外文翻译煤矿通风系统中瓦斯散发的控制.docx
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外文翻译煤矿通风系统中瓦斯散发的控制.docx
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外文翻译煤矿通风系统中瓦斯散发的控制
英文原文
MitigationofMethaneEmissionsfromCoalMineVentilationAir
PeterCarothersandMilindD.Deo
ABSTRACT
U.S.EPA’scoalbedmethaneoutreachprogram,(CMOP)haspreparedatechnicalassessmentoftechniquesthatcombusttraceamountsofcoalminemethanecontainedinventilationair.Controlofmethaneemissionsfrommineventilationsystemshasbeenanelusivegoalbecauseofthemagnitudeofatypicalairflowandtheverylowmethaneconcentrations.Oneestablishedandcost-effectiveusefeedstheairintoaprimemoverinlieuofambientcombustionair.Thismethodusuallyconsumesjustafractionoftheflowavailablefromeachventilationshaft.Theauthorsevaluatedthetechnicalandeconomicfeasibilityoftwoemergingsystemsthatmayacceptupto100%oftheflowfromanearbyshaft,oxidizethecontainedmethane,andproducemarketableenergy.Bothsystemsuseregenerative,flow-reversalreactors.Onesystemoperatesat1000℃,andtheotherusesacatalysttoreducethecombustiontemperaturebyseveralhundreddegrees.Abovecertainminimummethaneconcentrationsthereactorscanexchangehighqualityheatwithaworkingfluidsuchascompressedairorpressurizedwater.Thispaperdiscussestwoillustrativeenergyprojectswherethereactorsproduceenergyrevenueandgreenhousegascreditsandyieldanattractivereturnoninvestedcapital.
KEYWORDS:
Coal,Methane,Mining,Ventilation,Combustion,Regenerative,andGreenhouseGas.
INTRODUCTION
ThispaperpresentsasummaryofadraftU.S.EnvironmentalProtectionAgency(U.S.EPA)report.Itisatechnicalassessmentofexistingandemergingprocessescapableofremovingtraceamountsofmethanecontainedinventilationairstreamsatgassyundergroundcoalmines.
Coaledmethane(CBM)ismethanethatisformedduringthecoalificationprocessandthatresideswithinthecoalseamandadjacentrockstrata.Coalminingactivityreleasesmethanethathasnotbeencapturedwithdrainagesystems.Themethanethenpassesintomineworkingsandontotheatmosphere.Gassyundergroundminesreleasesignificantquantitiesofsuchmethane,whichisreferredtoascoalminemethane(CMM).Whenallowedtoaccumulateinmineworking,CMMpresentsasubstantialdangeroffireandexplosion.Toassureminersafetyandmaintaincontinuousproduction,operatorsofgassyminesmustdegasifytheirmines.
Themostuniversallyusedmethodofdegasificationisdilutionbyventilation.Ventilationsystemsconsistofinletandexhaustshaftsandpowerfulfansthatmovelargevolumesofairthroughthemineworkingstomaintainasafeworkingenvironment.Exhaustedventilationaircontainsaverydilutedamountofmethane;typicalconcentrationsrangebetween0.2to0.8%methane,wellbelowtheexplosionlimits.Todate(withveryfewexceptions)ventilationsystemsreleasetheair-methanemixturetotheatmosphere,thusemittingorliberatingthemethanewithoutattemptingtocaptureanduseit.Operatorsmaysupplementventilationwithanotherformofdegasification,methanedrainagetechnology,whichforciblyextractsmethanefromcoalstratainadvanceof,orafter,mining.
Someoperatorstoemployavarietyofprovenmethods,captureandusedrainedCMMbutthemajorityofdrainedventilationair.MethaneemissionsfromventilationaircomprisethelargestportionofallCMMliberationworldwide,andtheyarethemostdifficulttocontrol.Thispaperexaminesthecurrentandfuturepossibilitiesfordestroyingandpotentiallyusingventilationairmethane.
GlobalImportanceofVentilationAirEmissions
Methaneisapotentgreenhousegas,approximately21timesmoreeffectiveperunitofweightthancarbondioxideintermsofcausingglobalwarmingovera100-yeartimeframe.Coalminemethaneemissionsaccountforapproximately10%ofanthropogenicmethaneemissionsworldwide,andtheyarethefourthlargestsourceofmethanereleaseintheUS.Byfarthelargestportionofthismethaneleavestheminesthroughtheventilationsystem.Therefore,themostlogicalanddirectwaytoreduceCMMemissionswouldbetofindmethodstocapture,process,andusemethanethatexitstheventilationshaft.Thispaperassessestechnologiesthatcanbeexpectedtohandletheentireventilationstreamfromasingleshaft.AtypicalshaftatagassymineintheU.S.willmovebetween100to250cubic-metersofairpersecond(m3/s)orapproximately212,000to530,000cubicfeetperminute(cfm).Illustrationsinthispaperassumeaunitcapacityof100m3/s,apracticalmodularsizethatminescouldusesinglyorinmultiples.A100m3/sventilationflowcontaining0.5%methanewillemit43,200mofmethaneperdayorabout1.525mmcfd.
BarrierstoCurrentRecoveryandUse
Ventilationairflowsareverylarge,andthecontainedmethaneissodilutedthatconventionalcombustionprocessescannotoxidizeitwithoutsupplementalfuel.Ventilationairscharacteristicsmakeitextremelydifficulttohandleandprocessandconstitutetechnicalbarrierstoitsrecoveryanduse.
CostlyAirHandlingSystems
Typicalventilationairflowsaresoenormousthataprocessingsystemwillhavetobeverylargeandexpensive.Eachprocessingsystemwillhavetoincludeafantoneutralizeanypressuredropcausedbythereactorandavoidhavingtheminesfacecostlyincreasesinelectricpower.
Lowmethaneconcentrations.
Amethane-in-airmixtureisexplosiveinaconcentrationrangebetweenabout4.5and15%.below4.5%methanewillnotigniteorsustaincombustionunlessitcanremaininanenvironmentwheretemperaturesexceed1,000.therefore,anyconventionalmethodproposedtouseventilationairasafuel,oreventodestroyit,wouldrequireanendothermicreaction.
Variableflowsandchanginglocations
Mineoperatorswillfacetheflowvariationstypicallyexhibitedbyaventilationsystem.Asmineoperationsprogressundergroundtheworkingfacetendstomoveawayfromtheoriginalventilationshaft.Aprocessingsystembuilttoacceptagivenflowwillexperienceshort-termperiodicfluctuationsandaprobabledeclineovertimeasother,moredistantexhaustshaftstakeover.
IDENTIFICATIONOFAPPLICABLETECHNOLOGIES
Thetechnologiesavailabletomitigateventilationairemissionsdivideintotwobasiccategories:
ancillaryusesandprincipaluses.
Ancillaryuses
Thefocusofprojectsinthiscategoryisonaprimaryfuelthatisnotventilationair;thusemploymentofventilationairisancillaryandrestrictedtoamountsthatareconvenientfortheproject.Forexample,apowerplantofotherprimemovermayuseventilationair(insteadofambientair)ascombustionair.Projectsofthistypenormallyuseonlyafractionoftheventilationair.Thetechniquerequiresamodestairhandlingandtransportsystemthatservestobringventilationairfromtheshaftexittotheprimemoversairintake.TheAppinandtowerprojectsownedbyBHPsteelcollieriesdivisioninAustraliaprovideanoutstandingexampleofancillaryuse.Twofacilitiestotaling40and54MWeachproduceelectricpowerwithaseriesofone-megawattcaterpillarinternalcombustionenginegenerators.Gobgasdrainedfromthetwominesistheprimaryfuel,butitissupplementedwithmethane(averagingabout0.7%)containedinthemineventilationairthatisusedaseachunit’scombustionairinplaceofambientair.Thisstrategyincreasesthequantityoffuelavailabletotheprojectbyabout10%andconsumesupto20%ofventilationemissions.SincetheprojectmustrelyonnaturalgastosupplementitsprimaryfuelduringperiodsoflowCMMavailability,themethanefromventilationairrepresentsasignificantcostsavings.WhileBHPhasnotidentifiedseparatecapitalandoperatingexpendituresfortheairsubstitutionpartoftheproject,acaterpillarspokesmanstatedthattheseweremodest.Theyconsistedofductinginstalledfromjustabovetheventilationfantoeachengine’sairintake,theairfiltrationsystem,andsomeadditionalprogrammingatthecontrolcenters.Therearenoadditionalfansintheductworkbecausetheenginesgenerateenoughsuctionpowertomoveventilationairtotheirintakesystems.Onecanconcludefromtheforegoingthattheventilationairsubstitutionsystemisasimple,practical,andprofitabletechniqueforCMMusethatcouldbereplicatedatmanygassyminesettingswhereelectricgenerationusinggobgasmaybeviable.
Combustionturbines,orgasturbines,mayalsouseventilationairascombustionair.Sinceitcontainsuseablefuel,theoperatorcancutbackonthequantityofprimaryfuel.SolarTurbines,adivisionofCaterpillerInc.,hasinvestigatedthisstrategyforusewithsmall(e.g.,3to8MW)turbineslocatednearmineventilationshafts.Althoughthecompanyhasnofieldexperiencewiththeapplications,albeitwithinverystrictmethaneconcentrationlimitsthattheyimposetoguaranteethesafeoperationoftheequipment.
Principaluses
Technologiesinthiscategorywoulduseventilationairastheprimaryfuelandattempttoconsumeupto100%ofthe,ethaneemittingfro,asingleexhaustshaft.Asdiscussedbelow,thesesystems,ayalsoemploymoreconcentratedfuelssuchasgobgastoenhancetheutilityorprofitabilityofagivenproject.Theauthorsidentifiedtwoprocesses:
athermaloxidationprocesscalledtheVOCSIDIZER,andacatalyticoxidationprocesscalledtheCatalyticFlow-ReversalReactor(CFRR).Adescriptionofeachsystemfollows:
CFRR
In1995researchersatERDL/NaturalResourcesCanadainVarennes,Quebec(alsoknownasCANMETandNRCan)conceivedofanddevelopedtheCatalyticFlow-ReversalReactorexpresslyforuseoncoalmineventilationair.TheresearchteamwasawareofandwishedtoimproveupontheTFRRtoprocessmineventilationairatlowertemperatures,CANMETselec
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