Ease of control of imperfectly mixed continuous DTB crystallizers

This study examines the effects of imperfect mixing on the ease of control in continuous crystallization processes. A compartment model was employed t o describe imperfect mixing in a crystallizer vessel, and size-dependent cl assification functions were introduced to describe the internal classificat ion of crystals. The size-dependent classification functions were built by performing intensive CFD (computational fluid dynamics) calculations. The n ucleation rate equation used in the perfect mixing model was extended to al low the domination of nucleation by crystal-impeller collision to be consid ered. The index of ease of control was used to evaluate how easily a crysta llizer can be controlled. This index indicates the strength of control action relative to that of the physical feedback effects which cause oscillation. In this work, the idea of ease of control was extended so that the ease of control could be evalua ted based on the compartment model. It was shown that the imperfect mixing and the internal classification stro ngly influence the operating conditions under which a crystallizer can be c ontrolled easily. The internal classification also strongly affects the spa tial distribution of supersaturation in the crystallizer vessel.