When adjusting the firing rate of a boiler, why should air be increased to the burner before fuel?

Increasing the air supply to the burner before adjusting the fuel is crucial for ensuring complete combustion within the boiler. When air is introduced prior to any additional fuel, it allows for optimal mixing of the fuel and air. This mixing is essential because adequate oxygen needs to be present when the fuel ignites; otherwise, incomplete combustion may occur, leading to inefficient fuel use and the production of undesirable byproducts, such as carbon monoxide.

Complete combustion relies on having enough oxygen to fully oxidize the fuel. When adjustments are made to the burner, if fuel is increased without a corresponding increase in air, there may not be sufficient oxygen to support combustion. This can result in the generation of soot and potentially harmful gases. Therefore, adjusting the air first is a best practice to ensure that when fuel is introduced, the combustion process can occur effectively and safely.

Lower emissions, improved air quality, and other benefits are secondary effects that stem from ensuring complete combustion. However, the primary focus of this practice is to prevent incomplete combustion, which can lead to significant operational and safety issues.