DOSSIER Edited by/sous la direction de : P.-L. Carrette. PART 2 Post Combustion CO 2. Copyright 2014, IFP Energies nouvelles

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1 Photos: DOI: 1.516/ogst/146, Fotola/yuladarlng, IFPEN, X. D o s s e r Ths paper s a part of the hereunder thematc dosser publshed n OGST Journal, Vol. 69, No. 6, pp and avalable onlne here Cet artcle fat parte du dosser thématque c-dessous publé dans la revue OGST, Vol. 69, n 6, pp et téléchargeable c DOSSIER Edted by/sous la drecton de : P.-L. Carrette PART Post Combuston CO Capture Captage de CO en postcombuston Ol & Gas Scence and Technology Rev. IFP Energes nouvelles, Vol. 69 (14), No. 6, pp Copyrght 14, IFP Energes nouvelles 977 > Edtoral 989 > Post-Combuston CO Capture by Vacuum Swng Adsorpton Usng Zeoltes a Feasblty Study Captage du CO en postcombuston par adsorpton modulée en presson avec désorpton sous vde sur zéolthes étude de fasablté G. D. Prngruber, V. Carler and D. Lenekugel-le-Cocq 15 > Membrane Separaton Processes for Post-Combuston Carbon Doxde Capture: State of the Art and Crtcal Overvew Procédés membranares pour le captage du doxyde de carbone : état de l art et revue crtque B. Belassaou and É.Favre 11 > Pressure Drop, Capacty and Mass Transfer Area Requrements for Post-Combuston Carbon Capture by Solvents Pertes de charge, capacté et ares de transfert de matère requses pour le captage du CO en postcombuston par solvants A. Lassauce, P. Alx, L. Raynal, A. Royon-Lebeaud and Y. Haroun 135 > Hollow Fber Membrane Contactors for Post-Combuston CO Capture: A Scale-Up Study from Laboratory to Plot Plant Captage postcombuston du CO par des contacteurs membranares de fbres creuses : de l échelle laboratore à l échelle plote ndustrel É. Chabanon, E. Kmball, É. Favre, O. Loran, E. Goetheer, D. Ferre, A. Gomez and P. Broutn 147 > Hollow Fber Membrane Contactors for CO Capture: Modelng and Up-Scalng to CO Capture for an 8 MW e Coal Power Staton Contacteurs à membrane à fbres creuses pour la capture de CO : modélsaton et mse à l échelle de la capture du CO d une centrale électrque au charbon de 8 MW e E. Kmball, A. Al-Azk, A. Gomez, E. Goetheer, N. Booth, D. Adams and D. Ferre 169 > Development of HCapt+ TM Process for CO Capture from Lab to Industral Plot Plant Développement du procédé HCapt+ TM pour le captage du CO : du laboratore au plote ndustrel É. Lemare, P. A. Boullon and K. Lettat 181 > A Techncal and Economcal Evaluaton of CO Capture from Fludzed Catalytc Crackng (FCC) Flue Gas Évaluaton technco-économque du captage du CO présent dans les fumées d une unté FCC (Fludzed Catalytc Crackng) R. Dgne, F. Feugnet and A. Gomez 191 > Plot Plant Studes for CO Capture from Waste Incnerator Flue Gas Usng MEA Based Solvent Étude du captage du CO dans des gaz de combuston d un ncnérateur de déchets à l ade d un plote utlsant un solvant à base de MEA I. Aoun, A. Ledoux, L. Estel and S. Mary 115 > Amne Solvent Regeneraton for CO Capture Usng Geothermal Energy wth Advanced Strpper Confguratons Régénératon d un solvant de captage du CO utlsant l énerge géothermque et des confguratons amélorées pour le régénérateur D.H. Van Wagener, A. Gupta, G.T. Rochelle and S.L. Bryant 111 > ACACIA Project Development of a Post-Combuston CO capture process. Case of the DMX TM process Projet ACACIA Développement d un procédé de captage du CO postcombuston Cas du procédé DMX TM A. Gomez, P. Brot, L. Raynal, P. Broutn, M. Gmenez, M. Soazc, P. Cessat and S. Saysset 159> Regeneraton of Alkanolamne Solutons n Membrane Contactor Based on Novel Polynorbornene Régénératon de solutons d alcanolamne dans un contacteur à membrane basé sur un nouveau polynorbornène A.A. Shutova, A.N. Trusov, M.V. Bermeshev, S.A. Legkov, M.L. Grngolts, E.Sh. Fnkelsten, G.N. Bondarenko and A.V. Volkov

2 Ol & Gas Scence and Technology Rev. IFP Energes nouvelles, Vol. 69 (14), No. 6, pp Copyrght 13, IFP Energes nouvelles DOI: 1.516/ogst/146 Dosser Post Combuston CO Capture Captage de CO en postcombuston Hollow Fber Membrane Contactors for Post-Combuston CO Capture: A Scale-Up Study from Laboratory to Plot Plant E. Chabanon 1, E. Kmball *, E. Favre 1, O. Loran 3, E. Goetheer, D. Ferre 4, A. Gomez 4 and P. Broutn 4 1 Laboratore Réactons et Géne des Procédés, LRGP (UPR CNRS 3349), 1 rue Grandvlle, 54 Nancy - France TNO, Leeghwaterstraat 46, 68 CA Delft - The Netherlands 3 Polymem, mpasse du Palayré, 311 Toulouse - France 4 IFP Energes nouvelles-lyon, Rond-pont de l'échangeur de Solaze, BP 3, 6936 Solaze - France e-mal : elode.chabanon@ensc.npl-nancy.fr - ern.kmball@tno.nl - erc.favre@ensc.npl-nancy.fr - o.loran@polymem.fr - earl.goetheer@tno.nl danel.ferre@fpen.fr - adren.gomez@fpen.fr - paul.broutn@fpen.fr * Correspondng author Résumé Captage postcombuston du CO par des contacteurs membranares de fbres creuses : de l échelle laboratore à l échelle plote ndustrel Depus des décennes, les contacteurs membranares sont proposés pour ntensfer les procédés de transfert de matère. Le captage postcombuston du CO par absorpton dans un solvant chmque est actuellement l un des sujets le plus ntensvement examné. Un grand nombre d études ont déjà été reportées dans la lttérature, malheureusement, elles ne concernent pratquement que des expérences menées à l échelle laboratore sur de petts modules. Étant donné les débts de fumées qu dovent être tratés dans une applcaton ndustrelle du captage du CO, une étude consstante à plus grande échelle est nécessare à l obtenton d un desgn rgoureux du procédé. Dans cette étude, les possbltés et les lmtes de l échelle laboratore et de l échelle plote ndustrelle ont été évaluées et seront dscutées. Les expérences (absorpton du CO d un mélange gazeux par une soluton aqueuse de MEA à 3 %mass.) ont été menées à la fos sur un mn-module à l échelle laboratore et sur un module de talle ndustrelle (1 m ), tous deux consttués de fbres PTFE. L approche des résstances en sére a ensute été utlsée pour smuler les résultats. Un seul paramètre ajustable est utlsé : le coeffcent de transfert de matère dans la membrane (k m ) qu joue logquement un rôle clé. Les dffcultés et les ncerttudes des calculs lées au changement d échelle, plus partculèrement sur la valeur de k m, sont présentées et dscutées. Abstract Hollow Fber Membrane Contactors for Post-Combuston CO Capture: A Scale-Up Study from Laboratory to Plot Plant Membrane contactors have been proposed for decades as a way to acheve ntensfed mass transfer processes. Post-combuston CO capture by absorpton nto a chemcal solvent s one of the currently most ntensvely nvestgated topcs n ths area. Numerous studes have already been reported, unfortunately almost systematcally on small, laboratory scale, modules. Gven the level of flue gas flow rates whch have to be treated for carbon capture applcatons, a consstent scale-up methodology s obvously needed for a rgorous engneerng desgn. In ths study, the possbltes and lmtatons of scale-up strateges for membrane contactors have been explored and wll be dscussed. Experments (CO absorpton from a gas mxture n a 3%wt MEA aqueous soluton) have been performed both on mn-modules and at plot-scale (1 m membrane contactor module) based on

3 136 Ol & Gas Scence and Technology Rev. IFP Energes nouvelles, Vol. 69 (14), No. 6 PTFE hollow fbers. The results have been modeled utlzng a resstance n seres approach. The only adjustable parameter s n fttng the smulatons to expermental data s the membrane mass transfer coeffcent (k m ), whch logcally plays a key role. The dffcultes and uncertantes assocated wth scaleup computatons from lab scale to plot-scale modules, wth a partcular emphass on the k m value, are presented and crtcally dscussed. NOMENCLATURE c Concentraton (mol.m -3 ) C p Heat capacty (J.K -1.kg -1 ) D Dffuson coeffcent (m.s -1 ) H Enthalpy of reacton (J.mol -1 ) K Equlbrum constant of reacton (-) k app Apparent constant of equlbrum (-) r Radal coordnate (m) r Inner fber radus (m) r o Outer fber radus (m) r g Inner radus (m) R Reacton rate (mol.m -3.s -1 ) T Temperature (K) v Intersttal velocty (m.s -1 ) z Axal coordnate (m) ϕ Packng rato (-) κ Thermal conductvty (W.m -1.K -1 ) ρ Densty (kg.m -3 ) ABBREVIATIONS MEA MonoEthanolAmne PP PolyPropylene PTFE PolyTetraFluoroEthylene PVDF PolyVnylDeneFluorde INTRODUCTION The rse of greenhouse gases n the atmosphere s commonly accepted to be caused by anthropologcal emssons and could be responsble for global clmate change. Ths results n serous damage to the envronment n the forms of retreatng glacers, rsng sea-level and ncreasng storm ntensty [1]. It s establshed that CO s one of the most mportant greenhouse gases due to the mmense volumes and ncreasng rates at whch t s emtted to the atmosphere. Ths s mostly due to the constantly growng demand for energy, an ndustry whch emts around 3 bllon tons of CO each year worldwde []. In January 7, the European Commsson recommended to the member states to cut ther collectve greenhouse gas emssons by % from the 199 levels by [3]. Carbon Capture and Storage (CCS) s thus consdered to be an essental component n the strategy to meet the ambtous emssons reducton goals and must be appled to both new power plants and as a retroft to exstng plants [4]. For exstng power plants, the CO must be removed after the fuel combuston. Ths results n a dlute stream of CO, about 14% vol. [5], n ntrogen for a coal power plant. The condtons of the flue gas are mld at atmospherc pressure and about 4 C, but the flow rates are mmense, around 6 m 3 /s for an 8 MW coal fred power plant. The typcal systems requred to separate the CO at low concentratons nvolve contactng the flue gas wth a solvent, whch reacts chemcally wth the CO and s later regenerated by ether a pressure or temperature swng [6]. In order to acheve a capture rate of about 9%, huge contact surface areas are requred, about 7 m for the example above. The conventonal desgn for provdng such hgh contact surface areas s wth one or more large towers flled wth a structured packng materal. The flue gas s ntroduced at the bottom of the column and flows counter-currently to the solvent lqud ntroduced at the top. The sze of these columns, at least 1 m n dameter and at least four tmes as hgh, makes them both expensve and dffcult to nstall when space s lmted. As an alternatve, the utlzaton of membrane contactors could be a promsng process for CO capture [7, 8]. Wth Hollow Fber Membrane Modules (HFMM), the lqud solvent flows nsde the membrane fber tubes ( sde) whle the CO -rch gas flows around the outsde of the fbers ( sde) [9-11] or vce versa [1-14]. The gas s transported through the (deally) lqud-free pores of the membrane to come nto contact wth the lqud where t reacts wth MEA. Thousands of fbers are bundled tghtly together wthn each module, wth several modules n parallel to acheve the desred capture rate of CO. In comparson to packed columns, HFMM avod several operatonal problems ncludng floodng, channelng, foamng and entranment. Gas absorpton membrane systems offer further advantages, such as ndependent control of the gas and lqud flows, lnear scale-up [15] and a sgnfcant sze reducton, wth a specfc surface area (m.m -3 ) between two and ten tmes greater than wth packed columns [16]. The focus of much of the work nvestgatng the operaton of HFMM has been on modelng and predctng the mass transfer characterstcs of the CO across the membrane, usually wth lmted expermental data for comparson. The earler models solve the mass balances n two dmensons n order to compare the radal and axal concentraton profles at dfferent gas flow rates, lqud flow rates and temperatures [17, 18]

4 E. Chabanon et al. / Hollow Fber Membrane Contactors for Post-Combuston CO Capture: A Scale-Up Study from Laboratory to Plot Plant 137 and also wth varyng solvents [19, ]. More recent work has looked at the transent behavor of gas absorpton nto a lqud [1], predctons usng computatonal flud dynamcs [] and effects of the wettng behavor of the membrane [3-5]. In addton to CO capture, HFMM are also beng nvestgated for H S absorpton, by expermentally lookng at the effect of dfferent solvent concentratons [6] and by both expermentally and theoretcally lookng at the effects of module desgn and flow rates [7]. The work dscussed here has extended the tradtonal approach to nvestgate the mplcatons of scale-up for these systems. A lab-scale membrane module system was constructed n order to valdate a mass transfer model smlar to those dscussed above. The valdated model was then used for smulaton of a full scale system. The results of the full scale smulaton were then compared wth expermental data from an ndustral plot-scale membrane system utlzng the same materals as those for the lab-scale. In general, ths study ntends to evaluate and dscuss the possbltes and lmtatons of scale-up strateges for membrane contactors through these two case studes. 1 MATERIAL AND METHODS 1.1 Membrane Characterzaton In the frst step, a lterature revew combned wth the partners experence n membrane testng [8] and contactor development [9] showed that even though a very large number of studes on CO absorpton n membrane contactors have been reported [9-14, 3-33], several key ssues reman largely unexplored. Among them, the stablty n tme of the materal whch s used for the membrane n the contactor appears to be of prmary mportance but poorly documented. Most studes report lab-scale experments only on a short term bass (.e. on an hours or days scale [34-36]). Consequently, the followng prorty targets are defned, n order to select the most approprate materals for module preparaton: a seres of 1 dfferent commercally avalable flat sheet membrane materals, based on 4 dfferent polymer types polypropylene (PP), polyvnyldenefluorde (PVDF), polytetrafluoroethylene (PTFE) and nylon are selected for expermental tests; natve membrane materal propertes, such as gas permeablty and contact angle, are determned; the evoluton of the prevous propertes when the samples are put n contact wth a 3%wt monoethanolamne (MEA) aqueous soluton are nvestgated on a long tme bass (.e. up to months exposure) at temperatures of 93.15, and K. In parallel, compatblty tests of the solvent soluton wth dfferent glue and casng canddate materals were also performed. The results of the agng tests (evoluton of contact angle and gas permeablty wth tme) unambguously and consstently show that: PTFE (5 dfferent samples) demonstrates a remarkable stablty wth tme n terms of gas permeablty and stablty of the non wettng propertes, both at and K; PP (1 sample) and PVDF (3 dfferent samples) present a far to reasonable stablty of gas permeablty and contact angle wth tme at K, but degrade sgnfcantly at K; nylon does not show a good stablty n MEA solutons, both at and K. From the conclusons of ths prelmnary work, PTFE s selected as the most approprate membrane materal for the membrane contactor desgns. A talor made PTFE hollow fber has been provded by Polymem and samples are characterzed more fully. Several studes are done to characterze the porosty of the fbers. The frst s the Hg method (mercury ntruson technque) as t s the usual method for catalysts. The man result s that the nternal structure of the sample s manly macro-porous. The pores are comprsed of szes between 1 and 1 μm, wth a mean value of 5-6 μm and a mean porosty of.8 ml/g. The second study s an X-rays analyss done at the European Synchrotron Radaton Faclty n Grenoble (France). A typcal reconstructed 3D vew s shown n Fgure 1. Globally, the pores form nterconnected compartments, flattened n the drecton of the length of the fber (ansotropc texture). From the zoom-ns n the rght part of the fgure, one can see that the pores are very well connected n the axal drecton and that the superfcal porosty s very hgh, both on the nner and outer sdes of the fbbers. The flattened aspect of the pores s not adequate for the usual defnton of the pore szes whch supposes an sotropc dstrbuton. In good accordance wth the Hg 5 μm Fgure 1 Synchrotron analyss of the PTFE hollow fber tested at lab and plot-scale n ths study (mage obtaned at the European Synchrotron Radaton Faclty).

5 138 Ol & Gas Scence and Technology Rev. IFP Energes nouvelles, Vol. 69 (14), No. 6 analyss, t s agan found that 5 μm s the typcal dmenson of the pore n the radal drecton, but the straght pass length s qute scattered wth an apparent mean value of about 3 μm and some passes reachng almost 1 μm. 1. Expermental Set-Up 1..1 Lab-Scale The lab-scale membrane contactor s constructed utlzng the chosen PTFE fbers for the membrane polymer, as descrbed above. A photo and dagram of the module setup are shown n Fgure and the module s geometrcal propertes are summarzed n Table 1. Mxtures of CO and N are prepared usng two mass flow controllers and fed to the sde of the membrane fbers. An aqueous 3%wt MEA soluton s prepared by dluton of hgh purty MEA n dstlled water. The lqud phase flows n the sde, counter-currently to the gas phase. The lqud flow rate s controlled by a hgh precson pump and the pressure s regulated by a valve placed at the lqud outlet. Durng the experments, the pressure and temperature are both at ambent condtons (1 bar and ~ C). The nlet CO volume fracton s 14-15%vol. wth total gas flow rates of L.mn -1. Fresh 3%wt MEA soluton s used n each case wth flow rates of (1 1-3 ) - (5 1-3 ) L.mn -1. An Infra-Red (IR) analyzer s used to measure the CO volume fracton n the gas at both the nlet and outlet of the module. A bubble meter s used to measure the gas flow rate at the nlet and at the outlet of the module. Partcular attenton s pad to acheve steady-state condtons for each measurement, reflected by a constant CO volume fracton at the outlet. Module 1.. Industral Plot-Scale TABLE 1 Detals of the lab-scale HFMM Inner dameter (m) Effectve length (m).3 Length (m).35 Number of fbers (-) 119 Packng rato (-).59 Specfc nterfacal area (m.m -3 ) Inner dameter (m) Fber Outer dameter (m) Porosty (-).336 The plot-scale module s constructed to be more than two orders of magntude larger than the mn-module, both by ncreasng the length of the module and the number of fbers. Approxmately equal specfc nterfacal areas (m.m -3 ) and lqud phase Reynolds numbers of the same order of magntude ensured dmensonal smlarty between the mn-module and plot-scale. Due to the large number of fbers requred for the ndustral membrane module, 8 51, the bundle s supported by a plastc grd whch s rolled nto a spral nsde the fber bundle. The grd s needed to support the fbers durng the mplementaton of the resn sealng to make the bundle. An X-rays analyss showng the cross-secton of the bundle and the plastc grd are gven n Fgures 3a and 3b, respectvely. The presence of the grd does not appear to dsrupt the dstrbuton of the fbers over the length of the bundle to a large degree; however, the dark spaces n Fgure 3a ndcate CO Pressure regulator MFC Mxng Pressure gauge Pressure gauge MFC N Pressure regulator Compressed gas cylnder Pump Lqud feed IR analyser Ventng Fgure Photo and dagram of the lab-scale set-up for the CO absorpton experments wth mn HFMM.

6 E. Chabanon et al. / Hollow Fber Membrane Contactors for Post-Combuston CO Capture: A Scale-Up Study from Laboratory to Plot Plant a) b) Fgure 3 X-rays analyss of the plot-scale HFMM. a) Fber bundle cross-secton. b) Plastc grd wound nsde the fber bundle Gas Lqud No scale drawng Gas Module TABLE Detals of plot-scale HFMM Inner dameter (m).15 Length (m).88 Effectve length (m) 1 Number of fbers (-) 8 51 Packng rato (-).648 Specfc nterfacal area (m.m -3 ) 1 39 Inner dameter (m) Fber Outer dameter (m) Porosty (-).336 some vod spaces where preferental channelng of the gas flow may occur. The fnal parameters of the ndustral module are gven n Table. A dagram of the setup of the entre system s shown n Fgure 4. The lqud flows axally from bottom to top and an nlne transparent secton () follows the lqud outlet, allowng for observaton of possble bubbles. Keepng the countercurrent mode, the gas, therefore, flows from top to bottom and an nlne transparent flter (1) s nstalled at the gas outlet to catch any lqud that could percolate through the membrane. The absorpton of CO s tested usng a CO /N mxture. The flow rate of N and the concentraton of the CO are kept constant durng each test-run usng control valves. The lqud crcut s a closed loop ncludng a 6 L storage tank open to the atmosphere. The MEA solvent reaches the module through a pump-controlled valve-flow meter system and flows back to the tank by gravty. A bend and a valve placed at the lqud outlet of the module are used to mantan a constant pressure n the lqud phase. Ths faclty s used for the Lqud hghest gas flow rates to prevent the gas from passng through the hollow membrane fbers. The pressure drops of the gas phase and the lqud phase are measured by four relatve-to-atmosphere pressure transducers connected to the nlet and the outlet of each phase. For both types of modules (mn and plot), the pressure of the gas phase had to be montored so as not to be hgh enough to cause bubblng nto the lqud phase. Two small lnes from the gas nlet and outlet runnng down to the control room and made of capllary tubes are connected to IR sensors to measure the CO concentraton. Fnally, the lqud nlet and outlet are equpped wth bleed valves whch allow for samplng of the lqud phase n order to measure the mass fracton of MEA and the CO loadng of the lqud phase over tme. As wth the lab-scale experments, each measurement s taken when steady state condtons are reached. THEORETICAL STUDIES In ths study, a D mathematcal model s developed for the transport of CO from the gas phase nto an aqueous MEA soluton wthn an HFMM. Ths model s developed for a sngle hollow fber, as shown n Fgure 5. The setup of the Fgure 4 Dagram of the plot-scale HFMM setup. EL 1555 SL

7 14 Ol & Gas Scence and Technology Rev. IFP Energes nouvelles, Vol. 69 (14), No. 6 z = L r = r = r Lqud Gas r = ro z = rg z = Fgure 5 Schematc dagram of the membrane fber smulated n the D model. model s smlar to those most commonly found n the lterature [17, 19, -4, 6, 37] wth the three layers, membrane and treated separately accordng to a resstance-n-seres approach. The dfferental mass and energy balances n the axal and radal drectons over a sngle fber are consdered: sde (gas phase): dffuson and convecton, no reacton ( = CO, N ): c c sh D (1) + 1 ell c vz = r r r z T T s κ + 1 hell T ρ Cv () p z = r r r z membrane: dffuson only ( = CO, N ): mem mem mem c 1 c D (3) + = r r r mem mem κ mem T 1 T + = (4) r r r sde (lqud phase): dffuson, convecton and reacton ( = CO, H O, MEA): c 1 c lu D v (5) + men c z + R = r r r z T 1 T l κ + umen T ρ Cv p z + R H = (6) r r r z In the equatons above, D s the dffuson coeffcent of the speces n each layer (m.s -1 ), c s the concentraton of the speces n each layer (mol.m -3 ), v s the ntersttal velocty defned as below (m.s -1 ), R s the reacton rate (mol.m -3.s -1 ), r s the radal coordnate (m), z s the axal coordnate (m), T s the temperature (K), ρ s the densty (kg.m -3 ), κ s the thermal conductvty of each layer (W.m -1.K -1 ), H s the enthalpy of reacton of the speces wth the MEA (J.mol -1 ) and C p s the thermal capacty (J.K -1.kg -1 ). The three layers consdered are connected by the followng nterface relatons and boundary condtons: axal drecton (assumng counter-current flow pattern): radal drecton: T c r =, =, = for = all speces r r mem c r = r, T = T, = for = amne speces, r mem c = m c for = CO, HO mem r = r T = T, c mem o, c z=, T = Tn, c = for = CO, c = cn, for = MEA, H O z= L, T = Tn, c = cn, for = CO, c = for = MEA, H O mem = for = MEA = c for = T c r = rg, =, = for = r r c = for = MEA CO, HO, CO, HO,

8 E. Chabanon et al. / Hollow Fber Membrane Contactors for Post-Combuston CO Capture: A Scale-Up Study from Laboratory to Plot Plant 141 Fgure 6 Membrane module cross secton and approxmaton of the gas surroundng the fbers accordng to the Happel s free surface model [6]. may result n a hghly non-unform dstrbuton of the fbers wthn the module. Therefore, the Happel s free surface model s mostly used to calculate the effectve dameter of the gas around each fber and the non-unformty of the gas flow s accounted for n the adjustment of the mass transfer across the membrane. For the membrane, the only mechansm of mass transfer consdered s dffuson. A smplfed mechansm for the knetcs s used to formulate the overall reacton rate expresson, as gven below: K RNH + HCO 1 3 RNHCOO + H O RNH + H + K + RNH 3 The mplementaton s based on the method of lnes and executed n Matlab. The specfcatons used are: gas flow on the sde of the fbers, lqud flow on the sde and counter-current flows. The key assumptons are as follows: neglgble axal dffuson (n the gas and lqud phases); amne compounds and water only present n the lqud phase (no evaporaton); no wettng of the membrane pores; unform fber shapes and packng. The flow of the lqud on the tube sde of the membrane s assumed to be fully-developed lamnar parabolc flow, as supported by low Reynolds numbers (on the order of 1) for the condtons tested n the experments: r c (7) = v 1 r where v s the average velocty (m.s -1 ) and r s the nner radus of the fber (m). It should be noted that non-dealtes n the fber shapes (bends, nconsstent dameters, etc.) ntroduce mxng n the sde of the fbers, but ths s not consdered n the model. The flow of gas on the sde of the membrane s modeled usng Happel s free surface model [38] (Fg. 6): v z r r o r r r o o ln g = v r r 1 g (8) r g + 4 ro ro 3 r 4 g r + 4ln r o g rg + ( ) 1 r (9) g = ro 1 ϕ where r o s the outer radus of the fber, r g s the gas radus (m) and ϕ s the packng rato of the module. Ths equaton assumes unform lamnar flow around each of the fbers. It s known that the constructon of HFMM CO + H O The full reacton mechansm for CO -MEA-H O systems s more complex than that gven here, nvolvng several acdbase reactons [39]. These acd-base reactons are not consdered here as they allow for the calculaton of the concentratons of H + ons and water. In ths case, expermental data are avalable for the equlbrum ph versus temperature and CO partal pressure, allowng for drect calculaton of the concentraton of H + ons based on the CO concentraton, assumng a fast reacton tme of the acd-base reactons relatve to the reactons wth CO and amne speces. Also, the concentraton of H O s assumed to be constant as there s a large excess of water (7%wt) n the soluton. The expressons for the equlbrum constants for the specfc reactons above are obtaned from lterature, ncludng forward and backward rate constants, and are dependent on temperature. Conservaton of mass for the amne speces (RNH group) s also used n dervng the fnal rate expresson: + k 3K1[ H ][ RNHCOO ] R (1) CO = k3[ CO] [ RNH ] The concentratons of CO, RNHCOO (carbamate) and RNH (MEA) are calculated at each pont of the model grd dscretzaton by solvng the correspondng model dfferental equatons. 3 RESULTS AND DISCUSSION K 3 H + + HCO 3 k app CO + RNH RNHCOO + + RNH Results from Lab-Scale Setup The membrane mass transfer coeffcent, k m (m.s -1 ), s defned by: mem D ε km = τδ

9 14 Ol & Gas Scence and Technology Rev. IFP Energes nouvelles, Vol. 69 (14), No. 6 where D mem s the membrane dffuson coeffcent (m.s -1 ), ε s the membrane porosty (-), τ s the membrane tortuosty (-) and δ s the membrane thckness (m). By adjustng the value of k m for CO, the expermental results from the lab-scale module ft very well wth the model predctons. The value of k m s ft to the data by hand usng one lqud flow rate of L.mn -1 and an ntermedate gas flow rate of 3. L.mn -1. The value s adjusted n the model untl the calculated CO percentage at the outlet s about equal to the expermental value. The best ft s found usng a value of: k m = m.s 1 The results of the smulatons from the model compared to the expermental data are shown n Fgure 7, gven n terms of both the volume fracton of CO at the outlet of the gas phase (Fg. 7a) and as the capture rate of CO (Fg. 7b), both versus the gas flow rate at the nlet of the sde. All of the ponts shown are wth an nlet CO volume fracton of approxmately 15%, fresh 3%wt MEA and an nlet solvent flow rate of ether or L.mn -1. The results for the hgher lqud flow rate, Q l = L.mn -1, ft extremely well over the range of gas flow rates, from to 6. L.mn -1, where the data also follows a smooth trend. At the lower lqud flow rate, Q l = L.mn -1, there are larger dfferences between the expermental and model results but more fluctuatons n the data are also observed. Wth the close ft between the model and expermental results, the model s consdered to be valdated and able to descrbe the D mass transfer of CO across the membrane and ts absorpton nto the solvent. 3. Results from Plot-Scale Setup Several experments wth varyng lqud and gas flow rates were conducted wth the ndustral plot-scale HFMM. The results consdered here are for a range of lqud flow rates of L.mn -1 and gas flow rates of 5-3 L.mn -1. The MEA s recrculated and so s already partally loaded wth CO, whch s also measured at the start of each experment. The nlet volume fracton of CO n the N s kept approxmately constant at about 15%. The expermental results are then compared wth smulaton results from the D mass transfer model. Followng the valdaton of the D model wth the data from the lab-scale module, the parameters of the model descrbng the module desgn and MEA condtons are adjusted to smulate the plot-scale module. The fbers n both modules are made from the same materal, allowng for the membrane mass transfer coeffcent determned from the ft wth the lab-scale module expermental data to also be used n the smulatons of the larger module. However, the results of the plot-scale module smulatons usng the prevously determned k m value show a sgnfcant over-predcton of the CO capture for all of the gas and lqud flow rates, ndcated by very low values for the CO volume fracton at the outlet of the gas phase, as shown n Fgure 8. In order to have the model ft the expermental data at an ntermedate gas flow rate of 1 L.mn -1, the membrane mass transfer coeffcent s adjusted to: k m = m.s -1 CO volume fracton outlet of the gas phase (%) 14 Model Q l = 5 1 Exp. Q l = 5 Model Q l = 1 1 Exp. Q l = a) Gas flow n (L/mn) (~15% CO n N ) b) Capture rate (kg CO /h) Model Q l = 5 Exp. Q l = 5 Model Q l = 1 Exp. Q l = Gas flow n (L/mn) (~15% CO n N ) Fgure 7 Comparson of smulaton results and expermental data for the mn HFMM for gas nlet flow rates of to 6. L.mn -1 and two lqud flow rates, Q l = and L.mn -1. a) Results for CO volume fracton at the outlet of the sde. b) Results for calculaton of the capture rate (kg CO captured per hour).

10 E. Chabanon et al. / Hollow Fber Membrane Contactors for Post-Combuston CO Capture: A Scale-Up Study from Laboratory to Plot Plant Model Q g = 3 Model Q g = 1 Model Q g = 5 Exp. Q g = 3 Exp. Q g = 1 Exp. Q g = Model Q g = 3 Model Q g = 1 Model Q g = 5 Exp. Q g = 3 Exp. Q g = 1 Exp. Q g = 5 CO outlet concentraton (%) CO outlet concentraton (%) Lqud nlet flow rate (L/h) Fgure 8 Comparson of smulaton results and expermental data for the plot-scale module utlzng the k m value from the ft wth the mn-module data. Values are gven as CO volume fracton at the outlet of the gas phase for lqud nlet flow rates of L.mn -1 and gas nlet flow rates of 5, 1 or 3 L.mn -1. The nlet volume fracton of CO s about 15% n every case and the accuracy of the CO detector s ±.1% Lqud nlet flow rate (L/h) Fgure 9 Comparson of smulaton results and expermental data for the plot-scale module utlzng a k m value of m.s -1. Values are gven as CO volume fracton at the outlet of the sde for lqud nlet flow rates of L.mn -1 and gas nlet flow rates of 5, 1 or 3 L.mn -1. The nlet fracton of CO s about 15%vol. n every case and the accuracy of the CO detector s ±.1% (same expermental data as n Fg. 8). 5 and gves good results over the range of lqud flow rates, as shown n Fgure 9 (red markers). However, for the lower gas flow rate of 5 L.mn -1 (green markers), the smulatons show a lower predcton of the CO volume fracton at the outlet and at a hgher gas flow rate of 3 L.mn -1 (blue markers), the predcton of the percent CO s hgher than what s observed expermentally. The effects of the dfferent parameters on the results are nvestgated separately but the smulaton results cannot be made to ft well wth all of the data sets wth one set of parameter values. Ths ndcates that the non-dealtes n the larger plot-scale system are much more sgnfcant than wth the lab-scale module, as logcally expected. The D mass transfer model wth the stated assumptons cannot account for the dfferent phenomena occurrng n the plotscale module. 3.3 Comparson between Lab-Scale and Plot-Scale The sgnfcant dfferences n the results between the lab- and plot-scale modules show the dffcultes n predctng the performance of larger scale systems wth smple models. It s mportant to stress that the modelng approach tested n ths study corresponds to the basc D equatons classcally proposed n membrane contactor studes. The comparson performed here shows that sgnfcant mprovements need to be ncorporated nto the D mass transfer model before the operaton of a full scale module wll be acceptably smulated over a wde range of condtons. When smulatng the plotscale module, the over-predcton of the CO capture may be due to errors n the mass transfer parameters, knetcs or assumptons of unformty. Gven that the k m value s set by fttng the data from the small lab-scale module, t s thought that the maldstrbuton of gas flow around the fbers of the plot-scale module, especally wth the mesh grd that s ncorporated nto the fber bundle, s the most sgnfcant source of error. Ths would effectvely make the resstance of the gas flow through the membrane appear hgher. The mass transfer resstance of the gas flow close to the fbers s stll relatvely low, but not all of the gas flows n the of a fber, as defned by Happel s free surface model. The resstance to mass transfer through the membrane for some fracton of the CO n the gas phase would then be essentally nfnte. Another source of error that would be much more sgnfcant wth the plot-scale module than wth the lab-scale module s the effect of the temperature rse due to the heat of the absorpton reacton. The model assumed no evaporaton of water from the of the fbers to the gas phase. However, evaporaton may be a sgnfcant factor, gven that the gas s dry at the nlet and the smulatons predcted about a 1 C temperature rse over the length of the fber, for the plot-scale module. Ths s supported by the fact that a large amount (approxmately 1 L but not precsely measured) of condensed water s present n the outlet of the expermental plot-scale system between tests. In contrast, the predcted

11 144 Ol & Gas Scence and Technology Rev. IFP Energes nouvelles, Vol. 69 (14), No. 6 temperature rse for the much smaller lab-scale module s less than 1 C and no water condensaton n the expermental setup s reported. The effect that the water evaporaton can have on the CO capture performance s to decrease the capture rato. As water evaporates nto the gas phase, the partal pressure of CO n the gas phase decreases; ths n turn decreases the drvng force for CO transport through the membrane and nto the absorpton lqud, thus resultng n a lower CO capture rato (hgher CO volume fracton at the outlet) than expected wth no evaporaton. It has to be noted that for power plant capture systems, the flue gas treated by the HFMM s usually hydrated to some degree. Consequently, the evaporaton of water from the lqud can be expected to be smaller than n the expermental system. 3.4 Ablty to Predct Operaton of Large Scale Modules Wth the constructon of large scale HFMM, the performance becomes harder to predct. The plastc grd, as shown n Fgure 3b, s one example of the non-unformtes that can exst wthn the module whch cause maldstrbuton of flows. Others nclude bends n the fbers, varatons n the local fber packng and varyng thckness of the membranes. The ablty to take nto account these effects n a rgorous model s a challenge. Attempts have been made to capture the effects of non-unformtes, such as by consderng a random dstrbuton of fbers [37], however experments at several dfferent scales of HFMM are needed. The two orders of magntude dfference n sze between the two HFMM consdered here caused large dfferences n the ablty to predct the operaton. In order to understand how the nonunformtes evolve wth each step ncrease n sze and each varaton n module constructon, expermental data from many more systems are needed. Ths wll then lkely allow for correlatons based on scale to be derved for the several parameters needed to accurately smulate HFMM operaton. CONCLUSIONS Two dfferent scales of HFMM are constructed and operated to provde nsght nto the ablty of predctng the behavor of HFMM at full scale. The results of the two-dmensonal model based on mass and energy balances showed a good predcton of the performance of HFMM. For the lab-scale HFMM, wth less non-dealty n the system, the model and expermental results ft very well for varyng gas and lqud flow rates. When smulatng the larger plot-scale module, the predcton of the performance over a range of gas flow rates s not as good. The maldstrbuton of the flows around and nsde the fbers s not accounted for n the D model and proved to be much more mportant n the plot-scale module. The assumpton of unform flow s one of the key assumptons used n the development of the model. Another s the hypothess of a neglgble evaporaton of water. Although only modest temperature rses of up to 15 C are predcted by the smulatons, ths may have an effect n several ways. For one, the evaporaton wll cause a coolng effect n the lqud and decrease the temperature rse. Ths has mplcatons for the dffuson of the compounds n the lqud, the densty of both the gas and lqud and the reacton rates. Another effect of water n the gas phase s to decrease the partal pressure of CO. Ths wll decrease the drvng force for CO to be absorbed nto the lqud and thus decrease the capture rato. It has not been possble to ncorporate evaporaton nto the mass transfer model for ths project, but ths should clearly be a major focus of future work. More generally, ths contrbuton s one of the frst attempts to expermentally evaluate the scale-up possbltes and lmtatons of membrane contactors from laboratory- to plotscale. Publcatons almost systematcally refer to laboratory scale membrane contactors, whle large scale applcatons (such as CCS) obvously requre adequate smulaton tools and extrapolaton strateges for much larger unts. Ths study has shown that the scale-up ssue of membrane contactors s far from straghtforward. Consequently, research and development efforts are urgently needed n ths drecton. ACKNOWLEDGMENTS Ths work was completed as part of the larger CESAR Project, part of the European Commsson 7th Framework Program. REFERENCES 1 IPCC (7) 4th Assessment Report (AR4), Clmate Change 7: Synthess Report. 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