Gas-liquid flow in bubble columns and loop reactors: Part I. Detailed modelling and numerical simulation

The state of the art of the modelling of gas-liquid flow in bubble columns and loop reactors is critically reviewed. Recent results obtained with dynamic multidimensional two-fluid models are compared with respective steady state simulations. It will be shown that no steady state solution for uniformly aerated bubble columns can be obtained above a certain gas velocity if a sufficiently fine space grid is used. A dynamic state is obtained instead where large and rising vortices are subsequently generated at the gas distributor. Only after a long time averaging is the well known flow structure with increased gas hold-up and liquid upflow in the column centre and reduced gas hold-up with downflow near the walls obtained. The above results are based upon a two-dimension Euler-Euler model. The underlying assumptions and simplifications are discussed and the advantages and drawbacks of a corresponding Euler-Lagrangian formulation are considered. The model is used in Part II of this contribution for a detailed comparison with the experimental results from a flat bubble column with various circulating flow patterns.