(467c) Gas Dispersion With Up-Pumping Maxflo W Impellers

Despite known advantages of up-pumping wide-blade axial-flow impellers for gas dispersion, little is known about the design guidelines of these impellers. In the present study, the gas dispersion capabilities of the up-pumping axial-flow Maxflo W in low-viscosity liquids have been characterized, and compared with those of an up-pumping pitch-blade turbine and radial-flow CD-6.  This comparison includes the speed, torque, and power requirements of the three impellers. 

Testing at three scales (approximate volumes of 20, 70, and 170 liters) indicates that the dispersion capabilities of the Maxflo W can be described in terms of a scale-independent aeration-number Froude number relationship.  Although a minimum impeller rotational speed is required to disperse low gas flows, the increase in dispersion speed is small with increasing gas flow rate.  The effects of geometric parameters such as impeller to tank diameter ratio, sparger size, sparger location and liquid height on flooded to dispersed conditions have been investigated.  Unlike radial-flow gas dispersion impellers that are not strongly affected by some geometric parameters, the up-pumping Maxflo W dispersion performance can be highly dependent on sparger size and location.  Additionally, small impeller to tank diameter ratio Maxflo W impellers have been found to perform poorly in gas dispersion operations because of their highly axial discharge flow. 

It was found that the up-pumping pitched-blade turbine exhibits time-dependent dispersion behavior that can permanently fail to disperse gas after appearing to be capable of dispersion for reasonably long periods of time.  For this reason, collection of design data required extended, meticulous testing.