By John Downey
Duke Energy Corp. is modifying its largest coal plants to burn natural gas for at least part of the power they produce in order to reduce coal use in the near term.
Changes needed to allow eight of Duke’s major coal units to burn gas are slated to cost $283 million. The work is complete at six of the units. The final two units will be finished later this year.
Some clean-energy advocates worry the work will just extend the life of coal plants, allowing Duke to continue to recover costs for plants they say are no longer economical to operate. But Duke contends the work saves customers money and improves the company’s environmental performance.
“For every pound of coal displaced with natural gas, sulfur dioxide will be reduced by an estimated 99% and carbon dioxide emissions will be reduced by about 40% (per megawatt-hour) because natural gas burns more cleanly than coal,” says Heather Danenhower, a Duke spokeswoman. “Co-firing also helps enable renewables, like solar, because natural-gas units can provide energy quickly when the sun isn’t shining.”
In August, the watchdog group NC WARN, the Center for Biological Diversity and the environmental group Appalachian Voices asked the N.C. Utilities Commission for a declaratory ruling that the modifications could not be done without its approval. Duke says that approval is only required if a new plant is built, not when an existing plant is being modified.
NC WARN Executive Director Jim Warren contends the modifications are just a ploy to allow Duke to continue to operate coal plants it should shut down. The commission has not yet ruled in the case. But if regulatory approval is required, Warren and his allies will contend customers should not be charged for the costs of modifying the plants.
While Duke has done some complete changes at three smaller units in South Carolina and Florida to rebuild them as gas-only plants, modifications that allow plants to burn both coal and gas are only being done in North Carolina.
That started in 2016, when Duke Energy said it would retrofit the 825-megawatt Cliffside 6 and 570-megawatt Cliffside 5 coal units at the Rogers Energy Complex in Mooresboro.
Unit 6 will be able to burn 100% natural gas, and Duke’s current plans call for using it as a gas-only plant as early as 2030. But Duke’s current baseline proposals for use of the plant say it could burn some coal until its closing in 2049.
Unit 5 will burn up to 40% gas and is slated to continue operating through 2026. The final work on those two units was completed in 2018.
Duke moved the project to its massive 2,240-megawatt Belews Creek Steam Station in Stokes County in 2017. Work on the 1,120-megawatt Unit 1 was completed in January 2020, and the 1,120-megawatt Unit 2 started operating as a co-fired plant at the beginning of this year. That project cost about $117 million for the two units, Danenhower says.
Duke currently expects to run the Belews Creek units through 2039, although they could close as early as 2029 under some of Duke’s planning proposals.
All the remaining units are at the 2,000-megawatt Marshall Steam Station in Sherrills Ford on Lake Norman. Work there started in 2018, and Marshall Units 3 and 4, about 650 megawatts each, have already been retrofitted and can each now burn up to 50% natural gas. Duke finished the work at Unit 3 in November and Unit 4 in January.
Danenhower says work is now being done on units 1 and 2, each rated at about 350 megawatts. Duke has installed pipeline infrastructure that will allow each of those units to burn up to 40% natural gas in their operations, she says. They are slated to be done by the end of the year.
The final price tag for all four Marshall units would be $101 million. Duke expects to run them through 2035 but could close them as early as 2028 under some planning proposals.