A cryogenic CO2 capture system coupled with boil-off gas re-liquefaction for LNG carriers

Abstract

With the rising global demand for liquefied natural gas (LNG) in various fields, the need for LNG carriers has increased, which causes elevated CO₂ emission. Thus, CO₂ capture technology to achieve carbon neutrality on large LNG carriers has become a research concern. Besides, boil-off gas (BOG) is constantly generated which is due to the unavoidable heat leaks during the voyage resulting in the vaporization of several LNG. Therefore, a novel cryogenic on-board carbon capture (COCC) system making full use of LNG cold energy coupled with a BOG re-liquefaction (COCC-RL) system is firstly proposed, and the full operation conditions are considered. In this integrated system, superior thermal matching allows for CO₂ capture in the exhaust, natural gas fuel vaporization and BOG re-liquefaction. It is astounding that the small capacity capture system could also produce a more competitive annual total profit (ATP) (4.13 × 10⁴ $/ton) at a higher CO₂ capture rate (56.69 %) compared to a high main load as design point. Therefore, a hitherto unexploited solution avenue has emerged, presenting a novel direction for designing a cryogenic on-board carbon capture system coupled with BOG re-liquefaction at variable engine loads and shows the potential of cryogenic CO₂ capture technology in the shipping industry.