Residue gas-derived hydrogen for decarbonizing steelmaking: A techno-economic-environmental analysis of a bridging pathway

Decarbonization of the steel industry increasingly depends on transitioning from the conventional blast furnace-basic oxygen furnace (BF–BOF) route to hydrogen-based direct reduction integrated with electric arc furnaces (DR–EAF) to reduce carbon emissions. However, large-scale deployment remains constrained by the high cost and limited availability of green hydrogen (GH₂). This study investigates an alternative hydrogen supply pathway based on residue gases generated from BF–BOF operations, including coke oven gas (COG), Linz–Donawitz gas (LDG), and blast furnace gas (BFG). A hydrogen production process employing combined steam and CO₂ reforming (CSCR) was designed, and its technical performance, economic feasibility, and carbon emission reduction potential were evaluated through an integrated techno-economic-environmental analysis. Multiple process configurations using single-feeding and co-feeding strategies were assessed to determine optimal operating conditions and an efficient residue gas-to-hydrogen pathway. The results indicate that CSCR-derived hydrogen can substantially reduce hydrogen production costs and near-term GH₂ supply requirements, thereby enabling flexible hydrogen deployment during the transition toward low-carbon steelmaking. While GH₂-based DR–EAF remains indispensable for achieving ultimate carbon emission mitigation under increasingly stringent carbon regulations between 2030 and 2050, country-specific integration of CSCR-derived hydrogen can alleviate short-term GH₂ demand and facilitate a more gradual and economically viable transition. Overall, residue gas valorization is identified as a critical system-level approach for supporting scalable decarbonization of the steel industry.