Direct reduction of iron to facilitate net zero emissions in the steel industry: A review of research progress at different scales

Abstract

The global annual production of steel is approximately 2 billion tons, accounting for 8 % of the world's energy demand and 7 % of carbon dioxide (CO2) emissions in the energy sector. Coal-based direct reduced iron (DRI) reduces CO2 emissions by 38 % compared with traditional blast furnace–basic oxygen furnace (BF-BOF) ironmaking. Using a combination gas of methane (CH4) and hydrogen (H2) + carbon monoxide (CO) in DRI reduces CO2 emissions by 61 % compared with BF-BOF. Substituting H2 for CH4 (H2-DRI) reduces CO2 emissions by 97 %. Meanwhile, H2-DRI competes with CH4-based DRI in greenhouse-gas emissions, but H2-DRI falls short in terms of economics, safety, and high-temperature reduction efficiency. This article reviews the latest advancements in DRI reaction at different scales, from molecular to particle, pellet, reactor, and industrial levels. Research on DRI primarily focuses on particle agglomeration, pellet expansion, and enhancing reduction efficiency. The reaction environment is characterized through theoretical calculations, numerical simulations, and improvements in reactor structure, reducing gas composition, and pellet-ore preparation processes within the existing technological framework. Ultimately, technological advancements in the steel industry are influenced by climate objectives, policy support, investment returns, and reducing the cost of green H2. Accelerating research on different scales of H2-DRI can help achieve net-zero emissions in the steel industry.