电站锅炉外文翻译改进煤粉锅炉的燃烧和传热文档格式.docx

电站锅炉外文翻译改进煤粉锅炉的燃烧和传热文档格式.docx

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Clinton,NJ08809-4000,USA

Stefan_Laux@

T.Rosin

TR-TechInt.Oy

FIN-20100Turku,Finland

TR@

Abstract

Theperformanceofpulverizedcoalcombustionsystemscommonlysuffersfromairandfuelimbalancesattheburners.StoichiometrieslocaltotheburnersmustbemaintainedinordertoachieveultralowNOxperformancewithoutsignificantlysacrificingcombustionefficiency.Inadditiontotheemissionbenefits,improvementoftheairandfuelbalanceresultsinlessslaggingandreducedfurnacewallcorrosion.

HepaperpresentsresultsandbenefitsassociatedwithoperatingcoalfiredboilersusingFosterWheelerandTR-Tech’sElectricChargeTransfer（ECT）coalflowmeasurementtechnology.ECTsystemsprovideboileroperatorswithcontinuouson-lineindicationofcoalflowdistribution,conduitvelocityandparticlefineness.Thepaperwillshowdevicesthatcontrolthecoalflowbalance.ECTtechnologyinconjunctionwithFosterWheeler’ssolutionsforcoalflowbalancingisopeningupanentirenewspectruminoperationalassessmentandimprovementaswellasemissioncontrol.

UltraLowNOxCombustion

NewNOxregulationsdemanddrasticallyreducedNOxemissionsfromfossilfiredboilers.Withafewexceptions,theNOxlimitsforozonecontrolduringthesummermonthsrequireapost-combustioncontrolmethodsuchasSCRoncoalfiredboilers,becauseLowNOxfiringsystemsalonecannotachievecompliance.However,investmentcostsandammoniacostsofanSCRDeNOxcatalystcanbereduced,iftheoutputNOxfromthefiringsystemislow.Thus,morestringentemissionlimitsandtheadditionofpostcombustionNOxcontrolcreatetheneedforimprovementsofNOxemissionsfromtheexistingLowNOxcoalfiringsystems.

RegardlessoftheNOxreductionapproach,manycurrentlowNOxsystemsarelimitedintheirabilitytoprovidesignificantadditionalreductionsinNOx.Newmultiairzoneburnerdesigns,specialcoalnozzletips,etcdon’tprovidethereductionsbeingsoughtbyutilitieswantingtominimizeoreliminatepostcombustionsystems.

Inanticipationoftheserequirements,FosterWheelerhasbeendevelopingnewtechnologiestogobeyondjust“burnercomponents”.OurevaluationofoperatingLNBsystemsshowsthatmanyarelimitedfromfurtherNOxreductionby“nonburner“barriers.Byaddressingandeliminatingeachofthese,significantreductionsarepossible.

OneofthemostcommonbarrierstolowerNOxisrelatedtopoorcoalandairdistribution.Thesecanincludehighunburnedcarbon,highCO,furnaceslagging,oxygenand/orsteamtemperatureimbalance,corrosion,etc.

AlllowNOxfiringsystemsdependonadefinedbalanceoftheairandcoalattheburners.Bymonitoringandcontrollingtheairandcoalflowtotheburners,existingaswellasnewsystemsgreatlybenefitfromloweremissionsandimprovedboileroperation.Or,ifyouusethefollowinganalogyforboileremissionimprovement:

Thistrendiscomparabletothechangefromcarburetorstofuelinjectionsystemsseenovertimeinthecarindustry.FosterWheelerstronglybelievesthatfutureultralowNOxfiringsystemsneedatightcontroloftheairandfuelbalanceateachburnerinthesystem,regardlesswhetheritistangential,wallorarchfired/1/.

Manypulverizedcoalboilersexperiencesomeoftheproblemsassociatedwithpoorairandfueldistribution:

*Pooremissionperformance

*IncreasedammoniaconsumptionofSCRandSNCRsystems

*Increasedunburnedcarbonintheflyash

*Distortedoxygenprofileatboileroutlet

*Unevensteamtemperatureprofiles

*Flameimpingement

*Increasedslagging

*Waterwallwastage

Anydeviationfromthedesignair/fuelbalanceatindividualburnersresultinsomeburnersoperatingatafuelleanorafuelrichcondition.ThefuelrichburnersareproducinglargeamountsofCO,highLOIandlongerflameswhilelocallyloweringtheoxygenlevelinthefluegas.Ontheotherhand,thefuelleanburnersproducehighNOxlevelsatelevatedO2.TheoutcomeattheboilerexitisafluegaswithhighCOandhighNOx.Inaddition,LOIiselevatedduetotheburnersoperatingatlowstoichiometries.Thispapershowssomeofthesuccessesachievedbybalancingairandfuelflowinaboiler.

MostLowNOxBurnersandallTangentialFiringSystemsallowairflowcontrolattheburners.TheseareadjustedmainlyduringinitialoptimizationoftheLowNOxsystemafteraretrofit.Usually,itwasnotnecessarytoaddressdistributionchangeswithloadanddegradationofsystemperformancewithtime.Intherecentpast,severalvendorsdevelopedcontrolstrategiesandsoftwaretoimproveboilerandemissionperformance.Whilethisisthestepneededforimprovement,mostofthesystemslackreliableflowmeasurementandcontrolofairandfuel.FosterWheelerusesburnerairmeasurementtodeterminethesecondaryairflowandusesthealreadyexistingcontroldevicestomodulatetheflow.

ECTCoalFlowMeasurement

Forcontinuousboileroptimization,anon-linemeasurementofthefuelflowineachconduitisrequiredforon-lineoptimizationoftheairandcoalbalanceateachburner.ThistechnologyisoneofthevitalstepstowardsanUltra-LowNOxFiringSystem.

FosterWheelerispartneringwithTR-TechInternationalOyofFinlandtomarkettheElectricChargeTransfertechnology（ECT）worldwide.FosterWheeleristheglobaldistributoroftheECTsystem.Thepatentedtechnologymeasurestheelectricchargespresentinanytwo-phaseflowtransportandusesthesignalstodeterminethefollowingcharacteristicsoftheflow.

*ECTmeasurestherelativecoaldistributionbetweentheconduits.Inaddition,thesystemcanbeconfiguredtomeasuretheflowvelocityandtheabsoluteflowineachconduit.CoalflowbalanceisthekeymeasurementforcontinuousUltraLowNOxcombustion.

*ThehighdatacollectionrateoftheECTsystemallowsmonitoringalsounsteadyphenomenaincoalconduitsthatcancauseproblemsduringplantoperation.Thesignalscanbeusedtodetectcoalconduitlayoutduetoinsufficientprimaryairflowfromthemillandcoalconduitsurgingwhichresultsinfurnacepressureandemissionsfluctuations/2,3/.

*Finally,theECTsystemcanbeappliedtomonitortheparticlesizechangesofthecoalflow.

Theantennasandthehardwareusedforthissystemarethesameasinthecoalflowdistributionapplication.Thus,theECTsystemcanbeusedtomonitormillperformanceon-lineassuringpropercoalfinenessismaintainedtominimizeunburnedcarbon.Theconfigurationofthesystemisdescribedinmoredetailin/4/.

TheECTsystemconsistsofreceivingantennasineachcoalconduitthatareconnectedtoasignalconditioningunithousedinacabinet.Thesignalsfromtheseconditioningunitisreceivedbypersonalcomputersthatareusedfordataprocessingandanalysis.TR-Tech’sproprietarysoftwareisusedtodeterminethebalancebetweentheconduitsofonemill,todisplaytheresultstotheoperatorandtofeedthedataviaanetworktotheplant’sDCSsystemoracontinuoscombustionoptimizationsoftwarerunningonaseparatecomputer.

Theantennasareeasilyinstalledthroughthehorizontalorverticalwalloftheexistingconduitandinsertedintothecoalstream.Threeantennasineachconduitareneededforcoalflowbalancemeasurementandsixforcoalflowandvelocitymeasurement.Theirlocationinthepipewallisdeterminedsothattheeffectsofcoalropesonthemeasurementresultsareminimized.Antennasaremadeoftungstencarbidetoensurelongoperatinglife.Theinstallationisverysimpleandrequiresonlyamilltakenoutofserviceforseveralhourswhichminimizeslostgeneratingcapacity.Afterinstallation,theECTmeasurementisverifiedbyastandardASMEorRotorprobesamplingproceduresandthesystemisthenreadytobeused.

TheECTsystemoffersseveraldistinctadvantages:

*Allinformationiscontinuousandon-line.

*TheECTmeasurementisnoteffectedbycoaltype,moisture,ashcontentorcoalroping.

*Theelectronicscanbelocatedupto1200feetfromtheconduits.Nocabinetsareneededontheburnerdecks.

*Theabrasionresistantantennasinthecoalconduitarepassiveandneednopowersupply.

*Theinstallationiseasy.Theantennascanbeinstalledduringshortmilloutages.

ECTsystemshavebeensuccessfullyinstalledonindustrialplantsandmanyutilitysteamgenerators.Ingeneral,theresultsoftheECTmethodcompareverywellwithastandardASMEprobetestevenatextremeshiftsofthecoalflowbetweentheconduits.Thisconfirmstheviabilityofthetechnologyforreal-timecoalbalancingapplications.Since1998ECTwasinstalledatnineutilitypowerplantsandfiveinstallationsarescheduledfor2001.

Distributors

Inmanytangentiallyfiredplantsriffleboxesareinstalledafteranexhaustertodistributethefuel.Thesedesignscanberetrofittedwithadjustableriffleboxestoachieveimprovedfueldistribution.Adjustableriffleboxes（Figure5）allowbiasingtheparticleflowtowardsindividualconduits.Thedesignissimilartothefixedrifflers,butadjustablevanesareusedattherifflerinlet.Thechangeofafuelsystemwithoutdistributorstothisdesignrequiresadditionalspaceabovethepulverizerswhichmightbelimitedinretrofitapplications.

TheFosterWheelerThree-WayDistributorisshowninFigure6ontopofaheart-shapedclassifier.Thesingleoutletofthemillisdistributedinaverticalpipetothreeoutlets.Distributionfingersthatcanbepushedintotheflowbiastheflowfromthecentralinletpipeat