Contained flame radiant burner

Abstract

Confined flame radiant burner. It consists, on the one hand, of a premix flame burner, producing a main flame (1) in the shape of a dart, and an annular pilot (2), in an ignition chamber (7), on the other hand, of a refractory monolith (11), composed of a plurality of longitudinal channels (11a), covering it, characterized in that the main flame (1) is confined in a main channel (11b) which intimately surrounds it, to the point of being able to produce, on the corresponding outer wall, an active source of radiation, while the entire outlet flow surface of this monolith is composed of cells, the size of which is sufficiently small, to prevent the ignition of an external explosive zone, or allows, if the length is sufficient, the catalytic after-combustion of the combustion products of the main flame (1) and the pilot (2).Only the introduction of an external element into a useful hood opening (13a) allows this burner to be a source of ignition. Figure for the abbreviation: Fig. 2.

Description

Title of the invention: Confined flame radiant burner technical field

[0001] In the context of gas burners with induced air mixing, the present invention relates to a heat production burner, essentially by radiation, capable of operating safely in an explosive atmosphere. Previous technique

[0002] From publication FR2664678B1 is known a device for lighting a cigarette.

[0003] Since this burner does not benefit from induced primary air, and the power per unit of active surface area is limited by the diffusion speed of the secondary air, the external volume of the burner is necessarily large. Furthermore, since a transient flame initiates the catalytic reaction, only a fibrous catalyst support is feasible. Consequently, the corresponding device is particularly fragile.

[0004] Apart from this example, the combustion methods of current gas lighters can be divided into three families: • Diffusion flame: the jet of gaseous fuel burns in the ambient air, producing a yellow flame • Premixed flame, "rigid flame", or blue flame: a combustible air-gas premix is, after the admixture of atmospheric air, most often distributed into a main blue conical axial zone, the flame, and a low-velocity annular zone ensuring the dynamic stability of the flame • Catalysis: based on the previous case, the addition of an active solid element improves combustion stability

[0005] In these three versions, a free flame, always visible, is a potential source of fire that is all the more critical, since the quantity available of these ignition devices is, on earth, on the order of one per inhabitant.

[0006] Moreover, to address this situation on the American market, a standard requires disposable lighters to incorporate ergonomic constraints making them "child-resistant", as, for example, described in WO0138795A1.

[0007] More generally concerning honeycomb type catalytic burners, FR2678356A1 shows that, while ensuring operational stability through premix distribution may seem effective, catalyst aging remains the major constraint: for this type of burner with high specific power, the use of catalyst inevitably leads to a limited lifespan.

[0008] Moreover, the design of conventional radiant burners (without catalyst) results in a flat burner using a refractory support, generally obeying two constraints: to have upstream channels whose small dimensions prevent, by jamming, the ignition, and wider downstream channels, of judiciously varied position and lengths, in order, due to the local penetration of the combustion front, to recover useful radiation: FR1297959A is an example of this. Description of the invention

[0009] With this present invention, because the flame tip is located upstream of the refractory support, the monolith, the corresponding heat exchange is optimal: the active part of the monolith intimately surrounds, along its length, an axial premixed flame, thus allowing for the efficient recovery of heat produced by the combustion front. The corresponding outer part thus ensures optimal radiation to the outside.

[0010] The present invention uses a monolith made from a robust honeycomb-type support. As the latter is uncoated (without high specific surface area coating or precious metal deposit), its lifespan is not limited by a reduction in catalytic activity, which is itself often due to a structural modification of added elements.

[0011] Since all combustion products, from the main flame and the pilot, exit through a downstream face of support equipped with cells of sufficiently small size to produce the jamming of combustion reactions, the invention allows operation in an explosive atmosphere without risk of ignition: the flame remains confined, at ignition, as during nominal operation.

[0012] This invention thus makes it possible, in particular, to offer an intrinsically safe cigarette lighter: the absence of a free flame when used empty, that is to say without the introduction of an external object such as a cigarette, avoids any risk of causing a fire, even if the ambient atmosphere is explosive. Brief description of the drawings

[0013] The present invention will be better understood by examining a particular embodiment taken by way of non-limiting example and illustrated by the accompanying drawings:

[0014] [Fig. 1] is a schematic longitudinal cross-sectional representation of the premix flame burner on which the active element according to the invention rests.

[0015] [Fig.2] is a schematic longitudinal sectional representation of the complete device according to the invention

[0016] [Fig.3] is a schematic representation according to a longitudinal half-section of the active element according to the invention

[0017] [Fig.3A] represents the upstream cross-section AA of the [Fig.3]

[0018] [Fig.3B] represents the active cross-section BB of the [Fig.3]

[0019] [Fig.3C] represents the downstream cross-section CC of the [Fig.3]

[0020] [Fig.4A] is the schematic longitudinal sectional representation of the device according to the invention, in a plane perpendicular to that of [Fig.3]

[0021] [Fig.4B] schematically illustrates the new flame profile after the doubling of the gas flow rate

[0022] [Fig.5] presents an improvement of the invention with regard to hygiene combustion

[0023] [Fig.6] shows a use of the invention as a cigarette lighter Detailed description

[0024] Since the device according to the invention consists mainly of a casing around a premixed flame, it is necessary to describe precisely the burner which is at the origin of this flame.

[0025] According to [Fig.1], this burner has a main axial flame in the shape of a conical dart (1) and an annular pilot (2).

[0026] This dart (1) is a cone, representing a visible blue combustion front. The corresponding reaction layer rests on this conical surface and uses most of the gas flow. In the example described, the total flow rate, including the pilot (2), is of the same order as that of disposable gas lighters: approximately 2 g / h of isobutane.

[0027] As shown in [Fig.1], the device includes an injector (3) which allows the admission of primary air through the four orifices (4), a tube (5) then allowing the formation of a homogeneous air-gas mixture.A distribution coil (6) separates this mixture into 2 parallel flows; the main axial flow, which supplies the dart (1), and several small secondary flows distributed symmetrically in an annular space, which supply the pilot (2): an electrode (8), thanks to the ground return of a piezoelectric element (9), allows the ignition of this ring of pilot flames (2), itself necessary to ensure the ignition and stability of the dart (1); the pilot flames (2) are protected along their height by a refractory insulating ignition chamber (7), thus improving their own stability against air currents; an external metallic protection, the protective cover (10), allows, at a temperature level acceptable to the touch, the diffusion to the outside of the heat produced.

[0028] With reference to [Fig.2], the present invention is based on the dressing of the flames (1) and (2) from, in our example, a honeycomb type monolith of cordierite with 400 cells / inch2 (11), commonly used as a catalyst support for the treatment of automotive exhaust gases, and whose channels are parallel to the flow axis.

[0029] It is the shaping of this monolith (11) to cover the flames (1) and (2) that results in the main element of the invention.

[0030] This support has the particularity of presenting cells (1 la) of sufficiently small size to prevent, by wedging, any propagation of the combustion front to the outside, that is to say that they chemically and thermally block any propagation of the combustion front downstream.

[0031] Furthermore, this support has thin walls ensuring an open cross-section of approximately 80% of the total surface area; its use downstream of the combustion flow, slightly modifying the overall pressure drop, makes it possible to maintain a sufficiently high primary aeration rate through the orifices (4). Reducing the aeration rate would be all the more detrimental as it would limit the useful power of the air-gas premix, which is already assumed to be rich: indeed, since the design of the flame burner is defined for a rigid flame which, when free, already benefits from a secondary air supply, the air supplied by induction is, in general, insufficient to ensure complete combustion on its own.

[0032] Furthermore, the insulating washer (12) covers the ignition chamber (7), thereby improving the wind stability of the pilot flames (2). The inner diameter of the washer (12) is slightly larger than the dimension of the channel (11b) to insulate the ignition chamber (7) from the internal thermal radiation of the monolith, while allowing the combustion products of the pilot flames (2) to pass into the channels located at the periphery of the main channel (11b).

[0033] The hood obtained from a stainless steel tube (13) allows the position of the monolith (11) to be maintained by means of flexible refractory insulators upstream (12) and downstream (14), acting both mechanically and thermally.

[0034] The four tabs (13b) of this tubular hood ensure, by means of internal clamping, the mechanical connection within the protective hood (10). The limited contact surface thus reduces heat transfer between the tubular hood (13) and the protective hood (10).

[0035] To mount the burner of [Fig.2], the element described by [Fig.3] is added to the burner of [Fig.1], without any modification of the latter; the understanding of this invention is thus facilitated by the perfect modularity of the device described.

[0036] On this [Fig.3], through a useful opening in the hood (13a) not cut, the apparent shape, illustrated by its useful face (1 le), is that which a truly “rigid” flame would have.

[0037] From this same [Fig.3], the description from upstream to downstream of the distribution of cells in cross-sections at different heights makes it possible to specify locally the different roles of the three constituent elements of this sub-assembly, the monolith (11), the metal cover (13) and the joints (12) and (14).

[0038] [Fig.3A], upstream zone: • The peripheral cells of the monolith and the presence of the seal (12) ensure that the premix does not escape to the outside, especially since the jet effect of the nozzle in the channel (11b) creates a negative pressure in this space; furthermore, all passages to the outside downstream of the pilot flames have a maximum dimension that guarantees that none of them escape, even at the moment of ignition. • The top of the metal hood's tabs (13b) shows their reduced contact surface, limiting upstream heat transfer • Also, at the electrode, the seal (12) allows, by moving the cover away from the electrode, to facilitate obtaining the ignition spark at the coil

[0039] [Fig.3B], active zone: • The outer rows of cells were removed to reveal the radiating plate (11c), with a thickness equivalent to two complete cells. Thus, the monolith, due to the short distance between the combustion front of the dart and the wall of the channel (11b), and its minimal thickness, reduced to that of a single wall, allows efficient heat transfer to the outer wall (11e), raising it to over 600°C with bright red radiation • The tubular hood guides the combustion products from the pilot, with an additional possibility of diffusion to the outside through the two symmetrical openings in the hood (13a) • These openings (13a) are sufficient to allow the external use of radiant heat produced by the two symmetrical surfaces (11c) facing them

[0040] [Fig.3C], downstream zone: • Starting from its minimum cross-section with four complete cells, the monolith quickly regains its maximum cross-section, which allows it to ensure, both along its axis, dimensions that guarantee the dart's grip, and on its periphery, its radial positioning • The seals (14) improve this centering while reducing heat transfer between the tubular hood (13) and the monolith (11)

[0041] In [Fig. 4A], an axial channel (11b) closely surrounds the combustion front defining the dart (1), to recover its heat along its entire length, via a sealed longitudinal wall insulating it from the outside. Of course, for combustion reactions to occur in the direction perpendicular to the flow, the transverse dimension of this channel (11b) is necessarily greater than those of the cells (1a): In our example, four contiguous cells were planned to form the square section of this channel (11b).

[0042] We can then specify safe operation in an explosive outdoor area; it is necessary to consider: • On the one hand, as already mentioned, the direct jamming of the combustion reaction in homogeneous phase due to a maximum cell size (lia), for the control (2) as for the main flame (1) • On the other hand, the limitation of the risk of ignition by hot surface: in the presence of an external explosive atmosphere, the combustion products from the pilot ring (16) shown in [Fig.4A] generate a relatively cold layer which dilutes this atmosphere to the point that, when moving away from the wall (11c), i.e., in the vicinity of this wall (11c), the oxygen content is significantly less than 12%, i.e., in the vicinity of the hood (13), the temperature of the gas flow is less than 300°C: thus, the radiant surface (11c), even at 600°C, cannot be the source of ignition of an external flammable gas mixture; the invention is thus safer than any ignition device using a direct electrical source.

[0043] The design of this example was initially intended to maximize the heat exchange between the dart (1) and the channel (11b) by surrounding the dart (1) over its entire height, thus consuming an average theoretical specific power of approximately 50 W / cm2.

[0044] But, surprisingly, the doubling of the gas flow rate, observed by the doubling of the flame height of the burner in [Fig.1], increases the radiant power of the radiant surface (11c): in [Fig.4B] we see that the dart has been tipped (17); the possibility of ignition of a flame downstream of our burner by a match shows that the level of unburned gas is nevertheless high; but, the system responds favorably to more flow rate, resulting in more radiated power, and a great flexibility of operation is thus guaranteed: the stability of a combustion tube (17) is, in fact, ensured as long as the pilot flames (2) exist.

[0045] Figure 5 proposes a variant of the invention which, in particular, in this case, improves the combustion hygiene of our burner. To ensure sufficient contact time between the chemical species, the FF section of Figure 3 is lengthened and treated to make it active—for example, with a high specific surface area coating supporting finely dispersed platinum (thus eliminating any jamming)—to ensure low-temperature catalytic afterburning. • For the combustion products of the pilot flames, a secondary air supply (17) is already sufficient to improve combustion hygiene, even if the primary gas-air premix remains rich • As for the main flame, if the burner design described in [Fig.1] allows, when hot, operation close to stoichiometry, a post-combustion, ensured by a hetero-homogeneous catalytic reaction (19), makes it possible to reduce the rate of unburned gas: as it is a low-load post-treatment, in the presence of a strong dilution by the combustion products of the "dart" (18), the structural integrity of this part can be ensured.

[0046] The height of the active part added to our initial module of [Fig.3] is, advantageously, slightly greater than the length of the visible flame, which would have been observed after an external ignition of the unburned gases of the dart from this module.

[0047] Moreover, regardless of the flow rate, once ignition has been achieved by the spark from the piezoelectric element, a portion of the blue flame remains visible from the outside through the downstream channels (lia).

[0048] Thus, according to the invention, it is possible to propose a hybrid version of burner composed of a piloted flame trunk (18) upstream of a hetero-homogeneous catalytic reaction (19) which has a negligible rate of unburned gas: it is a long-form burner, whose structural stability is mainly linked to the distribution of the thermal load over this length. Examples

[0049] The device according to the invention meets any requirement, requiring both a high volumetric power density and safe operation in a potentially explosive area.

[0050] In particular, the use of this radiant burner could be well suited for high-temperature bonding or polymerization in the presence of solvent.

[0051] For gas-powered tools (soldering iron, glue gun, immersion heater), this device is advantageous whenever minimal radial space is required. Provided the product design allows for efficient heat recovery from the protective cover, this elongated burner offers numerous benefits: integrated piezoelectric ignition, compact size, high specific power output, and smooth, stable operation over time.

[0052] It is also particularly suited to the field of lighters: [Fig.6] shows what the use in this form could be, applied to the cigarette alone (20).

[0053] Due to the multiple outlet surfaces, the introduction of this cigarette (20) into one of the two orifices (13a) only slows down a portion of the combustion products of the pilot. Thus, since lighting a cigarette does not cause a significant decrease in the aeration rate, the useful power supplied remains constant.

[0054] Furthermore, if this type of design were made mandatory for all cigarette smokers, the number of accidental deaths (fires) would be drastically reduced. Even with improper use, producing an ignition would require, in addition to the actions required by normal use, the deliberate approach of an external solid object to the opening (13a).

[0055] Thus, this burner is a cigarette lighter that is less dangerous than any electric lighter and, in terms of safety, significantly safer than any gas lighter equipped with a child safety lock.

[0056] The object of this invention is a radiant burner comprising a piloted air-gas premix flame, equipped with an ignition electrode (8), producing a main combustion front in the form of an axial dart (1) characterized in that it comprises, downstream, a refractory support (11) equipped with channels (lia) parallel to the flow axis, totally covering the annular pilot (2) in its ignition chamber (7), intimately surrounding, at least at its base, the axial dart, to efficiently recover the heat produced, and having, for each output cell, a dimension sufficiently small, to prevent, including at ignition, any propagation of the combustion reaction to the outside.

[0057] The external shape of the refractory support is a truncated cone, the length of which is slightly greater than that of the main channel (11b) and the minimum section of which is that of this channel surrounded by a single peripheral wall.

[0058] On two symmetrically opposed planes, extending from a downstream zone close to the base of the cone to integrate the minimum section zone, a single longitudinal sealed wall separates the main channel (11b) from this external flat surface (1 le), the active source of radiation.

[0059] A flexible refractory insulating washer (12), with an inner diameter slightly greater than the equivalent diameter of the main channel (11b), limits the mechanical and thermal stresses transmitted to the upstream ignition chamber (7) while allowing the combustion products of the pilot flames (2) to pass through.

[0060] To maintain the refractory support (11) in position, it is extended downstream until it matches the diameter of its base, and a tubular metal cover (13), equipped with openings having an equivalent surface area facing each active radiating surface (1 e), ensures its centering and fixation. The sweeping of each radiating surface (1 e) by the combustion products of the pilot (2) prevents, by dilution, the ignition of an external explosive area that it would be likely to ignite as a hot surface.

[0061] In the latter case, the downstream part of the refractory support can, by an appropriate impregnation and over a sufficient height, be made catalytically active, to ensure the post-combustion of a premix flow rate too high for the channel (11b), thus ensuring a contact time of the reactants sufficient to facilitate the complete combustion of the premix from this main channel (11b), the combustion products of the pilot already benefiting from a supply of secondary air through each opening (13a).

[0062] The hood, having at least one opening with a diameter greater than that of a cigarette, allows ignition by proximity to the hot wall (11c) without significantly slowing the total flow of combustion products from the burner.

[0063] In the case of the example described, the refractory support used is of the cordierite honeycomb type with, at the downstream flow surface, 400 cells / inch2.

Claims

Demands

1. A radiant burner comprising a piloted air-gas premix flame, equipped with an ignition electrode (8), producing a main combustion front in the form of an axial dart, the main flame (1), characterized in that it comprises, downstream, a refractory monolith (11) equipped with channels (lia) parallel to the flow axis, including a main channel, completely covering an annular pilot (2), inside an ignition chamber (7), intimately surrounding, at least at its base, the axial dart, to efficiently recover the heat produced, and having, for any outlet flow cell, a dimension sufficiently small to prevent, including at ignition, any propagation of the combustion reaction to the outside

2. A burner according to claim 1 characterized in that the external shape of the monolith is a truncated cone, the length of which is slightly greater than that of the main channel (11b), the main channel intimately surrounding the nozzle, and the minimum cross-section of which is that of this channel surrounded by a single peripheral wall

3. Burner according to claim 2 characterized in that, on two symmetrically opposed planes, extending from a downstream zone near the base of the cone to integrate the minimum cross-section zone, a single longitudinal sealed wall separates the main channel (11b) from an external flat surface, defining an active radiation source (11c)

4. Burner according to claim 2 or 3 characterized in that a flexible refractory insulating washer (12), with an inner diameter slightly greater than the equivalent diameter of the main channel (11b), limits the mechanical and thermal stresses transmitted to the ignition chamber (7), while allowing the combustion products of the pilot (2) to pass through

5. A burner according to claims 3 and 4, characterized in that, to maintain the refractory monolith (11) in position, it is extended downstream until it reaches the diameter of its base, and a tubular metal cover (13), provided with two useful openings (13a) having an equivalent surface area facing each active radiation source (11), ensures its centering and fixation

6. Burner according to claim 5 characterized in that a sweep of each active radiation source (11c) by the combustion products of the pilot (16) prevents, by dilution, the ignition of an external explosive zone that it would be liable to ignite as a hot surface

7. Burner according to claim 6 characterized in that the downstream part of the refractory monolith is, by suitable impregnation over a sufficient height, rendered catalytically active to ensure low-temperature catalytic afterburning of the combustion products of the main flame (1) and the pilot flame (2) resulting from an excessively high premix flow rate

8. A burner according to claim 6 or 7 characterized in that, only the introduction of an external element into one of the two useful openings in the hood (13a) allows this burner to be a source of ignition for a cigarette (20), if this opening has a sufficient diameter

9. A burner according to any one of the preceding claims, characterized in that the refractory monolith used is of the cordierite honeycomb type with, at the downstream flow surface, 400 cells / inch2

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