生物质发电中英文对照外文翻译文献Word下载.docx

生物质发电中英文对照外文翻译文献Word下载.docx

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原文：

Biomassco-firingoptionsontheemissionreductionandelectricitygenerationcostsincoal-firedpowerplants

Abstract

Co-firingoffersanear-termsolutionforreducingCO2emissionsfromconventionalfossilfuelpowerplants.Viablealternativestolong-termCO2reductiontechnologiessuchasCO2sequestration,oxy-firingandcarbonloopcombustionarebeingdiscussed,butallofthemremainintheearlytomidstagesofdevelopment.Co-firing,ontheotherhand,isawell-proventechnologyandisinregularusethoughdoesnoteliminateCO2emissionsentirely.AnincrementalgaininCO2reductioncanbeachievedbyimmediateimplementationofbiomassco-firinginnearlyallcoal-firedpowerplantswithminimummodificationsandmoderateinvestment,makingco-firinganear-termsolutionforthegreenhousegasemissionproblem.Ifamajorityofcoal-firedboilersoperatingaroundtheworldadoptco-firingsystems,thetotalreductioninCO2emissionswouldbesubstantial.Itisthemostefficientmeansofpowergenerationfrombiomass,anditthusoffersCO2avoidancecostlowerthanthatforCO2sequestrationfromexistingpowerplants.Thepresentanalysisexaminesseveralco-firingoptionsincludinganoveloptionexternal（indirect）firingusingcombustionorgasificationinanexistingcoaloroilfiredplant.Capitalandoperatingcostsofsuchexternalunitsarecalculatedtodeterminethereturnoninvestment.Twooftheseindirectco-firingoptionsareanalyzedalongwiththeoptionofdirectco-firingofbiomassinpulverizingmillstocomparetheiroperationalmeritsandcostadvantageswiththegasificationoption.

1.Introduction

Theevidenceoftheeffectsofanthropogenicemissiononglobalclimateisoverwhelming[1].Thethreatofincreasingglobaltemperatureshassubjectedtheuseoffossilfuelstoincreasingscrutinyintermsofgreenhousegas（GHG）andpollutantemissions.Theissueofglobalwarmingneedstobeaddressedonanurgentbasistoavoidcatastrophicconsequencesforhumanityasawhole.

SocolowandPacala[2]introducedthewedgeconceptofreducingCO2emissionsthroughseveralinitiativesinvolvingexistingtechnologies,insteadofasinglefuturetechnologyoractionthatmaytakelongertodevelopandstrongerwillpowertoimplement.Awedgerepresentsacarbon-cuttingstrategythathasthepotentialtogrowfromzerotodaytoavoiding1billiontonsofcarbonemissionsperyearby2055.Ithasbeenestimated[3]thatatleast15strategiesarecurrentlyavailablethat,withscalingup,couldrepresentawedgeofemissionsreduction.

Althoughanumberofemissionreductionoptionsareavailabletotheindustry,manyofthemstillfacefinancialpenaltiesforimmediateimplementation.Somemeasuresareverysite/locationspecificwhileothersarestillinanearlystageofdevelopment.CarbondioxidesequestrationorzeroemissionpowerplantsrepresentthefutureofaCO2emissions-freepowersector,buttheywilltakeyearstocometothemainstreammarket.ThecostofCO2captureandsequestrationisintherangeof40e60US$/tonofCO2,dependingonthetypeofplantandwheretheCO2isstored[4,5].Thisisasignificanteconomicburdenontheindustry,andcouldpotentiallyescalatethecostofelectricityproducedbyasmuchas60%.

Canadahasvastamountsofbiomassinitsmillionsofhectaresofmanagedforests,mostofwhichremainuntappedforenergypurposes.Currently,largequantitiesoftheresiduesfromthewoodproductsindustryaresenttolandfillorareincinerated[6].Intheagriculturalsector,graincropsproduceanestimated32milliontonsofstrawresidueperyear.Allowingforastrawresidueof85%remaininginthefieldstomaintainsoilfertility,5milliontonswouldstillbeavailableforenergyuse.Duetoanincreaseinlandproductivity,significantareasoflandinCanada,whichwereearlierfarmed,arenolongerfarmed.Theselandscouldbeplantedwithfast-growingenergycrops,likeswitch-grassofferingpotentiallylargequantitiesofbiomassforenergyproduction[6].

LivingbiomassplantsabsorbCO2fromtheatmosphere.So,itscombustion/gasificationforenergyproductionisconsideredcarbonneutral.Thusifacertainamountofbiomassisfiredinanexistingfossil（coal,cokeoroil）fuelfiredplantgeneratingsomeenergy,theplantcouldreducefiringthecorrespondingamountoffossilfuelinit.Thus,apowerplantwithintegratedbiomassco-firinghasalowernetCO2contributionoverconventionalcoal-firedplants.

Biomassco-firingisonetechnologythatcanbeimplementedimmediatelyinnearlyallcoal-firedpowerplantsinarelativelyshortperiodoftimeandwithouttheneedforhugeinvestments.Ithasthusevolvedtobeanear-termalternativetoreducingtheenvironmentalimpactofelectricitygenerationfromcoal.Biomassco-firingofferstheleastcostamongtheseveraltechnologies/optionsavailableforgreenhousegasreduction[7].Principally,co-firingoperationsarenotimplementedtosaveenergybuttoreducecost,andgreenhousegasemissions（insomecases）.Inatypicalco-firingplant,theboilerenergyusagewillbethesameasitisoperatedatthesamesteamloadconditions（forheatingorpowergeneration）,withthesameheatinputasthatintheexistingcoal-firedplant.Theprimarysavingsfromco-firingresultfromreducedfuelcostswhenthecostofbiomassfuelislowerthanthatoffossilfuel,andavoidinglandfilltippingfeesorothercoststhatwouldotherwiseberequiredtodisposeofunwantedbiomass.Biomassfuelatprices20%ormorebelowthecoalpriceswouldusuallyprovidethecostsavingsneeded[8].

2.Co-firingoptions

Biomassco-firinghasbeensuccessfullydemonstratedinover150installationsworldwideforacombinationoffuelsandboilertypes[9].Theco-firingtechnologiesemployedintheseunitsmaybebroadlyclassifiedunderthreetypes:

i.Directco-firing,

ii.indirectco-firing,and

iii.gasificationco-firing.

Inallthreeoptions,theuseofbiomassdisplacesanequivalentamountofcoal（onanenergybasis）,andhenceresultsinthedirectreductionofCO2andNOxemissionstotheatmosphere.Theselectionoftheappropriateco-firingoptiondependsonanumberoffuelandsitespecificfactors.Theobjectiveofthisanalysisistodetermineandcomparetheeconomicsofthedifferentco-firingoptions.Briefdescriptionsofthethreeco-firingoptionsarepresentedhere.

2.1.Directco-firing

Directco-firinginvolvesfeedingbiomassintocoalgoingintothemills,thatpulverizethebiomassalongwithcoalinthesamemill.Sometimeseparatemillsmaybeusedorbiomassisinjecteddirectlyintotheboilerfurnacethroughthecoalburners,orinaseparatesystem.Thelevelofintegrationintotheexistingplantdependsprincipallyonthebiomassfuelcharacteristics.

Fourdifferentoptionsareavailabletoincorporatebiomasscofiringinpulverizedcoalpowerplants[10].Inthefirstoption,thepre-processedbiomassismixedwithcoalupstreamoftheexistingcoalfeeders.Thefuelmixtureisfedintotheexistingcoalmillsthatpulverizecoalandbiomasstogether,anddistributeitacrosstheexistingcoalburners,basedontherequiredco-firingrate.Thisisthesimplestoption,involvingthelowestleastcapitalcosts,buthasahighestriskofinterferencewiththecoalfiringcapabilityoftheboilerunit.Alkaliorotheragglomeration/corrosion-causingagentsinthebiomasscanbuild-uponheatingsurfacesoftheboilerreducingoutputandoperationaltime[11].Furthermore,differentcombustioncharacteristicsofcoalandbiomassmayaffectthestabilityandheattransfercharacteristicsoftheflame[12].Thus,thisdirectco-firingoptionisapplicabletoalimitedrangeofbiomasstypesandatverylowbiomass-to-coalco-firingratios.

Thesecondoptioninvolvesseparatehandling,metering,andpulverizationofthebiomass,butinjectionofthepulverizedbiomassintotheexistingpulverizedfuelpipe-workupstreamoftheburnersorattheburners.Thisoptionrequiresonlymodificationsexternaltotheboiler.Onedisadvantagewouldbetherequirementofadditionalequipmentaroundtheboiler,whichmayalreadybecongested.Itmayalsobedifficulttocontrolandtomaintaintheburneroperatingcharacteristicsoverthenormalboilerloadcurve.

Thethirdoptioninvolvestheseparatehandlingandpulverization

ofthebiomassfuelwithcombustionthroughanumberofburnerslocatedinthelowerfurnace,dedicatedtotheburningofthebiomassalone.Thisdemandsahighestcapitalcost,butinvolvestheleastrisktonormalboileroperationastheburnersarespecificallydesignedforbiomassburningandwouldnotinterferewiththecoalburners.

ThefinaloptioninvolvestheuseofbiomassasareburnfuelforNOxemissioncontrol.Thisoptioninvolvesseparatebiomasshandlingandpulverization,withinstallationofseparatebiomassfiredburnersattheexitofthefurnace.Aswiththepreviousoption,thecapitalcostishigh,butrisktoboileroperationisminimal.

2.2.Indirectorexternalco-firing

Indirectco-firinginvolvestheinstallationofacompletelyseparatebiomassboilertoproducelow-gradesteamforutilizationinthecoal-firedpowerplantpriortobeingupgraded,resultinginhigherconversionefficiencies.AnexampleofthisoptionistheAvedoreUnit2projectinCopenhagen,Denmark.InCanada,GreenfieldResearchInc.hasdevelopedasimilarCFBboilerdesignthatutilizesanumberofunitsoftheexistingpowerplantsystemslikeIDfanetc.toreducethecapitalcost.Inthissystem,asubcompactcirculatingfluidizedbedboilerisdesignedspecificallytohaveapiggy-backrideonanexistingpowerplantboiler.Sin