Sampling of Coal Dr kalyan sen Director, Central Fuel Research Institute, Dhanbad, 2003.
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Transcript of Sampling of Coal Dr kalyan sen Director, Central Fuel Research Institute, Dhanbad, 2003.
Sampling of CoalSampling of Coal
Dr kalyan sen
Director, Central Fuel Research Institute,
Dhanbad, 2003
04/18/23 2
Quality Monitoring (QM) of Coal is an essential requirement for process
control, plant performance or for any
commercial transaction between Consumer
and Producer
QM requires proper implementation QM requires proper implementation of standard sampling, preparation of standard sampling, preparation and test proceduresand test procedures
04/18/23 3
Objective
To collect a representative portion
of fuel (coal)
for determination
of quality parameters.
04/18/23 4
Purpose
Commercial Transaction Location Normally at Loading point
Parameters Ash, TM, 60% RH moisture,GCV
Quality Parameters for Power Generation
Location Normally at unloading point
Parameters Ash, TM, GCV, VM
S, N, Maceral composition
04/18/23 5
Steps for quality assessment
Sampling
Sample preparation
Analysis
04/18/23 6
Coal is heterogeneous material Very difficult to achieve highest level of
Sampling precision In terms of variance
80 % is from Sampling 20 % is from preparation & analysis
Overall precision is influenced primarily due to Sampling
Utmost importance need to be given for Sampling
04/18/23 7
Sampling methods depend onSampling methods depend on
mechanical or manual samplingmechanical or manual sampling
sampling from moving belt sampling from moving belt
sampling from stationary lot sampling from stationary lot
(wagon, stockpile, etc.)(wagon, stockpile, etc.)
04/18/23 8
Sampling types
Moving Stream
Auto-mechanical
sampling system
Manual
Stationary lot, Wagon, Stockpiles, etc.
Auto-mechanical Auger
Manual
04/18/23 9
Sampling variance is a function of product variability
i.e. different results can be obtained from
same increments for different coal
different increments for same coal
04/18/23 10
The objective is to reduce the The objective is to reduce the
sampling variance as far as sampling variance as far as
practicable practicable
04/18/23 11
Any Sampling scheme normally Any Sampling scheme normally conforms with the national or conforms with the national or international standards international standards (BIS/ISO/ASTM, etc.)(BIS/ISO/ASTM, etc.)
Constraint - technical, cost and Constraint - technical, cost and timetime
Thus modifications in sampling Thus modifications in sampling
procedures are necessary with mutual procedures are necessary with mutual
agreement between partiesagreement between parties
04/18/23 12
Precision
measures the closeness of data in given condition indicates the reproducibility of the results measures the chance error as expressed by
variance
SMALLER THE RANDOM ERROR, PRECISE IS THE METHOD
A commonly accepted index of precision is twice the population standard deviation
04/18/23 13
Precision depends onPrecision depends on
Variability of coal
number of samples from a lot
number of increments comprising each sample
mass of sample related to the nominal top size
04/18/23 14
Precision
PL = 2 * Sqrt [VI/m*n + VPT/m]
n = no. of increments m = no. of sub lots VI = Primary increment variance VPT = Preparation & testing variance PL = Overall precision
at 95% confidence level
04/18/23 15
Bias
Systematic error which leads to the
average value of a series of results being
persistently higher or lower than those
which are obtained using a reference
sampling method which is intrinsically
unbiased
04/18/23 16
Reference method of sampling Reference method of sampling
is ‘Stop Belt Method’is ‘Stop Belt Method’ (free of Bias)(free of Bias)
04/18/23 17
Design of Sampling Scheme
Basic Principles
Both for Mechanical & Manual systems
04/18/23 18
General scheme for sampling . . .General scheme for sampling . . . Decide purpose of sampling e.g. plant
performance, process control, commercial transaction
Identify the quality parameters, viz., general analysis, TM, size, washability, etc.
Define the lot Define the precision required Decide whether continuous or intermittent
sampling is required
04/18/23 19
Determine the number of sub-lots, increments to
achieve the required precision.
Determine the nominal top size of the coal
Determine the min. mass/ increment and the
min. mass of the total sample
Decide on the method of combining the different
increments for gross sample
Decide on drawing common or separate
samples, for analysis
General scheme for samplingGeneral scheme for sampling . . . . contd.contd...
04/18/23 20
General principle of SamplingGeneral principle of Sampling
Primary increments should account for the Variability
Equal probability to all particles to be selected and included in the sample
Largest particle of the lot should pass freely through the sample device
Sufficient mass of the sample to enable particles to be present in the same ratio as in the lot
04/18/23 21
SAMPLING SAMPLING FOR FOR COMMERCIAL COMMERCIAL TRANSACTIONTRANSACTION
Joint SamplingJoint Sampling• Washed coking coalWashed coking coal
• Power coalPower coal
04/18/23 22
Joint samplingJoint sampling at loading point - by customer and
producer on mutually agreed methods
at both ends - mean value
bonus/penalty to producer for values beyond agreed tolerance limits
requires periodic testing . . . Unfortunately rarely
practiced in India
04/18/23 23
Reasons for discrepancies in resultsReasons for discrepancies in results
level of precision not defined Non-identical procedures for sampling
at both ends manual sampling results in large human
error
deviation in procedures from agreed one
04/18/23 24
Primary requirements for development Primary requirements for development of a methodologyof a methodology
testing for estimation of the variances, Vi and Vpt decision on level of precision of the ash value calculation for no. of sub-lot and increment /sublot
at desired precision from known values of variances estimation of precision for the existing procedure estimation of min. mass/ sub-lot form the std. Table estimation of min. mass/ increment
04/18/23 25
SAMPLING SCHEME is designed SAMPLING SCHEME is designed based on the above testbased on the above test
The procedure can significantly The procedure can significantly
reduce the discrepancies in the reduce the discrepancies in the
results at both endsresults at both ends
04/18/23 26
Sampling of washed coking coalSampling of washed coking coal
Samples are drawn from the Automatic mechanical Sampler (AMS) Conveyor Belt
For day to day quality monitoring, samples For day to day quality monitoring, samples are reduced by offline and/or manual means are reduced by offline and/or manual means to analyze to analyze ASH & TOTAL MOISTUREASH & TOTAL MOISTURE
04/18/23 27
Sampling of Power CoalSampling of Power Coal
Best option: AMS at loading/ unloading pointBest option: AMS at loading/ unloading point
AMS for coal x200mm or above is not a AMS for coal x200mm or above is not a
proper choice to ascertain quality parameterproper choice to ascertain quality parameter
Suggestion: Suggestion: sampling on crushed coal sampling on crushed coal
below 50mm or preferably at 20mmbelow 50mm or preferably at 20mm
04/18/23 28
Where AMS is non-existing/ non-functioning , Where AMS is non-existing/ non-functioning ,
sampling may be done for the time being, at loading sampling may be done for the time being, at loading
point from the wagon by manual meanspoint from the wagon by manual means
Wagon top sampling is difficult, becauseWagon top sampling is difficult, because
• segregation occurs because of large sizesegregation occurs because of large size
• impractical to collect sample from the full depthimpractical to collect sample from the full depth
• introduces bias due to manual operationintroduces bias due to manual operation
Suggestion: smaller size (< 50mm) of the sampleSuggestion: smaller size (< 50mm) of the sample
04/18/23 29
Periodic tests
Estimate of overall precision
Estimation of increment variance
Estimation of preparation & testing variance
If the overall precision is different fromthe desired one then, number of increment
& sub lot to be modified accordingly.
04/18/23 30
Alternative
Long Term
Auto mechanical sampling system at
Sampling points
Auto mechanical Augers from the
wagons
04/18/23 31
Alternative
Short Term
Estimation of variance of sampling,
sample preparation & testing
Design a practical procedure for
routine implementation
Perform periodic test for checking
04/18/23 32
Conclusion:Conclusion:• Choice of Sampling methodology Choice of Sampling methodology depending on the purposedepending on the purpose
• Efforts to reduce the sampling Efforts to reduce the sampling variance to a min. possible limit variance to a min. possible limit
• Sampling on mechanically crushed Sampling on mechanically crushed coal below 50mm coal below 50mm
• Preferable size is 20mm ( feed to most Preferable size is 20mm ( feed to most power plants) power plants)
04/18/23 33
•Replacement of manual sampling Replacement of manual sampling method by AMSmethod by AMS
•In absence of AMS, manual wagon top In absence of AMS, manual wagon top
sampling of this size would give better sampling of this size would give better
resultsresults
• In absence of AMS, manual sampling In absence of AMS, manual sampling
from wagon top can be done as an from wagon top can be done as an
temporary option, following the temporary option, following the
prescribed methodologyprescribed methodology
Conclusion…………contd.Conclusion…………contd.
04/18/23 34
Ash Sample PreparationAsh Sample Preparation Gross Sample
Air dry & Crush to 12.5 mm
Air dry (if required oven dry at 35 deg but not more than 2 h at a time)
Reduce the sample to 2 kg
Divide into 4 parts
2 parts (Reserve); 1 part (212 micron) & 1 part (212 micron)
1 part preserve as check sample
1 part divide using laboratory divider (2 samples)
Sample A1 Sample A2
04/18/23 35
Total Moisture Sample PreparationTotal Moisture Sample PreparationGross Sample
Air dry Record wt.
Crush to 12.5mm
Reduce 2.5kgCrush to 2.8mm
Divide into 4 parts
Sample A Sample B RESERVE
Size12.5 mmabove ?
Record Initial wt.
Stage 1 loss%
Stage 2 loss%Oven dry 35deg
not exceed 2hRecord wt.
Stage 3 Moist.10g, 108deg, 2h
Y
N
04/18/23 36
Common Sample PreparationCommon Sample PreparationCommon Bottle Sample
Air dryRecord wt.
Crush to 2.8mm
Divide into 2 parts
Sample A Sample B
RESERVE
Record Initial wt.
Stage 1 loss%
Stage 2 loss%Oven dry 35degnot exceed 2hRecord wt.
Stage 3 Moist.10g, 108deg, 2h
Divide
Crush to 2.8mmCrush to 2.8mm
Sample C
Ash
Divide into 2 parts
04/18/23 37
THANKSTHANKS