Combustion burner assembly having low oxides of nitrogen emission

Abstract

A combustion burner assembly having low oxides of nitrogen emission includes a mixing section having an air inlet, a fuel inlet and a fuel mixture outlet. Air is tangentially supplied to the mixing section through the air inlet. A pocket portion in the mixing section receives fuel from a fuel inlet. A plurality of holes in the pocket portion transfer fuel to the mixing section to form a fuel mixture with the air in the mixing section. A diffuser is disposed within the mixing section adjacent the fuel mixture outlet. The diffuser has a plurality of overlapping vanes disposed around an aperture that form a plurality of passages between each of the plurality of overlapping vanes through which the fuel mixture exits the mixing section. A pilot assembly is substantially disposed within the mixing section and passes through the aperture in the diffuser. The pilot assembly is adapted to produce a pilot light downstream of the diffuser that ignites the exiting fuel mixture to produce a high swirling flame, thereby resulting in a combustion burner assembly having low oxides of nitrogen emission.

Description

FIELD OF THE INVENTION

The present invention relates to a combustion burner assembly providing low oxides of nitrogen emission. More particularly, the present invention relates to non-flue gas recirculating burner assembly that pre-mixes air and gas to provide a stable flame with low oxides of nitrogen emission. Still more particularly, the present invention relates to a mixing section of a combustion burner assembly that premixes air and gas to provide a uniform fuel mixture prior to combustion. The combustion burner assembly provides a uniform and lean fuel mixture to reduce flame temperatures and retard oxides of nitrogen emission.

BACKGROUND OF THE INVENTION

One problem with existing combustion burner assemblies is the emission of oxides of nitrogen, which are detrimental to the environment. Oxides of nitrogen have been found to be one of the primary causes of acid rain, a highly damaging result of the release of sulfur and oxides of nitrogen. Acid deposition has a variety of effects, including damage to forests and soils, fish and other living things, materials, and human health. U.S. Pat. No. 5,275,554 to Faulkner, the disclosure of which is hereby incorporated by reference in its entirety, discusses the emission of oxides of nitrogen by combustion burner assemblies.

Another problem with existing combustion burners is the use of a perforated screen or sheet at the fuel mixture exit of the combustion burner. The openings in the sheet, which are generally small, are prone to being plugged by air borne particulates, such as lint. Filters must be used to prevent the screens from capturing lint. The filters must be replaced frequently to maintain the efficiency of the burner. The sheets are also prone to harmonics generated as the fuel mixture passes through the openings, which sounds like a loud fog horn. Those harmonics provide a noisy burner that is a nuisance to those working in the vicinity. A need exists for a burner assembly that does not require a filter and does not create loud harmonics during operation.

A need exists for an improved combustion burner assembly that reduces oxides of nitrogen emission.

SUMMARY OF THE INVENTION

Accordingly, it is a primary objective of the present invention to provide an improved combustion burner assembly.

Accordingly, it is another objective of the present invention to provide a combustion burner assembly that provides low levels of oxides of nitrogen emission.

Accordingly, it is another objective of the present invention to provide a non-flue gas recirculating combustion burner that provides low levels of oxides of nitrogen emission.

Accordingly, it is another objective of the present invention to provide mixing section of a burner assembly that premixes air and gas prior to combustion to provide a uniform fuel mixture.

The foregoing objects are basically attained by providing a combustion burner assembly including a mixing section having an air inlet, a fuel inlet and a fuel mixture outlet. Air is tangentially supplied to the mixing section through the air inlet. A pocket portion in the mixing section receives fuel from a fuel inlet. A plurality of holes in the pocket portion transfer fuel to the mixing section to form a fuel mixture with the air in the mixing section. A diffuser is disposed within the mixing section adjacent the fuel mixture outlet. The diffuser has a plurality of overlapping vanes disposed around an aperture that form a plurality of passages between each of the plurality of overlapping vanes through which the fuel mixture exits the mixing section. A pilot assembly is substantially disposed within the mixing section and passes through the aperture in the diffuser. The pilot assembly is adapted to produce a pilot light downstream of the diffuser that ignites the exiting fuel mixture to produce a high swirling flame, thereby resulting in a combustion burner assembly having low oxides of nitrogen emissions.

The foregoing objects are also basically attained by providing a method of producing a combustion flame having low oxides of nitrogen emission. Air is supplied tangentially to a mixing section of the burner assembly to create swirling air flow within the mixing section. Fuel is supplied to the swirling air in the mixing section to form a premixed, swirling fuel mixture. A pilot assembly is ignited to produce a pilot light downstream of an exit of the mixing section. The premixed, swirling fuel mixture is passed through a diffuser in the mixing section upstream of the pilot light to spread out the fuel mixture. A combustion flame low in oxides of nitrogen emission is formed by discharging the premixed fuel mixture proximal the pilot light.

Other objects, advantages and salient features of the invention will become apparent from the following detailed description, which, taken in conjunction with the annexed drawings, discloses preferred embodiments of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

Referring now to the drawings that form a part of the original disclosure:

FIG. 1 is an exploded perspective view of a burner assembly according to a first embodiment of the present invention;

FIG. 2 is a front elevational view of a burner assembly according to a second embodiment of the present invention;

FIG. 3 is a side elevational view of the burner assembly of FIG. 2;

FIG. 4 is a front elevational view of the burner assembly of FIG. 1;

FIG. 5 is a side elevational view of the burner assembly of FIG. 4;

FIG. 6 is a side elevational view of the mixing section of the burner assembly of FIG. 1;

FIG. 7 is a side elevational view of the mixing section of FIG. 6 rotated so that a gas inlet is extending downwardly;

FIG. 8 is a front elevational view of the mixing section of FIG. 7;

FIG. 9 is a perspective view of a diffuser

FIG. 10 is a front elevational view of the diffuser of FIG. 9;

FIG. 11 is side elevational view of the diffuser of FIG. 9;

FIG. 12 is a rear elevational view of the diffuser of FIG. 9;

FIG. 13 is a front elevational diagrammatic view of the air flow entering the blower housing and the mixing chamber of a burner assembly according to a first embodiment of the present invention; and

FIG. 14 is a side elevational diagrammatic view of the air and gas flow in the mixing chamber of a burner assembly according to a first embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

As shown in FIGS. 1-14, a burner assembly 11 according to the present invention reduces the level of oxides of nitrogen emission. A uniform and lean fuel mixture is provided that reduces the combustion flame temperature, thereby resulting in the reduction of oxides of nitrogen (NO_X) emission.

The burner assembly 11 includes a mixing section 21 in which supplied air and fuel are premixed before being combusted in a heat exchanger 71 (FIG. 14). The burner assembly is rigidly coupled to the heat exchanger 71 by flange 23 at a combustion exit 22 of the mixing section 21, thereby positioning the combustion exit 22 of the mixing section within the heat exchanger. Preferably, the air inlet 20 is at a first end of the mixing section 21 that is opposite the fuel mixture (combustion) exit 22 at a second end of the mixing section. Fuel inlet 25 is preferably positioned between the first and second ends 20 and 22 of the mixing section 21, as shown in FIG. 14. Preferably, the mixing section 21 has a first portion 93 and a second portion 95. As shown in FIG. 14, the first portion 93 has a smaller width than the second portion 95, although the widths of the first and second portions may be substantially the same, or the width of the first portion may be larger than the width of the second portion. The first portion 93 has an inner surface 26. The second portion 95 has an inner surface 18. Preferably, the mixing section 21 is substantially cylindrical and has a flange 23 disposed at the transition from the first portion 93 to the second portion 95.

Fuel 81 from an independent source 24 is supplied to the mixing section 21 through fuel (or gas) inlet 25, as shown in FIG. 14. The path of the fuel 81 through the burner assembly 11 is represented in FIG. 14 by the open circles. The fuel 81 may be natural gas or liquid propane, but any suitable gas may be used. Flow control valve 27 controls the supply of gas from the gas source 24 to the burner assembly 11, as shown in FIG. 1. Handle 28 on the flow control valve 27 stops the supply of gas from the gas source 24. Fuel 81 is supplied to the mixing section 21 through fuel inlet 25. Preferably, the fuel inlet 25 is disposed between the first end 20 and the second end 22 of the mixing section 21.

Fuel is also supplied through first fuel pilot tubing 29 from the flow control valve to a pilot assembly 31. Fuel is also supplied to the pilot assembly 31 through second fuel pilot tubing 30. Providing additional fuel to the pilot assembly 31 enlarges the pilot light, thereby providing a rapid and smooth ignition of the fuel mixture in the mixing section 21.

Air 91 is drawn into the burner assembly 11 through an air damper assembly 41, as shown in FIGS. 1, 13 and 14. The path of the air 91 through the burner assembly 11 in FIGS. 13 and 14 is represented by the solid triangles. Motor 44 drives fan 46 to draw air into the air damper assembly (or blower housing) 41. First and second louvers 43 and 45 provide accurate control of the intake air, thereby controlling the fuel-air ratio. Air from the air damper assembly 41 is supplied to the mixing section 21 through adapter assembly 47. The adapter assembly 47 has a first end 48 rigidly coupled to the air damper assembly 41 and a second end 49 rigidly coupled to an intake end (or air inlet) 20 of the mixing section 21 to provide air 91 to the mixing section. The first end (inlet) 48 of the adapter assembly is offset from the second end (outlet) 49, thereby introducing the air 91 tangentially to the mixing section 21, as shown in FIGS. 1 and 13. A first vertical centerline 56 of the adapter assembly 47 is laterally offset from a second vertical centerline 57 through the air damper assembly 41, as shown in FIG. 13. The air 91 entering the mixing section 21 tangentially causes the air to spin, as shown by the solid triangles in FIG. 13, thereby swirling the air within the mixing section. The premixing of the air and fuel is facilitated by adding the fuel to the swirling air. Air 91 from the air damper assembly 41 is also supplied to the pilot assembly 31 through pilot air tubing 42.

The fuel inlet 25 supplies fuel to a pocket portion 83 of the mixing section 21, as shown in FIGS. 6, 7 and 14. The pocket portion 83 preferably extends entirely around the perimeter of the inner surface 26 of the mixing section 21. A plurality of holes 85 in an outer wall 84 of the pocket portion 83 allow the supplied fuel 81 to pass from the pocket portion 83 into the mixing section 21 to form a premixed fuel mixture with the supplied air 91.

Control panel 51 of the burner assembly 11 houses the burner operating controls, such as controls for supplying power to the motor 44 and the pilot assembly 31.

The pilot assembly 31 receives fuel from both the first and second fuel pilot tubing 29 and 30, as well as receiving air through pilot air tubing 42. The air and fuel (i.e., the fuel mixture) supplied to the pilot assembly 31 are premixed to improve light-off reliability and stability of the combustion flame. The pilot assembly 31 is positioned within the mixing section 21. The pilot assembly may include disk 33 to promote a low pressure zone in the mixing section 21, thereby facilitating thorough mixing of the air supplied through adapter assembly 47 and fuel supplied through inlet 25, as well as reducing the required pressures of the supplied fuel. The reduction in pressure results in increased velocity, which facilitates premixing of the air and fuel. Once the pilot assembly 31 has been ignited through the control panel 51, the thoroughly mixed fuel mixture is combusted and exhausted through the combustion exit (or fuel mixture outlet) 22 into the heat exchanger 71. A high swirling flame 73 is produced that increases recirculation and stability.

Premixing the supplied air and fuel mixture in the mixing section 21 ensures complete combustion of the fuel mixture with minimal levels of carbon monoxide and unburned hydrocarbons. The diffuser 61 and band 63 provided in the mixing section 21 facilitate reliable and consistent performance at the operating conditions necessary to provide low oxides of nitrogen emission. The diffuser 61 and band 63 facilitate mixing of the fuel 81 and air 91 in forming the fuel mixture, as well as providing a high swirl of the fuel mixture to provide enhanced flame retention. The diffuser 61 and band 63 also prevent flashback of the combustion flame into the mixing section 21 from the heat exchanger, which is a problem with existing combustion burners. The diffuser 61 may be used without the band 63.

The diffuser 61, as shown in FIGS. 9-12 preferably has eighteen blades 65. The blades overlap, preferably by about 50% of the blade width, to form a narrow passage 67 between the blades 65 through which the fuel mixture exits the burner assembly 11. The narrow and deep passages 67 prevent combustion flame flashback. Due to the overlapping of the blades 65, larger passages 67 are able to be created to eliminate clogging or plugging of the passages with air-borne particulates. Additionally, the flame front is stabilized by the high swirl generated by the diffuser 61 so that the burner assembly 11 is not prone to harmonic noise associated with existing burner assemblies.

The diffuser 61 has an outer member 62 and an inner member 64, as shown in FIGS. 9-12. The inner member 64 of the diffuser 61 forms an aperture 68. The plurality of vanes 67 extend between the inner member 64 and the outer member 62 of the diffuser 61. Preferably, the outer and inner members 62 and 64 are substantially circular, as shown in FIGS. 10 and 12. The ignition end 35 of the pilot assembly 31 passes through the aperture 68 in the diffuser 61, as shown in FIG. 1, such that the pilot light created by the pilot assembly 31 is formed downstream of the diffuser. For reasons of clarity, the pilot assembly 31 is not shown in FIGS. 13 and 14. The swirling, pre-mixed fuel mixture passes through the diffuser 61 at the fuel mixture outlet 22 of the mixing section 21. The fuel mixture is ignited by the pilot light as it passes through the diffuser 61 by the pilot light to create a flame 73. The swirling motion of the exiting fuel mixture results in a high swirling flame 73 that increases recirculation and flame stability.

The diffuser 61 is preferably rigidly fixed to the inner surface 18 of the exhaust portion 19 of the mixing section 21, as shown in FIGS. 1 and 14. Spacers may be disposed on the outer surface 62 of the diffuser 61 to space the diffuser from the inner surface 18 of the exhaust portion 19 of the mixing section 21 to prevent flashback into the mixing section. The spacers may be rods 66 affixed to the outer surface 62 of the diffuser, as shown in FIGS. 9-12, to maintain the gap between the diffuser and the inner surface 18 of the exhaust portion 19 of the mixing section. Alternatively, raised dimples (not shown) on the outer surface 62 of the diffuser 61 may be used to space the diffuser from the inner surface 18 of the exhaust portion 19 of the mixing section 21.

The mixing section 21, or venturi section, premixes the supplied fuel 81 and air 91 to form an extremely uniform and lean fuel mixture, thereby providing uniform flame temperatures. The fuel mixture being uniform and lean reduces the combustion flame temperature, thereby reducing the oxides of nitrogen emission of the combustion burner assembly 11. Furthermore, the mixing section 21 reduces the required pressure of supplied fuel 81, which facilitates drawing fuel in from inlet 25 to be mixed with the supplied air 91 from the adapter assembly 47. The disk 33 disposed on the pilot assembly 31 is positioned proximal the injection point of the fuel 81 into the mixing section 21 to reduce the pressure within the mixing chamber, thereby increasing the velocity of both the supplied air and fuel. The disk 33 on the pilot assembly reduces the amount of open area in the mixing section 21, thereby reducing the pressure therein. The increased fuel mixture velocity provides a fuel mixture velocity larger than the flame speed velocity, which also facilitates flashback prevention. Furthermore, the depth of the gap (i.e., the width of the diffuser and/or the air band) and the cool temperature of the fuel mixture, maintain a cool air band (if used) and mixing section. If the combustion flame was to migrate upstream, the combustion flame would be cooled below its ignition temperature and quenched.

The second embodiment of the combustion burner assembly 111, as shown in FIGS. 2 and 3, is substantially similar to the first embodiment of the combustion burner assembly 11, as shown in FIGS. 1 and 4-8. The operation of the burner assembly 111 is substantially similar to that of the first embodiment of the burner assembly 11. The part numbers referred to in the second embodiment of the burner assembly 111 are similar to that of the first embodiment of the burner assembly 11, but the part numbers of the second embodiment are 100 larger than the first embodiment. The first embodiment of the burner assembly 11 is useful in applications requiring a low centerline, thus the mixing section 21 being positioned below the air damper assembly 41, as shown in FIG. 4. The second embodiment of the burner assembly 111 is useful when a low centerline is not required, thus the air damper assembly 141 being positioned below the mixing section 121, as shown in FIG. 2 and 3.

While advantageous embodiments have been chosen to illustrate the invention, it will be understood by those skilled in the art that various changes and modifications may be made therein without departing from the scope of the invention as defined in the appended claims.

Claims

1. A combustion burner assembly, comprising: a mixing section having an air inlet, a fuel inlet and a fuel mixture outlet, said air inlet supplying air tangentially to said mixing section; a pocket portion in said mixing section to receive fuel from said fuel inlet; a plurality of holes in said pocket portion to transfer fuel to said mixing section to form a fuel mixture with said air in said mixing section; a diffuser disposed within said mixing section adjacent said fuel mixture outlet, said diffuser having a plurality of overlapping vanes disposed around an aperture forming a plurality of passages between each of said plurality of overlapping vanes through which said fuel mixture exits said mixing section; and a pilot assembly substantially disposed within said mixing section and passing through said aperture in said diffuser, said pilot assembly adapted to produce a pilot light downstream of said diffuser to ignite said fuel mixture.

2. A combustion burner assembly according to claim 1, wherein said mixing section having a first end and a second end, said first end being said air inlet, said second end being said fuel mixture outlet.

3. A combustion burner assembly according to claim 2, wherein said first end is opposite said second end.

4. A combustion burner assembly according to claim 3, wherein said fuel inlet is positioned between said first end and said second end of said mixing section.

5. A combustion burner assembly according to claim 1, wherein said pilot assembly has a first tube supplying air and a second tube supplying fuel to produce the pilot light.

6. A combustion burner assembly according to claim 1, wherein each of said plurality of vanes has a width, each of said plurality of vanes overlapping by approximately half of said width.

7. A combustion burner assembly according to claim 1, wherein a plurality of spacers are disposed on an outer surface of said diffuser to space said diffuser from an inner surface of said mixing section.

8. A combustion burner assembly according to claim 7, wherein said plurality of spacers are a plurality of rods.

9. A combustion burner assembly according to claim 7, wherein said plurality of spacers are a plurality of dimples.

10. A combustion burner assembly according to claim 1, wherein a disk is disposed on said pilot assembly to reduce pressure within said mixing chamber to increase the velocity of the fuel mixture.

11. A combustion burner assembly according to claim 10, wherein said disk is disposed on said pilot assembly proximal said plurality of holes in said pocket portion.

12. A combustion burner assembly according to claim 1, wherein an air band is disposed around an outer surface of said diffuser to prevent flashback into said mixing section.

13. A combustion burner assembly according to claim 1, wherein an air damper supplies air to said air inlet of said mixing section, said air damper being positioned above said mixing section.

14. A combustion burner assembly according to claim 1, wherein an air damper supplies air to said air inlet of said mixing section, said air damper being positioned below said mixing section.

15. A combustion burner assembly according to claim 1, wherein a flange is disposed on an outer surface of mixing section, said flange being adapted to be rigidly secured to a heat exchanger.

16. A combustion burner assembly, comprising: a mixing section having a first end and a second end; an adapter assembly connected to said first end of said mixing section; an air damper connected to said air adapter, air being tangentially supplied to said adapter assembly to create swirling air flow through said mixing section; a pocket portion in said mixing section to receive fuel from a fuel inlet; a plurality of holes in said pocket portion to transfer fuel to said mixing section to form a swirling, premixed fuel mixture with said air in said mixing section; a diffuser disposed within said mixing section adjacent said second end of said mixing section, said diffuser having a plurality of overlapping vanes disposed around an aperture forming a plurality of passages between each of said plurality of overlapping vanes through which said fuel mixture exits said second end of said mixing section; and a pilot assembly substantially disposed within said mixing section and passing through said aperture in said diffuser, said pilot assembly adapted to produce a pilot light downstream of said diffuser to ignite said exiting fuel mixture.

17. A combustion burner assembly according to claim 16, wherein said first end is opposite said second end.

18. A combustion burner assembly according to claim 16, wherein said fuel inlet is positioned between said first end and said second end of said mixing section.

19. A combustion burner assembly according to claim 16, wherein said pilot assembly has a first tube supplying air and a second tube supplying fuel to produce the pilot light.

20. A combustion burner assembly according to claim 16, wherein each of said plurality of vanes has a width, each of said plurality of vanes overlapping by approximately half of said width.

21. A combustion burner assembly according to claim 16, wherein a plurality of spacers are disposed on an outer surface of said diffuser to space said diffuser from an inner surface of said mixing section.

22. A combustion burner assembly according to claim 21, wherein said plurality of spacers are a plurality of rods.

23. A combustion burner assembly according to claim 21, wherein said plurality of spacers are a plurality of dimples.

24. A combustion burner assembly according to claim 16, wherein a disk is disposed on said pilot assembly to reduce pressure within said mixing chamber to increase the velocity of said fuel mixture.

25. A combustion burner assembly according to claim 24, wherein said disk is disposed on said pilot assembly proximal said plurality of holes in said pocket portion.

26. A combustion burner assembly according to claim 16, wherein an air band is disposed around an outer surface of said diffuser to prevent flashback into said mixing section.

27. A combustion burner assembly according to claim 16, wherein said air damper is positioned above said mixing section.

28. A combustion burner assembly according to claim 16, wherein said air damper is positioned below said mixing section.

29. A combustion burner assembly according to claim 16, wherein a flange is disposed on an outer surface of mixing section, said flange being adapted to be rigidly secured to a heat exhanger.

30. A method of producing a combustion flame having low oxides of nitrogen emission, comprising the steps of: supplying air tangentially to a mixing section of the burner assembly to create swirling air flow within the mixing section; supplying fuel to the swirling air in the mixing section to form a premixed, swirling fuel mixture; igniting a pilot assembly to produce a pilot light downstream of an exit of the mixing section; passing the premixed, swirling fuel mixture through a diffuser in the mixing section upstream of the pilot light to spread out the fuel mixture; and forming a combustion flame low in oxides of nitrogen emission by discharging the fuel mixture proximal the pilot light.

31. The method of producing a combustion flame having low oxides of nitrogen emission of claim 30, further comprising increasing the velocity of the fuel mixture by decreasing the pressure within the mixing section by disposing a disk on the pilot assembly.