Hydrodynamics and gas-liquid mass transfer in internal loopairlift contactor with sea water

Abstract

Sea water was shown to alter the performance of airlift contactors (ALCs) particularly in hydrodynamic point of view. The increase in salinity level prevented bubble coalescence and smaller bubble size was observed in the ALC with sea water. This smaller bubble size led to several differences in the hydrodynamic behavior of the ALC. Firstly, higher gas holdup was obtained as small bubbles moved at slower speed allowing bubbles to spend more time in the contactor. This led to a higher gas holdup. Next, as bubble velocity was low, the momentum/energy transfer to the liquid was not as high as that in the air-water ALC. In addition, the difference between riser and downcomer gas holdup was not as much in the air-sea water as that in the air-water system. This meant that there was less driving force for liquid momentum and, hence, liquid velocity in the ALC with sea water was supposed not to be as high as that obtained from the air-water ALC system. However, experiment revealed that the difference in liquid velocity in the air-sea water and air-water system was small. This was, at this point, believed to be due to the presence of local internal liquid circulation which still could not be thoroughly characterized. In terms of mass transfer between gas and liquid, no strong conclusion could be made from this work. The data on the overall volumetric mass transfer coefficient showed very high scattering characteristics, which did not allow systematic evaluation with only the present set of experimental evidence.