Interphase Momentum Study in a Slurry Bubble Column

Transcription

1 A publication of 1507 CHEMICAL ENGINEERING TRANSACTIONS VOL. 3, 013 Chief Eitor: Sauro Pierucci, Jiří J. Klemeš Copyright 013, AIDIC Servizi S.r.l., ISBN ; ISSN The Italian Aociation of Chemical Engineering Online at: Interphae Momentum Stuy in a Slurry Bubble Column João Lameu Silva Jr. a, Eric Djin Mori a, Renato Soccol Jr. a, Marco A. Ávila b, Milton Mori*,a a School of Chemical Engineering, Univerity of Campina - UNICAMP, Albert Eintein avenue 500, CEP: , Campina, Brazil b School of Mechanical Engineering, Univerity of Campina - UNICAMP, Meneleyev treet 00, CEP: , Campina, Brazil mori@feq.unicamp.br Eulerian three-imenional tranient imulation have been conucte to tuy the hyroynamic of threephae flow inie a lurry bubble column with intermeiate an high concentration of oli particle. The preent wor evaluate the influence of interaction among phae, in the time-average numerical reult. Preiction were compare with experimental ata available in the literature. Analyi of rag moel for the liqui-oli an ga-oli interaction play an important role in the ynamic behavior of a ga-oli-liqui lurry bubble column. The CFD moel imulate wa capable to preict ga holup an (ga velocity) x (ga holup) profile imilarly to that foun experimentally. 1. Introuction Slurry bubble column are wiely ue in inutrie, a chemical reactor, ue the implicity in it contruction an operation, a well a, it compactne an abence of moving part. Depite all the previou avantage, bubble column are alo nown a complex flow. In orer to eign an cale up a bubble column effectively, it require a etaile ecription of the bubble characteritic, ma an heat tranfer parameter (Kantarci et al., 005) an i wiely accepte that characteritic are epenent on the hyroynamic prevailing in thi ytem. A ucceful way of tuying complex flow ha been mae through the Computational Flui Dynamic (CFD), an thee moel are able to achieve numerical reult with goo agreement compare to experimental ata. Here are till a large number of controverial theorie aroun the interphae force that govern momentum tranfer between ytem phae. It i well-nown that interphae force an turbulence play a crucial role in the correct moeling of hyroynamic in bubble column (Tabib et al., 008). In thi ene, the main objective of the preent wor i to preent a CFD coe that i capable of imulating a three-phae flow with intermeiate an high concentration of oli in laboratorial cale lurry bubble column. For thi purpoe, ifferent empirical correlation to repreent the interaction among phae are aopte in the imulation in a time-average approach. The commercial coe ANSYS CFX 14 i ue in all CFD imulation.. Mathematical moel The Eulerian approach i bae on enemble-average ma an momentum tranport equation for each of the three phae. The ma an momentum conervation tranport equation can be written in a general form for the three phae a: t ( α ρ ) + ( α ρ U ) = 0 (1)

2 1508 t T ( ( ) + M + ρ g ( α ρ U ) + ( α ( ρ U U )) = α P+ α μ U + ( U ),eff () where ρ i the enity, α i the phae holup, U i the velocity vector, µ i the vicoity, the ubcript eff enote the effective vicoity, g i the gravitational acceleration an M i the total interfacial force acting between the phae an the ubcript inicate the phae (g=ga; l=liqui; =oli). The momentum tranport equation of oli phae preent an aitional term ue to oli preure, an can be written a α ζ U + P where ζ i the bul vicoity an P repreent the aitional preure ue to preence of ( ) S particulate oli. Thee term were coniere only in imulation with Kinetic Theory of Granular Flow (KTGF). The KTGF with e = 0.9 wa coniere in our analyi. The rag force can be ecribe a: M = M D 3 C = 4 D ρ α c U U ( U U ) (3) c c where C D i the non imenional rag coefficient, i phae iameter. The ubcript c inicate the continuou phae an tan for ipere phae. The rag moel correlation applie to ga-liqui contact wa the Ihii-Zuber moel, bae on the goo reult obtaine by Silva et al. (011). The rag moel for liqui-oli an ga-oli interaction ue in thi wor are preente in the next ection..1 Liqui-oli rag force correlation a) Wen-Yu Moel: The Wen-Yu moel conier a warm of particle flowing i a function of oli holup. The moel moifie by Jia et al. (007) i mathematically repreente a: ( ( ) ) αre, CD, l = α max (4) αre b) Giapow Moel: The Giapow moel i uually recommene for enely itribute oli particle ytem an it can be repreente by: CD, l = CD(Wen Yu)if α < 0.0, M α μl 7 α ρ = S α 4 l p l U U l U U if α > 0.0 D, l p l (5). Ga-oli rag force correlation There are few wor in literature which coniere the ga-oli rag in three-phae flow. In thi wor, the importance of thi momentum tranfer wa evaluate uing two correlation: a) Schallenberg et al. Moel: Mathematically, the correlation propoe by Schallenberg et al. (005) i given a: CD, = 80,min[ 1,max( 0, ( 15αg +1.8) )] (6) b) Syamlal-O'Brien Moel: The moel propoe by Syamlal an O'Brien (1989) i bae on the claical rag correlation of Dalla Valle: C Re D, = ρg U U = μ g g 4.8 Re / V p, r, ( ) ( ) Vr = A 0.06Re Re +0.1Re B A + A 4.14 A = α g, B = 0.8αg if αg 0.85 an αg if αg > 0.85 (7).65 where V r i the ratio of the terminal ettling velocity of a multiparticle ytem to that of an iolate ingle particle, propoe by Garie an Al-Dibouni (1977)..3 Turbulence The turbulence i ecribe by the two-equation RNG -ε moel, a the Dipere Phae Inuce Turbulence. A a reult, the um of all thee contribution etermine an effective vicoity (µ eff ). In thi ene come:

3 1509 μ eff, l = μl + μt,l + μbi,l, eff, g = μ g + μt, g μ an μ eff, = μ + μ (8) where, µ t i the turbulent vicoity, which wa coniere for the ga phae by Zero-Equation moel, µ bi i the bubble inuce turbulence calculate by the Sato an Seoguchi (1975) moel, µ i the hear vicoity inuce by oli colliion, coniere only in the imulation with KTGF..4 Numerical proceure The numerical reult are valiate with experimental ata from the literature Wu et al. (008) in a column with a iameter of 10. cm an height of 1.05 m. The Euler moel i applie to all three phae. The initial conition i fill the column with the liqui an oli phae (the repective concentration) to the operating height equal 0.9 m, a in phyical experiment. I impoe atmopheric preure at the top of the column, non-lip conition for the liqui an free lip to the ga an oli phae in the wall. The ga enter to the column with a contant velocity by an area equivalent to 70 % the total cro ection. The liqui an oli phae are not loa/leave the omain. The ga an oli phae are treate a a ipere flui, where, it i aume that all the bubble have the ame iameter, 4.5 mm (8.5 mm to high ga flow) an 75 µm to oli phae. The lurry bubble column i coniere to be operate at 5 C an 1 atm at iothermal conition. No heat an ma tranfer occur. The apparent alumina upenion vicoity can be etimate through empirical correlation from imple parameter i given by a Krieger an Dougherty moel: μ = μ.5 α,max α l 1 (9) α,max where, µ i the apparent vicoity of upenion, α,max = 0.6 an α i the oli holup in the ytem. A well itribute hexaheral meh i ue to 3D an tranient imulation with the commercial CFD coe ANSYS CFX 14. A time tep of 0,01 wa ue along all the imulation, an a real time of 00 wa imulate, where the firt 30 wa ue to etablih a peuo-tationary conition. A high-orer interpolation cheme wa ue for the hyroynamic equation an upwin for the turbulence equation, with a convergence criteria of RMS et to The preure-velocity coupling wa obtaine uing the SIMPLEC algorithm. Four tet cae conition are hown in Table 1. The numerical reult are compare with experimental ata, in a plane locate at 56.1 cm from the bottom of the bubble column. Table 1: Stuie cae Cae Superficial ga velocity (U g, cm/) Ga flow (Q g, m 3 /) Soli Concentration (α, %v/v) A.0 0, B , C.0 0, D , Reult 3.1 Influence of liqui-oli interaction The influence of ifferent rag law for liqui-oli interaction are hown in Figure 1. Starting with qualitative analye of cae C (critical cae), analyzing the alumina holup fiel, all imulation how that alumina i in upenion, agreement with the experimental viualization reporte by Wu et al. (008). The numerical raial profile of ga holup are hown in Figure 1a an 1c. Thi profile ha a parabolic hape an agree with the experimental behavior. When increae the uperficial ga velocity, increae the ga holup an ga velocity maximal value in central core of column. In thi ene, the numerical imulation repreent thi feature. It i poible to note in imulation reult that the moifie Wen-Yu rag moel provie better preiction for the raial profile of ga holup an (ga velocity) x (ga holup), while the Giapow rag moel overetimate the experimental ata in the region near the column center. 3. Influence of ga-oli interaction Simulation reult for all cae (A to D) are how in Figure. It can be oberve in that the incluion of gaoli rag i not promote any improvement a compare to the reult obtaine when only KTGF moel i coniere. The reult uing ga oli interaction become wore for (ga velocity) x (ga holup) profile howe in Figure b. The KTGF moel with how a goo agreement almot in all the raial extenion.

4 1510 Neverthele, when ga-oli interaction i inclue the numerical profile in the center uneretimate an howe wore preiction with experimental ata. Figure 1: Raial profile of ga holup an (ga velocity) x (ga holup). Liqui-oli interaction analyi. Figure c an how the raial profile obtaine from cae B. It i note in Figure c an that the gaoli interaction improvement the reult. It can be ue the interaction ga-oli in high ga velocity i neee to be coniere. The moel propoe by Schallenberg promote a goo agreement with experimental ata for both flui ynamic variable invetigate. The Syamlal-O Brien moel uneretimate the prouct between bubble velocity an ga holup an overetimate ga holup. In Figure e an f, it coul be pointe out that for thi operating flow regime the ga-oli interaction can be neglecte. The better preiction for thi cae i howe by G-L + L-S + No G-S interaction + KTGF. Since in thi cae we are ealing with high concentration of oli an the oli-oli interaction play an important role a oberve from everal reearch wor in the pat. Figure g an h how the numerical profile for cae D with high oli concentration an high ga uperficial velocity. It can be een that a better preiction againt the experimental ata wa obtaine without ga-oli interaction (G-L + L-S + No G-S interaction + KTGF). However, all moel howe imilar behavior for the ga holup profile. In thi ene, the ga-oli interaction improve the reult only to an intermeiate oli concentration. In the cae of high oli concentration will increae the ize of bubble inie the column an ampe the ga circulation, an will ecreae the ga volume fraction (Kantarci et al., 005). For a final comparion, Figure 3 how for all cae liqui-oli an ga-oli interphae momentum tranfer rate. It i note that ga-oli momentum exchange increae with ga uperficial velocity an oli concentration. The ga-oli rag force in Figure 3 howe for all cae lower rate of momentum exchange. For cae D (high ga uperficial velocity an oli concentration) higher value of momentum exchange were oberve.

5 1511 Figure : Raial profile of ga holup an (ga velocity) x (ga holup). Ga-oli interaction analyi. Analyzing the liqui-oli rag momentum fiel obtaine in the imulation it i poible to ee that low ga uperficial velocitie promote more homogeneou fiel, ince the oli particle are well itribute throughout the lurry, in contrat for high ga uperficial velocitie the particle ten towar the wall, promoting a ene particle concentration in thi region. The liqui-oli momentum for cae C preente higher rate than in cae D, which operate with high ga uperficial velocity.

6 151 Figure 3: Momentum tranfer countour plot for liqui-oli an ga-oli interaction coniering G-L, L-S, KTGF an G-S by Schallenberg moel. 4. Concluion A CFD coe wa capable of imulating intermeiate an high oli concentration inie a lurry bubble column. In aition, the imulation preente how a goo agreement with experimental inicating a goo numerical conitency with the experimental operating conition. For the liqui-oli phae rag force the moifie Wen-Yu moel gave a better preiction of the alumina in upenion inie the ytem. The Kinetic Theory of Granular Flow (KTGF) promote a better agreement with experimental ata for all cae, except for intermeiate oli concentration an high ga velocity (cae B), in which the moel propoe by Schallenberg et al. (005) reulte in a better preiction of experimental ata. Reference Decwer W.D., 199, Bubble Column Reactor. John Wiley & Son Lt, Chicheter, UK. Garie J., Al-Dibouni M.R., 1977, Velocity-voiage relationhip for fluiization an eimentation in oliliqui ytem. In. Eng. Chem. Proce De. Dev. 16(), Jia X., Wen J., Feng W., Yuan Q., 007, Local Hyroynamic Moeling of a Ga-Liqui-Soli Three-Phae Airlift Loop Reactor, In. Eng. Chem. Re. 46, Kantarci N., Bora F., Ulgen K., 005, Bubble Column Reactor, Proc. Bioche. 40, Krihna R., van Baten J.M., 004, Eulerian Simulation Strategy for Scaling Up a Bubble Column Slurry Reactor for Ficher-Tropch Synthei, In. an Eng. Chemitry Reearch 43, Sato, Y., Seoguchi, K., 1975, Liqui velocity itribution in two-phae bubble flow, International Journal of Multiphae Flow, Schallenberg J.; En J.H., Hempel D.C., 005, The important role of local ipere phae hol-up for the calculation of three-phae bubble column, Chem. Eng. Science 60, Silva M.K., Ávila M.A., Mori M., 011, CFD Moelling of a Bubble Column with a External Loop in the Heterogeneou Regime, Canaian Journal of Chemical Engineering 89, Syamlal M., O Brien T.J., 1989, Computer Simulation of Bubble in a Fluiize Be. AIChE Symp. Serie 85, -31. Tabib M.V., Roy S.A., Johi J.B., 008, CFD Simulation of Bubble Column - An Analyi of Interphae Force an Turbulence Moel, Chemical Engineering Journal 139, Wu C., Suar K., Al-Dahhan M.H., 008, Bubble Dynamic Invetigation in a Slurry Bubble Column, AIChE Journal 54,