New clean coal technology provides energy without burning

It was a long and tiring week where we all shared shifts,” she said.

Fan agreed that the nine-day experiment was a success. “In the two years we’ve been running the sub-pilot plants, our CDCL and SCL units have achieved a combined 830 operating hours, which clearly demonstrates the reliability and operability of our design,” he said.

At any one time, the units each produce about twenty-five thermal kilowatts — that is, thermal energy, which in a full-scale power plant would be used to heat water and turn the steam-powered turbines that create electricity.

The researchers are about to take their technology to the next level: a larger-scale pilot plant is under construction at the U.S. Department of Energy’s National Carbon Capture Center in Wilsonville, AL. Set to begin operations in late 2013, that plant will produce 250 thermal kilowatts using syngas.

The key to the technology is the use of tiny metal beads to carry oxygen to the fuel to spur the chemical reaction. For CDCL, the fuel is coal that’s been ground into a powder, and the metal beads are made of iron oxide composites. The coal particles are about 100 micrometers across — about the diameter of a human hair — and the iron beads are larger, about 1.5-2 millimeters across. Chung likened the two different sizes to talcum powder and ice cream sprinkles, though the mix is not nearly so colorful.

The release notes that the coal and iron oxide are heated to high temperatures, where the materials react with each other. Carbon from the coal binds with the oxygen from the iron oxide and creates carbon dioxide, which rises into a chamber where it is captured. Hot iron and coal ash are left behind. Because the iron beads are so much bigger than the coal ash, they are easily separated out of the ash, and delivered to a chamber where the heat energy would normally be harnessed for electricity. The coal ash is removed from the system.

The carbon dioxide is separated and can be recycled or sequestered for storage.  The iron beads are exposed to air inside the reactor, so that they become re-oxidized  be used again. The beads can be re-used almost indefinitely, or recycled.

Since the process captures nearly all the carbon dioxide, it exceeds the goals that DOE has set for developing clean energy. New technologies that use fossil fuels should not raise the cost of electricity more than 35 percent, while still capturing more than 90 percent of the resulting carbon dioxide. Based on the current tests with the research-scale plants, Fan and his team believe that they can meet or exceed that requirement.

The DOE funded this research, and collaborating companies include Babcock & Wilcox Power Generation Group, Inc.; CONSOL Energy, Inc.; and Clear Skies Consulting, LLC.