Plant engineers are adept at managing and maintaining aged equipment at the 800-MW Michoud power station, located 10 miles east of New Orleans (Figure 3). From November 2006 to November 2007, the generating station’s two units were off line less than 116 hours. Michoud Unit 2 operated 6,770 service hours, and its Unit 3 provided an exceptional 6,946 hours of service.
3. Prime performer. Plant engineers are adept at managing and maintaining aged equipment at the 800-MW Michoud power station, located 10 miles east of New Orleans. From November 2006 to November 2007, the generating station’s two units were off line less than 116 hours. Michoud Unit 2 operated 6,770 service hours, and its Unit 3 provided an exceptional 6,946 hours of service. Courtesy: Hach Co.
One key area at the plant where O&M excellence is evident is in maintaining plant water quality to avoid boiler tube leaks and other problems that can occur when using water that is outside of specification. During the same 2006 – 2007 time period, the 45-year-old Michoud Unit 2 experienced only two boiler tube leaks. Michoud Unit 3, which is 41 years old, had no leaks.
"Protecting boiler and turbine components from repairs and unscheduled downtime is critical," says Vinny Gagliano, water environmental technician for Entergy New Orleans, the subsidiary of Entergy Corp. that owns and operates the plant. "Good sampling, monitoring, and analysis of the steam-water cycle is essential for this, and one of the things we monitor very closely is silica."
Subpar water quality can endanger boiler tubes and piping by promoting corrosion, scaling, and fouling. At high temperatures, water contaminants such as silica can volatilize in the steam and deposit on the turbines or piping. Controlling silica helps avoid scaling and other detrimental effects in boilers, drums, heat exchangers, and condensers, where impaired heat transfer efficiency could ultimately impair production efficiency.
"We want to hold silica to very low levels because we don’t want it to carry over to the turbine blades," Gagliano says. Deposition on turbine blades from silica carryover in steam can result in inefficient and imbalanced spinning as well as thrown blades that directly reduce the plant’s power output and revenue. "Water moving through our boilers, especially our supercritical boiler, must be extremely high quality, since it affects both performance and overall boiler life."
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