The Minnesota Pollution Control Agency (MPCA) is taking comment until July 5 on a draft air permit under which the Northern States Power subsidiary of Xcel Energy (NYSE: XEL) would add a simple-cycle peaker at its existing Black Dog power plant.
The Black Dog facility is composed of a natural gas-fired combined cycle gas turbine with duct burner, two emergency generators, one fire pump, and an auxiliary boiler. The turbine is equipped with low-NOx burners and NOx emissions are controlled by selective catalytic reduction (SCR). Coal-fired capacity at the site was retired in 2015.
Construction of a new simple cycle combustion turbine, designated as Unit 6, will be authorized by this permit action. The main pollutants of concern from the new turbine are NOx, CO, and CO2e. Unit 6 will be equipped with low-NOx burners. This major amendment also incorporates the April 2015 decommissioning of two coal-fired units, Unit 3 and Unit 4, and the cessation of all coal-related activities. The permit action includes a minor amendment to add requirements for an auxiliary boiler. The auxiliary boiler was installed in 2015 to provide heat to the facility, a role that was previously filled by the coal-fired boilers.
The new combustion turbine will have a maximum output at approximately 215 MW. It will operate as a peaking service at no more than a third of its annual capacity on a heat input basis. The turbine will be a simple cycle General Electric (GE) 7F5 Series model equipped with low-NOx burners. The F-Class model turbine utilizes compressed air and fuel to produce electricity and high temperature exhaust gas. These turbines have fast start capabilities, reaching 150 MW in 10 minutes from a cold start, and operate at 50% to 100% load with faster ramp rates over the load range.
The combustion turbine consists of the following equipment in series:
- an inlet air filter;
- a compressor, where air is drawn in and compressed;
- a combustor, where fuel is mixed with the compressed air and burned;
- a power turbine, where the combusted gases expand to rotate a turbine;
- an electric generator; and
- an evaporative cooler.
Air pollution control equipment will consist of low-NOx burners. These burners are designed to maintain a stoichiometric fuel-to-oxygen ratio by premixing and introducing the minimum amount of oxygen containing air into the combustion chamber allowing the fuel to burn. This lean ratio results in a relatively cool combustion zone and results in less NOx and CO formation.
In other news related to this project:
- The Minnesota Public Utilities Commission plans a June 16 hearing in Burnsville on a site permit application for this project. The commission noted that the project was selected in a competitive resource acquisition process by the Minnesota PUC. Xcel Energy stated that the project is designed to provide power directly to customers in the Twin Cities Metro Area and its surroundings.
- The Federal Energy Regulatory Commission said in a Feb. 23 notice that it will prepare an environmental assessment (EA) on the Cedar Station Upgrade Project, which involves construction and operation of facilities by Northern Natural Gas Co. Northern plans to construct and operate approximately 7.8 miles of 20-inch-diameter pipeline from its existing Rosemont Junction in Rosemont, Minnesota, to its existing Cedar Station Meter Station in Eagan, Minnesota. The Cedar Station Upgrade Project would allow Northern to increase the pressure from 400 pounds per square inch gauge (psig) to 650 psig at the Cedar Station. This project would accommodate a contractual obligation to meet a delivery pressure for the Black Dog power plant.