What is the importance of feedwater deaeration and how is it achieved?

• A. To maximize oxygen in water to enhance combustion.
• B. To remove all minerals from water.
• C. To increase CO2 in water for corrosion protection.
• D. To minimize dissolved oxygen and carbon dioxide to prevent corrosion; achieved with a deaerator or mechanical/thermal deaeration using steam.

Answer: (D)

Removing dissolved gases from feedwater is essential to prevent boiler corrosion. Oxygen in the water aggressively attacks boiler metals, and carbon dioxide forms carbonic acid, which lowers water pH and also promotes corrosion inside the boiler and feed piping. By reducing these gases to very low levels, the metal surfaces stay protected, helping maintain efficiency and extend equipment life.

This is achieved with a deaerator, which uses steam to heat the feedwater and to strip dissolved gases so they can be vented away. In practice, water is brought into contact with live steam—often by spraying it or passing it over trays—so the temperature rises and the gases come out of solution. The vent then removes the non-condensable gases, while the heated, gas-free water continues on to the boiler feedwater system. Because higher temperatures reduce gas solubility, this steam-assisted heating is key to effectively removing oxygen and carbon dioxide.