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Transcript of Coal Quality Monitoring
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Commission of the European Communities
t e c h n i c a l c o a l r e s e a r c h
COAL QUALITY MONITORING
Report
EUR 13351 EN
Blow-up from microfiche original
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y
Commission of the European Communities
t e c h n i c a l c o a l r e s e a r c h
COAL QUALITY MONITORING
BRITISH COAL
Headquarters Technical Department
Ashby Road, Stanhope Bretby
UK-Burton-on-Trent, Staffs. DE15 OQD
Contract No 7220-EA/812
FINAL REPORT
Research work carried out with financial aid from
the European Coal and Steel Community.
1991
Directorate-General Energy
|Ü MJ WI v
iV nL l i î RC P . B iblio th
£UR 13351 EN
| C E.
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Published by the
COMMISSION OF THE EUROPEAN COMMUN ITIES
Directorate-General
Telecommunications, Information Industries and Innovation
L 2920 LUXEMBOURG
LEGAL NOTICE
Neither the Comm ission of the European Com mun ities nor any person acting on behalf
of the Commission is responsible for the use which might be made of the following
information
Catalogue number: CD-NA-13351-EN-C
© ECSC — EEC — EAEC, Brussels - Luxemb ourg, 1991
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III
FOREWORD
This work was undertaken jointly by the Coal Preparation Division
of the Mining Research and Development Establishment (now Headquarters
Technical Department) and by Scientific Control Department.
Development and laboratory work was carried out at:-
M.R.D.E., Bretby (later HQTD)
HQ Scientific Control, Harrow
Scottish Area Laboratory, Edinburgh
Yorkshire Regional Laboratory, Wath (later SCL(N))
East Midlands Region Laboratory, Mansfield (later SCL(S))
On site work was carried out at:-
Bilsthorpe Colliery
Mantón Colliery
Askem Colliery
Markham Colliery
Longannet Colliery
This report was prepared by M P Armstrong (Coal Preparation) and D Page
(Scientific Control).
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SYNOPSIS
This work has been undertaken to advance the development and
application of on-line coal quality monitoring in response to the
increasing need for real-time information to improve quality and
increase operational efficiency. In particular, factors affecting the
application and performance of ash and moisture measurement have been
studied.
Laboratory studies of ash content measurement utilising low energy
gamma radiation have demonstrated that the lower limit of measurement
accuracy is mainly controlled by variations in ash composition, and
reliable estimates of potential accuracy can be made from a knowledge
of the ash composition.
On-belt trials of two commercial ash monitors have shown the potential
for significant errors arising from other sources and the need to
ensure that instruments are applied in such a way that a fully
representative portion of the coal stream is interrogated.
In some circumstances, it may be more practical to monitor a sub-stream
of coal and a presentation unit has been developed which is capable of
handling wet coal, up to 25 mm top size, and producing a continuous bed
of coal suitable for interrogation by ash or moisture meters.
A previously developed, single frequency, microwave moisture meter has
been improved and, in conjunction with a specially developed ultrasonic
bed depth meter, the feasibility of measuring moisture content of coal
directly on a conveyor belt demonstrated.
A new moisture meter, which is less sensitive to the disturbing
influences of coal type, particle size and sample geometry, and which
is based on the attenuation of continuously varying frequency
microwaves, has been developed and tested satisfactorily.
A new type of capacitance moisture meter has been designed and built.
Laboratory tests on an experimental unit have demonstrated that a
reasonable accuracy is obtainable but some technical problems remain.
Development to a commercial prototype was not considered justifiable
because of high cost estimates.
A capability study of nuclear magnetic resonance techniques for
measuring moisture in coal has been made. Although reasonable accuracy
is obtainable with small volume samples, translation of the technique
to large scale on-stream monitoring is not considered to be worthwhile
because of the necessity to develop high capital cost equipment.
A survey of the status of on-line neutron gamma analysers has been
made. Their capability to measure most of the quality parameters of
coal, to a useful degree of accuracy, has been demonstrated but
applications are restricted by the high capital cost of the equipment.
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VII
CONTENTS
Page
FOREWORD III
SYNOPSIS V
1. INTRODUCTION 1
1.1 General 1
1.2
Obj ectives
1
1.3 Programme of Work 1
1.4 Allocation of Work 2
2.
MAIN-STREAM ASH MONITORING - WULTEX ASHMETER 3
2.1 Design and Operation 4
2.2 Previous Investigations and Testing by British Coal 5
2.2.1 Preliminary Laboratory Calibration 5
2.2.2 Initial Trial at Mantón Colliery 5
2.3 Theoretical Assessment of Calibration Accuracy 7
2.4 Further Laboratory Investigations 7
2.4.1 Bed Depth Effects 7
2.4.2 Calibration Tests 9
2.4.3 Appraisal of Calibration Tests 10
2.5 Trial Installation at Bilsthorpe Colliery 11
2.5.1 Consideration of Requirements for Second Trial
Installation 11
2.5.2 Description of Trial Site at Bilsthorpe Colliery 11
2.5.3 Installation of Ashmeter 12
2.5.4 On-site Calibration Tests 12
2.5.5 Shift Integration Tests 14
2.6 Re-design of Ashmeter Electronics by SCL(N) 15
2.6.1 Original Polish design 15
2.6.2 Re-designed System 15
2.6.3 Information Available From Re-designed System 16
2.7 Further Trials at Mantón Colliery 17
2.7.1 Description of Installation 17
2.7.2 Dynamic Calibration Test Procedure 17
2.7.3 Dynamic Calibration Test Results 18
2.7.4 Train-load Integration 18
2.8 Further Installations 19
2.9 Summary 19
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VIII
3. MAIN-STREAM ASH MONITORING - COALSCAN 3500 ASH MONITOR 20
3.1 Principle of Ash Measurement 21
3.2 Description of Commercial Unit 21
3.3 Calibration, Operation and Standardisation 22
3.4 Laboratory Investigations 23
3.4.1 Arrangements and Objectives 23
3.4.2 Setting-up Procedure 24
3.4.3 Results 26
3.5 On-Line Trials at Askem Colliery 29
3.5.1 Purchase Agreement and Installation 29
3.5.2 Commissioning and Calibration of Coalscan 3500 30
3.5.2.1 Preparatory Investigations 30
3.5.2.2 Commissioning and Preliminary Calibration 31
3.5.2.3 On-line Dynamic Calibrations 1 to 5 31
3.5.3 Investigation of Segregation on Belt 32
3.5.4 Further Dynamic Calibrations and Investigations 33
3.5.5 Performance Test 34
3.5.6 Sampling Precision 35
3.5.7 Further Investigation of Cross-belt Segregation 35
3.5.8 Seventh Dynamic Calibration Test 36
3.5.9 Comparison of Static and Dynamic Calibrations 38
3.5.10 Shift Integration Performance and Comparison with
Phase 3A Ash Monitor 3g
3.6 Summary 42
4. SUB-STREAM ASH MONITORING
4 3
4.1 Previous UK Experience and Problems 43
4.2 Previous Development of New Presentation System 44
4.3 Design of Trial Site at Markham Colliery 46
4.4 Design and Construction of New Experimental Ram-feed Unit 47
4.5 Testing of Ram-feed Unit at Markham Test Site 47
4.6 Design and Manufacture of Pre-production Prototype Unit 50
4.7 Nucleonic Ash Measuring and Signal Processing System 51
4.7.1 Design of Ash Measuring and Control System 51
4.7.2 Operation of Ash Measuring and Control System 51
4.7.3 Radiation Safety Precautions 52
4.7.4 Manufacture and Testing 53
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IX
4.8 Summary 53
5. MICROWAVE MOISTURE MONITORING 54
5.1 Review of Previous Development and Testing by British Coal 54
5.1.1 Early Investigations 54
5.1.2 Microwave Bands 54
5.1.3 Earlier Applications 55
5.1.4 Previous Development and Application of X-band System 55
5.1.5 Previous Development and Application of an S-band System 56
5.1.6 Limitations to Application of S-band System 56
5.2 Developments for On-belt Microwave Moisture Monitoring 57
5.2.1 Instrumentation Requirements 57
5.2.2 Moisture Meter Electronics 57
5.2.3 Data Logger 59
5.2.4 Ultrasonic Bed Depth Meter 59
5.2.5 Trial Installation of On-belt, S-band Moisture Monitor 60
5.2.5.1 Description of Installation 60
5.2.5.2 Results of On-site Trials at Longannet 61
5.3 Swept Frequency Microwave System 61
5.3.1 Limitations of Single Frequency Systems 61
5.3.2 Principle of 2 Frequency Measurement 62
5.3.3 Effect of Variable Geometry 63
5.3.4 Experimental Laboratory Equipment 64
5.3.5 Laboratory Test Procedure 65
5.3.6 Testing of Seams from Blindwells Opencast Site 65
5.3.7 Appraisal of Test Results 65
5.4 Summary 66
6. CAPACITANCE MOISTURE MONITORING 67
6.1 Previous Investigations, Applications and Development by
British Coal 67
6.1.1 Early Investigations 67
6.1.2 Further Development and Testing 67
6.2 Insulated Plate Capacitance Moisture Monitor 68
6.2.1 Proposed Development 68
6.2.2 Design of Experimental Laboratory System 69
6.2.3 Laboratory Tests with Experimental Cell - Series I 71
6.2.4 Laboratory Testing of Experimental Cell - Series II 72
6.2.5 Proposed Further Investigations 72
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7. DETERMINATION OF MOISTURE IN COAL BY NUCLEAR MAGNETIC RESONANCE 73
7.1 Introduction 73
7.2 Principle and Measurement Techniques 73
7.3 Review of Work to Date 74
7.4 Potential For On-Line Monitoring 76
7.5 Summary 77
8. THE APPLICATION OF NEUTRON/GAMMA INTERACTIONS TO ON-LINE
COAL ANALYSIS 77
8.1 Basic Principles and Techniques 77
8.2 General Review of On-line Applications 79
8.3 Commercially Available Analysers 79
8.3.1 Science Applications International Corporation 79
8.3.2 MDH-Motherwell Inc. 81
8.3.3 Gamma-Metrics 82
8.3.4 Summary of Performance Capabilities 83
8.3.5 Installations 83
8.4 Summary 84
9. GENERAL CONCLUSIONS 85
9.1 On-stream Ash Monitoring 85
9.2 Sub-stream Ash Monitoring 86
9.3 Microwave Moisture Monitoring 86
9.4 Capacitance Moisture Monitoring 86
9.5 Nuclear Magnetic Resonance 87
9.6 Neutron/gamma Analysis of Coal 87
REFERENCES 89
APPENDICES
1. EXTRACT FROM HEADS OF AGREEMENT CONTRACT BETWEEN THE NCB AND
WULTEX MACHINE CO. LTD. FOR THE TRIAL OF A WULTEX RADIOMETRIC
ASHMETER, TYPE G-3, AT MANTÓN COLLIERY 95
2.
CALCULATION OOF CALIBRATION ACCURACY FROM COAL COMPOSITION. 97
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X I
3. TECHNICAL APPENDIX TO HEADS OF AGREEMENT CONTRACT FOR
EXPERIMENTAL USE OF WULTEX RADIOMETRIC ASHMETER EQUIPMENT -
OBJECTIVES, DIRECTION AND REVIEW OF TRIAL. 99
4. WULTEX RADIOMETRIC ASHMETER - SITE REQUIREMENTS FOR PROPOSED
SECOND TRIAL INSTALLATION. 103
5. HEADS OF AGREEMENT CONTRACT BETWEEN THE NCB AND WULTEX MACHINE
CO.
LTD. FOR THE TRIAL OF A WULTEX RADIOMETRIC ASHMETER AT
BILSTHORPE COLLIERY, NORTH NOTTINGHAMSHIRE AREA - APPENDIX II
ACCEPTANCE CRITERIA FOR TRIAL. 105
6. TECHNICAL APPENDIX TO AGREEMENT FOR THE TRIAL OF A COALSCAN 3500
ASH MONITOR - OBJECTIVES, DIRECTION AND REVIEW OF TRIAL. 109
7.
EXTRACT FROM HEADS OF AGREEMENT CONTRACT BETWEEN THE NCB AND
MAGCO LTD. FOR THE TRIAL OF A COALSCAN 3500 ASH MONITOR AT
ASKERN COLLIERY, SOUTH YORKSHIRE AREA - APPENDIX II, ACCEPTANCE
CRITERIA FOR TRIAL. Ill
8. SPECIFICATION FOR THE DESIGN AND MANUFACTURE OF A PRE-PRODUCTION
PROTOTYPE RAM-FEED UNIT. 115
9. ASH MEASURING AND CONTROL SYSTEM FOR RAM-FEED ASH MONITOR -
SPECIFICATION OF MAIN PROPRIETARY COMPONENTS. 119
10.
SPECIFICATION FOR X BAND MICROWAVE MOISTURE METER. 123
11.
SPECIFICATION FOR S BAND MICROWAVE MOISTURE METER. 125
12.
TECHNICAL SPECIFICATION FOR ULTRASONIC BED-DEPTH METER. 127
13. LABORATORY SWEPT FREQUENCY MICROWAVE MOISTURE SYSTEM -
SPECIFICATION OF MEASURING EQUIPMENT. 129
14.
SOME ASPECTS OF THE THEORY OF CAPACITANCE MOISTURE MONITORING. 133
15. SPECIFICATION FOR AN ELECTRONICS PACKAGE FOR EXPERIMENTAL
CAPACITANCE MOISTURE MONITORING. 137
TABLES
1. Results of Previous Testing of Wultex Radiometric Ashmeter. 145
2.
Summary of Results of Laboratory Calibration Tests with Wultex
Ashmeters at
SCL(N).
146
3. Results of Calibrations Tests with Wultex Ashmeter on Bllsthorpe
Blended Smalls. 147
4. Laboratory Investigations with Coalscan 3500 Ash Monitor •
Results of Tests to Assess Statistical Counting Error Using
Calibration Standard. 148
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XII
5. Laboratory Investigations with Coalscan 3500 Ash Monitor -
Variations in Log Ratio Values Due to Changes in Bed Thickness.
18.
Results of Second Series of Laboratory Tests with Experimental
Insulated Plate Capacitance Cell.
149
6. Laboratory Investigations with Coalscan 3500 Ash Monitor -
Effect of Magnetite Addition to Coal Sample. 150
7. Laboratory Investigations with Coalscan 3500 Ash Monitor -
Effect of Calcium Carbonate Addition to Coal Sample. 15]
8. Laboratory Investigations with Coalscan 3500 Ash Monitor -
Effect of Kaolin Addition to Coal Sample. 152
9. Laboratory Calibration Tests with Coalscan 3500 Ash Monitor. 153
10.
Laboratory Investigations with Coalscan 3500 Ash Monitor -
Effect of Increasing Number of Static Measurements with Prepared
Samples of 25-3 mm Askem Blended Coal. 154
11.
Coalscan 3500 Ash Monitor Trial, Askem Colliery - Summary of
On-site Calibration and Performance Tests. 155
12. Coalscan 3500 Ash Monitor Trial, Askern Colliery - Results of
Investigation of Cross-belt Segregation with Oscillating Head,
Barium Source and 2 second Counting Periods. 156
13.
Experimental Ram-feed Presentation Unit with Plutonium 238
Isotope Measuring Head and Fe Correction • Laboratory
Calibration Tests on Markham Power Station Blend and Comparison
with Telsec 350 Analyser. 157
14.
Experimental Ram-feed Presentation Unit Trial, Markham Colliery
- Typical Sizing Analyses of Power Station Blend and Crushed
Product with Different Size Crusher Grids. 158
15.
Analyses of Seams from Blindwells Opencast Site Tested with the
Laboratory Swept Frequency Microwave System. 159
16. Results of Laboratory Swept Frequency Tests on a Range of Seams
from Blindwells Opencast Site. 160
17. Results of First Series of Laboratory Tests with Experimental
Insulted Plate Capacitance Cell and Different Concentrations of
Ionic Salt Solutions. 161
162
19. Calibration Tests with the Newport Mark IIIA Analyser. 163
20.
Summary of work on Moisture Measurement by NMR Spectrometry. 164
21.
Commercially Available Multielement Analysers. 165
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XIII
22. Accuracy of CONAC (+1 s
wt%).
166
23.
Precision of CONAC (+1 s
wt%).
167
24.
Accuracy of ELAN (wt
) .
168
25. Precision and Accuracy of GM Coal Analyser. 169
26. Relative Accuracy of Neutron Gamma Analysis. 170
27. Units Currently Installed or Ordered. 171
FIGURES
1. Wultex Radiometric Ashmeter, Type G3 - General Arrangement on ,,-
Belt Conveyor.
2.
Wultex Radiometric Ashmeter, Type G3 - Sectional View of Isotope
Measuring Head. 174
3. Wultex Ashmeter - Theoretical Effect of Bed Depth on Countrate
for 3 Levels of Ash Content and 2 Levels of Bulk Density. 175
4.
Wultex Ashmeter - Variable Depth Sample Presentation Box for
Laboratory Investigations. 176
5. Wultex Ashmeter * Effect of Bed Depth on Ash Measurement at Two
Levels of Bulk Density with Sample from Bilsthorpe PSF Blend. 177
6. Wultex Ashmeter - Effect of Bed Depth on Ash Measurement at Two
Levels of Bulk Density with Sample from Mantón Middlings. 178
7. Wultex Ashmeter - Effect of Bed Depth on Ash Measurement at Two
Levels of Bulk Density with Sample from Gedling Middlings. 179
8. Laboratory Calibration for Mantón 50 mm - 0 Blended Coal with
Wultex (UK) Ashmeter. 180
9. Laboratory Calibration for Mantón 50 mm - 0 Blended Coal with
Wultex (Polish) Ashmeter.
10.
Laboratory Calibration for Mantón 50 mm - 0 Untreated Coal with
Wultex (UK) Ashmeter.
11.
Laboratory Calibration for Mantón 50 mm - 0 Untreated Coal with
Wultex (Polish) Ashmeter.
181
182
183
12.
Laboratory Calibration for Askem 25 mm - 0 Blended Coal with
Wultex (Polish) Ashmeter. 184
13.
Laboratory Calibration for As kem 25 mm - 0 Untreated Coal with
Wultex (Polish) Ashmeter.
185
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XIV
14.
Laboratory Calibration for Askem 25 mm - 0 Washed Coal with
Wultex (Polish) Ashmeter.
16. Laboratory Calibration for Bilsthorpe 50 mm - 0 Blended Coal
with Wultex (Polish) Ashmeter.
20.
Laboratory Calibration for Bilsthorpe 50 mm - 0 Washed Coal with
Wultex (Polish) Ashmeter.
186
15.
Laboratory Calibration for Bilsthorpe 50 mm - 0 Blended Coal
with Wultex (UK) Ashmeter. 187
188
17. Laboratory Calibration for Bilsthorpe 38 mm - 0 Untreated Coal
with Wultex (UK) Ashmeter. 189
190
8.
Laboratory Calibration for Bilsthorpe 38 mm - 0 Untreated Coal
with Wultex (Polish) Ashmeter.
19. Laboratory Calibration for Bilsthorpe 50 mm - 0 Washed Coal with
Wultex (UK) Ashmeter. 191
192
21.
Laboratory Calibration for Cotgrave 50 mm - 0 Blended Coal with
Wultex (UK) Ashmeter. 193
22. Laboratory Calibration for Cotgrave 50 mm - 0 Blended Coal with
Wultex (Polish) Ashmeter. 194
23.
Laboratory Calibration for Lea Hall 25 mm - 0 Blended Coal with
Wultex (UK) Ashmeter. 195
24.
Laboratory Calibration for Daw Mill 12.5 mm - 0 Untreated Coal
with Wultex (UK) Ashmeter. 196
25.
Laboratory Calibration for Cwm 50 mm - 0 Washed Coal with Wultex
(UK) Ashmeter. 197
26.
Laboratory Calibration for Sharlston 50 mm - 0 Washed Coal with
Wultex (UK) Ashmeter.
1 9 8
27. Laboratory Calibration for Grimethorpe 50 mm - 0 Blended Coal
with Wultex (UK) Ashmeter. I99
28.
Laboratory Calibration for Grimethorpe 50 mm - 0 Untreated Coal
with Wultex (UK) Ashmeter. 200
29. Laboratory Calibration for Grimethorpe 50 mm - 0 Washed Coal
with Wultex (UK) Ashmeter. 201
30.
Relationship between Standard Deviation Calculated from Full
Elemental Analysis and Measured Standard Deviation for
Laboratory Calibration Tests with Wultex Ashmeter. 202
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XV
31.
Relationship between Standard Deviation derived from Iron and
Ash Analysis only and measured Standard Deviation for Laboratory
Calibration Tests with Wultex Ashmeter. 203
32. Schematic Arrangement of Wultex Ashmeter Installation at
Bilsthorpe Colliery. 204
33.
Schematic Arrangement of Wultex Ashmeter Installation at Mantón
Colliery. 205
34.
Wultex Ashmeter Installation at Mantón Colliery - Dynamic
Calibration Test 1. 206
35.
Wultex Ashmeter Installation at Mantón Colliery - Dynamic
Calibration Test 2. 207
36. Schematic Illustration of the Principle of Operation of the
Coalscan 3500 Ash Monitor. 208
37. Radiation Spectrum for Coalscan 3500 Ash Monitor with americium
and barium Sources. 209
38.
Schematic Arrangement of Commercial Design of Coalscan 3500 Ash
Monitor. 210
39.
Laboratory Investigations with Coalscan 3500 Ash Monitor -
Variation of Log Ratio Standard Deviation with Duration of
Counting Period. 211
40.
Laboratory Investigations with Coalscan 3500 Ash Monitor -
Effect of Chemical Additions on Measurement of Ash Content. 212
41.
Laboratory Calibration for Askern Blended Coal (-212 pi) with
Coalscan 3500 Ash Monitor. 213
42.
First Laboratory Calibration for Gascoigne Wood Untreated Coal
(-212 p ) with Coalscan 3500 Ash Monitor. 214
43. Second Laboratory Calibration for Gascoigne Wood Untreated Coal
(-212 um) with Coalscan 3500 Ash Monitor. 215
44.
Laboratory Calibration for South Side (Grimethorpe) Blended Coal
(-212 p ) with Coalscan 3500 Ash Monitor. 216
45.
Laboratory Calibration for Askern Blended Coal (-212 p ) , from
Fourth Dynamic Calibration, with Coalscan 3500 Ash Monitor. 217
46.
Laboratory Calibration for Askern Blended Coal (-1 mm ), from
Fourth Dynamic Calibration, with Coalscan 3500 Ash Monitor. 218
47. Laboratory Calibration for Askern Simulated Blended Coal (25 -
3.18 mm) with Coalscan 3500 Ash Monitor.
2 1 9
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XVI
48.
Schematic Arrangement of Coalscan 3500 and NCB/AERE Phase 3A Ash
Monitors at Askem Colliery. 220
49. On-site Static Calibration for Askem Blended Coal (-212 pn)
with Coalscan 3500 Ash Monitor. 221
50.
First Dynamic Calibration for As kem Blended Coal (25 mm - 0)
with Coalscan 3500 Ash Monitor. 222
51.
Static Calibration for Askem Blended Coal Samples (-212 p»)
from First Dynamic Calibration with Coalscan 3500 Ash Monitor. 223
52. Third Dynamic Calibration for Askem Blended Coal (25 mm - 0)
with Coalscan 3500 Ash Monitor. 224
53.
Fourth Dynamic Calibration for Askem Blended Coal (25 mm - 0)
with Coalscan 3500 Ash Monitor. 225
54.
Fifth Dynamic Calibration for Askem Blended Coal (25 mm - 0)
with Coalscan 3500 Ash Monitor. 226
55. Sixth Dynamic Calibration for Askem Blended Coal (25 mm - 0)
with Coalscan 3500 Ash Monitor. 227
56. Coalscan 3500 Ash Monitor Trial at Askem Colliery - Variation
of Barium Countrate, in 2 second Periods, during Oscillation of
Measuring Head across Product Stream with 18 second Cycle Time. 228
57.
Coalscan 3500 Ash Monitor Trial at Askem Colliery • Variation
of Mean Calculated Ash Content with Mean Barium Countrate during
Oscillation of Measuring Head for 13 minute Test Period. 229
58.
Performance Test Calibration for Askem Blended Coal (25 mm - 0)
with Coalscan 3500 Ash Monitor. 230
59. Coalscan 3500 Ash Monitor Trial at Askem Colliery - Variation
of Barium Countrate and Ash Content Measurements as Measuring
Head Oscillated over Stationary Conveyor spread with Even Layer
of Well Mixed -1 mm Coal Sample. 231
60.
Coalscan 3500 Ash Monitor Trial at Askem Colliery - Variation
of Americium and Barium Countrates and Computed Ash Content as
Measuring Head, with Standardisation Radiation Absorbers 232
attached to Detector, Oscillated over Conveyor Running Empty.
61.
Seventh Dynamic Calibration for Askem Blended Coal (25 mm - 0)
with Coalscan 3500 Ash Monitor. 233
62. Static Calibration for Askem Blended Coal Samples (-212 pi)
from Seventh Dynamic Calibration with Coalscan 3500 Ash Monitor.
234
63.
Coalscan 3500 Ash Monitor Trial at Askern Colliery -
Relationship between Coalscan Shift Integration and Laboratory
Shift Analysis for 99 Shifts. 235
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XVII
64.
Coalscan 3500 Ash Monitor Trial at Askem Colliery -
Relationship between Coalscan Shift Integration and Laboratory
Shift Analysis for 104 Shifts. 236
65.
Phase 3A Ash Monitor Installation at Askern Colliery -
Relationship between Phase 3A Shift Integration and Laboratory
Shift Analysis for 104 Shifts. 237
66. Coalscan 3500 Ash Monitor Trial at Askern Colliery - Difference
between Coalscan Shift Integration and Laboratory Shift Analysis
for 99 Shifts. 238
67. Coalscan 3500 Ash Monitor Trial at Askern Colliery - Difference
between Coalscan Shift Integration and Laboratory Shift Analysis
for 108 Shifts. 239
68.
Phase 3A Ash Monitor Installation at Askern Colliery -
Difference between Phase 3A Shift Integration and Laboratory
Shift Analysis for 108 Shifts. 240
69. NCB/AERE Phase 3A Ash Monitor for Sub-Stream Monitoring
(9612/1).
241
70.
Sketch of Original Design of Experimental Ram-feed Sample
Presentation Unit for Sub-Stream Monitoring. 242
71.
Modified Experimental Ram-feed Presentation Unit incorporating
Stainless Steel Trough and Showing Nucleonic Measuring Head
Mounted on Indpendent Supports (9398/2). 243
72.
Experimental Ram-feed Presentation Unit - Typical Relationship
between Backscatter Countrate and Material Compression. 244
73.
Experimental Ram-feed Presentation Unit - Hydraulic Pressure
required to produce increasing Material Compression at Different
Moisture Levels.
77. Trial of Experimental Ram-feed Unit at Markham Colliery - Sizing
Curves for 50 mm - 0 Blended Coal and Products from Crusher with
Different Size Crusher Grids.
245
74.
Schematic Arrangement of Colliery Sampling System and Ram-feed
Unit Trial Circuit at Markham Colliery. 246
75.
Re-designed,Experimental Ram-feed Presentation Unit, for
Installation at Colliery Trial Site, with Second Outlet for
Scrapings and Proposed Feed and Reject Screw Conveyors. 247
76. Re-designed, Experimental Ram-feed Unit Installed at Colliery
Trial Site with Feed Screw Conveyor delivering to Feed Hopper
and Compacted Material in Presentation Trough (12,056/1). 248
249
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X V I I I
78. Trial of Experimental Ram-feed Presentation Unit at Colliery
Site - Surface Profile of Compacted Bed with Coarse (-25 mm)
Material
(12,056/3).
250
79.
Trial of Experimental Ram-feed Presentation Unit at Colliery
Site - Surface Profile of Compacted Bed with Fine (-6 mm)
Material
(12,056/2).
251
80.
Diagram illustrating Main Design Features of Prototype Ram-feed
Presentation Unit. 252
81. General Arrangement Drawing of Prototype Ram-feed Presentation
Unit.
253
82. General View of Prototype Ram-feed Presentation Unit with
Polypropylene Trough Section following Stainless Steel
Compression Zone (Ramsey
10958).
254
83.
Rear View of Prototype Ram-feed Presentation Unit showing
Cut-outs in Feed Chute Casing for Level Sensors and Hydraulic
Cylinder Enclosure (Ramsey
10960).
255
84.
Block Diagram of Ash Measuring and Control System for Prototype
Ram-feed Ash Monitor. 256
85.
Block Diagram of Solid State X Band Microwave Moisture Meter. 257
2 5 8
6.
NCB/AERE Phase 3A Ash Monitor incorporating X Band Microwave
Moisture Meter.
87. Colliery Computer at Longannet Mine used for Computing Tonnage
Weighted Calorific Value from Ash/Moisture Monitor and Belt
Weigher Signals.
88.
Dedicated Microprocessor System at Monktonhall Colliery for
Display and Print-out of Integrated Ash, Moisture and Computed
Calorific Values.
2 5 9
2 6 0
89.
Prototype S Band Discrete Sample, Microwave Moisture Meter. 261
90.
Schematic Diagram of Re-designed Fixed Frequency, Microwave
Moisture System with High (60 dB) Dynamic Range. 262
91. Diagram of Data Logger recording signals from Phase 3A
Ash/Moisture Monitor. 263
92. Diagram of Data Logger recording signals from Belt Weigher and
Bed Depth and Moisture Meters. 264
93.
Block Diagram showing Design of Ultrasonic Bed Depth Meter. 265
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X I X
94.
Schematic Arrangement of On-belt S Band Moisture Meter,
Ultrasonic Bed-depth Meter and Phase 3A Ash/Moisture Monitor
with Data Loggers at Longannet Mine. 266
95.
Trial Installation of S Band Microwave Moisture Meter and
Ultrasonic Bed-depth Meter on 25 mm - 0 Raw Coal Conveyor at
Longannet Mine with Instrumentation and Data Logger located
alongside in Protective Cabinet
(12,399/1).
267
96. Trial Installation S Band Moisture Meter at Longannet Mine
showing Microwave Transmitting Horn and Ultrasonic Bed-depth
Meter mounted above Belt Conveyor and Microwave Receiving Horn
located below (12,399/2). 268
97. Trial of S Band, On-belt, Microwave Moisture Meter and
Ultrasonic Bed-Depth Meter at Longannet Mine - Traces of
Bed-depth, Attenuation and Belt Loading plotted at 1 Minute
Intervals on 22 January 1988. 269
98.
Trial of S Band, On-belt, Microwave Moisture Meter and
Ultrasonic Bed-depth Meter at Longannet Mine • Traces of
Bed-depth, Attenuation and Belt Loading averaged over 5 Minute
Intervals on 22 January 1988. 270
99. Trial of Ultrasonic Bed-depth Meter at Longannet Mine -
Calibration Graph of Belt Weigher Readings against Bed-depth
Meter Readings integrated over 5 Minute intervals during 5 hour
period on 22 January 1988. 271
100.
Schematic Diagram of Proposed Two Frequency Microwave Moisture
Meter. 272
101. Schematic Arrangement of Laboratory Swept Frequency Microwave
System. 273
102. Laboratory Swept Frequency Microwave System - Attenuation Scan
(5-7 GHz) and Linear Regression for Parrot Crop Seam with 14.3%
Moisture. 274
103. Laboratory Swept Frequency Microwave System - Attenuation Scan
(5-7 GHz) and Linear Regression for Parrot Crop Seam with 16.2%
Moisture. 275
104. Laboratory Swept Frequency Microwave System - Attenuation Scan
(5-7 GHz) and Linear Regression for Parrot Crop Seam with 18.7%
Moisture. 276
105. Laboratory Swept Frequency Microwave System - Attenuation Scan
(5-7 GHz) and Linear Regression for Parrot Crop Seam with 20.0%
Moisture. 277
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XX
106. Laboratory Swept Frequency Microwave System - Attenuation Scan
(5-7 GHz) and Linear Regression for Parrot Crop Seam with 21.7%
Moisture. 278
107. Laboratory Swept Frequency Microwave System - Attenuation Scan
(5-7 GHz) and Linear Regression for Parrot Crop Seam with 23.2%
Moisture. 279
108. Laboratory Swept Frequency Microwave System - Attenuation Scan
(5-7 GHz) and Linear Regression for Parrot Crop Seam with 25.2%
Moisture. 280
109. Laboratory Swept Frequency Microwave System - Attenuation Scan
(5-7 GHz) and Linear Regression for Parrot Crop Seam with 27.2%
Moisture. 281
110. Laboratory Swept Frequency Microwave System - Calibration Graph
of Moisture Content against Attenuation/Frequency Gradient for
Parrot Crop Seam. 282
111. Laboratory Swept Frequency Microwave System - Calibration Graph
of Moisture Content against Weighted Attenuation/Frequency
Gradient for Parrot Crop seam. 283
112.
Laboratory Swept Frequency Microwave System - Calibration Graph
of Moisture Content against Attenuation/Frequency Gradient for
Seven Seams from Blindwells Opencast Site. 284
113. Laboratory Swept Frequency Microwave System - Calibration Graph
of Moisture Content against Weighted Attenuation/Frequency
Gradient for Seven Seams from Blindwells Opencast Site. 285
114. Electronic Measurement System for Experimental Insulated Plate
Capacitance Cell. 286
115. Electronic Measurement System for Experimental Insulated Plate
Capacitance Cell with Automatic Stabilisation of Buffer
Amplifier Output Signal. 287
116.
Laboratory Tests with Experimental Insulated Plate Capacitance
Cell - Relationship between Instrument Reading and Added
Moisture with Increasing Ionic Salt Content. 288
117. Laboratory Tests with Experimental Insulated Plate Capacitance
Cell - Calibration Graph for Washed Small Coal from Markham
Colliery. 289
118.
First Derivative Absorption Spectrum for Wet Coal. 290
119. Free Induction Decay Signal for Wet Coal. 291
120.
Regression Calibration for Suites 5 and 6. 292
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XXI
121. Effect of Magnetite Additions on N.M.R. Instrument Reading. 293
122. S.A.I.C. 'CONAC' - Schematic Section 294
123.
MDH - Motherwell Inc. 'ELAN' - Schematic Section. 295
124.
Gamma Metrics 'Coal Analyser' - Schematic Section. 296
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1. INTRODUCTION
1.1 General
The need for rapid or continuous monitoring of coal quality
continues to increase as customer requirements become more closely
specified and as producers and users seek to increase the efficiency of
operations to meet those demands. Ash and moisture contents are key
parameters in the assessment of the quality of coal in the majority of
its uses. Other factors of growing importance to the user, both for
operational and environmental reasons, are sulphur and chlorine contents
and ash analysis. The availability of real-time information on some or
all of these parameters will assist in the control of coal preparation
processes to meet specifications and to optimise operations, in terms of
cost and quality, and allow the confirmation of consignment quality
before despatch to the customer.
The classical methods of assessing coal quality by sampling,
preparation and laboratory analysis take at least 2 hours, and often
24 hours, to complete and, consequently, are of little use for plant
control purposes or pre-dispatch quality confirmation. Continuous coal
quality monitors, particularly for ash content, have been under
development and in use for 30 years but, until recently, were mainly
designed for use on sub-streams. Consequently, they often required a
considerable amount of expensive ancilliary equipment for sample
conditioning and were prone to handlability problems with many products.
1.2 Objectives
It was considered that the above problems could be largely overcome
if it was possible to make the necessary measurements, with sufficient
accuracy, directly on the product conveyor belt. Work on the
development of suitable methods and instrumentation is ongoing in a
number of countries and some commercially produced equipment has
appeared on the market. Às yet, however, reported experience on the
application of such techniques is fairly limited or confined to specific
areas of interest. It is also realised that in some circumstances the
nature of the product, the design and layout of a plant and a possible
requirement for more accurate measurements than are obtainable from
on-belt measurements could make a sub-stream monitoring system a more
suitable option.
The main objectives of this project are to advance the development
and application of main-stream on-belt monitoring for ash and moisture
contents and to develop sub-stream monitoring equipment which will
tolerate coals of difficult handlability with little or no conditioning.
1.3 Programme of work
In the field of on-belt ash monitoring the programme of work
undertaken was designed to include the on-site calibration and
performance testing of proprietary instruments based on the
back-scattering and transmission of low energy gamma radiation. In
addition, the influence of such factors as coal bed depth, and coal
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composition variability on measurement accuracy was to be assessed in
both laboratory and on-site trials. On-belt moisture measurement had
not reached a commercial stage and work to study the extension of the
application of
a
British Coal developed sub-stream monitor
to direct
on-belt measurements was planned. The development of
a
new
microwave
technique, which should overcome some shortcomings of the
existing
system, was also to be pursued.
In the field of sub-steam monitoring, a major effort was to be
aimed at the production of a presentation unit which, with a minimum of
conditioning, could accept and present for interrogation by suitable ash
and moisture monitoring transducers, coal of particle sizes up to 50 mm.
Development of an improved capacitance-based moisture monitor
and
assessment of the potential for the use of nuclear magnetic resonance
was also to be undertaken.
Growing interest in the on-line measurement of other elements in
coal has resulted in the development of multi-element analysers based on
neutron-gamma techniques. An assessment of the performance, and
potential for application, of these analysers was also included in the
programme.
1.4 Allocation of work
This project was undertaken within British Coal by the Coal
Preparation Division of HQ Technical Department and Scientific Control
Department. The main division of the work was as follows:-
Coal Preparation Division
a) On site calibration trials of the Wultex and Coalscan ash meters
(in cooperation with Scientific Control)
b) Development and on-site trial of the Ram Feed Presentation Unit
c) Development of the Insulated Plate Capacitance Moisture Meter
Staff involved included:-
Coal Preparation Engineer
Engineer/Physicist
Electrical/Electronics Engineer
Scientific Control
i) Headquarters
a) Nuclear magnetic resonance studies
b) Assessment of neutron/gamma interaction applications
Staff involved included:-
Senior Scientist/Nuclear Physicist
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ii) Scottish Area Laboratory
Development and on-site trials of microwave moisture measurement
systems.
(This work subsequently transferred to Scientific Control Laboratory
(South)
SCL(S)).
Staff involved included:-
Senior Scientist/Control Engineer
Scientist
Electronics Engineers
Coal Analysts and Technicians.
iii) Yorkshire Regional Laboratory (later Scientific Control Laboratory
(North) SCL(N))
a) Laboratory trials of on-stream ash monitor systems
b) On-site calibration trials of Wultex and Coalscan Ash Monitors
c) Ashmeter electronics redesign
Staff involved included:-
Senior Scientists
Physicist
Process Engineer
Electronics Engineer and Technicians
Coal Analysts and Technicians
iv) East Midlands Regional Laboratory (later SCL(S))
On site calibration trial of Wultex Ashmeter.
Staff involved included:-
Senior Scientists
Coal Analysts and Technicians
Throughout the on-site trials assistance was also received in the
organisation and execution of the trials, in the installation of
equipment and in the collection of samples from operational engineers
and other staff located at the collieries.
2.
MAIN-STREAM ASH MONITORING - WULTEX ASH METER
Main-stream ash monitoring is the continuous measurement of the ash
content of coal, in either a raw or prepared condition, by the
continuous examination of the main production stream at some suitable
location. The first of two types of main-stream ash monitors that have
been investigated and tested both in the laboratory and in a production
situation is the Wultex Radiometric Ashmeter.
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2.1.
Design and Operation
The Radiometric Ashmeter was developed In Poland by the state coal
industry Research and Development Centre for Mining Mechanisation,
Electrotechnics and Automation Systems,
(EMAG).
It was designed for the
continuous measurement of the ash content of a small coal product
directly on a belt conveyor using a nucleonic backscatter technique(l).
The nucleonic measuring head is mounted behind a profiling plough
suspended by a parallelogram system from a supporting structure which
spans the belt conveyor, see Figure 1. The parallelogram system is
counterweighted so that the pressure of the profiling plough on the coal
is sufficient to produce a smooth surface profile and the required
degree of material compaction. The plough riding on the coal bed also
fulfills the important function of maintaining the measuring head at a
fixed height above the coal surface. If the flow of coal decreases such
that the coal bed reduces below the minimum depth the suspended frame
comes to rest against buffer stops and activates a switch to discontinue
the ash measurements. Hydraulic dampers are incorporated in the
parallelogram system to absorb any shocks to the system caused by sudden
changes in belt loading which might otherwise affect or damage the
measuring head. Because of the requirement to contact the coal and
produce a smooth surface profile the application of the Ashmeter is
restricted to coals which contain sufficient fines to facilitate this
and it is therefore not applicable to graded coals of large particle
size. The depth of material on the belt after profiling must also be
sufficient to ensure total absorption or backscatter of all the
radiation at the lowest ash content to be measured.
The measuring head, Figure 2, comprises the radioactive source
holder and the scintillation detector which continuously measures the
amount of radiation backscattered from the moving coal stream. Since
the ash forming elements in the coal absorb a higher proportion of the
radiation than the combustible elements the amount of backscattered
radiation measured by the detector decreases as the ash content of the
coal increases. A sliding shutter below the measuring head serves as
both a backscatter reference and as a radiation shield. On a later
design this shutter could be operated remotely by an electric actuator.
The radiation received by the scintillation detector produces
electrical pulses which are amplified for transmission to the electronic
signal processing and display unit which can be located up to 3 km from
the measuring head. The pulses are counted over a period of either
40 seconds or 2 minutes, as selected, and the pulse count is converted
to an ash value according to a pre-determined calibration for the
particular coal being monitored. The ash value is shown on a LED
display. A separate printer unit was required with the original design
of Ashmeter to provide a print out of the ash content every 40 seconds
or 2 minutes but a later design of the processing and display unit
incorporated a printer.
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Technical Data - Polish Instrument
Coal size 30 mm (maximum) - 0
Depth of profiled material 150 mm minimum
Range of ash measurement 3% - 40%
Permissible variation in
moisture content + 4% on moisture content at calibration
Radioactive source Americium -241 50 mCi
Radiation detector Scintillation detector with sodium
iodide crystal
Electrical supply Instrument 240 V AC
Power requirements Instrument 100 VA (approx)
Accuracy of Ash Measurement - Based on Polish Installations
Ash
3 -
10 -
20 -
Previous
Range
10%
20%
40%
Investigations
(Root
Accuracy
Mean Square Deviation)
+ 1% ash
±1 . 5 % ash
+2.0 % ash
and Testing by British
Coal
.2
2.2.1 Preliminary Laboratory Calibration
A licence for the manufacture and supply of the Radiometric
Ashmeter outside Poland was negotiated with EMAG by Wultex Machine Co
Ltd of Huddersfield in early 1981. In May 1981, a Polish manufactured
ashmeter was made available to British Coal by Wultex for preliminary
laboratory tests at the Scientific Control Laboratory North (SCL(N)) -
formerly Yorkshire Regional Laboratory. The tests were conducted with
50 mm -0 blended power station coal from Mantón Colliery, where
production was coming only from the Parkgate seam, and gave a
calibration standard deviation of 1.02% ash for a quadratic regression.
This result was sufficiently encouraging to proceed with a trial
installation, under a Heads of Agreement Contract, at Mantón Colliery in
August 1981. Because of the possibility of coal from the neighbouring
Steetley Colliery being treated at Mantón in the near future, this coal
was also tested in the laboratory and gave a much poorer calibration
standard deviation of 1.96% ash for a quadratic regression.
2.2.2 Initial Trial at Mantón Colliery
Following on-site calibration checks at Mantón, a series of 100
tests were conducted during October 1981 in accordance with the
procedure laid down in the Heads of Agreement Contract, Appendix 1,
which required that for 95 tests out of 100 the measured ash content
should be within +2.5% of the laboratory determined ash content. Each
test extended over a 4 minute integration period during which time
between 30 and 32 sample increments were taken by a mechanical sampler
to provide a composite sample for laboratory analysis.
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In addition to these acceptance tests the Ashmeter readings were
recorded and averaged over 1000 tonne train loads, corresponding to
approximately 4 hours production, and compared with laboratory ash
determinations for each consignment.
The results of these early investigations are given in Table 1.
The 100 test acceptance trials at Mantón gave an accuracy (2s) of ash
measurement of +2.58%. Only 4 tests lay outside the specified limits of
+2.5% ash after allowing for a mean bias of 1.1% between the Ashmeter
reading and the laboratory analysis. Only a small improvement in
accuracy (2s) to +2.3% ash was obtained when increasing the integration
period from 4 minutes to approximately 4 hours for train loads.
The reduced level of accuracy of the on-site ash measurements at
Mantón, as compared with the laboratory accuracy, was attributed in part
to the insufficient and variable depth of material on the conveyor belt.
Only by building up the levels in the blending bunkers, prior to each
4 minute test period, was it possible to maintain a reasonably
consistent flow rate of power station blend of around 300 t/h, which
corresponded to a bed depth of approximately 100 mm. During the loading
of each 1000 tonne train considerable variations could have occurred in
the belt loading so that the improvement in accuracy, that would have
been expected from a longer period of integration, was only partially
achieved.
The trial at Mantón continued for a period of six months in order
to check the mechanical and electrical reliability of the instrument, in
accordance with the terms of the Heads of Agreement, and no mechanical
or electrical problems arose during that period.
It was concluded from this trial that although the equipment had
proved mechanically and electrically reliable, there may be only a few
British collieries where the Wultex Ashmeter might be applied with
advantage. There would be many collieries where the inability to ensure
a sufficient and consistent material bed depth or where the production
of coal from several seams would adversely affect the accuracy of the
instrument. It was therefore decided to resume laboratory
investigations with the objectives of:-
(i) Evaluating the effect of material bed depth and bulk density
with the aim of devising a method of material presentation
so as to optimise the accuracy of the Ashmeter where the
required bed depth could not be achieved with the existing
material handling system
(ii) Assessing the possible wider application of the Ashmeter by
examining coals from multi-seam collieries and determining
the effect of variations in ash composition, in particular
the iron content, on the accuracy of the instrument.
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2.3. Theoretical Assessment of Calibration Accuracy
The Wultex Ash Meter is based on the fact that at relatively low
energies (<100 keV) the intensity of radiation backscattered from a
substance is a function of its average atomic number (Z). If coal is
considered to be a 2 component mixture of ash forming minerals (Z
a
- 12)
and combustible elements (Z
c
- 6) then Z, and hence backscattered
intensity, can be related to the concentration of mineral matter, which
itself correlates with ash content.
This relationship between backscattered intensity and ash content,
however, is subject to variations from a number of sources, not least
being the assumptions that coal is a simple 2-component mixture and that
the atomic number of the ash-forming minerals (Z
a
) is constant. Given
that the coal is presented to the detector system in a well defined
geometry which allows representative interrogation of the sample, then
variability in the composition of the coal is the major perturbing
factor, usually due to changes in iron content of the ash
minerals(2).
The magnitude of composition variations can then be regarded as
controlling the lower limits on the accuracy of the method.
By using a simple model of the backscatter method and inserting
data on the composition of the coal and relevant gamma ray attenuation
coefficients it is possible to calculate the relative backscattered
radiation intensity from any sample of coal (Appendix 2). If this
procedure is followed for a range of coal samples the correlation
between calculated relative backscattered intensity and ash content can
be assessed and an estimate of ash concentration error predicted for
that set of coals.
This procedure has been followed for all the coals used in the
Wultex laboratory trials. The theoretical values of calibration
standard deviation are given in Table 2, together with the measured
values obtained in the laboratory trials.
2.4 Further Laboratory Investigations
A further Heads of Agreement Contract, Appendix 3, was negotiated
with Wultex Machine Co Ltd for a second Ashmeter to be made available on
loan for the proposed programme of laboratory investigations at
SCL(N).
This unit would be one of the first batch to be manufactured in the UK
by Wultex. Because of problems encountered by Wultex in the manufacture
of these units, in particular the reliability of the scintillation
detector, the start of this work was delayed until 1984. To try and
reduce the delay the original Polish Ashmeter was withdrawn from Mantón
Colliery to the laboratory but it required attention and no advantage
was gained. Eventually both the Mantón Ashmeter and the new Wultex
Ashmeter were used to duplicate the laboratory investigations.
2.4.1 Bed depth effects
A theoretical study of the possible effect of material bed depth
and bulk density on the ash measurement with the Wultex Ashmeter was
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8
undertaken by Headquarters Scientific Control prior to the commencement
of laboratory trials. The theoretical effect of bed depth on the ash
measurement for three levels of ash content and two levels of bulk
density is shown in Figure 3. It was decided that the laboratory
investigations into the effect of bulk density would be limited to
confirming the validity of the theoretical curves but investigations
into bed depth would continue as originally planned.
Initial tests at SCL(N) to quantify the effects of bed depth and
compaction, using samples from normal commercial grades of coal, were
unsuccessful as the magnitude of the random errors made such effects
difficult to identify. The errors were further compounded by a degree
of detector instability present in the equipment at the time. The tests
were repeated using three prepared samples, each closely sized and
within a narrow range of relative density so that the inherent variation
in the density of the sample was minimised. The samples were presented
to the Ashmeters at a range of bed depths and were either loose-filled
or hand-compacted in the presentation container to give two levels of
bulk density.
The design of the presentation container used for these tests is
shown in Figure 4. The container comprised a rectangular wooden frame,
measuring 457 mm x 305 mm, with a loose wooden base which could be
positioned at four different levels to give depths of 80, 120, 160 and
200 mm. Â series of extension frames with depths varying from 6 mm to
32 mm, could be fitted to the top of the container to allow it to be
overfilled by a pre-determined amount. The material was then compacted
to the top of the container using a compression plate fitted with
spacers, selected to correspond with the extension frame being used, and
provided with compression stops to contact the top of the extension
frame and ensure that the surface of the compacted material corresponded
with the top of the original container. The extension frame was removed
before presentation to the measuring head. The lower degrees of
compaction could be achieved by hand but for greater compaction a
vibrating table was used.
The effect of varying bed depth on the measured ash content with
the three samples is shown in Figures 5, 6 and 7. The instrument
countrate readings were converted to ash content using appropriate
calibrations for the particular type of coal sample and Ashmeter. In
all cases the test results confirm the theoretical curves and show that
as the bed depth reduces below 200 mm there is a fall in countrate which
results in an increase in the indicated ash content. The effect of
reducing bed depth is slightly less with the compacted material but in
both cases the effect on ash measurement becomes significant when the
bed depth reduces below 150 mm and quite an appreciable error arises
when the depth falls to 100 mm. The tests also showed that a much more
uniform bulk density was achieved with a compacted bed than with a loose
fill.
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2.4.2 Calibration Tests
Laboratory investigations into the possible range of application
of the Wultex Ashmeter to UK coals had started in 1984, prior to the
ECSC Project, and by March 1985 a total of 9 products from 4 collieries
had been tested. The selection of collieries had to be modified from
those originally planned because of the intervention of the industrial
action in 1984/5 in British Coal and coals from the Nottinghamshire
coalfield had to be substituted for those from Yorkshire. A further 7
products had been tested by mid-1986 and a summary of all 16 laboratory
calibration tests is given in Table 2.
All tests were conducted in accordance with a standard procedure.
Initial tests to investigate the repeatability of the countrate
measurements showed that the standard deviations for the 40 and 120
second counting periods were of the same order and there was no
advantage in extending the counting period beyond 40 seconds. These
preliminary tests also showed that a minimum of 10 separate
presentations were required for each sample.
Although on-site the Ashmeter would be calibrated against the
'as-received' laboratory analysis, this was not considered possible in
the laboratory because of the progressive loss of moisture that would
occur with the preparation and repetitive handling of the samples. The
laboratory tests were therefore conducted with all the samples in an
'air dried' condition. It was initially considered necessary for all
samples to be reduced below 25 mm top size to assist laboratory handling
and avoid segregation but this size reduction was not found to be
necessary and the majority of the products were tested at the original
size,
as shown in Table 2.
A standard bed depth of 200 mm, after a compaction of
approximately 9%, was used for all tests. The presentation box was
filled 5 times for each sample, with thorough mixing between each fill,
and the box was presented twice to the measuring head at each filling,
with the box being rotated through 180° for the second presentation.
Following the countrate measurements, each sample was prepared in
accordance with the requirements of BS1017 "Methods for the sampling of
coal and coke, Part 1: Sampling of Coal
(1977)"
to produce laboratory
samples for moisture, ash and ultimate analysis in accordance with the
relevant parts of BS1016 "Methods for analysis and testing of coal and
coke". In addition, the ash from each sample was subjected to full
chemical analysis.
For the first 9 calibration tests the isotope measuring heads for
both the UK manufactured Ashmeter and for the Polish made Ashmeter were
set up on the same test rig and the samples were presented to each
instrument in turn. However, because of the failure of the detector on
the UK instrument, tests 4 and 5 were conducted using only tne Polish
Ashmeter. Tests 10 onwards were conducted using only the UK Ashmeter
because the Polish instrument was being prepared for re-installation at
Mantón Colliery.
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10
Where the calibration tests were conducted with both the UK and
Polish meters the results in Table 2 show that, with the exception of
Test 3 in which the detector on the UK meter was suspect, the level of
accuracy was approximately the same for both instruments.
2.4.3 Appraisal of Calibration Tests
A summary of the coal analysis and results of all 16 laboratory
calibration tests conducted with the Wultex Ashmeter is given in Table 2
and the calibration graphs are shown in Figures 8 to 29. With the
exceptions of Test 13, Sharlston Washed Coal, Test 15, Grimethorpe
(South Side) Untreated Coal and Test 3, Askem Blended Smalls using the
UK meter, all results show a good correlation between ash content and
count rate (Corr. coeff >0.87). The poor result for Test 3 (UK meter)
is attributed to the failing detector crystal and the low correlations
(<0.8) for Tests 13 and 15 to the highly variable iron content of ash.
Comparison of the measured calibration standard deviation values
with the theoretical values calculated from the full elemental analysis
shows a reasonable correlation, as illustrated in Figure 30. The
correlation coefficient between the measured and calculated standard
deviation was 0.853 and the standard deviation of the calculated values
with respect to the measured values was 0.31% ash.
The calibration accuracy for each test and, where appropriate, for
each instrument was also related to those characteristics of the
individual coals which were considered to have the greatest influence on
the calibration accuracy. These characteristics were:-
(a) the variability of the iron content of the coal, as measured
by the standard deviation; the greater the variability of
iron the poorer the expected accuracy.
(b) the relationship between the iron content and the ash
content, as given by the correlation coefficient; the
higher the correlation the greater the expected accuracy.
(c) the mean ash content of the coal; the higher the mean
ash the poorer the accuracy in absolute terms.
A multiple regression analysis, to 7 terms, between the measured
calibration accuracy and these three characteristics gave a very high
correlation coefficient of 0.973 and a standard deviation of 0.16% ash.
The graph of calculated calibration standard deviation from the
regression analysis against the measured standard deviation is shown in
Figure 31.
For this series of laboratory calibration tests the relationship
of the measured standard deviation with the combination of ash and iron
analysis was much closer than with the theoretical standard deviation
calculated from the full elemental analysis of the coal. The
possibility of using only the ash and iron analysis of the coal rather
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11
than the full elemental analysis to predict the probable calibration
accuracy for ash measurement would result In a considerable saving both
in time and money, and would justify further investigations with other
nucleonic ash measuring systems.
2.5 Trial Installation at Bilsthorpe Colliery
2.5.1 Consideration of Requirements for Second Trial Installation
The requirement of a minimum bed depth of 150 mm for the effective
application of the Wultex Ashmeter would considerably restrict its use
on existing conveyors in the UK where, to limit capital cost, most coal
preparation plants were equipped with narrower and faster belt conveyors
resulting in reduced belt loading per unit length and bed depths in the
order of 75-125 mm. The first trial installation at Mantón Colliery was
monitoring a single seam output and, therefore, it was considered that
the second trial installation should be set a more severe test of
monitoring a multi-seam output. A further problem which occurred at
Mantón after the initial acceptance testing was that variable quantities
of coal from neighbouring collieries were sent for treatment to Mantón
which impaired the accuracy of the Ashmeter that had been calibrated for
the single seam output at Mantón. This situation would be avoided, if
possible, for the second trial.
One means of overcoming the problem of material bed depth on
conveyors would be to install the Ashmeter on a belt feeder. Although a
considerable number of belt feeders are in use in British Coal coal
preparation plants, most are for regulating the tonnages of the washed
and untreated components of power station blends and are not handlingthe final blended product which it would be preferable to monitor.
Also, many of the existing belt feeders incorporate weigh sections and
they would have been affected by the Ashmeter profiling plough which
would still be required on a constant depth feeder to increase the
compaction and bulk density of the material being monitored and give
improved accuracy.
To find the most suitable site for the second trial installation
of the Ashmeter a specification, included in Appendix 4, was drawn up
and circulated to Area Coal Preparation Engineers in British Coal.
2.5.2 Description of Trial Site at Bilsthorpe Colliery
A number of proposed sites were inspected and the one which came
nearest to meeting the preferred conditions stated in Appendix 4 was at
Bilsthorpe Colliery in the Nottinghamshire Area. The output at
Bilsthorpe was produced in approximately equal proportions from two
seams, Parkgate and Low Main, and no other coal was treated at the
colliery.
The blending and bunkering system for power station fuel at
Bilsthorpe is shown schematically in Figure 32. The 50 mm - 0 power
station blend is prepared by the proportional addition of
38 mm - 0 untreated coal to 50 mm - 0 washed coal and filtered fines.
After mechanical mixing, samples are taken automatically to feed an
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existing NCB/AERE Phase 3A Ash Monitor, although problems were being
experienced with the feed presentation system of this monitor because of
the handlability of the product particularly after crushing below 6 mm.
The total make of power station blend is delivered to an open stockpile
over a ground hopper. When the site was initially inspected the product
was discharged from the ground hopper by a vibrating feeder, but plans
were being made to replace this arrangement with a variable speed belt
feeder which would hold a bed of coal 450 mm deep and approximately 2 m
in length and 1 m wide.
The belt feeder would discharge onto a 1050 mm belt conveyor which
elevates the product to the top of a battery of rapid-loading bunkers
where it is transferred to a tripper conveyor for distribution into the
individual bunkers. At this conveyor transfer point there was a second
automatic, traversing bucket sampler which was arranged to discharge a
sample increment at each end of its traverse. The minimum cycle time
for the sampler to complete 2 traverses was originally understood to be
40 second but was later found to be 1 minute.
The existing blending facilities at Bilsthorpe would allow the ash
content of the power station product to be intentionally varied for
short periods over a wide range of values to permit the on-site
calibration. The subsequent homogenising effect of the tripper conveyor
and the rapid-loading bunkers would tend to even out these variations
and restore the consistency of the final product.
2.5.3 Installation of the Ashmeter
The Ashmeter was supplied and installed at Bilsthorpe under a
Heads of Agreement by Wultex Machine Company in March/April 1985. It
was mounted over the coal bed on the belt feeder and, to allow access
for maintenance and belt changing, the standard supporting structure was
dispensed with and the parallelogram system was supported from the roof
of the underground chamber below the ground hopper. Some modifications
were necessary to the standard profiling plough and counterweight arms
because of the restricted space above the feeder. The feeder was fitted
with coal bed level sensors which reduced the belt speed to a creep
condition and interrupted the Ashmeter integration when the coal level
fell below normal. The sensors also activated the closing mechanism for
the source radiation shield. The feeder was completely fenced round for
radiation protection and the access for maintenance was interlocked with
the source radiation shield. Illuminated signs were provided to
indicate SOURCE EXPOSED or SOURCE SHIELDED.
2.5.4 On-site Calibration Tests
Completion of the Ashmeter installation was followed by several
days of stability tests, counting backscattered radiation from a
reference surface. Work was then started on the on-site calibration
tests by British Coal Scientific Control Laboratory, South (formerly
East Midlands Regional Laboratory).
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The calibration tests were carried out in accordance with the
procedure set out in Appendix II of the Heads of Agreement, reproduced
in Appendix 5 of this report. However, the minimum cycle time for the
automatic sampler proved to be 1 minute and the duration of each
calibration test had to be increased from 12 minutes to 19 minutes in
order to collect sufficient increments to comply with BS1017. This
extended test period provided 9 print-outs of 2 minute countrate
measurements. A total of 31 calibration tests were carried out over a 5
week period.
The results for all 31 tests, covering a range of ash content of
6.6 - 36.6% (as received), are given in Table 3, column 2 alongside the
results in column 1 of the previous laboratory calibration tests on
Bilsthorpe blended smalls. Column 3 gives the results for the
25 on-site calibration tests where the ash content lay within the same
limits as the previous laboratory tests. The quadratic regression of
ash content against Ashmeter countrate for all 31 tests gave a standard
deviation of 2.9% ash, corresponding to an accuracy for 95% confidence
limits of +5.8% ash compared with the laboratory calibration of +2.64%
ash.
The calibration accuracy of the Ashmeter was well outside the
standard of operating accuracy of +3.0% ash required by the Heads of
Agreement for the trial and it was agreed with Wultex representatives
that there was no purpose in proceeding with the trial programme until
the unsatisfactory calibration accuracy had been fully investigated.
It was considered that the poor on-site calibration accuracy must
be attributable to:
either (a) segregation on the belt feeder so that the material
being examined by the Ashmeter was not representative of the whole
product stream being sampled.
or (b) changes in the analysis of the coal being mined at
Bilsthorpe in the 12 months since the laboratory calibration tests were
conducted on the Wultex static test rig at SCL(N) and gave a calibration
accuracy (for 95% confidence limits) of +2.6% which was used as a basis
for setting the performance standards for the colliery trial.
Some size segregation was evident around the conical pile which
formed over the ground hopper but before each calibration test run a
funnel shape was allowed to form in the heap by ensuring that there was
a net withdrawal from the stockpile. This withdrawal was maintained
throughout the test so that the material being examined was mainly the
current make of blend. However, there were some reports of visual
evidence of segregation across the width of the belt feeder but the
pattern was not consistent. A quantitative investigation of the
suspected segregation on the feeder was not practicable due to the .
difficulty in obtaining properly representative samples of different
parts of the coal stream at that point. Consequently, arrangements were
made to look further at the second possible cause of the poor
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performance and to repeat the laboratory calibration tests on a second
set of coal samples.
A suite of 24 samples was collected over a 2 week period and the
laboratory calibration tests conducted using an alternative presentation
technique in addition to the method used previously. The alternative
method involved taking count readings in a five position lattice pattern
over the surface of the sample for each of two fillings of the
presentation box, compared with the previously established method of
2 count measurements for each of 5 box fillings. The alternative method
was included as possibly giving a closer simulation to the on-site
presentation and the samples were tested in an "as received" condition.
For the established presentation method the samples were 'air dried' to
allow direct comparison with the earlier laboratory calibration test.
The results of these tests are presented in Columns 4 to 7 of Table 3.
The results were evaluated for all the samples tested and also for only
those samples falling within the range of ash content of the original
tests (Column 1 ).
The calibration accuracy of the repeat laboratory calibrations
showed an appreciable deterioration from the original calibration but
was very much better than for the on-site calibration. The alternative
method of laboratory presentation with the 'as received' materials gave
a significantly higher accuracy than the previous presentation method
with the 'air dried' sample.
The results show a much lower standard deviation, or spread, of
iron in the coal for both the on-site calibration and for the repeat
laboratory calibration and this would have been expected to correspond
to an improved calibration accuracy. However, the beneficial effect of
the decreased spread of the iron content would appear to be more than
lost by the poor correlation between the iron and the ash in the coal.
The on-site calibration, having a higher iron/ash correlation than the
second laboratory calibration, would have been expected to give a level
of accuracy between the two laboratory calibrations. However, the
on-site calibration accuracy was much worse than the repeat laboratory
calibration and it must therefore be concluded that the poor on-site
calibration is not due to the chemical composition of the coal but to
other factors peculiar to the on-site monitoring conditions.
2.5.5 Shift Integration Tests
Following the failure of the Ashmeter to give a satisfactory
calibration, with short term integration periods of 20 minutes, it was
considered that it might still fulfill a useful role if an acceptable
calibration could be obtained over a shift's integration by reducing the
effect of the variations in the proportions of the two seams being mined
at Bilsthorpe. An investigation was conducted in the early part of 1986
to relate the ash content of routine shift samples to the average of the
2 minute countrate print-outs throughout the shift. The investigation
covered 28 shifts and a range of average shift ashes of 9.4% to 17.4%
but no correlation was found between the shift ash and the mean
countrate.
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A further investigation was conducted in July 1986 to attempt to
correlate the shift ash with the average countrate print-out. The
investigation covered 15 shifts, with the shift ash varying from 11.5%
to 19.0% but again there was no correlation with the average countrate.
It was therefore concluded that despite ensuring an adequate bed depth
the Ashmeter was incapable of measuring the ash content of the
50 mm - 0 blended smalls at Bilsthorpe with an acceptable level of
accuracy. The instrument was finally removed from Bilsthorpe in 1987 in
accordance with the terms and conditions of the Heads of Agreement.
2.6 Re-design of Ashmeter Electronics by SCL(N)
2.6.1 Original Polish Design
The nucleonic/electronic measuring system of the Polish designed
Ashmeter comprised three distinct units. These were:-
(a) The isotope measuring head, Figure 2, which consisted of the
radioactive source holder, designed to produce a vertically
collimated beam of radiation, and the sodium iodide
scintillation detector which produced electrical pulses
according to the intensity of the backscattered radiation and,
in turn, the ash content of the coal being tested.
(b) The power supply and amplifier unit which required locating
within 2.5 m of the measuring head. This contained the high
voltage (800 - 1600 V) generator for the scintillation detector
and a pulse pre-amplifier which performed a linear
amplification, by a factor of 100, of the electrical pulses
from the detector. An amplitude discriminator then selected
pulses within a defined range of amplitude for onward
transmission and processing.
(c) The signal processing and display unit which could be located
at a distance of up to 3000 m from the measuring head. This
unit had only limited pulse counting, processing and display
capabilities and was the main drawback of the original system.
After more than four years plant and laboratory service the
original Polish manufactured Ashmeter was becoming unreliable and
difficult to maintain. Furthermore, the limited information available
from the processing system, consisting of either counts per second or a
relatively crude conversion to ash content, was found to be inadequate
and a new and more reliable processing system, capable of providing
additional information, was considered necessary.
The UK version of the Ashmeter, manufactured by Wultex, closely
followed the Polish design except for the incorporation of a simple
printer and did not therefore satisfy the requirements of
SCL(N).
2.6.2 Re-designed System
The original isotope measuring head was retained unchanged except
for the addition of a small rotary shutter to blank off the source when
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not in use. The intermediate unit, incorporating the H.T. generator,
pulse pre-amplifier and simple pulse energy discriminator was also
retained. The re-design therefore mainly concerned the signal
processing and display unit and was undertaken by
SCL(N).
The new system, comprised three IP65 cabinets containing, in turn,
an intelligent terminal, a computing system and a power supply. The
IP65 cabinets vere chosen to combat the coal preparation environment and
to ensure the exclusion of dust and moisture.
The display cabinet, which can interface with the plant sequence
control system houses a four line, LCD display with 40 characters per
line, two 4 x 4 key pads and a simple paper strip printer for local hard
copy.
The computer cabinet contains a card frame and 9 printed circuit
boards. The boards contain the necessary electronics to interface to
plant signals such as 'belt standing' and 'low coal flow'. They also
receive signals from the isotope measuring head and drive outputs to the
display cabinet.
The power supply cabinet contains the battery support mechanism and
associated charging facilities.
2.6.3 Information Available from Re-designed System
The following information is displayed by the new LCD unit:
(i) Time-of-day
(ii) The length of the current integration period, which can be
selected by the operator in hours and minutes,
(iii) The time the current integration period ends,
(iv) The measurement of backscattered radiation in counts per
second, updated every minute,
(v) The ash content, corresponding to the counts per second
measurement, as determined by any form of calibration
equation,
(vi) The average ash content over a moving time period of
selected duration,
(vii) The average ash content from the beginning of the current
integration period to the present time,
(viii) The average ash content for the previous integration period.
The printer records the time of day and the running average ash
value, in addition to the times for conveyor belt standing and low coal
flow.
The setting of system variables, such as the Time of Day,
Integration Period and the time period for Running Average, is
facilitated by the terminal and menu driven interface on the display
terminal.
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2.7 Further Trials at Mantón Colliery
2.7.1 Description of Installation
Following the completion of the laboratory investigations at
SCL(N) the original Polish Ashmeter was re-conditioned and re-installed
at Mantón Colliery towards the end of 1986 for further on-site trials.
The Ashmeter was equipped with the new electronics package, designed by
SCL(N),
for signal processing and display.
A schematic arrangement of the blending and outloading system for
the power station fuel at Mantón Colliery is shown in Figure 33. The
blend constituents, comprising clean coal -50 mm, clean coal 25 mm - 0
and untreated coal 8 mm - 0, were held in three separate bunkers, each
being discharged by a variable speed belt feeder regulated by a blending
control system. The belt feeders delivered the constituents onto a
common conveyor and the combined product passed through a mechanical
mixer in transferring to the inclined bunker feed conveyor, with a belt
width of 1050 mm and speed of 1.65 m/s, which was housed in an enclosed
gantry. The Ashmeter was located near the tail-end of this conveyor
which delivered to the outloading bunker. The blended product was
sampled at the conveyor delivery by a chain bucket sampler which
discharged the sample increments into a small hopper from which they
were fed at a controlled rate by a belt feeder to a sample crusher and
divider to provide the final consignment sample, with the excess
returning to the product stream. The belt feeder could be reversed to
by-pass the crusher and provide occasional increments for a moisture
sample.
2.7.2 Dynamic Calibration Test Procedure
The calibration samples were collected over a period of 10 minutes
and comprised 25 increments taken at 24 second intervals using the
mechanical sampler. The samples were collected in total, after the
sample crusher and before the sample divider, and returned to SCL(N) for
preparation and analysis.
The Wultex Ashmeter was operated locally, under manual control,
and the new signal processing and display system provided a reading of
the average counts per second over the 10 minutes duration of the test.
A time lag of 11 seconds between the coal passing the Ashmeter and being
sampled had to be allowed for by starting the Ashmeter 11 seconds in
advance of the sampler and stopping 11 seconds earlier.
A minimum bed depth of approximately 90 mm had to be maintained on
the conveyor to ensure the Ashmeter continued to operate. The blend
ratio was adjusted after each test to provide a different ash level in
the product. A series of at least 20 tests was conducted to provide a
calibration between ash content and countrate.
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2.7.3 Dynamic Calibration Test Results
Two dynamic calibration tests were conducted in December 1986 and
February 1987 with the original Polish supplied, nucleonic measuring
head. A third test was conducted in October 1987 following the
replacement of the crystal in the scintillation detector but, due to an
error in the window settings, the results were invalidated. The
calibration graphs for the first and second tests are shown respectively
in Figures 34 and 35 and the results are summarised below.
Calibration Test
Dates conducted
No.
of samples
Range of Ash % (A.R.)
Mean Ash % (A.R.)
Regression Analysis
Correlation Coefficient
Standard Deviation Ash %
1
3.4.5./12/86
21
12.6 - 24.4
17.7
Linear
0.871
1.54
2
5,6,10/2/87
24
15.1 - 24.8
21.0
Linear
0.893
1.79
Comparison of these results with the plant performance test
conducted during the initial trial at Mantón, Table 1, shows an
improvement in correlation between ash content and countrate but a
reduction in calibration accuracy, particularly in Test 2, which may
have been due, in part, to deterioration in the scintillation detector.
Following the calibration the Ashraeter was used by the plant
operators to assist in controlling the quality of the blended product.
2.7.4 Train-load Integration
The loading of trains with power station blend through a single,
small capacity bunker at Mantón, rather than through rapid-loading
bunkers, made it possible to identify and sample individual train-loads.
This was the normal procedure at Mantón and it provided information on
the quality of each train-load. Following the re-installation and
calibration of the Wultex Ashmeter it was manually controlled to
integrate the ash measurement over each train-load and to provide a
print-out for comparison with the laboratory analysis.
For 114 train-loads produced in May and June 1987, ranging in ash
content from 12.3% to 21.1% the standard deviation between the average
ash content measured by the Ashmeter and the laboratory analysis was
1.73%. The failure of the detector crystal in July and problems
associated with its replacement, resulted in unreliable measurements for
several months. Following the correction of the detector problem, a
further comparison between the Ashmeter measurement and the laboratory
analysis for 237 train-loads, ranging from 11.7% to 22.6% ash, in the
four month period December 1987 to March 1988 gave a standard deviatie
of 1.64% ash.
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2.8 Further Installations
Following a change of ownership the Wultex Machine Company
terminated the licence agreement with EMAG and ceased manufacture and
support for the Ashmeter from mid-1986.
However, the Ashmeter which had been withdrawn from Bilsthorpe
Colliery was retained by British Coal and installed early in 1988 on a
weigh-feeder handling 50 mm - 0 untreated coal on the South Side Central
Coal Preparation Plant at Grimethorpe Colliery. It will be used for
controlling the blending of washed and untreated coal for power
stations. The instrument was undergoing calibration tests at the end of
this Project.
2.9 Summary
Earlier work with the Polish G2 Radiometric Ashmeter had shown
that the instrument was mechanically and electrically reliable and could
be applied with a reasonable degree of success to the continuous on-belt
monitoring of the ash content of a blended power station fuel produced
at a single seam colliery. This degree of success, however, was
conditional on the depth of the bed of coal being sufficient to ensure
total backscatter of the radiation and on the variations in coal
composition staying fairly constant. Since neither of those conditions
were likely to be met at many installations, laboratory work was
undertaken with the Wultex Ash Meter to assess the extent of these
effects.
Measurements confirmed that the accuracy of the instrument would
be affected when the coal bed depth was reduced below 200 mm and even
with the maximum compaction which could be expected to be applied to
coal on a conveyor, the effect would be significant at bed depths less
than 150 mm. As far as the UK coal industry, which generally uses
narrow, rapidly moving belts, is concerned this effect would severely
restrict its application to those few situations where low speed belt
feeders are in use.
The effect of coal composition on accuracy was assessed by
undertaking laboratory calibration trials on 16 suites of coals from a
range of sources. Results, in terms of standard deviation of ash
content about the calibration line, ranged from 0.19% to 2.31% ash. On
average, these results represent a relative accuracy (Is) of +5% , which
would be acceptable for many applications if it could be reproduced in
an on-belt situation.
A method for calculating the expected calibration standard
deviation from the total composition of the coal has been developed and
the results correlate with the measured values with an accuracy (+ls) of
0.31% ash absolute. The major factors, however, which affect the
accuracy of the calibration standard deviation are the level of ash
content, the variability of the iron content in the coal and the degree
of correlation between iron content and ash content. Using these three
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factors in an empirical relationship with the measured calibration
standard deviation shows that it is possible to predict, from a
knowledge of the ash and iron contents of the coal only, the expected
calibration accuracy to +0.16% ash absolute at one standard deviation.
An on-site trial was undertaken at Bilsthorpe Colliery, a two seam
mine,
where the meter was installed on a belt feeder outloading the
power station blend. A calibration trial comparing instrument readings,
integrated over 20 minutes, with the laboratory analysis of 31
corresponding samples of coal, taken from the coal stream by an
automatic sampler, gave a standard deviation of 2.8% ash, much higher
than the value of 1.8% obtained in static laboratory tests for the same
coal. Further laboratory tests confirmed that the larger on-site
calibration error could not be attributed to variations in coal
composition. There was visual evidence of cross-belt segregation of the
coal on the belt feeder but it was not practicable to quantify this or
the size of its contribution to the total error of the on-site
calibration. Two further trials, comparing instrument values integrated
over a full shift with the corresponding laboratory analyses, showed no
significant correlation. It was concluded that in the conditions found
at this site the Wultex Ashmeter was unable to provide a measurement of
ash content of sufficient accuracy to be of practical value to the plant
operations.
Throughout these plant trials the instrument was found to be
mechanically and electrically reliable. However, the signal processing
and display facilities of the meter were very limited and new units
based on microprocessors were designed and built to provide a wider
range of output data, including time-averaged values over
operator-selected periods of time. A modified meter was installed on
the power station fuel belt at Mantón Colliery, a single seam mine,
where dynamic calibration trials gave values of standard deviation of
1.5% ash and 1.8% ash, which compared with a static laboratory
calibration of 0.76% ash for the same coal. The long term performance
of the meter was assessed at this site by comparing the instrument
values integrated over individual train loads with average ash values
found by laboratory analysis. Two trials, covering 2 month and 4 month
periods,
gave standard deviations of 1.7% ash and 1.6% ash respectively.
The results obtained at this colliery are considered to be operationally
useful and instrument data are being used to assist in the manual
control of blending operations.
3. MAIN-STREAM ASH MONITORING - COALSCAN 3500 ASH MONITOR
The Coalscan 3500 Ash Monitor is the commercial version of the
SIROASH Low Energy Transmission (LET) gaug ed ) developed in Australia by
the Commonwealth Scientific and Industrial Research Organisation
(CSIRO).
It is designed for the continuous measurement of the ash
content of coal on a belt conveyor and is manufactured under licence by
Mineral Control Instrumentation Pty Ltd (MCI) of Adelaide.
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3.1 Principle of Ash Measurement
The ash content measurement is based on the transmission through
coal of highly collimateci beams of low and high energy gamma rays. The
absorption by the coal of the lower energy gamma rays depends on the ash
content of the coal and the weight per unit area, while the absorption
of the higher energy gamma rays depends essentially on the weight per
unit area of coal in the beam. The transmitted intensities are combined
to give ash content independent of the weight per unit area:-
Ash - Ki + K2 log(I/Io)low
log(I/Io)high
where I and Io are transmitted intensities with and without coal in the
beam and "low" and "high" refer respective to low and high energy gamma
rays. The calibration constants
K\
and K2 are found from measurements
on samples of a particular coal of known ash content. The instrument
must therefore be calibrated for each particular coal.
The low energy (60 keV) gamma radiation is provided by americium
241 and, depending on the range of coal depths being encountered, the
high energy radiation is provided at either 356 keV by barium 133 or at
660 keV by caesium 137. In practice, both the low and high energy
sources are mounted in a single source holder located below the conveyor
belt, and a single detector, with energy analysis facilities, above the
belt and resolves the transmitted intensities of the 2 different energy
levels. The arrangement of the source, collimator and detector about
the conveyor is shown in Figure 36 and the gamma radiation spectrum for
Americium and barium in Figure 37.
3.2 Description of Commercial Unit
The commercial design of the Coalscan 3500 Ashmeter, Figure 38,
comprises the following system units:-
(i) C-Frame: this houses both source and detector in precise
alignment, together with the EHT supply unit and the
pre-amplifier. The sources are housed in the lower arm of
the C-frame in a tungsten block with a fail-safe shutter.
The radiation detector, which is of the scintillation type,
is housed in the upper arm together with a thermostatically
controlled heater, the EHT supply unit and the pulse
pre-amplifier.
(ii) C-Frame Support: this is a substantial stand which is
located alongside the conveyor to provide a pivoted support
for the C-frame so that it can either be positioned over
the conveyor or swung to the side of the conveyor and
stationed on the off-belt standards holder, depending on
whether or not the belt is running.
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iii C-Frame
Actuator:
this
drives
the
C-frame
and
is
either
a
double acting pneumatic or hydraulic cylinder or a linear
electric actuator depending on the services available on
site.
iv Frame
Cabinets:
there
are
two
cabinets
mounted
directly
on
the C-frame, the first, which is thermostatically
controlled,
contains
the
Multi-Channel
Analyser
while
the
second houses the electrical terminations.
v Main Electronics Control Cabinet: this houses the control
computer,
which
handles
and
processes
all
the
signals
from
the
measuring
system,
and
the
programmable
logic
controller
PLC which controls the physical operation of the ash
monitor. The cabinet, which can be located up to 100 ■
from
the
measuring
station,
should
preferably
be
housed
in
a
protected
environment.
vi Operator Terminal: this is an RS232 terminal with a display
and
is
the
means
of
communicating
with
the
measuring
and
control systems through the main control cabinet.
vii Output Display Cabinet: this is suitable for siting in a
plant
control
room
or
plant
office
and
may
be
located
up
to
500 m from the main control cabinet. It houses a 100 m
wide, 2-pen strip chart recorder which displays both the
instantaneous
and
average
ash
content
of
the
coal.
The
instantaneous ash corresponds to the current integration
period,
typically
of
one
minute
duration.
The
average
ash
is
the
average
for
the
current
period,
e.g.,
8
hours
or
24
hours,
commencing
from
a
reference
time
of
day
or
froa
an
operator reset. This feature allows the recording of the
average
ash
content
of
the
coal
produced
during
a
particular
period.
The
display
cabinet
also
includes
a
cluster of annunciatiors which show the status of various
components in addition to high and low ash alarms.
3.3 Calibration, Operation and Standardisation
The monitor has to be calibrated for each particular application
by
measuring
the
transmitted
intensities
of
high
and
low
energy
gamma
radiation
with
coals
of
known
ash
content.
The
manufacturer
claims
that
the
instrument
can
be
calibrated
statically
in
an
off-belt
position.
It
is recommended that a set of 20 prepared samples of known analysis,
covering
the
full
range
of
ash
variation
of
the
particular
coal,
is
used.
The
coal
samples
should
each
weigh
2
kg
and
be
less
than
1
mm
particle size. They are presented to the instrument in a special sample
container and the countrates recorded. A calibration equation is
derived
from
a
regression
analysis
of
ash
content
against
the
log
countrate
ratio
and
keyed
into
the
instrument.
The
facility
to
conduct
an off-belt calibration is claimed by the manufacturers as a particular
advantage
of
the
Coalscan
3500
system
since
it
can
be
performed
with
small
samples
of
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more accurately known ash content and without the need to sample from
the coal stream.
Following calibration, a reference standard is placed in the
off-belt measuring position. In operation the monitor positions itself
over the conveyor only when it is running and whenever the belt stops
the monitor returns to the off-belt position and commences an internal
check and standardisation routine. After completing the routine the
source is shut off and the system awaits the re-starting of the belt.
The instrument only measures the ash content when the depth of
coal on the belt exceeds approximately 50 mm (depending on bulk
density).
It automatically determines when the coal layer is too thin
and stops recording. The instantaneous ash measurement provided by the
instrument is the average over a short time interval, normally 1 minute.
In some cases it may be necessary to integrate over longer periods to
allow for variations in the thickness of the conveyor belting. The
cumulative average ash content can be provided over any period
determined by the operator. The averaging procedure takes account of
the mass per unit area of coal in the measuring beam and therefore the
cumulative average ash is claimed to be a close approximation to a
tonnage weighted ash value.
3.4 Laboratory Investigations
3.4.1 Arrangements and Objectives
In view of a proposal for the trial installation of a Coalscan
3500 Ash Monitor at As kem Colliery, agreement was reached with Mineral
Control Instrumentation, the Australian manufacturers, for the loan of a
second Coalscan 3500 instrument for static laboratory evaluation at
British Coal's Scientific Control Laboratory (North).
The loan of the equipment was the subject of a Heads of Agreement
Contract covering the installation, maintenance and the programme of
test work to be carried out during the loan period which was initially
set at 6 months but later extended. The Technical Appendix to the
Agreement outlining the objectives, duration and review of the
laboratory trials is included as Appendix 6 of this report.
These trials had two main objectives which were:-
(a) to investigate fundamental factors, such as basic error in the
statistical count, the effect of changes in elemental
composition and the effect of bed depth.
(b) to investigate the suitability of the instrument to specific
applications by testing different coals in the laboratory and
to develop a calibration procedure to simulate the dynamic
operation of the monitor in practice.
The equipment, comprising items (i), (iv), (v) and (vi) of the
standard plant system was installed and commissioned at SCL(N)
early in 1986.
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3.4.2 Setting-up Procedure
The commissioning of the Coalscan 3500 Ash Monitor was carried out
in accordance with the setting-up procedure laid down in the instruction
manual and comprised the following stages : -
(i) Multi Channel Analyser (MCA)
The MCA supplied had optimum default settings for most
of its variables. However, three variables are required
to be set specifically for each installation and are the
EHT voltage for the scintillation detector and the low
and high energy levels for the Americium window. The
EHT voltage is found using a peak-seeking algorithm
contained in the MCA software. The latter two variables
are found by running another MCA software routine which
produces the energy spectrum and the energy levels are
chosen to include the main americium peak.
(it) Natural Background Correction
Under normal conditions the natural background radiation
is less than 50 counts per second and the correction
factor is set to zero. Alternatively, measurements are
taken with the sources removed and the countrates
obtained in the americium and caesium windows are used
as correction factors.
(iii) Background Stripping Factor
The countrate in the americium channel is principally
from americium gamma rays, however there is a degree of
interference due to gamma rays which originated from the
caesium source but have lost energy due to the
scattering processes. The process of removing these
degraded caesium gamma rays is called "background
stripping". The procedure involves introducing a 1-2 mm
thick sheet of lead in the beam which filters out the
americium gamma rays, without significantly reducing the
caesium countrate. The background stripping factor is
the ratio of the counts in the americium window divided
by the counts in the caesium window with the lead sheet
in place.
(iv) Dead Times and Standard Countrates
When countrates are high the electrical pulses
representing each count tend to overlap due to the
nature of the electronics employed. While a count is
being measured the counting system closes down for the
duration of the count measurement and is termed to be
'dead'. Measurement of the 'dead time' allows the
computer to make a statistical correction for the counts
received during this period.
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The Coalscan has to be set up to measure ash
independently of mass loading. To carry out this
procedure the values for the counts in the americium and
caesium windows, with no intervening samples in the
beam, are required. These values cannot be measured
directly because of the high countrates produced under
these conditions and have to be determined indirectly.
The procedure to obtain values for dead times and
standard countrate involves taking measurements of
varying attenuation using standard blocks of perspex and
glass or perspex and tin. These measurements are
processed using a computer program provided to give the
dead times and standard count rates.
(v) Log Correction Factors
The log correction factors ensure that the measured ash
is independent of mass per unit area at high and low
belt loadings.
At low mass per unit area the instrument response is
non-linear. To cater for this condition a linear
approximation is employed which is used as a sub-routine
to modify the ash estimate when the Caesium countrates
are above a predetermined value. At very low mass per
unit area, equivalent to less than about 50 mm depth of
coal,
this approximation is unsatisfactory and the
instrument is set to reject such readings.
At high belt loadings, i.e.,low caesium countrates, a
theoretically calculated factor is applied.
(vi) Sample Container Factors
During off-belt calibration and standardisation it is
necessary to measure the countrates without attenuation
due to the sample container. This value cannot be
measured directly because of the high countrates
involved and is obtained indirectly by measuring a set
of standard blocks with and without the sample
container.
(vii) Calibration Standard
A calibration standard is made from three or four
standard blocks and kept separately. The Coalscan 3500
uses the measurements it obtains from this off-belt
calibration standard to correct for source decay and any
drift in the measuring equipment.
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3.4.3 Results
(i) Basic Data
(i)(a) Statistical Counting Error
The Coalscan 3500 calculates an ash value every
50 milliseconds which is averaged over the number of
50 millisecond periods in the sampling time. In a series
of tests using the calibration standard the log ratio was
measured over 2, 4, 8, 15, 30 and 60 second periods. Two
further series of tests were conducted over 60, 120, 300
and 600 second periods. The results of all three series,
made up of tests 1-6, 7-10 and 11-14 respectively, are
given in Table 4 and Figure 39.
The two series of tests 7-10 and 11-14 show good
repeatability in terms of standard deviation. The mean
log ratio, however, is different and arose because the
instrument had not been standardising properly due to
software errors in the program. According to the
manufacturers of Coalscan 3500 a typical coal would give
a calibration gradient of between 0.01 and 0.03 log ratio
units per 1 percent ash, depending on ash composition.
For a counting period of 300 seconds the standard
deviation of the log ratio is 0.0017 and hence the
contribution of the counting statistics to the overall
precision of the ash estimate would be less than 0.1%
(absolute).
On standardising, the computer checks that the countrates
are within an acceptable band, determined by the user.
If the readings are outside this band the standards are
not revised and the readings are assumed to be caused by
system errors, e.g., incorrect alignment of the source,
standards block and detector. However, because of the
natural decay of the sources the standards countrate
gradually reduces and on this occasion it fell below the
lower acceptable limit. Adjustment of the limit brought
the standards log ratio back to normal. On the later
version of the software the band width was set
automatically as a percentage of the last valid reading
and would therefore take account of normal decay.
(i)(b) Coal Thickness
The log correction factors, described in the setting-up
procedure (3.4.2(v)), are designed to take account of
variations at deep and shallow coal depths. Measurements
made during the initial setting-up procedure to check
that compensation occurred are given in Table 5. This
table shows that the log ratio values are practically
constant over the wide range of attenuation equivalent to
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a 4:1 ratio in bed thickness. The variation in log ratio
values is no greater than the counting statistics error
on a 300 second counting period (equivalent to 0.1% ash).
(i)(c) Chemical Composition
To investigate the effect on the Coalscan 3500 of
variations in the chemical composition of the coal ash, a
series of tests were conducted in which increasing
amounts of chemically pure reagents were added
invididually to an air-dried coal sample crushed to minus
212 microns. The reagents used were magnetite
(Fe304),
calcium carbonate (CaC0
3
) and kaolin (AI2O32SÌO22H2O).
Two readings of 5 minutes each were taken for three fills
of the container with each level of reagent addition.
The total sample weight was approximately 800 g.
The results of the tests with each of the reagents is
given in Tables 6, 7 and 8. The percentage addition of
each reagent was converted to represent the oxides
normally present in ash, i.e. % Fe3Û4 converted to %
F6203, % Ca CO3 converted to % CaO, % AI2O32SÌO22H2O
converted to % AI2O32SÌO2. The addition of each reagent
was continued until the corresponding oxide comprised
approximately 10% of the sample. For a typical coal, an
increase on log ratio of 0.012 corresponds to an increase
in ash content of 1%. Using this relationship the
increase in the log ratio measurement above that of the
original coal sample, for each level of reagent addition,
was converted to the corresponding increase in ash
content. This content was plotted against the equivalent
oxide addition for each reagent in Figure 40.
The graph shows that the effect of AI2O32SÌO2 corresponds
closely to that of typical ash. It also shows the
considerable effect that variations in iron would have on
the Coalscan measurement. For a typical coal a 1%
increase in Fe2Û3 would give rise to a 6% increase in the
Coalscan measurement of ash content. Where the
instrument is to be used on a coal which has been cleaned
using a magnetite dense medium process, particular
attention must be paid to the rinsing of the coal leaving
the process to ensure efficient removal of adhering
magnetite. The effect of variations in calcium is
approximately half that of the iron.
(ii) Accuracy of Ash Measurement
(ii)(a) Samples - 212 Microns
Suites of coal samples were collected from several
collieries, where Coalscan applications were considered
possible, and prepared to provide air-dried test samples
with a top size of 212 microns. Each sample was
presented to the Coalscan instrument 5 times, each time
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for 5 minutes. Samples were mixed between
presentations. The samples were then analysed for ash
content and a linear regression of ash content against
log ratio calculated. The results of these tests are
summarised in Table 9 and the calibration graphs are
shown in Figures 41 to 45.
The Askern blended small coal gave a very good
calibration over quite a wide ash range and was
confirmed by the second test over a slightly reduced ash
range. By comparison, the first test with Gascoigne
Wood untreated small coal gave a poor calibration over a
fairly limited ash range of 13% . The calibration
deteriorated considerably when the ash range was
increased to 23%. The calibration for the South Side
(Grimethorpe) blended small coal was only moderately
good considering the quite narrow ash range.
(ii)(b) Samples - 1 mm
Sub-samples of the second suite of Askern blended small
samples were also tested at the slightly coarser size of
1 mm - 0 and the results are also included in Table 9,
Test 7, and Figure 46. As was expected, the calibration
accuracy was slightly worse than with the samples
reduced below 212 microns but the coarser material was
easier to handle.
Performing calibration tests under laboratory conditions
with samples reduced to such fine sizes must be regarded
as producing the most favourable results. Testing using
coarser sizes and on a colliery site could be expected
to give poorer results. On this basis of the coals
tested the only potentially suitable application was
Askern blended smalls.
(iii)(c) Samples 25 mm - 3.18 mm
A further laboratory calibration test was conducted on
Askern coal with samples prepared from known proportions
of washed smalls and raw smalls. Gross samples of
washed smalls and raw smalls were collected and air
dried. The fines below 3.18 mm in size were removed
from both samples to give products 25 mm - 3.18 mm which
were representatively sub-sampled and analysed for ash
content. Limiting the bottom size of the samples to
3.18 mm would avoid the migration of the fine material
during handling and thereby minimise bulk density
variations. Nine samples of 25 kg were prepared,
ranging from washed coal to raw coal with progressively
reducing proportions of washed coal and increasing
proportions of raw coal. The air dried ash content
ranged from 6.2% to 41.8%. The samples filled the
sample box, which was approximately 450 mm long, 300 mm
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wide and 160 mm deep, and was presented to the Coalscan
instrument such that 12 measurements were made at 25 mm
intervals along the centre line of the box over a
distance of 275 mm. Similar readings were also taken
along two lines at one quarter and three quarters of the
width of the presentation box to give three parallel
lines of test measurements. This procedure was repeated
for the same sample after emptying, re-mixing and
re-filling the box. The sample was then analysed for
ash content. The whole test routine was repeated for
each of the 9 samples, and a summary of the results is
given in Table 10.
The linear regression for the mean of all 72
measurements for both fillings of the presentation
container against the laboratory ash for each sample,
see Figure 47, gave a calibration standard deviation of
0.83% ash
(A.D.).
Although the upper size limit of the
material was 25 mm, the very intensive examination of
these samples gave a result which was comparable with
results from previous laboratory tests with Askem
blended coal reduced to finer sizes (Table 9 ). These
gave standard deviations of 0.64% ash (A.D.) and 0.59%
ash (A.R.) for minus 212 micron material and 0.80% ash
(A.R.) for minus 1 mm material.
The mean standard deviation for the linear regression of
each individual line of measurements from both box
fillings was 1.75% ash
(A.D.).
This pattern of
measurements, comprising a single row of closely spaced
spot measurements, could be considered to simulate the
continuous, single-line measurement made by an on-belt
Coalscan installation.
On the basis of the results of this series of laboratory
tests the standard deviation for an on-belt calibration
would be expected to be 2-1 times the standard deviation
for an off-belt, static calibration. This relationship
will be investigated further in the appraisal of the
results of the Coalscan trial at Askern Colliery.
3.5 On-Line Trials at Askern Colliery
3.5.1 Purchase Agreement and Installation
Askern Colliery, in the South Yorkshire Area of British
Coal,
was
chosen for the first on-line trial of a Coalscan 3500 ash monitor which
was purchased under a Heads of Agreement Contract from Magco Ltd., the
recently appointed UK agents for
M.C.I.,
the Australian manufacturers.
The instrument was installed by Magco Ltd. in March/April 1986 to
monitor the 25 mm - 0 blended power station fuel on the final conveyor
feeding the rapid-loading bunkers.
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The Heads of Agreement Contract document included the acceptance
criteria for the trial, see Appendix 7, which covered both the measuring
performance and reliability of the equipment. Following satisfactory
on-site calibration of the instrument, the performance criteria required
that at least 57 out of 60 tests, each conducted over an 8 minute
sampling period, should give ash measurements within +2.5% of the
laboratory ash analysis. The criteria for reliability was that the
instrument should operate continuously for a period of 60 workings days
without operational, mechanical or electrical problems and a continuous
period of 120 working days without the replacement of mechanical or
electrical components.
A schematic arrangement of the installation at the Askero coal
preparation plant is included in Figure 48. The plant, which has a
capacity of 500 t/h, produces 200/250 t/h of power station fuel. Only
part of the 25 mm - 0 raw coal is cleaned, using dense medium Vorsyls
and froth flotation, and the remainder is kept untreated. The resulting
washed smalls and untreated smalls are blended using a system of
blending bunkers and weigh feeders to produce a 25 mm - 0 power station
fuel with an ash content around 15% . An automatic traversing bucket
sampler at the discharge of the blend conveyor provides the feed to a
NCB/AERE Phase 3A ash monitor, with regularly spaced increments being
diverted to a moisture sample. From the blend conveyor the mixture of
washed and untreated smalls falls through a vertical mixer and is
delivered sideways to the 1050 mm wide inclined belt conveyor feeding
the rapid-loading bunkers.
The Coalscan instrument was installed a short distance along the
inclined bunker feed conveyor at a position adjacent to an existing area
of open platform. Some modifications were necessary to the height and
spacing of the troughing idlers to accommodate the lower arm of the Ci
frarne below the belt. Fencing was provided around the Coalscan unit for
radiation protection. The main electronics control cabinet was sited in
the plant motor control centre and the Output Display Cabinet located in
the central control room.
3.5.2 Commissioning and Calibration of Coalscan 3500
3.5.2.1 Preparatory Investigations
A suite of 20 samples of Askem power station fuel (blended
smalls) had previously been used for laboratory calibration trials with
the Wultex Radiometric Ashmeter, Table 2, Test 3, and had been analysed
for ash composition. The calibration standard deviation attributable to
the elemental compositon had been calculated as 0.84% ash and the
performance criteria for the Heads of Agreement was based on this
evaluation.
A further suite of 20 samples of As kem 25 mm - 0 blended smalls
was collected in March 1986 and, after air drying and crushing to minus
212 microns, they were tested on the Coalscan 3500 ash monitor which had
already been set up in the laboratory at
SCL(N),
Table 9, Test 1. The
calibration standard deviation for these samples was found to be 0.64%
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ash (A.D.). thereby tending to confirm that an accuracy of +2.5% ash
should be within the capabilities of the on-line installation at Askem.
3.5.2.2
Commissioning and Preliminary Calibration
The final installation and commissioning of the equipment at
Askem was supervised by an engineering representative from the
Australian manufacturers and was completed towards the end of April,
1986. To test the system, an off-belt calibration was performed on
26-27 April using the suite of samples of As kem blended smalls reduced
to minus 212 microns and previously tested on the laboratory Coalscan
instrument, as described above. The plant off-belt calibration,
Table 11, Test 0 and Figure 49, gave a calibration standard deviation of
0.99% ash (A.D.) compared with the laboratory result of 0.64% ash
(A.D.).
3.5.2.3 On-line Dynamic Calibrations 1 to 5
The Heads of Agreement Contract specified that the instrument
would be calibrated on-belt over a range of ash content of 10-26% and
over a minimum of 30 eight minute sampling periods. A representative
2 kg sub-sample, crushed to minus 1 mm or less, would be prepared from
each calibration sample and used to perform an off-belt calibration.
The manufacturer would then have the option of entering either the
on-belt or off-belt calibration into the instrument for the performance
testing.
The first on-belt dynamic calibration was carried out on 30th
April and 1st May 1986 with 12 acceptable samples being collected on the
first day and 17 on the second day giving a total of 29 samples for
evaluation. Regression analysis of the results gave a calibration
standard deviation of 1.51% ash (A.R.), Table 11, Figure 50. The minus
212 micron sub-samples obtained from the dynamic calibration samples
were used to perform an off-belt calibration which gave a calibration
standard deviation of 0.85% ash (A.D.), Table 11, Figure 51. The
on-belt calibration standard deviation of 1.51% ash would produce an
accuracy of ash measurement (2s) of +3.02% (A.R.) which was well outside
the required accuracy of +2.5%. The off-belt calibration accuracy of
+1.7% indicated that the errors in the on-belt calibration contained a
significant contribution due to factors other than coal composition.
After examining these results the reaction of the manufacturer was
two-fold:-
(i) the larger errors had occurred at either high or low flow
rates as indicated by the caesium countrate,
(ii) the instrument had not had sufficient time to standardise
after being switched on.
It was therefore decided that a second dynamic calibration should
be carried out after the instrument had again been set up and the
standard countrate stabilised.
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The second dynamic calibration commenced on 16th May 1986 when 12
acceptable samples were collected. This calibration exercise had,
however, to be abandoned when the Hagco representative was unable to
attend due to illness. A regression analysis was performed on the 12
samples collected and this gave a calibration standard deviation of
0.97% ash
(A.R.).
The trial suffered a further delay when the electric actuator,
controlling the movement of the C- frame, burnt out at the end of Hay
1986 and had to be replaced in early June. At the same time, Magco
installed a new version of the computer software and, following this, a
third dynamic calibration was carried out on 4-6th June 1986 when 23
samples were collected. The regression analysis gave a calibration
standard deviation of 1.76% ash
(A.R.),
Table 11, Figure 52.
The Australian manufacturers, MCI, were sent all the available
data and information for investigation and they discovered that an error
had occurred in entering the software into the instrument such that a
variable had been wrongly signed. This variable was the slope of the
flowrate correction and the effect had been to exaggerate errors at low
material flowrates.
An MCI representative came to the UK towards the end of September
1986 to discuss the progress of the trial and it was agreed to fit new
software. The comparatively low flowrates and consequent shallow bed
depths,
which were at the lower end of the range for the caesium source,
was considered to have contributed to the poorer calibrations. It was
therefore agreed to replace the caesium source with a lower energy
barium source which would be more sensitive at low flowrates.
After again setting up the instrument a fourth dynamic calibration
was conducted from 30th September to 2nd October 1986 when a total of 21
samples were taken. A regression analysis of the results gave a
calibration standard deviation of 1.39% ash (A.R.), Table 11, Figure S3.
Although this was an improvement on the third dynamic calibration it
would still not meet the accuracy requirements of the Heads of Agreement
Contract.
A fifth dynamic calibration was therefore undertaken on the 13th
and 14th November 1986 when a total of 22 samples were taken. The
regression analysis gave a calibration standard deviation of 1.39% ash
(A.R.),
Table 11, Figure 54. Although this gave a similar outcome to
the fourth calibration, when the two sets of data were combined, the
calibration standard deviation increased to 1.87% ash (A.R.).
3.5.3 Investigation of Segregation on Belt
One possible reason for the worse than expected calibration
results was that there was substantial variation in the coal quality
across the belt. A visual examination of the material on the belt prior
to the Coalscan installation revealed some size segregation but it had
not been considered significant. A series of tests were conducted in
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which the Coalscan measuring head moved from one position to another
across the width of the belt, remaining for a period of 96 seconds in
each position. Five separate tests were carried out on the 21st October
1986 over periods ranging from approximately 15 to 100 minutes. A
further test was conducted on 19th December 1986 with the Bretby
vertical mixer inoperative. For the purpose of these tests the fifth
calibration was entered into the instrument to provide readings directly
in terms of ash content. The results of all six tests are given below:-
Mean ash content readings at two positions across the belt
Position A Position B
Test Mean Mean
Ash % (A.R.) Ash % (A.R.)
1 20.64 16.18
2 19.94 15.60
3 20.72 16.644 16.92 15.05
5 17.40 14.83
Average 19.12 15.66
A statistical analysis showed that the difference in the mean ash
contents was significant in Test 3 and highly significant in Tests 1, 2,
4 and 5. In all five tests the mean ash content was higher at positon A
than position B. This result confirmed the presence of segregation with
respect to ash content across the belt.
Following these tests,
M.C.I,
decided that the C- frame, which had
maintained a fixed position over the belt, should be made to oscillate
across the belt with an amplitude of about 200 mm and a period of about
18 seconds. To achieve this oscillation the electric actuator would be
replaced by a hydraulic ram and power pack.
There was a further delay in implementing this modification and
the oscillating head was not installed until early April 1987.
3.5.4 Further Dynamic Calibrations and Investigations
The sixth dynamic calibration, using the oscillating C- frame, was
conducted over 4 days in mid-April 1987, and a total of 32 samples were
collected. The regression analysis gave a calibration standard
deviation of 1.56% ash
(A.R.),
Table 11, Figure 55. The oscillating C-
frame had therefore failed to produce any improvement in the calibration
accuracy.
A test was then conducted using the oscillating C- frame to
investigate further the variation of ash content across the belt. With
the measuring head oscillating over a 200 mm band over a period of about
18 seconds, countrate measurements were recorded every 2 seconds over a
period of 13 minutes. The pattern of variation of barium countrates
against time, Figure 56, follows the 18 second period of oscillation and
shows a progressive reduction in barium countrate, corresponding to an
increase in belt loading, from one side of the measuring band to the
other. The results were also grouped into ranges of decreasing barium
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countrate and the mean ash content was calculated for each range,
Table 12. The calculated ash contents were plotted against the mean
barium countrate for each of the ranges In Figure 57, and this provides
an approximate indication of the variation of ash across that section of
the belt traversed by the measuring head.
3.5.5 Performance Test
Although the level of calibration standard deviation, which had so
far been achieved from the on-site dynamic calibrations, had not reached
the level of accuracy, for 95 confidence limits, (2s), of +2.5
required by the Heads of Agreement for the trial, it was never-the-less
decided to proceed with the performance testing during May and June
1987.
The performance testing was undertaken on two days a week,
alternating between Tuesday and Thursday one week and Wednesday and
Friday the following week. Up to 9 samples a day of the blended smalls
were taken, in the same way as for the calibration procedure, by using
the automatic sampler to collect a minimum of 35 increments over a
period of about minutes. The samples were analysed for ash content
for comparison with the Coalscan measurements. The performance tests
were carried out under normal plant operating conditions, with no
deliberate variations to the composition and ash content of the blended
smalls.
Because no satisfactory calibration equation had been obtained
for the Coalscan instrument the output was given in log ratio units
which could be converted to ash content retrospectively.
A regression analysis of the results of the 57 performance tests,
which all fell within a narrow range of ash content of 10.4 - 16.1
(A.R.),
gave a standard deviation of 1.03 ash
(A.R.),
Table 11,
Figure 58 . However, the coefficient of 0.617 showed only a poor
correlation for the tests, and the comparatively low value of standard
deviation was due to the narrow range of ash content of only 5.7
encountered during the tests. When the calibration equations derived
from the results of the sixth dynamic calibration test, in total and for
individual day s samples, were applied to the log ratio measurements
obtained from the performance tests the number of performance test
samples falling outside the acceptable limits of +2.5 ash were as given
below.
Evaluation of performance test results
6th Dynamic Calibration Performance Test
Sample Range of Std. Dev. No of samples
outside
Nos Ash (A.R.) Ash (A.R.) +2.5 ash
limits
7
2
8
23
1 ■
1 ■
1 3 •
2 4
■
■ 32
• 1 2
■ 2 3
■
32
8 . 9 ■
1 0 . 8 ■
8 . 9 ■
1 2 . 7
■
• 2 4 . 7
■ 2 1 . 1
■ 2 1 . 3
■
2 4 . 7
1 . 6 7
1 . 1 5
1 . 7 9
2 . 7 5
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The Heads of Agreement Contract required that the calibration of
the instrument was based on a minimum of 30 samples but it is evident
from the above data that if the calibration samples were collected over
a number of days the calibration standard deviation for the individual
days could vary considerably on this application.
3.5.6 Sampling Precision
An exercise was carried out to determine the contribution of the
sampling error to the calibration standard deviation. The samples were
taken, prepared and analysed using the same procedure as for the dynamic
calibration tests except that the sample increments were placed
alternately into sub-samples A and B. The results from 14 pairs of
increments was a sampling precision (2s) of +1.02% ash which was in line
with British Coal normal sampling precision.
This result was applied to the fourth dynamic calibration test
which had given the lowest standard deviation:-
(overall precision)2 - (sampling precision)2 + (Coalscan precision)2
1.39
2
- 0.51
2
+ (Coalscan precision)
2
Coalscan precision - 1.29% ash at 1 standard deviation
Having taken into account the sampling precision the accuracy of
the Coalscan instrument was still outside the acceptance requirements.
3.5.7 Further Investigation of Cross-belt Segregation
The lack of improvement in the accuracy of the Coalscan since the
installation of the oscillating head mechanism in April 1987 suggested
that the instrument was not examining a representative proportion of the
coal on the conveyor due to cross-belt segregation and the uneven
distribution of material on the belt. The scanning range of the
measuring head across the belt had been Increased but without any
improvement in results. Finally, in January 1988, a plough was attached
to the conveyor sideplate, on the opposite side of the belt to the C-
frame support, in an attempt to produce a more uniform distribution of
coal on the belt.
A series of ten tests was conducted to investigate cross-belt
segregation and the effect this might be having on the performance of
the Coalscan instrument. Countrates were recorded every 3 seconds as
the measuring head was traversing the bed, the profile of which was
modified by alterations to the plough position and the flowrate. A
computer plot of barium countrate, indicating material bed depth, and
computed ash content against time was produced for each test and
examined for evidence of segregation. The plots showed certain
inconsistencies and two further tests were devised to examine them
further.
In the first test, Test 11, the conveyor was kept stationary and a
coal sample, crushed to minus 1 mm and well mixed, was spread evenly on
the belt. The measuring head was moved backwards and forwards across
the belt with the traversing system under manual control. The plot of
barium countrate and computed ash content against time, Figure 59,
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showed a sudden, large reduction in ash content and a lower barium
countrate with the measuring head in the extended position, towards the
far side of the belt. The chart also showed a longer time for the
outward travel of the measuring head and a shorter return time
indicating that the instrument was traversing the belt with different
speeds for outward and return travel.
In the final test, Test 12, the radiation absorbers, used for
the off-belt standardisation procedure, were secured to the underside of
the detector and with the conveyor running empty, the measuring head
traversed the belt with a cycle time of 108 seconds. The plot of barium
and americium countrates and computed ash content is shown in Figure 60.
The chart shows sudden increases in both barium and americium countrates
corresponding to a sharp fall in the ash content with the measuring head
in the extended position, at the far side of the belt. This effect was
found to correspond with a longitudinal section of the belt where the
outer cover was badly worn.
The following conclusions were drawn from this series of tests:-
(i) the apparent low ashes were mainly due to factors other
than just cross-belt segregation,
(ii) there was a section of the transverse scan width which was
giving rise to unrepresentative results and this seemed to
correspond to a section of the belt where the plastic
cover was worn,
(iii) the effect did not seem to vary significantly with
belt loading,
(iv) the scan cycle time was varying with time and confirming
previous experience.
The results of these cross-belt segregation tests were reported in
full to the manufacturer and a representative from MCI visited the
Askem installation from 9th to 12th February 1988 to investigate the
problem. The scan width was reduced from 200 mm to approximately 140 mm
to ensure that the measuring head was confined to a section of the belt
in consistently good condition. The instrument settings were also
examined and corrected where necessary, prior to a further dynamic
calibration test.
3.5.8 Seventh Dynamic Calibration Test
This test was carried out on the 14, 16 and 17th March 1988 when
7,
15 and 8 samples and measurements, respectively were taken. The
sample increments were collected at 16 second intervals over a period of
9 minutes 36 seconds, which corresponded to six complete circuits of the
conveyor belt. The odd and even increments were kept separate to enable
the sampling precision to be determined from the subsequent analysis.
whilst the samples were being collected the tracking of the conveyor was
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monitored by taking measurements from a datum to the edge of the belt.
The belt factors were also checked before and after the calibration
test.
The samples were prepared and analysed for moisture, ash and
elemental ash composition. The standard deviation for the 7th dynamic
calibration, Table 11, Figure 61, was found to be 1.7% ash (A.R.) and
the sampling precision was calculated at 1.2% ash at the 95% confidence
level.
A static calibration was also conducted on-site on 29 and 30 March
1988 with approximately 1 kg of each sample, reduced to minus
212 micron, and the standard deviation, Table 11, Figure 62, was found
to be 0.9% ash (A.D.).
The outcome of this calibration test was considered in relation to
the following factors : -
(i) Belt factor - representative of the attenuation due to the
belt and used by the instrument to determine the radiation
intensities at the underside of the coal bed. Measurements
of the belt factor immediately before and after the dynamic
test were very similar to those obtained by MCI when setting
up the instrument a month earlier and therefore no
significant changes had taken place.
(ii) Belt drift - the lateral movement of the belt relative to
the measuring head which may occur as the belt is running,
particularly under load. During the setting up by MCI the
mean position of the belt edge from the datum was 80 mm and
the scan width was adjusted to accommodate 25 mm movement
either way without significantly affecting the belt factor,
i.e. the belt edge to datum could vary between 55 and
105 mm. The measurements taken during the test were within
these limits.
(iii) Iron content - the iron oxide in the ash and the ash % for
this test is compared below with the available analysis from
previous dynamic tests.
Calibration Test
1st Dynamic
4th Dynamic
6th Dynamic
7th Dynamic
Ash
Mean
16.4
22.2
17.9
19.1
% (A.R.)
Std. Dev.
4.7
5.1
4.7
4.2
Fe203
Mean
11.4
10.7
11.5
13.4
in Ash
Std. :
2.4
1.7
2.2
2.4
Dev
Although the iron in ash is slightly higher than previously
encountered the standard deviation is similar to previous
dynamic calibration tests and no significant change has
occurred in elemental composition from the original analysis
submitted to the manufacturers.
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(iv) Errors - the overall error In ash measurement for the
installation could be attributed to the following sources : -
(a) Coal composition - the error attributable to variation in
coal composition can be taken as the standard deviation from
the static calibration, i.e. 0.9% ash.
(b) Sampling - the error due to sampling can be taken as the
precision of sampling, i.e. 0.6% ash at 1 standard
deviation, which is similar to a previous estimate and in
line with operational experience.
(c) Moisture - the error due to moisture was taken as 0.5% ash
at 1 standard deviation in accordance with information
received from CIRSO, Australia.
(d) Residual - that error which remains unexplained after
accounting for all other known sources of error.
This can be calculated from the known errors as follows,
where S is the standard deviation:-
(S
overall)
2
- (S
coal)
2
+ (S
sampling)
2
+ (S
moisture)
2
+ (S residual)
2
(1.7)2 - (0.9)2 + (0.6)2 +
(0.5)
2
+ (S
residual)
2
S residual - 1.2% ash
The residual error is therefore 1.2% ash and represents half
the overall measured variance. If the residual error could
be eliminated, the best achievable error of the Coalscan at
Askem would be : -
(S best
overall)
2
- (S
coal)
2
+ (S sampling)
2
+
(S moisture)
2
- (0.9)
2
+ (0.6)
2
+ (0.5)
2
S best overall - 1.2% ash
3.5.9 Comparison of Static and Dynamic Calibrations
It was originally intended, as stated in the Heads of Agreement
Contract, that the on-belt dynamic calibration test would be followed by
an off-belt static calibration using part of the laboratory sample from
the dynamic test. However, it was not anticipated that it would be
necessary to repeat the dynamic calibration so many times and, because
of the additional work involved the original procedure, was only
followed in the case of the first and seventh calibration but, in
addition, static calibrations were conducted with the laboratory
Coalscan instrument on the samples from the fourth dynamic test at -1 mm
and -212 micron sizes. The results of the dynamic and static
calibrations for these tests are summarised below with the dynamic
calibration converted to an air dried basis to enable a comparison of
accuracy to be made on a common basis. The value of standard deviation
used for Test 4
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4
7
1.51
1.39
1.70
1.70
1.57
1.92
0.85
0.70
0.91
Mean Ratio
3?
Is derived from the mean of the variances for the two tests conducted at
different particle sizes.
Coalscan 3500 Ash Monitor Calibrations
Dynamic Static Ratio
Test Std. Dev. Std. Dev. Std. Dev. Dynamic Std. Dev. (A.D.)
% Ash (A.R.) % Ash (A.D.) % Ash (A.D.) Static Std. Dev. (A.D.)
2.0 : 1
2.24 : 1
2.11 : 1
2.12 : 1
The mean ratio of dynamic to static calibration accuracy of
2.12 : 1 compares with the ratio of 2.1:1 given by the dynamic simulation
tests with the laboratory Coalscan instrument, Table 10, between the
calibration accuracy from the comprehensive examination of samples and
from a single row of measurements. This simulation technique warrants
further investigation as a possible means of predicting on-line
performance from laboratory testing.
3.5.10 Shift Integration Performance and Comparison with
Phase 3A Ash Monitor
Following the failure of the Coalscan 3500 to meet fully the
required level of accuracy in the performance tests conducted over short
integration periods of about 10 minutes, two series of tests were
conducted to investigate the accuracy of the instrument with full shift
integration and in the second series to compare the performance with a
Phase 3A ash monitor. The calibration derived from the performance test
was entered into the Coalscan instrument and the integration period set
to correspond to the shift sampling period.
In the first series of tests the integrated ash measurement was
compared with the laboratory shift analysis for a total of 99 shifts
during the latter part of 1987. A summary of the results is given
below:-
No of shifts
Range of ash % (A.R.)
Mean ash % (A.R.)
Standard deviation
ash % (A.R.)
Laboratory
Shift Analysis
99
10.9 - 20.3
15.1
1.72
Coalscan
Shift Integration
99
11.5 - 16.7
13.3
1.0
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Correlation coefficient
Standard deviation % ash
Calibration
0.
1.
617
03
Shift Integration
0.71
0.71
From the above results the Coalscan instrument showed much less
variability in the ash measurement than the laboratory analysis and also
a mean bias of
-1.8%.
The correlation between the Coalscan and the
laboratory analysis was not particularly good and the limited range of
ash variation resulted in a comparatively low value of standard
deviation. The relationship is shown graphically in Figure 63.
The second series of shift integration tests, including the
integrated ash measurement from the existing NCB/AERE Phase 3A ash
monitor, was conducted over 108 shifts between January and June 1988.
The Phase 3A monitor examined the total sample taken automatically from
the production stream and crushed below 5 mm. The laboratory sample was
obtained by sample division after the Phase 3A monitor. The results of
this series of tests are summarised below:-
Laboratory
Analysis
Coalscan
Integration
Phase 3A
Integration
No.
of shifts
Minimum ash % (A.R.)
Maximum ash % (A.R.)
Mean ash % (A.R.)
Std dev ash % (A.R.)
108
11.9
19.3
15.05
104
11.9
19.3
15.04
108
11.5
21.4
16.1
104
11.5
21.4
16.15
1.53 1.55
1.66 1.66
108
10.1
21.9
16.04
1.72
104
12.0
21.3
16.05
1.36
Coalscan 3500 Ash Monitor
Correlation Coefficient
Standard deviation ash %
Phase 3A Ash Monitor
Correlation Coefficient
Standard deviation ash %
Calibration
0.892
1.70
Calibration
0.98
0.84
Shift Integration
108 shifts 104 shifts
0.266 0.290
1.61 1.59
Shift Integration
108 shifts 104 shifts
0.398 0.629
1.59 1.06
The Coalscan and the Phase 3A both showed slightly more
variability in the integrated ash measurement than the laboratory
analysis over the 108 shifts. The Coalscan gave a mean bias of -1-1.05%
and the Phase 3A a mean bias of +0.99% . The correlation between the
shift integration and the laboratory ash for both the Coalscan and the
Phase 3A for the 108 shifts was extremely poor and the standard
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deviation for the Phase 3A was much worse than would have been expected
from past experience.
The Phase 3A results showed two very low measurements around 6-7%
below the laboratory ash and also two very high measurements between
6-8% above the laboratory ash. Although there was no record of any
special circumstances to account for these large differences it was
considered that they were the result of some abnormal condition and were
well outside the range of error normally experienced with the Phase 3A
ash monitor. Since the standard deviation was also much worse than
normally achieved with this instrument, and with the calibration value,
the performance of the Phase 3A was also assessed on the basis of 104
shifts. This gave a significant increase in the correlation coefficient
and also a substantial improvement in the standard deviation to a level
nearer to that normally associated with this instrument. The
relationship between the shift integration for each instrument and the
laboratory shift analysis is shown in Figures 64 and 65.
The difference between the Coalscan measurement and the laboratory
ash, for both series of tests, and between the Phase 3A measurement and
the laboratory ash have been plotted in Figures 66, 67 and 68. In the
first series of tests the Coalscan shows a pronounced drift away from
calibration in a negative direction from an initial bias of around -0.7%
to -2.8% after 99 shifts and suggests some instability in the
instrument. In the second series of tests the Coalscan showed a
pronounced positive drift in bias from an initial bias of -1.2% to a
final figure, after 108 shifts, of +3.2%. This drift tended to confirm
instability in the Coalscan system. The plot of the difference between
the Phase 3A measurement and the laboratory ash showed an almost
constant bias of around 1% over the period, and suggested a more stable
instrument than the Coalscan.
In order to make a strict comparison of the performances of the
Coalscan 3500 and the Phase 3A ash monitor on the basis of instrument
error (Si) only, it is necessary to take recognition of the errors which
arise in the sampling (Ss), sample preparation (Sp) and analysis (Sa) of
the laboratory samples to which they are compared. Both instruments are
compared to the same laboratory sample but since the instruments are
located at different positions in the flow scheme, Figure 48, the
actual measured standard deviations (Sm) reflect the errors which arise
in the determination of the laboratory value to different degrees.
(Sm)2 - (Si)
2
+ (Ss)
2
+ (Sp)
2
+ (Sa)
2
In the case of the Coalscan 3500 Sm includes all the errors from
the determination of the laboratory value (Ss + Sp +
Sa).
Previous
tests at As kem had shown that these errors had a combined value of
0.51% ash.
Thus (Si)
2
- (Sm)
2
- (Ss + Sp + Sa )
2
-
(1.59)
2
-
(0.51)
2
Hence Coalscan Si - 1.51 % ash
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In the case of the Phase 3A ash monitor, which was interrogating
the whole of the primary sample (after crushing to 5 mm) but before
sample preparation and analysis, the sampling errors are not included in
the comparison. Earlier work on the development of the Phase 3A ash
monitor (4) indicated that the error due to sample preparation and
analysis (Sp+Sa) amounts to approximately 1.25% of the average ash level
and hence, for this As kem trial, can be considered to be 0.19% ash.
Thus (Si)2 - (Sm)2 - (Sp+Sa)2
- (1.06)2.(0.19)2
Hence Phase 3A Si - 1.04 % ash
On the basis of instrument error, only the Coalscan 3500 showed a
50%
greater standard deviation on shift integrated ash measurement than
the Phase 3A ash monitor in this series of 104 shift results.
3.6 Summary
One of the significant advantages claimed for a two energy
transmission system is its insensitivity to coal bed thickness and
consequent suitability for application directly to coal on a conveyor.
Laboratory tests using standard absorbers representing a wide range of
coal bed thicknesses confirmed this advantage and substantiated the
claim that the instrument could be used with coal bed thickness down to
50 mm.
The effect of some coal composition factors on accuracy was
assessed experimentally, showing that the largest effect was due to iron
where a 1% addition of Fe2Û3 was found to be equivalent to an increase
of 6% in ash content.
A limited number of coals from potential sites for a trial
installation of the Coalscan Monitor were tested in the laboratory on a
static test rig. Calibration accuracy (+ls) using coal crushed to
-212 pi ranged from 0.64% to 3.67%.
An assessment of the effect of particle size on the accuracy of
the static calibration procedure was obtained by making additional
measurements on one suite of coals at coal at 1 mm - 0 and at 25-3 mm
particle size. A calibration standard deviation value of 0.64% for
-212 pa coal compares with 0.80% for 1 mm - 0 coal and 0.83% for 25-3 mm
coal which has been intensively interrogated by multiple-pass
measurements. When the pattern of measurements is reduced to a single
pass,
simulating the dynamic, on-belt situation, the value for 25-3 mm
coal is reduced to 1.75%. This suggests that the on-belt accuracy of
measurement may be significantly less than that obtained from a static
calibration and is associated with the degree of interrogation of the
sample.
The Coalscan monitor was installed on the final power station fuel
conveyor at As kem Colliery and subjected to a series of dynamic
calibration tests giving calibration standard deviation values of 1.4 to
1.8% compared with an agreed, expected performance target of less than
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1.25%. Static off-belt calibrations with the same coals showed that the
lower than expected accuracy must be attributed to factors other than
coal composition. Evidence of cross belt segregation of ash levels and
a significant effect due to a damaged section of the conveyor were found
but when these were avoided by rectifying the operating procedures no
significant improvement in accuracy was achieved. Taking into account
the errors due to coal composition, sampling and laboratory analysis and
moisture content variations, a residual error of 1.2% ash remained and
could not be explained.
A comparison of the accuracy of dynamic calibration tests with
static tests using the same samples gave an average ratio of 2:1, the
same as found in the earlier simulated dynamic test.
A performance test, comparing instrument readings interpreted over
10 minutes with laboratory analysis, for 57 samples and two subsequent
comparisons of shift-integrated values, each comprising about 100
samples, showed only a poor correlation (r - 0.7 or
less).
During these
longer term comparisons, a significant drift in the calibrations was
also observed resulting in a pronounced bias (3% ash) at the end of each
period.
4. SUB-STREAM ASH MONITORING
Sub-stream ash monitoring involves the examination, on a
continuous or intermittent basis, of a representative proportion of the
main production stream which has been obtained by some continuous or
intermittent sampling or diversion technique. The sub-stream material
may be conditioned in some way, i.e. crushing, drying etc. prior to
examination in order to assist the presentation to the measuring system
or to improve the accuracy of ash measurement. However, conditioning
the sample usually results in delaying the ash measurement and,
therefore, a compromise has to be made between the speed and accuracy of
the measurement, depending on the purpose of the monitoring, with
continuous quality control requiring a faster response than consignment
verification. Sub-stream monitoring can be combined with a sampling
system for quality control or commercial analysis purposes and,
therefore, does not necessarily involve additional sampling facilities.
4.1 Previous UK Experience and Problems
A sub-stream ash monitor, which had been successfully applied for
a number of years at several UK collieries, was the NCB/AERE Phase 3A
ash monitor, Figure 69. This instrument was developed jointly, in the
UK, by the National Coal Board (now British Coal Corporation) and the
Atomic Energy Research Establishment
(AERE),
Harwell, in the late I960's
and was subsequently re-designed and manufactured under licence in the
UK by Gunson's Sortex Ltd.(5), The phase 3A unit had a capacity of 1 t/h
and the feed material had to be crushed below 5 mm prior to presentation
to the nucleonic ash measuring system in a 38 mm thick layer, with a
smooth profiled surface, on a rotating table. The backscatter measuring
system employs a Plutonium 238 source with a low energy gamma radiation
level of 17 KeV which limits the depth of penetration of the coal and,
consequently, the size of material which can be examined.
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The increase in the fines content and consequently the moisture
content of most small coal products, as a result of intensive
mechanisation, resulted in difficult handlability problems on most Phase
3A installations with the eventual withdrawal from service of many
units. The difficult handlability affected all stages of the sample
handling and crushing arrangements as well as the ash monitor
presentation unit, and the requirement to crush the samples to below
5 mm in size further aggravated these handlability problems.
Investigations conducted in 1978/79 indicated that it was possible
with some coals to increase the size of the feed to the Phase 3A ash
monitor to 12 mm or even 15 mm without adversely affecting the accuracy
of ash measurement. This modification was implemented at a number of
installations by increasing the aperture of the grids on the sample
crusher from 12.5 mm to 25 mm to give a 12 mm - 0 product and provide
some alleviation of the handleability problem.
At the same time, investigations were also being made by British
Coal into the possibility of developing other presentation techniques
which would produce a consistent degree of material compaction and a
smooth surface profile but would tolerate material of more difficult
handlability. Two alternative techniques were tested and compared with
the Phase 3A turntable system. These alternatives were a belt feeder
and a screw feeder with an extension tube, both units being provided
with vertically adjustable compression plates to vary the degree of
material compaction. With coal -5 mm the free (or surface) moisture
tolerance level of the belt feeder was around 12.5% before deformation
of the coal bed occurred, with the screw feeder this level increased to
between 12.5 and 14.5% compared with around 10.5% for the Phase 3A
turntable. Tests conducted with coarser feeds showed an increase in the
moisture tolerance level and also that a smooth surface profile could be
produced by increasing the degree of material compaction.
4.2 Previous Development of New Presentation System
To assist with the handling of more difficult material and ensure
a positive flow through a compaction system it was proposed that a
horizontal, reciprocating ram be used to displace material from the
bottom of a hopper and through a compaction zone while in contact with a
short belt feeder. The belt travel would be dependent on the forward
movement of the material. An experimental laboratory unit, Figure 70,
incorporating a hydraulic ram and power pack, demonstrated that this
technique was capable of successfully handling material with a high
fines content and up to 20% free moisture and producing a smooth surface
profile. However, with no independent drive to the belt feeder the
drive transferred through the material was Insufficient to overcome the
resistance caused by particles becoming trapped in the clearance between
the belt and the side-plates. The belt feeder was therefore replaced by
a horizontal, stainless steel open top rectangular trough. It was found
that the action of the ram was capable of moving forward the compacted
bed of material a distance of at least 600 mm while maintaining a
constant bed depth.
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A number of calibration tests were conducted on the experimental
laboratory rig, Figure 71, using the plutonium 238 backscatter system,
with proportional counter, from the Phase 3A ash monitor. This system
was independently mounted to prevent shocks from the reversal of the
hydraulic ram affecting the measuring system. These tests included a
series conducted with a suite of 34 samples of blended power station
smalls from Markham Colliery, Central Area, British Coal. The same
samples were tested successively at 50 mm, 25 mm and 5 mm top size.
After reduction to minus 212 micron for laboratory analysis the samples
were also tested on a Telsec 350 laboratory analyser using a plutonium
238 source.
A summary of the sample analysis and calibration test results are
given in Table 13. The samples covered a wide range of ash content but
the total moisture, sulphur and chlorine contents were fairly
consistent. The calibration accuracy showed only a slight deterioration
from a standard deviation of 0.81% ash at 5 mm top size to 0.90% ash at
25 mm top size and this was attributed to the degree of compaction and
the smooth surface profile produced by the ram-feed unit. There was a
poorer correlation and a marked increase in standard deviation to 1.67%
ash with the 50 mm top size material which was too coarse to give a
smooth surface profile. The much lower standard deviation given by the
quadratic regression, compared with the linear regression, pointed to
the necessity for having a signal processing system with this new ash
monitor which, unlike the Phase 3A unit, would be capable of applying a
quadratic calibration equation to the countrate measurements. The
calibration accuracy given by the Telsec instrument probably represented
the optimum that could be achieved with that particular product due to
variations in the chemical composition of the ash.
The level of accuracy achieved by the ram-feed presentation system
handling 25 mm top size material from Markham Colliery was considered
very encouraging, particularly since the colliery output was drawn from
a number of seams with differing characteristics. Discussions were
therefore started regarding a colliery trial site at Markham for an
experimental ram-feed unit, possibly replacing the existing Phase 3A ash
monitor which had failed to operate regularly because of the difficult
handlability of the material.
Using the plutonium 238 isotope head, tests were also conducted to
determine the degree of compaction of the feed material necessary to
achieve a stable level of countrates. The tests were conducted with
four different coals, one sized 50 mm - 0, two sized 25 mm - 0 and the
fourth sized 12.5 mm - 0. The entry to the compaction zone had a depth
of 120 mm and countrate measurements were made with vertical
compressions ranging, where possible, from 0 to 21mm at intervals of
3 mm. The tests were conducted under choke-feed conditions from a
part-filled hopper, with material being recirculated as necessary to
maintain this condition. All the coals tested required a minimum
vertical compression of around 12 mm, i.e. 10%, in order to achieve a
stable countrate, as illustrated in Figure 72. Measurements of the
loose and compacted bulk densities of the samples showed that this
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degree of vertical compression corresponded to a volumetric compaction
of around 30% . Measurements were also made of the hydraulic pressure
required for vertical compressions of up to 21 mm using coal samples
with three different levels of moisture. The results were plotted in
Figure 73 and show that the pressure required to compress the material
increases with moisture content but, more significantly, the pressure
required increases dramatically for a vertical compression in excess of
12 mm for all levels of moisture tested.
4.3 Design of Trial Site at Markham Colliery
Proposals by the former North Derbyshire Area and Scientific
Control for the reorganisation of the sampling arrangements for the
50 mm - 0 power station blend at Markham Colliery in 1983, including the
removal of the Phase 3A ash monitor because of severe handlability
problems, provided an
opportunity for the incorporation of a trial site for the ram-feed
presentation unit. The design of the new sampling system and the
arrangements for the inclusion of the ram-feed unit are shown
schematically in Figure 74.
The existing mechanical sampler would be replaced by a new linear
motor driven, traversing bucket sampler at an in-line transfer point on
the conveyor system for the 50 mm - 0 blended power station product,
which was produced at a maximum rate of 850 t/h. Because of the high
flowrate the sampler would discharge an increment at each end of its
travel,
after a single pass through the falling stream of material. The
sample increment collected on the forward travel would be used for
normal laboratory analysis. It would discharge onto a slow moving belt
feeder, or pacemaker conveyor, which would regulate the feed to a swing
hammer crusher for reduction below 5 mm. The crushed sample would be
fed to a sample divider and a representative proportion diverted into a
container for laboratory analysis. The remainder of the sample was
returned by conveyor to the main product stream. At regular intervals,
increments would be automatically diverted before the crusher to provide
a moisture sample. The increments collected on the reverse travel of
the sampler were to be returned directly to the product stream but a
manual by-pass was provided to collect increments for bias testing.
Agreement was reached with both the Area and Scientific Control
that the sample increments collected on the reverse travel of the new
sampler would be used to feed a test circuit for the ram-feed unit. A
second pacemaker conveyor would be installed to collect the increments
and provide a controlled feed to a second swing hammer crusher. Tests
with Markham blended smalls at the at the manufacturer's works had
confirmed that the top size of the crushed product could be selected at
6 mm, 12.5 mm or 25 mm by changing the crusher grid plates. A larger
top size could be obtained, if required, by removal of the grid plates.
An automatic by-pass would return the sampler discharge directly to the
product stream when the ram-feed circuit was not in operation.
The crushed material would be transferred by conveyor to the
original ash monitoring room, which previously held the Phase 3A unit,
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where the ram-feed presentation unit would be sited. A short screw
conveyor would make the final delivery to the feed hopper on the
ram-feed unit. A second screw conveyor would collect the discharge from
the ram-feed unit and also pick up any scrapings from the ram and
deliver to the reject conveyor for return to the product stream. An
intermediate, slide operated, discharge from the screw conveyor would
provide for sampling the discharge from the ram-feed unit or for
collecting the whole throughput when conducting a calibration procedure.
The ram-feed circuit would have a separate electrical control
panel from the colliery sampling system but it would be interlocked with
the sampler and the reject conveyor. Adequate access would be provided
around the circuit for operation and maintenance, and platform areas
provided for instrumentation equipment.
The reorganisation of the colliery sampling system was completed
in 1983 but the completion of the test circuit was delayed by industrial
action until March 1985. The experimental ram-feed unit was installed
by August 1985 but was not commissioned until the end of the year
because of a fire on the coal preparation plant which necessitated
replacement of the electrical switchgear, cabling and control system.
4.4 Design and Construction of New Experimental Ram-feed Unit
A new experimental ram-feed unit, Figure 75 was designed and
constructed in-house for the site trials. The trough and the feed
hopper were constructed in stainless steel, and the trough was provided
with a second outlet in the position of the retracted ram to allow any
material to be drawn back by the ram to be discharged. A proprietory
screw conveyor was adapted to operate in conjunction with the ram-feed
unit and accept the material discharged at both outlets.
The ram, 38 mm bore hydraulic cylinder and guide rails were
transferred from the previous unit. A new proprietary hydraulic power
pack was provided, complete with the necessary valves, to allow the
speed of travel of the ram to be controlled independently in both
directions. This design would permit the slow forward travel of the ram
and the faster return travel to be adjusted more precisely than the
previous improvised arrangement. The power pack was provided with both
level and temperature sensors for connection in to the electrical
control system, as required by British Coal regulations.
The ram-feed unit and the screw feeder are shown in position at
the trial site in Figure 76.
4.5 Testing of Ram-feed Unit at Markham Test Site
The installation of the ram-feed unit at the test site at Markham
Colliery, including all electrical sequence and safety interlocks to
allow automatic running, was finally completed at the beginning of 1986.
However, some teething problems with the test circuit caused
interruptions to the operation of the system during the first few months
and regular operation was not achieved until the end of April of that
year.
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The initial trials of the ram-feed unit were intended to determine
whether:-
(a) the unit is capable of tolerating material of difficult
handlability, resulting from excessive proportions of filter
cake or recovered fines or inadequate dispersion of these
components in the blended product.
(b) this difficult material can be handled satisfactorily when
the product is crushed below 25 mm, 12.5 mm or 6 mm.
(c) the unit is capable of producing a continuous and uniformly
compacted bed under conditions of varying increment size and,
consequently, variable fcedrate and
(d) the unit can produce a continuous, smooth surface profile to
enable the measurement of iron fluorescence as a correction
factor.
By the end of June 1986 the unit had been in operation for about
300 hours, as recorded by the elapsed time meter on the system, with
only occasional attention from the colliery sampling staff. Sample
increments were being taken at 6 minute intervals and fed into the test
circuit over a period of 3-5 minutes. Under this trickle feed condition
some malformation of the coal bed occurred, probably due partly to the
feed screw delivering to one side of the feed hopper.
During the second half of 1986 the compression plate on the
ram-feed unit was increased in length from 100 mm to 300 mm to apply a
more gradual compression to the material being advanced by the ram. The
feed screw conveyor discharge chute was also modified to centralise the
material delivery into the feed hopper on the ram-feed unit. These
changes were successful in overcoming the problem of bed malformation at
low feed rates and the unit was able to produce a smooth, continuous
surface profile under both choke-feed and trickle-feed conditions. By
the end of 1986 the ram-feed unit had completed 1000 hours of operation
with no handlability problems encountered within the unit Itself.
The hydraulic pressure required by the 38 mm bore, double acting
hydraulic cylinder to produce the necessary degree of material
compaction resulted in a severe hydraulic shock to the whole unit when
the ram was reversed. It was feared that this mechanical shock would
seriously affect any nucleonic ash measuring system mounted on or over
the unit. This problem was overcome in the first half of 1987 by two
modifications to the hydraulic system:-
(a) the hydraulic cylinder was replaced by a larger unit of
63.5 mm bore to reduce the hydraulic pressure requirement
under normal feed conditions and to increase the maximum
thrust available to deal with excessive fines in the feed
material.
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(b) the existing AC operated reversing valves were replaced by
time-delayed DC operated valves which gave a more gradual
reversing action and cured the hydraulic shock and vibration
on the unit.
At the beginning of the trial the sample crusher was fitted with
50 mm aperture grid plates to provide a product for the ram-feed unit
with an upper size of around 25 mm. During the first 9 months of the
trial the ram-feed unit proved capable of handling this size of material
with no problems, and in January 1987 the crusher was fitted with 25 mm
aperture grid plates to reduce the upper size of the crushed product to
around 12 mm. After a further 2 months of satisfactory operation these
were in turn replaced by 12.5 mm aperture grid plates to give a product
of around 6 mm top size. The trial of the experimental ram-feed unit
continued for 11 months with this size of feed, before replacement by
the prototype unit, with no handlability problems.
The sizing analysis of the original 50 mm - 0 product and the
crushed product with each size of grid plates is given in Table 14 and
plotted in Figure 77.
Throughout the trial, regular checks were made on the condition of
the coal bed produced by the ram-feed system. The bed remained
consistently at the same level along the length of the trough and there
was no tendency for it to expand after emerging from the compression
plate. Sections taken periodically from the bed had a relative density
close to 1.0 which did not appear to be measurably affected by the size
of the feed material as a result of changing the crusher grid plates.
However, the smoothness of the surface profile improved as the top size
of the feed was reduced from 25 mm to 6 mm, Figures 78 and 79.
When operating under choke-feed conditions, each 254 mm forward
stroke of the ram of advanced the coal bed by 120 mm. With a trough
width of 180 mm and a bed depth of 108 mm the volume of material
extruded per stroke was 2.33 litres which with a coal bed of relative
density 1.0, corresponded to 2.33 kg of material per stroke. The ram
had a minimum cycle time of 12 seconds, 5 seconds forward travel,
5 seconds reverse, and 1 second reversing time at each end, which gave a
maximum rate of operation of 300 strokes per hour and a maximum capacity
of 700 kg per hour. The average weight of a sample increment was around
25 kg, so the maximum possible rate of sampling would be once every 2
minutes. In practice, the sampling frequency was limited to every six
minutes by the requirements of the colliery sampling system.
During the first fifteen months of the trial a check was kept on
the sample handling system with regard to any problems with material
handlability. The build-up of fines was found to occur at the following
locations
: -
(a) sample crusher outlet chute
(b) transfer chute from transfer conveyor to screw feeder
(c) ram-feed unit feed hopper
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The inside surfaces of these components were treated with a
proprietary epoxy paint finish to reduce fines adhesion and build-up.
This treatment overcame the problem and no further attention was
required.
Also, in the second half of 1987, an additional control panel was
introduced into the ram-feed control system to ensure that the feed rate
from the product sampling system was within the capacity of the
presentation unit. Two capacitance-type proximity switches were mounted
in cut-outs on the rear of the feed hopper; one near the top and the
other near the bottom. If the level in the feed hopper reached the
upper switch the feed system was stopped as far back as the pacemaker
conveyor and sample increments were diverted back to the product
conveyor. The feed system was re-started when the level fell below the
bottom level switch. The capacitance proximity switches were, however,
dependent on a certain level of moisture in the feed material and an
alternative type of level switch, such as a vibrating reed, may be
necessary with drier material.
4.6 Design and Manufacture of Pre-production Prototype Unit
In December 1986, when the experimental ram-feed unit at Markham
had completed 1000 hours operation with no material handlability
problems, it was decided to proceed with the design and manufacture of a
pre-production prototype unit. The design would be based on the
experimental unit and provision would be made for the incorporation of
both ash and moisture measuring systems. A specification, included in
Appendix 8, was drawn up by British Coal for the design, manufacture and
installation by an outside firm and tenders invited.
A contract was finally placed in July 1987 with Ramsey Process
Controls of Byfleet, Surrey, a firm which already had many years
experience in the supply, installation and maintenance of
instrumentation, including nucleonic equipment, in coal preparation
plants.
Following agreement on the main design features, Figure 80, the
first pre-production prototype unit was manufactured and installed at
Markham Colliery, in place of the experimental unit, in February 1988
and was in operation by 21st March 1988.
The general arrangement of the prototype unit is shown in
Figure 81 and a photograph of the completed unit prior to installation
in Figure 82. The unit, designed for floor mounting, was constructed
mainly using stainless steel. The feed hopper, with a capacity of
approximately 35kg, was lined with high molecular weight polyethylene to
reduce fines adhesion and avoid material build-up. The rear of the feed
hopper, Figure 83, included cut-outs in the stainless steel for the
positioning of upper and lower level senors. The rear view also shows
the hydraulic cylinder which, in this design, was mounted directly
in-line with the ram, and the length of the unit to the rear of the feed
hopper was minimised by allowing the ram to retract around the cylinder.
The unit was provided with two interchangeable trough sections,
made in polypropylene, which were flange connected after the compaction
zone. The longer section, 485 mm, would accommodate both ash and
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moisture monitors, the shorter section, 285 mm, was intended for ash
monitoring only. The width and depth of the trough section were kept at
180 mm and 120 mm respectively as in the experimental unit.
The prototype unit was fitted with the longer trough and operated
successfully under surveillance, for the 6 months to September 1988.
The hydraulic power pack for this installation, supplied by British
Coal,
had a capacity of 8.41 litres/min at a maximum pressure of
8621 kPa which, in combination with a cylinder of 63.5 mm bore was
capable of producing a maximum thrust of 27.3 kN.
A second prototype unit was ordered by British Coal early in 1988
to extend the on-site trials to a second colliery.
4.7 Nucleonic Ash Measuring and Signal Processing System
4.7.1 Design of Ash Measuring and Control System
The nucleonic ash measuring system for the Ram-fed ash monitor was
based on that currently used on the NCB/AERE Phase 3A ash monitor which
had been developed and proved over a number of years. The system
employs plutonium 238 isotopes emitting 12-17 keV gamma radiation and
the ash measurement is dependent on the radiation backscattered from the
upper layers of the coal bed. The system also detects and isolates iron
fluorescence to provide a means of correcting the ash measurement for
variations in the iron content of the coal.
The design of the system is illustrated in Figure 84, and the
specification for the principal components is given in Appendix 9. The
system comprises three functionally distinct and physically separate
sections : -
(i) The radiation emission and detection units, comprising radioactive
sources and proportional counter, were designed to be mounted
immediately above the coal bed on the ram-feed unit with the pulse
pre-amplifier in close proximity.
(ii) The pulse analysing and counting section comprised standard
Nuclear Instrumentation Modules
(NIM),
of reliable manufacture,
which plugged into a standard housing, i.e. a NIM bin, complete
with a power distribution system. This unit was, in turn, housed
within an environment-proof enclosure and located in the vicinity
of the ram-feed unit.
(iii) The computing and control section comprised a micro-computer, in
an industrial housing, for the computation and display of ash
content, and a programmable logic controller (PLC) which controls
the operation of the Ram-feed unit and co-ordinates the ash
measuring system.
4.7.2 Operation of Ash Measuring and Control System
The proportion of the radiation from the plutonium sources
absorbed by the coal bed is directly related to the ash content of the
coal and the proportion backscattered is, therefore, inversely related
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to ash content. The backscattered radiation, together with iron
fluorescence, is detected by the proportional counter which produces a
stream of charge pulses, with the magnitude of the charge dependent on
the energy of the detected radiation. The charge pulses are converted
by the pre-amplifier into amplified voltage pulses which are transmitted
to the spectroscopy amplier where it is further amplified before passing
to the spectrum stabiliser.
The spectrum stabiliser dynamically compensates the overall gain
of the counting system for any slight variations in system gain that
occur principally in the proportional counter. The voltage pulses pass
to the energy analyser which separates them into two channels. The
lower energy channel is the iron fluorescence and the higher energy
channel the backscattered radiation.
The two channels of pulses are presented individually to the dual
scaler timer module, which is under the control of the microcomputer,
and, on the instruction to start, the scaler timer accumulates counts in
two separate registers. On the command to stop counting the scaler
timer transfers the contents of the two registers to the computer, in
addition to the duration of the actual counting period. The computer
calculates the ash content from the two countrates using a previously
determined calibration equation for the particular coal under
examination. The computer screen displays the current ash content from
the last countrate measurement, the average ash content so far for the
shift and the target ash content for the particular product.
The PLC controls the operation of the Ram-feed unit and also
passes signals to the computer to instruct the dual scaler timer to
start and stop accumulating counts corresponding to the movement of the
coal bed in the Ram-feed trough. In this timing operation an allowance
is made for the initial forward movement of the ram to compress the new
coal charge before the bed itself starts to move. By taking the count
reading only from the moving coal bed it avoids the ash measurement
being biased by any interruptions to the product flow or sampler
operation when the instrument would, as a consequence, be making
repetitive measurements on the same material. Since the measurement is
made only on moving material the shift ash will be weighted according to
the size of the sample increment and, consequently, to the flowrate of
the product.
4.7.3 Radiation Safety Precautions
It was considered possible, although highly unlikely that one or
both of the plutonium 238 radioactive sources being used in the ash
measurement system could become dislodged from the source holders and
become a radiological hazard. To avoid this possibility, two
independent protection systems were incorporated in the measuring
system:-
(i) Source Loss Detector
If the countrate of backscattered radiation should
fall below a pre-set level an electronic circuit
would operate a trip and stop the Ram-feed unit.
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(ii) Optical Bed Level Trip
In the unlikely event of an obstruction in the Ram-feed
trough, due to a foreign object or a build-up of material,
there would be the possibility of the coal bed rising
and causing damage to the isotope measuring head which might
dislodge the sources.
To prevent this happening, a bed level sensor has been
incorporated in the system. It involves an infra-red
transmitter/receiver and uses fibre optic cable to
transmit and detect a beam of infra-red light across
the Ram-feed trough immediately below the radioactive
sources. Any interruption of this light beam will
activate a trip which will stop the ram-feed unit.
4.7.4 Manufacture and Testing
At the close of the ECSC Research Project all the proprietary
items of the ash measuring system had been obtained and the assembly of
the system had been completed. Only the provision of the necessary
supporting and guarding arrangements for the isotope measuring head over
the Ram-feed trough were required before installation of the system at
the trial site could proceed.
4.8 Summary
One of the limitations of the earlier British Coal designed
sub-stream ash monitors, the Phase 3A system, was the requirement for
coal to be crushed to less than 5 mm and its inability to handle some
wet coals. Work on an alternative presentation system, which would use
a Phase 3A backscattered radiation monitor head and could handle coals
up to 25 mm particle size, had established the basic principles upon
which an experimental system, the Ram-Feed Unit, was designed and built.
This experimental unit was installed at a colliery site where it
proved its mechanical and electrical reliability and its ability to
handle coal at 25 mm, 12.5 mm and 6 mm particle size over 1000 hours of
operating experience.
Based on this experience, a prototype presentation unit, modified
to allow the addition, at a later stage, of a moisture monitoring head,
has been built and successfully operated for a period of 6 months at the
colliery site.
A second prototype presentation unit was manufactured and fitted
with a backscattered radiation detector head linked to a specially
designed signal analysis and processing system and a microcomputer-based
computing and control unit. A microwave moisture monitoring system,
based on work described in Section 5 of this report, was also fitted and
the whole assembly installed at a colliery site for trials at the end of
this project.
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5. MICROWAVE MOISTURE MONITORING
5.1 Review of Previous Development and Testing by British Coal
5.1.1 Early Investigations
Investigations by British Coal, Scientific Control, into the
possible application of microwave attenuation for the determination of
moisture in coal began in the former North East Region in the mid I960's
and continued in that Region into the early 1970's. This early work
included both laboratory investigations (6) and plant trials (7) with
apparatus based on the proprietary equipment available at that time.
The laboratory investigations concluded that there was a useful
relationship between microwave attenuation and moisture content for any
particular coal and this might be used to monitor the moisture content
to an accuracy of about +1% . The plant trials, using an on-belt
microwave monitor and 12.5 mm - 0 washed coking coal from up to six
seams,
confirmed that the moisture content could be determined to about
+1%
on a daily basis. These investigations demonstrated that the
relationship between moisture content and microwave attenuation was
dependent on the rank of the coal and also on the size consist, so that
it would be necessary to determine a calibration for each coal to be
monitored.
5.1.2 Microwave Bands
The early investigations covered microwaves in two wavebands; the
first waveband, term X- band, covered frequencies in the range 8 to
13 GHz and the second, termed S- band, covers frequencies between 2 and
4 GHz. The range of frequency and wavelength for each band, together
with possible applications and particle size limits, are given below:-
Microwave Frequency Wavelength Possible
Band Range Range Application
X 8 - 1 3 GHz 3.75 - 2.3 cm Sampled and part-
prepared material,
Top size 15 mm
S 2 - 4 GHz 15 - 7.5 cm Unprepared material
• direct on-belt,
Top size 50 mm
The X- band microwaves have the greater attenuation due to water
and should therefore give greater accuracy. However, since the particle
size should be kept small in relation to the radiation wavelength, to
minimise resonance effects, the X- band is restricted to a top size of
15 mm. Its application is therefore mainly limited to samples which
have been subjected to some size reduction for the purposes of sample
division or ash monitoring. The S- band would be required for larger
material, as in the case of direct measurement of the product on a
conveyor belt.
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5.1.3 Earlier Applications
Following the early investigations, a number of MX100 microwave
moisture meters, manufactured by Rank Precision Instruments
(RPI),
were
applied in the former Scottish Area of British Coal. These meters
operated in the X- band and were used mainly with 5 mm - 0 material as
discrete sample instruments. One unit was installed for continuous
measurement of 5 mm - 0 material on a sample reject conveyor. Another
unit was incorporated into a plough assembly for monitoring a 25 mm - 0
power station fuel directly on the main product conveyor. On this
latter installation the 95% confidence limits for a single determination
were +1.2% over a range of 12-20% moisture.
Also in the Scottish Area, a system manufactured by Associated
Electrical Industries (AEI) and operating in the S- band was used with
limited success on discrete samples with a 25 mm top size.
5.1.4 Previous Development and Application of X-band System
In the late 1970's, the development of a new X-band microwave
instrument by the former Scottish Area Scientific Department was
prompted by the fact that the Rank units were becoming obsolete, with
spares difficult to obtain, and AEI were no longer producing microwave
moisture meters. In 1979, a new instrument was produced which employed
all solid state electronics and a highly stable, low power generator
which permitted the use of a simple "straight through" system without
the need for balancing or reference facilities to compensate for
instability, Figure 85.
Laboratory calibration tests of the new instrument confirmed its
ability to measure moisture to around +1% on discrete 5 mm - 0 samples,
and a number of discrete sample instruments were manufactured for plant
trials.
The manufacture was later passed to a private firm to produce
commercial units.
Attempts were made to monitor the 5 mm- 0 reject material from a
Phase 3A ash monitor on a small conveyor but difficulties were
experienced in maintaining a continuous uniform bed. It was then
realised that the profiled, constant depth bed of material on the
rotating table of the ash monitor would form an ideal presentation for
continuous moisture measurement. The steel turntable of the ash monitor
was replaced by a PVC turntable which was transparent to microwaves and
this allowed the microwave moisture meter to be incorporated as an
integral part of the Phase 3A ash monitor, Figure 86, to form a combined
ash/moisture instrument. The four Phase 3A ash monitors in the Scottish
Area were then converted to include moisture measurement, while discrete
sample instruments were used at other collieries.
The continuous moisture meters gave a linear calibration accuracy,
for 95% confidence limits, varying from +0.6% to +0.9% over a range of
moisture of 8%. Over the same range of moisture the discrete sample
moisture meter gave a calibration accuracy varying from +0.35% to +1.1%.
In operational use, however, the discrete sample unit gave greater
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accuracy (+0.7% to +1.0%) compared with the laboratory analysis, on a
daily basis, than the continuous instrument (+1.3% to +1.4%).
With the facility to continuously measure of both ash and moisture
content using the Phase 3A ash monitor, subject to the handlability of
the coal, it became possible to compute the calorific value of the
product provided the dry ash free calorific value of the product
remained reasonably constant. This arrangement was introduced at two
collieries.
At the first colliery use was made of the existing colliery
computer system, Figure 87, which, together with an existing belt
weigher, allowed tonnage weighted values to be used. Vith no existing
computing facilities at the second colliery a microprocessor-based
integration system was developed. This system, Figure 88, was able to
produce short term integrations as well as shift and daily averages, all
of which could be displayed and printed. Also, in the absence of a belt
weigher, a coal flow detector was used to suspend integration during
periods of no coal. With a sample fed monitor, such as the Phase 3A, a
degree of weighting was achieved since the quantity of sample was
dependent on the coal flowrate.
5.1.5 Previous Development and Application of an S-band System
The increasing requirement to monitor products directly on-belt
and avoid the growing handlability problems associated with sample
preparation and presentation led to the development in the early 1980's
of a new S-band instrument to allow moisture measurements on material up
to 50 mm top size.
The prototype S-band discrete sample instrument, Figure 89,
operated with a coal bed up to 300 mm thick and used a variable
frequency microwave source with a modified version of the X-band
instrument electronics. Laboratory calibration tests with 25 mm top
size material and consistent sample presentation box filling gave an
accuracy for 95% confidence limits of +0.6% . However, site trials at a
port with shipments of blended coal gave an accuracy of +2% which was
attributed to the variability of the blend and inconsistent presentation
box filling by different operators.
5.1.6 Limitations to Application of S-band System
Three main factors limited the more widespread application of the
S-band moisture meter. These were:-
(a) the analogue electronics, designed originally by Scottish
Area Laboratory, for the X-band meter, and a considerable
improvement on the older RPI unit, was limited to a range of
attenuation of about 30 dB and then only after careful
setting up.
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(b) single frequency moisture measurement was susceptible to
changes in the geometry of the presentation system and
required, as far as possible, constant bed depth and packing
density.
(c) single frequency moisture measurement was also affected by
variations in coal type requiring separate calibration for
each particular coal.
The work carried out by the former Scottish Area Scientific
Control under this Project was directed towards overcoming these
limitations and producing a moisture meter which could be applied
directly on a conveyor belt with the minimum of presentation
requirements and which would tolerate a wide range of coal types and
moisture levels.
5.2 Developments for On-belt Microwave Moisture Monitoring
5.2.1 Instrumentation Requirements
In order to improve the performance of the fixed frequency
microwave systems, when applied directly on-belt, it was necessary to
overcome the limitations of the inadequate dynamic range of the existing
instrumentation and the problem of the variations in the geometry of the
coal bed on the belt. It would also be necessary to provide suitable
equipment for the collection and processing of the measurement data
generated in a plant trial. To meet these requirements, a range of
equipment was either modified or designed and assembled.
5.2.2 Moisture Meter Electronics
Considerable effort went into re-designing the existing
electronics to increase the dynamic range from 30 dB to 60 dB. The new
design, shown in Figure 90, comprises the following main component
parts:-
(a) Microcomputer
The electronics are designed around a RCA 1802 central
processing unit which carries out all the control functions,
synchronisation and calculations.
(b) Microwave Generation
The design allows for two versions of the computer controlled
moisture meter, the X-band (10 Ghz) and the S-band (3 Ghz).
Depending on the version the appropriate microwave oscillator
is driven by a modulator, synchronised to the microcomputer.
To provide a high degree of electrical isolation between the
microwave source and the microwave detection the
synchronisation is effected by using an optical fibre link.
The sources generate either 10 Ghz or 3 Ghz microwaves,
modulated at approximately 1 Khz.
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(c) Microwave Detection and Amplification
The detected microwave power is fed through the amplifier
chain Al to A4. These four amplifiers each have a precision
gain which is a multiple of ten for ease of logarithmic
conversion by the computer. The actual system gain is
controlled by the computer software selecting the required
combination of amplifiers to produce a value of the required
order.
(d) Analogue to Digital Conversion (ade)
The a/d conversion is performed by an 8 bit high speed
converter. The input signal to the ade has to be in the
range 0 - 2.55 Volts. The computer selects the correct
combinations of amplifiers so that the input to the ade is
always within the required voltage range.
The computer controls the actual instant the a/d conversion
is performed. It initiates the conversions at the peak and
troughs of the modulations and subtracts one from the other
to obtain a value. This operation is performed a number of
times and the values averaged. This technique allows more
accurate readings to be obtained for low input signals,
corresponding to higher moisture contents, since random noise
is averaged out.
(e) Logarithmic Conversion
The computer software constructs a number, the exponent of
which is determined by the computer-selected amplifiers. The
mantissa, in the range 0 - 2.55, is the output from the ade.
Within the computer memory is a series of look-up tables and
the computer uses the number it constructed to look-up the
corresponding logarithmic value from the tables.
(f) Indicators
The unit has two L.E.D. indicators, one green and one red.
Green indicates that the output reading is valid and red that
the computer is going through the process of selecting the
required amplification, averaging the a/d conversions and
making the logarithmic conversion.
(g) Outputs
The computer provides a number of outputs. A digital to
analogue (d/a) converter produces an analogue signal which
gives an indication of attenuation in dbm's on a meter. The
analogue signal also drives a 4-20 mA current source for
remote indication and control purposes. The computer also
provides a standard RS 232 signal for communication with
other computers.
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Detailed specifications for both the X-band (3 cm) and S-band
(10 cm) microwave moisture meters are included in
Appendices 10 and 11.
5.2.3 Data Logger
The data logging units, which were designed and constructed in the
Scottish Area Laboratory to record colliery trials of microwave moisture
monitoring systems, were built around a RCA 1802 microprocessor. The
same design was used with a Phase 3A ash/moisture monitor and with an
on-belt moisture monitoring system. Figures 91 and 92 show the basic
components of the logger and the incoming signals for both applications.
The data logger has three input channels; the first channel is
stored as a 2 byte number and the other two channels are stored as
single byte numbers. The input signals are sampled at one minute
intervals, converted to digital form and stored in battery-backed RAM.
Every hour the data is transferred from RAM to a disc, together with the
time and date from a real time clock in the microprocessor. The data on
the disc is structured so that it can be easily read and analysed by a
BBC microcomputer. With a one minute sampling rate the data logger can
store up to 30 days data on one disc.
5.2.4 Ultrasonic Bed Depth Meter
In order to apply microwave moisture monitoring successfully to a
product directly on-belt it was necessary, as a first step, to overcome
the problem of varying bed depth. This could be done either by
profiling the coal bed to a constant depth or employing a method of
continuously measuring the depth of material on the belt and correcting
the attenuation measurement accordingly. Since it would not be
practical, in most cases, to produce a constant bed depth it was
necessary to develop a means of continuously measuring the depth of
material in the same line of the belt as the attenuation measurement.
This measurement was achieved using ultrasonics to measure the position
of the coal surface below a fixed point at a location where the level of
the belt itself was constant, e.g. immediately over a support roller,
thereby providing an indirect measure of the bed depth.
The bed depth meter, designed and constructed at the Scottish Area
Laboratory, used components from an Ultrasonic Ranging System Designers
Kit, manufactured by the Polaroid Corporation of the USA and marketed by
Polaroid (UK) Ltd. A technical specification for the bed depth meter is
included in Appendix 12 and the main components are shown in Figure 93.
The ranging board generates a high voltage (300 V) pulse which is
applied to the ultrasonic transducer. The resulting pulse of sound
energy from the transducer is directed at the coal surface normal to the
belt, and the returning echo detected by the transducer. The ranging
board provides a control level which allowes the pulse counter to count
the incoming oscillator pulses from the time of the transmitted pulse
until the detection of the returning echo. The number of pulses counted
is therefore proportional to the distance between the transducer and the
coal surface.
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The digital-to-analogue converter converts this count to an
analogue voltage which is proportional to distance. The
distance-to-depth converter inverts this voltage and an offset
compensates for the distance between the transducer and the empty
conveyor belt, thus providing an output to the display which shows the
depth of coal on the belt in millimetres. The frequency of the depth
measurements was 5 per second and the display updated at 0.5 second
intervals.
The output from the distance to depth converter is further
conditioned to provide a 0 - 1.6 V signal of bed depth to the data
logger. A 0.4 - 2.0 V output is also made available, together with a
4 - 20 mA signal for remote display or control purposes.
5.2.5 Trial Installation of On-belt, S-band Moisture Monitor
5.2.5.1
Description of Installation
Early in 1987, the fixed frequency S-band moisture monitoring
equipment was installed on a conveyor designed for handling up to
980 t/h of 25 mm - 0 blended raw coal at the Longannet Mine complex in
the former Scottish Area. The installation is illustrated schematically
in Figure 94 and photographs of the installation are Included in
Figures 95 and 96.
The moisture meter was installed with the microwave transmitting
horn mounted on a framework above the conveyor belt and the receiving
horn situated immediately below the top belt. The moisture meter
electronics, together with a data logger, were housed in an
environment-proof cabinet mounted alongside the belt.
The ultrasonic bed depth meter, which had already been undergoing
site trials at another colliery which was to be closed, was transferred
to Longannet and installed in-line with and immediately before the
moisture meter and as close as possible to a troughing idler. An
existing belt weigher was located about 9 metres before the moisture and
bed depth meters and the signals from all three instruments were passed
to the same data logger.
A further 5 metres before the belt weigher was an existing Birtley
automatic sampler which swept sample increments sideways off the belt at
intervals of either 2 or 3 minutes depending on whether or not coal was
being introduced from outside sources to maintain the quality of the
power station blend. The sample increments were fed via a crusher to a
Phase 3A ash monitor which had been modified to incorporate an X-band
microwave moisture meter. A second data logger was installed in the
second half of 1987 to record the ash and moisture signals from this
monitor.
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5.2.5.2 Results of On-site Trials at Longannet
The trials at Longannet continued under the close supervision of
Scottish Area Scientific Staff until the end of 1987 when, as part of a
general re-organisation of Scientific Services in British Coal, the
Scottish Area laboratory was closed and the staff who had been involved
in this work were either re-located at the HQ Technical Department at
Bretby or left the service of British Coal. This re-organisation caused
considerable disruption to this part of the Project, with the Longannet
trial having to be terminated early in 1988 before any on-belt
calibration could be undertaken on the moisture monitor. It also
prevented a full appraisal of the data which had been collected during
the trial.
However, prior to the closure of the Scottish Area laboratory,
software was developed to analyse some of the data from the on-belt
moisture meter data-logger. This development included a program to plot
the microwave attenuation, material bed depth and flowrate over each 24
hour period against a common time base. The data for the 22nd January
1988 is shown plotted at 1 minute intervals in Figure 97. The program
was further developed to set limits of acceptable data which eliminated
data indicating saturation of the system or transient spikes. The
facility was provided to average the remaining data over selected time
intervals ranging from 2 minutes to 60 minutes. The data for the 22nd
January was averaged over 5 minute intervals and is shown in Figure 98.
The non-valid data was replaced by a zero ordinate value and these
values would be ignored in subsequent data processing.
The traces for bed depth, microwave attenuation and belt loading
in Figure 98, all respond to the main changes in flowrate. When the
belt load and bed depth measurements fell to zero the attenuation fell
to a constant level of just below 12 dB, due to the combined effect of
the conveyor belt and, in particular, the constant air gap between the
transmitting and receiving horns. During the periods of coal flow the
traces for bed depth and belt load showed a particularly close
similarity with all the main changes, and many minor changes, in coal
flow being evident on both traces. The trace of microwave attenuation
showed differences in detail from the other two.
Consecutive values of bed depth and belt weigher readings,
integrated over 5 minutes, were taken for a period of approximately
5-6 hours from 8.00 hours on the 22 January and were plotted in
Figure 99. The correlation coefficient for the quadratic regression
between flowrate and bed depth was 0.93 and the standard deviation for
the flowrate was 43.3 t/h. The bed depth meter therefore provided only
an approximate measure of the flowrate.
5.3 Swept Frequency Microwave System
5.3.1 Limitations of Single Frequency Systems
Early experience with single frequency microwave moisture meters
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had shown that coal samples of similar moisture content but of different
rank, ash content and size consist gave different values of
attenuation (6). For each coal the calibration between attenuation and
moisture had shown a characteristic 'dog-leg' shape with the sudden
change in the attenuation/moisture relationship corresponding to the
change from inherent to free (or surface) moisture. However, apart from
this feature, the calibration for different coals varied widely,
particularly in the free moisture range, and the single frequency
moisture meter had to be calibrated for a particular coal. This
requirement was, consequently, a severe limitation where the instrument
was required for use with a blended product of variable composition.
Microwave attenuation is also dependent on the presentation
geometry and, therefore, single frequency meters ideally prefer constant
presentation conditions such as bed depth, material compaction and
distance from source to coal surface. This preference particularly
affects on-belt applications unless some compensation could be made for
bed depth variations, as was being attempted with the ultrasonic depth
meter at Longannet.
5.3.2 Principle of 2 Frequency Measurement
To endeavour to overcome the above limitations the absorption of
microwaves by water had to be examined in more detail. The water
molecule is electrically polarised and, if an electric field is applied,
the molecule will tend to align itself with the field. In doing so,
energy is extracted from the field to overcome the small but finite
inertia of the water molecule. If an alternating field of increasing
frequency is applied the water molecule will rotate faster and absorb
more power. This rising characteristic continues from low radio
frequencies and reaches a maximum in the microwave region at about
17GHz. Thereafter, the power absorbed declines as the inertia of the
molecule is too great to follow the rapidly alternating field.
The total attenuation produced by a coal sample can be represented
as:
-
A (total) - A(water) + A(coal)
The attenuation due to the water can be predicted as described
above. The attenuation due to the dry coal itself depends on the
molecular constituents and cannot be predicted. It is this factor which
adversely affects the accuracy of microwave moisture meters when
operating with blended products of varying composition.
If attenuation measurements were made at two frequencies (1) and
(2),
two equations would result:-
Ai (total) - Ai (water) + Ai (coal)
A2 (total) - A2 (water) + A2 (coal)
The two coal terms would be approximately equal and, therefore, by
subtraction
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A2 (total) - Ai (total) - A2 (water) - A^ (water)
The effect of the dry coal would therefore be eliminated and the
resulting value would depend only on the water in the sample. Some
preliminary experimental work was undertaken using a variable frequency
microwave source set to various frequencies and the differences in
attenuation correlated to moisture with encouraging results. Resulting
from this work, a two frequency design was proposed which mixed the two
microwave frequencies for transmission through a single microwave path
and subsequently separated them, Figure 100.
At the start of this Research Project the two frequency system was
being superseded by a swept frequency approach which, in addition to
overcoming the problem of differing coal types, also compensated for the
effect of varying geometry.
5.3.3 Effect of Variable Geometry
In a microwave measuring system the electromagnetic radiation
encounters several physical boundaries such as air/coal, coal/container
wall,
and container wall/air. At each of these boundaries some of the
incident radiation is reflected as well as transmitted.
At the first air/coal boundary there will be a large amount of
reflected energy which will set up a pattern of standing waves between
the transmitting horn and the coal surface. The effect of this pattern
is to produce local variations in microwave power density. Although the
total power delivered by the source is known the actual power density at
the coal surface is determined by the standing wave pattern which, in
turn, is critically dependent on the distance between the horn and the
coal surface.
In a single frequency system these errors can be minimised by
fixing the geometry, as far as possible, but, with the changes in
geometry inherent in an on-belt system, this would be extremely
difficult to achieve. The two frequency system would be more
susceptible to the geometry since if it were set up accurately for one
wavelength it would not be correct for another unless it were carefully
chosen.
If measurements were to be taken at a large number of intervals
over a range of frequencies then the attenuation would vary cyclically
as the position of the standing wave is shifted in space. The frequency
range would have to be wide enough to include several cycles of this
variation. Using a microprocessor, a linear regression would be applied
to the attenuation measurements and the straight line obtained would
even out the cyclic variations.
The intercept and the gradient of this linearised
attenuation/frequency relationship would both increase with the moisture
content of the coal. The intercept would also be dependent on the
attenuation of the dry coal, while the gradient would depend only on the
moisture. Therefore if the gradient of the attenuation/frequency
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relationship were used as the measurement of moisture, an instrument,
based on this technique, would be largely independent of both coal type
and the geometry of the system.
5.3.4 Experimental Laboratory Equipment
This aspect of the Research Project commenced with the
specification and procurement of the specialised microwave equipment
required for laboratory investigations of the swept frequency technique
and its incorporation in the system illustrated in Figure 101. A
detailed specification of the system components and computer software is
given in Appendix 13.
The system was designed around the Automatic Amplitude Analyser,
manufactured by Marconi Instruments, and referred to alternatively as a
scaler analyser. This instrument is an advanced processing unit capable
of accurately analysing the inputs from broadband microwave detectors
and displaying the results on a screen. Three independent channels,
designated A, B and R (reference), are provided for the connection of
the diode detectors. Each channel has an associated data store and
memory which can hold a sweep of 422 measurements over the frequency
range being used. The detector signal undergoes a digital/log
conversion process and this value was placed in the channel data store.
The value is further corrected for square law deviations and temperature
effects in the detector head. The dynamic range of the instrument is
around 70 dB.
The display shows the channel measurements in line or histogram
form with the frequency scale horizontal and the attenuation vertical.
The front panel keyboard controls a number of functions such as display
sensitivity, frequency windowing, subtraction of reference channel,
cursor position, sweep speed etc. Any of the keyboard functions can
also be accessed through the IEEE interface bus for remote computer
control.
The operation of the experimental arrangement is explained with
reference to Figure 101. Three variable sources are used to cover the
total frequency range 2-12 GHz in band-widths 2-4, 4-8 and 8-12 GHz,
corresponding to S, Q and X bands. Each band requires different
waveguides and horns. The X band components, which are relatively
inexpensive and easily available, were purchased. The larger Q and S
band components were manufactured in the laboratory workshop together
with various coal presentation systems, with sectional containers to
provide different coal bed depths.
Having positioned the coal sample, in its container, between the
transmitting and receiving horns, each test consisted of a sweep across
the relevant frequency range while measuring the transmitted and
received power through channels R and A respectively. The value A-R
then represents the power loss through the coal sample. Because of the
large number of tests carried out, and the amount of data generated, the
instrument is controlled remotely through the IEEE bus. A BBC
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microcomputer was programmed to set the control parameters, initiate the
scan, capture the data, perform the linear regression and store the
results on disc.
5.3.5 Laboratory Test Procedure
After some preliminary trials the following procedure was adopted
for obtaining a range of samples of progressively increasing moisture
content for a particular coal. A bulk sample of approximately 30kg of
coal was crushed below 4.5 mm and dried. After thorough mixing the bulk
sample was divided into two equal and representative parts. Each part
was subjected to a further mixing and sub-division and the procedure
repeated until a suite of 16 samples of approximately 2 kg was obtained.
These samples were weighed to determine the amount of water to be added
to each sample to produce a series of samples of increasing moisture
content within a given range. The water was added using a small, manual
spray gun while the sample was being continuously hand mixed. The
samples were then sealed in plastic bags and allowed to stand for
24 hours.
The samples were taken in turn for presentation to the microwave
measuring system. Using a standard filling technique the sample was
transferred to the sample presentation tube which comprised an aluminium
tube, 150 mm diameter and 100 mm deep, with a perspex base. The sample
was placed between the vertically arranged transmitting and receiving
horns and a scan of 100 milli-seconds' duration initiated over the range
5 GHz to 7 GHz, using the middle section of the Q band microwave source.
The sample container was emptied, the sample re-mixed, the container
re-filled and the measuring procedure repeated. The whole process was
repeated a further three times to give a total of 5 scans for each
sample. The samples were then analysed for total moisture content.
5.3.6 Testing of Seams from Blindwells Opencast Site
The foregoing test procedure was applied to coal samples from
seven different seams which occurred at the Blindwells Opencast Site in
Scotland. Typical analyses for six of the seven seams, which were all
low rank, are given in Table 15. The coal samples were prepared as
described above, with each seam sample providing a suite of 16 test
samples with total moisture contents ranging from 11% to 27% .
After being weighed, each of the test samples was presented five
times to the swept frequency measuring system. The resulting scan from
each presentation was transferred from the scaler analyser to the
computer and labelled. The linear regression analysis was performed and
the gradient of the straight line fit and the intercept at 5 GHz were
determined before transferring the data to disc storage. After the
fifth presentation the sample was resealed in a plastic bag while
awaiting analysis for total moisture content.
5.3.7 Appraisal of Test Results
The plots of 8 individual scans, representing different levels of
moisture content, for the Parrot Crop seam are included in Figures 102
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to 109 They include the straight line fit for each scan and illustrate
the change in both gradient and intercept as the moisture content
increases. The average gradient and intercept of the straight line fit
for the five presentations was determined for each of the 16 test
samples from each seam.
The calibration graph of total moisture content plotted against
the average attenuation/frequency gradient (dB/GHz) for the Parrot Crop
seam is shown in Figure 110 The quadratic regression for this
calibration gave a correlation coefficient of 0.957 and a standard
deviation of 1.28% moisture. Taking into account the mass of the
sample, the graph of total moisture against the weighted gradient
(dB/GHz/kg) is included in Figure 111. The quadratic regression in this
case showed an improvement in correlation coefficient to
0.979
and in
standard deviation to 0.91% moisture.
The data for the remaining six seams was processed using the same
method and the results of the quadratic moisture calibrations with both
the unweighted and weighted gradient for all seven seams is given in
Table 16. In addition, the results for all seven seams, totalling 108 in
all, were aggregated and plotted against the unweighted and weighted
gradients in Figures 112 and 113 respectively. The results of the
quadratic regression, included in Table 16 showed an improvement in
correlation coefficient from
0.964
to 0.973 and in standard deviation
from 1.14 to 0.99% moisture when the mass of the sample is taken into
account in the calibration.
The calibration accuracy for the combined results of all seven
seams is of the same order as for the individual seams and confirms that
the swept frequency, microwave measuring technique has considerable
potential for providing a measure of moisture content which is largely
independent of the particular coal. However, the seams tested were all
low rank and a much wider range of seams must be investigated to
determine whether a universal calibration is feasible.
5.4 Summary
Following the earlier demonstration of a British Coal moisture
meter based on the attenuation of microwaves at a single frequency to
moisture measurement of discrete samples and to a continuous sub-stream,
work was undertaken to extend the scope of applications of this
technique for on-belt measurement and to a wide range of coal types.
A new S-band meter, with an increased dynamic range, has been
designed and built, and a unit installed on a conveyor belt at a
colliery site. An ultrasonic bed depth meter has also been installed at
this site and data on microwave attenuation, bed depth and tonnage, from
an existing belt weigher, were collected on a specially designed data
logging unit. Correlations between these signals have been
demonstrated, but a reorganisation of scientific services within British
Coal resulted in termination of work at this site before a full
calibration of the moisture meter could be carried out. Arrangements
for a continuation of these trials at another site are in hand. A
second meter of this type is also being fitted to the Ram Feed Ash
Monitor for sub-stream trials.
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A single frequency microwave moisture meter of the above type is
limited in its application by sensitivity to variations in coal type,
particle size and coal bed geometry. A system designed to minimise
these problems, by measuring the attenuation of microwaves swept through
a range of frequencies, has been developed and an experimental
laboratory unit built. Tests with samples from a range of coal seams
have shown that it is relatively insensitive to coal type and gives a
calibration accuracy of +0.4% to +1.3% moisture at one standard
deviation.
6. CAPACITANCE MOISTURE MONITORING
6.1 Previous Investigations, Applications and Developments by British
Coal
6.1.1 Early Investigations
Initial investigations into the possible application of a
capacitance technique for the on-belt monitoring of the moisture content
of coal in the UK was undertaken in the former North Durham Area of
British Coal in the mid I960's (8).
The equipment used was developed in the United States of America
by Messrs Foxboro-Yoxall. The primary measuring element consisted of a
ski plate designed to ride on the bed of coal on a conveyor. Extending
from the underside of the ski plate was a vertical keel plate which was
insulated from the ski plate. In operation the underside of the ski and
the keel plate were in contact with the coal, the coal acting as the
dieletric. The measuring system also comprised a measuring head
assembly and a capacity Dynalog recorder.
The capacitance technique depends on the very large difference in
the dielectric constant between water, at 80, and coal, at around 6, for
excitation frequencies below 10 GHz. Laboratory tests, using the
Foxboro instrument, on eleven different coals covering the full range of
coal rank and each adjusted to a standard size grading, gave standard
deviations ranging from 0.25 to 0.75% moisture for ten of the eleven
coals tested.
The instrument was then installed at a colliery to continuously
monitor 25 mm - 0 raw coal directly on a conveyor and the trial extended
for a period of two and a half years. The main problem encountered was
wear on the primary element particularly affecting the insulation
between the ski and the keel plate. The wear was partially overcome by
the use of glass instead of epoxy resin as the insulating material.
Frequent checks were made on the instrument calibration over the
duration of the trial and a calibration standard deviation of 0.5%
moisture was regularly achieved.
6.1.2 Further Development and Testing
The Foxboro moisture meter was no longer commercially available in
the UK after about 1970 and, some time later, work was begun at the
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former Mining Research and Development Establishment (MRDE) of British
Coal to design a replacement. Initial testing of a prototype unit by
the former North East Area of British Coal indicated that results of
similar accuracy to that achieved with the Foxboro monitors was
possible. Subsequently, up to six of the MRDE developed moisture
monitors were used by the North East Area for both laboratory and plant
trials extending over a period of two years.
The very comprehensive testing by North East Area (9) led to a
number of conclusions regarding the MRDE moisture monitor in particular
and on-belt moisture monitoring in general. These were:-
(i) In situations where the coal product was well mixed and suitably
presented to the ski sensor the MRDE instrument was capable of an
accuracy (2 s) of better than +2% based on an integration period
of 4 minutes. Over longer periods, an increased accuracy was
expected.
(ii) Tests showed that the MRDE designed ski, with the two additional
vertical earthed plates, was as accurate as the original Foxboro
type ski with its single keel plate.
(iii) The insulation of the keel plate remained a problem even with the
glass inserts bedded in silicone rubber. The problem was one of
damage to the glass due to the impact of larger material or
foreign objects rather than wear.
(iv) Apart from the problem of insulation, wear on the keel plate
limited the life of the ski to an average of 9 months, depending
on the belt speed and coal nature.
(v) The monitor would not give reliable results on plants where the
washery water had a high and variable dissolved salts content
because of the effect on the conductivity of the coal.
(vi) The monitor had to be calibrated individually for each coal and,
therefore, it would not be suitable for blended products of
highly variable composition.
(vii) Because of the many problems of on-belt monitoring, consideration
should be given to monitoring moisture with a sample fed system.
The limitations of capacitance moisture monitoring had also been
reported earlier by Hampel and Hoberg (10).
6.2 Insulated Plate Capacitance Moisture Monitor
6.2.1 Proposed Development
It was considered that a number of the above limitations might be
overcome by the development of an insulated plate capacitance system for
incorporation in a sample fed, Ram-feed presentation unit.
The complete insulation of the capacitor plates would eliminate
the effect on the capacitance measurements of variations in the
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electrical conductivity of the coal due to variations in the presence of
ionic salt solutions. In addition to increasing the electrical
conductivity of the coal, ionic salts increase the relative interfacial
dielectric permittivity of the sample due to the accumulation of salt
ions at grain boundaries, i.e. the Maxwell-Wagner effect.
The incorporation of the insulated capacitance system in a sample
fed, Ram-feed presentation unit would considerably reduce the problems
of material presentation, wear and damage. It would also simplify the
calibration procedure, which was much more complicated for on-belt
systems.
6.2.2 Design of Experimental Laboratory System
A theoretical study, reproduced in Appendix 14, was first
undertaken to examine the factors involved in the design of an insulated
capacitance monitor. This study was followed by the design of a
discrete sample cell and an electronic measuring system to investigate
the technique further in the laboratory.
(i) Design of Insulated Plate Capacitance Cell
The test cell comprised an open wooden box of internal dimensions
185 mm wide, 300 mm long and 200 mm deep. It was provided with
two aluminium plates measuring 300 mm long by 100 mm deep and
2 mm thick which were arranged against opposite sides of the box
to form a parallel plate capacitor. The inside of the cell was
lined with plastic sheet of 0.235 mm thickness.
The final effective size of the experimental cell was 180 mm
wide, 300 mm long and 100 mm deep. These dimensions corresponded
to a 300 mm long section of the trough of the Ram-feed sample
presentation unit where the insulated capacitance plates could be
incorporated into the opposite side walls of the trough.
(ii) Measurement Electronics - Design Parameters
Before designing the electronic measurement system it was
necessary to establish the following parameters:-
(a) the operating frequency
(b) the maximum value of capacitance
The operating frequency was chosen to be in excess of 10 MHz.
The maximum value of capacitance likely to be encountered could
not, however, be accurately pre-determined.
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The equation defining the capacitance (C) of a parallel plate
capacitor is:-
C - Eo Er A
where Eo - Permittivity of free space (- 10'9 F/m"l)
3671
Er - Relative permittivity of the sample
A - Capacitor plate area
D - Capacitor plate separation
The maximum capacitance value would be obtained if the
measurement cell was completely filled with water (Er - 80) and
it would be given by:-
C - 80 x 10-9
x
o.l x 0.3
367T .
0.18
.-. C - 118. 10-12
F
i.e. C - 118 pF
This value represents the upper limit of capacitance which the
system was initially designed to measure.
Subsequent tests with the measurement system showed that an
operating frequency of 12.3 MHz was the most applicable.
(iii) Measurement Electronics - Description
The electronic measurement system developed for the insulated
plate capacitance cell comprised the following components,
arranged as illustrated in Figure 114.
(a) high frequency signal generator
(b) buffer amplifier
(c) measurement amplifier
(d) oscilloscope
The high frequency generator was the source of the radio
frequency signal which was used to drive the buffer amplifier.
The output from the buffer amplifier was applied across the
measurement cell and measurement resistor network. The voltage
developed across the measurement resistor was amplified and
buffered by the measurement amplifier and displayed on the
oscilloscope. Short circuited quarter-wave filters were
connected to the measurement system at positions A, B, C and D.
In addition, a 4.7pF capacitor was connected in shunt with the
measurement cell to help stabilise the measurement system by
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providing a small fixed value of capacitance when the cell was
empty. The effect on the measurement was to cause a small
offset.
During the first series of laboratory tests it was necessary to
manually reset the high frequency generator signal level at each
change of sample moisture because of the electrical loading of
the output stage of the buffer amplifier. Prior to the second
series of laboratory tests the electronics system was modified to
include automatic output signal level stabilisation, as shown in
Figure 115. This was achieved by comparing the output signal
level from the buffer amplifier with the input level to a
differential video amplifier which was arranged as a buffer
driven amplifier. The difference between these two signals was
used to generate a control signal which was applied to the
automatic gain control input of the differential video amplifier.
6.2.3 Laboratory Tests with Experimental Cell - Series I
The first series of tests with the experimental insulated plate
capacitance cell was conducted using a bulk sample of 12.5 • 0.5 mm
washed coal from Markham Colliery Coal Preparation Plant where the trial
site for the Ram-feed sample presentation unit was located. The bulk
sample was allowed to dry in the laboratory to a final moisture level of
1.7% and was then divided into three equal sub-samples, of approximately
6 kg, and designated 1A, IB and 1C.
The moisture content of Sample 1A was successively increased by 2%
intervals, using distilled water, up to a final level of 18% added
moisture. After each moisture addition the sample was thoroughly mixed
and presented to the capacitance cell for measurement.
A similar procedure was followed with Sample IB but, instead of
distilled water, a solution of 5g/litre of sodium chloride was used to
increase the moisture content at 2% intervals. With Sample 1C the
procedure was repeated using a log/litre solution of sodium chloride.
The results obtained are presented in Table 17 and plotted in
Figure 116.
The results show that the output signal from the measuring system
increases significantly with the increasing concentration of ionic
salts. The results also show quite a marked change in the relationship
between the added moisture content and the instrument reading which up
to about 1000 mV, corresponding approximately to 8% added moisture,
appeared approximately linear. For future testing the measuring system
gain was reduced to extend the effective range and any results in excess
of 1000 mV were discarded.
The results from this first series of tests showed that variations
in the ionic salt content of moist coal samples can appreciably affect
the measurements made with an insulated plate capacitance moisture meter
and were therefore not particularly encouraging.
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6.2.4 Laboratory Testing of Experimental Cell - Series II
A second series of tests were conducted following modifications to
the measurement system found necessary from the initial tests. The
samples were again obtained from Markham Colliery Coal Preparation Plant
and comprised 12.5 - 0.5 mm washed coal taken from the feed to the
dewatering centrifuges and, therefore, contained a high level of free
moisture. Four separate coal samples were obtained, with a 4 month
interval between the first two and second two.
A representative sub-sample, of approximately 6 kg, was taken from
the main sample in the as-sampled condition, loaded into the
experimental cell and a measurement made. The sub-sample was emptied,
mixed and re-loaded and a second measurement made. The procedure was
repeated a third time and the measurements averaged. A representative
portion of the sub-sample was then subject to moisture analysis and the
remainder mixed back into the original sample which was then allowed to
air-dry for a short time. A second sub-sample was taken and a further
set of measurements and moisture determination were made. This
procedure was repeated until the main sample reached an air-dried
condition. The same procedure was followed with the remaining three
samples and the results reported in Table 18.
The graph of total moisture content plotted against the instrument
reading, Figure 117, shows a good linear relationship extending over a
wide range of moisture content of 4.28% to 19.17%. The linear
regression analysis of total moisture with respect to instrument reading
gave the following values : -
Correlation coefficient 0.98
Standard deviation 0.88% moisture
The samples used for this second series of tests were analysed for
chlorine as an indication of the presence of ionic salts. The chlorine
level was found to be consistently low.
Taking into account that the output from Markham Colliery is drawn
from as many as five seams and that the samples were collected four
months apart the accuracy level achieved in the second series of tests
was considered particularly encouraging. It was therefore considered
possible that an insulated plate capacitance moisture meter might be
sufficiently accurate, given a suitable material presentation system, to
be useful in some coal preparation applications.
6.2.5 Proposed Further Investigations
Laboratory investigations were conducted using a comparatively
simple measuring system. A more elaborate system, capable of measuring
both the real and imaginary components of the relative permittivity of a
sample, might enable some correction for ionic salt variability to be
made. Using this more advanced measuring equipment to examine discrete
samples, further investigations could be conducted at several
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representative colliery sites to provide information on the variability
of ionic salts between spot samples and the possible scope of
application of the measuring technique.
It was proposed to proceed with these investigations as outlined
above. A specification for a suitable measuring system was prepared and
is included in Appendix 15. The specification was put out to tender to
a number of private companies. However, the high cost of developing the
equipment together with the introduction of two proprietry moisture
monitors, suitable for use with coal, led to the suspension of further
work in this direction until both proprietary monitors had been assessed
and evaluated.
7. DETERMINATION OF MOISTURE IN COAL BY NUCLEAR MAGNETIC RESONANCE
7.1 Introduction
The potential for the use of nuclear magnetic resonance
measurements for the determination of the moisture content of solids has
long been recognised and was reported as being applicable to coal more
than 25 years ago (11). The technique is unique among those, such as
microwave attenuation, capacitance measurement and neutron modetation,
which have been tried for this purpose in that it can be so arranged as
to give a response related directly to water. This study briefly
reviews work in this field to date, includes measurements made with a
laboratory analyser and comments on the potential for the technique to
be used for on-line analysis.
7.2 Principle and Measurement Techniques
For a full understanding of nuclear magnetic resonance, reference
should be made to some suitable text book (12); for the purpose of this
report a very general outline of the principles will suffice.
Basically, the technique exploits the interactions which occur
between the magnetic moments associated with the nuclei of many nuclides
and an external field. In particular, at a given magnetic field
intensity a resonance between the external field and the magnetic
moments of the nuclei is established at a frequency which is specific to
the nuclide involved and which has an amplitude proportional to the
number of nuclei present in the interrogated volume of material. In
addition, the characteristics of the response are modified by themolecular environment of the nuclei of interest and, consequently, it is
possible to differentiate a response originating from hydrogen in liquid
water from that due to hydrogen combined with carbon in a hydrocarbon
molecule.
Two basic approaches are available for the detection of the
resonance effect, the continuous wave method and the pulsed method:-
In the continuous wave approach the material under interrogation
is placed in a homogeneous high intensity field between the poles of a
magnet and subjected to a much weaker electromagnetic field, at right
angles,
from a radiofrequency coil around the sample. At appropriate
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combinations of these two fields, resonant absorption of energy occurs
as a result of transitions between energy levels associated with the
nuclear dipoles. The energy change is detected in the coil and
amplified. A spectrum of the energy changes in the expected region of
the resonance may be obtained by the application of a suitably varying
current to coils around the magnet poles which produces a slow linear
sweep of the magnetic field intensity within appropriate limits.
Fig 118 shows the kind of spectrum obtainable for wet coal. The
resonance signal from hydrogen in water occurs at a closely defined
value while that from hydrogen in solid hydrocarbons is broadened over a
wide range of values. Careful choice of the signal gate excludes most
of the latter giving a signal predominately arising from water.
In the pulsed approach the material is again interrogated by two
electromagnetic fields, a steady, high intensity field from a magnet and
a pulsed, lower intensity radiofrequency field which, together, meet the
energy requirements for a resonance response from hydrogen. Application
of the rf field disturbs the magnetic moment established in the presence
of the static field. Following the application of an rf pulse of
suitable duration the nuclei re-establish the original equilibrium
Boltzmann population distribution in the static field with the emission
of a transient signal known as the Free Induction Decay
(FID).
The
time-related characteristics of this signal are a function of the
molecular environment of the hydrogen nuclei. The decay time of the
response originating with hydrogen in the coal substance is much more
rapid than that associated with water, and the resulting composite
signal, Figure 119, can be readily analysed using suitable curve fitting
functions to give a signal related only to water.
7.3 Review of Work to Date
Initial studies on the quantitative determination of the moisture
content of coal were made in the I960's using an nmr spectrometer based
on the continuous wave measurement technique. These studies indicated
that the technique could be applied to a wide range of coal ranks and
was applicable to the measurement of total moisture content, including
that portion of the water absorbed into the pores of the coal(13).
Using a derivative of the nmr signal it was shown that the moisture
content correlated well with the signal height, particularly if
variations in bulk density were corrected for by including a
mass-related factor. Low ash crushed coal, with a maximum particle size
of 1.6 mm, was tested and it was shown that values of moisture content
determined in this manner were within 1% of the standard
laboratory-determined values in a range up to 30% moisture. It was even
demonstated that similar results could be obtained from a slowly moving
(grams per second) stream of coal contained within a glass tube. The
work was further extended to show that neither ash content, up to 50% ,
nor particle size, up to 6 mm, had any significant effect on the
accuracy of measurement(14).
Although measurement of moisture content using this method was
reasonably accurate and rapid, taking only a few minutes, the equipment
was complex and expensive. In particular, the requirement for a
homogeneous, high intensity magnetic field contributed significantly to
the high cost which, together with the associated technical problems,
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restricted the magnet size and, consequently, the available volume for
interrogation of the sample. (In the case of Ladner's work(13) the
volume of coal interrogated was approximately 15 cm^.) Development of
'low resolution' continuous wave instruments in the 1970's, using a
lower intensity magnetic field, reduced the cost of nmr spectrometers
suitable for the determination of moisture in coal and further studies
of the potential accuracy of this method for static samples were made.
Using a commercial analyser with a sample volume of 40 cm^ and
measurement times of 2 minutes, Robertson (15) obtained a calibration
standard deviation of +1.3% for a suite of coals covering a wide range
of coal ranks, with moisture contents up to 23% and at a maximum
particle size of 3.8 mm. A study by Page (16), which extended tests
using the same type of instrument to a sample volume of 100 cm^, showed
that for coals with moisture contents ranging up to 11% , calibration
standard deviations of 0.2 to 0.4% moisture were obtainable irrespective
of sample volume, Table 19. Figure 120 combines the results from suites
with different maximum particle size, indicating that particle size has
no significant effect on accuracy
(+0.26%).
The individual samples
represented in this relationship were drawn from coals of NCB Coal Rank
Code numbers 300 to 700 and ranged from 4 to 47% in ash content.
This work has shown that the nmr technique is relatively
insensitive to a number of variables which occur in coal but also draws
attention to the serious errors which can result from the presence of
magnetic materials. Naturally occurring magnetic materials are rare in
coal but the widespread use of magnetite as a medium for coal cleaning
in dense medium plants means that it is likely to be present, as a
contaminant, in many products. The extent to which magnetite
contaminates prepared coal products can vary considerably but typically
could be of the order of 0.1 to 0.2% on a cleaned coal. Results
presented by Robertson indicate that addition of magnetite to samples of
coal produced significant errors. Measurements by Page confirm this and
indicated that the addition of 0.1% magnetite is equivalent to a
reduction of 0.8% in moisture content, Figure 121. Addition of
magnetite produces a broadening of the nmr spectrum as determined by the
continuous wave method, which, at least up to 0.1% addition, is
proportional to the level of contamination. This proportionality allows
some correction of the measured value to be made by making a second
measurement to include the broadened
spectrum(15).
The first reported results of the application of pulsed nmr
spectrometry to the quantitative determination of moisture in coal are
those of King (17) in 1983. The work of King is particularly relevant
to this project in that it was specifically aimed at the development of
apparatus for the measurement, using magnetic resonance methods, of a
range of parameters, including moisture content, in flowing coal. Using
specifically designed apparatus, the nmr response from moisture was
measured in powdered (<0.1 mm) coal pneumatically conveyed through a
10 mm diameter pipe at flow rates of a few kilograms per second.
Results for a range of coal types with moisture contents up to 31%
indicated that measurements with a maximum error of 1.5% moisture were
possible under these conditions. It was suggested that such
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measurements should be feasible on coal being transported in a different
manner (e.g., on a conveyor) but no such applications have yet been
reported.
Pulsed nmr determination of moisture in coal has also been
investigated using 5 cm
3
samples of fine coal (<1 mm) in a laboratory
spectrometer (18). Over a range of moisture contents up to 26% and for
measuring periods of 20 seconds, calibration accuracies (+ls) of 0.4 to
0.7% moisture were obtained by a measurement method which was
independent of sample density. Proposals to investigate the accuracy of
measurement obtainable in sample by-lines up to 50 mm diameter and using
lower magnetic field homogeneity were made but so far have not been
reported.
7.4 Potential For On-Line Monitoring
Table 20 summarises the results of work to date showing that with
currently available equipment it is possible to measure the moisture
content of static or moving samples of coal to an accuracy of the order
of +1-2% moisture, a level which would be acceptable for on-line control
of coal quality. These measurements are substantially independent of
coal type, ash content or particle size up to 6 mm. The problem of
magnetic contamination of the sample could restrict the accuracy of the
technique when applied to products which may contain varying amounts of
magnetite carried over from dense medium coal cleaning processes. There
does,
however, appear to be some potential for the introduction of some
degree of compensation for such errors by modification of the
measurement technique.
The major restriction to the application of nmr spectrometry to
on-line measurement of moisture in coal is the requirement for a large
volume, homogeneous magnetic field. In the reported work the largest
volume of coal interrogated was 100 cm
3
. Adaptation of such
instrumentation to accept a flowing stream of coal is possible, but
would place considerable restrictions on particle size and throughput of
samples and lead to severe handlability problems with higher moisture
content coals.
To handle wet coal, as produced at a plant, it would be necessary
to have, at least, a sample sub-stream of dimensions similar to those
obtained with the Ram-feed Ash Monitor (100 x 180
mm).
This, in turn,
would necessitate a large increase in the dimensions of the magnet
required to produce a magnetic field of sufficient volume and adequate
homogeneity to allow measurements at the same level of accuracy as those
reported with smaller instruments. No such applications to the
determination of moisture in coal have been reported, but the technology
to detect relatively small amounts (0.6% by volume) of other nuclides
displaying nuclear magnetic resonance within a sensing region having a
cross sectional area of 36 cm x 58 cm and a total volume of 0.08 ra
3
has
been developed (19).
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7.5 Summary
Work on relatively small (up to 100 cm^) volumes of coal has shown
that it is possible to determine the moisture content of coal in a
reasonably short response time to an accuracy of +1 to 2% absolute using
the phenomenon of nuclear magnetic resonance.
This degree of accuracy is obtained for over measuring periods of
20 seconds to 2 minutes and is not significantly affected by coal type,
ash content or particle size. The technique can be applied to static or
moving coal.
Bulk density variations affect the accuracy to a degree but
compensation for such effects can be readily applied.
Magnetite contamination has a significant effect on accuracy and,
although some compensation may be possible, errors from this source
present a problem which has to be addressed.
Data so far obtained relate only to small volume samples; scaling
up the technique to accommodate the larger samples normally associated
with a product sub-stream or, indeed, to full stream monitoring would
require the application of large magnets. Such a step would be costly.
In view of the progress achieved in the field of on-line moisture
in coal measurement by other techniques (e.g., microwaves), where a
similar level of performance has already been demonstrated, it is
considered that the nmr technique does not offer any substantial
technical advantages which would warrant the considerable expense in
equipment and development costs which would be required for application
to large volume coal samples.
8. THE APPLICATION OF NEUTRON/GAMMA INTERACTIONS TO ON-LINE COAL
ANALYSIS
Interest in the application of neutron/gamma interactions to coal
analysis has grown considerably in recent years, to the extent that
on-line analysers are now commercially available and operating at a
number of locations
(20-22).
8.1 Basic Principles and Techniques
When coal is subjected to a flux of fast neutrons some
interactions with nuclei result in the production of high energy gamma
radiation, at a variety of energy levels, which are specific to the
types of nuclei involved and which, under particular conditions of
measurement, can be related quantitatively to the concentrations of the
nuclei involved. Spectroscopic analysis of this gamma flux yields
information on the elemental composition of the coal. Both the incident
neutrons and the resulting gamma radiation are highly penetrating,
allowing the interrogation of substantial volumes (0.2m3) of coal and
thus reducing or eliminating the need for crushing and preparation of
the coal before analysis. The gamma ray emissions can be classed as
prompt, occurring within 10
_1
0 seconds of the interaction, or delayed,
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arising from the decay of induced radioactivity with a half-life
measured in seconds, minutes or even longer.
Application of techniques involving delayed gamma emissions to
on-line analysers have been studied (23-24) but only a very limited
number of interactions produce emissions suitable for coal analysis and
most effort has been made in the field of prompt gamma neutron
activation analysis
(PGNAA).
Two mechanisms predominate in the
application of PGNAA to coal: (a) neutron capture interactions, which
occur mainly with neutrons at thermal energies (~10 2eV) and (b) in
elastic scattering interactions which occur with fast neutrons at energy
levels above nuclide-specific thresholds (-1 to 6 MeV for important
elements in
coal).
A convenient isotopie source of neutrons is
californium -252 (predominately 0.5 to 4 MeV) (25). Use of a 14 MeV
neutron generator has also been suggested and tried (26) but is much
less suited for an industrial environment.
In order to utilise the thermal capture interactions, moderation
of the fast neutron flux to thermal energies is necessary and, in the
case of coal, this is conveniently achieved within the bulk sample,
mainly as a result of elastic scattering interactions with hydrogen
present in the coal substance and any associated water. With a suitable
detection system, useful signals may be obtained from the thermal
neutron interactions with H, C, N, Na, Al, Si, S, CI, K, Ca, Ti, and Fe,
i.e. most of the major and minor elements present in coal and its
associated mineral matter except 0 and Mg. The spectra obtained are
complex, including significant gamma responses at more than 50 energy
levels from the 12 elements and interpretation, in terms of elemental
concentration, has to take into account the gamma ray energy response of
the detector and the effects of variations in both neutron and gamma ray
transport within the coal, due to changes in coal composition and
density. Nevertheless, it has been possible to derive algorithms which
are relatively insensitive to the major sample-related effects for
particular detector configurations and which are capable of giving
results of an accuracy, acceptable for operational purposes, for most
elements over measurement periods of a few minutes (27, 28) .
The absence of data for oxygen and the large statistical
uncertainty on the thermal neutron gamma signal from carbon impose a
significant degree of uncertainty on the measurements for some of the
other elements in coal. It has been shown that these measurement
precisions can be considerably improved if the system is set up to
generate, in addition to the thermal neutron capture gamma events, those
capture gamma events which arise as a result of Inelastic scattering of
the neutrons (29). This may be achieved by using 241 Am/Be as the
neutron source which gives strong signals for oxygen, carbon and silicon
inelastic scatter gamma radiation.
In order to obtain adequate data for total elemental analysis it
is generally considered that a high resolution semiconductor detector is
necessary (29). These devices, however, have quite low counting
efficiencies and are subject to fast neutron damage. With present
technology it is difficult to reconcile the conflicting requirements of
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high total count rates, necessary to allow sufficient statistical
precision on individual element measurements within the time constraints
of operational requirements, without subjecting the detector to a high
intensity neutron flux which shortens its life to an unacceptable
degree. Scintillation detectors do not have this problem but their low
resolution means that only data for a few of the elements in coal are
readily resolved from the detected spectrum. One attempt to overcome
this problem has been the development of a pair spectrometer array using
up to 19 scintillation detectors (30). This system gives much improved
resolution over a simple scintillator and has a better data rate
performance than a germanium semiconductor detector.
8.2 General review of on-line applications
The feasibility of the application of neutron gamma interactions
to the analysis of bulk coal and demonstrations of results for a limited
range of elements on experimental closed loop coalflow systems were
reported in the early I960's
(31-32).
Further development of one of
these projects (33) resulted in a prototype demonstration system,
installed at a coal preparation plant in the USA, which monitored the
sulphur content of metallurgical coal flowing through a bin 4.0 m high
and 1.0 m in diameter at a rate of 6 tonnes per hour (34). Using a
large (150 x 180 mm) sodium iodide scintillation detector and a
californium -252 neutron source this installation achieved a precision
(+ls) of 0.05% sulphur over a 2 minute measuring period.
The growing importance of coal as a primary fuel in the 1970's brought
about a resurgence of interest in on-line coal analysis and a number of
research interests undertook work aimed at the development of systems of
coal analysis based on neutron activation interactions. In particular,
the Electric Power Research Institute (EPRI) in California sponsored a
programme to develop on-line analysers in 1976 which led to the
development of a family of designs for PGNÂÂ analysers by Science
Applications International Corporation (SAIC) of California (35). At
the same time MDH - Motherwell Inc. of California began a study of the
technique and subsequently designed an analyser for bulk stream (36).
In 1983 Gamma-Metrics, also of California entered the market with a Bulk
Coal Analyser.
8.3 Commercially Available Analysers
At present, SAIC, MDH and Gamma-Metrics are the only manufacturers
who have reached the commercial stage with neutron/gamma analysers and
have units operating in the field. Table 21 compares some of the
principle features and dimensions of the three analysers.
8.3.1 Science Applications International Corporation
Assisted by EPRI sponsorship, SAIC undertook a series of
experimental and theoretical programmes to establish basic design
parameters for an on-line analysis system and the potential for
application at mines and power plants. This work is reported in a
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series of EPRI reports under the general title of 'Nuclear Assay of
Coal(37). The main conclusions arrived at were:-
(i) Given suitable constraints on coal bed thickness and density, and
on source, sample and detector configuration it was possible to
generate prompt gamma spectra in which all the main elemental
constituents of coal (except oxygen and magnesium) can be
identified.
(ii) For full elemental analysis, a high resolution germanium detector
is preferred but for some elements a low resolution sodium iodide
scintillation detector is adequate.
(iii) The susceptibility of germanium detectors to damage by neutrons
and their low counting efficiency results in a lower measurement
precision than is acceptable within the short response times
required for plant control purposes. Sodium iodide detectors do
not have this limitation.
(iv) The most accurate way of determining total hydrogen content is by
measurement of epithermal neutron flux leakage from the coal bed
with a helium -3 detector.
(v) A full elemental analyser is best served with a hybrid detector
system containing all the above types of detector.
(vi) A separate measurement of moisture content is required and can be
obtained with adequate precision using a moisture meter based on
microwave attenuation.
(vii) Mass flow information required in the data processing can be
obtained from conventional mass/density gauges.
A prototype elemental analyser (CONAC) based on these findings is
illustrated in Fig. 122.
Coal up to 75 mm particle size from the inlet feed hopper is
transferred on a flat bed conveyor between a californium -252 neutron
source and the detector assembly containing a High Purity germanium
detector, a sodium iodide scintillation detector and a helium -3
epithermal neutron detector. The belt speed is adjusted to give a flow
rate up to 30 tonnes per hour in a bed 30 cm deep and 90 cm wide. A
microwave moisture meter and a caesium -137 density gauge are installed
between the feed hopper and the neutron analyser section. The CONAC is
fitted with adequate radiation shielding and safety interlocks,
including a level detector on the feed hopper which stops the belt in
the event of an interruption to the coal feed, to ensure that radiation
levels at external surfaces meet safety regulations.
The signals from the two gamma detectors are processed to remove
pulse pile up and other unwanted effects, and subjected to suitable
stripping routines to give spectra from which the net areas of various
peaks can be related to the elements of interest. This information,
together with the output from the other detectors, is processed in the
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microcomputer to give elemental analysis of the major and minor elements
in coal (except Mg and 0) and moisture content, ash content and
calorific value. The ash content is inferred from the sum of the ash
elements, expressed as oxides, and including empirical values for
magnesium oxide and sulphur trioxide. The calorific value is calculated
from the heats of combustion of carbon and hydrogen (modified Dulong and
Petit formula) or from the relationship between ash, moisture and dry,
ash-free calorific value. Data for elemental analysis is integrated
separately for the Ge and Nal detectors on different time bases. Data
from the Nal detector system, which gives information on H, C, S, Cl, N
and Fe, on a short time basis, is normalised against the corresponding
values from the Ge detector system, which reports on a much longer time
base.
Initially these reporting periods were 20 minutes and 3 hours
respectively (38) but subsequent improvements to the system allowed the
same analysis precision to be reached over periods of 5 and 20 minutes
(39).
The reported values for accuracy and precision are given in
Tables 22 and 23 (40).
Prototypes of two other instruments based on the same technology
have been produced. These are the SAIC Sulfurmeter (41), which is
similar in design to the CONAC but uses only a Nal detector for prompt
gamma radiation measurement, and the SAIC Rapid Sulfurmeter (42), which
also uses a Nal detector but consists of a horizontal cylinder 1.8 m
long by 1.2 m diameter with a vertical chute 0.35 m by 0.30 m which is
fitted with a bottom door and has a capacity of 110 kg of coal. This
latter instrument operates on a 6 minute batch measurement basis over a
15 minute cycle. Calibration accuracy for the Belt Sulfurmeter is
reported as 0.08% s over a range 0.4 to 4.4%. The Batch Sulfurmeter
returned a similar initial calibration accuracy and a 6 minute precision
of measurement ranging from 0.04 to 0.09% sulphur.
8.3.2 MDH - Motherwell Inc.
With a primary interest in the rapid on line measurement of
sulphur in coal, MDH chose to develop a system centred on
californium -252 and a sodium iodide scintillation detector. Their
preferred method for coal presentation was a gravity-fed vertical,
rectangular chute through which the coal passed at a rate controlled by
a feeder at the bottom outlet. Figure 123 is a schematic representation
of the instrument(ELAN). The chute is over 2.5 m high and has a cross
section of 0.35 x 0.25 m. Enclosed within a suitable radiological
shield, the source/detection system consists of two 252 Cf sources at
one side of the chute and a large Nal detector at the other. Coal, at a
maximum particle size of 100 mm, flows between the two at any convenient
rate up to 100 tonnes per hour. The top of the chute is fitted with a
microwave moisture meter and a nucleonic level gauge which is linked to
the outlet discharge feeder to ensure that the chute remains full of
coal at all times.
The signal from the detector is stripped of pulse pile-up events
to give a spectrum which is considered to be a linear superposition of
the individual spectra of the gamma radiation from thermal neutron
capture interactions with all the detectable elements in coal, together
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with those which arise from inelastic scatter events for carbon and
oxygen and spectra representing background and neutron/detector
interactions (43). Information on these 23 component spectra is derived
from standards measured at the factory before despatch and installation
of the unit (44). The measured spectrum is decomposed into its
components giving a factor for each element which is related to its
weight fraction by normalisation to all the contributing elemental
factors. The factor for oxygen is inferred from its known relationship
with the ash elements, carbon, hydrogen and moisture. Ash content is
inferred from the sum of the ash elements, expressed as oxides,
including a value for sulphate taken from an assumed relationship with
total sulphur content, and corrected by a scaling factor for magnesium
and other undetermined ash constituents. Moisture content is obtained
directly from the microwave moisture meter. Calorific value is
calculated from the heats of combustion of carbon and hydrogen using the
Hott-Spooner relationship. Response times were initially quoted as
8 minutes for major elements and 1 hour for minor elements (45) but
current data sheets claim accurate analysis within 2 to 5 minutes.
Table 24 indicates the reported accuracy for a limited selection of
tests (46). Ån accuracy, usually within the limits of ASTM
reproducibility by normal laboratory analysis, is claimed for a 20
minute measurement period (47).
8.3.3 Gamma-Metrics
The Gamma-Metrics Coal Analyser (Model 3612C) was introduced in
1983 and designed to be a fully self-contained, portable, weatherproof
unit requiring no special housing facilities (48). The system chosen is
based on a californium -252 neutron source and scintillation detectors.
Figure 124 is a schematic representation of the instrument. Coal
presentation is via a vertical, rectangular chute 0.9 m by 0.3 m and the
flow of coal is controlled by a belt feeder at the bottom outlet. The
source/detection system consists of three 252 Cf sources, spaced
horizontally on one of the larger faces of the chute, with two large Nal
scintillation detectors on the other face. Immediately above and below
the neutron interrogation zone a 137 Cs transmission density gauge is
fitted to provide bulk density data. An ultrasonic level sensor, in the
mouth of the chute, is linked to the discharge belt feeder to ensure
that the chute remains full at all times. Coal at a maximum particle
size of 100 mm, is fed into the top of the chute at a rate up to
500 tonnes per hour.
Signals from the detector are stripped of pile-up events and other
unwanted signals to give a spectrum in which the contributions measured
in various chosen energy channels are correlated by regression
techniques to the elemental concentrations of known standards. An
initial generic calibration is made at the factory and subsequently
refined using coals from the site. Signal conditioning and data
processing is carried out within the unit and resulting values
transmitted to a display terminal. Moisture content was originally
calculated from hydrogen content, assuming a fixed C/H ratio in coal
substance. More recently, a microwave moisture meter has been offered
as an optional extra. Ash content is inferred from the sum of the ash
elements, and calorific value is calculated from the dry ash-free value
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for the coals being measured. Response times of one minute are claimed
for the instrument. Reported values for precision and accuracy are
listed in Table 25
(49-51).
In 1986, Gamma-Metrics introduced another version of their
analyser, with a smaller chute (0.45 m x 0.3
m),
and a maximum
throughput of 100 tonnes per hour (Model
1812C).
Precision is similar
to Model 3612C but with a response time of 2 minutes.
8.3.4 Summary of Performance Capabilities
Although reported values of accuracy and precision have been given
in Tables 22-25, it is difficult to make a comparison since the
composition of test coals used and the details of the procedures often
differ. In particular, the measurement times adopted are often
different or even not clearly defined, which has had a considerable
effect on estimates of precision. The minimum response times reported
in Table 21 do not necessarily reflect the optimum required to achieve
an acceptable value, especially for the minor constituents of ash. An
estimate of the relative accuracy at present obtainable for various
parameters has been made from the available data and is given in
Table 26.
8.3.5 Installations
At present, a total of 20 neutron gamma analysers are installed or
on order. Table 27 shows the distribution among the manufacturers and
the current status of the units. Six of the analysers are at power
plants and 14 at mines; all are situated in North America.
Of the SAIC analysers, only the Batch Sulfurmeter is in use where
it monitors the quality of the clean coal product from the coal
preparation plant, with respect to sulphur content, ash content and
calorific value to facilitate SO2 emission control, which is applied in
terms of a limit on the S02/calorific value ratio. The analyser is
integrated with the cleaning plant process control. The CONAC is also
at the same plant and linked to the same product stream but also has
facilities for the testing of imported coals on a re-cycle system (52).
Its primary role as a demonstration unit has been fulfilled and it is
now out of use and under consideration for transfer to another location.
The Belt Sulfurmeter at Monroe Power Plant has been used extensively to
control the blending operations for incoming coal with respect to
sulphur content, to ensure compliance with SO2 emission regulations. It
has been shown to accurately and rapidly track sulphur variations in the
coal stream and to show a good correlation between sulphur content of
the feed to the boiler and SO2 emissions from the stack (53). Changes
in the quality of coal supplies to the power station have rendered this
application redundant and it is now out of use.
The first of the MDH ELANS was installed on a clean coal product
line at Homer City Power Plant where it measures sulphur and ash
content, moisture and calorific value to ensure compliance with SO2
emission limits (45). As with the SAIC sulfurmeter at Monroe, control
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of the sulphur content of the feed coal to the boiler was chosen as an
alternative to flue gas de-sulphurisation to meet regulations. Of the
other 3 MDH units, two are at power plant and one at a mine, two are
recent installations and not yet commissioned while the third is still
in manufacture.
Gamma-Metrics have installed 12 units, two of which are the larger
3612C Model, and have one more under construction. They also maintain
the original production unit which is mounted on a lorry trailer with a
recirculation rig to give a self contained mobile demonstration unit.
Most of these installations have been made within the last three years
and there is as yet little published information. One unit is not in
use due to closure of the mine. The others are all at producing mines
where they provide data on the quality of coal shipments and offer a
basis for control by blending (6 units) cleaning plant control (3
units),
sorting (2 units) and direction of mining operations (1
unit).
Sulphur is the primary product quality parameter of interest but ash and
calorific value are also measured.
The majority of the analysers have been installed within the last
three years and consequently published information on operating
experience and instrument reliability is very limited. The SAIC
sulfurmeter at Monroe was put into service at the end of 1981 and was in
use,
somewhat intermittently due to problems outside the analyser
system, until 1988. The SAIC Batch sulfurmeter at Paradise has been
running as an operational tool since late 1983. The Homer City Elan has
been operating since mid-1983 but delays in the installation of a
parallel ASTM sampling system held up its full use as a plant control
instrument until mid 1985. The first Gamma-Metrics Analyser to be put
into operational use was at the Pyramid Surface Mine in early 1986. No
major reliability problems have been reported for these instruments and
operational availability is understood to be good. Capital costs are
high, ranging from £200,000 to over £500,000. Potential economic
benefits are also high, at least in the American market, where
application of this technology can result in operational cost reductions
of millions of dollars per year (54).
8.4 Summary
The principles involved in the application of neutron/gamma
interactions to coal analysis have been studied for a long time with the
result that three manufacturers now offer, and have operational
experience with analysers based on this technique. A fourth
manufacturer is just entering the market.
The analysers are capable of accepting large volume streams of
coal, up to 500 tonnes per train, with little or no preparation. They
are capable of measuring all the major and minor elements in coal
(except oxygen and magnesium) plus ash, moisture and calorific value,
and other analysis-derived parameters like ash fusion, on a continuous
basis.
Response times are of the order of tens of minutes and accuracy
is acceptable for control purposes. Accuracy ranges from relative values
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of less than 5% for hydrogen, carbon, ash content and calorific value to
more than 30% for sodium, calcium and titanium.
Some 20 analysers have been ordered or installed and are mainly in
use in connection with the control of coal quality to specifications
designed to meet SO2 emission standards in the USA. Their potential for
use in the operation of power station boilers is under study and an
extension of their use to other areas can be expected, provided the high
capital costs of the equipment can be justified.
9. GENERAL CONCLUSIONS
9.1 On-stream Ash Monitoring
Laboratory trials of both the backscatter and transmission low
energy (60 keV) gamma radiation techniques show that calibration
accuracies for well homogenised samples range from ±0.2% ash to +3.86%
ash with an average relative value of 5%. These values are
predominantly influenced by variations in coal composition, in
particular iron content where the effect of 1% of Fe203 on the
instrument reading is equivalent to that of 6% of ash.
Using a simple mathematical model of the backscatter system, it is
possible to calculate, from the composition of the coal, the expected
calibration standard deviation of ash content for well homogenised
samples,
with a reasonable degree of accuracy. The prime compositional
factors affecting calibration accuracy are level of ash content in the
coal, variability of iron content in the coal and the degree of
correlation between iron content and ash content. A good empirical
relationship between calibration accuracy and these factors has been
found.
The sensitivity of the Wultex backscatter system to bed depth
variations limits its use to belts where coal bed thickness exceeds
150-200 mm.
On-site calibration trials at two locations indicate that other
factors,
perhaps related to lack of homogeneity throughout the coal bed
at the point of measurement, introduce significant errors. Compared
with laboratory measurements, accuracy (+ls) is reduced by a factor of
about 2 to about +10% to 20%. Increasing the integration period to
several hours offers no improvement in accuracy.
Generally, the Wultex backscatter instrument is mechanically and
electrically reliable but, at the levels of accuracy found, offers only
data of limited value for the control of processes in the preparation of
the type of blended power station fuel commonly used in the UK.
The Coalscan two-energy transmission system is relatively
insensitive to variations in coal bed depth.
Given a reasonably thorough interrogation procedure the accuracy
of static calibrations is degraded only slightly as particle size
increases from 0.2 mm to 25 mm. Simulation of the on-belt situation,
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however, indicates that the calibration accuracy is reduced by a factor
of two to a relative value of +10% . On-belt trials confirm this level
of accuracy and integration over longer periods offers no improvement.
 significant proportion of the measured error is not accounted for by
coal composition variations (including moisture) or sampling and
analysis of the reference samples. Direct comparison with an existing
Phase 3A sub-stream monitor taking samples from the same production
stream indicates that the on-belt monitor is less accurate. The
equipment is generally mechanically and electrically reliable but some
evidence of long term calibration drift was seen. The level of accuracy
obtained again limits its potential for blending control purposes but
this geometry should be applicable to most belts.
Trials with both on-belt systems demonstrated the considerable
difficulties of performing dynamic on-belt calibrations.
9.2 Sub-stream Ash Monitoring
A sub-stream presentation unit (the Ram Feed Unit) has been
developed, which is capable of accepting coals of difficult handlability
and up to 25 mm particle size, to produce a continuous bed of coal, with
a smooth surface profile, suitable for radiometric examination. The
unit is also designed to accept a microwave moisture meter system and
has proved to be mechanically and electrically relaible over long
periods.
Equipped with a Phase 3A type backscatter ash monitor head, it
should be capable of measuring ash content (and with a suitable moisture
meter, moisture
content),
to a higher accuracy than can be achieved with
on-belt systems.
9.3 Microwave Moisture Monitoring
An improved, single frequency, microwave moisture meter has been
developed, together with an ultra-sonic bed depth system and their
ability to monitor appropriate parameters directly on a main product
belt demonstrated. This system should form the basis of an on-belt
moisture monitoring system. This type of moisture meter is also
suitable for application in the Ram Feed sub-stream presentation unit.
A moisture meter, based on a new measuring technique which
measures microwave attenuation over a range of frequencies, has been
developed and shown to give acceptable calibration accuracy. This Swept
Frequency System will be relatively insensitive to variations in coal
type, particle size and coal bed geometry and should be capable of
application to main-stream or sub-stream monitoring.
9.4 Capacitance Moisture Monitoring
An experimental version of a new type of capacitance moisture
meter (Insulated Plate Capacitance Monitor) has been developed and
tested in the laboratory. Calibration accuracy is similar to that of
microwave systems but some sensitivity to dissolved salts, in the water
associated with coal, remains. Quotations for the production of a
prototype instrument were much higher than expected. As a result of
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this cost and the satisfactory progress in microwave techniques it is
not considered to be economically justifiable to continue this work at
the present time.
9.5 Nuclear Magnetic Resonance
À study of the application of this technique to moisture
monitoring shows that it has the ability to measure moisture in coal to
an accuracy similar to that obtainable for microwave and capacitance
techniques.
The present state of the development, however, is restricted to
very small (100 cm^) volumes of coal and extension of the technique to
larger volumes, either in sub-streams or main-streams, will require
substantial technical effort and, if successful, is expected to result
in equipment with high capital cost. In these circumstances, it is not
considered worthwhile to pursue this particular line of work further.
9.6 Neutron/gamma Analysis of Coal
A total of 20 analysers, based on this principle, have been
ordered or installed and significant operational experience gained,
mainly in the control of product quality to meet SO2 emission standards.
These analysers are capable of real-time measurement of most of the
important elements in coal on a continuous basis, using large volume
coal streams, to an accuracy which is acceptable for some operational
purposes. An extension of their use, particularly to the field of power
station boiler control, can be expected, provided the returns can
justify the high capital cost of the equipment.
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APPENDIX 1
EXTRACT FROM HEADS OF AGREEMENT CONTRACT BETWEEN THE NCB AND WULTEX MACHINE
CO LTD FOR THE TRIAL OF A WULTEX RADIOMETRIC ASH-METER, TYPE G-3,
AT MANTÓN COLLIERY
ACCEPTANCE CRITERIA FOR TRIAL
The Plant will be deemed to have completed the Trial satisfactorily if
the following criteria are fulfilled:-
(i) Operational Reliability
To demonstrate operational reliability the Plant must be
regularly capable of operating under all feed conditions for
continuous periods of 5 working days without requiring operator
attention. This capability is to be demonstrated over a
continuous period of 60 working days. If during any 5 day
period operational attention is required then the Trial period
so far as operational reliability is concerned will revert back
to zero time and a further attempt to demonstrate this
capability for 60 workings days will be required.
(ii) Mechanical Reliability
To demonstrate mechanical reliability the Plant must be capable
of operating for a continuous period of 60 working days without
requiring any mechanical maintenance and for a continuous period
of 120 working days without requiring any replacement mechanical
parts.
If mechanical attention or replacement mechanical parts
are required within the specified periods then the Trial period
with respect to either of these requirements will revert back to
zero time and a further attempt to demonstrate the capability
for the specified period will be required.
(iii) Electrical Reliability
To demonstrate electrical reliability the Plant must be capable
of operating for a continuous period of 60 working days without
requiring electrical attention and for a continuous period of
120 working days without requiring any replacement electrical
parts. If electrical attention or replacement electrical parts
are required within the specified periods then the Trial period
with respect to either of these requirements will be considered
to revert back to zero time and a further attempt to demonstrate
the capability for the specified period will be required.
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(iv) Performance Standards
The Radiometrie Ash-Meter, Type G-3, having been calibrated
on-stream in accordance with the Contractors instructions
against the incinerated ash content of coal samples
representing the normal range of variation of the coal stream
being monitored, will be demonstrated to be capable of ash
measurements with the degree of accuracy specified in
paragraphs (a) and (b) below.
(a) The integrated ash measurement over a period of coal flow
of one hour shall be within +1.5% ash of the incinerated
ash content for a minimum of 95% of at least fifty such
measurements made within a period of 3 months from the
date of calibration and where the mean total moisture
content during such measurements lies within +4% of the
mean total moisture content of the coal samples on which
the calibration was based.
(b) The integrated ash measurements over a period of coal flow
of four minutes shall be within +2.5% ash of the
incinerated ash content for a minimum of 95% of at least
one hundred such measurements made within a period of 3
months from the date of calibration and where the mean
total moisture content during such measurements lies
within +4% of the mean total moisture content of the coal
samples on which the calibration was based.
A second calibration of the Radiometric Ash-Meter will be
made within 4 months of the date of the first calibration
or by agreement. If the ash measurements made in
accordance with paragraphs (à) and (b) above should show a
progressive drift away from the initial calibration and if
over the period of these measurements a change should
occur in the proportion of the seam outputs at the Mine
such that the change in the output from any seam exceeds
20%
of the Mine output then the accuracy of the ash
measurements will be assessed on the basis of the mean of
the first and second calibrations.
For the purpose of assessing the performance all sampling
will be conducted in accordance with BS 1017, Part 1, 1977
and all total moisture and incinerated ash contents will
be determined in accordance with BS 1016, Part 3, 1973.
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APPENDIX 2
CALCULATION OF CALIBRATION ACCURACY FROM COAL COMPOSITION
The relationship between backscattered Intensity and the composition
of the coal containing i elements in concentrations r is given by:-
1
'
k I
°
/ U
i
« i
r
i
£
i
(H
+ F')i ri
where
I - intensity of backscattered radiation
k - geometrical factor
I
0
- intensity of incident radiation
0* - sum of the Compton and coherent scattering coefficients
at the incident radiation energy
p - mass attenuation coefficient at the incident energy
u' - mass attenuation coefficient at the backscattered energy
From the elemental composition of the coal and tabulated values for
the scattering and attenuation coefficients, a value for relative
backscattered intensity (I/kI
0
) is calculated for each sample in a suite of
coal covering the range of ash content required. Regression analysis of
the ash content on the relative backscattered intensity provides
information on the extent of the correlation between the two parameters and
an estimate of the accuracy of ash content determination in terms of the
standard deviation of the results about the regression line.
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APPENDIX 3
NATIONAL COAL BOARD
HEADS OF AGREEMENT CONTRACT FOR EXPERIMENTAL USE OF WULTEX RADIOMETRIC
ASHMETER EQUIPMENT
TECHNICAL APPENDIX TO AGREEMENT
OBJECTIVES, DIRECTION AND REVIEW OF TRIAL
1. OBJECTIVES OF LABORATORY INVESTIGATIONS
Introduction
NCB experience so far with the Wultex Radiometric Ashmeter has been
restricted to a trial installation at Mantón Colliery where the output has
been drawn from a single seam, although some limited information has been
gained on the affect of introducing coal from other collieries mining
different seams. The conclusion drawn from the trial was that although
there may be collieries where the Ashmeter can be employed to advantage,
there are other collieries where inability to maintain an appropriate
material bed depth and bulk density, or where production is on a multi-seam
basis, may influence the accuracy of ash measurement.
Data originating from Poland and made available to the NCB by Wultex
has suggested that certain material presentation parameters, principally
material bed depth and bulk density, could have an appreciable effect on
the accuracy of ash measurement. Laboratory investigation with the
objective of quantifying the affect of these variables is considered
necessary. The NCB, Yorkshire Regional Laboratory, is prepared to
undertake this work; and with the further objective of assessing the
factors affecting the design of a method of presentation of the coal to the
Ashmeter in order to optimise the degree of accuracy of the Ashmeter in
circumstances where the required bed depth cannot be achieved without some
modification to the presentation-conveyor layout.
Variations in the elemental composition of the ash in different seams
affect the relationship between the ash content and the backscattered
radiation. In particular, iron is known to affect the backscattered
radiation disproportionately to its mass concentration and, therefore,
variations in iron content between different seams could have a significant
affect on the accuracy of ash measurement. The iron content of the Mantón
coal was found to be reasonably consistent during the performance tests on
the Ashmeter conducted under the initial Heads of Agreement Contract.
Therefore, to assess the possible wider application of the Ashmeter the
laboratory investigations will include the examination of coal from a
multi-seam colliery with the objective of assessing the affect of
variations in ash composition and iron content on the accuracy of the
Ashmeter.
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Stage 1 - Laboratory Investigations using Mantón Coal
It is currently proposed to conduct tests initially using samples of
part-treated smalls from Mantón Colliery since this would assist in
deciding the direction and extent of further trials with the existing
Ashmeter installation. However, the test procedures necessary to examine
different bed depths and bulk densities would encounter problems resulting
in possible errors if these investigations were attempted on a laboratory
scale with 50 mm top size material. It is therefore proposed that all coal
samples from Mantón would be screened at 25 mm and the material above this
size would be crushed below 25 mm and mixed back into the sample.
A suite, comprising a minimum of 20 calibration samples, of Mantón
part-treated smalls, and excluding any foreign coal being treated
temporarily at Mantón, will be collected. The samples will cover the
normal range of ash variation of 11% - 21% as found with the performance
tests conducted in October 1981 under the previous Heads of Agreement
Contract trials.
The laboratory tests will be conducted using the laboratory
presentation rig, modified as necessary and loaned to the NCB by the
Contractor. The NCB will provide a variable depth sample presentation
container of suitable design and means of achieving reproducible degrees of
sample compaction. Each coal sample will be tested at bed depths of 200,
160, 120 and 80 mm after a standardised compaction procedure which will
consist either of uniform dead-weight loading or subjection to vibration
for a fixed time dependent on preliminary tests. Each sample will be
presented to the Ashmeter a minimum of 10 times at each bed depth. A
measurement of the bulk density of the compacted material will be made for
each filling of the presentation container.
Additional tests to investigate the affect of variation of the bulk
density of the material will be conducted on at least three of the
calibration samples representing the lower, middle and upper portions of
the 11 - 21% ash range. These tests will be conducted at one or more
selected bed depths and at least two additional levels of bulk density
which will be achieved by varying the degree of compaction of the material.
Following the completion of testing on each of the calibration
samples it will be subjected to laboratory analysis for moisture, ash, iron
and sulphur content. A calibration for the Ashmeter, between the radiation
count readings and the laboratory ash determinations, will be obtained for
each bed depth and will permit assessment of the calibration accuracy of
the Ashmeter reading. The radiation count readings for the bulk density
tests will be converted to ash readings, according to the calibration for
the appropriate bed depth, and the affect of bulk density variations on the
ash readings will be obtained.
Stage 2 - Laboratory Investigations with Multi-seam Coal
For the second stage of the investigations it is proposed to use coal
samples, not exceeding 25 mm top size, from a multi-seam colliery where
there is a significant difference between the levels of iron content
between the seams so as to introduce a greater variability in the iron
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content of the samples. The procedures followed in Stage 1 will be
modified and simplified, wherever possible, to reduce the amount of test
work, according to the experience and findings of Stage 1.
2.
WULTEX PARTICIPATION IN DIRECTION OF INVESTIGATIONS
The objectives of the investigation shall be as detailed in the above
Introduction unless varied by mutual written agreement between the NCB and
the Contractor.
The NCB reserve the right to determine the laboratory procedures for
the investigations but undertake to consult fully with Wultex in order to
achieve agreement before the start of the investigations and before any
significant changes are made during the course of the investigations.
Nominated Wultex Engineers will be allowed reasonable access to
observe the progress of the investigations provided each visit is agreed in
advance with the Scientist in charge of the investigations.
3. REVIEW OF PROGRESS OF INVESTIGATIONS
The NCB will hold regular meetings with nominated representatives of
Wultex to review the progress of the investigations. The frequency of such
meetings would be dependent on the progress of the work and would normally
take place not more than once per month. The results of the investigations
would either be presented at such meetings or communicated by letter to
Wultex.
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APPENDIX
4
WÜLTEX
RADIOMETRIC
ASHMETER
SITE REQUIREMENTS FOR PROPOSED SECOND TRIAL INSTALLATION
Preparation Plant Feed
A
multi-seam
output
drawn
from
two
or
more
seams.
Any
foreign
coal
treated
should
be
on
a
regular
basis
where
it
comprises
an
appreciable
proportion
of
the
plant
throughput
(i.e.,
greater
than
10%).
Product
to
be
Monitored
Preferred
Product
Size Range
Ash
Variation
Alternative
Product
Size
Range
Ash
Variation
Monitoring Location
Preferred
Location
■
Alternative
Location
Blended
power
station
smalls
Preferably 30 mm - 0 but maximum of
50
mm
considered
At
least
+3%,
in
shift
or
train-load
samples,
in
the
range
10-20%
ash
Untreated
smalls
Preferably
less
than
30
mm
but
maximum
of
50
mm
considered
At
least
+5%
in
ash
range
20-40%
A
belt
feeder
with
a
minimum
bed
depth
of
200 mm and at least a 2 m length of
accessible
coal
surface
either
before
or
after
any
weigh
section.
Effective
product
mixing
prior
to
feeder
and
good
access
for
either
manual
or
mechanical
sampling
at
discharge
of
feeder.
A
belt
conveyor
with
belt
speed
not
greater
than 2.5 m/s, centralised product loading and
a bed depth not normally less than 150 mm
after
profiling.
Prior mixing of product either by mixer or
multiple
transfer
points.
Mechanical
sampler
at
either
return
or
head
end
of
proposed
conveyor.
Access to both sides of conveyor at monitor
location.
Headroom of 1.8 m above centre-line of belt.
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APPENDIX 5
HEADS OF AGREEMENT CONTRACT BETWEEN THE NCB AND WULTEX MACHINE CO. LTD.
FOR THE TRIAL OF A WULTEX RADIOMETRIC ASHMETER
AT BILSTHORPE COLLIERY, NORTH NOTTINGHAMSHIRE AREA
APPENDIX II - ACCEPTANCE CRITERIA FOR TRIAL
The Plant will be deemed to have completed the Trial satisfactorily
if the following criteria are fulfilled:-
(i) Operational Reliability
To demonstrate operational reliability the Plant must be
regularly capable of operating under all feed conditions for
continuous periods of 5 working days without requiring operator
attention. This capability is to be demonstrated over a
continuous period of 60 working days. If during any 5 day
period operator attention is required then the Trial period so
far as operational reliability is concerned will revert back to
zero time and a further attempt to demonstrate this capability
for 60 working days will be required. An example of operator
attention would be the necessity to remove a build-up of wet
fines from the contact surface of the plough unit in order to
maintain the measuring system at the correct height above the
coal surface.
(ii) Mechanical Reliability
To demonstrate mechanical reliability the Plant must be capable
of operating for a continuous period of 60 working days without
requiring any mechanical maintenance and for a continuous
period of 120 working days without requiring any replacement
mechanical parts. If mechanical attention or replacement
mechanical parts are required within the specified periods then
the Trial period with respect to either of these requirements
will revert back to zero time and a further attempt to
demonstrate the capability for the specified period will be
required.
(iii) Electrical Reliability
To demonstrate electrical reliability the Plant must be capable
of operating for a continuous period of 60 working days without
requiring electrical attention and for a continuous period of
120 working days without requiring any replacement electrical
parts.
If electrical attention or replacement electrical parts
are required within the specified periods then the Trial period
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with respect to either of these requirements will be considered
to revert back to zero time and a further attempt to
demonstrate the capability for the specified period will be
required.
(iv) Performance Standards
To enable the Vultex Ashmeter to provide a direct reading of
the ash content of the coal to be monitored it will be
necessary to obtain the relationship between the countrate of
the backscattered radiation and the incinerated ash content of
the coal over the normal range of ash variation, and for this
relationship to be entered in the instrument.
The Ashmeter will therefore be calibrated on site for Bilsthorpe
50 mm - 0 Blended Power Station Fuel in accordance with the following
procedure.
(a) The calibration will be based on a minimum of 30 calibration tests
each extending over a period of approximately 12 minutes and covering
a minimum range of ash content of 10% to 27%.
(b) For each calibration test the preparation plant will be operated so
as to provide sufficient current make of Power Station Fuel to
sustain a continuous flow of coal over the belt feeder at normal
flowrates for the required period of the test.
(c) The Ashmeter will be set to print out the countrate measurement every
2 minutes for 6 consecutive 2 minute periods and the arithmetic mean
of all 6 measurements will be taken to represent all the coal which
passed over the belt feeder during these measurements.
(d) The existing automatic sampler, located at the head end of the belt
conveyor which receives the coal from the belt feeder, will be used
to collect a sample, comprising a minimum of 35 full stream
increments taken at regularly spaced time intervals, from that parcel
of the coal which passed over the belt feeder during each of the
calibration tests and with due allowance being made for the time
delay in the material travelling between the Ashmeter and the
sampler.
(e) The coal samples collected during each calibration test will be
prepared and analysed in accordance with British Standard methods to
determine the total moisture and the ash content, both of which will
be reported on an 'As Received' basis.
(f) The Contractor will provide suitably experienced staff to participate
in the calibration procedure and be responsible for the operation of
the Ashmeter and obtaining the countrate print-outs for each test.
The Contractor's representatives will also be responsible for
calibrating the Ashmeter in accordance with the relationship obtained
between the countrate and the 'As Received' ash content.
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(g) The NCB will provide experienced staff to liaise with the
Contractor's representatives and carry out the sampling and
laboratory analysis procedures.
The Ashmeter, having been calibrated for the Bilsthorpe Power Station
Fuel in accordance with the foregoing procedure, will be tested according
to the following method and the accuracy of ash measurement determined.
(a) The accuracy of the Àshmeter will be assessed in a series of tests
conducted within 2 months of calibration by comparing the average ash
reading over a 12 minute period with the incinerated ash content of a
representative, full stream sample of the product which passed over
the belt feeder during the same time period.
(b) The performance assessment will be conducted and the samples analysed
by experienced NCB staff and the Contractor's representatives will
have access to observe the testing at all stages.
(c) For each performance test the preparation plant will be operated so
as to provide sufficient current make of Power Station Fuel to
sustain a continuous flow of coal over the belt feeder at normal
flowrates for the required period of the test.
(d) The Àshmeter will be set to print out the average ash content at
2 minute intervals for 6 consecutive 2 minute periods and the
arithmetic mean of all six measurements will be taken as the measured
ash content of the coal passing over the belt feeder in the 12 minute
test period.
(e) A representative sample of the coal, which has passed over the belt
feeder during the 12 minute test period, will be taken in a minimum
of 35 regularly spaced increments by the automatic sampler, at the
delivery of the belt conveyor following the belt feeder, with due
allowance for the time delay in the material travelling from the
Ashmeter to the sampler.
(f) The coal sample for each performance test will be prepared and
analysed for total moisture and ash content.
(g) The performance testing will be continued until 60 tests have been
conducted in which the total moisture during each test is within +4%
of the mean total moisture content of the samples on which the
calibration was based and the incinerated ash content is within the
range of incinerated ash contents of the calibration samples.
(h) To satisfy the requirements of the NCB the average Ashmeter
measurement for the 12 minute test period shall be within +3.0% of
the incinerated ash content for at least 95% of the 60 tests which
comply with the total moisture and ash content limitations specified
in paragraph (g) above.
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For the purposes of calibrating the Ashmeter and assessing the
performance all the sampling will be conducted in accordance with BS 1017
Part 1, 1977 and all total moisture and incinerated ash contents will be
determined in accordance with BS 1016, Part 3,1973.
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APPENDIX 6
TECHNICAL APPENDIX TO AGREEMENT FOR THE TRIAL OF A
COALSCAN 3500 ASH MONITOR
OBJECTIVES, DIRECTION AND REVIEW OF TRIAL
1. Objectives of Laboratory Investigations
Introduction
The Board has no experience of the Coalscan 3500 ash meter but from
information gained and a description of the principles involved there are
certain advantages to be gained which are unique to this equipment.
Notwithstanding this there are doubts as to the extent to which the
technique can be successfully and usefully applied to UK coals.
From theoretical considerations, the measuring principle should
tolerate variability in bulk density, bed depth, top size and surface
profile, particularly well and without significant loss of accuracy. Its
limitations are expected to arise mainly from variations in elemental
composition of the mineral matter which provides the basis for ash content
assessment. A further limitation affecting its resolution capability
(sensitivity) could arise from excessive attenuation of the transmitted
radiations by high ash coal or high bed depths or, more particularly, a
combination of the two.
There is a clear need to quantify these parameters thoroughly and
objectively so that the limitations and possible applications can be
broadly defined. The Yorkshire Regional Laboratory are prepared to
undertake this work on behalf of the Board making use of test facilities
sited within their Coal Sample preparation area.
2.
Test Procedure
The tests fall naturally into 2 distinct categories, those directed
to the derivation of basic data and those intended to give guidance on
which plants may be suitable for any proposed installation.
2.1 Basic data - it is required to know:-
1. The magnitude of the basic error inherent in the statistical
count.
2.
The effect of changes in "iron in ash" in terms of the error in
the reported ash value at both high and low levels of ash
content.
3. The effect of changes in "calcium in ash" in terras of the error
in the reported ash at both high and low levels of ash content.
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no
4.
The effect of bed depth on both resolution capability and
accuracy at both high and low ash levels. Deterioration in
performance might be expected, for example, where there is
either very little attenuation, for example shallow beds of low
ash material, or excessive attenuation as in the case of deep
beds of high ash material.
To reduce the workload in terms of replicate testing, these
tests will be conducted under idealised conditions specifically
designed to eliminate other variables or other sources of high
random errors. The coal will be ground to below 2.8 mm and
accurately profiled. Changes in iron, calcium and "ash" will be
done by controlled weighed additions of chemically pure
materials.
2.2 Suitability of Coalscan for Potential Applications at Specific
Locations
whilst it may be possible to pre-judge to some extent a likely site
for successful operation, this will be aided considerably by the results
obtained from the basic studies. When a likely plant has been selected,
taking into account coal preparation procedure, a suite of at least
20 samples will be taken from site over a period of (say) 1 shift. Each
sample will be composed of no more than a single increment large enough to
fill the test container. Each will be scanned several times for each of
several separate filling operations with the same sample and here a
knowledge of the effective beam width and count rate times are required to
decide on a presentation method more likely to simulate the "dynamic"
system which characterises the practical use of the instrument.
The whole test will be replicated using fresh samples derived from
other shifts/days. All samples so obtained will be separately prepared for
analysis by established BS techniques and analysed for ash content and ash
composition. The results will be analysed in depth and the implications
considered. The work will be repeated, refined or extended if considered
necessary. The Board reserve the right to determine the laboratory
procedures for the investigations but undertake to consult fully with the
Contractors as the UK Agents of Coalscan, in order to achieve agreement
before tests are commenced and before any significant changes are made to
the test programme during the course.
The Contractor will be allowed reasonable access to observe progress
provided each visit is agreed in advance with the Board Scientist in charge
of the investigations.
3. Review of Progress
The Board will hold regular meetings with representatives of the
Contractor to review progress of the investigations. The frequency of such
meetings would be dependent on progress but would normally take place not
more than once per month. The results of tests would either be presented
at such meetings or communicated by letter to the Contractor.
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n i
APPENDIX 7
EXTRACT FROM HEADS OF AGREEMENT CONTRACT BETWEEN THE NCB AND MAGCO LTD
FOR THE TRIAL OF A COALSCAN 3500 ASH MONITOR AT ASKERN COLLIERY.
SOUTH YORKSHIRE AREA
APPENDIX II
ACCEPTANCE CRITERIA FOR TRIAL
The Plant will be deemed to have completed the Trial satisfactorily
if the following criteria are fulfilled:-
(i) Operational Reliability
To demonstrate operational reliability the Plant must be regularly
capable of operating under all feed conditions for continuous periods
of 5 working days without requiring operator attention. This
capability is to be demonstrated over a continuous period of
60 working days. If during any 5 day period operator attention is
required then the Trial period so far as operational reliability is
concerned will revert back to zero time and a further attempt to
demonstrate this capability for 60 working days will be required.
(ii) Mechanical Reliability
To demonstrate mechanical reliability the Plant must be capable of
operating for a continuous period of 60 working days without
requiring any mechanical maintenance and for a continuous period of
120 working days without requiring any replacement mechanical parts.
If mechanical attention or replacement mechanical parts are required
within the specified periods then the Trial period with respect to
either of these requirements will revert back to zero time and a
further attempt to demonstrate the capability for the specified
period will be required.
(iii) Electrical Reliability
To demonstrate electrical reliability the Plant must be capable of
operating for a continuous period of 60 working days wihout requiring
electrical attention and for a continuous period of 120 working days
without requiring any replacement electrical parts. If electrical
attention or replacement electrical parts are required within the
specified periods then the trial period with respect to either of
these requirements will be considered to revert back to zero time and
a further attempt to demonstrate the capability for the specified
period will be required.
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(iv) Performance Standards
To enable the Coalscan ash monitor to provide a direct reading of the
ash content of the coal to be monitored it will be necessary to
obtain the relationship between the countrate of the transmitted
radiation and the incinerated ash content of the coal over the normal
range of ash variation, and for this relationship to be entered in
the instrument.
The Board will require to establish any difference between the
on-belt and off-belt calibration of the ash monitor. It will
therefore be calibrated for Askem 25 - 0 mm blended power station
fuel both on-belt in accordance with the following procedure and
off-belt in accordance with the procedure specified by the
manufacturer.
(a) The on-belt calibration will be based on a minimum of 30 calibration
tests each extending over a minimum period of 8 minutes or such time
interval as agreed with the Board's Engineer and covering the normal
range of ash content of 10% to 26%.
(b) For each calibration test the preparation plant will be operated so
as to provide sufficient current make of Power Station Fuel to
sustain a continuous flow of coal along the belt conveyor at normal
flowrates for the required period of the test.
(c) The ash monitor will be set to give the countrate measurement for the
test period which will be taken to represent all the coal which
passed along the belt conveyor during these measurements.
(d) The existing automatic sampler, located at the head end of the belt
conveyor which feeds to the Blended Smalls conveyor, will be used to
collect a sample, comprising a minimum of 35 full stream increments
taken at regularly spaced time intervals, from that parcel of coal
which passed along the belt conveyor during each of the calibration
tests and with due allowance being made for the time delay in the
material travelling between the sampler and the ash monitor.
(e) The coal samples collected during each calibration test will be
prepared and analysed in accordance with British Standard methods to
determine the total moisture and ash content, both of which will be
reported on an 'As Received' basis.
(f) The laboratory preparation of the on-belt calibration samples will be
designed to provide a 2 kg sub-sample, crushed below 1 mm or less,
from each calibration sample. Each sub-sample will be presented in
turn to the ash monitor in the off-belt position and count readings
will be taken in accordance with the manufacturers instructions. The
sub-samples will then be subjected to separate laboratory analysis.
The contractor will then have the option of using either the on-belt
or the off-belt data to derive the calibration equation which he will
then enter into the instrument.
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(g) The Contractor will provide suitably experienced staff to participate
in the calibration procedure and be responsible for the operation of
the ash monitor and obtaining the countrate readings for each test.
The Contractor's representatives will also be responsible for
calibrating the ash monitor in accordance with the relationship
obtained between the countrate and the 'As Received' ash content.
(h) The NCB will provide experienced staff to liaise with the
Contractor's representatives and carry out the sampling and
laboratory analysis procedures.
The ash monitor, having been calibrated for the Askern Fuel in
accordance with the foregoing procedure, will be tested according to the
following method and the accuracy of ash measurement determined.
(a) The accuracy of the ash monitor will be assessed in a series of tests
conducted within 2 months of calibration by comparing the average
ash
reading over an 8 minute period or period agreed with the Board's
Engineer with the incinerated ash content of a representative, full
stream sample of the product which passed along the belt conveyor
during the same time period.
(b) The performance assessment will be conducted and the samples analysed
by experienced NCB staff and the Contractor's representatives will
have access to observe the testing at all stages.
(c) For each performance test the preparation plant will be operated so
as to provide sufficient current make of Power Station Fuel to
sustain a continuous flow of coal along the belt conveyor at normal
flowrates for the required period of the test.
(d) The ash monitor will be set to give an output signal equivalent to an
integrated ash content over the test period such that the reading at
the end of the period represents the average ash content over that
period.
(e) A representative sample of the
coal,
which has passed over the belt
during the test period, will be taken in a minimum of 35 regularly
spaced increments by the automatic sampler, at the delivery of the
belt which feeds to the Blended Smalls conveyor, with due allowance
for the time delay in the material travelling from the sampler to the
ash monitor.
(f) The coal sample for each performance test will be prepared and
analysed for total moisture and ash content.
(g) The performance testing will be continued until 60 tests have been
conducted where the incinerated ash content is within the range of
incinerated ash contents of the calibration samples.
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(h) To satisfy the requirement of the NCB the average Coalscan ash
monitor measurement for the test period shall be within +2.5% of the
incinerated ash content for at least 95% (ie 57) of the 60 tests
which comply with the ash content limitations specified in paragraph
(g) above.
For the purposes of calibrating the ash monitor and assessing the
performance all the sampling will be conducted in accordance with BS1017,
Part 1 1977 and all total moisture and incinerated ash contents will be
determined in accordance with BS1016, Part 3, 1973.
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APPENDIX
8
Specification for the Design and Manufacture of a
Pre-production Prototype Ram-Feed Unit (RFU)
1. INTRODUCTION
1.1 Scope
This specification covers the design, manufacture, delivery,
installation and commissioning of a pre-production prototype Ram-Feed
Ash Monitor Presentation Unit (RFU).
1.2 Delivery
The pre-production RFU is to be delivered to, and installed at
Markham Colliery Coal Preparation Plant, British Coal Central Area,
Duckmanton.
1.3 Exclusions
The following items shall be excluded from the tender,
(i) All Nucleonic and electronic equipment,
(ii) The hydraulic power pack.
( H i ) The inductive proximity switches.
1.4 Schematic Diagrams and Drawings
All schematic diagrams and other drawings which are necessary to
fully illustrate the proposed design will be made available to the
Supervising Officer on completion of the design phase.
1.5 Documentation
(i) On completion the contractor shall supply two complete sets of all
arrangement and manufacturing drawings. Two sets of maintenance and
operating manuals complete with listings of, and specifications for,
all components used will also be supplied.
(ii) Final manufacturing drawings are to be prepared on British Coal
pre-numbered Drawing Sheets, which will be provided free of charge.
All drawings shall comply with British Coal's Codes of Practice,
details of which are available through the Board's Engineer.
1.6 Standard of Workmanship
The equipment to be supplied shall be constructed to a high standard;
consistent with good engineering practice.
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1.7 Phasing
The Contract shall comprise design, manufacturing and installation
phases. The Contractor will not proceed to the manufacturing phase
until the design has been agreed with the Board's Engineer.
2.
BACKGROUND INFORMATION
Some years ago, the NCB, in conjunction with AERE Harwell, developed
the Phase 3A Ash Monitor. This ash monitor was designed to be fed at
a rate of up to 1 tonne/hour with -5 mm material. It was equipped
with a nucleonic measuring system which enabled a correction for
variations in product iron content to be made to the measured ash
reading.
Though the accuracy of this ash monitor was acceptable, it was
susceptible to blockage by material of difficult handlability and in
some installations, required constant attention.
The Ram-Feed Unit (RFU) was conceived as being a positive feed system
which would solve the problem of blockages and provide a constant
geometry coal bed compatible with the established Phase 3A nucleonic
principle.
Development of the RFU has now progressed to point where a
pre-production prototype RFU is required. This specification defines
the modifications to the present experimental RFU that are required
to be included into the pre-production prototype.
3. TECHNICAL REQUIREMENTS
It will be assumed that the tenderer has a firm appreciation of the
existing experimental RFU installation.
References will be made to the attached schematic diagram of the
experimental RFU.
It is required that the pre-production prototype RFU will be of the
same materials and manufacture as the experimental RFU except for the
inclusion of modifications detailed below in paragraphs 3.1 to 3.7
inclusive, or where specifically stated otherwise.
3.1 The trough shall be extended in length such that the free trough
length (Dimension A) is 1 metre. The design should also allow for
the trough length (Dimension A) to be reduced to the existing length,
should that be necessary.
3.2 The bottom of the trough is to be constructed such that the section
at the reject end only (Dimension B) is made from Ultra High
Molecular Weight (UHMW) Polyethylene. It shall be of sufficient
thickness and mechanical strength to prevent distortion or breakage.
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3.3 The compression plate is to be extended to a length of 300 mm. The
hinged pivot point of the compression plate is to be designed so as
to prevent the spillage of fines from that point.
3.4 The feed chute is to be lined with UHMW polyethylene. The rear face
of the stainless steel structure of this chute is to contain two
holes each of dimension 75 mm x 75 mm, and positioned as shown on the
attached schematic diagram. These holes are to allow level switching
transducers to be incorporated into the RFU. Angle brackets, shall be
arranged on each of the vertical sides of these windows to facilitate
installation of the level sensors.
3.5 The pre-production prototype RFU is to be designed so as to minimise,
as far as practicable, the overall length of the RFU. this may be
achieved by mounting the hydraulic cylinder underneath the RFU
trough. If this option is adopted, the design will be such as to
prevent damage, or excessive build-up due to fines being scraped back
by the ram. Facility shall be available to allow for monitoring of
the limits of travel of the hydraulic cylinder.
3.6 The hydraulic cylinder is to be uprated from the existing 38 mm bore
to a 63.5 mm bore cylinder. The existing stroke length is to be
retained.
3.7 All moving parts shall be shrouded with plain mild steel safety
guards.
4. STATUTORY REQUIREMENTS
The pre-production prototype RFU will be designed and constructed in
accordance with the requirements of the Mines and Quarries Act 1954
and subsequent amendments, the Health and Safety at Work Act, and any
relevant NCB specifications and Codes of Practice.
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APPENDIX 9
ASH MEASURING AND CONTROL SYSTEM FOR RAM-FEED ASH MONITOR
Specification of Main Proprietary Components
(Refer Figure 84)
Radioactive Sources
Number of sources
Isotope type
Emission energy
Nominal activity
Supplier
Proportional Counter
Type
Gas filling
Window material
Supplier
Plutonium 238
12 ~ 17 KeV
370 MBq per source
Amersham International
PX425
Argon/helium
Beryllium
Centronics
Preamplifier (charge sensitive)
Type
Detector voltage (max)
Sensitivity
Output voltage (max)
Power requirements
Supplier
High Tension Supply
Type
Output voltage
Power requirements
Supplier
Spectroscopy Amplifier
Type
Input range (max)
Input impedance
Output range (max)
Output impedance
Power requirements
Supplier
N.E.5289B
2kV
0.2V/pC
+8V
+24V
Nuclear Enterprises
N.E.4660
0-2kV or 0-5kV
+12V, +24V
Nuclear Enterprises
N.E.4658
+10V
=
IK ohm
+10V
~50 ohms
+12V, +24V
Nuclear Enterprises
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S p e c t r u m S t a b i l i z e r
Type
Input range
Output range
Correction range
Power requirements
Supplier
Energy Analyser
Type
Input range
Output lower threshold
in window
upper threshold
Threshold range
Window range
Power requirements
Supplier
Dual Scaler Timer
Type
Input range
Threshold range
Outputs
Power requirements
Supplier
Power Supply Bin
Type
Supply voltage
Output voltages
Supplier
FCL 6000 Computer
Type
Supply voltage
System
Additional facilities:
Disk drives
Supplier
(i)
(ii)
(iii)
<iv)
(v)
(vi)
2050
0-10V
0-10V
-50%
to +100%
+12V, +24V
Canberra Industries Incorporated
N.E.4664
0-10V
5v TTL
5v TTL
5v TTL
0.1V to 10V
0.01V to IV or 0.1V to 10V
+12V, +24V
Nuclear Enterprises
N.E.4681
0.2V to 10V positive
0.2V - 5V
20mA current loop and RS232
+6V, +12V
Nuclear Enterprises
N.E.4601
240V A.C., 50Hz
0V, +6V, +12V, +24V to N.I.M. foi
Nuclear Enterprises
Industrial (I.P.67) Apple H e
240V
Autoprom board
RS232 board (4 channel)
32 digital I/O board
16 Opto-isolator board
Time, day, date board
Printer board
2 x disk drives (I.P.55)
Flex Controls Limited
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Programmable Logic Controller
Type Mitsubishi F2-40
Number of inputs 24
Input voltage 24V
Number of outputs 16
Output voltage User defined
Supply voltage 110V/240V A.C.
Supplier Radio Spares
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123
APPENDIX 10
SPECIFICATION FOR X BAND MICROWAVE MOISTURE METER
Applications
Coal - size
- moisture range
Other materials
Material presentation
Basis of Measurement
Measurement system
Dynamic range
Resolution
Sample rate
Accuracy of measurement
Microwave Source
Make/type
Frequency
Power
Frequency drift
Modulation frequency
Aerial systems
General
Power requirements
Main displays
End of determination indicator
Ranging indicator
Temperature range
Warm up time
Control unit dimensions
Transmitter and
receiver dimensions
less than 15 mm
5-20 %
Most particulate material such
as grain, bran, etc.
Individually designed installation
on material handling system
or Discrete sample cell for on-site
and laboratory application.
Auto-ranging microwave attenuation
meter with microprocessor control
60 dB
0.2 dB
25 per minute (approx)
+0.5% to +2% moisture dependent on
coal and method of presentation
Mullard CL8630
10.686 GHz
8 mW
0.25 MHz/degree K
1.0 kHz
18 dB pyramidal Horns
240 V, 45-50 Hz, 1.0 A
3*i digit LCD
Green LED
Red LED
5 to 40°C
10 minutes
Height 300 mm, width 400 mm,
depth 195 mm
Height 250 mm, width 120 mm,
depth 100 mm
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APPENDIX 11
SPECIFICATION FOR S BAND MICROWAVE MOISTURE METER
Applications
Coal - size
- moisture range
Other materials
Material presentation
Basis of Measurement
Measurement system
Dynamic range
Resplution
Sample rate
Accuracy of measurement
less than 50 mm
5 - 24 %
Most particulate material such as
grain, bran etc.
Individually designed installation
on material handling system or
Discrete sample cell for on-site
and laboratory application.
Auto-ranging microwave attenuation
meter operating with microprocessor
control
60dB
0.2 dB
25 per minute (approx)
+0.5% to +2.0% moisture dependent on
coal and method of presentation
Microwave Source
Make/type
Frequency
Power
Frequency drift
Modulation frequency
Aerial systems
General
Power requirements
Main displays
End of determination indicator
Ranging indicator
Temperature range
Warm up time
Control unit dimensions
Transmitter and
receiver dimensions
Avantek 8240
3.26 GHz
25 mW
30 MHz over operating temperature
range
1.0 kHz
13 dB pyramidal Horns
240 V, 45-50 Hz, 1.0 A
34 digit LCD display
Green LED
Red LED
5-40°C
10 minutes
Height 300 mm, width 400 mm
depth 195 mm
Height 255 mm, width 230 mm,
depth 260 mm
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APPENDIX 12
TECHNICAL SPECIFICATION FOR ULTRASONIC BED-DEPTH METER
Proprietory Components
Electrical requirements
Supply voltage
Supply current
Range
Resolution
Temperature coefficient
Accuracy
Transducer ultrasound frequency
Transmitter output level
Acceptance angle
3 dB full angle beamwidth
Measurement frequency
Outputs
Polaroid instrument-grade
electrostatic transducer.
Polaroid ultrasonic circuit board
(modified)
240 V A.C. or 110 V A.C.
(selectable within instrument)
30 mA
26 cm to 53.6 cm
(can be increased to max of 10.7 m)
1 mm in range 26 cm or 53.6 cm
5 cm in range 26 cm to 10.7 m
- 0.175%/°C
+3.5% over range 0° to 40°C
50 KHz (approx)
118 dB SPL at 1 metre (approx)
20 degrees (approx)
15 degrees (approx)
5 per second
Liquid crystal display in mm
- updated at 0.5 second intervals
0.4 to 2V (analogue)
0 to 1.6V (analogue) for
input to data logger
4 to 20 mA (analogue)
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APPENDIX 13
LABORATORY SWEPT FREQUENCY MICROWAVE MOISTURE SYSTEM
Specification of Measuring Equipment - refer Figure 101
Swept Frequency Microwave Source - Mainframe
Make
Type
Power requirements
Frequency range
Sweep control input
Response time
Resolution
Accuracy
Marconi Instruments Limited
6700B Sweep oscillator (mainframe)
240 V, 0.5 A
Determined by plug-in unit
10 V ramp
1 mS for full sweep
Better than 0.05% of R.F. unit bandwidth
As for R.F. unit frequency accuracy
Swept Frequency Microwave Source - R.F. Plug-in Unit
Make
Type
Frequency range
Frequency accuracy
Frequency linearity
Frequency stability
Power output
Spurius signals
3 dB Splitter
Make
Type
Frequency range
Detectors
Make/type
Frequency range
Maximum input
Marconi Instruments Limited
6754A R.F. Unit
4.0 - 8.0 GHz
+0.5%
0.25%
750 kHz/°C
lOmW
20 dB below fundamental at maximum power
Marconi Instruments Limited
Part No. 2200335
2 - 18 GHz
Marconi Instruments Limited / 6511
0.01 - 20 GHz
+26dB(m) average, +30dB(m) peak
Transmitting and Receiving Horns
Make
Centre frequency
Scaler Analyser
Make
Type
Power requirements
Frequency range
Dynamic range
Frequency resolution
Amplitude resolution
British Coal, Scottish Area Laboratory
6 GHz
Marconi Instruments Limited
6500 Automatic Amplitude Analyser
240 V, 0.5 A
0-126 GHz (dependent on detector)
66 dB
within 10 MHz
+0.01 dB(m)
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Specification of Computer Hardware - refer Figure 101
IEEE Interface
Make Acorn Computers Limited
Type IEEE 488 Interface
Power requirements 240 V, 12.5 mA
Manufactured in accordance with BS415/79 Class 1.
Microcomputer
Make Watford Electronics
Type BBC "B" with 32K extra memory
Power requirements 240 V, 0.2 A
Monitor
Make/type Microvitec / 1456
Power requirements 240 V, 0.3 A
Screen size 35.6 cm
Resolution 653 horizontal, 585 vertical
Disc Drive
Make/type Teac FD55FR 13.3 cm floppy disc drive
Power requirements 240 V, 20 mA
Disc type 13.3 cm double sided, 80 tracks/side
Printer
Make/type R. S. Components Limited / RS105 matrix printer
Power requirements 240 V, 0.15 A
Computer Software Facilities
(a) Transfer of data from Scaler Analyser to Computer Memory
(i) The displayed scan information comprising, horizontally,
422 frequency intervals with a vertical resolution of 256 points
(ii) The lower and upper frequency limits of the scan, i.e. the X
axis scale.
(iii) The datum and range of attenuation, i.e. the Y axis scale.
(iv) The period over which the 422 data pairs are measured, i.e.
the sweep speed.
(v) The position and corresponding frequency of an X axis cursor
used to measure the attenuation at a single point of the
scan, i.e. the brightline frequency.
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(b) Display, print-out and Analysis of Data
(i) Display listing of frequency/attenuation data pairs.
(ii) Provide print-out of listing of frequency/attenuation data
pairs.
(iii) Display plot of frequency scan. In this mode a replica of the
scan as displayed on the scalar analyser is reproduced on the
computer monitor. Each scan can be identified by up to 78
characters.
(iv) Print-out plot of frequency scan thereby allowing a permanent
record of the scans display on the Marconi analyser to be
obtained.
(v) Perform a linear regression on the scan data and superimpose
the straight line fit on the displayed scan.
(vi) Copy the block of data transferred from the Marconi analyser on
to disc storage.
(vii) Recall data previously stored on disc and process it in
accordance with any of the above options.
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APPENDIX 14
SOME ASPECTS OF THE THEORY OF
CAPACITANCE MOISTURE MONITORING
1. Complex Relative Permittivity
When an electric field is applied across a capacitor formed with a
dielectric containing polar molecules they tend to align in the direction of
the applied field. The rotation of these polar molecules, whilst aligning
with the applied field, is retarded because of viscous drag between the
polar molecules and the host material. This retardation results in energy
absorption from the applied field. The alignment of the polar molecules
within the applied field causes surface charges on the capacitor plates to
be neutralised. Additional charge can thus flow onto the capacitor plates
resulting in an increase in accumulated charge per applied unit of electric
field and the capacitance thereby increases.
The energy absorbed from the applied field by the rotation of the polar
molecules within the field is observed as a power loss. The relative
permittivity of such a material can be expressed as a complex number:-
i.e., Er + E'r - j E"
r
when j - -1
E'
r
represents the relative increase in capacitance
E"
r
represents the power loss to the dielectric
2.
Model of Insulated Plate Capacitance Moisture Meter
In order to design a suitable measurement system a model of the
insulated plate capacitance moisture meter was required. There were two
basic systems which could be used to model a capacitor:-
(i) a series model in which a resistor is assumed to be
connected in series with the capacitor.
(ii) a parallel model in which a resistor is assumed to
be connected in parallel with the capacitor.
In both cases the resistor, whether in series or parallel, models the
power loss to the dielectric from the applied field. For the particular
geometry, dielectric and frequency range of the proposed measurement cell, a
parallel resistor model was appropriate.
In order to show that a measure of capacitance can be obtained from the
voltage developed across a small series resistance an analysis of a parallel
model with a series connected measuring resistance is given below.
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With reference to the attached figure
Z(s)
™
SCi
Rl + 1
SCi
Rl + R
m
(1 +
+ R
m
(1 + SCiRi)
SCiRi)
The transfer function relating input voltage to output voltage is given by
Vo(s) - Rm - R
m
(1 + SCjRl) ....... (1)
Vi(s) "zCs3 Rl + R
m
d + SC]Ri)
-
R
m + SClRlRm
Rl + Rm d + SCiRn,) R
X
+ R„, + SCiRiR
m
Converting to Fourier Transforms gives
Vo(Jw ) - Rm + j w C j R i R m
Vi ( j w) R i + Rm + jwC iR iR
m
Rl + Rm + jwC iRiRm
now i f R i » R
m
a n d l » w C i R
m
t he n ( 2 )
Vo( jw) ~ jwC iR
m
V i ( J w )
->
Ao(jw)/
wCiRn/VKjw)/
(3)
The voltage developed across the measuring resistance Rm is therefore
proportional to the capacitance.
/
I f t h e c o n d i t i o n s ( 2 ) d o n o t a p p l y t h e n i t c a n b e sh ow n t h a t :
o ( j w y i J R¿
m
+ Ri +
w
2 c 2
1
R 2
l R
2
m
) 2 + ( w C ^ i R a T ^ y ^ i Ç J w ) / ( 4)
(Rl + R
m
)
2
+ ( wC iR iRm)
2
Numerical comparison of equations (3) and (4) show good agreement when
values of w exceed 2 x 10
7
rads/sec, R
m
- 20 ohms and other values lie
within their expected ranges.
It was therefore decided to use the voltage developed across a small
(20 ohms) series resistance as the primary measurement in determining the
capacitance.
It should be noted further that if the conditions proposed in (2) are
applied, in the Laplace domain, to (1) then we find that:-
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Vo(s)
^
SCiR
m
Vi(s)
Taking inverse transforms gives
Vo(t)^d(Vi(t)) CiR
m
dt
assuming zero initial conditions.
Now if Vi(t) contains a component of high frequency noise
then Vi(t) -
Vi(t)*
+ n(t)
b
If the frequency spectrum of n(t) - ) n^sinw^t
a
and
Vi(t)*
- Vi sin wt
b
Then Vo (t) - d(V¿sinwt +r~n i
c
sinwj
c
t) C]R
m
d t
Thus
Vo(t) - CiR
m
(wVicoswt + w
a
n
a
cosw
a
t + w
a
+i + n
a+
icosw
a+
it+ Wbn
D
coswbt)
That is the magnitude of noise signal components are amplified by
their frequencies.
For this reason the Bandwidth of the measurement oscilloscope would be
limited to 25 mHz and quarterwave filters would need to be connected to the
measurement circuit at appropriate points.
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i_
sc,
/¿(s)
Z(s)
m
V
o
(s)
V¿(s) - Laplace Transform of Excitation Voltage
V
0
(s) - Laplace Transform of Output Voltage
Z(s) - Laplace Transform of Input Impedance
SCi
Rl
Mn
Laplace Transform of Capacitor Impedance
Laplace Transform of "Power Loss" Resistance
Laplace Transform of Measuring Resistance
PARALLEL RESISTOR MODEL
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1 3 7
A P P E N D I X 15
SPECIFICATION FOR AN ELECTRONICS PACKAGE FOR EXPERIMENTAL
CAPACITANCE MOISTURE MONITORING
INTRODUCTION
1.1 Scope
This specification covers the design, development, construction,
testing and delivery of an electronics package for use with an
experimental moisture monitoring system.
1.2 Prices
The tenderer is requested to submit a listing of the tender price as
stated in the documents accompanying this specification.
1.3 Exclusions
The following items shall be excluded from the tender:
(i) The supply of the microcomputer
(ii) The supply of any moisture monitoring transducers
1.4 Completion time
The tenderer shall supply a listing of the estimated time for the
completion of each of the design, development, construction and testing
phases of the contract as stated in the document accompanying this
specification.
1.5 Schematic diagrams
The tender shall include such schematic and other diagrams as are
necessary to fully illustrate the proposals.
1.6 Documentation
The contractor shall supply two complete sets of all necessary circuit
and other diagrams. Two sets of maintenance and operating manuals,
complete with testing procedures shall also be supplied. Complete
listings of, and specifications for, all components used will be
included within the documentation.
1.7 Standard of Workmanship
The equipment to be supplied shall be constructed to a high standard
and consistent with good engineering practice.
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2.
BACKGROUND INFORMATION
Water has a dielectric constant of approximately 80 and a typical coal
has a dielectric constant of approximately 5. By arranging for moist
coal to form the dielectric material of a capacitor, a measurement of
the moisture content of the coal can be determined by measuring
capacitance. Further, since the loss tangent of water is large
compared to that of dry coal, a measure of loss tangent can also
provide a useful correlation. Practical experimentation has shown that
effective impedance measured in the radio frequency range will also
exhibit a useful correlation.
The subject of this specification is the design, construction, testing
and delivery of an electronics package for use with such experimental
moisture monitoring transducers. The specification is designed to
indicate the desired physical arrangement of, and the functions
associated with, the component parts of the electronics package.
Schematic diagrams designed to further explain the specification are
attached as Diagrams 1 and 2.
3. GENERAL REQUIREMENTS
The electronics package is to be used for two different types of
application. These are, an on-stream system in which the transducer is
mounted as to ride on a moving bed of coal, and a discrete sample
system. Considering the on-belt application, there is a need for a
part of the electronics package to be mounted statically, adjacent to
the transducer (Unit A). The other part is to be mounted inside a
compartment within the transducer (Unit
B).
The two parts are to be
connected by a flexible armoured multicore cable. The ambient
operating temperature for the electronics package is expected to be
-10°C to +50°C. The functions associated with each part of the
electronics package, and the specifications for each of those parts are
detailed in the following sections of this specification.
4. DETAIL REQUIREMENTS - UNIT A
4.1 Unit A - Duty
This unit will provide the dc power supplies for use by both Unit A and
Unit B. It will house such local electronics and analogue displays as
are necessary to satisfy the requirements of the specification. It
will provide sockets for connection to unit B and to a local computer.
The physical layout may be similar to that shown in Appendix 1.
4.2 Unit A - Specification
This unit will comprise three compartments; X, Y and Z. The functions
and specifications for each compartment are as detailed below.
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(X) Power supplies compartment requirements
This compartment will house such components as are necessary for
the provision of dc supplies for use by units A and B. The
mains transformer shall be fitted with an earthed interwinding
screen and shall be supplied from a 110 V/240 V, single phase,
50 Hz supply. The compartment will be wired such that the mains
(primary) wiring is segregated from the secondary and dc supply
wiring. The mains cable entry to this compartment will be by a
brass 20 mm compression gland suitable for use with 3 core
single wire armoured pvc cable with nominal core sections of
1.5 mm'. The removable cover giving access to this compartment
shall be fitted with a securely screw mounted white traffolyte
plate bearing the legend 'CAUTION. ISOLATE ELSEWHERE BEFORE
REMOVING THIS COVER', in red letters. The 110 V/240 V, single
phase,
50 Hz supply to this unit can be expected to be
contaminated with electrical noise. Provision shall be provided
such that any electrical noise does not interfere with the
operation of the electronics package. Internal earth straps and
connections shall be provided in order to maintain efficient
earth continuity. The secondary voltages and dc supplies shall
be at a voltage no greater than 25 or + 12.5 V.
(Y) Electronics compartment requirements
(i) This compartment will house the local electronics and analogue
displays. The local electronics will comprise such circuitry as
is necessary to convert the signals transmitted from Unit B into
a form in which they can be displayed on the local analogue
displays. Four displays will be available and arranged to
simultaneously display representations of the modulus and
argument of the transducer impedance and the capacitive and
conductive components of the impedance. Four 4 - 20 mA analogue
outputs representative of the above signals will also be
available and will be wired to a socket for connection to a
local computer.
Such testpoints as are necessary for the thorough testing of the
unit shall be provided on the circuit board(s) used in the
construction of unit A.
Facility shall be provided such that the gains and offset bias
of each of the signal channels can be individually and
independantly adjusted within ranges such that calibration can
be achieved.
All outputs and supplies from the unit shall be continuously
shortcircuit protected or rated, and be tolerant to any faults
likely to occur by compressive damage to or stretching of the
multicore cable linking units A and B.
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(ii) The analogue displays shall be formed by the generation of
suitable displays on a solid state dot matrix type display.
Facility shall be provided such that the range of each of the
displays can be individually set and displayed at suitable
points adjacent to the displays. The ranges should be retained
via battery backed memory when power is removed from the unit.
The display should be arranged such that it is clearly visible
under normal or poor lighting conditions.
Such additional space and electrical supplies shall be available
as are necessary for the retrofitment of two 127 mm x 127 mm, 5V
microprocessor boards for moisture calculation.
A red 'power on' light will be provided in order to indicate
that the electrical supply to the unit is healthy. This is to
be supplied from a low voltage dc source.
Test switches, test sockets and additional circuitry such as are
necessary for the testing of all the dc voltages and all the
datalinks to and from unit A shall be included within this
compartment. A transparent high impact plastic lockable cover
shall be provided to cover all the analogue displays, indicator
lamps, controls, test switches and test sockets. It will
provide environmental protection to at least IP 55 standard.
A removable cover will be provided giving direct access to the
interior of this compartment.
(Z) Termination Compartment
This compartment will house the main termination point and
sockets for connection to Unit B and to the local computer. A
removable cover will be provided giving access to the
compartment.
4.3 General Requirements - Unit A
A carrying handle is to be provided on top of the unit. Four
mounting points are to be provided near the rear corners of the unit
and the unit is to be stable when placed on its base.
The unit is to be environmmentally protected to at least IP 55
standard and shall be of a rugged substantial construction suitable
for direct installation in a coal prpeparation plant. Sockets
provided for connection to Unit B and the local computer shall be
environmentallly protected to at least IP 55 standard. Protection
caps shall be attached to the sockets such that the sockets can be
sealed to this standard when not in use.
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141
PROPOSED EXPERIMENTAL INSULATED-PLATE CAPACITANCE
MOISTURE METER - UNIT A
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1 2 7 MM
L E A D
TO
TRANSDUCER
A k
0 MM
-A
k
50 MM
LEAD
TO
TRANSDUCER
rs>
io MM
PROPOSED EXPERIMENTAL INSULATED-PLATE CAPACITANCE MOISTURE METER
-
UNIT
B
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143
5. DETAIL REQUIREMENTS - UNIT B
5.1 Unit B - Duty
This unit will generate radio frequency (RF) signals for use in the
measurement of the impedance of the moisture transducer. It will house
such subsequent signal processing electronics as are necessary for the
generation of signals accurately related to the modulus and argument of
the moisture monitor complex impedance. Further subsequent signal
processing electronics will be included in order to convert these
signals into a form suitable for transmission to Unit A.
5.2 Unit B - Specification
(i) Enclosure - mechanical considerations
Unit B will comprise an RF shielded enclosure of external
dimensions 127 mm x 254 mm x 50 mm. Circuit board(s) containing
the necessary electronic components will be securely mounted and
supported within this enclosure such that their operation is
unaffected by any vibration or by likely levels of impact.
Mounting points will be provided on the unit such that the unit can
be securely fastened inside the transducer. See Diagram 2 for
further details.
(ii) Electronic considerations
The RF generator output frequency will be infinitely variable by
local adjustment within the range 10 MHz to 15 MHz, and shall be
stable to within 1% of the set frequency. The output voltage from
this generator should be sufficiently large (but less than 25 V)
and stable under conditions of loading for measurements of
capacitance within the range 5 pF to 200 pF to be made with a
resolution of at least 0.1 pF. The range of the shunt resistance
will be of interest between 20 ohms and 5 k ohms.
The circuitry should be pass bandwidth limited as necessary such
that all measurements are performed only at the set frequency.
The measurement electronics should be designed such that variation
of the signal supply frequency within the stated range
(10 • 15 MHz) does not require alteration of, or manual adjustment
to any circuitry.
Such testpoints as are necessary for the thorough testing of the
unit shall be provided on the circuitboard(s). Unit B's enclosure
should be designed and arranged such that any testing can be
performed with the circuitboards in their enclosure.
With regard to temperature effects, the design and construction of
Unit B should recognise that the unit is to be housed within a
sealed compartment of limited volume.
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Ì44
Full consideration must be given to any effects likely to cause
inaccuracies or mal-operation owing to stray couplings to the unit
from the transducer whilst in both static and dynamic operation.
All outputs from the unit shall be continuously shortclrcuit
protected or rated, and tolerant to any faults likely to occur by
compressive damage to or stretching of the multicore cable linking
Units A and B.
(iii) Connections
Leads for connection to the transducer shall be attached to Unit B
at the centre of both sides of the unit - see Diagrams 2.
The leads will be 150 mm long and should be arranged to prevent any
dc bias from occurring across the transducer.
A multi-way socket will be provided for attachment to the body of
the transducer. This socket shall be of the same type as fitted to
the outputs of Unit A and will be fitted with a removable
environmentally protective cap to at least IP 55 standard.
A multi-way socket shall be fitted to Unit B from which all
connections between Unit B and unit A will be made. A set of
wanderleads of length 0.5 m, fitted with a plug for connection to
Unit B, will also be providded.
6. DETAIL REQUIREMENTS - MULTICORE CABLES
Two multicore cables shall be supplied with the unit, both complete
with appropriate mechanically strong plugs. The cable lengths shall
be 10 m and 2 m. The cables shall be suitable as regards liability
to mechanical and chemical damage, and will be of a flexible
armoured, fire resisting construction.
A screened multicore cable of length 5 m, and fitted with a plug for
attachment to the computer output socket of Unit A will be provided.
It will be capable of carrying all data links to the computer
simultaneously.
7.
STATUTORY REQUIREMENTS
Both units will be designed and constructed in accordance with the
requirements of the Mines and Quarries Act 1954 and subsequent
amendments, the Health and Safety at Work Act, and any relevant NCB
specifications and Codes of Practice.
8. CONFIDENTIALITY
No information contained in this specification or in any subequent
document or discussion shall be made public or disclosed to any third
parties without the agreement of the National Coal Board.
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TABLE 1 - RESULTS OF PREVIOUS TESTING OF WULTEX RADIOMETRIC ASHMETER
Laboratory
Laboratory
Laboratory
COLLIERY/
PRODUCT
Mantón
Blended Smalls
Mantón
Blended Smalls
Steetley
Blended Smalls
Manton/Steetley
Blended Smalls
Plant Train j
(4 hr)
Mantón
Blended Smalls
Mantón
Blended Smalls
SAMPLES
/TESTS/
TRAINLOADS
NO.
11
16
15
33
100
75
TOTAL
MOISTURE %
RANGE
6.4-9.3
6.4-9.3
7.8-13.6
5.6-13.6
7.2-10.9
7.3-11.5
ASH %
(A.R.)
RANGE
3.4-38.6
3.4-38.6
3.5-29.5
3.4-38.6
11.6-21.2
12.4-19.8
CALIBRATION
REGRESSION
ANALYSIS
Linear
Quadratic
Linear
Quadratic
Linear
Quadratic
Linear
Quadratic
Linear
Linear
CORR
COEFF
0.959
0.999
0.953
0.996
0.964
0.972
0.966
0.988
0.781
0.514
STD
DEV
% ASH
3.79
1.12
3.28
1.02
2.14
1.96
2.73
1.63
1.29
1.15
% SULPHUR
(A.D.)
RANGE
% IRON |
(A.D.) |
RANGE j
2.12-2.4 | 1.17-1.51 |
( Tests 46 - 100) |
<J1
(A.R. - AS RECEIVED, A.D. - AIR DRIED)
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COLLIERY
MANTON
ASKERN
BILSTHORPE
COTGRAVE
LEA HALL
DAM HILL
CWM
SHARLSTON
GRIMETHORPE
CENTRAL
NASHERY
(SOUTH SIDE)
SEAN(S)
PARKGATE
KARREN HOUSE
LON MAIN,
PARKGATE
DEEP HARD
BLACK SHALE
LOWER DEEP
DEEP. SHALLOW
THICK COAL
YARD
SIX FEET
WARREN HOUSE
LOW BARNSLEY
PARKGATE,
FENTON,
NEWHILL
PRODUCT
NON. SIZE
BLENDED
PSF
5 0 - 0
UNTREATED
SMALL COAL
5 0 - 0
BLENDED
PSF
2 5 - 0
UNTREATED
SMALL COAL
2 5 - 0
WASHED
SMALL COAL
2 5 - 0
BLENDED
PSF
5 0 - 0
UNTREATED
SMALL COAL
3 8 - 0
WASHED
SMALL COAL
5 0 - 0
BLENDED
PSF
5 0 - 0
BLENDED
PSF
2 5 - 0
UNTREATED
SMALL COAL
12.5 - 0
WASHED
SMALL COAL
5 0 - 0
WASHED
SMALL COAL
5 0 - 0
BLENDED
PSF
5 0 - 0
UNTREATED
SMALL COAL
5 0 - 0
WASHED
SMALL COAL
5 0 - 0
ASHNETER
UK METER
POLISH METER
UK METER
POLISH METER
UK METER
POLISH METER
UK METER
POLISH METER
UK METER
POLISH METER
UK METER
POLISH METER
UK METER
POLISH METER
UK METER
POLISH METER
UK METER
POLISH METER
UK METER
UK METER
UK METER
UK METER
UK METER
UK METER
UK METER
NUMBER
OF
SAMPLES
20
11
28
28
20
20
20
20
20
20
20
20
20
20
20
20
40
23
18
24
18
16
13
SIZE
TESTED
2 5 - 0
2 5 - 0
2 5 - 0
2 5 - 0
2 5 - 0
5 0 - 0
3 8 - 0
5 0 - 0
5 0 - 0
2 5 - 0
12.5 - 0
5 0 - 0
5 0 - 0
5 0 - 0
5 0 - 0
5 0 - 0
RANGE OF
MOISTURE
* (A.D.)
1.8 - 3.4
1.8 - 3.2
1.9 - 3.5
3.4 - 7.6
4.6 - 6.9
4.4 - 9.3
4.0 - 5.8
2.1 - 4.3
2.9 - 8.7
2.3 - 8.4
2.3 - 10.0
3.7 - 7.2
0.2 - 0.7
1.4 - 2.2
1.0 - 1.6
1.3 - 2.5
1.0 - 1.35
RANGE
OF ASH
% (A.D.)
7.0 - 22.3
16.1 - 22.2
30.4 - 47.0
18.1 - 28.2
32.9 - 45.6
2.8 - 11.6
10.5 - 27.7
30.2 - 48.0
3.8 - 8.8
14.6 - 30.2
13.5 - 39.8
13.0 - 23.3
4.2 - 8.4
10.6 - 17.9
4.1 - 29.2
21.4 - 34.5
2.8 - 5.6
RANGE
OF IRON
X (A.D.)
0.99 - 1.75
1.37 - 1.75
1.89 - 2.45
1.40 - 1.90
1.66 - 1.94
0.50 - 0.96
0.70 - 1.70
1.33 - 2.21
0.41 - 0.99
0.54 - 1.17
0.90 - 2.17
0.59 - 1.11
0.21 - 0.50
1.84 - 2.50
0.76 - 2.53
2.33 - 3.23
0.47 - 1.24
STD.
DEV.
OF IRON
X Fe
0.17
0.11
0.15
0.12
0.083
0.119
0.246
0.218
0.175
0.155
0.315
0.119
0.073
0.21
0.55
0.246
0.278
CORR. COEFF.
BETWEEN
X Fe C ASH X
0.946
0.877
0.697
0.527
0.520
0.955
0.941
0.695
0.829
0.588
0.868
0.783
0.904
0.490
0.959
0.027
0.978
BEST CALIBRATION
CORR.
COEFF.
0.984
0.955
0.918
0.914
0.486
0.951
0.946
0.992
0.950
0.957
0.892
0.885
0.932
0.906
0.952
0.964
0.973
0.965
0.965
0.770
0.998
0.767
0.983
STD.
DEV.
X ASH
0.76(0)
0.73(Q)
1.67U)
1.75(0)
2.34(L)
0.83(L)
1.37(L)
0.36(L)
1.32(Q)
1.23(Q)
2.15(L)
1.95U)
0.52(L)
O.flO(L)
1.24(L)
1.10(L)
1.58(Q)
0.68U)
0.28U)
1.36(g)
0.54(g)
2.31(0)
0.19(0)
CALC.
STD.
DEV.
0.46(g)
0.38(L)
1.30(L)
0.84U)
l.Ol(L)
0.28U)
0.68(L)
1.10(L)
0.49(L)
0.75(L)
1.3KL)
0.63U)
0.18U)
1.23(L)
0.94(0)
2.82(L)
0.16(0)
o i
- POWER STATION FUEL (L) LINEAR REGRESSION (0) QUADRATIC REGRESSION
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TABLE 3
RESULTS
OF
CALIBRATION TESTS WITH WULTEX ASHMETER
ON
BILSTHORPE BLENDED SMALLS
TEST LOCATION
Column Number
of
Samples
of Ash
of
Moisture
of Sulphur
Fe? O3 in Ash
( )
( )
Fe in
coal
( )
( )
Fe
and Ash in
Coal
on dry
(1
- Ash
-
Corr. Coeff.
in Coal
lasis
standard
|
YRL
| 2 present-
| ations x 5
|
box
fills
| AD
|
1
| 20
110.5
- 27.7
| 4.4 - 6.1
11.32
- 1.90
| 8.53
| 0.71
|
1.08
|
0.25
|
0.943
deviation)
|
1.32
|
0.950
BILSTHORPE COLLIERY
9 x 2 minute
integration periods
AR
2
31
6.6 - 36.6
9.6 - 15.8
0.98 - 1.61
6.88
1.61
0.77
0.19
0.849
2.93
0.905
3
25
10.7 - 27.5
10.7
- 15.4
1.0 - 1.50
6.65
1.13
0.76
0.14
0.680
2.77
0.754
YRL (REPEAT LABORATORY CALIBRATION)
|
5 presentations
x
2 box
fills
AR
4
| 5
24 | 19
6.3 - 37.4|11.4 - 23.6
9.0 -
14.7|11.4
- 14.5
0.85 - 1.5310.85 - 1.5
6.57 | 6.69
1.73 | 1.53
0.79 | 0.77
0.19 | 0.12
0.773 | 0.380
1.60 | 1.79
0.982 | 0.860
2 presentations |
x
5 box
fills
|
AD
|
6
24
7.0 - 39.6
3.0 - 5.2
0.94 - 1.66
6.57
1.73
0.86
0.20
0.773
1.93
0.976
7 |
19 |
12.6
- 26.11
3.0 - 5.2|
0.94 - 1.66|
6.69 |
1.53 |
0.85 |
0.13 |
0.380 |
2.10 |
0.841 |
(AR - AS RECEIVED, AD - AIR DRIED)
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148
TABLE 4 LABORATORY INVESTIGATIONS WITH COALSCAN 3500
ASH MONITOR - RESULTS OF TESTS TO ASSESS
STATISTICAL
COUNTING ERROR USING CALIBRATION
STANDARD
| TEST
| 1
1
2
1
3
1
4
| 5
1
6
|
7
1 8
1
9
1 io
1 11
1 12
1 13
1 14
COUNTING
PERIOD
SECONDS
2
4
8
15
30
60
60
120
300
600
60
120
300
600
| LOG RATIO |
MEAN
2.4700
2.4688
2.4682
2.4672
2.4672
2.4693
2.4613
2.4613
2.4616
2.4613
2.4701
2.4686
2.4693
2.4685
STANDARD |
DEVIATION |
0.0182
|
0.0134
|
0.0099
|
0.0071
|
0.0050
|
0.0014 |
0.0037 |
0.0024 |
0.0016
|
0.0012
|
0.0038 |
0.0025
|
0.0017
|
0.0012 |
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149
TABLE 5 LABORATORY INVESTIGATION WITH COALSCAN 3500
ASH MONITOR - VARIATIONS IN LOG RATIO VALUES DUE
TO CHANGES IN BED THICKNESS
| EQUIVALENT
| COAL BED
| THICKNESS
1 (MM)
1 85
| 128
| 168
| 202
| 230
| 253
| 272
AMERICIUM
CHANNEL
COUNTRATE
(CPS)
79114
42149
22428
12185
6769
3877
2287
MEAN
CAESIUM
CHANNEL
COUNTRATE
(CPS)
33053
25677
19877
15416
11950
9290
7186
STANDARD DEVIATION
LOG |
RATIO |
2.6026 |
2.5986 |
2.6006 |
2.6017 |
2.6008 |
2.6027 |
2.5998 |
2.6010 |
0.0015
|
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150
TABLE 6 LABORATORY INVESTIGATIONS WITH COALSCAN 3500 ASH MONITOR
- EFFECT OF MAGNETITE ADDITION TO COAL SAMPLE
I TEST
1 NÇL
| 1
1 2
1 3
1
4
| 5
1 6
| 7
1 8
1 9
1
io
1 11
1 12
1 13
1 14
1 15
1 16
% ADDITION |
Fe
3
0
4
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
5.0
6.0
7.0
| 8.0
| 9.0
10.0
Fe2Û3
0.0
0.52
1.03
1.55
2.07
2.59
3.10
3.62
4.14
4.65
5.17
| 6.20
| 7.24
| 8.27
| 9.31
10.34
LOG
RATIO
2.294
2.329
2.370
2.414
2.462
2.494
2.534
2.577
2.610
2.672
2.700
2.790
2.874
2.958
3.062
3.126
INCREASE |
IN ASH % i
0.0 |
2.96 |
6.36 |
10.04 |
14.05 |
16.71 |
19.98 |
23.63 |
26.37 |
31.53 |
33.84 |
41.36 |
48.31 |
55.31 |
| 64.01 |
69.38 |
(NOTE For a typical coal an Increase In log ratio of 0.012 corresponds
to an Increase in ash content of 1%.
Therefore Increase in ash - log ratio - 2.294 % )
0.012
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151
TABLE 7 LABORATORY INVESTIGATIONS WITH COALSCAN 3500 ASH MONITOR
- EFFECT OF CALCIUM CARBONATE ADDITION TO COAL SAMPLE
I TEST
1 NJL-
| 1
1 2
1 3
1
4
| 5
1 6
| 7
1 8
1 9
1 io
1 11
1 12
1 13
1 14
1 15
1 16
1 17
1 18
1 19
| 20
1 21
| 22
| 23
1 24
% ADDITION |
CACO3
0.0 |
0.5 |
1.0 |
1.5
2.0
2.5
3.0
3.5
4.0
4.5
5.0
6.0
7.0
8.0
9.0
10.0
11.0
12.0
13.0
14.0
15.0
| 16.0
| 17.0
18.0
CAO
0.0
0.28
0.56
0.84
1.12
1.40
1.68
1.96
2.24
2.52
2.80
3.36
3.92
4.48
5.04
5.60
6.16
6.72
7.28
7.84
8.40
8.96
9.52
10.08
LOG |
RATIO
2.289
2.301
2.313
2.325
2.337
2.348
2.360
2.372
2.384
2.396
2.408
2.431
2.455
2.479
2.502
2.526
2.550
2.573
2.597
|
2.620
|
2.644
|
2.668
| 2.691
2.715
INCREASE |
IN ASH % |
0.0 |
0.83 |
1.88 |
2.83 |
3.66 |
4.66 |
5.65 |
6.64 |
7.58 |
8.63 |
9.68 |
11.48 |
13.40 |
15.25 |
17.37 |
19.29 |
21.18 |
23.20 |
25.17 |
| 27.28 |
| 29.28 |
| 31.37 |
| 33.48 |
| 35.35 |
(NOTE For a typical coal an increase In log ratio of 0.012 corresponds
to an Increase In ash content of 1%.
Therefore Increase in ash - log ratio -
2.289
% )
0.012
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152
TABLE 8 LABORATORY INVESTIGATIONS WITH COALSCAN 3500 ASH MONITOR
- EFFECT OF KAOLIN ADDITION TO COAL SAMPLE
I TEST
1 N<L_
| 1
1 2
1 3
1
4
| 5
1 6
| 7
1 &
1 9
1 io
1 11
1 12
1 13
1 14
1 15
1 16
1 17
1 18
% ADDITION
AI2O32SÌO22H2O | AI2O32SÌO2
0.0 | 0.0
0.5 | 0.43
1.0 | 0.86
1.5 | 1.29
2.0 | 1.72
2.5 | 2.15
3.0 | 2.58
3.5 | 3.01
4.0 | 3.44
4.5 | 3.87
5.0 | 4.31
6.0 | 5.17
7.0 | 6.03
8.0 | 6.89
9.0 | 7.75
10.0 | 8.61
11.0 | 9.47
12.0 | 10.33
LOG
RATIO
2.290
2.294
2.298
2.302
2.306
2.310
2.314
2.318
2.322
2.326
2.331
2.339
2.347
2.355
2.363
2.371
2.379
2.387
INCREASE I
IN ASH % |
0.0 |
0.1 |
0.63 |
0.79 |
1.25 |
1.37 |
1.61 |
2.16 |
2.38 |
2.78 |
3.05 |
3.55 |
4.29 |
4.92 |
5.58 |
6.39 |
7.28 |
7.98 |
(NOTE For a typical coal an increase in log ratio of 0.012 corresponds
to an increase in ash content of 1%.
Therefore increase in ash - log ratio - 2.290 % )
0.012
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TABLE 9
LABORATORY CALIBRATION TESTS WITH COALSCAN 3500 ASH MONITOR
1
2
3
4
5
6
7
COLLIERY/
COAL PREPARATION
PLANT (CPP)
Askern
Gaseoigne Wood
Cascoigne Wood
South Side CPP
(Grimethorpe)
Askern
Askern
Askern
PRODUCT
Blended Smalls
Untreated Smalls
Untreated Smalls
Blended Smalls
Blended Smalls
(From 4th Dynamic Calib)
Blended Smalls
(From 4th Dynamic
Simulated Blended
Smalls
Calib)
NO.
OF
SAMPLES
20
20
20
16
21
21
9
SIZE
RANGE
TESTED
-212 micron
-212 micron
-212 micron
-212 micron
-212 micron
-1.0 mm
25-3.18 mm
RANGE
OF ASH %
(A.D.)
11.3-40.5
10.6-23.4
10.2-33.4
22.0-30.2
14.0-32.4
14.0-32.4
6.2-41.8
CALIBRATION |
CORR
COEFF
0.997
0.844
0.827
0.895
0.993
0.988
0.998
STD.
DEV. |
% ASH (A.D.)j
0.64 |
1.69 |
3.67 |
1.15 |
0.59 |
0.80 |
0.83 |
en
co
(A.D.
- AIR DRIED)
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TABLE 10 - LABORATORY INVESTIGATIONS WITH COALSCAN 3500 ASH MONITOR - EFFECT OF INCREASING
NUMBER OF STATIC MEASUREMENTS WITH PREPARED SAMPLES OF 25 - 3 mm ASKERN BLENDED COAL
I ONE BOX FILL | TWO BOX FILLS |
1 1 LINE | 2 LINES | 3 LINES | 1 LINE | 2 LINES | 3 LINES |
| EITHER FILL j EITHER FILL | EITHER FILL j EACH FILL | EACH FILL | EACH FILL |
| | CALIB. | | CALIB. | | CALIB. | | CALIB. | | CALIB. | | CALIB. |
| LINE j STD. DEV. j LINES | STD. DEV. | LINES j STD. DEV. | LINES j STD. DEV. | LINES | STD. DEV. | LINES | STD. DEV. |
1 1 % ASH | | % ASH | | % ASH | | % ASH | | % ASH | | % ASH |
| A | 2.059 | AB | 1.522 | ABC | 1.315 | AD | 1.466 | ABDE | 1.009 | ABCDEF |
0.834
|
1 B | 2.157 | AC | 1.151 | DEF | 1.284 | AE | 1.662 | ABDF |
0.936
| | |
| C | 1.308 | BC J 1.652 | | | AF | 1.427 | ABEF | 1.051 | | |
1 D 1 1.362 | DE 1 1.313 | | | BD | 0.757 | ACDE | 0.976 | | |
I E | 1.570 | DF 1 1.423 | | | BE | 1.157 | ACDF |
0.933
| | |
| F | 2.043 | EF 1 1.437 | | | BF | 1.388 | ACEF |
0.989
| | |
I I I I ¡ j | CD j 0.649 | BCDE j 0.728 | | |
I I I I I I j CE j
0.846
j BCDF |
0.865
| j |
1 1 1 I j | j CF j 1.208 j BCEF | 0.961 j | |
| MEAN | 1.750 | MEAN | 1.416 | MEAN | 1.299 | MEAN | 1.173 | MEAN |
0.939
| | |
| S.D. | 0.381 | S.D. | 0.172 | | | S.D. |
0.352
| S.D. |
0.095
| | |
BOX FILL 1
BOX FILL 2
| LINE
| LINE
| LINE
A
B
C
12
12
12
READINGS |
READINGS |
READINGS |
| LINE
| LINE
| LINE
D
E
F
12
12
12
READINGS 1
READINGS |
READINGS |
CJl
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TABLE 11 - COALSCAN 3500 ASH MONITOR TRIAL. ASKERN COLLIERY - SUMMARY OF ON-SITE CALIBRATION AND PERFORMANCE TESTS
Static Calib |
| NO.
1 o
| 1
• 1
2
3
4
5
6
7 |
7 |
¡ DATE(S)
| 26-27.4.86
| 30.4.86
|
1.5.86
16.5.86
4-6.6.86
30.9.86
1.10.86
2.10.86
13.11.86
14.11.86
9.4.87
14.4.87
15.4.87
16.4.87
May/June 1987
14.3.88
16.3.88 |
17.3.88
29-30.3.88 |
| NUMBER
OF
SAMPLES
| 20
12)
17)
29
12
23
5)
7)
9)
12)
10)
5)
7)
11)
9)
57
7)
15)
8)
60
29
21
22
32
30
SIZE
| RANGE
TESTED
-212 micron
| 25 mm - 0
-212 micron
25 mm - 0
25 mm - 0
25 mm - 0
25 mm - 0
25 mm - 0
25 mm - 0
25 mm - 0
-212 micron
RANGE
| OF
| ASH %
11.3-40.5 A.D.
6.9-24.6 A.R.
7.5-27.2 A.D.
6.9-31.4 A.R.
12.9-28.7 A.R.
11.2-22.0 A.R.
8.9-24.7
A.R.
10.4-16.1 A.R.
10.0-23.6 A.R.
11.0-26.5 A.D.
CALIBRATION |
CORRELATION
COEFFICIENT
0.993
0.941
0.985
TEST ABANDONED
0.963
0.954
0.906
0.934
0.617
0.892
0.976
| STD. DEV 1
% ASH |
0.99 (A.D.) |
1.51 (A.R.) |
0.85 (A.D.) |
1.76 (A.R.) |
1.39 (A.R.) |
1.39 (A.R.) |
1.56 (A.R.) |
1.03 (A.R.) |
1.70 (A.R.) |
0.91 (A.D.) |
(A.R. - AS RECEIVED, A.D. - AIR DRIED)
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156
TABLE 12 COALSCAN 3500 ASH MONITOR TRIAL, ASKERN COLLIERY -
RESULTS OF INVESTIGATION OF CROSS-BELT SEGREGATION WITH
OSCILLATING HEAD, BARIUM SOURCE AND 2 SECOND COUNTING
PERIODS
| BARIUM
| COUNTRATE
| RANGE
| C.P.S.
| >14000
| 13500-13999
| 13000-13499
| 12500-12999
| 12250-12499
| 12000-12249
| 11750-11999
| 11500-11749
NO.
OF
2 SECOND
PERIODS
98
25
40
68
41
69
25
9
BARIUM COUNTRATE
MEAN
COUNTRATE
C.P.S.
15017.9
13692.7
13257.8
12705.6
12373.1
12139.4
11897.3
11679.3
STD.
DEV.
C.P.S.
686.6
131.3
137.8
135.6
72.6
74.0
64.4
50.8
CALCULATED ASH |
MEAN
ASH
%
13.1
14.5
14.3
14.4
15.1
14.6
14.4
13.8
STD. |
DEV. |
ASH % |
1.5 |
1.6 |
1.8 |
1.7 |
1.6 |
1.7 |
1.5 |
1.5 |
(C.P.S.
- counts per second)
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157
TABLE
13
EXPERIMENTAL RAM-FEED PRESENTATION UNIT WITH
PLUTONIUM
238
ISOTOPE MEASURING HEAD
AND Fe
CORRECTION
- LABORATORY CALIBRATION TESTS
ON
MARKHAM POWER
STATION BLEND
AND
COMPARISON WITH TELSEC
350
ANALYSER
Sample Analysis
Number
of
samples
Total moisture
,
range
Ash content
(A.R.) range
Sulphur content
(A.R.) range
Chlorine content %(A.R.) range
34
7.43 -
10.95
-
1.65 -
0.17 -
10.42
34.4
2.00
0.22
Calibration Results
| EQUIPMENT/
| INSTRUMENT
| Experimental
| Ram-Feed Unit
| Telsec
350
| Analyser
FEED
SIZE
50
mm - 0
25
mm - 0
5
mm - 0
212 micron
-
0
LINEAR REGRESSION
CORR.
COEFF.
0.831
0.965
0.922
0.989
STD.
DEV.
ASH
1.93
0.91
1.34
0.51
QUADRATIC
CORR.
COEFF.
0.954
0.987
0.989
0.997
REGRESSION
|
STD.
|
DEV.
|
ASH
1.67 |
0.90 |
0.81 |
0.44 |
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158
TABLE 14 EXPERIMENTAL RAM-FEED PRESENTATION UNIT TRIAL.
MARKHAM COLLIERY - TYPICAL SIZING ANALYSES
OF POWER STATION BLEND AND CRUSHED PRODUCT
WITH DIFFERENT SIZE CRUSHER GRIDS
| SIZE
| FRACTION
| mm
| +16
| 1 6 - 8
| 8 - 4
| 4 - 2
1 2 - 1
| 1 - 0
| TOTAL
UN-CRUSHED
PRODUCT
WT.%
17.7
10.8
21.3
18.6
15.0
16.6
100.0
CUM
WT.%
U/S
100.0
82.3
71.5
50.2
31.6
16.6
50.1
WT.%
1.3
15.0
29.6
20.0
14.4
19.7
100.0
CRUSHER GRID APERTURE
i mm
CUM
WT.%
U/S
100.0
98.7
83.7
54.1
34.1
19.7
25
WT.%
2.1
10.8
32.1
22.3
14.4
18.3
100.0
.4 mm
CUM
WT.%
U/S
100.0
97.9
87.1
55.0
32.7
18.3
12.-
WT.%
0.9
8.5
26.3
25.2
18.2
20.9
100.0
1 mm |
| CUM |
WT.% |
U/S |
100.0 |
99.1 |
90.6 |
64.3 |
39.1 |
20.9 |
(u/s - undersize)
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4 Foot Upper East Crop
3 Foot East
3 Foot Normal
TABLE 15 - ANALYSES OF SEAMS
TOTAL
MOISTURE
%
19.8
17.9
19.3
19.2
21.9
21.9
LABORATORY
ASH
CONTENT
%
6.3
13.0
18.8
7.0
10.2
10.2
FROM BLINDWELLS
SWEPT FREQUENCY
VOLATILE
MATTER
%
29.5
27.2
25.2
30.8
25.9
25.9
OPENCAST
SITE
MICROWAVE SYSTEM
SULPHUR
%
0.72
0.61
2.13
N.A.
0.96
0.96
TESTED WITH
| CALORIFIC |
j VALUE |
| KJ/KG |
24,460 |
22,620 |
19,980 |
24,840 |
21,920 |
21,920 |
THE
VOLATILE
MATTER
(D.A.F.)
%
40.0
39.4
40.8
41.7
38.1
38.1
CALORIFIC |
VALUE |
(D.A.F.) |
KJ/KG j
33,120 |
32,740 |
32,280 |
33,660 |
32,280 |
32,280 |
on
N.A. - NOT AVAILABLE
D.A.F. - DRY ASH FREE
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160
TABLE
16
RESULTS
OF
LABORATORY SWEPT FREQUENCY TESTS
ON A
RANGE
OF
SEAMS FROM BLINDWELLS OPENCAST SITE
| SEAM
| Parrot Crop
|
4
Foot Upper
| East Crop
| Dover
| Lower Craw
| Normal
| Lower Craw
| Crop
|
3
Foot East
|3 Foot Normal
|
All
seams
TOTAL
|
MOISTURE
RANGE
%
14.3-27.2
11.1-24.4
13.2-27.0
13.4-26.8
11.4-26.0
13.5-25.5
13.1-26.3
11.1-27.2
QUAD. REGRESSION
|
TOTAL MOISTURE/
ATTENUATION GRAD.
CORR.
COEFF.
0.957
0.996
0.984
0.975
0.991
0.969
0.961
0.964
STD.
DEV.
% MOIST.
1.28
0.43
0.80
0.99
0.68
1.05
1.25
1.14
QUAD. REGRESSION
|
TOTAL MOISTURE/WEIGHTED
|
ATTENUATION GRAD.
|
CORR.
|
COEFF.
0.979
0.986
0.978
0.980
|
0.991
| 0.984
|
0.965
|
0.973
STD.
DEV. |
% MOIST.
j
0.91 |
0.82 |
0.94 |
0.88 |
0.67 |
0.77 |
1.17 |
0.99 |
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161
TABLE 17 RESULTS OF FIRST SERIES OF LABORATORY TESTS WITH
EXPERIMENTAL INSULATED PLATE CAPACITANCE CELL AND
DIFFERENT CONCENTRATIONS OF IONIC SALT SOLUTIONS
| | | SAMPLE | SAMPLE | SAMPLE |
j TEST | ADDED j 1A | IB | IC |
I
NO. |
MOISTURE
I I I 1
I 1 * 1 INSTRUMENT READING mV |
1 1 1 1 1 1
I 1 | 0 | 107 | 107 | 107 |
1 1 1 1 1 1
| 2 | 2 | 220 | 225 j 238 |
1 1 1 1 1 1
I 3 | 4 | 450 | 517 | 570 |
1 1 1 1 1 1
I 4 | 6 | 680 | 758 | 960 |
1 1 1 1 1 1
I 5 | 8 | 900 | 970 | 1200 |
1 1 1 1 1 1
I
6 | 10 | 1050 | 1120 | 1270 |
1 1 1 1 1 1
I 7 | 12 | 1160 | 1180 | 1350 |
1 1 1 1 1 1
| 8 | 14 | 1240 | 1280 | 1400 |
1 1 1 1 1 1
I
9 | 16 | 1310 | 1390 | 1460 |
1 1 1 1 1 1
| 10 | 18 | 1350 | 1430 | 1470 |
1 1 1 1 1 1
SAMPLE 1A - moisture content increased with distilled water
SAMPLE IB - moisture content increased with 5g/l solution of sodium chloride
SAMPLE IC - moisture content increased with 16g/l solution of sodium chloride
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162
TABLE 18 RESULTS OF SECOND SERIES OF LABORATORY TESTS WITH
EXPERIMENTAL INSULATED PLATE CAPACITANCE CELL
| | | TOTAL | INSTRUMENT |
| TEST | | MOISTURE | READING |
1 NO. j SAMPLE | % | mV |
| 1 | 2AA | 14.54 | 753 |
| 2 | | 13.37 | 707 |
| 3 | | 11.81 | 596 |
| 4 | | 11.81 | 553 |
| 5 | | 8.40 | 433 |
| 6 | | 8.49 | 410 |
| 7 | | 7.51 | 395 |
| 8 | | 7.42 | 284 |
| 9 | | 6.29 | 249 |
| 10 | | 5.03 | 247 |
| 11 | | 4.28 | 212 |
| 12 | 2AB | 16.75 | 791 |
| 13 | | 14.42 | 713 |
| 14 | | 11.71 | 596 |
| 15 | | 8.53 | 505 |
| 16 | | 7.25 | 417 |
| 17 | | 6.65 | 383 |
| 18 | | 5.61 | 315 |
| 19 | | 4.64 | 270 |
| 20 | 2BA | 19.17 | 903 |
| 21 | | 15.21 | 715 |
| 22 | | 11.70 | 615 |
| 23 | | 9.15 | 432 |
| 24 | 2BB | 18.24 | 953 |
| 25 | | 12.10 | 680 |
| 26 | | 9.93 | 555 |
| 27 | | 7.79 | 428 |
| 28 | | 7.14 | 365 |
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163
TABLE 19 CALIBRATION TESTS WITH THE NEWPORT
MARK IIIA ANALYSER
| SAMPLE VOLUME (cm
3
) | 40 | 100 |
1 I I I
| SAMPLE WEIGHT (g) | 20 - 30 | 50 - 80 |
1 I I I
| SUITE | NO. | NO. | MAX. | MOISTURE | STANDARD DEIVATION |
| | COALS | SAMPLES | PARTICLE | RANGE | (MOISTURE %)
¡ I I I S I Z E | (%) | | |
l l l l ( n m ) J i ¡ ¡
1 1 1 1 1 1 1 1
1 1 1 1 1 1 1 1
1 1 1 6 1 17 1 0.2 1 1 - 9 1 0.42 j 0.34 j
1 1 1 1 1 1 1 1
| 2 | 7 | 16 | 3.0 | 2 - 11 | 0.42 | 0.33 |
1 1 1 1 1 1 1 1
| 3 | 4 | 16 | 0.2 | 1 - 10 | 0.40 | 0.34 |
1 1 1 1 1 1 1 1
| 4 | 4 | 15 | 3.0 | 1 - 9 | 0.34 | 0.38 |
1 1 1 1 1 1 1 1
| 5 | 5 | 19 | 0.2 | 1 - 6 | 0.18 | 0.23 |
1 1 1 1 1 1 1 1
] 6 | 12 | 20 | 3.0 | 1 - 8 | 0.17 | 0.23 |
1 1 1 1 1 1 1 1
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TABLE
20
SUMMARY OF WORK ON MOISTURE MEASUREMENT BY NMR SPECTROMETRY
REFERENCE
LADNER 1964
LADNER 1966
ROBERTSON
1979
PAGE 1981
KING 1983
CUTMORE
1986
NMR
METHOD
Ctf
CU
CU
CU
PULSED
PULSED
FREQUENCY
(MHz)
16
16
2.7
2.7
10, 30
10-60
PRESENT-
ATION
STATIC
MOVING
STATIC
STATIC
STATIC
MOVING
STATIC
SAMPLE
VOLUME
(cm3)
15
15
40
40
100
0.5
PARTICLE
SIZE
(mm)
0
-
1.6
0.5 - 1.6
0
-
6.0
0.2 - 3.8
0 - 0.2
0 - 3.0
< 0.1
<1
MOISTURE
RANGE
(%)
3
3
3
4
0
1
1
1
0
- 30
- 15
- 25
- 27
- 14
-
10
- 11
-
31
-
30
ACCURACY
|
(-+
2s)
|
(%) |
1
|
1 |
1 |
2.6 |
0.6
|
0.4 - 0.8 |
0.5
-
0.7
|
1.5 |
1 - 2
|
en
■i*
(CU - CONTINUOUS UAVE)
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TABLE 21
COMMERCIALLY AVAILABLE MULTIELEMENT ANALYSERS
| Manufacturer | Science Applications | MDH-Motherwell Inc. | Gamma-Metrics |
| | International Corporation | | j
| | 1200 Prospect Street | 426 West Duarte Road | 5550 Oberlin Drive |
| | la Jolla | Monrovia j San Diego |
| | California 92037 | California 91016 | California 92121 |
j | USA | USA | USA j
| Instrument | CONAC* | ELAN | COAL ANALYSER (3612C)+ |
| Length (m) | 7.3 | 2.0 | 4.3 |
| Depth (m) | 1.7 | 1.9 | 2.4 |
| Height (m) | 2.1 | 2.4 | 2.6 |
j Presentation System j Horizontal belt j Vertical chute | Vertical chute j
j Coal bed x-section (m) j 0.9 x 0.3 j 0.35 x 0.25 j 0.9 x 0.3 j
j Max. coal flow (tph) | 30 | 100 | 500 |
j Max. particle size (mm) | 75 | 100 j 100 |
| Detectors | 1 x Nal | 1 x Nal | 2 x Nal |
j | 1 x HpGe | | j
1 | 1 x
3
He | | j
j Density measurement j 137Cs/NaI | None | 137Cs/NaI j
j Moisture measurement j Microwave | Microwave j C/H correlation (or microwave)j
| Minimum response time ¡ 5 - 2 0 j 2 - 5 j 1 j
j (minutes) I I I 1
0\
* Belt and batch (chute) 'Sulfurmeters' also made
+ Model 1812C with smaller chute also made
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166
TABLE 22 ACCURACY OF CONAC (ils wt% )
| YEAR
| REF
| TEST
| TEST
LOCATION
TYPE
| NO. SAMPLES
1 H
1 c
1
s
1 ci
1
N
1
Si
1 Al
1 Fe
| Ca
1 Ti
1 Ash
1 Moist
| C.V.
(kJAg)
1983
LABORATORY
CALIBRATION
17
0.08
1.4
0.13
0.005
0.18
0.14
0.11
0.05
0.008
1983
LABORATORY
ACCEPTANCE
5
0.12
2.74
0.29
0.006
0.18
0.69
0.55
644
1983
FIELD
ACCEPTANCE
5
0.04
1.8
0.05
0.006
0.16
1.7
0.52
4.30
1985 |
FIELD |
|
4 1
0.12 |
1.31 |
0.13 |
0.05 |
0.99 |
1.18 |
247 |
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167
TABLE
23
PRECISION
OF
CONAC
(± Is wt )
| YEAR
|
REF.
| TEST LOCATION
| REPORTING PERIOD
1 H
1 c
1 s
1
ci
1
N
|
Ash
1 Moisture
1
C.V.
(kJAg)
1983
LABORATORY
3h
0.03
1.39
0.08
0.006
0.04
0.74
0.03
347
1983
FIELD
3h
0.02
1.27
0.06
0.002
0.02
1.22
0.01
323
1985
|
FIELD
|
20m
|
00.02
|
1.88 |
0.11 |
0.10 |
0.49 |
0.16 |
286
|
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168
TABLE 24 ACCURACY OF ELAN (wt %)
| YEAR
| REF
| TEST
| NO.
| ASH
1 H
1 c
1 s
1 ci
1
N
1 Si
1 Al
1
F«
| Ca
1 Na
1 K
1
Ti
1 Ash
1 C.V.
TYPE
OF SAMPLES
RANGE
(%)
(kJAg)
1983
INITIAL
COMPARISON
2
6-7
MEAN DIFF.
0.26
1.1
0.05
0.01
0.03
0.07
0.03
0.02
0.05
0.005
0.06
0.03
0.23
1983
CALIBRATION
7
4-27
r.m.s.
0.04
| 0.20
| 214
1983
COMPARISON
35
r.m.s.
0.04
1985 |
COMPLIANCE |
DEMONSTRATION |
32 |
4-7 |
r.m.s. |
0.04 |
| 0.23 |
145 |
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170
TABLE 26 RELATIVE ACCURACY OF NEUTRON/GAMMA ANALYSIS
| RELATIVE ACCURACY
1
(±is)
| < 2%
| 2 - 5 %
| 5 - 1 0 %
| 10 - 20%
| 20 - 30%
| 30 - 50%
| > 50%
PARAMETER |
Calorific value j
H, C, Ash |
S, Si |
N, CI, Fe |
Al, K 1
Na,
Ti 1
Ca j
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171
TABLE 27 UNITS CURRENTLY INSTALLED OR ORDERED
|
|
SAIC
| MDH - |
GAMMA-
|
TOTAL
|
|
| |
MOTHERWELL
|
METRICS
| |
| Installed
and
Operating
j 1 j 3 j 11 | 15 j
| or Commissioning | | j j j
| Installed
not in use | 2 | j 1 | 3 |
| Ordered
| j 1 | 1 j 2 |
| TOTAL
| 3 | 4 | 13 | 20 |
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ISOTOPE
MEASURING
HEAD
STATUS
CONTROL
^
< > .
CONVEYOR WIDTH
160 mm
F I G U R E
1 .
W ULTEX RAD IOMET RIC AS HME T ER, T YPE
G3 -
GENERAL ARRANGEMENT
ON B ELT CONVEYOR
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174
HINGED
COVER
(LOCKABLE)
RADIATION
_
SOURCE (Am241)
SOURCE
CONTAINER
SCINTILLATION
DETECTOR
SHUTTER
4 9 0
mm
FIGURE 2. WULTEX RADIOMETRIC ASHMETER, TYPE G3 -
SECTIONAL VIEW OF ISOTOPE MEASURING HEAD
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0 . 8 8 - ,
BULX DENSITY
0 . 9 0 -
0 . 9 2 -
0.94 _
O
u
w 0 . 96 .
I—I
3
w
OS
0 . 9 8 -
1.00 -
900 KG/M
3
700 KG/M
3
10
ASH
15 ASH
20 ASH
u i
1-02
50
100
-nr
150
200
BED DEPTH (MM)
" I
250
FIGU RE 3 . W ULTEX AS HMET ER
*
T H E R O T E I C A L E F F E C T O F B E D D E P T H ON C O U N T R A T E F OR
3 L E V E L S O F A S H C O N T E N T A N D 2 L E V E L S O F B U L K D E N S I T Y
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176
SPACERS
1 .
T
TT-+Í
COMPRESSION STOPS
7
COMPRESSION PLATE
ADJUSTABLE BASE
=
\
EXTENSION
FRAME
BOX FRAME
SAMPLE COMPRESSION WITH POSSIBLE BED DEPTH/FRAME COMBINATIONS
BED
DEPTH
(D)
mm
80
120
160
200
FRAME DEPTH (E) mm
6
8 12 16 20
32
( E 100)
COMPRESSION ; - — - ' ;
( E + D )
7.0
4.8
3.6
2.9
9.1
6.25
4.8
3.8
13.0
9.1
7.0
5.7
16.7
11.8
9.1
7.4
20.0
14.3
11.1
9.1
-
21.1.
16.7
13.8
COMPRESSION SYSTEM SPACERS FOR EACH EXTENSION FRAME
EXTENSION
FRAME DEPTH
mm
6
8
12
16
20
32
FRAME LESS
COMPRESSION
PLATE mm
-
2
6
10
14
26
SPACERS
mm
-
2
6
10
14
10+10+6
FIGURE 4. WULTEX ASHMETER - VARIABLE DEPTH SAMPLE PRESENTATION
BOX FOR LABORATORY INVESTIGATIONS
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12
-i
10 _
8
_
o
■ <
< 6 -
LOOSE FILL
BULK DENSITY 769-791 KG/M
3
LABORATORY ASH
40
1
8 0
1
1 2 0
BED DEPTH (MM)
1
16 0
1
20 0
12 - I
10 -
8
-
SB
in
6 -
4 -
COMPACTED FILL
BULK
DENSITY
8 6 5 - 8 6 7
KG/M
3
UK METER
LABORATORY ASH
40
n
1
r
80 120 160
BED
DEPTH
(MM)
1
200
»J
««4
FIGURE 5. VULTEX ASHHETER - EFFECT OF BE D DEPTH ON ASH MEASUREMENT AT TW O E ELS
OF BULK DENSITY WITH SAMPLE FROM BILSTHORPE PS F BLEND
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20 -,
18
16
14
3 12
10 -
POLISH METER
LOOSE FILL ,
BULK DENSITY 739-776 KG/M
J
^
1 H
_ L A B O R A T O R Y ASH
40
i
1 r~
80
120 160
BED DEPTH (MM)
1
2 0 0
2 0 -i
1 8 -
1 6 -
1 4
_
o
«e
ac
v)
1 2
—
1 0 —
P O L I S H M E T E R
C O M P A C T E D F I L L
B U L K D E N S I T Y 8 1 6 - 8 2 1 K G / M
3
LABORATORY
AS H
40 80
120
160
B ED DEP T H
(MM)
200
0 0
F I G U R E 6 . W U LT EX Ä S HK E T E R - E F F E C T O F B E D D E P T H ON A S H ME A S U R E ME N T A T TWO L E V E L S O F
B U L K D E N S I T Y W I TH S A M P L E F RO M M A NT ÓN M I D D L I N G S .
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28 -,
28 -,
LOOSE FILL
BULK DENSITY 826-829 KG/M3
27 _
27 _
26 _
POLISH METER
o
•<
•4
25
24
23
26 —
o
•<
25 _
24 —
40
1—
8 0
1
120
BED
DEPTH
(MM)
— T
160
"I
200
23
COMPACTED
BULK DENSITY 913-916 KG/M
3
POLISH METER
LABORATORY ASH
40
"I 1 1 1
80 120 160 200
BED DEPTH (MM)
FIGURE 7. WULTEX ASHMETER - EFFECT OF BED DEPT H ON ASH MEASUREME NT AT TWO LEVEL S
OF BULK DENSITY WITH SAMPLE FROM GEDLING MIDDLINGS
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180
25 -
<r
<r
2
o
8
20 -
15
-
10 -
■
- •
1 . . . . 1
H ' ' M
i....R>v...
. . . . i
i • • • •
Da
iP
i i i i i
i i i i i
^ x
. . . . i
i
' ■ ' ■ i
. . . . i
i i i i
c
. . . . i
■ i—i—r-T -H
■ ■ ■ -*■ 1
1—
• -
2600 2100 2200 2300 2.4øø 25øø
ASHMETER
READING
(COUNTS/SECOND)
2600
2700
FIGURE 8. LABORATORY CALIBRATION FOR MANTÓN 50 mm - 0
BLENDED
COAL
WITH
fU T X
UK)
ASHMETER
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181
■
N
5-
g
5
24
-
22
-
29
18
16
14
T
1
•
T 1 1 1 1 1 1 r
T r
: ; ;
:
^ V ^ Q .
j
\
^TrR^ü
neo
X
_L
■
1150
1200
1250
ASHMETER
READING
<COUNTS/SECOND)
1300
FIGURE
9.
LABORATORY
CALIBRATION
FOR
MANTÓN
50
nun
-
0
BLENDED
COAL
WITH
WULTEX
(POLISH)
ASHMETER
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182
■
r
N
2
s
3
58
45
-
48
35
3ø
25
T — i — —
r
i i i I
^ ^ L
□
¿fvgp
p
ü
. . . . ^ s ^
b
Ía. . . . l^Í .
1609
X
_L _L _L
1630
1700
1750
1800
ASHMETER
READING
(COUNTS/SECOND)
1850
FIGURE 10. LABORATORY CALIBRATION FOR MANTÓN 50 nun - O
UNTREATED
COAL
WITH
WULTEX
(UK)
ASHMETER
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183
n
m
< r
X
< r
g
i -
2
o
m
850 900 950 1000
ASHMETER READING (COUNTS/SECOND)
1050
FIGURE 11. LABORATORY CALIBRATION FOR MANTON 50 mm - O
UNTREATED COAL WITH WULTEX (POLISH) ASHMETER
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184
■
fi
O
t-
r
cc
o
m
<r
30
28
26
24
22
20
18
16
—1
i . .
i i 1 i i
—r
; ;
; ;
; ;
; ;
;
j
> S
\
D
i— \
i — i — i — i — i —
d
: i :
. . i . . . . i . . . . i
\ D D
fla\ o
\ n
o
_ J ■ ■ ■ 1
1 ■ 1 I 1 1
• ;
• •
;
;
;
; ;
;
;
N.
•
N x i i ;
. . . . 1 . . . . 1
1—
-
-
-
-
m
1888 1050 1100 1150 1200
ASHMETER
READING
COUNTS/SECOND)
1250
1300
FIGURE
12.
LABORATORY
CALIBRATION
FOR
ASKERN
25
mm
-
0
BLENDED
GOAL
WITH
WULTEX
POLISH)
ASHMETER
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185
50
T — r
i — r
■
< r
fi
>
o:
o
(£ .
O
m
45
40
35
30
-•
.1 „ha™ D
D \
Ö \ n
•
-L
_L
■
_L
_L
i
i
i
i
850 900
950
1000
1050
ASHMETER
READING
(COUNTS/SECOND)
lløø
FIGURE
13.
LABORATORY
CALIBRATION
FOR
ASKERN
25
mm
-
O
UNTREATED COAL WITH WULTEX (POLISH) ASHMETER
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186
s
■
<r
N
12
-
10
-
8
-
ó
-
— 1
1
1— 1— 1— 1— 1— 1— 1— 1— 1— 1 — I
D
N 3
1 — i — ■ — — — 1
D\
I
r i 1 1
\ a
i
r I — I — |
— i — i — i — i — i
i
i
i
i
i
1—
-
1309
1400
1500
1600
1700
ASHMETER
READING
COUNTS/SECOND
1800
FIGURE
14.
LABORATORY
CALIBRATION
FOR
ASKERN
25
mm
-
0
WASHED COAL WITH WULTEX POLISH ASHMETER
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187
■
<L
N
<E
2200
2400
2600
2800
3øøø
ASHMETER
READING
(COUNTS/SECOND)
3200
FIGURE
15.
LABORATORY
CALIBRATION
FOR
BILSTHORPE
50
mm
-
0
BLENDED COAL WITH WULTEX (UK) ASHMETER
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188
■
o
3
ieeø
1180
1208
1388
1488
ASHMETER READING (COUNTS/SECOND)
1588
GURE
16.
LABORATORY
CALIBRATION
FOR
BILSTHORPE
50
mm
-
0
BLENDED
COAL
WITH
WULTEX
(POLISH)
ASHMETER
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189
B
<I
N
1909
i i i
2000 2100 2200 2300
ASHMETER READING (COUNTS/SECOND)
2400
FIGURE 17. LABORATORY CALIBRATION FOR BILSTHORPE 38 mm - O
UNTREATED COAL WITH WULTEX (UK) ASHMETER
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190
■
>
g
50
-•
45
-
4ø -
35
-
30
-
-
■
-• i
— —l— — — — I ~ I — i — i — T — r — i — r — r —
° n P
o
I — I — i i i
3
^ \ .
I
i
i
i
i
j—r—i—i—i—
i
1—
•
• -
800
_L _L
X
X
850
900
?5ø
løøø
1050
ASHMETER
READING
(COUNTS/SECOND)
Uøø
FIGURE
18.
LABORATORY
CALIBRATION
FOR
BILSTHORPE
38
mm
-
O
UNTREATED
COAL
WITH
WULTEX
(POLISH)
WULTEX
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191
■
<E
M
>
o
S
O
m
<r
2800
3000 3200 3400 3600
ASHMETER READING COUNTS/SECOND
3800
FIGURE 19. LABORATORY CALIBRATION FOR BILSTHORPE 50 mm - 0
WASHED COAL WITH WULTEX UK ASHMETER
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192
18
■
îi
2
O
5
4
2
— i
1380
1400
1500
1600
1700
ASHMETER
READING
(COUNTS/SECOND)
1800
FIGURE
20.
LABORATORY
CALIBRATION
FOR
BILS
THORPE
50
nun
-
0
WASHED
COAL
WITH
WULTEX
(POLISH)
ASHMETER
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193
■
N
O
H
2
O
o c
2400
2Ó00
2800
3000
ASHMETER
READING
(COUNTS/SECOND)
3200
FIGURE 21.LABORATORY CALIBRATION FOR COTGRAVE 50 mm - O
BLENDED
COAL
WITH
WULTEX
(UK)
ASHMETER
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194
■
■
NX
(f l
>
o
<C
OC
o
m
<r
35
-
30 -
25 -•
20
-
15
-
10
-
1100
1200
1300
1400
ASHMETER
READING
COUNTS/SECOND)
1500
FIGURE
22.
LABORATORY
CALIBRATION
FOR
COTGRAVE
50
mm
-
0
BLENDED
COAL
WITH
WULTEX
POLISH)
ASHMETER
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195
■
■
<I
X
CO
<t
o
45
40
35
38
25
20
15
10
- • i s :
. ;
- j
O
1
D
D
-
.
1 I I I
, . ,
^ \ n
D
.
r *
T
■ '
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■
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:
i
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n nnìTriL ri
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'
. ._
-
-
. ._
. ._
1
1800
2000
2200
2400
2600
ASHMETER
READING
(COUNTS/SECOND)
2800
FIGURE
23.
LABORATORY
CALIBRATION
FOR
LEA
HALL
25
mm
-
0
BLENDED COAL WITH WULTEX (UK) ASHMETER
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196
25 -■
O
■
r
N
S
28
15
10
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- ■ i
1
1 1 1 1 1
_ . . * . .
J
.
1
: o V
. . . . i
D :
. . . . i
r-i—i i i
—t 1
1
i
i
i
i
T
-
' — i — i — • — 1 —
a n i
D > v : :
D D ^ Q :
:
-
i — i — i — i i 1 i i ■ ■ i
2400
2500
2609
27øø
2800
ASHMETER
READING
(COUNTS/SECOND)
2900
3000
FIGURE
24.
LABORATORY
CALIBRATION
FOR
DAW
MILL
12.5
mm
-
O
UNTREATED
COAL
WITH
WULTEX
(UK)
ASHMETEÄ
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197
■
< r
fi
< r
>
CC
o
I
g
s
3
9 -
8 -•
7 -•
5
-
4
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_ .
- •
1
| \ c
IfflS
| I - T I I - T • « TI
;
0
> EFSJ
n
:
D
:
'
■
'
'
1
— « — « — • — « — i i —
,._
-
3208 3300 3400 35øø 36øø 37øø 38øø
ASHMETER READING (COUNTS/SECOND)
3900
FIGURE 25. LABORATORY CALIBRATION FOR CWM 50 mm - 0
WASHED
COAL
WITH
WULTEX
(IJK)
ASHMETER
7/24/2019 Coal Quality Monitoring
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198
■
p
B
< r
M
X
CO
<E
>
œ
o
5
20
18
16
14
12
10 -
8 — i
2500
2550
2600
2650
2700
2750
ASHMETER
READING
<COUNTS/SECOND)
2800
FIGURE 26. LABORATORY CALIBRATION FOR SHARLSTON 50 mm - 0
WASHED COAL WITH WULTEX (UK) ASHMETER
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199
3ø -
25 -
Q
M
fi
<r
cc
om
<r
20
15 -
10
-
5 -
0 -•
2200 2400 2600 28øø 3øøø 3299
ASHMETER READING (COUNTS/SECOND)
3400
FIGURE 27. LABORATORY CALIBRATION FOR GRIMETHORPE 50 mm - 0
BLENDED COAL WITH WULTEX (UK) ASHMETER
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200
■
< t
s/
N
g
2
O
m
5
2ø
»
i
■ ■ ■ ■ i ■ ■ ■ ■ i ■ ■ ■ ■
■ . . .
i . . . . i . . . . i . . . . i . . . . i
2868 2850 2188 2158 2288 2258 2388 2358 2488
ASHMETER
READING
(COUNTS/SECOND)
FIGURE
28.
LABORATORY
CALAIBRATION
FOR
GRIMETHORPE
50
mm
-
0
UNTREATED
GOAL
WITH
WULTEX
(UK)
ASHMETER
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201
a
<i
N
CO
O
m
<£
5 -
4 -
3008 3108 3288 3388 3488 3588
ASHMETER READING (COUNTS/SECOND)
3600
3788
FIGURE 29. LABORATORY CALIBRATION FOR GRIMETHORPE 50 mm - 0
WASHED COAL WITH WULTEX (UK) ASHMETER
7/24/2019 Coal Quality Monitoring
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202
x
/>
i
U
a
e
(O
i
2 .5
2
1.5
1
0 .5
- •
- •
- •
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1
'
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D
. . . .
^
n ^ D
.
. . .
i
. . . .
i
— — ■ — ■ — —
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. . . .
. . -
m
.._
-
0.5 1 1.5 2
CALIB
STD
DEV
-
LABORATORY
MEASUREMENTS
2.5
FIGURE
30.
RELATIONSHIP
BETWEEN
STANDARD
DEVIATION
CALCULATED
FROM
FULL ELEMENTAL ANALYSIS AND MEASURED STANDARD DEVIATION
FOR
LABORATORY
CALIBRATION
TESTS
WITH
WULTEX
ASHMETER
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203
2.5 -
co
I-I
O)
5-
i
o
I
s
0)
1.5
0.5
0.5 1 1.5 2
CALIB STD DEU - LABORATORY MEASUREMENTS
2.5
FIGURE 31. RELATIONSHIP BETWEEN STANDARD DEVIATION DERIVED
FROM IRON AND ASH ANALYSIS ONLY AND MEASURED
STANDARD DEVIATION FOR LABORATORY CALIBRATION
TESTS WITH WULTEX ASHMETER.
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Œ
RAW
COAL
FILTER
CAKE
CLEAN
COAL
IV J
MIXER
BELT FEEDER
\
7^
BELT WEIGHER
3D
MECH
SAMPLER
BELT
WEIGHER
SHIFT
SAMPLE
RAPID
LOADING
BUNKERS
O
■Ck
FIGURE
3 2 .
SCHEMATIC
ARRANGEMENT
OF
WULTEX
ASHMETER
INSTALLATION
AT
BILSTHORPE
COLLIERY
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CLEAN
COAL
-25 mm
MECHANICAL SAMPLER
I
V
<r t»|
CRUSHER
f
STATION O*"* ^ O
Ù
CONSIGNMENT
SAMPLE
o
en
FIGURE 33. SCHEMATIC ARRANGEMENT OF WÜLTEX ASHMETER INSTALLATION AT MANTON COLLIERY
7/24/2019 Coal Quality Monitoring
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206
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: ^ \
1
1
1
1
1
1
1
1
1
L
_
I
__L
L_
1
1
1
i —
—
• -
.
1300
1350
1400
1450
1500
ASHMETER
READING
(COUNTS/SECOND)
1550
FIGURE 34. WULTEX ASHMETER INSTALLATION AT MANTÓN COLLIERY
DYNAMIC
CALIBRATION
TEST
1
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207
3ø
cc
< r
M
X
CO
< c
>
cc
o
<i
25 —
20
15
—
10
— 1 — 1 — 1 — 1 — 1 — 1 — 1 — 1 — 1 — 1 — 1
-
- •
1
c
iSkn
D
i — i — i — i — i — ; — i — i — i —i — i
n
D
D
o
i — ' — « — ' — ■ — —
D
. . Q . . ^ . ^ ^
1 — 1 — 1 — 1 — 1 — 1 — 1 — 1 — 1 — 1 — 1 — 1 — 1 — 1 — 1 — 1 — 1 — 1 — 1 — 1 — 1 — 1 — J _ _
1
1 1
-
, . -
1
1250
1300
135 14 145
ASHMETER READING (COUNTS/SECOND)
1500
FIGURE
35.
WULTEX
ASHMETER
INSTALLATION
AT
MANTÓN
COLLIERY
-
DYNAMIC
ALIBRATION
TEST 2.
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208
H T • — - j r-*~ Signal to
amplifier
Scintillation
detector
M l . _IJS_
Am S Bo
FIGURE 36. SCHEMATIC ILLUSTRATION OF THEpRiNCIILE OF OPERATION 01
THE COALSCAN 3500 ASH MONITOR.
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209
Americium ( low )
channel
Borium ( high ) chonnel
60 keV
3 5 6
Energy , keV
FIGURE 37. RADIATION SPECTRUM FOR COALSCAN 3500 ASH MONITOR WITH
AMERICIUM AND BARIUM SOURCES.
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CONVEYOR
SOURCE
HOUSING
ELECTRONICS UNIT
SIGNAL CA3LE
DETECTOR
?=n
PRE AM?
±=és
S?
LOCAL CONTROL UNIT
J ^ = q ^
RADIOISO- S H U T T E R
TOPES POSITION
LIMITS
I
POWER UNITS
1-
FRAME CONTROL
SHUTTER CONTRC
,
D
FRAME POSITION LIMITS
cq
MULTI ÇHANNEI
ANAT.VSF.R
TERMINAL
I
COMPUTER
S
INPUT/
OUTPUT
POWER
SUPPLIES
RETRACTABLE FRAME
o
FIGURE 38. SCHEMATIC ARRANGMEITT~ OF COMMERCIAL DESIGN OF COALSCAN 3500 ASH MONITOR
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211
0 . 0 2 0
o 0 .01 6 _
D
o
~ 1 2
g 8
Q
O C
<r
a 4
-]—i—i—i—i—|—i—i—i—i—|—i—i—i—i—|—i—i—i—i—|—i—i i
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_L
J L.
J
i
i_i
i
L
■ ■ ■ i i i i i__i_
1
200 300 400
COUNTING PERIOD <SECS)
■COO
6
FIGURE 39. LABORATORY INVESTIGATIONS WITH COALSCAN 3500 ASH MONITOR -
VARIATION
OF
LOG
RATIO
STANDARD
DEVIATION
WITH
DURATION
OF
COUNTING
PERIOD
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212
70 - i
60
50 _
40 _
K
SC
CO
w 30
CO
¡3
OS
o
20 -
10 _
* Fe20
3
© C a O
V TYPICAL ASH
0
A
l
2
0
3
2 S i 0
2
%
A D D I TI ON
FIGURE 40. LABORATORY INVESTIGATIONS WITH COALSCAN 3500 ASH MONITOR -
EFFECT OF CHEMICAL ADDITIONS ON MEASUREMENT OF ASH CONTENT
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213
A
o
<r
X
w
<c
>
<z
o
»-
< t
cc
o
m
<x
45
40
35
30
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20
15
10
—
•
1
. . . . . . . .
| 1 1 1 1 1 1 1 1 1 1 r— i 1 1 1
_ J 1 1 1 . 1 1 1 1 1
/ : -
: -
; -
j -
2 .5 2 .ó
2 . 7 2 . 8 2 . 9
LOG.
RATIO
3.1
FIGURE 41. LABORATORY CALIBRATION FOR ASKERN BLENDED COAL (-212 pn)
WITH COALSCAN 3500 ASH MONITOR.
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214
a
< z
f i
X
0 1
24
22
28
18
là
14
12 -
10 -
' ' *
T — ■ — — — ■ — 1 — ■ — • — • — — 1
p
° 0 ^ ; q
:
J
y ^
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D :
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\y ^
\ :
J I L.
2 . 3 5
J i i i i L
J
L.
j i L _ l
2.4
2.45 2.5
LOG. RATIO
2.55
2.6
FIGURE
42.
FIRST
LABAORATORY
CALIBRATION
FOR
GASCOIGNE
WOOD
UNTREATED
COAL (-212 pin) WITH COALSCAN 3500 ASH MONITOR.
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215
•N
a
<r
X
CO
< c
>
oc
o
I
o
m
<c
35
-•
30
-
25
-
20
15
—
10
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;
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i
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D
y
i . . . . ¡ . . . .
. . . .
■ i i i
■
■
.
■
D
„ u i i 1
• -
• -
-
2.5 2.6
2.7 2.8
2.9 3
LOG.
RATIO
3.1
3.2
3.3
3.4
FIGURE
43.
SECOND
LABORATORY
CALIBRATION
FOR
GASCOIGNE
WOOD
UNTREATED
COAL
(-212
pu)
WITH
COALSCAN
3500
ASH
MONITOR
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276
<x
I
(O
< r
I
s
5
32
-
3ø -
28
-
26
-
24 -
22
-
2ø -
- :
■
: : D n j -
:
:
□ \s^ \ \ '.
P
o^P
0
^ i i
D
-
:
Ü
l^^
:
-
i n / r n ; i -
^ ^ : :
D
= : :
i i i 1 i i i 1 i i i 1 i i i 1 i i i.- L i i ■ 1 . . . 1 . . . 1
2.6
2.62
2.64
2.66
2.68
2.7
2.72
2.74
2.76
2.78
LOG.
RATIO
FIGURE 44. LABORATORY CALIBRATION FOR SOUTH SIDE (GRIMETHORPE)
BLENDED
COAL
(-212
pi)
WITH
COALSCAN
3500
ASH
MONITOR
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217
< r
Ni »
M
I
CO
< c
>
o c
o
< r
o
m
< r
35
30
-
25
-
20
-
15 -
10
— 1
- •
-
J
1 — — I — — — 1
. . . .
0D
i . . . i
Pu
i i i i
i — i — i — i i j — ■ — ■ — i - - » i
1 i i i i
. . . .
-
™
2.55
2.6
2.65
2.7
LOG.
RATIO
2.75
2.8
2.85
FIGURE
45.
LABORATORY
CALIBRATION
FOR
ASKERN
BLENDED
COAL
(-212
pi)
FROM
FOURTH
DYNAMIC
CALIBRATION,
WITH
COALSCAN
3500
ASH
MONITOR
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218
35 —
38 -
N
CO
<E
>
£.
O
I-
<£
OC
O
m
<E
25
20 —
15 -
18
...J
. . . .
1 1 1 1
D P^
3
i i i i 1
°rfJ
1 1 1 1,
D ^ Q
ÏS^
i i i i
1 i i i i 1
i —
-
2.55
2.6 2.65 2.7 2.75
LOG. RATIO
2.8
2.85
FIGURE 46. LABORATORY CALIBRATION FOR ASKERN BLENDED COAL (-1 nun),
FROM FOURTH DYNAMIC CALIBRATION, WITH COALSCAN 3500
ASH MONITOR
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219
<z
X
CO
<z
>
CC
o
tr
o
m
<E
45
40
35
30
25
28
15
10
5
— i
-
- ■
- •
-
i l i 1 1 i i 1 1 — — — — — j 1 1 1
r——j
1 1 1 i j
: :
Jr
: : : > / :
S5 :
: y f : :
j y ^ •
-
_
, . -
. -
r~
i i i i . i. J i i i i i i i i i i I _ I ■ ■ ' ■ ' ■ i l
2 .4
2 .5
2 .6 2 . 7
LOG. RATIO
2 . 8 2 . 9
FIGURE 47. LABORATORY CALIBRATION FOR ASKERN SIMULATED BLENDED
COAL
25
-
3.18
mm)
WITH
COALSCAN
3500
ASH
MONITOR
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RAW
COAL
CLEAN
COAL
WEIGH-
FEEDER
PHASE
3A
ASH
MONITOR
MECHANICAL
.
.
_ _
SAMPLER
Y
CRUSHER
ro
ro
o
[ J LABORATORY SAMPLE
FIGURE
4 8 .
SC HEMA TIC ARRANGEMENT
O F
C O A LS C A N 3 5 0 0
A N D
N C B / A E R E P H A S E
3 A A S H
MONITORS
A T
ASKERN C OLLIERY
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221
f i
I
co
<r
>
cc
o
I
<r
ce
o
m
<r
45
40
35
30
25
20
15
10
— i
- •
-
;
•
•
C
jdß
P%
1 i—_i i i i i i i i 1
: •
¿s
''■
-
:
jr
•
'
: s S ^ :
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:
-
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:
-
:
:
:
-
: : : -
i
i
i
i
i
i
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i
i
■
i
■
i
i
2 .5
2 . 6
2 . 7
2 . 8
LOG.
RATIO
2 . 9
FIGURE
49.
ON-SITE
STATIC
CALIBRATION
FOR
ASKERN
BLENDED
COAL
(-212
pn)
WITH
COALSCAN
3500
ASH
MONITOR
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222
c c
<E
v
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X
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o
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o c
s
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7ñ
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1 0
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i ■■ ■| ■■■ i
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¿\.JQ
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L_i ,_ i . .1
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.
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T
2
L_I
J
,
1 1
D y
L i i i i l
-
-
-
m
-
.
-
• -
-
-
2 .3 2 35 2 4 2 45 2 5
LOG.
RATIO
2.55
2 . 6
2.65
FIGURE
50.
FIRST
DYNAMIC
CALIBRATION
FOR
ASKERN
BLENDED
COAL
(25
mm
-
0)
WITH
COALSCAN
3500
ASH
MONITOR
7/24/2019 Coal Quality Monitoring
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223
m
a
x
co
<c
>
o
h -
< Z
CC
o
m
<r
39
25
28
15
18
5
— i
- •
i — « —
r
~ >
— « — i
□
. . . .
i — i — i — i — i — |
U
. . . .
D
J
2
®
n
:
1 1 1 1 1 1 1 L_l 1 1
D
—i—i—i—i—i—i—i—i
_I_J
- 1 — 1 — . r - ,
D
s
. . . .
,.-
■
-
2.45
5 55 6 65
LOG.
RATIO
2 . 7
2 . 7 5
2 . 8
FIGURE
51. STATIG CALIBRATION
FOR ASKERN BLENDED COAL SAMPLES
212
)iin)
FROM
FIRST
DYNAMIC
CALIBRATION
WITH
COALSCAN
3500 ASH MONITOR
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224
O C
< r
N
c o
< c
< r
c e
o
m
<E
35
30
25
20
15
10
5
' '
i . .
o
Q
— y
k j . S ^ i . n
: / Q
sĂac
1
■ t i i i i i i i i i i i i i ■ i
Uy
D
. . . .
1
. . . .
1
. . .
.
:
i
-
: -
: -
: -
: -
: -
-
: -
i
. . . .
i
2.45
2 .5
2.55
2 .6
2.65
2 .7
2.75
LOG.
RATIO
2 . 8 2 . 8 5
FIGURE 52. THIRD DYNAMIC CALIBRATION FOR ASKERN BLENDED COAL
25
mm
-
0 WITH
COALSCAN
3500
ASH
MONITOR
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225
3ø
Q:
<r
?£
ft
<I
>
CC
O
I
<r
cc
o
m
<r
25 —
20 -
15
10
: : : Jf
D
:
: :
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•
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- : °:
J
: -
I
I
p é
u
\
i I -
- ;
J ?
-
-■■
X Ş o
I
i
i
i - -
:
¿¿ □ : : : :
1.95
2 . 0 5
2 . 1
LOG.
RATIO
2 . 1 5
2 . 2
FIGURE
53.
FOURTH
DYNAMIC
CALIBRATION
FOR
ASKERN
BLENDED
COAL
(25
mm
-
0)
WITH
COALSCAN
3500
ASH
MONITOR
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226
C C
m
< x
f i
X
(O
<E
>
O C
o
»
< r
o c
s
1.95
2 . 8 5
LOG.RATIO
2.1
2.15
FIGURE 54. FIFTH DYNAMIC CALIBRATION FOR ASKERN BLENDED COAL
(25 mm - 0) WITH COALSCAN 3500 ASH MONITOR
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227
■
< x
n
>
cc
o
»
< t
a.
o
m
< t
25
-
29
-
15
10
i i i i i i i i
T ' ' ' ' 1 f
D
aX
3 D
D
n . .
„s
D 5 ^ :
x ^ à
D
' L I
■ i L ■ i L
j i L
1.9
1.95
2.85
2.1
LOG.
RATIO
FIGURE
55.
SIXTH
DYNAMIC
CALIBRATION
FOR
ASKERN
BLENDED
COAL
(25
mm
-
0)
WITH
COALSCAN
3500
ASH
MONITOR
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228
16 -
(À
■
O.
■
o
©
<9
«-•
LU
<I
o:
i
z
g
o
s
h-l
18
27
36
45
COUNTING PERIOD <No>
54
63
FIGURE
56.
COALSCAN
3500
ASH
MONITOR
TRIAL
AT
ASKERN
COLLIERY
-
VARIATION
OF BARIUM COUNTRATE, IN 2 SECOND PERIODS, DURING OSCILLATION
OF
MEASURING
HEAD
ACROSS
PRODUCT
STREAM
WITH
18
SECOND
CYCLE TIME
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229
UJ
H
Z
O
O
X
CO
< r
UJ
15 . 5
15
14 . 5
14
13 . 5
13
¡ . . . .
- •
1
-,
1
„i
J_.
i
i -
•
•
*• •
\
■
. . . .
i
. . .
.
. . . .
11.5
12
12.5
13
13.5
14
14.5
MEAN
BARIUM
COUNTRATE
(1808
C.P.S.)
15
15.5
FIGURE
57.
COALSCAN
3500
ASH
MONITOR
TRIAL
AT
ASKERN
COLLIERY
-
VARIATION
OF
MEAN
CALCULATED
ASH
CONTENT
WITH
MEAN
BARIUM
COUNTRATE
DURING
OSCILLATION
OF
MEASURING
HEAD
FOR
13
MINUTE
TEST
PERIOD.
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230
cc .
m
z
g
16
-
15
-
14
13
12
11
18
T ■ » » — ţ — i ' ■» • i ■ » - • » | • ■ i J i ' i -
- •
_ .
D
: D
:
q
□
: D
O-jG D ^ -
:
s^
n
jS a?
m □
D
□
' - V
1
n i n i ¡ J B P ^
■ E L J ?
d
0
D
□ i *
D
D
I
I
J L.
■
■
1.94
1.96
1.98
2
LOG.RATIO
J
i
i
i
L
2.62
2.84
FIGURE
58.
PERFORMANCE
TEST
CALIBRATION
FOR
ASKERN
BLENDED
COAL
(25
mm
-
0)
WITH
COALSCAN
3500
ASH
MONITOR.
7/24/2019 Coal Quality Monitoring
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l/l
Q.
O
O
O
o
tu
r
^ I ■ » ■ '■ » I »■aHIII IJIIM IIHIII I I I II I I I | I IWHIIII I II I I I I I I[ IIHIII I l l l ll l l l l l l | ll l l l l l | | l| | l | | | | | |J|
l
| | | |U||| | | | | |
l
| |p||| | | | | | |ni| | ITII | l l l | l l l || l | | | | | | || | | | | | | . | || | | | |niMI^
12:1ú
1 2 : 1 /
12 :1»
1^: iy
12 :20 12:2.2
12:2.i-
12 :24 12 :2ü 12:2.7 12 : 2« 12.2Ü
TIM
f
co
FIGURE
5 9 .
COALSCAN
3 5 0 0
ASH
MONITOR
TRIAL
AT
ASKERN
COLLIERY
-
VARIATION
OF
BARIUM
COUNTRATE AND ASH CONTENT MEASUREMENTS AS MEASURING HEAD OSCILLATED OVER
STATIONARY CONVEYOR SPREAD WITH EVEN LAYER OF WELL MIXED - 1 MM COAL SAMPLE.
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i/l
CL
Ü
O
O
O
c -
' \
4
CD
I
5
anin
[HIIWMIUIIII
HN|unM iiiiiiniiiii|M M iniiiniiiiiii
[iiiiii
imiiiiii
i i i[iiii i i i i
II
i i i i i i i i i|ii i iMi
II
iiiii
M I
ii|iiii
I I I
IIIIIIIMI
■
■■■■■■¡■■l|HIIIIIIUIIUIIII|IIIHMIIIUMIHmnnill
HIHI
13:04
3: b 2: 6 3:ü7
1 3:0Ü
2: 9 3: 2: 2: 2 2: 2 2: 4
12:1
5
'I IM E
ro
co
ro
FIGURE 60. COALSCAN 3500
ASH MONITOR TRIAL
AT ASKERN COLLIERY
VARIATION
OF AMERCIUM
AND BARIUM
COUNTRATES
AND
COMPUTED
ASH
CONTENT
AS
MEASURING
HEAD,
WITH
STANDARDISATION
RAnTATTON
ABSORBERS ATTACHED TO DETECTOR, OSCILLATED OVER CONVEYOR RUNNING EMPTY.
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233
C E
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oc
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f-
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24 -•
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15
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,
,
,
,.-
. ._
.,
1.92
1.94
1.96
1.98
2
2.82
2.84
2.86
2.88
L06. RATIO
FIGURE
61.
SEVENTH
DYNAMIC
CALIBRATION
FOR
ASKERN
BLENDED
COAL
(25
mm
-
0)
WITH
COALSCAN
3500
ASH
MONITOR.
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234
■ i i
N
X
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C C
O
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:
:
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2.82
1 1 1 , 1 1
■ ■ i ■ ■
2 . 9 6
2 . 1
LOG. RATIO
2 . 1 4 2 . 1 8
FIGURE
6 2 .
STATIC
CALIBRATION
FOR
ASKERN
BLENDED
COAL
SAMPLES
( - 2 1 2 p i ) FROM SEVENTH DYNAMIC CALIBRATION WITH COALSCAN
3 5 0 0 ASH MONITOR.
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235
fi
t o
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z
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14
16
18
LABORATORY
ANALYSIS
ASH
V.
28 22
FIGURE 63. COALSCAN 3500 ASH MONITOR TRIAL AT ASKERN COLLIERY
-
RELATIONSHIP
BETWEEN
COALSCAN
SHIFT
INTEGRATION
AND
LABORATORY
SHIFT
ANALYSIS
FOR
99
SHIFTS.
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236
X
<L
(D
<r
o
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22 -
2ø
18
16
14
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i ■ ■ ■ i ■ ■ ■ » ■ ■ » L__L
10
12
14
16
18
LABORATORY
ANALYSIS
ASH
'/.
20
22
FIGURE 64. COALSCAN 3500 ASH MONITOR TRIAL AT ASKERN COLLIERY
-
RELATIONSHIP
BETWEEN
COALSCAN
SHIFT
INTEGRATION
AND
LABORATORY
SHIFT
ANALYSIS
FOR
104
SHIFTS.
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237
x
•H
22
20
18
16
—
14
12
10
—
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-
10
12
14
lé 18
LABORATORY ANALYSIS ASH V.
28
22
FIGURE 65. PHASE 3A ASH MONITOR INSTALLATION AT ASKERN COLLIERY
RELATIONSHIP
BETWEEN
PHASE
3A
SHIFT
INTEGRATION
AND
LABORATORY
SHIFT
ANALYSIS
FOR
104
SHIFTS.
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X
Ol
<
>
Œ
O
<
cr
o
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2
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-4 -
-6
-
- a
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20
40 »
m
BO
a o
100
120
ro
cs
FIGUR E 66. COALSCA N 3500 ASH MONITOR TRIAL AT ASKERN COLLIER Y - DIFFE RENCE BET WEEN COALS CAN SHIF T
INTEGRATION AND LABORATORY SHIFT ANALYSIS FOR 99 SHIFTS.
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6 r
r
en
<
ir
o
B -
<
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O
tn
<
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u
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BO
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ISO
co
ID
-6 r
- a »-
FIGURE 67. COALSCAN 3500 ASH MONITOR TRIAL AT ASKERN COLLI ERY - DIF FERE NCE BETWEEN COALS CAN
SHIFT INTEGRATION AND LABORATORY SHIFT ANALYSIS FOR 108 SHIFTS.
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I
en
<
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o
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40
60
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ISO
-2
«
•te
o
-B
«
-a
S H I F T S
FIGURE
68.
PHASE
3A
ASH
MONITOR
INSTALLATION
AT
ASKERN
COLLIERY
-
DIFFERENCE
BETWEEN
PHASE
3A
SHIFT
INTEGRATION
AND
LABORATORY
SHIFT
ANALYSIS
FOR
108
SHIFTS.
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1 Conveyor Unit
2 Inlet Chute
3 Clean-off Scraper
4 Scraper
5 Turntable
6 Outlet Chute
7 Drive Motor/Gearbox Unit
8 Discharge Detecting Doppler
Unit Optional)
9 Air Blower Duct
10 Compression Plate
11 Eccentric Guide
12 Peripheral Side wal I
13 Proportional Counter and
Pulse Amplifier assembly
14 Radiation Source
ţ DISCHARGE
FIGURE 6 9 . NCB/AERE PHASE 3A ASH MONITOR FOR SUB-STREAM MONITORING 9 6 1 2 / 1 )
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COMPACTION CHAMBER
COMPRESSION PLATE
NUCLEONIC MEASURING'
HEAD
FEED HOPPER
BELT FEEDER
WITHOUT DRIVE UNIT
DOUBLE-ACTING HYDRAULIC CYLINDER
FIGURE 70. SKETCH FOR ORIGINAL DESIGN OF EXPERIMENTAL RAM-FEED SAMPLE PRESENTATION UNIT FOR SUB-STEAM MONITORING.
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243
.•*•* ìC-
tG U R E 7 1 . M O D I F IE D E X PE R IM E N T A L RA M - FE E D PR E S E N T A T I O N U N I T I N C O R P O RA T I N G
STAINLESS STEEL TROUGH AND SHOWING NUCLEONIC M EASURING HEAD M OUNTED
ON IN D E PE N D E N T S U PPO RT S ( 9 3 9 8 / 2 ) .
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244
1200H
1100—
1000-
800.
T
3
12
~r
15
18
n
21
COMPRESSION (MM)
FIGURE 72. EXPERIMENTAL RAM-FEED PRESENTATION UNIT - TYPICAL RELATIONSHIP
BETWEEN BACKSCATTER COUNTRATE AND MATERIAL COMPRESSION.
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245
uu «,
9 12 15
COMPRESSION (MM)
FIGURE 73. EXPERIMENTAL RAM-FEED PRESENTATION UNIT - HYDRAULIC PRESSURE
REQUIRED TO PRODUCE INCREASING MATERIAL COMPRESSION AT DIFFERENT
MOISTURE LEVELS.
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246
B L E N DE D C O A L 8 5 0 t / h
- 5 0 nun
N
C
D I V E R T E R
A U T O M A T I C
X
M A N U A L
D I V E R T E R
T R A V E R S I N G S UC KE T S A M P L E R
F E E D E R
C R U S H E R
D O
- 2 5
mm
— C A L I B R A T I O N
S A M P L E S
FEEDER
0 0
C R U S H E R
- 5
mm
M O I S T U R E I
I
S A M P L E L J
1 - 5 0
mm
A
X A U T O M A T I C
*
N
D I V E R T E R
I I M O I S T U R E
S A M P L E
P N
D
D I V I D E R
L A 3 0 R A T 0 R Y
S A M P L E
T O R A P I D
L O A D I N G B U N K E R S
FIGURE 74. SCHEMATIC ARRANGEMENT OF COLLIERY SAMPLING SYSTEM AND RAM-FEED
UNIT TRIAL CIRCUIT AT MARKHAM COLLIERY.
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REJECTS
COAL
ED
["RAM HEAD (RETRACTED)
rHYDRAULIC CYLINDER
STROKE
RAM HEAD
(ADVANCED)
U.
"- GUIDE
BLOCKS
? REJECT
SCAPINGS
.SUPPORT
STRUCTURE
ffî
&
M
ro
J»
FIGURE 75.
ü^fíÜÜ™
E X P E R I M E N T A L
RAM-FEED PRESENTATION UNIT. FOR INSTALLATION AT COLLIERY TRIAL SITE
WITH SECOND OUTLET FOR SCRAPINGS AND PROPOSED FEED AND REJECT SCREW CONVEYOR.
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248
FIGURE 76. RE-DESIGNED, EXPERIMENTAL RAM-FEED UNIT INSTALLED AT COLLIERY TRIAL
SITE WITH FEED SCREW CONVEYOR DELIVERYING TO FEED HOPPER AND COMPACTED
MATERIAL IN PRESENTATION TROUGH (12,056/1)
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249
100 - |
iu
N
M
t/5
Oí
W
Q
z
>
H
<
80 -
60 -
40 -
20 -
SCREEN SIZE
MM
x UN-CRUSHED PRODUCT
• 50.8 MM CRUSHER GRIDS
© 2 5 . 4
MM
CRUSHER GRIDS
0
12.7 MM
CRUSHER GRIDS
FIGURE 77. TRIAL OF EXPERIMENTAL RAM-FEED UNIT AT MARKHAM COLLIERY -
SIZING CURVES FOR 50 mm - 0 BLENDED COAL AND PRODUCTS FROM
CRUSHER WITH DIFFERENT SIZE CRUSHER GRIDS.
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250
FIGURE 78. TRIAL OF EXPERIMENTAL RAM-FEED PRESENTATION UNIT AT COLLIERY
SITE - SURFACE PROFILE OF COMPACTED BED WITH COARSE (-25 mm) MATERIAL
(12,056/3).
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251
FIGURE 79. TRIAL OF EXPERIMENTAL RAM-FEED PRESENTATION UNIT AT COLLIERY SITE
- SURFACE PROFILE OF COMPACTED BED WITH FINE (-6 mm) MATERIAL
(12,056/2).
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252
FEED
HOPPER
FUTURE NUCLEONIC
MEASURING HEAD
LEVEL
SENSORS
HYDRAULIC
CYLINDER
SCRAPINGS
MATERIAL
DISCHARGE
SECTIONAL ELEVATION
1 —
1
—
T
_ L _
—r
i _
H
■ n
i
i
: z ]
s
PUN
FIGURE
80 DIAGRAM
ILLUSTRATING
MAIN
DESIGN
FEATURES
OF
PROTOTYPE
RAM FEED PRESENTATION UNIT
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L t
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-
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IGUR
81. GENERAL ARRANGEMENT DRAWING OF PROTOTYPE RAM FEED PRESENTATION
UNIT.
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254
*/.
,
*, ¿t
f
4
' IGURE 8 2 . GENERAL VIEW OF PROTOTYPE RAM - FEED PRESE NTA TION UN IT WITH
P O L Y P R O P Y L E N E T R O U G H S E C T I O N F O L L O W I N G S T A I N L E S S S T E E L C O M P R E S S I O N
ZON E (R A MS E Y 1 0 9 5 8 ) .
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255
FIGURE 83. REAR VIEW OF PROTOTYPE RAM-FEED PRESENTATION UNIT SHOWING
CUT-OUTS IN FEED CHUTE CASING FOR LEVEL SENSORS AND
HYDRAULIC CYLINDER ENCLOSURE (RAMSEY
10960).
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PLUTONIUM 238
BACKSCATTER
1
PROPORTIONAL
COUNTER
(PX 425)
y
CHARGE
SENSITIVE
PREAMPLIFIER
(NE5289/B)
H.T.
SUPPLY
(NE 4660)
SPECTROSCOPY •
AMPLIFIER
(NE 4658)
SPECTRUM
STABILISER
(CANBERRA 2050)
in
oí
ENERGY
ANALYSER
(NE 4664)
DUAL
COUNTER
TIMER
(NE 4681)
RS 232
DATA PATH *""
m
DTGTTAI.
~~ CONTROL
ASH CALCULATION
AND DISPLAY
COMPUTER
(FCL 6000)
PROGRAMMABLE
LOGIC
CONTROLLER
(MITSUBISHI F2-40)
FIGURE 84 . BLOCK DIAGRAM OF ASH MEASURING AND CONTROL SYSTEM FOR PROTOTYPE RAM-FEED ASH MO NITOR.
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RECEIVING
HORN
TRANSMITTING
HORN
DETECTOR
COAL
SAMPLE
VARIABLE
ATTENUATOR
QUNN
DIODE
l \>
1<s
TUNED RECTIFIER LOO
FILTER CONVERTER
L.J
DISPLAY
MODULATED
POWER SUPPLY
FIGÖRE 8 5 . BLOCK DIAGRAM OF SOLID STATE X BAND MICROWAVE MOISTURE METER.
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258
/ T r a n a m m a r
Vartteal Prof»« Plat*
SMawaH
Scraper
FIGURE 86. NCB/AERE PHASE 3A ASH MONITOR INCORPORATING X BAND
MICROWXAVE MOISTURE METER.
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ASH
MONITOR
M O I S T
UftC
METER
BELT
WEIGHER
INTERFACE
OTHER
COLLIERY
SIGNALS
FERRANTI
ARGUS
COMPUTER
1 1
TELETYPE
*
no
U3
FIGURE
8 7 .
£««£?£££
i S ? T S S i s
a w a
'
1
"
0
— *
WEIGHTKD
C M
™
ÏAU
*
« -
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ASM MONITOR ELECTRONICS
MONITOR
OS
O
FIGURE 88 . DEDICATED MICROPROCESSOR SYSTEM AT MOMKTONHALL COLLIERY FOR DISPLAY AND PRINT-OUT OF
INTEGRATED ASH, MOISTURE AND COMPUTED CALORIFIC VALUES.
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T M N S M I T T I N S
MOWN
MOOULATCO
POWER
SUPPLY
COM.
SAMPLE
MEAO
AMPUTIER
ro
MICROPROCESSOR
20mA
SERIALLINK
FIGURE 89. PROTOTYPE S BAND DISCRETE SAMPLE, MICROWAVE MOISTURE METER.
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MICROWAVE SOURCE
RCñ l 8 0 2 n i CROCOf l P UT E R
DETECTOR & AMPLIFIER
NDICATORS
M
HIGH SPEED
ANALOGUE TO
DIGITAL CONVERTER
no
OUTPUTS
FIGURE 90. SCHEMATIC DIAGRAM OF RE-DESIGNED FIXED FREQUENCY, MICROWAVE MOISTURE SYSTEM WITH H IGH
(GO dB) DYNAMIC RANGE.
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263
Pj±ASE3A_ASH/MOISTURE MONITOR
ASH SIGNAL MOISTURE SIGNAL
—
ANALOGUE
INTERFACE
ANALOGUE TO DIGITAL
CONVERTER
&
MULTIPLEXER
RCA1802
MICROCOMPUTER
3.5"
DISC
DATA LOGGER
FIGURE 91. DIAGRAM OF DATA LOGGER RECORDING SIGNALS FRON PHASE 3A ASH/NOISTURE
MONITOR.
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264
BELT
WEIGHER
SIGNñL
ULTRASONIC
BED DEPTH
SIGNAL
—
MOISTURE
SIGNñL
ñNñLOGUE
INTERFñCE
ANALOGUE TO DIGITAL
CONVERTER
&
MULTIPLEXER
RCñl802
MICROCOMPUTER
3,5
U
DISC
DñTñ LOGGER
FIGURE 92. DIAGRAM OF DATA LOGGER RECORDING SIGNALS FRON BELT WEIGHER
AND BED DEPTH AND MOISTURE METERS.
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RANGING
BOARD
PULSE
COUNTER
DIGITAL TO
ANALOGUE
CONVERTER
DISTANCE
TO
DEPTH
CONVERTER
LIQUID
CRYSTAL
DISPLAY
AMPLIFIER
TRANSDUCER
OUTPUT
ø.ifV - 2.0V)
D
ro
in
OUTPUT
0-1.GV)
SIGNAL
PATH
VOLTAGE TO
CURRENT
CONVERTER
-a
OUTPUT
H — 20mA)
CONVEYOR
BELT
FIGURE 93. BLOCK DIAGRAM SHOWING DESIGN O F ULTRASONIC BED DEPTH METER.
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BIRTELY
SAMPLER
t
c
l
SAMPLE
CRUSHER
PHASE3A
ASH MOISTURE
MONITOR
4
DATA
LOGGER
SAMPLE
REJECT
r
MICROWAVE
MOISTURE
LABORATORY
SAMPLE
n
BELT
WEIGHER
L
ULTRASONIC
t
BED
DEPTH
r^
METER
■
METER
i
5mm
-
0
BLENDED
COAL
ro
oí
DISTRIBUTING
SCRAPER
I
I
DATA
LOGGER
MICROWAVE
MOISTURE
METER
ELECTRONICS
EXCHANGE
BUNKER
A
A
Œ
TO
POWER STATION
FIGURE 94. SCHEMATIC ARRANGEMENT
OF
ON-BELT
S
BAND MOISTURE METER, ULTRASONIC BED-DEPTH METER
AND
PHASE
3A
ASH/MOISTURE
MONITOR
WITH
DATA
LOGGERS
AT
LONGANNET
NINES.
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267
FIGURE 95. TRIAL INSTALLATION OF S BAND MICROWAVE MOISTURE METER AND ULTRASONIC
BED-DEPTH METER ON 25 mm - O RAW COAL CONVEYOR AT LONGANNET MINE WITH
INSTRUMENTATION AND DATA LOGGER LOCATED ALONGSIDE IN PROTECTIVE
CABINET
(12,399/1).
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268
FIGURE 96. TRIAL INSTALLATION S BAND MOISTURE METER AT LONGANNET MINE SHOWING
MICROWAVE TRANSMITTING HORN AND ULTRASONIC BED-DEPTH METER MOUNTED
ABOVE BELT CONVEYOR AND MICROWAVE RECEIVING HORN LOCATED BELOW
(12,399/2).
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6 38 -
u
269
2 0 - -
Q.
0)
•o
,
e
T3
tt)
OQ o
1
12 IS IB 21
24
-C 1BB8-
1 2 0 0 - -
T3
O
O
— 688-
01 8-
m i
3 E 9 12 15 IB 21 24
12 15
T i m e ( h o u r s )
FIGURE 97. TRIAL OF S BAND, ON-BELT, MICROWAVE MOISTURE METER AND
ULTRASONIC BED-DEPTH METER AT LONGANNET MINE - TRACES OF
BED-DEPTH, ATTENUATION AND BELT LOADING PLOTTED AT
1 MINUTE INTERVALS ON 22 JANUARY 1988.
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270
S
M
-
-C
28
+
a
w
T3
J B - -
O
CD
e
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;
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15
18
21
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m
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e
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8
12
15
1B
r ^ \ p ~ ~ ^ ~
v
r
^ Y
21 24
; g 12 15 18 21 24 12 15 18
T i m e h o u r s
FIGURE
9 8 .
TRIAL
OF S
BAND,
ON-BELT,
MICROWAVE
MOISTURE
METER
AND
ULTRASONIC
BED-DEPTH METER ATIONGANNET MINE -TRACES
OF BED-DEPTH, ATTENUATION
AND
BELT
LOADING
AVERAGED
OVER
5
MINUTE
INTERVALS
ON
22
JNAUARY
1 9 8 8
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271
u i
x
(9
Li
680 -
509
—
400
-
300
-
200 -•
løø
-
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, , , . , , , . , . . . , , , , , , , , , , , , j T - n - r | . . . ¡
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.
.
.
h
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™
: -
:
-
L_L
1
1
1
6
8
19
BED
DEPTH
METER
<CM>
12
14
16
FIGURE 99. TRIAL OF ULTRASONIC BED-DEPTH HETER AT LONGANNET NINE -
CALIBRATION
GRAPH
OF
BELT
WEIGHER
READINGS
AGAINST
BED
DEPTH
METER
READINGS
INTEGRATED
OVER
5
MINUTE
INTERVALS
DURING
5
HOUR
PERIOD
ON
22
JANUARY
1988.
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22GHz
SOURCE
1
1200 Hz
FREQUENCY
SOURCE
MICROWAVE
r u r t o o r à i í "
LnüPrlNG
CIRCUIT
HORN .
COMBINER f V -* -4
V^LJ b^
3 8GHZ
SOURCE
2
i i r w n j w z n
9 2
H z
SSÄ
SAMPLE
U n ü r r l N ü
CIRCUIT
SEPARATOR
. H O R N
V V . . M 1
RECEIVER,
CHOPPING
FREQUENCY
SOURCE
i.
SIGNAL
k .
SIGNAL OUT
PROPORTIONAL
TO MOISTURE
SIGNAL
SUBTRACTOR
^ t r A K A J U K
INJ
««J
FIGURE 100 . SCHEMATIC DIAGRAM OF PROPOSED TWO FREQUENCY MICROWAVE MOISTURE
METER.
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273
SWEPT
RF
SOURCE
3 dB
SPLITTER
DETECTOR
RAMP
6500 SCALER ANALYSER
m
A B R
o
o
IEEE
BUS
INTERFACE
t
TRANSMITTING
HORN
RECEIVING
HORN
DETECTOR
FIGURE 101. SCHEMATIC ARRANGEMENT OF LABORATORY SWEPT FREQUENCY
MICROWAVE SYSTEM.
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d B
- 2 8 , 8 8 -
- 2 5 . 8 8
-î
- 3 8 . 8 8 -
■
-35.88-î
-48.88
ì
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-i
7 188fts
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ro
■Ck
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5.88 5.22 5.44 5.67 5.89 6.11 6.33 6.56 6.78 7.88
6 H Z
FIGURE
102.
LABORATORY
SVEPT
FREQUENCY
MI
CROWS
E
SYSTEM
-
ATTENUATION
SCAN
(5-7
GHz)
AND
LINEAR REGRESSION FOR PARROT CROP SEAM WITH 14.3% MOISTURE.
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d B
0 . 6 8
- 5 . 8 8 -i
- 1 8 . 8 8 - i
- 4 8 . 8 8 -
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11
;
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1 1 1
1 1 1 11
1 1 1
1 1 1
1 1
1 1 1
1 1 1 11
1 1 1 11
5 . 8 8 5 . 2 2 5.44 5 . 6 7 5.89 6.11 6.33 6.56 6.78 7.88
G H Z
ro
en
FIGURE 103. LABORATORY SWEPT FREQUENCY MICROWAVE SYSTEM - ATTENUATION SCAN (5-7 GHz) AND
LINEAR
REGRESSION
FOR
PARROT
CROP
SEAM
WITH
16.
2
MOISTURE.
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e
■ ■ ■ ■ ■
■
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d B
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-
1 8 8 n s
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|
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I
5 . 8 8 5.22 5.44 5.67 5.89 6.11 6.33 6.56 6.78 7.88
6 H Z
ro
FIGURE
104.
LABORATORY
SWEPT
FREQUENCY
MICROWAVE
SYSTEM
-
ATTENUATION
SCAN
(5-7
GHz)
AND
LINEAR
REGRESSION
FOR
PARROT
CROP
SEAM
WITH
18.7 MOISTURE.
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d
8,1
-5 . 88
-18 .88
-3
- 1 5 . 8 8 - ;
-28 .88 -
- 2 5 . 8 8 - i
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i
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r
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i
i
i
i
i
i
|
i
i
r
f
188ns
Sweep
ro
5.88 5 .22 5 .44 5 .67 5 .89 6 .11 6 .33 6 .56 6.78 7 .88
GHZ
105.
LABORATORY
SWEPT
FREQUENCY
MICROWAVE
SYSTEM
-
ATTENUATION
SCAN
(5-7
GHz)
AND
LINEAR
REGRESSION
FOR
PARROT
CROP
SEAM
WITH
20.0 MOISTURE.
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d B
8.88
-5.88
-18.88 -3
-15.88
-28.88-i
-25.88
-,
-38.88
ì
-35.88-i
-48.88
-45.88 «i
i
i
i
i
i
i
i,
i
M i i L
i
i
i
;
i
i
i
■
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i
i
i
i
r
188ns
Sweep
' 5 8 . 8 8 - 1 1 1 1 1 1 1 1 1 1 » ' i i [ 1 1 i i 1 1 1 1 1 1 1 1 1 ' 1 1 1 1 1 1 1 ' i i i 1 1 i
5.88
5.22
5.44
5.67
5 .89
6 .11
6 .33
6.56
6 .78
7.
G H Z
r o
00
FIGURE 106. LABORATORY SWEPT FREQUENCY MICROWAVE SYSTEM - ATTENUATION SCAN (5-7 GHz) AND
LINEAR REGRESSION FOR PARROT CROP SEAM WITH 21.7% MOISTURE.
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dB
-48 .88 -i
- 4 5 . 8 8 - i
I I • I I ' I L
1 I I I I
\r 168ns
Sweep
5 8 . 8 8 i i i 1 1 i i i i i | i i i 1 1 1 1 1 i 1 1 1 1 i | i 1 1 i 1 1 1 1 i 1 1 ' i i 1 1 i i i
5.88 5 .22 5 .44 5 .67 5 .8 9 6 .11 6 .33 6 .56 6 .7 8 7 .
GHZ
1 0
FIGURE 107. LABORATORY SWEPT FREQUENCY MICROWAVE SYSTEM - ATTENUATION SCAN (5-7 GHz)
AND LINEAR REGRESSION FOR PARROT CROP SEAM WITH 23.2 % MOISTURE.
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Q Q [ ■ ■ ■ t l i : ■ 1 ' I I ■■
I
I
'
I
I
I
I
i
I
I ■
I
I
II
d B
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-18.88-;
-15.88-i
-28.88
-25.88
-38.88
-35.88
-48.88
-45.88
-58.88
7
188ns
Sweep
1 1 1 1 1 1 1 1 1 1 1 1 1 i c 1 1 1 1 1 1 1 1 1 1 1 » i 'i 1 1 1 1 1 1 1 1 > i 1 1 1 1 1
5.88
5.22
5.44
5.67
5.89
6.11
6.33
6.56
6.78
7.88
6HZ
00
o
FIGURE 108. LABORATORY SWEPT FREQUENCY MICROWAVE SYSTEM - ATTENUATION SCAN (5-7 GHz) AND
LINEAR REGRESSION FOR PARROT CROP SEAM WITH 25.2% MOISTURE.
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d B
- 5 . 8 8 H
- 1 8 . 8 8
-
- 1 5 . 8 8 - i
- 2 8 . 8 8 - i
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1
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f
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.
i
5.88
5 .22
5.44
5.67
5.89
6 .11
6 .33
6 .56
6 .78
7.
GHZ
FIGURE 109. LABORATORY SWEPT FREQUENCY MICROWAVE SYSTEM - ATTENUATION SCAN (5-7 GHz) AND
LINEAR
REGRESSION
FOR
PARROT
CROP
SEAM
WITH
27.2%
MOISTURE.
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282
25 -
iu
a.
Z3
l -l
o
JE
<Z
O
20
-
15
-
10 -
— 1
-
-
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D
f
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D
i ■ ' ' ' i
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D
1—1—1—1—1—1—1—1—1—1—1—1—1—1—1—1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1_._1 1
-
■ -
2 3 4 5 6 7 8 9
ATTEN / FREQ GRADIENT <dB/ GHz>
FIGURE
110.
LABORATORY
SWEPT
FREQUENCY
MICROWAVE
SYSTEM
-
CALIBRATION
GRAPH
OF
MOISTURE
CONTENT
AGAINST
ATTENUATION/FREQUENCY
GRADIENT
FOR
PARROT
CROP
SEAM.
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283
M
IU
OC
c o
o
<I
o
39
25
28
15
18
— ¡
D
— ■ — » — i — ■ — i
yu
o
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^ / D
E
a
n
-
•
-
— i — i — i — i — i — i — i — i — i — i — i — i — i — i — i — i — i — i — i — i — i — i — i — i — i — i — i — i — i — i — i — i
i
i
i
i
3 4 5 ó 7 8
WEIGHTED ATTEH/FREQ GRADIENT (dB'GHz'KG)
FIGURE 111. LABORATORY SWEPT FREQUENCY MICROWAVE SYSTEM -
CALIBRATION GRAPH OF MOISTURE CONTENT AGAINST
WEIGHTED ATTENUATION/FREQUENCY GRADIENT FOR
PARROT CROP SEAM.
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284
M
ÜJ
CC
»
tft
O
E
30
25
28
15
10
5
— i
- •
1
Bjj
a
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riJpr
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. . . .
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1
. . .
.
1 —
•
-
-
L .
.
4
5
6
7
ATTEN
/
FREQ
GRADIENT
<dB/GHz)
8
FIGURE 112. LABORATORY SWEPT FREQUENCY MICROWAVE SYSTEM - CALIBRATION
GRAPH OF MOISTURE CONTENT AGAINST ATTENUATION/FREQUENCY
GRADIENT FOR SEVEN SEAMS FROM BLINDWELLS OPENCAST SITE.
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285
(/)
1-4
O
I-
o
30 -
25
20
-
15 -•
10
-
5
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;
.
.
.
.
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. . . .
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n
C
1
D
. . . .
t • —
•
3
4
5
6
7
8
WEIGHTED
ATTEN/FREQ
GRADIENT
<dB/6Hz/KG)
FIGURE
113.
LABORATORY
SWEPT
FREQUENCY
MICROWAVE
SYSTEM
-
CALIBRATION
GRAPH
OF
MOISTURE
CONTENT
AGAINST
WEIGHTED
ATTENUATION/
FREQUENCY GRADIENT FOR SEVEN SEAMS FROM BLINDWELLS OPENCAST
SITE.
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HIGH
FREQUENCY
GENERATOR
BUFFER
AMPLIFIER
-+•+■
CZÏ
OSCILLOSCOPE
m
MEASUREMENT
AMPLIFIER
03
CT*
FIGURE
114.
ELECTRONIC
MEASUREMENT
SYSTEM
FO R
EXPERIMENTAL
INSULATED
PLATE
CAPACITANCE CELL.
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HIGH
FREQUENCY
GENERATOR
OSCILLOSCOPE
PUFFER
AMPLIFIER
- * < ►
FEEDBACK
NETWORK
-IZZF
< \
1
^ M P E M R
ro
oo
««4
lv
m
FIGURE 115.
ELECTRONIC MEASUREMENT SYSTEM FOR EXPERIMENTAL INSULATED PLATE
CAPACITANCE
CELL
WITH
AUTOMATIC
STABILISATION
OF
BUFFER
AMPLIFER
OUTPUT
SIGNAL
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288
LÜ
S
I
0
O
E
a
a
<r
20
15
18
5
e
. . .
. . .
i . J_..J_I_J i 1..J..J
i •
A / ; B / C /
J&&;
^XŞ
L _ . .
e
200
400
600
800
1000
INSTRUMENT READING <»V>
1200
1400
1600
FIGURE 116. LABORATORY TESTS WITH EXPERIMENTAL INSULATED
CAPACITANCE CELL RELATIONSHIP BETWEEN INSTRUMENT
READING AND ADDED MOISTURE WITH INCREASING IONIC
SALT
CONTENT.
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289
ui
te
< r
i -
o
20
16
12
8
4
e
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yS
.
1
•-
. ._
• -
-
-
1
200
400
600
INSTRUMENT READING (mV)
800
løøø
FIGURE 117. LABORATORY TESTS WITH EXPERIMENTAL INSULATED PLATE
CAPACITANCE CELL - CALIBRATION GRAPH FOR WASHED SMALL
COAL FROM MARKHAM COLLIERY.
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290
HYDROGEN
IN WATER
w
H
as
►J
55
M
en
HYDROGEN
IN
CO AL
MAGNETIC FIELD INTENSITY
FIGURE
118
FIRST DERIVATIVE ABSORPTION SPECTRUM
FOR
WET
COAL
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291
i
w
I
M
Cu
.HYDROGEN
IN
COAL
AND
WATER
HYDROGEN IN WATER
T
100
T
200
300
TIME gjs)
FIGURE 119. FREE INDUCTION DECAY SIGNAL FOR WET COAL.
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292
8 -
> >
LÜ
CC
ID
h-
tt
»-t
O
g
í -
2
O
m
< i
ó —
4
-
2
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m
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: + < 0 . 2 mm:
X
< 3 . 0
mm:
X
S
///
—
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' — ' — ■ — —
j T *
„...i i . i i 1
:
-
-
o
0 . 6 3 0 .1 0 . 1 5
METER
READING
(SIGNAL/GRAM)
0.2
0.25
FIGURE
120.
REGRESSION
CALIBRATION
FOR
SUITES
5
AND
6.
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293
4.1 -
LU 3.7
3.3
CD
£ 2.9
a
<r
m
ce
z 2.5
LU
S 2.1
1.7 -•
,
,
,
,
, . . . j
,
,
,
,
- L
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> p
-
;
Q
: :
c
1
■
■
■
■
■
*
i _ _ l
i ^ ^ ^ ^
■ ■ ■ — i
-
• -
-
. . . L 1 . . . . 1
0.1 0.2 0.3
ADDED MAGNETITE (K>
0.4
FIGURE 121. EFFECT OF MAGNETITE ADDITIONS ON N.M.R. INSTRUMENT READING.
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DISPLAY/
CONSOLE
AIR
CONDITIONING
UNIT
ENVIRONMENTAL
ENCLOSURE
LEVEL
DETECTOR
COAL FEED
COAL
DISCHARGE
2.4 m
ro
FIGURE 122. S.A.I.C. 'CONAC' - SCHEMATIC SE CTION
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295
CONTROL/
DISPLAY UNIT
POWER AND
LOGIC UNIT
DETECTOR
COAL
FEED
LEVEL DETECTOR
MOISTURE METER
NEUTRON
SOURCES
T
2.4 m
— SHIELDING
1
2.0 m
FIGURE 123. MDH - MOTHERWELL INC. 'ELAN' - SCHEMATIC SECTION.
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2.1 m
COAL
FEED
FEED
HOPPER
LEVEL
DETECTOR
SIGNAL
PROCESSOR
H DISPLAY/
CONSOLE
NEUTRON
SOURCE
SHIELDING
7.3 m
COAL
DISCHARGE
FIGURE 124 . GAMMA METRICS 'COAL ANALYSER' - SCHEMATIC SECTION.
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