Crystallization kinetics of potassium sulfate in an MSMPR stirred crystallizer

Abstract

Experimental work on a potassium sulfate-water system was carried out using ten and fifty liter crystallizers. Different impeller velocities and suspension densities were used. The crystal size distribution was determined over the range from 0.1 μm to the largest crystals, which have been produced in the crystallizers, by the combination of Coulter LS-130 light scattering laser and by Vidas image analyzer results. Experimental evidence from continuous crystallizers frequently shows, at least for small crystals, deviation from the McCabe ΔL law. In this case, the estimation of kinetics of both nucleation and growth rate becomes more complicated. In this work the crystal size distribution was determined experimentally. The relation between growth rate and particle size is investigated. The methods of estimation of kinetics for industrial use are discussed. The experimental data of population density distribution was fitted directly by the three-parameter model presented by Mydlarz and Jones for a steady state MSMPR crystallizer. Then the relation between growth rate and particle size was calculated by the corresponding three-parameter growth rate model. The relation between growth rate and particle size shows that the apparent crystal growth rate increases linearly with the crystal size when the crystal size is smaller than about 10 μm, is strongly size-dependent when the crystal size is between 10–700 μm, and is size-independent when the crystal size is greater than 700 μm. A mechanism of growth rate dispersion is suggested.