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A radiant tube burner system comprises a novel flue gas recirculating assembly for reducing nitrous oxides emissions. In the burner system, the combustion air conduit running to the radiant tube burner intersects the exhaust conduit at a location between the radiant tube and the eventual exhaust out

A radiant tube burner system comprises a novel flue gas recirculating assembly for reducing nitrous oxides emissions. In the burner system, the combustion air conduit running to the radiant tube burner intersects the exhaust conduit at a location between the radiant tube and the eventual exhaust outlet. A venturi is formed at this intersection. The venturi is configured to suction a portion of the flue gas from the exhaust conduit into the combustion air flow. The assembly includes a may be interposed along the exhaust conduit mounted directly between the radiant tube and a downstream section of the exhaust conduit.

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What is claimed is: 1. A radiant tube burner system for combusting fuel and combustion air, thereby forming flue gas, the radiant tube burner system comprising: a burner having a combustion air inlet, a fuel inlet, and a burner head, the burner adapted to convey combustion air and fuel from the com

What is claimed is: 1. A radiant tube burner system for combusting fuel and combustion air, thereby forming flue gas, the radiant tube burner system comprising: a burner having a combustion air inlet, a fuel inlet, and a burner head, the burner adapted to convey combustion air and fuel from the combustion air inlet and the fuel inlet to the burner head for combustion; a radiant tube receiving the burner head; an exhaust conduit connected to the radiant tube, the exhaust conduit adapted to convey flue gas toward an exhaust outlet; a blower adapted to generate a pressurized source of combustion air; a combustion air conduit connecting the blower to the combustion air inlet, the combustion air conduit intersecting the exhaust conduit at a location fluidically between the radiant tube and the exhaust outlet; and a venturi formed at an intersection between the combustion air conduit and the exhaust conduit, the venturi arranged to suction a portion of flue gas from the exhaust conduit into the combustion air conduit. 2. The radiant tube burner system of claim 1, wherein said exhaust conduit includes a tubular conduit section, the tubular conduit section including a flue gas entrance port and a flue gas exit port communicating flue gas through the exhaust conduit, the tubular conduit section further including an oxidant entrance port and an oxidant exit port, the flue gas entrance and exit ports connected by a flue gas passageway for communicating flue gas through the exhaust conduit, the tubular conduit section further including a throat portion integral extending transversely relative to the flue gas passageway, the throat portion connecting the flue gas passageway to the oxidant exit port; and wherein the combustion air conduit includes an oxidant inlet pipe extending through the oxidant entrance port, the oxidant inlet pipe terminating in a nozzle directed toward the oxidant exit port. 3. The radiant tube burner system of claim 2, wherein the oxidant inlet pipe is formed separately from the tubular conduit section and is movable relative to the tubular conduit section, further comprising a mounting device releasably securing the oxidant inlet pipe to the tubular conduit section, whereby a position of the nozzle can be adjusted relative to the oxidant exit port. 4. The radiant tube burner system of claim 3, wherein said mounting device comprises a screw mounted into a threaded hole in the tubular conduit section, the screw clamping the oxidant inlet pipe to the tubular conduit section. 5. The radiant tube burner system of claim 4, further comprising a threaded sleeve slidably mounted coaxial about the oxidant inlet pipe screwed into a threaded opening in the tubular conduit section, and a seal retained between the threaded sleeve and the tubular conduit section. 6. The radiant tube burner system of claim 2, further comprising a restrictor mounted on an oxidant outlet pipe arranged to restrict flow from the flue gas passageway through the throat portion. 7. The radiant tube burner system of claim 6 further comprising means for adjusting a position of the restrictor on the oxidant outlet pipe. 8. The radiant tube burner system of claim 2 wherein a recirculation passage is defined generally between the throat portion and the oxidant inlet pipe connecting the flue gas passageway to the oxidant exit port, wherein when oxidant flows through the oxidant inlet pipe and flue gas flows through the flue gas passageway, a portion of the flue gas is suctioned into the oxidant exit port through the recirculation passage. 9. An apparatus for introducing flue gas from an exhaust conduit into oxidant flowing in an oxidant conduit, the apparatus comprising: a tubular conduit section adapted to be interposed along the exhaust conduit, the tubular conduit section including a flue gas entrance port and a flue gas exit port, an oxidant entrance port and an oxidant exit port, the flue gas entrance and exit ports connected by a flue gas passageway for communicating flue gas through the exhaust conduit, the tubular conduit section further including a throat portion integral extending transversely relative to the flue gas passageway, the throat portion connecting the flue gas passageway to the oxidant exit port; and an oxidant inlet pipe extending through the oxidant entrance port, the oxidant inlet pipe terminating in a nozzle directed toward the oxidant exit port, wherein the flue gas passageway fluidically intersects the oxidant conduit. 10. The apparatus of claim 9, wherein the oxidant inlet pipe is formed separately from the tubular conduit section and is movable relative to the tubular conduit section, further comprising a mounting device releasably securing the oxidant inlet pipe to the tubular conduit section, whereby a position of the nozzle can be adjusted relative to the oxidant exit port. 11. The apparatus of claim 10, wherein said mounting device comprises a screw mounted into a threaded hole in the tubular conduit section, the screw clamping the oxidant inlet pipe to the tubular conduit section. 12. The apparatus of claim 11, further comprising a threaded sleeve slidably mounted coaxial about the oxidant inlet pipe screwed into a threaded opening in the tubular conduit section, and a seal retained between the threaded sleeve and the tubular conduit section. 13. The apparatus of claim 9 wherein the oxidant inlet pipe is connected to a blower, the blower adapted to generate a combustion air flow, and wherein the throat portion is connected to a combustion air inlet of a radiant tube burner. 14. The apparatus of claim 9 wherein the throat portion projects generally perpendicular relative to the flue gas passageway. 15. The apparatus of claim 9, further comprising a restrictor mounted on an oxidant outlet pipe arranged to restrict flow from the flue gas passageway through the throat portion. 16. The apparatus of claim 15 further comprising means for adjusting a position of the restrictor on the oxidant outlet pipe. 17. The apparatus of claim 9 wherein a recirculation passage is defined generally between the throat portion and the oxidant inlet pipe connecting the flue gas passageway to the oxidant exit port, wherein when oxidant flows through the oxidant inlet pipe and flue gas flows through the flue gas passageway, a portion of the flue gas is suctioned into the oxidant exit port through the recirculation passage.