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In this study, cargo boil-off gas (BOG) re-liquefaction systems for ammonia-fueled liquefied carbon dioxide (LCO2) carriers were analyzed. These systems use cold energy from ammonia to reliquefy the CO2 BOG. In this study, a system that can completely reliquefy the CO2 BOG at all engine loads using only one heat exchanger is proposed, instead of the existing cascade system that requires multiple components. R744, which has a low global warming potential, was used as the working fluid for the refrigeration cycle in the CO2 BOG re-liquefaction system. The organic Rankine cycle (ORC) was used to reduce the net power consumption of the system. The existing and proposed systems were classified into Case 1 (existing system), Case 2 (our proposed system), and Case 3 (Case 2 combined with an ORC). Thermodynamic and economic analyses were conducted. Case 2 is a system with a simpler configuration than Case 1, but it has a similar thermodynamic performance. Case 3 has a higher exergy destruction rate than Cases 1 and 2, owing to the ORC, but it can significantly reduce the net power consumption. The economic analysis shows that Cases 2 and 3 reduce the total annual costs by 17.4% and 20.1%, respectively, compared to Case 1. The proposed systems are significantly more advantageous for long-term operation than existing systems. [ABSTRACT FROM AUTHOR]

The combined use of generation and propulsion gas turbines and steam turbines is efficient and can meet the environmental regulations. In this study, the thermodynamic performance of waste heat recovery systems of a marine gas turbine was analyzed. These systems combine the steam Rankine cycle and the organic Rankine cycle to form a dual-loop cycle. Working fluids R32, R134a, R152a and R1234yf, that are low-global warming potential, were selected for the organic Rankine cycle. All of the working fluids exhibited better performance than for the single-loop cycle, and R134a exhibited the greatest efficiency with energy and exergy efficiencies of 29.50 % and 45.58 %, respectively. The most important components contributing to the exergy destruction of the cycle were the heat exchangers. Therefore, it is essential to select the optimum heat exchanger as well as the working fluid in the waste heat recovery system for marine gas turbines. [ABSTRACT FROM AUTHOR]