Designing safe CO₂ carriers for a growing CCS market

Carbon capture and storage (CCS) is rapidly emerging as a critical enabler of global decarbonization. DNV’s recent Energy Transition Outlook (ETO) estimates that 210 million tonnes per annum (MTPA) of CO₂ will be captured by 2030 and 1.3 gigatonnes per annum by 2050, equating to about 6% of global emissions. The ETO estimates that 42 MTPA will be captured in Europe by 2030 already, and a large part of this volume will be transported by ship to offshore injection sites. Therefore, the development of supporting infrastructure, including a fleet of CO₂ carriers, must continue.

Transformation of the CO₂ carrier sector

While CO₂ has been transported over long distances by sea for many decades, this has mainly been on smaller vessels with limited cargo capacities serving the food and beverage industry.

Taking this to a larger scale will involve the construction of a fleet of much larger specialized vessels, which will provide flexible transportation of CO₂ globally. This will also be complemented by the development of wider maritime infrastructure, including floating terminals and floating offshore units.

An expanding global CO₂ carrier fleet

The CO₂ carrier fleet is still in its early stages. Two vessels dedicated to specific CCS projects have been delivered in 2025, with two more under construction. Many more vessels are expected to follow over the coming years as CCS markets expand.

“The nature of the future CO₂ carrier fleet will vary from region to region,” says Mathias Sørhaug, Business Development Director CO₂ Shipping at DNV. “It can be split into three broad categories: short sea trading with vessels up to about 20,000 m³, offshore injection projects with vessels up to 50,000 m³, and vessels for long-haul trades typically serving the Asia-Pacific market.”

Adapting the new fleet to the CCS value chain

As regions like the EU, and countries like Japan and Korea, ramp up their CCS capacities over the coming decade and beyond, the need for CO₂ carriers will grow.

As this happens and maritime CO₂ transport evolves, the storage and transport conditions of the cargo will need to be adapted to the design and operation of the whole value chain. This includes capturing, intermediate storage, transport, as well as injection and permanent storage in the CO₂ reservoir.

“The most cost-efficient solution for shipping may not necessarily be optimal for the full chain,” Sørhaug notes. “Due to the strong interdependencies between the maritime elements in the logistics chain and the rest of the CCS infrastructure, collaboration across the full chain is essential to find the optimal and the most cost-efficient solutions.”

Critical design aspects for CO₂ carriers

The design, construction and operation of CO₂ carriers involve several critical aspects, which are governed by the International Code of the Construction and Equipment of Ships Carrying Liquefied Gases in Bulk (the IGC Code). This defines the specific requirements for CO₂ transport, including outlining the most common types of containment systems used for storing and transporting liquefied gases in bulk.

Given the similar storage conditions of CO₂ and LPG, it is natural for CO₂ carrier designs to draw inspiration from conventional semi-refrigerated LPG carriers. However, CO₂ presents its own considerations.

“The design of CO₂ carriers must take into account the unique properties of CO₂, which differ from other liquefied gases transported at sea,” Sørhaug adds. “This includes its combination of high density, elevated pressure conditions and low temperature, which brings challenges and design uncertainties into the design phase.”

Ensuring the feasibility of CO₂ tanks

Due to the strong interdependency between cargo tank design, tank material and overall ship design, full confidence in the feasibility of a CO₂ ship or offshore unit can only be achieved once the cargo tank concept itself is proven feasible. This creates a development dilemma in the planning and design of CCS infrastructure.

“Novel cargo tank concepts may offer cost-saving potential and enable broader optimization of the ship and potentially also the CCS value chain, for example by allowing for larger vessel capacities,” says Sørhaug. “However, such innovations require substantial development time and efforts, which can delay progress in the ship design as well as the planning of connected infrastructure.”

On the other hand, using established cargo tank technologies with qualified materials reduces the design uncertainty and can provide early confidence in the feasibility of the chosen concept. However, this approach may limit opportunities for the optimization of the ship design and overall CCS chain efficiency.

Offshore discharge and injection options of captured CO₂

The sequestration of captured CO₂ is a crucial part of the decarbonization value chain. While the options for this will be varied, it is likely that large quantities will be sent to depleted offshore oil and gas reservoirs or aquifers located offshore.

“For shorter distances and when CO₂ volumes are large, subsea pipelines will be used to transport the captured CO₂ from onshore collection points to the subsea injection point,” says Sørhaug. “However, CO₂ carriers are also expected to play a major role in transporting the CO₂ to the injection sites.”

The actual injection of the CO₂ transported to an injection site may be achieved by different measures, including direct injection from the shuttle tanker, injection via a permanently positioned bottom-fixed injection installation, and injection via a permanently located floating injection unit with or without storage.

“This will require precise control of temperature and pressure to ensure the CO₂ is stored safely and efficiently,” adds Sørhaug.

Managing CO₂ impurities in CCS transport and storage

For the large-scale CCS market, CO₂ will be captured from a wide range of industrial emitters, such as industries associated with the production of cement, ammonia, blue hydrogen or waste for power generation. Each of these industries produces a CO₂ stream with a unique contamination profile, hence potentially introducing impurities not covered by current industry experience.

The presence of impurities can affect the stream with respect to toxicity, physical properties, phase behaviour and the solubility of key components.

“Understanding the implications and limitations associated with impurities throughout the CCS value chain is essential for the cargo handling and cargo management processes, with these having commercial impacts,” says Sørhaug. “It is crucial to manage these variations to balance technical concerns and prevent issues such as corrosion and phase changes, particularly during transport and storage.”

DNV at the forefront of rules development for CO₂ carriers

In a rapidly evolving CO₂ shipping market, the development and application of dedicated notations and rules provides designers and shipbuilders with a clear regulatory foundation, enabling innovation while ensuring safety and compliance at every stage of vessel construction. DNV has taken a leading role in this space through the publication of the CO₂ RECOND notation – a world’s first class notation in the CO₂ carrier space – which sets requirements for vessels or offshore units intended for offshore injection.   

“CCS infrastructure with offshore injection may offer significant cost savings potential for the overall value chain. To support the development of these types of vessels or units we have used our experience from gas carriers and FSRUs to develop the dedicated CO₂ RECOND class notation,” adds Sørhaug.

A new fleet of CO₂ carriers within the CCS value chain

CCS markets are set for exponential growth over the coming years and decades. As more CO₂ carriers are added, it is vital that this expansion is done safely and reliably and – crucially – is well integrated into the entire CCS value chain.

“This will require close collaboration with a range of different actors so that the CCS industry as a whole can evolve in step,” concludes Sørhaug.