An innovative new process that releases the energy in coal without burning . . . while capturing the greenhouse gas carbon dioxide . . . has passed a milestone on the route to possible commercial use at a US university.
The results of a 200-hour test on a sub-pilot scale version of the technology using two inexpensive but highly polluting forms of coal are said to be encouraging.
Liang-Shih Fan and colleagues at Ohio State University advocate that carbon capture and sequestration ranks high among the approaches for reducing coal-related emissions of the carbon dioxide linked to global warming. This approach involves separating and collecting carbon dioxide before it leaves smokestacks.
Fan’s team has been working for more than a decade on two versions of carbon capture termed Syngas Chemical Looping (SCL) and Coal-Direct Chemical Looping (CDCL).
They involve oxidising coal, syngas or natural gas in a sealed chamber in the absence of the atmospheric oxygen involved in conventional burning. Metal compounds containing oxygen are in the chamber. They provide the oxygen for oxidation, take up coal’s energy, release it as heat in a second chamber and circulate back for another run in the first chamber.
The team has reported that the CDCL trial operated successfully for 203 hours without an involuntary shutdown.
The system used sub-bituminous and lignite coals, which are the main source of carbon dioxide emissions at US and many other coal-fired power plants worldwide. Carbon dioxide captured during the trial had a purity of 99.5%.
This represents the “longest integrated operation of chemical looping technology anywhere in the world to date,” according to the US Department of Energy, which helped fund the work through the agency’s Carbon Capture Program.
The unit produced 25 kilowatts of thermal energy, which in a power plant would have been used to produce electricity.
A larger test plant is now being built in Alabama.
“The chemical looping LS Fan is demonstrating is completely new,” said Lynn Brickett, division director of the Existing Plants Emissions Control division of the US Department of Energy’s National Energy Technology Laboratory (NETL) in Pittsburgh.