Excess air

*      Excess air is necessary for complete combustion and for temperature control.


*      If  excess air is not provided, there is a large risk for incomplete combustion and combustible gases such as CO will leave with the flue gas. CO is poisonous, unstable and represents an energy loss.


* On the other hand too much excess air will increase the risk of thermal NOx production (see later this chapter) and increase the amount of energy lost with the flue gas.


* Thus, the excess air should be as little as possible, but enough for complete combustion.


*      The air excess factor for combustion is often denoted m. For stoichiometric conditions m=1, i.e. the stoichiometric air amount was supplied for the combustion process.


*      If excess air is supplied, m > 1.