Investigation of CO₂ Photoreduction in an Annular Fluidized Bed Photoreactor by MP-PIC Simulation

Carbon dioxide (CO₂) photoreduction is a promising process for both mitigating CO₂ emissions and providing chemicals and fuels. A gas-solid two-phase annular fluidized bed photoreactor (FBPR) would be preferred for this process due to its high mass-transfer rate and easy operation. However, CO₂ photoreduction using the FBPR has not been widely researched to date. The Lagrangian multiphase particle-in-cell (MP-PIC) simulation with computational fluid dynamic models is a new and robust approach to explore the multiphase reaction system in the gas-solid fluidized bed. Therefore, the purpose of this paper is to investigate CO₂ photoreduction in the FBPR by MP-PIC modeling to understand the intrinsic mechanism of solid flow, species mass transfer, and CO₂ photoreaction. The MP-PIC models for solid flow in the FBPR were validated by the bed expansion height and bubble size. The results showed the particle stress of the Lun model, the drag of the Ergun-WenYu (Gidaspow) model, and the coefficient of restitution e = 0.95 with the wall parameters e_w = 0.9 and μ_w = 0.6 are the best fit to the experimental empirical correlations. The MP-PIC models developed in this work proved to be better than the Eulerian two-fluid modeling in the prediction of the bed expansion height and bubble size. It was also found from the simulation results that the maximum radiation intensity is in the half reactor height area, and the photocatalytic reaction mainly occurred around the inner wall. It showed that the gas velocity and catalyst loading were two crucial operating parameters to control the process. The results reported here can provide guidance for the operation and reactor design of the CO₂ photoreduction process.