(359a) Mixing Nuclear Waste Using Airlift Circulators: Performance Measurements and Parameter Optimization

Airlift circulators (ALCs) were investigated as a supplement to the primary mixing system, i.e., pulse jet mixers, in Waste Treatment and Immobilization Plant (WTP) vessels designed for high solids processing on the Hanford site. ALCs use air confined in a riser tube to generate a bulk recirculation flow in the vessel.  The velocity (or volumetric flow) created by the ALC is a complex function of several geometric parameters, air flow rate, and fluid properties.  By varying several of these parameters in a 7.5-ft diameter test vessel, a simple relationship between velocity, air flow rate, and geometry was established over the range of test conditions.   The relationship is similar to expressions available in the literature; however, previously developed expressions did not produce reasonable estimates of velocity for this experimental system because of differences in scale.

The velocity exiting the riser tube is one useful performance metric that was studied.  Others of particular interest to mixing nuclear waste are the ability of an ALC to transport settling solids from bottom regions of the vessel to the top (particularly in Newtonian fluids) and the mobilization (or yielding the fluid to the point of motion) of non-Newtonian yield stress fluids in the upper portion of the vessel.  Both of these mixing functions were tested independent of a pulse jet mixing system to assess the performance of the ALCs alone.  The tests used simulant fluids in the 7.5-ft diameter vessel and the results from these tests will be presented.  Implications of these test results on selection of optimum ALC system parameters will be discussed.