How does the attemperator control the temperature of superheated steam?

• A. By injecting small amounts of boiler feed water into the steam header
• B. By removing condensate
• C. By adjusting burner fuel
• D. By venting steam to atmosphere

Answer: (A)

The key idea is that temperature control of already superheated steam is done by desuperheating through water spray. An attemperator injects a carefully metered amount of boiler feedwater into the steam header. The colder feedwater mixes with the hot steam, and as it absorbs heat (and some of it flashes to steam), the overall temperature of the steam drops to the desired setpoint while the pressure remains effectively controlled downstream. This direct in-line cooling is the purpose of the attemperator and is why injecting feedwater is the correct method.

Other actions don’t provide the same controlled temperature adjustment: removing condensate mainly handles liquid water content and flow issues, not the steam’s temperature; changing burner fuel affects boiler output upstream rather than adjusting the existing steam’s temperature in the header; venting to atmosphere wastes energy and does not maintain a stable, controlled steam temperature.