This study proposes a feasible solution for boil-off gas (BOG) treatment to facilitate NH₃ fuel use by ocean-going ships, which is currently considered an alternative fuel for ships. Two systems were designed and analyzed for BOG in IMO Type-A NH₃ fuel storage tanks for 14,000 TEU container ships. First, BOG lost inside the storage tank minimized economic losses through the onboard re-liquefaction system. The total energy consumed by the system to process NH₃ gas generated in the fuel tank at 232.4 kg/h was 51.9 kW, and the specific energy consumption (SEC) was 0.223 kWh/kg. Second, NH₃ was supplied to the direct Low-Pressure Selective Catalytic Reduction (LP-SCR) system to treat marine pollutants generated by combustion engines. The feasible design point was determined by calculating the NH₃ feed flow rate using three methodologies. The energy consumed by the direct LP-SCR system was 3.89 and 2.39 kW, and the SEC was 0.0144 at 0.0167 kWh/kg at 100% and 25% load, respectively. The feasibility was indicated via economic analysis. Depending on the life cycle cost, the competitiveness of the re-liquefaction system depends on the price of NH₃, where a higher price yields a more economical solution. In conclusion, the direct LP-SCR system has a low overall cost because of its low energy consumption when supplying NH₃ and its reduced amount of core equipment.

This study evaluates the thermodynamic performance of the following two CO₂ liquefaction processes for onboard carbon capture and storage (OCCS) on a 174,000 m³ LNG carrier: the Linde–Hampson and vapor compression refrigeration cycles. The cycles were designed based on realistic vessel operating conditions and compared using the specific energy consumption (SEC) as the primary performance indicator, alongside the coefficient of performance (COP). To enable a fair comparison of the two distinct cycles, a complementary COP metric was validated for the open-loop Linde–Hampson cycle by establishing a system-level definition of heat removal. The validity of this metric was confirmed by demonstrating that its optimal point (maximum COP) aligns with that of the primary metric (minimum SEC), ensuring thermodynamic consistency. The analysis reveals that the vapor compression cycle demonstrates superior performance, achieving an 8.35% higher COP and an 11.45% lower SEC than the Linde–Hampson cycle. This work provides a consistent methodology for the comparative assessment of open- and closed-loop liquefaction systems.

As environmental concerns increase globally, the International Maritime Organization has been strengthening regulations to limit pollution from ships, attracting increasing interest in ammonia as a zero-carbon marine fuel. This study aimed to establish safe bunkering procedures for ammonia-fueled ships through thermodynamic analysis. The research analyzed two bunkering scenarios, ship-to-ship and truck-to-ship, calculating the boil-off rate and return boil-off gas for each scenario. A thermal analysis showed that the ship-to-ship scenario generated 271.9 kg/h of return boil-off gas with a total heat ingress of 92.84 kW. The truck-to-ship scenario produced 243.95 kg/h of return boil-off gas with a total heat ingress of 84.4 kW. Based on these findings, comprehensive bunkering procedures were developed for both scenarios, consisting of 14 steps for ship-to-ship and 13 for truck-to-ship, addressing the unique challenges of ammonia handling. These procedures include evaporated gas recovery systems, ammonia catch systems, and nitrogen purging to minimize leakage and explosion risks. The results of this study contribute to the development of safety regulations for ammonia-fueled ships by establishing systematic operational procedures that consider the toxicity and corrosiveness of ammonia.