Information
-
Patent Grant
-
6508207
-
Patent Number
6,508,207
-
Date Filed
Wednesday, February 7, 200123 years ago
-
Date Issued
Tuesday, January 21, 200321 years ago
-
Inventors
-
Original Assignees
-
Examiners
Agents
- Schnader Harrison Segal & Lewis LLP
-
CPC
-
US Classifications
Field of Search
US
- 122 1301
- 122 1431
- 122 141
- 126 307 A
- 126 39 E
- 431 266
- 431 354
-
International Classifications
-
Abstract
A water heater including a water container; a combustion chamber adjacent the container, the combustion chamber having at least one air inlet to admit air and extraneous fumes into the combustion chamber and confine ignition and combustion of the extraneous fumes within the combustion chamber; a burner associated with the combustion chamber and arranged to combust fuel to heat water in the container; and an air diverter positioned between the air inlet and the burner and adapted to channel at least a portion of combustion air passing through at least a portion of the air inlet to a position for mixture with the fuel prior to entering the burner to slow combustion and thereby reduce combustion temperatures and NOx emissions.
Description
FIELD OF INVENTION
This invention relates to water heaters, particularly to improvements to gas fired water heaters adapted to render them safer for use and to reduce NO
x
emissions.
BACKGROUND OF INVENTION
The most commonly used gas-fired water heater is the storage type, generally comprising an assembly of a water tank, a main burner to provide heat to the tank, a pilot burner to initiate the main burner on demand, an air inlet adjacent the burner near the base of the jacket, an exhaust flue and a jacket to cover these components. Another type of gas-fired water heater is the instantaneous type which has a water flow path through a heat exchanger heated, again, by a main burner initiated from a pilot burner flame.
For convenience, the following description is in terms of storage type water heaters but the invention is not limited to this type. Thus, reference to “water container,” “water containment and flow means,” “means for storing or containing water” and similar such terms includes water tanks, reservoirs, bladders, bags and the like in gas-fired water heaters of the storage type and water flow paths such as pipes, tubes, conduits, heat exchangers and the like in gas-fired water heaters of the instantaneous type.
A particular difficulty with many locations for water heaters is that the locations are also used for storage of other equipment such as lawn mowers, trimmers, snow blowers and the like. It is a common procedure for such machinery to be refueled in such locations.
There have been a number of reported instances of spilled gasoline and associated extraneous fumes being accidently ignited. There are many available ignition sources, such as refrigerators, running engines, electric motors, electric and gas dryers, electric light switches and the like. However, gas water heaters have sometimes been suspected because they often have a pilot flame.
Vapors from spilled or escaping flammable liquid or gaseous substances in a space in which an ignition source is present provides for ignition potential. “Extraneous fumes,” “fumes” or “extraneous gases” are sometimes hereinafter used to encompass gases, vapors or fumes generated by a wide variety of liquid volatile or semi-volatile substances such as gasoline, kerosene, turpentine, alcohols, insect repellent, weed killer, solvents and the like as well as non-liquid substances such as propane, methane, butane and the like.
Many inter-related factors influence whether a particular fuel spillage leads to ignition. These factors include, among other things, the quantity, nature and physical properties of the particular type of spilled fuel. Also influential is whether air currents in the room, either natural or artificially created, are sufficient to accelerate the spread of fumes, both laterally and in height, from the spillage point to an ignition point yet not so strong as to ventilate such fumes harmlessly, that is, such that air to fuel ratio ranges are capable of enabling ignition are not reached given all the surrounding circumstances.
One surrounding circumstance is the relative density of the fumes. When a spilled liquid fuel spreads on a floor, normal evaporation occurs and fumes from the liquid form a mixture with the surrounding air that may, at some time and at some locations, be within the range that will ignite. For example, the range for common gasoline vapor is between about 2% and 8% gasoline with air, for butane between 1% and 10%. Such mixtures form and spread by a combination of processes including natural diffusion, forced convection due to air current drafts and by gravitationally affected upward displacement of molecules of one less dense gas or vapor by those of another more dense. Most common fuels stored in households are, as used, either gases with densities relatively close to that of air (e.g. propane and butane) or liquids which form fumes having a density close to that of air, (e.g. gasoline, which may contain butane and pentane among other components is very typical of such a liquid fuel).
In reconstructions of accidental ignition situations, and when gas water heaters are sometimes suspected and which involved spilled fuels typically used around households, it is reported that the spillage is sometimes at floor level and, it is reasoned, that it spreads outwardly from the spill at first close to floor level. Without appreciable forced mixing, the air/fuel mixture would tend to be at its most flammable levels close to floor level for a longer period before it would slowly diffuse towards the ceiling of the room space. The principal reason for this observation is that the density of fumes typically involved is not greatly dissimilar to that of air. Combined with the tendency of ignitable concentrations of the fumes being at or near floor level is the fact that many gas appliances often have their source of ignition at or near that level.
Earlier efforts, such as those disclosed in U.S. Pat. No. 5,797,355, substantially raised the probability of successful confinement of ignition of spilled flammable substances from typical spillage situations to the inside of the combustion chamber. Other following structures, such as those disclosed in U.S. Pat. Nos. 5,950,573; 6,003,477; 6,082,310; 6,085,699; and 6,085,700, for example, have built on the break through success of '355.
Although the water heaters described in the above-identified patents have been well received and highly successful with respect to increasing the resistance to ambient flammable vapors, certain portions of the U.S., especially California have stringent low NO
x
emissions regulations and requirements. We have discovered an ongoing challenge associated with meeting these limits with such structures for the following reasons.
An important element of such flammable vapor resistant water heaters is a flame arrestor or flame trap placed strategically in the air intake opening to the combustion chamber of the water heater. This is accomplished by creating a controlled opening for combustion air and otherwise sealing off the combustion chamber. It was discovered that placement of the flame arrestor relative to the pilot is important in consistently igniting the flammable vapors in different spill scenarios. Both the pilot and main burners must be able to light the flammable vapors soon after they enter the combustion chamber.
There are also preexisting conditions that dictate the relative positioning of the pilot to the burner that it is to ignite. Thus, the design wherein the same pilot that would light the burner would also ignite the flammable vapors, if present, had the effect of setting a relationship of the inlet air relative to the burner. The result was that the air inset for the flame trap is off center and not symmetrical.
Most natural gas burners used in storage water heaters are “pan” burners. They are made of sheet metal making them a very economical choice and their flame pattern is well suited for heating a typical storage tank bottom. Such pan burners are designed to operate with air evenly distributed around the inlet to the mixing chamber of the burner. They have the opening to the mixing chamber placed at a specific distance and concentricity from a gas orifice. This allows the gas to flow from the orifice and mix with the combustion air consistently and unencumbered.
However, in that design, the relationship of the flame arrestor to pilot to burner creates imbalances in the availability and locations of primary and secondary air through out the combustion chamber. This imbalance can cause several side effects in the combustion process. It leads to higher levels of NO
x
production as the flame temperature runs hotter on the non-arrestor side due to lack of excess air to help cool the process. The air at the mixing chamber opening is also distributed unevenly. This also contributes to higher NO
x
production by disturbing the ratio of primary and secondary air. This can deprive the burner of enough air to mix with the amount of fuel. The fuel and air may also not mix as intended. With the air availability skewed from side to side, the mixture may not be as homogenous as a mixing chamber in a symmetrical environment and, therefore, produce pockets of rich mixture and pockets that are too lean. This has been found to increase NO
x
production due to having isolated hot spots. It is known that one of the primary factors of NO
x
production is flame temperature exceeding 2800 degrees F. Formation of thermal NO
x
increases exponentially with combustion temperature, and increases by a square root relationship with the presence of oxygen in the combustion zone. This excessively rich primary mixture is also more likely to flashback on extinction when using alternate higher BTU input fuels that are required for ANSI testing. (Butane-Air). Accordingly, it has been a primary objective to produce a water heater that simultaneously addresses the issue of resistance to flammable vapors and can meet ever increasingly stringent low NO
x
emissions regulations and requirements by the various regulatory bodies.
SUMMARY OF THE INVENTION
The invention relates to a water heater including a water container and a combustion chamber adjacent the container. The combustion chamber has at least one flame trap to admit air and extraneous fumes into the combustion chamber. The flame trap (sometimes also referred to as an “air inlet” or “air inlet plate”) has a plurality of ports. The ports are sized and shaped to cause air and extraneous fumes to pass through the ports, yet confine ignition and combustion of the extraneous fume species within the combustion chamber. The water heater includes a burner associated with the combustion chamber and arranged to combust fuel to heat water in the container. A low NO
x
draft hood is positioned relative to the burner and the flame trap to enhance combustion dynamics to reduce production of NO
x
emissions.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1
is a schematic partial cross-sectional view of a gas-fueled water heater having an air inlet and low NO
x
hood according to the invention.
FIG. 2
is a schematic perspective view of the combustion chamber of a water heater of the type shown in FIG.
1
.
FIG. 3
is a top plan view of the combustion chamber shown in FIG.
2
.
FIG. 4
is a cross-sectional view of the combustion chamber taken through the line A—A in FIG.
3
.
FIG. 5
is a schematic perspective view of a burner and low NO
x
hood according to the invention.
FIG. 6
is an inverted plan view of the burner and low NO
x
hood of FIG.
5
.
FIG. 7
is a cross-sectional view of the burner and low NO
x
hood taken through the line VII—VII of FIG.
6
.
FIG. 8
is an elevation view of a prior art combustion chamber generally similar to that shown in
FIG. 4
, partially cut-away to show a conventional burner.
DETAILED DESCRIPTION OF THE INVENTION
It will be appreciated that the following description is intended to refer to the specific embodiments of the invention selected for illustration in the drawings and is not intended to limit or define the invention, other than in the appended claims.
Turning now to the drawings in general and
FIGS. 1-4
in particular, there is illustrated a storage type gas water heater
62
including jacket
64
which surrounds a water tank
66
and a main burner
74
in an enclosed chamber
75
that addresses and solves the longstanding problems described above. Water tank
66
is preferably capable of holding heated water at mains pressure and is insulated preferably by foam insulation
68
. Alternative insulation may include fiberglass or other types of fibrous insulation and the like. Fiberglass insulation surrounds chamber
75
at the lowermost portion of water tank
66
. It is possible that heat resistant foam insulation can be used if desired. A foam dam separates foam insulation
68
and the fiberglass insulation.
Located underneath water tank
66
is a pilot burner
73
and main burner
74
which preferably use natural gas as fuel or other gases such as LPG, for example. Other suitable fuels may be substituted. Main burner
74
receives combustion air through air inlet plate
90
and low NO
x
draft diverter
91
and then combusts gas admixed with air and the hot products of combustion rise up through flue
70
, possibly with heated air. Water tank
66
is lined with a glass coating to provide corrosion resistance against the hot water content. It is also coated on part of the exterior surface with a glass coating to provide corrosion resistance to that portion particularly that forms the upper wall of the combustion chamber
75
and contacts the hot and corrosive products of combustion. The external glass coating is applied to about half the thickness of that of the internal lining since this results in a protective coating more resistant to cracking under the influence of sudden changes in temperature. Such cracking if it happens causes the coating to resemble a fish scale appearance and such scales could detach eventually and possibly partly block the air inlet plate
90
. However, without this external protective coating, the steel surface of the tank
66
and lower portion of the flue
70
may shed flake-like rust products, which could risk blocking the air inlet plate
90
.
Fuel gas is supplied to both burners
73
,
74
through a gas valve
69
and a fuel line
71
. Flue
70
in this instance, contains a series of baffles
72
to better transfer heat generated by main burner
74
to water within tank
66
. Near pilot burner
73
is a flame detecting thermocouple (not shown) which is a known safety measure to ensure that in the absence of a flame at pilot burner
73
the gas control valve
69
shuts off the gas supply. The water temperature sensor
63
, preferably located inside the tank
66
, co-operates also with the gas control valve
69
to supply gas to the main burner
74
on demand.
The products of combustion pass upwardly and out the top of jacket
64
via flue outlet
76
after heat has been transferred from the products of combustion. Flue outlet
76
discharges conventionally into a draught diverter
77
which in turn connects to an exhaust duct leading outdoors.
Water heater
62
is mounted preferably on legs
84
to raise the base
86
of the combustion chamber
75
off the floor. In base
86
is an aperture
28
which is closed gas tightly by an air inlet plate
90
which admits all air for combustion of the fuel gas combusted through the main burner
74
and pilot burner
73
, regardless of the relative proportions of primary and secondary combustion air used by each burner. Air inlet plate
90
is preferably made from a thin metallic perforated sheet of stainless steel.
Where base
86
meets the vertical combustion chamber walls
79
, adjoining surfaces are thoroughly sealed by a circumferential seam
81
to prevent ingress of air or flammable extraneous fumes. Instead, the base
86
and walls
79
may be one piece. The underside of the base
86
is recessed inwardly from the lower end of the seam to create an air space
82
between it and a flat-bottomed support pan
56
illustrated in FIG.
8
. This support pan
56
is used with the present invention also but is omitted from
FIGS. 1-4
for clarity of illustration. The support pan
56
is provided with at least one hole
83
vertically below the air inlet plate in the base
86
to admit air into the air space
82
.
Pilot flame establishment can be achieved by a piezoelectric igniter. A pilot flame observation window
93
can be provided which is sealed. Cold water is introduced at a low level of the tank
66
and withdrawn from a high level in any manner as already well known.
Referring to
FIGS. 4-7
, specifics of a burner
74
and air diverter
91
\ are shown. Burner
74
is constructed of an upper sheet metal plate
100
and a lower sheet metal plate
102
that are fixed together in a known manner such as by spot welding or the like at a multiplicity of nodes
104
. The diameter of upper sheet
100
is smaller than the diameter of lower sheet
102
. The nodes are elongated in a radially-extending direction and form a series of elongated radially-extending channels
106
through which a mixture of fuel and combustion air pass prior to combustion of the fuel. An opening
108
is located at the outer terminus of substantially all of channels
106
.
Upper sheet
100
is substantially “bowl-shaped”, as is lower sheet
102
, except that lower sheet
102
has an opening
110
centrally located which is formed by a downwardly-extending lip
112
.
Diverter
91
includes a pair of substantially vertically oriented side walls
114
and an end wall
116
connected therebetween. The side walls
114
and end wall
116
are also connected together by a cover
118
as well as a lower floor
120
. The side walls
114
taper towards each other in the direction which terminates in end wall
116
. Floor
120
is sized such that it leaves a substantial opening
122
in a lowermost portion of air diverter
91
. There is also an opening
124
formed by a lip
126
that is connected directly to lip
112
of burner
74
. Lower floor
120
also has an opening
128
that is sized to receive fuel line
71
. Fuel line
71
is terminated at opening
128
with a fuel injecting nozzle
129
. Cover
118
has a curved portion
130
that is especially designed to cause an even flow of air into diverter
91
as air passes through opening
122
and towards opening
124
. Curved portion
130
also causes the air flow to be such to maximize mixing with fuel prior to passage through opening
110
of burner
74
and through channels
106
of burner
74
prior to combustion.
During normal operation, water heater
62
operates in substantially the same fashion as conventional water heaters except that all air for combustion enters through air inlet plate
90
. A portion of the air entering through air inlet plate
90
passes into air diverter
91
through opening
122
, assisted by aspiration from a pressure drop in fuel flow through nozzle
129
as the fuel's velocity is increased by passing through the small opening in it. The fuel and air mix prior to passing through opening
110
and channels
106
.
The invention, including the use of diverter
91
, corrects the imbalance described above. We found that the diverter
91
increases the amount of primary air available by about 25%. This lowers the NO
x
levels below the industry-accepted value of 40 Ng/J or 55 ppm corrected to 3% oxygen. This structure also completely neutralizes tendencies of the burner to flashback to the orifice on flame extinction. Although we do not wish to be bound by any particular theory, we believe that air diverter
91
increases the velocity of the air mixing may contribute to this factor being so effectively answered. Because of the robustness of this design, concerning this flashback solution, we can also lower costs by using inexpensive burners with relatively low port loading that would normally flashback in this environment. Low port loads in natural gas burners are known to produce less NO
x
.
This mode of combustion is brought about so that NO
x
emissions are reduced due to the proportioning and premixing of the air and fuel in proper ratios and so that combustion takes place in a slower and substantially even manner. Moreover, the multiplicity of holes
108
supply further even quantities of air calculated to lower flame temperatures, thereby reducing NO
x
emissions still further. This configuration inhibits soot formation or “candling” at nozzle
129
. The remainder of the air in the combustion chamber can flow freely around the outer edge of the lower sheet
102
to contribute further secondary air to the main burner.
It is important that the lower edge of diverter
91
, where opening
122
is located, does not physically contact air inlet plate
90
. This could reduce the ability of air inlet plate
90
to confine potential ignition within the combustion chamber. It is accordingly preferred that a space or gap of at least about ¼-inch is maintained. Also, it is important that the curved portion
130
of cover
118
not extend across both elongated side edges of air inlet plate
90
inasmuch as this will potentially disturb the even flow of air currents around and through air inlet plate
90
.
Also, it is preferable that opening
122
be aligned over the center of the perforated area of the air inlet plate
90
because the velocity profile of the air entering the combustion chamber is greatest above the center of plate
90
. By taking air into the opening
122
of cover
118
at the highest available upward velocity a higher aeration is achieved in the primary stage of combustion, believed to amount to about 2 to 20% additional primary aeration. The higher upwardly then horizontally directed flow of incoming fresh air across the vertically emerging stream of gas or fuel from nozzle
129
is believed also to be a reason for the inhibiting of candling as mentioned above.
As best illustrated in
FIG. 3
, both air diverter
91
and pilot burner
73
are located side by side generally as close to the center of the perforated area of the air inlet plate
90
where the velocity of incoming air is highest. When flammable extraneous fumes enter the combustion chamber
75
the alignment of the pilot burner
73
generally over the center of the plate
90
(or near the center) has been found to minimize instances of high velocity or explosive initial ignition of fumes in the chamber.
If spilled fuel or other flammable fluid is in the vicinity of water heater
62
then some extraneous fumes from the spilled substance may be drawn through plate
90
by virtue of the natural draft characteristic of such water heaters. Air inlet
90
allows the combustible extraneous fumes and air to enter but confines potential ignition and combustion inside the combustion chamber
75
.
The spilled substance taken into water heater
62
is burned within combustion chamber
75
and exhausted through flue
70
via outlet
76
and duct
78
. Because flame is confined by the air inlet plate
90
within the combustion chamber, flammable substance external to water heater
62
will not be ignited.
With reference to
FIG. 1
, the size of air inlet plate
90
is dependent upon the air consumption requirement for proper combustion to meet mandated specifications to ensure low pollution burning of the gas fuel. Merely by way of general indication, the air inlet plate should be conveniently about 3700 mm
2
perforated area when fitted to a water heater having between 35,000 and 50,000 Btu/hr (approximate) energy consumption rating to meet ANSI requirements for overload combustion. Air diverter
91
is sized accordingly and preferably made from the same or similar material as air inlet plate
90
.
With reference to
FIG. 8
, the lower portion is quite similar to
FIGS. 2 and 4
and corresponding reference numerals are used. The burner
74
lacks the extended lower sheet
102
of FIG.
5
and the holes
108
therein. The diverter
91
is absent. The support pan
56
is included although this is also used in the invention but not illustrated, for clarity reasons only. The support pan
56
and base
86
define an air space
82
below the combustion chamber. Combustion air enters the air space
86
upstream of the combustion chamber
75
via the entry hole
83
.
It is to be understood that the invention disclosed and defined herein extends to all alternative combinations of the individual features mentioned or evident from the text or drawings. All of these different combinations constitute various alternative aspects of the invention. The foregoing describes embodiments of the present invention and modifications, obvious to those skilled in the art can be made to them, without departing from the scope of the present invention.
Claims
- 1. A water heater comprising:a water container; a combustion chamber adjacent the container, said combustion chamber having at least one air inlet to admit air and extraneous fumes into said combustion chamber and confine ignition and combustion of said extraneous fumes within said combustion chamber; a burner associated with said combustion chamber and arranged to combust fuel to heat water in said container; and an air diverter operatively positioned between said air inlet and said burner which channels at least a portion of combustion air passing through at least a portion of said air inlet such that said combustion air and said fuel are mixed in the air diverter prior to entering said burner.
- 2. A water heater comprising:a water container; a combustion chamber adjacent the container, said combustion chamber having at least one air inlet to admit air and extraneous fumes into said combustion chamber and confine ignition and combustion of said extraneous fumes within said combustion chamber; a burner associated with said combustion chamber and arranged to combust fuel to heat water in said container; an air diverter operatively positioned between said air inlet and said burner and adapted to channel at least a portion of combustion air passing through at least a portion of said air inlet to a position for mixture with said fuel prior to entering said burner; and a fuel line positioned to introduce said fuel into said diverter.
- 3. A water heater comprising:a water container; a combustion chamber adjacent the container, said combustion chamber having at least one air inlet to admit air and extraneous fumes into said combustion chamber and confine ignition and combustion of said extraneous fumes within said combustion chamber; a burner associated with said combustion chamber and arranged to combust fuel to heat water in said container; an air diverter operatively positioned between said air inlet and said burner and adapted to channel at least a portion of combustion air passing through at least a portion of said air inlet to a position for mixture with said fuel prior to entering said burner; and wherein said diverter comprises a draft hood including a pair of substantially vertically oriented side walls, a substantially vertically oriented end wall connected between said side walls, and a cover connected to edge portions of said walls, at least said side walls forming a lower opening to receive said air and said cover having an upper opening oriented to pass premixed fuel and air to an opening in said burner.
- 4. The water heater defined in claim 3, wherein said cover has a downwardly curved portion extending over said air inlet.
- 5. The water heater defined in claim 3, wherein said lower opening is positioned over said air inlet.
- 6. The water heater defined in claim 3, wherein said lower opening is spaced about ¼-inch above said air inlet.
- 7. The water heater defined in claim 3, wherein said diverter further comprises a lower floor connected between at least a portion of said walls.
- 8. The water heater defined in claim 7, wherein said lower floor has an opening connected to a fuel line extending into said combustion chamber.
- 9. The water heater defined in claim 3, wherein said burner has an opening connected to said cover to receive premixed fuel and air from said diverter.
- 10. A water heater comprising:a water container; a combustion chamber adjacent the container, said combustion chamber having at least one air inlet to admit air and extraneous fumes into said combustion chamber and confine ignition and combustion of said extraneous fumes within said combustion chamber; a burner associated with said combustion chamber and arranged to combust fuel to heat water in said container; an air diverter operatively positioned between said air inlet and said burner and adapted to channel at least a portion of combustion air passing through at least a portion of said air inlet to a position for mixture with said fuel prior to entering said burner; and wherein said burner comprises two metallic sheets fixed together and wherein an upper sheet thereof has a smaller diameter than a lower sheet thereof.
- 11. The water heater defined in claim 10, wherein said metallic sheets are shaped to form a multiplicity of radially extending channels through which premixed gas and air flow prior to combustion.
- 12. The water heater defined in claim 11, wherein the lower sheet has an opening positioned at a distal end portion of substantially all of said channels.
- 13. A water heater comprising:a water container; a combustion chamber adjacent the container, said combustion chamber having at least one air inlet to admit air and extraneous fumes into said combustion chamber and confine ignition and combustion of said extraneous fumes within said combustion chamber; a burner associated with said combustion chamber and arranged to combust fuel to heat water in said container; an air diverter operatively positioned between said air inlet and said burner and adapted to channel at least a portion of combustion air passing through at least a portion of said air inlet to a position for mixture with said fuel prior to entering said burner; and wherein said diverter extends across one side of said air inlet, but not across a corresponding opposed side of said air inlet.
- 14. The water heater defined in claim 3, wherein said side walls taper towards one another in the direction of said end wall.
- 15. A water heater comprising:a water container; a combustion chamber adjacent the container, said combustion chamber having at least one air inlet to admit air and extraneous fumes into said combustion chamber and confine ignition and combustion of said extraneous fumes within said combustion chamber; a burner associated with said combustion chamber and arranged to combust fuel to heat water in said container; and an air diverter connected to said burner and a fuel line and positioned to receive at least a portion of combustion air passing through at least a portion of said air inlet and having an opening to said burner through which mixed fuel and combustion air pass for combustion at said burner.
US Referenced Citations (3)
Number |
Name |
Date |
Kind |
5341767 |
Smith |
Aug 1994 |
A |
6109216 |
Reynolds et al. |
Aug 2000 |
A |
6190163 |
Maricic et al. |
Feb 2001 |
B1 |