Flammable vapor resistant water heater with low NOx emissions

Information

  • Patent Grant
  • 6446581
  • Patent Number
    6,446,581
  • Date Filed
    Friday, November 16, 2001
    23 years ago
  • Date Issued
    Tuesday, September 10, 2002
    22 years ago
Abstract
A water heater including a water container, a combustion chamber adjacent the container, the combustion chamber having a side wall and at least one flame arrestor to admit air and extraneous fumes into the combustion chamber and confine ignition and combustion of the extraneous fumes within the combustion chamber, and a burner having a multiplicity of burner ports associated with the combustion chamber and arranged to combust fuel to heat water in the container, and an air diverter including a baffle plate with an upper surface and an outer edge portion, the diverter positioned in the combustion chamber and having a lower portion of the upper surface positioned at about the same height as at least a portion of the burner ports, the baffle plate sized to form a gap between the outer edge portion and the side wall such that flames generated by combustion of the fuel tend to attach to at least a portion of the lower portion, and a flange attached to and angled upwardly from the outer edge portion and adapted to channel combustion air passing through at least a portion of the flame trap through the gap to ensure uniform combustion and meter the relative amounts of primary and secondary air, with the net effect of optimizing combustion and minimizing NOx and CO emissions.
Description




FIELD OF THE 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




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 capable of enabling ignition are or 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. 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.




One attempt to limit NO


x


emissions is U.S. Pat. No. 5,645,413 to Benedek et al., which discloses a water heater designed to operate with unlimited burner primary air, and a key feature is to recirculate secondary air to the primary combustion flame region. In '413, the flame guide and burner are an integral system such that the burner does not function separately from the flame guide.




SUMMARY OF THE INVENTION




This invention relates to a water heater including a water container and a combustion chamber adjacent the container. The combustion chamber has a side wall and at least one flame arrestor 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 having a multiplicity of burner ports is associated with the combustion chamber and arranged to combust fuel to heat water in the container.




An air diverter including a baffle plate with an upper surface, an inner portion and an outer edge portion is positioned in the combustion chamber. The baffle plate has a lower portion of its upper surface positioned at about the same height as at least a portion of the burner ports. The baffle plate is sized to form a gap between the outer edge portion and the side wall such that flames generated by combustion of the fuel tend to attach to at least the inner portion of the baffle plate. A flange is attached to and angled upwardly from the outer edge portion and adapted to channel combustion air passing through at least a portion of the flame arrestor through the gap.











BRIEF DESCRIPTION OF THE DRAWINGS





FIG. 1

is a schematic partial cross-sectional view of the lower half of a gas-fueled water heater having an air inlet and low NO


x


air distributor according to the invention.





FIG. 2

is a schematic partial cross-sectional view of the water heater of

FIG. 1

rotated by 60°.





FIG. 3

is a schematic perspective view of the lower portion of the water heater of

FIGS. 1 and 2

according to the invention, broken apart for ease of understanding.





FIG. 4

is an exploded partial cross-sectional view taken from the phantom line IV of FIG.


1


.





FIG. 5

is an exploded partial cross-sectional view taken from the phantom line V of FIG.


1


.





FIG. 6

is an exploded partial cross-sectional view taken from the phantom line VI of FIG.


2


.











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 and 2

in particular, there is illustrated a storage type gas water heater


2


including jacket


4


which surrounds a water tank


6


and a main burner


74


in a combustion chamber


15


. Water tank


6


has a bottom


7


and is preferably capable of holding heated water at mains pressure and is further preferably insulated by foam insulation


8


. Alternative insulation may include fiberglass or other types of fibrous insulation and the like. Fiberglass insulation


9


surrounds chamber


15


at the lowermost portion of water tank


6


. It is possible that heat resistant foam insulation can be used if desired.




Located underneath water tank


6


is a pilot burner (not shown) 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 flame arrestor


30


, which is installed in an aperture/opening


28


in base


26


, and then combusts gas admixed with air and the hot products of combustion rise up through flue


10


, possibly with heated air. Water tank


6


is lined with a glass coating (not shown) for corrosion resistance. The thickness of the coating on the exterior surface of water tank


6


is about one half of the thickness of the interior facing surface to prevent “fish scaling”. Also, the lower portion of flue


10


is coated (not shown) to prevent scaling that could fall into combustion chamber


15


and possibly partially block off flame arrestor


30


.




The fuel is supplied to both burner


74


through a gas valve (not shown) and fuel line


84


. Flue


10


contains a series of baffles (not shown) to better transfer heat generated by main burner


74


to water within tank


6


. Near the pilot burner is a flame detecting thermocouple (not shown) which is a safety measure to ensure that, in the absence of a flame at the pilot burner, the gas control valve shuts off the gas supply. The water temperature sensor


67


, preferably located inside the tank


6


, co-operates also with the gas control valve (not shown) to supply gas to the main burner


74


on demand.




The products of combustion pass upwardly and out the top of jacket


4


via a flue outlet after heat has been transferred from the products of combustion. The flue outlet discharges conventionally into a draught diverter which in turn connects to an exhaust duct leading outdoors.




Water heater


2


is mounted preferably on legs


24


to raise the base


26


of the combustion chamber


15


off the floor. As noted above, an aperture


28


is closed gas tightly by flame arrestor


30


which admits air for combustion of the fuel gas combusted through main burner


74


and the pilot burner, regardless of the relative proportions of primary and secondary combustion air used by each burner. Flame arrestor


30


is preferably made from a thin metallic perforated sheet of stainless steel, such as described in U.S. Pat. No. 6,085,699, for example.




Where base


26


meets the vertical combustion chamber wall or skirt


79


, adjoining surfaces can be either one piece or alternatively sealed thoroughly to prevent ingress of air or flammable extraneous fumes. Gas, water, electrical, control or other connections, fittings or plumbing, wherever they pass through combustion chamber wall


79


, such as at opening


80


, are sealed with a closure plate (not shown). The combustion chamber


15


is air/gas tight except for means to supply combustion air through flame arrestor


30


and to exhaust combustion products through flue


10


.




Pilot flame establishment can be achieved by a piezoelectric igniter (not shown). A pilot flame observation window (not shown) can be provided which is sealed. Cold water is introduced at a low level of the tank


6


and withdrawn from a high level in any manner as already well known.




Referring now to

FIGS. 1-6

, the invention also includes an air distribution, metering, and combustion staging apparatus


99


for combustion chamber


15


of water heater


2


equipped with flame arrestor


30


. We found that flame arrestor


30


imposes a large flow restriction of the combustion air entering combustion chamber


15


as well as asymmetry in air distribution to burner


74


. We also found that this flow imbalance produces nonuniform stoichiometry around the periphery of the typically axisymmetric burner


74


, with resulting performance penalties in NO


x


production in the regions where stoichiometry is not optimal. These nonuniformities arise in both the primary combustion zone, where there may be incomplete mixing of the gas and primary combustion air, and the secondary region where combustion is completed by additional air available at the exit of the burner ports.




The reactions by which NO


x


is formed are strongly dependent on temperature, with higher flame temperatures producing substantially more NO


x


than the amounts created at lower temperatures. Since these high flame temperatures occur in mixtures closest to stoichiometric air/fuel ratios, it is desirable to avoid operating in such a regime. Generally, this is accomplished by ensuring that the overall combustion air is sufficient to increase the stoichiometric ratio well above a value of 1.0, typically to a value of 1.2 or above. Local stoichiometries, however, can vary significantly from the bulk value if air is provided in a nonuniform distribution to the burner and is incompletely mixed prior to combustion at the burner ports. Thus, some regions of the burner can be operating in a manner which produces high levels of NO


x


while other regions do not, resulting in an elevated average NO


x


concentration in the total flow of combustion products in the flue. Similar mechanisms can produce undesirable levels of CO emissions in nonuniform or poorly mixed gas/air mixtures if localized stoichiometries are such that the oxidation of CO to CO


2


cannot be completed before flame temperatures drop below a critical level.




Apparatus


99


of the invention improves the performance of the combustion system by providing a means to more evenly distribute the air entering chamber


15


via the flame arrestor


30


and thus produce a more uniform stoichiometry around the burner periphery. Referring particularly to

FIGS. 3 and 6

, a circular baffle plate


100


having an upper surface


152


is installed in chamber


15


substantially concentric with burner


74


. An inner portion


150


of the surface


152


is located at about the same height as burner ports


102


formed between adjacent nodes


154


of upper metallic sheet


156


and lower metallic sheet


158


of burner


74


. Plate


100


is positioned to allow burner


74


to be inserted and removed while plate


100


remains fixed in combustion chamber


15


.




Inner portion


150


extends radially outwardly from inner edge


160


, which forms a central opening


162


, at an angle relative to horizontal in a range of about 5° to about 10° and terminates at a flat portion


164


. The width of inner portion


150


is preferably about 1.5 times the width of flat outer portion


164


. Inner edge


160


is most preferably substantially vertically oriented and rests upon or is supported by a lower lip


166


of burner


74


.




The diameter of plate


100


is sized to create a gap


104


(see

FIG. 2

) between outer edge


106


of outer portion


164


and skirt


79


of combustion chamber


15


that is small relative to the overall diameter of combustion chamber


15


. The gap


104


is preferably between about 0.25 and about 0.75 inches. The impingement and subsequent redistribution of air on the underside of plate


100


results in a more even flow to and around burner


74


. Additionally, the pressure drop of the secondary air around outer edge


106


of plate


100


can be adjusted by the width of gap


104


between plate


100


and skirt


79


and/or gap between the top of flange


115


(see below) and bottom


7


of water storage tank


6


, thus allowing more or less secondary air to be admitted.




Since the overall airflow into the chamber is restricted by flame arrestor


30


, control of the secondary air accordingly provides a means to control the amount of primary air entering burner


74


and thus the overall primary fuel/air ratio. Additionally attached to upper surface


152


of plate


100


is flange


115


comprising a substantially vertically oriented ring located at outer edge


106


. Flange


115


has a height, typically in the range of about 1-1.25 inch, that is relatively small compared to the diameter of baffle plate


100


.




The upward slope/angle of inner portion


150


and the proximity of burner ports


102


causes the flames to attach substantially continuously to surface


152


of baffle plate


100


, thereby transferring heat from the flames to the baffle plate


100


which reduces peak temperatures and minimizes NO


x


production. Baffle plate


100


and flange


115


control both radiative heat loss and the time the combustion gases spend in the primary combustion zone prior to secondary air being introduced. This in turn controls various combustion processes such as formation of NO


x


and the burnout of carbon monoxide.




Apparatus


99


is at least partially supported by a plurality of positioning brackets


168


. Brackets


168


extend substantially horizontally outwardly from flange


115


at gap


104


and have an opening


170


sized and shaped to receive a bracket engager tab


172


that extends substantially horizontally inwardly from skirt


79


into gap


104


. Each engager tab passes through opening


170


and enables baffle plate


100


to be substantially horizontally and vertically fixed into a desired position. This is especially important to maintain gap


104


substantially even between skirt


79


and outer edge


106


/flange


115


.




Also, the lowermost portion of inner edge


160


concentrically contacts burner


74


at lower lip


166


of lower metallic sheet


158


of burner


74


. Such contacts provide for additional support and stabilization of apparatus


99


with respect to burner


74


and the remainder of the components associated with combustion chamber


15


. As noted above, burner


74


is formed from upper metallic sheet


156


and lower metallic sheet


158


, which are connected together at nodes


154


, preferably by spot-welding or the like. Upper sheet


156


has a diameter that is less than lower sheet


158


. Also, the diameter of upper sheet


156


is less than the diameter of opening


162


, which permits the entire burner assembly, including burner


74


, to be removed from combustion chamber


15


by way of opening


80


without disturbing and/or removing apparatus


99


.




Bracket


168


preferably engages extender tabs


172


in a manner that provides substantially no lateral or vertical movement of baffle plate


100


. Most preferably, extender tabs


172


are integral with an upper portion of skirt


79


, although this is not required.




Thus, the invention serves to control the combustion processes by distributing total combustion air more uniformly, preferably substantially uniformly, and metering the relative proportions of the primary and secondary air, as well as by controlling the heat release and staging. Optimization of the overall burner system can include, but is not limited to, improvements in the emissions of NO


x


and carbon monoxide, the efficiency of heat transfer to the water storage tank, and the peak metal temperatures of the combustion apparatus.




Installation of apparatus


99


into combustion chamber


15


is preferably accomplished as follows:




Baffle plate


100


with flange


115


is installed permanently in combustion chamber


15


prior to attaching tank


6


to skirt


79


. This is accomplished by engaging extender tabs


172


with their respective brackets


168


. Later, burner


74


and the manifold assembly are installed into combustion chamber


15


through opening


80


such that burner


74


is raised up through the center of plate


100


and a seal is substantially formed between edge


160


of plate


100


and the extended lower lip


166


of burner


74


. Burner


74


is then supported by the tip


82


of fuel line


84


at support bracket


86


and by the combustion chamber door. Of course, opening


80


is also sized and shaped for removal of burner


74


from combustion chamber


15


.




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 a side wall and at least one flame arrestor 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 having a multiplicity of burner ports associated with said combustion chamber and arranged to combust fuel to heat water in said container; an air diverter comprising a baffle plate with an upper surface formed from an inner portion and an outer portion, said diverter positioned in said combustion chamber and having the upper surface of the inner portion positioned at about the same height as at least a portion of said burner ports, said baffle plate sized to form a gap between an edge of the outer portion and said side wall such that flames generated by combustion of said fuel tend to attach to at least the inner portion of the baffle plate; and a flange attached to and angled upwardly from the outer portion and adapted to channel combustion air passing through at least a portion of said flame arrestor through said gap.
  • 2. The water heater defined in claim 1, wherein the inner portion of the baffle plate is angled upwardly from a central axis extending through the baffle plate.
  • 3. The water heater defined in claim 2, wherein about half of the baffle plate is angled upwardly.
  • 4. The water heater defined in claim 1, wherein the outer portion of the baffle plate is substantially horizontal.
  • 5. The water heater defined in claim 1, wherein the baffle plate inner portion has a central opening with an edge, the edge contacting a lower portion of the burner.
  • 6. The water heater defined in claim 5, wherein the edge of the inner portion is substantially vertically oriented.
  • 7. The water heater defined in claim 1, wherein the inner portion of the baffle plate is oriented at an angle of about 5° to about 10°.
  • 8. The water heater defined in claim 1, wherein said gap is from about 0.25 to about 0.75 inches.
  • 9. The water heater defined in claim 1, wherein said burner comprises two metallic sheets fixed together and wherein an upper sheet thereof has a smaller diameter than a lower sheet thereof.
  • 10. The water heater defined in claim 9, wherein said metallic sheets are shaped to form a multiplicity of elongated and radially extending channels through which premixed gas and air flow prior to combustion.
  • 11. The water heater defined in claim 9, wherein the lower sheet has a lower step portion upon which an edge of the baffle plate inner portion is supported.
  • 12. The water heater defined in claim 1, wherein the flange is substantially vertical.
  • 13. The water heater defined in claim 1, wherein the burner is removable from the combustion chamber without moving the diverter.
  • 14. The water heater defined in claim 1, further comprising at least one positioning bracket extending outwardly from the flange and engaging the side wall.
  • 15. The water heater defined in claim 14, wherein positioning bracket maintains the baffle plate in a selected position.
  • 16. The water heater defined in claim 14, wherein the positioning bracket has an opening sized and shaped to receive a bracket engager tab extending inwardly from the side wall.
  • 17. The water heater defined in claim 1, wherein the side wall has an opening sized to permit removal of the burner from the combustion chamber.
  • 18. The water heater defined in claim 1, wherein attachment of the flames to the baffle plate upper surface lowers flame temperature and thereby reduces NOx emissions.
  • 19. The water heater defined in claim 1, wherein the baffle plate and the gap are positioned to cause combustion air passing to the burner to be substantially uniform in flow rate around the burner outer edge portion.
  • 20. The water heater defined in claim 1, wherein the baffle plate and the gap are positioned to meter the relative amounts of primary and secondary air.
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Number Name Date Kind
796924 McCartney Aug 1905 A
4869232 Narang Sep 1989 A
4940042 Moore et al. Jul 1990 A
5020512 Vago et al. Jun 1991 A
5335646 Katchka Aug 1994 A
5427525 Shukla et al. Jun 1995 A
5448969 Stuart et al. Sep 1995 A
5646413 Benedek et al. Jul 1997 A
5649822 Gertler et al. Jul 1997 A
5797355 Bourke et al. Aug 1998 A
5937796 Sebastiani Aug 1999 A