Influence of Hydrogen Injection on the Isothermal Reduction of Iron Ore Pellets under Simulated Blast Furnace Conditions

Cutting down CO2 emissions from blast furnace (BF) ironmaking is a critical area of research. Utilization of hydrogen as a reducing agent has been regarded as one of the most promising solutions to address this challenge. This study examined the impact of using hydrogen injection on the isothermal reduction of commercial iron ore pellets under conditions simulating the center and wall areas of a BF. The effect of distinct reducing conditions, influenced by the radial position within a BF and the amount of hydrogen injected, on the reducibility, swelling, cracking, and porosity of pellets was investigated. A high-temperature furnace with a thermogravimetric analyzer was utilized to simulate the atmospheres of CO–CO2–H2–H2O–N2 at 700, 900 and 1 100°C in 300-minute experiments. The changes in volume and porosity of the pellets were determined based on the results obtained using a gas pycnometer and manual measurement. The phase transformations were studied using microscopy and X-ray diffraction. The results show that the addition of hydrogen had an accelerating effect on the reduction rates excluding the experiment conducted at 700°C under center conditions of a BF, during which the high level of water vapor led to oxidation of the pellet on the surface rather than reduction at the beginning of the wüstite–metallic iron reduction stage. Furthermore, the pellets swelled less in hydrogen-enriched atmospheres. Also, it should be highlighted that the reduction was significantly faster near the center of a BF compared to the areas near the walls. © 2025 The Iron and Steel Institute of Japan.