Effect of solid media addition on mass transfer and bubble dynamics in bubble column reactor

The development of a bubble column reactor (BCR) has been investigated in terms of various related aspects for improving gas-liquid mass transfer. However, a comprehensive analysis of additional solid media in the multi-phase reactor for enhancing oxygen transfer performance is still limited. Therefore, the present work aims to analyze the relative effect of different solid media types and operating conditions on oxygen mass transfer coefficient (KLa) and hydrodynamic bubble parameters, i.e., bubble size distribution (DB) and bubble rising velocity (UB), in BCR. It was tested with different types of solid media (plastic ring, scouring sponge, scouring pad, and activated carbon foam), superficial gas velocities (Vg) (0.18 – 0.94×10-2 m.s-1), and solid media loading (3% – 10%). The result found that the addition of solid media in BCR can enhance KLa value with rising Vg about 9% – 80% compared to the free solid media due to its effect on bubble break-up and bubble increasing velocity. Furthermore, the scouring sponge and scouring pad resulted in the optimum KLa at a loading of 3%, but the plastic ring and activated carbon foam reached the optimum KLa at the highest loading (10%). However, at higher loading (>3%), the scouring pad tended to lower KLa. This could be because too much loading promotes bubble coalescence and accumulates at the reactor bottom due to its higher density. At Vg 0.94×10-2 m.s-1, the bubble size distribution was found to be smaller DB by scouring pad and plastic ring, 4.24mm and 4.47mm, and larger DB by scouring sponge and activated carbon foam, 4.73mm and 4.61mm, respectively, compared to without adding solid media, 4.51mm. Indeed, due to the reduction of the free movement of rising bubbles by solid media, all solid media types appeared to decrease UB by approximately 26% – 67% compared to non-additional media. Remarkably, the scouring sponge could provide the highest enhancement of KLa due to the effect of reducing bubble rising velocity, resulting in increased bubble retention time, not bubble break-up rate. Overall, the study concludes that a scouring sponge is recommended as the most effective solid media for improving oxygen mass transfer by enhancing bubble retention time in BCR.