Which component in the boiler feedwater system removes dissolved gases from the feedwater?

• A. Deaerator
• B. Economizer
• C. Feedwater pump
• D. Steam separator

Answer: (A)

Dissolved gases in feedwater, especially oxygen and carbon dioxide, drive corrosion inside the boiler and tubes. The component designed to remove these gases is the deaerator. In a deaerator, feedwater is heated (often with steam in an atmospheric vessel) so the solubility of gases drops, and the non-condensable gases are vented to the stack. This leaves feedwater with very low levels of dissolved gases before it goes into the boiler, protecting metal surfaces and improving reliability. The deaerator also serves as a feedwater heater, using exhaust steam to raise water temperature and boost overall efficiency.

Other parts have different roles. An economizer uses flue gas heat to preheat feedwater but doesn’t strip dissolved gases. The feedwater pump increases pressure but doesn’t remove gases. A steam separator removes entrained steam from the water but not dissolved gases.