| Summary: | The pipeline has historically been the preferred means to transport CO<sub>2</sub> due to its low cost for short distances and opportunities for economies of scale. However, interest in vessel-based transport of CO<sub>2</sub> is growing. While most of the literature has assumed that CO<sub>2</sub> shipping would take place at low pressure (at 7 barg and −46 °C), the issue of identifying best transport conditions, in terms of pressure, temperature, and gas composition, is becoming more relevant as ship-based carbon capture and storage chains move towards implementation. This study focuses on an in-depth comparison of the two primary and relevant transport pressures, 7 and 15 barg, for annual volumes up to 20 MtCO<sub>2</sub>/year and transport distances up to 2000 km. We also address the impact of a number of key factors on optimal transport conditions, including (a) transport between harbours versus transport to an offshore site, (b) CO<sub>2</sub> pressure prior to conditioning, (c) the presence of impurities and of purity constraints, and (d) maximum feasible ship capacities for the 7 and 15 barg options. Overall, we have found that 7 barg shipping is the most cost-efficient option for the combinations of distance and annual volume where transport by ship is the cost-optimal means of transport. Furthermore, 7 barg shipping can enable significant cost reductions (beyond 30%) compared to 15 barg shipping for a wide range of annual volume capacities.
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