WO2003062705A1 - Gas burner comprising a two-part combustion surface and a boiler equipped with one such burner - Google Patents

Abstract

The invention relates to a gas burner in the form of a case (1) that defines a chamber (E) which receives the air/gas mixture (A+G) to be burnt and which houses a perforated distribution partition (3) through which said mixture passes. According to the invention, one part of the wall of said case forms the combustion surface (FC). The external face of the combustion surface comprises a layer (6) of flexible, porous, thermally-insulating material, said layer being provided with numerous perforations (60) which are evenly distributed and which are used for the discharge and combustion of the air/gas mixture (A+G) once it has passed through the distribution partition (3). The inventive burner is characterised in that the internal face of said combustion surface (FC) comprises a perforated support plate (5) which supports the aforementioned layer (6). The holes (50) in said plate are (i) disposed opposite a perforation (60) in the layer (6) and (ii) provided with dimensions greater than those of said perforations (60). The invention also relates to a boiler which is equipped with one such burner.

Description

 GAS BURNER, WITH BIPARTITE COMBUSTION FACE AND BOILER EQUIPPED WITH SUCH A BURNER

The present invention relates to a gas burner and to a boiler equipped with a burner.

Many types of burners are known, which make it possible to ensure the combustion of a gas, for domestic or industrial uses. Commonly used burners have the form of a box which delimits an enclosure in which the air / gas mixture to be burned is received. A part of the wall of the housing constitutes a combustion face through which the air / gas mixture escapes while being burned.

According to their type of design, these burners make it possible to ensure the combustion of the gas, this with a more or less good efficiency, and in a power range which can vary from 1 to 3 approximately. The noise level of such burners is sometimes high and depends in particular on the richness of the air / gas mixture.

Other types of burners have been proposed which also have the form of a box delimiting an enclosure but, with a part of the wall of the box forming a combustion face consisting of a sheet of porous flexible material and thermal insulator, traversed by 'a plurality of perforations.

Such a sheet is for example made up of ceramic or metallic fibers coated with silicon carbide or alumina oxide.

With such a burner, a large part of the air / gas mixture escapes through the perforations in the sheet, which results in flames of good size. Furthermore, due to the porous nature of the sheet, the remaining part of the stream crosses the random network of fibers and escapes outside while being burnt, in the form of small flames surrounding the main flames.

In a way, the small flames catch the large flames on the combustion face, and the phenomenon known as "reentry of flames" (risk of seeing the flame descend under the combustion face), is avoided by the insulation of the fibers which provide a low temperature on the internal face of the sheet.

This type of burner ensures excellent combustion of the air / gas mixture, with a power range which can vary from approximately one to approximately thirty. Furthermore, such a burner has a relatively low noise level.

The ply of flexible material as mentioned above is in principle intended to be self-supporting, which means that it is normally able to support itself, without deformation under the effect of its own weight. She has simply need to be held at the periphery to become one with the burner housing.

However, in practice, it appears that this sheet-like material withstands impact very poorly and deforms relatively easily. There may therefore be situations in which the sheet is already damaged during its mounting in the burner, for example following a handling error. This is of course not technically and aesthetically acceptable.

In addition, problems of deformation of this sheet are also encountered when the pressure of the air / gas mixture in the burner is high. Such a phenomenon also occurs in the event of a high overpressure caused by a malfunction or a sudden ignition of the burner, for example due to electrodes or to a defective ignition system.

Document US-A-4,657,506 describes a gas burner comprising a tubular sleeve pierced with a multitude of radial openings. Its external face carries a sheet of porous woven metal. In this sleeve is mounted a shorter coaxial tube, of smaller diameter, also pierced with radial openings. The tube acts as a distribution wall, while the sleeve and the fabric constitute a combustion face.

GB-A-2 292 794 relates to a gas burner whose noise emission, due to combustion, is reduced.

The burner body has a double structure wall, namely a perforated outer wall and an inner wall also perforated. These are separated from each other by an interval between 0.5 and 1.2 mm.

The density of openings of the external wall is higher than that of the internal wall.

In the example of FIGS. 4 and 5, the openings of the external wall are distributed in patterns constituting a central opening surrounded by equidistant peripheral openings.

According to this document, the openings of the internal wall are placed opposite the central openings.

In view of this state of the art, there is still a need to provide a gas burner of the type described above, the sheet of flexible porous and insulating material being not or practically not subject to deformations due to impacts. external or burner operation problems. The present invention also aims to achieve the above objective, without calling into question the general structure of existing burners. The invention therefore relates to a gas burner which has the form of a box delimiting an enclosure in which is received the air / gas mixture to be burned and which contains a perforated partition called "distribution" through which said mixture, a part of the wall of said housing forming a combustion face comprising, on the outside, a sheet of flexible, porous and thermal insulating material, traversed by a plurality of perforations, distributed in a homogeneous manner and provided for ensuring the exhaust and combustion of said air mixture / gas after it has passed through said distribution wall.

This gas burner is remarkable in that said combustion phase also comprises, on the inside, a perforated support plate on which said sheet is in support, the openings of which are, on the one hand, each arranged opposite one another. a perforation of said ply and, on the other hand, of dimensions greater than those of said perforations.

Being thus supported by a perforated plate, the ply of flexible material sees its rigidity increase, which very significantly improves its resistance in the event of shock or overpressure.

Furthermore, the fact that the openings of this plate have dimensions greater than those of the perforations of the sheet, we will be able to keep the two "families" of flames which are characteristic of the burners according to the state of the art as described more high.

The advantages of these known burners are therefore preserved and their disadvantages eliminated.

According to other advantageous and non-limiting characteristics of this burner: - said sheet consists of ceramic fibers coated with silicon carbide or alumina oxide;

- The perforations of the sheet and the openings of the plate are circular and centered with respect to each other;

- The perforations of the sheet have a diameter of around 1.5 millimeters, while the openings of the plate have a diameter of around 2.4 millimeters;

- The support plate has a small thickness, for example between about 0.3 and about 0.8 millimeters;

- The perforations of the sheet and the openings of the plate are distributed regularly, in particular according to patterns in the form of isosceles triangles; - The housing is substantially in a cylinder whose height is significantly less than its diameter, said ply corresponding to one of the large faces of the cylinder, while the second large face has an access opening of the air / gas mixture; - Said support plate is slightly curved, its concavity being turned towards the inside of the housing;

- The housing is substantially in a cylinder whose height is significantly greater than its diameter, said ply materializing at least part of its surface of revolution, and one of its large faces is closed, while the second has a air / gas mixture access opening;

- Said distribution wall is cylindrical, coaxial with the housing, the arrival of the air / gas mixture being directed axially.

The invention also relates to a gas boiler equipped with at least one burner as described above. Other characteristics and advantages of the present invention will appear on reading the detailed description which follows, of a few exemplary embodiments. This description will be made with reference to the accompanying drawings in which:

- Figure 1 is a sectional view, along a longitudinal median plane, of a first embodiment of the burner;

- Figure 2 is a diagram showing in section a fraction of the combustion face of the burner, this diagram being intended to explain the combustion phenomena encountered there;

- Figure 3 is a partial top view of said combustion face;

- Figure 4 is a schematic view in longitudinal and median section, of another embodiment of the burner.

The burner shown in Figure 1 has a structure generally known per se. It has the shape of a housing 1, in this case cylindrical, the height of which is clearly less than the diameter. As an indication, these height and diameter are respectively of the order of 3 and 10 centimeters.

The housing consists of a ferrule 11 whose lower edge 111 is folded outwards, while its upper edge 110 is folded inwards. It also includes a flange 10 which corresponds to one of the large faces of the cylinder which constitutes the housing 1. Its peripheral rim 102 is crimped on the lower rim 11 of the ferrule.

The flange is open axially, the corresponding opening 101 being delimited by a cylindrical flange 100.

The housing contains an annular spacer 2, for example a height of one centimeter, which bears on the upper face of the flange 10. Its outside diameter is slightly less than the inside diameter of the ferrule 11. In other words , the spacer 2 is pressed against the ferrule. It may consist of an open and elastically deformable ring, the bringing together of its two ends giving it a circular shape of the desired diameter.

On this spacer rests a perforated partition 3, which has the shape of a thin disc. Its diameter is equal, apart from play, to the inside diameter of the ferrule 11. The openings of this partition 3 are referenced 30. They extend axially, that is to say parallel to the longitudinal axis XX 'of the housing.

On this partition is supported a second spacer 4, which has the same characteristics as the previous one. However, it has a lower height, for example of the order of 5 millimeters. In any event, the height of the spacer stack 2 / plate

3 / spacer 4 is less than the height of the ferrule 11.

All the parts described above are metallic, preferably made of stainless steel. They can also be in protected steel, in particular bichromate, or in sheet metal with aluminum coating. The last part of the housing 1 constitutes what can be described as the FC combustion face. As will be seen later, it is indeed at this face that the combustion of the air / gas mixture admitted into the burner takes place.

This combustion face FC is bipartite.

On the inside of the housing, it consists of a cylindrical support plate 5, for example made of the same metal as the other parts of the housing.

In the case described here, it is a thin disc, for example of the order of 0.3 to 0.8 millimeters.

The plate has a diameter similar to that of the wall 3 and rests on the spacer 4. As can be seen in Figures 1 and 2, the support plate 5 is slightly curved, its concavity being turned towards the inside of the housing. As an indication, the deflection of this plate is of the order of 2 to 4 millimeters, for a diameter of the order of 10 centimeters. The advantage of giving the plate such a curve will be explained later in the description. However, this is a preferential but not mandatory characteristic, embodiments not shown of the burner which may include a strictly planar support plate.

The second part of the combustion face FC is, on the outside, made up of a sheet 6 of a flexible, porous and thermal insulating material. As an indication, its thickness is of the order of 2 to 5 millimeters.

In a particularly preferred manner, this sheet consists of ceramic fibers coated with silicon carbide or alumina oxide. The one sold by the company SCHOTT GAS SYSTEMS hic, under the brand SCHOTT CERAMAT is perfectly suitable.

However, this ply can also be made of metallic fibers.

In the structure of FIG. 1, the ply 6 corresponds to one of the two large faces constituting the housing 1, opposite the second face constituted by the flange 10.

Against its periphery is folded up the upper edge 110 of the flange 11. in a way, it is sandwiched between this edge and the plate 5.

The plate 5 and the sheet 6 each have perforations for the passage of the air / gas mixture to be burned. According to the invention, the openings 50 of the plate 5 are arranged opposite the perforations 60 of the sheet. In addition, they have dimensions greater than those of said perforations. The advantage of such characteristics will be explained later.

The perforations 60 of the sheet pass through it in the direction of its thickness. They should not be confused with the passages which are present in the structure of the sheet and which give it its porosity.

In the embodiment presented here, the openings and perforations are circular and centered with respect to each other.

According to an advantageous embodiment, the diameter d ₂ of the openings 50 is approximately 2.4 millimeters, while that of the perforations is 1.5 millimeters. The distribution of the perforations 50 and the openings 60 is homogeneous and regular. According to the embodiment of FIG. 3, they are distant from their neighbors by a pitch N, for example of 3.5 millimeters. They are therefore distributed according to patterns in the form of isosceles triangles, the perforations / openings materializing three to three, the vertices of one of these triangles. In the example which has just been described, the housing 1 has a substantially cylindrical shape. It is particularly suitable for equipping a food cooking appliance.

However, in variants not shown, this box can have different shapes, in particular parallelepiped. In this case, the shape of the parts that the housing contains is adapted accordingly.

In Figure 4 is shown an embodiment of a burner more particularly intended to equip a boiler.

In this figure, the elements bearing identical references to those used above denote identical or similar parts.

The housing of this burner also has a cylindrical shape.

However, its height is much greater than its diameter. One 12 of its end faces is blind, while the second 10 has an opening 101 for admitting the air / gas mixture to be burned. The admission of the air / gas mixture into the housing is therefore carried out along the longitudinal axis XX 'of the housing 1.

The ply 6 materializes here the surface of revolution of the cylinder and is supported on a plate 5, also cylindrical, but of smaller diameter. As for the distribution partition 3, it is cylindrical and coaxial with the housing.

For the sake of simplification, the connecting or wedging elements of the different parts together have not been shown. The choice of their shape and dimensions is within the normal competence of those skilled in the art.

We will now explain the operation of the burner according to the invention, more specifically with reference to FIGS. 1 to 3.

On these, we have designated by the reference A + G, the air / gas mixture to be burned, and by the reference E, the interior space of the housing.

The mixture A + G is brought into the space E of the housing 1, for example using a fan, not shown, through the opening 101. In the space Ai located between this opening and the partition 3, the mixture A + G is established at a certain pressure. This mixture is then forced through the openings 30 of the partition to enter the space referenced A ₂ , disposed above this partition. This transfer from one space to another makes it possible to distribute the air / gas mixture evenly in space A ₂ . It will therefore be able to be distributed in a homogeneous manner at the level of the combustion face FC.

As already said above, the plate 5 has the function of supporting the ply 6.

In the case presented here, this plate has a certain curve, its concavity being turned inward. In this way, even if it expands under the effect of the heat of combustion, this "pre-deformation" ensures that it retains a curved shape and, thus, continues to fulfill its role of supporting the web.

A strictly flat plate would also be suitable. However, by a phenomenon of dilation, one runs the risk that it will collapse and that it will no longer fulfill its supporting role.

The diameter of the perforations 50 of the plate 5 and the pitch N are parameters which make it possible to define the maximum power of the burner per square centimeter of surface, as well as the range of variation of this power, without causing reentry of flame under the plate 5.

For a power range from 1 to 30, the diameter of the openings is 2.4 millimeters, for a pitch of 3.5 millimeters. Insofar as the openings 60 of the ply 6 are arranged in coincidence with the perforations 50 of the plate and have a smaller diameter, there is no problem of tolerance between them.

Most of the evacuation of the A + G mixture out of the housing is done through the openings 60 of the ply 6, and its combustion at the FC face is manifested by the presence of main darts or flames referenced 7 to the figure 3.

In addition, since the dimensions of the openings 50 of the plate 5 are larger than those of the perforations 60, there is a region R at the base of the latter which is accessible to the mixture A + G, since it is not supported by the plate.

The porous, aerated structure of the sheet 6, means that this secondary flow of air and gas can migrate to the outside, which results in darts 8 of reduced dimensions surrounding the main darts 7. It is these auxiliary darts 8 which keep the flame attached to the outside of the combustion face FC. Preferably, the peripheral zone of the ply 6 is free of perforations 60, so as to prevent the flames from overheating the upper rim 110 of the ferrule 11.

Being supported by the plate 5, the ply 6 is more resistant to shocks and deformations, and gives the burner the same combustion characteristics as a burner without a support plate.

The burner of Figure 4 works in the same way, except that the combustion takes place on the outer surface of a sheet of cylindrical shape. Such a burner is particularly suitable for being integrated in a boiler for private or industrial use.

Claims

1. Gas burner, which has the form of a box (1) delimiting an enclosure (E) in which is received the air / gas mixture (A + G) to be burned and which contains a perforated partition (3) called " distribution "crossed by said mixture, a part of the wall of said housing forming combustion face (FC) comprising, on the outside, a sheet (6) of flexible, porous and thermal insulating material, crossed by a plurality of perforations ( 60), distributed in a homogeneous manner and provided to ensure the exhaust and combustion of said air / gas mixture (A + G) after it has crossed said distribution wall (3), characterized in that said face of combustion (FC) also comprises, on the inside, a perforated support plate (5) on which said sheet (6) is supported, the openings (50) of which are, on the one hand, each arranged opposite a perforation (60) of said ply (6) and, on the other hand, of dimensions greater than those of said perforations (60). 2. Burner according to claim 1, characterized in that said ply (6) consists of ceramic fibers coated with silicon carbide or alumina oxide. 3. Burner according to one of claims 1 and 2, characterized in that the perforations (60) of the ply (6) and the openings (50) of the plate (5) are circular and centered with respect to the other. 4. Burner according to claim 3, characterized in that the perforations (60) of the ply (6) have a diameter of the order of 1.5 millimeters, while the openings (50) of the plate (5) have a diameter of around 2, 4 millimeters. 5. Burner according to one of claims 1 and 4, characterized in that the support plate (5) has a small thickness, for example between about 0.3 and about 0.8 millimeters. 6. Burner according to one of claims 1 and 5, characterized in that the perforations (60) of the sheet (6) and the openings (50) of the plate (5) are distributed evenly, in particular according to patterns in the form of isosceles triangles. 7. Burner according to one of claims 1 and 6, characterized in that the housing (1) fits substantially in a cylinder whose height is significantly less than its diameter, said ply (6) corresponding to one of large faces of the cylinder, while the second large face (10) has an opening (101) for access to the air / gas mixture (A + G). 8. Burner according to one of claims 1 to 7, characterized in that said support plate (5) is slightly curved, its concavity being turned towards the inside of the housing (1). 9. Burner according to one of claims 1 and 6, characterized in that the housing (1) fits substantially in a cylinder whose height is significantly greater than its diameter, said ply (6) materializing at least a part of its surface of revolution, and that one (12) of its large faces is closed, while the second (10) has an opening (101) for access to the air / gas mixture (A + G). 10. Burner according to claim 9, characterized in that said distribution wall (3) is cylindrical, coaxial with the housing, the arrival of the air / gas mixture being directed axially. 11. Gas boiler equipped with at least one burner according to one of claims 1 to 10.