US20110311923A1

US20110311923A1 - Induced-Draft Burner With Isolated Gas-Air Mixing

Info

Publication number: US20110311923A1
Application number: US13/160,638
Authority: US
Inventors: Scott A. Liljenberg; Michael R. Carey; Jeffrey M. Cohen
Original assignee: Carrier Corp
Current assignee: Carrier Corp
Priority date: 2010-06-22
Filing date: 2011-06-15
Publication date: 2011-12-22

Abstract

A furnace with a burner is disclosed. The burner may include an area expansion plenum, a burner tube, a heat exchanger, a gas valve, an igniter, and an induced-draft blower. The gas valve may meter gas into the area expansion plenum, while the induced-draft blower may draw air into the area expansion plenum, wherein air and gas may mix to produce a lean gas/air mixture. The lean gas/air mixture may then be pulled through the burner tube and into the heat exchanger. Within the heat exchanger, the lean gas/air mixture may be ignited and energy may be produced, exciting acoustic energy in the heat exchanger. The acoustic energy may be distributed out of the heat exchanger by the area expansion plenum. In order to distribute the acoustic energy, the cross sectional area of the area expansion plenum may be greater than the cross sectional area of the burner tube.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a non-provisional U.S. patent application, which claims priority under 35 U.S.C. §119(e) to U.S. Provisional Patent Application Ser. No. 61/357,286 filed on Jun. 22, 2010, the entirety of which is incorporated by reference herein.

FIELD OF THE DISCLOSURE

The present disclosure generally relates to furnaces and, more particularly, relates to a furnace with an induced-draft burner with isolated gas-air mixing.

BACKGROUND OF THE DISCLOSURE

Gas furnaces, particularly induced-draft furnaces, are widely installed in homes for heating purposes. Gas furnaces contain a combustion chamber typically at the inlet of a heat exchanger, wherein a mixture of gas and air are burned, creating hot gaseous products of combustion. The combustion of gas and air also results in combustion emission being emitted into the atmosphere. One combustion emission component, NO_x(oxides of nitrogen), is of increasing concern due to the health and atmospheric concerns it creates. Moreover, regulations are mandating stricter emission limitations. The South Coast Air Quality Management District (SCAQMD) of California is one example of a regulatory body dictating a maximum emission rate of NO_xfrom furnaces. Given the current climate and popular opinion regarding the environment, these standards are likely to only get more restrictive in the future.
A known technique for reducing NO_xis to premix gas and air before burning it. Such premixing allows the gas and air to mix fully at a gas-air mixture that reduces NO_xproduction. As a result of such regulations, prior art burners have had to be redesigned. Certain prior art burners, known as “in-shot” burners, included two sources of air: a primary source providing air to the inlet of the burner for mixing with the gas, and a secondary source at the outlet of the burner and prior to introduction of the flame in the heat exchanger. The primary source of air is premixed with gas at the inlet of the burner, producing a gas-air mixture. The secondary source of air is introduced at the outlet of the burner to decouple the burner from the heat exchanger. However, introducing the secondary source of air limits the reduction of NO_xemission to a certain level since the secondary source of air is not fully premixed into the gas-air mixture at the outlet of the burner upon ignition. In order to further reduce NO_xemissions and meet continually more restrictive emission limitations, the secondary source of air has to be eliminated and an improved burner design must be developed, particularly for induced-draft furnaces. Improved burners for use with induced-draft furnaces which satisfy the emissions standards have not yet been introduced.

SUMMARY OF THE DISCLOSURE

In accordance with one aspect of the disclosure, a burner for a furnace is disclosed. The burner may include an area expansion plenum, a gas valve, a burner tube, a combustion chamber, an induced-draft blower, and an igniter. The gas valve may meter gas into the area expansion plenum, while the induced-draft blower may pull air into the area expansion plenum. Within the area expansion plenum, gas and air may mix to produce a lean gas/air mixture. The lean gas/air mixture may then be pulled by the induced-draft blower through the burner tube and into the combustion chamber. In the combustion chamber, the igniter may ignite the lean gas/air mixture, thus, producing energy. The energy may excite acoustic energy in the combustion chamber. The acoustic energy in the combustion chamber may be distributed out of the combustion chamber by the area expansion plenum.
In accordance with another aspect of the disclosure, a method for isolating gas-air mixing in an induced-draft furnace is disclosed. The method may include metering gas into an area expansion plenum; drawing air into the area expansion plenum; mixing gas and air within the area expansion plenum to produce a lean gas/air mixture; pulling the lean gas/air mixture through a burner tube and into a heat exchanger; igniting the lean gas/air mixture within the heat exchanger, wherein the ignition may produce energy, thus, exciting acoustic energy in the heat exchanger; and distributing the acoustic energy in the heat exchanger out of the heat exchanger and into the area expansion plenum.
In accordance with yet another aspect of the disclosure, a furnace with a burner is disclosed. The furnace may include a cabinet housing therein at least one area expansion plenum, a gas valve, at least one burner tube, an igniter, at least one heat exchanger, an induced-draft blower, and a flue pipe. The at least one area expansion plenum may mix gas and air to produce a lean gas/air mixture. The gas valve, coupled to the at least one area expansion plenum, may meter gas into the at least one area expansion plenum. The at least one heat exchanger, downstream of the at least one area expansion plenum, may have an igniter which may ignite the lean gas/air mixture to produce combustion products. The induced-draft blower, downstream to the at least one heat exchanger, may draw air into the at least one area expansion plenum, wherein air and gas may mix to produce a lean gas/air mixture. The induced-draft blower may then pull the lean gas/air mixture through the at least one burner tube and into the at least one heat exchanger. The induced-draft blower, coupled in-between the flue pipe and the at least one heat exchanger, may also pull the combustion products out of the at least one heat exchanger, and may push the combustion products through the flue pipe and out into the atmosphere.
Other advantages and features will be apparent from the following detailed description when read in conjunction with the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the disclosed system and method, reference should be made to the embodiments illustrated in greater detail in the accompanying drawings, wherein:

FIG. 1 is a perspective view of an embodiment of a furnace constructed in accordance with the teachings of the present disclosure;

FIG. 2 is a block diagram of an embodiment of a burner constructed in accordance with the teachings of the prior art; and

FIG. 3 is a block diagram of an embodiment of a burner constructed in accordance with the teachings of the present disclosure and intended to be employed in combination with the furnace of FIG. 1.

It should be understood that the drawings are not necessarily to scale and that the disclosed embodiments are sometimes illustrated diagrammatically and in partial views. In certain instances, details which are not necessary for an understanding of the disclosed methods and systems or which render other details difficult to perceive may have been omitted. It should be understood, of course, that this disclosure is not limited to the particular embodiments illustrated herein.

DETAILED DESCRIPTION OF THE DISCLOSURE

In FIG. 1, an induced-draft furnace 10, which may be operated according to the principles of the present disclosure is illustrated. The induced-draft furnace 10 may include a cabinet 15, housing therein a burner assembly 11, a gas valve 18, a primary heat exchanger 13, a condensing heat exchanger 14, an induced-draft blower 23 supporting an inducer motor 24, and a circulating air blower 26 supporting a drive motor 27. The burner assembly 11 may communicate with the primary heat exchanger 13. Fluidly connected at the other end of the primary heat exchanger 13 may be the condensing heat exchanger 14 whose discharge end may be fluidly connected to a collector box 16 and an exhaust vent 17. In operation, the gas valve 18 may meter the flow of gas to the burner assembly 11 where atmospheric air from an air inlet 19 may be mixed and ignited by an igniter assembly 21. The hot gas combustion products may then be passed through the primary heat exchanger 13 and the condensing heat exchanger 14. The relatively cool exhaust gases may then pass through the collector box 16 through a condensate drain line 22 from where it may be suitably drained. Flow of the combustion air into the air inlet 19 through the heat exchangers 13 and 14, and exhaust vent 17, may be enhanced by the induced-draft blower 23 which may be driven by the motor 24 in response to control signals from a furnace control assembly 29 contained therein. Household air may be drawn into the blower 26 which may be driven by the drive motor 27 in response to signals received from the furnace control assembly 29.
Induced-draft furnaces, such as the one depicted in FIG. 1, commonly utilize a burner, such as, but not limited to, an air induced combustion system. Induced burners operate with negative pressure, wherein air and gas may be pulled into a combustion chamber for combustion, and then upon ignition, combustion products may be pulled out of the combustion chamber. Induced-draft furnaces commonly utilize a heat exchanger as a combustion chamber. In FIG. 2, a burner 20 commonly designed with an “in-shot” burner is illustrated. As previously discussed, there exist limitations in reducing NO_xemission due to the secondary source of air being introduced with the “in-shot” burner.
While advancements in eliminating the secondary source of air may have been achieved by operatively coupling the burner and the heat exchanger into one unit, build-up of dynamic pressure in the system may have been created as a secondary by-product. Dynamic pressure may be a known and unwanted by-product in any enclosed system generating high energy. Typically, enclosed systems may have a natural acoustic resonance. With the right frequency, an energy source may excite the natural acoustic frequency of the system. Once the acoustic frequency of the system is excited, dynamic pressure starts to build-up in an enclosed system. Dynamic pressure may not only make the system noisy, but also may impact the performance of the system. A noisy inefficient induced-draft furnace in a home may not be desired.
In FIG. 3, a burner 30 which may be operated according to the principles of the present disclosure is illustrated. The burner 30 may include a heat exchanger 102, a burner tube 104, a gas valve 106, an igniter 108, an induced-draft blower 110, and an area expansion plenum 112. In operation, the gas valve 106 may meter the flow of gas into the area expansion plenum 112. It should be understood that gas may be injected in multiple ways including axial, radial, single orifice, or multiple orifices. Simultaneously, the induced-draft blower 110 may pull atmospheric air from an air inlet 114 of the area expansion plenum 112 into the area expansion plenum 112, wherein air and gas may be mixed. A lean gas/air mixture may then be pulled through the burner tube 104 and into the heat exchanger 102, wherein the lean gas/air mixture may be ignited by the igniter 108. Upon combustion, a flame 116 may be produced and hot gaseous combustion products emitted from the flame 116 may then be drawn out of the heat exchanger 102 by the induced-draft blower 110 and expelled out into the atmosphere. It should be understood that hot gaseous combustion products may be pulled through other components in the induced-draft furnace 10 as depicted in FIG. 1, such as the exhaust vent 17, before being emitted out into the atmosphere.
As depicted in FIG. 3, the heat exchanger 102 may be operatively coupled to the burner tube 104. Although the close coupling of the burner tube 104 with the heat exchanger 102 lowers NO_xemission by eliminating the secondary source of air, it may also result in system 30 instability and noisy operation. In an induced-draft burner, mixing gas and air may occur near atmospheric pressure. Furthermore, combustion in an enclosed area, such as the heat exchanger 102, may create dynamic pressure when energy expelled from the flame 116 may not be able to dissipate. As the dynamic pressure builds-up, it may start propagating into the burner tube 104. If the mixing region occurred in the burner tube 104, the dynamic pressure generated by the flame 116 or natural dynamics of the burner 30 may alter the mixing region by fluctuating the inlet air flow from the ambient. Since gas may be relatively insensitive to the dynamics due to a high pressure drop across the gas orifice, the resulting gas/air mixture strength may take on the dynamic characteristics of the burner 30. Thus, the gas-to-air ratio to the flame region varies dynamically, resulting in enhanced pulsation of the flame 116. Pressure pulsation may result in instability and noisy operation of the burner 30.
Therefore, the area expansion plenum 112 may be operatively coupled to the burner tube 104. The area expansion plenum 112 may enhance the isolation of the gas/air mixing region from the flame region. By isolating the two regions, dynamic pressure from the flame region may be decoupled from the mixing region. Within the area expansion plenum 112, air and gas may be mixed before the lean gas/air mixture may be pulled by the induced-draft blower 110 into the burner tube 104, and then ignited by the igniter 108 in the heat exchanger 102.
As the flame 116 expels energy into the heat exchanger 102, dynamic pressure, also referred to as acoustic energy, may build-up and may propagate into the burner tube 104 and the area expansion plenum 112. However, once the dynamic pressure reaches the area expansion plenum 112, the amplitude of the dynamic pressure may be reduced by the area expansion plenum 112. In other words, the area expansion plenum 112 may help distribute the acoustic energy built-up in the heat exchanger 102. In one exemplary embodiment, the area expansion plenum 112 may have a concave and convex surface and may be oriented in axial or vertical position. It should be understood that the area expansion plenum 112 may be any shape or orientation as long as the cross sectional area of the area expansion plenum 112 is greater than the cross sectional area of the burner tube 104. The amount of amplitude reduction of the dynamic pressure may be determined by the area ratio from the area expansion plenum 112 to the burner tube 104. In one exemplary embodiment, the plenum-to-tube area ratio may be at least 10:1. With the cross sectional area of the area expansion plenum 112 being at least ten times greater than the cross sectional area of the burner tube 104, dynamic pressure may be adequately distributed. It should be understood that the area ratio may be as small or as large as desired. Moreover, the cross sectional area increase in the area expansion plenum 112 may also provide an increased residence time for better mixing of the gas and air.
Although the description for the burner 30 herein has been made in reference with an induced-draft furnace, it should be understood that the present disclosure contemplates incorporating any other type of system or device utilizing an induced combustion system, such as, but not limited to, engines, boilers, commercial rooftop units, and cooking equipment.
While only certain embodiments have been set forth, alternatives and modifications will be apparent from the above description to those skilled in the art. These and other alternatives are considered equivalents and within the spirit and scope of this disclosure and the appended claims.

Claims

1) A burner for a furnace, comprising:

an area expansion plenum capable of mixing gas and air to produce a lean gas/air mixture;

a gas valve operatively coupled to the area expansion plenum and capable of metering gas into the area expansion plenum;

a combustion chamber downstream of the area expansion plenum;

a burner tube operatively coupled between the area expansion plenum and the combustion chamber;

an induced-draft blower downstream of the combustion chamber and capable of drawing air into the area expansion plenum, and pulling the lean gas/air mixture through the burner tube and into the combustion chamber; and

an igniter associated between the burner tube and the combustion chamber and capable of igniting the lean gas/air mixture.

2) The burner of claim 1, wherein the igniter produces a flame upon ignition of the lean gas/air mixture, the flame produces energy in the combustion chamber, the energy excites acoustic energy in the combustion chamber, and wherein the area expansion plenum provides a fluid communication path to distribute the acoustic energy out of the combustion chamber.

3) The burner of claim 1, wherein the combustion chamber is part of a heat exchanger.

4) The burner of claim 1, wherein a cross sectional area of the area expansion plenum is greater than a cross sectional area of the burner tube.

5) The burner of claim 4, wherein the cross sectional area of the area expansion plenum is at least ten times greater than the cross sectional area of the burner tube.

6) The burner of claim 1, wherein the area expansion plenum has one of a concave and convex surface.

7) The burner of claim 1, wherein the area expansion plenum is oriented in a vertical position.

8) The burner of claim 1, wherein the area expansion plenum is oriented in an axial position.

9) A method for isolating gas-air mixing in an induced-draft burner, comprising the steps of:

metering gas into an area expansion plenum;

drawing air into the area expansion plenum;

mixing gas and air within the area expansion plenum to produce a lean gas/air mixture;

pulling the lean gas/air mixture through a burner tube and into a heat exchanger;

igniting the lean gas/air mixture within the heat exchanger, the ignition producing energy in the heat exchanger, the energy exciting acoustic energy in the heat exchanger; and

distributing the acoustic energy in the heat exchanger out of the heat exchanger and into the area expansion plenum.

10) The method of claim 9, wherein a cross sectional area of the area expansion plenum is greater than a cross sectional area of the burner tube.

11) The method of claim 10, wherein the cross sectional area of the area expansion plenum is at least ten times greater than the cross sectional area of the burner tube.

12) The method of claim 10, wherein the acoustic energy distribution rate increases as the area ratio of the area expansion plenum to the burner tube increases.

13) The method of claim 9, wherein air is drawn by an induced-draft blower into the area expansion plenum and gas is metered by a gas valve into the area expansion plenum to produce the lean gas/air mixture, the lean gas/air mixture being pulled by the induced-draft blower through the burner tube and into the heat exchanger.

14) A furnace with a burner, comprising:

at least one area expansion plenum capable of mixing gas and air to produce a lean gas/air mixture;

a gas valve operatively associated with the area expansion plenum and capable of metering gas into the area expansion plenum;

at least one heat exchanger downstream of the area expansion plenum;

at least one burner tube operatively coupled between the area expansion plenum and the heat exchanger;

an induced-draft blower downstream of the heat exchanger and capable of drawing air into the area expansion plenum, and pulling the lean gas/air mixture through the burner tube and into the heat exchanger; and

an igniter associated between the burner tube and the heat exchanger and capable of igniting the lean gas/air mixture to produce combustion products;

a flue pipe downstream of the induced-draft blower, wherein the induced-draft blower is adapted to pull the combustion products through the heat exchanger and push the combustion products through the flue pipe and out into the atmosphere; and

a cabinet housing therein the area expansion plenum, the gas valve, the burner tube, the igniter, the heat exchanger, the induced-draft blower, and the flue pipe.

15) The furnace of claim 14, wherein a cross sectional area of the at least one area expansion plenum is greater than a cross sectional area of the at least one burner tube.

16) The furnace of claim 15, wherein the cross sectional area of the at least one area expansion plenum is at least ten times greater than the cross sectional area of the at least one burner tube.

17) The furnace of claim 14, wherein the at least one area expansion plenum has one of a concave and convex surface.

18) The furnace of claim 14, wherein the at least one area expansion plenum is oriented in an axial position.

19) The furnace of claim 14, wherein the at least one area expansion plenum is oriented in a vertical position.

20) The furnace of claim 14, wherein the igniter produces a flame upon ignition of the lean gas/air mixture, the flame produces energy in the at least one heat exchanger, the energy excites acoustic energy in the at least one heat exchanger, the acoustic energy in the at least one heat exchanger is distributed out of the at least one heat exchanger by the at least one area expansion plenum.