EP0840061B1 - Flameholder for gas burner and burner comprising such flameholder - Google Patents

Abstract

The flame spreader (1) contains a set of rings (2) made from knitted metal wire with non-porous spacers (20) between them. These have internal diameters which are more or less equal to those of the rings, while there outer diameters are smaller. The spacers are thinner than the metal wire rings, and the difference between their outer diameters is equivalent to the spacers' thickness. The two end rings in the set have collars (132,232) which cover some four fifths of their outer surfaces, while the free end of the stack is closed by a blank cover (26) made from a heat resistant material. The burner also has a gas distribution chamber (81) fed with combustive air and fuel gas, connected to a combustion chamber (82) containing the flame spreader.

Description

The field of the invention is that of fastening devices for flames usable in particular on a cylindrical gas mixture burner.

We already know devices of this type on which we are looking to stabilize the flames produced, so as to promote their development as homogeneous as possible. Other expressions refer to also these devices, such as "flame hanging plates" or "grids of combustion ".

These devices are generally made of various materials such as than ceramic or metal, and are finely perforated with size holes and suitable distribution to allow the passage of gases and a the most homogeneous combustion possible. They are typically arranged in the burner, between the mixture distribution and combustion chambers they separate

• la stabilisation des flammes par ces dispositifs n'est pas toujours satisfaisante. Il peut y avoir des retours de flammes dans la chambre de répartition du mélange, des flammes trop décollées du dispositif qui viennent chauffer les parois de la chambre de combustion, ou des flammes trop collées au dispositif portant celui-ci au rouge,
• la production de gaz nocifs ou polluants (oxyde de carbone, oxydes d'azote) est souvent trop importante,
• la structure même de ces dispositifs rend difficile une modulation importante de la puissance des brûleurs,
• l'inter-allumage des flammes est très faible, voire nulle,
• l'adaptation de ces dispositifs à des brûleurs cylindrique est difficile, chère et peu efficace.

Among the drawbacks which have been observed on such devices in the burners of the prior art, it may be noted:

• flame stabilization by these devices is not always satisfactory. There may be flashbacks in the distribution chamber of the mixture, flames that are too loose from the device which heat the walls of the combustion chamber, or flames that are too stuck to the device carrying the latter in red,
• the production of harmful or polluting gases (carbon monoxide, nitrogen oxides) is often too high,
• the very structure of these devices makes it difficult to significantly modulate the power of the burners,
• the inter-ignition of the flames is very low, even zero,
• the adaptation of these devices to cylindrical burners is difficult, expensive and ineffective.

There is also known a flame attachment device for gas mixture burners described in GB-2 231 949, comprising in its structure corrugated sheets for the circulation through them of gases, the device hooking consisting of a substantially coaxial stack of rings between which are arranged annular spacers not porous.

The insertion between two consecutive rings of an annular spacer made of non-porous metallic material preferably resistant to temperatures above 1000 ° C improves the ventilation flexibility (variation of the air factor n ) and the flame stability, limit manufacturing costs and overcomes the problem of separation of the flame in the case of strong ventilation for rings superimposed axially

Faced with GB-A-2 231 949, the invention aims in particular to allow a substantially uniform passage of gases over the entire surface of the device, with regular flame spread and good porosity, in order to reduce pressure drops and emissions of harmful or polluting gases.

US-A-3,144,073 describes a (single) ring constituted by a structure comprising a compressed network of flexible intermeshed metallic wires.

On the other hand, EP-A-0 635 677 describes the use of a trellis consisting of a compressed network of flexible metallic threads knitted for the gas flow through it.

• les anneaux soient constitués chacun par un réseau comprimé de fil(s) métallique(s) souple(s) tricotés(s) pour la circulation desdits gaz à travers eux,
• le diamètre externe de chaque entretoise soit inférieur au diamètre externe des anneaux.

However, the solutions proposed both by US-A-3 144 073 and by EP-A-0 635 677 for solving the problems which the invention aims to solve compared to the embodiment described in GB-A-2 231 949 n ' not being completely satisfactory, the invention proposes that:

• the rings are each constituted by a compressed network of flexible metallic wire (s) knitted for the circulation of said gases through them,
• the outer diameter of each spacer is less than the outer diameter of the rings.

The external diameter of the external spacer, less than the diameter outer ring, forms an annular groove generating two zones of piloting on each side of each ring. On each of these two areas, a gas flow comes out perpendicular to the main flame which emerges on the outer periphery of the spacer, at the outlet of the groove. When the dimensions of the annular spacers are optimally defined, and in particular depending on the dimensions of the ring, the two gas flows are meet and form a pilot flame parallel to the main flame. This pilot flame develops at the exit of the throat and is detached from the edge of the spacer in order to obtain a homogeneous flame front with inter-ignition of flames. The respective dimensions of the rings and annular spacers are defined to optimize the stabilization of the main flame by the pilot flame, while maintaining good inter-ignition.

Preferably, the spacer will have a substantially internal diameter identical to the internal diameter of the ring.

A second consideration looked at the performance of the flame attachment device (flame stability and homogeneity, inter-ignition), which largely depend on the respective dimensions rings and spacers. Preferably, the thickness of the spacer annular will be less than the thickness of the ring, the difference between the external radius and the internal radius of the annular spacer will be substantially equal to its thickness (substantially square or rectangular section), and the difference between the outer diameter of the ring and the outer diameter of the annular spacer will be substantially equal to the thickness of the spacer annular. In this way, the best flame control, the better flame front stability and maximum ventilation flexibility, while having low emissions of harmful or polluting gases.

A third consideration focused on solving the problem piloting the first (upstream) and the last (downstream) ring of the stack The solution is to partially seal, preferably in a 4/5 ratio, the peripheral surface of these two rings where the flame develops main to release only one piloting area (representing the fraction a fifth remaining).

A fourth consideration focused on solving the problem shutting off the flame attachment device at its downstream end. The solution is to have the hanging device on the downstream ring flame, a non-porous circular blanking plate made of material resistant to high temperatures (above 1000 ° C). Preferably, the blanking plate will have an external diameter substantially equal to the diameter outer of a ring and a thickness such that it does not curl under the effect heat.

In connection with this fourth consideration, the invention is proposes to solve the problem of the removable fixing of the device hanging flames on the burner. These removable fastening means preferably have the form of a threaded rod axially passing through the flame attachment device and connected to the burner by lugs and to the blanking plate with a nut. These means may also be made up several threaded rods arranged on an imaginary circle, the diameter will be close to the internal diameter of the device and coming to connect directly the burner to the cover plate (without legs). Finally, these means may still be placed outside the device and take the form of flanges.

A fifth consideration is concerned with the centering of the ring (s) and annular spacer (s) to obtain a perfectly axially aligned stack. The solution is to provide the annular spacer of centering pins, preferably at least eight, staggered on either side of the thickness of the spacer. These lugs are integral, in particular by welding, with the internal walls of the spacer and are distributed around the internal periphery thereof, preferably at 90 ° from each other.

The invention also relates to a cylindrical burner of the type general gas mixture, comprising a distribution chamber of the mixture supplied with combustion air and combustible gas, communicating with a combustion chamber, with interposition between them of the device according to the invention.

The device of the invention can be used in particular for domestic burners (of a few tens of kilowatts of power nominal), for example with total air / gas premix and blue flame, making possible in particular a large power modulation, which can, for example, range from about 5 to 25 kilowatts, or a modulation of power of 1: 5. The device of the invention can also be used for collective boilers (a few hundred kilowatts of power nominal) by adapting the size of the burner to the required power. In these different cases, the outer diameter of the rings will be chosen according to the size of the combustion chamber.

• la figure 1 montre en perspective un anneau conforme à l'invention ;
• la figure 2 montre un détail de réalisation du réseau tricoté de la figure 1, à l'endroit du repère III de cette figure ;
• la figure 3 montre, vue en coupe, le dispositif d'accrochage de flammes de la figure 5 muni d'entretoises annulaires insérées entre deux anneaux consécutifs ;
• la figure 4 est une vue du dessus de la figure 4 représentant une entretoise munie de ses moyens de centrage;
• la figure 5 montre en demi-vue éclatée en perspective les moyens de fixation d'obturation et de recouvrement du ou des anneaux du dispositif;
• la figure 6 montre, en coupe verticale médiane, une utilisation possible du dispositif de l'invention, sur un brûleur à gaz ;
• la figure montre un détail de la figure 6 représentant un front de flamme obtenu avec les entretoises ;

Other characteristics and advantages of the invention will appear from the description which follows, given with reference to the appended drawings given solely by way of examples, and in which:

• Figure 1 shows in perspective a ring according to the invention;
• Figure 2 shows a detail of the knitted network of Figure 1, at the location of the reference III of this figure;
• Figure 3 shows, in section, the flame attachment device of Figure 5 provided with annular spacers inserted between two consecutive rings;
• Figure 4 is a top view of Figure 4 showing a spacer provided with its centering means;
• FIG. 5 shows in exploded half-view in perspective the means for fixing the closure and covering the ring or rings of the device;
• FIG. 6 shows, in median vertical section, a possible use of the device of the invention, on a gas burner;
• the figure shows a detail of figure 6 representing a flame front obtained with the spacers;

Referring to Figure 1, we see a ring 2, here perfectly circular, of diameter external D2, with internal diameter d2 and thickness E2, and has an axis main or normal axis symbolized by the letters yy '. This type of ring is manufactured and sold by the company TISSMETAL (Reims, FRANCE). It's clear that the ring can take all possible forms (square, triangle, star, ellipse ...) along a plane P perpendicular to its normal axis yy ', the shape circular (both on its external and internal perimeter) being preferred.

In FIG. 2, it can be seen that the ring 2 comprises, in its constitution, a network of flexible metallic wire (s), with interlaced parts, leaving between it passages 4 (or openings) formed by the meshes "knitting" and through which the gases will circulate. It is quite possible to make the network with intertwined parts by knitting one (or more) yarn (s) or by weaving several threads perpendicular to each other (weft threads) by compared to the others (son of chain). This network of wire (s), or interlacing, is presented here as a knitted work consisting of at least one thread. In in this case, this knitted work is made with a single yarn 6 made up of a flexible metallic material which is easy to knit, such as for example "304L" stainless steel from 1 to 3 tenths of a millimeter in diameter. In any condition cause, the material used to make the device should preferably keep its characteristics (mechanical in particular) until high temperatures, from around 1000 ° C to 1200 ° C.

From Figure 2, we see that the thread 6 is somehow "knitted" like knitting a sock but we could consider using other known crossing or braiding modes (weaving for example). In this figure, we schematically illustrated the manner in which the loops 8a and 8b in "Q" (OMEGA) of wire 6 can be intertwined between them. Sections 10 of wire 6, which overlap upside down, thus present interlacing zones as referenced in 11, these sections 10 forming "upper" loops 8a which pass through their loops 8b lower, thus delimiting the passages 4. For the clarity of the representation, these passages of the knitted work have been represented in a state relatively loose, these same passages being found distributed throughout the network structure in compressed state according to shape, size and layout which vary according to the compressive forces exerted.

Figure 3 shows a device flame attachment 1 in which we find inserted between two 2 consecutive rings, an annular spacer 20 made of a material non-porous metal. This spacer 20 has an internal diameter d20 substantially equal to the internal diameter d2 of the ring 2 and a diameter outer D20 smaller than the outer diameter D2 of said ring 2. The dimensions of this annular spacer 20 are very important. The spacer 20 is preferably provided with several means 21 for centering the rings 2, taking the form of lugs (21a, 21b, ...) welded on either side of the thickness E20 thereof on its internal diameter d20.

FIG. 4 shows, seen from above, a spacer 20 provided with eight centering pins (21a, 21b, ...) divided into two groups of four pins arranged on either side of the thickness E20 thereof, preferably arranged at 90 °, the two groups being staggered (45 ° offset) one relative to each other as shown. Each group of four centering means defines a virtual ring of external diameter D21 substantially equal to the internal diameter d20 of the spacer 20 and the diameter internal d2 of ring 2 so that it comes to center on the spacer 20. The thickness E21 of these pins will be small, of the order of a few millimeters, so as to create a good centering without interfering with the circulation of gases through passages 4 of the device 1. For the same reasons, the internal diameter d21 of the two virtual rings defined by lugs 21a and 21b will be slightly smaller than the external diameter D21 to avoid excessive disturbance the gas flow.

FIG. 5 shows the covering means 132 and 232 of a upstream ring 102 and a downstream ring 202, the latter being the last ring of the stack or the ring arranged furthest downstream with respect to the direction of gas circulation, symbolized by the letters AM (upstream) and AV (downstream). In the case where there is only one ring 2, these covering means 132 and 232 become useless. These recovery means 132 and 232 consist of by a first strapping 132 disposed around the upstream ring 102, and a second strapping 232 disposed around the downstream ring 202. Preferably, each strapping 132 and 232 will have a thickness E132 and E232 such that it will cover approximately four-fifths (4/5) of the thickness of each upstream 102 and downstream 202 rings so as to allow good steering of flame. These straps 132 and 232 will have an internal diameter d132 and d232 slightly greater than the outer diameter D2 of the rings 102 and 202, and a external diameter D132 and D232 slightly greater than their internal diameter d132 and d232. They will also be made of a non-porous material preferably resistant to temperatures above 1000 ° C.

Figure 5 also shows the sealing means 24 and fixing 25 of the flame attachment device 1, in an alternative embodiment where the device 1 is made up of several rings 2 and several spacers 20 inserted between two consecutive rings 2 (by measuring clarity, a single spacer 20 is shown between a ring 2 and the ring downstream 202). These shutter means 24 consist of a plate terminal 26 circular and solid, preferably resistant to temperatures higher than 1000 ° C. This end plate 26 is disposed on the ring downstream 202 and is fixed, for example by welding, by means of covering 232 of the downstream ring 202. In this way, the gases are forced to pass to the through the flame attachment device 1, therefore through the passages 4 defined by the compressed mesh of knitted yarn (s). The diameter D26 of the end plate 26 will preferably be substantially equal to the external diameter D2 of the downstream ring 202, and its thickness E26 will be sufficient to prevent the end plate 26 from curling under the effect of the heat.

The fixing means 25 are represented by a threaded rod 27 passing axially through the center of the flame catching device 1 and the end plate 26, legs 28 and 29 which are fixed on the burner and a nut 30 coming to tighten the end plate 26 on the burner 80. Thus, or the rings 2 (with or without spacers) are slightly compressed between the end plate 26 and the burner 80, and are fixed thereto removable. The flame attachment device 1 can therefore be easily replaced, or even a single ring 2 or a single spacer 20.

Referring now to Figure 6, there is shown a device 1, mounted in a known type of burner, referenced in its together in 80, such as a domestic premix burner total and blue flame.

This burner 80 essentially comprises a distribution 81, which has the general shape of a truncated cone box, substantially circular section, connected at its most rear side narrow 81a to separate supply lines 83, 84 respectively combustion air and combustible gas. In this figure, the acronyms AM and AV allow to locate the "upstream" and "downstream" sides of the burner respectively, with reference to the circulation of the combustible mixture, in the burner, such as shown diagrammatically by arrows 87, 87 'and 88. This distribution chamber 81 is separated from a combustion chamber 82, on its front face, by the device flame attachment 1. In this case, this device is under the form of several superimposed rings 2 and fixed to the burner 80 by fastening means 25 such as a threaded rod 27, tabs 28 and 29 and a nut 30. The flame catching device 1 is closed, on a ring downstream 202, by a rigid non-porous plate 26 through which can insert the threaded rod 27. In the variant where the flame hanging device consists of a single ring, the ring downstream 202 is formed by this single ring 2 and the end plate 26 is disposed on this ring 2. As can be seen in FIG. 6, the pipe 84 fuel gas supply line meets the supply line 83 air just upstream of the distribution chamber (at 85). Of course, we here plans to install a fan upstream of duct 83 (supply of pressurized air), but it is possible to provide that the premix of the gases (gas + air) is done before the distribution chamber 81.

As illustrated, the ignition of the burner is ensured by an electrode 97 suitably insulated and supplied with high voltage by a cable power supply not shown, ignition taking place by sparks or arc between the tip 97a of the electrode and, for example, the neighboring wall a spacer or a ring.

For example, the flame attachment device will be consisting of a reference stainless steel wire mesh "304L" and may consist of a stack of rings of diameter external D = 90 mm, internal diameter d = 60 mm and thickness E = 15 mm.

As an indication, the air factor ( n ) obtained in a gas burner with a nominal power of 25 kW fitted with the device according to the invention varies from 1.15 to 1.45 without an annular spacer, and from 1.16 to 1 , 62 with annular spacer, while it varies from 1 to 1.29 for a standard burner with a nominal power of 31 kW.

FIG. 7 shows, in detail, the flame front obtained by the assembly consisting of flame attachment device and the burner associated with FIG. 6. Between two adjacent rings 2, a groove 40 making the device tour is defined, opposite the spacer 20. On the edges upper and lower rings, out of the jets J1 and J2 of mixture air + gas which go around the device. These jets are parallel to the axis yy 'and are directed towards each other. If the dimensions of the spacer are correct chosen, then these two gas jets will meet in throat 40 and create a pilot flame F 'perpendicular to the axis yy' and detached from the slice of the spacer. This pilot flame F 'ensures the stabilization and the homogeneity of the flame front F, avoiding any rupture thereof in ring / spacer contact areas. It develops as much flame pilot F 'that there is a spacer. Preferably, there will be no spacer between the burner and the upstream ring 102, nor beyond the downstream ring 202. Thanks to the additional space freed up between the rings 2 by the spacers 20, we can thus reduce the number of rings, which is favorable for the reduction the cost of the burner.

Claims (11)

1. Device (1) for flame retention for use on a gas mixing burner (80), the construction of which incorporates :

   at least two rings (2) substantially coaxially stacked,

   a non-porous annular stay (20) interposed successively between two adjacent rings (2),

   caracterised in that:

   each of the rings is constituted by a compressed gauze of knitted flexible metal wire or wires through which said gases will flow,

   the external diameter (D20) of each stay (20) is less than the external diameter (D2) of the rings (2).
2. Device (1) according to claim 1, characterised in that the internal diameter (d20) of each stay (20) is substantially the same as the internal diameter (d2) of the rings (2).
3. Device (1) according to any of the preceding claims, characterised in that the thickness (E20) of each stay (20) is less than the thickness (E2) of the rings (2).
4. Device (1) according to any of the preceding claims, characterised in that the difference between the external diameter (D20) and the internal diameter (d20) of each stay (20) is substantially double the thickness (E20) thereof.
5. Device (1) according to any of the preceding claims, characterised in that the difference between the external diameter (D2) of the rings (2) and the external diameter (D20) of each stay (20) is substantially the same as the thickness (E20) of said stay (20).
6. Device (1) according to any of the preceding claims, characterised in that each annular stay (20) has an internal diameter (d20) and is fitted, on said internal diameter (d20), with centring means (21) which help to align the stacked rings (2), such as welded lugs (21a, 21b,...).
7. Device (1) according to any of the preceding claims, characterised in that an upstream ring (102) and a downstream ring (202) are fitted with circular cover means (132, 232) which preferably obturate four-fifths of the external peripheral surface of said rings (102) and (202).
8. Device (1) according to any of the preceding claims, characterised in that a downstream ring (202) is fitted with obturating means (24), such as a solid, circular, heat-resistant end plate (26), having an external diameter (D26) substantially the same as the external diameter (D2) of said downstream ring (202).
9. Device (1) according to claim 8, characterised in that the end plate (26) and the cover means (232) of the downstream ring (202) are fixed, for example by welding.
10. Device (1) according to any of the preceding claims, characterised in that it is fitted with removable fixing means (25) which connect it internally or externally to the burner (80) and/or to the end plate (26), such as a threaded rod (27) fitted with tabs (28) and (29) and with a nut (30).
11. Gas burner (80) having a gas distribution chamber (81) supplied with oxygen-carrying air and fuel gas and communicating with a combustion chamber (82), there being interposed between these chambers a flame retention device (1) according to any of the preceding claims.

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