Reduction of Iron Oxides with Hydrogen—A Review

Abstract

This review focuses on the reduction of iron oxides using hydrogen as a reducing agent. Due to increasing requirements from environmental issues, a change of process concepts in the iron and steel industry is necessary within the next few years. Currently, crude steel production is mainly based on fossil fuels, and emitting of the climate‐relevant gas carbon dioxide is integral. One opportunity to avoid or reduce greenhouse gas emissions is substituting hydrogen for carbon as an energy source and reducing agent. Hydrogen, produced via renewable energies, allows carbon‐free reduction and avoids forming harmful greenhouse gases during the reduction process. The thermodynamic and kinetic behaviors of reduction with hydrogen are summarized and discussed in this review. The effects of influencing parameters, such as temperature, type of iron oxide, grain size, etc. are shown and compared with the reduction behavior of iron oxides with carbon monoxide. Different methods to describe the kinetics of the reduction progress and the role of the apparent activation energy are shown and proofed regarding their plausibility.

Decarbonization of the Iron and Steel Industry with Direct Reduction of Iron Ore with Green Hydrogen

“…At high temperatures, the rate of chemical reaction is higher than the transport rate or mass transfer rate of reactants and products. This observation is in accordance with the Arrhenius equation [37]. In a solid-gas reaction at high temperatures, diffusion of reactants and products is often the rate-limiting step.…”

“…Direct reduction of iron ore refers to the conversion of solid iron ore to metallic iron without conversion to the liquid phase [37]. Majority of the direct reduced iron (DRI) [38] is produced by reacting iron oxide with hydrocarbon-based reducing gases produced from reforming natural gas or coal gasification [39][40][41][42].…”

“…The reduction reactions are depicted in Equations (4)-(6) [52]. The reduction reaction is endothermic and energy in the form of heat needs to be supplied to carry the reaction forward [37]. The reaction propagation and the different processes involved in the reaction are depicted in Figure 1.…”

“…The large variation in the values of apparent activation energies is due to its dependence on multiple factors. Thermo-physical properties of the input material, reducing gas composition, reduction temperature, particle size and the experimental set-up are some of the variables listed by [37]. There is a need for a more thorough investigation to evaluate the apparent activation energy required for iron ore reduction reaction with pure hydrogen.…”

“…(a) Shrinking core model depicting the evolution of iron ore reduction reaction with hydrogen [56]. (b) Process steps in the reduction of iron ore pellets with hydrogen [37]. The location of the process steps is represented from numbers 1 to 5 (1b), which are also depicted in the shrinking core model (1a).…”