Design and Optimization of a LNG Cold Energy and BOG Driven CCHP System Integrating Carbon Capture

To address the issues of cold energy waste during the liquefied natural gas （LNG） regasification process and the treatment of boil-off gas （BOG） generated in LNG storage tanks, while also reducing the carbon emissions in the production process, this study proposes an LNG cold energy and BOG-driven combined cooling, heating, and power （CCHP） system integrated with carbon capture. An optimization model targeting exergy efficiency, net electrical power, and total cost ratio was developed. The Elitist Non-dominated Sorting Genetic Algorithm （NSGA-II） and Multi-objective Particle Swarm Optimization （MOPSO） were employed for multi-objective optimization. Linear Programming （LINMAP） and the Technique for Order of Preference by Similarity to Ideal Solution （TOPSIS） were subsequently applied to identify the optimal performance point. Performance analyses were then conducted at this point to evaluate the system’s optimized performance. The results indicate that the optimal system performance is achieved when the LNG vaporization pressure is 7200 kPa, the gas expander outlet pressure is 140 kPa, the ORC expander inlet pressure is 19500 kPa, the BOG combustion pressure is 990 kPa, and the expander T-4 outlet pressure is 2500 kPa. At this point, exergy efficiency, net electrical power, and total cost ratio reach 58.22%, 2505.73 kW, and 0.531 M/year, respectively. Through process integration, the optimized system achieves efficient cascade utilization of energy, with CO₂ capture, freshwater production, and nitrogen output reaching 1981 kg/h, 1620 kg/h, and 9689 kg/h, respectively, ensuring the economic operation of the system. The carbon capture efficiency reaches 99.58%, achieving near-zero carbon emissions. The system wastes only 42.35 kW of cold energy, accounting for just 2.23% of the total cold energy.This provides a replicable technical solution for energy conservation and emission reduction in LNG receiving terminals.