Question 60 AEL01 - Assistant Engineer - Limited

The Correct Answer is D **Explanation of why option D is correct:** 1. **When the boiler is steaming (under pressure/firing):** A surface blowdown is most effective when the boiler is actively steaming or under light load. This is because the impurities (excess chemicals, dissolved solids, and salinity) that the surface blow targets tend to concentrate and skim the top layer of the water (the steam drum water level) due to density differences and the circulatory patterns caused by heating. If the boiler is secured, the water is stagnant, and the impurities are less concentrated at the surface exit point. 2. **Level maintained above normal:** When performing a surface blow, the boiler water level must be intentionally raised slightly above the normal operating level (but below the high alarm trip) before and during the operation. This ensures that the water being skimmed off is purely surface water, maximizing the removal of floating impurities and concentrated solids. Raising the level allows for a more controlled, thorough skimming action while reducing the risk of dropping the level too low during the operation. **Explanation of why the other options are incorrect:** * **A) The surface blow would be performed when the boiler is secured AND the level would be maintained above normal during the duration of the blow.** * **Incorrect:** Performing the blow when the boiler is secured (not steaming) is inefficient because the impurities are not concentrated at the surface due to lack of circulation and boiling action. * **B) The surface blow would be performed when the boiler is steaming AND the level would be maintained normal during the duration of the blow.** * **Incorrect:** While steaming is correct, maintaining the level strictly at "normal" (mid-gauge) makes the blowdown operation difficult and risky, as the level will rapidly drop below normal during the procedure. Furthermore, intentionally raising the level slightly maximizes the skimming efficiency of the surface layer. * **C) The surface blow would be performed when the boiler is secured AND the level would be maintained normal during the duration of the blow.** * **Incorrect:** Both conditions are incorrect. The boiler should be steaming for efficiency, and the level should be maintained above normal to ensure safe and effective skimming.