(Inside Science) -- For decades, researchers have discussed possible methods for capturing excess carbon dioxide from the air to manage climate risks, including a warming planet and increasing levels of acid in the oceans. But these CO2 molecules --composed of one carbon atom and two oxygen atoms -- are thinly dispersed in the air. Theoretical calculations of the cost to capture them vary wildly -- anywhere between $50 and $1,000 per ton of CO2.
Now for the first time, scientists have calculated the cost to design and engineer an industrial-sized facility that not only removes CO2 from the air but converts it into fuel that could power parts of the transportation sector, which is responsible for about 20 percent of carbon emissions worldwide. The analysis, based on the direct air capture pilot plant in Squamish, Canada, Carbon Engineering, shows that it would cost between $94 and $232 to pull one ton of CO2 from the air.
According to their findings, the pilot plant could extract almost 1 million tons of CO2 from the air per year. The process could be coupled with a method to store the CO2 underground. Carbon Engineering has also demonstrated that they can make fuel for vehicles. One million tons of CO2 could be converted into 30 million gallons of jet fuel, diesel, or gasoline, the researchers report. Although using the CO2 as a fuel would not reduce the total amount of CO2 from the atmosphere, it would flatten emission levels from the heavy transportation industry -- airplanes, ships, trucks and trains -- which is unlikely to become electrified for decades.
“What I hope this does is give people some confidence that our technology and some of the competitive technologies really can work at cost,” said David Keith, founder and chief science officer of Carbon Engineering, and a professor of engineering and public policy at Harvard University in Cambridge. Keith and his colleagues published the details of their analysis in today’s issue of the journal Joule.
Costs were kept down by including proven technologies from the chemical, cooling tower, and pulp and paper industries in the pilot plant's design, said Steve Oldham, CEO of Carbon Engineering.
The way it works is fairly straightforward. Giant fans suck in ambient air, which passes over a thin plastic surface that has a solution of potassium hydroxide flowing over it. The potassium hydroxide binds to CO2 molecules, capturing them. The CO2-laden solution is piped into a reactor where it’s mixed with calcium hydroxide to form tiny pellets of calcium carbonate about a millimeter across. During this process, the potassium hydroxide gets released and is recirculated for use during the initial stage. A machine called a calciner heats the pellets, releasing the CO2 as a gas that can be sequestered or mixed with hydrogen to form a hydrocarbon fuel.
“It’s the only carbon-neutral fuel in the world,” said Oldham. The company plans to license their technology to plants that would turn the CO2 into fuel. That resulting fuel would then be compatible with all gasoline-powered vehicles and filling stations, which means the technology doesn’t require that any changes be made to the transportation infrastructure.
Christoph Gebald, the founder and director of Climeworks, a direct air capture firm based in Zurich, Switzerland, said that Keith’s estimates for capturing CO2 are in line with numbers that he and his team have calculated, but have not published.
“Climeworks is confident that we will reach a cost level of $200 per ton of CO2 in the next three to five years on a small scale,” he said. As part of a much larger scale effort, he said they could achieve a cost slightly below $100 in five to 10 years.
Climeworks has nine plants around the world, two of which sell CO2 to greenhouses and beverage makers. Another six demonstration facilities are developing methods to produce fuel, and one plant in Iceland stores CO2 gas underground, where the geology and temperature mineralizes the gas into calcium carbonate rock.
Gebald said that although the cost to capture CO2 from the air is lower than originally thought, it’s still about twice as expensive as extracting fossil fuels from the ground. That creates a challenge for any company that wants to convert CO2 into fuel.
ButGebald said that CO2 gas captured from air has no impurities and could be sold as a premium fuel, or to niche markets such as the cosmetics industry. In addition, the fuel wouldn’t incur the carbon taxes that countries impose on fossil fuels, said Oldham.