Gas composition and carbon deposition in a shaft furnace using coke oven Gas: A Lab experimental study

• This study investigated gas composition and carbon deposition in a shaft furnace. • CH 4 conversion to H 2 and CO is influenced by the filling material. • Effects of key process parameters on CH 4 conversion and carbon deposition were identified. • Optimal conditions were identified: NG addition ratio < 30 %, and temperature in 900–1000 °C. The coke oven gas (COG)-based shaft furnace is a promising technology for low-carbon ironmaking. However, carbon deposition in this process is unavoidable, and the behaviour of carbon deposition and gas composition changes is unclear. In this study, the effects of initial gas composition (such as natural gas (NG) ratio), temperature, and filling material on the direct reduction in the shaft furnace were examined in terms of gas phase reduction potential, the CH 4 effective conversion ratio, and carbon deposition behaviour. The results show that the extent of CH 4 conversion to H 2 and CO is significantly influenced by the type of filling material, where under the same temperature conditions, the CH 4 conversion ratio increases in the order: Al 2 O 3 pellets (3.92 %) < low-reducibility oxide pellets (6.55 %) < high-reducibility oxide pellets (10.69 %) < pre-reduced pellets (11.40 %). Increasing the NG ratio leads to a reduction in the effective gas content (H 2 + CO), thereby lowering the reduction potential and intensifying carbon deposition. When the NG ratio > 30 %, the effective conversion ratio declines significantly. Additionally, when the reduction zone temperature exceeds 900 °C, the total amount of effective gas (H 2 + CO) at the outlet remains nearly constant, indicating that the gas-phase reduction potential within the reaction zone does not significantly change beyond 900 °C. Therefore, it is recommended that the NG ratio remain below 30 %, and the reduction zone temperature be maintained between 900 °C and 1000 °C to ensure stable and efficient operation. Furthermore, thermodynamic analysis indicates that carbon deposition is likely to occur at the shaft furnace inlet in industry practice. This study proposes optimal process parameters for the COG-based direct reduction process operation and provides guidance to support the broader development of hydrogen-rich direct reduction technologies for low-carbon ironmaking.