What is the approximate amount of excess air required for firing pulverized coal?

When firing pulverized coal, the amount of excess air required is a critical factor for efficient combustion. Typically, firing pulverized coal necessitates an excess air supply to ensure that the coal burns completely. The range of 15-20% excess air is commonly recommended because it strikes a balance between providing enough oxygen for complete combustion and minimizing heat losses associated with excess air.

Excess air is essential to prevent incomplete combustion, which can lead to the generation of carbon monoxide and other unburned hydrocarbons. However, if too much air is used, it can dilute the combustion gases and reduce the overall temperature of the combustion zone, resulting in lower efficiency and increased heat losses.

Thus, in the context of pulverized coal combustion, an approximate excess air requirement of 15-20% is considered optimal to achieve effective combustion while maintaining energy efficiency and minimizing pollutants.