环境省请负业务

1617DDT7POPs1970POPsPOPsPOPs13522POPs/POPsPOPsPOPsPOPsPOPs17316()()()()POPs()())¾¾¾¾¾¾¾¾¾¾¾¾==(2)(410132114g)8007506505ppmTCLP2ppb8Preventionandcontroltechnologiesandpractices8.3Reducingmercuryreleases8.3.1Natureofmercuryemissions629.Inordertofullyappreciatetherelevanceofvariousemissioncontroltechnologies,itisfirstnecessarytoreviewthecontextofthesemercuryemissions(PacynaandPacyna,2000,asmodifiedbyUScommentstoanearlierdraftofthisreport).•Concentrationsofmercuryincoalsandfueloilsvarysubstantiallydependingonthetypeoffuelanditsorigin.Themercuryincoalmaybeassociatedwiththeorganicortheinorganicconstituents(mineralmatter)ofcoal.Whenitisassociatedwithmineralmattersuchassulfidesitcanoftenberemovedbyphysicalcoalcleaningtechniques.Theremovalofmercuryfromtheorganicfractionofcoalismuchmoredifficultandcostly.•Mostoftheprocessesgeneratingatmosphericemissionsofmercuryemployhightemperature.Duringtheseprocesses,includingcombustionoffossilfuels,incinerationofwastes,roastingandsmeltingoperationsinnon-ferrousandferrousmetallurgy,andcementproduction,mercuryintroducedwithinputmaterialvolatilizesandisconvertedtoelementalmercury(Hg0)inthehightemperatureregionoftheprocess.AsthefluegasiscooledtofluegascleaningtemperaturesthemercurymayremainasHg0orpartofitmaybeoxidizedtoionicmercury[Hg(II)].Further,Hg0and/orHg(II)maybeadsorbedontoparticlestoformparticle-boundmercury[Hg(p)].TherelativemagnitudeofHg0,Hg(II),andHg(p)influegasiscalledthespeciationofmercury.•Mercuryoxidizationcanresultfromgas-phaseorgas-solidreactions(heterogeneousreactions).Laboratoryexperimentsandthermal-chemicalstudieshaveimplicatedatomicchlorine(Cl-)andnitrogenoxide(NO2)astwopotentialoxidizingagents.Thermal-chemicalequilibriumstudiesindicatethatthepreferredoxidationproductisHgCl2whensufficientchlorineispresentinthefuelorwaste(i.e.,whentheconcentrationofchlorineissubstantiallyhigherthantheconcentrationofmercuryinthefluegas).Flyashandothersurfaceswithinthecombustionsystemcancatalyzeormediatemercuryoxidizationreactions.Majorfactorsthataffectmercuryspeciationarethefuel(orwaste)composition,thecombustionconditions,andthetypeoffluegascleaningmethodsused.•Varioustechnologieswithinthesameindustrymaygeneratedifferentamountsofatmosphericemissionsofmercury.Itcanbegeneralizedforconventionalthermalpowerplantsthattheplantdesign,particularlytheburnerconfiguration,flyashcharacteristics,etc.,haveanimpactontheemissions.3•Themajorparametersthatdeterminetheamountandcharacteristicsofmercuryemittedtotheatmospherefromhigh-temperatureprocessesaretheamountandspeciationofmercuryenteringthefluegascleaningdevices,thetypeoffluegascleaningdevicesused,theconcentrationsofotherconstituents(chlorine,NOx),andthetemperatureatwhichthefluegascleaningdevicesareoperated.8.3.2Availableoptions630.Theoptionsavailableforreducingmercuryreleasesfromvariousprocessesmaybeorganizedintwocategories:non-control-technologyoptions,andcontrol-technologyoptions.631.Thebest-knownnon-control-technologyoptionsincludesuchmeasuresas:•Conversiontonaturalgas,oil,oranon-fossilpowergeneratingtechnology;•Improvedenergyefficiency(reductionsofCO2-emissionsasforeseenintheKyotoProtocoltotheUNFrameworkConventiononClimateChangeareexpectedtohelpreducemercuryemissionsfromfossilfuelpowergeneration);•Banningmercuryinproducts;•Taxesorotherdisincentivestotheuseofmercuryinproducts;and•Productlabeling.3Cyclone-andpulverizedcoal-(PC)firedboilersbothoperateattemperaturesthatvolatilisethemercuryincoalandconvertittoHg0inthehigh-temperatureregionsofthefurnace.Thedifferenceinstackemissionsofmercuryfromthesetwotypesofunitsisprobablyduetotheamountandcharacteristicsofflyash.Incyclone-firedunitsmostofthemineralmatterisconvertedtoslag,whichisremovedinamoltenforminthebottomofthecombustionunit.Arelativelysmallamountofthemineralmatterisconvertedtoflyash,whichinturncontainsarelativelysmallamountofunburnedcarbon.InPC-firedboilers,approximately90percentofthecoalmineralmatterisconvertedtoflyash.Theuseoflow-NOxburnerstendstoincreasetheamountofcarboninflyash,increasingtheamountofmercurythatisadsorbedandsubsequentlycapturedasHg(p)inadownstreamelectrostaticprecipitator(ESP)orfabricfilter(FF).Asimilarphenomenonhasbeenobservedinsystemsthatburnmunicipalsolidwaste.Somemass-burn-water-wallincineratorsexhibitverygoodcombustionandlowflyashcarbonconcentrations.Welloperatedmass-burnunitsequippedwithspraydryerandfabricfilters(SD/FFs)exhibitlittleifanymercurycapture.Alternatively,UStestsononerefuse-derived-fuel(RDF)combustorequippedwithaSD/FFexhibitedmercurycapturesrangingfrom96to99percent.Inasimilarfashion,fluidizedbedincineratorstypicallyemitrelativelylargeamountsofflyashwithahighcarboncontent.WhileimprovedmercurycapturebyflyashsometimescorrelateswithlowNOxemission,theredoesnotappeartobeacause632.Banningandtaxesarereasonablyself-explanatory.Productlabellinghasadvantagesanddisadvantages,buthasprovenrathereffectiveinsomecases,incombinationwithothermeasures.Forexample,inthecaseofconsumerbatteries,consumerspaidsignificantattentiontolabelsconcerningthecontentofmercuryandcadmium.633