Seabound: Closing the loop

Global Cement (GC): Please can you introduce Seabound to our readers?

Alisha Fredriksson (AF): Seabound is a start-up based in London, UK. It is focused on decarbonising the shipping industry by capturing ships’ CO₂ emissions directly on board using calcium looping technology. The company was established in late 2021 by myself and Roujia Wen and it now has a team of 20 people, many of whom are engineers.

GC: How does the technology work?

AF: The process uses calcium-looping technology, which is a well-established carbon capture technique. We pass the unprocessed ship exhaust gas through a carbon capture unit that is the size of a 20ft shipping container. The unit is filled with ~100mm-diameter pebbles of calcium hydroxide (Ca(OH)2), which reacts with the CO₂ to produce calcium carbonate (CaCO₃) and water.

The key difference compared to other calcium-looping systems is the use of pebbles instead of powders. Powder systems use fluidised beds, which are clearly impractical on the high seas!

GC: How well developed is the technology?

AF: The technology is robust and well-developed. So far, Seabound has carried out two pilot projects. The first was in 2023 with Lomar Shipping and its charterer Hapag Lloyd. We essentially pulled the prototype out of our London warehouse and temporarily installed it on a 3200-container vessel. The team and I took turns sailing on the vessel for months to run all the trials. We managed to capture CO₂ at about 80% efficiency and SOx at 90% efficiency. This was our first technical milestone and proof of principle in the real world.

The key learning outcome was that we found a way to modularise the system, which we then spent a year developing for our second trial, with decarbonisation technology firm STAX Engineering in Longbeach, California, in collaboration with the Norwegian ship owner Wallenius Wilhelmsen. We have discovered that the system is most effective when we position the containers close to the engines, otherwise the exhaust gas may not be at a sufficient temperature for the process to work. Preheating the gas would be a solution to this, but it goes against the sustainability ethos of what we’re trying to achieve.

Following these successful pilot projects, we are about to deploy our first full-scale commercial units, which we call Seabound Containers. This is in collaboration with Hartmann Group, InterMaritime Group and Heidelberg Materials Northern Europe. The project will equip the UBC Cork, a 5700 gross tonne cement carrier, with four Seabound Containers, as an initial commercial demonstration. More Seabound Containers will be added later.

The calcium carbonate produced in the Seabound Containers will be offloaded at Heidelberg Materials’ Brevik plant in Norway, the host plant of the first industrial-scale carbon capture facility in the cement sector. This represents a circular solution, in which the CO₂ from the ship will end up in long term undersea storage after it has passed through the Brevik plant. In the longer term, green lime, made using alternative fuels and carbon capture, will be used for the ships. We are already working with lime producers on this. There’s a lot of sustainability synergies that can be developed.

GC: How much of the ships’ cargo will be taken up by Seabound Containers?

AF: This will depend on the type of fuel, the type of ship, its speed, the distance of the voyage and other factors. However, a good rule of thumb is that the Seabound Containers will need just 1-2% of any given ship’s cargo capacity.

GC: What’s next for Seabound?

AF: We are currently starting the detailed engineering for the Heidelberg Materials project and will retrofit the UBC Cork towards the end of 2025. We will be learning on the job, as this is only the first cement carrier we have worked on – hopefully the first of many. We are looking forward to learning a lot from our first commercial deployment. It’s at a completely different scale to the pilots.

GC: What are the main barriers to rolling out this technology?

AF: I'd probably say that sourcing green lime is going to be difficult at first. It is something that the lime industry is working on, both incumbents and start-ups, but it's moving along fairly slowly. That’s why we're starting to team up with them to accelerate production.

GC: Is this predominantly a lime-sector technology, where you can offer the perfect carbon / calcium loop?

AF: There is space for both the closed loop system to operate in the lime sector and for early cement sector adopters like Heidelberg Materials. Its commitment demonstrates that there is an appetite. Another angle that we're exploring is developing a dedicated sulphur capture unit using calcium hydroxide that would produce gypsum. That’s another potential string to our bow.

GC: What impact would you like Seabound's process to have by 2030?

AF: We would like to see Seabound Containers on hundreds of vessels essentially capturing CO₂ emissions. The technology is there. The most difficult aspect is working out the process and getting buy-in from the different necessary partners. Thankfully, there are regulatory tailwinds that help us.

GC: Thank you for speaking with us today Alisha.

AF: Thank you – It was great to talk!