气候变化领域集成服务门户

[Photo: Heirloom + CarbonCure] By Adele Peters5 minute Read

Hidden behind a long white warehouse in an industrial neighborhood south of San Francisco, the first direct air capture facility in the U.S. is sucking CO2 out of the air.

Inside a tall structure covered in chicken wire and netting, stacks of trays stretch 20 feet into the air, each filled with calcium oxide. In nature, the mineral captures CO2 over geologic timescales and forms limestone. By tweaking that process, Heirloom Carbon, the startup running the plant, can speed it up to happen in around three days.

The technique is based on academic research from five scientists, and the company is racing to make it a feasible way to fight climate change at a large scale.

At the beginning [in the lab], it was petri dishes with grams of CO2 capture potential, says CEO Shashank Samala. That s where we were a couple of years ago. We ve increased the tray size about 100 times, and then we engineered a system that is fully automated . . . that can capture thousands of times more CO2.

The startup has an audacious goal: It wants to be able to pull 1 billion tons of CO2 from the air every year by 2035. (That s roughly the size of the airline industry s annual emissions; in total, society emitted around 40 billion tons of CO2 last year.) By the middle of the century, we ll need to be able to remove as much as 10 billion tons of CO2 from the atmosphere annually to keep the world from heating up 1.5 degrees Celsius. That s in addition to all the work that businesses and governments need to do to cut emissions from cars and power plants and every other part of society.

Dozens of companies are working on new ways to capture CO2 from the air reliably and permanently. But it s often expensive. The world s first carbon removal plant, in Iceland, uses fans to suck air through large carbon-collecting equipment before the CO2 can be injected underground for storage; the technology costs hundreds of dollars per ton of CO2 captured.

Heirloom s approach has the potential to become affordable more quickly, with the aim to sell carbon removal credits for less than $100 per ton by 2035. The company starts with crushed limestone, heating it up in an electric kiln that runs on renewable electricity. The heat breaks the rock down into pure CO2, which the company captures, and calcium oxide powder. When the powder is placed outside in trays and mixed with water, it begins to capture CO2 from the air, forming limestone.

I think one of the really big strengths of what they re doing is they have a fairly simple chemistry, says Anu Khan, deputy director of science and innovation at Carbon180, a nonprofit focused on carbon removal. It s not super complicated. . . . They re starting with something that is naturally occurring. And that lets them focus on all of the other engineering challenges that arise when you re trying to do direct air capture.

Two other companies, Calcite and Parallel, are working on similar approaches.

At Heirloom s pilot site near San Francisco, nearly 90 trays sit in each stack, though the towers can go higher. A machine moves up and down the stacks of trays, using sensors to analyze each tray and add water to optimize the process. After a few days, when the limestone has formed, it goes back into the kiln and the CO2 is removed, compressed, and put into cylinders that can be delivered elsewhere for permanent storage. When the calcium oxide powder comes out of the kiln, it can go back on the trays.

The circular process from limestone to powder to limestone, on repeat keeps costs and the company s environmental footprint low. The process also uses less energy than other techniques. We want to use as little energy as possible by working with nature, Samala says. It also uses little land, unlike some other limestone-based approaches that spread crushed rock over large areas.

There are nature-based ways to capture CO2 from the air, including protecting and restoring forests. Such methods are important, but they aren t permanent solutions; if a tree burns in a wildfire, the carbon goes back in the atmosphere. It s hard to measure exactly how much carbon is stored in a forest. (Heirloom, by contrast, can weigh its CO2 cylinders to measure the total amount captured.) It s also hard to prove that a particular project definitely prevented deforestation; many offsets may not actually help.

Relying on trees also requires large amounts of land. One recent study calculated that there isn t enough land available to feasibly meet climate pledges that countries have made under the Paris Agreement. Heirloom says its current configuration uses land around 5,000 times more efficiently than a tree. We need to plant as many trees as possible, Samala says. And in addition to that, we need to also look for land-efficient ways to remove carbon, like this one.

Last week, the company announced that it had partnered with CarbonCure Technologies, a company with technologies designed to sequester CO2 in concrete. Heirloom sent its first batch of its CO2 to a local concrete company a client of CarbonCure s which successfully injected it into concrete. The process both reduces the carbon footprint of the final concrete and makes it stronger. When it s mineralized into concrete, the CO2 is permanently sequestered, even if a road or building made from the concrete is later demolished.

Heirloom plans to build plants next to geological storage sites places where CO2 can be injected underground for permanent storage by partner companies. The federal government is working to speed up the process of permitting sites where this can happen. In the meantime, Samala says, the CO2 can be sequestered in concrete. And Heirloom can sell its carbon removal services to companies that want to offset their own carbon footprints.

There s growing corporate interest in this type of permanent, measurable CO2 capture. The tech company Stripe, an early corporate pioneer in supporting permanent carbon removal, committed to buy carbon removal services from Heirloom before the startup had built its first pilot. Microsoft, Shopify, and other companies are also customers. But finding more corporate customers is crucial for the company to succeed, Samala says.

Fundamentally, it s all driven by corporate offtake, Samala says. That demand signal that we get from customers allows us to invest in mass manufacturing and scale up, and also lots of R D investment to simplify and optimize our process.

Companies like Stripe helped us start the race, he adds. We need 1,000 more corporate [partners] for us to continue the race.

Correction: This post was updated to clarify the nature of CarbonCure s business.

Adele Peters is a staff writer at Fast Company who focuses on solutions to some of the world's largest problems, from climate change to homelessness. Previously, she worked with GOOD, BioLite, and the Sustainable Products and Solutions program at UC Berkeley

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