Comparative study of local gas-liquid hydrodynamics and mass transfer between conventional and modified airlift reactors

Abstract

Modified airlift reactor (MALR) was developed for improving the oxygen transfer coefficient (KLa) by installing the slanted baffles in the riser compartment. MALR can enhance KLa value up to 97% compared to a regular reactor. However, insufficient analysis of the hydrodynamics and other oxygen transfer parameters of this new reactor has been performed to date. Therefore, this paper aims to analyse local gas-liquid dynamics and evaluate the oxygen transfer performance in MALR compared to regular reactors using clean water as a liquid phase. Air bubble distribution was employed in terms of bubble diameter, rising velocity, and interfacial area. Slanted baffles maintained the bubble size between 3.88 and 4.63 mm for the studied superficial gas velocity (Ug), which is smaller than that in airlift reactor (ALR) by approximately 0.2 mm. Bubble rising velocity (UB) is relatively increased with Ug, regardless of reactor classes. New reactor could extend the bubble residence in the water by lengthening the bubble stream path of the slanted baffles leading to decrease UB values about 39% and 52% compared to bubble column reactor (BCR) and ALR, respectively. These performances consequently resulted in an interfacial area almost two times higher than in regular reactors. Oxygen transfer improved in MALR with an extra amount of oxygen transfer efficiency of 1.57% and 0.63% over BCR and ALR, respectively. This resulted in the highest aeration efficiency (AE) compared to other examined reactors, following a trendline expression of AE ˜ 0.046 Ug−0.6. Insertion of slanted baffles produced 5% and 12.8% more dead zone volume than ALR and BCR, respectively. In conclusion, MALR can significantly enhance oxygen transfer performance due to the ability to maintain bubble size and extend the gas-liquid transfer period.