外文翻译循环流化床锅炉中燃烧煤泥炭或木材时灰特性.docx
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外文翻译循环流化床锅炉中燃烧煤泥炭或木材时灰特性.docx
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外文翻译循环流化床锅炉中燃烧煤泥炭或木材时灰特性
英文原文
AshbehaviourinaCFBboilerduring
combustionofcoal,peatorwood
Bengt-JohanSkrifvarsa,RainerBackmana,MikkoHupaa,
GeorgeSfirisb,TomasAbyhammarbandAndersLyngfeltC
AboAkademiUniversity,Turku,Finland
VattenfallAB,Stockholm,Sweden
ChalmersUniversityofTechnology,Gothenburg,Sweden
(Received19November1996;revised16June1997
Abstract
Thispaperpresentsselectedresultsfromanextensiveon-sitemeasurementcampaignwheretheashbehaviorsina12MWCFBboilerwasstudiedduringfiringofcoal,peatandwood.Samplesweretakenfromallin-going(bedmaterial,fuel)andout-goingsolidmaterialstreams(secondarycycloneandbagfilter)aswellasfromthebedandthereturnleg.Depositsampleswerefurthercollectedfromthecycloneinletandfromtwodifferentlocationsintheconvectivepath.Inaddition,theboileroperationwasmonitored,includingcollectionofoperationaldata,fluegastemperatureprofilesandemissions.Thepaperdiscussesthedifferencesintheashchemistrythatweredetectedbetweenthethreedifferentcombustioncasesanddrawsconclusionsontheimpactofthechemistryonthebedagglomerationandfoulingtendencyforeachfuel.
(Keywords:
ashbehaviors;CFBcombustion;depositformation).
INTRODUCTION
Circulatingfluidizedbedcombustionisoccasionallyconnectedwithfuelmineralmatterrelatedproblems.Thereleasedfuelmineralmatter,theash,maycausebothbedagglomerationinthefurnaceoftheboileraswellasdepositsinotherlocations.Theheatexchangersurfaces,thecycloneandthereturnlegaretypicallysensitiveareaswheredepositsmaycauseextensiveoperationalproblems.Inadditiontophysicalparameterssuchasfluidizationcharacteristicsandmixing,theashchemistryplaysanimportantroleintheashbehaviour.Thispaperpresentsresultsfromanextensiveon-sitemeasurementcampaignwheretheashbehaviourina12MWCFBboilerwasstudiedduringthefiringofcoal,peatandwood.Focusisontheimpactofashchemistryonslagging,foulingandbedagglomeration.
EXPERIMENTAL
Theboilerinwhichthemeasurementswereconducted,isasemi-fullscaleCFB,thatproduceshotwaterforlocaldistrictheating.Theboilerisalsoaverysuitableresearchfacilityandhaspreviouslybeensuccessfullyusedwhenaddressing,forexample,emissionquestionsfromCFB.TheCFBboilerisequippedwithanumberofoperationalcontrol1systems,suchasanadvancedairdistributionandpossibilitiesforfluegasrecirculation,bedparticlecooler,primaryairpreheaterandflyashrecirculationpossibilities.Thisenablesawiderangeofoperatingoptionstobetestedundercontrolledconditionsinawideloadrange(3-12MW).Theunitisalsoequippedwithanalyticalinstrumentationforcontinuousmonitoringandrecordingoftheoperation.Numerousinstrumenttappingsenablemeasurementsinmanylocationsintheboiler.AschematicviewoftheboilerispresentedinFigureI.
Duringthecombustiontests,samplesfromallin-going(bedmaterial,fuel)andout-goingsolidmaterialstreams(secondarycycloneandbagfilter)aswellasfromthebedandthereturnlegwerecollectedtwiceadayandanalysedquantitativelyfortheelementsSi,Al,Fe,Ca,Mg,P,Na,K,ClandSbywetchemicalanalyses.Depositsampleswerecollectedatthecycloneinlet(TFG=850°C)andfromonelocationintheconvectivepath(TN=680°C)withasamplingtimevaryingfrom15minto21h.ThesamplinglocationsareindicatedinFigureIasLot.1and2.Thesamplingwascarriedoutusingspeciallydesignedsurfacetemperaturecontrolleddepositprobes.TheprobeswerealsoequippedwitharemovableringforlaterSEM/EDAXanalyses.Theprobesurfacetemperatureinthetestswassetat450°Ctosimulateasuperheatertube.Alltheprobesampleswerephotographedandthecollecteddepositiswerecharacterizedwithrespecttotheircollecteddeposits.Selectedsamplesfrombothfront(windward)sideandback(leeward)sideofthesamplingprobeswereanalysedquantitativelyfortheelementsSi,Al,Fe,Ca,Mg,P,Na,K,ClandS.
Inaddition,theboileroperationwasmonitored.Thisincludedcollectionofoperationaldata(fuelandsorbentfeed,airdistributionandtotalair),fluegastemperatureprofilesandemissions(CO,CO2,SO2,NO,andN2O).ThedatarelevantforslaggingandfoulingevaluationsaresummarizedinTableI.
RESULTS
Fuelanalyses
ThefuelanalysesaresummarizedinTable2.Theashcontentinthewoodwasapproximately0.8wt%.Thecorrespondingvalueswere4.5wt%forpeatand11.9wt%forcoal.Thesulphurcontentinthewoodwaslow,0.03wt%.Thecorrespondingvalueforpeatwas0.41wt%.Thefiredcoalwasahighsulphurcoalwith1.9wt%sulphur.Thechlorinecontentinwoodisgenerallylow,typically0.01-0.05wt%.Atypicalvalueforcoalsofthekindthatwasusedinthesetestsis0.1-0.5wt%.Inpeatthechlorinewasanalysedtobe0.04wt%.
Themainashelementinwoodwascalcium(23.2wt%inash)followedbypotassium(12.8wt%inash)andmagnesium(3.5wt%inash).Inpeatthemainelementwassilicon(16.6wt%inash)followedbycalcium(11.8wt%inash)andaluminium(7.9wt%inash).Thebedmaterialusedduringthecombustionofwoodandpeatwasaquartzsandwithaparticlesizeofapproximately350mm.DuringthecoalcombustiontestscalciumcarbonatewasaddedtothebedintheCa:
S-ratioof2.7.
Figure1AschematicviewoftheCFBboilerinwhichthecombustiontestswerepreformed.Samplinglocationsareindicatedinthefigure.
Table1AsummaryoftherunningconditionsintheCFBduringthecombustiontests
Table2Fuelandashanalysesofthecoal,peatandwood,usedduringthecombustiontests.
Ashanddepositanalyses
Noheavyslaggingorfoulingwasexperiencedduringthetests.Generallythedepositswerethin,0.l-1mm.Thethickestdepositswereroughly3mminthicknessafterasamplingtimeof12h.Thesedepositswerecollectedfromsamplinglocation2duringthewoodcombustiontests.Thecoalandpeatfiringcausedhardlyanydepositsinthesamplelocationsoftheboiler.
Figure2summarizesthechemicalanalysesfortheashesanddeposits.Inthisfiguretheanalysedelementsarerecalculatedtotheircorrespondingoxides.Nobaghousesamplescouldbecollectedduringthewoodcombustion
testssincetheamountoftheashreachingthebaghousewastoolow.Neithercouldanyquantitativewetchemicalanalysesbeperformedonthedepositsamplescollectedatthecycloneinlet,orduringthecoalandpeatcombustiontests,onthefrontsidedepositintheconvectivepartofthefluegaschannel,becauseofthesmallamountofsample.Sometrendscanbeextractedfromthefigurethatareinterestingfromtheashbehaviourpointofview.
Onetrendisthedecreasingshareofsiliconandtheincreasingproportionofashelementsinthesamplescollectedfromthewoodandpeatcombustiontestsfromthebedmaterialandprimarycycloneashtothesecondarycycloneandbaghouseashes.Thereasonforthistrendisthatthelargersizedquartzbedmaterialisseparatedattheprimarycycloneandremainswithintheinternalloop,furnace-primarycyclone,whilesmallersizedparticles,suchascondensedashparticles,smallfragmentsofthebedandallgasesworktheirwayouttotheconvectivepartofthefluegaschannel.Forthesamplescollectedfromthecoalfiringteststheproportionofthesulphurabsorbentcalciumisclearlyseeninthebedandprimarycyclonesamples.Todistinguishbetweenelementsoriginatingfromthebedandfromthefuelinthesecondarycycloneandbaghouse
samplesis,however,verydifficult,sincebothcontainedcalciumandsilicon.
Asecondtrendisthedecreaseinthetotalamountofanalysedelementsinthedifferentsamplesaswemovefromthebedandprimarycyclonesamplestothesecondarycycloneandbaghouseashes.Inthebedandprimarycyclonesamples,theanalysedelementscalculatedtotheircorrespondingoxidesadduptoapproximatelyl00%,whichshowsthatmostoftheelementsinthesamplesaretakenintoaccount.However,inthesecondarycycloneashaswellasinthedepositsamplescollectedduringthewoodcombustiontests,thesumofoxidesremainbelowl00%,indicatingsomemissingcomponent.Thiscanalsobeseentosomeextentinthecorrespondingsamplesfromthepeatcombustiontest.AssumingpartoftheanalysedcalciumtobecalciumcarbonateandestimatingtheamountofcarbonasCO2,acorrectioncanbemadeforthemissingfraction.Thesecondarycycloneandbaghousesamplesfromthecoalcombustiontestscontainedahighamountofunburntcarbon,makingitlessvalidtomakeasimilarcorrection.
Athirdnoteworthytrendistheproportionofsulphurandchlorineinthedifferentsamples.Inthebedandprimarycyclonesamplescollectedduringthewoodandpeatcombustiontestsbothvaluesareverylow.Inthewoodcombustiontestschlorineappearstobeenrichedinthedepositsamples,whilethepeatcombustiontestsdonotshowanysimilartrend.Inthecoalcombustiontestssulphurisfoundtoaverylargeextentinthebedandprimarycyclonesamples,andtoalesserextentinthedeposits,secondarycycloneandbaghouseashesandinthefluegasasSO2(g).Chlorineisabsentfromallthesamplescollectedduringthecoalcombustionruns.Theresultsindicatethatchlorineescapesoutthroughtheprimarycycloneinallthecasestested.Inthecaseofwoodcombustion,chlorineappearedtobestronglyenrichedinthedeposits,whileforpeat,tosomeextent(<0.2wt%),itwasfoundinthebaghousesamples.Forcoal,chlorinealsoescapedthebaghouse.
DISCUSSION
Basedonthequantitativewetchemicalanalyses,theamountofthedifferentcompoundsinthedepositswas
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