Which device removes dissolved gases from feedwater before it enters the boiler?

• A. Deaerator
• B. Soot blower
• C. Blowdown valve
• D. Water softener

Answer: (A)

Dissolved gases like oxygen and carbon dioxide in feedwater cause corrosion and pitting in boilers, which hurts metal integrity and heat transfer. Removing these gases before the water enters the boiler is essential for protecting the system and maintaining efficiency. The deaerator is designed for this purpose. By heating the feedwater toward its boiling point and venting the released gases, it strips out the dissolved oxygen and CO2, delivering deaerated water to the boiler. The effectiveness relies on the fact that gas solubility decreases with increasing temperature, so heating drives off the gases that would otherwise corrode the boiler internals.

Soot blowers, in contrast, clean soot from the furnace tubes to keep heat transfer efficient but don’t remove dissolved gases from feedwater. A blowdown valve is used to purge boiler water to control dissolved solids, not to purge gases. A water softener removes hardness minerals to prevent scale, not to remove gases. So the deaerator uniquely fulfills the role of removing dissolved gases before the water enters the boiler.