Question 83Steam Plants - 1st Asst/Chief

The correct answer is B) efficient combustion. The absence of carbon monoxide (CO) in the flue gas of a boiler indicates that the combustion process is efficient, meaning the fuel is being burned completely with the proper air-to-fuel ratio. When combustion is efficient, the fuel is fully oxidized, and CO is not present in the exhaust. This is the desired outcome, as the presence of CO would indicate incomplete combustion and potential safety/efficiency issues. The other answer choices are incorrect because: A) low carbon content of fuel would not necessarily lead to the absence of CO; C) insufficient air would actually cause incomplete combustion and the presence of CO; and D) contaminated fuel oil would more likely result in the presence of CO, not its absence.