Influence of hydrogen flow rate on multistep kinetics of hematite reduction

Hydrogen ironmaking is the most ideal approach to reduce industrial carbon emissions. In this study, the isothermal reaction characteristics and multistep kinetics of hematite particles with hydrogen are investigated using thermogravimetric analysis (TGA) at 650–725 °C. The two steps of Fe₃O₄–FeO and FeO–Fe of hematite reduction are discovered to proceed simultaneously. The reduction is divided into three stages according to the derivative thermogravimetry (DTG) curves. For the three stages, the optimal kinetic models are the phase boundary and the 2D growth of nuclei. In the range of 75–130 mL/min, there is a critical hydrogen flow rate below which the apparent activation energy increases and above which it remains constant, which is 30.44 ± 3.30, 77.33 ± 0.41, and 49.56 ± 0.49 kJ/mol, respectively. A significant linear correlation between hydrogen flow rate above the critical value and the pre-exponential factor is found.