大氣污染控制Lecture9-2ControlofPrimaryParticulates

AirPollutionLecture9-2

ControlofPrimaryParticulatesⅠTypesofParticlescollectiondevicesⅡSurfaceFilterⅢDepthFilterⅣScrubbersforparticulatecontrolⅤSummaryⅠTypesofParticlescollectiondeviceselectrostaticprecipitatorsgravitysettlerswallcollectiondevicecycloneseparator(壁式收集設(shè)備）(重力沉降式室)(旋風(fēng)除塵器）(靜電除塵器）HHD型寬間距臥式電除塵器寬間距臥式電除塵器ⅠTypesofParticlescollectiondevicesscrubbersurfacefilterdividingcollectiondevice(表面式過濾器）(縱深式過濾器）（分離式收集設(shè)備）(氣體洗滌器）depthfilterLSB型布袋除塵器LYDZA型布袋除塵器旋風(fēng)水膜脫硫除塵器高效脫硫消煙除塵器ThegeneralideaofDividingcollectiondevices①Dividingthedirtygasflowintosmallparts.②Insmallparts,theparticlescontactfiltersorwaterdropsandbecollected.③Thedirtyfiltersarecleaned,orthedirtyfiltersandwaterarethrownaway,orseparated.ⅡSurfaceFilter(1)ParticlescollectingprocessbythesurfacefilterParticleswhichcausesignificantairpollutionareinsizerangesfrom0.01to10μ.Typicalsizeoftheholesintheclothismorethan100μ.Howtheclothactsasasieveforsmallerparticles?(1)ParticlescollectingprocessbythesurfacefilterⅡSurfaceFilterDirtygasstream△xCleanedgasflow①Firstly,largeparticlesarecaughtonthesidesoftheholesofaholesofafilter.②Particlesincrease,thefiltercakeformsandbecomestherealfilter.However,thefiltermediumservesonlytosupportthecake.③Thefiltercakebecomethickerandthicker,thepressuredropincreasestosomevalue.Atthistime,theremustbesomewayofremovingthecakeofparticlesthataccumulatesonthefilters.Cleaningoperatingisveryimportantforbaghouse.FiltercakeFiltermedium布袋除塵器結(jié)構(gòu)(2)Twotypicalbaghouses

shake-deflatebaghousepulse-jetbaghouse(震動反吹清灰袋式除塵器)(脈沖噴吹清灰袋式除塵器）(2)TwotypicalbaghousesThedifferenceofthesetwotypesofbaghouseCleaningwayshake-deflatepulse-jetShake+aweakflowofgasinthereversedirectionIntermittentjetsofcompressedairCleaningoperatingBaghouseisoutofservice,anddirtygasflowhasbeenswitchedoff.Baghouseisinservice,anddirtygasflowisinwardthroughthebags.Page261,Fig.9.5shake-deflatebaghouseLDB型布袋除塵器shake-deflateLPP系列脈沖袋式除塵器LPJ系列高壓噴管脈沖袋除塵器Jet-Pulse大風(fēng)量的煙氣PPC系列氣箱脈沖袋收塵器這種類型的收塵器，集合分室反吹和噴吹脈沖等諸類收塵器的優(yōu)點(diǎn)，克服了分室反吹時(shí)動能強(qiáng)度不夠、脈沖噴吹過濾與清灰同時(shí)進(jìn)行的缺點(diǎn)。采用高能清灰和分式結(jié)構(gòu)離線清灰。玻纖袋收塵器該收塵器適應(yīng)性強(qiáng)、即能在高溫(氣溫達(dá)250℃)，高濕（露點(diǎn)在60℃時(shí)）。LFSF型反吹風(fēng)玻纖袋除塵器立窯烘干機(jī)y煙氣溫度一般在60－300℃范圍內(nèi)波動。LCXS型玻纖袋收塵器(3)collectedefficiencyflowrateorAirtoclothratioQ—volumeflowrateA—filterarea,A=n×A0A0—filterareaofeachbag△P—pressuredropμ—viscosityK—permeability,determinedbyexperiment.△x—thickoffiltercakeorfiltermedium.Page283(3)collectedefficiencym—massofsolidsremoved,whichisthecollectedparticlesonthesurfaceoffilter.t—timeC—particleconcentrationindirtyairη—collectedefficiencyFiltercakePage287EffectoffabricloadingandfacevelocityoncollectedefficiencyFabricloadingρ

△x,g/m20Outletconcentrationc,g/m33.35m/min1.52m/min0.61m/min0.39m/minEffectoffabricloadingEffectoffabricloadingandfacevelocityoncollectedefficiency1)Atzerofabricloading(neworfreshlycleanedcloth),theoutletconcentrationishighandpracticallyequalstotheinletconcentrationofabout0.89g/m.2)Asthecakebuildsup,theoutletconcentrationdeclines.3)Finallyoutletconcentrationremainsconstant,about0.001timestheinletconcentration.1%particlespassthroughthepinholesandwillnotbecollected.EffectoffabricloadingPinholesareregionswherethecakedoesnotestablishproperly.Effectofsuperficialvelocity(vs)Ifthesuperficialvelocityincreases,efficiencyfalls.ⅢDepthFilterDepthfilterisdifferentfromsurfacefilter,doesnotformafiltercakeonthesurface,butinsteadcollectsparticlesthroughouttheentirebody.ExamplesFilter–tippedcigarettesFamilyairfilter(1)DepthfiltermodelAVy-particleVy-gasVrelative=Vy-gas-Vy-particleDirtyairwithparticlesdirectionisfrominnertoouter.Fy-inertialFy-dragFlowofgasandparticlesaroundacylinderDb,ObstacleorTargetPage293(1)DepthfiltermodelGasflowmustbendtoflowaroundthefiber.Particlestendtocontinuegoingstraightbecausethedensityofparticleismuchlargerthangas,andtheinertiaofparticlewilldriveparticlealongtheinitialdirection.Howtoevaluatethechanceofparticlesimpactingthetargetbyinertialmechanism?(2)InertialImpaction①②resistingforce(inertialforce) Page293(2)InertialImpaction③Inbalance(2)InertialImpaction(2)InertialImpactionSeparationNumberImpactionparameterInertiaparameter分離指數(shù)碰撞參數(shù)慣性參數(shù)慣性碰撞參數(shù)Page294(2)InertialImpactionXstokes’stopping(2)InertialImpactionHowNsaffectsTargetefficiency?SeparationNumber,Targetefficiency,ηt0.10.01LangmuirandBlodgettPage293Fig.9.18Targetefficiency(ηt)Targetefficiencyηtrepresentsthenumberofparticlesthatactuallycontactthetarget,dividedbythenumberthatwouldhavecontacteditifallparticleshadmovedperfectlystraightandnonehadbeendrawnaroundthetargetbythegasstream.

Targetefficiency(ηt)TargetParticlesinthisregionmayimpingeontarget(2)InertialImpactionDNsηtForlargeparticlesNsislarge,sotheinertialforceislarge,andtimedecreasesomuchthatparticleshavenotenoughtimetomovearoundthetarget.Therefore,thetargetefficiencyηtwillincrease.Ns∝D2Ns∝1/△t0.10.01

ηt(2)InertialImpactionNsisfrom0.01to0.1,ηtislow.Ns∝D2Nsissosmallthattheparticlehaspracticallyzerochanceofimpactingthetarget.Foraverysmallparticle0.10.01

ηtHowsmallparticlesarecollectedbythefilters?(3)DiffusioncollectionmechanismandinterceptionmechanismThesmallparticlespasssoclosetothetargetthatBrownianmotionmovestheparticlestothetarget.Target(3)DiffusioncollectionmechanismandinterceptionmechanismDiffusivity,m2/s擴(kuò)散系數(shù)Kinematicsviscosity,m2/s運(yùn)動粘度Page296Freidlander(3)Diffusioncollectionmechanismandinterceptionmechanismμ運(yùn)動粘度動力粘度m2/skg/(m·s)1cp=10-3kg/(m·s)(3)Diffusioncollectionmechanismandinterceptionmechanismk___BoltzmannconstantC___CunninghamcorrectionfactorT___temperatureD___diameteroftheparticleμ

___theviscosity(3)DiffusioncollectionmechanismandinterceptionmechanismFirsttermEfficiencyfordiffusioncollection∝Dηt(3)DiffusioncollectionmechanismandinterceptionmechanismSecondtermEfficiencyforinterceptionInterceptionmechanismmeanscollectionbynoninertialcontactwhenparticlescenterpasseswithinDb/2ofthetarget.Page297Target(4)ComparisonofcollectionmechanismsImpactionandinterceptionDiffusionDηtηtVηtηtDbηtηtPage297Table9.3ⅣScrubbersforparticulatecontrolThecommonexampleofscrubberisrainstormMostfineparticleswilladheretoaliquiddropiftheycontactit.Manyraindropsdividethedirtygasintoalotofsmallstream.0.5μ50μ(Particles)(Waterdrops)ⅣScrubbersforparticulatecontrol(1)ComponentpartsofascrubberinstallationGas-liquidseparator(cyclone)MixedgasandliquidCleangasDirtyliquidLiquid-solidseparatorGas-liquidContactor(scrubber)DirtygasLiquidrecirculatingpumpCleanliquidPage299Fig.9.20ⅣScrubbersforparticulatecontrol①M(fèi)akingthewaterdropsandtheparticlestoucheachother,theparticleswillbecaughtonthedrop.②Gasandliquidseparating.③particlesareseparatedfromwater.④Cleanliquidrecirculating(1)Componentpartsofascrubberinstallation(2)ThetypesofscrubbersⅣScrubbersforparticulatecontrolCrossflowscrubberGasflowinGasflowoutLiquidflowinLiquidflowout(2)ThetypesofscrubbersⅣScrubbersforparticulatecontrolCounterflowscrubberQL,inQG,outQG,inQL,out(2)ThetypesofscrubbersⅣScrubbersforparticulatecontrolCo-flowscrubberGasflowinGasflowoutLiquidflowinLiquidflowout(2)ThetypesofscrubbersⅣScrubbersforparticulatecontrolCo-flowscrubberPage308,Fig.9.26Typicaldownflowventuriscrubbers并流向下文丘里管濕式洗滌塔Page308,Fig.9.26旋風(fēng)水膜脫硫除塵器GasinGasoutLimeliquidinliquidout高效脫硫消煙除塵器GasinLimeliquidinliquidoutⅤSummarySurfacefilterDepthfilterscrubberTypicalequipmentBaghouseCigarettefilterCo-flowventuriscrubberFilterortargetCloth