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.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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