Non-burning coal technology nears pilot-scale development

The concept of clean coal doesn’t get a lot of respect from environmentalists who tend to describe it as an oxymoron (like “military intelligence”). A research team at Ohio State University in the US has, however, pioneered a new combustion technology which is now ready for larger scale testing, having successfully produced heat from coal while capturing 99 percent of the carbon dioxide produced in the reaction over 203 hours of continuous operation.

The process is highly-efficient in terms of CO2 capture compared with post-combustion capture technologies that can be retrofitted to existing coal-fired power plants, or pre-combustion technologies that can be applied to new plants. While it may not be enough to stop the rise of gas-fired power generation in North America and Western Europe, it could be a promising development for Asia’s coal-dependent giants: China and India.

Liang-Shih Fan, professor of chemical and bimolecular engineering and director of Ohio State’s Clean Coal Research Laboratory, pioneered the technology called Coal-Direct Chemical Looping (CDCL), which chemically harnesses coal’s energy and efficiently contains the carbon dioxide produced before it can be released into the atmosphere.

“In the simplest sense, combustion is a chemical reaction that consumes oxygen and produces heat,” Fan 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.”

The Ohio State group typically studies coal in the two forms that are already commonly available to the power industry: crushed coal feedstock, and coal-derived syngas. The latter fuel has been successfully studied in a second sub-pilot research-scale unit, through a similar process called Syngas Chemical Looping (SCL).  Both the CDCL and SCL research reactors are contained in 25-foot-high insulated metal cylinders that resemble a very tall home water heater tank.

No other lab has continuously operated a coal-direct chemical looping unit as long as the Ohio State lab did last September and the test was only ended because Fan and his research students had grown tired of fueling and monitoring the reactor after eight days of shifts.

“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,” said Fan.

At any one time, the units each produce about 25 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 National Carbon Capture Center run by the US Department of Energy (DOE). Set to begin operations in late 2013, that plant will produce 250 thermal kilowatts using syngas.