In what situation is a draft fan most critical?

A draft fan is most critical during the combustion process because its primary function is to supply the necessary airflow for burning fuel efficiently in a boiler. Proper combustion requires a specific air-to-fuel ratio, and the draft fan helps maintain that balance by controlling the amount of air entering the combustion chamber. When the draft fan operates effectively, it ensures complete combustion, which maximizes energy output and minimizes harmful emissions.

During this phase, the fan also helps in managing the flue gases by creating a pressure difference that facilitates their removal from the combustion area to the exhaust stack. Insufficient airflow can lead to incomplete combustion, resulting in increased emissions such as carbon monoxide and unburned hydrocarbons, along with potential operational issues like soot buildup.

While draft fans play important roles during boiler shutdown, fuel delivery, and maintenance checks, their function is paramount during combustion to maintain efficiency, safety, and compliance with environmental regulations. This underscores the critical nature of draft fans in the operational effectiveness of boiler systems.