What is the primary role of an induced draft fan in steam generating plants?

The primary role of an induced draft fan in steam generating plants is to maintain a slightly lower pressure than atmospheric pressure in the firebox. This is critical for ensuring proper combustion and efficient operation of the furnace. When the pressure inside the firebox is lower than atmospheric pressure, it helps to pull air into the combustion system, facilitating the necessary airflow for burning the fuel efficiently.

Creating a slight negative pressure not only aids in achieving optimal combustion but also helps to manage flue gases and prevents potential backdrafts that could compromise safety and performance. This controlled environment in the firebox is essential for maximizing energy extraction from the fuel and minimizing pollutant emissions.

Other options may imply functions that are not directly related to the induced draft fan's role in maintaining combustion efficiency and safety within the firebox. Thus, maintaining a lower pressure is fundamental to the effectiveness of the fan in a steam generating system.