What is the purpose of the external desuperheater?

• A. To reduce the temperature of the auxiliary steam for the 150 psi auxiliary steam system
• B. To increase steam pressure in the main line
• C. To dry the steam
• D. To remove moisture from condensate

Answer: (A)

The key idea is that steam often leaves the boiler hotter than what downstream equipment can safely handle. An external desuperheater cools that steam by spraying water into the flow; the water absorbs heat as it evaporates, lowering the steam temperature to the level required by the 150 psi auxiliary steam system. This keeps auxiliary components from being damaged by excessive heat. It doesn’t raise pressure, dry the steam, or remove condensate—those are handled by other parts of the system.