FEEDBACK-CONTROL OF CRYSTAL SIZE DISTRIBUTION IN A CONTINUOUS COOLING CRYSTALLIZER

Control of crystal size distribution (CSD) in a 21.8 L continuous cooling KCl crystallizer was attempted. Feed saturated at 54-degrees-C with potash, nearly saturated with NaCl and containing 0.75 g MgSO4/100 g of H2O was cooled to the crystallizer temperature at 40-degrees-C. The control scheme consisted of a proportional-integral controller with the rate of fines dissolution/removal as the input variable and the fines suspension density (crystals smaller than 150-mu-m) as the output variable. The measured/controlled variable was a temperature difference, DELTA-T, corresponding to the temperature of a slurry sample containing representative fines, before and after the fines were dissolved by heating. An increase in the product weight-mean crystal size and a decrease in the coefficient of product were observed in the controlled runs.