GB2225732A

GB2225732A - Heating device with a catalytic burner

Info

Publication number: GB2225732A
Application number: GB8926001A
Authority: GB
Inventors: Philippe Botazzi
Original assignee: Application des Gaz SA
Current assignee: Application des Gaz SA
Priority date: 1988-11-17
Filing date: 1989-11-17
Publication date: 1990-06-13
Also published as: FR2639093A1; GB8926001D0; JPH02223709A; DE3936265A1; FR2639093B1

Abstract

A heating device incorporating an induced-air catalytic burner (8), includes means (22) for confining a flame, for initiating the catalytic combustion, in the downstream zone (10a) of a heating element (10), but at a distance from the outlet face (8b) of the catalytic structure (8). After ignition, heat spreads from means 22 - preferably a screen or disc - by conduction and convection to the burner 8. This, when it reaches a particular temperature, catalyses the combustion of the fuel; the initiating flame downstream of means 22 thus goes out. Means 23 upstream of the catalytic burner 8, becomes hot and so preheats the fuel. Tube 9, at its downstream end, forms an air-tight seal with means 23 and, upstream, accepts a mixture of ambient air and fuel from an injector. The device may be used in a hair-curler. <IMAGE>

Description

i HEATING DEVICE WITH CATALYTIC BURNER The present invention relates

generally to a heating device with an induced-air catalytic burner. In particular, a device of this type may have various applications according to the use of the heat generated by the catalytic burner, for example as portable curling tongs, as a soldering iron, etc.

French Patent Application 8,714,747 filed by the Applicant on 20th October 1987, describes a portable heating device and in particular a gasoperated soldering iron. Such a heating device comprises an optional member for controlling a current of pressurised fuel gas, for example butane, obtained from an interchangeable cartridge, for example a cartridge with an aerosol valve. This cartridge may be releasably coupled to the device, in other words simultaneously integrated with the latter and connected internally and in a leaktight manner with the said device. An injector injects a jet of the fuel gas, from the said current and this jet of gas is then mixed with ambient air, so as to obtain a flow of combustible mixture.

A catalytic combustion structure, permeable to the flow of combustible mixture, has an inlet face which receives the said mixture and an outlet face which, during operating, give out the combustion vapours. This structure consists of a permeable refractory core, having a plurality of channels which extend, according to the direction of circulation of the mixture to be burned, from the inlet face to the outlet face of the core.

A heating element, made of metal is arranged outside and around the catalytic combustion structure and extends according to the direction of circulation of the gases, from a zone, situated downstream from the outlet face of the catalytic structure, to a zone situated upstream from the inlet face of the catalytic structure. This heating element receives some of the combustion heat and dissipates it towards the outside of e X the device, for example towards a bit of a soldering iron.

A tube, which is continuous and leaktight, except in the region of the means for mixing in primary air, is in contact, at the upstream end, with the outlet of the injector, and is connected, at the downstream end, to the inlet face of the catalytic structure.

For a heating device as defined above, and for certain applications, in particular in the home as curling tongs, the induced-air catalytic burner must in practice conform to the following requirement. The heating device must be quickly brought to the temperature which initiates the catalytic burner, in particular so as to allow repeated use of the same device. Any rapid activation of the device, and in particular any accelerated heating up of the heating element from the ambient temperature, is by way of a catalytic burner capable of generating a relatively high caloric power, at least during the start-up period.

When designing or constructing a heating device such as defined above, there may therefore be a contradiction between the need for a burner with a low power for the intended application, but at the same time the need for a burner with a high power for rapid startup of the device.

In the prior art, it has already been proposed to overcome such a dilemma by employing means for regulating the catalytic burner, these means consisting, in a general manner, of regulating the flow rate of the feed current of fuel gas as a function of the temperature of the heating element. This solution necessitates recourse to various mechanisms, which are relatively accurate and incorporate numerous components, in order to obtain precise regulation.

other solutions have also been proposed in the prior art, which consist of providing several burners in

1 1 a same device, operating together upon start-up but only one of which operates once the nominal operating temperature has been reached. Such a solution complicates construction and hence the cost of the heating devices. In addition, this complexity is often incompatible with satisfactory reliability.

The present invention proposes to overcome these disadvantages for a heating device having an induced-air catalytic burner.

A heating device according to the present invention comprises an injector for injecting a jet of fuel gas from a source, towards means for mixing ambient air with the jet, so as to obtain a flow of combustible mixture, a catalytic combustion structure, permeable to the flow of the combustible mixture, being connected to a tube which is continuous and leaktight, except in the region of the means for mixing with ambient air, and which is in contact, at the upstream end, with the outlet of the injector, a heating element being arranged outside and around the catalytic combustion structure, and extending, according to the direction of circulation of the gases, from a zone situated downstream from an outlet face of the catalytic structure, to a zone, situated upstream from the inlet face of the catalytic structure, the said heating element receiving some of the combustion heat and dissipating it towards the outside of the device, and means for confining a flame in the downstream zone of the heating element at a distance from the outlet face of the catalytic structure, for initiating the catalytic combustion.

In such a heating device, the catalytic burner can be rapidly initiated or activated, but the catalytic operating range of the burner is capable of generating a nominal caloric power, which is restricted to a relatively low value. This initiating flame serves to activate the heating element.

The means for confining the flame preferably consists of a perforated screen arranged transversely opposite the outlet face of the catalytic structure.

Means for heating the catalytic structure up to the temperature which initiates the catalytic combustion are suitable arranged in the upstream zone of the heating element. The reheating means may consist of a perforated screen, arranged transversely, opposite the inlet face of the catalytic structure, having the flow of the combustible mixture passing through it.

The width of the heating element, from the inside towards the outside of the catalytic structure, may have an average size which is greater in its mid zone, in other words the zone in the region of the catalytic structure, than in its downstream and upstream zones.

The catalytic structure preferably consists of a permeable refractory core, having a plurality of channels, extending, according to the direction of the mixture to be burned, from the inlet face to the outlet face of the said core, the internal surface of each channel being coated with a combustion catalyst.

The temperature of the catalytic structure necessary to initiate the catalytic combustion, is suitable identical to or close to the nominal operating temperatures of the said device.

A device according to the invention allows a rapid and controlled startup of the catalytic burner to be obtained, according to the following procedures:

When the fuel gas is released, a flame is ignited at the outlet of the catalytic burner, but at a distance from the catalytic structure. This flame generates a caloric power which is much greater than the nominal caloric power of the catalytic burner but this flame cannot heat up the catalytic structure directly, since it is not in contact with the latter.

1 This flame, which is confined in the downstream zone of the heating element, subsequently heats up the latter progressively to a temperature equal to, or slightly greater than, the nominal operating temperature of the heating device.

At the same time, the quantities of heat received by the downstream zone of the heating element are in part then transmitted to the catalytic structure, on the one hand from the mid zone of the said element, and on the other hand by reheating the combustible mixture in the upstream zone of the said element, and passing the reheated mixture into the catalytic structure. The catalytic structure then also reaches the nominal operating temperature, but after the heating element, since, as indicated above, the catalytic structure receives heat only by means of the said element.

If the selected temperature for initiating the combustion of the catalytic burner is equal to or near the nominal operating temperature, the catalytic combustion is then initiated. This combustion brings the gas mixture which is at the outlet of the catalytic burner to below its inflammability limit and consequently the initiating flame is extinguished.

Catalytic combustion continues, with a relatively low caloric power, which is sufficient to maintain the nominal operating temperature at a relatively low value.

The present invention therefore allows the heating device to be brought rapidly to its nominal operating temperature, but no higher than that, in view of the two successive, but never concomitant, combustion modes which are obtained, namely a naked-flame mode, and then a catalytic mode, this being achieved without the intervention of the user or an appropriate mechanism or automatic control.

The present invention intrinsically allows the starting-up of the catalytic burner to be ensured once the nominal operating temperature has been reached, and not before, since the burner, during the flame mode, receives quantities of heat only from the heating element, which forms the part of the device which is put into use.

The present invention will now be described by way of example with reference to the accompanying drawings, in which:

- Figure 1 diagrammatically illustrates, in axial section, a heating device according to the invention, and, to be more particular, gasoperated curling tongs; - Figure 2 shows an enlarged view, still in axial section, of the catalytic burner which forms part of the device shown in Figure 1; - Figure 3 shows a front view of one of the perforated screens which form part of a catalytic burner according to the invention; - Figure 4 shows the development over time (expressed in minutes) of the operating temperature of the device, to be more precise that of the heating element, following ignition of the burner of the said device.

The present invention is now described with reference to Figures 1 and 2, for portable and selfcontained curling tongs which operate by means of an interchangeable cartridge of butane. However, it must be understood that this particular description does not limit the general nature of the present invention, as expressed and defined in the claims.

The device comprises a body (2), which has, at its upstream end, means (3) for coupling to a cartridge (4), of pressurised fuel gas, and, at its downstream end, an injector (5) for ejecting a jet of the fuel gas from the feed current issuing from the cartridge or source (4) towards means (6) for mixing ambient air with the jet, so as to obtain a flow of combustible mixture.

A catalytic burner (7), comprising a catalytic combustion structure (8), permeable to the flow of the combustible mixture coming from the means (6) for mixing in primary air, is located downstream from the injector (5). As shown in Figure 2, the inlet face 8a of the catalytic structure receives the combustible mixture and the face 8b gives out combustion vapours.

A tube (9) which is continuous and airtight, except in the region of the means (6) for mixing in primary air, connects, at the upstream end, with the outlet of the injector (5), and connects, at the downstream end, in an airtight manner with the inlet face (8a) of the catalytic structure (8).

A heating element (10) made of metal, is arranged outside and around the catalytic combustion structure (8), extending, according to the direction of circulation of the gases, from a zone (10a) situated downstream from the outlet face (8b) of the catalytic structure (8) to a upstream zone (10c), situated upstream from the inlet face (8a) of the structure (8), passing through a mid zone (10b) situated in the region of the catalytic structure (8). This heating element absorbs some of the combustion heat and dissipates it towards the outside of the device.

A cap (11) fits over the heating element (10), and is separated from the latter by a transverse grid (12). An orifice (11a) is provided in the cap for discharging the vapours from the device. A tube (13) with radial fins which act as a comb, fits over the heating element (10) and the cap (11).

A piezoelectric ignition system has an electrode (14), the sparking end of which is situated in the downstream zone (10a) of the heating element (10). bar of the element is electrically insulated from the heating element (10) by a sheath (15). The piezoelectric mechanism (16) is fastened onto the body (2), and generates an electrical voltage under the influence of a push rod (16a).

The various components of the device will now be described in more detail.

The cartridge (4) contains a pressurised fuel gas, for example butane or isobutane, and is of the type described in the French Patent FR-A-2,580, 376 filed by the Applicant; this cartridge therefore has a valve of the aerosol type.

The coupling means (3) allows the cartridge (4) to be fixed and integrated onto the device, in a releasable manner and allows the cartridge to be opened whilst at the same time ensuring a leaktight connection with the device.

To be more precise, the coupling means (3) comprises a cylinder (17) capable of containing the cartridge, which can be screwed onto the body (2) of the device and allows the head of the aerosol valve to be applied against a sealing strip (18). A drawing-off hollow needle (19) is fastened in a leaktight manner onto the body (2) of the device and penetrates the aerosol valve of the cartridge (4), as illustrated diagrammatically in Figure 1, allowing the latter to be opened. The head of this aerosol valve is, moreover, guided by a cylindrical inner collar (2a) of the body (2). The sealing sleeve (18) is held tightly between the collar (2a) of the body (2) and another collar belonging to the hollow needle (19). This sleeve (18) has an annular sealing lip, to make corresponding contact with the periphery of the aerosol valve.

A spring (20), which is compressed and is supported between the body (2) and the front face of the cartridge (4), allows the above mentioned cartridge to be pushed out of the body (2) when the cylinder (17) is unscrewed.

The means (6) for mixing ambient air combines the -g- injector (5) and a component (21) in the form of a Venturi tube seated inside the upstream end of the connecting tube (9). A space is provided between this upstream end of the tube (9) and the injector (5) so as to allow the entry of ambient air, which is impelled by the jet given out by the injector (5).

According to Figure 2, the heating element (10) has a generally H-shaped cross-section, the downstream zone (10a) and the upstream zone (10c) of which have the form of a tubular sleeve with a small thickness.

A mid zone (lob) has an average transverse size, that is from the inside towards the outside of the device, which is greater than the thickness of the downstream (loa) and upstream (10c) zones. This mid zone comprises an axial cylindrical housing for the catalytic structure (8), and has two collars on either side for housing the perforated screens (22) and (23) respectively, which will be referred to below.

The catalytic structure is of the "honeycomb" type, in other words it consists of a permeable refractory core, run through by a plurality of channels (8c) extending, according to the direction of circulation of the mixture to be burned, from the inlet face (8a) to the outlet face (8b) of the core. The internal surface of each of these channels is coated or impregnated with an appropriate combustion catalyst. By design, and in particular by the choice of the combustion catalyst, this catalytic structure has a temperature initiating catalytic combustion which is specified by the manufacturer or may be established with ease by persons skilled in the art. As indicated above, the catalytic structure retained according to the invention has an initiating temperature which is identical to or close to the nominal temperature aimed at for operating the device.

The two perforated screens (22) and (23) each consist-, as shown in Figure 3, of a disc having a 1 perforated central or axial part, (23a) a plurality of peripheral notches, (23b) each being V-shaped in profile, and a solid part, (23c), between the central perforation and the notches. If one disregards the solid parts between the notches, the solid part, (23c), may be likened to a ring.

Each of these discs (22), (23) is arranged transversely in an abovedescribed collar of the heating element (10). The disc or perforated screen (22) forms the means for trapping the flame which initiates the catalytic combustion, this being achieved at a distance from the opposite to the outlet face (8b) of the catalytic structure (8).

The disc or perforated screen (23), forms the means for reheating the catalytic structure (8) up to the temperature necessary to initiate the catalytic combustion. This disc (23) is arranged transversely opposite the inlet face (8a) of the catalytic structure (8), and consequently the combustible mixture to be burned, which, once heated, in turn reheats the catalytic structure (8), passes therethrough.

As the above description indicates, the perforated screens (22) and (23) are therefore arranged respectively in the downstream zone (10a) and the upstream zone (10c) of the heating element (10).

Moreover, the downstream end of the connecting tube (9) is connected in a leaktight manner with the inlet face (8a) of the catalytic structure (8), in view of the seal existing between this end and the heating element (10).

The operation of the catalytic burner, and therefore of the heating device, according to the invention, is as follows.

By placing a cartridge (4) in the cylinder (17), and by screwing the latter onto the body (2), the coupling means (3) causes the aerosol valve of the cartridge (4) to open, and therefore the heating device k to be fed with fuel gas. If it is desired to stop the device, the opposite procedure must be adopted, in other words the cylinder (17) must be unscrewed relative to the body (2), so as to uncouple the cartridge (4), and the aerosol valve of the latter must be closed.

The mixing means (6), at the outlet of the injector (5), allows a combustible mixture combining the fuel gas and the oxidant air to be obtained in the connecting tube (9). This mixture becomes homogeneous as it circulates in the conduit (9). The mixture then passes through the perforated screen (23), through the catalytic structure (8) and through the perforated screen (22) so as to finish in the downstream chamber of the heating element (10).

By applying pressure to the piezoelectric mechanism (16), by means of the push rod (16a), a spark, which ignites a flame at the outlet of the disc (22), is created at the free end (14) of the electrode.

This flame is confined to the downstream zone (10a) of the heating element but has no direct thermal contact with the "honeycomb" catalytic structure (8) in view of it being trapped on the disc (22) which separates it from the outlet face (8b) of the structure (8).

As shown in Figure 1, this flame will therefore subsequently progressively heat up the heating element (10), the quantities of heat transferred from the zone (10a) being distributed towards the mid zone (10b) and upstream zone (10c). The heating element (10) is therefore subsequently rapidly heated up to the nominal operating temperature of the device, for example in the order of 1600 C, and even a little above this.

At the same time, the quantities of heat received by the heating element (10) are returned in part to the catalytic structure (8) in two ways: on the one hand, there is a beat transfer by conduction or convention between the mid zone (10b) and the structure (8) and, on the other hand, the perforated screen or disc (23), in 4 J thermal contact with the upstream zone (10c), allows the combustible mixture to be heated before it is introduced into the channels (8c), this heated mixture in turn heating up the catalytic structure (8).

The result of all this is that the catalytic structure is also brought rapidly to the nominal operating temperature of the device, that is to the temperature initiating the catalytic combustion, since, by design, the selected catalyst has an initiating temperature close to or identical to this nominal operating temperature. This temperature, however, is reached by the structure (8) only after the heating element (10) has reached the desired temperature in view of the above-described forms of heat transfer.

As soon as the initiating temperature of the catalytic combustion is reached, for example, after five minutes according to Figure 4, catalytic combustion occurs, consuming some of the fuel gas present in the mixture circulating in the conduit (9). It is then no longer possible to support and maintain the flame for initiating the catalytic combustion. Consequently, this flame goes out, and combustion takes place entirely in the catalytic mode.

The catalytic combustion can then take place with an operating temperature which remains, by design, close to or identical to its nominal value, as shown by the plateau illustrated in Figure 4.

Claims

CLAIMS: 1. Heating device comprising an injector for injecting a jet of

fuel gas from a source, towards means for mixing ambient air with the jet, so as to obtain a flow of combustible mixture, a catalytic combustion structure, permeable to the flow of the combustible mixture, being connected to a tube which is continuous and leaktight, except in the region of the means for mixing with ambient air, and which is in contact, at the upstream end, with the outlet of the injector, a heating element being arranged outside and around the catalytic combustion structure, and extending, according to the direction of circulation of the gases, from a zone situated downstream from an outlet face of the catalytic structure, to a zone, situated upstream from the inlet face of the catalytic structure, the said heating element receiving some of the combustion heat and dissipating it towards the outside of the device, and means for confining a flame in the downstream zone of the heating element at a distance from the outlet face of the catalytic structure, for initiating the catalytic combustion.
2. Device according to Claim 1, wherein the confining means consist of a perforated screen arranged transversely opposite the outlet face of the catalytic structure.
3. Device according to either Claim 1 or 2, in which means for heating up the catalytic structure to a temperature which initiates the catalytic combustion are arranged in the upstream zone of the heating element.
4. Device according to Claim 3, wherein the heating means consist of a perforated screen, arranged transversely, opposite the inlet face of the catalytic structure having the flow of the combustible mixture passing through it.
5. Device according to any preceding Claim, in which the width of the heating element, from the inside towards the outside of the catalytic structure, has an average size which is greater in its mid zone, in other words the zone in the region of the catalytic structure than in its downstream and upstream zones.
6. Device according to any preceding Claim, in which the catalytic structure consists of a permeable refractory core, having a plurality of channels. extending, according to the direction of the mixture to be burned, from the inlet face to the outlet face of the said core, the internal surface of each channel being coated with a combustion catalyst.
7. Device according to any preceding Claim, in which the temperature of the catalytic structure, necessary to initiate the catalytic combustion, is identical to or close to the nominal operating temperature of the device.
8. Device as claimed in Claim 1 in which means are provided for producing the flame, the means comprising an electrode of piezoelectric material and means for applying stress to the electrode so as to produce a spark.

Hojse66-71 High Holborn.London WG1R4TP- Further copies maybe obtainedfrom The PatentOffice,led IsgoatThe. atentOffice.St-m Sales Branch, St Mary Cra-7;. Or-,ing-On. Kent BR5 3RD. Printed by Multiplex techniques ltd. St Mar,,, Cray. Ken'. Cc n 187