The percent of primary air is determined by the type of kiln.
It is very low for cement kilns and kilns having shell coolers.
Primary air would seldom exceed 30% unless required to enhance
the total combustion air for special reasons such as the
additional air often required by calcined petroleum coke kilns
The Bluff-Body(R) elements are radial so that the primary air, while highly turbulent, is without any rotative spin about the burner axis which results in a non-divergent flame emission. A non-divergent flame transfers more heat to the load via radiation than a divergent flame.
The Bluff-Body(R) register
allows the introduction of NCGs to be central and intimately
mixed with the fuel and primary air for extremely low PPM of
sulfide emissions to the atmosphere.
The incineration of NCGs is literally without parallel and their introduction being central (rather than offset) does not chill the flame even when large volumes are incinerated.
If there is a problem with condensate carry-over, a separator can be added to trap the condensate so that condensate carry-over does not reach the lime bed.
Turbulence and Flame Radiation
The primary air is supplied at up
to 25" w.c. for 30% primary air and higher pressure for
lower primary air pressure drop is virtually all across the
These relatively high primary air pressures are to maximize turbulence (without rotative spin) and therefore greatly enhances the flame's radiation which allows the non-divergent flame to be most effective.
The Bluff-Body(R) register section is refractory lined to promote nascent combustion and raise the flame temperature within the register quickly. This lining does not suffer however as each Bluff-Body(R) element serves as a heat sink and the average refractory temperature is not excessive. Thus, thermal shock and spalling are completely avoided.
All liquid, gaseous or pulverized solid fuels may be used with the Bluff-Body(R) technology. All fuels are used at low or moderate pressures as most of the mixing work is by the primary air. Due to the use of transport air for solid fuels, low percent primary air at higher pressure would be used for high-ash content pulverized fuels to have a moderate register lining temperature and avoid any slagging.
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