Effect of mixing on the crystal size distribution of borax decahydrate in a batch cooling crystallizer

The effect of the impeller speed upon the metastable zone width, supersaturation level, crystal growth and the crystal size distribution of borax decahydrate have been investigated to find operating conditions of a batch cooling crystallizer. The importance of impeller speed was studied in baffled stirred crystallizer with a volume of about 2 dm3, equipped with four straight blade turbine (4-SBT) cooling at a constant cooling rate. The metastable zone width was determined by visual method, while concentration changes during the process were monitored in line using ion-selective electrode. The crystal size distribution was determined by optical microscope and sieve analysis respectively. The power consumption measurements were performed for all impeller speeds examined as well. On the basis of the experimental results and observations it is evident that in an agitated batch crystallizer the above mentioned parameters are significantly influenced by hydrodynamic regime in the system determined by impeller used and its revolution speed.