Question 312Steam Plants - Assistant Engineer

The correct answer is D) a decrease in boiler efficiency. Excessive carbon deposits on the boiler burner throat ring and diffuser can restrict the flow of air, reducing the amount of excess air available for combustion. This decreased air flow leads to incomplete combustion, which in turn reduces the overall efficiency of the boiler. The carbon deposits act as an insulator, hindering heat transfer from the flame to the boiler water, also contributing to the decrease in boiler efficiency. The other options are incorrect because: A) reduced fuel oil pressure is not a direct result of carbon deposits, B) increased heat transfer and overheating would not occur due to the insulating effect of the carbon deposits, and C) too much excess combustion air is the opposite of what happens when carbon deposits restrict air flow.