Effects of configurations of external loop airlift contactor on hydrodynamics and gas-liquid mass transfer

Abstract

Various configurations of external loop airlift contactor (ELALC) were examined for their hydrodynamic and mass transfer behavior using tap water. These behaviors was manipulated by changing the length of connection tubes (L[subscript c]), height of riser and downcmoer (L[subscript h]) and other configurations while keeping the ratio between downcomer and riser cross sectional area constant at 0.269. The results showed that the change of configuration could have effects on: gas holdup, liquid velocity, and gas-liquid mass transfer. Increasing L[subscript c] and L[subscript h] seemed to pose the same effect on the airlift performance. For instance, an increase in L[subscript c] from 20 to 40 cm, and Lp[subscript h] from 100 to 140 cm, could increase liquid velocity at 11.3 and 7.2%, decreased overall gas holdup at 8.6 and 3.3% and decreased the overall volumetric mass transfer coefficient at 8.2 and 5.6%, respectively. The effect of configurations on ELALC was investigated. ELALCs with inclined connection tubes and with close downcomer were compared with regular ELALC in terms of hydrodynamic and gas-liquid mass transfer behaviors. The two configurations presented large agglomerate of gas bubbles on the top connection tubes which resulted in more gas holdups and less downcomer liquid velocity when compared with regular ELALC. The mathematical model was developed based on the mass conservation principals to predict the gas-liquid mass transfer in the ELALC. Basically ELALC was represented by a series of reactors, i.e. the riser, downcomer, top and bottom connection tubes were represented by the dispersion model, and the two gas separators represented by the stirred tank model. The simulation results were found to be reasonably accurate for all experimental conditions employed in this work.