By Brian K. Schimmoller,
Great River Energy’s Coal Creek Station in central North Dakota has twin 550 MW lignite-fired units. The Alstom (CE) split furnaces, completed in 1979 and 1980, are among the largest in the world at 90 feet wide, 45 feet deep and 210 feet tall. Eight pulverizers feed lignite to 64 burners and the boilers have been retrofit with separated overfire air for NOx control. Each unit is equipped with an electrostatic precipitator and wet lime flue gas scrubbers. The primary transmission outlet for the station is a 400 kV DC transmission line from the station to just west of Minneapolis, Minn.
For the three-year period between 2000 and 2002, the gross plant heat rate averaged about 10,360 Btu/kWh and the net plant heat rate averaged about 11,085 Btu/kWh. Net running plant capacity factor measured 90.9 percent, and station availability averaged 94.7 percent. Major outages are scheduled on a three-year interval, so the availability factor reflects availability loss due to scheduled outages as well as forced outages.
John Weeda, Coal Creek Plant Manager
“Employees are the key ingredient to maintaining high availability,” says John Weeda, Coal Creek Plant Manager. “Employees are taught to consider the economic impact of their work, to continually seek to improve on their work processes and to be accountable for the system they operate and maintain.” Employees are organized into ‘core’ areas aligned with the plant’s physical processes: turbine area, boiler area, flue gas area, and fuel and ash handling area. Other employees are organized in support groups and operating groups. Each employee ‘owns’ a set of equipment. “This sense of ownership has translated into cost effective and reliable operating and maintenance practices,” says Weeda. “For example, the operators quickly noticed that there were fewer equipment failures requiring personnel to be called in for emergency maintenance as employees sense of ownership increased.
Coal Creek nurtures a benchmarking culture at the plant, but considers it ‘benchmarking the future instead of the past.’ This practice examines work processes to see if they are aligned with processes that have produced world-class results at other locations. For example, EPRI Plant Maintenance Optimization techniques are incorporated into training for maintenance personnel. At one training class, craft, planning and supervisory personnel rated 20 parameters of the maintenance processes and compared their rating with world-class organizations. “Such training, coupled with process improvements and employee dedication, has resulted in numerous maintenance success stories,” says Weeda. “Intervals between pump overhauls have been increased at least two to three times, cooling tower maintenance budgets are one-fourth what they were just a few years ago, and ash NUVA feeder maintenance costs are down substantially.”
Maintenance planners only schedule work that is cross-functional between core groups. If an ash line is scheduled to be out of service, there may be work in the scrubber that can be done at the same time since scrubber blowdown is dependent on the ash line in service. If a pulverizer overhaul requires more craft employees than are available within the core work group, planners schedule that work so craft resources from other areas can be coordinated. For other maintenance, the planners provide parts support, but, contrary to conventional wisdom, maintenance craft employees are responsible for keeping track of the backlog of work on their equipment and for integrating work orders together for efficient conduct of the work. They are also encouraged to identify needed work on their own and to perform maintenance proactively before equipment reaches the failure point.
Since the market value of electricity produced by the plant typically exceeds maintenance costs by several multiples, coordination of any work involving load reduction or shutdown is carefully coordinated with market conditions. Maintenance options are weighed against the lost revenue opportunity or the cost of replacement power in the market. The Outage Manager keeps track of the market cost of all outages and load reductions, says Weeda, and this information is shared with employees whose work has an impact on the outage. For example, the leader of the boiler core area discusses the cost of a boiler tube outage with the employees in that area, enabling the operators to see the impact of shutdown, cooldown and startup time on the overall outage cost.
Fly ash and SO2 allowances are also treated as important products at Coal Creek. Fly ash quality control begins with the mining plans in the adjacent lignite mine; pulverizer fineness and the combustion process are also watched carefully to maintain quality. Finally, any ash affected by oil fires or other problems is diverted to a waste silo. On-site storage of around 100,000 tons provides flexibility to deliver fly ash when the market demands it.
Employees in the flue core area take SO2 allowances very seriously. The condition of the scrubber modules and the accuracy of the Continuous Emission Monitor system determine the number of SO2 allowances that can be saved for sale in the emissions market. The available SO2 allowances are updated monthly and a corporate-wide team meets periodically to review marketing strategy, to time sales to market price, and to meet company financial objectives.
The plant has been very successful in implementing improvements that result in low-cost or fuel-free megawatt-hours. Station service power requirements have been reduced by 1.5 percent in recent years, according to Weeda, via optimizing fan and motor sizes, selecting more efficient equipment, improving valve maintenance and providing operators with better information. For example, Coal Creek realized a 25 percent reduction in power requirements through installation of variable speed drives on the ash pumps, and a recent digital control system upgrade gives operators tighter control over steam conditions and other controllable parameters.
Coal Creek carefully monitors its workforce staffing levels and incentive programs. “Each time an opening has occurred during the past several years, plant staffing has been reviewed,” says Weeda. “The review included looking at processes that had been improved and determining if there was any way to shuffle assignments to take advantage of the improvement to avoid filling the opening. As a result, the plant staff has been reduced approximately 20 percent.” The GRE corporate Success Sharing Plan includes incentives for the hourly and salaried workforces. The incentive measures are tied to safety and to performance supporting the plant’s mission to be a low-cost provider to member cooperatives.
Weeda sees two major challenges in the next several years: “A large number of the current long-term employees will reach retirement age in 5-10 years. Retaining their knowledge and transferring that to incoming employees will be critical for continued success. Also, in that same time frame, changes in environmental regulation will pose challenges on how to remove mercury from the flue gas and how to make further reductions in NOx and SO2 for regional haze considerations.”