Modeling industrial shaft furnaces and investigation of CH4-related side reactions

The shaft furnace is a promising low-carbon ironmaking technology, but its complex internal processes pose challenges for efficient operation and control. Numerical simulation provides an effective method for revealing the internal states, whereas many existing models incorporate simplifications that limit prediction accuracy. This study presents a CFD model for industrial MIDREX shaft furnaces, incorporating major reactions, including CH 4 -related side reactions. An improved unreacted shrinking core model (USCM) is introduced for reduction based on the thermodynamic equilibrium diagram. It allows for the decoupling of reaction and diffusion layers, reducing the reaction layers and enabling variable diffusion structures. Consequently, the reaction model provides a more physically realistic and thermodynamically consistent representation of the multi-step reduction process, is valid for H 2 –CO mixtures, and increases computational efficiency by 65–75 %. The model is validated using four sets of laboratory and industrial data, covering inner states and overall performance parameters. It also successfully captures the influence of CH 4 , an inevitable component arising from reforming. A high CH 4 content causes substantial heat loss near the gas inlet and reduces metallization, primarily due to the combined effects of endothermic reduction and side reactions. Based on simulation results, an optimal CH 4 level is identified to balance metallization, gas utilization, and energy efficiency. The model can serve as a valuable tool for analyzing shaft furnace performance and has the potential to support the evaluation of advanced decarbonization strategies such as high H 2 content operation.