The Wisconsin Department of Natural Resources on Jan. 15 went out for comment on a plan to approve air permitting that would allow upgrades by Wisconsin Electric Power d/b/a We Energies at the Port Washington Generating Station, a nominal 1,090-MW natural gas-fired station consisting of two similar units.
Each unit consists of two combustion turbine generators (CTG) and one steam turbine electric generator. Each CTG is equipped with a heat recovery steam generator (HRSG) which provides steam to the steam turbine common to that unit. Each HRSG is equipped with duct burners for supplemental natural gas firing, oxidation catalysts for the control of carbon monoxide (CO) and organic compound (VOC) emissions, and selective catalytic reduction (SCR) systems for the control of NOx emissions.
We Energies is proposing two projects, the Advanced Gas Path (AGP) Project and the Duct Burner Pyro- Bloc Project.
- The work proposed for the AGP will provide improved materials, design, and extended component life of the CTGs by replacing the existing turbine components exposed to hot combustion gases with new, improved components. The new turbine components are expected to allow for increased firing temperatures and result in improved turbine efficiency and increased electric output. At design conditions, the output of each CTG is expected to increase from approximately 169 MW to approximately 180 MW, and the overall power block heat rate is expected to improve by about 0.9%.
- The Duct Burner Pyro-Bloc Project will include changes to the HRSG insulation downstream of the duct burner to prevent insulation problems from limiting utilization of the duct burners. The Pyro-Bloc insulation is a ceramic fiber system designed for high temperature furnaces.
The Port Washington Power plant is located in Port Washington on the west shore of Lake Michigan. The site includes the plant proper which houses the boilers, turbines, and electrical switching equipment.
Under the AGP Project, the maximum nominal CTG heat input is expected to increase from 2,096 to 2,242 MMBtu/hour. The Pyro-Bloc Project is expected to result in a change in the duct burner firing rate from the current de-rated value of about 184 MMBtu/hour to the design capacity of 371 MMBtu/hour.
These units were initially permitted under a construction permit issued in December 2002.
The current Port Washington CTGs are General Electric (GE) Model 7FA.03 combustion turbines. The AGP Project will replace the existing combustion liners and all turbine components that are exposed to the hot combustion gases. The new components will have improved materials which will allow for increased firing temperatures. The redesigned turbine components and improved cooling/sealing features are expected to result in improved turbine efficiency and increased electric output. We Energies noted in its June 2015 permit application for this project that GE states the following general performance benefits for AGP:
- Up to a 4.8% increase in combined cycle output.
- Up to 7% increase in CTG output.
- Up to a 1% increase in fuel efficiency.
- Up to 32,000 hour or 900 factored start gas path maintenance intervals, which can extend outage intervals by up to 33%.
- Extension of certain gas turbine components life out to as much as 96,000 hours.
After the AGP Project, the CTs will be designated as GE Model 7FA.04.
The Duct Burner Pyro-Bloc Project will include changes to the heat recovery steam generator (HRSG) insulation downstream of the duct burner to restore the performance of the duct burners back to the original design capacity. The duct burners are located between the two high pressure (HP) superheater sections of each HRSG. The duct burners are used to increase the temperature of the flue gas flow through the HRSG to increase steam production and are generally used to meet peak power requirements for the facility.
The use of the duct burners has been limited because of flame impingement causing damage to the side walls downstream of the duct burners. The duct burner frame supports the burner elements while allowing for thermal expansion. A firing duct, located downstream of the duct burner elements, directs the gas flows from the duct burner to the HP Superheater #2 section of the HRSG and prevents flame impingement on the heat exchanger surfaces. The firing duct is instrumented with a temperature sensor for control of the duct burner firing. The Pyro-Bloc insulation is a ceramic fiber lining system designed for high temperature furnaces. This insulation is installed in modules which have a better heat resistance than conventional blanket systems. This insulation will be installed on the side walls of the firing duct.