Method for reducing NOx emissions with minimal increases in unburned carbon and waterwall corrosion

An apparatus for reducing NOx emissions in a furnace having a main combustion zone with a waterwall and means for supplying main combustion air and fuel to the main combustion zone, and which reduces unburned carbon and waterwall corrosion in the furnace, the apparatus comprising:

• a plurality of lower overfire air injectors at a first level over the main combustion zone of the furnace for supplying overfire air to create a lower overfire air zone in the furnace over the main combustion zone;
• means for articulating the plurality of lower overfire air injectors for directing the overfire air at the first level to produce an oxygen rich environment along the waterwalls in the lower overfire air zone;
• a plurality of upper overfire air injectors at a second level over the lower overfire air zone for supplying overfire air to create an upper overfire air zone in the furnace over the lower overfire air zone;
• and
• means for supplying the overfire air in the lower overfire air zone at a rate to produce a stoichiometry of 0.7 to 1.0 in the main combustion zone, and for providing overfire air in the upper overfire air zone at a location to permit combustion gases from the lower zone to be resident for about 0.1 to 0.2 seconds prior to being mixed with overfire air from the upper overfire air injector for reducing the stoichiometry in the main combustion zone which reduces unburned carbon and a corrosive reducing atmosphere in the furnace.