Australian Coal Preparation—a 2000 Review
Australian coal preparation—a 2000reviewby A. Swanson*The Australian coal industry has been subdued in recent years andonly a few new plants have been constructed, but the drive forgreater efficiency has seen continued technological developments.The paper lists the new plants and major upgrades, plussummarizes technical developments in the areas of dense mediumprocessing, fine coal treatment, froth flotation, dewatering and online analysers.IntroductionThis paper is a reflection on the developmentsin coal preparation in Australia for the periodsince late 1997, when an excellent summarywas prepared for the last IOC seminar on coalpreparation developments in each country(Hornsby and Partridge1998). Fortuitously, theEighth Australian Coal Preparation Conferencewas held in November 2000 and much of thetechnology developments discussed belowcome from the papers presented at theconference.Note, that the views expressed arepersonal and do not necessarily represent theviews of the Australian Coal PreparationSociety.General coal industry viewThe last three years for the Australian coalindustry have been very difficult, perhaps thetoughest since the early 1980s. Low priceshave prevailed for much of the time butexports have continued to grow for the threeyear period and the relevant statistics aregiven in Table I. While contract prices werelow, spot thermal coal prices were very low forperiods of time, but these have dramaticallyimproved over 2000; the lower A /US exchange rate enhanced profitability for coalmining operations in the latter part of 2000.The focus has very much been on reducingcosts which has inevitably led to restructuringand lower employment levels in the industry.The Journal of The South African Institute of Mining and MetallurgyPlant construction activityThe difficult period for the industry resulted inonly limited construction activity for new andupgraded preparation plant facilities. Some ofthe more significant projects brought on line inthe period 1998–2000 were:Burton Coal—second module commissioned; 400 t/h of feed in each module withtwo-stage processing of coarse coal in 1300mm diameter dense medium cyclones, sandsfraction in spirals and Jameson cell flotation on* Quality Coal Consulting, Newcastle, Australia.Australian Representative InternationalOrganising Committee, XIV ICPC. The South African Institute of Mining andMetallurgy, 2001. SA ISSN 0038–223X/3.00 0.00. First presented at Colloquium: CoalPreparation, 14 February 2001.MAY/JUNE 2001107 SynopsisRecently focus has switched back to improvingthe efficiency of operations, prompted by animproved outlook for the industry.One of the notable features for 2000 in theAustralian coal industry, has been the changesto, and consolidation of, the ownership ofAustralian coal mining operations (Table II).However, the significant passive minorityownership by Japanese trading companies hasnot changed. There have also been a numberof smaller operations open up, with manymaking use on contracted services for mining,preparation and haulage. Such venturesinclude Coppabella, Foxleigh, Whitehaven,Cullen Valley, Glennies Creek, Nardell andDonaldson.The Australian industry relies heavily onexports, as shown in Table I, so the future ofthe Australian coal industry depends substantially of overseas sales. Current projectionsfrom government and industry sourcesindicate only very minor increases in cokingcoal exports but substantial increases inthermal coal exports, to 147 Mt/y in 2010(Haraldson2000). Such an increase will requiresubstantial projects to come on line, which willnot only require the increased demand, butalso the likelihood of a reasonable return onthe capital invested.
Australian coal preparation—a 2000 reviewTable IProduction statistics for Australian coal industry(2000 data are provisional; source Aust. Coal Report)Saleable outputMetallurgical exportsThermal exportsTotal exportsExports to JapanExports to Asia zone1999 Production (Mt)QldNSW Total2000 Production (Mt)QldNSW 8235.3100.586.4186.987.8127.8Table IISignificant operators in the Australian coal industry(covering approximately 90% of saleable production; sourceAust. Coal Report)CompanyAnglo dyPowercoal**QCTRAGRio TintoShellSumitomo CorpWesfarmersDecember 1999Capacity (Mt/y)Managed .718.24.34.3December 2000Capacity (Mt/y)Managed Owned 1*1136080212003* Sale pending** Sale of assets under considerationthe ultrafine fraction. Later the first module was modified inlight of technological advantages from second module, whichincluded the 1 m diameter classifying cyclones and theClimax magnetic separators.Moranbah North Coal—complete new plant wasconstructed to treat 1500 t/h in two modules; in each modulecoal is processed in a Teska Bath, two 1 m diameter cyclonesand three Jameson flotation cells.Coppabella—a new plant was installed to treat 600 t/h ofraw coal in a large diameter dense medium cyclone ( 1.4 mmw/w) and spirals (deslimed –1.4 mm w/w).Saraji—replacement of conventional flotation cells byMicrocel columns. Eight 4 m diameter cells were installed totreat 400 t/h of –0.5 mm coal.Warkworth—addition of a module to treat the ultrafinefraction in Jameson cells and screenbowl centrifuges toprovide a Beneficiated Dried Tailings (BDT) product to thespecifically designed Redbank Power Station (Mills,et al.2000). Classifying cyclone overflow, normally sentdirectly to the thickener, is processed to provide 58 t/h (dry)of product coal with an ash of less than 15% and total 108MAY/JUNE 2001moisture of 26–30%. The plant was commissioned in late2000 and is undergoing operational trials.South Walker Creek—preparation plant capacity wasincreased by installing a larger diameter dense mediumcyclone (1300 mm) and additional spirals.Blair Athol Coal—a 250 t/h contractor supplied andoperated plant upgrades coal that contains too much dilutionand so has been excluded from the raw coal export steamproduct. The plant consists of dense medium and spiralcircuits.Callide—two ROMJIGS, capable of handling around 350t/h each of very coarse coal, have been installed to treat–350 75 mm coal (-75 40 mm can be optionally included);commissioning is expected March 2001. Raw coal from themine (2000 t/h) is broken to 350 mm topsize and screened,with the coarse coal washed and the undersize coal passingstraight to product. The product coal, consisting of washedand crushed coarse coal, and raw undersize coal, is suppliedto regional power stations. Overseas studies indicated thatcutpoints of 1.77 to 2.0, at Eps of 0.07 to 0.10, could beachieved (Sanders, et al.2000).Technology developmentsWashability dataWith lower levels of operating profits, it is becomingincreasingly important that mine planning procedures arereliable and accurate, and that all options to optimize returnsare considered. The projection of likely yields from coalpreparation is a crucial step in such a process. Also, thedesigners and operators need to provide coal preparationplants that have minimum capital cost and maximumefficiency. Thus reliable sizing and washability data areessential.Industry and government have funded extensive investigations into better sample pretreatment (Swanson2000).These were derived from an understanding of the breakagethat occurs in coal handling and preparation facitities, asshown conceptually in Figure 1. The procedures developedare now finding common usage in the testing of largediameter bore cores and strip samples. The procedureinvolves drop shattering to the point of ‘inevitable breakage’,further drop shatter to model the breakage in handlingsystems, dry tumbling to incorporate abrasion and fiveminutes of wet tumbling to achieve the in-plant wet sizing.When detailed float-sink work is carried out on a number ofsize fractions, and these data used in a simulation model,close matches to plant performance can be achieved (Esterle,et al.2000, Figure 2).However, large diameter cores are relatively expensive toobtain and test, so the number and spread of results areusually quite limited. To obtain sufficient volumes of data forgeological modelling and mine planning, it is common to uselarge numbers of slim cores. Such cores have only a smallmass and so the detailed data required for reliable projectionof preparation plants have not been traditionally obtained. Aspart of a larger project on fragmentation, adjacent slim andLD cores were drilled and the washability results were usedin simulations to compare to plant results (Esterle, et al.2000).It was found that by pretreatment of the slim core, and byThe Journal of The South African Institute of Mining and Metallurgy
Australian coal preparation—a 2000 reviewRate of DegradationDryconditionsWetconditionsBreakage directly relatedto energy input5 minutewet-tumble pointInitial easydegradationLess-easy breakageBreakdown due towet screeningInitial easy breakageROMcircuits to be designed. As a result, most new installationsemploy such units.Banana screens have been widely used in desliming anddrain and rinse applications because of their increasedscreening capacity per unit of footprint area, compared toconventional sieve bend/low head screen combinations.However, the ‘drain’ performance is critical to the operationof dense medium circuits and an ACARP study hasinvestigated this aspect of banana screen operation (Meyers,et al.2000). The findings from this project were that the drainbehaviour of banana screens were, for the same apertures,inferior to sieve bend/low head screen combinations (Figures3 and 4). However, the rinse performance of banana screenswas superior and overall the total screen performance showsbetter moistures and lower magnetite losses. The poor drainperformance of banana screens is marked below effective cutsizes of 1 mm and the different balances of drain and rinseflows need to be taken into account at the design stage.The replacement of sieve bend/low head screens withbanana screens has focused attention back on the operationEnergy InputFitted Model Partition Number858075706560555045891011120.1 R27 Slim pre-treatR23 LD R27 LDR23 Slim Explo. R23 Slim pre-treat R27 Slim Explo.B2C1C2D1E11.0E2100F1Figure 3—All modified Whiten model fitted drain section data(B2 sieve bend/low head with 0.55 mm aperture; C1, C2, F1banana screens with aperture 0.56 to 0.8 mm; the rest bananascreens with apertures 1.1 to 1.7 mm)doing more detailed float-sink work, better yield estimateswere obtained than from standard exploration techniques, asshown in Figure 2. Results were not as good as for largediameter cores but because of the potential wider geographicdistribution, the use of pretreated and fully tested slim coreswarrants further consideration.Dense medium processingThe trend continues to the use of modules with single largediameter dense medium cyclones, with units up to 1300 mmin diameter that can process 450 t/h of coal and more. Inplant refurbishments, single large diameter DMCs arereplacing pairs of smaller diameter units. There are someemerging concerns about the efficiency of separation for thesmaller coal (say -4 1 mm) and this will be the subject of anACARP- funded study in 2001.The Climax style magnetic separators, which feature acounter rotation technique, offer higher unit capacities, betterefficiencies and higher concentrate densities. These styles ofunits have allowed simpler and more effective dense mediumEffective Cut Point—S50 (mm)Figure 2—Comparison between plant performance and simulations ofbore core dataThe Journal of The South African Institute of Mining and MetallurgyB11Geometric Mean Size (mm)13Product Ash % 00.01A17Plant (2-hourly) 1009080706050403020101.4R2 0.931.21.00.80.60.40.20.06065707580859095100Solids Drain Rate % Banana ScreensxS/Bend L/Head Screen — Regression LineFigure 4—Solids drain rate% v effective cut point (S50) with sievebend/low head data point shownof density control systems (Leach and Meyers2000). Avariable drain rate, particularly a low one induced by theretrofit of a banana screen, more strongly impacts on thetraditional DSM system (using an overdense sump to correctmedium density in feed), than the now more common risingMAY/JUNE 2001109 Product Wet YieldFigure 1—Conceptual breakage model for coal handling andpreparation
Australian coal preparation—a 2000 reviewdensity system (concentrated medium from dilute circuitreturned immediately and make up water used to correctdensity). Thus the replacement of sieve bend/low headscreens by a banana screen, in a plant employing atraditional DSM density control circuit, can have catastrophiceffects if the density control system is not upgraded.The Macquarie coal preparation plant has benefitedgreatly from a project to improve the magnetite control circuit(van Barneveld, et al.2000). The original design had separatedilute medium treatment for the DM bath, primary DMC andsecondary DMC circuits. The new design had a single dilutecircuit with just two Climax magnetic separators and there isa controlled redistribution of magnetite back to each circuit.The simplified circuit contains 17 pieces of equipmentcompared to the original 58. Magnetite consumption hasfallen from 1.3 kg/t to 0.4 kg/t, plant availability hasincreased to 87%, control has become simpler and operationshave greatly improved.While the operation of dense medium cyclones is wellunderstood in overall terms, a better understanding ofmedium behaviour, and the prediction of underflow andoverflow densities, will enhance modelling and processcontrol. As a result a project has commenced at JKMRC thatuses gamma ray tomography to determine the internalmedium gradients (Lyman, et al.2000). A rig has beendeveloped using a 350 mm diameter DSM style densemedium cyclones, and techniques to extract useful data havebeen established, so results should become available over thenext year or so.A novel cyclone concept has been developed by theJKMRC (Rong and Napier-Munn,2000) that, by using specialprofiles for the body, vortex finder and spigot, increasescentrifugal forces and mitigates short-circuiting (see Figure5). The objective is to improve the efficiency of densemedium processing of smaller particles, say –4 mm. Pilottesting of the dense medium separation of a 100 mmdiameter new cyclone and a DSM type cyclone showed someimproved performance using tracers and coal (-1 0.125 mm)—sharper separation, lower cutpoint offset, good efficiency atlow cutpoints. Work is progressing to a 200 mm diameterdesign.cation (Rong and Napier-Munn2000). Pilot testing was carriedout comparing the performance with two commerciallyavailable 100 mm diameter classifying cyclones. Generallythe JKMRC cyclone gave a sharper separation and, for a givenfeed pressure, the JKMRC cyclone gave a lower separationsize, demonstrating the higher centrifugal force present.Also, under similar test conditions, the novel design gave alower flow ratio to underflow. The next steps are evaluationsat 200 mm diameter and then plant trials.After a series of pilot trials and simulation studies,Bayswater Colliery Company decided to upgrade their coalpreparation plant by employing a Teetered Bed Separator(TBS) to process the –2 0.5 mm size fraction. The treatmentof this fraction took load off the water washing cyclones andspirals and was a cost effective upgrade. Overall plantcapacity increased by around 100 t/h and yield increases of1.5–2.5% were expected. The plant flowsheet is given inFigure 6, with installation occurring in April 2000, commissioning in May 2000 and successful operation since.Froth flotationApart from the two major installations of Microcels at PeakDowns and Saraji, new plants and upgraded plants haveincluded Jameson cells, e.g. Burton Downs, Moranbah North,Blackwater. As the technology has become more accepted,further development has been undertaken (Murphy, et al,2000). Carrying capacities are historically difficult to predictfor column flotation, and Jameson cells in particular; investigations have derived more accurate methodology to reducethe conservatism in design. High Intensity Conditioning(HIC) has shown that with no additional reagents microagglomerates can be generated which improve the flotationresponse of difficult to float ultra-fine coal. A thirdgeneration Jameson cell is now available that incorporates aSpinFlow wash water system, to improve wash water distribution, and an air isolating slurry eliminating valve, tominimise ingress of solids into the air distribution system.Fine coal processingA one metre diameter classifying cyclone, cutting between0.2 mm and 0.3 mm, offers a number of distinct advantagesover traditional multiple cyclones carrying out the sameduty—reduction in capital and maintenance costs, simplerlayout, elimination of slurry subdivision step. Performancedata are difficult to establish due to the volume of samplesthat are required and so ACARP funding was made availableto obtain such information (O’Brien, et al.2000). It was foundthat similar efficiencies to banks of smaller cyclones wereobtained and that similar relationships are found with respectto the impact of variables such as flowrate, pressure, andgeometry on separation size. Increasing feed solids from 10%to 20% increased the cut size from 0.2 mm to 0.3 mm. Thebehaviour of particles of different densities was marked withthe high density particles separating at 0.07 mm and thecleanest coal separating at 0.3–0.5 mm.The novel cyclone design described above in densemedium processing, also can be used for fine coal classifi- 110MAY/JUNE 2001Figure 5—Schematic drawing of the new cyclone design conceptfrom JKMRCThe Journal of The South African Institute of Mining and Metallurgy
Australian coal preparation—a 2000 reviewPRE-TREATMENT-125 mmCLEANINGSUBSEQUENT TREATMENTJIGRAW COALSCREEN 8 mmPROD. DEWSCREEN 19 mm PLANT FEEDSIZER-19 0.5ww/mm-8 2.5w/w mmSPIRALSSMALL COALCENTRI.PRIM. CLASS.CYCLONESPRIM.WWCFINE COALCENTRI.SEC. WWC-2.5w/w 0.125WASHED COALTBSTHICKENERSIEVEBENDFINES PROD.SCREENFINES REJECTSCREEN-0.5 0.125 mmTAILINGSWASHERY REJECTFigure 6—Bayswater TBS plant upgrade as-built process flowsheetThe Journal of The South African Institute of Mining and MetallurgyFigure 9). The information provided includes bubble size,froth texture and froth velocity, and control strategies havebeen developed using such data. Prototypes were trialed atPeak Downs and full commercial systems are being installedat both Peak Downs and Saraji Mines.DewateringWhen looking to dewater fine flotation products, the choicehas been usually a horizontal belt vacuum filter, such hasbeen the case at Burton Downs and Moranbah North. ForStatic in-line mixerProductXXXXXFlow controlvalveJet ejectorXSeparation cellTailingsCentrifugal pumpFigure 7—The TurboFlotation systemMAY/JUNE 2001111 The CSIRO-developed TurboFlotation process hascontinued its development with the trial of a 1 m diameterunit at the Coppabella mine, treating the –0.1 mm fraction inone or two stages (Ofori, et al.2000). The process aims toprovide low cost, compact high capacity flotation cells byimproving residence times by an order of magnitude byisolating the sub-processes of bubble generation,particle/bubble contacting, froth/slurry separation and frothcrowding/removal (Figure 7). Successful trialing at bench(90 mm diameter) and pilot (300 mm diameter) providedconfidence to scale up by a factor of 40 times to 1 mdiameter. The demonstration plant has been operating sinceJune 2000, and while a number of application-specific issueshave been identified, there have been some scale-up issuesthat need to be attended to before the unit can achieveoptimum performance.Studies have indicated that cavitation forces ca
Australian coal preparation—a 2000 review the ultrafine fraction. Later the first module was modified in . are now finding common usage in the testing of large diameter bore cores and strip samples. The procedure .
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