Advanced process design of subcooling re-liquefaction system considering storage pressure for a liquefied CO2 carrier

Because carbon capture and storage methods are considered greenhouse gas reduction technologies, demand for a large liquefied CO2 (LCO2) carrier to transport captured CO2 to storage sites has arisen. To prevent the emission of boil-off CO2 gas during transport, a CO2 re-liquefaction system would be required. This study suggests a new type of LCO2 subcooling re-liquefaction system for an LCO2 carrier and demonstrates its effectiveness by comparing its performance with that of conventional re-liquefaction systems considering LCO2 storage pressure. The results show that the suggested LCO2 subcooling system has lower specific energy consumption than that of conventional LCO2 re-liquefaction systems, even with a simpler configuration. At 15 bar of storage pressure, the LCO2 subcooling system has a lower specific energy consumption of 176.91 kJ/kgCO2, which is 18.2 and 5.3 % lower than that of the Linde–Hampson cycle and vapor-compression refrigeration cycle using NH3 as a refrigerant, respectively. Additionally, economic benefits can be obtained because the boil-off CO2 compressor is not required in an LCO2 subcooling system. Finally, considering CO2 re-liquefaction performance and the design constraints of the LCO2 carrier, 15 bar LCO2 storage conditions with a subcooling system are considered the most economical LCO2 carrier design.