Mechanism and Kinetics of Carburization in Direct Reduced Iron via the Boudouard Reaction

In direct reduction ironmaking process, CO₂ emissions, energy consumption, and the carbon content in direct reduced iron (DRI) are closely linked. Therefore, understanding the DRI carburizing behavior is essential. This study examined Boudouard reaction - one of the primary reactions - under pressurized conditions equivalent to those in commercial reactors. Experiments revealed a significant radial carbon gradient in DRI and a reaction rate peak at a temperature different from that in pure iron plates. In addition, a newly developed numerical model, based on detailed reaction mechanisms, reproduced this behavior and showed: 1. CO₂ retention causes the gradient and deviation from iron plate behavior, 2. Gas diffusion follows Fick's law via molecular diffusion only, 3. Pores < 5 μm are inactive, and 4. Fe3C acts catalytically equivalent to 12% Fe on a molar basis.