Hydrogen direct reduction of Iron ore to metalic Iron

Hydrogen Direct Reduction of Iron Ore: System-Level Realities This note summarises the practical, physical, and system-level considerations associated with the direct reduction of iron ore using green and blue hydrogen. While hydrogen-based DRI is often presented as a straightforward decarbonisation pathway, real-world deployment is constrained by energy intensity, reactor hydrodynamics, and system integration challenges. 1. Fundamental Physical Mismatch Hydrogen is the lightest gas (molecular weight 2 g/mol), while iron ore is among the heaviest industrial solids (bulk density ~2,000–3,500 kg/m³). Achieving effective gas–solid interaction between such mismatched phases is intrinsically difficult. Reduction success depends not only on chemical reactivity, but also on momentum transfer between gas and solid. 2. Gas–Solid Hydrodynamics Challenge Drag force in a shaft or fluidised reactor scales with gas density and velocity. Hydrogen’s very low density means that, compared to CO or syngas, substantially higher gas velocity, pressure, and temperature are required to deliver equivalent momentum. This leads to unavoidable design penalties. 3. Pressure Requirement Hydrogen-based DRI systems typically require operation at elevated pressures (5–10 bar) to increase gas density and avoid channelling and bypassing. Higher pressure increases: • Reactor wall thickness and capital cost • Compression energy demand • Operational complexity 4. Temperature and Sticking Risks Hydrogen reduction kinetics favour high temperatures (>800–900 °C). However, at these conditions: • Iron ore pellets soften • Metallic iron forms early • Sintering and sticking occur • Bed permeability collapses These effects are more severe with hydrogen than with CO-based systems, leading to defluidisation risks in fluidised beds and operability limits in shaft furnaces. 5. Gas Bypass and Non-Uniform Reduction Hydrogen’s low density and viscosity promote preferential flow paths, resulting in: • Channelling • Uneven reduction • Hot spots • Lower productivity Achieving uniform metallisation therefore requires careful pellet design, high recycle ratios, and precise control. 6. Energy Penalties Beyond Chemistry Hydrogen DRI imposes significant indirect energy loads: • Compression energy to reach operating pressure • Recirculation and blower power • Electrolyser electricity demand (~2.7–3.0 MWh per tonne of DRI) Even if direct emissions are near zero, total system energy demand remains very high unless firm, carbon-free power is available. 7. Green vs Blue Hydrogen Pathways Green hydrogen offers the lowest direct emissions but is constrained by electricity demand, intermittency, water use, and cost. Blue hydrogen provides industrial-scale continuity today but retains residual emissions and CBAM exposure. Neither pathway alone fully resolves the system challenge. 8. Core Insight Hydrogen is an excellent chemical reductant, but a poor momentum carrier. CO-based systems succeed not only due to chemistry, but because heavier molecules naturally stabilise gas–solid hydrodynamics. Decarbonising ironmaking therefore requires system redesign, not molecule substitution alone. 9. Strategic Implication Effective green iron production depends on: • Continuous, firm energy supply • Integrated hydrogen production • Carbon management at the system level • Avoidance of abrupt technology lock-in System-integrated approaches that stabilise energy supply and manage carbon flows are essential to make hydrogen-based ironmaking scalable, operable, and CBAM-robust.