Premix Flashback Control
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.
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This application claims the priority benefit of provisional U.S. Patent Application No. 61/418,096, filed Nov. 30, 2010, which is incorporated by reference.
TECHNICAL FIELDThis technology relates to a furnace with a premix burner in which flashback may occur.
BACKGROUNDAs shown in
Mixer tubes 30 are located within the oxidant plenum 17. The mixer tubes 30 are preferably arranged in a circular array centered on a longitudinal axis 31. Each mixer tube 30 has an open inner end 32 that receives a stream of combustion air directly from within the oxidant plenum 17. Each mixer tube 30 also receives streams of fuel from fuel injector conduits 34 that extend from the fuel plenum 19 into the open inner end 32. These streams of fuel and combustion air flow through the mixer tubes 30 to form a combustible mixture known as premix.
An outer portion 40 of the burner 10 defines a stabilized combustion chamber 41 with an outlet port 45. The premix is ignited in the combustion chamber 41 upon emerging from open outer ends 46 of the mixer tubes 30. Ignition is initially accomplished by use of an igniter before the combustion chamber 41 reaches the auto-ignition temperature of the premix. Combustion continues as the premix is injected from the outlet port 45 into the furnace process chamber 15.
As further shown in
The controller 60 has hardware and/or software that is configured for operation of the burner 10, and may comprise any suitable programmable logic controller or other control device, or combination of control devices, that is programmed or otherwise configured to perform as described and claimed. As the controller 60 carries out those instructions, it operates the valves 62 to initiate, regulate, and terminate flows of reactant streams that provide the premix at the outlets 46 of the mixer tubes 30. The controller 60 is preferably configured to operate the valves 62 such that the fuel and combustion air are delivered to the burner 10 in amounts that form premix having a lean fuel-to-oxidant ratio. The fuel-lean composition of the premix helps to avoid the production of NOx.
Flashback can occur in a premix of fuel and oxidant when the flame speed exceeds the velocity of the reactants. Specifically, flashback can occur in a boundary layer of premix at the inner wall surface of a mixer tube 30. It is believed that a flame propagates/flashes back upstream through the premix in the lower velocity portions of the boundary layer that are spaced away from the wall at a distance greater than the quenching distance for the given fuel/oxidant mixture. The quenching distance is the distance from a wall where combustion is prevented by heat loss and chemical radical absorption by the wall. Accordingly, the likelihood of flashback is increased when the thickness of the boundary layer is greater than the quenching distance.
SUMMARYAn 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. In one embodiment, the flashback control means includes means for electrically charging the tube. In another embodiment, the flashback control means includes means for cooling the tube.
In other embodiments, the flashback control means responds to flashback in the tube by changing the flame speed of the fuel provided to the tube to form premix. Some embodiments include one or more inner tubes within an outer tube. Those embodiments provide stratified flammability that increases radially inward of the outer tube.
In another embodiment, the flashback control means injects non-flammable fluid across the tube to form a curtain that blocks flashback of the premix. An additional embodiment controls flashback by adding diluent fluid to the premix fuel.
Each of
The embodiments shown in
In the example of
In the example of
In the example of
The inlet structure 152 receives the non-flammable fluid from a surrounding annular duct 154. As shown schematically in
The porous inlet structure 152 is formed of solid material that is permeable to fluids and, although sintered metal is preferred, may comprise any such material or materials that can withstand the high temperatures of combustion in the burner 10. It has a skeletal structure called the matrix or frame that has voids. A porous medium has distinct advantages over a solid with manufactured holes, which are known as through holes. A porous medium can have a pore size and density that is not attainable through machining or fabrication techniques. Introducing a flow along the inner wall surface of the mixer tube 30 is effective through the use of a porous medium because the permeability of the porous section will allow the non-flammable fluid to gradually displace the bulk mixer flow radially inward from the wall surface to form a more uniform boundary layer composition that is more resistant to flashback. With proper porous medium selection the flow passing through the medium will have a low exit velocity at the wall of the mixer tube 30 which reduces its interaction with the bulk mixer flow.
The embodiment of
In the embodiment of
As shown in
In operation of the embodiment of
The controller 60 is configured for the inner tubes 180 and 182 to receive combustion air from the plenum 17 and fuel from the injector conduits 188 and 190 at respective ratios that differ from each other. Specifically, the first inner tube 180 receives unmixed fuel and oxidant at a first ratio, and the second inner tube 182 receives unmixed fuel and oxidant at a second ratio that is more fuel rich that the first ratio. Premix then flows from the first inner tube 180 into the mixing section 193 at the first ratio, and from the second inner tube 182 into the mixing section 193 at the second, relatively fuel rich ratio. This inhibits flashback upstream from the outlet 46 by providing stratified ratios of fuel-to-oxidant that increase radially inward of the outer tube 30.
In a variation of the embodiment of
The embodiment of
Each mixer tube 30 in the embodiment of
This written description sets forth the best mode of carrying out the invention, and describes the invention so as to enable a person of ordinary skill in the art to make and use the invention, by presenting examples of the elements recited in the claims. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those of ordinary skill in the art. Such other examples are intended to be within the scope of the claims if they have elements that do not differ from the literal language of the claims, or if they have elements with insubstantial differences from the literal language of the claims.
Claims
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.
Type: Application
Filed: Nov 30, 2011
Publication Date: May 31, 2012
Applicant: Fives North American Combustion, Inc. (Cleveland, OH)
Inventors: Mark C. Hannum ( Hudson, OH), John J. Nowakowski (Valley View, OH), Thomas F. Robertson (Medina Township, OH)
Application Number: 13/307,570
International Classification: F23D 14/78 (20060101); F23N 5/24 (20060101); F23D 14/02 (20060101);