大气复习资料含答案共11页.docx

大气复习资料含答案共11页.docx

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大气复习资料含答案共11页

大气复习资料

一、概念解释

（1）Globewarming:

GlobalwarmingistheincreaseintheaveragemeasuredtemperatureoftheEarth'snear-surfaceairandoceanssincethemid-twentiethcentury,anditsprojectedcontinuation.

（2）Temperatureinversions：

Atemperatureinversionsisathinlayeroftheatmospherewherethedecreaseintemperaturewithheightismuchlessthannormal（orinextremecases,thetemperatureincreaseswithheight）.

（3）ESP:

Electrostaticprecipitator,whichislikeagravitysetterorcentrifugalseparator,butelectrostaticforcedrivestheparticlestothewall.

（4）HEPA:

HighEfficiencyParticulateAir

（5）Leanbum：

Leanburnreferstotheuseofleanmixturesinaninternalcombustionengine.Theair-fuelcanbeashighas65:

1,sothemixturehasconsiderablylessfuelincomparisontothestoichiometriccombustionratio（14.7forpetrol,forexample）.

（6）Plumerise:

theplumerisingadistance△habovethetopofthestackbeforelevelingout.

（7）Wetscrubber:

Adevicethatcollectsparticlesbycontactingthedirtygasstreamwithliquiddrops.

（8）Photochemicalsmog：

（9）ThermalNO:

ThermalNOxreferstoNOxformedthroughhightemperatureoxidationofthediatomicnitrogenfoundincombustionair.

（10）A/Fratio:

Airtofuelratioforautoengines.

（11）PM2.5:

particlewiththeaerodynamicdiameterlessthan2.5um,whichisalsocalledRespirableParticles.

（12）Alternativefuel:

Severalotherfuelsexceptofconventionalgasolineanddiesel,whichhavebeenusedformanyyearsinslighutlymodifiedautomobileengines,forreasonsofcostandavailability.

（13）VOCs:

Volatileorganiccompoundsarethoseorganicliquidsorsolidswhoseroomtemperaturevaporpressurearegreaterthanabout0.01psia（=0.0007atm）andwhoseatmosphericboilingpointsareuptoabout500℉,whichmeansmostorganiccompoundswithlessthan12carbonatoms.

（1）SCRandSNCR:

6NO+4NH3→5N2+6H2O,4NO+4NH3+O2→4N2+6H2O

2NO2+4NH3→3N2+6H2O.

Thesereactionscanbecarriedoutoveravarietyofcatalysts,thetemperatureisbetween1600℉and1800℉,oncethetemperatureincreases,thedominantreactionis

NH3+O2→NO+1.5H2O,thecatalyticprocessesarecalledSCR,andthehigher-temperatureones,withoutcatalysts,callSNCR.

（2）Aerodynamicdiameter:

Airborneparticleshaveirregularshapes,andtheiraerodynamicbehaviorisexpressedintermsofthediameterofanidealizedsphericalparticleknownasAerodynamicdiameter.

（3）PrimaryParticles:

Particlesfoundintheatmosphereintheforminwhichtheywereemitted,forexamples,NO,CO,SO2

（4）PointSources:

smallnumberoflargesourcesthatemitlargeramountspersource,athigherelevations（powerplants,smelters,cementplants,etc.）calledpointsources

二、Answerfollowingquestions

（1）Whicharethemainconstituentsforthegroundlevelozone

formation?

Ozoneisformedwhenthefollowingconstituentsarepresent.

Nitrogenoxides,VolatileOrganic,Compounds,Sunlight,Hightemperature（>18℃）

NO+VOC+O2+Sunlight→NO2+O3

（2）Pleaselistfivemajortypesofwetscrubbers.

PlateScrubber（板式）PackedScrubber（填料式）PreformedSprayScrubber（喷雾式）Gas-AtomizedSprayScrubber（气体雾化）CentrifugalScrubber（离心式）Impingement-EntrainmentScrubber（冲击夹带式）MechanicallyAidedScrubber（机械辅助式）MovingBedScrubber（移动床式）

（3）HowtocontrolVOCspollutionbyprevention?

Twoexamples.

Substitution（代替）,Replacinggasolineasamotorfuelwithcompressednaturalgasorpropaneisaformofsubstitution.

ProcessModification（过程修改）,Replacinggasoline-poweredvehicleswithelectric-poweredvehiclesisaformofprocessmodification.

Leakage（渗漏）Control,Storinglargeamountsofgasolineinfloatingrooftanks.

（4）Pleaseintroducetheprocessofforced-oxidationLimestoneWet

Scrubbingbriefly？

（5）WhatarethemostdifferentpointsbetweenSCRandSNCR?

（6）CanTWCbeappliedinthetreatmentofdieselexhaust（=emission

ofdieselengine）?

Why？

·Thecharacteristicofemissionofdieselengine:

AmplePMandExcessiveO2,Lowertemperature;

·Thedifficultyinthereactionofsolid-gas-solid.

Key:

Themixtureprocessoffuelandairforgasenginesisdistinguishedfromthatfordieselengines,hencethecharacterofonetypeengineisdifferentfromtheotherone:

therearemainlyfivegases（NOX,HC,COandO2,CO2）intheexhaustofgasmotors,whilethereareampleO2andfourothergasesmentionedaboveinthetailpipeemissionofdieselengine.AndthepresenceofabundantO2wouldinhibittheperformanceofTWC.

Moreover,thecontactandreactionofsolid-solid-gasresultinginthedifficultiesforcatalyststooxidationtheparticulateintheexhaustofdieselengine,whilethecontactandreactionofsolid-gas-gasoccurintheexhaustofgasolineengineandthelatterreactioniseasier.

（7）Whatkindsofindoorairpollutantsaremostlyconcernedby

public?

a）Random

b）Combustionby-products

1.CO,CO2,SO2,Formaldehyde,Hydrocarbons,NOx

2.Particulates,polyaromatichydrocarbons

c）Cigarettesd）Volatileorganiccompounds

f）Biologicalcontaminants

（8）Listthetechnologystrategyforthecontrolofparticles.

（9）Givenamesofthreetypicalkindsofcombustionreactors.Which

haslowestoperatortemperatureamongthosereactors?

1.Directflameincineration2.Thermalincineration

3.Catalyticincineration（haslowestoperatortemperature）

（10）WhatarethemajordevelopmentproblemsofForced-oxidationlimestonewetscrubbing?

（11）Whatareprimaryairpollutantsandsecondaryairpollutants?

Anyexample?

primaryairpollutantsaredirectlyfromthesources,forexamples,NO,CO,SO2.

Thesecondaryairpollutantsarefromtheprimarypollutants,suchasNO2,NO3,fineparticles.NO+CH+O2+sunlight→NO2+O3

（12）Basicstrategyofcontrolforparticulatepollutants（three

aspects）?

Impaction碰撞Interception截留Diffusion扩散

Byforcingtheindividualparticlestocontacteachother,

Bycontactingthemwithdropsofwater,

BypreventingtheemissionofgaseousPollutants.

（13）HowtoreducetheformationofNOxinfluegasbymodifyingthecombustionprocesses?

p459

（14）Pleaseexplaintheformationofacidrain?

Sulfuroxidesandnitrogenoxides

NONO2HNO3nitricacidSO2H2SO4sulfuricacid

（15）WhatarebasicprinciplesofelectrostaticPrecipitators（six

activities）?

·Ionization-Chargingofparticles

·Migration-Transportingthechargedparticlestothecollectingsurfaces

·Collection-Precipitationofthechargedparticlesontothecollectingsurfaces

·Chargedissipation-Neutralizingthechargedparticlesonthecollectingsurfaces

·Particledislodging-Removingtheparticlesfromthecollectingsurfacetothehopper

·Particleremoval-Conveyingtheparticlesfromthehoppertoadisposalpoint

三、Calculation

1）Estimatetheconcentrationofcarbonmonoxideatthedownwindedgeofacity.Thecitymaybeconsideredtoconsistofthreeparallelstrips,locatedperpendiculartothewind.Forallofthestripsthewindvelocity

equals3m/s.Thepropertiesofeachofthestripsaredescribedinthefollowingtable,

Nameofstrip

Length,km

Emissionrate

q,g/s·km2

Mixingheight

H,m

Upwindsuburbs

5

100

400

Downtown

2

500

500

Downwindsuburbs

5

100

400

solution：

c1=0+（100*5000）/（3*400）=416.7μg/m3

c2=416.7+（500*2000）/（3*500）=1083.4μg/m3

c3=1083.4+（100*5000）/（3*400）=1500.1μg/m3

2）AnESPisdesignedtotreat540,000acfm（actualcubicfeetperminute）with99%efficiency.Assuminganeffectivedriftvelocityof0.12m/s,calculatetherequiredplateareaandthenumberofplates.Theplatesizeis5.4mtallby3mlong（A=－Q×㏑（1－η）/ωp,acfm＝1ft3/min,1m=3.28ft,1m2＝1550in2＝10.7639ft2）.

solution1ft3/min=（1/3.28）3m3/min=0.0283m3/min

540000acfm=540000*0.028315282m3/min=254.7m3/s

A=-（254.7/0.12）ln（1-0.99）=9774.47m2

N=9774.47/514.3=604

3）Wewishtotreatanairstreamcontaining0.005molfraction（0.5%,5000ppm）toluene,movingataflowrate2240m3/hat0℃and1atm,soastoremove99%ofthetoluenebywaterabsorption.Estimatetherequiredwaterflowrate.HereHenry’slawconstantis10000atm.

Solution：

4）Apowerplantfluegascontains1000ppmofSO2andisemittedatarateof224m3/sat546Kand1atm.AForced-oxidationlimestonewetscrubbingsystemistobeusedtoachieve90%removaloftheSO2.CalculatetheamountofCaSO4·2H2Ocontainedinthefinalsolidproductint/d.

Solution：

=（101325*224*1000*10-6）/（8.315*546）=4.999mol/s

SO2~CaSO4·2H2Oson（caso4）=n（so2）=4.999mol/s*90%=4.4991mol/s

m=4.4991mol/s*172g/mol*3600*24s/d*10-6t/d=66.86t/d

5）Apowerplantemits36kg/hofSO2atheightH=120mandthewindspeedis2m/s.DispersionCoefficients:

σy=40mandσz=30m,Estimatetheground-levelconcentrationofSO2fromthissourceatadistance1kmdirectlydownwind?

Solution：

u=2m/s,H=120m,Q=36kg/h=10g/s,y=0,z=H=120,x=1000m

=0.40

6）Apowerplantfluegascontains1000×10-6（1000ppm）ofNOx，andisemittedatarateof89.6m3/sat546Kand1atm.TheNOxis90%molNO,balanceNO2.AselectivecatalyticreductionsystemistobeusedtoremovetheNOx.Calculatetheminimumofammonianeededinkg/h.

Solution:

4NO+4NH3+O2→4N2+6H2O2O+4NH3+O2→3N2+6H2O

PV=nRTn=（101325*89.6*1000*10-6）/（8.315*546）=2.0mol/s

n（no）=0.9*2mol/s=1.8mol/sson（no2）=2.0-1.8=0.2mol/s

n（NH3）=n（no）+2*n（no2）=1.8+0.4=2.2mol/s

m=2.2mol/s*17g/mol=37.4g/s=134.64kg/h

7）TheefficiencyofanESPis98%.TheefficiencyoftheESPdropsto93%asaresultofflowratechanges.Calculatetheratioofflowratesfortheabovesituation.Useappropriateassumption

Solution:

A=－Q×㏑（1－η）/ωpSOQ=-A*ωp/㏑（1－η）

AssumetheplateareaAandtheeffectivedrivevelocityωpareunchanged.

Then

Q1/Q2=（-A1*ωp/㏑（1－η1）/（-A2*ωp/㏑（1－η2）

=㏑（1－η2）/㏑（1－η1）

=㏑（1－0.93）/㏑（1－0.98）

=0.68

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