EP0679838A1 - Improvements to gas burners - Google Patents

Abstract

The gas burner consists of a distribution chamber (1) to receive air and a combustible gas, partially delimited by a thin perforated panel (2) which acts as a burner bar. The distribution chamber has an upper end with a series of feed apertures (3b) facing the perforated panel, while the perforated zones of the latter are not situated directly in line with some of the apertures. The offset perforated sections (2a) are curved, with convex sides facing towards the distribution chamber and located between its feed apertures. Apart from the curved sections, the perforated panel is generally flat, and the gas feed apertures in the distribution chamber, which are set in a plane parallel to the perforated panel, are connected to feed ducts (4) in the form of Venturi tubes fed by individual nozzles. <IMAGE>

Description

The invention relates to gas burners, and more particularly to those which comprise at least one distribution chamber which is intended to receive air and a combustible gas, and which is partially delimited by a thin perforated wall constituting a ramp combustion chamber and forming a downstream end of the distribution chamber, this distribution chamber further comprising an upstream end provided with a plurality of supply orifices arranged opposite the perforated wall and supplying the distribution chamber with air and in gas, the perforated wall comprising perforated zones which are not located directly opposite a supply orifice.

Such a gas burner is disclosed, for example, in document FR-A-2,695,457.

These burners are intended in particular to equip heating and domestic hot water production appliances running on gas, whose nominal power does not exceed 70 kW thermal.

The invention applies more particularly, but not exclusively, to gas burners of the atmospheric type.

Gas burners of the kind mentioned above have the drawback that the sheet of flames which develops above the perforated wall in the areas which are not located directly opposite a supply orifice, tends to to remain "stuck" to the perforated wall, because the speed of the gas premix leaving the perforated wall is relatively low in these areas.

This phenomenon can cause local overheating of the perforated wall, up to bringing it to red. These overheating risks causing deterioration of the perforated wall, due to its thinness.

In addition, especially when using certain combustible gases, flames may tend to form. inside the distribution chamber, which can make the operation of the burner dangerous.

The present invention aims in particular to remedy these drawbacks.

To this end, according to the invention, said perforated areas of the perforated wall which are not located directly opposite a supply orifice constitute parts hollowed out towards the upstream end of the distribution chamber.

Thus, it can be seen that the flame layer is no longer "stuck" to the perforated wall in the hollowed-out parts, and said hollowed-out parts no longer tend to be subjected to significant overheating.

• les orifices d'alimentation sont disposés alignés selon une direction longitudinale, et les parties creusées de la paroi perforée sont disposées entre les orifices d'alimentation ;
• les parties creusées de la paroi perforée ont une forme sensiblement cylindrique présentant un axe parallèle à la paroi perforée et perpendiculaire à la direction d'alignement des orifices d'alimentation ;
• les parties creusées ont une forme cylindrique à section arrondie ;
• les parties creusées ont une forme cylindrique à section sensiblement en forme de V ;
• la paroi perforée présente une forme générale plane, en dehors des parties creusées, et dans lequel les orifices d'alimentation sont disposés dans un plan commun parallèle à la paroi perforée ;
• chaque orifice d'alimentation est relié à un conduit d'alimentation qui, au moins au voisinage de l'orifice d'alimentation, présente un axe sensiblement perpendiculaire à la paroi perforée ;
• les conduits d'alimentation sont des tubes venturis alimentés chacun en gaz combustible par un injecteur ;
• les différents tubes venturis présentent des axes rectilignes parallèles et coplanaires.

In preferred embodiments, use is also made of one and / or the other of the following arrangements:

• the feed orifices are arranged aligned in a longitudinal direction, and the hollowed out portions of the perforated wall are arranged between the feed orifices;
• the hollow parts of the perforated wall have a substantially cylindrical shape having an axis parallel to the perforated wall and perpendicular to the direction of alignment of the supply orifices;
• the hollowed parts have a cylindrical shape with rounded section;
• the hollowed parts have a cylindrical shape with a substantially V-shaped section;
• the perforated wall has a generally planar shape, apart from the hollowed out parts, and in which the supply orifices are arranged in a common plane parallel to the perforated wall;
• each supply orifice is connected to a supply duct which, at least in the vicinity of the supply orifice, has an axis substantially perpendicular to the perforated wall;
• the supply conduits are venturis tubes each supplied with combustible gas by an injector;
• the different venturi tubes have parallel and coplanar rectilinear axes.

Other characteristics and advantages of the invention will appear during the following description of three of its embodiments, given by way of nonlimiting examples, with reference to the accompanying drawings.

• la figure 1 est une vue schématique partielle en perspective d'un brûleur à gaz selon l'invention,
• la figure 2 est une vue en coupe transversale de la plaque de support et de la paroi perforée d'une des rampes de combustion du brûleur de la figure 1,
• la figure 3 est une vue en coupe longitudinale partielle d'une rampe du brûleur de la figure 1,
• la figure 4 est une vue en coupe transversale de la plaque de support et des parois perforées d'une variante du brûleur de la figure 1, et
• la figure 5 est une vue similaire à la figure 4, pour une variante de la figure 4.

In the drawings:

• FIG. 1 is a partial schematic perspective view of a gas burner according to the invention,
• FIG. 2 is a cross-sectional view of the support plate and of the perforated wall of one of the combustion ramps of the burner of FIG. 1,
• FIG. 3 is a view in partial longitudinal section of a ramp of the burner in FIG. 1,
• FIG. 4 is a cross-sectional view of the support plate and the perforated walls of a variant of the burner of FIG. 1, and
• FIG. 5 is a view similar to FIG. 4, for a variant of FIG. 4.

In the different figures, the same references designate identical or similar elements.

In the following description, terms such as "vertical", "horizontal", "high", "low" are given with reference to the most common position of use of the burner, but are not limiting.

The burner shown in Figures 1 to 3 is of the atmospheric type, and has five juxtaposed combustion ramps, only one of which is shown.

• une pluralité de tubes venturis 4 s'étendant respectivement selon des axes verticaux situés dans un même plan vertical, chaque tube venturi comprenant, d'amont en aval, un court tronçon convergent, un col cylindrique, puis un long tronçon divergent,
• une nourrice 6 d'alimentation en gaz combustible, dotée d'autant d'injecteurs 5, chaque injecteur 5 étant orienté vers le haut et disposé selon l'axe d'un tube venturi 4, légèrement au-dessous de son tronçon convergent de façon à rendre possible l'admission d'air à ce niveau,
• une plaque de support 3 massive, réalisée en un matériau bon conducteur thermique tel que l'aluminium, cette plaque de support ayant une forme générale plane et étant orientée horizontalement, ladite plaque de support étant traversée par des alésages verticaux 3b qui sont en nombre égal aux tubes venturis 4 et qui comportent chacun une partie inférieure élargie 3c dans laquelle est emboîtée l'extrémité aval d'un tube venturi,
• une chambre de répartition 1 qui est définie dans un évidement 3a en partie supérieure de la plaque de support 3 et dans laquelle débouchent tous les tubes venturis, susmentionnés,
• et une paroi perforée 2 de faible épaisseur (par exemple quelques dixièmes de millimètres) au-dessus de laquelle a lieu la combustion du prémélange gazeux provenant de la chambre de répartition 1.

Each combustion rail includes:

• a plurality of venturi tubes 4 extending respectively along vertical axes situated in the same vertical plane, each venturi tube comprising, from upstream to downstream, a short convergent section, a cylindrical neck, then a long divergent section,
• a fuel gas supply manifold 6, provided with as many injectors 5, each injector 5 being oriented upwards and arranged along the axis of a venturi tube 4, slightly below its section converging so to make it possible to admit air at this level,
• a massive support plate 3, made of a material which is a good thermal conductor such as aluminum, this support plate having a generally planar shape and being oriented horizontally, said support plate being traversed by vertical bores 3b which are of equal number to the venturis tubes 4 and which each comprise an enlarged lower part 3c in which the downstream end of a venturi tube is fitted,
• a distribution chamber 1 which is defined in a recess 3a in the upper part of the support plate 3 and into which all the venturis tubes, mentioned above, open out,
• and a thin perforated wall 2 (for example a few tenths of a millimeter) above which the combustion of the gas premix from the distribution chamber 1 takes place.

The feeders 6 of the burner are each supplied from a source of pressurized combustible gas 7, via pipes 8 and valves 9 specific to each feeder. Preferably, each valve 9 can operate in all or nothing, as disclosed for example in the document FR-A-2 695 475 cited above, so that each combustion rail is always supplied with an optimal gas flow rate.

The perforated wall 2 can be made, for example, of stainless steel and has numerous perforations in the form of parallel rectilinear slots arranged perpendicular to the longitudinal direction of said perforated wall.

These slots represent for example a proportion of the upper surface of the perforated wall 2 which is greater than 30%, and which can be for example approximately 35%. Thus, the perforated wall 2 has good transparency to the thermal radiation emitted by the flames F formed above it, which decreases the temperature of the flames.

This high density of perforations also allows a better distribution of the layer of flames above the perforated plate, with a surface power preferably less than 250 W / cm², which contributes to reducing the temperature of the perforated wall. Furthermore, the high density of the perforations is also favorable for reducing the pressure losses in the gas flow.

The perforated wall 2 has laterally two longitudinal edges 2b folded vertically towards the support plate 3. Thus, the perforated wall 2 can fit onto the support plate 3 by overlapping it and the horizontal part of the wall 2 rests on the face upper of the support plate 3 at the periphery of the recess 3a of this plate. This mounting allows sufficient sealing between the perforated wall 2 and the support plate 3.

As can be seen in particular in Figure 3, the perforated wall 2 has stamped parts 2a which are hollowed out or curved towards the inside of the distribution chamber 1 above each portion of the support plate 3 which separates two bores 3a, 3b. According to an advantageous embodiment, these stamped parts can have a cylindrical shape, possibly with an arc or V-shaped section, having an axis perpendicular to the vertical plane common to the vertical axes of the venturis tubes.

This arrangement makes it possible to compensate for the non-uniformity of the speed field of the gaseous premix leaving the perforated wall 2, and prevents the flame blanket F from remaining stuck to the perforated wall 2 between two venturis tubes.

Indeed, the speed of the gas premix leaving the perforated wall 2 is lower between the outlets of two venturis tubes 4, so that, without the stamped parts 2a, the flame sheet F would tend to form in contact with the perforated wall 2 in these locations, or even to enter inside the distribution chamber 1 with certain types of combustible gas.

The formation of flames F in contact with the perforated wall risks causing local overheating of the perforated wall 2, overheating which can cause deterioration of the perforated wall due to its thinness.

In addition, if the flames F tend to form inside the distribution chamber 1, the operation of the burner can be dangerous.

The support plate 3 has a thickness e, below the distribution chamber 1, which can be greater than 8 mm, and for example between 8 and 15 mm. This plate is therefore massive enough to withstand without damage the thermal energy it receives by conduction from the perforated wall 2, and by radiation from the flames and from the perforated wall 2. In addition to its mechanical connection and sealing functions between the venturis tubes and the perforated wall, this support plate thus ensures a function of absorption and thermal diffusion.

The support plate 3 can be treated, at least in the part of its surface which is arranged opposite the perforated wall 2, so that it has a good coefficient of absorption of thermal radiation. For example, the surface of the solid plate 3 can be treated so that it has a dark color (in particular by means of a special paint, by means of an anodization, or by means of an oxidation), and / or so that it has a rough wall.

In order to collect a sufficient part of the thermal radiation from the flame table and the grid in the venturis tubes 4, for reasons which will be seen below, it is advantageous that the bores 3b of the support plate 3 occupy a fairly large proportion of the surface of the support plate. For example, these bores 3b can have a diameter D substantially equal to the width of the recess 3a of the support plate and the spacing d between two successive bores 3b of the support plate can for example be less than half of this diameter D.

The venturis tubes 4 can be made, for example, of stainless steel or aluminized steel, and they absorb by their internal surface the thermal radiation coming from the layer of flames located above the perforated wall 2, and also coming from the perforated wall. herself.

In addition, the venturis tubes 4 receive heat by conduction from the support plate 3.

The heat received by radiation or by conduction by the venturis tubes 4 is transmitted to the flow of air and combustible gas which passes through these venturis tubes. Optionally, to increase this heat exchange with the gas flow, it is possible to produce axial fins (not shown) inside the venturis tubes.

Preheating of the mixture of air and combustible gas is thus obtained, which makes it possible to obtain better flammability of the mixture, hence greater stability of the flame front above the grate.

As can be seen in FIG. 1, the venturis tubes 4 can each be made by assembling half-shells 4a, 4b, from stamped sheet metal, these two half-shells being assembled in a sealed manner against each other, in particular by crimping or welding.

During the assembly of the combustion ramp, the upper parts of the half-shells 4a, 4b are received in a groove 3d formed longitudinally in the lower part of the support plate 3, and in the parts enlarged 3c bores 3b.

As shown in Figure 4, the support plate 3 may optionally be common to the different burner combustion ramps, so as to form a one-piece assembly. In this case, the support plate 3 may comprise, in the upper part, longitudinal grooves 3f which receive the folded longitudinal edges of the perforated walls 2. This arrangement makes it possible to reduce the cost of the burner and to simplify its production, and also facilitates diffusion heat by the common support plate 3, all the more so since all of the burner combustion ramps are not necessarily simultaneously in operation.

Optionally, as shown in FIG. 5, the support plate 3 can be similar to that of FIG. 4 and be equipped with a perforated wall 2 also common to the different combustion ramps. This perforated wall 2 may optionally include parallel longitudinal folds 2c which penetrate into the grooves 3f of the support plate 3, in order to achieve a sufficient seal between the distribution chambers 1 of the different combustion ramps.

The use of a common perforated wall 2 is advantageous insofar as it reduces the cost of the burner and simplifies it. This arrangement is not likely to disturb the proper functioning of the burner, for example by transmission of heat from one part to another of the common perforated wall, insofar as the massive support plate tends precisely to effectively reduce the temperature of this perforated wall.

According to another variant, not shown, the support plate 3 of each combustion ramp, or possibly a monobloc plate common to all the combustion ramps, could be tightly connected to the upper part of a chamber receiving a mixture of air and combustible gas under pressure, the burner then being supply air type.

Instead of a massive plate 3 mounted between the venturis tubes 4 and the perforated wall 2, each burner combustion ramp according to the invention could possibly include a piece of non-massive sheet metal, possibly cooled by water.

In addition, each burner combustion ramp could possibly not include an intermediate part between the venturis tubes 4 and the perforated wall 2, the venturis tubes then being produced for example as disclosed in document FR-A-2 695 475 by assembly. two stamped sheets common to all venturis tubes, these stamped sheets also forming the side walls and the bottom of the distribution chamber 1.

Claims (9)

Gas burner comprising at least one distribution chamber (1) which is intended to receive air and a combustible gas, and which is partially delimited by a thin perforated wall (2) constituting a combustion ramp and forming a downstream end of the distribution chamber, this distribution chamber further comprising an upstream end provided with a plurality of supply orifices (3b) arranged opposite the perforated wall (2) and supplying the distribution chamber (1) with air and gas, the perforated wall (2) comprising perforated zones (2a) which are not located directly opposite a supply orifice (3b),
characterized in that said perforated areas of the perforated wall which are not located directly opposite a supply orifice (3b) constitute hollowed out parts (2a) towards the upstream end of the distribution chamber (1). Burner according to claim 1, in which the feed orifices (3b) are arranged aligned in a longitudinal direction, and the hollowed out parts (2a) of the perforated wall are arranged between the feed orifices (3b). Burner according to claim 2, in which the hollowed-out parts (2a) of the perforated wall have a substantially cylindrical shape having an axis parallel to the perforated wall and perpendicular to the direction of alignment of the supply orifices (3b). Burner according to claim 3, in which the hollowed out parts (2a) have a cylindrical shape with rounded section. Burner according to claim 3, in which the hollowed out portions (2a) have a cylindrical shape with a substantially V-shaped section. Burner according to any one of the claims previous, in which the perforated wall (2) has a generally planar shape, apart from the hollowed out parts (2a), and in which the supply orifices (3b) are arranged in a common plane parallel to the perforated wall (2) . Burner according to any one of the preceding claims, in which each supply orifice (3b) is connected to a supply duct (4) which, at least in the vicinity of the supply orifice (3b), has a axis substantially perpendicular to the perforated wall (2). Burner according to claim 7, in which the supply conduits are venturi tubes (4) each supplied with combustible gas by an injector (5). Burner according to claim 8, in which the different venturi tubes (4) have parallel and coplanar rectilinear axes.

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