Interoperability and energy optimization in low pressure ship to medium pressure terminal interfacing

• CO₂ shipping is vital for transporting captured CO₂ from scattered sources to storage sites, enabling large-scale CCS deployment. • Lack of standard specs for CO₂ state, pressure, and temperature complicates transport system compatibility. • During unloading, the LP CO₂ is pressurized and heated at subcooled conditions, to match MP terminal pressure and reduce terminal vapor displacement. • During LP loading, the terminal outgoing MP stream is depressurized to LP conditions, requiring subcooling to prevent two-phase flow. While subcooling reduces vapor displacement, it demands more energy than using a high-capacity vapor return compressor. Large-scale deployment of Carbon Capture and Storage (CCS) is essential to meet global climate change mitigation goals, with CO₂ shipping playing an important role in enabling cost-effective transport from dispersed sources to storage sites. However, transporting CO₂ is facing interoperability challenges due to the absence of standardized specifications for transport conditions, including state (gas, liquid, or dense phase), pressure and temperature levels. To address this, the authors propose a compatibility framework between Low Pressure (LP, 7–10 bara) ships and Medium Pressure (MP, 12–20 bara) terminals, serving liquefied CO₂ (LCO₂) shipping. The aim is to identify machinery systems and operating strategies that ensure cost-effective LCO₂ transfer. A thermodynamic model is used to simulate and optimize performance during loading and discharging operations, by quantifying energy and equipment needs and proposing ship-terminal interface solutions. The model is applied in a case study featuring a ship with three 7300 m³ tanks (simulated range: 5840–8760 m³) and evaluated across varying pressures, temperatures, and flow rates. The study concludes that: • During LP discharging, the LCO₂ is pressurized and heated to MP saturation conditions. To reduce vapor displacement from the terminal tank, subcooled inlet conditions are applied. Vapor returned to the ship is cooled via heat integration before being depressurized to LP. • During MP loading, the fluid stream is depressurized to LP, requiring subcooling to avoid two-phase flow and excessive vapor return. A sub-cooler reduces vapor displacement but demands more energy than a high-capacity vapor return compressor.