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By Valerie Volcovici
WASHINGTON, Sept 20 (Reuters) - The Obama administration will unveil on Friday new regulations expected to set strict limits on the amount of carbon pollution generated by any new U.S. power plants, and which is certain to face legal challenges and a backlash from congressional supporters of the coal industry.
The Environmental Protection Agency's long-awaited guidelines are expected to make it more difficult for new coal-fired power plants to be built.
The rules, which are a revision of a previous attempt by the EPA to create emissions standards for fossil fuel plants, are the first salvo in President Barack Obama's climate change package, announced in June.
EPA Administrator Gina McCarthy is expected to discuss the new rules and defend Obama's climate plan, which opponents in Congress say amounts to a "war on coal," during a speech at the National Press Club in Washington on Friday morning.
Any new coal plant built in the United States would need to install technology to capture its carbon emissions, according to sources familiar with the plan.
That technology is controversial because it is currently not yet operational on a commercial scale, an issue that could become central to legal challenges to the EPA.
The EPA previously issued a version of the rule last year but made changes to it to address potential legal weaknesses and to factor in over 2 million public comments.
Unlike last year's version, the new proposed rule would create separate emissions rates for coal and gas-fired power plants. Legal experts had warned that a single standard, which had been set at 1,000 lb of carbon dioxide per megawatt hour, deviated from the federal Clean Air Act.
The new version would let new coal plants emit up to 1,100 lb of CO2/MWh, according to sources who have viewed the proposal, slightly higher than the 1,000 lb rate in the previous proposal.
A new coal plant could also be built at the current average emissions rate, around 1,800 lb/MWh, but the plant owners would have seven years to bring down its emissions rate to between 1,000 and 1,050 lb/MWh, according to sources who have seen the rule.
This provision is a significant change from the first version, which gave a coal plant 30 years to achieve a 1,000 lb/MWh emissions performance rate.
Under the new rules, newly built large natural gas-fired power plants could emit up to 1,000 lb of carbon dioxide per megawatt hour. Smaller, less efficient natural gas-fired plants could emit up to 1,100 lb of CO2/MWh or less, sources said.
Obama had set a Sept. 20 deadline for the EPA to issue the proposal. The agency will launch a public comment period after the rule's release.
It is due to issue a proposal to address emissions from existing power plants - which account for nearly 40 percent of U.S. greenhouse gas emissions - by June 2014.
Reporting by Valerie Volcovici; Editing by Eric Beech