| Abstract
| - This study deals with the effects of electrolyte and particle concentrations on the gas holdup inboth the homogeneous and the heterogeneous flow regimes in a slurry bubble column. Gas holdupmeasurements 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 additions of electrolyte (sodium gluconate,0.05−0.2 M) and of solid carbon particles (diameter 30 μm, 0.1−1.0 g L-1) both lead to aconsiderable increase in gas holdup. In both cases, critical concentrations exist above which nofurther increase in gas holdup is observed. The transition from the homogeneous to theheterogeneous regime is not significantly affected by electrolyte but is increased by the presenceof particles. Three mechanisms are proposed that might account for the gas holdup increaseresulting from particle and electrolyte addition. It is suggested that a layer of carbon particlesaround the gas bubbles results in a lower average bubble rise velocity. Both the addition ofcarbon particles and the addition of electrolyte lead to bubble stabilization, a decreased rate ofcoalescence, and thus a higher gas holdup. It is further suggested that the presence of electrolytechanges the surface tension, leading to smaller bubbles, a lower average bubble rise velocity,and thus a higher gas holdup. The combined addition of electrolyte and carbon particles confirmsthese hypotheses.
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