Optimisation of carbon dioxide pressurisation pathways for pipeline offshore delivery

To maximise economies of scale of future CO₂ transport infrastructure, new CO₂ pipelines within the carbon capture utilisation and storage (CCUS) value chain, should ideally have excess capacity to satisfy future transportation demand. However, in scenarios where booster compressors cannot be employed along the pipeline, the rise in pipeline mass flow rate over time culminates in higher energy consumption of upstream compression/liquefaction. This work explores the optimisation of various CO₂ pressurisation pathways and assesses their flexibility in handling a variability in pipeline mass flow rates whilst delivering a captured CO₂ stream at a fixed final pressure of 100 barg. The study is based on the Dunkirk 3D Project, which has a planned nameplate capture capacity of 1 MtCO₂/y, with other CO₂ point sources taking up additional pipeline utilisation capacity. Two categories of CO₂ pressurisation pathways are considered, gas compression and subcritical liquefaction and pumping. These pathways are optimised to enable a fair comparison, considering the number of compression stages, compression ratio, and cooling/liquefaction system. Modelling results indicate that the temperature of the cooling utility has the greatest influence in reducing the overall work duty and sensitivity to a variability in pipeline mass flow rate. Furthermore, the utilisation of 5 °C seawater as a cooling and liquefaction utility reduces the work duty of the conditioning process by 25.4% and requires fewer compression stages relative to conventional gas compression utilising cooling water at 30 °C.