Numerical simulation of the hydrodynamic behavior and the synchronistic oxidation and reduction in an internal circulation micro-electrolysis reactor

[Display omitted] •Modeling of hydrodynamics of internal circulation micro-electrolysis (ICE) reactor.•Important design parameters were optimized and identified.•The dissolved oxygen distribution was simulated with the optimized parameters.•Synchronistic oxidation and reduction was verified to occur in the reactor.•ICE reactor can avoid problems of traditional reactors for wastewater treatment. The filter packing of traditional iron–carbon micro-electrolysis reactors is prone to hardening and passivation during operation. In this study, internal loop airlift reactors were used to contain iron–carbon fillings in order to solve these problems and realize a synchronistic oxidation and reduction environment in an internal circulation micro-electrolysis (ICE) reactor. The hydrodynamics of the novel gas–liquid–solid three-phase reactor were investigated through a computational approach. A 2D and 3D transient Eulerian–Eulerian multiphase model was carried out with the standard k − ε turbulence model. Important design parameters of the ICE reactor were identified: the solid velocity, radial profiles of the axial gas holdup and water distribution. The effects of the mesh grid size sensitivity, superficial gas velocity, riser diameter (Dr), height–diameter ratio (H/D), draft tube axial height (Hd) and number of water distribution pipes were considered. The key observations were as follows. The minimum fluidization velocity was 1 m·s−1. With the increase in the number of distribution pipes, the distribution of water was more uniform, but the solid flow resistance increased. When Dr = 30 mm, H/D = 4:1, Hd = 90 mm, and the number of distribution pipes was 4, the hydrodynamic performance was observed to be better. The dissolved oxygen distribution was simulated based on the optimum structural parameters. The experimental results have the same trend as the simulation results, and synchronistic oxidation and reduction was verified in the ICE reactor. Therefore, the optimum structural design and operating parameters and the three-phase system theory were obtained through the CFD simulation, and these findings will provide a basis for the design and enlargement of the ICE reactor.