How to stash carbon dioxide: Turn it into stone.
Dissolved in water and pumped underground, CO2 becomes limestone.
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The scientists are in early discussions with a large oil company in Oman about field tests. They also have a pending patent on part of the injection process they are developing. Professor Kelemen says any proceeds would be the property of Columbia University.Skip to next paragraph
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Peridotite occurs in sizable and accessible quantities on every continent except Antarctica, according to Kelemen. Basalt is one of the Earth’s most common rock formations, making up 10 percent of the continental crusts.
Basalt is also found on the seafloor surrounding most continents, as well as inland. There is storage space in geologic formations worldwide for at least 2 trillion tons of carbon dioxide, according to the United Nations’ Intergovernmental Panel on Climate Change. The human population produces roughly 30 billion tons of CO2 annually.
As Kelemen says, “There is a huge amount of rock, compared with CO2, in the atmosphere.”
But even if suitable geologic formations abound, the question remains: Does CO2 mineralization make economic and practical sense?
Capturing carbon dioxide and injecting the dry gas into the ground takes large amounts of energy and money – as much as $110 per ton of CO2 to capture and transport, according to a recent paper by Carnegie Mellon University environmental engineer Edward Rubin. But to start the mineralization quickly by dissolving CO2 into water before injection would also require a lot of water.
“When you talk about sequestration at scale for commercial operations,” says Peter McGrail, an environmental engineer with the Pacific Northwest National Laboratory, “you end up having to deal with extraordinarily large volumes of water.” To dissolve a ton of CO2 requires about 27 tons of water, as well as significant pressure and heat.
Another potential problem occurs after injection, as carbonate minerals precipitate from the water solution into the porous rock. The minerals might plug up areas into which the water solution is migrating. If this happens, new wells and pipelines would be required to continue the sequestration project.
“This is really the core problem with this idea,” says Dr. McGrail. “It may be possible [to surmount it], but whether it’s cost-effective to do so and whether the risk associated with having to drill many more wells early in a project [is] hard to say.”
The process of injecting CO2 underground – whether combined with water or just as a gas – uses relatively little energy. It is carbon capture, compression, and transport that demand significant amounts of power.
According to researcher McLing, conservative estimates find that with most of our existing coal-fired power plants, at least 25 percent of the electricity produced would go toward capture and compression technology. So for every three electricity plants built with carbon capture capabilities, a fourth would be needed just to power the process.
“I’m pretty strongly pro-CO2 capture and sequestration,” says McLing. “But ... is it the right thing in terms of resource conservation? To get rid of the carbon dioxide, we have to burn an additional 20 to 40 percent more coal or natural gas or petroleum. What was formerly a 200-year supply of a resource may now only be a 100-year supply of a resource.
“Those are things we have to balance,” McLing concludes. “Are conservation and sequestration compatible?”