Thermodynamic analysis of a transcritical CO2 heat recovery system with 2-stage reheat applied to cooling water of internal combustion engine for propulsion of the 6800 TEU container ship

Abstract

The study on a novel waste heat recovery system that comprises transcritical carbon dioxide Rankine cycle with 2-stage reheat and 3-stage turbine was carried out. This power generation system which converts waste heat into electric power was theoretically applied to cooling water for scavenge air and engine water jacket in a main engine for a 6800 TEU container ship's propulsion, as a stand-alone type. The thermodynamic performance depending on changes in the dimensionless turbine inlet pressures was investigated. The results showed that the heat recovery system could produce a maximum net output of 383 kW for the representative operation condition in the main engine. Moreover, when considering the variation of seawater temperature in the ship's regular route, it was found that the maximum output was inversely proportional to the dimensionless temperature for the seawater. Based on energy analysis, the cycle and system efficiencies were maximized at 9.27 and 7.87%, respectively, with respect to the heat effectiveness of 84.95%. Based on exergy analysis, the maximum efficiencies of exergy and system exergy were 6.60% and 5.94%, respectively, with respect to the exergy effectiveness of 90.12% under the same initial condition of the energy analysis. As a result of the detailed analysis, the importance was confirmed that the optimal output assignment for the 3-stage turbine considering the minimization of the exergy destruction in the reheater 1 and 2 was required in order to achieve the maximum performance of the present system.