Abstract: To achieve the green hydrogen replacing gray hydrogen initiative in refineries and address the associated cost increase, a synergistic efficiency enhancement pathway of green hydrogen substitution + system integration optimization is constructed. First, by establishing a material balance model for the hydrogen production/consumption system, the impacts of green hydrogen replacing gray hydrogen on the refinery's hydrogen source structure, fuel gas system, and resource utilization efficiency are quantitatively analyzed. The results show that replacing the gray hydrogen produced by the refinery's dry gas hydrogen production unit with 4600 m³/h of green hydrogen leads to an increase in the enterprise's production cost. Therefore, two cost optimization strategies are proposed and verified: Using the PSA unit of the decommissioned dry gas hydrogen production unit to raise the purity (φ) of reformed hydrogen from 85% to over 99%, thereby reducing the fresh hydrogen consumption of downstream hydrogenation units by approximately 300 m³/h.Adopting the liquid-phase absorption method to recover 13 kt/a of liquid hydrocarbons from the high C₃+ content fuel gas across the entire plant. The economic accounting results indicate that after system integration optimization, the new C₃+ recovery unit and the "green hydrogen replacing gray hydrogen" initiative cause the total plant cost to increase by 33.81 million yuan per year. Meanwhile, the recovery of high C₃+ liquid hydrocarbons and the total savings from full processing fee reduction amount to 34.94 million yuan per year, boosting the enterprise's annual benefit by 1.13 million yuan after the project implementation. In addition, the total plant CO₂ emission reduction reaches approximately 23 kt/a, and the increased carbon sink benefit (calculated at a carbon price of 100 yuan/t) is about 2.31 million yuan. Thus, implementing green hydrogen replacing gray hydrogen can serve as a critical opportunity for refineries to restructure resources and optimize systems, enabling deep carbon emission reduction while maintaining the sustainability of economic benefits.

Key words: green hydrogen, grey hydrogen, reforming hydrogen, green hydrogen refining, light hydrocarbon recovery