International shipping is responsible for 80% of world trade and around 3% of global CO2 emissions. Yet shipping is currently not on track to meet climate targets.
A year ago, the International Maritime Organization, the UN agency that regulates shipping, tightened emissions targets for the shipping sector, aligning it with other sectors that are aiming for net-zero emissions by 2050. But low-emission fuels such as methanol, hydrogen and ammonia are not coming available fast enough.
Now Jess Adkins, a chemical oceanographer at the California Institute of Technology (Caltech), thinks he can help by equipping cargo ships with reactors that can convert the carbon dioxide (CO2) released by burning fuel into sea salt, which he says can be stored for 100,000 years.
The process is similar to what already happens naturally in the oceans. “This is a reaction that the planet has been doing for billions of years,” said Adkins, who founded Calcarea, a startup that designs and tests the reactors.
“If we can just speed it up, we have a chance of a safe and permanent way to store CO2.”
Sure, but faster
Seawater naturally absorbs about a third of the CO2 emitted into the atmosphere, making the water more acidic and dissolving calcium carbonate, which is abundant in the ocean. “Calcium carbonate is what coral skeletons, shells and all the things that make up most of the sediments on the bottom of the ocean are made of,” Adkins said.
The dissolved calcium carbonate then reacts with the CO2 in the water to form bicarbonate salts, which locks in the CO2. “There are already 38,000 gigatons (38 trillion tons) of bicarbonate in the ocean,” Adkins added.
Calcarea aims to mimic this natural process by routing the ship’s exhaust fumes into a reactor in the ship’s hull, where the fumes are vigorously mixed with seawater and limestone — a type of rock made mostly of calcium carbonate that’s a common ingredient in concrete. The CO2 in the exhaust fumes reacts with the mixture, creating saltwater that traps the CO2 as bicarbonate salts. Adkins says he hopes a full-scale reactor could capture and store about half of a ship’s carbon emissions.
In nature, the reaction takes more than 10,000 years, Adkins said, but in Calcarea’s reactors it takes about a minute, he said. This is accomplished by bringing the CO2 and the limestone into close contact with each other.
The resulting saltwater is simply discharged into the ocean, where it poses no threat to marine life or the chemical balance of the seawater, Adkins said. He added that the company is also considering adding a pre-filter to the system to remove other pollutants from the exhaust that could end up in the water, such as particulate matter and unburned fuel, as well as other contaminants.
After working on the project for two years, he spun the company off from Caltech in January 2023, where he remains a professor, albeit on leave. He was joined by three co-founders: Caltech student Melissa Gutierrez, engineer Pierre Forin, and professor and geochemist Will Berelson of the University of Southern California (USC).
They raised $3.5 million in funding and set their sights on the shipping industry. “The beauty of it is that the ship is a natural water pump,” Adkins said, noting that the system requires water to be constantly moving for the reaction between the different elements to occur, something that is naturally provided by the motion of a ship.
So far, Calcarea has built two prototype reactors, one at the USC parking lot and one at the Port of Los Angeles. In late May, the company announced a partnership with the research and development arm of international shipping company Lomar. Adkins is confident that this will lead to the first full-scale prototype of his reactor being placed on a ship.
The reactors will be sized for various ship sizes, including “the largest out there,” the Newcastlemax class, which can carry 180,000 tons of cargo. “On one of these, we would take up about 4 to 5 percent of the deadweight and carry about 4,000 tons of limestone. But we won’t use all of that,” Adkins said.
Carbon capture at sea
Before Calcarea is ready to install its first reactor, there are still technical challenges to be solved. For example, how exactly the reactor will fit on the ship and the logistics of loading the limestone and setting up the supply chain to deliver it. These can be slow steps, Adkins warns.
The cost of the system is currently estimated at around $100 per ton of CO2 captured at the tailpipe. This includes the revenue the ship loses by making room for the reactor at the expense of commercial cargo.
Some cargo ships already have similar devices aboard, called scrubbers. They are designed to capture and discharge sulfur emissions — harmful to human health and the environment — but not carbon dioxide. As of June 2023, they had been installed on about 5% of the global merchant fleet, according to the British Port Association, although studies have shown that scrubber wastewater “can be acutely toxic to aquatic organisms.” Calcarea’s reactors also capture sulfur as part of their carbon removal process.
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There is also a technology that is more directly similar to Calcarea’s. For example, a British company called Seabound makes a device that captures between 25% and 95% of a ship’s carbon emissions. However, it produces solid carbonate pebbles that have to be unloaded at a port.
According to Daniel Sigman, a professor of geological and geophysical sciences at Princeton University who is not involved with Calcarea, the company’s approach has several advantages over similar strategies being pursued. First, it’s an acceleration of a natural process that would happen anyway. Second, because the reaction takes place in a designed reactor on the ship and doesn’t completely consume the CO2 supply, it won’t increase the ocean’s acidity or contribute to the problem of ocean acidification, which is harmful to marine life.
Because Calcarea’s founders are experts in the ocean’s carbon cycle, he added, they are well positioned to avoid potential pitfalls in removing CO2: “Many other companies seeking to improve ocean alkalinity don’t understand the carbon cycle at all relevant scales and therefore tend to adopt approaches that are ineffective — or even counterproductive.”
Adkins believes Calcarea can help the industry decarbonize the energy sector as it transitions to greener fuels. In the more distant future, the reactors could even take up the entire space on special vessels designed to capture CO2 from the atmosphere that has been captured on land, as an alternative to underground storage.
“We think ships can actually compete with underground CO2 storage,” he said. “Purpose-built ships that pick up CO2 and limestone in a port, go out to sea and just do our reaction — they will be just machines to efficiently and safely store carbon in the ocean as bicarbonate.”
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