[font face=Serif][font size=5]A Cleaner Way to Use Coal[/font]

[font size=4]A technology for generating electricity from coal without pollution achieves a milestone.[/font]

By Kevin Bullis on February 7, 2013

[font size=3]Coal is abundant and cheap, but burning it is a dirty business. This week researchers at Ohio State University announced a milestone in the development of a far cleaner way to use the energy in coal—a process called chemical looping that has the potential to reduce or eliminate a wide range of pollutants, including carbon dioxide and smog-forming nitrogen oxides.

One version of the technology ran continuously for over a week in a 25-kilowatt test facility, the researchers reported, the longest any such process has run. The successful test clears the way to ramp up the technology in a one-megawatt demonstration plant that’s being planned in collaboration with the energy company Babcock and Wilcox.

In ordinary coal plants, coal is pulverized to make a fine powder and then burned in air to produce steam to drive turbines. This process makes very hot flames that can create the pollutant nitrogen oxide, and the carbon dioxide generated is difficult to isolate and capture because it makes up only a small fraction of the exhaust gases.

In chemical looping, coal doesn’t react with air. Instead, it’s exposed to oxygen-bearing materials such as iron oxide. The coal reacts with these materials, and the energy bound up in coal breaks the bond between the oxygen and the iron. The reaction produces nearly pure carbon dioxide gas and iron metal (along with the mineral wüstite). Electricity is generated when the iron is moved out of the reaction chamber and is essentially burned—that is, allowed to react with oxygen in air. This releases heat to produce steam.

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