This paper studies re-liquefaction properties of CO₂ and introduces feasible designs of boil-off CO₂ re-liquefaction processes suited for a large-scale transport ship. There are additional design considerations besides re-liquefaction efficiency due to the ship. Firstly, re-liquefaction facilities should be located within a limited space of a transport ship, which induces the number of main equipment as a constraint. Secondly, if an external closed-loop refrigeration is necessary, refrigerants should be re-chargeable and safe. From this perspective, CO₂ would be the most appropriate one due to the availability in a liquefied CO₂ ship and its safety if it can have similar performance to conventional refrigerants. According to CO₂ liquefaction simulation, CO₂ as a refrigerant shows similar performance to C₃H₈ and NH₃ with additional 5–7% power consumptions. With this preliminary investigation, four boil-off CO₂ re-liquefaction processes for a large-scale transport ship are designed. A re-liquefaction process which employs a distillation column shows 99.7% of re-liquefaction fraction but it has disadvantages of power consumption and the number of main equipment. On the contrary, another re-liquefaction process which has an external closed-loop refrigeration cycle with a CO₂ refrigerant meets the re-liquefaction target (>70.0%) with the lowest power consumption. This process also requires nominal level of the number of main equipment and the capital expenditure. Given these results, an external closed-loop CO₂ refrigeration cycle based re-liquefaction process is expected to be appropriate for a large-scale liquid CO₂ transport ship. Hopefully, the results addressed in this study will contribute to further development of liquefied CO₂ transport ships in near future.

本文研究了CO _2的再液化特性，并介绍了适用于大型运输船的蒸发式CO ₂再液化工艺的可行设计。除了船的再液化效率外，还有其他设计注意事项。首先，再液化设施应位于运输船的有限空间内，这会限制主要设备的数量。其次，如果需要外部闭环制冷，则制冷剂应可充电且安全。从这个角度来看，由于液化的CO ₂船的可用性及其安全性（如果它可以具有与常规制冷剂相似的性能），CO ₂将是最合适的。根据CO₂液化模拟显示，作为制冷剂的CO ₂具有与C ₃ H ₈和NH ₃相似的性能，但功耗却增加了5-7％。通过该初步研究，设计了用于大型运输船的四个蒸发式CO ₂再液化工艺。使用蒸馏塔的再液化方法显示出99.7％的再液化率，但是它具有功耗和主要设备数量的缺点。相反，另一种再液化过程具有外部闭环制冷循环和CO ₂制冷剂以最低的能耗达到了再液化目标（> 70.0％）。此过程还需要名义水平的主要设备数量和资本支出。鉴于这些结果，预期基于外部闭环CO ₂制冷循环的再液化过程适用于大型液态CO ₂运输船。希望这项研究中提出的结果将有助于在不久的将来进一步发展液化CO ₂运输船。