The role of gas disengagement and surface active agents on hydrodynamic and mass transfer characteristics of airlift reactors

Abstract

Abstract The hydrodynamics and mass transfer characteristics of a 0.7 m 3 external loop airlift reactor were experimentally investigated for superficial gas velocities between 0.02 and 0.18 m s −1 . The reactor was made of QVF glass sections with 6.5 m in height and 0.225 m in diameter of both riser and downcomer. The effects of the addition of minute quantities of silicone polymer, polypropylene glycol and octanol, on airwater systems were examined. In general, the addition of surface active agents led to significant reductions in volumetric mass transfer coefficients and liquid circulation velocities, relative to the values determined for the air-water system. However, for the gas hold-up, surfactants produced higher values in contrary to antifoams which reduced the gas hold-up due to enhancement of bubbles coalescence. The gas disengagement section was found to have a great effect on the reactor performance, especially when foaming increased in the system. Of the two gas disengagement sections used (namely, closed and open channel) the closed channel configuration failed to remove the increasing small bubbles and the reactor continuity disrupted at high gas throughputs. In contrast, the open channel configuration improved the reactor performance with substantial reduction in downcomer gas hold-up and increase in volumetric mass transfer coefficient.