Gas-liquid and liquid-liquid system modeling using population balances for local mass transfer

Gas-liquid and liquid-liquid stirred tank reactors are frequently used in chemical process industries. The design and operation of such reactors are very often based on empirical design equations and heuristic rules based on measurements over the whole vessel. This makes it difficult to use a more profound understanding of the process details, especially local phenomena. The scale-up task often fails when the local phenomena are not taken into account. By using CFD, the fluid flows can be taken into closer examination. Rigorous sub-models can be implemented into commercial CFD codes to calculate local two-phase properties. These models are: Population balance equations for bubble/droplet size distribution, mass transfer calculation, chemical kinetics and thermodynamics. Simulation of a two-phase stirred tank reactor proved to be a reasonable task. The results revealed details of the reactor operation that cannot be observed directly. It is clear that this methodology is applicable also for other multiphase process equipment than reactors.