Boiler feedwater — high-pressure units use deaeration chiefly to reduce which dissolved constituent and thereby limit corrosion?

Introduction:
Corrosion in boilers is strongly accelerated by dissolved oxygen. Mechanical and thermal deaeration, often followed by chemical scavengers, is standard practice in high-pressure systems. The question asks what deaeration primarily reduces.

Given Data / Assumptions:

• System: high-pressure boiler feedwater.
• Process: deaeration (mechanical/thermal).
• Goal: corrosion control via removal of dissolved gases.

Concept / Approach:
By heating and contacting water with steam in a deaerator, oxygen solubility drops and oxygen is stripped out. Remaining traces are scavenged (e.g., hydrazine or sulfite in some systems).

Step-by-Step Solution:

Verification / Alternative check:
Boiler water treatment guidelines prioritize oxygen removal to protect economizers and feed lines from pitting.

Why Other Options Are Wrong:

• Foaming: controlled by antifoams, proper alkalinity, and solids management, not by deaeration alone.
• Silica: addressed via demineralization; deaeration does not remove silica.
• Caustic embrittlement: managed through alkalinity control and metallurgy; not solved directly by deaeration.

Common Pitfalls:
Assuming deaeration is a substitute for full water treatment; it targets gases, not dissolved salts.

Final Answer:
Deaeration reduces the dissolved oxygen content of boiler feedwater.