DNV supports innovations in CO2 carrier design
To have any hope of meeting the Paris and Glasgow Agreement goals we need to remove 6–7 gigatonnes of CO2 from the atmosphere every year from 2050 onwards. Alternative fuels and energy saving will help, but too much CO2 is being emitted all the time, also as a by-product of basic industries such as steel and cement. CCS is a key element in tackling the decarbonization challenge, and time is of the essence.
Several hundred new ships needed in the next decades
Putting CO2 back underground where it came from, mostly in seabed reservoirs, is an optimal environmental solution. Northern Europe is currently leading the way with the Northern Lights joint venture developing the infrastructure from capture to storage. The government-supported Longship project, comprising capture facilities in the eastern part of Norway, will be the first end-to-end pilot to utilize that infrastructure. “Around 260 million tonnes of CO2 have been injected and stored on the Norwegian Continental Shelf since the mid-1990s as part of enhanced oil recovery (EOR) processes to maximize oil and gas extraction, so we have a lot of experience already,” says Erik Mathias Sørhaug, Business Development Leader, DNV Maritime Advisory.
“We need to rapidly deploy and scale the entire value chain from capture, storage and transport to offloading and injection for CCS to have a meaningful impact. A large proportion of the total volume, at least in the initial stages, will need to be transported by ship, making marine transport a key holistic component,” he adds. “We foresee a completely new ship segment developing on the back of increased transport demand for liquid CO2, with potentially several hundred ships coming onstream towards 2050.”
Different pressure regimes can increase CO2 cargo capacity
But different CCS applications and levels of scale may require liquid CO2 to be shipped at different pressure levels, requiring the development of low-, medium- and high-pressure tank solutions. Today CO2 is transported for commercial use in northern Europe using a handful of small ships at medium pressure. The planned Northern Lights ships will be medium pressure (15 bar at −28°C) as well, and able to carry LPG if necessary. The technology is operationally well known, but has limits in terms of tank size and materials.
Both low- and high-pressure solutions can potentially increase cargo capacity, but are novel technologies presenting new risks and challenges in ship design, construction and operations. These include tank size and optimal arrangement, material selection, condition of the captured CO2, holding time and the need for re-liquefaction, the corrosive effects of impurities in the cargo, safety considerations, reliable monitoring systems and achieving the optimal balance between cost and complexity.
High pressure technology requires less energy
“A holistic approach is decisive for choosing the most effective solution. Cost viability boils down to distance to the final storage site, the amount of CO2 to be transported (per load and on an annual basis) and the concept for offloading and injection,” says Sørhaug. Here the industry needs a clearer picture to make sound business decisions.
High-pressure (35–45 bar) technology is an interesting alternative to low- and medium-pressure solutions when looking at the cost for the whole value chain, as the ambient temperature conditions (0–10°C) require less energy to cool the gas to a cryogenic level for loading, and reheating at the unloading point. The flexibility and scalability of the cargo containment systems potentially allows the construction of very large CO2 carriers of up to 80,000 cubic metres or even more.
KNCC forges ahead in high pressure
In the vanguard of high-pressure developments is Knutsen NYK Carbon Carriers (KNCC). DNV recently awarded the joint venture between Knutsen Group and NYK Group an Approval in Principle for its new PCO2 tank concept applying principles adopted from Knutsen’s proprietary pressurized natural gas (PNG) carrier solution developed 15 years ago to carry compressed natural gas (CNG).
The CO2 is stored in bundles of vertically stacked, small-diameter pressure cylinders instead of in large cylindrical tanks.
The small diameter mitigates the risk of pressure variations within the tubes, avoids dry-ice formation and eliminates the sloshing effects of liquid CO2 in part or fully loaded condition. KNCC believes the concept will result in significant cost savings versus cryogenic strategies.