Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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TITLE OF INVENTION
Burner for reducing nitrogen oxides and carbon monoxide
BACKGROUND OF THE INVENTION
Field of the Invention
The present invention relates to an atmospheric burner. More particularly, the
invention relates to an atmospheric burner for use in gas-fueled appliances
which reduces
emissions of NO, NOZ and carbon monoxide.
Description of the Related Art
Atmospheric burners are commonly used in appliances which use a gas as a fuel.
Gaseous hydrocarbons such as methane (natural gas) or propane (bottled gas)
may be used as
a fuel in such appliances. Common appliances of these types include water
heaters, furnaces,
boilers, space heaters, ranges and clothes dryers.
When fuels such as hydrocarbon gases are burned in air and the flame
temperature
exceeds certain levels, it is known that nitrogen present in the air will
combine with oxygen
to form oxides of nitrogen such as nitrogen monoxide (NO) and nitrogen dioxide
(NO2).
These oxides of nitrogen are usually formed simultaneously in the mixed
combustion
emission gases and are referred to collectively as NOX, or "nitrogen oxides".
Nitrogen oxides
are air pollutants, and government regulations set strict limits on the
maximum nitrogen oxide
emissions from appliances. Consequently, considerable effort has been expended
in the area
of burner design with the goal of lowering NOX emissions.
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Several approaches for lowering NOX emissions have been tried, but all to
date have required expensive modifications to burner design. U.S. Patent
4,904,179
to Drago and Ripka discloses a burner where a perforated metal screen is
disposed in
the flame to conduct heat from the flame in an attempt to lower NOX emissions.
This approach disadvantageously requires the screen as a separate component of
the
burner assembly as well as some provision for mounting of the screen in an
appropriate relationship to the rest of the burner assembly.
A gas burner using metal flame inserts in the form of slotted, inverted
channel shaped members is disclosed in U. S. Patent 4,616,994 to Tomlinson.
The
flame inserts of the Tomlinson disclosure are disposed on each side of the gas
flames of the burner in contact with the inner cones of the burner flames.
This burner
design requires a separate assembly from the burner itself, the assembly then
being
mounted on the burner. The shape of these inserts is complicated and requires
a
number of manufacturing steps to fabricate.
A different system of flame inserts is disclosed in U.S. Patent 4,652,236 to
Viessmann. Flat vertical parallel fins are disposed between slot-shaped gas
ports
and extend perpendicularly above the gas burner. This arrangement places the
fins in
contact with the flames to draw heat from the flames. A chimney effect is also
said
to be produced with secondary air entering the flames and cooling the insert
fins.
The fins of this invention are disclosed as being separate pieces of material
attached
to a burner tube. The manufacture of this type of burner is complicated by the
need
to fabricate these fins separately and then attach them to the burner tube.
This
approach also reduces efficiency by removing energy intended for heating an
external item.
U.S. Patent 4,525,141 to DeWerth et al. describes flame inserts which are
rod-shaped rather than flat. The rod-shaped flame inserts are arranged
radially
around a gas burner and spaced between the flames of the operating burner.
Each
flame is flanked by two inserts with the insert rods sized so as to have these
rods in
contact with the inner cones of the flames, which is said to lower the flame
temperature by carrying heat away from the flame and radiating this heat.
Although
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the burner allegedly reduces emissions of nitrogen oxides, the design
disadvantageously requires more components for its manufacture than most
conventional burners. The assembly of the additional components into the
finished
burner also requires a more complicated manufacturing process resulting in
very
high production costs.
U.S. Patent 4,629,415 to DeWerth et al. discloses the use of rods formed into
concentric rings supported around a circular gas burner. The rods are spaced
from
the burner ports and arranged vertically so that the gas flames project
between the
ring shaped rods. The ring-shaped rods of this burner design require
additional
component parts beyond the conventional burner housing: supports for the rods
are
needed to hold the rods in the proper position in relation to the burner ports
so that
the flames will properly contact the rods. These additional components and
associated supporting structures increase the production costs associated with
this
burner.
Secondary air shields have also been used to control nitrogen oxide
emissions from burners. Secondary air shields are believed to work by limiting
the
rate at which air needed for combustion diffuses into a flame. In conventional
burners, primary air (air which is mixed with a fuel gas prior to combustion)
is
normally maintained below the stoichiometric amount required for complete
combustion of the fuel gas to prevent detonation. Once ignited, the gas-
primary air
mixture burns in a flame, but additional air (secondary air) is required for
complete
burning of the fuel. Secondary air diffuses into a flame from the surrounding
space
to supply the balance of oxygen needed for complete stoichiometric combustion.
By
placing a barrier or shield in proximity to a flame, diffusion of secondary
air into the
flame is slowed. This is believed to affect the fuel gas burning rate in the
flame in a
manner which reduces emissions of nitrogen oxides.
A conventional use of secondary air shields can be seen in the burner
disclosed in Minimizing Emissions of Nitrogen Oxides from Domestic Water
Heaters, technical report ES66052D of the Southern California Gas Company,
March, 1973, by W. S. Zawada. This report discloses the advantages of a gas
burner
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provided with a solid annular air shield. disposed below the flames of a
burner. The
air shield is shown as an additional member affixed to the burner assembly,
thereby
adding to the complexity of the burner design and to its manufacturing cost.
Further,
the accompanying increase in size renders the burner impractical as a
replacement in
existing gas appliances.
Thus, known burners have not satisfied the long-felt need in the art for a
burner which is inexpensive to produce and efficiently burns gaseous
hydrocarbon
fuel while producing lower nitrogen oxide emissions.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide such a burner for use in
water heaters and other appliances. It is a further object of the present
invention to
provide a gas burner which meets the following goals relative to a burner of
conventional design:
1. Increased Recovery Efficiency
2. Reduced NO,, and Carbon Monoxide Emissions
3. Quiet Operation
4. Multiple Fuel Utilization
5. Smooth Ignition and Extinction
6. Low Cost
Other objects of the invention will become apparent from the description
provided
below.
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The gas burner of the present invention comprises a coupled burner body and
burner lid. A plurality of gas ports in a substantially circular and planar
arrangement
are interposed between the coupled body and lid and are directed radially from
the
body and lid. An air shield member is co-formed to and extends radially from
the
5 burner body or burner lid. Extending radially from the air shield member in
substantial radial alignment with the gas ports is a plurality of flame
partitions, the
number of flame partitions being preferably equal to the number of gas ports.
Each
flame partition is an elongated member comprising two attached tabs which are
substantially perpendicular to each other when the flame partition is observed
in
cross-section.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a top plan view of a body of a burner in accordance with the
invention.
Fig. 2 is a side sectional view of a burner body, air shield member, and flame
partition in accordance with the invention.
Fig. 3 is a bottom plan view of a burner lid in accordance with the invention.
Fig. 4 is a side elevation view of the burner lid of Fig. 3.
Fig. 5 is a transverse sectional view of the burner lid of Fig. 3.
Fig. 6 is a top plan view of a burner in accordance with the invention.
Fig. 7 is an side elevation view of the burner of Fig. 6.
Fig. 8 is a transverse sectional view of a burner in accordance with the
invention.
Fig. 9 is a detailed view of a portion of Fig. 7, showing details of a flame
partition.
Fig. 10 is a bottom plan view of a burner lid of a second embodiment in
accordance with the invention.
Fig. 11 is a side elevation view of the burner lid of Fig. 10.
Fig. 12 is a transverse sectional view of the burner lid of Fig. 10.
Fig. 13 is a top plan view of a burner of the second embodiment in
accordance with the invention.
Fig. 14 is a transverse sectional view of the burner of Fig. 13.
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Fig. 15 is a perspective view of a third embodiment in accordance with the
invention.
Fig. 16 is a top plan view of the embodiment of Fig. 15.
Fig. 17 is a bottom plan view of the embodiment of Fig. 15.
Fig. 18 is a side elevation view of the embodiment of Fig. 15, showing a gas
port.
Fig. 19 is a detailed view of a portion of Fig. 18, showing a detail of the
air
shield member.
Fig. 20 is a perspective view of a fourth embodiment of a burner in
accordance with the invention.
Fig. 21 is a top plan view of the embodiment of Fig. 20.
DETAILED DESCRIPTION OF THE INVENTION
The burner of the present invention surprisingly overcomes the performance
shortcomings of previous burner designs. It accomplishes this through an
elegantly
simple design, comprising only two low-cost stamped metal parts. More
specifically,
it was discovered by the inventors that the combined performance advantages of
a
flame insert and a secondary air shield are surprisingly realized from the
easily-manufactured burner of the invention. The advantages of the invention
are
realized while also keeping the burner to a two piece design.
The invention exhibits several performance advantages when compared with
a conventional gas burner for water heater use. A burner made according to the
invention disclosed here satisfies the objects outlined above. When compared
with a
conventional burner of similar design and configuration, but the conventional
burner
having a burner body with a smooth lip in place of the flame partitions of the
invention, a burner in accordance with the invention gave the following
improvements in performance. Table I shows the results of a comparison trial
of the
conventional burner with the burner according to the invention. Recovery
efficiency, excess air, and ignition time were all significantly improved with
use of
the burner of the invention. Emissions of carbon monoxide and nitrogen oxides
were
greatly reduced while carbon dioxide emission increased, showing improved
overall
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combustion efficiency. The cost of manufacturing a burner in accordance with
the
invention was estimated to be approximately 66% lower than for a conventional
burner. A burner according to the present invention is capable of operating
with a
variety of fuel gases at a wide range of line pressures, and can operate with
methane
as a fuel with a burner input range of from about 30,000 to about 80,000 Btu
per
hour. This corresponds to a port loading of about 1,550 Btu per port or
224,543 Btu
per square inch.
Parameter Performance of Performance of Performance Percentage
Conventional Burner of the Improvement Performance
Burner Present Invention Improvement
Recovery 0.742 0.763 increased 2.8%
Efficiency
Carbon 106 ppm 74 ppm reduced 30%
Monoxide
NOX 88.9 ppm 69.6 ppm reduced 22%
Carbon Dioxide 9.20% 9.95% increased 8%
Excess Air 3.32% 2.74% reduced 17%
Ignition Time 1.4 sec 0.5 sec reduced 64%
Table 1.
The invention's design allows for the insertion of a burner in accordance
with the invention through the access port of conventional water heaters, thus
facilitating its installation as an environmentally-friendly replacement
burner for
existing water heaters. Burners according to other low-NOx designs require the
disassembly of a conventional water heater for their installation therein,
because the
burners of these other designs cannot fit through the standard access port of
a water
heater.
The burner of the invention combines the performance advantages of a flame
insert and a secondary air shield into a single structure co-formed either
with the
burner body or burner lid. The invention can be fabricated from sheet metal
using
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conventional stamping techniques, and does not require the use of relatively
expensive materials such as stainless steel or ceramics. The burner is formed
from
two generally circular pieces. A preferred embodiment of the invention is
shown in
the accompanying drawings which will now be discussed in detail. Those skilled
in
the art of burner design and construction will readily understand the method
of
manufacture of the novel burner disclosed herein, and its operation and
advantages.
In the included drawings, similar reference numbers are used to indicate
corresponding elements in the different illustrated embodiments.
Figures 1 through 9 show a first embodiment of a burner according to the
invention.
Referring to Fig. 1, an overhead view of a burner body 10 in accordance with
the invention is shown. Starting from the center of Fig. 1, burner body 10
comprises
a venturi 12, which possesses a plurality of primary air entrance points (not
shown),
90 degrees to each other. Moving radially, burner body 10 also comprises
bosses 14,
each boss forming approximately one half of a gas port when the burner body is
coupled coaxially with the burner lid to form a complete burner assembly. The
preferred embodiment has 42 such bosses corresponding to 42 gas ports.
Integral to
burner body 10 is air shield member 16, which further toward the periphery is
divided and formed into a skirt comprising a plurality of flame partitions 18
equal in
number to the bosses and ports. Flame partitions 18 comprise a first tab and a
second
tab, said tabs at approximately right angles to each other (the tabs are
clearly shown
in Fig. 9). While the exact mechanism is not known, it is thought that these
tabs
function both as a flame insert and a secondary air shield to lower NOX and
carbon
monoxide emissions.
Fig. 2 is a transverse section of a burner body in accordance with the
invention. The overall length of flame partition 18 measured radially from the
air
shield member 16 is preferably in the range of about 5/16 inch (7.9 mm) to
about 1
inch ( 2.5 cm). The first tab can extend from about 1/32 inch (0.08 cm) to
about 3/8
inch (9.5 mm) in a direction substantially perpendicular to the second tab,
and the
second tab can extend from about 3/16 inch (4.8 mm) to about 9/16 inch (14.3
mm)
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in a direction substantially perpendicular to the first tab, and the sum of
the lengths
of the first and second tabs in these directions preferably does not exceed
9/16 inch
(14.3 mm). A flame partition 18 may be in any orientation about its
longitudinal axis
so long as the tabs remain substantially perpendicular to each other and at
least one
of the tabs extends in a direction that would intersect the plane of the gas
ports.
The burner also comprises a burner lid, an example of which is shown for the
first embodiment in Fig. 3 in bottom plan view. Burner lid 20 comprises a
generally
circular central portion 21 having a profile concave as seen from the top of
the lid.
The generally circular central portion 21 is from about 3.0 inches (7.6 cm) to
about
3.5 inches (8.9 cm) in diameter. Burner lid 20 also comprises an array of
bosses 22
formed on the burner lid, the bosses arranged radially around the generally
circular
central portion, each of the bosses constituting approximately one half of
each gas
port when the burner lid is coupled with the burner body described above.
Coaxial
coupling of a burner lid and a burner body into a complete burner assembly may
be
accomplished by a variety of methods known to those skilled in the art of
metal
fabrication, and is preferably achieved through spot welding. Fig. 4 shows the
burner
lid 20 of Fig. 3 in perspective, while Fig. 5 shows the burner lid 20 of Fig.
3 in
transverse section.
Referring to Fig. 6, a burner 24 in accordance with the invention may be seen
in a top view with flame partitions 18 extending from below burner lid 20.
Fig. 7
shows the burner of Fig. 6 in perspective, and shows a venturi 12. Fig. 8
shows a
complete burner in accordance with the invention, in transverse section to
more
clearly illustrate the relationship of the elements of the invention to one
another.
Referring now to Fig. 9, a detailed view of a portion of Fig. 7 is shown. In
this figure the "L" shape of a flame partition 18 clearly depicted. First tab
26 of
flame partition 18 is substantially perpendicular to second tab 28, said tabs
being
connected at fold 32. In this preferred embodiment, flame partition 18 extends
radially at an angle of about 35 degrees to the planar arrangement of gas
ports while
remaining in substantial radial alignment with port 30. The angle between
flame
partitions 18 and the planar arrangement of gas ports preferably ranges from
about 0
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to 90 degrees, more preferably from about 20 to 50 degrees, and most
preferably
from about 35 degrees. Second tab 28 is positioned to contact and divide the
flame
that would emanate from the port 30. First tab 26 is positioned below the
flame. In a
preferred embodiment as shown, the first tab is extended and disposed below a
5 flame proceeding from gas port 30, where it may shield the flame from
diffusion
from below of secondary air. The second tab is disposed in the flame, where it
may
function as a flame insert, elongating and removing heat from the flame.
A second, alternative embodiment of a burner in accordance with the
invention is shown in Figures 10 through 14. Referring to Fig. 10, an
alternative
10 form of a burner lid 40 comprises an array of bosses 22. The burner lid 40
also
comprises a generally circular central portion 41 having a truncated concave
shape
as viewed from the top of the lid. The generally circular central portion 41
is from
about 3.0 inches (7.6 cm) to about 3.5 inches (8.9 cm) in diameter. The
generally
circular central portion 41 is capped by a generally circular planar portion
43
forming the truncation, and the generally circular planar portion having a
diameter of
from about 1/4 inch (0.6 mm) to about 2 inches (5.1 cm), and preferably having
a
diameter of about 1 1/2 inches (3.8 cm).
Fig. 11 shows a side elevation of the alternative burner lid of Fig. 10. This
latter figure clearly shows the truncated dome shaped generally circular
central
portion 41, and the circular planar portion 43. Fig. 12 shows a transverse
section of
the alternative burner lid of Fig. 10.
Fig. 13 shows a top plan view of a complete mated burner according to the
invention, where the alternative burner lid 40 is used with the burner body of
Fig. 1.
Coaxial coupling of the burner lid with the burner body may be accomplished by
a
method such as spot welding, as described above for the first embodiment.
In Fig. 14 is shown the transverse section of the second alternative
embodiment of a burner in accordance with the invention, showing the
relationship
of the circular planar portion 43 of the burner lid to the venturi 12.
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It has also been discovered that improvements in burner performance can be
achieved by use of the flame partitions of the invention, even when the number
of
flame partitions is fewer than the number of gas ports in a burner. Although
it is
preferred to have these two numbers equal, a burner's operation can still
benefit
from providing the inventive flame partitions disposed around the burner.
Fig. 15 illustrates a third embodiment of a burner in accordance with the
invention. In this embodiment the burner is ringed around its periphery with
flame
partitions 18 in similar construction and arrangement to the embodiments
disclosed
above except for a sector 48, that is devoid of a flame partition. As shown in
the
figure, the sector 48 may be repeated at four spaced apart locations around
the
burner embodiment. A burner according to the teachings of the present
invention
may have such a sector that is devoid of a single flame partition, or may have
a
plurality of sectors devoid of a single flame partition. If a plurality of
such sectors is
present, it is preferred that the sectors be equally spaced apart from one
another. For
example, if four such sectors are present in a burner according to the
invention, it is
preferred that the four sectors be disposed at twelve, three, six and nine
o'clock
positions about the burner.
Fig. 16 illustrates a top plan view of a complete mated burner of the third
embodiment according to the invention, where the embodiment lacks a flame
partition, providing a sector 48 that is repeated at three other spaced apart
locations
around the burner of this embodiment.
Fig. 17 illustrates a bottom plan view of the third embodiment according to
the invention. Clearly visible is the sector 48 without flame partitions, with
the
sector at the twelve o'clock position being repeated at the three, six and
nine o'clock
positions.
Turning to Fig. 18, an elevation view of the third embodiment may be seen
that shows a gas port visible within the sector without flame partitions. Fig.
19
provides a detailed view of this gas port, the gas port having no flame
partition 18
disposed before it.
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Fig. 20 illustrates a fourth embodiment of a burner in accordance with the
invention. In this embodiment the burner is ringed around its periphery with
flame
partitions 18 except for a sector 52, that is devoid of three flame
partitions. As
shown in the figure, the sector 52 is present at four spaced apart locations
around the
burner embodiment. The construction and arrangement of the fourth embodiment
is
similar to the third embodiment disclosed above except for the size of the
sector 52.
A burner according to the teachings of the present invention may have such a
sector
that is devoid of a plurality of flame partitions, or may have a plurality of
sectors
devoid of a plurality of flame partition. If a plurality of such sectors are
present, it is
preferred that the sectors be spaced apart from one another. For example, if
four
such sectors are present in a burner according to the invention, it is
preferred that the
four sectors be disposed at twelve, three, six and nine o'clock positions
about the
burner. Fig. 21 shows a top plan view of the fourth embodiment.
Flame 42 38 34 30 26 22
Partitions:
Combustion 81.85 80.77 80.4 79.99 79.49 79.17
Efficiency (%)
Carbon 9.40 9.40 9.40 9.40 9.45 9.40
Dioxide (%)
Carbon 15 15 15 15 15 15
Monoxide
(ppm)
NOx (ppm) 58 56.8 58.7 59.8 60.4 61.7
Table 2.
In Table 2 are seen data from a comparison of the performance of a burner
according to the invention having 42 of the inventive flame partitions,
compared
with burners having fewer than 42 flame partitions. The data of Table 2 were
obtained from tests with burners installed in a water heater, with a different
water
heater being used than that used for the tests of Table 1. The Table 2 data
show that
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as fewer flame partitions are used with a burner of the inventive
construction, there is a trend
for the NO, being produced by the burner to increase. As may be seen in Table
2, the NOX
output of a burner increased from 58 ppm to 61.7 ppm as the number of flame
partitions was
reduced from 42 to 22. With 22 flame partitions on the test burner used, four
sectors, each
devoid of five flame partitions were spaced about the burner.
The novel design of the invention permits inexpensive manufacture with a
minimum
of parts. Further, the elongated elements of the invention surprisingly
provide the
performance advantages of both a flame insert and a secondary air shield. As a
result, the
invention provides an efficient, low NOX and low carbon monoxide burner at low
cost. The
invention is particularly suited for use in appliances such as water heaters,
and burners of the
invention can be readily installed as a replacement for less efficient, higher
NOX burners in
older water heaters and appliances.
Although four embodiments of a burner according to this invention have been
shown
and described in detail above, those skilled in the art will readily
appreciate that many
modifications may be made to these embodiments without departing from the
spirit and scope
of the invention defined in the appended claims.
McCarthy Tetrault LLP TDO-RED #8373438 v. 2
