Dear Colleagues,

The direct reduction iron is considered the primary actor in the transition to sustainable steelmaking. Reducing iron ores with H₂ yields water vapor instead of CO₂ with a carbon-based reductant. H₂ is currently produced from fossil fuels (natural gas, coal, oil) by biomass gasification and from non-carbon sources, such as water electrolysis. An important factor in the production of DRI in industrial practice is the dynamic control of the process in the reactors. This dynamic control, along with optimization of the process, is essential for ensuring both a smooth operation process and the quality of the products, for example the metallization degree and cementite fraction in the reduced pellets. Despite the renewed efforts in the technological research and development of hydrogen and fuel cells, the hydrogen economy is not yet developed, and several technological and non-technical barriers remain. In the industrial sector, the direct reduction of hydrogen is considered a technically viable option in Europe from 2030 onwards. This is considered one of the most innovative technologies with the highest future potential in the iron and steel sector in the long-term. DRI processes can reduce CO₂ emissions using natural gas instead of coal due to the replacement of the carbon reductant by hydrogen from methane. Midrex and HYL Energiron are the processes with the highest capacities that are currently used worldwide. H₂ can also be used as the reductant in conventional direct reduction reactors. One issue, though, is preventing the sticking of the DRI. If H₂ is produced by water electrolysis using hydro or nuclear electricity, then CO₂ emissions could be lowered to less than 300 kg/t HRC. In view of current developments with regard to GHG-neutral hydrogen-based reduction processes producing H₂-reduced DRI and the subsequent melting in the EAF, there is still a need to introduce carbon into the system either to carburize the steel or to create foaming slag to improve the energy efficiency of the melting process. Therefore, in the future, if a substantial part of steel production shifts to a direct reduction and EAF-based route to reach the international goals of GHG emission reduction, there will still be a need to use alternative carbon sources to produce green and carbon neutral and/or fully circular steel. In a route based on hydrogen and direct reduction, the output after the reduction process is the porous material of DRI, or sponge iron, which can potentially be transported to an EAF in a different location (or pressed to hot briquetted iron, HBI, which is favorable for transportation). As the hydrogen content in the mixture increases, the total energy consumption in the reactor decreases. A strong decrease in electricity consumption is recorded as the hydrogen content increases, and the availability of DR-grade pellets is limited with respect to the total international steel production. Therefore, the main obstacles to the direct conversion of steel production are mainly represented by the availability of such grade raw materials. In fact, the successful and productive operation of a DR-EAF line requires the use of high-grade pellets (gangue less than 5%, possibly basic). Taking into account all the described aspects, a good solution appears to be the integration of a direct reduction with large smelting furnaces. In this way, BF-grade pellets could be reduced in the DR reactor by overcoming the problem of the availability of high-quality DR-grade pellets.

For all the described aspects, this Special Issue aims to present the latest research findings in the field of hydrogen-based direct reduction. This Special Issue is open to all the researchers involved in this field and invites them to contribute their most recent results.

Prof. Dr. Pasquale Cavaliere
Guest Editor

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• global warming
• energy
• CO₂ emissions
• energy transition
• hydrogen
• renewables
• decarbonization
• steel industry
• hydrogen storage
• best available technologies
• hydrogen “color”
• coal
• biomass
• nuclear
• iron ores reduction
• reducing gases
• hydrogen reduction
• kinetics of hydrogen reduction
• thermodynamic of hydrogen reduction
• energy efficiency
• hydrogen metallurgy
• direct reduced iron
• sponge iron
• hydrogen direct reduced iron
• electric arc furnace
• hot briquetted iron