Carbon-efficient production planning for long-chain integrated refinery-petrochemical processes: A material-energy-carbon optimization perspective

The integrated refinery-petrochemical plant produces multiple oil products and petrochemical materials, which process consumes large amounts of energy and generates considerable quantities of CO2. Meanwhile, due to the long production chain, and a wide variety of carbon emissions sources, the CO2 generated by the production process is difficult to be quantified accurately. To achieve the low-carbon and energy-saving targets, a multi-objective production planning model for the integrated refinery-petrochemical plant is developed in this work. Firstly, an accurate top-down carbon accounting model is established. Then, a multi-aspects process carbon efficiency index is proposed, considering production capacity and energy consumption. A multi-objective production planning model aiming at maximizing total profit and process carbon efficiency is constructed and formulated as a large-scale MINLP problem. Additionally, the FP-growth algorithm is used to analyze the multi-level coupling of emission-material-energy, identifying association and synergy effects. Finally, a case study on a practical integrated refinery-petrochemical plant with a 16000 kilotons annual processing capacity is presented. The results are: (1) Introducing the process carbon efficiency index is able to increase CO2 emissions reduction potential while ensuring more profit. Specifically, CO2 emissions are significantly reduced by 10%, and energy consumption is reduced by 289.1 tce after optimization. (2) The FCC unit generates the highest CO2 emissions, accounting for 34.4% of overall CO2 emissions. The highest proportion of CO2 emissions from process emission sources exceeded 75% of the total emissions. (3) The integrated reforming-hydrogenation unit has the highest CO2 emissions reduction potential, with the unit's CO2 emissions reduced by 25.3%, and energy consumption reduced by 3.15 tce after optimization. The refinery is proven to have higher CO2 emissions reduction potential than the chemical plant, achieving a CO2 emissions reduction of 11.4%. (4) The multi-level association analysis for emission-material-energy can provide qualitative and quantitative information for decision-makers.