Particle Residence Time Distribution in a Continuous Flow Stirred Reactor: Experimental Characterization and CFD Modeling

Residence time distribution of catalyst particles in a continuous flow stirred vessel plays an important role in determining the final particle size distribution in processes where product is formed on catalyst particles. It is therefore necessary to control the mixing conditions in the vessel to improve the final particle size distribution. In this work, experimental characterization and a computational fluid dynamics (CFD) model were used to identify the appropriate mixing environment in a continuous flow stirred vessel to improve the final particle size distribution. Particle residence time distribution was first measured in a stirred vessel using two different vessel internal designs. A CFD model was then developed to predict the particle residence time distribution. The predicted particle residence time distribution was found to show reasonably good agreement with experimental data. The validated computational model was then used to evaluate different internal designs. It was observed that the particle size distribution could be made more plug-flow like by decreasing the off-bottom clearance of the upper two impellers and replacing the rotating discs with stationary discs (horizontal baffles) extended to the vessel wall. The resulting residence time distribution was demonstrated to more favorable than the existing design.