Premix Flashback Control

Abstract

An apparatus includes a furnace structure defining a combustion zone, and a tube that discharges fuel-oxidant premix into the combustion zone through an outlet from the tube. A reactant supply system provides the tube with unmixed fuel and oxidant for forming the premix. A flashback control means inhibits or extinguishes flashback in the tube.

1 . An apparatus comprising:
 a furnace structure defining a combustion zone;   a tube that discharges fuel-oxidant premix into the combustion zone through an outlet from the tube;   a reactant supply system that provides the tube with unmixed fuel and oxidant for forming the premix; and   means for inhibiting or extinguishing flashback in a boundary layer of fluid that extends along the length of the tube upstream from the outlet, including means for electrically charging the tube.   
     
     
         2 . An apparatus comprising:
 a furnace structure defining a combustion zone;   a tube that discharges fuel-oxidant premix into the combustion zone through an outlet from the tube;   a reactant supply system that provides the tube with unmixed fuel and oxidant for forming the premix; and   means for inhibiting or extinguishing flashback in a boundary layer of fluid that extends along the length of the tube upstream from the outlet, including means for cooling the tube.   
     
     
         3 . An apparatus as defined in  claim 2  wherein the cooling means is configured to apply a cooling medium to a surface of the tube. 
     
     
         4 . An apparatus as defined in  claim 2  wherein the cooling means includes a thermoelectric element coupled to the tube. 
     
     
         5 . An apparatus comprising:
 a furnace structure defining a combustion zone;   a tube configured to form premix from fuel and oxidant flowing along the length of the tube, having an open inner end configured to receive unmixed fuel and oxidant, and having an outlet configured to discharge the premix into the combustion zone;   an injector configured to inject fuel into the open inner end of the tube; and   a reactant supply system that provides the injector with fuel, including flashback control means for responding to flashback in the tube by changing the overall flame speed of the fuel provided to the injector.   
     
     
         6 . An apparatus as defined in  claim 5  wherein the reactant supply system is configured to provide the injector with a first fuel from a first source, and the flashback control means responds to flashback in the tube by providing the injector with a second fuel from a second source, with the first fuel having a first overall flame speed in fuel-air premix under a given set of conditions of temperature, pressure and fuel-to-air ratio, and the second fuel having a second, lower overall flame speed in fuel-air premix under the given set of conditions of temperature, pressure and fuel-to-air ratio. 
     
     
         7 . An apparatus as defined in  claim 6  wherein the flashback control means responds to flashback in the tube by providing the injector with fuel including only the second fuel from the second source. 
     
     
         8 . An apparatus comprising:
 a furnace structure defining a combustion zone;   a tube configured to form premix from fuel and oxidant flowing along the length of the tube, having an open inner end configured to receive unmixed fuel and oxidant, and having an outlet configured to discharge the premix into the combustion zone;   an injector configured to inject fuel into the open inner end of the tube; and   a reactant supply system that provides the injector with a first fuel selected from the group consisting of hydrogen, acetylene, ethylene, propylene, ethylene oxide, and mixtures thereof, including flashback control means for responding to flashback in the tube by providing the injector with a second fuel selected from the group consisting of methane, ethane, propane, butane, and mixtures thereof.   
     
     
         9 . An apparatus as defined in  claim 8  wherein the flashback control means responds to flashback in the tube by providing the injector with only the second fuel. 
     
     
         10 . An apparatus comprising:
 a furnace structure defining a combustion zone; and   a tube having an outlet that discharges fuel-oxidant premix into the combustion zone, an open upstream end that receives unmixed fuel and oxidant for forming the premix, and a fluid inlet at an intermediate location between the outlet and the open upstream end;   wherein the fluid inlet comprises a porous media fluid inlet structure.   
     
     
         11 . An apparatus as defined in  claim 10  further comprising a source of non-flammable fluid coupled to the fluid inlet. 
     
     
         12 . An apparatus comprising:
 a furnace structure defining a combustion zone;   an outer tube configured to form fuel-oxidant premix from fuel and oxidant flowing within the outer tube, having an open inner end, and having an outlet configured to discharge fuel-oxidant premix into the combustion zone;   an inner tube configured to form fuel-oxidant premix from fuel and oxidant flowing within the inner tube, the inner tube reaching longitudinally within the outer tube to define an annular flow space between the inner and outer tubes, having an open inner end, and having an outlet configured to discharge fuel-oxidant premix into the outer tube at a location upstream of the outlet of the outer tube; and   a reactant supply system configured to provide the annular flow space with only a reactant stream that is free of fuel, and to provide the open inner end of the inner tube with unmixed reactant streams of fuel and oxidant.   
     
     
         13 . An apparatus as defined in  claim 12  wherein the inner tube is a first inner tube, and further comprising a second inner tube nested within the first inner tube, with each of the inner tubes having an open inner end, and with each of the inner tubes having an outlet configured to discharge a respective stream of fuel-oxidant premix into the outer tube at a location spaced upstream from the outlet of the outer tube. 
     
     
         14 . An apparatus as defined in  claim 13  wherein the reactant supply system is configured to provide the open inner end of the first inner tube with unmixed reactant streams of fuel and oxidant at a first fuel-to-oxidant ratio, and to provide the open inner end of the second inner tube with unmixed reactant streams of fuel and oxidant at a second fuel-to-oxidant ratio that is more fuel rich than the first fuel-to-oxidant ratio. 
     
     
         15 . An apparatus as defined in  claim 13  wherein the reactant supply system is configured to provide the open inner end of the first inner tube with fuel that has an overall flame speed in fuel-air premix under a given set of conditions of temperature, pressure and fuel-to-air ratio, and to provide the open inner end of the second inner tube with fuel that has a second, higher overall flame speed in fuel-air premix under the given set of conditions of temperature, pressure and fuel-to-air ratio. 
     
     
         16 . An apparatus comprising:
 a furnace structure defining a combustion zone;   an outer tube configured to form fuel-oxidant premix from fuel and oxidant flowing within the outer tube, having an open inner end, and having an outlet configured to discharge fuel-oxidant premix into the combustion zone;   an inner tube configured to form fuel-oxidant premix from fuel and oxidant flowing within the inner tube, the inner tube reaching longitudinally within the outer tube to define an annular flow space between the inner and outer tubes, having an open inner end, and having an outlet configured to discharge fuel-oxidant premix into the outer tube at a location upstream of the outlet of the outer tube; and   a reactant supply system configured to provide the annular flow space with unmixed streams of fuel and oxidant at a non-flammable fuel-to-oxidant ratio, and to provide the open inner end of the inner tube with unmixed streams of fuel and oxidant at a flammable fuel-to-oxidant ratio.   
     
     
         17 . An apparatus as defined in  claim 16  wherein the inner tube is a first inner tube, and further comprising a second inner tube nested within the first inner tube, with each of the inner tubes having an open inner end, and with each of the inner tubes having an outlet configured to discharge a respective stream of fuel-oxidant premix into the outer tube at a location spaced upstream from the outlet of the outer tube. 
     
     
         18 . An apparatus as defined in  claim 17  wherein the reactant supply system is configured to provide the open inner end of the first inner tube with unmixed reactant streams of fuel and oxidant at a first fuel-to-oxidant ratio, and to provide the open inner end of the second inner tube with unmixed reactant streams of fuel and oxidant at a second fuel-to-oxidant ratio that is more fuel rich than the first fuel-to-oxidant ratio. 
     
     
         19 . An apparatus as defined in  claim 17  wherein the reactant supply system is configured to provide the open inner end of the first inner tube with fuel that has a first overall flame speed in fuel-air premix under a given set of conditions of temperature, pressure and fuel-to-air, and to provide the open inner end of the second inner tube with fuel that has a second, higher overall flame speed in fuel-air premix under the given set of conditions of temperature, pressure and fuel-to-air ratio. 
     
     
         20 . An apparatus comprising:
 a furnace structure defining a combustion zone;   an outer tube configured to form fuel-oxidant premix from fuel and oxidant flowing within the outer tube, having an open inner end, and having an outlet configured to discharge fuel-oxidant premix into the combustion zone;   an inner tube configured to form fuel-oxidant premix from fuel and oxidant flowing within the inner tube, the inner tube reaching longitudinally within the outer tube to define an annular flow space between the inner and outer tubes, having an open inner end, and having an outlet configured to discharge fuel-oxidant premix into the outer tube at a location upstream of the outlet of the outer tube; and   a reactant supply system configured to provide the annular flow space with unmixed streams of oxidant and a first fuel, and to provide the open inner end of the inner tube with unmixed streams of oxidant and a second fuel, with the first fuel having a first overall flame speed in fuel-air premix under a given set of conditions of temperature, pressure and fuel-to-air ratio, and the second fuel having a second, higher overall flame speed in fuel-air premix under the given set of conditions of temperature, pressure and fuel-to-air ratio.   
     
     
         21 . An apparatus as defined in  claim 20  wherein the inner tube is a first inner tube, and further comprising a second inner tube nested within the first inner tube, with each of the inner tubes having an open inner end, and with each of the inner tubes having an outlet configured to discharge a respective stream of fuel-oxidant premix into the outer tube at a location spaced upstream from the outlet of the outer tube. 
     
     
         22 . An apparatus as defined in  claim 21  wherein the reactant supply system is configured to provide the open inner end of the second inner tube with fuel that has a third overall flame speed which, in fuel-air premix under the given set of conditions of temperature, pressure and fuel-to-air ratio, is higher than the second overall flame speed. 
     
     
         23 . An apparatus as defined in  claim 21  wherein the reactant supply system is configured to provide the open inner end of the first inner tube with unmixed reactant streams of fuel and oxidant at a first fuel-to-oxidant ratio, and to provide the open inner end of the second inner tube with unmixed reactant streams of fuel and oxidant at a second fuel-to-oxidant ratio that is more fuel rich than the first fuel-to-oxidant ratio. 
     
     
         24 . An apparatus comprising:
 a furnace structure defining a combustion zone;   a tube that discharges fuel-oxidant premix into the combustion zone through an outlet from the tube;   a reactant supply system that provides the tube with unmixed fuel and oxidant for forming the premix; and   flashback control means for injecting non-flammable fluid across the tube, whereby the non-flammable fluid can form a curtain to block flashback of the premix.   
     
     
         25 . An apparatus as defined in  claim 24  wherein the flashback control means injects non-flammable fluid across the outlet of the tube, whereby the non-flammable fluid can form a curtain to block flashback of the premix from the outlet. 
     
     
         26 . An apparatus as defined in  claim 24  wherein the flashback control means includes a line configured to provide non-flammable fluid to the injector, a valve in the line, a flashback sensor, and a controller configured to operate the valve in response to the flashback sensor. 
     
     
         27 . An apparatus comprising:
 a furnace structure defining a combustion zone;   a tube configured to form fuel-oxidant premix from fuel and oxidant flowing along the length of the tube, and having an outlet configured to discharge the fuel-oxidant premix into the combustion zone;   an injector configured to inject fuel into the tube; and   a reactant supply system configured to provide the injector with fuel, and to respond to flashback in the tube by providing the injector with diluent fluid.   
     
     
         28 . An apparatus as defined in  claim 27  wherein the reactant supply system includes a line configured to provide diluent fluid to the injector, a valve in the line, a flashback sensor, and a controller configured to operate the valve in response to the flashback sensor. 
     
     
         29 . An apparatus as defined in  claim 27  wherein the reactant supply system is configured to respond to flashback in the tube by interrupting the flow of fuel to the injector until the flashback is extinguished.