Experimental study on bubble rising and descending velocity distribution in a slurry bubble column reactor

To determine bubble rising and descending velocity simultaneously, a BVW-2 four-channel conductivity probe bubble parameters apparatus and its analysis are used in gas-liquid and gas-liquid-solid bubble columns. The column is 100 mm in internal diameter and 1500 mm in height. The solid particles used are glass beads with an average diameter of 17.82 mu m, representing typical particle size for catalytic slurry reactors. The effects of superficial gas velocity (1.0 cm/s <= U-g <= 6.4 cm/s), solid holdup (0 % <= epsilon(s) <= 30%), and radial location (r/R = 0, 0.4, and 0.7) on bubble velocity distributions are determined. It is found that increasing U-g can increase the velocity of bubbles but do not exert much influence on bubble velocity distribution. Solid holdup mainly affects the distribution of bubble velocity while the radial direction affects bubble velocity distribution only slightly. The ratio of descending bubbles to rising bubbles increases from the bubble column center to the wall. It can be proved experimentally that large bubbles do not always rise faster than small bubbles at higher Ug (for example 6.4 cm/s).