Secondary nucleation in a stirred vessel cooling crystallizer

Abstract

The effect of the crystal concentration, stirrer type and -speed, and the supersaturation on the total net nucleation rate were examined in a continuous stirred vessel cooling crystallizer. A model for nucleation in suspensions is proposed, which is based on collision breeding. This type of secondary nucleation is treated in the literature, but until now its mechanism has not been established. To evaluate the results of the experiments, all possible collisions of each crystal during its movement through the crystallizer are considered. The model shows a linear relationship between the net nucleation rate and the energy dissipated by the stirrer, which is verified by the experiments.The experiments also show that the net nucleation rate is proportional to the crystal concentration.From the model, it can be concluded that the nucleation rate is determined by the nucleation due to crystal-stirrer collisions.Another result is an apparent low order dependence of supersaturation on the net nucleation rate.