Advanced overfire air system for NO.sub.x control

In a fossil fuel-fired furnace having a plurality of walls embodying therewithin a burner region, the improvement comprising an advanced overfire air system for accomplishing NO.sub.x control in the fossil fuel-fired furnace, said advanced overfire air system comprising:

• a. a windbox mounted in supported relation within the burner region of the fossil fuel-fired furnace, said windbox embodying a plurality of elevations;
• b. a first fossil fuel nozzle supported in said windbox at a first elevation thereof operative for introducing fossil fuel in a first direction into the burner region of the fossil fuel-fired furnace through said windbox at said first elevation thereof;
• c. a combustion supporting secondary air nozzle supported in said windbox at a second elevation thereof operative for introducing combustion supporting secondary air in the first direction into the burner region of the fossil fuel-fired furnace through said windbox at said second elevation thereof;
• d. a second fossil fuel nozzle supported in said windbox at a third elevation thereof operative for introducing fossil fuel in the first direction into the burner region of the fossil fuel-fired furnace through said windbox at said third elevation thereof;
• e. a plurality of overfire air compartments mounted in supported relation in the burner region of the fossil fuel-fired furnace above and in spaced relation to said windbox;
• f. a first overfire air nozzle supported in one of said plurality of overfire air compartments operative for introducing overfire air in a second direction opposite to the first direction into the burner region of the fossil fuel-fired furnace through said one of said plurality of overfire air compartments;
• g. a second overfire air nozzle supported in another one of said plurality of overfire air compartments operative for introducing overfire air in a direction other than the second direction into the burner region of the fossil fuel-fired furnace through said another one of said plurality of overfire air compartments;
• h. a third overfire air nozzle supported in said windbox at a fourth elevation thereof operative for introducing overfire air in the first direction into the burner region of the fossil fuel-fired furnace through said windbox at said fourth elevation thereof;
• and
• i. air supply means connected to said first overfire air nozzle, said second overfire air nozzle and said third overfire air nozzle for supplying overfire air thereto, said air supply means being operative to supply to said first overfire air nozzle and said second overfire air nozzle more overfire air for introduction into the burner region of the fossil fuel-fired furnace through said plurality of overfire air compartments than is supplied by said air supply means to said third overfire air nozzle for introduction into the burner region of the fossil fuel-fired furnace through said windbox at said fourth elevation thereof.