EP1050712B1 - Full premix gas burner with cooling system - Google Patents

Abstract

The cooled gas burner with total premixing comprises burner rods mounted between cooling pipes (2). Each burner rod (16) has profile which follows the shape of the cooling pipe and has transverse grooves across its whole length which exit on the side of rod where the flame is to be situated.

Description

The present invention relates to a gas burner cooled to total premix.

Such a burner is for example intended to equip a boiler with hot water for central heating. The invention relates more particularly a burner which can modulate in power over a range ranging for example from 30 to 100% of its nominal power.

A burner of this type has a grid which is cooled naturally by the gas premix which burns at the outlet of the burner. In hyperstochiometric regime, the sheet metal of the grid heats up and there are risks of backfire. It is then known to cool the sheet. This cooling is then carried out using pipes in which water circulates from the circuit heating associated with the burner.

It is known, for example, to have a burner comprising a multitude of pieces stacked on top of each other and mounted between heating circuit water pipes. The premix then passes between the parts and burns outside of them.

Once this assembly mounted, its handling is quite difficult and disassembly almost impossible. It is therefore quite difficult to clean.

In particular, document DE 37 10 244 A describes a burner delimited by two plates as well as by the walls of the cooling forming a loop. Slots are present in the plate superior. A premix arrival leads into the room. The elements delimiting the chamber are fixed by welding. Disassembly of such assembly is very difficult.

The present invention therefore aims to provide a gas burner cooled to total premix whose handling and disassembly are more easier than the devices of the prior art. This burner can preferably modulate in power over a large range, for example from 30 to 100% of its nominal power.

For this purpose, the gas burner it offers is of the type cooled to total premix comprising burner grates mounted between cooling lines.

According to the invention, each burner grate is presented under the shape of a shaped bar adapted to the shape of the pipes cooling on which it rests, having transverse slots distributed along the bar, these slots opening on the side of the grid intended to be the seat of a flame and being deep enough to allow the passage of the gas premix from the inside of the burner to the outside of this one.

This design of the burner grate makes it possible to have a grate of easy handling which can be assembled, disassembled and cleaned very easily compared to the grids of the prior art.

The height of the profiled bars is preferably of the same order larger than the diameter of the tubes between which they are located. This height is for example greater than the diameter of these tubes.

For good support of the profiled bars on the tubes and also to ensure proper cooling of the burner grate, staples are provided for fixing the grilles on the cooling pipes, these staples passing through a slot in the grid, this slot being possibly wider than the slots intended only for passage premix.

It is also possible to provide a fixing of the bars profiled using screws. In this case then, each burner grate for example has bores extending parallel to the slots, these bores being intended to receive screws for fixing the grid burner on a distribution grid, the areas in which are located the bores not having a slot.

In a preferred embodiment, the burner grate has a flared section reminiscent of a V, the outer faces of the branches of the V being concave to properly support each on a cooling line and slots for the premix passage extending between the branches of the V.

To limit the surface of the slots and thereby limit their width variations due in particular to expansion problems thermal, we can predict that each slot extends over a half only from the profiled bar located on the side of a cooling. In a preferred embodiment, the slots are distributed longitudinally in pairs on the profiled bar, a rib separating each time two slots arranged in the same plane transverse.

Thermal expansion problems also appear at the ends of the profiled bars. To avoid having at these ends a passage of combustible gas mixture which may cause a return of flame, each profiled bar may have at each of its ends, on the side intended to be the seat of a flame, a fixing lug extending longitudinally and over the entire width of the profiled bar.

The burner grate is for example made of an alloy metallic based on aluminum or copper. These alloys are generally easily spinnable, which is advantageous for producing a profiled bar. In addition, these alloys are good conductors of heat.

The cooling pipes, for example, are made of steel, preferably stainless steel.

The slots made in the profiled bars present by example a depth between 20 and 40 mm and a width between 1 and 1.5 mm.

The passage of the premix through the grid being done on a relatively large height, it is possible to provide slots fairly wide without fear of flashback. This is advantageous because with wide slits, any dust present in the burner do not foul the burner grate.

Profiled bars with slots can be obtained by several processes. Advantageously, they are obtained by sawing a profiled bar. This process makes it possible to have an attractive cost price by report for example to an embodiment by molding.

To minimize the amount of air / gas fuel premix present in the burner and maintain an almost constant speed of the premix over the entire height of the burner, an advantageous form of embodiment provides that the cooling pipes are arranged so as to define a circular cylinder and a stepped tapered part, said distribution cone, is arranged inside the cylinder thus formed by the cooling tubes.

Figure 1 est une vue en coupe longitudinale d'un brûleur selon l'invention,

Figure 2 est une vue en coupe à échelle agrandie selon la ligne de coupe II-II de la figure 1,

Figure 3 est une vue en coupe longitudinale selon la ligne de coupe III-III de la figure 2 d'une barre utilisée pour réaliser la grille de brûleur,

Figure 4 est une vue en coupe selon la ligne de coupe IV-IV de la figure 3,

Figure 5 est une vue correspondant à la figure 1, à plus grande échelle, d'une seconde forme de réalisation d'un brûleur selon l'invention, et

Figure 6 est une vue en coupe selon la ligne VI-VI de la figure 5.

In any case, the invention will be clearly understood with the aid of the description which follows, with reference to the appended schematic drawing showing by way of nonlimiting examples two embodiments of a burner according to the invention.

FIG. 1 is a view in longitudinal section of a burner according to the invention,

FIG. 2 is a section view on an enlarged scale along the section line II-II of FIG. 1,

FIG. 3 is a view in longitudinal section along the section line III-III of FIG. 2 of a bar used to make the burner grate,

FIG. 4 is a sectional view along the section line IV-IV of FIG. 3,

FIG. 5 is a view corresponding to FIG. 1, on a larger scale, of a second embodiment of a burner according to the invention, and

Figure 6 is a sectional view along line VI-VI of Figure 5.

Figure 1 is a schematic view of a burner body. This the latter comprises tubes 2 made of metallic material, for example steel, copper, stainless steel or other, arranged in a cylinder and mounted between two tubular plates 4. On each tubular plate 4 is mounted a water box 6 allowing irrigation and circulation of water in the tubes 2 of the burner. Between the tubes 2 are placed profiled elements which form the burner grate at the level of which the combustion of a premix. This burner grate will be described in more detail below.

In the center of the burner is a tapered frustoconical piece called distribution cone 8. Its functions are to reduce the volume inside the burner to minimize the amount of fuel premix air / gas present in the burner and maintain an almost constant speed premix over the entire height of the burner. At the top of the cone of distribution 8, a helical part, called deflector 10, is mounted, the blades are drilled and tilted. The purpose of this deflector 10 is to create turbulence intended to mix air and gas well to obtain a homogeneous premix. Between the distribution cone 8 and the burner tubes 2, there is a grid with holes, called a distribution grid 12, the loss of which load makes it possible to distribute the premix evenly over the entire burner surface. At the top of the distribution cone 8, we can see also a thin tube, called a vent tube 14. If the temperature in the burner, this vent tube 14 makes it possible to avoid pressure increase in the cone due to volume expansion internal. This vent tube 14 opens into an air zone only.

Between two tubes 2 neighbors is each time an element section 16 which is shown in more detail in FIGS. 3 and 4. Thus, at the periphery of the burner, there is an alternation of profiled elements 16 and of tube 2.

Each profiled element 16 has a head 18 intended to be placed outside the cylinder formed by the tubes 2, a body 20 intended to be substantially at the height of the tubes 2 and a foot 22 intended to be inside the cylinder defined by the tubes 2. Each profiled element 16 has a height greater than the diameter of the tubes 2.

The outer surface of the head 18 is rounded. Its radius of curvature is greater than the radius of curvature of tube 2 but less than radius of curvature of the cylinder formed by the set of tubes 2.

The body 20 has a shape reminiscent of a V. The point of the V is on the side of the foot 22 of the profiled element 16 while the part flared from the V is on the side of the head 18 of this profiled element 16. The flared part of the body 20 fits the outside surface of the tubes 2 between which is the profiled element 16.

The foot 22 of the profiled element has a section substantially circular to which the base of the body 20 is attached.

The profiled element 16 extends over the entire length of the burner between the two tubular plates 4. It is placed each time between two tubes 2 and extends parallel to them. Cross direction tubes 2 and profiled elements 16, and over the entire length of each profiled element 16, there are slots 24. These slots extend over the entire height of the body 20 and of the head 18 of the profiled element 16. We have then a set of substantially V-shaped lamellae 26 which are all attached to a common foot 22.

As seen in Figure 3, all of the slots 24 are of same width, with the exception of a few slots 28 which have been shown wider in the drawing.

The wider slots 28 are provided for fixing the profiled elements 16 on the tubes 2. A clip 30 then takes place in this slot 28 to hold the profiled element 16 between two tubes 2. This clip 30 exerts an elastic force on the profiled element 16 so as to press the head 18 of the profiled element on the face outside of the cylinder formed by the tubes 2. This head 18 is of course substantially wider than the free space left between two neighboring tubes 2. The staples 30 are made of a spring steel wire for example which is folded to allow the profiled element to be hooked between the two tubes 2. Such a clip 30 is visible in FIG. 2. One end of the wire comes take support at the bottom of the wide slot 28 on the side of the foot 22. Then this wire follows the outside surface of a tube 2, then joins the neighboring tube 2 and also marries its outer surface.

The other slots 24 have a width which is calculated so that, whatever the burner charge rate or the air / gas ratio, the flame does not can go back up in the burner (phenomenon called "flashback"). The premix which has become homogenized on passage of the deflector 10 and which is uniformly distributed over the entire burner surface thanks to the cone distribution 8 and the distribution grid 12 passes through the slots 24 of the profiled elements 16 and ignites on the external periphery of the burner, that is to say at the periphery of the cylinder formed by the tubes 2 and the elements profiles 16. This configuration modulates the burner output between 30% and 100% of its nominal power without any problem.

The width of the slots 24 can be of the order of 1.2 mm. This is very interesting because the dust possibly present in the burner are not likely to be blocked at these slots. this is an advantage compared to punched sheets used in burners of the prior art and which have small diameter holes. The width significant slits is allowed here by the relatively thick large (of the order of 30 mm) of the profiled element 16 and the slots 24.

Figures 5 and 6 show a second embodiment of a burner according to the invention. We find in this burner tubes 2 in stainless steel arranged in a cylinder and mounted between two plates tubular 4. We also find each time a water box 6 mounted on a tubular plate 4. Here also, profiled elements form the burner grate. We also find here a helical deflector 10 and a distribution grid 12. In this embodiment, there is no cone distribution.

In this second embodiment, the profiled parts 16 forming the burner grate have the same general shape as that described with reference to Figures 1 to 4 but have shaped slots different and are fixed in the burner body differently than the profiled bars described above.

Note in Figure 6 that the section of profiled bars 16 remains unchanged. This profiled bar similarly follows the shape of tubes 2.

Cross slits 25 are made along the bar profiled. Unlike the slots 24, which extend over the entire width of the profiled bar, the slots 25 are only made at the level of one half of the profile bar. These slots 25 are each in a half of the profiled bar located on the side of a tube 2. These halves are by example separated by a longitudinal plane of symmetry 32. Of course, the slots 25 are not made over the entire half of the profiled bar 16 as can be seen in FIG. 6. These slots 25 create a passage at the level of each tube 2 between the interior space of the cylinder delimited by the cooling tubes and the outer space of this cylinder. Without the presence of the slots, the profiled bar would completely obstruct the passage between the inside of this cylinder and the outside of it.

The slots 25 are obtained for example by sawing the bar profiled. In the embodiment shown in Figures 5 and 6, we makes in the same transverse plane two slots 25, one in each half of the profiled bar 16. There remains between the two slots 25 a rib 34. It would also be possible to provide slots 25 offset at each longitudinally. This would make a slot 25 on one side of the profiled bar 16 then a neighbor on the other side of profiled bar 16 and and so on.

This embodiment allows for surface slots less important. The width of the slits therefore varies less when the temperature within the burner varies. This limits the problems of thermal expansion. Compared to the embodiment of FIGS. 1 to 4, it is as if we had come to add the rib 34 to connect to each times two solid sections adjacent to the profiled bar in order to maintain them at equal distance and therefore keep the width substantially constant of a slot 24. This prevents a slot from becoming too wide and causing then a flashback.

In this embodiment, the profiled bar 16 is fixed not using staples on the cooling tubes 2 but using screws on the distribution grid 12. Bores 36 are then provided in the profiled bar 16 for the passage of the fixing screws. At the location corresponding, a nut 38 is welded to the distribution grid. Account given the thermal expansion problems, an assembly can be carried out elastic using the fixing screws. The profiled bar 16, at the level of the bores 36, is not provided with slots 25.

To avoid flashback problems in the ends of profiled bars 16, these rest at each end on supports 40 are for example fixed using screws on nuts 38 also welded to the distribution grid 12. At each end, each profiled bar then has a fixing lug 42 coming to rest on the support 40 and extending over the entire width of the profiled bar 16. The support 40 also extends over the entire width of the profiled bar 16. The passage between the inside of the cylinder defined by the cooling tubes 2 and the outside of this cylinder while allowing expansion of the profiled bars. This dilation takes place mainly in the longitudinal direction of profiled bars. Thus during this expansion, the fixing lugs 42 slide on the supports 40. Whatever the space between the front surface of a profiled bar and the tubular plate or the support 40, the gas premix cannot pass at the ends of the burner grates. This avoids any backfire problem.

The configuration according to the invention allows good cooling of the burner grate. Indeed, the contact surface between the tubes 2 and the profiled elements 16 is relatively large. This good cooling significantly reduces polluting emissions (CO, NOx, ...) of the burner during its operation.

The burner grate as described above has many advantages. Its handling is very easy. Its dismantling and cleaning can be done very easily. In addition, the elements profiles are easy to produce and their cost is appreciably lower than the cost price of the burner grates of the prior art. It is enough to cut a profile to the desired length and to make the slots by sawing. Of course, other obtaining methods are possible. We can imagine that the profiled elements are obtained by molding.

This burner design allows a wide choice of material for the burner grate. The profiled elements can be produced by for example aluminum or copper or any other conductive material easily spun or moldable.

It goes without saying that the invention is not limited to the form of preferential embodiment described above by way of nonlimiting example; on the contrary, it embraces all variants within the framework of claims below.

Thus, for example, the invention can also be applied to a burner with in-line cooling tubes.

Claims (11)

1. Total premix cooled gas burner having burner grates mounted between cooling pipes (2), characterised in that each burner grate is in the form of a profiled bar (16) with a shape adapted to the shape of the cooling pipes between which it is situated and on which it rests, having transverse slits (24; 25) distributed along the bar, these slits opening out on the side of the grate intended to be the seat of a flame and being deep enough to permit the passage of the gas premix from the inside of the burner to the outside thereof.
2. Burner according to Claim 1, characterised in that clips (30) are provided for fixing the grates (16) on the cooling pipes (2), these clips (30) passing through a slit (28) of the grate, this slit (28) being optionally wider than the slits (24) intended solely for the passage of the premix.
3. Burner according to Claim 1, characterised in that each burner grate (16) has bores extending parallel to the slits (25), these bores being intended to receive screws for fixing the burner grate (16) on a distribution grate (12), the areas in which the bores are located not being provided with slits (25).
4. Burner according to one of Claims 1 to 3, characterised in that the burner grate has a splayed cross-section resembling a V, the outer faces of the legs of the V being concave so as to each bear snugly on a cooling pipe (2) and the slits (24; 25) for the passage of the premix extending between the legs of the V.
5. Burner according to one of Claims 1 to 4, characterised in that each slit (25) extends over only half of the profiled bar (16) situated on the side of a cooling pipe.
6. Burner according to Claim 5, characterised in that the slits (25) are distributed longitudinally in pairs over the profiled bar, a rib (34) in each case separating two slits arranged in the same transverse plane.
7. Burner according to one of Claims 1 to 6, characterised in that each profiled bar (16) has at each of its ends, on the side intended to be the seat of a flame, a fixing lug (42) extending longitudinally and over the entire width of the profiled bar (16).
8. Burner according to one of Claims 1 to 3, characterised in that the burner grate (16) is made of a metal alloy based on aluminium or copper.
9. Burner according to one of Claims 1 to 5, characterised in that the slits (24) have a depth of between 20 and 40 mm and a width of between 1 and 1.5 mm.
10. Burner according to one of Claims 1 to 6, characterised in that the slits (24, 25) are obtained by sawing a profiled bar.
11. Burner according to one of Claims 1 to 10, characterised in that the cooling pipes are arranged so as to define a circular cylinder and in that a multistage frustoconical part, called a distribution cone (8), is arranged inside the cylinder thus formed by the cooling tubes.

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