Importantly, the proposed decarbonization strategy does not rely on deployment of renewable energy sources hence offers a solution which is not dependent on the growth of renewables sectors. Through comparing the emissions from sub-systems under the optimal solution, we found that the GHG emissions in utilization dominate the whole CCU system, so optimizing the utilization path can be more rewarding than the capture path. This finding benefits from optimizing the sub-systems simultaneously. The GHG emissions breakdowns indicate that heating is the most significant contributor to GHG emissions of the whole system, accounting for 60%. Electrifying heating fully by CCS electricity and fully producing methanol in the utilization pathways can reduce GHG emissions by 47% compared to the conventional process.