Question 58 AEL01 - Assistant Engineer - Limited

The Correct Answer is C ### Why Option C is Correct: The purpose of a bottom blowdown in a boiler is to remove sludge, suspended solids, and concentrated chemical solids that have settled at the lowest point (mud drum or bottom header). These impurities tend to remain suspended while the boiler is firing or steaming, due to turbulent water circulation. To effectively remove them, the circulation must be minimized, allowing sufficient time for gravity to pull the solids out of suspension and onto the bottom surface. Therefore, the correct procedure is to perform the bottom blowdown **when the boiler has been secured (shut down or placed on standby) long enough for most solids to settle**. This maximizes the amount of contaminants removed per blowdown. ### Why Other Options Are Incorrect: **A) when the boiler has been cooled to ambient temperature** This is incorrect. While blowdown should ideally be performed when the boiler is secured, waiting until it reaches ambient temperature is unnecessary and impractical. Boiler pressure should be reduced, but the blowdown is typically most effective when the boiler is secured but still warm, shortly after circulation has stopped. Furthermore, cooling to ambient temperatures takes many hours and is not a required or beneficial part of the standard bottom blow procedure. **B) only after raising the water level to within 1/2 inch of the high water cutout** This is incorrect and potentially dangerous. While performing a blowdown does lower the water level, deliberately raising the level excessively close to the high water cutout is not part of the standard procedure and introduces a risk of carryover (water entering the steam line) or tripping the high water cutout, which would likely shut down the boiler or alarm unnecessarily. The operator should ensure the normal operating water level is maintained, but not intentionally raise it to an extreme high level beforehand. **D) only after bypassing the low-pressure pressuretrol** This is incorrect. Bypassing the low-pressure pressuretrol (a control that sets the operating range) does not affect the physical process of solids settling or the mechanical safety of the blowdown. The blowdown procedure is a mechanical operation designed to remove sediment, independent of the pressure control settings. Bypassing operational controls is generally discouraged unless absolutely necessary for maintenance or specific testing.