NEW HAVEN, W.Va.—A 100-story smokestack belches a roiling, white cloud of water vapor, carbon dioxide and other leftover gases after burning daily as much as 12,000 tons of coal at the Mountaineer Power Plant—a total of 3.5 million tons a year. The facility just outside the town of New Haven boasts a single 65-meter-high boiler capable of generating enough steam to pump out 1,300 megawatts of electricity—enough to power nearly one million average American homes a month—continuously. And now roughly 1.5 percent of the CO2 billowing from its stack is being captured in an industrial unit rising from the concrete in its shadow and then pumped underground for storage. In case you were wondering, this last phase is called "clean coal".

"Mountaineer is the turning point," says Philippe Joubert, president of Alstom Power, a subsidiary of France-based Alstom, SA. "We believe coal is a must, but we believe coal must be clean."

View a slide show of the world's first carbon capture and storage facility in operation

The small stream of flue gas travels to the carbon-capture unit through plastic pipes reinforced with fiberglass and is cooled to between –1 and 21 degrees Celsius from the 55-degree C temperature at which it emerges from the other environmental technology add-ons that strip out the fly ash, sulfur dioxide and nitrogen oxides. The carbon-capture machine's loud hum comes primarily from the whirring of fans to further cool the flue gas, along with the steady jostling of the agitator that keeps solids from settling out in the tall tank where the CO2 is captured. There is also the continuous chug of the compressors pressurizing that captured CO2 into a liquid at 98 kilograms per square centimeter. An incessant rumble also emanates from the regenerator stacks, as well, where steam heat and pressure combine to turn ammonium bicarbonate (part of the CO2-stripping process) back into baker's ammonia (ammonium carbonate), siphoning off the captured CO2 in the operation. A little bit of ammonium sulfate—a fertilizer—is also produced; it is shipped to a farmer's cooperative just across the river in Ohio.

"It's just like a shower," says Robert Hilton, vice president of power technologies and government affairs at Alstom. "The gas is coming up and the liquid is coming down."

This carbon-capture unit built by Alstom and dubbed the "chilled ammonia" process, consumes 25-kilogram bags of baker's ammonia to strip CO2 from the cooled flue gas and then, by reheating the resulting ammonium bicarbonate, captures that CO2 and recycles the reconstituted ammonia back into the industrial process. Many power plants already employ such ammonia in selective catalytic reduction units to strip nitrogen oxides out of the flue gas.

But the primary benefits of the chilled-ammonia process for capturing CO2 are lower electricity and steam consumption, compared with other potential technologies for carbon capture, such as using amines, another ammonia compound, which can consume as much as 30 percent of the plant's power just to run, says Shawn Black, product manager for Alstom. The goal here is to get that number down to under 15 percent.

"The challenge is going to be more on the storage side," argues project manager Brian Sherrick of Columbus, Ohio–based American Electric Power (AEP), the utility that owns the facility, because storage depends on the local geology and cooperative federal and local governments as well as the concerns of local residents. The first demonstration of chilled-ammonia technology, done at We Energies's Pleasant Prairie power plant in Wisconsin, did not bother to store the CO2, because the geology beneath that state is not capable of such sequestration.

All told, the carbon-capture machine at Mountaineer can capture 5.5 metric tons of pressurized CO2 per hour, which flows out through a five-centimeter-diameter insulated pipe. It's pumped 300 meters or so to the injection site, where its pressure is increased to more than 140 kilograms per square centimeter before being pumped through one of two wellheads. Down the well dubbed AEP 2, the CO2 flows 2,375 meters straight down into the Rose Run sandstone, a 35-meter-thick layer with a nine-meter-thick band of porous rock suitable for storage. Down AEP 1, the CO2 flows directionally into Copper Ridge dolomite, which has much thinner strata for possible storage, more than 2,450 meters down. Thick bands of shale and limestone that lie on top ensure that the CO2 does not escape back to the surface.

"Old wells are your most likely leakage path," Sherrick says, and there is one old coal gas well that pierces the earth to 1,200 meters below the surface, which AEP will monitor closely. In addition, the company has three wells explicitly drilled to monitor the CO2 as it spreads out in the deep subsurface.

After five years of injection—an estimated 500,000 metric tons of the milky liquid—the sequestered CO2 plume may become big enough to cross into Ohio. "It's supposed to be better down there than in the air," says Mayor Scott Hill of the town of Racine, Ohio, directly across the river. "I wonder what happens long-term." He adds that he is fine with it "until something happens. You know, they just tell you what you want to hear."

The next step will be scaling up the whole unit, making it capable of capturing CO2 emissions associated with 235 megawatts of the plant's power, or roughly one fifth of its output, Sherrick says. Of course, that will take up more space, roughly eight to 12 acres according to preliminary engineering; a unit big enough to capture the plant's full emissions could be as big again as the plant itself. And it will cost at least $700 million, half of which AEP has applied to receive from the federal government.

Alstom, for its part, plans to offer such chilled-ammonia technology commercially by 2015, according to Pierre Gauthier, president and CEO of Alstom USA. "It's not tomorrow morning, but it's not 2030 either."

"Decarbonizing the electric sector is job one for the electricity industry," adds Henry "Hank" Courtright, a senior vice president at the Palo Alto, Calif.–based Electric Power Research Institute (EPRI). "If we can do that, we can help them decarbonize the rest of the economy" through alternative technologies such as electric cars. In fact, EPRI estimates that a 41 percent reduction in U.S. greenhouse gas emissions by 2030 could be achieved through a combination of carbon capture and storage (CCS), increased generation from renewable energy sources, and new nuclear power plants—as well as efficiency improvements.

Of course, right next door to Mountaineer is the Philip Sporn Power Plant, whose multiple smokestacks and four smaller boilers show no visible signs of activity other than coal continually being added to its sprawling pile. But that is because there are no pollution controls whatsoever on the old plant, whose emissions are detectable, if at all, as a faint haze. In addition, Sporn's fly-ash ponds, hidden behind a grassy berm directly behind Mountaineer's CCS unit, have been cited by the U.S. Environmental Protection Agency as having "high hazard potential."

Coal may get cleaner as pollution controls minimize the emissions that cause acid rain and smog as well as cut the greenhouse gases changing the climate, but there are still plenty of leftovers from coal burning: toxic ash, mercury and other issues. And old plants like Sporn, running since 1950, will never get such pollution controls. Instead, they will continue to run until utilities like AEP are forced to shut them down, which will also add to the cost of electricity.

Cleaner coal will be more expensive, too, adding at least 4 cents per kilowatt-hour to the power Mountaineer produces at roughly 5 cents per kWh. Nevertheless, "this is the first time in the world carbon capture has been carried on and sequestration has been part of it," West Virginia Sen. Jay Rockefeller notes. "Some say it's only a very small part of it, but that's not the point. It's taken 90 percent of the carbon out of a small section."

View a slide show of the world's first carbon capture and storage facility in operation