Reburn Zone
Reburn fuel injection creates a reducing
region within which the reburn
fuel molecules break down to hydrocarbon
fragments (CH, CH2, etc.)
that react with NOx, producing reduced
nitrogen species (mainly N2). The optimum
reburn zone stoichiometric ratio
is 0.85-0.95. This is achieved by injecting
reburn fuel at a rate corresponding
to 10-30% of the total heat input,
depending on the primary zone excess
air level. The lower the primary combustion
zone excess air, the lower
the reburn fuel requirement. Introduction
of FGR through the reburn fuel
injectors may also be employed to increase
the momentum of the injected
reburn fuel to improve furnace penetration
and mixing. Because recirculated
flue gas has a low oxygen
content, FGR has only a minor impact
on the reburn zone fuel requirement
and the burnout zone air rate