Hydrogen-Based Fluidized Bed Direct Reduction of Iron Ore: Fundamentals, Process Evolution, and Industrial Challenges

The iron (Fe) and steel industry is responsible for a significant share of global carbon dioxide (CO2) emissions, primarily owing to its reliance on carbon (C)-based reduction routes such as the blast furnace (BF)-basic oxygen furnace (BOF) process. In response to increasingly stringent decarbonization targets, hydrogen (H2)-based direct reduction has emerged as a promising pathway toward low- to near-zero-C ironmaking. Within this context, fluidized bed technologies offer unique advantages, including the direct utilization of Fe ore fines, enhanced gas–solid contact, high heat and mass transfer rates, and the potential elimination of energy-intensive pelletization. This review provides a comprehensive assessment of fluidized bed (FB) technologies for Fe ore reduction, with a particular focus on their applicability to H2-based direct-reduced Fe production. The fundamental thermodynamics and kinetics of Fe oxide reduction are discussed, alongside key aspects of particle behavior and fluidization regimes relevant to fine ores. A detailed historical and technical overview of major FB direct-reduction and smelting-reduction processes (including FIOR, FINMET, FINEX, HIFRI, HYFOR, HyREX, NU-Iron, H-Iron, Iron-Carbide, Circored, and Circofer) is presented, highlighting their operating principles, performance, and industrial outcomes. This review concludes by assessing the key operational challenges associated with fluidized bed reduction, particularly under H2-rich conditions, and by summarizing recent laboratory- and pilot-scale developments aimed at overcoming these limitations and enabling industrial deployment.