U.S. patent application number 13/160638 was filed with the patent office on 2011-12-22 for induced-draft burner with isolated gas-air mixing.
This patent application is currently assigned to Carrier Corporation. Invention is credited to Michael R. Carey, Jeffrey M. Cohen, Scott A. Liljenberg.
Application Number | 20110311923 13/160638 |
Document ID | / |
Family ID | 45328988 |
Filed Date | 2011-12-22 |
United States Patent
Application |
20110311923 |
Kind Code |
A1 |
Liljenberg; Scott A. ; et
al. |
December 22, 2011 |
Induced-Draft Burner With Isolated Gas-Air Mixing
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.
Inventors: |
Liljenberg; Scott A.;
(US) ; Carey; Michael R.; (US) ; Cohen;
Jeffrey M.; (US) |
Assignee: |
Carrier Corporation
|
Family ID: |
45328988 |
Appl. No.: |
13/160638 |
Filed: |
June 15, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61357286 |
Jun 22, 2010 |
|
|
|
Current U.S.
Class: |
431/12 ; 239/316;
431/354 |
Current CPC
Class: |
F23D 2210/00 20130101;
F23D 14/04 20130101; F23M 20/005 20150115 |
Class at
Publication: |
431/12 ; 431/354;
239/316 |
International
Class: |
F23D 14/04 20060101
F23D014/04; F23N 1/02 20060101 F23N001/02; F23D 14/60 20060101
F23D014/60 |
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.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This is a non-provisional U.S. patent application, which
claims priority under 35 U.S.C. .sctn.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
[0002] 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
[0003] 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.sub.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.sub.x
from furnaces. Given the current climate and popular opinion
regarding the environment, these standards are likely to only get
more restrictive in the future.
[0004] A known technique for reducing NO.sub.x is 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.sub.x production. 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.sub.x emission 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.sub.x
emissions 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
[0005] 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.
[0006] 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.
[0007] 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.
[0008] 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
[0009] 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:
[0010] FIG. 1 is a perspective view of an embodiment of a furnace
constructed in accordance with the teachings of the present
disclosure;
[0011] FIG. 2 is a block diagram of an embodiment of a burner
constructed in accordance with the teachings of the prior art;
and
[0012] 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.
[0013] 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
[0014] 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.
[0015] 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.sub.x emission due to the secondary source of air being
introduced with the "in-shot" burner.
[0016] 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.
[0017] 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.
[0018] 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.sub.x emission 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.
[0019] 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.
[0020] 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.
[0021] 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.
[0022] 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.
* * * * *