Application of Fuel Cold Energy in CO₂ Bog Reliquefaction System on Ammonia-Powered CO₂ Carrier

A CO₂ boiled off gas (CO₂ BOG) reliquefaction system using liquid ammonia cold energy is designed to solve the problems of fuel cold energy waste and the large power consumption of the compressor in the process of CO₂ BOG reliquefaction on an ammonia-powered CO₂ carrier. Aspen HYSYS is used to simulate the calculation, and it is found that the system has lower power consumption than the existing reliquefaction method. The temperature of the heat exchanger heater-1 heat flow outlet node (node C-4) is optimised, and it is found that, with the increase of the node C-4 temperature, the power consumption of the compressor gradually increases, and the liquefaction fraction of CO₂ BOG gradually decreases. Under 85% conditions, when the ambient temperature is 0°C and the temperature of node C-4 is -9°C, the liquid fraction of CO₂ BOG reaches the maximum, which is 74.46%, and the power of Compressor-1 is the minimum, which is 40.90 kW. According to this, the optimum temperature of node C-4 under various working conditions is determined. The exergy efficiency model is established, in an 85% ship working condition with the ambient temperature of 40°C, and the exergy efficiency of the system is the maximum, reaching 59.58%. Therefore, the CO₂ BOG reliquefaction system proposed in this study could realise effective utilisation of liquid ammonia cold energy.