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Part 1 of 4: Overview

Protecting the boiler, the most important component of a power plant, presents unique challenges. The quality of the water moving through the boiler is key to both performance and overall boiler life. This series of articles discusses challenges specifically related to water quality in boiler applications:

• Carryover of impurities
• Management of blowdown
• Cooling water in-leakage to condensate
• Water Conditions: Raw Water and Process Water

Feedwater

Challenge: Carryover of Impurities
Impurities in the feedwater system transport to the boiler where they deposit on surfaces. This results in heat transfer loss, reduced efficiency, and an increased risk of boiler tube failure. From the boiler, impurities carry over into steam causing scaling and turbine blade corrosion. Deposits on the turbines reduce efficiency, directly reducing the plant's power output and resulting revenue.

Potential sources of impurities can include:

• Return condensate
• Makeup water
• Chemical cleaning
• Water treatment chemicals
• Condensate polishers
• Condenser leaks
• Glycol (antifreeze) from plant equipment
• Paints and solvents
• Air in-leakage
• Corrosion products
• Combustion products

Measurements to fight corrosion and minimize carryover include close control of pH and oxygen levels. Silica must be held to exceptionally low levels in high-pressure boilers to prevent carryover into steam and deposition on turbine blades. In addition, ammonia or neutralizing amines may be applied to neutralize CO2, an acidic byproduct that promotes corrosion. Filming amines are often used to form a protective coating on steam system metal surfaces.

Online monitoring of key parameters such as pH, conductivity, Dissolved Oxygen (DO), silica, sodium, and, if applicable, phosphate and hydrazine help maintain optimum boiler chemistry and minimize solids carryover. Refer to the table below for details.

SOURCE: Hach Company