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

Increasing the air supply to the burner before introducing fuel is crucial for ensuring complete combustion. This practice helps prevent the situation where fuel is introduced without enough air to support its combustion, which can lead to incomplete combustion. Incomplete combustion generates carbon monoxide, soot, and unburned hydrocarbons, all of which are detrimental to both operational efficiency and safety.

By allowing air to enter first, the burner creates the optimal conditions for combustion, ensuring there is sufficient oxygen available when the fuel is introduced. This not only maximizes the efficiency of fuel utilization but also reduces the risk of hazardous emissions and improves the overall performance of the boiler. Ultimately, maintaining a proper air-to-fuel ratio is essential for both efficient energy production and compliance with environmental regulations.