A Computational and Experimental Study of Mixing and Chemical Reaction in a Stirred Tank Reactor Equipped with a Down-pumping Hydrofoil Impeller using a Micro-Mixing-Based CFD Model

In this work the following fast parallel competing reactions scheme (Bourne and Yu, Ind. Eng. Chem. Res. 33, 41-55. 1994).A+B-->P+RA+C-->Q+Swas modeled in a stirred tank reactor using CFD, and the results compared with original experimental data. The experimental system comprised a cylindrical stirred tank reactor fitted with an axial down-pumping hydrofoil impeller (Chemineer HE-3) operated in semi-batch mode, with the limiting reagent being slowly added to the contents of the reactor. The final yield, X-S, of the undesired product S was experimentally measured. The flow field in the reactor was simulated using the Iieynolds Stress turbulence model. The full impeller geometry was incorporated in the CFD simulation using the Multiple Reference Frames (MRF) model. The reaction zone was modeled in a Lagrangian way using a multi-phase model (Volume of Fluid (VOF) model). The interaction of turbulence and reaction was accounted for by means of the engulfment model for micro-mixing (Baldyga and Bourne, Chem. Eng. J., 42, 83-92. 1989). The agreement between previously published experimental velocity distribution data (Jaworski. Nienow and Dyster, Can. J. Chem. Eng., 74, 3-15, 1996) and the results of the simulations was generally good. The micro-mixing model, in conjunction with CFD, predicted a final value of X-S in close agreement with the experimental data, demonstrating that the proposed approach can be successfully used to model turbulent reactive systems without the need for experimental inputs.