What is the function of the windbox in a boiler?

The windbox in a boiler serves as the chamber through which combustion air is introduced to the boiler furnace. Its main purpose is to ensure that the combustion process receives a steady and controlled flow of air, which is essential for efficient burning of fuel. The windbox helps to distribute the air evenly across the furnace area, promoting optimal combustion and maximizing efficiency.

By directing the combustion air into the furnace, the windbox plays a critical role in maintaining proper air-to-fuel ratios, which is vital for effective operation. If the combustion air does not enter the furnace adequately, it can lead to incomplete combustion, increased emissions, and reduced efficiency.

In this context, the other choices do not accurately represent the primary function of the windbox. It is not primarily maintained at a negative pressure, nor is it a collector for exhaust gases before they exit the boiler. While the mixing of fuel and air for combustion is essential, the windbox specifically focuses on the introduction of combustion air rather than being responsible for the mixing process itself.