What issue may arise due to fouling in a boiler system?

Fouling in a boiler system refers to the accumulation of unwanted materials on the heat transfer surfaces, such as heat exchangers, tubes, and the walls of the boiler. This buildup disrupts the normal flow of heat and gases, leading to several operational issues.

When fouling occurs, the insulation effect due to deposits decreases the heat transfer efficiency between the combustion gases and water or steam in the boiler. As a result, to maintain the required temperature and steam production, the system must operate at higher temperatures and pressures. This can lead to an increase in stack temperature because the system compensates for the heat loss caused by fouling by burning more fuel to reach desired performance levels.

Higher stack temperatures indicate that more heat is being released into the flue gases, which is not being effectively utilized for heating. This not only diminishes the energy efficiency of the boiler but can also lead to increased emissions and operational costs. Therefore, increased stack temperature is a direct consequence of fouling in the boiler system, making it the correct answer to the question.