外文翻译天然气Word格式文档下载.docx
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外文翻译天然气Word格式文档下载.docx
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Forotheruses,seeNaturalgas(disambiguation).
Naturalgasisanaturallyoccurringhydrocarbongasmixtureconsistingprimarilyofmethane,withupto20percent[1]concentrationofotherhydrocarbons(usuallyethane)aswellassmallamountsofimpuritiessuchascarbondioxide.Naturalgasiswidelyusedandisanimportantenergysourceinmanyapplicationsincludingheatingbuildings,generatingelectricity,providingheatandpowertoindustryandvehiclesandisalsoafeedstockinthemanufactureofproductssuchasfertilizers.
Naturalgasisfoundindeepundergroundnaturalrockformationsorassociatedwithotherhydrocarbonreservoirs,incoalbeds,andasmethaneclathrates.Mostnaturalgaswascreatedovertimebytwomechanisms:
biogenicandthermogenic.Biogenicgasiscreatedbymethanogenicorganismsinmarshes,bogs,landfills,andshallowsediments.Deeperintheearth,atgreatertemperatureandpressure,thermogenicgasiscreatedfromburiedorganicmaterial.[2]
Beforenaturalgascanbeusedasafuel,itmustundergoprocessingtocleanthegasandremoveimpuritiesincludingwaterinordertomeetthespecificationsofmarketablenaturalgas.Theby-productsofprocessingincludeethane,propane,butanes,pentanes,andhighermolecularweighthydrocarbons,hydrogensulphide(whichmaybeconvertedintopuresulfur),carbondioxide,watervapor,andsometimesheliumandnitrogen.
Inthe19thcentury,naturalgaswasusuallyobtainedasabyproductofproducingoil,sincethesmall,lightgascarbonchainscameoutofsolutionastheextractedfluidsunderwentpressurereductionfromthereservoirtothesurface,similartouncappingabottleofsodapopwherethecarbondioxideeffervesces.Unwantednaturalgaswasadisposalproblemintheactiveoilfields.Iftherewasnotamarketfornaturalgasnearthewellheaditwasvirtuallyvaluelesssinceithadtobepipedtotheenduser.Inthe19thcenturyandearly20thcentury,suchunwantedgaswasusuallyburnedoffintheoilfields.Today,unwantedgas(orstrandedgaswithoutamarket)associatedwithoilextractionoftenisreturnedtothereservoirwith'
injection'
wellswhileawaitingapossiblefuturemarketortorepressurizetheformation,whichcanenhanceextractionratesfromotherwells.Inregionswithahighnaturalgasdemand(suchastheUS),pipelinesareconstructedwheneconomicallyfeasibletomovethegasfromthewellsitetotheendconsumer.
Anotherpossibilityistoexportthenaturalgasasaliquid.Gas-to-liquids(GTL)isadevelopingtechnologythatconvertsstrandednaturalgasintosyntheticgasoline,diesel,orjetfuelthroughtheFischer-TropschprocessdevelopedduringWorldWarIIbyGermany.Suchfuelcanbetransportedtousersthroughconventionalpipelinesandtankers.ProponentsclaimGTLburnscleanerthancomparablepetroleumfuels.MostmajorinternationaloilcompaniesareinanadvancedstageofGTLproduction,withaworld-scale(140,000barrels(22,000m3)aday)GTLplantinQatarscheduledtobeinproductionbefore2010.[datedinfo]
Naturalgascanbe"
associated"
(foundinoilfields)or"
non-associated"
(isolatedinnaturalgasfields),andisalsofoundincoalbeds(ascoalbedmethane).Itsometimescontainssignificantamountsofethane,propane,butane,andpentane—heavierhydrocarbonsremovedforcommercialusepriortothemethanebeingsoldasaconsumerfuelorchemicalplantfeedstock.Non-hydrocarbonssuchascarbondioxide,nitrogen,helium(rarely),andhydrogensulfidemustalsoberemovedbeforethenaturalgascanbetransported
.[3]
Naturalgasiscommerciallyextractedfromoilfieldsandnaturalgasfields.Gasextractedfromoilwellsiscalledcasingheadgasorassociatedgas.Thenaturalgasindustryisextractinggasfromincreasinglymorechallengingresourcetypes:
sourgas,tightgas,shalegas,andcoalbedmethane.
Theworld'
slargestprovengasreservesarelocatedinRussia,with4.757×
1013m³
(1.68×
1015cubicfeet).WiththeGazpromcompany,Russiaisfrequentlytheworld'
slargestnaturalgasextractor.Majorprovenresources(inbillioncubicmeters)areworld175,400(2006),Russia47,570(2006),Iran26,370(2006),Qatar25,790(2007),SaudiArabia6,568(2006)andUnitedArabEmirates5,823(2006).
Itisestimatedthatthereareabout900trillioncubicmetersof"
unconventional"
gassuchasshalegas,ofwhich180trillionmayberecoverable.[4]Inturn,manystudiesfromMIT,Black&
VeatchandtheDOE--seenaturalgas--willaccountforalargerportionofelectricitygenerationandheatinthefuture.[5]
slargestgasfieldisQatar'
soffshoreNorthField,estimatedtohave25trillioncubicmeters[6](9.0×
1014cubicfeet)ofgasinplace—enoughtolastmorethan420years[citationneeded]atoptimumextractionlevels.ThesecondlargestnaturalgasfieldistheSouthParsGasFieldinIranianwatersinthePersianGulf.LocatednexttoQatar'
sNorthField,ithasanestimatedreserveof8to14trillioncubicmeters[7](2.8×
1014to5.0×
1014cubicfeet)ofgas.
Becausenaturalgasisnotapureproduct,asthereservoirpressuredropswhennon-associatedgasisextractedfromafieldundersupercritical(pressure/temperature)conditions,thehighermolecularweightcomponentsmaypartiallycondenseuponisothermicdepressurizing—aneffectcalledretrogradecondensation.Theliquidthusformedmaygettrappedastheporesofthegasreservoirgetdeposited.Onemethodtodealwiththisproblemistore-injectdriedgasfreeofcondensatetomaintaintheundergroundpressureandtoallowre-evaporationandextractionofcondensates.Morefrequently,theliquidcondensesatthesurface,andoneofthetasksofthegasplanttocollectthiscondensate.Theresultingliquidiscallednaturalgasliquid(NGL)andhascommercialvalue.
Towngas
Towngas,asyntheticallyproducedmixtureofmethaneandothergases,mainlythehighlytoxiccarbonmonoxide,isusedinasimilarwaytonaturalgasandcanbeproducedbytreatingcoalchemically.Thisisahistoricaltechnology,notusuallyeconomicallycompetitivewithothersourcesoffuelgastoday.Buttherearestillsomespecificcaseswhereitisthebestoptionanditmaybesointothefuture.
Mosttown"
gashouses"
locatedintheeasternUSinthelate19thandearly20thcenturiesweresimpleby-productcokeovenswhichheatedbituminouscoalinair-tightchambers.Thegasdrivenofffromthecoalwascollectedanddistributedthroughnetworksofpipestoresidencesandotherbuildingswhereitwasusedforcookingandlighting.(Gasheatingdidnotcomeintowidespreaduseuntilthelasthalfofthe20thcentury.)Thecoaltar(orasphalt)thatcollectedinthebottomsofthegashouseovenswasoftenusedforroofingandotherwater-proofingpurposes,andwhenmixedwithsandandgravelwasusedforpavingstreets.
Biogas
Mainarticle:
biogas
Whenmethane-richgasesareproducedbytheanaerobicdecayofnon-fossilorganicmatter(biomass),thesearereferredtoasbiogas(ornaturalbiogas).Sourcesofbiogasincludeswamps,marshes,andlandfills(seelandfillgas),aswellassewagesludgeandmanure[8]bywayofanaerobicdigesters,inadditiontoentericfermentation,particularlyincattle.
Methanogenicarchaeaareresponsibleforallbiologicalsourcesofmethane,someinsymbioticrelationshipswithotherlifeforms,includingtermites,ruminants,andcultivatedcrops.Methanereleaseddirectlyintotheatmospherewouldbeconsideredapollutant.However,methaneintheatmosphereisoxidized,producingcarbondioxideandwater.Methaneintheatmospherehasahalflifeofsevenyears,meaningthatifatonneofmethanewereemittedtoday,500kilogramswouldhavebrokendowntocarbondioxideandwateraftersevenyears.
Othersourcesofmethane,theprincipalcomponentofnaturalgas,includelandfillgas,biogas,andmethanehydrate.Biogas,andespeciallylandfillgas,arealreadyusedinsomeareas,buttheirusecouldbegreatlyexpanded.Landfillgasisatypeofbiogas,butbiogasusuallyreferstogasproducedfromorganicmaterialthathasnotbeenmixedwithotherwaste.
Landfillgasiscreatedfromthedecompositionofwasteinlandfills.Ifthegasisnotremoved,thepressuremaygetsohighthatitworksitswaytothesurface,causingdamagetothelandfillstructure,unpleasantodor,vegetationdie-off,andanexplosionhazard.Thegascanbeventedtotheatmosphere,flaredorburnedtoproduceelectricityorheat.ExperimentalsystemswerebeingproposedforuseinpartsofHertfordshire,UK,andLyoninFrance.
Oncewatervaporisremoved,abouthalfoflandfillgasismethane.Almostalloftherestiscarbondioxide,buttherearealsosmallamountsofnitrogen,oxygen,andhydrogen.Thereareusuallytraceamountsofhydrogensulfideandsiloxanes,buttheirconcentrationvarieswidely.Landfillgascannotbedistributedthroughutilitynaturalgaspipelinesunlessitiscleaneduptolessthan3%CO2,andafewpartspermillionH2S,becauseCO2andH2Scorrodethepipelines.[9]Itisusuallymoreeconomicaltocombustthegasonsiteorwithinashortdistanceofthelandfillusingadedicatedpipeline.Watervaporisoftenremoved,evenifthegasiscombustedonsite.Iflowtemperaturescondensewateroutofthegas,siloxanescanbeloweredaswellbecausetheytendtocondenseoutwiththewatervapor.Othernon-methanecomponentsmayalsoberemovedinordertomeetemissionstandards,topreventfoulingoftheequipmentorforenvironmentalconsiderations.Co-firinglandfillgaswithnaturalgasimprovescombustion,whichlowersemissions.
Gasgeneratedinsewagetreatmentplantsiscommonlyusedtogenerateel
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