HYDRODYNAMICS OF A GAS-LIQUID REACTOR STIRRED WITH A MULTI-IMPELLER SYSTEM

The behaviour of a sparged vessel agitated by two impellers is examined. Three stirrer configurations were tested: double Rushton turbine, Rushton turbine plus a pumping downward mixed flow turbine and a Rushton turbine plus a pumping upward mixed flow turbine. Hydrodynamic regimes, dissipated power and mixing time of the liquid were considered, several regimes were identified both for the bottom impeller and for the upper one. As far as the dissipated power is concerned, it was found that above the flooding conditions, the gassed power number is slightly affected by stirrer speed and depends on gas flow rate mainly. The mixing time of nonareated liquid showed a linear dependance on N-1, but it is always much higher than that in a single stirrer system. The presence of gas, above the flooding conditions, increases the mixing time, due to the lower pumping capacity of the stirrers.