Which statement best describes the role of oxygen scavengers in boiler feedwater treatment?

• A. They increase dissolved oxygen to improve oxidation.
• B. They remove minerals from water.
• C. They neutralize acid in feedwater.
• D. They remove dissolved oxygen from feedwater to minimize corrosion.

Answer: (D)

Oxygen in boiler feedwater is a major cause of corrosion, especially on hot metal surfaces. Oxygen scavengers are added to remove that dissolved oxygen before it reaches the boiler by acting as reducing agents that react with O2 to form harmless products like water or nitrogen. This keeps the oxygen level very low and protects the metal from rust and pitting, extending the life of boiler components. For example, sodium sulfite reacts with dissolved oxygen to form sulfate, while hydrazine converts oxygen and water into nitrogen gas and water. The goal is to minimize corrosion, not to increase oxygen, remove minerals, or neutralize acid, which do not address the dissolved oxygen problem in the feedwater.