Fuel injector for low NOx furnace

Abstract

A fuel injector for use in a furnace causes a primary stream of a carrier gas and fuel to be mixed with heated air, oxygen or a mixture of oxygen and CO 2 or re-circulated flue gas, within the injector by a secondary stream of heated air, before the primary stream exits the injector as a fuel stream and flows into a combustion zone of the furnace. The interaction of the primary stream with the heated air of the secondary stream increases stoichiometry at the center of the fuel stream exiting the injector, so as to minimize NO x creation and maximize combustion of fuel in the furnace.

1 . A fuel injector for use in a furnace comprising:
 a housing having an inlet end and an outlet end, wherein the housing defines a passageway extending between the inlet and outlet ends, wherein the inlet end is for receiving a primary stream of a carrier gas and fuel, wherein a central axis extends along the length and through the center of the passageway;   means for introducing a secondary stream of a heated gas into the passageway; and   wherein, when the primary stream is supplied to the passageway at the inlet end and the secondary stream is introduced into the passageway by the introducing means, the primary stream flows through the passageway towards the outlet end and the secondary stream mixes with and heats, and increases oxygen concentration of, a portion of the primary stream along and around the central axis of the passageway, before the primary stream exits the passageway at the outlet end.   
     
     
         2 . The fuel injector of  claim 1 , wherein the gas of the secondary stream is air and the fuel is pulverized coal. 
     
     
         3 . The fuel injector of  claim 2 , wherein the air in the secondary stream is between about 400° F. and 1000° F. 
     
     
         4 . The fuel injector of  claim 1 , wherein the introducing means defines at least one aperture for introducing the secondary stream into the passageway, wherein the aperture is between the inlet end and the outlet end. 
     
     
         5 . The fuel injector of  claim 4 , wherein the aperture is defined by an adjustable air register. 
     
     
         6 . The fuel injector of  claim 4  further comprising:
 a baffle extending from the housing into the passageway and towards the central axis, wherein the baffle is disposed upstream of the aperture to facilitate penetration of the secondary stream toward the central axis.   
     
     
         7 . The fuel injector of  claim 6 , wherein the baffle is substantially adjacent to the aperture. 
     
     
         8 . The fuel injector of  claim 6 , wherein the baffle extends in the direction of the outlet end. 
     
     
         9 . The fuel injector of  claim 4  further comprising:
 a diverging cone disposed along the central axis upstream of the aperture, wherein the cone diverges in the direction of the outlet end.   
     
     
         10 . The fuel injector of  claim 9  further comprising:
 a baffle extending from the housing into the passageway and towards the central axis and disposed downstream of the cone, wherein the baffle is disposed upstream of the aperture to facilitate penetration of the secondary stream toward the central axis.   
     
     
         11 . The fuel injector of  claim 1  further comprising:
 a segmented nozzle at the outlet end for receiving from the passageway the primary stream in combination with the secondary stream, wherein the segmented nozzle separates the combination of the primary and secondary streams into a plurality of substantially elliptically shaped fuel streams for delivery from the injector at the outlet end.   
     
     
         12 . The fuel injector of  claim 1 , wherein the secondary stream is 100% oxygen, a mixture of air and oxygen, a mixture of CO 2  and oxygen, or a mixture of re-circulated flue gas and oxygen. 
     
     
         13 . A fuel injector for use in a furnace comprising:
 a housing having an inlet end and an outlet end, wherein the housing defines a passageway extending between the inlet and outlet ends, wherein a central axis extends along the length and through the center of the passageway and wherein the inlet end is for receiving a primary stream of a carrier gas and fuel;   an air distributor for distributing the secondary stream substantially along and around the central axis upstream of the outlet end; and   wherein, when the primary stream is supplied to the passageway at the inlet end and flows through the passageway towards the outlet end and the secondary stream is distributed by the air distributor, the secondary stream exiting the distributor mixes with and heats, and increases oxygen concentration of, a portion of the primary stream along and around the axis before the primary stream exits the passageway at the outlet end.   
     
     
         14 . The fuel injector of  claim 13  further comprising:
 a hollow conduit for supplying the secondary stream to the distributor, wherein the distributor is a divergent cone defining a hollow interior in communication with the hollow conduit.   
     
     
         15 . The fuel injector of  claim 14 , wherein the hollow conduit extends from the inlet end to the distributor. 
     
     
         16 . The fuel injector of  claim 14 , wherein the housing defines at least one aperture between the inlet end and the outlet end and the hollow conduit extends from the aperture to the distributor. 
     
     
         17 . The fuel injector of  claim 13 , wherein the gas of the secondary stream is air and fuel is pulverized coal. 
     
     
         18 . The fuel injector of  claim 17 , wherein the air in the secondary stream is between about 400° F. and 1000° F. 
     
     
         19 . The fuel injector of  claim 13  further comprising:
 a segmented nozzle at the outlet end for receiving the from the passageway the primary stream in combination with the secondary stream, wherein the segmented nozzle separates the combination of the primary and secondary streams into a plurality of substantially elliptically shaped fuel streams for delivery from the injector at the outlet end.   
     
     
         20 . The fuel injector of  claim 13 , wherein the secondary stream is 100% oxygen, a mixture of air and oxygen, a mixture of CO 2  and oxygen, or a mixture of re-circulated flue gas and oxygen. 
     
     
         21 . A method for delivering fuel from a fuel injector to a combustion zone of a furnace comprising:
 providing a fuel injector, wherein the fuel injector comprises a housing having an inlet end and an outlet end, wherein the housing defines a passageway extending between the inlet and outlet ends, wherein a central axis extends along the length and through the center of the passageway;   supplying a primary stream of a carrier gas and fuel to the passageway at the inlet end, wherein the primary stream flows through the passageway towards the outlet end; and   supplying a secondary stream of a heated gas into the passageway, wherein the secondary stream mixes with and heats, and increases oxygen concentration of, a portion of the primary stream along and around the axis, before the primary stream exits the passageway at the outlet end.   
     
     
         22 . The method of  claim 21 , wherein the gas of the secondary stream is air and the fuel is pulverized coal. 
     
     
         23 . The method of  claim 22 , wherein the air in the secondary stream is between about 400° F. and 1000° F. 
     
     
         24 . The method of  claim 21  further comprising:
 supplying the secondary stream into the passageway through at least one aperture in the housing disposed between the inlet end and the outlet end.   
     
     
         25 . The method of  claim 24 , wherein the aperture is defined by an adjustable air register. 
     
     
         26 . The method of  claim 24  further comprising:
 interrupting the flow of the primary stream upstream of the aperture to facilitate penetration of the secondary stream toward the central axis.   
     
     
         27 . The method of  claim 26 , wherein the flow is interrupted substantially adjacent to the aperture. 
     
     
         28 . The method of  claim 24  further comprising:
 diverting flow of the primary stream away from the central axis upstream of the aperture.   
     
     
         29 . The method of  claim 21  further comprising:
 separating the primary stream as heated by the secondary stream into a plurality of substantially elliptically shaped fuel streams for delivery from the injector at the outlet end.   
     
     
         30 . The method of  claim 21  further comprising:
 supplying the secondary stream to generate a fuel stream exiting the outlet end having a predetermined stoichiometry on and surrounding the central axis of the passageway.   
     
     
         31 . The method of  claim 21  further comprising:
 supplying the secondary stream along and around the central axis.   
     
     
         32 . The method of  claim 31 , wherein the secondary stream is supplied from a hollow conduit extending from the inlet end. 
     
     
         33 . The method of  claim 31 , wherein the secondary stream is supplied from an aperture in the housing, through a hollow conduit and to an air distributor for distributing the secondary stream along and around the central axis 
     
     
         34 . The method of  claim 21 , wherein the secondary stream is 100% oxygen, a mixture of air and oxygen, a mixture of CO 2  and oxygen, or a mixture of re-circulated flue gas and oxygen.