Techniques for reducing NOx emissions
from fossil-fuel-fired boilers can be classified
into two fundamentally different categories:
combustion controls and post-combustion controls.
Combustion controls reduce NOx formation
during the combustion process, while
post-combustion controls reduce NOx after it
has been formed.
Combustion controls include low-NOx burners
(LNBs), reburning, overfire air (OFA), flue
gas recirculation (FGR), and operational modifications.
Post-combustion controls include selective
catalytic reduction (SCR) and selective
noncatalytic reduction (SNCR). The primary
technology currently used for NOx reduction to
meet Title IV standards is combustion modification
using LNBs, often in combination with OFA.