Fundamentals of Green Steel Production: On the Role of Gas Pressure During Hydrogen Reduction of Iron Ores

Abstract

Out of the multitude of researched processing routes for sustainable ironmaking, hydrogen-based direct reduction and hydrogen plasma smelting reduction (HyPSR) are currently the most promising candidates for a successful industrial application. Both processes operate under gaseous atmospheres, which turn the partial and absolute pressure of hydrogen into a relevant process parameter. Here, we present first insights into the influence of total pressure and concentration of hydrogen on the reduction of hematite, focusing on the more pressure-sensitive route (HyPSR). The effect of pressure on the dissociation of H2 molecules into metastable H atoms or H+ ions,- and the overall hydrogen utilization is discussed using a thermodynamic approach. Validation experiments were conducted to testify the practical feasibility of adjusting these parameters. A decrease in the total pressure of the system from 900 mbar to 450 mbar resulted in an improved hydrogen utilization, thus suggesting that a larger population of H atoms can exist in the plasma arcs ignited under 450 mbar. An increase in the hydrogen concentration to 20 vol.% lead to undesired evaporation, likely because of a parallel increase in plasma temperature. Possibilities and challenges for exploiting these pressure-related phenomena for the industrial production of green steel are outlined and discussed.