Carbon Dioxide (CO₂) transport is the intermediary step in the carbon capture value chain, where CO₂ shipping is increasingly playing a more important role in global decarbonisation efforts via transport for CO₂ storage or utilisation. Although technical challenges remain in CO₂ shipping, the technologies for transport are maturing, making the business case more favourable for widespread adoption.
Carbon Capture is regarded as a necessary technology to be deployed in conjunction with zero-carbon energy to reach the IPCC 1.5C scenario by 2050 (IPCC). This means that global CO₂ emissions must be reduced by 5 gigatons per year - the equivalent to the total CO₂ emissions from about ten thousand factories and power stations. It is estimated that CCS can contribute to eliminating 14-17 percent of these emissions (SINTEF).
The transport of CO₂ by pipeline has been practised for three decades, and international standards such as ASME B31.4 are widely adopted. Liquid transportation systems for hydrocarbons, liquid petroleum gas, anhydrous ammonia and alcohols are subject to the widely applied Norwegian standard (DNV, 2000) with explicit mention of Carbon Dioxide.
Globally, CO₂ shipping is growing to accommodate offshore geological storage. For decades commercial CO₂ shipping has served markets seeking food grade, or high-purity CO₂ for utilisation purposes. Although technical challenges remain in CO₂ shipping the technologies for transport are increasingly maturing, making the business case more favourable for widespread adoption.
Current CO₂ shipping practices
CO₂ transportation by ship requires a pressure system to maintain the CO₂ in a liquid state. CO₂ tankers generally operate at conditions near the triple point – the temperature and pressure where CO₂ can coexist in thermodynamic equilibrium, or where the solid, liquid and gas states converge—but new research suggests that CO₂ can be shipped at varying pressure and temperature conditions to help integrate shipped CO₂ into the existing carbon capture and storage value chain.
Because liquid CO₂ can only exist at a combination of low temperature and pressures exceeding atmospheric pressure, CO₂ cargo tanks therefore should be pressurised or semi-refrigerated. The semi-refrigerated generally preferred for similarities with LPG carriers, and the design point of the cargo tank would be approximately –54C per 6 bar to –50C per 7 bar, which is near the triple point of CO₂.
For purposes of loading and unloading liquid CO₂ to ships, liquified CO₂ is discharged from intermediate storage tanks to the onboard cargo tanks with process systems suitable for high pressure and low temperature CO₂ handling. Before discharge, the onboard cargo tanks are prepared for the cargo with pressurised gaseous CO₂ to prevent contamination by humid air and the formation of dry ice. To prevent CO₂ diffusion resulting from heat transfer during transfer and storage additional refrigeration units are used to capture any potential boil-off and emissions from the CO₂ vessel.
CO₂ vessels generally have a capacity of 800m3 upwards to 22,000m3, which is not massive in the grand scheme of CO₂ capture mitigation, but it is a superior option to decarbonise industries in remote areas over longer distances. The alternative to shipping is using a CO₂ pipeline, where there is a high-cost associated with maintaining stable temperature and pressure over long distances, hence shipping of smaller volumes over longer distances is more economical.
CO₂ shipping economics
Costs of a marine transport include many elements: apart from the investment for vessels, other investments include loading and unloading facilities, temporary storage and liquefaction units. Additionally, operational costs include labour, ship fuel, harbour fees and maintenance. According to a report by the IPCC, the optimal use of installations and ships in the transport cycle is crucial for the business case for CO₂ shipping. In some cases, extra storage facilities are required to account for any potential disruption to the marine based CO₂ value chain.
In 2004 Equinor (then Statoil) estimated marine transport costs of 5.5Mt CO₂ per year by 17 20,000m3 tanker (upgraded LNG tankers) over a distance of 7600km per sailing, with liquefaction and loading/unloading costs to be USD 300million. The IEA conducted a comparable study demonstrating lower costs: for the same CO₂ cargo using 30,000m3 ships over a distance of 7600km the cost is estimated to be USD 35million – suggesting a stronger cost correlation with distance and cargo load.
The implementation of carbon capture technologies in shipping will result in an increased need for infrastructure supporting off and on-loading of CO₂. Innovative technologies can successfully mitigate the environmental impact of CO₂ when refitting industries towards a sustainable future.
Various ECONNECT IQuay solutions can be utilised for marine-based transfer of liquid CO₂. Featuring industry-leading cryogenic floating hoses, CO₂ can be safely and efficiently transferred between CO₂ vessels to marine structures for offshore storage or land-based storage areas. The universal skid-mounted or semi-submersible IQuay design provides pressurised, continuous flow between structures and the operating pressure is managed by an integrated safety and control process system.
The IQuay jettyless solution can be scaled according to a project’s need, enabling the carbon capture and utilisation value chain. Benefits include:
A high degree of flexibility and can be deployed quickly and without the environmental impact of building conventional marine infrastructure
Along with transportation through pipelines, CO₂ can be transported on ships either at high-pressure state or at liquid state by cooling the gas down to the liquefaction point
Jettyless IQuay systems are fast and flexible, de-risking carbon capture projects and utilising high safety standards from the LNG industry which will be valuable lessons learned for the management of CO₂
Minimal footprint: hoses can be reeled and platform moored close to shore while not in use
Cost Efficient: significant CAPEX reduction compared to fixed infrastructure
Flexible to demand and easy to re-deploy in other CCS locations, thereby simplifying asset investment and increasing utilisation across several projects.
Stian is ECONNECT Energy’s Chief Innovation Officer and co-founder. His passion for technology development and innovation can be backed by the multiple patents to his name and he is continuously improving the technology and ensuring technical superiority within the energy and maritime industries through development schemes and prototype development. Stian also operates as Technical Manager for engineering studies, allowing customers to gain full access to his team’s key domain expertise.