Method and apparatus for a dual mode burner yielding low nox emission

Abstract

A method of operating a burner includes providing supplying a combustible mixture containing a ratio of fuel and air that is incapable of maintaining a stable flame to a combustion chamber. The combustible mixture is ignited by an igniter, and presence of a flame is sensed. The igniter is maintained active to sustain combustion of the combustible mixture within the combustion chamber so that a space exterior to the combustion chamber is heated to a temperature at or above an auto-ignition temperature of the combustible mixture. The temperature of the space exterior is monitored and the combustible mixture is provided at a second flow rate, which is higher than the first flow rate, to extinguish the flame in the combustion chamber such that combustion occurs in the space exterior to the combustion chamber. When combustion occurs in the space exterior to the combustion chamber, the igniter is deactivated.

What is claimed is: 
     
         1 . A method of operating a burner, comprising:
 providing a combustion chamber in the burner, which is adapted to receive at least a fuel stream and an air stream;   activating an igniter within the combustion chamber;   supplying a combustible mixture containing a ratio of fuel and air to the combustion chamber at a first flow rate, the combustible mixture being incapable of maintaining a stable flame;   igniting a flame in the combustible mixture in the combustion chamber by activating an igniter;   sensing a flame presence within the combustion chamber;   maintaining the igniter active to stabilize the flame within the combustion chamber;   heating a space exterior to the combustion chamber to a temperature at or above an auto-ignition temperature of the combustible mixture;   monitoring the temperature of the space exterior; and   deactivating the igniter to destabilize the flame in the combustion chamber such that combustion occurs in the space exterior to the combustion chamber when the temperature of the space exterior is at or above the auto-ignition temperature.   
     
     
         2 . The method of  claim 1 , further comprising providing a secondary air stream, which represents at least a portion of the air stream, to the combustion chamber in a direction disposed at an angle relative to a flow direction of the fuel stream. 
     
     
         3 . The method of  claim 2 , wherein the secondary air stream is provided through at least one opening formed in a sidewall of a hollow body that defines the combustion chamber. 
     
     
         4 . The method of  claim 2 , further comprising forming a flame region within the combustion chamber in an area where the secondary air stream and the fuel stream meet and overlap with the igniter. 
     
     
         5 . The method of  claim 2 , wherein the secondary air stream and a remaining portion of the air stream are provided at different pressures. 
     
     
         6 . The method of  claim 2 , further comprising selectively adjusting a flow rate of the secondary air stream. 
     
     
         7 . The method of  claim 1 , wherein the igniter is one of a hot surface igniter, a direct spark igniter, a plasma igniter, an arc igniter, a pilot flame igniter, or an electric, magnetic or electromagnetic field generator igniter. 
     
     
         8 . The method of  claim 1 , wherein the space exterior to the combustion chamber is a furnace chamber in a furnace, and wherein the space exterior to the combustion chamber is a radiant tube disposed in the furnace chamber. 
     
     
         9 . The method of  claim 1 , wherein a controller automatically adjusts at least one of a flow rate of the fuel stream, a flow rate of the air stream, and a flow rate of an oxidant stream, which oxidant stream is included in the combustible mixture, based on signals provided to the controller that are indicative of the sensing of the flame presence and the monitoring of the temperature of the space exterior, 
     
     
         10 . The method of  claim 1 , wherein the burner further comprises a nozzle for the fuel and air streams to pass through and intermix in the combustion chamber. 
     
     
         11 . A method of operating a burner, comprising:
 activating an igniter;   providing a fuel stream, a first air stream, and a secondary air stream to a combustion chamber of the burner;   intermixing the fuel, first and secondary air streams to form a combustible mixture at a first flow rate, said combustible mixture being incapable of maintaining a stable flame within the combustion chamber;   igniting the combustible mixture in the combustion chamber with the igniter;   sensing a flame presence within the combustion chamber;   maintaining the igniter active to sustain combustion of the combustible mixture within the combustion chamber;   heating a space exterior to the combustion chamber to a temperature at or above an auto-ignition temperature of the combustible mixture;   monitoring the temperature of the space exterior;   providing the combustible mixture at a second flow rate, which is higher than the first flow rate, to extinguish a flame in the combustion chamber such that combustion occurs in the space exterior to the combustion chamber; and   when combustion occurs in the space exterior to the combustion chamber, deactivating the igniter and discontinuing the secondary air stream.   
     
     
         12 . The method of  claim 11 , further comprising providing the secondary air stream to the combustion chamber in a direction disposed at an angle relative to a flow direction of the fuel stream. 
     
     
         13 . The method of  claim 12 , wherein the secondary air stream is provided through at least one opening formed in a sidewall of a hollow body that defines the combustion chamber, wherein the burner further comprises a nozzle for the fuel and air streams to pass through and intermix in the combustion chamber, and wherein the at least one opening is different than nozzle openings provided for the fuel and first air streams. 
     
     
         14 . The method of  claim 11 , further comprising forming a flame region within the combustion chamber in an area where the secondary air stream and the fuel stream meet and overlap with the igniter. 
     
     
         15 . The method of  claim 11 , wherein the first and secondary air streams are provided at different pressures. 
     
     
         16 . The method of  claim 11 , further comprising selectively adjusting a flow rate of the secondary air stream, 
     
     
         17 . The method of  claim 11 , wherein the igniter is one of a hot surface igniter, a direct spark igniter, a plasma igniter, an arc igniter, a pilot flame igniter, or an electric, magnetic or electromagnetic field generator igniter. 
     
     
         18 . The method of  claim 11 , wherein the space exterior to the combustion chamber is a furnace chamber in a furnace, and wherein the space exterior to the combustion chamber is a radiant tube disposed in the furnace chamber. 
     
     
         19 . The method of  claim 11 , wherein a controller automatically adjusts at least one of a flow rate of the fuel stream, a flow rate of the first air stream, and a flow rate of an oxidant stream, which oxidant stream is included in the combustible mixture, based on signals provided to the controller that are indicative of the sensing of the flame presence and the monitoring of the temperature of the space exterior. 
     
     
         20 . A method for operating a burner, comprising:
 activating an igniter;   providing a combustible mixture to a combustion chamber;   sensing a flame presence in the combustion chamber;   maintaining activation of the igniter to stabilize a flame in the combustible mixture within the combustion chamber;   sensing an external temperature when a flame is sensed in the combustion chamber;   comparing the external temperature with an auto-ignition temperature of the combustible mixture; and, when the external temperature is greater or equal than the auto-ignition temperature,   transitioning the flame from the combustion chamber to an area external to the combustion chamber; and   deactivating the igniter.