Burner Pilot With Virtual Spinner

Abstract

A method and apparatus for preheating a furnace during a warm-up phase of furnace operation. The furnace has main burners with a tubular fuel supply surrounded by a main combustion air duct defining an annular space between the supply and the duct that extends in an axial direction of the main burner. A pilot nozzle in the annular space extends in an axial direction of the burner towards an interior of the furnace and discharges readily ignitable fluid fuel jets through orifices in the nozzle toward the interior of the furnace. Combustion air from the duct is directed past the nozzle and is mixed with the fuel discharged from the orifices to form an ignitable mixture that is ignited to form the furnace heating pilot flame downstream of the nozzle. The flame is stabilized and anchored to the pilot nozzle by recirculating portions of the flame and its constituents from the furnace interior back towards the nozzle by protecting the air passing through the primary ignition zone from being directly affected by air flowing through the main combustion air conduit, diverging the fuel jets relative to the axial direction by an angle between about 20° to 80°, and giving the fuel jets a tangential directional component relative to the axial direction to spin the flame about the axis of the pilot.

1 . A method of anchoring a high heat output pilot flame to a pilot nozzle associated with a coal burner for industrial furnaces, comprising
 flowing combustion air along an exterior of a coal supply conduit having a downstream end for discharge of the air into a furnace interior,   placing a pilot nozzle proximate to the downstream end of the coal supply conduit,   delivering fuel gas to the nozzle through a pipe placed in the combustion air flow,   shielding the pipe delivering fuel to the pilot nozzle in the part adjacent to the nozzle with a tubular hood that is open in a downstream direction, while permitting a limited amount of the combustion air to flow into inside the hood,   directing a plurality of pilot fuel jets from the pilot nozzle into the furnace interior,   discharging at least one igniter fuel jet into an interior of the hood,   aspirating air into the hood with the fuel gas jets from at least one of the pilot nozzle or the igniter jet in a quantity to create a flammable mixture inside the hood,   igniting the flammable mixture inside the hood to generate an igniter flame that extends past the open downstream end of the hood, and   orienting the pilot fuel jets so that they diverge relative to a longitudinal axis of the pilot nozzle and so that the pilot fuel jets have a tangential component relative to the pilot nozzle axis for spinning the fuel about the pilot axis and recirculating a portion of the mixture of fuel with air from the location downstream of the nozzle back to the pilot nozzle.   
   
   
       2 . A method of anchoring a high heat output pilot flame to a pilot nozzle associated with a coal burner for industrial furnaces, the coal burner including a coal supply conduit extending in an axial direction into an interior of the furnace, the method comprising
 flowing combustion air along an exterior of the coal supply conduit for discharge into the furnace interior,   shielding the pilot burner from the combustion air flowing along the exterior of the supply conduit while permitting a limited, controlled amount of air from the combustion air to flow past the pilot nozzle by placing a tubular hood over the pilot nozzle which is open in a downstream direction,   discharging at least one high velocity igniter fuel jet into an interior of the hood to thereby lower a pressure inside the hood,   using the lower pressure inside the hood to aspirate an amount of air from the combustion air into the hood which depends on the lowered pressure inside the hood,   igniting fuel from the igniter jets and air inside the hood to generate an igniter flame that extends past the open downstream end of the hood,   directing a plurality of pilot fuel jets from a downstream end portion of the pilot nozzle into the furnace interior, and   orienting the pilot fuel jets so that they diverge relative to a longitudinal axis of the pilot nozzle and so that the pilot fuel jets are tangential relative to the pilot nozzle axis for spinning the fuel about the pilot axis and recirculating a portion of the pilot fuel from the pilot fuel jets in an upstream direction toward the pilot nozzle.   
   
   
       3 . A method for preheating a furnace during a warm-up phase of furnace operation, the furnace including at least one main burner having a tubular fuel supply surrounded by a main combustion air duct defining an annular space between the fuel supply and the duct that extends in an axial direction of the main burner, the method comprising
 positioning a pilot nozzle in the annular space so that the nozzle generally extends in an axial direction of the burner towards an interior of the furnace,   discharging readily ignitable fuel jets through orifices in the nozzle oriented toward the interior of the furnace,   directing air from the annular space past the nozzle and mixing the air with the fuel discharged from the orifices to form an ignitable mixture,   igniting the mixture to form a flame downstream of the nozzle,   stabilizing the flame and recirculating portions of the flame and/or the mixture from the furnace interior back towards the nozzle by
 protecting the air directed past the nozzle from being directly affected by air flowing through the main combustion air conduit, and 
 diverging the fuel jets relative to the axial direction between about 20° to 80° and giving the fuel jets a tangential directional component relative to the axial direction. 
   
   
   
       4 . A method according to  claim 3  including positioning the nozzle outside the furnace interior. 
   
   
       5 . A method according to  claim 3  wherein the angle is between about 20° and 80°. 
   
   
       6 . A method according to  claim 3  wherein a heat output of the fuel discharged through the orifices is between about 4 and 50 million BTU per hour. 
   
   
       7 . A method according to  claim 6  wherein the nozzle comprises a pilot burner, and including limiting a maximum width of the pilot burner transverse to the axial direction to no more than about five inches. 
   
   
       8 . A method according to  claim 3  wherein the fluid fuel comprises a gas. 
   
   
       9 . A method according to  claim 3  wherein protecting the air comprises placing a tubular hood having an open downstream end about the nozzle, and inhibiting the flow of air from the combustion air duct into the hood with an air flow restrictor positioned proximate an upstream end of the hood. 
   
   
       10 . A method of generating a high BTU output pilot flame during a warm-up phase of operation of a furnace having a main production burner that includes a first conduit for directing coal into an interior of a furnace and a combustion air duct surrounding the conduit defining an annular combustion air passage into the furnace for mixing the coal with combustion air and ignition of the coal, the method comprising
 placing a pilot nozzle in the combustion air passage so that a downstream of the nozzle is proximate a downstream end of the burner,   surrounding the nozzle with a tubular hood having an open downstream end proximate the downstream end of the nozzle and an upstream end,   preventing combustion air flowing through the combustion air passage from directly entering the hood through the upstream end thereof while maintaining flow communication between the combustion air passage and an inside of the hood via the upstream end thereof,   flowing a pressurized fluid fuel through igniter orifices in the nozzle located inside the tubular hood at a sufficient rate to lower a pressure inside the tubular hood to draw combustion air from the combustion air passage via the upstream end of the hood into the hood,   discharging a major portion of the fluid fuel from a plurality of pilot orifices in a downstream end portion of the nozzle,   orienting fuel from the plurality of pilot orifices so that fuel jets emitted therefrom angularly diverge in a downstream direction toward the furnace interior and have a tangential flow direction relative to a longitudinal axis of the pilot nozzle,   generating an igniter flame that propagates past the downstream end of the hood by igniting the fuel emitted by the igniter orifices inside the tubular hood, and   igniting a mixture of fuel from the pilot orifices and combustion air from the combustion air conduit downstream of the main production burner to generate a pilot flame that extends into the furnace interior for heating the furnace interior while portions of the pilot flame and its constituent gases recirculate from the furnace interior rearwardly towards the downstream end of the nozzle while simultaneously spinning relative to the nozzle axis for maintaining a stable pilot flame.   
   
   
       11 . A method according to  claim 10  wherein the pilot flame generates a heat output between 5 to 50 million BTU per hour. 
   
   
       12 . A method according to  claim 10  wherein preventing combustion air from flowing directly into the hood comprises placing a flow restrictor proximate to and spaced apart from the upstream end of the hood to define a gap between the flow restrictor and the upstream end of the gap through which the combustion air enters the hood. 
   
   
       13 . A method according to  claim 12  wherein the flow restrictor is a plate, and varying a width of the gap by moving the plate relative to the upstream end of the hood. 
   
   
       14 . A method according to  claim 10  wherein the nozzle includes a fuel supply tube, and wherein the igniter orifices are formed in the fuel supply tube. 
   
   
       15 . Apparatus for preheating a furnace during a warm-up phase of operation and prior to a production phase of operation of the furnace comprising
 at least one main burner adapted to be extended in an axial direction through a wall of the furnace including a production fuel conduit for directing a production fuel into a furnace interior during the production phase of the furnace,   a combustion air duct surrounding the production fuel conduit for flowing combustion air along an annular passage past the main burner into the furnace interior,   an elongated pilot fuel nozzle positioned in the air duct arranged substantially parallel to the conduit and the duct and having a transverse extent slightly less than a width of the annular passage, the nozzle including at least one igniter orifice located upstream of a downstream end of the nozzle and a plurality of pilot fuel orifices located proximate the downstream end of the nozzle which angularly diverge in a downstream direction relative to an axis of the nozzle and which are tangentially positioned relative to the nozzle axis,   a tubular hood disposed in the annular passage and having an open downstream end proximate the downstream end of the nozzle,   a flow inhibitor positioned proximate an upstream end of the tubular hood for preventing combustion air from flowing from the annular passage directly into the hood, and   an igniter located inside the tubular hood and proximate the igniter orifices for igniting the fuel emitted by the igniter orifices and generating an igniter flame inside the tubular hood which extends in a downstream direction past the tubular hood for igniting a mixture of fuel emitted by the pilot orifices and combustion air from the annular passage downstream of the tubular hood,   whereby the mixture generates a pilot flame downstream of the hood and portions of the pilot flame recirculate from the downstream part of the flame back to the nozzle and spin relative to a longitudinal axis of the nozzle.   
   
   
       16 . Apparatus according to  claim 15  wherein the flow inhibitor comprises a plate extending transversely across and axially spaced from the upstream end of the hood to form a gap between the plate and the upstream end of the hood through which air must flow in order to enter the interior of the hood. 
   
   
       17 . Apparatus according to  claim 15  wherein the hood has an interior cross-section, and wherein the nozzle has a lesser cross-section than the hood and is positioned adjacent a wall of the hood to define an enlarged space inside the hood where the igniter flame is generated. 
   
   
       18 . Apparatus according to  claim 15  wherein the elongated fuel nozzle includes a fuel supply tube, and wherein the igniter orifices are formed in the fuel supply tube.