As a main growing greenhouse gas emitter, petroleum refining is responsible for 4%–10% of the global carbon dioxide (CO2) emissions, of which approximately 25% is derived from fluid catalytic cracking (FCC) units. The flue gas released by FCC units has a high CO2 content (11–17 vol%), creating potential for methanol production when the methane and hydrogen in the dry gas as a byproduct of FCC are considered. To unlock this low-carbon opportunity for refineries, we employed Aspen Plus to develop a methanol synthesis system by recovering the CO2 in the flue gas and the methane and hydrogen in the dry gas of an FCC unit. Based on pinch theory, a process heat integration technique was designed and optimized to reduce the energy penalty of the system. The developed system enables an annual CO2 mitigation of 2.80 million tons and boosts the energy efficiency of the FCC units by 2.8%. The system developed by this study is more economically favorable than traditional coal-to-methanol production. The developed system provides technological routes for refineries to achieve large-scale CO2 mitigation, thus advancing the green transition of the petrochemical industry.