Improved Crystallizer Stirrer Performance through CFD Modelling

An experimental pilot crystallizer was constructed at the Commonwealth Scientific and Industrial Research Organisation (CSIRO), and numerous trials were performed to obtain velocity data at selected positions within the crystallizer for different impeller designs and operating conditions. The measurement technique was based on laser doppler velocimetry (LDV). Factory trials were also conducted on a stirred batch crystallizer and velocity measurements obtained using hot film anemometers. CFD models were developed for the different impeller designs and conditions for both the laboratory and factory crystallizers. The data from the CFD modelling were matched against the laboratory data from the CSIRO velocity profiles and the factory data to validate the CFD models. The CFD models showed very good agreement to the CSIRO velocity profiles and also predicted the torque (power) applied to the impeller reasonably well. The CFD models also showed reasonable agreement to the factory data. Using the validated CFD model, an improved impeller design was generated for batch evaporating crystallizers. The new impeller design was retrofitted into a stirred crystallizer at an Australian factory in 2004, and its performance was evaluated against data collected using the original impeller. The results show the new impeller blades consume more power but improve the circulation substantially towards the outer regions of the crystallizer and increase the heat transfer coefficient by 15–40%