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Using Electrochemical Protection to Prolong Service Life of Scrubbers and Associated Equipment

Published: 19980301 by NACE International
Author(s): Winston Shim
Co-Author(s): Eldon Dille - Sargent and Lundy Engineers

Austenitic chromium-nickel-molybdenum-iron alloys (904L 316L 317 L, etc.) used to construct Flue Gas Desulfurization (FGD) scrubbers and associated equipment in coal fired generating stations can experience localized corrosion. The problem may be alleviated by using more costly materials such as higher grades of stainless steel or high nickel alloys. An alternative and more cost-effective method of prolonging equipment service life is the use of Papritection@, an electrochemical protection system (EP). Weight-loss coupon results in environments similar to FGD scrubbers have shown that the use of electrochemical protection prolongs the life of stainless steels in oxidizing acid-chloride environments by an average of 3 to 5 times.
This paper discusses an EP system that was recently supplied to an electric power utility company to protect a 316L thin metallic lined (wallpapered) FGD scrubber reaction tank. Acidic effluent from the absorber section of the scrubber is piped into this reaction tank for limestone neutralization and hence formation of calcium sulfate. Inspection of the protected reaction tank after one year of operation as well as in-situ coupon test results indicated that the EP system was very effective in mitigating localized corrosion of the scrubber reaction tank. The results are presented in this paper.