EP0549416A1 - Grid burner and heating installation comprising same - Google Patents

Abstract

Gas burner comprising a gas distribution chamber (3) supplied with combustion air and combustible gas and communicating with a combustion chamber (15) through a main flame stabilization grid (11) having a sparse structure, porous to the mixture air / gas. Preferably, the means (23) for igniting the burner will be arranged outside the distribution chamber but will pass through the grid (11), the ignition being effected either from one side of this grid, or from of its periphery. Such a burner can in particular be used with a compact submerged tube on an installation for heating industrial baths. <IMAGE>

Description

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

• une chambre de répartition pour favoriser le mélange d'air comburant et de gaz combustible,
• une chambre de combustion communiquant avec la chambre de répartition, avec interposition entre elles d'une grille de stabilisation de flammes,
• une arrivée d'air comburant pour approvisionner en air la chambre de répartition,
• et une arrivée de gaz combustible pour approvisionner en gaz cette même chambre de répartition,
• ladite grille de stabilisation de flammes présentant des premiers orifices de relativement large section la traversant, pour le passage du mélange d'air et de gaz vers la chambre de combustion.

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

• a distribution chamber to promote the mixture of combustion air and combustible gas,
• a combustion chamber communicating with the distribution chamber, with interposition between them of a flame stabilization grid,
• a combustion air supply to supply air to the distribution chamber,
• and a fuel gas supply to supply gas to the same distribution chamber,
• said flame stabilization grid having first orifices of relatively large section passing through it, for the passage of the mixture of air and gas towards the combustion chamber.

Many heating systems for industrial baths are known today using the compact submerged tube technique.

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, some solutions, one of which is set out in French patent application FR-A-2 606 492 filed on November 7, 1986.

With a permanent aim of improvement, the applicant now proposes an improved combustion and heating installation, even more reliable and easier to maintain, taking into account the increasing requirements in this area.

This material also makes it possible to increase the overall efficiency of the installation by increasing the intrinsic performance of the burner.

The solution proposed in the invention consists in particular in that the grid of this burner is crossed not only by said first orifices, but also by second orifices of smaller section giving the grid a incomplete structure, porous to the air / gas which thus circulates through these two series of orifices.

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 the said second orifices.

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

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

According to another characteristic of the invention, the burner will also advantageously comprise means for igniting and controlling the flames placed next to the distribution chamber and opening into the combustion chamber.

Preferably, these ignition and control means will receive the mixture flow necessary for ignition via an isolated or separate ignition chamber from the distribution chamber with independent or autonomous power supplies to authorize air / gas dosages specific to each. of these rooms.

For 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.

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, the combustion chamber of which is immersed in said bath, is connected to at least one exchanger tube. also immersed in this bath and in which can circulate, before their evacuation, the combustion products generated by the burner.

• 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 figue 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 in a section made along line II of FIG. 2,
• Fig 2 is a top view of the same burner in the direction of arrow II in Figure 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 limited transversely 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 mm²), 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 formed 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 19a₁ 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 23 may be disposed 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 the igniter support 29 fitted with autonomous fuel gas 31 and combustion air 33 inlets (see Figures 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 shape 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 the 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 outwardly, 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, can 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, identified 10 includes, 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 be issued 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 supplying respectively 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 open into the chamber 32, it will be possible not to only to ensure an 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 attached to the secondary grid 52 will therefore be extinguished. But the air will continue to escape through this grid 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 completely 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 including: - a distribution chamber (3, 30) in which a mixture of combustion air and combustible gas circulates, - an ignition chamber (35, 46) located next to the distribution chamber from which it is isolated by a partition (36, 48) and in which a mixture of combustion air and combustible gas circulates, means (5, 31, 33, 38, 50) for supplying air and combustible gas to said distribution and ignition chambers, respectively, a combustion chamber (15, 32) with which said distribution and ignition chambers communicate at one end, through grid-shaped flame stabilization means, and - means (23) for igniting the burner extending partially in the combustion chamber, characterized in that the flame stabilization means comprise two grids, a main grid (11, 34) and a secondary grid (37, 52) extending respectively across said end of the distribution chamber (3, 30) and of the ignition chamber (35, 46), the latter being traversed by the ignition means (23) which, being disposed apart from said distribution chamber, also pass through the secondary grid to open into the combustion chamber. 2 - Burner according to claim 1 characterized in that the distribution and ignition chambers are supplied with combustion air and combustible gas by conduits (5, 31, 33, 38.50) separate to make the air proportions and independent gases from one said chamber to another, the distribution chamber (3, 30) being connected to a single conduit (5, 38) for common supply of a premix of air and combustible gas, l at least the supply of combustion air to the ignition chamber (35, 46) taking place tangentially to it to improve mixing of the mixture. 3 - Burner according to any one of the preceding claims, characterized in that the main grid (11) is presented as a plate through which is formed on one side, away from its center, a passage (27) in through which extends said secondary grid (37) which also appears as a plate. 4 - Burner according to claim 3 characterized in that next to said passage (27) occupied by the secondary grid (37) and the ignition means (23), the main grid (11) is crossed by a second passage ( 45) extending a well (43) formed in a wall of the burner next to said distribution and ignition chambers, this well receiving flame control means which thus open into the combustion chamber through a substantially peripheral zone of said main grid. 5 - Burner according to any one of the preceding claims, characterized in that the ignition chamber (35) has, on the side of the secondary grid (37), the shape of an extended disc, opposite to said grid , by an annular column surrounding a central cavity open to the air in which a spark plug (23) is mounted so as to pass through the discoid part of the ignition chamber. 6 - Burner according to any one of the preceding claims, characterized in that an obstacle (13) is interposed in the distribution chamber on the path of the gases going towards the combustion chamber, to promote 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 less than that of the main grate (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 flange (49) which extends at the connection between the chambers of distribution (3) and combustion (15), this flange locally defining a substantially annular cavity (51), external to said chambers and where a retaining means (53), thus relatively thermally insulated, maintains the peripheral border with a certain amount of play of said grid. 9 - Burner according to any one of the preceding claims, in which said main grid (11, 34) has, through it and for the passage of the mixture of air and combustible gas towards the combustion chamber, first orifices (19a ) of relatively large section as well as second orifices (19b) of smaller section, so that the flames developed in the combustion chamber by the burner in operation include darts of relatively large length (21a) substantially in the extension of the first orifices and an area (21b) of relatively short flames distributed opposite said second orifices (19b), characterized in that the section of these second orifices is approximately two to four times smaller than that of the first orifices (19a). 10 - Burner according to any one of the preceding claims, characterized in that the main grid (11, 34) is produced from materials and structures belonging to the following list: sintered bronze, stack of perforated metal sheets, fibrous ceramics, fabrics metallic. 11 - Burner according to any one of claims 1, 2, 9 or 10 characterized in that the distribution chamber (30) comprises a turbine (40) conducive to the mechanical resistance over time of the main grid (34) and promoting the mixture of air and gas, said turbine being disposed facing this main grid, substantially at the level where said distribution chamber is tangentially supplied with air and combustible gas. 12 - Burner according to any one of the preceding claims, characterized in that the ignition chamber (46) extends all around the distribution, for ignition of the burner by the periphery of the combustion chamber. 13 - Installation for heating a liquid bath comprising the burner according to any one of the preceding claims, the combustion chamber (15, 32) immersed in said bath (55) is connected to at least one heat exchanger tube (57 ) also immersed in this bath and in which circulate, before their evacuation, combustion products generated by the burner.

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