“Technically, anything is possible”: retrofitting for carbon capture

Onboard carbon capture could help existing ships cut emissions, but fitting it to vessels never designed for it raises hard questions about space, stability, energy and delivery.

As shipping looks for ways to cut emissions, attention is not only on the fuels and vessels of the future. Ships already in service will also need options for reducing their carbon footprint. Onboard carbon capture offers one possibility.

Rather than preventing carbon dioxide (CO₂) from being produced, the technology captures it from a ship's exhaust before it reaches the atmosphere, with the captured carbon stored onboard for later offloading.

The challenge for existing vessels is, of course, that they were never designed to have the systems on board in the first place. “Technically, anything is possible,” says Su Len Quach, General Manager, Integration Engineering & Market Development at Wärtsilä. “Rather than starting with the technology, the bigger question is what makes sense commercially and operationally for the customer.”

A question of space, weight, and placement

Invariably, installing carbon capture equipment requires space. As a general rule of thumb, the more carbon a shipowner wants to capture, the more storage – and thus space needed. What space is available – or in the case of cargo vessels, how much capacity a shipowner is willing to give to the system – is a crucial question for retrofitting. Other considerations include “weight and where the installation would happen on the ship, as these impact stability,” says Quach.

Carbon capture systems need to connect with the exhaust gas, which can push some equipment relatively high on the vessel. The CO₂ tanks, meanwhile, can be much heavier than the capture plant itself and may benefit from being placed lower on the vessel.

Existing equipment and pipework add another layer of difficulty. As Chara Georgopoulou, Head of Maritime R&D and Advisory Greece at DNV, points out, technical adaptability includes considering whether “there is space available, there is enough power available” and whether the retrofit would require “re-routing of some pipes.”

“Everything needs to be designed to interact in a safe way with the rest of the machinery.”

The energy equation

Like all onboard systems, carbon capture requires energy to operate. That energy can come from two sources – electricity and heat. For the latter, the aim is to make use of heat the vessel is already producing rather than adding further fuel demand.
“We want to utilise waste heat,” says Quach, “because otherwise you would kind of burn fuel just to take out CO2.”

But that does not mean waste heat is a simple solution. The vessel also needs heat for other purposes, while a higher capture rate increases the heat demand from the carbon capture system itself. Quach says part of a retrofit project could include optimising the vessel’s own heat consumption to make more available for the carbon capture system.

Georgopoulou also points to the interaction between the capture system and the ship’s existing machinery. Some carbon capture processes can be energy intensive and may require additional technologies to improve the net performance of the overall system.

A good example, Georgopoulou says, is auxiliary engine economisers. Liquefying carbon dioxide onboard can increase engine load and produce more exhaust heat. With the right design, “that recovered heat can be used to produce steam for the capture process, helping the system meet part of its own heat demand,” says Georgopoulou.

From design to delivery

Even after feasibility work, the challenge does not end with a design that looks workable on paper. Retrofit projects can still bring surprises once the vessel reaches the yard.

“Every retrofit project brings surprises. The key is being prepared to manage them,” says Quach.

Reflecting on his experience retrofitting the LPG tanker Clipper Eris with a carbon capture system, Quach says, collaboration between the technology provider, shipowner and yard is central to making retrofitting projects work.

“You need a strong partnership with all stakeholders and a shared goal – to deliver a high-quality vessel. Close relationships help teams navigate challenges quickly when inevitable surprises arise.”

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Main image: Two container ships navigating a busy shipping lane
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