By Bob Geiger
Dolan Media Newswires
Minneapolis — Xcel Energy’s Black Dog Plant is expected to become an all-natural, gas-powered facility, significantly cutting emissions of sulfur dioxide, nitrogen oxide, mercury and carbon in the Minnesota River Valley.
Part of the Burnsville plant, originally designed in the 1950s to burn coal, was converted in 2002 to gas, which cut pollution and boosted power generation with two boilers transformed into a combined-cycle unit that includes a jet-like turbine to produce energy.
“When we look at coal plants, we have to look at the life of those facilities,” said Steve Hjermstad, manager of capital projects for Xcel Energy. Black Dog “is a nice location, it’s within the beltway, and it makes a lot of sense to consider that a brownfield application.”
The conversion of the first two coal-fired units cost $122 million, some $34 million below budget, Hjermstad said.
If it is converted to natural gas, it would be the third Minneapolis-St. Paul area Xcel Energy power plant to abandon coal as a fuel, partly because the utility expects the federal government to limit greenhouse-gas emissions.
Also converted, under the auspices of the Metro Emissions Reduction Project are the St. Paul High Bridge Plant and the Riverside Plant in Minneapolis.
Jim Zyduck, plant director at High Bridge, oversaw conversion of the aging coal-fired plant to cleaner-burning natural gas between 2002 and 2007.
“We basically doubled the output of the plant,” said Zyduck, whose plant generates an average of 550 megawatts.
Among challenges posed by the High Bridge conversion, which Hjermstad termed a “brownfield repowering,” was cutting the amount of coal in the plant’s yard from 180,000 tons to 30,000 tons.
The other challenge was assembling a 2 million-pound boiler assembly on site and moving it into the plant.
“The boiler had to be slid into the plant on two super-modules,” Zyduck said. “It creates a lot of safety hazards.”
Xcel Energy hired Atlanta-based engineering and construction consultant CH2M Hill Inc. to work on the conversion of High Bridge.
Construction jobs, particularly needed in a persistently dour economy for contractors, could be created if Xcel Energy includes the Black Dog plant’s remaining coal burners in its resource plan submitted to the Minnesota Public Utilities Commission.
Hjermstad said the High Bridge plant project totaled 1.7 million craft hours.
The result of the coal-to-natural-gas conversion is more bang per burn and fewer emissions. Even with the increased productivity, Zyduck and Hjermstad said, the cost of fuel required to generate a megawatt hour of energy ranges from $17 to $19 for coal. Natural gas, on the other hand, is $25 for each megawatt hour, and has spiked above $40.
If Black Dog completes its conversion to natural gas, the Burnsville plant, like High Bridge in St. Paul, would have a coal yard to deal with.