Abstract
The suspension of settling solids with gassed impellers has been studied taking into account the influence of cavity formation behind the impeller blades in gassed systems. It is shown that the increase of stirrer speed that is required to maintain complete suspension under gassed conditions correlates strongly with the power drop that results from cavity formation. Many different impellers have been compared, both at low and high solids concentrations. Downward pumping types can be used only at very low and stable gassing rates. In most cases a disc turbine will operate satisfactorily at a bottom clearance of about 0.25 tank diameter especially when used in a vessel with a dished bottom. Although the ungassed stirrer speed for complete suspension depends among other things on the particle concentration, the increase with gassing rate is practically independent of the solid phase because the whole process is dominated by the gas—liquid impeller hydrodynamics. Scale up correlations for the just-suspended power consumption are given.
Published Version
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