CFD modeling of ethylene degradation in gas-phase photocatalytic reactors

Photocatalytic oxidation is a promising technology to degrade volatile organic compounds. The performance of photocatalytic reactors is affected by the hydrodynamics, radiation transfer, mass transfer and reaction kinetics. Baffles may improve the hydrodynamics. The effect of baffles on heterogeneous photocatalytic oxidation of gas-phase ethylene in three annular reactors is simulated using computational fluid dynamics. ANSYS Fluent is used to solve all governing equations. Baffles can improve the uniformity of flow and prolong the residence time. The residence time of the C-type reactor and B-type reactor is 0.5% greater than the unbaffled reactor. Baffles have little effect on the radiation distribution. The concentric arrangement of lamp and the reactor leads to a radial dominance of radiation. The effect of baffles on the diffusion of ethylene is complex. The effective diffusion coefficient at the catalyst surface in the C-type reactor decreases 9.5% and that in the B-type reactor increases 3% with respect to the unbaffled reactor. The outlet ethylene concentration is 4.19 ppmv for the U-type reactor, 3.93 ppmv for the C-type reactor and 3.62 ppmv for the B-type reactor. The optimal performance in the B-type reactor is due to the large diffusion coefficient of ethylene. The arrangement of baffles should enlarge the effective diffusion coefficient at the catalyst surface as far as possible.