Low NO
Emissions of NO X and/or CO are reduced at the stack by systems and methods wherein a primary fuel is thoroughly mixed with a specific range of excess combustion air. The primary fuel-air mixture is then discharged and anchored within a combustion chamber of a burner. Further, the systems and methods provide for dynamically controlling NO X content in emissions from a furnace by adjusting the flow of primary fuel and of a secondary stage fuel, and in some cases controlling the amount or placement of combustion air into the furnace.
1. A method of discharging fuel and an amount of air into a furnace space wherein the fuel is burned such that flue gases having low NOx content and low CO content are formed therefrom, the method comprises:
mixing a first portion of the fuel and substantially all of the air to form a lean primary fuel-air mixture;
discharging the lean primary fuel-air mixture into the furnace space within a primary combustion zone defined by a burner tile such that there is a furnace environment surrounding the burner tile;
burning the lean primary fuel-air mixture in the primary combustion zone to produce a flame and thus generated flue gases, wherein the primary combustion zone has a first end and a second end, and the lean primary fuel-air mixture is introduced so that the flame is anchored adjacent the first end and the generated flue gases are discharged into the furnace environment at the second end.
2. The method of claim 1 , wherein the discharging of the lean primary fuel-air mixture is through at least one tube in which the first portion of the fuel and substantially all the air are mixed to form the fuel-air mixture, and wherein the first end of the combustion zone is closed to air introduction other than through the at least one tube.
3. The method of claim 1 , further comprising introducing a second portion of fuel into the furnace outside of the primary combustion zone such that the second portion of fuel forms a secondary combustion zone downstream of the primary combustion zone and substantially all the air for the secondary combustion zone is provided by the lean primary fuel-air mixture.
4. The method of claim 3 , wherein substantially all the air is at least 97% of the air needed for combustion of the fuel based on the air needed to combust the first portion of the fuel, and the second portion of the fuel.
5. The method of claim 3 , further comprising:
determining the composition of the fuel;
determining a flow rate of the first portion of the fuel and a flow rate of the second portion of the fuel;
determining an adiabatic flame temperature (AFT) for the composition of the fuel;
determining the excess air quantity required to produce a predetermined NOx emission level based on the AFT; and
based on the excess air quantity required to produce the predetermined NOx emission level, adjusting at least one of the flow rate of the first portion of fuel, the flow rate of the second portion of fuel, the amount of air, and the distribution of air within the burner.
6. The method of claim 5 , wherein the step of adjusting comprises adjusting both the flow rate of the first portion of fuel and the flow rate of the second portion of the fuel.
7. The method of claim 6 , wherein the flow rate of the first portion of the fuel and the flow rate of the second portion of the fuel are adjusted simultaneously.
8. The method of claim 7 , wherein the discharging of the lean primary fuel-air mixture is through a plurality of tubes in which all the air for the primary combustion zone and secondary combustion zone, and the first portion of the fuel are mixed to form the fuel-air mixture, and wherein the fuel-air mixture is supplied to the first combustion zone only through the tubes.