Scale‐up of mixing in gassed multi‐turbine agitated vessels

Abstract

A mixing model previously developed for the determination of mixing time in gassed tanks stirred by multiple Rushton turbines (Vasconcelos et al., 1995) was verified for the additional scales of 0.39,0.56 and 0.72 m vessel diameter. It is now shown that the single adjusted parameter previously required by the model, the air-induced axial velocity parameter v,,, is scale-independent with an invariant value of 7 x m/s. Model simulations, with tank and turbine diameters and the number of stages as the only required parameters, deviate 5% on average from the experimentally determined mixing timeThe model is thus a valuable tool for scale-up of this type of vessels.Un modkle de mClange mis au point antkrieurement pour la dktermination du temps de mClange dans des rCservoirs en milieu aCrC agitCs par des turbines de Rushton multiples (Vasconselos et al., 1995), a Ctt vkrifiC pour de nouvelles Cchelles de diamktre de rkservoir de 0,39,0,56 et 0,72 m. I1 est maintenant montrC que le paramktre d'ajustement unique auparavant exigC par le modkle, soit le paramktre de vitesse axiale induite par l'air vp, est un invariant de 1'Cchelle dont la valeur est 7 x m/s. Des simulations utilisant comme paramktres uniques les diamktres de rkservoirs et de turbines et le nombre de phases, donnent des dCviations de 5% par rapport au temps de mClange to,os determink expCrimentalement. Le modkle est donc un outil valable pour la mise B I'Cchelle de ce type de rkservoirs.

Gas hold-up distribution and mixing time in gas–liquid stirred tanks

“…The increase of the mixing time above a critical impeller speed under sparged conditions is in general agreement with previous findings [6,21] based on results collected with different techniques.…”

“…Several aspects of the complex hydrodynamics of the two-phase turbulent flow in stirred gas-liquid contactors have been investigated in the past decades [1], moving over the years from the overall characteristics of systems of different geometries under variable operation conditions (such as power consumption [2,3], overall gas hold-up [2][3][4][5], gas dispersion regimes [4,5], liquid mixing time under gassed conditions [2,3,6,7]) to, more recently, local variables based on advanced techniques (liquid and gas velocity fields [8][9][10], bubbles size distribution [11][12], local gas hold-up [13][14][15][16][17]). …”

Mixing and mass transfer in a pilot scale U‐loop bioreactor

“…( a ) the U‐loop fermenter (Eq. ), ( d ) STR Equation with H = 2 D v (Vasconcelos et al, ), ( b ) STR Equation with H = D v (Van't Riet, ), ( c ) predicted curve for a U‐loop fermenter if a centrifugal pump with a lower head is used (three times smaller motor). ( C and D ) Comparison of the mass transfer coefficients ( k L a ) for the 0.15 ⋅ m 3 U‐loop fermenter and mechanically stirred systems at two different volumetric gas flow rates ( Q g ) equal to 0.67 and 1.33 vvm.…”

“…( a ) the U‐loop fermenter (Eq. ), ( d ) STR Equation with H = 2 D v (Vasconcelos et al, ), ( b ) STR Equation with H = D v (Van't Riet, ).…”

Flow Induced by Dual-Turbine of Different Diameters in a Gas-Liquid Agitation System: the Agitation and Turbulence Indices

“…The gas -liquid dispersion process in stirred tanks with standard geometry, equipped with a ring sparger and dual-turbine agitation system, where the liquid height is larger than the tank diameter (H > T) has been widely reported (Abrardi, et al, 1988;Hudcova, et al, 1989;Roman & Gavrilescu, 1994;Vasconcelos et al, 1998). However, in the literature is scare the experimental data concerning aeration-agitation system with all the following characteristics: a) H = T (Kuboi & Nienow, 1982), b) baffles fixed away from the wall and the bottom, c) tanks with curved bottom (Bouaifi & Roustan, 1998), and d) dual-turbine impellers.…”