With the specter of global warming seared into our national consciousness, reducing carbon dioxide emissions has become a priority. Now, researchers have invented a phone-booth-size device that can take back those emissions we can't prevent--the ones that have already reached the atmosphere.
The Atmospheric Carbon CapturE SystemS (ACCESS) Air-Capture System, developed by Global Research Technologies in Tucson, Ariz., holds sheets of material capable of capturing CO2 molecules directly from open air. (The chemical makeup of the fabriclike sorbent is being kept under wraps.) While that may sound tricky enough, "the hard part," says Klaus Lackner, a geophysicist at Columbia University, "is prying the carbon dioxide loose once you absorb it." Lackner worked with Global Research to create the technology.
To remove the molecules, the sheets are sprayed with a chemical solution that bonds to the carbon dioxide. The solution is then drained off to a separation unit, where the CO2 is isolated as pure gas through electrodialysis. A design goal was to avoid using toxic or corrosive chemicals that would require special handling, so ordinary PVC pipe is used to transfer the solution back to a collection unit so that it can be recycled.
Ideally, the ACCESS machines would be placed in clusters, similar to windmill groupings, near facilities capable of storing the carbon permanently. Unlike turbines, however, these devices can be placed anywhere. Locating them in windy areas would increase their efficiency by moving air across the surfaces more quickly, but they are not dependent on a strong breeze. "A windmill is not producing energy when the wind isn't blowing, but the carbon-capture device can capture carbon, no matter what," Lackner says.
The current prototype captures less than 100 kilograms of CO2 per day, but Lackner predicts future models will capture 1 ton per day--several hundred times the amount saved by an equal-size windmill. New versions of ACCESS could capture carbon at a rate of about 3 kg per second, the same amount an average tree absorbs in a year. Still, millions of these devices would be needed to significantly cut global emissions. The Department of Energy estimates that the United States alone released 7075.6 million tons of CO2 in 2006.
Skeptics of the technology point to carbon emissions coming from ACCESS and similar devices themselves. Because it uses electricity from the grid to separate gas from the solution, the prototype barely breaks even in CO2 savings. Global Research hopes to run future models on solar power, which would take fossil fuels out of the equation. The price of capturing the CO2 is also high, predicted to cost several hundred dollars per ton once commercially developed. "In the long term, the price will come down to $30 per ton," Lackner says, "but this will not happen overnight."
The usefulness of carbon-capture technology hinges on the development of practical methods for storing carbon, which the industry does not predict to be commercially viable before 2020 or later. Lackner says the ACCESS system could be paired with any form of carbon sequestration being developed, including underground or underwater storage. His preferred method is to pack carbon away Han Solo-style with mineral carbonation, a process that turns CO2 into a solid by mi it with other compounds. In addition to storage, the captured CO2 could be used commercially for oil recovery, preserving food and increasing plant growth in greenhouses.
The next step in developing the carbon-hungry machine is to design a model that can be easily mass produced. The technology won't be ready tomorrow, but it's not far off. "If it's five years," Lackner says, "we run an awfully slow outfit."