COMPARTMENT MODEL APPROACH AS A DESIGN TOOL FOR LARGE AERATED VESSELS WITH MULTIPLE IMPELLERS

摘要

The occurrence of local concentration gradients in large scale bioreactors is determined by mixing of the micro-environment. Prediction of the local conditions is therefore of major importance for the design of aerated reactors with multiple impellers such as commonly used in industry. As an alternative tool to computational fluid dynamics a compartment model approach has been used to simulate the global flow pattern in stirred vessels. The usefulness of this approach is demonstrated by an optimization of a substrate feeding setup using single and multiple dip pipes for a 50 m~3 reactor. It is shown that the mixing time can be reduced substantially if the substrate is injected by more dip pipes. However two conditions have to be fulfilled: the injection has to be done symmetrically with respect to the axial centre of the dispersion volume and the multiple dip pipes have to be evenly distributed along the axial co-ordinate of the dispersion volume. The simulations show that this holds, independently of the impeller configuration and the assumed axial flow structure.