Role of Perforated Plates in the Airlift Contactor.

Abstract

This work investigated the effects of perforated plates on the performance of an airlift contactor. The result showed that the rate of gas-liquid mass transfer in the airlift contactor with perforated plates was significantly greater than those found in a conventional airlift contactor and in a bubble column. This was because the perforated plates induced resistance to fluid flows which lengthened the residence time of gas bubbles in the riser. This in turn gave a greater local gas holdup and also a higher rate of mass transfer between gas and liquid. On the other hand, perforated plates reduced the liquid velocity in the system which was found to negatively influence the gas-liquid mass transfer rate. However, in most cases, the effect of the increase in riser gas holdup on the gas-liquid mass transfer rate overwhelmed that from the low liquid velocity, and the resulting overall volumetric mass transfer coefficient was found to increase in the system with perforated plates. In this work, it was reported that there existed the optimal hole size and the optimal number of holes which gave the highest gas-liquid mass transfer rate. The number of perforated plates in the ALC was also examined and the investigation revealed that there was a maximum number of plates that could be inserted in the ALC above which no further enhancement of overall volumetric mass transfer rate was obtained.