MODELING OF TURBULENT-FLOW IN A BUBBLE-COLUMN REACTOR

A comprehensive mathematical model for describing flow, turbulence and gas hold-up distribution in a bubble column reactor is developed. For large diameter bubble columns (> 0.1 m), operated with the zero or lo w liquid throughput, sparged gas tends to pass preferentially through the central portion of the column. This non-uniform gas hold-up distri bution leads to macroscale circulation and turbulence in the reactor. Two new mechanisms are proposed and modelled to explain such a non-uni form gas hold-up distribution in bubble columns. The influence of acco mpanying wakes and of the column wall on the motion of gas bubbles is accounted for for the first time. Turbulent, dispersed gas-liquid flow is described by the time averaged two phase momentum equations. The t urbulent stresses are simulated using a k-epsilon model. Extra terms a rising from the gas hold-up fluctuations and pressure gradients are in cluded in the model. The predicted flow characteristics of the bubble column reactor are verified by comparison with the published experimen tal data over a wide range.