The influence of water vapour on hydrogen reduction of iron ore pellets

This study investigates the influence of water vapour on the hydrogen reduction of iron ores, focusing on conditions closely aligned with industrial processes, including high temperatures and realistic gas compositions. Single-pellet reduction experiments were conducted isothermally in gas atmospheres with varying ratios of water vapour and hydrogen (30% H2O + 70% H2, 20% H2O + 80% H2, 10% H2O + 90% H2 and 100% H2) over a temperature range of 800 degrees C to 1000 degrees C. The results demonstrate a consistent increase in the reduction rate with rising temperature across all gas compositions, highlighting the impact of water vapour on reduction kinetics under near-industrial conditions. At 30% H2O, reduction was limited to w & uuml;stite, with no metallic iron formation observed. At 20% H2O, reduction degrees increased from 36% at 800 degrees C to 77% at 900 degrees C, where a thick metallic iron layer formed, and to 95% at 1000 degrees C, leaving only trace w & uuml;stite. Under 10% H2O, reduction exceeded 97%, approaching completion. The study reveals that high water vapour content hinders hydrogen diffusion and blocks active sites on w & uuml;stite, impeding its reduction to metallic iron. These findings, supported by kinetic modelling, underscore a complex interplay of diffusion and chemical reaction as the controlling mechanisms. By examining the reduction process under conditions that closely replicate those in industrial hydrogen-based direct reduction, this study provides critical insights into optimising reduction efficiency for sustainable ironmaking.