The Minnesota Pollution Control Agency on Aug. 2 went out for comment until Aug. 31 on a draft air permit covering a plan by a Calpine Corp. (NYSE: CPN) subsidiary to expand the existing, gas-fired Mankato plant.
Mankato Energy Center II LLC proposes to install a new combustion turbine/heat recovery steam generator (HRSG) train converting the existing facility to a 2×1 combined cycle unit. The new combustion turbine (CT)/HRSG train will be owned by Mankato Energy Center II (MEC II) and operated by Calpine Operating Services. It will generate an additional 345 MW at peak load at winter ambient conditions.
The CT will be fired by natural gas only and exhaust to a separate HRSG having a supplementary duct firing capacity of 824 mmBtu/hr. The duct burners will be fired with natural gas. Steam generated by the new HRSG will exhaust to the existing steam turbine. MEC II will install selective catalytic reduction (SCR) and dry low-NOx (DLN) burners to reduce NOx emissions and a catalyst oxidation system to control CO and VOC emissions. The HRSG low-NOx duct burner will be controlled by the SCR and oxidation catalyst.
To provide additional cooling due to increased steam flow to the steam turbine, four new cells will be added to the existing cooling tower. The facility also is adding a diesel-fired emergency generator.
Mankato Energy Center LLC (MEC I) owns the existing plant with a capacity of 375 MW at winter conditions, which is a 1×1 Siemens-Westinghouse combined cycle power block consisting of one combustion turbine, one HRSG and one steam turbine. This turbine is fired primarily by natural gas with distillate fuel oil as backup. The combustion turbine exhausts to a separate HRSG with supplementary duct firing capacity of 800 mmBtu/hr. Steam generated in the HRSG exhausts into the steam turbine.
MEC II will install the new combustion turbine/HRSG train converting the facility to a 2×1 combined cycle power block. The new CT/HRSG train will generate an additional 345 MW for a total of 720 MW at winter conditions.
The new combustion turbine will be an F-Class turbine with similar characteristics to the existing turbine. An anhydrous ammonia tank will be installed to provide reagent to the new SCR. The facility also will add a water tank, condensate tank, a small diesel tank for the proposed diesel emergency generator, natural gas piping and electrical equipment insulated with sulfur hexafluoride (SF6). The facility has an existing bath heater that is included in this permit action.
Calpine said about this project in its July 29 quarterly earnings statement: “By order dated February 5, 2015, the Minnesota Public Utilities Commission concluded a competitive resource acquisition proceeding and selected a 345 MW expansion of our Mankato Power Plant, authorizing execution of a 20-year PPA between Calpine and Xcel Energy. The PPA was executed in April 2015 and satisfied final regulatory approval requirements in March 2016. Commercial operation of the expanded capacity is expected by June 1, 2019.”