Modeling of industrial crystallizers for control and design purposes

The design of forced circulation (FC) crystallizers, which are widely used for the bulk crystallization of inorganic salts, is hindered by the lack of rules for scale-up, caused by the lack of reliable process models. The absence of a stirrer in the crystallizer and the relatively high temperature increase in the circulation line result, as expected, in a strong deviation from the well-mixed vessel approach often used in modeling. To improve process models, a compartmental approach is presented here to describe the crystallization process of evaporative and cooling suspension crystallizers. The model has been implemented in the dynamic flowsheeting program, speedup, and applied to simulate a 200-l evaporative FC crystallizer, with five compartments. Preliminary simulation results indicate that large supersaturation profiles are present in the crystallizer and that only a part of the crystallizer volume is effectively used for the growth of crystals.