CFD modelling of gas-liquid flow in an industrial scale gas-stirred leaching tank

The performance of a gas-stirred tank for cyanide leaching relies on the good mixing between solid particles and reagents, as well as sufficient oxygen mass transfer through gas bubbles. In this study, a gasliquid two phase computational fluid dynamics (CFD) model has been applied to investigate the gas-slurry flow in an industrial scale leaching tank. Following model validation using measurement data from a laboratory gas-stirred reactor, the CFD model has been extended to study flow dynamics in an industrial scale Pachuca tank with different designs. The likely effects of the introduced gas bubble size and the draft tube diameter on tank performance are assessed in terms of the overall flow patterns, gas holdup, bubble residence time distribution, slurry mixing, as well as the solid sedimentation region. It was found that the slurry flow in the tank is dominated by strong global re-circulations with slurries being pumped up inside the riser, followed by a downward motion in the downcomer before re-joining the riser from the draft tube bottom. There are no local re-circulations observed in the riser and downcomer regions for the original design and the proposed new designs. The new design with either reducing the gas bubble size or increasing the draft tube diameter increases gas holdup, promotes solid mixing and reduces the solid sedimentation region. Simulation results obtained demonstrate the feasibility of the present modelling approach as a useful numerical tool to help potential improvement of industrial scale Pachuca tank design and/or operation. Crown Copyright (C) 2015 Published by Elsevier B.V. All rights reserved.