Thermodynamic analysis and multi-objective optimization of a transcritical CO2 waste heat recovery system for cruise ship application

To develop the energy-efficient and flexible waste heat recovery process for cruise ship application, a novel combined system with transcritical CO2 Rankine cycle and ejector refrigeration cycle (ETCRC) is presented. The proposed system driven by main engine exhaust gas can be selectively operated in a specific mode with adjustable capacities of heating, cooling and power to satisfy shipboard demands. The simulation model is developed for performance analysis from the thermodynamic aspect. Moreover, a typical transcritical CO2 Rankine cycle coupled with valve-expansion refrigeration process (VTRCR) and a conventional regenerative organic Rankine cycle (RORC) using R123 are considered as reference systems. Parametric investigation and performance comparison between the present system and each considered reference system in different operation modes are respectively conducted. Furthermore, based on artificial bee colony (ABC) algorithm and fast non-dominated sorting technique, multi-objective optimization for the proposed system is performed to maximize useful energy productions. According to the results, the proposed combined cycle is found to be more efficient than the reference cycle in each of the specified operation mode. Under the optimal conditions, the maximum cooling effect and net power of the ETCRC in Mode-S operation are 863.3 kW and 202.9 kW, respectively. And the maximum high-temperature heating output and net power of the ETCRC for Mode-SAW operation are 960.5 kW and 272.7 kW, respectively. The performance characteristics of the proposed cycle theoretically demonstrate its advantages for application in cruise ships.