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Carbon Capture Heads Out to Sea

Seabound is out to scrub carbon from shipping exhaust.

Mirror images of ships.
Heatmap Illustration/Getty Images

If the global shipping industry were its own nation, it would be the sixth largest emitter of carbon dioxide, belching about a billion tons of the stuff into the atmosphere every year. And not to state the obvious, but the sector isn’t going anywhere. Not only is cargo shipping the means by which 80% of global trade is carried out, but transporting goods via ship is actually much more fuel-efficient than the alternatives.

That means that slashing shipping emissions, which account for nearly 3% of the global total, is 100% necessary for a decarbonized future. But unlike most other industries, there’s a global regulatory body — the International Maritime Organization — that can set goals and mandates to ensure that decarbonization happens on schedule. The IMO is targeting net-zero shipping emissions by 2050, with a 40% reduction in the carbon intensity of international shipping by 2030 compared to 2008. And while these goals aren’t binding, forthcoming measures set to be developed and adopted late next year will be.

Shipping decarbonization is still in its early infancy though, meaning the pathway to net zero remains highly unclear — and that there’s lots of room for technological innovation. One company that’s gained traction in the past few years is aiming more at the “net” than the “zero” part of that equation — rather than develop clean fuels, UK-based startup Seabound is retrofitting ships with onboard carbon capture devices. The process uses a technology called calcium-looping that allows the company to capture carbon from the ship’s exhaust system, essentially locking it up in a limestone rock, and then process it later on land.

Though it’s relatively unproven, onboard carbon capture has the potential to gain ground quickly if it can be shown to work at scale. But precisely because thetechnology is unproven, the industry is far from unified in the idea that it will play a consequential role in the final decarbonization picture. “Alternative fuels are probably going to be the dominant solution,” Aparajit Pandey, shipping decarbonization lead at the think tank RMI, told me.

Indeed, low and zero-carbon fuels made from green methanol or ammonia (which are themselves made from green hydrogen) are widely considered the leading contenders in this space — while methanol does produce some CO2 when burned, it’s much cleaner than fossil fuels due to its low carbon and high oxygen content, and ammonia contains no carbon at all. But it could take a while to ramp up production to meet the industry’s ravenous fuel demand. Plus, repowering an existing ship with ammonia or methanol requires an expensive and time-consuming engine retrofit, and turning over the entire global fleet could take decades.

Other ideas and approaches abound. Biofuels? They come with a familiar host of concerns, plus fuel production is inherently limited by the amount of biomass that’s available. Solar-powered ships? Folks are trying, but current panels aren’t nearly energy dense enough to power a freighter on their own. Electrifying ships? It definitely makes sense for smaller vessels like ferries and tugboats, but batteries also take up a lot of space that could otherwise be used for freight. They also need to be either charged or swapped, requiring infrastructure that just doesn’t exist yet.

“Carbon capture is probably the only way that you can get a meaningful amount of emissions reduction in any near term way,” Clea Kolster, partner and head of science at Lowercarbon Capital, told me, referring to the cargo shipping industry. Lowercarbon led Seabound’s $4.4 million seed round two years ago.

This is not a zero sum calculation, however. Seabound CEO Alisha Fredricksson told me that she believes both methanol and ammonia fuels have a significant role to play. “They’re just taking a long time to develop. And so we won't have sufficient supply for another 10, 20 years or so.”

Seabound’s system works by reacting the CO2 in a ship’s exhaust gas with calcium oxide to form solid calcium carbonate (aka limestone). This essentially locks the carbon away in small pebbles, which are unloaded when the ship docks. Because Seabound doesn’t purify or compress the CO2 onboard, the company says its system requires “negligible” amounts of additional fuel to operate. Once on land, the plan is for Seabound to either sell the limestone for use as a building material or to separate the CO2 and calcium oxide; the latter could then be reused to capture more carbon, while the former could either be used to produce methanol shipping fuel or geologically sequestered.

There are other companies attempting onboard carbon capture: Value Maritime, Mitsubishi, and Wartsila, among others, all of which rely on amine-based systems, a well-proven technology for carbon removal on land. But Fredricksson told me that miniaturizing these systems to work on ships is much more capital and energy intensive than Seabound’s decoupled approach, which allows the company to capture the CO2 at sea and process it later on land. This older tech also produces liquified CO2, which she says ports are less equipped to handle than a solid material like limestone.

Seabound completed its maiden voyage earlier this year, leaving from Turkey and traveling around the Middle East in a months-long trip that put their tech to the test in the real world for the first time. The system was installed on a freighter from Lomar Shipping, and was able to capture carbon at 78% efficiency and sulfur, a pollutant that can cause respiratory problems and acid rain, at about 90% efficiency while it was running.

Fredricksson and the company’s backers deemed the voyage a great success. “We hit the results we were looking for,” she told me. But in the grand scheme of things, the pilot was still quite small-scale. Seabound’s system only captured about 1 metric ton of carbon per day, a tiny percent of the ship’s overall emissions. That’s because the system was only running for a total of around 100 hours during the two months it was at sea. The objective, Fredricksson told me, was not to capture as much CO2 as possible, but to demonstrate the technical feasibility of the system and prepare for future scale-up.

Ultimately, the company hopes to capture up to 95% of a ship’s carbon emissions. But similar to batteries, this involves a space-related tradeoff. A larger, more effective carbon capture system would mean less room for cargo. “So I think the main goal for our engineering team over time will be to increase the efficiency to pack more and more tons of CO2 into each container,” Fredricksson told me. Right now, she says that 10- to 14-day voyages are Seabound’s sweet spot, given the size of its systems. The company hopes to build its first full scale system by the end of this year and start delivering to commercial customers in 2025.

The degree of interest in Seabound’s systems will depend in no small part on forthcoming directives from the IMO. As of now, there’s a rule mandating that ships calculate their energy efficiency and report it to the organization. Fredricksson says it’s already getting harder to sell ships with lower ratings. Pandey said he thinks future regulations could resemble the FuelEU initiative, which requires a steady decrease in the emissions intensity of shipping fuels over time, from 2% in 2025 to up to 80% by 2050.

While it’s unclear how a rule like this would incorporate onboard carbon capture into its framework, Pandey told me that if Seabound can prove out its tech on a larger scale, the approach is promising. “Of the carbon capture solutions that are out there, they’re probably the most innovative,” he told me. But he’s not sure that the company’s aim to commercialize by next year is realistic. “From now to prove it out to scale, who knows? Five years, six years, seven years, something like that,” Pandey guessed, “I think it could be viable, but it's so early.”

A recent report on the potential of onboard carbon capture from DNV, an organization that maintains technical standards for ships, agrees that a longer timeline is more likely, stating that, “With the wider [carbon capture, utilization, and storage] infrastructure in development, scaling up of the maritime carbon capture network will take time and is expected to reach a broader uptake after 2030.”

Since returning from its first voyage, Seabound has reconfigured its system to fit into modified shipping containers that are intended to reduce retrofit time and costs. Now, if a shipowner wants to use Seabound’s system, the primary modification involves installing pipes to route exhaust from the ship’s smokestack or funnel to the company’s carbon capture device. Fredricksson estimates installation costs will be on the order of $100,000 per ship, though that will vary greatly depending on vessel size and type.

But if that estimate is in the right ballpark, it would be orders of magnitude cheaper than retrofitting a ship with an engine built for ammonia or methanol fuels. And yet Pandey isn’t so sure ship operators will be keen on either upgrade. “My strong guess is if they’re not going to retrofit a vessel for a new engine, they’re also not going to retrofit it for carbon capture,” Pandey told me.

Fredricksson expects Seabound will raise a Series A round later this year or early next, to help get its first commercial units off the line. And apparently, there’s been loads of investor interest. “Shipping and maritime is new for the climate tech ecosystem,” Fredricksson told me, meaning there’s lots to be gained by moving quickly and early. “There is so much CO2 out there being emitted by ships,” Fredricksson said, “and not a lot of solutions yet going after them.”

Katie Brigham profile image

Katie Brigham

Katie is a staff writer for Heatmap covering climate tech. Based out of the Bay Area, she formerly worked as a reporter and producer for


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