热能与动力工程专业毕业设计论文翻译1.docx

热能与动力工程专业毕业设计论文翻译1.docx

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热能与动力工程专业毕业设计论文翻译1

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ACOMPARISONSTUDYOFACFBANDPCFBASHCHARACTERISTICS

K.M.SellakumarandR.Conn

FosterWheelerDevelopmentCorporation,12PeachTreeHillRoad,Livingston,NJ07039,USA

A.Bland

Forpersonaluseonlyinstudyandresearch;notforcommercialuse

WesternResearchInstitute,365N.9thSt,Laramie,WY,82070,USA

Abstract:

Theadventoffluidizedbedcombustiontechnologyhasprovidedavenues

forenvironmentalissues-freeuseofalltypesoffossilfuels.WiththepotentialcommercialapplicationofPressurizedCirculatingFluidizedBedCombustion（PCFB）technologyintheverynearfuture,thereisaneedtounderstandthesimilaritiesanddifferencesinthecharacteristicsofsolidby-productsfromtheconventionalAtmosphericCirculatingFluidizedBedCombustion（ACFB）andthePCFB.Similarto

Forpersonaluseonlyinstudyandresearch;notforcommercialuse

ACFBresidues,themaincomponentsinPCFBresiduesarefrom:

-theinorganicconstituentsinthecoalandincorporatedsediments（Al,Fe,andSi）,

-theinorganicconstituentsinthecoalandincorporatedsediments（Al,Fe,andSi）,

Forpersonaluseonlyinstudyandresearch;notforcommercialuse

And

-sulfurreleasedfromthecoalduringcombustionthatiscapturedbythesorbent.

However,theconcentrationofeachcomponentintheresiduesmayshowgreatvariations,dependingonthefeedsandoperatingconditionsintheunit.Ingeneral,theresiduesdischargedfromPCFBunitswiththesametypesoffeedsandsulfurretentionshouldhavearelativelylowercontentofcalciumbutahighercontentofcoal-derivedconstituentsthanthosefromACFBunits,becausealowersorbentfeedisrequiredforpressurizedsystems.Also,thesorbent-derivedcomponentsintheresiduesfrombothsystemsaredifferentduetothevarioussulfationmechanismsunderatmosphericandpressurizedconditions.

Forpersonaluseonlyinstudyandresearch;notforcommercialuse

AshsamplesfromthecommercialACFBplantsandtheFosterWheeler10MWthPCFBpilotplantinKarhulahavebeenusedinthisstudy.Inthispaper,theashcharacteristicsandwhereonetypeofash-ACFBashorPCFBash–hasbetterapplicationovertheotheraredescribed.

INTRODUCTION

CFBcombustionhasproventobeoneofthemostpromisingtechnologiesforburningawiderangeofcoalsandotherfuelsandhandlingwidevariationsinfuelquality,whilestillachievingstrictairemissionrequirements.Low-gradefuelsthathavelargeashcontentandveryhighsulfurdonotnormallyfindacceptanceinpulverizedcoal（p.c.）units.ThesefuelsareburnedefficientlyinCFBsystems.However,ifthesulfurcontentislarge,thennecessarysorbenthastobeaddedtocaptureSO2insolidform.

Forpersonaluseonlyinstudyandresearch;notforcommercialuse

CFBboilersgeneratetwomajorwastestreams,flyashandbottomash,whichareamixtureoffuelash,unburnedcarbonresidues,andlimeparticlescoatedwithsulfatelayers.Theashpropertiesaresubstantiallydifferentfromthep.c.ashestypicallymarketedasASTMClassCandFflyashes.TheoperatingconditionsforCFBCunits,inadditiontothefuelandsorbentcharacteristics,directlycontributetothechemicalcharacteristicsoftheashes.CFBashesgenerallycontainahighercontentofcalciumasanoxideandasasulfate,butalowercontentofsilicaandaluminathanashesgeneratedfromp.c.boilers.Onenotableexceptionisashesresultingfromthefiringoflowsulfuranthracitesandbituminouscoals;theseby-productsarecomposedprimarilyoffuelashconstituents,sincesorbentdoesnotdominateashchemistry.Consequently,theutilizationoptionsforCFBashesaresomewhatmorediversethanp.c.ash,duetotheeffectofsorbentontheoverallashchemistry.

Pressurizedfluidizedbedcombustion（PFBC）representsoneofthemostpromisingemergingCleanCoalTechnologies（CCT）.CirculatingPFBCtechnologyisbeingdemonstratedatthepilot-scaleatFosterWheelerEnergiaOyinKarhula,Finland.WesternResearchInstitute（WRI）hascompletedathree-yearprojectundersponsorshipoftheElectricPowerResearchInstitute（EPRI）,FosterWheelerEnergyInternational,Inc.,andtheU.S.DepartmentofEnergy（DOE）FederalEnergyTechnologyCenter（FETC）thataddressedashusemarketsandoptionsforPFBCtechnologies.FWsuppliedrepresentativeashsamplesfromtheKarhulaPCFBpilotcombustoroperationforthisstudy.TheoverallobjectivesofthisstudyweretodeterminethemarketpotentialandthetechnicalfeasibilityofusingPFBCashinhigh-volumeuseapplications.

TheEnvironmentalProtectionAgency（EPA）madeafinalrulethateffectiveSeptember2,1993,fourlarge-volumefossilfuelcombustion（FFC）wastestreamsfromelectricutilitypowerplantsareexemptedfromRCRA（ResourceConservationandRecoveryActof1976）SubtitleCforhazardouswasteregulations（FederalRegister1993）.Thewastestreamsincludeflyash,bottomash,boilerslags,andfluegasdesulfurization（FGD）sludge.Nevertheless,thefluidizedbedcombustion（FBC）wastestreamswerenotincludedinthisfinalregulatorydeterminationduetothelackofinformation.Sinceearly1990s,extensivestudieshavebeenconductedontheACFBandPCFBashes（Young,1996;ConnandSellakumar,1997,Conn,Wu,andSellakumar1997;Bland,1998）.

Inthispaper,areviewoftheACFBandPPCFBprocesses,keychangesintheby-productconstituents,andattendantdifferencesinthephysicalandchemicalpropertiesaredescribed.Inaddition,thecurrentandpotentialusesoftheby-productsareoutlined.

ACFBANDPCFBPROCESSES

Influidizedbedcombustors,limestoneisaddedinthebedforsulfurcapture.ProbablesulfurcapturemechanismsintheACFBandPCFBcombustorshavebeensummarizedearlier（Koskinenetal.,1993）.Numerousstudieshaveconfirmedthatatatmosphericconditions,thefirststepinthesulfurcaptureprocessisthecalcinationofCaCO3.

CaCO3（s）→CaO（s）+CO2（g）

（1）

Thecalcinationreactionproceedssignificantlyfasterthanthenextstepthatisthesulfurcapturestep,calledthesulfationreaction.

CaO（s）+SO2（g）+1/2O2（g）→CaSO4（s）

（2）

Underpressurizedfluidizedbedcombustionconditions,thehighpartialpressureofCO2thatexistsbyvirtueofthehighcombustorpressure,preventsthedecompositionofCaCO3.AthighO2partialpressures,thedesulfurizationreactioninpressurizedconditionsisviathe"direct"sulfationofCaCO3.

CaCO3（s）+SO2（g）+1/2O2（g）→CaSO4（s）+CO2（g）（3）

However,inthepresenceofsomecatalystsSO2（g）canbeconvertedtoSO3（g）,andthefollowingreactionisalsopossible（Hajaligoletal.1988）:

CaCO3（s）+SO3（g）®CaSO4（s）+CO2（g）（3a）

ThermaldecompositionofCaSO4innormalpressurizedfluidizedbedcombustionconditionsisnotprobablebecauseoflowtemperaturesandhighpressuresinthereactor.However,accordingtoLygnfeltandLeckner（1989）significantamountsofSO2maybereleasedfromthesorbentinthepressurizedfluidizedbedcombustionifconditionsbecomereducinginthereactor.

Insummary,itcanbeconcludedthatunderPCFBconditions:

-thesulfationofsorbentstakesplacebyadirectreactionbetweenCaCO3andSOx..

-thesulfationrateincreaseswithtemperatureand

-thetotalpressureinthecombustordoesnotlimitthesulfurcapturebythesorbent.

-ThesurfacestructureoftheashparticlesfromthePCFBprocessislikelytobedifferentfromthatoftheashfromtheACFBprocess.

CHARCTERIZATIONOFACFBASH

ChemicalProperties:

KeyoxidesofinterestforashuseintypicalACFBbottomashandflyasharepresentedinTable1.Thechemicalcharacterizationtestingincludedmajorelementcomposition,aswellasphaseanalysis.ThereisageneraldecreaseinCaOandSO3withdecreasingsulfurcontentofthefuelburned.Fuelashcontributessilica,alumina,andcertainamountsofalkalis.TheflyashandthebedashwerealsoanalyzedbyX-raydiffraction（XRD）forphasecomposition.Thedataconfirmtheobservationthattheashesarecomposedprincipallyofanhydrite[CaSO4],lime[CaO],quartz[SiO2],andassociatedoxidesofiron,magnesium,anddehydroxylatedclaysoriginatingfromthefuelashcomponents.

PhysicalProperties:

Thegeneralphysicalpropertiesoftheasheswerealsodetermined,includingpouredandpackedbulkdensities,specificgravity,particlesizedistribution,andmoisture.Theflyashesallwererelativelyfinewithgreaterthan80%passinga200-meshscreen（74mm）.Asaresult,theseashescanreadilybemadeintocement-typepasteswithoutfurthermilling.Thepouredbulkdensityoftheflyashesrangedfromabout540（lowSfuel）to916（highSfuel）kg/m3;thecompactedbulkdensityoftheflyasheswereslightlyhigherandrangedfrom840（lowS）to1167（highS）kg/m3.Thespecificgravityrangedfrom2.2（lowS）to2.7（highS）fortheflyashes.

CHARACTERIZATIONOFPCFBASH

ThestudyofPFBCashuseoptionshasincludedtwodifferentashes:

ashfromthecombustionoflow-sulfurPowderRiverBasinsubbituminouscoal（BlackThunder）withlimestonesorbentandthecombustionofhigh-sulfurIllinoisBasincoalwithalimestonesorbent.（Bland,1998）.

GeneralChemistry:

Withtheexceptionofrelativelyhighmineralcarbon,thechemistryofthePCFBashesistypicalofashesfromACFBoflow-sulfurandhigh-sulfurcoalsusinglimestoneanddolomitesorbents.PhaseanalysesoftheashesbyX-raydiffractionshowthatthePCFBashesarecomposedprincipallyofanhydrite（CaSO4）,calcite（CaCO3）,coalashoxides,anddehydroxylatedclays.Thelackoflime（CaO）inthePFBCashesisdistinctlydifferentfromAFBCashes,whichcontainlargeamountsoflime.Asstatedearlier,inPFBCsystems,thepartialpressureofCO2favorsbothcalcinationandrecarbonization.T