ESTIMATION OF NUCLEATION AND ATTRITION KINETICS FROM CSD-TRANSIENTS IN A CONTINUOUS CRYSTALLIZER

Crystal attrition is an important mechanism which is often neglected in the models of crystallization proceses. In order to account for attrition effects an appropriate model is required. In this investigation experimental attrition results were used to formulate a simple empirical attrition model which relates crystal attrition to the crystal attrition to the crystal size and the crystal hold-up. It is assumed that crystal abrasion is the predominant mechanism by which attrition occurs. The process of abrasion is modelled by a negative growth rate, which implies the assumption that the fragments produced dissolve immediately. As a result, an increase in the rate of abrasion enhances the kinetic growth rate, which in turn increases the nucleation rate. The attrition parameters are estimated simultaneously with the parameters which determine crystal birth from CSD-transients in a 20 litre continuous crystallizer which produces ammonium sulphate. Attrition causes a reduction in the number of larger crystals, a fact which is experimentally observed. A very significant improvement of the predicted transients and an increase in the accuracy of the estimated nucleation parameters results therefore when crystal attrition is included in the model.