CHAPTER-5.-BRIEF-INTRODUCTION-TO-COAL-MINING

CHAPTER5.BRIEFINTRODUCTIONTOCOALMININGCoalmining[01]istheremovalofcoalfromtheground.Theminingmethodemployedtoextractthecoaldependsonthefollowingcriteria:a.seamthickness[02],b.theoverburdenthickness,c.theeaseofremovaloftheoverburden,d.theeasewithwhichashaft[03]canbesunktoreachthecoalseam,e.theamountofcoalextractedrelativetotheamountthatcannotberemoved,andf.themarketdemandforthecoal.Thetwotypesofminingmethodsaresurfacemining[04]andundergroundmining[05].Insurfacemining,thelayersofrockorsoiloverlyingacoalseamarefirstremovedafterwhichthecoalisextractedfromtheexposedseam.Inundergroundmining,ashaftisdugtoreachthecoalseam.Currently,undergroundminingaccountsforapproximately60percentoftheworldrecoveryofcoal.5.1SurfaceMiningSurfaceminingisusedtoreachcoalreservesthataretooshallowtobereachedbyotherminingmethods.Typesofsurfaceminingincludeopen-pitmining[06],driftmining[07],slopemining[08],contourmining[09],andaugermining[10].A.Open-pitMiningInopen-pitmining,orstripmining,earth-movingequipmentisusedtoremovetherockyoverburdenandthenhugemechanicalshovels[11]scoop[12]coalupfromtheunderlyingdeposit.Themoderncoalindustryhasdevelopedsomeofthelargestindustrialequipmentevermade,includingshovelscapableofholding290metrictonsofcoal.Toreachthecoal,bulldozers[13]clearthevegetationandsoil.Dependingonthehardnessanddepthoftheexposedsedimentaryrocks,theserockylayersmaybeshatteredwithexplosives.Todothis,workersdrillblastholes[14]intotheoverlyingsedimentaryrock,filltheseholeswithexplosives[15],andthenblasttheoverburdentofracturetherock.Oncethebrokenrockisremoved,coalisshoveledfromtheunderlyingdepositintogiantearth-movingtrucks[16]fortransport[17].B.DriftMiningDriftminingisusedwhenahorizontalseam[18]ofcoalemergesatthesurfaceonthesideofahillormountain,andtheopening[19]intotheminecanbemadedirectlyintothecoalseam.Thistypeofminingisgenerallytheeasiestandmosteconomicaltypebecauseexcavationthroughrockisnotnecessary.Ifcoalisavailableinthismanner,itislikelytobemined.C.SlopeMiningSlopeminingoccurswhenaninclinedopeningisusedtotapthecoalseam(orseams).Aslopeminemayfollowthecoalseamiftheseamisinclinedandexposedtothesurface,ortheslopemaybedriventhroughrockstrataoverlyingthecoaltoreachaseam.Coaltransportationfromaslopeminecanbeaccomplishedbyconveyor[20]orbytrackhaulage[21](usingatrolleylocomotive[22]ifthegradeisnotsevere)orbypullingminecars[23]uptheslopeusinganelectrichoist[24]andsteelrope[25]ifthegradeissteep.Themostcommonpracticeistouseabeltconveyor.D.ContourMiningContourminingoccursonhillyormountainousterrain,whereworkersuseexcavationequipmenttocutintothehillsidealongitscontourtoremovetheoverlyingrockandthenminethecoal.Thedepthtowhichworkersmustcutintothehillsidedependsonfactorssuchashillslopeandcoalbedthickness.E.AugerMiningAugerminingisfrequentlyemployedinopen-pitmineswherethethicknessoftheoverburdenistoogreatforopen-pitminingtobecost-effective[26].Open-pitminingwouldrequirethelengthyandcostlyremovaloftheoverburden,whereasaugerminingismoreefficientbecauseitcutsthroughtheoverburdenandremovesthecoalasitdrills.Inthistechnique,theminersdrillaseriesofhorizontalholesintothecoalbedwithalargeauger(drill)poweredbyadieselorgasolineengine[27].Theseaugersaretypicallyabout60m(200ft)longand0.6to2.1m(2to7ft)indiameter.Astheseenormousdrillsboreintothecoalseam,theydischargecoallikeawooddrillproducingwoodshavings.Additionalaugerlengthsareaddedasthecuttingheadoftheaugerpenetratesfartherintothecoal.Penetrationcontinuesuntilthecuttingheaddriftsintothetoporbottomofthecoalseam,intoaprevioushole,oruntilthemaximumtorque[28](energyrequiredtotwistanobject)oftheaugerisreached.F.SatelliteAids[29]toSurfaceMiningInthelate1990ssomecoalminingenterprisesusedtechnologiessuchastheglobalpositioningsystem(GPS)[30]tohelpguidethepositioningofminingequipment.SatellitesoperatedbytheUnitedStatesAirForceSpaceCommandandleasedtocompaniesforcommercialusetrackthepositionofminingequipmentagainstamapofamine’stopography[31].Thismapusescolorstodistinguishsoilthatshouldbeexcavated,soilthatshouldremaininplace,andareasthatshouldbefilledin.Theequipmentdriverobservesthisvisualinformation[32]onamonitor[33]whileoperatingtheequipment.SomecoalminingenterpriseshaveusedGPStoincreaseminingefficiencyupto30percent.5.2UndergroundMiningUnderground,ordeep,miningoccurswhencoalisextractedfromaseamwithoutremovaloftheoverlyingstrata.Minersbuildashaftminethatenterstheearththroughaverticalopeninganddescendsfromthesurfacetothecoalseam.Inthemine,thecoalisextractedfromtheseambyvariousmethods,includingconventionalmining[34],continuousmining[35],longwallmining[36],androom-and-pillarmining[37].A.ConventionalMiningConventionalmining,alsocalledcyclicmining,involvesasequenceofoperationsthatproceedinthefollowingorder:a.supportingtheroof[38],b.ventilation[39],c.cutting[40],d.drilling[41],e.blasting[42],f.coalremoval[43],andg.loading[44].First,minersmaketheroofabovetheseamsafeandstablebytimbering[45]orbyroofbolting[46],processesintendedtopreventtherooffromcollapsing[47].Atthesametime,theycreateventilationopeningssothatdangerousgases[48]