TM 5-810-15
(6) Combustion modifications primarily deal
in the combustion air at high temperatures. At very
with the control of fuel and air. Vertical staging
low levels of NOx prompt NOx is formed when
includes overfire air (OFA) ports above the main
intermediate hydrocarbons present in the flames
combustion zone. Horizontal staging use registers
oxidize.
or other devices to introduce air at different points
(5) NOx control techniques can be defined as
along the flame. Fuel staging establishes a fuel rich
either combustion modifications or post combus-
zone above an air lean main combustion zone.
tion reduction. The goals of combustion modifica-
Burner out of service (BOOS) techniques direct
tion include redistribution of air and fuel to slow
fuel to lower burner levels, while operating upper
mixing, reduction of O2 in NOx formation zones,
burners with air only. Flue gas recirculation (FGR)
and reduction of the amount of fuel burned at peak
flame temperatures.
cools the flame. In addition to low NOx burners
3-14
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