Mixing system for introducing and dispersing gas into liquids

Abstract

A mixing system utilizes up pumping impellers which entrain gas into the liquid both at the surface (the gas liquid interface) and below the surface by induction to draw gas down below the surface where it is dispersed into the circulation produced by the impellers. The impellers are the axial flow type. Tubes disposed on the suction sides of the impeller blades, and providing gas outlets near the tips of the blades, rotate with the impellers. The tubes may extend along the shaft above the surface or into a hollow shaft having a breathing opening above the surface. The rotation of the impeller produces a suction at the tube outlets to draw gas into the liquid while the upward circulation produces surface turbulence for gas entrainment. The entrained gas from the surface and the gas discharged from the tubes is circulated. The system is less sensitive to variations in the level of the liquid between the impeller and the surface than is the case with the systems operating by surface gas entrainment or induction alone and even systems using induction and vortices created by down pumping impellers, as have heretofore been proposed. The gas transfer, as measured by the mass transfer co-efficient (kLa), is less sensitive to liquid level and the decrease of the mass transfer co-efficient with increasing liquid level is reduced.