Corrosion-control Coatings Protect Power Plant FGD Systems

by Ed Sullivan

One of the main problems that put flue-gas desulfurization (FGD) plants out of operation is corrosion. Severe problems in FGD installations are caused when condensates of acids are formed, which accelerate pitting and crevice corrosion, particularly in scrubbers with high sulfate solutions.

Scrubbers lined with 2205 duplex stainless are among the most vulnerable, failing frequently because of pit or crevice corrosion from chlorides and fluorides.

A Dec. 17 article in the Pittsburgh Post-Gazette advises that corrosion problems in power plant FGD scrubbers are widespread.

“The corrosion problem in the scrubber vessel has occurred at as many as 70 other power plants across the country and appears to be caused by the type of metal alloy used for that part of the equipment,” writes environment reporter Don Hopey. “GenOn will install protective liners and coatings to correct the problem and expects to have those repairs finished by early March.”

The FGD failure that spawned Hopey’s article is at GenOn Energy’s Cheswick coal-fired plant near Pittsburgh.

According to a Dec. 7 GenOn letter to the Allegheny County Health Department, the emissions-control equipment installed during summer at the 637-MW power plant is already so severely corroded that it can’t be used, the article says.

The scrubber failures because of corrosion might be more common than the 70 problematic plants cited in the article, said Art Rak, CEO of Ultimate Corrosion Control (UCC) in Clarkston, Mich. He attributes much of the problem to the use of 2205 duplex stainless as FGD linings.

“While all FGD systems are somewhat different, over a 15-year history of working in the power plant market, abrasion, pit corrosion and chlorides in FGD systems have commonly caused failures,” Rak said. “Given the potentially aggressive corrosive conditions present in FGD systems–dew point, acidity, high temperature, concentrations of chlorides and fluorides, wet-dry cycles and gas velocity–no two systems are exactly the same. When it’s all said and done, what is really needed is the combination of chemical, abrasion and permeation resistance.”

The latter has worked well for UCC, which uses vinyl ester products called VE 62 and VE 62-AR manufactured by KCC Corrosion Control in Houston.

“The properties of this vinyl ester material have other significant advantages over other linings, especially its permeation resistance,” Rak said.

Permeation resistance of a polymer lining is the greatest determinant of life expectancy of a polymer lining system.

KCC VE 62 / VE 62 AR was used to coat test panels in an FGD ductwork section–specifically the gas cooler–ahead of a part of a Chiyoda CT-121 FGD system, said registered professional engineer Bryan Louque, of the Pipeline & Hazardous Materials Safety Administration.

“The FGD unit served a 500-plus-megawatt power station located in the Midwest,” Louque said. “Other coatings that were tested included troweled-on, thick film vinyl esters, a spray epoxy and vulcanized rubber. After six months of operation, the VE 62 test coupons showed no visible signs of abrasion or delamination from the test coupon.”

Louque said that KCC VE 62 exhibits abrasion and chemical resistance for a spray-applied vinyl ester. Temperature performance is similar to that of other spray-applied vinyl ester systems, he said.

Rak said the vinyl ester coating’s design also provides high performance when it comes to chemical and temperature resistance.

“It is a spray-applied, vinyl ester polymer that is easier to apply while outperforming trowel-applied linings, which is what power plants have to install to even approach the same performance,” Rak said. “Also, trowel-applied linings consume great quantities of field labor and waste a lot of material because a trowel is a very imperfect means of application and is extremely difficult to obtain a uniform thickness that is easily obtained by an airless, spray-on coating.”

Evidence of this savings and consistency as well as dramatically lower VOC of styrene is demonstrated by the vinyl ester (VE 62) coating’s normal thickness when spray applied. A 30-mil wet coat yields a 30-mil dry coat.

Author
Ed Sullivan is a Hermosa Beach, Calif.-based writer. He has researched and written about high technologies, health care, finance and real estate for more than 25 years. Email questions regarding VE 62 and VE 62-AR to kcc@kcccontrol.com.

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