System-level analysis of CO2 utilization from steelworks residue gases for fuel production: Superstructure-based optimization and techno-economic assessment

The steelmaking industry is a major source of industrial CO 2 emissions and generates large quantities of carbon-rich residue gases with substantial calorific value, yet conventional combined heat and power (CHP) still underexploit their energetic and economic potential. This study develops a superstructure-based optimization framework for CO 2 utilization from steelworks residue gases, such as coke oven gas (COG) and Linz–Donawitz gas (LDG) into value-added fuels, namely hydrogen (H 2 ), methanol (MeOH) and Fischer–Tropsch (FT) fuels. A technology superstructure comprising 30 alternative gas-to-fuels routes is formulated, and rigorous steady-state process models are developed in Aspen Plus to quantify mass and energy balances as well as key cost parameters. Based on these models, network optimization problems are solved to identify optimal residue gas utilization strategies under four design objectives: minimum total energy consumption, minimum fuel production cost, minimum process-level CO 2-eq emissions and maximum profit. The optimization also accounts for different residue gas availability scenarios and production scales representative of industrial steelworks. The results show that MeOH Route #5 achieves an energy efficiency of up to 82%. H 2 Route #1 produces high-purity hydrogen at a unit cost of 18.0 $/MWh at medium scale, corresponding to a 68% reduction relative to reported market prices. FT Route #10 yields the lowest CO 2 footprint at 95 kg CO 2-eq /MWh among the considered options. Overall, the proposed framework provides steel plants with practical decision-support tools to design economically viable and environmentally favorable residue gas-to-fuels portfolios, thereby enabling new revenue streams while facilitating compliance with increasingly stringent carbon regulations.