CFD model of a self-aerating flotation cell

The effect of impeller speed on the air flow in a self-aerated Denver laboratory flotation cell was investigated using computational modelling. Air is induced into the slurry by the impeller's rotating action. The rate of air flow is determined by the suction pressure created by the impeller, the hydrostatic head of the slurry and the frictional losses along the delivery shaft from the inlet valve to the impeller. From two-phase simulations of the flotation cell at varying impeller speeds, the predicted air flow rates have been found to compare favourably against measured values reported in the literature. The effect of increasing impeller speed is to increase the air flow rate and gas holdup in the cell. Simulations with flotation kinetics showed that the gravitational force acting on the attached particles is significant. The effect is a decrease in the bubble rise velocity which in turn affects the flotation rate as predicted by the model. The effects of the local turbulence level on the local attachment rate and bubble loading have been discussed and quantified.