A state-of-the-art review on the utilization of biochar as renewable energy for the sustainable steel industry

The steel industry is a major contributor to global anthropogenic CO₂ emissions, accounting for nearly 10 % of the total. Within this sector, ironmaking processes, particularly those using the traditional blast furnace-basic oxygen furnace route, are responsible for almost 90 % of the industry's CO₂ emissions. Biochar, derived from renewable feedstocks, offers a sustainable and eco-friendly alternative to fossil fuels for ironmaking. This review examines the cutting-edge techniques for producing biochar and recent advancements in utilizing biochar across various ironmaking processes, including sintering/pelletizing, coke making, blast furnace injection, and direct reduction iron processes, with a focus on reducing CO₂ emissions. Despite demonstrated benefits such as reduced pollution, improved burden permeability, and enhanced gas utilization efficiency in pilot and industrial trials, large-scale biochar application remains limited by the varying quality requirements of different processes. Innovatively, a green hydrogen-metallurgical route that utilizes hydrogen-rich syngas derived from biomass and biochar is proposed in this work, serving as a comprehensive solution to address the challenges associated with the quality discrepancies of biochar produced by different carbonization methods and the diverse quality requirements for biochar in various ironmaking processes. This solution not only underscores its potential to significantly transform the iron and steel industry towards a more sustainable and low-carbon future, but also highlights the innovative contributions of this research to the fields of renewable energy, solid waste resources, metallurgical industry, and global climate change.