Scrubber---Copy

2020/9/10Aerosol&ParticulateResearchLab1ParticulateScrubbers•Typesofscrubbers:spraychamberandventuriscrubber•Theoryanddesignconsideration•Pressuredrop•ContactingpowerReading:Chap.7(countercurrentflow)Collectingmedium:LiquiddropsWettedsurfaceQ:Whatparameterswillaffectthecollectionefficiency?Q:Anyotherarrangementofair&water?2020/9/10Aerosol&ParticulateResearchLab3Q:Isthegasvelocityofanyconcern?Isdropletsizeimportant?2020/9/10Aerosol&ParticulateResearchLab4CycloneSprayChamber&ImpingementScrubberFlagan&Seinfeld,FundamentalofAirPollutionEngineering,1988Q:Isusedwaterrecirculated?2020/9/10Aerosol&ParticulateResearchLab5VenturiScrubberHandbookofAirPollutionControlEngineering&Technology,Mycock,McKenna&Theodore,CRCInc.,1995.HighefficiencyevenforsmallparticlesQ:ESPforsticky,flammableorhighlycorrosivematerials?QL/QG:0.001-0.003VG:60-120m/s2020/9/10Aerosol&ParticulateResearchLab6Theory:SprayChamberDropletconcentrationinthechamberdcdLdcddVAdQVANn36Vd:dropletfallingvelocityrelativetoafixedcoordinateVtd:dropletterminalsettlingvelocityinstillair(i.e.relativetothegasflow)Volumeofeachdroplet36dddTotalnumberofdropletsthatpassthechamberpersecond3366dLdLdLddQdQQNVtdVGVdGtddVVVQL:volumetricliquidflowrate2020/9/10Aerosol&ParticulateResearchLab7Volumeofairthatflowsthroughthecross-sectionareaofasingledropletduringthetimedtdzVVddtVddtddtdd22singleair,44VTotaleffectivevolumeofgassweptcleanpersecondbyalldropletsindz32allair,64VdLdtddddQdzVVdAtagiventimedt,thedistanceadropletfallsisdtVdzdTotalnumberofparticlessweptcleanpersecondbyalldropletsindzzpdLdtdddpndQdzVVddN,32642020/9/10Aerosol&ParticulateResearchLab8QLQGzN2/dzzN2/dzzNTotalnumberofparticlesremovedpersecondoverdx2/,2/,dzzpdzzpcGpnnAVdNGdtddGtddGdtdLdQVAVVdQzVQexp)(23expPParticlepenetrationinacountercurrentverticalspraychamberCross-sectionalareaofallthedropletsGtddLddcdLcdVVdzQdVAdQzAA2346232020/9/10Aerosol&ParticulateResearchLab9)(1012.6expP4GtddGdtdLdVVdQzVQIfQLingal/minandQGincfm,zinftandddinmmGdtddddGLdQVAzdQQexp23expPParticlepenetrationinacross-flowspraychamberQ:Howdowehavehighercollectionefficiency?Q:Whatarethecollectionmechanisms(weneeditford)?2020/9/10Aerosol&ParticulateResearchLab102020/9/10Aerosol&ParticulateResearchLab11SingledropletcollectionefficiencydpddGLmmDiameterratioViscosityratiodGGtddVdmReDScGGmdGtdppcdVdCStm182ParticleReynolds#ParticleSchmidt#ParticleStokes#DepositionofParticlesonaSphericalCollector(diffusion)(interception)(impaction)2020/9/10Aerosol&ParticulateResearchLab12Impactiononly235.0StStIdp=2g/cm3Q:Whyisthereanoptimalsize?Q:Theoperatingconditionofaverticalcountercurrentspraychamberare:QL/QG=1L/m3,VG=20cm/s,dd=300mmandz=1m.Calculatethecollectionefficiencyof8mmparticlesthroughthischamber.Assumeatmosphericpressure,25oCandpof1g/cm3.(ImpactionparameterKpisusedintextbook;Kp=2St)2020/9/10Aerosol&ParticulateResearchLab13VenturiScrubbers:CalvertDesignpopopopoGGdLGLdKfKfKfKQdVQ17.049.07.07.0ln4.17.055expPmParticlepenetrationthroughaventuriscrubberKpo=2St(aerodynamicdiameter)usingthroatvelocityf=0.5forhydrophilicmaterials,0.25forhydrophobicmaterialsSautermeandropletdiameter5.145.05.05.011000597GLLLLGdQQVkdmk1=58600ifVGisincm/s=1920ifVGisinft/s,LandmshouldbeincgsQLandQGshouldbeofthesameunit2020/9/10Aerosol&ParticulateResearchLab141163)1(22422LdGDdtGLGLdClXXXXkQQVkpPressureDropVenturiScrubberlt:venturithroatlengthX:dimensionlessthroatlengthEx:10”water,2mm,=?2020/9/10Aerosol&ParticulateResearchLab15ContactingPowerApproach)exp(1tNTtPNContactingpower,hp/1000cfmWhencomparedatthesamepowerconsumption,allscrubbersgivethesamedegreeofcollectionofagivendisperseddust,regardlessofthemechanismsinvolvedandregardlessofwhetherthepressuredropisobtainedbyhighgasflowrateorhighwaterflowrate(PTinhp/1000acfm)Nt:Numberoftransferunit(unitless)(1inchofwater=0.1575hp/1000cfm)VenturiscrubbercollectingametallurgicalfumeQ:Testsofaventuriscrubbershowtheresultslistedontheright.Estimatethecontactingpowerrequiredtoattain97%efficiency.Frictionloss(inH2O)(%)12.75638.1892020/9/10Aerosol&ParticulateResearchLab162020/9/10Aerosol&ParticulateResearchLab17QuickReflection