Question 470Steam Plants - Assistant Engineer

The correct answer is B. When an automatic auxiliary boiler is prepurged, the damper on the inlet side of the furnace is moved to the open position for a given number of seconds to allow for the removal of any unburnt fuel or gases from the furnace prior to ignition. This is done to ensure a safe and complete combustion process. The damper is then moved to the low fire position to prepare the boiler for ignition at a reduced firing rate. The other options are incorrect because they do not accurately describe the sequence of events that occurs during the prepurge of an automatic auxiliary boiler. Option A describes the damper being moved to the closed position, which would not allow for the necessary air flow and purging of the furnace. Options C and D describe actions that are not specific to the prepurge process for an automatic auxiliary boiler.