Northern States Power seeks site permit for 215-MW Black Dog 6 project

The Northern States Power subsidiary of Xcel Energy (NYSE: XEL) applied Oct. 15 at the Minnesota Public Utilities Commission for a site permit on the 215-MW Black Dog Unit 6 Project, which is a new gas-fired unit at the existing Black Dog power plant.

The commission had previously approved this project as part of the utility’s recent Competive Resource Acquisition case. Black Dog Unit 6 Project is a simple-cycle natural gas-fired combustion unit designed to provide approximately 215 MW of nominal peaking capabilities. The project will be located at the Black Dog Generating Plant in Burnsville, Minnesota.

Construction is scheduled to begin in June 2016 with foundation work for the new unit. Initial startup is planned for early 2018, with commercial operation in April 2018, the utility noted.

The combustion turbine (CT) will be a simple-cycle unit with dry low-nitrogen oxide (NOx) burners and the use of good combustion practices for emissions control. No add-on emission controls are anticipated.

Black Dog Unit 6 will provide approximately 215 MW of nominal peaking capabilities and will be built in the existing powerhouse building for Unit 4. Both Units 3 and 4 were retired in early spring 2015.

The Black Dog Generating Facility is located south of the Minnesota River, about 15 miles south of Minneapolis and west of the City of Eagan.

New project to use old infrastructure

Black Dog Unit 6 will utilize existing infrastructure at the plant and feed power directly to the existing 115-kV transmission system that serves distribution substations throughout the largest load center – the Minneapolis-St. Paul metropolitan area. The Black Dog Unit 6 Project is designed to ensure generation at the Black Dog Plant to provide power to the lower voltage system delivery directly to customers. This system configuration exposes customer power supply in the Twin Cities metropolitan area to fewer equipment failures and thus enhances reliability.

Numerous remediation activities at the Black Dog Plant are underway and will continue concurrently during the construction and operation of the proposed Unit 6 Project. These remediation activities have been separately approved and permitted and are not part of this site permit application, but are described to provide context and background information.

The existing plant was initially developed as a coal- and gas-fired generating station. The original Unit 1 boiler/turbine and the Unit 2 boiler, installed in the 1950s and fired with coal, were replaced in 2002 with a natural gas-fired combined cycle unit (Unit 5), which includes a natural gas-fired combustion turbine-generator combined with a heat recovery steam generator (HRSG) and utilizes state-of-the-art technology for controlling NOx. Exhaust heat from Unit 5 produces steam in the HRSG that powers the Unit 2 steam turbine. The Unit 5/2 repowering project, completed in the summer of 2002, increased output from the two original units by more than 100 MW, and resulted in greater operating efficiency and cleaner generation. Unit 5/2 is summer rated at 283 MW. These units will not be modified as part of the Unit 6 Project.

Units 3 and 4 were retired in April 2015. Units 3 and 4 were dual-fuel boilers with steam turbines that utilized low-sulfur western coal as the primary fuel. Natural gas was used as a backup or topping fuel to obtain maximum generation for both units. Unit 3, completed in 1955, was rated at 89 MW. Unit 4 was rated at 164 MW and was completed in 1960. There is no further coal-fired generation at the Black Dog Plant.

The existing coal yard and ash ponds are currently being decommissioned. Xcel Energy enrolled in the Minnesota Pollution Control Agency’s (MPCA) Voluntary Investigation and Cleanup (VIC) program in 2011 for the purpose of obtaining a “No Further Action” letter for the coal yard and ash pond operational areas (VIC Site).

Unit 6 based on an F class combustion turbine

The Unit 6 Project will consist of installing a simple-cycle natural gas-fired combustion turbine unit in the existing powerhouse where retired Unit 4 is currently located. The exhaust stack will be approximately 200 feet tall and will be located adjacent to the unit and exit through the existing Unit 4 boiler roof.

Northern States Power will operate Unit 6 as a peaking generator, with an anticipated annual capacity factor of 4% to 10%. It is expected that the annual availability will be greater than 95%, and that its service life will exceed 35 years. The peaking capacity design is based on the performance characteristics of F class combustion turbines. Upon completion, the project will provide a nominal generating capacity of about 215 MW, which is the net capacity during summer conditions when the combustion turbine is operated at full capacity. The total summer generating capacity of the Black Dog Generating Plant will be 498 MW once Unit 6 is operational.

The model F class combustion turbines have fast start capability, reaching 150 MW in 10 minutes from a cold start, and operating in a range of at least 50% to 100% load while meeting emission limits, with faster ramp rates over the load range. Maximum output during summer heat and humidity conditions is approximately 215 MW.

Unit 6 will be fueled entirely by natural gas. CenterPoint Energy currently serves the plant site. Because Unit 6 will increase the plant’s high pressure natural gas need, Northern States Power is conducting a competitive process for gas supply to the plant. The new pipeline is expected to commence at or near Northern Natural Gas Co.’s Cedar Town Border Station yard. The new pipeline will extend approximately two miles to terminate in the Black Dog Generation Plant yard. Permitting for the new line will be the responsibility of the fuel supplier. Bids were due to the company by Aug. 30, 2015, and bid selection is expected in October 2015.

The estimated capital cost of the Unit 6 project is approximately $100 million, based on a March 2018 commercial operation date. This includes design and engineering, procurement of equipment, site preparation, building construction, equipment installation, plant start-up and testing, and other costs associated with the development and construction of the project. Annual operating costs will vary depending on how often the unit is run but are anticipated to be between $0.05/kWh and $0.09/kWh including fuel, labor, materials, maintenance and applicable taxes. 

A project contact is: Amy S. Fredregill, Manager, Resource Planning and Strategy, 414 Nicollet Mall, 7th Floor, Minneapolis, MN 55401, (612) 215-5367,

About Barry Cassell 20414 Articles
Barry Cassell is Chief Analyst for GenerationHub covering coal and emission controls issues, projects and policy. He has covered the coal and power generation industry for more than 24 years, beginning in November 2011 at GenerationHub and prior to that as editor of SNL Energy’s Coal Report. He was formerly with Coal Outlook for 15 years as the publication’s editor and contributing writer, and prior to that he was editor of Coal & Synfuels Technology and associate editor of The Energy Report. He has a bachelor’s degree from Central Michigan University.