A Comparative CFD Study on Gas-Liquid Dispersion in A Stirred Tank with Low and High Gas Loadings

Abstract

Abstract The computational fluid dynamics (CFD) combined with a population balance model (PBM) was applied to simulate gas-liquid dispersion in a stirred tank with low and high gas loadings. The model predictions were validated by using the data in the literature. The simulation results show that the flow patterns and gas dispersion characteristics are very different in the stirred tank for low and high gas loadings. A typical two-loop flow pattern forms as that in single-phase stirred tank for low gas loadings, while a triple-loop flow pattern, with two recirculation loops above and one below the impeller is found in the tank for high gas loadings. Shaft power input of impeller agitation plays a major role for gas dispersion with low gas loadings. For high gas loadings, the potential energy due to gas sparging has significant effect on gas dispersion and can not be neglected. Compared to low gas loading, high gas loading causes average gas holdup increased in the stirred tank, while relative local gas holdup in the lower circulation-loop region and near-wall region reduced. The ability of impeller agitation for gas dispersion reduces with high gas loadings, and mean bubble size becomes larger and the volume-averaged bubble size distribution is wider.