Toward sustainability in the iron and steel industry: Eco-efficient design and optimization of an integrated COG-based polygeneration system incorporating the Allam cycle and seawater desalination

• Development of a high-efficiency and cost-effective process for hydrogen recovery from COG. • Parametric study and sensitivity analysis to investigate the influence of key operational variables on system performance. • Thermal integration of the Allam power cycle with a seawater desalination unit. • Multi-objective optimization to minimize cost and enhance the thermodynamic efficiency of the process. Coke oven gas (COG), a byproduct of steel plants, contains a relatively high hydrogen content. Proper utilization of industrial byproducts such as COG can mitigate environmental pollution and energy losses. Key factors in sustainable energy development include improving the efficiency of energy conversion from available resources and minimizing environmental impacts. This study employs a nitrogen expansion–based cryogenic separation process for hydrogen recovery from COG. Furthermore, the proposed configuration integrates an Allam cycle and a seawater desalination unit, enabling the co-production of hydrogen, electricity, hot water, and freshwater. The Allam cycle supplies all on-site power demands and is integrated with the desalination unit to meet its process-heat requirement, enabling self-sustained operation without grid electricity. Under steady-state conditions, the system achieves energy, exergy, and electrical efficiencies of 86. 27%, 52. 58%, and 15. 18%, respectively, with a specific energy consumption of 0. 987 kWh/kg, an LCOP of 0. 035/kWh, and an NPV of 45. 23 million. The influence of key independent operating parameters on the performance of the developed process was systematically investigated. Moreover, based on the parametric study results, a SHAP-based sensitivity analysis was conducted to quantify the impact of these parameters on the economic performance of the process. Finally, multi-objective optimization using the weighted-sum method was performed to enhance the thermodynamic and economic performance of the system. The suggested system offers a promising pathway for improving the conversion of COG into useful outputs and can also serve as a strategy to reduce CO 2 emissions and promote sustainability in the iron and steel industry.