Question 277Steam Plants - Assistant Engineer

The correct answer is B) too much excess air. If the stack temperature is higher than normal, this could indicate that there is too much excess air in the boiler system. Excess air results in higher stack temperatures because the extra air carries more heat out of the boiler, reducing the overall efficiency. This is a common issue that can arise from improper boiler tuning or air/fuel ratio imbalances. The other answer choices are incorrect because they do not directly relate to the specific symptom of a high stack temperature. High feed water pressure, external casing leakage, and low fuel oil back pressure would not necessarily cause elevated stack temperatures on their own.