What is the role of Excess Air in the Combustion Process of a boiler?

When fuel is burned in the combustion chamber of the boiler, the calculated amount of air which is required for the fuel to burn is never sufficient.  Excess air needs to be fed to the combustion chamber.  This air which is in excess of the calculated amount is known as excess air.

Excess Air refers to the additional air which is fed to the combustion chamber of the boiler to ensure that the fuel gets burnt properly.  Excess Air is provided by means of blowers.  in the case of supercharged boilers, it is provided by compressors. 

Different types of fuel have different requirements for excess air. Gas may require up to 10% of excess air.  Fuel will require up to 20 % and coal will require large amounts of excess air up to 60 %