Holdup and velocity profiles of monosized spherical solids in a three-phase bubble column

Abstract

Non-invasive laser detective techniques, Phase Doppler Anemometry (PDA), were used to measure solids holdup and velocity profiles in a three-phase gas–liquid–solid bubble column. The cylindrical bubble column was driven by a point air source made of a 30-mm diameter perforated air stone centrally mounted at the bottom. It had an inner diameter of 152mm and was filled with liquid up to 1m above the point source. Monosized acrylic beads with a nominal diameter of 3mm were used as the solid phase. With added salt, the liquid density was adjusted to 1.0485kg/m3 for matching the density of the solid phase which was 1.05kg/m3. The bubble diameters generated were within the range of 600–2400μm. The turbulent characteristics of the bubbles and the solid phase were measured at five different air rates, namely 0.4, 0.6, 0.8, 1.0 and 1.2L/min (corresponding to the superficial gas velocities of 0.375, 0.549, 0.752, 0.919 and 1.128mm/s, respectively). The time averaged velocity measurements indicated tProd. Type: FTPhat a large circulation flow pattern exist in the column. Driven by the bubbles, the solid motion was upward in the center region and downward near the walls in the bubble column. The solid holdup values decrease slightly along the radial position in the lower part of the bubble column, and it became uniform in the upper part. The mean solid phase concentration is exponential decay with the height z. The solids velocity and holdup distribution presented here can improve the understanding of the flow behavior in a three-phase bubble column.