Trapping Carbon, Freeing Coal
Capture begins with a new technology from the New Hampshire company Powerspan. In a large industrial box, Powerspan passes the airy remnants of coal combustion through an ammonium carbonate solution. The carbon dioxide in this flue gas--roughly 10 percent to 15 percent of it--bonds with the solution to form ammonium bicarbonate, while the other elements pass through on their way to smokestack release. From a given stream of waste gas, the technology captures 90 percent of the CO2 or about 20 tons a day for every 24 megawatt-hours of electricity produced.
When heated, the ammonium bicarbonate releases a relatively pure stream of CO2. This CO2 can then be compressed by pressures of up to 2,000 pounds-per-square-inch, making it into a supercritical gas with the density of a liquid but the easy flow of its unpressurized state. It costs about 10 percent of the electricity generated by the coal burning to capture and compress the greenhouse gas, according to Frank Alix, Powerspan's chairman and CEO--far less than the 30 percent required for other proposed technologies.