IMPROVEMENTS MADE AT COLLINSVILLE COAL PREPARATION PLANT …
Transcript of IMPROVEMENTS MADE AT COLLINSVILLE COAL PREPARATION PLANT …
99
特 別
講 演IMPROVEMENTS MADE AT COLLINSVILLE
COAL PREPARATION PLANT TO
ALLEVIATE PRODUCTION
CONSTRAINTS
M. M. WILLIAMSON R. G. BUCKLEY
D. B. HAIGH J. M. CHADDERTON
ABSTRACT
Following a brief description of the location and features of the Collinsville coal mine , the basic concepts of the coking coal expansion project are described in order to give an appreciation of the origins of the operational problems which caused cokimg coal production losses in 1984 and 1985.
The paper gives explanations of the symptoms and causes associated with the early low production levels of the Coal Preparation Plant.
A description of the significant changes to design and equipment to bring the plant to satisfactory
performance is presented.
1. INTRODUCTION
The Collinsville coal mine is situated at the Northernmost extremity of the Bowen Basin
Coalfield in Central Queensland, Australia. (See Plate 1) Coal has been mined at this location for
approximately 65 years supplying energy for North Queensland industry and for production of
electrical power by the State's Generating Board. A large proportion of the mine's output is used
to supply coal for copper smelting and power generation at Mount Isa, and coking coal is supplied
to the State Cokeworks, located in Bowen, where it is carbonised to produce hard coke for utilisation
in the lead blast furnace, also at Mount Isa.
Plate 1. Location MAP
*昭 和61年6月10日 本会第76回 例会 において発表
** MIM (Holdings) Limited** Collinsville Coal Company Pty. Ltd
昭和61年5月10日 受理
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Expansion of the mine was undtrtaken in 1983 by Mount Isa Mines Limited as part of a
development known as the Newlands-Collinsville-Abbot Point project (N. C. A. project). The
project was developed to produce four mtpa of export steaming coal from Newlands mine, and one mtpa of coking coal from Collinsville for exclusive supply to the Japanese Steel Mills with whom
a long term agreement was signed in April 1980.
The large capacity, deep water port facility constructed at Abbot Point is capable of loading
vessels from 20, 000 t to 200, 000 t capacity and provides world-class loading facilities for a wide
variety of vessels receiving the Collinsville and Newlands products.
2. DESCRIPTION OF COLLINSVILLE COAL PROJECT
2.1 General
The project incorporated the expansion of a 140 tph coal preparation plant commissioned in
1979, built to process coal for carbonisation at the State Cokeworks and, in addition, provided
coal handling and stockpiling facilities for the existing steaming coal products.
The present 400 tph coal preparation plant comprises the original 140 tpa plant expanded to
provide the extra processing capacity to produce 1.0 Mtpa of high grade coking coal of 9.0°o ash from three coal seams named Garrick, Scott and Denison. Scott and Denison seams are virtually
one combined seam in the project's mining areas, and are therefore mined and processed as one
entity from each of two locations. These areas are known as Scott/Denison North (SDN) and
Scott/Denison West (SDW).
2.2 Scope of Operations
The coal preparation complex consists of four major components : a 1200 tph run-of-mine
(ROM) coking coal crushing, screening and blending plant, a 400 tph coal preparation plant, a 2000 tph product reclaiming section and a 2500 tph train loading plant.
Raw Coking Coal Handling
The ROM coking handling section was expanded to include transient storage, blending and
homogenisation of the preparation plant feed. The system has been designed to produce a 2:2:1
blend of Scott/Dension West, Scott/Denison North and Garrick West seams. Coal from these
areas is mined on a campaign basis and placed as inclined strata in the raw coal stockpile. The
portal reclaimer cuts across the layered stockpile thereby blending the seams together. Stockpiled coal is reclaimed to the 1200 t preparation plant feed bin by a portal reclaimer at a maximum
rate of 800 tph.
Preparation Plant
The Preparation Plant consists of two principal sections. (See Fig. 1) The coarse fraction
(32 mm to 0.5 mm) is processed in three DUTCH STATE MINES' (DSM) 700 mm diameter,
heavy medium cyclones. The minus 0.5 mm fraction is deslimed at 0.125 mm in classifying cyclones
and then processed in two-stage DSM water washing cyclones.
The dewatered, cleaned coal is conveyed to a product stockpile within the rail loading loop
and the reject to a 400 t bin for truck disposal. Fine rejects from two thickeners are pumped into
old mine workings.
Product Coal Reclaiming and Train Loading
Coking coal for shipment is reclaimed by front end loader into track mounted, reclaim hoppers
fitted with vibrating feeders and mounted over the reclaim conveyor. The coal is reclaimed at
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Improvements made at Collinsville Coal Preparation Plant to Alleviate Production Constraints101
Fig.1. Simplified Flow Diagram-Collinsville Coal Preparation Plant
2000 tph to a 2400 t capacity train loading bin from which it is loaded into unit trains at a rate of
2500 tph.
Plant Control
Plant and field operations are fully automated with a distributed control system being used
for startup and shutdown, process control and alarm monitoring. Operations are directed from a
central control room in the preparation plant. Product reclaim and train loading are directed from
a separate control desk at the loadout bin.
2.3 Design Philosophy
Prior to the N. C. A. development, Collinsville mine had been supplying a variety of specialised
steaming coal products to the industries of Central and Northern Queensland by the blending of
raw coal from several open-cut and underground mining areas . In order to improve and rationalise
these facilities, and to enable an orderly overall mine development, new conveying, stockpiling and
Fig. 2. Relationship Between % Recovery & % Ash for the Three Blend Components
(Data From Large Bore Core Analysis)
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loadout facilities for the steaming coal were integrated with the new coking coal developments.
The extensive mechanical handling and processing plant developments were integrated into a single
operational and management unit.
The three components of the coking coal blend, SDN, SDW, and Garrick, whilst of similar
rank and complementary caking properties, differ widely in washability characteristics, necessitating
precise blending of the raw coal. (See Fig. 2) A portal reclaimer system was selected in order
to provide maximum operational flexibility.
Since it was known that the Garrick seam contained significant quantities of sulphur in the
form of pyrites, the plant was designed to reduce this component of the blend to 20 mm top size.
The Scott & Denison seams are reduced to 32 mm top size only. In pre mining studies, tests on
bore cores had demonstrated that there was a diverse range of washability characteristics and that
gravity separation of the fines would result in higher yields and lower sulphur than would be the
case using froth flotation techniques.
The original 140 tph plant was part of a concept for an eventual 560 tph modular plant. The
original module successfully treated Bowen seam coal using manual soda ash addition for pH control;
corrosion/erosion was not an apparent problem. The concept of a 560 tph plant was later changed
to a single, integrated 400 tph plant with lime dosing providing pH control to cope with the higher
content of pyrites in the coal for the NCA project. This change in concept resulted in poor opera-
tion and maintenance access and also eliminated the possibility of conducting maintenance work
on equipment in part of the plant whilst at the same time producing coal from the remaining,
operating plant.
3. DESIGN FEATURES
3.1 Materials Handling
The Collinsville coal project development, which necessitates the handling and blending of
coal from some seven coal producing areas for several different markets of coking and steaming
coal has resulted in a major conveying installation. Approximately 5 km of conveyors transfer
approximately 2.4 mtpa of coal across a site covering some 3 sq km. These extensive conveying
facilities are essential to provide the necessary operational flexibility using a minimum of labour,
however, they also require skilled labour resources for operating, inspection and repair. (See Plate 2)
3.2 Process Plant
The coal preparation plant makes use of extensive hydraulic distribution and processing circuits
Plate 2. View of Site
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Improvements made at Collinsville Coal Preparation Plant to Alleviate Production Constraints 103
for the cleaning of the coal. The constraints imposed by the incorporation of the existing plant
facilities resulted in design compromise by perpetuation of existing, low capacity, processing plant
items such as pumps, tanks, pipes etc. Hence the number of pump units installed per unit capacity
is approximately double that of conventional coal processing plants in the Bowen Basin. As a
direct consequence, the number and extent of pipe-runs is, similarly, above the normal level.
3.3 Control
Control of the preparation plant is carried out by a TOSHIBA TOSDIC 246 Distributed
Process Control system. This was a relatively novel application for this equipment requiring the
development of new hardware and extensive programme formulation. With a commitment to such
a high technology control philosophy, it followed that a significant proliferation of remote sensors,
transducers and controllers would also ensue, and high level skills would need to be developed by
the mine's technicians.
3.4 Materials of Manufacture
The equipment used, and materials selected, for the process plant were standard specification
items (e. g. vibrating screens, centrifugal pumps etc) ; carbon steel fabrications and pipe ranges,
together with Nihard castings and stainless steel screen decks, were used in a conventional manner.
Protection of some carbon fabrications from wear was incorporated by the use of basalt and
quarry tiles and epoxy/aggregate materials. Nevertheless, a large proportion of the fabrications were in direct contact with the plant process water.
3.5 Process Water
The water used for the preparation plant, as well as other mine sections, is obtained from the
Bowen River. Water quality is of quite high purity ; it is very low in dissolved solids and lacks
capacity to buffer. Typically the alkalinity of this water (measured as mg CaCO3/1), for hydroxyl,
carbonate and bicarbonate ions, totals only 113. At this level the effect of the addition of relative
small proportions of acid or alkali results in major changes in pH.
4. OPERATIONAL & PRODUCTION PROBLEMS
4.1 Early Symptoms
Load commissioning of the Preparation Plant commenced on 22 November 1983.
This phase of the operation identified the need for processing adjustments. The major changes
were associated with water balance, heavy medium circuitry control, fines plant cyclones, and the
control logic.
Despite these constraints to plant capacity, load commissioning, at reduced feed rates, continued
until the three week Christmas 1983 shutdown period, to provide additional operator training.
Simultaneously production was interrupted by a series of electrical problems associated with
the central control system. Many hardware and firmware problems were eventually identified as
communications problems which were subsequently rectified by the manufacturer. Changes to
software were made progressively as the need was identified. By April 1984 the majority of
electrical control problems had been resolved.
Extentive premature wear on pumps, cyclones, pipes and linings was apparent by early
February 1984 and the plant was shutdown one month later for major repair and replacement of
this equipment. During the shutdown, the lime dosing plant, which had been found to be
unsuitable for the available lime quality, was modified, increased in capacity and the plant's control
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logic extensively modified to enhance overall control. The electric power supply was also modified
and improved, and coal was reintroduced in early April.
A gradual improvement in plant availability over a two month period was then experienced.
However, a number of further problems gradually became evident which were found to be
symptomatic of deep seated difficulties.
These symptoms included the blinding of screen cloths with lime and calcium sulphate
deposits, failures of the screen bowl centrifuge, blockages caused by large coal contamination in
the fines plant. Operational difficulties with the thickeners resulted in continual contamination of
clarified water and further corrosion of processing equipment resulted again in extended mainte-
nance shutdowns. Low recovery of coal and persistent faults to the raw coal reclaimer also
appeared as significant problems.
At this stage it was increasingly apparent that extraordinary corrosion and erosion was being
experienced which would require a continuing, extensive maintenance commitment. It was difficult
to determine whether the other causes of lost production such as blockages, low product recovery
and clarified water contamination were secondary consequences of the corrosion/erosion problem or
whether they resulted from separate causes.
The problem of gypsum deposition on screen decks at first appeared to indicate an adequate
or excessive level of pH control, however, subsequent investigations showed that this was caused
by periodic excessive pH corrections whilst at other times, and other places in the circuit, very low
pH levels persisted which were the ongoing cause of continuing high corrosion and erosion.4.2 Causes of Production Constraints and Remedies
Maintenance
By mid 1984 it was obvious that maintenance requirements were accelerating at a rate greater
than could be dealt with by the engineering department's human resources even after providing
additional support from other sections of the mine. As the months progressed all hope of achieving
budgeted production in the short to medium term was abandoned and a significant commitment
to major changes was made.
In September 1984 a contract was placed with a local engineering company to progressively
replace all carbon steel piping by corrosion and abrasion resistant materials. After evaluation of
various options a general decision was made to the use of Acrylonitrile Butadiene Styrene (A. B. S.)
piping for general application supplemented with polyurethane lined steel pipe for high abrasion areas.
Simultaneously investigations were carried out regarding the suitability and application const-
raints of available corrosion and abrasion resistant materials, which would reduce the general
maintenance burden, particularly in association with critical processing equipment such as cyclones,
pumps, and fabrications. Various materials were selected and tested with a view to eliminating contact between carbon steel and process water. A description of the philosophy adopted and
measures taken to overcome the corrosion/erosion problem is described in section 5.4.
Plant Feed Variations
Problems of thickener control and a perceived high variation in fines dewatering screens
loading, tegether with significant variations between predicted and actual plant recoveries instigated
an investigation into the size consist of the plant feed. The results of sizing testes on raw coal
received at the preparation plant are shown in Fig.3. It was apparent that the strata mode of
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Improvements made at Collinsville Coal Preparation Plant to Alleviate Production Constraints105
Fig.3. Variation of Fines Content of Recovered Coal From Raw Coal Stockpile
(per half hour sample period)
Fig.4. Zones of Accumulation of Coarse Coal in Raw Coal Stockpiles
stacking was responsible for severe size segregation in the stockpile. Since stockpile reclaim is by
a portal mounted, scraper conveyor, pivoting from the toe of the pile on the stacker side, the size
consist of the reclaimed material varies according to the size segregation established during the
building of the stockpile. Low fines contents are encountered when reclaiming the first face of
the stockpile and the lower layers. (See Fig.4)
The diverse range of fines plant loading coupled with inefficient clean coal classifying cyclone
performance due to high corrosion rate of spigots was determined as being responsible for the variation of slurry concentration to the fines dewatering screens, causing wet classification rather
than dewatering on the 0. 4 mm aperture wedge wire decks. As a consequence of all these
factors, thickener feed loading was extremely variable and was beyond the control flexibility of
the manual flocculant dosing system.
Compounding these problems was the extremely high corrosion/erosion rate of primary
classifying and water washing cyclones which resulted in very variable separating and concentration
performance of the fines, dependant upon the condition of spigots and vortex finders. The process life of some items of the various cyclones was as low as two weeks in some circumstances.
A series of remedial actions were taken to resolve these difficulties. The stockpiling
programme was modified to minimise rilling of the coal down the face of the pile. The control of flocculant addition to the thickeners was automated. "Clarometers" are now installed which
assess the flocculant requirement by testing the settling rate of the slurry at periodic intervals,
after which flocculant addition is modified to achieve a desired settling rate . The introduction of
corrosion/erosion resistant materials has minimised problems associated with variations in cyclone
configuration.
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Lime Plant
The initial changes made to the lime plant in March 1984 overcame the immediate difficulties
of severe pH fluctuation. However, the modified plant utilised lime inefficiently because of
minimal slaking time. In excess of 7 kg of quicklime per tonne of product coal was being
consumed. An investigation of pH levels around the plant identified that the single point dosage
system was inadequate. Table 1 compares the pH and water assays at various points in the
plant with that at the pH probe located in the clarified water head tank.
The present design of lime dosing and mixing plant comprises a storage silo fitted with rotary
valve which delivers in batch mode to a mixing tank. Recirculation of the slurry mixture by
pumping enhances the slaking process. Slaked lime solution is pumped via a degritting cyclone
to a rising main which distributes the milk-of-lime, on demand, to three locations via modulating
dosing valves-which ensure correct dosing of both fine and coarse processing circuits.
Whilst the addition of lime has resulted in a reduction in the acidic conditions within the plant,
deposits of insoluble salts have resulted. Analysis of the deposits occurring at various locations
in the plant from time to time have been analysed and shown to be composed of mainly gypsum
(CaSO4•E2H2O) with sodium jarosite (NaFe3(SO4)2(OH)6) and ferrihydrite (Fe2O3•xH2O). Recently,
additions of a solution of sodium hexametaphosphate polymer have been made to complex soluble
calcium resulting in reduced gypsum formation.
Plant Modularisation
The decision was made to convert the plant to modular concept in October 1984. This decision
was made to enable maintenance of equipment in the plant to be carried out whilst the remainder
of the plant continued operation.
Table 1 Table Showing Variation of pH and Water Analysis at Several Plant Locations
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Improvements made at Collinsville Coal Preparation Plant to Alleviate Production Constraints 107
The modular concept required the plant to be divided into one module of 160 tph and one of
260 tph i. e. the original plant as module 1; the extension as module 2 with some drives (e. g.
conveyors to and from the plant) common to both modules.
This conversion required only relatively small changes in process configuration. The mechanical
changes included the introduction of splitter boxes and valves to allow hydraulic isolation of
equipment.
The major change was the reprogramming of the Tosdic system. A complete rewrite of
startup, shutdown and trip sequence logic was undertaken which took account of the need to
operate either module separately or both combined. A satisfactory level of "user friendliness" was
achieved by rearranging the VDU screen display format and process graphics. This better
enabled operators to control the plant in the new "modularised" configuration. Operator guidance
messages were also introduced to warn of the failure of process valves etc. to reach final, safe
limits. At the same time the opportunity was grasped to make further improvements to the
operating programme to allow operating staff to bypass "non-essential" production equipment
(such as centrifuges) to further improve potential plant availability.The modifications were completed during the Easter plant shutdown period in 1985. The
programme rewrite was of major proportions and required minor programme correction and debugging after start up, as had been the experience in early operations of the plant. Operator
and maintenance staff familiarisation and corrective measures to eliminate production aberrations
took approximately 2 months during which time there was no apparent improvement to production
levels.
Co-ordination of Expertise
By June/July 1985 the materials upgrade programme to combat corrosion and erosion
problems was well advanced and bringing benefits of a reduction in the extent of "crisis mainte-nance" leading to a gradual reinforcement of the planned maintenance programme. This situation
coupled with the plant modularisation provided the potential, at last, to attain production targets.
A small select committee comprising production and maintenance foremen, engineers and
plant metallurgist began daily meetings to review plant status in order to optimise throughput and recovery. The condition of all items which could influence the operational and metallurgical
status of the plant was assessed, reported and maintenance priorities determined.
The effects of this approach were virtually immediate and significant. Within a matter of a
few weeks the production levels increased by some 30% and by October 1985 actual plant
performance consistently exceeded budgetted performance with respect to both production tonnage and coal recovery. The plant was being utilised at a 100% level, and only the lack of raw coal
at the blending stockpiles caused the plant availability to remain at unchanged levels. Advantage
of this situation was taken to undertake more inspections and maintenance work during the
periods when the plant was awaiting coal.
5. COMBATTING CORROSION & EROSION
5.1 General
Three methods were adopted to overcome the problems associated with corrosion and erosion.
These addressed :
the reduction of corrosive forces within the plant by pH control ;
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the reduction or modification of erosive forces by innovation to change the magnitude and
angle of impact ;
the replacement of highly corrosion and abrasion prone materials by superior fabrications
materials, linings and castings.
5.2 Reduction of Corrosive Forces
The need for an effective and responsive pH control system was recognised. A system
utilising lime had been selected because of its ready availability, and because of coal market
considerations.
A description of the modifications and improvements to the lime mixing and dosing plant was
given in section 4.2. Whilst pH levels are now controlled to acceptable limits, this aspect of plant operation will continuously require careful aeetntion.
5.3 Reduction of Erosive Forces
It is often the case that the intial design of some particular aspect of a coal preparation
plant is not the optimum. Where the consequences of a less-than-optimum design are significant, changes are made. In view of the severe erosion experienced at Collinsville, several aspects of
the plant were redesigned to extend the replacement intervals where these measures were considered
to be cost effective.
One example was the replacement of pipe launder off-takes from the wet-distributor which
divides the 32 mm X 0 feed coal, suspended in water, to the three desliming screens. The original
mild steel pipes were corroded and eroded within 12 weeks of startup. After making stopgap
repairs and replacements in mild steel, new pipe launders were designed which took a more direct
route, and these were lined with cast basalt. The greater part of this launder remains unworn
after 18 months of operation. Some upgrade using special impact resistant lining on the sharp
bends at the start of the launders is still required to totally resolve the problem.
In another example of attacking the corrosion/erosion problem through design changes, the
original circulating medium tank agitation system was changed. The initial concept, known as
the "figure of eight" system comprised a series of valves and pipes which, on startup, withdrew
supernatant liquid from the top of the sump and pumped it into the settled, thickened, magnetite
slurry at the base. After several minutes of operation in this mode, the thoroughly mixed medium
was then pumped normally, from the bottom of the sump to the process.
Whilst this system has in other, less corrosive, environments been very successfully used, in
this case the high maintenance requirement outweighed the operational advantages.
Air injection points at the base of the sump and in the pump suction line have now been
installed and the original system removed.
5.4 Corrosion & Abrasion Resistant Materials
General
There is a wide range of materials available which can be used to inhibit corrosion and
increase component life. Each type of material has particular advantages associated with variable
costs. Some materials have disadvantages also. In selecting which material to use, reference to
the experience of others who have suffered similar problems is of advantage. Ultimately however,
local circumstances will influence the final selection and the most cost effective materials will be
used.
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Improvements made at Collinsville Coal Preparation Plant to Alleviate Production Constraints 109
Piping
When corrosion unexpectedly affects a processing plant, the most noticeable effects are associated
with the pipework. The pipe runs quickly develop leaks creating an untidy environment and
causing losses of process fluids.
The effects of corrosion/erosion depend upon the velocity and size of solids and the configu-
ration of the pipework.
Where pipes contain solids of fine sizes which travel at moderate speeds there is only abrasion
adjacent to locations of high turbulence. Slurries containning larger particles cause abrasion by
impact where the pipe changes direction but may not cause significant erosion in straight flow.If a slurry attains very high velocities, as in pipe launders for example , the effects of impact
are severe and special attention to design and materials is required .At Collinsville three types of remedy have been applied to resolve the corrosion/erosion problem
dependant upon the severity of the abrasion in each situation.
The original carbon steel pipes which contain pumped slurries of particles up to 5 mm in
rising mains, have generally been replaced using ABS piping.
Where the flow of this type of material is turbulent (e. g. after butterfly valves) or has high
impact energy (e. g. in direction changes in pipe launders) polyurethane lined carbon steel , 3Cr12, or high density polyethylene pipes and bends have been used .
For highly abrasive situations, where large particles are handled in slurries , cast basalt lined pipes and bends, 27% chrome castings and linings of Alumina Oxide have been applied.
Cyclones
The severity of corrosion and erosion of cyclones varies with the function of the cyclone . Heavy medium cyclones are recognised as forming a highly abrasive environment and are normally
constructed of thick Nihard castings. At Collinsville these cyclones have approximately 60°0 of the normal life expectancy (i. e. 6 months) . The life of these cyclones have not been unacceptable in relation to some other corrosion and abrasion experiences , nevertheless cyclones cast from 270 chrome alloy have been tested and found to give a life expectancy of 12 to 18 months . Ceramic lined cyclones are on site awaiting to be tested.
The cyclones which had the shortest life of 2 to 6 weeks were the water washing cyclones . Since these cyclones depend for their performance on the spigot aperture , vortex finder length and diameter and area of the cyclone inlet, the rapid wearing rate of these items caused serious coal
recovery and plant balance problems. The presently preferred materials specification comprises
ceramic spigots using 94% A1203, in association with polyurethane bodies and vortex finders . Using this combination the maintenance interval has been extended to six months .
Classifying cyclones are used at Collinsville to prepare feed for the water washing cyclones . Premature wear of the cyclone spigots resulted in unnecessary slimes contamination in this circ uit. It was established that consistent control of the cyclone underflow quality could be achieved by the
use of the correctly sized polyurethane spigots. This material increased the maintenance interval
several fold.
A similar situation in the clean coal classifying cyclones , which concentrate and deslime the feed to the slurry dewatering screens, again resulted in the selection of polyurethane . In the case of these cyclones it is necessary to achieve a cyclone underflow solids concentration of approximatel
y 40 to 50% for the slurry dewatering screens to operate efficiently . At approximately 25% solids
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the function of the screen changes from dewatering to wet classification and the fine clean coal
product is lost to the coal thickener through the 0.4 mm apertures of the screen decks. Strict control of the cyclone spigots is therefore essential.
Pump Components
A feature of the high maintenance demands during 1984 was the frequency of replacement of
impellers and liners of the centrifugal process pumps. Regular pump rebuilds after periods of
only 6 weeks to 6 months characterised the early months of operation. (See Plates 3 & 4)
With the co-operation of the pump manufacturer, 27% chrome alloy replacements have been
obtained and tested. Good success has been achieved in the case of pumps operating on slurries
of fine coal. Inspections at the end of 12 months operation give a predicted life of up to four
years for many pumps. Where the 27%o chrome alloy components have been applied to pumps in the heavy medium plant, premature failures have occurred and at present a life expectancy in
excess of 8 months has not been achieved.
Trials of other materials in pumps are currently being carried out and include
(1) impellors and throat bushes cast in polyurethane
(2) all wet end components sprayed with a ceramic coating.Eventually it is hoped to achieve a satisfactory specification for all pump components.
Tanks, Chutes and Fabrications
Factory cast polyurethane and site sprayed steel plate fabrications have been successfully
applied where slurries contain particles of less than 5 mm. Trowelable grade polyurethane used
on-site has been found to be effective but difficult to satisfactorily bond to steelwork.
Baytec brand polyurethane has been spray applied to a variable thickness to suit different
applications. The finished lining has a Durometer Hardness of between 72 and 79. A particular
advantage of this type of material is the short curing period of approximately 3 minutes. Applica-
tion in confined spaces is difficult due to the physical size of the spray gun used to apply the
material.
Where high impact forces are present in an abrasive situation, as in the case with conveyor
transfer chutes, cyclone underflow collecting chutes, raw coal distributor, dense medium mixing
tanks and centrifuge casings, it has been determined that a high degree of protection can be
attained using 85%o alumina tiles. The tile lining has not been totally satisfactory if too wide a
space between tiles has existed or if the receiving surface has not been rigid and has flexed
causing failure of the adhesive bond.
Plate 3. Corroded Heavy Medium Pump Throat BushPlate 4. Corroded Heavy Medium Pump Impellor
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Improvements made at Collinsville Coal Preparation Plant to Alleviate Production Constraints 111
Historically, stainless steel has been effective in combatting corrosion but has been an expensive
solution to the problem. However a lower cost corrosion resistant steel has become available and
is now in wide use. Named 3Cr12, the metal is a low friction, high chrome content alloy which
can be easily fabricated and, in addition to its corrosion resistance, is highly abrasion resistant.
An example of the successful application of 3Cr12 is in the lower part of the rejects bin. The
bottom 1 metre of the cone, the transition piece, exit chutes and gates were fabricated in 6 mm
thick 3Cr12. In the 25 months of service up to December 1985, the most severe wear in this
section was estimated to be 15%. Earlier experience with mild steel indicated a replacement
interval of 12 months with that material.
Miscellaneous Applications
Several other materials have been used and tested and found to be successful in various
specific applications. A variety of plastics and low friction linings have been used in chutes.
Linatex and reinforced rubber pipes have found specialist applications, and a variety of the linings
ranging from simple quarry the to high density alumina tiles have been successfully applied.
As other materials are developed or become available, it will be mine policy to test and
evaluate performance.
6. PRESENT OPERATIONAL STATUS
Fig. 5 indicates the level of plant performance from plant commissioning in November 1983,
to the middle of the current year. The gradual improvement in performance is evidenced by the
trends in plant utilisation and production. It can be expected that plant availability will continue
at approximately 75 to 80% since this provides sufficient operating time to produce budgetted
tonnage. The essential feature of recent successful plant operation has been that when the plant
is not under maintenance it has been capable of operating without risk of failure, thereby giving
high utilisation.
To demonstrate the improvements which have been achieved Table 2 has been prepared which
compares the important operational parameters in two similar periods in the consecutive years
1984/85 and 1985/86. The operations in 1984/85 were characterised by low levels of utilisation,
poor coal recovery and low production rates compared with the 1985/6 period when plant produc-tion was high and constrained primarily by the limited availability of coal for processing. Most
of the maintenance carried out in 1985/86 was planned and controlled in direct contrast to the
previous year where maintenance work was dominated by the frequency of equipment failures.Despite the recent satisfactory plant performance results, research and development work is
Fig.5. Variation of Plant Throughput, Availibility & Utilisation With time
Vol. 33. No. 2 ('86-‰Ä) (69)
112 M. M. WILLIAMSON • R. G. BUCKLEY • D. B. HAIGH and J. M. CHADDERTON
Table 2 Table Showing Comparative Plant Performance for Corresponding Periods in 1984/85 and 1985/86
continuing in the expectation of improving both the reliability and the performance of the plant .Greater reliability can be anticipated as better corrosion and erosion resistant materials are
found and applied and as the formal planned-maintenance procedure is complied with.
Plans are already in hand to reduce the rejection of fine coal to tailings. Higher efficiency
classifying cyclones and more fines dewatering screens are soon to be purchased. Test work on
the potential to recover coal in the minus 74 micron sizes is being started and will result in plant
modifications if shown to be cost effective.
7. SUMMARY
The Collinsville Coal Preparation Plant has been brought to a satisfactory level of performance
despite a diverse, complex and debilitating range of problems. This has been achieved by the
careful analysis of a variety of discernable symptoms and rectification of the deeply underlying
causes of the difficulties. The plant is now well able to satisfy the contractual requirements for
the supply of 1.0 Mtpa of high grade coking coal to the Japanese Steel Mills. The resolution of
the problems must be credited to the high dedication of technicians, engineers, craftsmen and
operators who overcame considerable difficulties in bringing the plant to full productive capacity .The present satisfactory level of performance is however not the end of the story , improvements
will continue to be made as more effective and economical solutions to problems emerge.
ACKNOWLEDGEMENTS
The authors wish to thank the management and staff of Collinsville for their support and
assistance in the preparation of this paper.
Contributions from K. S. Gilmour, K. Tosi and A. Tilney are acknowledged.
Thanks are extended to colleague R. Hoare for assistance in editing and assembly of the
paper.Thanks also go to M. I. M. Holdings Limited (MIM) Collinsville Coal Company Pty. Limited
(CCP) for the opportunity to prepare and present this paper.
(70) 資源処理技術(浮 選)
Improvements made at Collinsville Coal Preparation Plant to Alleviate Production Constraints 113
DISCLAIMER
The views expressed herein are those of the authors and not necessarily those of MIM and
CCP.
Vol. 33. No. 2 ('86-‰Ä)(71)