01:00 AM EST on Monday, January 31, 2005

"Clean-coal technology" may bring memories of the 1980s and early '90s, when the technology was hailed as a partial solution to the harmful environmental effects of coal -- used in the generation of about half of all U.S. electricity.

Back then, much taxpayer money was shoveled into the technology, but the results were pretty paltry -- mainly "scrubbers," which withdraw harmful gases and particulates from stack emissions. The scrubbers have been only moderately successful in reducing such air pollutants as sulfur and nitrogen oxides, mercury, and arsenic -- not enough to bring many industrial plants into compliance with the Clean Air Act (under which the plants continue to operate because of special exemption). And the scrubbers have had no effect on carbon-dioxide emissions, the chief factor in global warming.

But much of the "clean-coal" research and development was promising. The energy industry's failure to exploit it was mainly due to the companies' seeking the least allowable compliance with the Clean Air Act -- and having the political clout to do so.

Some of the technology involves processing the coal into a cleaner-burning mixture before combustion. Tempering high-sulfur and -moisture coal with heat and pressure to change its chemical composition can yield a 60-percent increase in heat per unit.

Another promising process converts coal into a gas that can be cleaned of tars and oils, and burned in a turbine. This would ease the generating companies' removal of carbon dioxide from exhausts, while allowing more efficient combustion.

These technologies would bring the plants that are exempted from the Clean Air Act into compliance.

So why aren't these measures being taken in the Ohio Valley, where coal-burning plants cause ozone-alert days and acid rain in the Northeast -- harming both public health and the ecosystem?

Cost. Natural gas is a lot cheaper than processed coal. Yet with dwindling natural gas (due partly to opposition to liquefied natural gas) and surging gas prices, expect to hear more about "clean coal."