Design and optimization of a zero carbon emission system integrated with the utilization of marine engine waste heat and LNG cold energy for LNG-powered ships

Aiming at promoting LNG-powered ships to achieve zero carbon emission, this paper presents an efficient energy utilization system, which can fully recover the marine engine waste heat and LNG cold energy while realizing zero carbon emission. A combination of transcritical CO2 and organic Rankine cycles is adopted to replace the original ship's waste heat generation system. Based on balancing the ship's application constraints and energy efficiency indicators, the existing land air separation system is modified to recycle the products' cold energy and the oxygen-enriched combustion of the main engine is constructed. Then, through a sensible energy gradient design and adjusting the circulating flue gas parameters, the design goals are achieved while meeting the host power. The feasibility of the system's application is assessed through thermodynamic and economic analysis, and the optimal technical parameters are determined after working fluids matching and optimization of sensitive parameters based on the genetic algorithm. The results indicate that the system's CO2 capturing purity, exergy efficiency, net output power and annual net profit are 97.09%, 51.78%, 318.36 kW, US$485,165, respectively, demonstrating significant features such as high effective energy conservation and zero carbon emission.