环境工程专业英语 课件 U2L2 Air Pollution Emission Control Devices for Stationary

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AirPollutionEmissionControlDevicesforStationary

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StationarysourcespowerplantssteelmillssmelterscementplantsrefineriesotherindustrialprocessesContaminantsparticulatesaerosolsvaporsgasesAirPollutionEmissionControlDevicesforStationaryStationarysourcesofairpollutionemission

CommonmethodsforeliminatingorreducinggaseouspollutantsDestroyingpollutantsbythermalorcatalyticcombustionChangingpollutantstolessharmfulformsthroughchemicalreactionsCollectingpollutantsusingairpollutioncontrolsystemsbeforetheyreachtheatmosphereAirPollutionEmissionControlDevicesforStationaryAirpollutioncontroldevices

Electrostaticprecipitators(wetanddrytypes)Fabricfilters(alsocalledbaghouses)WetscrubbersCyclones(ormulticlones)AirPollutionEmissionControlDevicesforStationary

ThemostcommonlyuseddevicesforcontrollingparticulateemissionsThermaloxidizersCatalyticreactorsCarbonadsorbersAbsorptiontowersBiofiltersAirPollutionEmissionControlDevicesforStationaryCommoncontroldevicesforgaseousandvaporpollutantsScrubbingScrubbingisaphysicalprocesswherebyparticulates,vapors,andgasesarecontrolledbyeitherpassingagasstreamthroughaliquidsolutionorsprayingaliquidintoagasstream.Wateristhemostcommonlyusedabsorbentliquid.Asthegasstreamcontactstheliquid,theliquidabsorbsthepollutants,inmuchthesamewaythatraindropletswashawaystrongodorsonhotsummerdaysAirPollutionEmissionControlDevicesforStationaryAbsorption&WetScrubbingEquipment

WetScrubbingEquipment

GasabsorptionGasabsorptioniscommonlyusedtorecoverproductsortopurifygasstreamsthathavehighconcentrationsofwater-solublecompounds.Absorptionequipmentisdesignedtogetasmuchmixingbetweenthegasandliquidaspossible.Commontypesofgasabsorptionequipmentincludespraytowers,packedtowers,traytowers,andspraychambers.AirPollutionEmissionControlDevicesforStationaryAbsorption&WetScrubbingEquipment

GasabsorptionPackedtowersarebyfarthemostcommonlyusedcontrolequipmentfortheabsorptionofgaseouspollutants.However,whenusedwithheavy,particulate-ladengas,theycanbepluggedbyparticulatematter(PM).WetcollectiondevicesusedforPMcontrolincludeventuriscrubbers,bubblingscrubbers,spraytowers,andinsomeinstances,wetelectrostaticprecipitators(ESPs).AirPollutionEmissionControlDevicesforStationaryAbsorption&WetScrubbingEquipment

PackedtowersAdsorptionTheprocessofadsorptioninvolvesthemolecularattractionofgasesorvapors[usuallyvolatileorganiccompounds(VOCs)]ontothesurfaceofcertainsolids(usuallycarbon,molecularsieves,and/orcatalysts).Thisattractionmaybechemicalorphysicalinnatureandispredominantlyasurfaceeffect.AirPollutionEmissionControlDevicesforStationaryAbsorption&WetScrubbingEquipment

AdsorptionActivatedcarbon(charcoal),whichpossessesthelargeinternalsurfaceareaneededtoadsorblargequantitiesofgaseswithinitsstructure,isoftenusedtoremoveVOCsfromfluegases.AftertheactivatedcarbonissaturatedwithVOCs,itisoftentreated(byheatand/orsteam)tostripoffthecollectedVOCs.TheVOCsarethensentforfurthertreatment,andthecarbonisreusedintheadsorptionreactor.AirPollutionEmissionControlDevicesforStationaryAbsorption&WetScrubbingEquipment

AdsorptionAdsorptionisaffectedbythetemperature,flowrate,concentration,andmolecularstructureofthegas.Adsorptioniscommonlyusedforremovinggasesfromcontaminatedsoil,oilrefineries,municipalwastewatertreatmentplants,industrialpaintshops,andsteelmills.AirPollutionEmissionControlDevicesforStationaryAbsorption&WetScrubbingEquipment

AdsorptionTowerFabricFiltersorBagHousesFabricfilters,alsocommonlyreferredtoasbaghouses,areusedinmanyindustrialapplications.Theyoperateinamannersimilartoahouseholdvacuumcleaner.Dust-ladengasespassthroughfabricbagswherethedryparticulatesarecapturedonthefabricsurface.Afterenoughdusthasbuiltuponthefilters,asindicatedbyabuildupinpressureacrossthefabric,dustisperiodicallyremovedbyblowingairbackthroughthefabric,pulsingthefabricwithablastofair,orshakingthefabric.AirPollutionEmissionControlDevicesforStationaryAbsorption&WetScrubbingEquipment

FabricFiltersorBagHousesBaghousesareusedtocontrolairpollutantsfromcoal-firedpowerplants,steelmills,foundries,andotherindustrialprocesses.Fabricfilerscancollectover99.9%oftheenteringparticulates,evenfinePM.Baghousesalsoaresometimesusedaspartofamultistagegascleaningsystemwheretheyareusedasareactoraswellasaparticulateremovaldevice,suchasinsemi-dryfluegasdesulphurizationsystems.Recentlysomebaghousesarebeingequippedwithcatalyticbagswheretheyalsoactasachemicalreactorwhiletheyarecollectingparticulate.AirPollutionEmissionControlDevicesforStationaryAbsorption&WetScrubbingEquipment

CatalyticReactorsCatalyticreactors,referredtoasselectivecatalyticreduction(SCR)systems,areuseextensivelytocontrolNOx,emissionsarisingfromtheburningoffossilfuelsinindustrialprocesses.AmmoniaisinjectedandmixedwiththefluegasesupstreamoftheSCRreactor.IntheSCRreactor,ammoniaandNOx,reacttoformnitrogenandwater.Greaterthan90%NOx,removalispossiblewiththesesystems.AirPollutionEmissionControlDevicesforStationaryAbsorption&WetScrubbingEquipment

CatalyticReactorsCatalyticreactorsalsoperformthermaldestructionfunctionslikeincinerators,butatlowertemperaturesandforselectedwastegasesonly.Theyincorporatebedsofsolidcatalyticmaterialthattheunwantedgasespassthrough,typicallyforoxidationorreductionpurposes.Catalyticreactorshavetheadvantageofloweringthethermalenergyrequirements.Destructionefficienciesof99.99%arepossiblewithsignificantlyreducedenergyandoperatingcostsascomparedtoanincinerator.AirPollutionEmissionControlDevicesforStationaryAbsorption&WetScrubbingEquipment

CyclonesDust-ladengasiswhirledrapidlyinsideacollectorshapedlikeacylinder(orcyclone).Theswirlingmotioncreatescentrifugalforcesthatcausetheparticlestobethrownagainstthewallsofthecylinderanddropintoahopperbelow.Thegasleftinthemiddleofthecylinderafterthedustparticleshavebeenremovedmovesupwardandexitsthecylinder.CyclonesoperatetocollectrelativelylargesizePMfromagaseousstream,andcanoperateatelevatedtemperatures.AirPollutionEmissionControlDevicesforStationaryAbsorption&WetScrubbingEquipment

CyclonesCyclonesaretypicallyusedfortheremovalofparticles50microns(μm)orlarger.Efficienciesgreaterthan90%forparticlesizesof10μmorgreaterarepossible,andefficiencyincreasesexponentiallywithparticlediameterandwithincreasedpressuredropthroughthecyclone.Cyclonesarewidelyused;theycontrolpollutantsfromcottongins,rockcrushers,andmanyotherindustrialprocessesthatcontainrelativelylargeparticulateinthegasstream.Heavydustattheinletofthecyclonecanalsoleadtopluggingofthecyclonehopper.AirPollutionEmissionControlDevicesforStationaryAbsorption&WetScrubbingEquipment

ElectrostaticPrecipitators(ESPs)ESPsarerelativelylarge,lowvelocitydustcollectiondevicesthatremoveparticlesinmuchthesamewaythatstaticelectricityinclothingpicksupsmallpiecesoflint.Transformersareusedtodevelopextremelyhighvoltagedropsbetweenchargingelectrodesandcollectingplates.Theelectricalfieldproducedinthegasstreamasitpassesthroughthehighvoltagedischargeintroducesachargeontheparticles,whichisthenattractedtothecollectingplates.AirPollutionEmissionControlDevicesforStationaryAbsorption&WetScrubbingEquipment

ElectrostaticPrecipitators(ESPs)Periodicallythecollecteddustisremovedfromthecollectingplatesbyahammerdevicestrikingthetopoftheplates(rapping)dislodgingtheparticulate,whichfallstoabottomhopperforremoval.Electrostaticprecipitatorsareoftenconfiguredasaseriesofcollectingplatestoimproveoverallcollectionefficiency.Efficienciesexceeding99%canbeachieved,andESPsareusedinmanyofthesameapplicationsasbaghouses,includingpowerplants,steelandpapermills,smelters,cementplants,andpetroleumrefineries.AirPollutionEmissionControlDevicesforStationaryAbsorption&WetScrubbingEquipment

IncineratorsIncinerationinvolvesthehighefficiencycombustionofcertainsolid,liquid,orgaseouswastes.Thereactionsmaybeself-sustainingbasedonthecombustibilityofthewaste,ormayrequiretheadditionofauxiliaryfuels,suchasnaturalgasorpropane.Theymaybebatchoperationsorcontinuousaswithflaresusedtoburnoffmethanefromlandfills.Whennotburningsolids,theyarealsocalledthermaloxidizers,andthesedevicescanoperateatefficienciesof99.99%(aswithhazardouswasteincinerators).AirPollutionEmissionControlDevicesforStationaryAbsorption&WetScrubbingEquipment

IncineratorsThermaloxidizersareusedtodestroyodorousortoxicVOCs.Achievingtherequiredtemperatures(upto2000℉)requiresalargefuelusage,andcostscanbehigh.Regenerativethermaloxidizers,though,canachieveveryhighheatrecoveries(upto95%),greatlyreducingfuelcosts.AirPollutionEmissionControlDevicesforStationaryAbsorption&WetScrubbingEquipment

BiofiltersBiofiltersoperatetodestroyVOCsandodorsbymicrobialoxidationoftheseproblemcompounds.Theyaremosteffectiveonwater-solublematerials.Thepollutedairispassedthroughawettedbed,whichsupportsabiomassofbacteriathatabsorbandmetabolizepollutants.Efficienciesover98%arepossiblewiththisapplication.AirPollutionEmissionControlDevicesforStationaryAbsorption&WetScrubbingEquipment

英语翻译的词义选择

根据词的单复数确定词义(1)Electronicsisabranchofsciencethatdealswiththestudyandapplicationofelectrondevices.

译文：电子学是有关电子装置的研究和应用的一门科学。(electronics看似为复数，实则单数，在句中为“电子学”的意思)Translation

英语翻译的词义选择

根据词的词类确定词义(1)Itistheatomsthatmakeupiron,water,oxygenandthelike.

译文：正是原子构成了铁、水、氧等类物质。(like在句中作为名词，表示“相同之物”)Translation

英语翻译的词义选择

根据词的专业领域确定词义

(1)Assumethattheinputvoltagefromthepowersupplyremainsconstant.

译文：假定由电源输入的电压保持不变。(power在句中作“电源”)Translation

英语翻译的词义选择

根据词语境确定词义

(1)Womenwhodrinkandsmokeheavilyarelikelytodevelopcancersoftheoralandtongueatayoungerage.

译文：大量饮酒并吸烟的妇女很可能在年轻时就患上口腔癌和舌癌。(develop在句中表示“患病”)Translation

英语翻译的词义选择

根据词的汉语习惯搭配确定词义

(1)Volcanicrocksfrominsidethefieldwerefoundtobenon-magnetic.

译文1：热田内的火山岩以前被发现是非磁性的。

译文2：以前的调查表明，这个热田的火山岩为非磁性岩石。buildaship造船

buildabridge架桥universalmeter万用表

universalmotor交直流两用电动机universaldividingheading多用分度表头universalconstant通用常数

universalrules一般法则Translation

英语翻译的词义选择

根据词的同义