Coal Mining - basics - gpph.com.augpph.com.au/aus/data/uploads/papers/Coal Mining - basics.pdf ·...
Transcript of Coal Mining - basics - gpph.com.augpph.com.au/aus/data/uploads/papers/Coal Mining - basics.pdf ·...
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Coal Mining - basics
Coal Mining MethodsUnderground
Bord & PillarLongwall
SurfaceOpen Cut StripOpen Pit
HighwallAugerContinuous Highwall MinerPunch
Bord & PillarContinuous Miner & shuttle cars or continuous haulageHighly flexible, high cost – can handle geological variability1.5-3m per pass, but can take up to 3 passes in good conditionsPreferably less than 10o dip and less than 500m depth of coverMultiple units possible to vary coal source and increase productionBest with good floor and roof plus strong coalWorking section may include roof and floor but coal may be left on roof or floor to improve conditionsSingle seam – reasonably constant productionPillar extraction to improve coal recovery to a maximum of around 65%
Continuous Miner
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LongwallSpecialised equipment consisting of hydraulic face supports, shearer, chain conveyor, sizer, etcInflexible technique requiring a block of 200-400m wide by 2-4km long for a single faceHigh capital requirement, but can be low operating costStandard longwall has a face height of 1.5-4.5m with a dip preferably less than 10o and less than 1000m depth of coverCan mine through small faults and dykes with increased dilution, and can mine thicker seams using top coal caving at the expense of up to 20% dilutionLarge production peak generally greater than 3 times averageOne month delay during face relocationUsually single longwall coal source plus development unitsCoal recovery up to 85%
Longwall Face
Unplanned Longwall Delay Open Cut StripFlat lying with less than 10o dip and a single or multi-seam depositLong narrow strips less than 100m wide and 2-15km long with a maximum pit depth less than 200mDragline and/or shovel/truck stripping of blasted overburden, possibly assisted by production dozingCoal mining by front end loader or excavator into trucksCoal mining rate relatively uniform but subject to surges due to availability of exposed coalMining exposed coal gives supply from a single source for an extended period. Blending from multiple seams/areas is possibleDilution is from weak floor & cleanup due to waste not separating from coal and coal contact irregularities. Increases with poor drainage & blast damage. May also include weathered, spon. com. or contaminated U/G coal.
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Open Cut Strip Layout Dragline Strip Mining
Coal Hot Out of the Open Cut Open PitAny dip:
Shallow dip with benches on seamsSteep dip with benches on horizontal levels
Smaller pit dimensions, generally multi-seam with greater than 30% of waste hauled out of pit. Mining progresses in large cut-backs or panelsVaries from small, shallow operations to large capacity mines up to 400m deepShovel or excavator & truck waste removalExcavator or front end loader coal mining with rear dump truck haulageMultiple coal sources available from a number of seams giving a uniform production rateDilution from similar sources to open cut, but may be greater with steep dips due to through seam blastingCoal recovery generally greater than 90%
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Layout and Section of Steep Dip Open Pit
-300RL
-200RL
-100RL
0RL
100RL
200RL
300RL
Open pit with spontaneous combustion
Augering1.35-1.8m dia. auger or a 1.5m dia. twin augerReliably excavate to 160-200m from the open cut highwallCan multi-pass in thicker seamsRecovery 30-60% with limited dilutionRelatively unaffected by weak strataApproximately 0.5Mtpa
Single & Twin Augers
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Continuous Highwall Miner1.5-3m extraction height from a rectangular heading using a continuous miner and highwall miner continuous haulageReliably excavate to 350-500m from the highwallCan double pass in thicker seams leaving a septumRecovery 45-60% with dilution similar to underground miningMust have strong strataApproximately 1.0Mtpa
Punch MiningLongwall or bord and pillar mining with panel access directly from an open cut highwallSimilar mining conditions and constraints to underground mining by these techniques
Mine Planning & Technical ServicesPit design to maximise economic recoverable coal (NPV?, meet product specifications, maximise production)Scheduling to keep primary stripping equipment busy and meet production targeted quantity & qualityMining method and geology provide iterative economic relationshipProvide communication, coordination and monitoring from pit to market (survey, geology, coal quality)Other issues
Water management Geological and geotechnical problemsEnvironmental control and rehabilitationBlasting design and monitoringProduction monitoringHauls and Dump locationMedium & long term planning
ProductionMoving overburden is main focus in most surface mining operationsMajority of equipment is used on overburden removalCoal mining is a minor cost item but can have a major impact on profitabilityWeather and underground drainage is important
Rain affects blastingWater disrupts coal ripping, blasting and mining
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Drill & BlastingWhy blast
To break up overburden for diggingAlternatives ripping and surface miners
IssuesEnvironmental (overpressure and vibration)Damage to coal roof and edgeGood blasting vital for productivity
Drilling & BlastingHow to control blast damage
Correct depth for holesSet standoff based on material typeTouch drillingIncrease standoff at edges
Charge and initiation sequence
Check true depths Edge damage
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By Courtesy of Peak Downs
DraglineAdvantages
Low cost per bcm movedHigh productivityCan coal close to face
DisadvantagesHigh capital costRequires good conditions, less flexibleDepth of mining limitedBlending from pit more difficultCable handling and power demand
ShovelsAdvantages
More flexible than draglinesCan be very productive in right conditions
Need wide faces, good blasting, flat floors
DisadvantagesCost per bcm higher than draglineAssociated equipment (trucks, dozers, graders, road maint)Several passes may be needed hence coal not availableCable handling
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Hydraulic ExcavatorsAdvantages
More flexible than shovelsLower capital costCan be very productive in right conditionsGood coaling tool
DisadvantagesCost per bcm higher than shovels (but not by much)
Associated equipment (trucks, dozers, graders, road maint)Dig depth limited (5m under) - several passes may be needed hence coal not availableShorter lifespan
Front end loadersAdvantages
Most flexible machine (though needs good floor)Most mobile
DisadvantagesCost per bcm higher than shovels/excavatorsAssociated equipment (trucks, dozers, graders, road maint)Dig depth limited - several passes may be needed hence coal not availableWater control on floor
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Coal Preparation - miningClean roof
Dozer to push roof materialDoes parting stick to roofHow variable is the seam contactWhat is clean – how dirty is the top coalAim to minimise roof losses and dilutionRubber tyred equipment gives lower lossGrader cleanup can improve coal recovery
Coal Preparation - miningRip coal
Dozer to rip for loaderDepth limited by ripper tyne, hardnessRip and push generates finesWhat ripping spacing, is cross ripping neededFines generation can be reduced by optimum ripping
Thick seam - rip and pushTwo passes if coal quality differentSingle pass if blending needed
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Coal Preparation - miningBlast coal
Seam must be thick enough (3m?)Stemming material in holePlastic nonel blast lines in coalCrush zone around each hole
Stemming
Crush zone
Coal Preparation - miningClean floor and edges
Dozer to push floor coal and along highwallDoes coal stick to floorWhat is cleanAim to maximise coal recovery but minimise dilutionWhat coal should be mined – bypass vs. wash –selection of working sectionSoft floor and poor drainage give higher dilutionThrow blast can place coal toe under spoil and increase edge dilution
Selective miningTo recover high value intervals
Eg recover a SS Coking coal section out of a thicker seamNormally slows productionLeaves higher ash productTotal value added must be determined
New machines being introduced to eliminate blasting can also be selective
Surface miner
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SummaryMining is a compromise between:
maximum productivityminimum cost/tcoal recovery vital over long term
Underground & highwall mining characteristics:Single coal type with potentially high dilutionMines a working section based partly on geotechnical considerationsVery high peak productionAll coal is cut by pick with high fines contentNo selective mining possible – limited range of cutting heights
Surface mining characteristics:Multiple coal sources with dilution dependant on seam thickness and mining conditionsWorking sections based on economics and practicalityUniform production rateCoal may be ripped, pushed, blasted or dug unshot with varying fines generationSelective mining possible to provide feed for different products or blendsMining from multiple sources can assist in overcoming problems (blinding screens, excessive rejects or slimes) but can also result in surging due to cyclical loading