CFD-PBM numerical simulation and experimental investigation of hydrodynamics in a multistage internal loop reactor with guide cones

Multistage internal loop reactors demonstrate a powerful application in biological wastewater degradation and with high solid concentrations fields. Due to the complexity of the gas-liquid-solid flow, the hydrodynamic characteristics of a multistage internal loop reactor are still ambiguous. This research focuses on a self-designed multistage internal loop reactor with guide cones and investigates the hydrodynamic characteristics by combining experiment and computational fluid dynamic-population balance model (CFD-PBM) numerical simulation. Meanwhile, validating the simulation results using particle image velocimetry (PIV) technique shows that the results are plausible. The investigation results indicate that the increment in superficial gas velocity can increase the gas holdup and volumetric mass transfer coefficient and decrease the mixing time. The addition of solid particles would get the opposite effects. In addition, the effects of bubbles on particles are summarized as driving and collision, and the particles motion in the riser and downcomer is analyzed based on the above effects. Research on the flow field of the liquid phase has found that an increase in superficial gas velocity and the addition of solid particles can generate vortices. Finally, A study of the bubble size distribution reveals larger bubble sizes in the second and third-stage riser.