外文翻译天然气.docx

外文翻译天然气.docx

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外文翻译天然气

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英文原文

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Naturalgas

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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]

Theworld'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