Question 413Steam Plants - Assistant Engineer

The correct answer is D) Economizer drain valve. Before lighting off a boiler, the economizer drain valve should be closed. The economizer is a heat exchanger that preheats the boiler feedwater, and the drain valve is used to remove any accumulated sediment or water from the economizer. Closing this valve ensures that the economizer is properly filled and ready for operation when the boiler is fired up. The other answer choices are not the valves that need to be closed before lighting off a boiler. The superheater vent and drain valves are used to control the flow of superheated steam, while the air cock valve is used to vent air from the boiler system. These valves do not need to be closed specifically before lighting off the boiler.