Simplified system for feeding over-fire air to a heater for a low NOx emission

Abstract

A system for feeding over-fire air to a combustion chamber ( 10, 24, 42 ) of a steam or hot water generation plant of low-medium capacity, using solid, liquid or gaseous fuel or a combination thereof, comprising a main combustion air duct ( 5 ) supplied to a burner unit ( 11, 25, 43 ) in the combustion chamber and an over-fire air duct ( 12, 27, 44 ), which extends within said combustion chambers and is provided at its end with nozzle means ( 17, 27, 47 ) for said over-fire air.

1 . A system for feeding over-fire air to a combustion chamber ( 10 ,  24 ,  42 ) of a steam or hot water generation plant of low-medium capacity, using solid, liquid or gaseous fuel or a combination thereof, comprising a main combustion air duct ( 5 ) supplied to a burner unit ( 11 ,  25 ,  43 ) in said combustion chamber and an over-fire air duct ( 12 ,  27 ,  44 ), characterized in that said over-fire air duct ( 12 ,  27 ,  44 ) extends within said combustion chamber and is provided at its end with nozzle means ( 17 ,  27 ,  47 ) for said over-fire air.  
     
     
         2 . Over-fire air feeding system according to  claim 1 , wherein said over-fire air duct ( 12 ) extends within said combustion chamber coaxially to said burner unit ( 11 ) from a wall opposite thereto and ends with a nozzle ( 17 ) for radially injecting the over-fire air in said combustion chamber.  
     
     
         3 . Over-fire air feeding system according to  claim 2 , wherein said nozzle ( 17 ) in axially sliding.  
     
     
         4 . Over-fire air feeding system according to  claim 2 , wherein said radial over-fire air outlet is continuous.  
     
     
         5 . Over-fire air feeding system according to  claim 2 , wherein said radial over-fire air outlet are air jets.  
     
     
         6 . Over-fire air feeding system according to  claim 2 , wherein said over-fire air duct ( 12 ) adjustably extends within said combustion chamber ( 10 ).  
     
     
         7 . Over-fire air feeding system according to  claim 1 , wherein said nozzle means ( 29 ,  47 ) for the over-fire air are located close to the side walls of said combustion chamber ( 24 ,  42 ) and are arranged on an injection duct ( 28 ,  46 ) crosswise extending within said combustion chamber and communicating with said over-fire air duct ( 27 ,  44 ).  
     
     
         8 . Over-fire air feeding system according to  claim 7 , wherein said nozzle means ( 29 ,  47 ) are equally spaced tubular nozzles.  
     
     
         9 . Over-fire feeding system according to  claim 7 , wherein said nozzle means are formed by a continuous slit along said injection duct ( 28 ,  46 ).  
     
     
         10 . Over-fire air feeding system according to  claim 7 , wherein said over-fire air duct ( 27 ,  44 ) is entered said combustion chamber ( 24 ,  42 ) through a manhole ( 45 ).  
     
     
         11 . Over-fire air feeding system according to  claim 7 , wherein said over-fire air duct ( 27 ,  44 ) is entered said combustion chamber ( 24 ,  42 ) through an opening formed in a not-pressurized part of the generator.  
     
     
         12 . Over-fire air feeding system according to  claim 7 , wherein said over-fire air duct ( 44 ) is entered said combustion chamber ( 42 ) coaxially to said burner unit ( 43 ).  
     
     
         13 . Over-fire air feeding system according to  claim 1 , wherein a portion of the exhaust gas is added either to the overall combustion air flow or to the air supplied to all or some of the burners or to the over-fire air flow only.