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Three geometric configurations of gas–liquid separators were used in split‐channel airlift reactors (0·1 m3 liquid volume; riser‐to‐downcomer cross‐sectional area ratio = 0·7; aspect ratio = 3.6) to test the effect of geometry on hydrodynamic performance and oxygen transfer behaviour. For otherwise fixed conditions, the design of gas–liquid separators affected the induced liquid circulation rate, the depth of penetration of the bubble layer in the downcomer, the gas holdup in the downcomer, the mixing time and the overall volumetric gas–liquid oxygen transfer coefficient. The gas holdup in the riser was only marginally affected by the design of the separator. The impact of the various separator designs on hydrodynamic behaviour could be explained as emanating from a combination of the gas–liquid separating ability of the design and its hydraulic resistance.

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Abstract:The effects of the horizontal connection length (0.1 < L, d 0.5 m), the cross-sectional area ratio of downcomer-to-riser (0.1 1 d A , / A , < 0.53), and the superficial gas velocity on gas phase holdups in the riser and downcomer were studied. The circulation liquid velocity, the mixing performance and the volumetric mass transfer coefficient in the external-loop airlift reactors were also measured. The horizontal connection length and A J A , were major parameters which strongly affected the performance of external-loop airlift reactors. Useful correlations in the external-loop airlift reactors were obtained for gas holdups, the volumetric mass transfer coefficient, the circulation liquid velocity, and the mixing time.Key words: external-loop airlift reactor, horizontal connection length, circulation liquid velocity, gas holdup, volumetric oxygen transfer coefficient.

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