CFD Study of Local Crystal Growth Rate in a Continuous Suspension Crystallizer.

Abstract

The objective of the present work is to determine the local crystal growth rate in an imperfectly mixed suspension crystallizer. Experiments were carried out in pure potassium sulphate-water solution. The steady-state Crystal Size Distributions (CSDs) were measured at four different heights of the crystallizer using an in-situ particle image analyzer. Experimentally obtained CSD was used to determine the overall growth rate. Then, Computational Fluid Dynamics (CFD) was used to calculate the Particle Size Distributions (PSDs) of the same kind of suspension which was used in the experiments. The computational study was focused to simulate the mass transfer coefficient between particles and solution, and supersaturation. These quantities were determined from hydrodynamics of suspension in a crystallizer. The multi-fluid model was applied to describe suspension flow in the crystallizer. One continuous phase (water) and six dispersed phases, which were taken to be particles in six size classes, were used to approximate PSD. The crystal growth rate model was based on the diffusion process and was implemented into a CFD environment. The local growth rates were calculated from the slip velocity or from energy dissipation rate at the local temperature and supersaturation.