Apparatus and method for NOx reduction in natural gas furnaces

Abstract

An improved combustion system for reducing NOx in a furnace 10 is provided having a primary flame zone 12. The primary flame zone 12 includes a plurality of burners 14 located therein which are operated on a sub-stoichiometric level thereby producing uncombusted natural gas (or hydrocarbon). The burners 14 also facilitate the passage of the uncombusted natural gas (or hydrocarbon) from the primary flame zone 12 into a secondary flame zone 18 above the primary flame zone. The secondary flame zone 18 is provided with a natural draft port 20, having a predetermined cross-sectional area, formed therein at a predetermined distance above the primary flame zone 12. As a result, air of a predetermined volume is induced into the secondary flame zone 18 so that uncombusted natural gas (or hydrocarbon) in the secondary flame zone is combusted thereby reducing NOx emissions from the furnace 10.

What is claimed:  
     
         1 . An improved combustion system for reducing NOx in a furnace including: 
 a primary flame zone for burning fuel which produces flue gas without NOx;    a secondary flame zone above the primary flame zone;    means in the primary flame zone for facilitating the passage of uncombusted natural gas into the secondary flame zone; and    means in the secondary flame zone for inducing a predetermined amount of air into the secondary flame zone so that uncombusted natural gas in the secondary flame zone is combusted thereby reducing NOx emission from the furnace.    
     
     
         2 . An improved combustion system as defined in  claim 1  wherein the means for facilitating the passage of uncombusted natural gas into the secondary flame zone includes a plurality of burners which are activated so that the burners are operated at sub-stoichiometric levels.  
     
     
         3 . An improved combustion system as defined in  claim 2  wherein the burners are operated at a 0.9 sub-stoichiometric factor.  
     
     
         4 . An improved combustion system as defined in  claim 3  wherein the means in the secondary flame zone for inducing a predetermined amount of air into the secondary flame zone includes a port having a predetermined cross-sectional area, formed at a predetermined distance above the primary flame zone.  
     
     
         5 . An improved combustion system as defined in  claim 4  wherein the port includes a door aligned adjacent to the aperture to facilitate the opening and closing of the aperture.  
     
     
         6 . An improved combustion system as defined in  claim 5  wherein the aperture has a cross-sectional area of one and eight-tenths square feet.  
     
     
         7 . An improved combustion system as defined in  claim 6  wherein the aperture is aligned in the secondary flame zone thirty feet above the primary flame zone.  
     
     
         8 . An improved combustion system as defined in  claim 7  wherein the port facilitates the induction of fifteen hundred lb.-mole per hour of air into the secondary flame zone to complete combustion of natural gas therein.  
     
     
         9 . A method of reducing NOx emissions in a furnace including the steps of: 
 operating a primary flame zone of the furnace so that uncombusted natural gas passes into a secondary flame zone of the furnace; and    inducing a predetermined amount of air into the secondary flame zone at a predetermined level above the primary flame zone so that the uncombusted natural gas is combusted thereby reducing NOx emissions from the furnace.    
     
     
         10  A method for reducing NOx emissions in a furnace as defined in  claim 9  wherein the primary flame zone is operated at sub-stoichiometric levels.  
     
     
         11 . A method for reducing NOx emissions in a furnace as defined in  claim 10  wherein the primary flame zone is operated at a 0.9 sub-stoichiometric factor.  
     
     
         12 . A method for reducing NOx emissions in a furnace as defined in  claim 11  wherein the air induced into the secondary flame zone is thirty feet above the primary flame zone.  
     
     
         13 . A method for reducing NOx emissions in a furnace as defined in  claim 12  wherein the induction of air into the secondary flame zone is facilitated by an aperture formed therein having a cross-sectional area of one and eight-tenth square feet.  
     
     
         14 . A method for reducing NOx emissions in a furnace as defined in  claim 13  wherein fifteen hundred lb.-mole per hour of air is induced into the secondary flame zone.  
     
     
         15 . An improved furnace including: 
 a primary flame zone for burning fuel which produces flue gas without NOx;    a secondary flame zone above the primary flame zone;    means in the primary flame zone for facilitating the passage of uncombusted natural gas into the secondary flame zone; and    means in the secondary flame zone for inducing a predetermined amount of air into the secondary flame zone so that uncombusted natural gas in the secondary flame zone is combusted thereby reducing NOx emissions from the furnace.    
     
     
         16 . An improved combustion system as defined in  claim 15  wherein the means for facilitating the passage of uncombusted natural gas into the secondary flame zone includes a plurality of burners which are activated so that the burners are operated at sub-stoichiometric levels.  
     
     
         17 . An improved combustion system as defined in  claim 16  wherein the burners are operated at a 0.9 sub-stoichiometric factor.  
     
     
         18 . An improved combustion system as defined in  claim 17  wherein the means in the secondary flame zone for inducing a predetermined amount of air into the secondary flame zone includes a port having an aperture having a predetermined cross-sectional area formed at a predetermined distance above the primary flame zone.  
     
     
         19 . An improved combustion system as defined in  claim 18  wherein the port includes a door aligned adjacent to the aperture to facilitate the opening and closing of the aperture.  
     
     
         20 . An improved combustion system as defined in  claim 19  wherein the aperture has a cross-sectional area of one and eight-tenths square feet.  
     
     
         21 . An improved combustion system as defined in  claim 20  wherein the aperture is aligned in the secondary flame zone thirty feet above the primary flame zone.  
     
     
         22 . An improved combustion system as defined in  claim 21  wherein the port facilitates the induction of fifteen hundred lb.-mole per hour of air into the secondary flame zone to complete combustion of NOx therein.  
     
     
         23 . An improved combustion system for reducing NOx in a furnace including: 
 a primary flame zone for burning fuel which produces flue gas without NOx;    a secondary flame zone above the primary flame zone;    means in the primary flame zone for facilitating the passage of uncombusted natural gas into the secondary flame zone; and    means in the secondary flame zone for injecting a predetermined amount of air into the secondary flame zone so that uncombusted natural gas in the secondary flame zone is combusted thereby reducing NOx emissions from the furnace.    
     
     
         24 . An improved combustion system as defined in  claim 23  wherein the means for facilitating the passage of uncombusted natural gas into the secondary flame zone includes a plurality of burners which are activated so that the burners are operated at sub-stoichiometric levels.  
     
     
         25 . An improved combustion system as defined in  claim 24  wherein the burners are operated at a 0.9 sub-stoichiometric factor.  
     
     
         26 . An improved combustion system as defined in  claim 25  wherein the means in the secondary flame zone for injecting a predetermined amount of air into the secondary flame zone includes an injector formed therein at a predetermined distance above the primary flame zone.  
     
     
         27 . An improved combustion system as defined in  claim 26  wherein the injector is aligned in the secondary flame zone thirty feet above the primary flame zone.  
     
     
         28 . An improved combustion system as defined in  claim 27  wherein the injector facilitates the injection of fifteen hundred lb.-mole per hour of air into the secondary flame zone to complete combustion of natural gas therein.  
     
     
         29 . A method of reducing NOx emissions in a furnace including the steps of: 
 operating a primary flame zone of the furnace so that uncombusted natural gas passes into a secondary flame zone of the furnace; and    injecting a predetermined amount of air into the secondary flame zone at a predetermined level above the primary flame zone so that the uncombusted natural gas is combusted thereby reducing NOx emissions from the furnace.    
     
     
         30 . A method for reducing NOx emissions in a furnace as defined in  claim 29  wherein the primary flame zone is operated at sub-stoichiometric levels.  
     
     
         31 . A method for reducing NOx emissions in a furnace as defined in  claim 30  wherein the primary flame zone is operated at a 0.9 sub-stoichiometric factor.  
     
     
         32 . A method for reducing NOx emissions in a furnace as defined in  claim 31  wherein the air injected into the secondary flame zone is thirty feet above the primary flame zone.  
     
     
         33 . A method for reducing NOx emissions in a furnace as defined in  claim 32  wherein fifteen hundred lb.-mole per hour of air is injected into the secondary flame zone.