GB2243310A

GB2243310A - Catalytic burner

Info

Publication number: GB2243310A
Application number: GB9106895A
Authority: GB
Inventors: Paul A Browne; Kirk A Dobbs
Original assignee: Atomic Energy of Canada Ltd AECL
Current assignee: Atomic Energy of Canada Ltd AECL
Priority date: 1990-04-27
Filing date: 1991-04-02
Publication date: 1991-10-30
Also published as: GB9106895D0; DE4111607A1; ITMI911159A1; ITMI911159A0; FR2661481A1; CA2015620A1

Abstract

A natural draft, catalytic heater (10) comprises a tubular body (16) which defines an elongated fluid flow passage (24) having an air/fuel mixture inlet (26) at one end and a combustion product outlet (34) at the other end thereof. A secondary catalytic burner (52) is disposed within the passage (32) downstream of the primary catalytic burner (50) for completing combustion of any un-oxidised fuel in the exhaust from the primary catalytic burner (50). Low pressure drop through the primary burner (50) is achieved by a tubular burner construction held against the passage wall and combustion of most of the reactants is achieved by providing an appropriate catalyst surface area. A stirring element (76) may be placed within the burner (50) for gently urging reactants outwardly towards the catalyst. A low pressure drop through the secondary burner (52) is achieved by providing a plurality of axial passages which present relatively little resistance to gas flow. The surfaces of the passages are coated with a catalyst material to ensure that any un-oxidized reactants are oxidised. <IMAGE>

Description

1 W 1 A CATALYTIC HEATER ---1-1. 0 1 The present invention relates, in

general, to catalytic heating devices and, more specifically, to natural draft catalytic heaters which can be used in applications which do not have access to electricity and which use alcohols, preferably methanol, as the source of fuel.

There are many applications in which non-electric, safe, simple and inexpensive heaters could be used. For example, heaters of this type could be used in cottage and marine refrigerators and stoves, water heaters, coolers, engine and battery heaters. Existing products have not served these markets well. many devices currently available for these markets require electricity and therefore are completely unsuitable for these applications. Others require fuels which are gaseous at room temperature. The fuels must be pressurized and are relatively unsafe as compared with fuels, such as alcohols, which are liquid at room temperature. Not only are pressurized fuels relatively hazardous, they require relatively complex flow control mechanisms for operation.

It is now well known that some materials, notably noble metals such as platinum, palladium and the like, cause some combustible gases to react with oxygen resulting in release of heat. These materials are referred to as "catalysts" and the combustion process is generally referred to as "catalytic combustion". Catalytic combustion has received much favour in recent years. Indeed, the process has been applied to domestic appliances such as curling irons, soldering irons and the like. Most catalytic appliances of this type use pressurized fuel cartridges containing butane, propane and the like and therefore suffer from the same drawbacks mentioned earlier. Further, many catalytic burners require electricity to cause a spark to initiate catAlytic combustion while others require preheating, even at room temperature.

Many catalytic burners are operated in an open environment which causes some problems. The term "open environment" means that the burner element itself releases heat to surrounding air. The difficulty with this arrangement is that it may allow the catalyst material to be exposed to temperatures (about 500'C) which are known to cause premature failure of the catalyst. This arrangement also includes constructions in which the combustion chamber itself is open to some extent to the atmosphere and permits gases to escape without undergoing complete oxidation. Other designs do not provide any mechanism for ensuring complete combustion. In either case, unburnt fuels create a safety hazard that may not be easily detected by the human nose.

Insofar as fuels are concerned, alcohols provide several advantages. In comparison with some other liquid fuels and fuels which are gaseous at room temperature, the likelihood of inadvertent ignition of alcohols is low. It is therefore, a relatively safe fuel. If a mishap does occur, it can be easily extinguished with water. Alcohols burn cleanly and require only ordinary heat exchange equipment. Importantly, consumers are familiar with alcohol fuels for table top burners. Being liquid at room temperature, alcohols are stored in unpressurized containers and are sold off store shelves. Their cost is reasonably competitive with other hydrocarbon fuels.

Natural draft operation is essential if a burner is to be used in an environment where electricity is not available. As compared with forced draft, the driving force for natural draft is relatively small. Thus, it is important that the pressure drop across the burner elements be kept as low as possible to ensure satisfactory air flow so as to not only sustain catalytic combustion but also ensure complete combustion.

In summary, there is a need for a natural draft catalytic heater which can be operated without electricity, which is simple and reliable in operation, simple in construction and inexpensive to manufacture, safe, causes complete combustion of combustible fuel and uses a liquid fuel such as alcohol.

The present invention seeks to provide a natural draft, catalytic heater which overcomes many of the above described disadvantages of the prior art.

One aspect of the present invention relates to a catalytic burner arrangement which causes a minimum pressure drop but which results in substantially complete catalytic combustion of the reactants. In accordance with this aspect of the invention, there is provided a tubular body which defines an elongated fluid flow passage having an air/fuel mixture inlet at one end and a combustion product outlet at the other end thereof. A primary catalytic burner is disposed within the passage adjacent the inlet for reacting most of the air/fuel mixture introduced into the inlet. A secondary catalytic burner is disposed within the passage downstream of the primary catalytic burner for completing combustion of any un-oxidized fuel in the exhaust from the primary catalytic burner. Low pressure drop through the primary burner is achieved by a tubular burner construction held against the passage wall while combustion of most of the reactants is achieved by providing an appropriate catalyst surface area. A stirring element may be placed within the burner for gently urging reactants, which tend to flow axially through the burner, outwardly towards the catalyst. A low pressure through the secondary burner is achieved by providing a plurality of axial passages which present relatively little resistance to gas flow. The surfaces of the passages are coated with a catalyst material to ensure that any un-oxidized reactants are oxidized.

Another aspect of the invention relates to a burner housing construction which is particularly well suited for use with alcohol fuels and for natural draft operation. In accordance with this aspect, there is provided a generally U-shaped tubular body which defines an elongated fluid flow passage. The tubular body is formed with a pair of parallel arms and a connecting portion which joins adjacent ends of the arms. The fluid flow passage has an air inlet section in a free end of one of the arms, an air/fuel mixing section downstream of the inlet section for forming a vaporized air/fuel mixture, the mixing section having a fuel port for receiving a supply of liquid fuel, an air/fuel combustion section in the other of the arms for receiving and oxidizing the air/fuel mixture delivered by the mixing section and a combustion product exhaust section in a free end of the other of the arms. A catalytic burner is disposed within the combustion section for catalytically reacting the air/fuel mixture delivered thereto by the mixing section.

There are a number of benefits offered by a U-shaped bumer body. Liquid fuels, such as alcohols, must be vaporized before burning. The U-shaped tube allows heat from combustion to be fed back, by conduction, to the mixing section to vaporize the fuel. The U-shaped tube is forgiving in this respect in that it allows a puddle of fuel to form in the connecting portion at the base of the tube during start-up conditions. In addition, to some extent, the configuration allows a mixture to be formed prior to contact with the catalyst, in contrast to other designs where reactants first meet in the combustion zone. This pre-mixing improves combustion.

The U-shaped configuration also acts as a safety device in the event that combustion is prevented. If, for some reason, the combustion duct is plugged, the burner will simply flood to the level of the fuel reservoir, provided that the reservoir is below the elevated inlet and outlet openings. Thus, fuel is not spilled to create a safety hazard. The Ushaped tube also improves start-up.

Methanol-air mixtures are heavier than air so that on start-up, a combustible mixture is formed naturally and is retained in the duct.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features of the invention will become more apparent from the following description in which reference is made to the appended drawings wherein:

FIGURE 1 is schematic drawing illustrating a natural draft, flameless catalytic heater in accordance with a preferred embodiment of the present invention; FIGURE 2 is a partially broken, schematic perspective view of a primary catalytic burner in accordance with a preferred embodiment of the present invention; FIGURE 3 is an edge view of a secondary catalytic burner in accordance with a preferred embodiment of the present invention; FIGURE 4 is a schematic perspective view of a secondary catalytic burner in accordance with a preferred embodiment of the present invention; FIGURE 5 is a schematic drawing of a mechanism for controlling the operating temperature of the heater; FIGURE 6 is a cross-sectional view of a non-U7tube embodiment according to the present invention; and FIGURE 7 is a schematic view similar to FIGURE 1, but illustrating an optional fuel line which bypasses the thermostatic valve illustrated in FIGURE 5 to provide idle fuel flow.

DESCRIPTION OF PREFERRED EMBODIMENT

FIGURE 1 of the drawings illustrates a preferred embodiment of the natural draft, flameless catalytic heater 10 of the present invention. Heater 10 includes a generally U-shaped tubular body or housing 12 having a pair of parallel arms 14 and 16 and a connecting portion 18 joining adjacent ends 20 and 22 of the arms. Body 12 defines a fluid flow passage or duct 24 having an air inlet section 26 in the free end 28 of arm 14, an air/fuel mixing section 30 in the lower end of arm 14 and in connecting portion 18, an air/fuel combustion section 32 in the lower end of arm 16 and a combustion product exhaust section 34 in a free end 35 of the other of arm 16. The inlet section includes an air inlet opening 36.

A fuel port 38 opens into mixing section 30 and communicates with a metal or plastic fuel reservoir 40 via a vinyl fuel delivery line 42. Line 42 is provided with a manual shut-off valve 44 and a flow restrictor 46, in the form of an A102 stick, for limiting the rate of flow of liquid fuel to the fuel port when valve 44 is open.

A primary catalytic burner 50 is disposed within combustion section 32 for catalytically reacting a major portion of the air/fuel mixture delivered to the combustion section by the mixing section. The primary burner is in intimate heat conducting contact with the inner surface of tube 16. The tube radiates heat acquired during combustion to surrounding ambient air. A secondary catalytic burner 52 is disposed in combustion section 32 downstream of the primary catalytic burner 50 for catalytically oxidizing fuel which may not have been oxidized by the primary burner.

The operation of the device described thusfar is as follows. When shutoff valve 44 is opened, a metered amount of fuel drips into air/fuel mixing section 30.

At least a portion of this fuel will vaporize, mix with air in the mixing section and be communicated to primary burner 50. Assuming the temperature of the mixture is above the auto ignition temperature of the catalyst, the mixture will oxidize and release heat to surrounding gases and the burner. The burner will transfer heat to the duct wall of tube 16 which in turn will transfer heat to ambient air. The heated products of combustion will rise and pass through secondary burner 52 where any unburnt gases will be oxidized. The combustion products will continue to rise, enter the exhaust section and ultimately emerge from the tube through exhaust opening 54. The upward flow of gases in arm 16 of tube 12 thus initiates a natural flow or draft through the tube. As the temperature within the combustion section increases and approaches normal operating temperature, heat will be conducted upstream of passage 24 into the air/fuel mixing section resulting in more efficient vaporization of the fuel and mixing of fuel and air.

Tube 12 is preferably made of thin-walled aluminum, although other materials may be used if desired. While tubular arms 14 and 16 may be of any desired shape, arm 14 and connecting portion 18 are preferably made of square 7- tubing stock and arm 16 is preferably made of round stock. The square stock is preferred because, for the construction shown, it is easier to manufacture tubes 14 and 18 from square stock. On the other, as explained more fully latter, circular stock is preferred for tube 16 because of the construction of the burner elements and their relationship with the tube wall.

The U-shaped burner body offers a number of benefits. Liquid fuels, such as alcohols, must be vaporized before burning. The U-shaped tube allows heat from combustion to be fed back, by conduction, to the mixing section to vaporize the fuel. The U-shaped tube is forgiving in this respect in that it allows a puddle of fuel to form in the connecting portion at the base of the tube during start-up conditions. In addition, to some extent, the configuration allows a mixture to be formed prior to contact with the catalyst, in contrast to other designs where reactants first meet in the combustion zone. This pre-mixing improves combustion. The U-shaped configuration also acts as a safety device in the event that combustion is prevented. If, for some reason, the combustion duct is plugged, the burner will simply flood to the level of the fuel reservoir, provided that the reservoir is below the elevated inlet and outlet openings. Thus, fuel is not spilled to create a safety hazard. The U-shaped tube also improves start- up.

Methanol-air mixtures are heavier than air. When starting, a combustible mixture is formed naturally and is retained in the duct. Notwithstanding these benefits, it is to be understood that the present invention is not strictly limited to a U-shaped burner design and that the advantages of other aspects of the invention may be realized with different burner configurations.

Prior art catalytic burners typically operate in an open environment and thus may experience excessively high temperatures. It is known that temperatures in excess of about 500'C significantly reduce the longevity of some catalytic burners. To avoid this problem, the primary burner of the present invention is placed in physical contact with the tube wall so that the tube wall functions as a heat sink and prevents overheating of the burner. This arrangement serves as one form of temperature control.

The operating temperature of the heater may also be controlled by periodically temporarily discontinuing fuel flow. This may be achieved by providing a needle valve 60 in fuel port 38 and a temperature responsive actuating device 62, such as a bi-metal thermostat, connected to the needle valve by any suitable linkage 64, as shown in FIGURE 5. The thermostat may be positioned at any convenient location adjacent arm 16 of the tube. Thus, when the temperature sensed by the thermostat exceeds a predetermined value, which will vary with the application in which the heater is used, the thermostat will close the needle and terminate fuel flow. As a result, only fresh, relatively cool air will flow through passage 24 passed primary burner 50. The burner will cool because of the lower air temperature and because there will be no fuel to react with the catalyst. Once the temperature has reached a predetermined minimum value, the thermostat will retract and open the needle valve and allow fuel to flow into the mixing chamber. It will be understood that fuel flow may not be fully ON or fully OFF. Temperature control may also be achieved by reducing or increasing the flow.

There are situations, cold conditions for example, in which it is preferable not to shut down the heater completely but keep it operating at a minimum temperature. To facilitate this in the embodiment of FIGURE 1, shut-off valve 44 may be left partially open to allow enough fuel to drip into passage 24 to sustain combustion. In the embodiment of FIGURE 5, there may be provided, as shown in FIGURE 7, a fuel line 66 which bypasses the thermostatic valve 62 and connects to a second fuel port 68. Line 66 would also be provided with an appropriate restrictor 69.

Turning now to FIGURE 2 of the drawings, primary catalytic burner 50 will be seen to comprise a fine mesh metallic, preferably stainless steel, screen 70 having a coating of a suitable catalyst material such as a noble metal, preferably platinum washcoated onto the screen, and a thin metallic, preferably stainless steel, sheet 72 of substantially the same size as the screen and fixedly secured to the screen by spot welding. The screen and sheet are rolled into a cylindrical shape, with sheet 72 on the outside, and inserted into the exhaust opening of arm 16 of the tube to the position shown in FIGURE I of the drawings. The natural resilience of the thus formed tubular primary burner urges stainless steel sheet 72 into intimate heat conducting contact with an inner surface of the tube. Sheet 72 serves as a heat sink to keep the operating temperature of the burner within predetermined limits. In order to maximize the heat transfer area between the burner and the tube, arm 16 is in the form of a cylindrical tube.

Wi.th a view of maximizing the combustion efficiency of the burner, the primary burner may be provided with a stirring element 76 for urging the air/fuel mixture into intimate contact with the inner surface of burner. Element 76 is a thin rectangular body disposed within the primary burner and has a width which is slightly less than the inner diameter of the burner and a length which is substantially the same as that of the burner. The strip is twisted about its long axis between about a 1/2 turn and a full turn. The air/fuel mixture enters the burner axially. As it moves through the burner, the stirring element urges the mixture radially outwardly toward the inner surface of the burner, into contact with the catalyst material. The stirring element may be coated with a catalyst material if desired. However, this is not essential in order to achieve complete combustion of the vapour or the optimum operating temperature.

With reference to FIGURES 3 and 4, secondary catalytic burner 52 will be seen to be formed with a plurality of parallel axial fluid flow passages 80 washcoated with a catalyst material. Passages 80 provide a relatively large surface area for catalytic combustion, so as to maximize the possibility of achieving complete combustion of the air/fuel mixture entering the combustion chamber, without substantially increasing the pressure drop across the secondary burner.

As best shown in FIGURE 4, secondary burner 52 is iD the form of a lamination of a flat stainless steel sheet 84 and a corrugated stainless steel sheet 86 secured to the flat metallic sheet and rolled into a spiral about an axis paralleling the corrugations of the corrugated metallic sheet to a diameter corresponding to in the inner diameter of tube arm 16. The burner is inserted into exhaust opening 54 and slid to the position shown in FIGURE 1 where it is held by friction.

Various means may be provided to facilitate start-up of the catalyst in temperatures below the self or auto ignition temperature of the catalyst, typically O'C. Conveniently, the primary catalytic element may be preheated by contacting the outside of the duct with a temporary flame, which will consume fuel held in a wick 88 in close proximity to the duct. Since the mesh supporting the catalyst is electrically conductive, another way of preheating the element to a suitable temperature is to pass an electric current through the duct. Still another means of preheating is to employ a separate electrical heater of conventional design.

FIGURE 6 illustrates a alternative embodiment 100 of the present invention. The primary differences between this embodiment and the embodiment of FIGURE 1 is that the body 102 is not U-shaped. Body 102 includes a fuel reservoir 104 which contains wicking material 106 and which is formed with a plurality of air inlet openings 107 in its upper wall 108.. A tube 110 extends from the upper surface of the reservoir 104 and communicates therewith.

The tube is identical in construction with arm 16 of the U-shaped embodiment and includes a primary catalytic burner 112, stirring element 114 and a secondary catalytic burner 118 which operate in the same manner as the earlier version. A butterfly valve 120 is provided at the outlet end 122 of the tube to control the flow of combustion gases.

It will be understood that various modifications and alterations may be made to the device described herein without departing from the spirit of the appended claims.

t

Claims

CLAIMS 1. A natural draft, flameless, catalytic heater comprising: a

tubular body defining an elongated fluid flow passage having an air/fuel mixture inlet at one end thereof and a combustion product outlet at the other end thereof; a primary catalytic burner disposed within said passage adjacent said inlet for reacting most of the airlfuel mixture introduced into said inlet; and a secondary catalytic burner disposed within said passage downstream of said primary catalytic burner for completing combustion of any unburnt fuel in the fluid exhausted from said primary catalytic burner.
2. A heater as defined in Claim 1, said primary catalytic burner including a fine mesh metallic screen having a catalyst coating thereon, said screen being in intimate heat conducting contact with an inner surface of said body.
3. A heater as defined in Claim 2, said primary catalytic burner further including a thin metallic sheet of substantially the same size as said screen and fixedly secured to said screen, said sheet being interposed between said screen and said inner surface of said body.
4. A heater as defined in Claim 2, further including means for controlling the temperature of said primary catalytic burner.
5. A heater as defined in Claim 4, said temperature controlling means being a heat sink fixedly secured to said screen.

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6. A heater as defined in claim 5, said temperature controlling means including a thin metallic sheet of substantially the same size as said screen and fixedly secured to said screen, said sheet being interposed between said screen and said inner surface of said body.
7. A heater as defined in claim 1, said secondary catalytic burner having a plurality of parallel a.-dal fluid flow passages, said a)dal passages being coated with a catalyst material whereby to provide a relatively large surface area for catalytic combustion without substantially increasing the pressure drop across said secondary catalytic burner.
8. A heater as defined in claim 7, said secondary catalytic burner comprising a lamination of a flat fine mesh metallic screen having a catalyst coating thereon and a corrugated sheet secured to said screen, said lamination being rolled about an axis paralleling the corrugations in said corrugated sheet to a diameter corresponding to the inner dimension of said elongated fluid flow passage so as to define said plurality of axial passages.
9. A heater as defined in claim 1, further including means disposed within said elongated flow passage for urging said air/fuel mixture into intimate contact with said primary catalytic burner.
10. A heater as defined in claim 9, said means for urging comprising a thin rectangular body disposed within said primary catalytic bumer, said thin body having a width which is slightly less than the internal Pimension of said primary catalytic burner and a length which is substantially the same as that of said primary catalytic burner, said strip being helically twisted about its long axis between about 1/2 turn and a full turn.
i i 11. A heater as defined in claim 4, said elongated passage further including a mixing section for forming said air/fuel mixture, said mixing section being downstream of said inlet and upstream of said primary catalytic burner and having a fuel port for receiving a liquid fuel from a liquid fuel reservoir.
12. A heater as defined in claim 11, said temperature control means including means for controlling the flow of liquid fuel from said fuel port.
13. A heater as defined in claim 12, said temperature control means comprising a fuel reservoir, a fuel line connecting said reservoir and said fuel port, a flow restrictor in said line for limiting the flow of fuel to said fuel port, a needle valve for opening and closing said fuel port and a thermostatic element connected to said needle valve for closing said valve when the combustion temperature exceeds a predetermined upper temperature limit and for opening said valve when said combustion temperature drops below a predetermined lower temperature limit.
14. A heater as defined in claim 1, further including means for initiating catalytic combustion of said air/fuel mixture when the ambient temperature is below the automatic ignition temperature of said primary catalytic burner.
15. A heater as defined in claim 14, said means for initiating comprising a wick disposed about the exterior of said combustion section of said tube for receiving a supply of liquid fuel whereby said fuel may be ignited by an open flame and burnt in the vicinity of said primary catalytic burner so as to raise the temperature within said combustion section above said automatic ignition temperature of said catalyst.
16. A heater as defined in claim 1, said elongated passage further including an air and fuel mixing section between said inlet and said primary catalytic burner for forming an said airlfuel mixture, said mixing section having a fuel port for receiving liquid fuel from a liquid fuel reservoir, said mixing section being proximate said primary catalytic burner whereby heat generated by said burner is communicated upstream to said mixing section and causes vaporization of said fuel and mixing of vaporized fuel with air entering said inlet.
17. A heater as defined in claim 16, said inlet being at a higher elevation than said fuel port to prevent spillage of fuel if said elongated passage is blocked and catalytic combustion ceases.
18. A heater as defined in claim 16, said,body being a U-shaped tube having a pair of parallel arms and connecting portion joining adjacent ends of said arms, said pair of arms and said connecting portion defining said elongated fluid flow passage, one of said arms defining said inlet and including at least a portion of said mixing section and the other of said arms housing said primary catalytic bumer and said secondary catalytic burner.

A - is-
19. A natural draft, flameless, catalytic heater comprising: a generally U-shaped tubular body defining an elongated fluid flow passage, said tubular body having a pair of parallel arms and a connecting portion joining adjacent ends of said arms, said fluid flow passage having an air inlet section in a free end of one of said arms, an air/fuel mixing section downstream of said inlet section for forming a vaporized air/fuel mixture, said mixing section having a fuel port for receiving a supply of liquid fuel, an air/fuel combustion section in the other of said arms for receiving and oxidizing an air/fuel mixture from said mixing section and a combustion product exhaust section in a free end of the other of said arms; a primary catalytic burner disposed within said combustion section for catalytically reacting a major portion of the air/fuel mixture delivered thereto by said mixing section, said primary catalytic burner including a fine mesh metallic screen having a catalyst material coating thereon and a thin metallic sheet of substantially the same size as said screen and fixedly secured to said screen, said sheet being in intimate heat conducting contact with an inner surface of said body whereby to transfer heat to said body which, in turn, radiates heat to ambient air; a secondary catalytic burner disposed within said combustion section downstream of said primary catalytic burner for completing combustion of any unburnt fuel in the fluid exhausted from said primary catalytic burner, said secondary catalytic burner having a plurality of parallel axial fluid flow passages, said axial passages being coated with a catalyst material whereby to provide a relatively large surface area for catalytic combustion without substantially increasing burner; a liquid fuel reservoir; a fuel line connecting said fuel reservoir and said fuel port and a flow restrictor in said fuel line for limiting the flow of fuel to said port.

the pressure drop across said secondary catalytic
20. A heater as defined in claim 19, said secondary catalytic burner comprising a lamination of a flat fine mesh metallic screen having a catalyst coating thereon and a corrugated sheet secured to said screen, said lamination being rolled about an axis paralleling the corrugations in said corrugated sheet to a diameter corresponding to the inner dimension of said elongated fluid flow passage so as to define said plurality of axial passages.
21. A heater as defined in claim 19, further including means disposed within said elongated flow passage for urging said airlfuel mixture into intimate contact with said primary catalytic burner.
22. A heater as defined in claim 21, said means for urging comprising a thin rectangular body disposed within said primary catalytic burner, said thin body having a width which is slightly less than the internal dimension of said primary catalytic burner and a length which is substantially the same as that of said primary catalytic burner, said strip being twisted about its long aids between about 112 turn and a full turn.
23. A heater as defined in claim 19, further including means for controlling the temperature of said primary catalytic burner.
24. A beater as defined in claim 23, said temperature control means including means for controlling the flow of liquid fuel to said fuel port.
25. A heater as defined in claim 24, said temperature control means including a needle valve for opening and closing said fuel port and a thermostatic element connected to said needle valve for closing said needle valve when the combustion temperature exceeds a predetermined upper temperature limit and for opening said valve when said combustion temperature drops below a predetermined lower temperature limit.
26. A heater as defined in claim 19, further including means for initiating catalytic combustion of said air/fuel mixture when the ambient temperature is below the automatic ignition temperature of said primary catalytic burner.
27. A heater as defined in claim 26, said means for initiating comprising a wick disposed about the exterior of said combustion section of said tube for receiving a supply of liquid fuel whereby said fuel may be ignited by an open flame and burn in the vicinity of said primary catalytic burner so as to raise the temperature within said combustion section above said automatic ignition temperature of said catalyst.
28. A natural draft, flameless, catalytic heater comprising:

a generally U-shaped tubular body defining an elongated fluid flow passage, said tubular body having a pair of parallel arms and a connecting portion joining adjacent ends of said arms, said fluid flow passage having an air inlet section in a free end of one of said arms, an air/fuel mixing section downstream of said inlet section for forming a vaporized air/fuel mixture, said mixing section having a fuel port for receiving a supply of liquid futl, an air/fuel combustion section in the other of said arms for receiving and oxidizing an air/fuel mixture from said mixing section and a combustion product exhaust section in a free end of the other of said arms; a primary catalytic burner disposed within said combustion section for catalytically reacting most of the air/fuel mixture delivered thereto by said mixing section, said primary catalytic burner including a metallic fine mesh screen having a catalyst coating thereon and a thin metallic sheet of substantially the same size as said screen and fixedly secured to said screen, said sheet being in intimate heat conducting contact with an inner surface of said body whereby to transfer heat to said body which, in turn, radiates heat to ambient air, means disposed within said elongated flow passage for urging said air/fuel mixture into intimate contact with said primary catalytic burner, said means for urging comprising a thin rectangular body disposed within said primary catalytic burner, said thin body having a width which is slightly less than the internal dimension of said primary catalytic burner and a length which is substantially the same as that of said primary catalytic burner, said strip being twisted about its long axis between about 1/2 turn and a full turn; a secondary catalytic burner disposed within said combustion section downstream of said primary catalytic bumer for completing combustion of any unburnt fuel in the fluid exhausted from said primary catalytic bumer, said secondary catalytic burner having a plurality of parallel axial fluid flow passages, said axial passages being coated with a catalyst material whereby to provide a relatively large surface area for catalytic combustion without 0 t substantially increasing the pressure drop across said secondary catalytic burner, said secondary catalytic burner comprising a lamination of a flat fine mesh metallic screen having a catalyst coating thereon and a corrugated sheet secured to said screen, said lamination being rolled about an axis paralleling the corrugations in said corrugated sheet to a diameter corresponding to the inner dimension of said elongated fluid flow passage so as to define said plurality of axial passages; a liquid fuel reservoir; a fuel line connecting said fuel reservoir and said fuel port, a flow restrictor in said fuel line for limiting the flow of fuel to said port; means for controlling the temperature of said primary catalytic burner, said temperature control means including a needle valve for opening and closing said fuel port and a thermostatic element connected to said needle valve for closing said needle valve when the combustion temperature exceeds a predetermined upper temperature limit and for opening said valve when said combustion temperature drops below a predetermined lower temperature limit; and means for initiating catalytic combustion of said air/fuel mixture when the ambient temperature is below the automatic ignition temperature of said primary catalytic burner, said means for initiating comprising a wick disposed about the exterior of said combustion section of said tube for receiving a supply of liquid fuel whereby said fuel may be ignited by an open flame and burn in the vicinity of said primary catalytic bumer so as to raise the temperature within said combustion section above said automatic ignition temperature of said catalyst.
29. A natural draft, flameless, catalytic heater comprising: a generally U-shaped tubular body defining an elongated fluid flow passage, said tubular body having a pair of parallel arms and connecting portion joining adjacent ends of said arms, said fluid flow passage having an air inlet section in a free end of one of said arms, an air/fuel mixing section downstream of said inlet section for forming a vaporized air/fuel mixture, said mixing section having a fuel port for receiving a supply of liquid fuel, an air/fuel combustion section in the other of said arms for receiving and oxidizing an air/fuel mixture from said mixing section and a combustion product exhaust section in a free end of the other of said arms; and a tubular catalytic burner disposed within said combustion section for catalytically reacting the air/fuel mixture delivered thereto by said mixing section, said catalytic burner being in intimate heat conducting contact with an inner surface of said body whereby to transfer heat to said body which, in turn, radiates heat to ambient air.
30. A heater as defined in claim 29, said catalytic burner including including a metallic fine mesh screen having a catalyst coating thereon and a thin metallic sheet of substantially the same size as said screen and fixedly secured to said screen.
31. A heater as defined in claim 30, further including liquid fuel reservoir, a fuel line connecting said fuel reservoir and said fuel port and a flow restrictor in said fuel line for limiting the flow of fuel to said port.
32. A heater as defined in claim 30, further including a secondary catalytic burner disposed within said combustion section downstream of said primary catalytic burner for completing combustion of any unburnt fuel in the fluid exhausted from said primary catalytic burner and for controlling the exhaust temperature of fluid to prevent condensation from occurring within said passage, said secondary catalytic burner having a plurality of parallel axial fluid flow 1 V 1 1 passages, said axial passages being coated with a catalyst material whereby to provide a relatively large surface area for catalytic combustion without substantially increasing the pressure drop across said secondary catalytic burner.
33. A heater as defined in claim 32, said secondary catalytic burner comprising a lamination of a flat metallic sheet and a corrugated metallic sheet secured to said flat metallic sheet, said lamination being rolled about an axis paralleling the corrugations in said corrugated metallic sheet to a diameter corresponding to the inner dimension of said elongated fluid flow passage so as to define said plurality of axial passages.
34. A heater as defined in claim 29, further including means disposed within said elongated flow passage for urging said air/fuel mixture into intimate contact with said primary catalytic burner.
35. A heater as defined in claim 34, said means for urging comprising a thin rectangular body disposed within said primary catalytic burner, said thin body having a width which is slightly less than the internal dimension of said primary catalytic burner and a length which is substantially the same as that of said primary catalytic burner, said strip being twisted about its long axis between about 1/2 turn and a full turn.
36. A heater as defined in claim 29, further including means for controlling the temperature of said primary catalytic burner.
37. A heater as defined in claim 36, said temperature control means including means for controlling the flow of liquid fuel to said fuel port.
38. A heater as defined in claim 37, said temperature control means including a needle valve for opening and closing said fuel port and a thermostatic element connected to said needle valve for closing said needle valve when the combustion temperature exceeds a predetermined upper temperature limit and for opening said valve when said combustion temperature drops below a predetermined lower temperature limit.
39. A heater as defined in claim 29, further including means for initiating catalytic combustion of said airlfuel mixture when the ambient temperature is below the automatic ignition temperature of said primary catalytic burner.
40. A heater as defined in claim 39, said means for initiating comprising a wick disposed about the exterior of said combustion section of said tube for receiving a supply of liquid fuel whereby said fuel may be ignited by an open flame and burn in the vicinity of said primary catalytic burner so as to raise the temperature within said combustion section above said automatic ignition temperature of said catalyst.

Published 1991 at The Patent Office. Concept House. Cardiff Road, Newport. Gwent NP9 I RH. Further copies may be obtained from Sales Branch. Unit 6, Nine Mile Point, Cvnnfelinfach, Cross Keys. Newport. NP 1 7HZ. Printed by Multiplex techniques lid. St Mary Cray, Kent.