Diffuser plate for boiler burner feed assembly

Abstract

A diffuser or orifice plate is positioned across the bore of a feed pipe supplying a mixture of pressurized air and recycled flue gas to the combustion chamber of a gas burner associated with a boiler. The diffuser plate comprises inner and outer, radially spaced apart, annular baffles. The baffles define a central opening and an outer series of openings forming an annular array. Part of the gas mixture is accelerated as it passes through the restrictive outer openings and forms an annular stream. Part of the gas mixture passes through the central opening in the form of a lance-like stream. Fuel gas is injected into the annular stream immediately downstream of the diffuser plate. The resulting air/flue gas/fuel gas mixture mixes and adopts an elongated form in the combustion chamber. The burner feed assembly described contributes to maintaining the Ox content in the burner flue gas at a low level such as less than 15 ppm.

1 . A burner feed assembly for supplying a combustion mixture to the combustion chamber of a burner associated with a boiler, comprising: 
 means for supplying a stream of pressurized air;    a feed pipe, having a bore, for connecting the air supply means with the combustion chamber, said bore having upstream and downstream ends;    a diffuser plate, comprising inner and outer, generally annular baffles forming a central opening and at least one outwardly spaced, arcuate opening, said diffuser plate being positioned transversely across the downstream end of the bore of the feed pipe;    means for recycling flue gases, produced in the combustion chamber, to the feed pipe bore upstream of the diffuser plate, for mixing with the stream of air to form an air/flue gas mixture; and    means for feeding fuel gas into the air/flue gas mixture immediately downstream of the diffuser plate.    
   
   
       2 . The burner feed assembly as set forth in  claim 1  comprising radial connectors interconnecting the inner and outer annular baffles, said baffles and connectors combining to define a plurality of arcuate, outwardly spaced openings, collectively forming a substantially annular passageway.  
   
   
       3 . A method for controlling NOx emission from a burner having a feed pipe for supplying a flow of a mixture of air and flue gas under pressure into a burner combustion chamber, comprising: 
 providing an apertured diffusion plate extending across the bore of the feed pipe, said plate having a central opening and one or more outwardly spaced, arcuate openings;    forming part of the mixture flow into an inner stream having an elongated configuration, by passing it through the central opening;    forming another part of the mixture flow into an outer stream having a generally annular configuration by passing it through the outer openings;    the area of the outer openings being selected to be restrictive so that the mixture flow is accelerated as it passes therethrough; and    injecting fuel gas inwardly into the annular stream immediately downstream of the plate.