Making Green Steel with Hydrogen
Channel: Metallurgy Guru - Sustainable Metals & Green Steel
Date: 2022-02-13

More than 1.8 billion tons of steel are produced every year, making it the most important alloy in terms of volume and impact. While steel is a sustainability enabler, through lightweight car parts, wind farms and magnets, its primary production is not. Iron is reduced from ore using carbon. This produces 2t CO2/t of steel, standing for 33% of the global CO2 emissions in manufacturing. These emissions can be reduced when replacing carbon by hydrogen or its carriers as reductant [1,2]. 
The lecture presents some recent progress in understanding the key mechanisms of hydrogen-based direct reduction and hydrogen-based plasma reduction [3-5]. The kinetics of the reactions strongly depend on mass transport kinetics, nucleation during the multiple phase transformations, the oxide’s chemistry and microstructure, and on damage and fracture associated with the phase transformation and mass transport phenomena occurring during reduction. Understanding these effects is key to make hydrogen-based reduction of iron ores commercially viable, enabling massive CO2 reductions. 
Another aspect is that the production of hydrogen using renewable energy will remain as one of the bottlenecks at least during the next two decades, because making the gigantic annual crude steel production of 1.8 billion tons sustainable requires a minimum stoichiometric amount of ~97 million tons of green hydrogen per year. This means that turning the ironmaking sector more sustainable requires optimal utilization of green hydrogen and energy, thus reducing efforts for costly in-process hydrogen recycling [5].


[1] youtube: Sustainable Metallurgy and Green Metals https://www.youtube.com/watch?v=1kihsaLSxv0

[2] Raabe D, Tasan CC, Olivetti EA. Strategies for improving the sustainability of structural metals. Nature. 2019 Nov; 575 (7781): 64-74. 
https://www.nature.com/articles/s41586-019-1702-5

[3] SH Kim, X Zhang, Y Ma, IR Souza Filho, K Schweinar, et al. Influence of microstructure and atomic-scale chemistry on the direct reduction of iron ore with hydrogen at 700° C, Acta Materialia, 2021
https://www.sciencedirect.com/science/article/pii/S135964542100313X

[4] IR Souza Filho, Y Ma, M Kulse, D Ponge, B Gault, et al. Sustainable steel through hydrogen plasma reduction of iron ore: Process, kinetics, microstructure, chemistry, Acta Materialia, 2021
https://www.sciencedirect.com/science/article/pii/S1359645421003517

[5] IR Souza Filho, H Springer, Y Ma, A Mahajan, CC da Silva, M Kulse, D Raabe, Green steel at its crossroads: Hybrid hydrogen-based reduction of iron ores, Journal of Cleaner Production, Volume 340, 15 March 2022, 130805
https://www.sciencedirect.com/science/article/pii/S0959652622004437