Numerical simulation study on the reduction reaction and foaming behavior of hydrogen and slag containing FeO

Using hydrogen as a reducing agent can significantly reduce the carbon emissions in the steel industry. Research on H2 reduction and foaming of FeO slag is limited. Unlike prior numerical studies that only simulated inert gas injection (e.g., Ar) without chemical reaction, this study develops a 3D model that couples H2–FeO reduction kinetics with population balance modeling (PBM) for foaming. The model is validated against experimental data (discrepancy <4.4%). The results show that after injecting hydrogen into the slag for 10 min, vortices form in the liquid, the unreacted FeO is transported to the reaction interface. The presence of vortices is associated with enhanced mixing and lower local H2O concentrations near the reaction interface, which may facilitate the forward reaction. When the hydrogen injection time was extended from 10 to 30 min, the average height of the foam phase increased from 0.531 to 0.645 cm, the volume fraction of the foam phase rose from 0.54 to 0.83, the foaming index rose from 0.512 to 0.622, the average diameter of the bubbles rose from 0.86 mm to 2.57 mm. A practical strength of this validated model is its ability to predict foaming index and foam height for different slag compositions and gas flow rates without costly high-temperature experiments, accelerating the design of hydrogen-based smelting processes.