However, with new EPA rules on mercury, interstate pollution and other emissions, another 56 percent of U.S. coal plants could become as costly to run as natural gas plants, the Duke researchers found.
The study found that, with new EPA rules, the majority of natural gas plants would remain cost competitive with a majority of coal plants unless or until the gas-to-coal price ratio increase from the current 1.5 to 4.3.
"Even if natural gas prices rise, the U.S. electricity sector could still continue its shift away from coal plants and toward greater use of lower [carbon dioxide]-emitting natural gas plants," the Duke study said. "This is because the economics of natural gas vs. coal plants depends not only on the price of natural gas, but also on the price of coal and on the expense of meeting the stricter EPA regulations."
The Duke researchers made a number of assumptions, some of which could have inflated their estimates of regulatory costs, and others of which might have low-balled those costs.
For example, the report assumes that power plants that don't currently meet new EPA standards would have to install separate control equipment for each individual pollutant. But, some power companies have said expensive controls for one pollutant, such as sulfur dioxide, will also help them control for other emissions, such as mercury.
Also, the report takes into account only air pollution rules, not other potential regulations, such as coal-ash handling and disposal restrictions, which could affect coal-fired utilities.
A spokeswoman for the National Mining Association said her group is still reviewing the Duke study.
Melissa McHenry, a spokeswoman for American Electric Power, said the study outlines potential risks to power plants that are "much higher than the EPA projections of the impacts.
"We can't speak to the accuracy of their analysis, but this study certainly supports the concerns that we have been expressing for some time about the EPA regulations and the potential for regional reliability impacts that the closure of a significant amount of electricity generating units may cause," McHenry said in an e-mail message.
John Coequyt, an energy analyst with the Sierra Club, noted that the Duke study did not take into account any health or climate change benefits from reducing coal plant pollution.
"We believe that Congress told companies to clean up their coal plants a very long time ago," Coequyt said. "Once you start to deal with the air and water pollution problems from these coal plants, you have to start thinking about whether these plants can be competitive."
Reach Ken Ward Jr. at kw...@wvgazette.com or 304-348-1702.