Mass transfer and hydrodynamic characteristics of new carbon carbon packing: Application to CO2 post-combustion capture

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_{Alix, Pascal and Raynal, Ludovic and Abbé, François and}

Meyer, Michel and Prevost, Michel and Rouzineau, David (2011) Mass transfer

and hydrodynamic characteristics of new carbon carbon packing: Application

to CO2 post-combustion capture. Chemical Engineering Research and Design,

vol. 89 (n°9). pp. 1658-1668. ISSN 0263-8762



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Mass

transfer

and

hydrodynamic

characteristics

of

new

carbon

carbon

packing:

Application

to

CO2

post-combustion

capture

Pascal

Alix

a

_,

_Ludovic

_Raynal

a

_,

_Franc¸ois

_Abbe

b

_,

_Michel

_Meyer

c

_,

Michel

Prevost

c

_,

_David

_Rouzineau

c,∗

a_{IFP,BP.3,69360Solaize,France}

b_{SnecmaPropulsionSolide,GroupeSafran,Lescinqchemins33187LeHaillan,France}

c_{UniversitédeToulouse,INPT,ENSIACET,LaboratoiredeGénieChimique(UMR5503),4alléeEmileMonso,BP84234,31432Toulouse,} France

a

b

s

t

r

a

c

t

Anovelstructuredpacking,the4Dpacking,hasbeencharacterizedintermsofhydrodynamics,effectiveareaand gassidemasstransfercoefficient.Theincreaseofthe4Dopeningfractionallowstoreducepressuredropandto getabettercapacitythanMellapak500Yand750Y,forwhichthegeometricareasaresimilar.The50%open4D packing,4D-50%,leadstoeffectiveareaswhicharehigherthanMellapak500Yones,anddoubledcomparedwith MellapakPlus252Yones.Effectiveareasforthe4Ddonotdecreasewhentheopeningfractionincreasesfrom30to 50%,thisindicatesthatanon-negligibleamountofdropletsisgeneratedat50%.Gassidemasstransfercoefficient hadbeenmeasuredwithanoriginalexperimentalmethod:waterevaporation.Correspondingresultsseemtobe inagreementwiththeliterature,andwiththefactthatalargeamountofdropletsisgenerated.Correlationsare proposedforbotheffectiveareaandgassidemasstransfercoefficientforthe4D-50%.

The4D-50%packingcouldbeveryinterestingforpost-combustionCO2capturesinceitgenerateslowpressure

dropandaveryhighinterfacialarea.Thiswillbefurtherconfirmedbyaneconomicstudyforwhichtheabsorber plantwillbedesignedwitharatebasedmodel.

Keywords: Newpacking;Post-combustioncapture;Absorption;Pressuredrop;Masstransferefficiency

1.

Introduction

The captureand geologicalstorage of the CO2 emitted by

power plants is one important way to reduce greenhouse

gasesemissions.Hugegasflowratesmustbetreatedfor post-combustioncaptureofCO2,whichleadtoverylargecapture

amineplants.Theoptimizationofsuchhighvolumereactor designisthusofgreatimportanceinordertoreduceinvest costs.Sincecaptureprocessoperatesdownstreamthepower plant,itrequires verylowpressuredropinordertoreduce theboosterfanelectricconsumption,operatingcostsand effi-ciencylost.

Tominimizevolumereactorandpressuredrop,very effi-cientgasliquidcontactorsareneeded.Intheframeworkof

∗_{Correspondingauthor.}

E-mailaddress:david.rouzineau@ensiacet.fr(D.Rouzineau).

GASCOGNE project, supported by ANR, a novel structured

packinghasbeenconsideredforchemicalengineering stud-ies,the“4Dpacking”.Thelatterhadbeeninitiallydeveloped and ismanufactured bySPS. Tobuild-upmodels, testsare highlyneededtocharacterize4Dpackingsintermsof hydro-dynamicsandmasstransfer.Theaimofthepresentstudyisto determinethepressuredrop,theeffectivearea,ae,andthegas

sidemasstransfercoefficient,kG,forthreegeometric

config-urations.SinceoneassumesthatMEA30wt%isthebasecase fortheprocess(Knudsenetal.,2006;Feronetal.,2007),onecan considerthatfastreactionswilloccurincaptureplants.aeand

kGbecomethemainparameterstoestimatetheefficiencyof

anabsorber(Danckwerts,1970).Ithastobenoticedthat exper-imentshavebeenconductedwithbothIFPandLGCfacilities.

Nomenclature

AB distancebetweentwocrossingsoffibres

Ac columncross-section(m2)

ae effectiveoreffectiveareaofthepacking(m−1)

ae,4D effective oreffective areaofthe 4Dpackings

(m−1₎

ae,void effectiveoreffectiveareaoftheIFPempty

col-umn(m−1₎

ae,global effective or effective area ofcolumn section

(m−1₎

ag geometricarea(m−1)

C0

CO2 CO2 molar concentration in the liquid bulk

(molm−3₎

Cg concentration of gas phase needed for kgae

measurement(moll−1₎

Cl concentrationofliquidphaseneededforkgae

measurement(moll−1₎

C0

OH OH−ionsmolarconcentrationintheliquidbulk

(molm−3₎

C0

Na Na+ionsmolarconcentrationintheliquidbulk

(molm−3₎

d columninnerdiameter(m)

DCO2 CO2 diffusion coefficient in the liquid phase

(m2_s−1₎

Dm diameterofthemandrel

dp drippointdensityoftheliquiddistributor(m−2₎

dz heightofanelementofthecolumn(m)

E enhancementfactor

FG

CO2 CO2gasmolarrate(mols −1₎

FL

CO2 CO2liquidmolarrate(mols −1₎ FS gasF-factor=√G×VsG(Pa0.5)

FS|fl gasF-factoratthefloodingpoint(Pa0.5) G gasflowrate(kgh−1_m−2₎

G0 airflow(ms−1₎

h,hg,CO2,etc. contributionsofacation,ananion,anda

gas,respectively(lmol−1₎

H column’sheight(m)

He Henryconstant(Pam3_mol−1₎

Hw Henryconstantforwater(Pam3mol−1)

I ionicstrengthofsolution(moll−1₎ k2 kineticconstant(m3_mol−1_s−1₎

k∞

2 infinitely diluted solution kinetic constant

(m3_mol−1_s−1₎

kg gassidemasstransfercoefficient(ms−1)

KG overall gas side mass transfer coefficient

(molPa−1_m−2_s−1₎

kL liquidsidemasstransfercoefficient(ms−1)

Lf widthofcarbonfabric

Nf numberofspindle

P pressure,neededforkgaemeasurement(Pa)

PCO2 CO2partialpressure(Pa) Ptot totalpressureofthecolumn(Pa)

QL liquidload(m3m−2s−1)

S channelsideofthestructuredpacking(m)

T temperature(K)

TAS temperatureatadiabaticconditionsof

satura-tion(◦_C)

TGin,TGout inletandoutletgastemperatures(◦C)

TLin,TLout inletandoutletliquidtemperatures(◦C)

Tws waterstoragetemperature

VsG superficialgasvelocity(ms−1)

Y absolutehumidity, needed forkgae

measure-ment

YAS absolutehumidityatadiabatictemperatureof

saturation

Yin,Yout absoluteinletand outlethumiditiesofairin

column

yx molarfractionofthecomponentxinthegas

phase(mol/mol)

z axiscolumnposition(m)

1P/L pressuredropperunitlengthofthepackedbed (Pa/m)

1Ptot totalpressuredropofthecolumn(Pa)

Non-dimensionalterms

Ha Hattanumber

Greek

 braidangle(◦₎

ε voidfractionofthebed

fCO2 specific absorbed molar flux of CO2

(molm−3_s−1₎

wCO2 absorbedmolarfluxofCO2(molm−2s−1)

G gasdensity(kgm−3)

Inthefollowing,theexperimentalset-upsandmethodsare firstdescribed.Second,resultsareshownanddiscussed.Last, correlationstopredictpressure drop,effectiveareaandgas sidemasstransfercoefficientareproposed.

2.

Methods

and

materials

2.1. Packingstructure

Thesubjectofthisstudyfocusesonanewstructuredpacking technique(SPSPatent2005)developedbySnecmaPropulsion Solide(theSAFRANgroup).Itisconstructedwithinterwoven carbonfibres(Fig.1).Thetubesareformedwithcarbonfabrics whicharewovenonamandrelaccordingtoaparticularbraid angle(Fig.2a).Thebraidangle()correspondstotheangle formedbetweenabraidthreadandthebraidaxis(Fig.2b).

Fig.2–(a)Carbonfabricswovenonamandrel;(b)braid angle;(c)crossingoffibres.

Thedistancebetweentwofibrecrossings(Fig.2c)alongthe circumferenceisgivenby

AB= 2Dm Nf

, (1)

whereDmisthediameterofthemandrel(equivalenttothe

diameterofatube)andNfisthenumberofspindles(Fig.2a,

16spindles).If

AB≤_cosLf_, (2)

Fig.3–Onetubewithholes.

whereLfisthewidthofacarbonfabric,thenthereisnofree

spacebetweenthefibres(thereisnohole);butif AB> Lf

cos, (3)

then ahole isformed. Fig. 3representsatube withholes. Therefore,thevalueofthebraidangledeterminesthetube holesizes,andthelowerthebraidanglethebiggertheholes.

The diameter of the mandrel can vary from 4.5mm to

20mm,andthebraidanglecanvaryfrom15◦_to45◦_.The

open-ingsthereforeswingfrom0%to85%,correspondingtoahole surfaceareafrom0mm2_to735mm2_{.Thetubesarethenfitted}

togetheraccordingtothefourdiagonalsofacubeasshown inFig.4a,whichdemonstrateswhythispackingiscalled“4D packing”. Finally,thelayout isrepeated inthe threespatial directions(Fig.4b)toobtainthefinalstructure(Fig.4c).

Twopackingsstructuresweremadewith10mmdiameter

tubes.Thefirstgenerationwasmadewithabraidangleof30◦_,

soaholesizeof7.4mm2 _{(correspondingtoanapproximate}

openingof30%;named4D30%,Fig.5).Thispackingpossesses avoidfractionofapproximately94% andageometricarea,

ag,of420m2m−3(thesurfaceareaisevaluatedby

geometri-calcalculation,knowingthesurfaceoftubes,thediameterof holeandthenumberoftubeperpacking’svolumeinm3_).The

second generationisrelativelysimilar tothefirstonewith only8spindles(Nf)insteadof12,sotheholesizechangesand

becomes26.6mm2_{(relativetoanapproximateopeningof50%,}

named4D-50%).Thispackingmaintainsageometricarea,ag,

of330m2_m−3_{.Table1resumesthecharacteristicsofthesetwo}

packing.

Thisstructureisadvantageousbecausemanyparameters canbemodifiedatwilltooptimizetheperformancesofthe structuredpacking.Inparticular,itispossibletochangethe tubediameters,theholesizesoftubes(openings),thesizes ofcarbonfabric(numberoffibres),andthetubeangles. More-over,thispackingpossessesotherinterestingpropertiessuch asasmalltubethickness(0.2mm),assuggestedduringthe evolutionofstructuredpacking,and asignificantstructural cohesion(mechanicalstrength)duetogeometryofthe struc-ture(usingthefourdiagonalsofacube).

2.2. IFPfacilities

Experimentshavebeencarriedoutina0.73mheight,150mm internaldiametercolumn.Thepressureisclosetothe

atmo-Table1–Characteristicsofthetwogenerationofpacking.

Packing Voidfraction(tube) Dm Nf Lf ag Voidfraction

Sepcarb®

4D-30% 31.24% 10mm 12 2mm 420m2_m−3 _94%

Sepcarb®

4D-50% 49.84% 10mm 8 2mm 327m2_m−3 _95%

Fig.4–(a)Tubesfittingaccordingtothefourdiagonalsofa cube;(b)reproductionofthelayoutinonedirection;(c)final structure.

Fig.5–4Dpackingelements.

sphericpressure,thetemperatureistheroomtemperature. Liquidload,QL,variesfrom10to60m3m−2h−1,gasvelocity

variesfrom0to2m/swhichleadstoaF-factor,Fs,between0

and2Pa0.5_{.Thedrippointdensityoftheliquiddistributor,dp,}

whichisthenumberofliquidinjectorsbysurfacearea,isclose to3350m−2_{.AccordingtoFairandBravo(1990)orAroonwilas}

etal.(2001),itishighenoughtoensurethatthedistributor doesnotinfluencetheresults.

Table2givespackedbedcharacteristicsforthethreetested geometries.Ithastobenoticedthatthereisanon-negligible voidzoneforallexperiments.Forthe4D-50%,a100mmheight bloc had beentested. Elements of4Dpackingare oriented at45◦ _{fromeach other,and thebed heightsare comprised}

between0.2and0.6mapproximately.

2.3. LGCfacilities

Theexperimentalhydrodynamicsand masstransfer

coeffi-cientsetupforthisstudyisaglasscolumnwithaninternal diameterof150mmandheightof1m.Countercurrent

oper-ation with an air–water system was used and all studies

were carried out atroom temperatureand under standard

atmosphericpressure.Forthe pressuredropmeasurement,

the packedbed height is 0.9m, and forthe masstransfer measurementthreeconfigurationsareusedwithbedheights comprisedbetween0.1and0.3mapproximately(seeSection

2.6).

Theliquidflowsfromatankthroughapumpandflowmeter (withameasurementprecisionof±2.5%)andwassuppliedat thetopofthecolumnviathesameplatedistributorprovided byIFP.Theliquidisagaincollectedintothetankafterhaving passedthroughthepacking,withsuperficialliquidvelocities intherangefrom1to30m3_m−2_h−1_{.Thegasflowissupplied}

atthebottomofthecolumnandwasmeasuredbytwo

dif-ferentflowmeters(withaprecision±1.6%)forsuperficialgas velocitiesfrom0to2ms−1_{foranemptycolumn.The}

pres-suredroppermeterwasmeasuredusinganinclinedU-tube filledwithwater,whichyieldedpressuremeasurementswith aprecisionof0.05mbar.

2.4. PressuredropmeasurementsatLGC

Theexperimental procedure usedtomeasure thepressure

dropconsistsofaperiodicincreaseofgasflowforaconstant

Table2–Geometriccharacteristicsof4Dbeds.

4D-30% 4D-50%

Configuration 1 1 2

Packedbedheight(m) 0.441 0.20 0.315

Voidzoneheight(m) 0.289 0.53 0.415

Numberofblocs 9 4 5a

Geometricarea(m2_m−3_{) 420 327}

Voidfraction(%) 94 95

Material Carbon

Stateofsurface Smooth

liquidflowuntilfloodingisreached.Thefloodingpointcanbe definedasthepointwhereareversalliquidflowappears.At thismoment,theliquidisunabletoflowdownwardthrough thepacking,thepressuredropincreasesdrastically,andan

accurate pressure measurement is impossible due to the

instabilityofthesystem.Beforeeachtest,ahighliquidflow issuppliedandpassesthroughthebedfor30mintofullywet thepackingandavoiddryzones.

2.5. EffectiveareameasurementsatIFP

Inthepresentstudytheair/NaOHsystemhasbeenchosen.

Withinthepackedcolumn,hydroxidesareconsumedbythe

absorbedCO2accordingtothefollowingreactions(Pohorecki

andMoniuk,1988):

CO2(G)↔CO2(L) (4)

CO2(L)+OH−↔HCO3− (5)

HCO3−+OH−↔CO32−+H2O (6)

Reaction(4)correspondstogastoliquidabsorption; reac-tion(5)isthereactiontoconsiderforkineticssincereaction(6)

hasamuchhigherreactionratethanreaction(5).An enhance-ment factor, E, can be used to describe the impact ofthe chemicalreactionontheabsorptionrateofCO2(Danckwerts,

1970): CO2=ϕCO2.ae,global=



₁ kG + He E.kL

−1

.ae,global.

!

PCO2−He.C0CO₂

CO2=KG.ae,global.

!

PCO2−He.CCO2 0

(7)

Atcolumninlet,theCO2molarfractioninthegasphaseis

closeto400ppmv,whiletheconcentrationofNaOHinthe liq-uidphaseisequalto0.1moll−1_{andinlargeexcesscompared}

totheabsorbedCO2.Duringatest,a1m3storagetankensures

thatthesodiumhydroxideandbicarbonatesconcentrations areconstantandnegligible,respectively(Raynaletal.,2004). Thisleadstoapseudo-firstorderreactionandfastreaction regime(Seibertetal.,2005;AlixandRaynal,2008)forwhich (Danckwerts,1970):







E=Ha=

p

DCO2.k2.C 0 OH kL C0_CO 2=0mol m −3 (8)

Itcanalsobeassumedthatthegassideresistanceis negli-gible.Withoutgasresistance,thecombinationofrelations(7) and(8)gives: CO2=

p

DCO2.k2.C 0 OH He .PCO2.ae,global (9)

Withinthepackedcolumn,one-dimensionaland station-aryplugflowsofliquidandgasareassumed.Then,thepacked bedcanbesimulatedbyasuccessionofsingleelements(Fig.6) forwhichthemassbalanceleadstothefollowingsetof

equa-Fig.6–Singleelementtomodelpackedbedof

experimentalcolumns,andestimatemasstransfer

parameters. tions:























dFG_CO 2 dz =CO2.Ac FG CO2= yCO2 1−yCO2 ×FG N₂ yCO2= PCO2 Ptot (10)

TheCO2gasmolarfractionismeasuredattheinletand

attheoutletofthecolumnviainfraredmeasurements.The effectiveareaofthecolumnsection,ae,global,isassumedtobe

constant.Thecolumnisassumedtobeisothermandisobar, thisisjustifiedbythesmallamountofCO2whichisabsorbed,

the negligible correspondingtemperature increase,and the very littlepressure drop.Diffusioncoefficient, DCO2, kinetic

constant,k2, andHenryconstant,He,havebeen calculated withrelationsgivenbyPohoreckiandMoniuk(1988).Forthe presentchemicalsystem,thesodiumhydroxidesolutioncan beconsideredunloaded,andtheliquidviscosityisclosetothe waterviscosity.Thisleadsto:















































log



_H w He



=−I×h=−₂₀₀₀1

!

C0 Na+C0OH

×(0.091+0.066+hg,CO2) log



100 Hw



=9.1229−5.9044×10−2_{×T+7.8857×10}−5_×T2 log



_k 2 k2∞



=0.0221×I−0.016×I2 log(k∞ 2)=11.895− 2382 T log(D_CO2)=−8.1764+712.5_T −2.594×10 5 T2 (11)

FromtheinletCO2molarfraction,yCO2,in,relations(9)and

(10)showthatae,globalistheonlyparametertoadjustinorderto

fittheCO2outletmolarfraction.ThentheCO2profiledirectly

givesae,global.

Liquidsamplesaretakenatinletandatoutletofthe col-umn.CO2contentismeasuredbyHCltitration.Massbalance

betweenthegasandtheliquidphasehasthusbeenchecked.

2.6. Gassidemasstransfercoefficientmeasurements atLGC

Generallyusedmethodsofkgaedeterminationcanbe

classi-fiedintothreemaincategories:

Table3–Differentmethodsusedintheliteratureforkgaedetermination.

Absorption Evaporationofpurliquid Absorptionwith

chemicalreaction

Examples Air-CO2aorSO2aorNH3aorO2b/water Air/waterormethanolcorMEK... NH3d/H2SO4

SO2a/NaOH

Obligation Humidificationofgas Humidificationofgas

Measurements Cg,Cl,T,P,Ye,f,g T,P,Ye,f,h Cl,Cg,T,P,Ye,f,g

Difficulties Cg,Cl,noisotherm Tinterfaceh,i,j Cg,Cl,noisotherm

a _{Billet(1995).}

b _{PuranikandVogelpohl(1974).} c _{SuroskyandDodge(1950).} d _{NakovandKolev(1994).} e _{VidwansandSharma(1967).} f _{SharmaandDankwerts(1970).} g _{Hüpenetal.(2006).}

h _{Treybal(1965).} i _{Ondaetal.(1968).}

j _{KawasakiandHayakawa(1972).}

- theevaporationofapureliquidbyaninertgas, - theabsorptionwithchemicalreaction.

Table3givesthedifferentsystemsusedintheliteraturefor thedeterminationofkgae,andtheneedofmeasurementand

thedifficulties ofeach methodare presented.Followingthe analysisofthistable,themethodofevaporationofpure liq-uidisappliedheretowaterasthepureliquidandtoairasthe inertgas;despitethefactthatthemethodislessused nowa-days,itpresentshoweversomeadvantages.Indeed,usingthe methodofevaporationofpureliquid,weensurethatthe trans-ferresistanceistotallylimitedtogas-phase.

However,itisrecognizedthatdependingonoperating con-ditionsandincasesofabsorptionwithchemicalreactionmass transfer resistanceispractically confinedtothe gasphase. Theprocessbyphysicalabsorptionisnotsatisfying,becauseit doesnotallowtoreducesufficientlytheliquidfilmresistance inordertoobtainkgae.However,thenumberofmeasurement

carriedoutforthemethodofevaporationofapureliquidis lowcomparedtoothertwomethods,whichlimitsapriorithe uncertaintiesevaluationofkgae.

Regardingthequalityofresultsonecanexpectfromthis method,thearticleofSuroskyandDodge(1950)canserveas areferencebecauseitiscomprehensive,fullofuseful

infor-mation and details a clear methodology treatment of raw

experimentalvalues.Theresultsshowthatitispossibleto haveaprecisiononthekgaeof10%.Moreover,the

measure-mentofairhumidityisnowadaysachievedwithmoreefficient equipment.

Theoperatingmode istoobtain adiabatic conditionsof saturationbytakingintocontacttheairwithwaterat counter-currentundersteady-stateconditions.Theairhumidification ascoolingprocedureleadsthesystemtowardsastable oper-atingconditionsintermsofwatertemperatureatadiabatic conditions of saturation (TAS). The gathered experimental

data’satstableconditionoffunctioningpermitthe determi-nationofkgae,usingmassbalanceforgas-phase:

LnYAS−Yin YAS−Yout =

kgaeH

G0 (12)

WithYinandYout asabsoluteinletandoutlethumidities

ofair incolumn, G0 asairflow, Z as column’s heightand

YASasabsolutehumidityatadiabatictemperatureof

satura-tion.Inordertooverwhelmtheimpactofextremityeffects,

authors(SuroskyandDodge,1950)recommendrealisingthe

same measurements withatleast twodifferent heightsof

packing.So, ourpilotcontainsacolumnof150mm diame-ter,withwaterandairatcounter-current(Fig.7).Dryairflow ismeasured;thenitishumidifiedandheated(byan evapora-torfedbyameasuringmicro-pump)inordertoobtaindesired conditionsofbottom-column.

Temperatureanddewpointaremeasuredatinletand out-letsectionsbyahygrometer(hygrometerwithcooledmirror permittinganaccuracyof±0.1◦_{C ofthe dewpoint). Water}

circulatesinclosedloopthroughstorage,up-column,liquid distributor(withadjustableheighttodistribute5cmontopthe packing),gasdistributortocomebackintostorage.Flows,inlet andoutlettemperaturesofcolumn(TLin andTLoutforliquid

temperature and TGin and TGout forgastemperature),

abso-luteinletand outlethumiditiesofair(YinandYout),aswell

asstoragetemperature(Tws)aremeasured(Fig.7).Theliquid

storagehastobesolimitedintermsofvolume(10l)inorder toreducethetimeofstabilisation.Theoperatingconditions arepredictedtoobtainanadiabatictemperatureofsaturation closetothesurroundingtemperature.

Foreach test,thesteadystateisreached(observedafter 30minwhenallmeasurementsarestable).Inthiscase,the temperaturesTLin,TLoutandTwsareequal,andadiabatic

tem-peratureofsaturationisreached.Thistemperaturepermits tocalculateYAS,theabsolutehumidityatadiabatic

tempera-tureofsaturation.Andthefinalresultkgaeiscalculatedbythe

relation(12).

For thepresent study six4D-30%and4D-50%blocshad

beentested.

3.

Results

and

discussion

3.1. Pressuredropcurve

Fig.8givesthedrypressuredropof4Dpackingsasa func-tion oftheF-factor.Logarithmicscalesare usedinorderto checkthepressuredroppowerlawcoefficientwhichislinked

to the flow regime. Present measurements are compared

withcalculatedpressuredropforthreeMellapakstructured

packingscommercializedbySulzerChemtech:M252Y,M500Y

andM750Y.Ithastobenoticedthatthegeometricareasof selectedcommercialpackingsareclosedtothe4Dones(see

Tables2and4).Calculationshavebeencarriedoutwiththe manufacturersoftwareSulcol2.0.First,theexperimental

pres-Fig.7–Experimentalsetupforkgaemeasurement.

Table4–GeometriccharacteristicsoftestedMellapakpackingsforeffectiveareameasurement.

MellapakPlus252Y Mellapak250Ya _Mellapak

500Ya

Packedbedheight(m) 2 3 3

Columndiameter(m) 0.15 0.43 0.43 Geometricarea(m2_m−3_{) 250 250 500} Voidfraction(%) 98 98 97.5 Corrugationlength(mm) 19 19 9 Channelangle(◦_{) 45 45 45} Material 316L

Stateofsurface Textureonthewall,perforated

a _{Tsaietal.(2008).}

suredroponacolumnequippedwith4D-30%issimilartothe

onecalculatedonacolumnequippedwithMellapak750.Y.

Second,theuseofthe4D-50%allowstoreducethepressure

dropby50%approximately.Thepressuredroponacolumn

equippedwith4D-50%becomessimilartotheonecalculated

0.1 1.0 10.0 100.0 10.0 1.0 0.1 Fs (Pa0.5) ∆ P/L (mbar/m) 4D-30% 4D-50% M500Y, Sulcol 2.0 M750Y, Sulcol 2.0 M252Y, Sulcol 2.0

Fig.8–DrypressuredropasafunctionofFsfor4Dopen packings.Comparisonwithcalculatedpressuredropfor

Mellapak750Y,Mellapak500YandMellapakPlus252Y

(Sulcol2.0).

onacolumnequippedwithMellapak500Y.Ithastobenoticed thattheslopeofthecurveiscloseto1.9forboth4D-30%and 4D-50%,thisresultissimilartotheresultsobtainedbySpiegel andMeier(1992).Last,thecalculatedpressuredropona col-umnequippedwithMellapakPlus252.Y,whichisthereference caseforthepresentwork,is50%lowerthantheonemeasured

onacolumnequippedwith4D-50%.

Fig.9givesthewettedpressuredropof4Dpackingsasa functionoftheF-factorandforQL=28m3m−2h−1.Such

liq-uidloadisexpectedforCO2absorbers.Presentmeasurements

arecomparedwithcalculatedpressuredropforMellapak252Y, 500Yand750Y.Inthecaseof4Dpackings,thepressuredrop

is reduced by30% whilethe capacity is increased by 25%

whentheopeningfractionincreasesfrom30to50%.Below theloadingpoint,theexperimentalpressuredropona col-umnequippedwith4D-30%(respectively4D-50%)issimilarto theonecalculatedonacolumnequippedwithMellapak750.Y (respectively500Y).Thefloodinglimitofthe4D-30%issimilar totheonegivenforMellapak750Y,andthefloodinglimitof the4D-50%ishigherthanthosegivenforMellapak500Yand 750Y.Foracolumnequippedwith4D-50%whichoperatesat afloodingpercentageequals 70%,thepackedbedpressure dropwillbecloseto3mbar/m.Last,itshouldbenoticedthat thecapacityoftheMellapakPlus252Yis40%higherthanthe

4D-50%one.

3.2. Effectivearea

First,thevoidzoneimpactshouldbecharacterizedforopen 4Dpacking(cf.Table2).Fig.10giveseffectiveareawhichhas

0.0 0.1 1.0 10.0 100.0 10.0 1.0 0.1 Fs (Pa0.5) ∆ P/L (mbar/m) 4D-50% 4D-30% M500Y, Sulcol 2.0 M750Y, Sulcol 2.0 M252Y, Sulcol 2.0 slope=1.9

Fig.9–WettedpressuredropasafunctionofFsfor4D openpackings,QL=28m3_m−2_h−1_{.Comparisonwith}

calculatedpressuredropforMellapak750Y,Mellapak500Y andMellapakPlus252Y(Sulcol2.0).

beenmeasuredwithanemptycolumn,ae,void,asafunction

ofQLandFs.First,itappearsthatae,voiddoesnotdependon

thegasflowrateforthetestedrange.Second,ae,voidislowand

comprisedbetween20and60m2_m−3_{.Last,asimpleand}

accu-ratecorrelationcanbeusedtoestimateae,voidforthepresent

work:

ae,void=7.66×(3600×QL)0.492 (13)

CO2absorbedratemeasurementsgivetheaveraged

effec-tiveareafortheentirecolumn,ae,global(seeSection2.5).

Forthe4D-30%and4D-50%packings,thevoidzonecannot beneglected(seeTable2)andthepackedbedeffectivearea

y = 7.6558x0.492 0 10 20 30 40 50 60 70 60 50 40 30 20 10 0 Q_L (m3/m2/h) ae,void (m 2 /m 3 ) Fs = 0.85 Pa0.5 Fs = 1.2 Pa0.5 Fs = 1.5 Pa0.5

Fig.10–Effectiveareaforthevoidzone,asafunctionofQL

andFs.

willbegivenby:

ae,4D=ae,global×H−a_He,void×(H−H4D)

4D (14)

Twoconfigurationshavebeentestedwiththe4D-50%(see

Table2),thenrelation(14)leadstotwodifferentvaluesfor

ae,4D.Forthiswork,anarithmeticaverageofthesetwovalues

isretained.Fig.11givestheeffectiveareameasuredwiththe 4DpackingsasafunctionofFsandQL.Presentexperiments

arecomparedwitheffectiveareasmeasuredfordifferent com-mercialpackings:MellapakPlus252.Y(AlixandRaynal,2009), Mellapak250Yand500Y(Tsaietal.,2008).Ithastobenoticed thatMellapakPlus252.Yhadbeencharacterizedwiththesame

experimental columnas 4D packings, however 2%CO2/1N

sodiumhydroxidesystemwasused.Thelattercouldleadto underestimatetheeffectiveareaabout15%becauseofgas

lim-Fig.11–Effectiveareafor4DpackingsasafunctionofQL.ComparisonwithdifferentMellapakcommercialpackings(Alix andRaynal,2009;Tsaietal.,2008).

itationandnon-pseudo-firstorderreaction(AlixandRaynal, 2008).IthastobealsonoticedthatMellapak250.Yand500.Y hadbeencharacterizedbySRPwitha430mmdiameter

col-umn. Theuse ofdifferent columndiameters could impact

experimentalresults(Olujic,1999),however,sincethecolumn

diametersare always muchhigherthan channelsizes(see

Table4),thediameterimpactshouldbemoderate(Henriques de Britoet al., 1994). First,onecan observe that Mellapak-Plus252.YandMellapak250.Yeffectiveareasaresimilar,this wasexpectedsincebothpackingshaveverysimilargeometric characteristics(seeTable4).Thisresultindicatesthat chem-icalsystemanddiametereffectsshouldbemoderateforthis packing,thenitisreasonabletocomparepresentresultswith thoseobtainedwithMellapak250.YandMellapakPlus252.Y. SinceMellapak500Ychannel sizeislower than the Mella-pak250.Yone(seeTable4),scaleeffectshouldbelowerfor the500.Y.Thisalsoindicatesthatitisreasonabletocompare presentresultswiththoseobtainedwithMellapak500.Y.

Second,Fig.11showsthat,whatevertheopeningfraction, 4Deffectiveareasaresimilarwhileagdecreasesstronglywhen

theopeningfractionincreases.Thisresultcouldbeexplained bythefactthatmoredropletsaregeneratedwhenopening fractionincreases (Alix and Raynal, 2008). Then,the effec-tiveareacouldexceedthegeometriconefor4D-50%(ratioup to1.4).Third,experimentalvaluesaremorescatteredfor4D packingthanthoseobtainedwithMellapakpackings.Thisis explainedbythefactthattheeffectiveareaislesssensitiveto thegasflowrateforMellapakthanfor4Dpackings.Inthecase ofopen4Dpackings,thegasflowrateimpactislinkedtothe amountofdropletslikeforrandompackings.Last,4D interfa-cialareasaremuchhigherthanthoseobtainedwithMellapak packingsinspiteofthefactthattheMellapakgeometricareas couldexceed4Dones.Thisresultisveryinterestingsincethe absorberheightwillbedirectlylinkedtothe packing effec-tivearea,andthisefficiencygaincouldcompensatethelower capacityof4Dpackings(seeSection3.1).The4D-50% struc-tureisthemoreinterestinggeometrysinceitgivesthebest compromisebetweenefficiencyandcapacity.

Toestimatethegainrelativesto4D-50%packingforCO2

captureplants,oneshouldmodeltheoverallabsorber (includ-inghydrodynamics,massandheattransfer,thermodynamics, and kinetic).Then,acorrelation toestimatethe interfacial areaishighlyneeded.Fig.12givestheeffectiveareaforthe 4D-50%packingasafunctionofFsandQL.Thefollowingrelation

canbegivenwithanaccuracyof±5%:











ae,4D-50%=A×(3600×QL)B A=137.77×Fs+134.39 B₌0.085 (15)

3.3. Gassidemasstransfercoefficient

kgae measurementsare realisedwith 3differentheightsof

packinginordertodeducetheextremityeffects,i.e.1blocs, 2blocsand3blocsofpacking(0.1m,0.2m,and0.3m, respec-tively).First,thepacking4D-50%hadbeentestedforaliquid loadscaleof7–23m3_m−2_h−1_{,andforagasflowratescaleof}

3500–7200kgm−2_h−1_.

Thevaluesofkgaearepresentedinlogarithmicscaleasa

functiongasflowrate’slogarithminFig.13. Regardingthis figure,twostraightlines(dotted)areaddedwhichcorrespond at+10%and−10%oftheaveragevalue,andpointsareincluded betweenthesetwoboundaries.

y = 246.03x0.0929 y = 283.07x0.0879 y = 328.69x0.0745 200 250 300 350 400 450 500 550 600 80 70 60 50 40 30 20 10 0 QL (m3/m2/h) a e,4D (m 2 /m 3 ) 4D_50%, Fs=0.8, IFP 4D_50%, Fs=1.1, IFP 4D_50%, Fs=1.4, IFP

Fig.12–Effectiveareafor4D-50%asafunctionofFsandQL. Therefore,underfunctionalconditionsofthispacking,the resultspresentaquasi-independencyonliquidflowrate,and animportantdependencyongasflowrate.Thefollowing rela-tionshipisthensuggested:

kg∗ae=3.7488×10−3∗G0.843 (16)

withGinkgh−1_m−2_andkg*aeins−1_.

ThepowerofGisaround0.8against0.7formostof tradi-tionalpacking(Ondaetal.,1968).Evenifitisnottraditional, ithasbeenalreadyobservedforsomeotherinternalsof col-umn.AccordingtoDwyerandDodge(1941),thedependency ongasflowrateforringswith25mmdiameterisapowerof 0.77andfor12.5mmringdiameteris0.9.Forthe4Dpacking, thetubediameteris10mmwhichisclosedtothe12.5mmring diameter.Thatissuggestingthatforthe4D-50%the character-isticdimensionofflowislowandthetestsin150mmcolumn diameterarerepresentative.

However,itispossiblethatthisvalueislinkedtothefact thataeisverysensitivetothegasflowrate.Regardingits

par-ticularstructure,thispackinggenerates: - liquiddropletsthroughlargeopenings.

- liquid film which follows the assembly angle ofpacking tubesandthereforeanincreaseinmovementwithrespect toaverticalflow. 0,4 0,45 0,5 0,55 0,6 0,65 0,7 0,75 0,8 0,85 0,9 0,95 1 3,9 3,85 3,8 3,75 3,7 3,65 3,6 3,55 3,5 log(G) log(k g ae ) +10% -10%

Fig.13–Dependencyoflog(kgae)asafunctionoflog(G)for

0,6 0,65 0,7 0,75 0,8 0,85 0,9 0,95 1 1,05 1,1 1,15 1,2 1,25 1,3 3,9 3,85 3,8 3,75 3,7 3,65 3,6 log(G) lo g (kg ae ) +10% -10%

Fig.14–Dependencyoflog(kgae)onlog(G)forthe4D-30%.

- thepossibilityofcreatingtheequivalentofabubblingin themiddleoftubesofpackingstructureathighgasflow rates,withmaybeapossibleliquidupstreaminthechannels formedbytubes.

Second,the4D-30%packing istested withaliquidload equals16m3_m−2_h−1_{andthepreviousrangeofgasflowrate.}

TheresultsareillustratedinlogarithmicscaleinFig.14.One canobserveahighdependencyonLOG(G)(1.54powerofG),as forthe4D-50%.Thiscouldbealsoexplainedbythefactthat

aeisverysensitivetothegasflowrate.

kg∗ae=1.4612×10−5∗G1.54 (17)

withGinkgh−1_m−2_andkg*aeins−1_.

4.

Conclusions

and

perspectives

Anovelstructuredpacking,the4Dpacking,hadbeen char-acterizedintermsofhydrodynamicsandmasstransfer.The

4Dpackingismadeofcarbontubeswhichcouldbeopened

byadjustingmanufacturingparameters(suchasbraidangle). Withanopeningfractionof50%,thecapacityofthe4D

pack-ing is maximum and becomesbetter than those given for

Mellapak500Yand750Ywhichhavesimilargeometricareas. Howeverthecapacityofthe4D-50%is40%lowerthantheone givenfortheMellapakPlus252.Ywhichisourreferencecase. Theeffectiveareaofthe4Dpacking,ae,doesnotdecrease

whentheopeningfractionincreasesfrom30to50%.This indi-catesthatmoredropletsaregeneratedwiththe4D-50%,this isconfirmedbythefact thatae becomesmoresensitive to

thegasflowrate4D-50%.Theeffectiveareaismuchhigher thanthosemeasuredwithMellapakpackings.Inparticular, theeffectiveareaisdoubledcomparedtothe MellapakPlus 252Yone.Thenthe4D-50%packingshouldbeveryefficient forCO2capture.Thisshouldatleastcompensatethelower

capacityofthe4D-50%.

Thegassidemasstransfercoefficient,kG,hadbeen

mea-sured for 4D packing via water evaporation. This original methodgivesveryaccurateresults.Correlationsaregivento estimateae andkG*ae.Thesecorrelationswillbeused

after-wardstoprovidearate-basedmodelfortheabsorber(Aspen

ratesep). Themodelshows theperformance of4D packing

inCO2 capturewith 30wt%MEA. Experimentswill bealso

conductedwitha400mmdiametercolumninordertovalid presentresultsintermsofpressuredropcurvesandeffective area.

Acknowledgments

This work is supported byANR (French National Research

Agency)throughtheGASCOGNEproject.

TheauthorswouldliketothanktheANRforitsfinancial

supportundertheGASCOGNEproject.

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