LNG cold energy driven multi-generation system integrating light hydrocarbon separation, BOG helium extraction and two-stage ORC: multi-objective optimization and comprehensive evaluation

To achieve the cascade utilization of LNG cold energy, this paper presents a novel and efficient system known as LHS-HE-TSORC, which integrates light hydrocarbon separation (LHS), boil-off gas (BOG) helium extraction, and a two-stage organic Rankine cycle (ORC). The working fluid for the ORC and the separation membrane material used in the helium extraction system were meticulously selected. Sensitivity analysis assesses the impacts of key process variables on net electric power ( NEP ), exergy efficiency ( η ex ), and net present value ( NPV ). Multi-objective optimization is conducted using the Non-dominated Sorting Genetic Algorithm II (NSGA-II) and Multi-Objective Particle Swarm Optimization (MOPSO) to identify optimal system parameters. The results indicate that R290 is selected for the ORC subsystem, while PBO-co-PPL 28 is chosen as the membrane material for the helium extraction subsystem. The multi-objective optimization results demonstrate a performance characterized by an NEP of 12.69 × 10 3 kW, an η ex of 38.38 %, and an NPV of 3.67 × 10 9 $. Energy assessment results confirm that heat exchanger HX-3 exhibits the minimum energy loss and the highest heat transfer efficiency. Exergy assessment results indicate that the total exergy destruction amounts to 53,838.37 kW. The economic assessment reveals a dynamic payback period ( DPP ) of 2.695 years. The exergoenvironmental assessment confirms that the system shows improved environmental compatibility under colder conditions. Finally, the entropy generation assessment indicates that the highest entropy generation occurs in the heat exchanger, tower, and combustion chamber.