Influence of scale on the volumetric mass transfer coefficients in bubble columns

Abstract

The gas holdup, ε, and volumetric mass transfer coefficient, k L a, were measured for the air–water system in bubble columns of three different diameters, 0.1, 0.15 and 0.38 m. The superficial gas velocity U was varied in the range 0–0.35 m s −1, spanning both the homogeneous and heterogeneous flow regimes. The gas holdup ε shows a small decrease with increased column diameter; this effect is due to increased liquid recirculations with increasing scale. The volumetric mass-transfer coefficient, k L a, closely follows the trend in gas holdup. For U>0.08 m s −1, the value of k L a/ ε was found to be practically independent of column diameter and superficial gas velocity; the value of this parameter is found to be about 0.48 s −1. Our studies provide a simple method for estimation of k L a in industrial size bubble columns operated at high superficial gas velocities.