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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100 M. M. WILLIAMSON • R. G. BUCKLEY • D. B. HAIGH and J. M. CHADDERTON

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

(58) 資源処理技術(浮選)

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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102M. M. WILLIAMSON • R. G. BUCKLEY • D. B. HAIGH and J. M. CHADDERTON

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


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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104 M. M. WILLIAMSON . R. G. BUCKLEY • D. B. HAIGH and J. M. CHADDERTON

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


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



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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108 M. M. WILLIAMSON •E R. G. BUCKLEY. D. B. HAIGH and J. M. CHADDERTON

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.



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



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)


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.



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)

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IMPROVEMENTS MADE AT COLLINSVILLE COAL PREPARATION PLANT …