IMPORTANCE OF MACROMIXING IN BATCH COOLING CRYSTALLIZATION

The importance of spatial variations of the conditions in industrial-s cale, agitated batch cooling crystallizers is investigated by computer simulations. A three-compartment model is developed considering prima ry and magma density-dependent secondary nucleation. An increasing cry stallizer size is described by an increasing suspension turnover time. It is shown that accumulation of larger crystals in the bottom region , localized supersaturation generation and variations in the secondary nucleation rate due to varying local mixing intensity will, under nor mal conditions, exert a low and often negligible influence on the prod uct-size distribution of an industrial unit. In a batch process, the p roduct-size distribution is governed mainly by the conditions early in the process. During this period the supersaturation half-life is much longer than the suspension turnover time, and the influence of local variations becomes weak.