There is no denying that as power plants age, they grow more susceptible to increased maintenance, higher forced outage rates, reduced efficiency and emission excursions. By the same token, however, sustained investment in an aging plant can yield significant benefits and position the plant as a low-cost, low-emission source of power. DTE Energy has taken this philosophy to heart at the St. Clair Power Plant in St. Clair, Michigan. According to Ben Kiehl, St. Clair Plant Director, “We’re re-inventing ourselves by implementing an operating systems framework for doing business that relies on a set of core principles including safety, benchmarking, open communication, accountability, activity-driven decision-making, and waste elimination.”
The St. Clair Power Plant dates back to 1952, when Units 1-4 entered service. A total of seven coal-fueled boilers were ultimately built at St. Clair, although only six remain operational. Units 1-4 are 163 MW Babcock & Wilcox boilers tied to GE and Allis Chalmers steam turbines. Units 6 and 7 are tangentially fired Combustion Engineering boilers tied to Westinghouse steam turbines. Unit 6 is rated at 321 MW and Unit 7 is rated at 451 MW. Unit 5, a 300 MW cyclone boiler, was taken out of service in 1979.
Ben Kiehl, St. Clair Plant Director
St. Clair is ISO 14001 Environmental Management System certified and has recently been awarded the Clean Corporate Citizen designation by the Michigan Department of Environmental Quality.
Ben Kiehl, St. Clair Plant Director
St. Clair is essentially a baseloaded plant, dispatched after DTE Energy’s nuclear unit and the neighboring Belle River coal-fired power plant. Between 1999 and 2003, plant capacity factor averaged 57%, plant heat rate averaged 10,449 Btu/kWh, and the equivalent forced outage rate averaged 18%. “Admittedly, our numbers aren’t sterling, yet,” says Kiehl. “One of the reasons our availability has not been as good as it will be is that we’ve had a lot of extraordinary events – for example, an unexpected generator winding failure in Unit 2 took the unit off-line for six months in 2003.”
In the middle to late 1970s, the plant was converted to burn Western sub-bituminous coal. The conversion resulted in unit derates and necessitated the installation of larger electrostatic precipitators on Units 1-4 and Unit 6. In addition, low NOx burners and overfire air ports have been installed on Units 6 and 7, are currently being installed on Unit 3 and will be installed on the remaining three units by the end of 2005.
To help minimize furnace pluggage, St. Clair has to periodically de-slag the boilers, which are undersized for firing Western coal. For Units 1-4, load is lowered every other night for three hours in order to de-slag, according to Jack Guillaumin, Production Manager. For Units 6 and 7, de-slagging occurs every third night. St. Clair also closely adheres to furnace exit gas temperature limitations. “We use furnace exit gas temperature (FEGT) as an index to provide a repeatable point of reference that we avoid exceeding,” says Guillaumin. “Keeping FEGT below established guidelines reduces slagging and fouling, thereby reducing the rate of furnace pluggage and extending run length between furnace on-line and off-line cleanings” St. Clair is also investigating the use of a magnesium hydroxide additive to prevent fouling.
St. Clair burns a blend of low-sulfur Western coal (from the Decker and Spring Creek mines in Montana) and high-sulfur Pittsburgh-seam Eastern coal. Blending is done in the coal yard with variable speed feeders. Although the nominal blend is 85% Western and 15% Eastern coal, the exact blend depends on a number of factors including demand requirements, coal prices, stockpile inventory, and unit availability. In the summer months, for example, the blend trends toward 70/30 on Units 6 and 7 to gain additional generating capacity by firing more Eastern coal with its higher heating value. The higher sulfur content of the Eastern coal also helps prevent opacity excursions with the ESP on Unit 7, according to Don Snyder, St. Clair Fuel Supply Manager.
Fuel supply and stockpile management at St. Clair is unique. The Western coal is delivered to Superior, Wisconsin, by unit train and then barged to St. Clair on 60,000-ton vessels. Because the vessels typically can’t operate on the Great Lakes from late December until late March, the plant must stockpile between 2.1 and 2.4 million tons for the winter season. Eastern coal is delivered by rail. “We’re finding that Pittsburgh-seam coals are becoming scarce,” says Snyder. “We used to stock 140,000 tons heading into the winter; now we stock 20,000-30,000 tons, which equates to only about 10-15 days of inventory.”
Because St. Clair borders several residential areas, coal pile management and dust control take on added significance. Compaction using heavy scrapers is the plant’s main strategy. “If we keep the coal compacted, we can minimize spontaneous combustion,” says Snyder. “We can only sit on loose piles for about two weeks before having to move them.” St. Clair relies heavily on front-end loaders to dig out hot spots that develop when loose material is washed down the side of a given pile and accumulates at the bottom. To prepare Western coal piles for winter storage, St. Clair uses a latex sealant that is applied using a converted scraper equipped with a 10,000-gallon tank.
The single biggest source of downtime at St. Clair — as it is at most coal-fueled power plants — is boiler tube leaks/failures. Across St. Clair’s six units in 2003, 15 forced outages were related to boiler tube integrity problems. The plant is using EPRI’s Boiler WorkStation to track and trend the boiler tube problems, and is working with Washington Group International to identify the various failure mechanisms, ascertain root causes, and implement corrective actions.
“One of the things that will drive our future excellence is the concept that, if we take a unit down for a periodic outage, we’re going to do it correctly,” says Kiehl. “We’ll take fewer periodics, but invest more money during the window of opportunity to ensure we address all of the issues. In a forced outage situation such as a tube leak, we could historically get away with patching the problem and getting the unit back on-line in three or four days. Now, more commonly, if market conditions allow, we’ll extend the outage to address additional reliability issues in order to bring the unit back with more assured availability.”
In another unique program aimed at higher reliability, St. Clair has entered into a coal mill alliance with Babcock & Wilcox. Persistent maintenance problems associated with broken mill shafts on the EL-70 ball mills on Units 1-4 has led to an arrangement in which DTE Energy will compensate Babcock & Wilcox based on coal throughput ($/ton coal ground). St. Clair will supply the craft labor and B&W will provide the parts and technical expertise. “If the mills aren’t running, B&W won’t get paid, so this makes them an ‘owner’ in the reliability of the units,” says Kiehl. “We both stand to gain financially from this arrangement.”
Training has become a top-priority issue at St. Clair. “Because this is not an easy plant to operate, we’ve struggled with employee retention,” says Guillaumin. In October of 2001, 72% of plant operators had less than three years’ experience and 65% of them were control room operators. To reverse this trend, St. Clair greatly boosted its training program, hiring back two supervising/control room operators to support the training coordinator for the operations staff. Plant management also added two senior leaders to each operating shift. These senior leaders, who don’t have day-to-day operator duties, have a primary function to act as on-the-job trainers. “For example, if we’re having problems cutting in a boiler feed pump, the senior leaders will reserve a block of time during the month to work with each operator on a one-on-one basis to review critical procedures,” says Guillaumin.
The training emphasis has been a success. Operator turnover has dropped significantly. Currently, 46% of control room operators and 44% of plant operators have less than three years’ experience. By December 2004, St. Clair expects to be at 32% for control room operators and 16% for plant operators. Further, the more open communication style has enabled operators to learn from their mistakes and enabled management to pinpoint training deficiencies.
Maintenance planning at St. Clair is divided into forced and periodic outage categories. For forced outages, the head unit engineer for each unit doubles as the unit’s outage manager. This person is responsible for maintaining an outage plan to identify critical work under various scenarios, executing the plans when an outage occurs, and managing the budget. The plans are built around 3, 5, and 7-day outage schedules so the plant can muster the necessary resources when opportunities arise. The plan is reviewed weekly to ensure everyone knows exactly what to expect if and when a unit comes down.
For periodic outage maintenance planning, Detroit Edison’s Fossil Generation Organization (St. Clair’s parent organization) has developed a process handbook. The handbook contains 52 milestones, extending as far as 24 months in advance of the outage date, to define roles and responsibilities across a set timeline. The process also
provides a forum in which to discuss and formalize concepts for
managing cost during the outage, adhering to the schedule, utilizing labor, etc. Kiehl believes this formalized process provides a major “shot in the arm” for professionalism and accountability.
St. Clair has a Technical Group that supports Fuel Supply, Unit Operations, Water Chemistry, Environmental, Thermal Performance, and Predictive Maintenance. Engineers and technicians provide trouble-shooting services, make recommendations for capital improvement, manage outages, and provide numerous predictive tools and testing for maintenance.
St. Clair and its employees participate in DTE Energy’s incentive plan through its overall contributions to corporate goals (which make up 70% of the award), and through its more direct contributions to Fossil Generation Organization goals (which make up the remaining 30% of the award). At the fossil generation level, St. Clair has a number of specific targets. Safety goals are defined in terms of the number of OSHA recordable injuries per 200,000 work hours. The target value is 3.9, with minimum (threshold) and maximum levels of 5.0 and 2.5, respectively. One of the operational excellence goals is for opacity, measured in terms of the number of reportable six-minute average exceedances greater than 20% divided by the number of fan run hours. The target level is 0.129%, with minimum and maximum levels of 0.145% and 0.113%, respectively. A second operational goal is for equivalent availability factor, with a target of 80.5% and minimum and maximum levels of 78.5% and 82.5%, respectively.
DTE Energy’s St. Clair Power Plant in St. Clair, Michigan
To promote and drive continuous process improvement at St. Clair, DTE Energy has implemented a “four block” program across its fossil generation organization. “The four block system is a method for tracking and trending performance with an eye toward developing a road map to take you from current reality to some future better state,” says Kiehl. “It incorporates issue identification, Pareto diagrams (the 80/20 rule), trend charts and system cost analyses to define areas in which improvement is necessary and how such improvement can be achieved.” Individuals involved in this process are trained in six sigma techniques and statistical analysis, ultimately becoming “Operating System Specialists” and in some instances “Black Belts” charged with identifying and implementing quality optimization initiatives. “In simple terms, the intent is to define and measure performance against established metrics to determine if we’re doing better,” says Kiehl.
No task is too mundane for such quality analysis. “For example, the person responsible for plant cleaning and building maintenance began to question the cleaning specifications based on a cost analysis he performed,” says Kiehl. “He got a group together to examine the issue, and now we’re in the process of re-writing our cleaning specs to better utilize our labor.” The same individual learned statistics and was able to prove to several vendors that their costs for cleaning supplies had increased beyond acceptable limits.
The improvements at St. Clair have not, and will not, come cheaply. Kiehl is convinced, however, that the money is well spent, solidifying the facility’s position as a low-cost energy supplier and enhancing its reputation as a good neighbor, attractive employer, and valued corporate citizen.