Developments in the Understanding and Modeling of the Agglomeration of Suspended Crystals in Crystallization from Solutions

Abstract

The paper deals with the modeling of the agglomeration of crystals during their crystallization. Crystal agglomeration actually consists of two steps, i.e. particle collision and agglomerate strengthening by crystal growth. The expression of agglomeration rates can be written in terms of a collision rate coupled with an efficiency factor. However, the mechanisms and rates of collision and disruption are related to the type of liquid flow that the mother crystals and the agglomerate experience, which in turn are dependent on their respective sizes. In particular, the influences of the absolute and relative sizes of mother particles, of the local energy dissipation and of the fluid viscosity differ according to the three types of motions, i.e. Brownian, laminar, turbulent. Besides this, the rapidity of the crystal growth, which in turn is a function of the supersaturation, plays a major role in the strengthening rate. The question of the limit cases between two regimes is also treated. The method takes into account and unifies previous expressions obtained by other authors in the various regimes. The model is also able to calculate the average agglomeration degrees.The paper is illustrated by one example of crystal agglomeration from our recent work and introduces a general model.