Design and optimization of LNG-powered ship cold energy and waste heat integrated utilization system based on novel intermediate fluid vaporizer

Based on a novel integrated intermediate fluid vaporizer with liquefied natural gas (LNG) cold energy utilization proposed by the author's team, a full-power generation integrated system is constructed in this study. It is a two-stage cascade Rankine cycle with two-stage condensation and coupled with a trans-critical CO2 Rankine cycle. This study regards a river–sea direct transportation type of 25,000-ton LNG fuel-powered chemical ship as the application object and considers combined utilization of the medium-temperature waste heat of flue gas from the exhaust turbine power generation cycle outlet and the vaporization cold energy of LNG. Through the simulation and analysis of the scheme, circulating working fluid optimization and operation parameter optimization based on a genetic algorithm are conducted. The overall exergy efficiency of the optimized system reaches 45.1%, while the power generation of the system reaches 72.66 kW. Furthermore, economic analysis shows that the net annual income of the optimized system can reach 280,700 yuan, and the recovery cycle of initial investment cost is expected to be 6.11 years