Changing Boiler Feedwater Chemistry and Its Impact On Metal Transport
By Steven A. Dunn
A large three unit (2,400 pounds per square inch gauge [psig] drum) coal-fired generating station had recently been experiencing very high iron removal levels during recent boiler chemical cleanings. The units have full-flow, deep-bed condensate polishers with copper-based metals in the condenser and the first three feedwater heaters. The costs of the cleanings increased rapidly in recent years, spurring efforts to make changes to reduce iron corrosion product formation and transport to the boiler.
It is well known in the industry that most of the metal transport to a boiler originates from the pre-boiler system. The cause of the recent increase in iron levels during boiler chemical cleanings is thought to be due to the changing metallurgy of the pre-boiler feedwater heaters. Like many other power plants, this station is replacing the original copper metal based feedwater heaters with iron metal-based feedwater heaters as the old heaters fail. The change in the type of metallurgy in the pre-boiler system requires a change in pre-boiler chemistry (if possible) to minimize iron corrosion and iron metal corrosion product transport to the boiler.
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