"Fossil fuel supplies are plentiful, and what will limit the usage of fossil fuels is the potential climatic and ecosystem changes you may see as a result of rising CO2 levels in the atmosphere," said Los Alamos researcher Manvendra Dubey. "If you can capture atmospheric carbon dioxide, then you limit the environmental impact of fossil fuels and you can continue to use them. We have come up with a way to capture and sequester the carbon dioxide that we are putting in the atmosphere. Our approach is particularly well suited to capturing CO2 from numerous small sources such as automobiles that are largely being ignored."
While many scientists are working on capturing or sequestering carbon, Dubey and his colleagues' method differs because it works on a dilute stream of CO2 in the atmosphere as opposed to capturing more concentrated forms found in power plant exhausts. The method uses ordinary air with its average carbon dioxide concentration of about 370 parts per million.
It utilizes the wind and natural atmospheric mixing to transport CO2 to a removal site, and it is the only means available to capture CO2 generated from transportation sources and small, dispersed sources that account for nearly half of all carbon dioxide emissions.
The air is passed over an extraction agent, for example a solution of quicklime, the active agent in some cement. As the air passes over the extraction structure, the carbon dioxide in the air reacts with the quicklime and becomes converted to calcium carbonate (limestone), a solid that forms and falls to the bottom of the extractor.
The calcium carbonate is then heated to yield pure carbon dioxide and quicklime, which is recycled back into the extractor. The purified and liberated carbon dioxide can then be sequestered as a gas by direct injection into the ground or it could be reacted with minerals to form a solid. Carbon dioxide gas also can be sold commercially to the petrochemical industry, which uses large quantities of it to extract fossil fuels. Of course, because the process uses existing air, it does not need to be located near any particular elevated source of carbon dioxide. It captures carbon dioxide from all sources by harnessing wind as a no-cost transportation vector.
"The carbon dioxide comes to the facility on its own," Dubey said. "And because treated air is discharged, the overall concentration of carbon dioxide in the atmosphere gradually decreases over time. Using this method on a large enough scale, it may be possible to return atmospheric carbon dioxide levels to pre-Industrial-Age concentrations. Given the possibility our climate system can change abruptly, this possibility is very exciting."
Cost of the entire process is equivalent to about 20 cents/gal of gasoline—a nominal cost when one considers the recent price fluctuations at gasoline pumps across the nation, Dubey said. A typical extraction facility that could extract all current carbon dioxide emissions would require only an area of one square yard per person in the developed world. A facility of sufficient size could be located in arid regions, since discharged air that is deficient in carbon dioxide could have consequences on nearby plant life.
Large expanses of desert would not be affected by the CO2 deficit however, and could provide the wide-open spaces necessary both for the facility and to allow the discharged air to become well mixed with the atmosphere again.
The next step for Dubey and his colleagues is to use intense computer models to optimize the configuration of the extractor as well as design alternative chemicals for extraction.