Air and fuel staged burner

Abstract

A burner ( 10 ) for reducing NO x emissions where supply fuel ( 16 ) and supply air ( 20 ) are supplied to a combustion tunnel ( 52 ) at high and low velocities and secondary air ( 26 ) is supplied to a secondary combustion zone ( 60 ), wherein products of combustion ( 59 ) exiting into the secondary combustion zone ( 60 ) from the combustion tunnel ( 52 ) are drawn back into the combustion tunnel ( 52 ) and back into the secondary air conduit ( 54 ).

We claim:  
     
         1 . A burner ( 10 ) for reducing NO x  emissions comprising: 
 a main burner body ( 22 ) defining an internal cavity ( 13 ), an air connection ( 12 ) fluidly connected to the internal cavity ( 13 ), and a combustion tunnel ( 52 );    a distribution tee ( 30 ) positioned adjacent to the internal cavity ( 13 ) and spaced away from the combustion tunnel ( 52 ), the distribution tee ( 30 ) fluidly connected to the internal cavity ( 13 ); and    a burner nozzle ( 46 ) positioned in the interior cavity ( 13 ) of the main burner body ( 22 ), the burner nozzle defining a primary air orifice ( 32 ), a fuel annulus ( 47 ) having a first width (W 1 ), and a fuel orifice ( 48 ) having a second width (W 2 ),    wherein the first width (W 1 ) of the fuel annulus ( 47 ) is less than the second width (W 2 ) of the fuel orifice ( 48 ).    
     
     
         2 . The burner ( 10 ) as claimed in  claim 1 , wherein the main burner body ( 22 ) extends longitudinally about an imaginary burner centerline (C), and the primary air orifice ( 32 ) is oriented to form a convergent angle (∝) as measured from the imaginary burner centerline (C).  
     
     
         3 . The burner ( 10 ) as claimed in  claim 2 , wherein the convergent angle (∝) is approximately 30-60° as measured from the imaginary burner centerline (C).  
     
     
         4 . The burner ( 10 ) as claimed in  claim 1 , wherein the main burner body ( 22 ) extends longitudinally about an imaginary burner centerline (C) and the primary air orifice ( 32 ) is oriented to produce a swirl pattern in the combustion tunnel ( 52 ).  
     
     
         5 . The burner ( 10 ) as claimed in  claim 4 , wherein the swirl is approximately less than or equal to 0.7 times an internal diameter (D) of the combustion tunnel ( 52 ).  
     
     
         6 . The burner ( 10 ) as claimed in  claim 1 , further comprising a secondary air conduit ( 54 ) fluidly connected to the distribution tee ( 30 ), the secondary air conduit ( 54 ) having a secondary air jet ( 56 ) fluidly connected to a secondary combustion zone ( 60 ).  
     
     
         7 . The burner ( 10 ) as claimed in  claim 6 , wherein the main burner body ( 22 ) extends longitudinally about an imaginary burner centerline (C) and the secondary air jet ( 56 ) is oriented substantially parallel to the imaginary burner centerline (C) of the main burner body ( 22 ).  
     
     
         8 . The burner ( 10 ) as claimed in  claim 6 , wherein the main burner body ( 22 ) extends longitudinally about an imaginary burner centerline (C) and the secondary air jet ( 56 ) is oriented at an angle (β) convergent with the imaginary burner centerline (C) of the main burner body ( 22 ).  
     
     
         9 . The burner ( 10 ) as claimed in  claim 1 , further comprising a primary fuel path ( 42 ) and a secondary fuel path ( 44 ), the primary fuel path ( 42 ) fluidly connected to the annulus ( 47 ), the secondary fuel path ( 44 ) fluidly connected to the fuel orifice ( 48 ), and the primary fuel path ( 42 ) and the secondary fuel path ( 44 ) are fluidly connected to each other.  
     
     
         10 . A method of decreasing NO x  emissions in a burner ( 10 ) having a main burner body ( 22 ) defining a combustion tunnel ( 52 ) and a source of secondary air ( 26 ) comprising the steps of: 
 a. exhausting products of combustion ( 59 ) into a secondary combustion zone ( 60 ); and    b. drawing products of combustion ( 59 ) from the secondary combustion zone ( 60 ) to an combustion tunnel exit ( 62 ) and to the source of secondary air ( 26 ).    
     
     
         11 . The method as claimed in  claim 10 , further comprising the steps of: 
 c. flowing supply air ( 20 ) into the main burner body ( 22 );    d. dividing the supply air ( 20 ) into primary air ( 24 ) and secondary air ( 26 );    e. flowing the primary air ( 24 ) into the combustion tunnel ( 52 ) at a given velocity;    f. flowing primary fuel ( 38 ) into the combustion tunnel ( 52 ) at a velocity lower than the velocity of the primary air ( 24 );    g. flowing secondary fuel ( 40 ) into the combustion tunnel ( 52 ) at a velocity higher than the velocity of the primary fuel ( 38 );    h. flowing the secondary air ( 26 ) into the secondary combustion zone ( 60 ) at a velocity higher than the velocity of the primary fuel ( 38 ); and    i. igniting the primary fuel ( 38 ), the secondary fuel ( 40 ), and primary air ( 24 ) in the combustion tunnel ( 52 ) to form products of combustion ( 59 ).    
     
     
         12 . The method as claimed in  claim 11 , wherein the ratio of primary air ( 24 ) to secondary air ( 26 ) is approximately in the range of 40/60 to 70/30, respectively.  
     
     
         13 . The method as claimed in  claim 11 , wherein the primary air ( 24 ) flows into the combustion tunnel ( 52 ) at a rate of approximately 300-400 feet per second at rated input.  
     
     
         14 . The method as claimed in  claim 11 , wherein the secondary air ( 26 ) flows in the secondary combustion zone ( 60 ) at a velocity of approximately 150-400 feet/second at rated input.  
     
     
         15 . The method as claimed in  claim 11 , wherein the primary fuel ( 38 ) to secondary fuel ( 40 ) split ratio is in the range of approximately 20/80 to 40/60, respectively.  
     
     
         16 . The method as claimed in  claim 11 , wherein the primary fuel ( 38 ) flows into the combustion tunnel ( 52 ) at a velocity less than approximately 100 feet/second at rated input.  
     
     
         17 . The method as claimed in  claim 11 , wherein the secondary fuel ( 40 ) flows into the combustion tunnel ( 52 ) at a velocity approximately greater than 350 feet/second at rated input.  
     
     
         18 . A burner ( 10 ) for reducing NO x  emissions comprising: 
 a main burner body ( 22 ) defining an internal cavity ( 13 ), an air connection ( 12 ) fluidly connected to the internal cavity ( 13 ), and a combustion tunnel ( 52 );    a distribution tee ( 30 ) fluidly connected to the internal cavity ( 13 ); a burner nozzle ( 46 ) positioned in the interior cavity ( 13 ) of the main burner body ( 22 ), the burner nozzle defining a primary air orifice ( 32 ), a fuel annulus ( 47 ) having a first width (W 1 ), and a fuel orifice ( 48 ) having a second width (W 2 ), wherein the first width (W 1 ) of the fuel annulus ( 47 ) is less than the second width (W 2 ) of the fuel orifice ( 48 );    a fuel connector ( 14 ) defining a primary fuel path ( 42 ) and a secondary fuel path ( 44 ), the primary fuel path ( 42 ) fluidly connected to the annulus ( 47 ), the secondary fuel path ( 44 ) fluidly connected to the orifice ( 48 ), and the primary fuel path ( 42 ) and the secondary fuel path ( 44 ) fluidly connected to each other; and    a secondary air conduit ( 54 ) defining a secondary air jet ( 56 ), the secondary air conduit ( 54 ) fluidly connected to the distribution tee ( 30 ) and the secondary air jet ( 56 ) spaced away from the combustion tunnel ( 52 ).    
     
     
         19 . The burner ( 10 ) as claimed in  claim 18 , wherein the fuel orifice ( 48 ) and the fuel annulus ( 47 ) lie in the same plane, substantially perpendicular to an imaginary burner centerline (C).  
     
     
         20 . The burner ( 10 ) as claimed in  claim 19 , wherein the distribution tee ( 30 ) is positioned adjacent to the internal cavity ( 13 ) of the main burner body ( 22 ) and spaced opposite the combustion tunnel ( 52 ).