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

Abstract

The gas holdup, ε , and volumetric mass transfer coefficient, k_La, 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_La, closely follows the trend in gas holdup. For U> 0.08 m s⁻¹, the value of k_La/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_La in industrial size bubble columns operated at high superficial gas velocities.