2012-2014PollutionControlDr.Zhu’spart

Sulfurcompoundsareknowntooriginatefrompetroleumandnaturalgasandrichwastegases.

Brieflydescribethestrategiesinremovalofsulfurcompoundsfromthesetwosources.

Answer:

Forpetroleumandnaturalgas:Themostcommonmethodforremovingonecomponentfromagasstream—absorptionandstripping.Procedure:

①feedgasentersabsorber(gaspassesupwards,liquidsolventdownwards)

②bubblecaps,sievetrays,orpackingpresentintheinterioroftheabsorbertopromotegoodcountercurrentcontact

③whenthegashasreachedthetopofthecolumn,mostoftheunwantedcomponenthasbeendissolvedinthesolvent,thecleanedgaspassesontotheatmosphereortoitsfurtheruse

④theloadedsolventpassestothestripper,whichisoperatedatamuchlowerpressureandhighertemperaturethantheabsorber.

⑤Thestripped,orleansolventissentbacktotheabsorbercolumn.

Fortherichwastegases:Therichwastegascanbetreatedeconomicallyinplantsthatproducesulfuricacid:

SO2+1/2O2=SO3SO3+H2O=H2SO4

TheconversionofSO2toSO3isanequilibriumreactionanditisexothermic.Thereactionoscarried

outin3or4separatecatalystbedswithintercoolersbetweenthem.

ExplaindifferencesbetweenabsorberandstripperontheiroperationconditionsAnswer:

Inabsorber,thegaseshavetodissolveinthesolvent,sothepressurehastobehighandthetemperaturehastobelowinordertopushthegasesdissolveintotheliquidsolvent.

Instripper,thegaseshavetoescapefromthesolvent,sothepressurehastobelowandthetemperaturehastobehighinordertoextractgasesfromliquidsolvent.

Describethefunctionsofscrubber,effluentholdtank,thickenerofatypicallimestonewetscrubber.

Answer:

Scrubber:Scrubbersystemsareadiversegroupofairpollutioncontroldevicesthatcanbeusedtoremovesomeparticulatesand/orgasesfromindustrialexhauststreams

Effluentholdtank:Storetheeffluentofthesystem.RecirculatetheslurryandofferplaceforCaSO3oxidisedtoCaSO4.

Thickenerofatypicallimestonewetscrubber:reducethewatercontentofthewasteslurry;filtertoremovesolid.

OneofthelargestcoppersmeltersintheUSAproduces320000tonsofcopperperyear.Thecopperoresmeltedisprincipallychalcopyrite.IfallthesulfurwereemittedtotheatmosphereasSO2,howmuchwouldbeemitted?Ifallthesulfurintheorewereconvertedtosulfuricacid,howmuchsulfuricacidperyearwouldthesmelterproduce?

Answer: 2CuFeS2+5O2→2Cu+2FeO+4SO2

367.6 256

320000 x

X=222850.9t

SO2+1/2O2+H2O=H2SO4

64 98

222850.9 X

X=341240.4t

So,thesulflurdioxideis222850.9t,thesulfuricacidis341240.4t.

Namethethreeclassesofnitrogenoxidesfoundincombustiongases.Describetheioriginsandestimatetheircontributionstothetotalnitrogenoxideemissionsfromcoalcombustionatdifferenttemperatures.

Answer:

Threeclassesofnitrogenoxidesincombustiongases:Thermalnitrogenoxides,PromptnitrogenoxidesandFuelnitrogenoxides.

Origins:

Thermal:mostsignificant,formedbysimpleheatingofN2andO2,eitherinaflameorbysomeotherexternalheatingsuchaslightningbolt.

Prompt:FormedquicklyfromtheinteractionofN2andO2withsomeoftheactivecarbonspeciesderivedfromthefuelinflames-notformedsimplybyheatingN2andO2,notobservedinflamesoffuelswithnocarbon.

Fuel:formedbyconversionofsomeofthenitrogen(usuallyorganicnitrogen)originallypresentinthe

fueltoNOx.

EstimatedcontributionofthethreeNOmechanismstototalNOxformationincoalcombustion:

Describetwo-stagecombustionmethodandwhataretheadvantagesanddisadvantages?Answer:

Description:Two-stagecombustion,orreburning,isthemethodthatmixpartofthecombustionairwiththefuel,burnasmuchofthefuelasthatamountofairwillburn,thenaddtheremainingairandfinishthecombustion.

1ststage:Tmaxisloweredasnotallthefuelisburned,atthemaximumtemperature,allO2isusedup-notenoughtofromNO

2ndstage:heatreleasedinthefirststagehasbeenremoved,maximumtemperaturelowered,formationofNOsmall.

Advantages:cheap

Disadvantages:alargerfireboxisrequiredforthesamecombustionrate,difficulttogetcompleteburninginthe2ndstage.

Describehowthepeaktemperatureofaflamedependsonthesizeoftheflame,degreeoffuel-airpremixingandamountoffuel-airpreheat.

Answer:

Peaktemperatureofaflamedependson:fuelandoxidizerused,sizeofflame,degreeoffuel-airpremixingandamountoffuel–airpreheat.

Flamegeneratesheatbychemicalreactionandlosesittothesurroundingpartlybythermalradiation,partlybyconductionandpartlybymixingwiththesurroundingair-largerthesurfaceareaoftheflame,lowertheflametemperature.Surfaceareaofflamesdependsstronglyonhowmuchpremixingoffuelandoxidizer.Airandfuelarecompletelymixedbeforeignition.Preheatingcombustionairincreasestheflametemperature.

Forasamplecontaining78%N2and4%O2,howlongwouldthegashavetobeheldat2000KforthecalculatedthermalNOconcentrationtobe3000ppm?

Answer:

Accordingtothetableinhandout,

[NO]eat2000Kis3615ppm=3615×10-6(mg變g,L變毫升)×6.1×10-6mol/cm3(molardensity)=2.21×10-8mol/cm3

[O2]=0.04×6.1×10-6=2.44×10-7mol/cm3

Kb=4.1×1013exp(-9160