(364d) Comparison of Efficiency for Impellers Commonly Used in Anoxic Denitrification

The hydraulic efficiency of impellers operating in stirred
vessels can be defined in the same way as a pump - the ratio of the flowing
fluid's kinetic energy to the mechanical energy input by the mixing device.

In this presentation the hydraulic efficiencies of several
impeller types commonly used in the process industries are compared to the
efficiencies of impellers used for mixing in anoxic denitrification.  Values
for the impellers' efficiencies are compared with values previously reported in
the literature.

Results of a full-scale mixing trial in which the solids
distribution was measured for three impellers will also be presented and
results discussed in the light of the impellers' relative efficiencies.  The
local solids concentration was measured at several locations within the vessel
and the power input per volume determined when each local measurement was found
to be within ± 5 % of the average.  Hydrofoil impellers were found to be 3 ? 5
times more energy efficient than a Hyperboloid impeller in achieving this
target.