Split-channel rectangular airlift reactors: Enhancement of performance by geometric modifications

Two geometric configurations of gas-liquid separators were used in split-channel airlift reactors (0.1 m(3) liquid volume; riser-to-downcomer cross-sectional area = 1.45; aspect ratio = 3.6) to test the effect of geometry on hydrodynamic performance and oxygen transfer behaviour. One of the configurations consisted of the basic internal-loop airlift head region without added features; the other had a 45 degrees -inclined prism attached to the upper edge of the splitting baffle. For otherwise fixed conditions, the design of gas-liquid separators affected the induced liquid circulation velocity, the depth of penetration of the bubbles in the downcomer, the gas holdup in the downcomer and the mixing time. The overall volumetric gas-liquid oxygen transfer coefficient was not affected. The gas holdup in the riser was only marginally affected by the design of the separator; however, the relationship between the riser and the downcomer holdups was sensitive to separator configuration. Incorporation of the prism in the basic airlift configuration enhanced gas-liquid separation so much so that up to 30% reduction in the downcomer gas holdup could be obtained relative to the unmodified geometry. The impact of the 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.