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California Startup Capturing Carbon With Cheap and Plentiful Limestone

Capturing carbon dioxide by pulling it out of the air is one of the most effective ways to battle climate change, but the process has traditionally taken too much time and money to be cost-effective. California startup Heirloom Carbon Technologies thinks it has the answer by using cheap and plentiful minerals like limestone, to capture carbon quickly. High-profile investors like Bill Gates’s Breakthrough Energy Ventures are betting the company will succeed.

Heirloom, based in San Francisco, says it can remove carbon dioxide for $50 a ton once it reaches commercial scale – much cheaper than the estimated $94 to $232 a ton it would cost with other approaches. Heirloom’s goal is to remove 1 billion tons of carbon by 2035.

According to the MIT Technology Review, Heirloom’s process involves cooking ground limestone (also known as calcium carbonate) or other materials at high enough temperatures to break the materials down and release the carbon dioxide inside. The leftover limestone, or calcium oxide, is then spread out in hundreds of trays stacked 20-feet high and exposed to the air, where it bonds with carbon. 

Heirloom’s goal is to have the bonding occur within two weeks or less, whereas usually, it would take about a year. That carbon would then be captured, compressed and injected underground, where it would remain.

“It looks like cookies in a baking tray,” Heirloom CEO Shashank Samala told Bloomberg in a recent interview. “We’re trying to simplify as much as possible.”

Getting the infrastructure in place requires money. On March 17, the company raised $53 million in a Series A funding round co-led by Carbon Direct Capital Management, Ahren Innovation Capital, and Gates Breakthrough Energy Ventures. The Microsoft Climate Innovation Fund also participated. Additionally, Alice Newcombe-Ellis will join Heirloom’s board of directors.

The dollar amount represented one of the largest-ever private funding rounds in the field of direct-air carbon capture. Heirloom will use the money to fund research and development, and the company has tested different parts of the process. Part of the funds will be used to build a pilot plant by next year.

For investors, the main attraction is Heirloom’s ability to do the job quickly and inexpensively by relying on abundant and affordable minerals and proven technology at a commercially viable scale.

Photo Courtesy Roberto Sorin

“The costs of Direct Air Capture have to come way down to make a meaningful impact on climate change,” Samala said in a press release. “Utilizing low cost, earth abundant minerals as a sponge for CO2 is key to making the economics work. In the ten months since we launched, we’ve made a breakthrough in the rate we take up CO2 from the atmosphere, giving us a clear path to ultra-low cost, highly scalable carbon removal, and achieving our mission to help reverse climate change.”

Heirloom was founded in 2020 by a team of entrepreneurs and carbon renewal experts. Their mission was to enhance the natural carbon mineralization process so the minerals can absorb carbon dioxide from the ambient air in days rather than years. The company’s clients include Stripe, Shopify, Klarna Bank AB, and Wise Plc.

Stripe said it has agreed to pay more than $2,000 a ton to Heirloom, though that price will drop considerably as the technology scales up. Heirloom’s goal is to lower the cost to as little as $50 a ton.

Rivals in the direct-air carbon capture space include Switzerland’s Climeworks AG, which has sold credits to Gates for as much as $600 a ton; and Canada’s Carbon Engineering Ltd., which has been working with Occidental Petroleum to build a plant that could capture as much as 1 million tons each year.


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