Scale-up of a downflow bubble column: Experimental investigations

Abstract

Co-current downflow bubble columns provide advantages like high gas phase residence time and small bubble diameters, which result in high gas-liquid interfacial area and high mass transfer rates. The precise knowledge of gas fraction, bubble size distribution, interfacial area (a_) and volumetric mass transfer coefficient (kLa_) data is essential for the design of such downflow bubble columns. The present work investigates the effect of superficial gas velocity, liquid velocity and gas sparging location on the volume averaged gas fraction, axial and chordal gas fraction profiles, Sauter-mean bubble size, kLa_, and a_ in a downflow bubble column modified to operate via an array of downward pointing micro-jets. Experiments were performed for air-water system with 20 PPM SDS in two-different scale downflow bubble columns: (1) volume of 5 L (Height (H) = 0.6 m, Diameter (D) = 0.1 m, aspect ratio (H/D) = 6) and (2) volume of 120 L (H = 1.5 m, D = 0.3 m, H/D = 5). The experimental results of axial and chordal gas fraction profiles and bubble size distributions are presented. Further, the empirical correlations have been proposed to predict the gas fraction (∈G), Sauter-mean bubble diameter (dB) and effective gas-liquid interfacial area a_ for better understanding the scale-up process.