EP0334736A1 - Gas burners - Google Patents

Abstract

A gas burner is provided of the type distributing, through multiple nozzles (12), the flames (13) generated by the combustion of a pressurized fuel gas in air, comprising an air-fox (1) one wall (3) of which is perforated with a large number of closely spaced orifices (5), a gas feed-tank (7) connected to a pressurized fuel gas source and a plurality of hollow needles (11) each connecting the inside of the feed-tank (7) to the central zone of the inlet of an orifice (5) in the perforated wall (3) so as to define with this orifice one of the flame production sites (12). The air-box is connected to a pressurized air source, the orifices are cylindrical and a mechanical obstacle (16) is provided in the centre of the outlet of each orifice, for deflecting the gas jet leaving the needle and mixing it with the air stream which surrounds it.

Description

The invention relates to gas burners of the type distributing, through multiple nozzles, the flames generated by the combustion of a combustible gas under pressure in the air, this gas being able to be, for example, one or the other of the following: natural gas, butane, propane.

Such burners are used, for example, in water heaters, bath heaters, domestic or industrial central heating boilers, stoves, etc.

The invention relates more particularly, among these burners, those which include an air box of which an outer wall is perforated by a large number of close orifices, a gas manifold connected to a source of pressurized combustible gas, this manifold being arranged so as to present opposite the perforated wall of the air box a perforated partition sufficiently spaced from this perforated wall so that air can circulate freely between said wall and said partition and a plurality of hollow needles each connected in a manner watertight at the edge of a hole in the partition and each opening into the central zone of the entrance to an orifice in the perforated wall so as to define with the latter a nozzle for distributing the fuel air-gas mixture forming a site for flame production.

In the known embodiments of these burners, called "atmospheric", the air box communicates with the atmosphere and the air used for the formation of the flame-generating combustible mixture is entrained in the orifices by the stream of pressurized gas leaving the needles, said orifices having for this purpose a profile converging downstream.

It is therefore difficult to settle in a wide range the calorific power of the burner, in particular given the need to avoid, for low powers, the extinction of certain flames by re-entry of these upstream of the distribution nozzles and, for high powers, the extinction of certain flames by detachment of these downstream.

In addition, the flame-generating combustible mixture is not homogeneous, the relative proportion of the gas with respect to the air being higher in the area near the outlet axis of each needle, area in which the gas stream flows without being obstructed by any obstacle, only in the peripheral regions of each distribution nozzle: this results in imperfect combustion of said mixture and the production of undesirable toxic gases, in particular carbon monoxide and nitrogen oxides, in the products of combustion.

The object of the invention is, above all, to remedy these drawbacks.

To this end, the burners of the type in question according to the invention are essentially characterized in that the air box is connected to a source of pressurized air, in that each orifice is constituted by at least one cylindrical hole, and in that a mechanical obstacle is placed across the central zone of the outlet of each orifice, in the axial extension of the corresponding needle, so as to deflect the jet of gas leaving this needle towards the air stream surrounding this jet.

In preferred embodiments, use is also made of one and / or the other of the following arrangements:
- the mechanical obstacles are bridges dividing the corresponding orifices into two identical halves,
the perforated area of the perforated wall of the box is delimited laterally by at least one series of small holes passing through this wall from side to side and opening outwardly at the foot of a rim projecting outwardly from the wall,
- additional orifices are made in the perforated wall of the air box, regularly distributed between the above orifices and of cross section smaller than that of these orifices,
the orifices hollowed out in the perforated wall of the air box are circular and delimited by counterbores on the outside of this wall,
the orifices hollowed out in the perforated wall of the air box are joined together by grooves hollowed out in the external face of this wall,
the bridges constituting the mechanical obstacles consist of thin wires housed in the above grooves,
the perforated wall of the air box and the perforated partition of the manifold are spaced apart by a distance of the order of cm, the diameter of each orifice hollowed out in the perforated wall is of the order of 4 mm, the internal diameter of each needle is of the order of 0.6 mm to 0.7 mm, its external diameter is of the order of 1.2 to 1.4 mm, the distance between the axes of the neighboring needles is of the order of 6 to 8 mm, the diameter of each additional orifice, if provided, is of the order of 2 to 3 mm and that of the small border holes, if provided, is in the order of 2 to 3 mm,
- the perforated wall of the air box is composed of two adjoining walls, one interior and the other exterior, having perforations offset mutually so that the exterior wall forms opposite the central areas of the perforations of the interior wall bridges constituting mechanical obstacles,
the perforations hollowed out in the above walls have elongated shapes with parallel edges and are mutually aligned according to the direction of their elongation,
- the two adjoining walls are circular and their perforations are elongated radially,
the bridges formed between the perforations hollowed out in the inner wall are wider in the areas of the adjoining walls, the closest to the axis of these walls,
- the inner wall is thicker than the outer wall,
the face of the perforated wall of the air box, inside this box, is hollowed out in the immediate vicinity of each orifice by at least one air inlet capable of imparting a rotary movement to the air admitted into this orifice,
- The air box has the general shape of a cylindrical wafer and the nurse, that of a hollow ring coaxial with the box and contained in it.

The invention includes, apart from these main provisions, certain other provisions which are preferably used at the same time and which will be more explicitly discussed below.

• Les figures 1 et 2, de ces dessins, montrent respectivement en coupe axiale selon I-I, figure 2 et en demie vue en plan, un brûleur à gaz établi selon l'in­vention.
• La figure 3 est un détail agrandi de la figure 1.
• Les figures 4 et 5 montrent à plus grande échel­le, respectivement, un morceau de la face extérieure de la paroi perforée comprise par ledit brûleur et un mor­ceau de la face intérieure de cette paroi.
• La figure 6 montre en vue en plan une variante de brûleur à gaz établi selon l'invention.
• Les figures 7 et 8 montrent à échelle agrandie une portion de ce brûleur en coupe axiale selon VII-VII figure 8 et en vue en plan.

In what follows, two preferred embodiments of the invention will be described with reference to the accompanying drawings, of course in a non-limiting manner.

• Figures 1 and 2 of these drawings show respectively in axial section along II, Figure 2 and in half plan view, a gas burner established according to the invention.
• Figure 3 is an enlarged detail of Figure 1.
• Figures 4 and 5 show on a larger scale, respectively, a piece of the outer face of the perforated wall included by said burner and a piece of the inner face of this wall.
• Figure 6 shows in plan view a variant of gas burner established according to the invention.
• Figures 7 and 8 show on an enlarged scale a portion of this burner in axial section along VII-VII Figure 8 and in plan view.

The burner which is the subject of FIGS. 1 to 5 comprises an air box 1 in the form of a thick wafer, that is to say bounded by a cylindrical side wall of revolution 2 and by two transverse plane walls 3 and 4.

One of these planar walls 3 is perforated by a multitude of close orifices 5 whose inner face is cylindrical of revolution.

The other flat wall 4 is crossed by a pipe 6 connecting the box to an external source of pressurized air such as a fan (not shown).

Inside the box 1 is housed, with play in all directions, a gas manifold 7 which, like the box 1, has the shape of a cylindrical wafer, but smaller than the said box and hollowed out in the center by a fireplace 8.

This manifold is arranged coaxially with the box 1, it is connected by a pipe 9 to a source of pressurized combustible gas and its flat wall 10 parallel to the perforated wall 3 is bristling with a multitude of hollow needles 11 each connecting the inside the nurse 7 at the central area of an orifice 5.

The distance D between the opposite faces of the wall 3 and of the partition 10 is large enough for the air to circulate freely in the space Z created between these elements and, for the same reason, the spacings E between the different needles are large enough and the outside diameter d _e thereof, small enough.

The air pressure occupying space Z is then the same at all points in this space.

Likewise, the internal volume of the annular manifold 7 is large enough for the gas admitted into it through the pipe 9 to be subjected to the same pressure at all points in this volume.

It follows that the pressurized gas flows distributed respectively to the outlets of the different needles 11 are all identical to each other and that the pressurized air flows projected towards the outside of the box 1, around the outlets of needles, at through the holes 5, are also identical to each other.

Consequently, the compositions of the air-gas mixture to be burned which are distributed on the combustion sites themselves through the various nozzles 12 formed by the orifices 5 and the outlets of the needles 11 are identical to each other and very easy to adjust by acting on the air inlet pressure in the box 1 and / or on the gas inlet pressure in the manifold 7.

If therefore the two air and gas components of the combustible mixture are intimately mixed at the sites indicated, an excellent and homogeneous combustion is automatically obtained at these sites during the formation of the multiple flames 13 due to the ignition of said mixture at said sites.

To ensure this intimate mixing, a mechanical obstacle is provided in the central zone of each orifice 5, that is to say in the axial extension of each needle 11.

This obstacle deflects the jet of gas leaving the needle, creating a certain turbulence therein, which ensures its intimate mixing with the stream of pressurized air which surrounds it just before the distribution of the mixture obtained at the outlet of the corresponding nozzle.

In the embodiment of FIGS. 1 to 5, the obstacles in question are thin wires 16 made in particular of stainless steel, wires attached to the external face of the perforated wall 3 of the air box, diametrically across the orifices 5.

The quality and homogeneity of the combustion can be further improved by fitting the perforated wall 3 of the air box as follows:
- the orifices 5 are delimited, on the side of the external face of said wall, by counterbores 14,
- These counterbores 14 are joined together by grooves 15 hollowed out in said face and constituting a network of small channels facilitating the interignition as well as the attachment of the flames 13, some of these grooves 15 receiving the wires 16 above, which also serve as flame catchers,
- The perforated annular zone of the wall 3 is delimited laterally, both internally and externally, by a ring of small holes 17 passing through this wall right through and opening outwardly at the foot of a rim 18 which projects outwardly from said wall,
a plurality of small circular orifices 24 are regularly hollowed out in the perforated zone of the wall 3 regularly distributed between the orifices 5 and of diameter smaller than that of these orifices 5,
- At least one air inlet 19 (see FIGS. 3 to 5) is hollowed out in the inner face of the wall 3, in the immediate vicinity of each orifice 5, capable of imparting a rotary movement with the pressurized air admitted into this orifice, which improves its mixture with the combustible gas leaving the central needle 11, a particularly valuable advantage when this gas is butane or propane.

In practice, the various dimensions of the components of the circular nozzles 12 are advantageously given the following values:
distance D, which corresponds substantially to the length of each needle 11 protruding from the partition 10: 8 to 10 mm, preferably 9 mm,
- spacing E between the axes of the neighboring needles: 5 to 9 mm, preferably 6 to 8 mm,
- internal diameter d _i of each needle: 0.4 to 0.8 mm, preferably 0.6 mm to 0.7 mm,
- outside diameter d _e of each needle: 1 to 1.5 mm, preferably 1.2 to 1.4 mm,
- thickness e of the perforated wall 3: 2 to 5 mm,
- diameter T of each orifice 5: 3 to 5 mm, preferably 4 mm,
- diameter L of each counterbore 14: 5 to 7 mm, preferably 6 mm and depth thereof: approximately 1 mm.

The diameter of the holes 17 and that of the orifices 24, if provided, are advantageously of the order of 2 to 3 mm.

The number of needles is generally several tens, or even several hundreds.

The transverse plane into which each needle 11 opens is generally located axially a little below the level of the interior surface of the perforated wall 3 of the box 1, that is to say inside the box, but it can be located a little beyond this level towards the outside, without however exceeding that of the outside surface of the wall 3.

We can still see on the drawing:
screws 20 (FIG. 1) making it possible to fix the manifold 7 inside the box 1 and cooperating with complementary threaded bores 21 hollowed out in extra thicknesses 22 of this manifold,
- And an igniter 23 (Figure 2), for example of the piezoelectric spark type.

The air box 1 is generally formed by stamped metal sheets, for example stainless steel or aluminum, including its perforated wall 3, which could however be made of a molded or sintered ceramic, while the manifold 7 is made of a metal part, for example made of molded aluminum alloy.

The burner which is the subject of Figures 6 to 8 is of the same type as the previous one and differs only in the perforated outer wall of the air box.

This wall also has the general shape of a circular plate, but this plate is here composed of two flat discs 25, 26 joined against one another, one of these discs 25, arranged on the inside. of the box, preferably being thicker than the other disc 26, outside, the thickness of each disc being in particular of the order of 1 to 2 mm.

The orifices hollowed out in said wall are no longer here circular holes but radial slots each composed of a first slot 27 cut out in the inner disc 25 and by two radial slots 28 radially aligned with the outer disc 26, the inner lateral faces of said slots being all cylindrical.

The two radial slots 28 are separated by a bridge 29 located opposite the center of the corresponding slot 27, that is to say in the axial extension of the corresponding needle 11.

The bridges 29 play here the role of a deflecting obstacle and creator of turbulence, or even of flame catching device, which was played by the wires 16 in the previous embodiment.

The slots 27 are, in turn, separated by bridges 30 against which abut the streams of pressurized air tending to escape from the air box.

The different perforations of the two discs are drawn in such a way that the simple axial juxtaposition of these two discs, in well defined relative angular positions, results in the presence of a trigger guard 29 opposite the center of each slot 27.

In the embodiment illustrated in FIGS. 6 to 8, these perforations are all narrow radial slots and aligned radially, the width of the slots 27 hollowed out in the disc 25 being slightly greater than that of the slots 28 which is typically of the order of 2 mm- and the bridges 30 mutually separating the slots 27 are wider as they are closer to the common axis of the two discs.

The slots 27 and 28 could also have forms other than rectilinear and radial, extending for example according to rectilinear segments inclined on the corresponding radii, or according to concentric arcs of a circle, or even according to spiral arcs or even according to crosses.

In each case, these slots are delimited laterally by cylindrical walls, which allows them to be produced by simple stamping of sheets.

In each case, an obstacle is provided opposite the center of each slot, and this obstacle is bordered by voids large enough to allow through them an unimpeded distribution of the mixture of the flame-generating fuel to the outside of the box 1 .

The obstacle in question is generally, as before, a trigger guard crossing, at its exit, the associated dispensing orifice, which it divides into two identical halves.

Here again, additional holes allocated solely for the passage of pressurized air could be hollowed out in the discs.

The flow rate of the air-gas mixture can be adjusted once and for all by giving predetermined values to the flow rates of its two components, the ratio between these two flow rates corresponding to the stoichiometric formula. of the perfect combustion increased by the minimum excess air imposed by the standards, taking into account the possible contributions of air carried through the holes (17, 24) not associated with needles (11).

According to an advantageous variant, the flow rates or pressures of the two components can be adjusted as desired, taking care of course that the composition of the mixture remains close to its optimal value.

We can thus "modulate" the calorific power of the burner.

This modulation is possible here in an extremely wide range since it can go from 1 to 20 and even more whereas with the previously known embodiments with "atmospheric" burners it was difficult to exceed a ratio of 4 between the two extreme values of the calorific power likely to be generated by the burner.

Thus the burner described above can deliver at will a calorific power varying from 2 to 30 kW and even beyond, that is to say starting from an extremely low minimum value for which each flame is reduced to a tiny blue pearl visible only in the dark up to the maximum value corresponding to the pressure of the network or other source of gas and that of the blown air, taking into account the dimensions of the distribution orifices.

As a result of this, and whatever the embodiment adopted, there are finally burners whose constitution and operation result sufficiently from the above.

These burners have many advantages over those previously known, in particular:
- in that they allow excellent combustion over the entire "surface" of the burner, defined by the perforated area of its air box, which reduces, or even cancels, the proportion of unwanted toxic gases (such as carbon monoxide or nitrogen oxides) in the products of combustion,
- and in that they lend themselves to a very simple power adjustment in an extremely wide range which can exceed the ratio of 1 to 20 between its extreme values.

As is obvious, and as already follows from the foregoing, the invention is in no way limited to those of its modes of application and embodiments which have been more especially envisaged; on the contrary, it embraces all variants, in particular:
- those or the flames 13 would have an orientation other than ascending vertical, for example descending vertical, or horizontal,
- And those where the perforated wall from which the flame mat comes out would have a shape other than that illustrated with a flat washer, for example that of a flat disc, or that of at least one flat and elongated rectangle forming a kind of "lit ramp", or even that of at least the lateral surface of a cylinder, of revolution or not, or that of a hemisphere or a sphere excluding a portion of this sphere reserved for the necessary radial admissions of the gaseous components.

Claims (16)

1. Gas burner comprising an air box (1) of which an outer wall (3; 25,26) is perforated by a large number of close orifices, a gas manifold (7) connected to a source of combustible gas under pressure, this manifold being arranged so as to present opposite the perforated wall of the air box a perforated partition (10) sufficiently spaced from this perforated wall so that the air can circulate freely between said wall and said partition and a plurality hollow needles (11) each sealingly connected to the edge of a hole in the partition and each opening into the central zone of the inlet of an orifice (5; 27,28) of the perforated wall so as to define with the latter a nozzle (12) for distributing the fuel air-gas mixture forming a flame production site (13), characterized in that the air box (1) is connected to a source of pressurized air, in that each orifice (5; 27,28) is constituted by at least one cylindrical hole and in that a mechanical obstacle (16; 29) is arranged across the central zone of the outlet of each orifice, in the axial extension of the corresponding needle (11), so as to deflect the jet of gas leaving this needle towards the air stream surrounding this jet. 2. Burner according to claim 1, characterized in that the mechanical obstacles (16; 29) are bridges dividing the corresponding orifices (5; 27, 28) into two identical halves. 3. Burner according to any one of the preceding claims, characterized in that the perforated area of the perforated wall (3; 25,26) of the box (1) is delimited laterally by at least one series of small holes (17) crossing this wall right through and opening outwardly at the foot of a ledge (18) projecting outwardly from the wall. 4. Burner according to any one of the preceding claims, characterized in that complementary orifices (24) are formed in the perforated wall of the air box, regularly distributed between the above orifices and of cross section smaller than that of these holes. 5. Burner according to any one of the preceding claims, characterized in that the orifices (5) hollowed out in the perforated wall (3) of the air box are circular and delimited by countersinks (14) on the outside of this wall . 6. Burner according to claim 5, characterized in that the orifices (5) are joined together by grooves (15) hollowed out in the outer face of the wall (3). 7. Burner according to claim 6, characterized in that the bridges constituting the mechanical obstacles consist of thin wires (16) housed in the grooves (15). 8. Burner according to any one of the preceding claims, characterized in that the perforated wall of the air box (1) and the perforated partition of the manifold (7) are spaced apart by a distance (D) of l order of cm, in that the diameter (T) of each orifice (5) hollowed out in the perforated wall is of the order of 4 mm, in that the internal diameter (di) of each needle (11) is of the order of 0.6 mm to 0.7 mm, in that its external diameter (of) is of the order of 1.2 to 1.4 mm, in that the distance (E) between the axes of the neighboring needles is of the order of 6 to 8 mm, in that the diameter of each complementary orifice (24), if provided, is of the order of 2 to 3 mm and in that of the small border holes (17), if provided, is of the order of 2 to 3 mm. 9. Burner according to any one of claims 1 to 4, characterized in that the perforated wall of the air box is composed of two adjoining walls (25, 26), one inside and the other outside, having perforations (27,28) mutually offset so that the outer wall forms, opposite the central zones, perforations of the inner wall of the bridges (29) constituting the mechanical obstacles. 10. Burner according to claim 9, characterized in that the perforations (27,28) have elongated shapes with parallel edges and are mutually aligned in the direction of their elongation. 11. Burner according to claim 10, characterized in that the two adjoining walls (25, 26) are circular and in that their perforations (27, 28) are elongated radially, 12. Burner according to claim 11, characterized in that the bridges (30) formed between the perforations (27) hollowed out in the inner wall (25) are wider in the areas, of the adjoining walls, closest to the axis of these walls. 13. Burner according to any one of claims 9 to 12, characterized in that the inner wall (25) is thicker than the outer wall (26). 14. Burner according to any one of claims 9 to 13, characterized in that the adjoining walls <(25,26) have thicknesses of the order of 1 to 2 mm and in that the perforations (27,28) hollowed out in these walls are stamped slots whose width is of the order of 2 mm. 15. Burner according to any one of the preceding claims, characterized in that the face of the perforated wall of the air box, internal to this box, is hollowed out in the immediate vicinity of each orifice by at least one air inlet (19) suitable for imparting a rotary movement to the air admitted into this orifice. 16. Burner according to any one of the preceding claims, characterized in that the air box (1) has the general shape of a cylindrical wafer and the feeder (7), that of a hollow ring coaxial with the box and contained in it.

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