GB2249491A

GB2249491A - A catalytic heating element

Info

Publication number: GB2249491A
Application number: GB9123391A
Authority: GB
Inventors: John Andrew Sullivan
Original assignee: ADVANCED CERAMICS Ltd
Current assignee: ADVANCED CERAMICS Ltd
Priority date: 1990-11-06
Filing date: 1991-11-04
Publication date: 1992-05-13
Also published as: GB9123391D0; IE903998A1; ZA918780B

Abstract

A space heater (1) comprises a main housing (2) within which a gas dispersing housing (25) is mounted. A support member (44) of porous refractory material supports a catalytic heating element (26) in the dispersing housing (25) for converting gas to heat. The catalytic heating element (26) comprises a main catalyst element (60) with a high ignition and operating temperature and a plurality of secondary catalyst elements (61) with a low ignition temperature. A resistance wire heating element (65) ignites the secondary catalyst elements (61) whose operating temperature is greater than the ignition temperature of the main catalyst element (60) and in turn the secondary catalyst elements (61) ignite the main catalyst element (60). <IMAGE>

Description

"A Catalytic Heating Element" The present invention relates to a catalytic heating element, and in particular though not limited to a catalytic heating element for use in a gas powered space heater. The invention also relates to the gas powered space heater comprising the catalytic heating element.

Gas powered space heaters, in general, comprise a housing, and a catalytic heating element for converting gas to heat is mounted in the housing.

The catalytic heating element is normally porous to allow gas to pass therethrough. The gas is converted into heat on coming into contact with a catalyst in the catalytic heating element. Such catalytic heating element, in general, comprise a sheet of carrier matting, which is generally a fibrous material which carries a catalyst. An ignition means, for example, a pilot light, a flint and wheel or an electrically powered heating element is provided adjacent the catalytic heating element for bringing the catalytic heating element up to the ignition temperature so that the catalytic heating element can then operate to convert gas to heat.

Such gas powered space heaters are particularly suited to heating hazardous environments, for example, areas where there is a relatively high risk of fire or explosion. While these heaters are relatively safe once the entire catalytic heating element is operational, problems can arise at start up of such heaters. Two problems in particular arise at start up. Firstly, gas slippage may arise, while the catalytic heating element is being brought up to its ignition temperature. Gas slippage is the phenomena whereby unburnt gas passes through the catalytic heating element. A second problem is caused by the ignition means used for igniting the catalytic heating element in the first instance. If the temperature of the ignition means exceeds certain relatively low limits explosion or fire may occur in a hazardous environment.For example, if the ignition means for igniting the catalytic heating element is a spark, such a spark could cause an explosion in a hazardous environment. Even where a hot wire electrically powered heating element is used, great care has to be taken to ensure that the temperature of the electrical heating element, while being raised to the ignition temperature of the catalytic heating element does not exceed the flash point of chemicals which could exist in a hazardous environment. To overcome the latter problem, where an electrically powered heating element is used, the temperature of the heating element is generally kept relatively low. However, this results in relatively long preheat times, in other words, the time necessary to raise the temperature of the catalytic heating element to its ignition temperature. In many cases preheat times of twenty to thirty minutes are common.During the preheating, it is essential that the supply rate of gas to the catalytic heating element is controlled within very fine limits to avoid slippage. This, it will be appreciated, leads to a considerable number of disadvantages. It is clearly a major disadvantage to have a long preheat time, particularly in cases where heat is instantly or relatively instantly required. Further, significant costs are incurred in providing suitable control apparatus to control the supply rate of gas to the catalytic heating element during preheat.

Indeed, as well as requiring control apparatus, monitoring devices are also required for monitoring the temperature of the catalytic heating element and the rate of gas flow. This further adds to the cost and complexity of such devices.

There is therefore a need for a gas powered space heater which overcomes these problems. There is also a need for a catalytic heating element which likewise overcomes the problems.

The present invention is directed towards providing a catalytic heating element as well as a gas powered space heater.

According to the invention, there is provided a catalytic heating element comprising a first catalyst element, and a second catalyst element in close proximity to the first catalyst element, the first and second catalyst elements having respective ignition temperatures and respective operating temperatures, the ignition temperature of the second catalyst element being lower than the ignition temperature of the first catalyst element, and the operating temperature of the second catalyst element being sufficient to ignite the first catalyst element.

In one embodiment of the invention the operating temperature of the second catalyst element is at least equal to the ignition temperature of the first catalyst element.

Preferably, the operating temperature of the second catalyst element is higher than the ignition temperature of the first catalyst element.

Preferably, the operating temperature of the second catalyst element is at least 100C higher than the ignition temperature of the first catalyst element.

In one embodiment of the invention the ignition temperature of the second catalyst element is in the range of 500C to 2000C.

Preferably, the ignition temperature of the second catalyst element is in the range of 1000C to 1750C.

Advantageously, the ignition temperature of the second catalyst element is approximately 150 C.

In another embodiment of the invention the ignition temperature of the first catalyst element is in the range of 2000C to 3000C.

Preferably, the ignition temperature of the first catalyst element is in the range of 2250C to 2750C.

Advantageously, the ignition temperature of the first catalyst element is approximately 2500C.

In a further embodiment of the invention the operating temperature of the first catalyst element is in the range of 5000C to 8000C.

Advantageously, the operating temperature of the first catalyst element is in the range of 6000C to 7000C.

In an other embodiment of the invention the first catalyst element is in sheet form, and a plurality of second catalyst elements are providing at spaced apart locations over the surface of the first catalyst element.

In another embodiment of the invention the second catalyst element is provided in sheet form, the area of each second catalyst element being less than the area of the first catalyst element.

Advantageously, the area of each second catalyst element is approximately 600my2.

Preferably, the number of second catalyst elements per square metre of the first catalyst element does not exceed 25.

In a further embodiment of the invention ignition means is provided in close proximity to each second catalyst element for ignition thereof.

Preferably, the ignition means comprises an electrically powered heating element having an operating temperature of not less than 500C.

Advantageously, the operating temperature of the electrically powered heating element is not greater than 4000C.

Preferably, the operating temperature of the electrically powered heating element is not greater than 2200C.

In one embodiment of the invention the electrically powered heating element comprises an elongated resistance wire extending over at least portion of the surface of the first catalyst element, the second catalyst elements being spaced apart at intervals along the resistance wire.

Additionally, the invention provides a space heater comprising the catalytic heating element according to the invention, a support means for supporting the catalytic heating element, gas dispersing means for dispersing gas through the first and second catalyst elements, and means for delivering gas to the dispersing means.

In another embodiment of the invention the dispersing means comprises a dispersing housing defining a dispersing chamber and an open mouth to the dispersing chamber, the support means being mounted in the open mouth for supporting the catalytic heating element therein.

In another embodiment of the invention the support means comprises a support member of porous refractory material, the support member substantially closing the open mouth of the dispersing housing, and the catalytic heating element being provided on the downstream side of the support member.

Preferably, the second catalyst element is provided on the upstream side of the first catalyst element and the electrically powered heating element is provided on the upstream side of the first catalyst element.

Advantageously, the second catalyst element is provided between the first catalyst element and the support means.

In a further embodiment of the invention air delivery means is provided for delivering air across the downstream surface of the first catalyst element.

Preferably, the air delivery means comprises a motor driven fan.

Advantageously, the space heater comprises a main housing defining a hollow interior region for accommodating the dispersing housing, the main housing and the dispersing housing defining an annular opening for directing air across the downstream surface of the first catalyst element.

The invention will be more clearly understood from the following description of a preferred embodiment thereof, given by way of example only, with reference to the accompanying drawings, in which: Fig. 1 is a front perspective view of a space heater according to the invention, Fig. 2 is a rear perspective view of the space heater of Fig. 1, Fig. 3 is a side elevational view of the space heater of Fig. 1, Fig. 4 is a top plan view of the space heater of Fig. 1, Fig. 5 is a rear elevational view of the space heater of Fig. 1, Fig. 6 is a cross sectional view of the space heater of Fig. 1 on the line VI-VI of Fig. 5, Fig. 7 is an exploded perspective view of portion of the space heater of Fig. 1, Fig. 8 is a rear elevational view of another portion of the space heater.of Fig. 1, and Fig. 9 is a perspective view of a detail of the space heater of Fig. 1.

Referring to the drawings, there is illustrated a gas powered space heater according to the invention indicated generally by the reference numeral 1. The gas powered space heater 1 is particularly suitable for use in a hazardous environment. The heater 1 comprises a main housing 2 of fibre glass material comprising a rear wall 4, and top and bottom walls 5 and 6 and side walls 7 and 8, respectively, diverging outwardly from the rear wall 4 and defining with the rear wall 4 a hollow interior region 10. A main frame 12 comprising a top cross member 14 and a bottom cross member 15 joined by side members 16 and 17 is secured to the main housing 2 and defines an open mouth 19 to the hollow interior region 10. The cross members 14 and 15 and the side members 16 and 17 are of stainless steel formed by bending and are welded together.A rear flange 20 extending rearwardly from the main frame 12 is secured to the top and bottom walls 5 and 6 and the side walls 7 and 8 of the main housing 2 by screws 22.

A gas dispersing means comprising a gas dispersing housing 25 housing a gas catalytic heating element 26 also according to the invention is mounted in the hollow interior region 10 of the main housing 2 adjacent the open mouth 19. The gas catalytic heating element 26 is described in detail below.

The dispersing housing 25 is of sheet steel material formed by bending and comprises a rear wall 28 and top and bottom walls 29 and 30 joined by side walls 31 and 32, respectively, all extending from the rear wall 28. A flange 34 extends outwardly of and along the top and bottom walls 29 and 30 and side walls 31 and 32 and is secured to the main frame 12 by screws 35 as will be described below. The dispersing housing 25 defines a gas dispersing chamber 36 within which the catalytic heating element 26 is mounted, and which delivers and disperses gas to the catalytic heating element 26. Gas is delivered into the dispersing chamber 36 through an inlet 37 in the rear wall 28 through a conduit 39 and a controller 40 The controller 40 controls the supply of, and regulates the pressure at which gas is supplied into the dispersing chamber 36.An inlet connector 41 extends from the controller 40 through the rear wall 4 of the main housing 2 for connecting to a remote supply of gas.

A support means comprising a support member 44 is mounted in the dispersing chamber 36 for supporting and diffusing gas through the catalytic heating element 26. An inwardly directed flange 45 extending from the top and bottom walls 29 and 30 and side walls 31 and 32 of the dispersing housing 25 locates and retains the support member 44 in the dispersing chamber 36. The support member 44 is formed by a sheet of porous refractory material which extends over the entire cross section of the area of the gas dispersing chamber 36. Gas in the dispersing chamber 36 passes through the support member 44 and is diffused through a downstream surface 46 of the support member 44 into the catalytic heating element 26, which is mounted on the downstream side of the support member 44. A sheet of wire gauze material 48 extends across the dispersing housing 25 and retains the catalytic heating element 26 in abutting engagement with the support member 44. The gauze 48 overlays the flange 34 and is secured thereto by an intermediate frame 49 which clamps the gauze 48 in position against the flange 34. The screws 35 retain the frame 49, the gauze 48 and the flange 34 together as will be described below. Bars 50 welded to the top and bottom cross members 14 and 15 of the main frame 12 support the gauze 48.

Spacers 52 on the screws 35 space the intermediate frame 49 from the main frame 12 to form a substantially annular outlet from the hollow interior region 10 from which air is delivered across the open mouth 19 and in turn across the catalytic heating element 26. A motor driven fan 54 mounted in an inlet housing 55 on the rear wall 4 of the main housing 2 delivers air through the hollow interior region 10 of the main housing 2 and in turn through the annular outlet 53. Air is drawn through an opening 56 in the rear wall 4 of the main housing 2 through the inlet housing 55. A grill 57 closes the opening 56. A cable socket 58 is mounted in the rear wall 4 of the main housing 2 for delivering power to the motor driven fan 54.

Returning now to the catalytic heating element 26, the catalytic heating element 26 comprises a first catalyst element, namely, a main catalyst element 60 and a plurality of second catalyst element namely, secondary catalyst elements 61 arranged at spaced apart locations in close proximity to the main catalyst element 60 for igniting the main catalyst element 60. The main catalyst element 60 is of sheet form and comprises a carrier mat of fibrous material, namely, SAFFIL. The carrier mat carries a catalyst, in this case, a precious metal, namely, platinum. The secondary catalyst elements 61 are also of sheet form and comprise a carrier mat also of fibrous material, in this case, SAFFIL. The carrier mats of the secondary catalyst elements carry a catalyst, in this embodiment of the invention platinum.The ignition temperature of the main catalyst element 60 is approximately 2500C and its operating temperature is between 6000C and 7000C. The ignition temperature of each secondary catalyst element 61 is approximately 1500C, and the operating temperature of each secondary catalyst element 61 is sufficient to ignite the main catalyst 60. In this case, the operating temperature of the secondary catalyst elements 61 is similar to the main catalyst element 60. Accordingly, on the temperature of the secondary catalyst elements 61 exceeding 2500C, the main catalyst element 60 is ignited.

Ignition means for igniting the secondary catalyst elements 61 comprises an electrically powered heating element, namely, a resistance wire heating element 65 which extends over a substantial portion of the surface of the main catalyst element 60. The secondary catalyst elements 61 are wrapped around the resistance wire heating element 65 at spaced apart intervals along the resistance wire heating element 65. The resistance wire heating element 65 terminates in terminals 66 and 67 which extends through the dispersing housing 25 for connection to a 24 volt supply derived from a power supply (not shown) mounted in a sub-housing 68 on the top wall 4 of the main housing 2. The power supply (not shown) is powered from the socket 58.The resistance and the length of the resistance wire heating element 65 is such that the temperature of the wire element 65 never exceeds 4000C in free air when fed with a voltage of between 1 and 24 volts. In this embodiment of the invention the resistance wire heating element is fed with a 12 volt DC supply.

The 12 volt DC supply raises the temperature of the resistance wire heating element 65 rapidly to approximately 2000C which rapidly ignites the secondary catalyst elements 61.

In this embodiment of the invention the mat of the secondary catalyst elements 61 are highly loaded with platinum in order to provide the relatively low ignition temperature. The secondary catalyst elements 61 are fifteen second catalyst elements, in other words, they reach operating temperature in 15 seconds from ignition. The area of each secondary catalyst element 61 is less than the area of the main catalyst element 60 in this case the area of each secondary catalyst element 61 is of the order of 600mm2.

The catalytic heating element 26 is mounted in the dispersing chamber 36 against the downstream surface 46 of the support member 44. The secondary catalyst elements 61 are provided on the upstream side of the main catalyst element 60, and accordingly, the secondary catalyst elements 61 and the resistance wire heating element 65 are effectively sandwiched between the main catalyst element 60 and the support member 44.

A temperature sensor 69 is mounted in the dispersing housing 25 and extends through the dispersing chamber 36 and the support member 44 to engage the main catalyst element 60 for monitoring the temperature of the main catalyst element 60 to determine the presence or absence of combustion.

Suitable control circuitry (not shown) housed in the sub-housing 68 operates the controller 40 to control the supply of gas to the dispersing chamber 36 in response to the sensor 69. The control circuitry (not shown) comprises time delays (not shown) and other suitable interlocks (not shown) for preventing the controller 40 switching off the supply of gas during the ignition phase of the catalytic heating element 26.

Neon indicator lights 72 in the main frame 12 indicate the operating status of the heater 1.

The top wall 5, bottom wall 6 and side walls 7 and 8 of the main housing 2 extend from the rear wall 4 at an angle of approximately 450. Accordingly, the heater 1 may be mounted on a vertical wall of a building by the bottom wall 6 of the main housing 2, with the bottom wall 6 flush against the vertical wall. In which case, the surface of the gauze 48, and in turn, the main catalyst heating element 60 is at an angle of approximately 450 to the horizontal.

Thus, heat is directed outwardly, downwardly from the heater 1 into the space to be heated below. It has been found that 450 is the optimum angle for mounting such heaters on a wall. Furthermore, by virtue of the fact that the side walls 7 and 8 are also provided at 450 to the rear wall 4, a pair of heaters 1 can be mounted together by joining adjacent side walls 7 and 8 of adjacent heaters 1.

In which case, the surfaces of the wire gauze 48 of the heaters 1 are at 900 to each other. Other suitable mounting arrangements can be used by virtue of the fact that the top, bottom and side walls 5 to 8 are angled at approximately 450 to the rear wall 4. Such angled positions will be readily apparent to those skilled in the art.

In use, with the heater 1 mounted in a desired location, electrical power is connected to the socket 58 and a gas supply is connected to the inlet connector 41. To ignite the heater, the resistance wire heating element 65 is powered thus raising the temperature of the resistance wire heating element to approximately 2000C. This heats a portion of the secondary catalyst elements 61 adjacent to the wire heating element 65 likewise to approximately 2000C.

Gas is then delivered into the gas dispersing chamber 36 and diffused through the support member 44. The secondary catalyst elements 61 begin to oxidise, thereby burning the gas. The temperature of the secondary catalyst elements quickly rises past the ignition temperature of the main catalyst element 60 to their operating temperature of approximately 6000C within approximately 15 seconds of ignition. This thus raises the temperature of the portions of the main catalyst element 60 adjacent the secondary catalyst elements 61 to the ignition temperature of the main catalyst element 60. At this stage the main catalyst element 60 begins to oxidise, thereby burning the gas. The entire area of the main catalyst element 60 rapidly reaches ignition temperature and shortly thereafter reaches its normal operating temperature of between 6000C and 7000C.

The motor powered fan 54 delivers air across the open mouth 19 over the gauze 48 and in turn over the downstream surface of the main catalyst element 60 to facilitate oxidisation and combustion thereof.

While the catalytic heating element has been described as comprising a main catalyst element and a plurality of secondary catalyst elements, in certain cases, it is envisaged that a single secondary catalyst element may be sufficient. In which case, the secondary catalyst element may be of considerably lesser area than the area of the main catalyst element, or alternatively, in certain cases may cover the entire area of the main catalyst element. It will of course be appreciated that it is not necessary that the main catalyst element, or indeed, the secondary catalyst element be in the form of a sheet. They may be in any other suitable form, and may be of any suitable shape or construction.

It will of course be appreciated that the more secondary catalyst elements that are provided the quicker the main catalyst element will be raised to its ignition temperature, and in turn, the operating temperatures. It will of course be appreciated that while the secondary catalyst elements have been described as being wrapped around the resistance wire heating element, this while it is preferable is not essential. However, it is important that the resistance wire heating element should be provided in close proximity to the secondary catalyst elements. In certain cases, it is envisaged that the resistance wire heating element may merely pass over the surface of the secondary catalyst elements.

It is also envisaged that the resistance wire heating element may be wrapped with the secondary catalyst element. In other words, the secondary catalyst element would be wrapped completely around the resistance wire heating element along the full length of the heating element. This would render the resistance wire heating element safe in free air, and would avoid any danger of the wire heating element igniting flamable liquids or vapours in a hazardous environment. Furthermore, the secondary catalyst elements should be in close proximity to the main catalyst elements.

While the main and secondary catalyst elements have been described as comprising a carrier mat of fibrous material, any other suitable carrier may be provided, however, it is preferable that the carrier should be of a porous material.

While particular catalyst materials have been described, any other suitable catalyst materials may be used. While the main and secondary catalyst elements have been described as having particular ignition and operating temperatures, main and secondary catalyst elements of other ignition and operating temperature may be provided.

While the catalytic heating element according to the invention has been described as being mounted in a space heater, also according to the invention, it will of course be appreciated that the catalytic heating element may be mounted in any other heating device.

Needless to say, while the space heater has been described as being of a particular shape and construction, other shapes and constructions may be provided. It will also be appreciated that other construction of support means for supporting the catalytic heating element may be provided as indeed may other suitable dispersing and defusing means for the gas.

Claims

1. A catalytic heating element comprising a first catalyst element, and a second catalyst element in close proximity to the first catalyst element, the first and second catalyst elements having respective ignition temperatures and respective operating temperatures, the ignition temperature of the second catalyst element being lower than the ignition temperature of the first catalyst element, and the operating temperature of the second catalyst element being sufficient to ignite the first catalyst element.

2. A catalytic heating element as claimed in Claim 1 in which the operating temperature of the second catalyst element is at least equal to the ignition temperature of the first catalyst element.

3 A catalytic element as claimed in Claim 1 or 2 in which the operating temperature of the second catalyst element is higher than the ignition temperature of the first catalyst element.

4. A catalytic heating element as claimed in Claim 3 in which the operating temperature of the second catalyst element is at least 100C higher than the ignition temperature of the first catalyst element.

5. A catalytic heating element as claimed in any preceding Claim in which the ignition temperature of the second catalyst element is in the range of 500C to 2000C.

6. A catalytic heating element as claimed in Claim 5 in which the ignition temperature of the second catalyst element is in the range of 1000C to 1750C.

7. A catalytic heating element as claimed in Claim 6 in which the ignition temperature of the second catalyst element is approximately 1500C.

8. A catalytic heating element as claimed in any preceding Claim in which the ignition temperature of the first catalyst element is in the range of 2000C to 3000C.

9. A catalytic heating element as claimed in Claim 8 in which the ignition temperature of the first catalyst element is in the range of 2250C to 2750C.

10. A catalytic heating element as claimed in Claim 9 in which the ignition temperature of the first catalyst element is approximately 2500C.

11. A catalytic heating element as claimed in any preceding Claim in which the operating temperature of the first catalyst element is in the range of 5000C to 8000C.

12. A catalytic heating element as claimed in Claim 11 in which the operating temperature of the first catalyst element is in the range of 6000C to 7000C.

13. A catalytic heating element as claimed in any preceding Claim in which the firstcatalyst element is in sheet form, and a plurality of second catalyst elements are providing at spaced apart locations over the surface of the first catalyst element.

14. A catalytic heating element as claimed in Claim 13 in which each second catalyst element is provided in sheet form, the area of each second catalyst element being less than the area of the first catalyst element.

15. A catalytic heating element as claimed in Claim 13 or 14 in which the area of each second catalyst element is approximately 600mm2.

16. A catalytic heating element as claimed in any of Claims 13 to 15 in which the number of second catalyst elements per square metre of the first catalyst element does not exceed 25.

17. A catalytic heating element as claimed in any preceding Claim in which ignition means is provided in close proximity to each second catalyst element for ignition thereof.

18. A catalytic heating element as claimed in Claim 17 in which the ignition means comprises an electrically powered heating element having an operating temperature of not less than 500C.

19. A catalytic heating element as claimed in Claim 18 in which the operating temperature of the electrically powered heating element is not greater than 4000C.

20. A catalytic heating element as claimed in Claim 19 in which the operating temperature of the electrically powered heating element is not greater than 2200C.

21. A catalytic heating element as claimed in any of Claims 18 to 20 in which the electrically powered heating element comprises an elongated resistance wire extending over at least portion of the surface of the first catalyst element, the second catalyst elements being spaced apart at intervals along the resistance wire.

22. A catalytic heating element substantially as described herein with reference to and as illustrated in the accompanying drawings.

23. A space heater comprising the catalytic heating element of any preceding claim, a support means for supporting the catalytic heating element, gas dispersing means for dispersing gas through the first and second catalyst elements, and means for delivering gas to the dispersing means.

240 A space heater as claimed in Claim 23 in which the dispersing means comprises a dispersing housing defining a dispersing chamber and an open mouth to the dispersing chamber, the support means being mounted in the open mouth for supporting the catalytic heating element therein.

25. A space heater as claimed in Claim 23 or 24 in which the support means comprises a support member of porous refractory material, the support member substantially closing the open mouth of the dispersing housing, and the catalytic heating element being provided on the downstream side of the support member.

26. A space heater as claimed in any of Claims 23 to 25 in which the second catalyst element is provided on the upstream side of the first catalyst element and the electrically powered heating element is provided on the upstream side of the first catalyst element.

27. A space heater as claimed in any of Claims 23 to 26 in which the second catalyst element is provided between the first catalyst element and the support means.

28. A space heater as claimed in any of Claims 23 to 27 in which air delivery means is provided for delivering air across the downstream surface of the first catalyst element.

29. A space heater as claimed in Claim 28 in which the air delivery means comprises a motor driven fan.

30. A space heater as claimed in any of Claims 23 to 29 in which the space heater comprises a main housing defining a hollow interior region for accommodating the dispersing housing, the main housing and the dispersing housing defining an annular opening for directing air across the downstream surface of the first catalyst element.

31. A space heater substantially as described herein with reference to and as illustrated in the accompanying drawings.