Techno-economic analysis of large-scale CO2 ship transport with onboard boil-off gas reliquefaction

This study presents a comprehensive techno-economic analysis of large-scale CO₂ transport by ship over long distances, with a focus on the economic impact of onboard boil-off gas (BOG) reliquefaction. Besides ship size and transport distance, this study includes an extended analysis of the effect of varying seawater temperatures on the reliquefaction system. Various scenarios involving three different ship sizes (40 K, 80 K, 120 K m³) and transport distances ranging from 1,000 to 20,000 km were examined to evaluate the cost implications for cross-border Carbon Capture and Storage (CCS) projects. The analysis shows that larger ships reduce costs significantly for long distances and large annual CO₂ transport amounts. While the absolute cost of BOG reliquefaction increases with larger ship sizes and longer transport distances, its proportion relative to the total transport cost remains fairly constant at about 5 % of total CO₂ transport costs. Additionally, seawater temperature plays a crucial role in system performance, with higher temperatures significantly increasing cost of reliquefaction system. The study also finds that BOG reliquefaction costs account for approximately 15.1 % to 17.0 % of the ship capital expenditure (CAPEX). Sensitivity analysis identifies the fuel prices and ship CAPEX as the most significant factors influencing overall transport costs. These findings underscore the importance of optimizing ship size and managing fuel costs to design economical CO₂ maritime transport systems, particularly for long-distance CCS applications.