Staff at the Public Service Commission of Wisconsin on Sept. 26 filed an environmental assessment review of Wisconsin Electric Power’s plan to convert its coal-fired Valley Power Plant to burn natural gas.
Wisconsin Electric Power (WEPCO) applied in April for commission approval to convert the Valley plant, located near downtown Milwaukee, from a coal-fired cogeneration facility to a gas-fired cogen. Wisconsin Gas LLC (WG) would construct additional natural gas facilities to service the plant as part of the conversion. WEPCO is a unit of Wisconsin Energy (NYSE: WEC).
Though two entities are involved, the proposed work of both is considered a single project for this environmental assessment. Staff said the project can be adequately covered by this assessment and that no environmental impact statement is needed.
Valley has an electric capacity of about 280 MW and is the sole source of steam for the Downtown Milwaukee Steam System. It has two generating units of about 140 MW apiece. Steam for each unit is provided by two boilers (Generating Unit 1 is served by Boilers B21 and B22; Generating Unit 2 is served by Boilers B23 and B24). These four identical Riley dry bottom wall-fired boilers are currently fired by coal.
The gas conversion project consists of the removal, installation, and modification of the fuel-burning equipment at Valley to allow the plant to burn natural gas. It also includes removal, installation, and modification of the plant auxiliary systems to reliably supply steam to the WEPCO downtown Milwaukee steam system while significantly reducing minimum electrical output.
The project includes the removal of eight coal burners and associated coal piping and the installation of six to eight natural gas burners for each of the four Valley boilers, installation of the associated natural gas piping and valves inside the plant, and piping and valves between the plant and a metering station. The installation of flue gas recirculation fans to reduce NOX emissions is also included.
Because the baghouse would no longer be required, it would be removed from service and the induced draft fan discharge would run directly to the chimney. Boilers are to be sealed where existing burners, soot blowers, and bottom ash seal equipment are removed. Boiler to steam system let down valves are to be added to improve the reliability of the steam supply to the Downtown Milwaukee Steam System when only one turbine generator is operating.
All coal handling equipment, including the ash handling systems, would be retired. Prior to completion of the project, usable coal would be burned from the coal pile while boilers 3 and 4 are still capable of burning coal.
WEPCO plans to complete the conversion of Unit 1 in 2014 and the conversion of Unit 2 in 2015.
Wisconsin Gas would construct about 1,500 feet of 24-inch high pressure steel main from a point near North Emmber Lane and West Canal Street, east to the Valley plant, and a dedicated 300-foot, 24-inch steel service line from the 24-inch steel main in West Canal Street to a newly installed high pressure meter set without regulation on the Valley property.
Construction of the gas facilities is tentatively scheduled to begin on March 1, 2014, and to be completed by Aug. 31, 2014.
WEPCO estimates the cost of the Valley conversion to be $62m. Wisconsin Gas estimates the cost for the Valley natural gas main extension project to be $3.8m.
Other clean-air options included plant shutdown, replacement
This project is needed to meet requirements under the federal Mercury and Air Toxics Standards (MATS) and the SO2 National Ambient Air Quality Standards (NAAQS). The other compliance alternatives included:
- Continue to power Valley with coal and install Dry Sorbent Injection (DSI) to ensure compliance with MATS. However, when the U.S. Environmental Protection Agency implements stricter NAAQS for SO2, DSI will likely not be sufficient and a full Air Quality Control System may be needed at Valley if it continues to burn coal.
- Continue to power Valley with coal, but install a full Air Quality Control System, including selective catalytic reduction and an SO2 scrubber.
- Retire Valley, construct new transmission facilities to maintain electric system reliability, and install new gas-fired package boilers to supply steam only. The Valley plant is needed to maintain electric reliability and steam supply, so the plant could not be retired before new transmission and steam supply facilities are built.
- Retire Valley and build a new combined-cycle power plant, which would also be used to supply steam to the Downtown Milwaukee Steam System. This plant would be very expensive to build and would need to run with one or two units on line at all times for steam reliability and voltage stability, negating the primary advantage of cycling on and off daily to avoid operation at night when energy prices are lower than the plant’s operating costs.
The current coal-burning operations at Valley produce bottom ash and fly ash, which contain unburned coal combustion products. Currently, both the bottom ash and fly ash are trucked to WEPCO’s Pleasant Prairie Power Plant and reburned in the boilers. This ash constitutes less than 1% of the fuel input at Pleasant Prairie.
“In summary, the overall environmental impact of the project would be positive,” the staff environmental report said. “The exact reduction in emissions would depend on the amount of electricity generated at the site. Wastewater discharges related to the coal pile runoff would be eliminated.”