Hydrodynamics of gas-lift reactors with a fast, liquid-phase reaction

The reactive absorption of CO2 into concentrated KOH solutions was studied in an external-loop, gas-lift reactor. Three different inlet gas compositio ns were used: air, 50-50 vol% air-CO2, and pure CO2. The downcomer liquid v elocity and the axial profile of the cross-sectionally averaged gas holdup in the riser were measured. The reaction is so fast that the CO2 is consume d appreciably along the riser, and this causes a significant reduction in t he liquid circulation relative to a system with no reaction. A one-dimensio nal, pseudo-steady-state model has been developed to describe the interacti ons of hydrodynamics, mass transfer, and chemical reaction for the bubbly f low regime in the riser. The model considers mass transfer from the gas to the liquid phase and its enhancement due to the chemical reaction, and is b ased on the spatially averaged equations of continuity, momentum, and macro scopic mechanical energy. The rate of liquid circulation, and the axial var iation of gas holdup, gas composition, pressure, and gas and liquid velocit y, are predicted. The gas/liquid mass transfer coefficient and the bubble r adius at the sparger, neither of which was known a priori, were used to min imize the error of the data with respect to the model. (C) 1999 Elsevier Sc ience Ltd. All rights reserved.