Staging could be either applied to the burner design
itself, or could be achieved by fluid injection through
separate pipes. An example for the latter is over- or
undertiring in power plant boilers or waste incineration
boilers. A burner design for air staging is shown
in Fig. 4. The primary combustion takes place in a
combustion chamber, where the flame is stabilized by
a disk on the gas nozzle. The combustion products
enter the furnace with a high velocity of typically 100
m/s. The jet entrains exhaust gases from the furnace
to cool down the combustion products. Further
downstream secondary combustion takes place with
air, injected through concentric arranged nozzles.