Bubble Size "Bimodal" Distribution Enhances Mixing and Mass Transfer in Slurry Bubbling Column Reactor

To meet the needs of industrial installations to enhance mixing and mass transfer, solving the problem that the liquid turbulence caused by the microbubbles is weak and unfavorable for gas-liquid-solid phases mixing, we propose a concept of employing bubbles with a "bimodal" size distribution. Specifically, microbubbles are introduced to enhance mass transfer, while macrobubbles are utilized to promote mixing. Building upon this design philosophy, we developed a comprehensive gas distributor comprising a swirl-venturi microbubble generator and a ring-shaped gas distributor. This combined system aims to optimize the distribution of the bubble sizes. Experimental studies have been conducted to investigate the impact of bubble size distribution on gas holdup, solid holdup, liquid phase mixing, and the liquid volumetric mass transfer coefficient within the slurry reactor. From the experimental findings, we derive essential principles for the design of the "bimodal" bubble size distribution. First, the superficial gas velocity of the macro bubble should exceed the critical value, set at u(g,trans-tM), which equals 0.077 m/s in our experiments. Second, the proportion of air intake from the swirling-venturi microbubble generator to the total air intake should not surpass the critical ratio alpha(SVMG,trans) established at 30% in this experiment. These principles provide a solid foundation for optimizing the proposed "bimodal" bubble size distribution and improving the overall performance of the slurry reactor.