Burner system including a distal flame holder and a non-reactive fluid source

Abstract

A burner includes a distal flame holder, first and second fuel nozzles, a fuel and oxidant source, and a mixing tube disposed upstream from the distal flame holder. Fuel emitted from the first fuel nozzle mixes with oxidant from the oxidant source to form a fuel and oxidant mixture to support combustion in the distal flame holder. A non-reactive fluid source such as recirculated flue gas provides a non-reactive fluid for dilution of the fuel and oxidant mixture to prevent flashback.

1 . A burner system, comprising:
 a distal flame holder for disposition in a combustion volume and configured to receive and ignite a fuel and oxidant mixture;   a fuel source configured to contribute a fuel to the fuel and oxidant mixture;   an oxidant source configured to contribute an oxidant to the fuel and oxidant mixture; and   a non-reactive fluid source configured to deliver a non-reactive fluid in a dilution region between the distal flame holder and the non-reactive fluid source.   
     
     
         2 . The burner system of  claim 1 , further comprising:
 a mixing tube disposed in the dilution region and being open between the distal flame holder and the fuel source, the mixing tube configured to receive, and facilitate mixing of, the fuel and the oxidant; and   a pilot fuel nozzle disposed proximate the distal flame holder and downstream from a distal end of the mixing tube.   
     
     
         3 . The burner system of  claim 2 , wherein the non-reactive fluid is flue gas from downstream of the distal flame holder, and
 a flow of the fuel and oxidant from the fuel and oxidant source toward the distal flame holder draws the flue gas into a proximal end of the mixing tube from at least downstream of the distal flame holder along an outer surface of the mixing tube.   
     
     
         4 . The burner system of  claim 2 , wherein the proximal end of the mixing tube includes a flared portion. 
     
     
         5 . The burner system of  claim 1 , further comprising a pilot flame holding feature disposed to hold a pilot flame;
 wherein the non-reactive fluid source is configured to deliver the non-reactive fluid in a region disposed between the pilot flame holding feature and an ignitable portion of the fuel and oxidant mixture.   
     
     
         6 . The burner system of  claim 5 , wherein the non-reactive fluid includes a reactive component; and
 wherein the pilot flame held by the pilot flame holding feature generates at least a portion of the non-reactive fluid in the form of a fuel depleting combustion product.   
     
     
         7 . The burner system of  claim 6 , wherein the non-reactive fluid includes one or more components selected from the group consisting of:
 nitrogen, carbon dioxide, nitrogen oxide, nitrogen dioxide, sulfur oxide, sulfur dioxide, oxygen, and argon.   
     
     
         8 . The burner system of  claim 7 , further comprising: an ignitor configured to selectably ignite the fuel and oxidant mixture, the ignitor being disposed adjacent to the pilot flame and the fuel and oxidant mixture. 
     
     
         9 . The burner system of  claim 3 , wherein the non-reactive fluid further comprises combustion reaction products generated by a pilot flame. 
     
     
         10 . The burner system of  claim 1 , wherein
 the fuel source includes:
 a fuel supply configured to store the fuel, and 
 a first fuel nozzle in fluid connection with the fuel supply and positioned to deliver the fuel to the fuel and oxidant mixture; and 
   the non-reactive fluid source includes:
 a second fuel nozzle in fluid connection with the fuel supply, 
 an intermediate flame holder disposed between the second fuel nozzle and the distal flame holder, the intermediate flame holder configured to hold a flame supported by the oxidant and by the fuel, when the fuel is delivered from the second fuel nozzle, and 
 an ignition source configured to ignite the fuel and the oxidant at the intermediate flame holder to produce the flame. 
   
     
     
         11 . The burner system of  claim 10 , wherein combustion products from the flame constitute at least a portion of the non-reactive fluid. 
     
     
         12 . The burner system of  claim 11 , further comprising:
 a fuel flow control mechanism in fluid connection with the second fuel nozzle;   wherein the fuel flow control mechanism is configured to permit a first fuel flow rate to the second fuel nozzle during a startup period and is configured to permit a second fuel flow rate to the second fuel nozzle after the startup period.   
     
     
         13 . The burner system of  claim 12 , wherein the intermediate flame holder is disposed a distance from the distal flame holder sufficient at the first fuel flow rate to cool the combustion products below an auto-ignition temperature of the fuel and oxidant mixture. 
     
     
         14 .- 15 . (canceled) 
     
     
         16 . The burner system of  claim 1 , wherein the distal flame holder is configured to support a combustion reaction of the fuel and the oxidant upstream, downstream, and within the distal flame holder. 
     
     
         17 .- 23 . (canceled) 
     
     
         24 . A burner system, comprising:
 a distal flame holder configured to hold a combustion reaction of a fuel and an oxidant;   an oxidant conduit configured to direct the oxidant toward the distal flame holder;   a first fuel nozzle oriented to direct a first flow of the fuel into a combustion volume for mixture with the oxidant in a dilution region between the first fuel nozzle and the distal flame holder when a temperature of the distal flame holder is above a predetermined temperature;   a mixing tube disposed in the dilution region, and being open between the distal flame holder and the first fuel nozzle; and   a non-reactive fluid source oriented to provide a non-reactive fluid into the mixing tube when the distal flame holder is at an operating temperature.   
     
     
         25 . The burner system of  claim 24 , wherein the non-reactive fluid source comprises:
 a flue gas recirculation path;   wherein flue gas provided by via flue gas recirculation path constitutes at least part of the non-reactive fluid, and the flue gas is educed into a fuel and oxidant stream by the flow of at least the oxidant.   
     
     
         26 . The burner system of  claim 25 , further comprising;
 a pilot fuel nozzle configured to provide pilot fuel for a pilot flame, wherein the flue gas recirculation path includes at least a toroidal volume between the mixing tube and a wall of the combustion volume, and   the flue gas is educed into the fuel and oxidant stream at a proximal opening of the mixing tube for dilution of the fuel and oxidant stream.   
     
     
         27 . The burner system of  claim 26 , wherein the flue gas recirculation path is external to combustion chamber. 
     
     
         28 . The burner system of  claim 27 , further comprising a flue gas flow control mechanism configured to control at least one of a rate of flow and a direction of flow of the recirculated flue gas. 
     
     
         29 . The burner system of  claim 24 , wherein the mixing tube includes a flared portion at the proximal opening. 
     
     
         30 . The burner system of  claim 24 , further comprising;
 a pilot fuel nozzle disposed lateral to the first fuel nozzle; and   an ignition source disposed proximate the pilot fuel nozzle and configured to ignite a mixture of the oxidant and the fuel emitted from the pilot fuel nozzle.   
     
     
         31 . The burner system of  claim 30 , further comprising:
 a first valve configured to control a flow rate of the first flow of the fuel to the first fuel nozzle; and   a second valve configured to control a flow rate of a second flow of the fuel to the pilot fuel nozzle.   
     
     
         32 . The burner system of  claim 31 , further comprising:
 a controller having outputs configured to adjust at least one of the first valve and the second valve, wherein the controller is configured to cause the flow rate of the second flow of the fuel to be lower than the flow rate of the first flow of the fuel when the distal flame holder is at the operating temperature.   
     
     
         33 . The burner system of  claim 30 , wherein the pilot fuel nozzle and the first fuel nozzle are configured to emit the same fuel. 
     
     
         34 . The burner system of  claim 24 , further comprising:
 a heating apparatus configured to heat the distal flame holder to the predetermined temperature; and   a controller operatively coupled to the heating apparatus, the controller configured to receive an indication of the temperature of the distal flame holder and to control the heating apparatus based on the indication of the temperature.   
     
     
         35 . The burner system of  claim 34 , wherein the heating apparatus includes the non-reactive fluid source, and the non-reactive fluid source includes at least the pilot fuel nozzle configured to direct the second flow of the fuel for mixture and combustion with a portion of the oxidant in the dilution region, the combustion of the second flow of the fuel and the oxidant providing thermal energy that heats the distal flame holder, and
 wherein the controller is configured to cause the pilot fuel nozzle to emit the second flow of the fuel at a first fuel flow rate when the temperature of the distal flame holder is below the predetermined temperature, and to emit the second flow of the fuel at a second fuel flow rate when the temperature of the distal flame holder is at or above the predetermined temperature.   
     
     
         36 . The burner system of  claim 35 , wherein the first fuel flow rate is higher than the second fuel flow rate. 
     
     
         37 . The burner system of  claim 35 , further comprising an oxidant supply controller configured to control a flow rate of the oxidant, the oxidant supply controller including:
 a first oxidant flow control mechanism configured to control flow of the oxidant for mixture with the fuel alternately at the first fuel flow rate and the second fuel flow rate; and   a second oxidant flow control mechanism configured to control flow of the oxidant for mixture of the oxidant with the fuel from the first fuel nozzle.   
     
     
         38 . (canceled) 
     
     
         39 . A method for inhibiting flashback in a burner system, the method comprising:
 supplying an oxidant to a combustion volume;   directing a fuel via a first fuel nozzle to a dilution region of the combustion volume between the first fuel nozzle and a distal flame holder;   mixing the oxidant with the fuel from the first fuel nozzle in the dilution region to provide a mixture of the fuel and the oxidant; and   providing a non-reactive fluid to the mixture of the fuel and the oxidant in the dilution region.   
     
     
         40 . The method of  claim 39 , wherein said providing the non-reactive fluid includes:
 emitting the fuel from a second fuel nozzle at a velocity different from a velocity of the fuel supplied via the first fuel nozzle; and   combusting the fuel emitted from the second fuel nozzle in a portion of the dilution region proximate the second fuel nozzle, wherein combustion products from combusting the fuel emitted from the second fuel nozzle constitute the non-reactive fluid.   
     
     
         41 . The method of  claim 40 , wherein said combusting the fuel emitted from the second fuel nozzle in a portion of the dilution region proximate the second fuel nozzle comprises:
 supplying the oxidant proximate the second fuel nozzle toward an intermediate flame holder disposed in the dilution region;   igniting a second mixture of the fuel emitted from the second fuel nozzle and the oxidant supplied proximate the second fuel nozzle; and   holding a flame, resulting from the ignition of the second mixture, at the intermediate flame holder.   
     
     
         42 . The method of  claim 41 , wherein the intermediate flame holder is disposed proximate the second fuel nozzle. 
     
     
         43 . (canceled) 
     
     
         44 . The method of  claim 39 , wherein said providing the non-reactive fluid to the mixture of the fuel and the oxidant includes recirculating a flue gas, as the non-reactive fluid, sourced from downstream of the distal flame holder. 
     
     
         45 . The method of  claim 44 , further comprising:
 educing the flue gas into a proximal end of a mixing tube, the mixing tube disposed in the dilution region and open between the first fuel nozzle and the distal flame holder, for dilution of the mixture of the fuel and the oxidant.   
     
     
         46 .- 53 . (canceled) 
     
     
         54 . The multi-stage burner system of  claim 10 , wherein the intermediate flame holder comprises an electrode configured to provide an electrical charge to the second mixture of the fuel and the oxidant. 
     
     
         55 . A method of utilizing a multi-stage burner system, the method comprising:
 directing an oxidant into a combustion volume;   directing a fuel via a first fuel nozzle toward an intermediate flame holder disposed in a dilution region between the first fuel nozzle and a distal flame holder;   holding a flame at the intermediate flame holder supported by a mixture of the oxidant and the fuel from the first fuel nozzle; and   when the distal flame holder is at a predetermined temperature:
 directing the fuel via a second fuel nozzle toward the distal flame holder via the dilution region, 
 mixing the oxidant and the fuel from the second fuel nozzle to provide a second mixture of the fuel and the oxidant for combustion at the distal flame holder, 
 diluting the second mixture of the fuel and the oxidant with combustion products of the flame within the dilution region, and 
 burning the second mixture of the fuel and the oxidant at the distal flame holder. 
   
     
     
         56 . The method of  claim 55 , wherein said directing the fuel via the first fuel nozzle includes:
 emitting the fuel from the first fuel nozzle at a first fuel flow rate during a startup period in which the distal flame holder is heated by the flame to the predetermined temperature; and   emitting the fuel from the first fuel nozzle at a second fuel flow rate when the distal flame holder is at the predetermined temperature, the second fuel flow rate being lower than the first fuel flow rate.   
     
     
         57 . The method of  claim 55 , further comprising igniting, proximate the intermediate flame holder, the mixture of the oxidant and the fuel from the first fuel nozzle to produce the flame. 
     
     
         58 . The method of  claim 57 , wherein said igniting the mixture of the oxidant and the fuel from the first fuel nozzle includes providing an ignition source proximate the intermediate flame holder, the ignition source configured to ignite the mixture of the oxidant and the fuel from the first fuel nozzle. 
     
     
         59 . The method of  claim 55 , wherein said directing the fuel via the first fuel nozzle includes controlling a rate of the fuel toward the intermediate flame holder. 
     
     
         60 . The method of  claim 55 , further comprising:
 directing thermal energy from the flame toward the distal flame holder to heat the distal flame holder to the predetermined temperature.   
     
     
         61 . The method of  claim 55 , further comprising:
 directing the combustion products released by the flame as a non-reactive fluid for dilution of the mixture of the oxidant and the fuel from the second fuel nozzle in the dilution region.   
     
     
         62 . The method of  claim 55 , further comprising powering an electrode to produce an electric charge across the intermediate flame holder.