Gas Holdup in a Slurry Bubble Column: Influence of Electrolyte and Carbon Particles

This study deals with the effects of electrolyte and particle concns. on the gas holdup in both the homogeneous and the heterogeneous flow regimes in a slurry bubble column. Gas holdup measurements and video recordings of the bubble behavior were carried out in a 2D slurry column (0.015 * 0.30 * 2.00 m) under ambient conditions. The addns. of electrolyte (sodium gluconate, 0.05-0.2 M) and of solid carbon particles (diam. 30 mm, 0.1-1.0 g L-1) both lead to a considerable increase in gas holdup. In both cases, crit. concns. exist above which no further increase in gas holdup is obsd. The transition from the homogeneous to the heterogeneous regime is not significantly affected by electrolyte but is increased by the presence of particles. Three mechanisms are proposed that might account for the gas holdup increase resulting from particle and electrolyte addn. It is suggested that a layer of carbon particles around the gas bubbles results in a lower av. bubble rise velocity. Both the addn. of carbon particles and the addn. of electrolyte lead to bubble stabilization, a decreased rate of coalescence, and thus a higher gas holdup. It is further suggested that the presence of electrolyte changes the surface tension, leading to smaller bubbles, a lower av. bubble rise velocity, and thus a higher gas holdup. The combined addn. of electrolyte and carbon particles confirms these hypotheses. [on SciFinder (R)