The International Energy Agency (IEA) has heralded carbon capture, utilisation, and storage (CCUS) as a key enabler of emission reduction globally, representing a significant growth opportunity for the global shipping sector, especially for early movers. According to recent analysis, CCUS uptake1 needs to grow 120 times by 2050 for all countries to achieve their net zero commitments. But despite this potential, issues around CO2 transportation persist.
Pipelines vs shipping
For more than 50 years, pipelines on the seabed have been used to transport oil successfully, and this remains an option for CO2 transportation. In our recent whitepaper, CO2 impurities and LCO2 carrier design: practical considerations, we estimated that nearly 360 000 km of pipelines may be required to transport the CO2 captured from industrial processes by 2050.
Since many pipelines are still required for use in the oil and gas industry, they alone won’t meet demand. For example, the USA would need to construct somewhere between 17 700 and 37 000 km of additional CO2 pipelines before 2050.
Furthermore, terminal facilities will need to be built which connect land to subsea pipelines or to ships. Subsea pipeline and termination manifolds, as well as riser connections to fixed or floating offshore platforms, are already being studied as viable options, with trials underway.
When it comes to transporting CO2 in pipelines, there are many considerations. The CO2 must be set at a supercritical pressure of 73.8 bar and temperature of 31.1° C. In addition, constructing pipelines with the required temperature and pressure characteristics, using materials that avoid corrosion, pitting or cracking, will be necessary, taking into account the content of the CO2 stream (eg, accompanying water, nitrogen, hydrocarbons, oxygen, sulphur, and sulphides).
Although the use of pipelines in the energy sector is well established, they require a continuous flow of compressed gas, and their user costs are highly dependent on distance. Therefore, the shipping industry is increasingly being looked at as the most viable solution for safely transporting CO2, particularly when volumes are relatively low.
In fact, transporting CO2 by ship has been labelled essential by the European Commission’s EU Taxonomy for Sustainable Activities2, as well as the EU Emissions Tading System (EU ETS)3.
While transporting CO2 in pipelines requires supercritical conditions to be met, shipping it is simpler as it can be in liquefied form (LCO2). This means it can be shipped at varying temperatures and pressures, and a ship can take approximately 1/500th of the volume of CO2 transported in pipeline alternatives.
The existing fleet in operation that meets the criteria for LCO2 transportation is limited to only four carriers. They are currently serving the food and beverage industry at small capacities (~1700 tons CO2), and operating pressures in the range of 15-19 bar(a). There are currently two ships that can transport CO2 at the pressure level of 1318 bar(g).
The possibility of transporting CO2 in cryogenic conditions is being investigated. However, currently no ship can transport CO2 in the pressure range of 6-8 bar(g). Interestingly, joint industry projects, like that of ECOLOG, Hanwha Ocean, Babcock LGE, and the American Bureau of Shipping, are exploring this as a workable solution. Through the project, approval in principle has been issued for a low-pressure, 40 000 cbm LCO2 carrier.
ABS has recently issued approval in principle to Knutsen NYK Carbon Carriers (KNCC) for its novel design of a 40 000 cbm LCO2 carrier.
A first in the industry, the LCO2-EP carrier concept from KNCC aims to transport and store LCO2 at near ambient temperatures and under elevated pressure using a modular approach, allowing less cooling and potentially use of larger carriers for transport. ABS completed design reviews based on class and statutory requirements.
Trials and tribulations of shipping
Unlike onshore CO2 handling systems and transportation by pipelines, there is a lack of engineering data available on shipping CO2. This creates many challenges.
The demand for robust shipping infrastructure to allow the CCUS industry to mature, creates significant economic potential for the shipping industry, while supporting net zero targets. However, companies need to be aware that to capitalise on the opportunity, they need to invest and build dedicated LCO2 carriers to support the transportation of extensive volumes of CO2 captured.
Currently, there are no standards for shipping CO2 with impurities as cargo, only recommendations such as the ABS guide on liquefied carbon dioxide carriers. For shipping companies, following guides like these can help mitigate health and safety risks. Additionally, corrosion reactions could potentially impact the integrity of the ship and/or create harm to personnel. If liquid CO2 contains more water than gaseous CO2, it can become more corrosive
Also, a high-level of non-condensable impurities can substantially consume the volumetric capacity. For example, the presence of 10% hydrogen can reduce the capacity by 27%, which would incur a financial loss.
The density of the cargo must also be considered, in that lower-density LCO2 reduces a ship’s volumetric efficiency, and a higher pressure limits tank size, and requires increased wall thickness. The physical properties and transport conditions of CO2, and consequent issues like compression liquefaction system and power demand, need to be better understood in order to create definitive guidelines for handling and shipping.
The design of the cargo tanks should be in accordance with the International Code for the Construction and Equipment of Ships Carrying Liquefied Gases in Bulk, or IGC code. This code has been the basis for the design of cargo tanks for liquefied petroleum gas (LPG) since the 1960s.
Trials around carrier materials are also underway. New high-strength carbon-manganese steel materials are being developed by steel mills for example that could be used as CO2 carrier tank material subject to approval by the ship’s Classification Society. Trials like these are critical in that they provide more clarity around ideal pressure, temperature, and composition mechanisms so that we can create the right conditions for transporting CO2 in liquid form, throughout the shipping transport chain.
While there are some country-specific challenges, the CCUS industry globally is gathering pace, allowing many nations to unlock the possibilities of sustainable emissions reduction. However, the transportation of CO2 must be optimised in a way that takes into account human life, environmental protections, cost, and energy demand. If the industry, regulatory bodies, and government continue to collaborate on suitable CO2 applications internationally, the CCUS market will be able to thrive and support the transition to a net zero future.
1 https://www.mckinsey.com/industries/oil-and-gas/our-insights/scaling-the-ccus-industry-to-achieve-net-zero-emissions
2 https://finance.ec.europa.eu/sustainable-finance/tools-and-standards/eu-taxonomy-sustainable-activities_en
3 https://climate.ec.europa.eu/eu-action/eu-emissions-trading-system-eu-ets_en
