The Public Service Commission of Wisconsin on Dec. 16 issued an environmental assessment covering a plan to upgrade two units at the coal-fired Columbia power plant.
Wisconsin Power and Light (WP&L), Wisconsin Public Service Corp. (WPSC), and Madison Gas and Electric (MGE) applied to the PSC in July for authority to: construct, install, and place in operation 12 new coal pulverizers; and to upgrade two steam turbines at the Columbia Energy Center. If the commission approves the project, it will issue a Certificate of Authority (CA) to the applicant utilities.
WP&L (the plant operator) owns 46.2% of the plant, while WPSC and MGE own 31.8% and 22%, respectively.
Columbia consists mainly of two generating units, Units 1 and 2, each of which is a tangentially-fired boiler and an associated turbine generator. Columbia Units 1 and 2 were placed into operation in 1975 and 1978 and have nameplate generation capacities of 512 MW and 511 MW, respectively. The boilers each fire sub-bituminous Powder River Basin (PRB) coal from various mines, and each have six coal pulverizers and six elevations of burners.
Two additional project proposals for improvements at Columbia recently received CAs from the commission, and construction of both projects is still in progress.
- One project is the installation of dry flue gas desulfurization (FGD) systems and downstream baghouses for the Units 1 and 2 and modifications to the existing activated carbon injection (ACI) systems to reduce SO2 and mercury (Hg) emissions, at a cost of $627m.
- The other project, with a cost of $19.2m, is building two new cooling tower units to replace the existing ones because structural failure is occurring despite regular maintenance.
A fourth project, for which an application to the commission is expected soon, would install and operate a selective catalytic reduction (SCR) system for Unit 2 that could be in service by the end of 2018. The cost for this plant addition would be about $230m.
The low-pressure (LP) turbine rotors at these units are showing a corrosion condition known as “stress corrosion cracking” where the rotors have dovetail notches to attach the turbine blades to the rotor. In the most recent major turbine outage inspections, pitting and several small cracks were found on the rotors at the dovetail attachment sites. The turbines were returned to service, but the utilities determined that it is time to prepare for repair during the next turbine outage.
Twelve existing Combustion Engineering (now Alstom) coal pulverizers, six per unit, also date from the initial construction of the plant. The applicants state that the pulverizers have reached the end of their useful life. They cite erosion in the main housing and roofs that are leading to thinning, cracking, and deformation, which in turn will lead to increased coal leakage and fugitive dust. Fugitive dust is a safety issue at the plant, and the pulverizers must be shut down and repaired when coal leaks are identified.
Upgrades will lead to higher unit efficiency
“The Applicants state that proposed project is not needed to meet the Applicants’ near-term energy or capacity needs,” the environmental assessment noted. “The turbines and pulverizers are in need of major maintenance because of mechanical damage buildup in the pulverizers and corrosion buildup in the turbines. The Applicants have stated that the proposed combination of upgrades will enable greater efficiencies from the existing units.”
The efficiencies include:
- An estimated reduction in the heat rate of about 440 British thermal units (Btu) per kilowatt hour (kWh) on each unit, which reflects about a 4% increase in efficiency. The heat rate is the amount of fuel required to produce one kWh, so less fuel is projected to be needed.
- A total plant operating capacity increase of about 95 MW, an increase in the daily average energy production from each unit of about 9%.
- A reduction of air emission intensity in pounds per megawatt hour (MWh) due to improved operating efficiencies.
The applicants hope to improve the performance of the two Columbia units by:
- resolving the stress corrosion cracking concern in the LP steam turbine rotors by replacing the rotors and turbine casings; and
- improving the reliability and reducing the maintenance costs of the coal pulverizing systems by replacing them with newer systems.
These benefits, minus the capital and operating costs, would provide a net customer benefit of about $103m in present value revenue requirements (PVRR). The benefit would be increased by savings resulting from avoiding maintenance costs on the existing pulverizer equipment and steam turbines.
U.S. Energy Information Administration data shows that Columbia earlier this year was taking Powder River Basin coal from suppliers like Arch Coal (NYSE: ACI), Cloud Peak Energy (NYSE: CLD) and Alpha Natural Resources (NYSE: ANR).