Editor's note: The original online version of this story was previously posted.
Over the next five years at least half a million tons of carbon dioxide will be injected into rock deep underneath the Mountaineer power plant near New Haven, W.Va. Although that is less than 0.00001 percent of global emissions of the greenhouse gas and less than 2 percent of the plant’s own CO2 output, the sequestration, which began in September, marks the first commercial demonstration of the only available technological fix for the carbon problem of coal-fired power plants, one that many coal facilities around the world hope to emulate.
Coal accounts for roughly 50 percent of the electricity generated in the U.S. and as much as 75 percent of the electricity generated by American Electric Power, says Nick Akins, executive vice president of generation at the utility, which owns Mountaineer. The plant can pump out 1,300 megawatts of electricity, making it one of the single largest coal-fired power plants in the U.S. and a leading source of CO2 emissions. (The top emitters of global-warming pollution—China and the U.S.—burn nearly four billion tons of the dirty black rock a year.)
As a result, everyone from coal companies to environmental groups have identified carbon capture and storage, or CCS, as critical in enabling significant and rapid cuts in greenhouse gases. But there have been only a handful of demonstrations of the technology to capture the gas and, outside of using CO2 to pump more oil out of the ground, even fewer attempts to store it.
To capture CO2 from its smokestacks, Mountaineer will employ so-called chilled ammonia technology, which relies on ammonium carbonate chemistry to pull CO2 out of the exhaust gases. (The other two basic capture technologies either burn coal in pure oxygen to produce a CO2-rich emissions stream or siphon off the CO2 made during the gasification of coal.)
Mountaineer takes the captured CO2 and compresses it to at least 2,000 pounds per square inch, liquefying it and pumping it about 8,000 feet down into the ground. At that depth, the liquid CO2 flows through the porous rock formations, adhering to the tiny spaces, slowly spreading out over time and, ultimately, chemically reacting with rock or brine. “We’re not going into a salt cavern; we’re not going into an underground river. We’re going into microscopic holes,” explains geologist Susan Hovorka of the University of Texas at Austin, referring to CCS in general. “Add it up, and it’s a large volume.” In fact, the Department of Energy estimates that the U.S. has the geologic room for 3.9 trillion tons of CO2 underground, more than enough for the 3.2 billion tons that is emitted every year by large industrial sources.
The two geologic formations below Mountaineer are the Rose Run Sandstone and Copper Ridge Dolomite, which run underneath layers of relatively impermeable rock that will keep the CO2 trapped. “Part of our project is to kind of take those through their paces and get an idea of their acceptance of CO2,” says Gary Spitznogle, a CCS engineering manager at American Electric Power. After all, a similar effort in Ohio revealed that formations there stored less CO2 than expected. The company will monitor the CO2 via three specially drilled wells, in addition to the two wells for pumping the CO2 down in the first place.
The process of capturing and storing carbon dioxide may be simple chemistry and geology, but it has significant industrial costs. American Electric Power alone will pay $73 million for just the capture technology at Mountaineer and has asked for $334 million in federal stimulus—half the total cost, the company says—to scale up the project to nab roughly 20 percent of the plant’s emissions in future years.