265949 A Novel Euler-Lagrange Simulation Method for Gas-Liquid Stirred Reactors

Thursday, November 1, 2012: 8:30 AM
318 (Convention Center )
Radompon Sungkorn, Chemical and Materials Engineering, University of Alberta, Edmonton, AB, Canada, Jos Derksen, Department of Chemical & Materials Engineering, University of Alberta, Edmonton, AB, Canada and Johannes G. Khinast, Institute for Process and Particle Engineering, Graz University of Technology, Graz, Austria

         Various processes in chemical and biochemical industries involve dispersion of gas into liquid in stirred tank reactors. The complexity within the reactors are extremely high due to turbulent flow induced by impeller, interactions between the dispersed-gas and liquid phase, and interactions within the dispersed-gas phase. A simulation method that provides realistic description of the multiphase flow within the reactors is a valuable tool for design, optimization, and scale-up of such processes.

         We present a novel simulation method for gas-liquid stirred reactors including bubble breakage and coalescence [1]. The filtered conservation equations for the liquid phase are discretized using a lattice-Boltzmann scheme. A Lagrangian approach with a bubble parcel concept is used to represent the dispersed-gas phase. Bubble breakage and coalescence are modeled as stochastic events. The momentum coupling between phases is realized through the  source term in the conservation equations resulting in the so-called four-way coupling. The action of the reactor's components on the dispersed-gas and liquid phases is described using an immersed boundary condition.

         The present method was used to simulate gas-liquid flow in a stirred reactor following the experiments of Montante et al. [2]. The predicted number-based mean diameter and long-term averaged liquid velocity components agreed qualitatively well with the experimental data (Fig. 1). Effects of the presence of the dispersed-gas phase and the gas flow rate on the hydrodynamics were numerically studied.

         Furthermore, the present method was extended by including a power law model to represent shear-thinning liquids and empirical correlations for bubbles in shear-thinning liquids [3]. Simulations of aerated stirred reactors with shear-thinning liquids following the experiments of Venneker et al. [4] were carried out (Fig. 2). The predicted flow field of a single-phase stirred reactor with shear-thinning liquid showed reasonable agreement with the experimental data. For gas-liquid reactors, the predicted gas holdup distribution agreed qualitatively with the experimental data. Using the present method, it was found that a change in rheology significantly alters the number mean diameter, Sauter diameter, and the shape of bubble size distribution.

Figure 1. Comparison between experimental and predicted long-term average axial and radial liquid velocity.

Figure 2. Snapshot of predicted bubble dispersion pattern in an aerated stirred reactor with shear-thinning power law liquid.

References

[1] Sungkorn R., Derksen J.J., Khinast J.G. Euler-Lagrange modeling of a gas-liquid stirred reactor with consideration of bubble breakage and coalescence. AIChE J. 2012;58:1356-1370.

[2] Montante G., Paglianti A., Magelli F. Experimental analysis and computational modelling of gas-liquid stirred vessels. Trans IChemE. 2007;85:647-653.

[3] Sungkorn R., Derksen J.J., Khinast J.G. Modeling of aerated stirred tanks with shear-thinning power law liquids. Heat and Fluid Flows. 2012 (accepted).

[4] Venneker V.C.H., Derksen J.J., Van den Akker H.E.A. Population balance modeling of aerated stirred vessels based on CFD. AIChE J. 2002;48:673-685.


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