Effects of solid particles on bubble breakup and coalescence in slurry bubble columns

Abstract

Bubble size distribution (BSD) is a crucial parameter in the design and scale-up of slurry bubble columns (SBCs) as it affects the hydrodynamics, heat and mass transfers, and, consequently, the column overall performance. It is necessary to understand the impacts of various parameters on the bubble size to adequately predict the BSD. The population balance model is widely adopted to estimate the BSD by considering the bubble coalescence and breakup rates. Many bubble coalescence and breakup models have been proposed in literature to predict the BSD. However, the available models have been developed for two-phase (gas–liquid) systems. They are, hence, less appropriate for three phase (gas–liquid-solids) systems, as the presence of particles in these systems has considerable impacts on their hydrodynamics. Novel bubble breakup and coalescence models are developed in the present study to predict the effects of solids concentration and particle size on the bubble breakup and coalescence rates. The results showed that the presence of solids can increase both bubble coalescence and breakup rates, while the effect is more pronounced on the coalescence rate. In addition, an increase in the particle size increases the bubble breakup rate and decreases the bubble coalescence rate. An integrated population balance and hydrodynamic model was also developed to estimate the BSD and gas holdup in a slurry bubble column. The developed models in this study were successfully validated by experimental hydrodynamic data from literature and those obtained in our pilot-scale slurry bubble column. A set of parametric studies were accomplished to investigate the effects of solid particles on the bubble breakup, bubble coalescence, and BSD in two common industrial applications of SBCs.