APPARATUS AND METHOD FOR A BURNER ASSEMBLY

Abstract

A burner assembly having a blower housing, a blower to supply air to the burner assembly, a blast tube having a longitudinal axis, a fuel source to supply fuel to the burner assembly, a center tube that is substantially parallel to the longitudinal axis and conveys air and fuel to a center tube burner end opening, a plurality of premix tubes, each of which is substantially parallel to the longitudinal axis and conveys air and fuel to a premix tube burner end opening, a diffuser that is disposed in the center tube near the center tube burner end opening, a nozzle that is disposed in the center tube substantially perpendicular to the diffuser. The center tube air and fuel mixture is fuel rich and the premix tubes air and fuel mixture is fuel lean. A method for burning the center tube air and fuel mixture and the premix tubes mixtures.

Claims

1. A burner assembly, said burner assembly comprising: (a) a blower housing; (b) a blower, said blower being adapted to supply air to the burner assembly; (c) a blast tube, said blast tube having a longitudinal axis; (d) a fuel source, said fuel source being adapted to supply fuel to the burner assembly; (e) a center tube, said center tube being substantially parallel to the longitudinal axis and being adapted to convey a center tube air and fuel mixture to a center tube burner end opening; (f) a plurality of premix tubes, each of said plurality of premix tubes being substantially parallel to the longitudinal axis and being adapted to convey a premix tube air and fuel mixture to a premix tube burner end opening; (g) a diffuser, said diffuser being disposed in the center tube near the center tube burner end opening; wherein the center tube air and fuel mixture is fuel rich; and wherein the premix tubes air and fuel mixtures are fuel lean.

2. The burner assembly of claim 1 further comprising a blower motor.

3. The burner assembly of claim 1 further comprising a damper.

4. The burner assembly of claim 1 further comprising a mounting flange.

5. The burner assembly of claim 1 further comprising an access cover.

6. The burner assembly of claim 1 further comprising a fuel manifold.

7. The burner assembly of claim 7 wherein the fuel manifold comprises a plurality of orifices.

8. The burner assembly of claim 1 wherein the assembly comprises a scanner.

9. The burner assembly of claim 1 wherein the assembly comprises a pilot.

10. The burner assembly of claim 1 wherein the air comprises ambient air.

11. The burner assembly of claim 1 wherein the fuel comprises gaseous fuel.

12. The burner assembly of claim 1 wherein the fuel comprises liquid fuel.

13. The burner assembly of claim 1 further comprising a nozzle.

14. A burner assembly, said burner assembly comprising: (a) a blower housing, (b) a blower, said blower being adapted to supply ambient air to the blower housing; (c) a blast tube, said blast tube having a longitudinal axis; (d) a gaseous fuel source, said gaseous fuel source being adapted to supply gaseous fuel into the housing; (e) a center tube, said center tube being substantially parallel to the longitudinal axis and being adapted to convey a center tube ambient air and gaseous fuel mixture to a center tube burner end opening; (f) a plurality of premix tubes, each of said plurality of premix tubes being substantially parallel to the longitudinal axis and being adapted to convey a premix tube ambient air and gaseous fuel mixture to a premix tube burner end opening; (g) a diffuser, said diffuser being disposed in the center tube near the center tube burner end opening; wherein the center tube ambient air and gaseous fuel mixture is gaseous fuel rich; and wherein the mixture the plurality of premix tubes ambient air and gaseous fuel mixture is gaseous fuel lean.

15. The burner assembly of claim 14 further comprising a nozzle, said nozzle being disposed in the center tube substantially perpendicular to the diffuser;

16. A method for a burner assembly, said method comprising: (a) providing a burner assembly, said burner assembly comprising: (i) a blower housing; (ii) a blower, said blower being adapted to supply air to the burner assembly; (iii) a blast tube, said blast tube having a longitudinal axis; (iv) a fuel source, said fuel source being adapted to supply fuel to the burner assembly; (v) a center tube, said center tube being substantially parallel to the longitudinal axis and being adapted to convey a center tube air and fuel mixture to a center tube burner end opening; (vi) a plurality of premix tubes, each of said plurality of premix tubes being substantially parallel to the longitudinal axis and being adapted to convey a premix tube air and fuel mixture to a premix tube burner end opening; (vi) a diffuser, said diffuser being disposed in the center tube near the center tube burner end opening; wherein the center tube air and mixture is fuel rich; and wherein the premix tubes air and fuel mixtures are fuel lean; (b) burning the center tube air and fuel mixture and the plurality of premix tubes air and fuel mixtures.

17. The method of claim 16 further comprising mixing the center tube air and fuel mixture in the center tube.

18. The method of claim 16 further comprising mixing the plurality of premix tubes air and fuel mixture in each of the plurality of premix tubes.

19. The method of claim 16 further comprising mixing the center tube air and fuel mixture with the plurality of premix tubes air and fuel mixtures near the plurality of premix tubes burner end opening.

20. The method of claim 16 further comprising attaching a burner flame to the diffuser.

21. The method of claim 16 further comprising conveying the fuel to the center tube and the plurality of premix tubes via a manifold.

22. The method of claim 16 wherein the burner assembly further comprises a nozzle.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0014] The presently preferred embodiments of the invention are illustrated in the accompanying drawings, in which like reference numerals represent like parts throughout, and in which:

[0015] FIG. 1 is a partial sectional side view of the preferred embodiment of the burner assembly in accordance with the present invention.

[0016] FIG. 1A is a detailed partial sectional side view of the preferred nozzle and diffuser of the burner assembly illustrated in FIG. 1.

[0017] FIG. 2 is a burner end view of the preferred burner assembly illustrated in FIGS. 1 and 1A.

DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION

[0018] Referring now to the drawings, the preferred embodiment of the burner assembly in accordance with the present invention is illustrated by FIGS. 1 through 2. Referring now to FIG. 1, a partial sectional side view of the preferred embodiment of the burner assembly in accordance with the present invention is illustrated. As shown in FIG. 1, the preferred burner assembly is designated generally by reference numeral 20. Preferred burner assembly 20 comprises blower housing 30. Substantially surrounding preferred blast tube 110 is mounting flange 36. Preferred blast tube 110 has longitudinal axis 32 and comprises access cover 38. Preferred access cover 38 is adapted to permit easy access to the diffuser, the pilot, and the scanner.

[0019] Still referring to FIG. 1, preferred burner assembly 20 also comprises blower 40. Preferred blower is adapted to supply air to blower housing 30 and more particularly toward the burner end openings. Preferred blower 40 may be integrally mounted on burner assembly 20 or remotely located away from the burner assembly. Preferred blower 40 also comprises blower wheel 41 and mounting bracket 44. Preferably, the air supplied by blower 40 is ambient air. Preferred burner assembly 20 further comprises fuel source 50. Preferred fuel source is adapted to supply fuel to burner assembly 20 and more particularly to the burner end openings. Preferably, fuel is conveyed to preferred burner assembly 20 via fuel manifold 52. Preferred fuel manifold 52 comprises a plurality of orifices that are in fluid communication with the center tube and the plurality of premix tubes. Preferably, the fuel supplied by fuel source 50 is gaseous fuel. It is contemplated within the scope of the invention, however, that the fuel supplied by fuel source 50 is liquid fuel.

[0020] Still referring to FIG. 1, preferred burner assembly 20 still further comprises center tube 60. Preferred center tube 60 is substantially parallel to longitudinal axis 32 and is adapted to convey a center tube air and fuel mixture toward center tube burner end opening 62. Preferred center tube 60 comprises a plurality of center tube orifices 64 for receiving fuel from fuel manifold 52. In addition, preferred burner assembly 20 comprises a plurality of premix tubes 70. Preferred plurality of premix tubes 70 are substantially parallel to longitudinal axis 32 and each of them is adapted to convey a premix tube air and fuel mixture toward one of the premix tube burner end openings 72. Each of preferred premix tubes 70 comprises a plurality of premix tube orifices 74 for receiving fuel from fuel manifold 52.

[0021] Still referring to FIG. 1, preferred burner assembly 20 also comprises diffuser 80. Preferred diffuser 80 is disposed in center tube 60 near center tube burner end opening 62. Preferred burner assembly 20 further comprises nozzle 90. Preferred nozzle 90 is disposed in center tube 60 substantially perpendicular to diffuser 80. Preferred nozzle 90 may be a gaseous fuel or liquid fuel nozzle.

[0022] Still referring to FIG. 1, preferred burner assembly 20 further comprises burner housing or blast tube 110 which is adapted to convey air from blower 40 toward the burner end openings, burner head 130 which is disposed upstream from the burner end openings, and control panel 140 which is adapted to interface with a user to control the operation of the burner assembly.

[0023] Still referring to FIG. 1, in preferred burner assembly 20, the center tube air and fuel mixture is fuel rich and the premix tubes air and fuel mixtures are fuel lean.

[0024] Referring now to FIG. 1A, a detailed partial sectional side view of preferred center tube burner end opening 62, diffuser 80, and nozzle 90 of burner assembly 20 is illustrated.

[0025] Referring now to FIG. 2, a burner end view of preferred burner assembly 20 is illustrated. As shown in FIG. 2, preferred burner assembly 20 comprises blower housing 30, mounting flange 36, blower motor 42, mounting bracket 44, center tube 60, a plurality of premix tubes 70, diffuser 80, damper 120 which is adapted to control the flow of air from blower 40 toward the burner end openings, fuel control valve 150 which is adapted to control the flow of fuel from fuel source 50 to the burner assembly, pilot 160 which is adapted to provide a means for igniting a burner flame, and scanner 170 which is adapted to verify that a pilot flame is produced before introducing the main fuel and thereafter verify that the main flame is produced. Preferred scanner 170 may use Infrared, Ultraviolet, flamerod sensing, or any other suitable technology for verifying the pilot and main flames. Preferred burner assembly 20 still further comprises silencer 180 which is adapted to reduce noise produced by the burner assembly.

[0026] The invention also comprises a method for a burner assembly. The preferred method comprises providing a burner assembly as described above in detail. The preferred method also comprises burning the center tube air and fuel mixture and the plurality of premix tubes air and fuel mixtures. In other preferred embodiments of the method of the invention, the method further comprises mixing the center tube air and fuel mixture in the center tube, mixing the plurality of premix tubes air and fuel mixtures in each of the plurality of premix tubes, and mixing the center tube air and fuel mixture with the plurality of premix tubes air and fuel mixtures near the burner end openings. In other preferred embodiments of the method of the invention, the method still further comprises attaching a burner flame to the diffuser and conveying the fuel to the center tube and the plurality of premix tubes via a manifold.

[0027] In operation, several advantages of the preferred embodiments of the burner assembly are achieved. For example, the preferred embodiments of the burner assembly do not produce excessive amounts of the undesirable combination of nitric oxide (NO) and nitrogen dioxide (NO2) (collectively NOx). The preferred embodiments of the burner assembly also do not require either expensive and complex external flue gas recirculation piping and controls or burner geometry using internal flue gas recirculation systems to lower NOx emission levels. The preferred embodiments of the burner assembly further do not require undesirably high amounts of excess oxygen to reduce NOx emission levels. The preferred embodiments of the burner assembly still further do not have undesirably low combustion efficiencies. In addition, the preferred embodiments of the burner assembly do not produce undesirable acoustic coupling. The preferred embodiments of the burner assembly also do not dispose the burner head within the combustion chamber.

[0028] Additionally, in operation, combustion air from the blower is conveyed to the blast tube where it enters into the burner head. Uniform air flow is conveyed to each of the plurality of premix tubes and toward the premix tubes burner end openings. Uniform air flow is also conveyed to the center tube and toward the center tube burner end opening. In addition, gaseous fuel is conveyed to the gas manifold where it exits the manifold through a plurality of orifices. More particularly, gaseous fuel is conveyed to the plurality of premix tubes via a plurality of premix tube orifices, mixed with the combustion air in the premix tubes, and the mixture is conveyed toward the premix tubes burner end openings. A well-mixed lean fuel and air mixture is conveyed in each of the plurality of premix tubes. Simultaneously, gaseous fuel from the manifold enters the center tube via a plurality of center tube orifices and mixes with the combustion air in the center tube. It is also contemplated within the scope of the invention that the gaseous fuel may be conveyed via a center gas gun delivery system in order to more precisely control the fuel to air ratio. The center tube air and fuel mixture is conveyed through the flame stabilizing diffuser to produce a fuel rich stabilized center flame. The well-mixed fuel lean air mixtures exit the plurality of premix tubes burner end openings where the lean fuel mixtures are ignited by the fuel rich stabilized center flame. The well-mixed fuel lean mixture flames produce extremely low NOx levels, and the fuel rich stabilized flame is established on the diffuser.

[0029] More particularly, the high-velocity plurality of premix tubes surrounding the center tube produce very low NOx levels, e.g. less than thirty parts per million (30 ppm) and typically less than ten parts per million (10 ppm), due to operating at a relatively high level of oxygen (O2) (fuel lean). The center tube operates at a relatively low level of oxygen (O2) (fuel rich) or even at a sub-stoichiometric ratio and produces normal NOx levels, e.g. greater than approximately fifty parts per million (50 ppm). When the fuel lean and fuel rich mixtures are slowly combined, the sum of the flue gas results in low NOx levels (e.g., less than 30 ppm) and relatively low excess oxygen (3% or less). Typically, 3% excess oxygen is the desired level to maximize combustion efficiency while still having sufficient excess oxygen to ensure complete combustion.

[0030] In addition, the geometry of the plurality of premix tubes minimizes the risk of flashback, and the combination of the plurality of premix tubes with the standard nozzle mix burner defined in part by center tube minimizes the risk of acoustic coupling which premix burners experience. Further, because the fuel rich standard nozzle mix burner defined in part by the center tube has a very low oxygen level, the temperature of the flame it produces is lower than normal and it produces somewhat lower NOx levels. The fuel lean plurality of premix tubes produce very low NOx levels. Still further, the excess oxygen from the plurality of premix tubes is somewhat delayed in combining with the fuel rich mixture of the center burner and this further reduces NOx levels. The preferred embodiments of the burner assembly of the invention also produce almost no carbon monoxide (CO).

[0031] In testing preferred embodiments of the invention on multiple different-sized burner assemblies, the following results were achieved in one exemplary test: [0032] Rate: 6,900 Mbuth [0033] Excess O2: 2.5% [0034] NOx: 25.2 ppm [0035] CO: 0%

[0036] When the excess O2 level was increased to 3%, the NOx levels were reduced to 24.5 ppm.

[0037] As demonstrated above, the combination of a fuel rich center nozzle mix burner, which provides stability for the entire assembly and an flame in need of oxygen, and the plurality of pre-mix burners surrounding the center nozzle mix burner, which produce extremely low NOx levels and provide the oxygen needed by the center burner, produce low NOx levels with a relatively low amount of excess oxygen.

[0038] Although this description contains many specifics, these should not be construed as limiting the scope of the invention but as merely providing illustrations of some of the presently preferred embodiments thereof, as well as the best mode contemplated by the inventors of carrying out the invention. The invention, as described herein, is susceptible to various modifications and adaptations, and the same are intended to be comprehended within the meaning and range of equivalents of the appended claims.