What is the last valve to be closed before lighting off?

What is the last valve to be closed before lighting off?

• A. Economizer Vent
• B. Blowdown Valve
• C. Main Steam Stop Valve
• D. Feedwater Valve

Answer: (A)

During boiler start-up, you purge air from the system and line routes so combustion can begin safely and efficiently. The economizer vent is opened to vent air and non-condensables from the economizer and its piping. Once the purge is complete, you close that vent last so the economizer is sealed and the flue gases produced when lighting off flow through it to preheat the feedwater. If the vent were closed earlier, purge air could remain and hinder ignition; if kept open too long, heat transfer would be wasted through the vent. The other valves are dealt with earlier in the sequence: the main steam stop valve is closed to isolate the boiler from the steam system, the blowdown valve is closed to stop water loss, and the feedwater valve remains in a position that allows water to enter as the boiler heats up. Therefore, the economizer vent is the last valve to be closed before lighting off.

During boiler start-up, you purge air from the system and line routes so combustion can begin safely and efficiently. The economizer vent is opened to vent air and non-condensables from the economizer and its piping. Once the purge is complete, you close that vent last so the economizer is sealed and the flue gases produced when lighting off flow through it to preheat the feedwater. If the vent were closed earlier, purge air could remain and hinder ignition; if kept open too long, heat transfer would be wasted through the vent. The other valves are dealt with earlier in the sequence: the main steam stop valve is closed to isolate the boiler from the steam system, the blowdown valve is closed to stop water loss, and the feedwater valve remains in a position that allows water to enter as the boiler heats up. Therefore, the economizer vent is the last valve to be closed before lighting off.