Bubbling Behavior in Gas-Liquid Countercurrent Bubble Column Bioreactors

Abstract

Characteristics of bubbling behavior and bubble properties were investigated and diagnosed in a gas–liquid countercurrent bubble column bioreactor which is 0.152 m in inside diameter and 3.5 m in height. The effects of gas and liquid velocities and bubble distribution mode (even, wall-side, central or asymmetric distribution) on the bubble properties such as chord length, frequency, rising velocity, holdup and bubbling behavior were examined. For the analysis of resultant bubbling behavior, pressure fluctuation signals were measured and analyzed by adopting the concept of the chaos theory; the signals were interpreted by means of an attractor in the phase space portraits and correlation-dimension. It was found that the resultant bubbling behavior could be detected effectively and quantitatively in terms of the phase space portraits and correlation dimension of pressure fluctuations in the bubble column bioreactor. The bubble size, frequency and holdup increased with increasing gas (UG) or liquid velocity (UL). The rising velocity of bubbles increased with increasing UG, whereas decreased with increasing UL. The uniformity of bubble size distribution and bubble holdup decreased when the distribution mode of bubbles at the gas distributor was changed from even to wall-side, central or asymmetric. The central distribution of bubbles was better than the asymmetric mode but worse than wall-side distribution, on considering the bubble holdup and uniformity of distribution. The bubble holdup and size were well correlated in terms of correlation dimension of pressure fluctuations elucidating the bubbling phenomena in the gas–liquid countercurrent bubble column bioreactor.