Kinetics of Iron Oxide Reduction in \({\text{H}}_{2}/{\text{H}}_{2}{\text{O}}\) Gas Mixture: Global and Stepwise Reduction

In order to achieve lower \(\hbox {CO}_{2}\) 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 \(\hbox {H}_{2}/\hbox {H}_{2}\hbox {O}\) 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 \(\hbox {H}_{2}\hbox {O}\) in the reducing gas mixture. For global reduction of \(\hbox {Fe}_{2}\hbox {O}_{3}\), the effect of different mole fractions of \(\hbox {H}_{2}\) (and \(\hbox {H}_{2}\hbox {O}\)) in mix gas on the reduction kinetics was analyzed. The results suggested that when the \(\hbox {H}_{2}\hbox {O}\) mole fraction was lower, the reaction was only divided into the first and second stages (corresponding to \(\hbox {Fe}_{2}\hbox {O}_{3}\rightarrow \hbox {FeO}\) and \(\hbox {FeO}\rightarrow \hbox {Fe}\)), which were controlled by chemical reaction. When the \(\hbox {H}_{2}\hbox {O}\) 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 \(\hbox {H}_{2}\hbox {O}\) content in the reducing gas whereas it increased for second stage with increasing \(\hbox {H}_{2}\hbox {O}\) content i.e., from 34.97 kJ/mol (100 pct \(\hbox {H}_{2}\)) to 51.04 kJ/mol (90 pct \(\hbox {H}_{2}\)) and 69.6 kJ/mol (80 pct \(\hbox {H}_{2}\)). In addition, stepwise reduction experiments were designed by controlling the \(\hbox {H}_{2}\) mole fraction as 50 and 90 pct to decouple the \(\hbox {Fe}_{2}\hbox {O}_{3}\rightarrow \hbox {Fe}\) reaction into \(\hbox {Fe}_{2}\hbox {O}_{3}\rightarrow \hbox {FeO}\) and \(\hbox {FeO}\rightarrow \hbox {Fe}\) 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 \(\hbox {H}_{2}\hbox {O}\) were sintered more seriously at high temperature and hindered the further reaction.