U.S. patent number RE36,743 [Application Number 08/629,329] was granted by the patent office on 2000-06-20 for pre-mix flame type burner.
This patent grant is currently assigned to Carrier Corporation. Invention is credited to Chester D. Ripka.
United States Patent |
RE36,743 |
Ripka |
June 20, 2000 |
Pre-mix flame type burner
Abstract
A burner for burning a combustible gas comprising fuel gas and
air that has been mixed before being supplied to the burner. The
burner has a flame holder .[.concavely.]. .Iadd.axially and
radially .Iaddend.recessed into a flame outlet. The .[.concave.].
configuration of the flame holder focuses the individual flames on
the combustion surface toward a central location where the
individual flames interact with and reinforce one another in a
direction axial to the burner. Thus very little heat is transmitted
directly from the burner in a direction normal to the burner axis.
This characteristic of the burner allows it to be used to fire a
flue type heat exchangers where the walls of the heat exchanger are
very close to the burner without excessive temperatures being
produced in the heat exchanger walls adjacent the burner.
Inventors: |
Ripka; Chester D. (East
Syracuse, NY) |
Assignee: |
Carrier Corporation (Syracuse,
NY)
|
Family
ID: |
22918414 |
Appl.
No.: |
08/629,329 |
Filed: |
April 8, 1996 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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Reissue of: |
243353 |
May 16, 1994 |
05458484 |
Oct 17, 1995 |
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Current U.S.
Class: |
431/353; 126/109;
126/116R; 431/328; 431/329; 431/346 |
Current CPC
Class: |
F23D
14/02 (20130101); F23D 14/58 (20130101) |
Current International
Class: |
F23D
14/02 (20060101); F23D 14/58 (20060101); F23D
14/48 (20060101); F23D 014/82 () |
Field of
Search: |
;431/353,329,346,354,348,328 ;239/403 ;126/109 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
American Society of Heating, Refrigerating and Air-Conditioning
Engineers, Inc. Dec. 1992 Ashrae Heating, Ventilating and
Air-Conditioning Systems and Equipment Handbook, 15.1-15.3
(Atlanta) Dec. 1992..
|
Primary Examiner: Jones; Larry
Claims
I claim:
1. A flame type burner (510, 610, 710) for burning a combustible
gas comprising:
a burner body (511, 611, 711);
a combustible gas inlet means for mixing a fuel gas and air and
conveying it (512, 612, 712) into said burner body;
a flame outlet (513, 613, 713) from said burner body; and
a perforated flame holder (514, 614, 714) having a combustion
surface that is .[.concavely.]. .Iadd.axially and radially
.Iaddend.recessed into said flame outlet and that directs flames
toward a central focus.
2. The burner of claim 1 in which said flame holder is comprised of
a single thickness of a single material.
3. The burner of claim 1 in which at least one .Iadd.portion of an
axial .Iaddend.cross section of said flame holder is a .[.segment
of an parabola.]. .Iadd.straight line.Iaddend..
4. The burner of claim 1 in which at least one .Iadd.axial
.Iaddend.cross section of said flame holder is a segment of an
ellipse.
5. The burner of claim 1 in which at least one .Iadd.axial
.Iaddend.cross section of said flame holder is an arc of a
circle.
6. A flue gas-to-fluid heat exchanger (50, 60) and flame type
burner (510, 610, 710) assembly comprising:
a flue gas-to-fluid heat exchanger having a flue inlet (52, 62);
and
a flame type burner, positioned at said flue inlet, having a burner
body (511, 611, 711);
a combustible gas inlet means for mixing a fuel gas and air and
conveying it (512, 612, 712) into said burner body;
a flame outlet (513, 613, 713) from said burner body; and
a perforated flame holder (514, 614, 714) having a combustion
surface that is .[.concavely.]. .Iadd.axially and radially
.Iaddend.recessed into said flame outlet and that directs flames
toward a central focus.
Description
BACKGROUND OF THE INVENTION
This invention relates generally to burners for burning a
combustible gas comprised of a mixture of fuel gas and air. More
particularly, the invention relates to a burner of the pre-mix type
where the mixing of the fuel gas and air has occurred before the
combustible gas reaches the burner.
Burners for burning a combustible gas find use in a wide variety of
applications. One use is in hot air furnaces, where the burning gas
heats air for the purpose of warming the interior of a building
such as a house. In such a furnace, the burning gas and gases of
combustion are confined with a heat exchanger, such as heat
exchanger 50 in FIG. 1, while air to be heated passes over and
around the exterior of the heat exchanger. Heat exchanger 50 is of
the clamshell type and is typical of the heat exchangers found in
residential warm air furnaces. Such a heat exchanger is
manufactured by embossing two matching raised patterns into sheet
metal and joining the embossed patterns together to form heat
exchanger flue path 51. The joints are made so that flue path 51 is
gas tight except for flue inlet 52 and flue outlet 53. The typical
furnace has more than one heat exchanger, the number being
dependent on the size and heat transfer characteristics of each
individual heat exchanger and the desired furnace heating capacity.
Other furnace structure isolates the flue inlets and outlets from
the air to be heated. Other furnace designs use tubular heat
exchangers such as heat exchanger 60 shown in FIG. 2. Heat
exchanger 60 is functionally similar to heat exchanger 50 in that
air to be heated passes
around the exterior of flue 61 and the burning gas and gases of
combustion are confined to the interior of the flue path between
flue inlet 61 and flue outlet 62.
In the typical prior an hot air furnace, an inshot burner, such as
burner 30 depicted schematically in FIG. 3, burns fuel gas and air
to produce hot gases of combustion. Fuel gas is supplied to burner
30 through gas inlet 32. Air, introduced through primary air inlet
36, mixes with the fuel gas and burns, producing primary flame 33.
Other air, known as secondary air, mixes with the unburned gas in
primary flame 33 and produces secondary flame 34. The result is
that the total length of flame from an inshot burner is relatively
long. An inshot burner is positioned at the flue inlet, such as
flue inlet 52 (FIG. 1) or flue inlet 62 (FIG. 2), of each heat
exchanger in the furnace so that the flame projects into the heat
exchanger flue.
The combustion of a fuel gas such as methane, particularly at very
high temperatures can produce, as products of combustion, various
oxides of nitrogen, collectively known as NO.sub.x. These oxides
vent to the atmosphere with other combustion products. Limiting the
concentration of NO.sub.x .[.in.]. .Iadd.is .Iaddend.desirable, as
certain .[.jurisdiction.]. .Iadd.jurisdictions .Iaddend.may place
restrictions on NO.sub.x emissions. Furnaces sold in those
jurisdictions must comply with very stringent emission
standards.
Furnace designers have found that the use of pre-mix burners can
greatly reduce NO.sub.x emissions. Unlike an inshot burner, where
fuel gas and air mix in the burner, the fuel gas and air are mixed
to form a combustible gas at a point in the fuel gas and air supply
paths before reaching the pre-mix burner. FIG. 4 depicts
schematically a typical prior art pre-mix burner. Burner 40 has
burner body 41, combustible gas inlet 42 and flame holder 44. Flame
holder 44 is perforated so that combustible gas can pass through
the holder and burn as flames 49 slightly off its surface. In such
a burner as burner 40, the flames, and thus the heat output, are
concentrated in the immediate vicinity of the burner.
A pre-mix burner having physical and operating characteristics
similar to burner 40 would not be suitable for use with a heat
exchanger such as heat exchanger 50 or 60. The heat exchanger wall
would necessarily be in close proximity to the burner and thus the
concentration of the heat produced in the immediate vicinity of the
burner would result in excessively high temperatures in the wall of
the heat exchanger. Such high temperatures would increase surface
temperatures of the surrounding heat exchanger and shorten the life
of the heat exchanger. U.S. Pat. No. 4,960,102, issued 2 Oct. 1990
to Shellenberger, describes and depicts a furnace having a burner
like burner 40. The furnace avoids the problem of excessive
temperatures in the heat exchanger wall by constructing the wall to
be sufficiently far from the burner that excessive temperaures do
not occur.
The figures of U.S. Pat. No. 3,525,325, issued 25 Aug. 1970 to
Perl, appear to disclose a gas flame burner having a concave flame
holder but a close reading of the disclosure shows that the '325
burner is of the radiant infrared and not of the flame type.
Clamshell and tubular type furnace heat exchangers offer a number
of operational, cost and manufacturing advantages. Large numbers
are in use and they are still in production. What is needed is a
burner of the pre-mix type, with its low NO.sub.x emission
qualities, that can be used with a clamshell or tube type heat
exchanger. Such a burner should not have combustion characteristics
that would lead to excessive heat exchanger wall temperatures, even
if the wall is in close proximity to the burner.
SUMMARY OF THE INVENTION
The present invention is a burner of the pre-mix type in which a
combustible gas, comprised of a mixture of fuel gas and air, is
burned. The physical configuration of the burner affects the flame
that it produces so that excessive temperatures in the immediate
vicinity of the burner are avoided. It is thus possible to use the
burner in conjunction with a clamshell or tubular type heat
exchanger with little or no modification to the heat exchanger.
The burner has a flame outlet having a flame holder
.[.concavely.]..Iadd.which is axially and radially
.Iaddend.recessed into the outlet. The .[.concavity.]. .Iadd.shape
.Iaddend.of the flame holder causes the individual flames produced
on the flame holder to be directed to a central focus, where they
reinforce each other and combine to produce a flame that is
projected along an axis normal to the plane of the flame outlet for
some distance from the burner. In this way, the heat produced by
the flame is distributed over a greater distance than is possible
with prior art pre-mix burners. It is this distribution of heat in
an extended flame downstream of the burner that allows the burner
to be used with clamshell and tubular heat exchangers.
BRIEF DESCRIPTION OF THE DRAWINGS
The accompanying drawings form a part of the specification.
Throughout the drawings, like reference numbers identify like
elements.
FIG. 1 is a view of a clamshell heat exchanger.
FIG. 2 is a view of a tubular heat exchanger.
FIG. 3 is a schematic view of an inshot type burner.
FIG. 4 is a schematic view of a prior art pre-mix burner.
FIGS. 5A and 5B are respectively a schematic view and an isometric
view, partially broken away, of one embodiment of the burner of the
present invention.
FIGS. 6A and 6B are respectively a schematic view and an isometric
view, partially broken away, of another embodiment of the burner of
the present invention.
FIGS. 7A and 7B are respectively a schematic view and an isometric
view, partially broken away, of another embodiment of the burner of
the present invention.
FIG. 8 is a view of a portion of the flame holder of the burner of
the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Burner 510, shown in FIGS. 5A and 5B, is one embodiment of the
present invention. Combustible gas flows into rectangular burner
body 511 through combustible gas inlet 512. The gas flows through
flame holder 514 by means of a number of perforations. During
burner operation, combustion of the gas occurs on the outer or
downstream face of flame holder 514. The entire surface of flame
holder 514 contains perforations.
FIG. 8 depicts one satisfactory arrangement of perforations, with
groups of perforations 14 separated by imperforate zones 16. U.S.
Pat. No. 4,397,631, issued 9 Aug. 1983 to Fisher, fully discloses
and discusses the reasons for and advantages of such an
arrangement.
Combustion occurs at each perforation in flame holder 514. Because
flame holder 514 is configured to .[.concavely.]. .Iadd.axially and
radially .Iaddend.recess into burner body 511 from burner outlet
513, individual flames are directed inward toward a central focus
where they combine and reinforce and are projected out of burner
outlet 513 in a direction normal to the plane of outlet 513.
FIGS. 6A and 6B and 7A and 7B depict other embodiments of the
present invention. Burners 616 and 710 differ from burner 510
primarily in the shapes of their respective burner bodies 611 and
711 and in the configurations of their respective flame holders 614
and 714. The shape of burner 610 would make it suitable for use
with a tubular heat exchanger while the shapes of burners 510 and
710 are adapted for use with a clamshell type heat exchanger. The
oval shape of burner body 611 offers no operational advantage over
the rectangular shape of burner body 510 but burner 710 may offer
increased life as compared to burner 510 because it does not have
square corners. These corners could increase the thermal and
physical stresses present in burner body 511.
Theoretical work confirmed by experiments indicate that the precise
.[.concave.]. shape of flame holders 514, 614 and 714 is not
critical. FIG. 5A depicts a flame holder having one axial cross
section that is comprised of an arc of a circle and straight lines.
FIG. 6A depicts a flame holder having .[.a.]. .Iadd.an axial
.Iaddend.cross section that is the arc of a circle. And FIG. 7A
depicts a flame holder having an elliptical cross section. Any of
these shapes should provide satisfactory performance. It is merely
necessary to have a shape that directs the individual flames on the
outer surface of the flame holder toward a central focus.
I have built and tested a prototype of the burner of the present
invention. During bench operational testing at full burner feed
rate, it is possible for one to hold a hand within two centimeters
of the burner body continuously with only a slight increase in
temperature detectable. This is because the combined flame and
resultant heat from the burner is projected downstream from the
burner outlet. In addition, the unignited and relatively cool
combustible gas entering the burner body serves to remove heat from
the burner body wall.
* * * * *