Gas Fraction and Bubble Dynamics in Structured Slurry Bubble Columns

With the aim of structuring the flow and reducing backmixing in slurry bubble columns, we investigate the effect of needle spargers in three-phase systems. We apply optical probes in a 2D and 3D column to measure the bubble dynamics and gas fraction. Experimental results for air water glass beads show that an increase in solids volume fraction (1) decreases the gas fraction, (2) shifts the transition point from homogeneous to heterogeneous flow to a lower gas velocity, (3) increases the mean bubble velocity by 60-100% in the range of superficial gas velocities from 0.02 to 0.1 m/s, and (4) has only a limited effect on the bubble size distribution. Fitting our experimental data to the Richardson and Zaki and Gamier models shows that we cannot use the model coefficients they report in their papers. However, fitting our data results in realistic values for the terminal bubble velocity in a swarm. By using needle spargers, giving a very uniform gas supply, a first step toward structuring the hydrodynamics of slurry bubble columns has been taken.