The technology uses a chemical reaction to produce heat from coal while creating nearly no polluting emissions, including carbon dioxide.
The team at Ohio State successfully operated a research-scale combustion system for 203 continuous hours, producing heat from coal while capturing 99% of the carbon dioxide produced in the reaction.
The researchers are now ready to progress to larger-scale testing at the National Carbon Capture Center.
Ohio State Clean Coal Research Laboratory director and chemical and biomolecular engineering Professor Liang-Shih Fan pioneered the coal-direct chemical looping technology.
“In the simplest sense, combustion is a chemical reaction that consumes oxygen and produces heat,” he said.
“Unfortunately, it also produces carbon dioxide, which is difficult to capture and bad for the environment.
“So we found a way to release the heat without burning.
“We carefully control the chemical reaction so that the coal never burns – it is consumed chemically and the carbon dioxide is entirely contained inside the reactor.”
A research associate and one of the group's team leaders, Dawei Wang, described the technology’s potential benefits.
"The commercial-scale CDCL plant could really promote our energy independence,” Wang said.
“Not only can we use America's natural resources such as Ohio coal but we can keep our air clean and spur the economy with jobs.”
Fan’s lab studied the use of both crushed coal “feedstock” and coal-derived syngas, the latter fuel also being successful in a second study of a similar process called syngas chemical looping.
At any one time, the CDCL and SCL units at the university each produce about 25 thermal kilowatts – enough thermal energy for a full-scale thermal plant to heat water and turn the steam-powered turbines that create electricity.
The key to the technology is the use of tiny metal beads to carry oxygen to the fuel to spur a chemical reaction.
For CDCL, the coal feedstock and iron beads are heated to high temperatures where they 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,” an Ohio State press release detailed.
“Because the iron beads are 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-oxidised to be used again.
“The beads can be reused almost indefinitely, or recycled.”
The process captures nearly all of the carbon dioxide, exceeding the goals that US Department of Energy has set for developing clean energy.
According to these goals, technologies that use fossil fuels should not raise the cost of electricity more than 35% while still capturing more than 90% of the resulting carbon dioxide.
Based on current tests with the research-scale plants, Fan and his team believe they can meet or exceed that requirement.
The researchers are about to take their technology to the next level with a larger-scale pilot plant under construction at the DOE’s National Carbon Capture Center in Wilsonville, Alabama.
Set to begin operations in late 2013, the plant will produce 250kW using syngas.
The DOE funded the research and is collaborating with companies including Babcock & Wilcox Power Generation Group, CONSOL Energy and Clear Skies Consulting.