Kinetics of Iron Oxide Reduction in H2/H2O Gas Mixture: Global and Stepwise Reduction

In order to achieve lower CO(2 )emissions from iron and steel manufacturing, reduction of iron oxides using hydrogen is the most promising alternative. Kinetics of these reduction reactions will govern the overall efficiency of the process. In this study, reduction of iron oxide pellet powder was carried out in different H-2/H2O mix gas in temperature range of 1023 K to 1373 K using thermo-gravimetric analysis (TGA). A quantitative steam generator setup was designed and installed in connection with TGA setup for controlled use of H2O in the reducing gas mixture. For global reduction of Fe2O3, the effect of different mole fractions of H-2 (and H2O) in mix gas on the reduction kinetics was analyzed. The results suggested that when the H2O mole fraction was lower, the reaction was only divided into the first and second stages (corresponding to Fe2O3 -> FeO and FeO -> Fe), which were controlled by chemical reaction. When the H2O mole fraction was higher in the mix gas (20 pct), the reaction was diffusion controlled towards the end of the second stage. The apparent activation energy of the first stage was not affected with increasing H2O content in the reducing gas whereas it increased for second stage with increasing H2O content i.e., from 34.97 kJ/mol (100 pct H-2) to 51.04 kJ/mol (90 pct H-2) and 69.6 kJ/mol (80 pct H-2). In addition, stepwise reduction experiments were designed by controlling the H-2 mole fraction as 50 and 90 pct to decouple the Fe2O3 -> Fe reaction into Fe2O3 -> FeO and -> FeO Fe respectively. XRD and SEM analysis of the reaction products was carried out to identify the phases and morphological changes at each reaction step. It was found that the products formed by reduction with gas containing higher mole fraction of H2O were sintered more seriously at high temperature and hindered the further reaction. (C) The Minerals, Metals & Materials Society and ASM International 2022

Automated summary

The reduction of iron oxide using hydrogen in different H2/H2O mix gas was studied in this research, showing that the kinetics of the reduction reaction was influenced by the mole fraction of H2O in the mix gas. Higher H2O content in the gas mixture led to a diffusion-controlled reaction process, affecting the activation energy and hindering further reaction at high temperatures.