Xcel Energy wants to retire its last two coal-fired power plants (Units 3 and 4) at the Black Dog power plant in Burnsville, Minn., and replace them with natural gas–fired units. Black Dog Units 1 and 2 were converted to natural gas combined-cycle operation in 2002. Xcel says the conversion would be “more economical” than alternatives.

“Repowering this plant with state-of-the-art natural gas technology is more economical than any of the alternatives available to us, makes great use of an existing plant site and existing transmission resources and will help meet our customers’ needs in an environmentally sound manner,” said Judy Poferl, president and CEO of Northern States Power Co.-Minnesota, an Xcel Energy company. “The project presents a great opportunity to modernize our power supply in a way that takes advantage of Black Dog’s unique location and the infrastructure that has developed there over time.”

The company said it filed an application with state regulators on Monday for a “certificate of need” of a combined-cycle facility on the Black Dog site, separate from the main building. The new facility will include “two combustion turbines, two heat recovery steam generators and a steam turbine generator located in what is now the plant’s coal yard,” Xcel said.

The company added that integrating combustion turbine and steam turbine technology “provides an extremely efficient electricity production process.” Claiming combined-cycle technology would be “about 50% more efficient” than the existing traditional steam plant, the company also said that the plant would generate more power; the repowering is expected to replace 253 MW of coal-fired generating capacity with 700 MW of gas power. The project will include a new substation and connection to the on-site 345-kilovolt transmission lines. A higher-capacity natural gas line will also be installed to serve the facility.

The Black Dog proposal requires review and approval by various state agencies, including the Minnesota Pollution Control Agency and Minnesota Public Utilities Commission. As part of the certificate of need process, independent power suppliers will have the opportunity to propose alternative developments.

If the $600 million project is approved, site preparation could begin in 2012 and foundation construction could begin in 2013, Xcel said. It would then come online by 2016.

Xcel had last September shut down its 538-MW Black Dog plant after it was rocked by an explosion. No personnel were harmed, but three firefighters responding to a smoldering fire in a coal hopper received minor injuries, police said.

The company did not comment as to whether this was a factor in its decision to repower the plant. It said, however, that the project was similar to the company’s Minnesota Metro Emissions Reduction Project, which led to repowering the High Bridge and Riverside plants from coal to natural gas and upgrades at the Allen S. King plant.

“Combined with the previous emissions reduction project, the conversion of the Black Dog plant supports the utility’s overall goals to make strategic use of critical locations, expand generating capacity, keep rates reasonable and reduce emissions to meet environmental requirements,” it said.

Sources: POWERnews, Xcel Energy