Question 17Steam Plants - Assistant Engineer

The correct answer is D) 79.0%. When there is no excess air for combustion, the nitrogen content of the flue gas will be approximately 79%. This is because nitrogen makes up about 79% of the Earth's atmosphere, and in the absence of excess air, the flue gas will primarily consist of the nitrogen component of the air used for combustion. The other answer choices are incorrect because: A) 10.5% is too low for the nitrogen content in the absence of excess air. B) 14.0% is also too low for the nitrogen content in the absence of excess air. C) 21.0% represents the approximate oxygen content of air, which would not be the case without excess air for combustion.