US20200173689A1

US20200173689A1 - Inward fired low nox premix burner

Info

Publication number: US20200173689A1
Application number: US16/615,553
Authority: US
Inventors: Robert Shaw
Original assignee: Carrier Corp
Current assignee: Carrier Corp
Priority date: 2017-05-24
Filing date: 2018-05-23
Publication date: 2020-06-04
Also published as: WO2018217915A1

Abstract

A burner assembly (40) for providing a flame and combustion gas to a plurality of inlets includes a support member (70) having a back surface and an inner surface. An elongated opening (72) is formed in the support member. A burner (74) is connected to the support member adjacent the opening and extending upstream from the back surface. The burner is arranged in fluid communication with the plurality of inlets. An interior surface of the burner is contoured to direct flames generally inwardly.

Description

BACKGROUND OF THE INVENTION

The subject matter disclosed herein relates to heating systems. More specifically, the subject disclosure relates to burners for residential and commercial heating systems.
Heating systems, in particular furnaces, include one or more burners for combusting a fuel such as natural gas. Hot flue gas from the combustion of the fuel proceeds from the burner and through a heat exchanger. The hot flue gas transfers thermal energy to the heat exchanger, from which the thermal energy is then dissipated by a flow of air driven across the heat exchanger by, for example, a blower.
A typical prior art construction is shown in FIG. 1. A burner 10 is located external to a heat exchanger 12. The burner 10, often referred to as an inshot burner 10, receives a flow of fuel from a fuel source 14. An ignition source 16 combusts the flow of fuel to create a combustion flame 18.
Another type of burner is a premix burner in which fuel and air are mixed in a burner inlet tube prior to injection into a combustion zone 19 where the ignition source 16 ignites the mixture. Premix burners, compared to inshot burners, typically emit much lower levels of NO_x, the emissions of which are tightly regulated and restricted by many jurisdictions. Because of this advantage of premix burners, it may be desirable to utilize premix burners in furnaces.

BRIEF DESCRIPTION OF THE INVENTION

According to one aspect of the invention, a burner assembly for providing a flame and combustion gas to a plurality of inlets includes a support member having a back surface and an inner surface. An elongated opening is formed in the support member. A burner is connected to the support member adjacent the opening and extending upstream from the back surface. The burner is arranged in fluid communication with the plurality of inlets. An interior surface of the burner is contoured to direct flames generally inwardly.
In addition to one or more of the features described above, or as an alternative, in further embodiments the interior surface of the burner is concave.
In addition to one or more of the features described above, or as an alternative, in further embodiments the interior surface of the burner is contoured to direct flames from the interior surface to a focus.
In addition to one or more of the features described above, or as an alternative, in further embodiments an outlet of the burner is arranged within a plane, and the focus is arranged opposite the burner relative to the plane.
In addition to one or more of the features described above, or as an alternative, in further embodiments the interior surface of the burner is elliptical in shape.
In addition to one or more of the features described above, or as an alternative, in further embodiments the interior surface of the burner is circular in shape.
In addition to one or more of the features described above, or as an alternative, in further embodiments the burner is formed from a porous material.
In addition to one or more of the features described above, or as an alternative, in further embodiments an outlet end of the burner comprises a flange, the flange being mounted to the inner surface of the support member such that the burner extends through the opening.
In addition to one or more of the features described above, or as an alternative, in further embodiments comprising an igniter arranged adjacent a first end of the opening and a flame sensor positioned adjacent a second, opposite end of the opening.
In addition to one or more of the features described above, or as an alternative, in further embodiments the igniter is offset from the inner surface of the support member such that the igniter is positioned downstream from the burner relative to a direction of flow through the burner.
According to another embodiment, a furnace includes a heat exchanger having a plurality of coils and a burner unit. The burner unit includes a burner box defining a mixing chamber for receiving a mixture of fuel and air. A burner assembly includes a burner arranged within the mixing chamber and substantially aligned with the plurality of coils. An interior surface of the burner is contoured to direct flames generally inwardly.
In addition to one or more of the features described above, or as an alternative, in further embodiments the burner unit further comprises a support member having an opening, the burner being positioned generally adjacent the opening.
In addition to one or more of the features described above, or as an alternative, in further embodiments the interior surface of the burner is contoured to direct flames from the interior surface to a focus.
In addition to one or more of the features described above, or as an alternative, in further embodiments an outlet of the burner is arranged within a plane, the focus and the burner being disposed on opposing sides of the plane.
In addition to one or more of the features described above, or as an alternative, in further embodiments the interior surface of the burner is elliptical in shape.
In addition to one or more of the features described above, or as an alternative, in further embodiments the interior surface of the burner is circular in shape.
According to yet another embodiment, a method of operating a furnace includes providing a mixture of fuel and air to a mixing chamber, igniting the mixture of fuel and air as it flows from the mixing chamber through a burner assembly including a burner, and supplying flames and combustion from the burner to a plurality of coils of a heat exchanger.
In addition to one or more of the features described above, or as an alternative, in further embodiments comprising directing flames from an interior surface of the burner generally inwardly.
In addition to one or more of the features described above, or as an alternative, in further embodiments directing flames from an interior surface of the burner generally inwardly comprises directing the flames to a focus.
In addition to one or more of the features described above, or as an alternative, in further embodiments an outlet of the burner is arranged within a plane and the focus and the burner are disposed on opposing sides of the plane.
These and other advantages and features will become more apparent from the following description taken in conjunction with the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The subject matter, which is regarded as the invention, is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other features, and advantages of the invention are apparent from the following detailed description taken in conjunction with the accompanying drawings in which:

FIG. 1 is a cross-sectional view of an example of a typical prior art burner arrangement;

FIG. 2 is a schematic view of an embodiment of a furnace; and

FIG. 3 is a perspective view of an expanded burner unit according to an embodiment;

FIG. 4 is a perspective view of an expanded burner unit according to an embodiment; and

FIG. 5 is a cross-sectional view of a portion of the burner assembly according to an embodiment.

The detailed description explains embodiments of the invention, together with advantages and features, by way of example with reference to the drawings.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to the FIGS., an improved furnace 20 is illustrated. The furnace 20 may include a heat exchanger 22 having a plurality of individual heat exchanger coils 24. The heat exchanger coils 24, which may be metallic conduits, may be provided in a serpentine fashion to provide a large surface area in a small overall volume of space, the importance of which will be discussed in further detail below. Each heat exchanger coil 24 includes an inlet 26 and outlet 28. A burner unit 30 is operatively associated with each inlet 26, and a vent 32 is operatively associated with each outlet 28. The burner unit 30 introduces a flame and combustion gases (not shown) into the heat exchanger coils 24, while vent 32 releases the combustion gases to atmosphere (through a flue or the like) after the heat of the flame and combustion gases is extracted by the heat exchanger 22.
In order to extract the heat, a blower motor 36 may be provided to create a significant air flow across the heat exchanger coils 24. As the air circulates across the coils 24, it is heated and can then be directed to a space to be heated such as a home or commercial building for example, by way of appropriate ductwork as indicated by arrow 37. The furnace 20 may also include a return 38 to enable air from the space to be heated to be recirculated and/or fresh air to be introduced for flow across the heat exchanger coils 24.
Turning to FIG. 3, to generate the flame and hot combustion gases, a mixture of fuel and air is formed and then provided to a burner assembly 40 of the burner unit 30 for ignition. The fuel may be natural gas or propane introduced to an inlet 44 of a mixing tube 42 from a fuel source 46 via a fuel orifice or a jet 48. Substantially all of the air necessary for combustion is introduced into the burner assembly 40 via an upstream mixing chamber 49. Such air may be introduced by inducing an airflow using a motorized induction fan 50 (FIG. 2) downstream of a burner outlet. More specifically, a motor 52 having the fan 50 associated therewith may be operatively associated with the outlets 28 of the heat exchanger coils 24. When energized, the fan 50 may rotate and induce an air flow through the heat exchanger coils 24 and burners 30. Control of the motor 52, may be controlled by a processor 54 such as an integrated furnace control (IFC).
Returning to FIG. 3, in an embodiment, one or more openings 56 are formed in the sidewall of the mixing tube 42 generally adjacent the inlet 44. As the fuel moves through the mixing tube 42 towards the mixing chamber 49, air is drawn into the tube 42 through the openings 56 and becomes entrained within the fuel. As a result, the fluid expelled from an outlet 58 of the mixing tube 42 into the mixing chamber 49 is a mixture of both fuel and air.
With specific reference now to FIGS. 3-5, the burner unit 30 is illustrated in more detail. As shown, the burner unit 30 includes a burner box 60 having a generally hollow interior commonly referred to as the mixing chamber 49. The burner box 60 generally includes a top wall 62, bottom wall 64, back wall 66, and opposing sidewalls 68 such that one side of the burner box is open. The burner unit 30 additionally includes a burner assembly 40 mounted within the mixing chamber 49 of the burner box 60.
The burner assembly 40 generally includes a support member 70 having an opening 72 formed therein. In the illustrated, non-limiting embodiment, the opening 72 is generally elongated such that the opening 72 is substantially aligned with the inlet 26 of each of the plurality of heat exchanger coils 24. However, embodiments where the support member 70 includes a plurality of openings 72, each of which is associated with at least one of the heat exchanger coils 24, are also contemplated herein. A burner 74 configured to function as a flame retainer is connected to the support member 70 generally adjacent the opening 72. The burner 74 extends beyond a back surface 76 of the support member (see FIG. 4) into the mixing chamber 49. In an embodiment, the burner 74 is coupled to the support member 70, such as via a welding operation for example. The burner 74 may include a flange 78 (see FIG. 5) configured to couple to the back surface 76 of the support member 70. Alternatively, the flange 78 may be mounted in overlapping relationship with an opposite, interior surface 80 such that the burner 74 generally extends through the opening 72.
The burner 74 is formed from a porous material, such as a wire mesh or steel wool for example, so that a fluid is able to pass from the mixing chamber 49 through the burner 74. As best shown in the cross-sectional view of FIG. 5, the burner 74 has a generally tubular contour. The contour of the burner 74 may be selected such that at least a portion of the flames directed from an interior surface 82 of the burner 74 are angled generally inwardly. In an embodiment, the burner 74 has a generally curved shape that directs the plurality of flames formed about the interior surface 82 of the burner 74 towards a central focus 84. For example, the interior surface of the burner 74 is concave, having a generally circular or elliptical shape. In embodiments where the burner 74 has a generally circular or elliptical contour, the focus 84 is located on an opposite side of plane P defined by the inner surface 80 as the burner 74. By selecting a contour that positions the focus 84 at a position generally aligned with or in front of the plane P, the length of the jet of flames created by the burner 74 exceeds that of flames formed from conventional outward fired burners.
To light the burner 74, an igniter 86 (FIG. 3) is located near the burner 74, generally between an outlet of the burner 74 and the heat exchanger 24 to ignite the fuel/air mixture. As shown, the igniter 86 may be mounted to the support member 70 at a location offset from the interior surface 80 thereof such that the igniter 86 is generally downstream from the burner 74 relative to a direction of flow through the burner 74. The igniter 86 may be aligned with a portion of the opening 72 such that the igniter 86 is arranged in fluid communication with the fuel/air mixture within the burner 74. Similarly, a flame sensor 88 may be disposed on an opposite side of the support member 70 from the igniter 86. In an embodiment, the igniter 86 and the flamer sensor 88 are generally aligned. The flame sensor 88 is configured to determine if the ignition has carried over across the entire opening 72 by sensing the presence of a flame at an end of the opening furthest from the igniter 86.
The burner assembly 40 is positioned within the mixing chamber 49 of the burner box 60 such that an outlet of the burner 74 (generally aligned with plane P) is adjacent an open end 90 of the box 60. Connected to the support member 70 is a refractory panel 92 including at least one refractory opening 94 aligned with the inlet 26 of one or more heat exchanger coils 24. The refractory panel 92 is configured to protect not only the adjacent surface of the support member 70, but also the interface between the support member 70 and the heat exchanger coils 24, from overheating. The refractory panel 92 may overlay a portion or the entire support member 70. Alternatively, as shown in the illustrated, non-limiting embodiment, the refractory panel 92 may be received within a cavity (see FIG. 3) formed in the support member 70. In such embodiments, the refractory panel 92 has a size and shape generally complementary to the cavity.
In an embodiment, a gasket 96 having at least one opening 98 formed therein may be arranged between a pressure distribution bracket 100 and the cell panel 101 to provide a seal there between. Each of the openings 98 formed in the gasket 96 is substantially aligned with an opening 94 formed in the refractory panel 92 and/or an inlet 26 of a corresponding heat exchanger coil 24.
A burner unit having an elongated burner 74 as illustrated and described herein provides a system having consistently “smooth” ignitions during both normal and abnormal conditions. By eliminating multiple premix burners, the occurrence of pressure waves which can disrupt the attachment between the flame and the burner at the time of ignition is prevented.
While the invention has been described in detail in connection with only a limited number of embodiments, it should be readily understood that the invention is not limited to such disclosed embodiments. Rather, the invention can be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described, but which are commensurate with the spirit and scope of the invention. Additionally, while various embodiments of the invention have been described, it is to be understood that aspects of the invention may include only some of the described embodiments. Accordingly, the invention is not to be seen as limited by the foregoing description, but is only limited by the scope of the appended claims.

Claims

What is claimed is:

1. A burner assembly for providing a flame and combustion gas to a plurality of inlets, comprising

a support member having a back surface and an inner surface, an elongated opening being formed in the support member; and

a burner connected to the support member adjacent the opening and extending upstream from the back surface, the burner being arranged in fluid communication with the plurality of inlets, wherein an interior surface of the burner is contoured to direct flames generally inwardly.

2. The burner assembly of claim 1, wherein the interior surface of the burner is concave.

3. The burner assembly of claim 1, wherein the interior surface of the burner is contoured to direct flames from the interior surface to a focus.

4. The burner assembly of claim 3, wherein an outlet of the burner is arranged within a plane, and the focus is arranged opposite the burner relative to the plane.

5. The burner assembly of claim 4, wherein the interior surface of the burner is elliptical in shape.

6. The burner assembly of claim 3, wherein the interior surface of the burner is circular in shape.

7. The burner assembly of claim 1, wherein the burner is formed from a porous material.

8. The burner assembly of claim 1, wherein an outlet end of the burner comprises a flange, the flange being mounted to the inner surface of the support member such that the burner extends through the opening.

9. The burner assembly of claim 1, further comprising:

an igniter arranged adjacent a first end of the opening; and

a flame sensor positioned adjacent a second, opposite end of the opening.

10. The burner assembly of claim 9, w herein the igniter is offset from the inner surface of the support member such that the igniter is positioned downstream from the burner relative to a direction of flow through the burner.

11. A furnace comprising:

a heat exchanger including a plurality of coils; and

a burner unit including:

a burner box defining a mixing chamber for receiving a mixture of fuel and air; and

a burner assembly including a burner arranged within the mixing chamber and being substantially aligned with the plurality of coils, wherein an interior surface of the burner is contoured to direct flames generally inwardly.

12. The furnace of claim 11, wherein the burner unit further comprises a support member having an opening, the burner being positioned generally adjacent the opening.

13. The furnace of claim 11, wherein the interior surface of the burner is contoured to direct flames from the interior surface to a focus.

14. The furnace of claim 13, wherein an outlet of the burner is arranged within a plane, the focus and the burner being disposed on opposing sides of the plane.

15. The furnace of claim 14, wherein the interior surface of the burner is elliptical in shape.

16. The furnace of claim 13, wherein the interior surface of the burner is circular in shape.

17. A method of operating a furnace, comprising:

providing a mixture of fuel and air to a mixing chamber;

igniting the mixture of fuel and air as it flows from the mixing chamber through a burner assembly including a burner; and

supplying flames and combustion from the burner to a plurality of coils of a heat exchanger.

18. The method of claim 17, further comprising directing flames from an interior surface of the burner generally inwardly.

19. The method of claim 18, wherein directing flames from an interior surface of the burner generally inwardly comprises directing the flames to a focus.

20. The method of claim 19, wherein an outlet of the burner is arranged within a plane and the focus and the burner are disposed on opposing sides of the plane.