Does CCS stack up?

Carbon capture and storage (CCS) is gaining widespread attention as a way towards ‘Net Zero’ but a CO₂ value chain is required before the maritime industry can give serious consideration to the commercial transportation of this primary greenhouse gas. What’s more a number of technical obstacles need to be hurdled if there is going to be industry wide take up of CCS technology aboard all vessel types, including passenger ships.

Financial constraints have already resulted in delays to the planned 2026 commissioning of a carbon capture plant in Oslo, Norway, with inflation, geopolitical instability, energy and raw materials pushing cost calculations for Hafslund Oslo Celsio’s Klemetsrud plant way beyond the initial US$518.88 million price tag.

Any further delays to plant commissioning will inevitably have a knock-on effect on the 7,500cbm Northern Lights vessels being built to ship CO₂ from industrial sites in Europe to the receiving terminal in Øygarden, Norway, from where it would be injected into rock formations on the North Sea seabed. If we assume the same issues are impacting similar projects elsewhere, then meeting the Paris Protocol ambition of a 1.5°C temperature drop is improbable. The targeted Celsius reduction means limiting carbon emissions to 450ppm and “we are already at 420ppm. The time gap is narrowing very quickly,” one analyst revealed.

Transporting CO₂ in its gaseous form is technically feasible and transporting CO₂ as dry ice is also possible but the volumes make liquefaction a better solution, with most maritime projects looking at developing onboard liquefied CO₂ containment systems.

However, while a LCO₂ system is likely to be based on a bi-lobe, tri-lobe or cylindrical Type C cargo tank, simply using a tank designed for LNG or LPG containment is not an option. As Knut Erik Heggem, Sales Manager at Wärtsilä Gas Solutions (WGN), explained: “There are so many different implications [connected with] carrying liquid carbon dioxide that [we cannot] just have a conventional tank that’s already in common use; it’s got to be a new design, a new concept.”

Heggem furthered that CO₂ is about 45% heavier than LPG and LNG. And for larger LCO₂ carriers, containment tanks need to withstand different design pressures and temperatures. The operating envelope of a LCO₂ tank needs to be above the ‘triple point’ for pure carbon dioxide, which occurs at 0.5 MPa (5bar) and -54.4°C.

Essentially, CO₂ is stored at high pressures and low temperatures to maintain its liquid state. This means special attention must be given to insulation systems and pressure relief mechanisms to prevent excessive pressure build-up or temperature fluctuations during transportation.

While LCO₂ tanks would not need an inert gas system, they would need to be vented very carefully to protect crews entering the tank (CO₂ is toxic) but also to prevent ice from forming in the tank. Venting during transportation would be an important operation to prevent over-pressurisation, which, depending on the size of the tanks, could require several thousand cubic metres of dry air.

Knut Arild Kaupang, Sales Director with Survitec’s Maritime Protection division, the safety company WGS approached as part of its research into the development of a medium pressure LCO₂ containment system, said if you put in “ambient air with a high dew point it will start snowing inside. We already have the technology. It needs a slight redesign, but we basically have a solution ready. It is very similar to our dry inert gas systems, we just remove the inert gas part.”

Despite the potential for liquefied carbon dioxide to solidify into dry ice should relief valves fail and pressure falls below 5 bar, tanks will need to be built from sturdier, heavier materials which, due to stability reasons, will have to be accounted for at the ship design stage. This may also require larger ballasting requirements. Certainly, steel thickness above 50mm or high tensile steel could be difficult to achieve classification certification, while a 5% nickel steel could be too much of a financial stretch for a vessel transporting a waste product that currently has no discernible trade value.

Tank lifespan is also an issue. One analyst we spoke to suggested that containment and cargo handling systems could be capable of only three of four round trips before they need replacing due to structural fatigue. While this needs further exploration, tank fatigue is a challenge and no vessel would be accepted into class if it was capable of only a few years operational life.

Nevertheless, despite these technical challenges, classification society DNV – which is involved in a number of land-based and maritime CCS projects, including the aforementioned Northern Lights vessels – foresees a market in which a fleet of LCO₂ tankers would be chartered by shore-based industrialists, manufacturers and energy producers to ship the waste from A to B. However, substantially larger vessels than those currently on the drawing board would be required.

DNV’s Business Development Director, CO₂ Carriers, Erik Mathias Sørhaug, suggested that between 50 and 150 vessels would be required to transport 5.8Gt of CO₂ per year to meet emissions reduction targets. He said it could be more by 2050 “if we are to be close to meeting the Paris agreement targets.”

For those vessels using CCS to simply clean up exhaust emissions rather than carrying it as cargo, the same storage issues apply, albeit to a lesser scale. A burning question is which fuel is best for onboard capture.

Sørhaug said: “HFO it potentially cheaper than LNG, but HFO would require more treatment of the exhaust before capturing the CO₂. Depending on the extra fuel consumption onboard carbon capture may become a competitive alternative to green fuels which are expected to become more expensive.”

Internal data from Wärtsilä test stations show that 10% extra power is needed to capture 70% of CO₂ emissions. 80% capture is possible but then the extra power needed exceeds 10%, according to Heggem.

For passenger vessels, particularly cruiseships, there are the obvious safety concerns, but available space is currently the prohibiting factor. Carnival Corp, for instance, “thinks it has potential on a limited scale in cruise ships, due to the relatively small storage space available”, compared to other commercial vessels like bulk carriers or tankers. Certainly, retrofitting existing vessels with CCS technology poses challenges in finding suitable locations for installation without compromising passenger comfort or operational and energy efficiency.

The implementation of CCS technology involves substantial upfront costs, including the installation of equipment, infrastructure modifications, and ongoing operational expenses. These costs can be a significant barrier, particularly for merchant vessels that operate on tight profit margins. Assessing the economic viability and potential return on investment for CCS implementation can pose challenges, as the technology is still in its early stages and cost-effectiveness may vary depending on vessel type and operational profile.