Air Pollution Control Technology

Unit7ConventionalTechnologyofAirPollutionControl•TheprincipaltechnologiesofairpollutioncontrolConventionaltechnologies:Cyclones旋风除尘器Electrostaticprecipitators静电除尘器Fabricfilters织布过滤器（Baghouses袋式过滤器）Scrubbers洗涤器Biofiltration生物过滤Othertechnologies:Granularbed颗粒床Panelbedfilters平板床过滤Chargeddropletscrubbers带电荷液滴洗涤器CycloniccollectorsGasstreamentertangentially（切线地）intoaroundconically(锥形）shapedvesselsandfollowsaspiral（螺旋形的）pathtotheoutlet.Thespiralmotionproducesthecentrifugalforce（地心引力）thatcausetheparticulatetomovetowardtheperipheryofthevessel.theparticulatefallintothebottomofthevessel.CyclonicdustcollectorThelargediameter,lowefficiencycyclone.Characteristicsoflargecyclones:Lowefficienciesespeciallyonparticleslessthan50u.Lowinitialcostandusuallyoperateatpressuredrops(压力降）of1to3inchesofwater.Applications：Thelargercyclonesareoftenusedasapartoftheprocesswhenthegasstreamisheavilyladenwithpartofproductsuchascoaldryers(煤干燥机）,alfalfadehydrator（苜蓿干燥机）andmillingoperation（研磨机）.Theyarewidelyusedingrainelevators（谷物升降机）,sawmills（锯木厂）,asphaltplants（沥青制造厂）anddetergentmanufacture（清洁剂制造厂）.•Characteristicsofsmallcyclones:Themultitubecyclonesarecapableofefficienciesexceeding90%.Thecostishigherandtheirpressuredropsisusually3to5inchesofwater.Theyarealsomoresusceptibletoplugging（堵塞）anderosion.Thesmalldiameter,multitubehighefficiencycyclone.CyclonicdustcollectorFabricfiltersConsistsFabricfiltersystems,i.e.,baghouse,usuallyconsistoftubular（管状的）bagsmadeofwoven（织物）syntheticfabricorfiberglass（玻璃纤维）.Basically,theunitconsistsofcompartmentscontainingrowsoffilterbagsortubes.Principle:Thedirtygaspassthroughthefabricwhiletheparticlesarecollectedontheupstreamsidebyfilteringactionofthefabric.Andthenthedustretainedonthebagsisperiodicallyshakenoffandfallsintoacollectinghopper（收集斗）forremoval.Operationparameters•Theamountoffilterarearequiredisoftenbasedonanair-to-clothratioof11.5to3.0cfm(cubicfeetperminute)ofgas/ft2ofcloth.•Themaximumoperatingtemperatureforabaghouseis550F(Fahreheit)usingfiberglassbag.However,theremayalsobeaminimumtemperaturelimitationsoastomaintainthegastemperature50Fto75Fabovethedewpoint(露点）.•Inletdustloadingrangefrom0.1to10.0grains/ft3ofgas.•Higherconcentrationsinsomeindustriesareremovedbyaprecleaningdevice,suchasalowefficiencycyclone.Celsius摄氏的Baghouse•Applications:gascleaningbyfiltration（过滤）issuitedforapplicationswheredryparticulatesarehandledorwherewaterintheprocessgasesisinthevaporstage.Miningoperations(采矿）FoodprocessingGrainelevators（谷物升降机）Soapanddetergents（清洁剂）PlasticsmanufactureCarbonblackCementElectricarcfurnaces(电弧炉）Foundrycupolas（铸造化铁炉）Nonferroussmeltingoperation（有色金属冶炼）Removalefficienciesoffabricfilter•Thebasicfilterorbaghouseiscapableofoperatinginexcessof99%efficiency,althoughsatisfactoryoperationofthesystemiscontingentupon(dependon)thecharacteristicsofthegasstreamandtheparticulatematterbeingremoved.Wetscrubbers•Wetcollectorusewater“sprays”tocollectandremoveparticulatematter.•Theprincipalmechanisms:Increasingthesizeoftheparticlesbycombinationwithliquiddropletstherebyincreasingtheirsizesotheymaybecollectedmoreeasily.Trappingtheparticlesinliquidfilmandwashingthemaway.LowEnergyWetScrubbersConsists:Spraytower（喷射塔）Packedtower（填充塔）Impingementplatetower（板式撞击塔）Characteristics:Waterrequirementmaybe3to6gal/1000ft3ofgas.Collectionefficienciescanbeexceed90%to95%Applications:Incinerators(焚化炉）FertilizermanufacturingLimekilns(石灰窑）Ironfoundries（铸铁厂）VenturiScrubberCharacteristics:HigherenergyscrubberImpartshighvelocity（速度)tothegasstreambymeansofconverging-divergingductsection(收缩扩大管截面）。Requireadraftfan（通气风扇）withhighpowerinput.Applications:Steelfurnace(炼钢炉）Pulpmills（纸浆厂）Foundrycupolas（铸造化铁炉）.ElectrostaticPrecipitators•Applications:suitableforgasstreamwhichcanbeeasilyionized(离子化）andwhichcontaineitherliquidorsolidparticulatematter.Anion阴离子Cation阳离子ElectrostaticPrecipitatorsTopViewofESPSchematicDiagramThegasisionized（离子化）bythehighvoltageelectrode.Theparticulatematterischargedbytheinteractionofthegasions.Theparticlesmigratetothecollectingsurfacewhichhasanoppositepolarity（极性）andneutralized（中和）.Theparticle-ladengaspassthroughanelectrostaticfieldproducedbyahighvoltage（电压）electrode（电极）andgroundedcollectionsurface.SideviewofESPSchematicDiagramBasicstepsfortheoperationofelectrostaticprecipitationElectricalchargingofthesuspendedparticulatematter(悬浮颗粒物）.Collectionofthechargedparticulatematteronthegroundedsurface.Removaloftheparticulatematterfromthecollectingsurfacebymechanicalscrubbingorflushing（washing)withliquids.