How to disperse gases in liquids

Abstract

Mixing of a gas in a liquid is required in fermentation operations and a variety of oxygenation and hydrogenation processes. Agitation increases the mass transfer between the gas and the liquid phase. Gas-liquid reactors equipped with agitators are often operated at high power input and large gas holdup, making these units among the most difficult to design. Modern high-efficiency and concave-blade disc impellers provide the proper balance of flow, turbulence and shear for most applications. For an overview of the state of the art in gas-liquid agitation, a number of excellent reports are available. This article aims to present practical design guidelines while explaining the basics of gas-liquid mixing. It expands on design procedures presented in 1976 by Hicks and Gates and capitalizes on recent advances in flow-visualization techniques, development of new gas-dispersion impellers and improved understanding of the dispersion process itself. Methods to calculate power draw, gas holdup and mass-transfer rate are illustrated with examples. It is shown that concave-blade turbines provide better performance than the traditional flat-blade units.