Liquid-phase properties and sparger design effects in an external-loop airlift reactor

Abstract A synergistic effect of liquid-phase properties and sparger design on the performance of an external-loop airlift reactor was observed in our experiments. The absolute changes of gas holdup reflecting the variations of gas dispersion mode and system properties were, however, less pronounced than in the bubble column reactors due to the equalizing effect of induced liquid circulation on the riser hydrodynamics. The total increase of gas holdup observed in aqueous solutions of inorganic salts was independent of the type of salt and varied only with the gas dispersion mode. For all electrolytes studied, the respective limiting dependence e vs uG were obtained at concentrations close to the transition coalescence concentrations of individual electrolytes, while further increase of salt concentration had a negligible effect on gas holdup values. The Zuber and Findlay drift flux model fitted well the data of riser gas holdup for the heterogeneous bubbling conditions; it, however, failed to reflect the transition between the heterogeneous and homogeneous bubbling regimes. Data for the homogeneous bubbling regime were adequately described by the slip velocity concept when the functional relation between slip velocity and riser gas holdup was expressed by the modified equation of Davidson and Harrison.

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