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A burner assembly for a radiant burner includes a burner tube structure in the form of an elongated burner conduit having spaced inlet and outlet ends. The conduit is adapted and arranged for directing a fuel lean gaseous mixture comprising a portion of the total fluid fuel to be combusted and oxyge

A burner assembly for a radiant burner includes a burner tube structure in the form of an elongated burner conduit having spaced inlet and outlet ends. The conduit is adapted and arranged for directing a fuel lean gaseous mixture comprising a portion of the total fluid fuel to be combusted and oxygen therealong from the inlet end to the outlet end. The assembly also includes a main burner nozzle at the outlet end of the conduit, which nozzle has a central axis, a wall extending around a centrally located chamber therein, and a downstream end spaced from the outlet end of the conduit. The main burner nozzle is arranged and adapted for receiving the mixture from the conduit in the chamber and redirecting the same through a plurality of apertures in the wall and into a combustion zone in a direction transverse to the axis and at a velocity which is greater than the flame speed of the gaseous mixture. The apertures are distributed circumferentially around the wall, whereby the mixture is directed without substantial recirculation and with minimal pressure drop through said apertures and into the combustion zone in the form of a generally round flat pattern which is detached from the nozzle, surrounds the wall and extends outwardly across a radiant surface of a burner tile. The burner also includes an elongated fuel tube extending in a direction generally parallel to the axis, and the fuel tube has a downstream end portion. A secondary fuel nozzle includes a secondary fuel port on the downstream end portion of the fuel tube, which secondary fuel port is located and arranged so as to deliver secondary fuel to a position which is on the opposite side of the fuel pattern from the radiant surface and sufficiently remote from the combustion zone to permit the same to become intermixed with flue gases before entering said combustion zone.

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1. A high capacity, low NO x radiant wall burner including an elongated nozzle arrangement adapted for installation in a passageway in a wall of a furnace adjacent a combustion zone, said furnace wall providing a radiant surface surrounding said passageway and located adjacent said zone, said nozzl

1. A high capacity, low NO x radiant wall burner including an elongated nozzle arrangement adapted for installation in a passageway in a wall of a furnace adjacent a combustion zone, said furnace wall providing a radiant surface surrounding said passageway and located adjacent said zone, said nozzle arrangement comprising:an elongated burner tube including an elongated downstream portion configured to extend through said passageway and an elongated upstream portion, said portions having respective centrally disposed, longitudinally extending axes;a fuel-air mixture supply system providing a source of a fuel lean combustible fuel-air mixture for introduction into said burner tube, an upstream end of the upstream portion of the burner tube being connected in fluid communication with the fuel supply system for receiving the fuel lean combustible fuel-air mixture therefrom, said tube providing a conduit for flow of said fuel lean combustible fuel-air mixture therealong from said upstream end to a downstream end of the downstream end of the downstream portion of the burner tube;a main nozzle positioned at the downstream end of said downstream portion of the burner tube adjacent said radiant surface, said main nozzle having an internal cavity that is in fluid communication with the downstream end of the downstream portion of the burner tube for receiving the fuel lean combustible fuel-air mixture flowing along the tube, said main nozzle being arranged and configured to redirect the fuel-air mixture in the cavity and cause it to flow in a direction radially outwardly relative to said axis of the downstream portion of the burner tube, into said zone, and generally across said radiant surface, said main nozzle including a wall extending around the cavity and a series of radially extending opening in the wall of the main nozzle, said openings being arranged and configured to dispense said combustible fuel-air mixture in said radial direction at an initial velocity which exceeds the flame speed of the mixture and in a circular pattern which essentially surrounds said nozzle in a radial direction, whereby a detached round flame is created when the mixture is combusting; anda secondary fuel nozzle system including an elongated secondary fuel tube longitudinally of said downstream portion of the burner and having at least one fuel gas port that is configured, positioned and arranged to discharge a flow of secondary fuel and cause the same to travel in a direction outwardly away from said radiant surface to a location that is axially spaced from and out of contact with said zone, whereby the secondary fuel will have an opportunity become mixed with flue gases before undergoing combustion with excess air in the combustion zone, said secondary fuel constituting a substantial portion of the total fuel provided to said combustion zone by said fuel-air mixture supply system and said secondary fuel nozzle system. 2. A high capacity, low NO x radiant wall burner as set forth in claim 1, wherein said fuel-air supply system comprises an ejector including a fuel inlet connectable to a source of pressurized fluid fuel, a fluid fuel spud connected in fluid communication with said inlet and positioned for ejecting fluid fuel through a space in fluid communication with a source of air, and a fitting mounted at said upstream end of the upstream portion of the burner tube, said fitting having a mouth positioned for receiving a premix comprising the ejected fluid fuel and air carried along with it and directing the same into the upstream end of the burner tube. 3. A high capacity, low NO x radiant wall burner as set forth in claim 2, wherein said axes are superimposed whereby said burner tube is essentially straight and said main nozzle, said burner tube and said ejector are in essential alignment along said axes. 4. A high capacity, low NO x radiant wall burner as set forth in claim 2, wherein the axis of the upstream portion is disposed at an angle re lative to the axis of the downstream portion thereof, whereby said main nozzle and said downstream portion of the burner tube are disposed in essential alignment along the axis of said downstream portion, and said ejector and said upstream portion of the burner tube are disposed in essential alignment along the axis of said upstream portion. 5. A high capacity, low NO x radiant wall burner as set forth in claim 1, wherein said elongated secondary fuel tube is located outside said main nozzle. 6. A high capacity, low NO x radiant wall burner as set forth in claim 1, wherein said secondary fuel nozzle system includes a plurality of said secondary elongated fuel tubes, said fuel tubes all being located outside said main nozzle. 7. A high capacity, low NO x radiant wall burner as set forth in claim 5, wherein said port is configured, positioned and arranged to cause at least a portion of the secondary fuel to pierce the fuel-air mixture pattern and reach said location in the furnace without combusting. 8. A high capacity, low NO x radiant wall burner as set forth in claim 1,wherein said main nozzle includes an end cap having a hole in it, and wherein said secondary fuel tube extends through said cavity and a downstream portion thereof protrudes through said hole, said port being in said downstream portion of the fuel tube and positioned adjacent said location in the furnace. 9. A high capacity, low NO x radiant wall burner as set forth in claim 8, wherein a plurality of said ports are provided in said downstream portion of the fuel tube and said location in the furnace surrounds said downstream portion of the secondary fuel tube. 10. A high capacity, low NO x radiant wall burner as set forth in claim 1, wherein said radiant surface is essentially flat. 11. A high capacity, low NO x radiant wall burner as set forth in claim 1, wherein said radiant surface is concave. 12. A high capacity, low NO x radiant wall burner as set forth in claim 11, wherein said radiant surface is cup-shaped. 13. A high capacity, low NO x radiant wall burner as set forth in claim 8, wherein said secondary fuel system includes a segment of tubing which extends through a wall of said downstream portion of the burner tube, said segment being connected in fluid communication with an upstream end of the secondary fuel tube. 14. A high capacity, low NO x radiant wall burner as set forth in claim 8, wherein said end cap is convex relative to said cavity. 15. A high capacity, low NO x radiant wall burner as set forth in claim 1, wherein said openings comprise elongated slots which extend in a direction which is essentially parallel to the axis of the downstream portion of the burner tube. 16. A high capacity, low NO x radiant wall burner as set forth in claim 15, wherein said wall of the main nozzle comprises a series of circumferentially spaced bars presenting said slots therebetween, said bars having rounded surfaces adjacent said cavity to inhibit the formation of recirculation zones in the cavity. 17. A high capacity, low NO x radiant wall burner as set forth in claim 1, wherein said burner includes at least one baffle having a generally bell-shaped downstream portion located in said cavity, said bell-shaped portion having an outer, circumferentially extending edge disposed adjacent said wall of the main nozzle. 18. A high capacity, low NO x radiant wall burner as set forth in claim 15, wherein said burner includes at least one baffle having a generally bell-shaped downstream portion located in said cavity, said bell-shaped portion having an outer, circumferentially extending edge disposed adjacent said wall of the main nozzle. 19. A high capacity, low NO x radiant wall burner as set forth in claim 18, wherein said slots have an upstream end and a downstream end and said outer edge of the bell-shaped portion is located closer to the upstream end of the slot than to the downstream end of the slot. 20. A high capacity, low NO x radiant wall burne r as set forth in claim 19, wherein said outer edge of the bell-shaped portion is located approximately one-fourth of the distance from the upstream end of the slot to the downstream end of the slot. 21. A high capacity, low NO x radiant wall burner as set forth in claim 18, wherein said slots have upstream end surfaces that slope in a direction of fluid flow to inhibit the formation of recirculation zones in the cavity. 22. A high capacity, low NO x radiant wall burner as set forth in claim 1, wherein said fuel-air mixture supply system and secondary fuel system are configured and arranged such that the amount of said secondary fuel constitutes more than about 20% of the total fuel provided to the combustion zone. 23. A high capacity, low NO x radiant wall burner as set forth in claim 22, wherein said fuel-air mixture supply system and said secondary fuel system are arranged such that the amount of said secondary fuel constitutes at least about 30% of the total fuel provided to the combustion zone. 24. A high capacity, low NO x radiant wall burner as set forth in claim 23, wherein said fuel-air mixture supply system and said secondary fuel system are arranged such that the amount of said secondary fuel constitutes at least about 50% of the total fuel provided to the combustion zone. 25. A high capacity, low NO x radiant wall burner as set forth in claim 22, wherein said secondary fuel nozzle system is arranged for connection of the elongated fuel tube to a source of fuel gas at a pressure of at least about 2 psig. 26. A high capacity, low NO x radiant wall burner as set forth in claim 25, wherein said secondary fuel nozzle system is arranged for connection of the elongated fuel tube to a source of fuel gas at a pressure of at least about 3 psig. 27. A high capacity, low NO x radiant wall burner as set forth in claim 26, wherein said secondary fuel nozzle system is arranged for connection of the elongated fuel tube to a source of fuel gas at a pressure of at least about 5 psig. 28. A high capacity, low NO x radiant wall burner as set forth in claim 27, wherein said secondary fuel nozzle system is arranged for connection of the elongated fuel tube to a source of fuel gas at a pressure of at least about 10 psig. 29. A high capacity, low NO x radiant wall burner as set forth in claim 28, wherein said secondary fuel nozzle system is arranged for connection of the elongated fuel tube to a source of fuel gas at a pressure of at least about 15 psig. 30. A high capacity, low NO x radiant wall burner as set forth in claim 1, wherein an upstream extremity of said flame is positioned at least about 1 inch from said nozzle. 31. A high capacity, low NO x radiant wall burner as set forth in claim 30, wherein said upstream extremity of said detached flame is positioned no more than about 3 inches from said nozzle. 32. A high capacity, low NO x radiant wall burner as set forth in claim 4, wherein said burner tube includes a curved portion which interconnects said downstream and upstream portions thereof, and wherein said secondary fuel system includes a segment of tubing which extends through a wall of said curved portion of the burner tube, said segment being connected in fluid communication with an upstream end of the fuel tube. 33. A high capacity, low NO x radiant wall burner as set forth in claim 32, wherein said segment of tubing and said fuel tube extend essentially along the axis of said downstream portion of the burner tube. 34. A high capacity, low NO x radiant wall burner as set forth in claim 3, wherein said secondary fuel system includes a segment of tubing that is connected in fluid communication with an upstream end of the fuel tube, said segment extending through said fitting and through said spud, said spud including a plurality of orifices for ejecting fluid fuel, said orifices being arranged around said segment of tubing. 35. A high capacity, low NO x radiant wall burner as set forth in claim 1 wherein said f uel comprises natural gas. 36. A high capacity, low NO x radiant wall burner as set forth in claim 1 wherein said fuel comprises hydrogen. 37. A radiant wall burner as set forth in claim 1, wherein said fuel-air mixture supply system is arranged and adapted for supplying in said mixture all of the air needed for combustion of said total fuel. 38. A radiant wall burner as set forth in claim 2, wherein said fuel-air mixture supply system is arranged and adapted for supplying in said mixture all of the air needed for combustion of said total fuel. 39. A high capacity, low NO x radiant wall burner as set forth in claim 3, wherein said secondary fuel system includes a segment of tubing which extends through a wall of said downstream portion of the burner tube, said segment being connected in fluid with an upstream end of the fuel tube. 40. A high capacity, low NO x radiant wall burner as set forth in claim 2, wherein said fitting is generally bell-shaped. 41. A burner assembly for a radiant burner comprising:a burner tube structure comprising an elongated burner conduit having spaced inlet and outlet ends, said conduit being adapted and arranged for directing a fuel lean gaseous mixture comprising a portion of the total fluid fuel to be combusted and oxygen therealong from said inlet end to said outlet end;a main burner nozzle at the outlet end of said conduit, said burner nozzle having a central axis, a wall extending around a centrally located cavity therein, and a downstream end spaced from said outlet end of the conduit, said main burner nozzle being arranged and adapted for receiving said mixture from the conduit in said cavity and redirecting the same through a plurality of apertures in said wall and into a combustion zone in a direction transverse to said axis, said apertures being distributed around said wall, whereby the mixture directed into the combustion zone through said apertures is generally in the form of a round flat pattern that surrounds said wall and extends outwardly across a radiant surface; anda secondary fuel tube delivery system including an elongated fuel tube extending along said axis and a secondary fuel nozzle located at a downstream end portion of the fuel tube, said secondary fuel nozzle including a secondary fuel port that is located and arranged so as to discharge a flow of secondary fuel and cause the same to travel in a direction outwardly away from said surface to a location that is axially spaced from and out of contact with said combustion zone, whereby the secondary fuel will have an opportunity become mixed with flue gases before undergoing combustion with excess air in the combustion zone. 42. A burner assembly as set forth in claim 41, further comprising a fuel-air mixture supply system providing a source of a fuel lean combustible fuel-air mixture for introduction into the inlet end of said burner conduit, said fuel-air mixture supply system being arranged and configured to establish a fuel lean fuel to air ratio in said fuel-air mixture whereby the latter has a predetermined low flame speed, said apertures being arranged and configured to dispense said combustible fuel-air mixture in said transverse direction at an initial velocity which exceeds the predetermined flame speed of the mixture and in said pattern, whereby a round flame that is detached from the nozzle is created upon combustion of the mixture. 43. A high capacity, low NO x radiant wall burner as set forth in claim 42, wherein said secondary fuel nozzle system is configured and arranged such that the secondary fuel is pure fuel. 44. A high capacity, low NO x radiant wall burner as set forth in claim 42, wherein said a fuel-air mixture supply system and said main nozzle are configured and arranged such that said fuel-air mixture includes all of the air required for combusting said fuel. 45. A high capacity, low NO x radiant wall burner as set forth in claim 43, wherein said a fuel-air mixture supply system and said main n ozzle are configured and arranged such that said fuel-air mixture includes all of the air required for combusting said fuel. 46. A high capacity, low NO x radiant wall burner as set forth in claim 42, wherein said a fuel-air mixture supply system and said main nozzle are configured and arranged such that said fuel-air mixture includes no more than 55% of the total fuel combusted in said burner. 47. A high capacity, low NO x radiant wall burner as set forth in claim 43, wherein said a fuel-air mixture supply system and said main nozzle are configured and arranged such that said fuel-air mixture includes no more than 55% of the total fuel combusted in said burner. 48. A high capacity, low NO x radiant wall burner as set forth in claim 44, wherein said a fuel-air mixture supply system and said main nozzle are configured and arranged such that said fuel-air mixture includes no more than 55% of the total fuel combusted in said burner. 49. A high capacity, low NO x radiant wall burner as set forth in claim 45, wherein said a fuel-air mixture supply system and said main nozzle are configured and arranged such that said fuel-air mixture includes no more than 55% of the total fuel combusted in said burner. 50. A high capacity, low NO x radiant wall burner as set forth in claim 41, wherein the downstream end of the main burner nozzle has a hole in it and said elongated fuel tube extends axially through the cavity with the secondary fuel nozzle projecting through said hole. 51. A high capacity, low NO x radiant wall burner as set forth in claim 41, wherein said elongated fuel tube extends along an outer periphery of main burner nozzle. 52. A burner assembly as set forth in claim 41, wherein said mixture comprises a mixture of a gaseous fuel and air, and said burner tube structure comprises a venturi tube which uses a flow of said gaseous fuel to induce a flow of air, whereby to create said mixture. 53. A burner assembly as set forth in claim 41, wherein said mixture comprises a mixture of a gaseous fuel and air, and said burner tube structure comprises a plurality of venturi tubes arranged for parallel flow, each of said venturis being adapted and arranged to use a flow of said gaseous fuel to induce a flow of air, whereby to generate said mixture as an ultra fuel lean mixture of fuel and air. 54. A burner assembly as set forth in claim 41, wherein said elongated fuel tube is located externally of said main fuel nozzle and said secondary fuel port is located and arranged so as to deliver secondary fuel at a velocity and in a direction such that at least a portion of the secondary fuel pierces said pattern to reach said location. 55. A burner assembly as set forth in claim 41, wherein said fuel lean gaseous, mixture includes all of the oxygen needed for combustion of the total fuel. 56. A burner assembly as set forth in claim 53, wherein said fuel lean gaseous mixture includes all of the air needed for combustion of the total fuel. 57. A burner assembly as set forth in claim 41, wherein said radiant surface is part of a refractory burner tile inserted in a wall of a furnace, and wherein said main burner nozzle extends through a passageway in said tile. 58. A high capacity, low NO x radiant wall burner as set forth in claim 41, wherein said burner tube structure and said secondary fuel delivery system are arranged such that the amount of said secondary fuel delivered to said location constitutes at least about 30% of the total fuel provided to the combustion zone. 59. A high capacity, low NO x radiant wall burner as set forth in claim 58, wherein said burner tube structure and said secondary fuel delivery system are arranged such that the amount of said secondary fuel delivered to said location constitutes at least about 50% of the total fuel provided to the combustion zone. 60. A high capacity, low NO x radiant wall burner as set forth in claim 41, wherein said main burner nozzle is arranged and adapted for redirecting the gaseou s mixture at an initial velocity which exceeds the flame speed of the mixture, whereby said round flame is detached from the nozzle. 61. A burner assembly as set forth in claim 42, wherein said fuel-air mixing system comprises at least one venturi tube, said venturi tube being adapted and arranged to use a flow of said gaseous fuel to induce a flow of air, whereby to gene mixture as an ultra fuel lean mixture of fuel and air. 62. A radiant wall burner as set forth in claim 42, wherein said fuel-air mixing system is arranged and adapted for supplying in said mixture all of the air needed for combustion of said total fuel. 63. A radiant wall burner as set forth in claim 61, wherein said fuel-air mixing system is arranged and adapted for supplying in said mixture all of the air needed for combustion of said total fuel. 64. A method for operating a high capacity, low NO x radiant wall burner to heat a radiant surface adjacent a combustion zone in a furnace chamber, said method comprising:providing a fuel lean combustible fuel-air mixture;providing an elongated main nozzle having a longitudinal axis;causing the fuel-air mixture to flow radially outwardly from said main nozzle, into said combustion zone and generally across said radiant surface in a circular pattern which essentially surrounds said main nozzle in a radial direction;combusting said mixture in said zone; anddischarging a flow of secondary fuel into said furnace chamber and causing the same to travel in a direction outwardly away from said radiant surface to a location in said furnace chamber that is axially spaced from and out of contract with said zone, said location being sufficiently remote from said zone to permit the secondary fuel to become intermixed with flue gases before it has time to return to the zone for combustion with excess oxygen in the zone. 65. A method for operating a high capacity, low NO x radiant wall burner as set forth in claim 64, further comprising establishing a fuel lean fuel to air ratio in said fuel-air mixture at a level such that the flame speed of the mixture is less than the velocity of the same as its flows radially outwardly from said nozzle, whereby a flame that is detached from said nozzle results during combustion of the mixture. 66. A method for operating a high capacity, low NO x radiant wall burner as set forth in claim 64, wherein said secondary fuel constitutes more than 20% of the total fuel provided to the combustion zone. 67. A method for operating a high capacity, low NO x radiant wall burner as set forth in claim 66, wherein said secondary fuel constitutes at least about 30% of the total fuel provided to the combustion zone. 68. A method for operating a high capacity, low NO x radiant wall burner as set forth in claim 67, wherein said secondary fuel constitutes at least about 50% of the total fuel provided to the combustion zone. 69. A method for operating a high capacity, low NO x radiant wall burner as set forth in claim 64, wherein said secondary fuel is provided at said location using a secondary fuel nozzle which extends through said main nozzle. 70. A method for operating a high capacity, low NO x radiant wall burner as set forth in claim 66, wherein said secondary fuel is provided at said location using a secondary fuel nozzle which emits a jet of fuel that pierces said pattern without combusting. 71. A method as set forth in claim 66, wherein said fuel-air mixture supply system includes all of the air needed for combustion of said total fuel. 72. A high capacity, low NO x radiant wall burner as set forth in claim 64, wherein is included the step of causing the fuel-air mixture to flow outwardly from said main nozzle at an initial velocity which exceeds the flame speed of the mixture, whereby a detached round flame is created when the mixture is combusting. 73. A method for operating a radiant burner comprising:delivering a flow of a fuel lean combustible mixture comprising a portion of the total fuel to be combusted and air in a radial direction from an elongated nozzle having a central axis to a combustion zone surrounding said nozzle in the form of a round, flat pattern, said zone being located in a furnace chamber adjacent a radiant surface;establishing a fuel lean fuel to air ratio in said mixture at a level such that the flame speed of the mixture is less than the velocity thereof as the same is delivered to said combustion zone, whereby a flame that is detached from said nozzle results during combustion of the mixture;igniting said mixture to create a round flat detached flame which surrounds said nozzle in a radial direction and is located adjacent said radiant surface; anddischarging a flow of secondary fuel into said furnace chamber and causing the same to travel in a direction outwardly away from said radiant surface to a location in said furnace chamber that is axially spaced from and out of contact with said zone, said location being sufficiently remote from said zone to permit the secondary fuel to become intermixed with flue gases before it has time to return to the zone for combustion with excess oxygen in the zone. 74. A method as set forth in claim 73, wherein said fuel lean combustible mixture system includes all of the air needed for combustion of said total fuel. 75. A method as set forth in claim 73, wherein said radiant surface is part of a refractory burner tile inserted in a wall of a furnace, and wherein said elongated nozzle extends through a passageway in said tile. 76. A method for operating a high capacity, low NO x radiant wall burner as set forth in claim 73, wherein said secondary fuel constitutes at least about 30% of the total fuel provided to the combustion zone. 77. A method for operating a high capacity, low NO x radiant wall burner as set forth in claim 76, wherein said secondary fuel constitutes at least about 50% of the total fuel provided to the combustion zone. 78. A method as set forth in claim 73, wherein said mixture is an ultra fuel lean mixture of fuel and air. 79. A method as set forth in claim 78, wherein said mixture includes all of the air needed for combustion of said total fuel.