传质与分离习题含答案.docx

传质与分离习题含答案.docx

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传质与分离习题含答案

ProblemsforMassTransferandSeparationProcess

Absorption

1Theammonia-airmixturecontaining9%ammonia（molarfraction）iscontactwiththeammonia-waterliquidcontaining5%ammonia（molarfraction）.Underthisoperatingcondition,theequilibriumrelationshipisy*=0.97x.Whentheabovetwophasesarecontact,whatwillhappen,absorptionorstripping?

Solution:

y0.09x0.05y0.97x

y0.970.050.0485y0.09Itisanabsorptionoperation.

0

2Whenthetemperatureis10candtheoverallpressureis101.3KPa,thesolubilityof

4

oxygeninwatercanberepresentedbyequationp=3.2710x,wherep（atm）andxrefertothepartialpressureofoxygeninthevaporphaseandthemolefractionofoxygenintheliquidphase,respectively.Assumethatwaterisfullycontactwiththeairunderthatcondition,calculatehowmuchoxygencanbedissolvedinthepercubicmeterofwater?

Solution:

themolefractionofoxygeninairis0.21,henee:

p=Py=1x0.21=0.21amt

Becausethexisverysmall,itcanbeapproximatelyequaltomolarratioX,thatis

6.42*10

So

6.42*106（kmolO2）*32（kgO2/kmolO2）

1（kmolH2O）*18（kgH2O/kmolH2O）

3Anacetone-airmixturecontaining0.02molarfractionofacetoneisabsorbedbywaterinapackedtowerincountercurrentflow.And99%ofacetoneisremoved,mixedgasmolarflowfluxis0.03kmol•s1m-2,practiceabsorbentflowrateLis1.4timesasmuchastheminamountrequired.Undertheoperatingcondition,theequilibriumrelationshipisy*=1.75x.Volumetotal

—121

absorptioncoefficientisKya=0.022kmol•smy.Whatisthemolarflowrateoftheabsorbentandwhatheightofpackingwillberequired?

Lybya0.020.99

Vminx；xa0.021.75

1.4

2.43

L2.430.030.0729kmoLm2s

min

L2.43

NumberofmasstransferunitsNoy=（yi-y2）/y=12

（yb-ya）=0.02-0.0002

y=[（yb-y*b）-（ya-y*a）]/ln[（yb-y*b）/（ya-y*a）]

（yb-y*b）=0.02-1.75xb=0.0057

Xb=V/L（yb-ya）=（0.02-0.0002）/2.43=0.00815

（ya-y*a）=ya=0.0002

OrNoy-^ln[（ybmXa）（1S）S]=12

1SyamXb

HoyNoy1.3641216.37m

4ThemixedgasfromanoildistillationtowercontainsH2S=0.04（molarfraction）.Triethanolamine（absorbent）isusedasthesolventtoabsorb99%H2Sinthepackingtower,theequilibriumrelationshipisy*=1.95x,themolarfluxrateofthemixedgasis0.02kmol-m-2°s-1,overallvolumeabsorptioncoefficientisKya=0.05kmol-s1my‘ThesolventfreeofH2Sentersthetoweranditcontains70%oftheH2Ssaturationconcentrationwhenleavingthetower.Trytocalculate:

（a）thenumberofmasstransferunitsNoy,and（b）theheightofpackinglayerneeded,Z.

solution:

ya=yb（1-0.99）=0.04*1%=0.0004

xb*=yb/m=0.04/1.95=0.0205xb=0.7xb*=0.0144

yb*=1.95*0.0144=0.028

yb-yb*=0.04-0.028=0.012

△ym=0.0034

Z=HoyNoy

Noy=（yb-ya）/△ym=11.6

HoyGm/Kya0.02/0.050.4m

Z=11.6*0.4=4.64m

5Ammoniaisremovedfromammonia-airmixturebycountercurrentscrubbingwithwaterinapackedtoweratanatmosphericpressure.Given:

theheightofthepackinglayerZis6m,themixedgasenteringthetowercontains0.03ammonia（molarfraction,allarethesamebelow）,thegasoutofthetowercontainsammonia0.003;theNH3concentrationofliquidoutofthetoweris80%ofitssaturationconcentration,andtheequilibriumrelationisy*=1.2x.Find:

（1）thepracticalliquid—gasratioandtheminliquid—gasratioL/V=?

.

（2）thenumberofoverallmasstransferunits.

（3）ifthemolarfractionoftheammoniaoutofthetowerwillbereducedto0.002andtheotheroperatingconditionskeepunchanged,isthetowersuitable?

L

0.03

0.003,"

solution:

（1）

——

1.35

G

0.8

0.031.2

12

（2）

S

0.89

1.35

NOY

1

0.03

In0.110.896.26

1

0.89

0.003

Noy

0.9588.478.16.0mitisnotsuitable

6Purewaterisusedinanabsorptiontowerwiththeheightofthepackedlayer3mtoabsorbammoniainanairstream.Theabsorptivityis99percent.Theoperatingconditionsofabsorberare

02

101.3kpaand20c,respectively.ThefluxofgasVis580kg/（m.h）,and6percent（volume%）of

ammoniaiscontainedinthegasmixture.ThefluxofwaterLis770kg/（m2.h）.Thegasandliquid

*

iscountercurrentinthetoweratisothermaltemperature.Theequilibriumequationy=0.9x,andgasphasemasstransfercoefficientkGaisproportionaltoV0.8,butithasnothingtodowithL.

Whatistheheightofthepackedlayerneededtokeepthesameabsorptivitywhentheconditionsofoperationchangeasfollows:

（1）theoperatingpressureis2timesasmuchastheoriginal.

（2）themassflowrateofwaterisonetimemorethantheoriginal.3）themassflowrateofgasistwotimesasmuchastheoriginal

Solution:

Z3m,p1atm,T293K

Y2Y（10.99）0.000638

TheaveragemolecularweightofthemixedgasM=290.94+170.06=28.28

（10.06）19.28kmol/（m2