EP0549416B1 - Grid burner and heating installation comprising same - Google Patents

Abstract

Gas burner comprising a gas distribution chamber (3) fed with combustive air and combustible gas and communicating with a combustion chamber (15) through a main flame stabilization grille (11) having a lacunar structure, porous to the air/gas mixture. Preferably, the means (23) for ignition of the burner will be disposed outside the distribution chamber but will pass through the grille (11), the ignition being carried out either from one side of this grille, or from its periphery.

Description

The invention relates to a gas mixture burner and combustion grate (s) which can be used in particular on immersion tube heating installations.

• une chambre de répartition dans laquelle circule un mélange d'air comburant et de gaz combustible,
• une chambre d'allumage située à côté de la chambre de répartition dans laquelle elle est isolée par une cloison de séparation et dans laquelle circule un mélange d'air comburant et de gaz combustible,
• des moyens d'alimentation en air et en gaz combustible desdites chambres de répartition et d'allumage, respectivement,
• une chambre de combustion avec laquelle lesdites chambres de répartition et d'allumage communiquent à une extrémité, à travers des moyens de stabilisation de flammes en forme de grille, et
• des moyens d'allumage du brûleur s'étendant partiellement dans la chambre de combustion et à l'écart de la chambre de répartition.

More specifically, the invention relates first of all to a gas burner comprising:

• a distribution chamber in which a mixture of combustion air and combustible gas circulates,
• an ignition chamber situated next to the distribution chamber in which it is isolated by a partition wall and in which a mixture of combustion air and combustible gas circulates,
• means for supplying air and combustible gas to said distribution and ignition chambers, respectively,
• a combustion chamber with which said distribution and ignition chambers communicate at one end, through grid-shaped flame stabilization means, and
• ignition means of the burner extending partially in the combustion chamber and away from the distribution chamber.

Such a type of burner is described in DE-A-1401857.

It is claimed that this category of burner can be improved to be made in particular even more reliable and easier to maintain.

The invention proposes to solve this problem of improving reliability and ease of maintenance by the characteristics of the characterizing part of claim 1.

In DE-A-1401857, the problem is not solved since the flame stabilization means presented therein consists of a single "grid" or "ceramic plate" which therefore diffuses the heat of the flame over the entire surface of the wafer, even outside the ignition period, including next to the ignition chamber. In addition, the igniter is mounted away from the plate. To check the plate and the igniter, it is therefore necessary to disassemble both. Furthermore, such an arrangement of the igniter makes it sensitive not only to the heat of the combustion chamber, but also (if it is not thermally insulated) to that of the side wall of this chamber through which one can reasonably assume it is mounted.

The realization in a single part of the flame stabilization plate also requires that the entire plate be dismantled to control it and if necessary, that it be changed (entirely), even if only a control, or even a replacement, of its the most requested part facing the distribution chamber would have been sufficient.

A priori, the two-part grid of the invention could be produced from the materials and structures belonging to the following list: sintered bronze or stack of finely perforated metal sheets, fibrous ceramic, metallic fabric.

And according to another characteristic of the invention, the burner will advantageously comprise, in addition to said ignition means, flame control means also arranged next to the distribution chamber and opening into the combustion chamber.

Preferably, the ignition and control means in question will receive the mixture flow necessary for ignition by a supply to the ignition chamber independent or autonomous from that of the distribution chamber to allow clean air / gas dosages. to each of these rooms.

For the ignition of the burner, use may be made of a "local" ignition offset towards the outside of the main grate, or of a peripheral ignition by a flame zone then bordering the periphery of the combustion chamber.

To promote mechanical strength over time, in particular of the main grid, in particular facing thermal stresses, another characteristic of the invention provides for having a gas mixing turbine in the distribution chamber.

It will also be noted that, in the invention, the (each) burner grate will preferably be crossed not only by first orifices, but also by second orifices of smaller section giving the (each) grate a sparse, porous structure to the air / gas mixture in circulation.

Advantageously, these orifices will be distributed over substantially the entire surface of the grate, the number of second orifices being much greater than that of the first, so that, with the burner operating, the flames developed in the combustion chamber include darts of relatively great length substantially in the extension of the first orifices and a relatively short flame area, distributed opposite said second orifices.

In this way, the combustion efficiency should be optimum and the conventional problems of flame stability significantly less.

In addition to the burner which has just been presented, the invention also relates to an installation for heating a bath of liquid heated by such a burner whose combustion chamber immersed in said bath is connected to at least one exchanger tube also immersed in this bath and in which the combustion products generated by the burner can circulate before their evacuation.

Admittedly, numerous heating equipment for industrial baths is already known using the compact submerged tube technique.

And, often, these devices use so-called "nose-mix" burners, that is to say without distribution, combustion taking place directly in the area where air and gas meet.

However, experience has shown that this type of burner is not entirely satisfactory in particular on compact submerged tube installations and often leads to excessive production of carbon monoxide, as well as to noisy operation due in particular to turbulence problems.

The applicant has already proposed, in particular for this type of problem, a few solutions, one of which is set out in French patent application FR-A-2 606 492, filed on November 7, 1986, or in its associated European patent EP-A -269,488.

However, this document does not make it possible to optimize the maintenance and the reliability of the igniter and / or of the flame stabilization plate, since if the igniter is mounted through this plate, it is constantly immersed in the flame. . The plate is also unique and there is no independent ignition chamber.

• La figure 1 est une vue schématique locale du brûleur de l'invention suivant une coupe faite le long de la ligne I - I de la figure 2,
• La figure 2 est une vue de dessus du même brûleur dans le sens de la flèche II de la figure 1,
• la figure 3 est une vue locale agrandie en plan d'une grille poreuse utilisable dans le cadre de l'invention,
• la figure 4 est une autre vue locale du brûleur de l'invention le long de la ligne de coupe IV-IV de la figure 2,
• la figure 5 est une vue schématique du brûleur de l'invention utilisé sur une installation à tube immergé compact,
• et la figure 6 illustre une variante de réalisation.

In what follows, we will now describe in more detail an embodiment of the invention with reference to accompanying drawings given only by way of nonlimiting examples and in which:

• FIG. 1 is a local schematic view of the burner of the invention according to a section made along the line I - I of FIG. 2,
• FIG. 2 is a top view of the same burner in the direction of the arrow II in FIG. 1,
• FIG. 3 is an enlarged local plan view of a porous grid usable in the context of the invention,
• FIG. 4 is another local view of the burner of the invention along the section line IV-IV of FIG. 2,
• FIG. 5 is a schematic view of the burner of the invention used on a compact submerged tube installation,
• and Figure 6 illustrates an alternative embodiment.

Referring first to Figures 1 and 2, the burner identified as a whole 1 comprises a distribution chamber (also called "premix") into which opens, by a preferably radial opening 5, the combustion air and combustible gas that begins to mix.

In 7, the arrival of combustible gas has been identified, the flow of which is directed, via at least one front transverse orifice 7a or rear 7b (FIG. 2), substantially parallel to the flow of pressurized air (blown air) which arrives by the radial pipe 9.

The distribution chamber 3, which has the general shape of a cylindrical box with a substantially circular section, is transversely limited on its front face (AV) by a flame stabilization grid 11 crossed by the mixture of air and gas, after the latter has passed through a baffle or a distribution chute 12 defined or limited by a plate or any other transverse obstacle 13 favorable to the homogeneous mixture of gases.

The grid 11 has the function of ensuring a suitable distribution and good stabilization of the flames at the entrance to the combustion chamber 15 where these flames will develop.

To promote this, and as can be seen more clearly in FIG. 3, this grid which here has the general shape of a substantially flat plate, has been constructed to be crossed, over its thickness e , by preferably two series of orifices comprising first orifices 19a of relatively large section (a few mm ² ), as well as second orifices 19b of smaller section giving the grid a sparse structure, porous to the air / gas mixture.

In practice, these two series of orifices will advantageously be distributed over substantially the entire active surface of the grid. And the number of second diffusion orifices 19b will be much greater than that of the main orifices 19a, for example in a ratio substantially between 15 to 1 and 30 to 1. As for the cross section of these second orifices 19b, it will be preferably 2 to 4 times smaller than that of the first orifices 19a.

In this way, the burner operating, the flames developed in the combustion chamber (the cross section of which will preferably be slightly less than that of the grate) will include darts 21a of relatively great length extending substantially in the extension of the first orifices. 19a, while a general zone of relatively short flames 21b will be distributed opposite the second orifices 19b.

In practice, the grid may in particular be produced from materials and structures of the sintered bronze type or stack of finely perforated metal sheets or also of fibrous ceramic or metallic fabric.

For example, within the framework of a sintered bronze grid, provision could be made to use a plate of this material with a thickness of approximately 3 mm, pierced with holes of 2 mm in cross section in a square pitch of 8 mm, the degree vacuum corresponding to these holes being about 3 to 8%.

Tests have shown that such a grid works very well, the power represented by the small diffusion orifices 19b representing approximately 30 to 40% of the total power.

It will be noted that an additional advantage of such a structure is to ensure its internal cooling by circulation through it of the air / gas flow.

One could even provide that the second orifices 19b, advantageously arranged substantially regularly through the surface of this grid, for some of them open out randomly on such and such a main orifice 19a, thus increasing the cross section of the latter, as illustrated. for example at the location of the orifice 19a ₁ in FIG. 3.

Returning to the structure of the burner in FIGS. 1, 2 or 4, it will also be noted that it conventionally comprises ignition means 23 making it possible to initiate combustion, as well as means 25 for controlling the presence of the flames.

The ignition means could for example consist of a spark plug, of the automobile spark plug type, mounted through the main grid 11.

Like the control means 25, these ignition means will preferably be arranged outside, next to the distribution chamber 3.

More precisely, the igniter may be placed at the location of a passage 27 (see FIG. 4) formed from the side, through the grid 11, this passage receiving part of the burner head forming an igniter support 29 equipped autonomous arrivals of combustible gas 31 and combustion air 33 (see FIGS. 1 and 2) to supply an ignition mixture chamber 35. This chamber, preferably separated or isolated from the distribution chamber by a wall 36, can communicate with the combustion chamber 15 through an additional grid 37 for stabilizing the ignition flame, this grid then extending substantially parallel to the plane of the main grid 11 and being traversed by the igniter 23, so that the electrodes 23a of the latter open into the combustion chamber 15 to ignite the mixture there.

Thus arranged, the igniter 23 will preferably extend substantially parallel to the general axis 39 of the chamber 15, rather towards the periphery of the grid 11.

As for the ignition chamber 35, it may have in the upper part the form of a hollow, annular vertical column, surrounding a central cavity open to the open air of the igniter support, the head 23b of the igniter with its power cable 41 extending in this central cavity. In addition, thanks to a tangential air supply at its upper part, this same chamber will ensure mixing by rotary stirring of the gases until they meet, in the lower part, the transverse grid 37 at the place where the chamber ignition takes the form of a disc.

To control the presence of flames in the combustion chamber, the burner can therefore also be equipped with a control means 25, the probe of which, for example consisting of an electrode 25a, preferably rectilinear, will extend into the development zone. flames attached respectively to the main grid 11 and to the secondary ignition grid 37, as clearly appears in FIG. 4.

Thus arranged, the control means 25 can pass through a well 43 itself passing through a second passage 45 formed through the main grid 11 so that the probe 25a can communicate with the combustion chamber 15, the head 25b of this control means with its electric power cable 47 remaining of course away from the combustion zone to be cooled by the ambient air.

By comparing FIGS. 1 and 4, it will also be noted that the main grid 11 will advantageously be held at its periphery by a flange 49 extending externally, substantially at the level of the connection which can be removable between the upper part of the burner comprising the distribution 3 and the lower part comprising the combustion chamber 15.

To do this, the flange 49 will locally define an annular cavity 51 external to the chambers 3 and 15. In this cavity, a retaining means 53, such as a circlip, will be able to maintain with a certain possible play the peripheral edge of the grid 11 .

Thus, the holding zone of this grid will be relatively thermally insulated from the hot part of the burner and the grid will be able to absorb thermal stress more easily.

Let us now turn to FIG. 5, to briefly describe the preferred application of the burner 1 of the invention to the heating of an industrial bath of liquid 55 in which at least the combustion chamber 15 of the burner and a tube are immersed. heat exchanger 57 connected to the outlet 15a of the combustion chamber 15 and which winds in the bath 55, which is heated by heat exchange with the combustion products generated by the burner and circulating in the tube before being evacuated to the outlet 57a of the same tube emerging outside.

In Figure 6, there is shown an alternative embodiment of the burner of the invention which is characterized by a stirring turbine and a peripheral ignition.

This burner, marked 10 comprises, like the previous one, a distribution chamber 30 communicating with a combustion chamber 32 through a main combustion grate 34 of the same type as the previous one (11).

The distribution chamber 30 is here tangentially supplied with air and combustible gas (already at least preferably partially mixed) via an intake manifold 38 which can come from upstream of the air inlet 38a to which the gas inlet 38b is connected.

To improve the quality of the combustion and promote good resistance to the thermal stresses of the grate 32, a brewing turbine 40 is placed facing it, in the chamber 30. It appeared preferable to place this turbine substantially at the level of the zone, opposite the grid, where the lateral pipe 38 is tangentially connected to the chamber 30.

In this way, the blades of the turbine will be able to receive the gas mixture transversely and thus be naturally driven in rotation by creating recirculation currents favorable to the homogenization of the gases and the limitation of thermal stresses.

A boss 42 situated, in FIG. 1, towards the top of the chamber 30 supports the rotation shaft 44 of the turbine which can rotate there in a conventional manner, via ball bearings (not shown).

For the ignition of the burner, the solution adopted here consists of "peripheral" ignition, via an ignition chamber 46 extending all around the distribution chamber 30, a priori essentially in its front part (AV).

In particular so as to be able to regulate at will and autonomously the air and the gas respectively supplying the distribution and ignition chambers, it again appeared preferable to "isolate" them from one another by a partition 48 and ensuring that the ignition chamber 46 has its own mixture inlet, via a tangential supply pipe 50.

And, for the attachment of the ignition flame, a secondary combustion grate 52 has also been interposed between the ignition chamber and the combustion chamber.

The distribution and ignition chambers being preferably arranged concentrically, this secondary grid may in particular have the shape of a frame or of a crown surrounding the main grid.

Such an arrangement is advantageous.

In fact, if the above-mentioned means 23, 25 for igniting and controlling the flames are mounted in the chamber 46, in such a way that they pass through the grid 52, to lead into the chamber 32, it will be possible not only to ensure effective peripheral ignition, but also to improve the control conditions by limiting the thermal stresses supported by these accessories. For this it will suffice, when the ignition sequence of the burner start-up cycle is completed and the latter is kept lit by means of flame detection, to cut off the gas supply to chamber 46 while maintaining its supply in the air.

The flames hung up to the secondary grid 52 will therefore be extinguished. But the air will continue to escape through this grate towards the combustion chamber, this air flow then constituting an excellent means of continuous cooling at least of the spark plug 23 and of the control electrode 25.

It will be noted that this principle of blowing air after ignition is entirely adaptable to the case of the burner of FIGS. 1 to 5. Similarly, the principle of peripheral ignition could be retained on this burner, the ignition chamber 46 with its accessories which can thus come to surround the base (marked 3 'in FIG. 1) of the distribution chamber 3.

Claims (13)

1. Gas burner comprising:

   - a distribution chamber (3, 30) in which a mixture of combustion air and fuel gas circulates;

   - an ignition chamber (35, 46) situated beside the distribution chamber from which it is isolated by a partition (36, 48), and in which a mixture of combustion air and fuel gas circulates;

   - means (5, 31, 33, 38, 50) for the supply of air and fuel gas to the said distribution and ignition chambers, respectively;

   - a combustion chamber (15, 32) with which the said distribution and ignition chambers communicate at one end thereof through flamestabilizing means in the form of a grid; and

   - means (23) for igniting the burner, extending partially into the combustion chamber and at the side of the distribution chamber,

   characterized in that the flame-stabilization means comprise two grids: a main grid (11, 34) and a secondary grid (37, 52) extending across the said end of the distribution chamber (3, 30) and of the ignition chamber (35, 46), respectively, ignition means (23) extending through the latter and also through the secondary grid to emerge in the combustion chamber.
2. Burner according to Claim 1, characterized in that the distribution and ignition chambers are supplied with combustion air and fuel gas by separate ducts (5, 31, 33, 38, 50) in order to render the proportions of air and of gas independent from one said chamber to the other, the distribution chamber (3, 30) being connected to a single duct (5, 38) for the common supply of a premix of air and of fuel gas, the supply at least of combustion air to the ignition chamber (35, 46) being effected tangentially thereto in order to improve the mixing of the mixture.
3. Burner according to any one of the preceding claims, characterized in that the main grid (11) is formed as a plate through which there is provided, on one side, spaced from its centre, a passage (27) across which the said secondary grid (37), which is also formed as a plate, extends.
4. Burner according to Claim 3, characterized in that beside the said passage (27) occupied by the secondary grid (37) and the ignition means (23), a second passage (45) extends through the main grid (11), extending a hole (43) provided in a wall of the burner beside the said distribution and ignition chambers, this hole housing flame-monitoring means which also emerge in the combustion chamber through a substantially peripheral region of the said main grid.
5. Burner according to any one of the preceding claims, characterized in that, on the side with the secondary grid (37), the ignition chamber (35) has the shape of a disc which is extended towards the opposite side to the said grid by an annular upright portion surrounding a central cavity which is open to the open air and in which a spark plug is mounted so as to extend through the disc-shaped portion of the ignition chamber (35).
6. Burner according to any one of the preceding claims, characterized in that an obstruction (13) is interposed in the distribution chamber (3, 30) in the path of the gases directed towards the combustion chamber (15, 32) in order to favour the mixing of these gases.
7. Burner according to any one of the preceding claims, characterized in that the cross-section of the combustion chamber (15) is slightly smaller than that of the main grid (11).
8. Burner according to any one of the preceding claims, characterized in that the main grid (11) is held at its periphery by a collar 49 which extends at the level of the connection between the distribution chamber (3) and the combustion chamber (15), this collar defining locally an approximately annular cavity (51) outside the said chambers and in which a retaining means (53), which is thus relatively thermally insulated, holds the peripheral edge of the said grid with a certain possible play.
9. Burner according to any one of the preceding claims, in which the said main grid (11, 34) has first holes (19a) of relatively large cross-section as well as second holes (19b) of smaller cross-section extending through it for the passage of the mixture of air and fuel gas towards the combustion chamber, so that the flames developed in the combustion chamber by the burner in operation comprise relatively long inner cones (21a) extending approximately from the first holes and a region (21b) of relatively short flames distributed opposite the said second holes (19b), characterized in that the cross-section of the second holes is about two to four times smaller than that of the first holes (19a).
10. Burner according to any one of the preceding claims, characterized in that the main grid (11, 34) is made of materials and structures belonging to the following list: sintered bronze, packs of perforated metal plates, fibrous ceramics, metallic fabrics.
11. Burner according to any one of Claims 1, 2, 9 and 10, characterized in that the distribution chamber (30) includes a turbine (40) favourable to the mechanical strength over time of the main grid (34) and favouring the mixture of air and gas, the said turbine being disposed facing the main grid, approximately at the level at which the said distribution chamber is supplied tangentially with air and fuel gas.
12. Burner according to any one of the preceding claims, characterized in that the ignition chamber (46) extends around the entire distribution chamber for ignition of the burner via the periphery of the combustion chamber.
13. Installation for heating a bath of liquid including the burner according to any one of the preceding claims, of which the combustion chamber (15, 32) immersed in the said bath (55) is connected to at least one heat-exchanger pipe (57) which is also immersed in this bath and in which combustion products generated by the burner circulate before their evacuation.

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