47 th International Energy Agency Workshop on Larg

147thInternationalEnergyAgencyWorkshoponLargeScaleCFBZlotnicki,PolandOctober13th2003RecentALSTOMPOWERLargeCFBandScaleupaspectsincludingstepstoSupercritical.Jean-XavierMORINALSTOMWHYCFBTECHNOLOGYISAPROMISINGOPTIONThefluidbedcombustionprocessfacilitatespowerproductionfiringawiderangeoffuelswhilemeetingstringentrequiredemissionslimits.Thecurrenttrendofcosteffective,environmentallysensitivesolidfuelsteamgenerationhascreatedaneedforcontinuedscale-upoftheCFBoptiontocontinuetomeetthesedemands.CFBtechnologyhasdemonstratedanunparalleledabilitytoachievelowNOxproductionwithouttheneedforpost-combustionequipmentsuchasSCR.Thisispossibleduetolowcombustiontemperatures(1550-1650°F/845-900°C)andthestagingofairbyapplicationofsecondaryairadmissionzones.Furthermore,CFBtechnologyhasexhibitedafuelflexibilitywithanabilitytoburnwastematerialsandfuelspreviouslydeemeduneconomicaland/orimpossibletohandlebyconventionalboilerfiringsystemtechnologies.Currently,basedonitsdemonstratedscale-upease,lowemissionscapabilitiesandfuelflexibility,CFBtechnologyisaseriousoptionformanycustomersfortheirmid-sized(300-450MWe)andlarger(400-600MWe)utilityunitapplications.Inaddition,thankstoitsabilitytocopewithoxygenfiring,theCFBprocessappearsasasuitabletechnologyroutetoimplementefficientCO2capturesystemsabletomeetKyotoProtocolerequirementwithCO2sequestrationortomeetEnhancedoilrecoveryrequirements.TheproperdesignofthecombustorandtheappropriatescaleupfiguresarethekeytosuccessforsuchtechnologywhereAlstomhasthewidestrangeofexperiencewithlargeCFBunitsinoperationrespectivelyunderconstruction.THEMAJORSCALEUPTECHNICALCHALLENGESScale-upofCFBtechnologyhassteadilyprogressedoverthelastdecade.Asunitsarescaledupinsize,maintainingthebeddynamicssimilartosmallCFBsrequiresmoreengineeringexpertise.Bedfluidization,airdistributioninthecombustor,andfuelfeeddistributionareextremelycriticaltoobtainthesameprocessrequirementsasforsmallerCFBs.Themajorscale-uptechnicalchallengesarewithfourmajorcomponentsofCFBs:thecombustor,thecyclones,thebackpass,andthefluidbedheatexchangers.CombustorCarefulconsiderationisgiventothegeometryofthecombustorasthisimpactsfuel,air,andsorbentmixing.Inscaling-upCFBdesignfromexistingunits,ALSTOMincreasesthecombustorheightonlyslightlytoensurethesolidspressureprofile,andthereforeheattransfertothewaterwallsiswithinourprovenexperienceandknowledgebase.ThelowerfurnacedesignusedbyALSTOMenablesthefuel,air,andsorbenttomixinanareathatisroughlyone-halfoftheoverallcombustorplanarea.Astheunitsizeincreases,thedepthoftheunitremainsconstanttoensuregoodmixingoffuel,air,andsorbentinthelowerfurnace.Thewidthoftheunitincreasesandcyclonesareaddedasrequiredtomaintaingasvelocities2atoptimumlevels.Asunitsincreaseinsizetoapointwherefour(4)cyclonesarerequired,thecombustordesignchangestoapant-leg.Thecombustionofthefuel,sulfurcapture,andheattransfertothecombustorwallsandin-combustorsurfacearearesultoffluidizationofthebed.Thebedmaterialisfluidizedbyprimaryair,whichisintroducedintothecombustorthroughanozzlegridinthefloor.ThelocationofthesecondaryairalongthefrontandrearwallsaidsincombustionaswellascreatesconditionstominimizeNOxformation.TheproperdesignofthecombustorandtheappropriatescaleupfiguresarethekeytosuccesforsuchtechnologywhereAlstomhasthewidestrangeofexperiencewithlargeCFBunitsinoperationrespectivelyunderconstruction.CyclonesCyclonesinaCFBseparatetheentrainedparticlesfromthefluegasleavingthecombustorandreturnthehotsolidstothecombustor.Thehighrecyclerateofthecycleensuresauniformtemperatureinthecombustor.Theefficiencyofthecycloneimpactsthecapturerateofthefinesfractionofthesolidsenteringthecyclone.Thisinturnaffectslimestoneutilizationandcarbonburn-up.Inscaling-up,apointisreachedwherethecyclonesizegetssolargethatlimestoneutilizationandcarbonburn-uparenegativelyimpacted.Scale-uptolargersizecycloneshasbeengradual.Optimizationofthecyclonecollectionefficiencyhasbeenachieved,asaresultofALSTOMknowledgeandextensivelaboratoryresearch,throughchangestotheinletandoutletductdesign,andtothevortexfinderlengthandlocation.Astheunitsizeincreases,cyclonesizeisincreasedorcyclonesareaddedasrequiredtomaintainoptimumgasvelocities.13/10/20031Cyclonearrangements100MWe100-200MWe200-300MWe300MWe3FluidBedHeatExchangers(FBHEs)Recirculatedashfromthefurnacecanbedirectedfrombelowthecyclonehopperattemperaturesof1550-1650°F(845-900°C)toabubblingfluidizedbedheatexchangerforthepurposeofperformingadditionalboilerheatduty.Solidsaredivertedusingawatercooledashcontrolvalvetoaseriesofheatexchangerbundleswhichcanperformsuperheater,reheater,and/orevaporatorduties.AsCFBsgetlargerinsize,thecombustorsurface-to-volumeratiodecreasesanditisnotalwayspossibletoperformtherequiredheatdutyinthefurnaceandbackpass.TheFBHEsallowincrementaldutybypassingasufficientamountofrecyclesolidsintothebundles.AninherentbenefitofusingaFBHEistherelativelyhighheattransferratefromthehotsolidstothetubebundles.Bystandardizingtubebundlearrangementsandbyutilizingamodularapproach,anincreaseinunitsizecanbeaccommodatedwithoutdevelopingnewFBHEdesigns.FEATURESOF3