Stacking DAC for bankable carbon removal

Capture6 says it pairs direct air capture with water treatment plants to get around many of the bottlenecks facing carbon removal today.

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January 16, 2024
A river next to an industrial plant on a desert landscape

Photo credit: Capture6

Direct air capture has no shortage of industry enthusiasm — or government support. 

However, DAC remains among the most expensive forms of carbon removal, and struggles to scale in the face of barriers like high energy requirements. Today, removal projects are largely propped up by advance orders from the corporate world

Those are serious potential bottlenecks to meeting the goal outlined by the Intergovernmental Panel on Climate Change — up to 10 gigatons of removal by 2050 — explained Luke Shors, co-founder of DAC startup Capture6. But Shors and his team, who today announced a partnership to build a major removal facility in South Korea, think they’ve found a way to skirt the manifold challenges.

  • The top line news: Capture6 is partnering with a state-owned water utility in South Korea to build a fully integrated water management and carbon dioxide removal facility. The project includes construction of the country’s largest desalination facility, which, combined with Capture6’s technology, will process seawater to capture carbon dioxide, recover freshwater, and extract green chemicals.
  • The nuts and bolts: At the most basic level, Capture6’s DAC method requires a source of saltwater and a source of air. Carbon dioxide binds with salt stripped from the input water and creates solid, mineralized carbonates. That process generates not only freshwater, but green chemicals like hydrochloric acid and calcium carbonates, which Capture6 uses as additional revenue streams. However, the company’s solution is still untested at scale, with projects either planned or in demonstration mode.
  • The current take: “Being able to structure projects that do more than just capture carbon, but also address other environmental needs and community-driven needs, our projects are getting a lot of traction,” Shors told Latitude Media. “They’re not as reliant on the benevolence of the few corporates that are buying carbon removal.”

In Shors’ view, there are several barriers that could ultimately prevent most DAC solutions from scaling.

For instance, most DAC operates at very high temperatures, which means that in many cases equipment can’t be shut on and off without risking damage to certain components. That’s a big problem for a technology that relies on intermittent renewables — and one that restricts the tech’s geographic reach.

Then, Shors added, there’s the challenge that many of these projects are significant consumers of freshwater. By some estimates, removing one metric ton of carbon dioxide requires multiple metric tons of freshwater. (Liquid solvent-based DAC plants, like those created by Climeworks, are particularly water-intensive, requiring 9 metric tons of water per metric ton of removal.)

Finally, there’s the still-sky-high cost of most DAC. 

“If you take the current price that companies like Microsoft are paying for carbon removal, around $1000 a ton, and you extrapolate on those numbers, you get to something like we’re going to need to use 10% of the global GDP on carbon removal,” Shors said. 

(Of course, bringing the cost way, way down is a major focus of DAC innovators today, and is an explicit focus of the Department of Energy’s Carbon Negative Shot.) 

Taking DAC to the bank

Capture6’s solution to those problems is to “stack the benefits,” Shors said. “We’re not exclusively reliant on the voluntary carbon market. We can access financing because we can create bankable projects.”

Beyond carbon removal, the company's additional revenue streams include the production of freshwater and the elimination of brine waste created by industrial processes. Capture6 uses an electrochemical process to strip out salt from brine, separating sodium ions from chloride ions. Sodium ions bond with hydroxide groups from water molecules, creating sodium hydroxide, which, when exposed to carbon dioxide from the air, bonds to form sodium carbonate.

Capture6 repurposes technologies already available at desalination and water recovery plants, so its IP isn’t so much brand-new tech, but systems-level configuration of existing tech. 

Via Capture6' process, carbon dioxide binds with salt stripped from the input water and creates solid, mineralized carbonates. (Image credit: Capture6)

Typical desalination processes create one unit of brine for each unit of clean water, and often that brine gets dumped into the ocean and causes major problems for marine ecosystems. That makes both freshwater production and brine removal lucrative side gigs, Shors said.

Capture6’s “Monarch” demonstration project in Los Angeles County leans heavily on brine removal services, he added. In partnership with the city of Palmdale’s water district, the company will demonstrate its saltwater separation technology with the help of a grant from the California Energy Commission. 

Projects also produce various materials the company can recover from wastewater treatment, including lithium and magnesium. And the just-announced South Korea plant will produce hydrochloric acid and calcium carbonates as well, which the country currently imports.

“The challenge from a global perspective is we likely need to do carbon removal lots of places,” Shors said. “Although many groups are rushing towards building facilities in the U.S., we still need projects elsewhere, and this is where companies like ourselves are working on how to make this model viable across a wide range of places.”

Each Capture6 project is a bit of a puzzle of figuring out how to best deliver local value, profit, and benefits to the overall energy transition. Ideally, Shors said, Capture6’s work would ideally prompt the development of new renewable resources.

“In our ideal situation, we would bring a project that had existing offtakes for water and carbon removal to a renewable developer, who would use that offtake to launch a bigger project that would serve us and also other needs,” he added. “I don’t think there always has to be a zero sum game between DAC using renewables and taking renewables from consumers.”

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