Modelling of mass transfer in gas–liquid stirred tanks agitated by Rushton turbine and CD-6 impeller: A scale-up study

Abstract A combined computational fluid dynamics (CFD) and population balance model (PBM) approach has been applied to the simulation of gas–liquid stirred tanks agitated by (i) a Rushton turbine or (ii) a CD-6 impeller, operating at aeration numbers from 0.017 to 0.038. The multiphase simulations were realised via an Eulerian–Eulerian two-fluid model and the drag coefficient of spherical and distorted bubbles was modelled using the Ishii–Zuber equations. The effect of the void fraction on the drag coefficient was modelled using the correlation by Behzadi et al. [Behzadi, A., Issa, R.I. and Rusche, H., 2004, Modelling of dispersed bubble and droplet flow at high phase fractions, Chem Eng Sci, 59: 759–770]. The local bubble size distribution was obtained by solving the PBM using the quadrature method of moments (QMOM). The local k L a was estimated using both the Higbie penetration theory and the surface renewal model. The predicted gas–liquid hydrodynamics, local bubble sizes and dissolved oxygen concentration were in good agreement with experimental measurements reported in the literature. A slight improvement in the prediction of the aerated power number was obtained using the non-uniform bubble size distribution resulting from the coupled CFD–PBM simulation. Evaluation of the prospective scale-up approaches indicates a higher probability of maintaining a similar level of mass transfer in a larger tank by keeping the P g / V and VVM constant. Considering its predictive capability, the method outlined in this work can provide a useful scale-up evaluation of gas–liquid stirred tanks.

[1]  Yoshinori Kawase,et al.  Phenomenological model for bubble column reactors: prediction of gas hold-ups and volumetric mass transfer coefficients , 2000 .

[2]  Alvin W. Nienow,et al.  Blending of Miscible Liquids , 2004 .

[3]  R. D. Vigil,et al.  Quadrature method of moments for aggregation-breakage processes. , 2003, Journal of colloid and interface science.

[4]  H. Blanch,et al.  Bubble coalescence and break‐up in air‐sparged bubble columns , 1990 .

[5]  A. M. Al Taweel,et al.  CFD simulation of gas-liquid contacting in tubular reactors , 2007 .

[6]  K. Riet,et al.  Review of Measuring Methods and Results in Nonviscous Gas-Liquid Mass Transfer in Stirred Vessels , 1979 .

[7]  Zai-Sha Mao,et al.  Experimental and numerical study of gas hold-up in surface aerated stirred tanks , 2006 .

[8]  R. Higbie,et al.  The Rate of Absorption of a Pure Gas into a Still Liquid during Short Periods of Exposure , 1935 .

[9]  P. Lines.  Gas-Liquid Mass Transfer Using Surface-Aeration in Stirred Vessels, with Dual Impellers , 2000 .

[10]  A. K. Agrawal,et al.  Shape of liquid drops moving in liquid media , 1966 .

[11]  Daniele Marchisio,et al.  Two-scale simulation of mass transfer in an agitated gas-liquid tank , 2007 .

[12]  Alvin W. Nienow,et al.  The dependency on scale of power numbers of Rushton disc turbines , 1987 .

[13]  Pasi Moilanen,et al.  Local bubble size distributions in agitated vessel: Comparison of three experimental techniques , 2005 .

[14]  Alberto Brucato,et al.  Modelling and Simulation of Gas–Liquid Hydrodynamics in Mechanically Stirred Tanks , 2007 .

[15]  Milorad P. Dudukovic,et al.  Numerical simulation of bubble columns flows: effect of different breakup and coalescence closures , 2005 .

[16]  Robert McGraw,et al.  Description of Aerosol Dynamics by the Quadrature Method of Moments , 1997 .

[17]  Zai-Sha Mao,et al.  Experimental and Numerical Investigation on Gas Holdup and Flooding in an Aerated Stirred Tank with Rushton Impeller , 2006 .

[18]  Stefan Luther,et al.  Bubble shape and orientation determination with a four-point optical fibre probe , 2005 .

[19]  Ville Alopaeus,et al.  Modelling local bubble size distributions in agitated vessels , 2007 .

[20]  D. Mewes,et al.  Bubble‐Size distributions and flow fields in bubble columns , 2002 .

[21]  N. Zuber,et al.  Drag coefficient and relative velocity in bubbly, droplet or particulate flows , 1979 .

[22]  J. Bertrand,et al.  Effect of Dual Impeller-Sparger Geometry on the Hydrodynamics and Mass Transfer in Stirred Vessels , 2004 .

[23]  Tron Solberg,et al.  Flow Generated by an Aerated Rushton Impeller: Two‐phase PIV Experiments and Numerical Simulations , 2008 .

[24]  Jos Derksen,et al.  Population Balance Modeling of Aerated Stirred Vessels Based on CFD , 2002 .

[25]  António Joaquim Serralheiro,et al.  Bubble size in aerated stirred tanks , 2002 .

[26]  M. Barigou,et al.  Bubble-size distributions in a mechanically agitated gas—liquid contactor , 1992 .

[27]  Ville Alopaeus,et al.  Modelling mass transfer in an aerated 0.2 m3 vessel agitated by Rushton, Phasejet and Combijet impellers , 2008 .

[28]  Ak Allen Chesters.  The modelling of coalescence processes in fluid-liquid dispersions : a review of current understanding , 1991 .

[29]  J. Derksen,et al.  Three-dimensional LDA measurements in the impeller region of a turbulently stirred tank , 1999 .

[30]  A. Brucato,et al.  Particle drag coefficients in turbulent fluids , 1998 .

[31]  Sergio Bordel,et al.  Modeling of the evolution with length of bubble size distributions in bubble columns , 2006 .

[32]  J. M. Smith,et al.  Large multiphase reactors : Some open questions , 2006 .

[33]  G. Evans,et al.  Numerical modelling of gas-liquid flow in stirred tanks , 2005 .

[34]  Alessandro Paglianti,et al.  Gas–liquid flow and bubble size distribution in stirred tanks , 2008 .

[36]  Mark M. Clark,et al.  Turbulence in Flocculators: Comparison of Measurements and CFD Simulations , 1999 .

[37]  Juan C. Lasheras,et al.  On the breakup of an air bubble injected into a fully developed turbulent flow. Part 1. Breakup frequency , 1999, Journal of Fluid Mechanics.

[38]  Donald S. Scott,et al.  An eddy cell model of mass transfer into the surface of a turbulent liquid , 1970 .

[39]  E. L. Paul,et al.  Handbook of Industrial Mixing , 2003 .

[40]  P. V. Danckwerts.  Significance of Liquid-Film Coefficients in Gas Absorption , 1951 .

[41]  Bengt Andersson,et al.  On the breakup of fluid particles in turbulent flows , 2006 .

[42]  Ville Alopaeus,et al.  Modelling Local Gas–Liquid Mass Transfer in Agitated Vessels , 2007 .

[43]  Vivek V. Ranade,et al.  CFD simulation of gas–liquid stirred vessel: VC, S33, and L33 flow regimes , 2006 .

[44]  Pierre Proulx,et al.  Two-phase mass transfer coefficient prediction in stirred vessel with a CFD model , 2008, Comput. Chem. Eng..

[45]  Roy G. Gordon,et al.  Error Bounds in Equilibrium Statistical Mechanics , 1968 .

[46]  A. Bakker,et al.  A COMPUTATIONAL MODEL FOR THE GAS-LIQUID FLOW IN STIRRED REACTORS , 1994 .

[47]  Geoffrey M. Evans,et al.  Predicting gas–liquid flow in a mechanically stirred tank , 2002 .

[48]  A. Kolmogorov.  The local structure of turbulence in incompressible viscous fluid for very large Reynolds numbers , 1991, Proceedings of the Royal Society of London. Series A: Mathematical and Physical Sciences.

[49]  R. Clift,et al.  Bubbles, Drops, and Particles , 1978 .

[50]  R. I. Issa,et al.  Modelling of dispersed bubble and droplet flow at high phase fractions , 2004 .

[51]  Bjørn H. Hjertager,et al.  LDA measurements and CFD modelling of gas-liquid flow in a stirred vessel , 1996 .

[52]  Mark F. Reeder,et al.  Performance of a Gas Dispersion Impeller with Vertically Asymmetric Blades , 1999 .

[53]  H. Svendsen,et al.  Theoretical model for drop and bubble breakup in turbulent dispersions , 1996 .

[54]  Jie Wu,et al.  Measurement of gas-liquid mass transfer in an agitated vessel -A comparison between different impellers , 2001 .

[55]  A. Bannari,et al.  CFD MODELING OF GAS DISPERSION AND BUBBLE SIZE IN A DOUBLE TURBINE STIRRED TANK , 2006 .

[56]  Alvin W. Nienow,et al.  The Transition from Homogeneous to Heterogeneous Flow in a Gassed, Stirred Vessel , 2000 .