Reduced NOx method of combustion

Abstract

The present invention is a method for achieving low NO x single-stage combustion. A high velocity burner is run normally, with combustion occurring within both the burner combustion chamber and furnace chamber, until the gases within the furnace exceed the auto-ignition temperature of the gaseous fuel. The gaseous fuel is then shut off until the temperature within the burner combustion chamber drops below the auto-ignition temperature of the gaseous fuel. The gaseous fuel is then turned back on and the gaseous fuel auto ignites within the furnace chamber. The combustion then occurs only within the furnace chamber and not in the burner combustion chamber.

1 . A method for low NO x  combustion, comprising the steps of: 
 providing a burner, the burner comprising: 
 a combustion chamber disposed within the burner, the combustion chamber being in fluid communication with a combustion air supply, a gaseous fuel supply, and a furnace chamber; and  
 a flame stabilizer nested with the burner, the flame stabilizer being in fluid communication with the combustion chamber, a combustion air supply, and a gaseous fuel supply; and  
   flowing the combustion air into the combustion chamber;    flowing gaseous fuel into the combustion chamber;    mixing the gaseous fuel with the combustion air within the combustion chamber, forming a fuel/air mixture;    flowing the fuel/air mixture from the combustion chamber into the furnace chamber through a high velocity exit nozzle;    igniting the fuel/air mixture within the combustion chamber to form a flame, the flame being stabilized by the flame stabilizer;    combusting the fuel/air mixture, the combustion occurring in the combustion chamber, and in the furnace chamber, the combustion forming hot gases of combustion, hot gases of combustion produced in the combustion chamber flowing into the furnace chamber through the high velocity exit nozzle; then    continuing to combust the fuel/air mixture for a first preselected period of time until attaining a first preselected temperature of gases within the furnace sufficient to auto ignite the fuel; then    ceasing to provide gaseous fuel, causing combustion of the fuel/air mixture to cease; then    waiting for a second preselected period of time until the burner combustion chamber cools to a second preselected temperature below the auto-ignition temperature of the fuel, wherein the furnace gases remain sufficiently hot to auto ignite the fuel; then    restarting the provision of gaseous fuel, causing the auto-ignition of the fuel/air mixture solely within the furnace chamber, without igniting the fuel/air mixture in the burner combustion chamber, an exit velocity of the fuel/air mixture through the high velocity exit nozzle being sufficiently high to prevent flashback of flame into the burner combustion chamber.    
   
   
       2 . The method of  claim 1 , wherein the step of ceasing further comprises ceasing to provide combustion air and wherein the step of restarting further comprises restarting the provision of combustion air.  
   
   
       3 . The method of  claim 1 , wherein the gaseous fuel is selected from the group consisting of natural gas, methane, coke oven gas, blast furnace gas, and combinations thereof.  
   
   
       4 . The method of  claim 1 , wherein the combustion chamber is connected to the gaseous fuel supply through a gaseous fuel line, wherein a valve is attached to the gaseous fuel line, the valve controlling flow of gaseous fuel through the gaseous fuel line, and wherein the ceasing and restarting of the gaseous fuel is accomplished through the actuation of the valve.  
   
   
       5 . The method of  claim 4 , wherein the valve is a solenoid valve.  
   
   
       6 . The method of  claim 2 , wherein the combustion chamber is connected to the combustion air supply though a combustion air line, wherein a valve is attached to the combustion air line, the valve controlling flow of combustion air through the combustion air line, and wherein the ceasing and restarting of combustion air is accomplished through the actuation of the valve.  
   
   
       7 . The method of  claim 6 , wherein the valve is a butterfly valve.  
   
   
       8 . The method of  claim 1 , wherein the combustion air is preheated to a temperature of up to about 1000° F.  
   
   
       9 . The method of  claim 1 , wherein excess combustion air is provided in the range of about 0% excess combustion air to about 30% excess combustion air.  
   
   
       10 . The method of  claim 1 , wherein the combustion air is provided at a static air inlet pressure in the range of about 8 osig to about 20 osig.  
   
   
       11 . The method of  claim 1 , wherein excess gaseous fuel is provided in the range of about 0% excess gaseous fuel to about 10% excess gaseous fuel.  
   
   
       12 . A method for low NO x  combustion, comprising the steps of: 
 providing a burner, wherein the burner is self-recuperative, the burner comprising: 
 a combustion chamber disposed within the burner, the combustion chamber being in fluid communication with a combustion air supply, a gaseous fuel supply, and a furnace chamber;  
 a flame stabilizer nested with the burner, the flame stabilizer being in fluid communication with the combustion chamber, a combustion air supply, and a gaseous fuel supply; and  
 an exhaust housing comprising an exhaust passageway, the exhaust passageway being in fluid communication with the furnace chamber and an exhaust air outlet passage; and  
   flowing the combustion air into the combustion chamber;    flowing gaseous fuel into the combustion chamber;    mixing the gaseous fuel with the combustion air within the combustion chamber, forming a fuel/air mixture;    flowing the fuel/air mixture from the combustion chamber into the furnace chamber through a high velocity exit nozzle;    igniting the fuel/air mixture within the combustion chamber to form a flame, the flame being stabilized by the flame stabilizer;    combusting the fuel/air mixture, the combustion occurring in the combustion chamber, and in the furnace chamber, the combustion forming hot gases of combustion, hot gases of combustion produced in the combustion chamber flowing into the furnace chamber through the high velocity exit nozzle, the hot gases of combustion flowing back into the exhaust passageway and out of the burner through the exhaust air outlet passage; then    continuing to combust the fuel/air mixture for a first preselected period of time until attaining a first preselected temperature of gases within the furnace sufficient to auto ignite the fuel; then    ceasing to provide gaseous fuel, causing combustion of the fuel/air mixture to cease; then    waiting for a second preselected period of time until the burner combustion chamber cools to a second preselected temperature below the auto-ignition temperature of the fuel, wherein the furnace gases remain sufficiently hot to auto ignite the fuel; then    restarting the provision of gaseous fuel, causing the auto-ignition of the fuel/air mixture solely within the furnace chamber, without igniting the fuel/air mixture in the burner combustion chamber, an exit velocity of the fuel/air mixture through the high velocity exit nozzle being sufficiently high to prevent flashback of flame into the burner combustion chamber.    
   
   
       13 . The method of  claim 12 , wherein the step of ceasing further comprises ceasing to provide combustion air and wherein the step of restarting further comprises restarting the provision of combustion air.  
   
   
       14 . The method of  claim 12 , wherein the gaseous fuel is selected from the group consisting of natural gas, methane, coke oven gas, blast furnace gas, and combinations thereof.  
   
   
       15 . The method of claim  1 - 2 , wherein the combustion chamber is connected to the gaseous fuel supply through a gaseous fuel line, wherein a valve is attached to the gaseous fuel line, the valve controlling flow of gaseous fuel through the gaseous fuel line, and wherein the ceasing and restarting of the gaseous fuel is accomplished through the actuation of the valve.  
   
   
       16 . The method of  claim 15 , wherein the valve is a solenoid valve.  
   
   
       17 . The method of  claim 13 , wherein the combustion chamber is connected to the combustion air supply though a combustion air line, wherein a valve is attached to the combustion air line, the valve controlling flow of combustion air through the combustion air line, and wherein the ceasing and restarting of combustion air is accomplished through the actuation of a valve.  
   
   
       18 . The method of  claim 17 , wherein the valve is a butterfly valve.  
   
   
       19 . The method of  claim 12 , wherein excess combustion air is provided in the range of about 0% excess combustion air to about 30% excess combustion air.  
   
   
       20 . The method of  claim 12 , wherein the combustion air is provided at a static air inlet pressure in the range of about 8 osig to about 20 osig.  
   
   
       21 . The method of  claim 15 , wherein the combustion air is provided at a static air inlet pressure in the range of about 8 osig to about 20 osig.  
   
   
       22 . The method of  claim 12 , wherein excess gaseous fuel is provided in the range of about 0% excess gaseous fuel to about 10% excess gaseous fuel.