Dominion Mt. Storm

Dominion Mt. Storm

May 05 - Power Engineering

Tucked on the northern edge of the Allegheny Mountains in eastern West Virginia, Dominion Energy's three-unit Mt. Storm power plant generates low-cost baseload electricity for millions of people in the Mid-Atlantic region. Units 1 and 2, which came online in 1965 and 1966, respectively, are rated at 551 MW (summer). Unit 3, which came online in 1973, is rated at 553 MW (summer). All three units feature tangentially fired CE boilers with six levels of ignition and low-NOs burners. Units 1 and 2 have Westinghouse steam turbines; Unit 3 has an ABB steam turbine.

The plant's proximity to the Appalachian coalfields has historically kept fuel prices down. About 80 percent of the coal used at Mt. Storm is mined locally. About three-fourths of the coal consumed at Mt. Storm is under long-term contract, which also helps keep prices down. The recent gyrations in the coal market, however, have had an impact on plant operations, according to Roger Shears, Director of Fossil and Hydro Station III (Mt. Storm). "Historically, our coal has been in the 12,200 to 12,500 Btu/lb range, with 13 to 15 percent ash, and a Hardgrove Grindability Index of 70. Today, we're occasionally seeing coal at 10,500 Btu/lb, 25 percent ash and an HGI of 45. Such variation in fuel quality makes it difficult to optimize the coal mills and the boilers with respect to a particular fuel."

Mt. Storm is equipped with six coal mills. This has provided a measure of flexibility because only five are required for full-load operation, but plant personnel have had to make certain accommodations. Coal mill roll settings, for example, which typically are at 6 to 7 tons of compression on the springs, have been increased to 9 to 10 tons. "This setting is too heavy for the softer coals and not quite enough for the harder coals," said Shears, "so we're essentially splitting the difference to maintain throughput." Further, the use of higher volatile fuels has forced the plant to reduce mill outlet temperatures, from 180 F to 155 F, to lessen the chances of mill fires or explosions.

Mt. Storm's performance record is impressive. Capacity factor, 92 percent in January 2005, with an 85 percent average over the past few years. Forced outage rate, 4 percent in January, with an 8 to 9 percent average. Heat rate, 9,717 Btu/kWh in January, with a 9,800 to 9,900 Btu/kWh average in recent years. Dominion has devoted significant resources in several areas to improve these numbers. To address boiler tube leaks, Mt. Storm is working with the corporate engineering group on an aggressive program aimed at early detection, fleet-wide tube leak mapping, and tube replacement. Mt. Storm is specifically exploring changes in boiler tube materials in certain locations to reduce the frequency of leaks. For example, spiral welded tubing using Inconel 622 material for the weld overlay has been used in burner corners to reduce erosion; and superheat pendant platen tubes have been replaced with stainless steel material, SA 213-TP347H, to combat fire-side corrosion.

Mt. Storm has also paid particular attention to steam carryover and condenser tube leaks. The steam drums for Units 1 and 2 are marginally sized for the steam flow, leading to stresses that have caused cracks in the steam liner and carryover into the superheat section. The carryover has resulted in sulfate and phosphate build- up, leading to overheating and tube leaks.

"In the condensers, we were seeing some leakage and seepage past the machined and driven plugs used for the stainless steel tubes," said Shears. "The Unit 1 and 2 steam turbines were particularly susceptible to deposit build-up, and over a 90 to 120 day period, we'd lose 20 to 30 MW of generating capacity." Mt. Storm tried several of the conventional leak detection techniques, including saran wrap and gas inspection, but still encountered various leakage episodes. Borrowing a technology used at Dominion's nuclear facilities, Mt. Storm finally tried a technique called dimple plug testing. This technique uses a modified rubber stopper plug with the center hollowed out, creating a thin membrane on the head. Over four to six hours, even a small leak will cause the plugs to dimple in, identifying the leak.

"By tightening our condensers, which enabled us to switch from a phosphate-based water treatment program to an all-volatile treatment program, we reduced deposit build-up and reduced our lost capacity to just 10 to 12 MW," said Shears. "Also, because we had been running at a lower pressure to minimize carryover, we were able to increase the throttle pressure from 2450 psi to 2520 psi, recovering another 10 MW."

Mt. Storm has historically targeted a nominal 40/60 ratio of preventive to corrective maintenance tasks. A recent concerted effort to complete PM tasks on schedule has begun to reduce the amount of corrective maintenance needed. "This has required a disciplined effort," said Shears, "but once you get over the hump, the preventive maintenance investment quickly pays for itself."

The plant's condition-based maintenance group has also paid significant dividends. Lube oil analysis, for example, identified an impending bearing failure in a critical coal crusher. "The early identification allowed us to preplan the work, minimizing out- ofservice time as well as scheduling the work at a time that did not disrupt unit operation," said Shears. "A recent horizontal superheater inspection in the boiler revealed severe fly ash erosion to several tubes, creating impending tube leak outages. We were able to replace the damaged areas, correct the cause of the erosion and prevent costly forced outages."

Mt. Storm instituted a six-sigma program several years ago and currently has two black belts on staff. A recent sootblower maintenance project highlights the program's value. With more than 100 sootblowers in each boiler, mechanics spend a great deal of time keeping them operational. Through a six-sigma project, Mt. Storm determined that not all sootblowers are equal; some have a greater impact and value than others. As a result, Mt. Storm has begun categorizing individual sootblowers as high, medium and low impact. If a mechanic has limited time for sootblower maintenance, he will focus his efforts on those with higher impact.

Dominion has significantly refined its outage management approach to optimize turnarounds. A corporate outage group works with plant personnel up to one year in advance to examine the maintenance backlog, identify boiler and turbine needs, and coordinate outage activities. For a recent outage on Unit 2, the original schedule called for 98 days. By working with the various outage teams - boiler, steam turbine, scaffolding, cleaning, metallizing, etc. - the schedule was reduced to 75 days, and may come in under 72 days, according to Shears. Further, the integrated planning has enabled Mt. Storni to reduce expediting costs associated with overtime, headcount, and parts supply. We've essentially paid for the outage team's salary in reduced expediting costs," said Shears.

All three units at Mt. Storm are equipped with scrubbers and SCRs for SO^sub 2^ and NO^sub x^ control. The scrubbers are designed for 95 percent SO^sub 2^ removal, but have typically achieved 97 to 98 percent removal on a 30-day rolling average. Because the plant is remote from large metropolitan areas, wallboard gypsum is not produced. The scrubber byproduct, however, is reinjected into local coal mines for acid mine drainage neutralization. The SCRs, designed for at least 90 percent NO^sub x^ removal, currently only operate during the ozone season, but will operate year-round beginning in 2008. Mt. Storm has experienced some large-particle ash problems in the SCRs, but plant management has decided not to install a screen ahead of the SCR because of industry problems with such solutions. Instead, Mt. Storm will spend some time investigating the boiler conditions that are producing the ash in the first place. Mt. Storm also decided to install ceramic-coated cold-end baskets in the air preheater to eliminate damage from ammonia bisulfate production. As a result, the air preheaters have stayed clean.

Mt. Storm utilizes some cross-training for its 270 employees. For example, mechanics can perform limited electrical checks and operators can adjust packing. A recent agreement with the IBEW local enables welders to enter the mechanic's development program and vice versa. "The program is entirely voluntary, but most new trainees and even a number of long-term employees have decided to participate," said Shears. "Participants receive an increased hourly rate if they make it through the program."

The aging workforce issue has caught Mt. Storm's attention. One technique Dominion is exploring is an early employment program, where electricians and mechanics are hired two years early and operators are brought in three years early. "In the current marketplace, it is difficult to budget for this, but it could have tremendous benefits as more and more of our employees near 3 retirement age," said Shears.

BY BRIAN K. SCHIMMOLLER, MANAGING EDITOR