(371d) CFD Characterization of a Vertically Stacked 7-Stage Continuous Crystallizer Cascade

Mixing plays a crucial role in crystallization processes to obtain e.g., a homogeneous supersaturation profile and a better control on the particle size distribution. Parameters such as the impeller type, size, position, and speed can heavily influence the mixing in Mixed Suspension Mixed Product Removal (MSMPR) crystallizer, the most widely adopted type among the continuous crystallizers. In the presented work, a novel stacked 7-tank MSMPR cascade is studied where the slurry is displaced vertically, by intervention of two periodically inflating diaphragms, in the first and last stage. It is of fundamental importance to understand and optimize the impact of the impeller configuration on the hydrodynamics inside the spherical tanks of the novel crystallizer aimed at minimizing the settling of solids and ensuring swift micromixing of antisolvent. Therefore, Computational Fluid Dynamics (CFD) was used to numerically study different impeller configurations (type, size, position) to map out the crystallizers mixing characteristic and identify the optimized setting (lowest impeller speed to minimize crystal breakage). Simulations were conducted utilizing Ansys Fluent software with an unstructured computational grid employing the RNG k-ε model. The results in this work represent the first CFD study for the novel crystallizer design. It also addresses the demand of the scientific community to investigate the hydrodynamics in crystallizers.