Time-dependent hydrodynamics of bubble columns

Abstract

Bubble column reactors are widely used in chemical engineering. They often operate in the heterogeneous regime combining thus high gas concentrations and strong velocity fluctuations. Furthermore, processes are usually dynamic as the injected gas flowrate may be unsteady, they can suffer sudden change of operating parameters, etc…

We present experimental results for six different bubble columns (with 5 different column diameters) in both the homogeneous and the heterogeneous regime. We cover two different time-dependent situations. First, the startup of the bubble column is considered. This unsteady regime consists on injecting a fixed gas flowrate starting from zero. The time that bubbles require to reach the free surface and the duration of the unsteady regime are then analyzed. Later, we focus on the fluctuations of several quantities (void fraction, correlation times…) within stable operating conditions. Our results show that even within steady gas injection conditions, all studied parameters present significant fluctuations.