Economy‑carbon co-optimization of industrial multi-energy systems considering process coupling and the flexible utilization of by-product gas

As a pillar of energy-intensive heavy industry, the steel sector plays a critical role in achieving energy conservation and carbon mitigation. With the traditional blast furnace–basic oxygen furnace (BF–BOF) long process increasingly challenged to meet low-carbon demands, electric arc furnace (EAF) short process steelmaking has emerged as a viable pathway. Consequently, the coexistence of long and short processes will serve as a crucial transitional phase for steel enterprises undergoing low-carbon transformation. To improve the efficiency of both energy and carbon, this paper establishes an economy-carbon co-optimization model for the industrial multi-energy system (IMES) of steel enterprises during this transitional phase, which is modeled as a multi-objective optimization problem. By coupling combined heat and power (CHP), post-combustion carbon capture (PCC), and methanol synthesis processes, the by-product gases generated from BF-BOF process are flexibly utilized. To address the trade-off between economic and carbon objectives, an NSGA-II–TOPSIS algorithm is employed to solve the proposed model and determine the optimal operating strategy for the IMES. The case study shows that under single-objective economic optimization, the system reduces carbon emissions by 56.13% and operating costs by 0.66%. After multi-objective optimization, an increase of 7.51% in operating cost leads to a reduction of 69.87% in carbon emissions. Grounded in the steel industry's low-carbon transition needs, this study integrates electricity prices responsiveness with low-carbon objectives. By balancing economic and sustainability goals, it provides a decision-making framework for the sector's low-carbon transformation.