CFD-PBE simulation of premixed continuous precipitation incorporating nucleation, growth and aggregation in a stirred tank with multi-class method

Abstract

The continuous precipitation of BaSO4 with a premixed feed in a stirred tank is simulated. The population balance equation (PBE) is closed with the multi-class method. The effects of aggregation, feeding concentration, agitation speed, mean residence time, the crystal size distribution (CSD) at different locations and the net birth rate of each size bin due to aggregation are numerically studied. Size bin number tests show that at least 36 bins are needed for the size range in this work to achieve acceptable accuracy in both cases with and without aggregation. The predicted CSD is in good agreement with the reported experimental measurement. Narrower CSD and higher peak value are obtained with higher feed concentration. Aggregation broadens the CSD, decreases the peak value, and makes the CSD shift toward a larger size. The mean size L32 of crystals decreases significantly with increasing the inlet concentration, which is consistent with the experiments and model predictions reported in the literature. The effects of residence time and agitation speed on CSD and L32 are limited, which is very different from those in unpremixed cases. The CSD at the inlet region differs greatly from the outlet and near impeller regions, both in shape and value. A bimodal distribution appears around the inlet under some conditions. The net birth rate of the ith size bin due to aggregation increases dramatically with the inlet concentration. The detailed information, such as the bimodal distribution in a certain location under certain conditions and the aggregation rate of each size bin, could be useful for the precise and sophisticated control of precipitation in some novel processes like nano-particles production.