Mixing system for gas dispersion in liquids or liquid suspensions

Abstract

In order to obtain efficient gas dispersion (aeration where air is the gas) in mixing systems where the circulating impeller is offset from the center of the tank containing the medium in which the gas is dispersed or sparged while being circulated, flooding of the impeller due to entrainment of gas released by the sparging device (a pipe or ring having as outlets) because of the asymmetrical return flow of the medium circulating in the tank which entrains the gas and brings the gas into the area swept by the impeller as it rotates, is avoided by arranging the sparging device to prohibit the release of gas into a region, including a sector of the swept area, where the return flow responsible for flooding occurs. This sector has been found to lie along a line between the center of the tank and the axis of rotation of the impeller. The gas dispersion mixing system is especially useful in dispersion of gas into large volumes (e.g. 20,000 cubic feet). There, a plurality of axial flow impellers and associated sparging devices are circumferentially spaced around the center of the tank. The sparging devices are arranged so that gas is prohibited from being released in the region where the gas is subject to being entrained into the impellers swept area by the asymmetrical return flow, thereby avoiding flooding and increasing gas dispersion (mass conversion) in the mixing system.