Solar-aided direct reduction of iron ore with hydrogen targeting carbon-free steel metallurgy

Steel metallurgy accounts for about 7 % of global greenhouse gas emissions and its decarbonation is a major issue. The direct reduction of iron ore with H2 using concentrated solar heat offers a carbon-free route for the iron metallurgical process. Such a solar process for clean ironmaking has never been implemented before. This study aims to investigate the reaction characteristics of direct iron ore reduction and further proposes a first experimental demonstration of direct reduced iron production in a packed-bed solar reactor under real solar irradiation. Fe2O3 reduction with H2 was first studied by thermogravimetric analysis to unravel the effect of temperature, H2 mole fraction, and particle size. The reaction rate increased with temperature (400–800 °C) and H2 mole fraction (25–75 %), and the reaction reached completion with an initial conversion starting from 370 °C. An activation energy of 38.5 and 30.4 kJ/mol was determined for commercial Fe2O3 and iron ore, respectively. The size of iron ore particles after pellets crushing (in the range 0.25–2 mm) did not significantly affect the reaction rate. However, fine micron size powder with low bulk density showed improved conversion rates. Finally, the reduction process was demonstrated in a solar-heated packed-bed reactor up to 1000 °C, confirming the feasibility of renewable iron production from complete ore reduction at moderate temperatures (starting above 400 °C), and thus paving the way toward decarbonation of the iron and steel metallurgical industry.