In this work, a numerical simulation study on the mixing characteristics of multiphase flow in an autoclave was carried out using CFD technology. The Eulerian–Eulerian model and discrete phase model (DPM) were employed to investigate the solid holdup, critical suspension speed, nonuniformity of solid suspension, gas holdup distribution, bubble tracks, and residence time during stirring leaching in the autoclave. Experiments validate the accuracy of the numerical model, and the experimental values correspond well with the simulation results. The numerical simulation results show that the solid–liquid mixing is mainly affected by the axial flow, the best agitation speed is 400 rpm, and increasing the speed further cannot make the mixture more homogenous and buildup occurred above the autoclave. The calculated critical suspension speed is 406 rpm, which is slightly lower than that obtained from the empirical formula. The gas phase is mainly concentrated in the vortex area above the blade. When the gas phase is in a completely dispersed state (N = 300 rpm), the average residence time of the bubbles is 5.66 s.

The gas-liquid flow and oxygen content in a pressurized leaching stirred tank significantly influence the chemical reaction rates, while the specific dynamics of gas-liquid flow in the sulfuric acid system remain largely unexplored. In this study, a mathematical model of gas-liquid flow within a stirred tank is developed using the Euler-Euler approach, with the turbulence and drag force models being validated against experimental data. Utilizing this validated and reliable model, this study investigates the impacts of the sulfuric acid concentration, baffles, air inlet velocity, and bubble diameter on the flow field and gas holdup in a two-phase system consisting of a sulfuric acid solution and oxygen. The findings indicate that introducing a specific concentration of sulfuric acid decreases the solution velocity and increases the gas holdup within the tank. However, once the sulfuric acid concentration reaches a certain threshold, further increases have a diminished effect on the gas-liquid phases. The installation of baffles enhances the turbulent kinetic energy and increases the gas holdup while only resulting in a minimal 1.2% increase in power consumption. Additionally, the inlet velocity and bubble diameter have a relatively minor impact on the tank’s flow field. However, increasing the inlet velocity significantly boosts the gas holdup, whereas an increase in the bubble diameter marginally reduces it. Furthermore, introducing a sulfuric acid solution into the tank can enhance the gas holdup when the gas inlet velocity is low. Conversely, when the gas inlet velocity is high, the addition of sulfuric acid results in a decrease in the gas holdup. The conclusions from this study contribute to enhancing the mixing effectiveness and oxygen content within the tank, providing a substantial theoretical basis for optimizing the design and operating conditions of pressurized leaching stirred tanks.

Exploring the fluidization behaviors and chemical performance in silicon tetrachloride (SiCl₄) hydrochlorination processes within a fluidized bed reactor (FBR) poses significant challenges. In this study, we developed an Eulerian-granular model (EGM) by integrating the Eulerian–Eulerian two-fluid model with the kinetic theory of granular flow (KTGF). The effect of fluidization velocities on the flow regime, heat transfer, and chemical reaction performance were investigated. The applicability of the simulation method and the validity of the model were confirmed through comprehensive comparisons, including the simulated values of the maximum bed expansion height (H_max) with theoretical values derived from empirical formulas and the simulated gas temperature profile with Hsu’s experimental data. The results indicate that the present EGM can be feasible to describe the variation of the flow regime within the FBR. An increase in bed voidage over time, coinciding with transitions in the flow regime, can be observed. Particularly noteworthy was the attainment of a more uniform distribution of SiCl₄ under the bubbling fluidization state. Furthermore, the FBR possess high heat transfer characteristics, and the reaction gas can reach the set temperature of the bed after entering a small distance (about 10 mm). The presence of circulating bubbles within the FBR enhances the mixing uniformity of the SiCl₄ reaction gas and silicon particles, particularly in the central and upper regions of the bed under the bubbling fluidization state. As a result, the predicted highest concentration of SiHCl₃ was 13.08% and the conversion rate of SiCl₄ was 28.97% under the bubbling fluidization state. Our results can provide a theoretical basis for further understanding of the hydrochlorination process of SiCl₄ within the FBR.