Ships have the ability to store the carbon dioxide they produce beneath the water’s surface

Ships can capture their own carbon emissions by bubbling exhaust gases through seawater and limestone, and returning the water to the ocean. This has the potential to save space and energy compared to other systems, but it is unclear what the environmental impact will be.

This system utilizes the natural reaction between carbon dioxide and calcium carbonate (also known as limestone). “The ocean has been doing exactly this for billions of years.” jess adkins Calcarea, a startup that developed the technology.

When seawater absorbs CO2, it becomes acidic enough to break down limestone. The dissolved rocks react with CO2 in the water to form bicarbonate minerals, which can remain stable in the ocean for thousands of years. This is one of the main ways Earth removes CO2 from the atmosphere over long timescales.

For decades, Adkins and his colleagues Studied As oceans become more acidic due to rising levels of carbon dioxide in the atmosphere, a study shows how this dynamic affects organisms with shells and skeletons made of calcium, such as corals. They realized that by increasing the dissolution rate of limestone, more carbon dioxide could be converted into stable bicarbonate. One way to do this was to increase the concentration of carbon dioxide in contact with the limestone. “[the reaction] With pure CO2, it goes orders of magnitude faster,” Adkins says.

Researchers are currently designing a way to capture carbon from ships using this process. Ships account for about 3 percent of anthropogenic CO2 emissions, and options for reducing ship footprints are limited.

Tests in California demonstrated that the two prototypes can convert at least 30 percent of the CO2 in a diesel engine’s exhaust gas into bicarbonate, Adkins said. They are currently working with the research department of global shipping company Romer Shipping to test the system onboard ships.

Shipboard testing involves compressing the exhaust gas and foaming it in large volumes of seawater, using the ship’s motion as a water pump to save energy. The more acidic water flows over crushed limestone, forming bicarbonates, which are then released into the ocean.

Adkins said the technology does not consume as much space and is more flexible than other approaches, which require captured emissions to be stored onboard and unloaded at a dedicated port. states. Still, he estimates that the Calcarea system will take up about 4 percent of the space on large bulk carriers sailing long voyages.

Phil Renforth Researchers at Heriot-Watt University in the UK say the idea is interesting but could face some problems. For one thing, he says, this approach likely won’t be able to capture all the CO2 from the exhaust gas without an impractically large nuclear reactor. As options for low-emission marine fuels increase, it may prove to be a better option than capturing exhaust gases.

“We also need to know a lot about the consequences of scaling this up,” he says. Bicarbonate is abundant in seawater, so its release into the ocean is not a concern, but other compounds in exhaust gases can have negative effects on ecosystems, he said.

Many ships already use systems that drain sulfur pollution from their exhaust gases into the ocean. But the world’s shipping and high seas regulators remain divided over how to deal with plans to store CO2 in the ocean.