Simulation and performance optimization of a poly-generation system based on LNG cold energy utilization

In order to solve the problem that the organic working medium of a power generation system is easy to thermal decomposition at medium and high temperature, the waste heat was recovered with the supercritical and transcritical CO₂ used in combination on the principle of "appropriate temperature and cascade utilization", and a poly-generation system based on LNG cold energy utilization was established. Herein, the system was simulated by Aspen HYSYS in terms of the process flow and evaluated from the prospective of thermal performance and exergoeconomy. Besides, the effect of main parameters on system performance was analyzed, and on this basis, the multi-objective optimization of system performance was carried out using Matlab. The results show that the reduction of split ratio in supercritical CO₂ recompression Brayton cycle and compression ratio in refrigeration cycle can not only improve the system efficiency, but also reduce the average unit cost. In addition, the power generation efficiency, exergy efficiency and average unit cost of the optimized poly-generation system are 55.83%, 52.23% and 16.57 /GJ, respectively, and the power generation efficiency has been enhanced by 14.05% in comparison to the system integrated with the single supercritical CO₂ recompression Brayton cycle. Generally, the research results could provide an application idea for the utilization of LNG cold energy and the recovery of waste heat.