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Dec 26, 2023

Meet Direct Ocean Capture

Much of the discussion around carbon removal has centered around air capture,

Much of the discussion around carbon removal has centered around air capture, but traction is also building around ocean capture that would pull CO2 from the high seas. A prominent emerging player is Captura Technologies, which has gained financial backing from Equinor and Saudi Aramco through a recent series A financing round. The company believes it can bring down costs fast, its CEO Steve Oldham tells Energy Intelligence in an interview. "The big advantage of ocean-based carbon removal is the fact that the ocean already exists, it's really big, it's a proven carbon absorber, and it's available to everybody for free," Oldham says. His previous job was CEO of Canada's Carbon Engineering, the firm Occidental Petroleum picked to develop its grand DAC ambition.

While direct air capture (DAC) intends to suck CO2 from the atmosphere, Captura's direct ocean capture (DOC) technology aims at similarly capturing CO2 but from ocean water, and then either using it or storing it underground. The facilities could either be located near the shore or be placed offshore. Captura's technology is based on electrodialysis, a process involving electricity and ion-exchange membranes commonly used to purify or desalinate water. Unlike DAC — which "inherently involves moving a lot of air, for which you need machines" — Captura's process does not require CO2-absorbing chemicals and their subsequent regeneration. "The ocean serves as the air contactor, the absorbent, and we have no byproducts," says Oldham.

Efficient Process

Electrodialysis is energy intensive but Captura, which was founded by Caltech scientists, is using a proprietary process developed at the university that is "seven to 10 times more efficient than the best commercial electrodialysis today," Oldham explains. "As a result of that, our energy use for electrodialysis is much lower than it would be if somebody was looking for a solution using off-the-shelf technology. That's why we think we'll be one-third to one-quarter of the energy requirement of today's DAC systems."

Both DOC and DAC are energy intensive, with the former requiring water to be pumped into the system and the latter requiring similar effort with air. But the volumetric concentration of CO2 in the ocean is 150 times higher than in the air — so essentially you need to do comparably less water pumping with DOC vs. air-vacuuming with DAC to get comparable amounts of CO2, says Oldham. "It's more expensive to move water, but it's not 150 times more expensive."

Roles of Aramco, Equinor

Captura also intends to take advantage of existing facilities pumping and filtering large volumes of seawater, such as desalination plants and coastal power stations. "One of the interesting things with having Aramco as an investor is Saudi Arabia has the world's largest desalinating capacity," says Oldham. He believes Aramco could add Captura technology at Saudi desalinization plants, and then combine the resulting CO2 with clean hydrogen to make synthetic fuels.

Because DOC facilities could also be located offshore, this is where Equinor can step in. The Norwegian oil company is a major offshore wind power developer. Provided appropriate policies are in place, DOC units could be attractive offtakers for offshore wind farms and avoid building expensive high-voltage links to the shore, Oldham emphasizes. "The idea of using an offshore oil and gas platform and repurposing it using our technology to be a carbon removal platform is also very appealing; and of course, those oil and gas platforms are sat on top of candidate [possible] sequestration sites."

Captura has a first one ton per year unit installed at Newport Beach, California, is building the next 100 ton/yr one, and is expecting its "final" 1,000 ton/yr pilot to be deployed in 2024. "Then our plan is that a plant developer is ready to proceed with the first commercial plant on the basis of the work that we've done on the design for large plants and the results of the pilot plants," says Oldham. "If you compare with Carbon Engineering, Occidental committed to build the first large plant before the validation plant was even finished."

More generally, Oldham thinks DOC is three years behind DAC but "hopefully will catch up." A few years ago, DAC "wasn't widely understood or acknowledged." It is now part of the US' Inflation Reduction Act (IRA) and is eligible for several European funding schemes. The US' generous 45Q tax credit for carbon sequestration was "very much written" for DAC, says Oldham, but the US' Internal Revenue Service has recently launched a call for comment on that scheme, to which Captura responded. "If the 45Q was widened to include other forms of technological carbon removal like ocean capture, then I think you'll get to deployment pretty quickly."

Quick Cost-Cutting

In terms of cost, Captura is confident it can achieve removal and sequestration at less than $100 per ton. This is comparable to what DAC companies are targeting, but Oldham believes Captura can reach that level much more quickly because its technology is less capital intensive and more modular. "Fundamentally, with the technology that we have in-house today, we can achieve that price point; if somebody contracted us tomorrow to build a first industrial scale system, I'm confident we'd be at that price point."

Oceans absorb about 25%-30% of human CO2 emissions every year, according to scientists. While the ability of oceans to capture and store carbon has slowed the accumulation of atmospheric CO2 — and, hence, the pace of global warming — this has come at a cost. CO2 is causing seawater to become more acidic, with negative impacts on marine life, notably shells and corals. To address this, DOC promises to discharge decarbonized water back into the ocean and allow it to extract more CO2 from the atmosphere with minimal impacts.