EP1122494B1 - Gas burners for heating a gas flowing in a duct - Google Patents

Description

The subject of the present invention is a improvement to gas burners for heating of a gas flowing in a conduit.

The technical sector is the realization of so-called “vein” burners because placed directly at inside the gas circulation pipe, which burners being arranged in compound ramps in general of elementary blocks and arranged transversely by relative to the direction of gas flow.

In the present description, we will denote by burners indifferently the whole of a ramp composed of several elementary blocks or an elementary block in himself.

The main applications of the invention are the heating of the turbine gases in the co-generation facilities. This post burner combustion improves the overall efficiency of the installation, to modulate the production of steam by according to needs and incidentally to maintain this production in case of shutdown of the gas turbine. In this case, a fan that draws in ambient air supplies the oxidant necessary for the burners instead and place exhaust gases from the turbine.

Such burners must be able to operate with a stable flame under very conditions different either with turbine gas at temperature from 300 to 600 ° C and composed of 11 to 15% oxygen, i.e. with ambient air. An example of this type of burner is described in European patent 313,469 published on 23 April 1989 on behalf of MECANIQUE GENERALE TURBINE FIREPLACES.

French regulations concerning emissions from this type of installation were recently supplemented by the decree of the French Ministry of Spatial Planning and the Environment of August 11, 1999 which limits the emissions of nitrogen oxides and d '' carbon oxides, in particular for boilers used in post combustion, at given values which are a production maximum of 200 mg / Nm ³ for nitrogen oxides NOx and 250 mg / Nm ³ for carbon oxides CO .

The burners as described in the patent European mentioned above allow to respect this stopped during operation with turbine gas; however, and although some devices are described in this patent to reduce emissions of nitrogen oxides they don't allow in most cases of obtaining the regulatory values during the post combustion operation only in air ambient.

The problem is therefore to be able to realize and to operate a burner called "vein" in respecting the above regulatory values while preserving good flame stability.

A solution to the problem posed is a known type intended to be placed in a conduit for heating a gas circulating in this conduit and comprising a tube able to be arranged transversely relative to to the direction of circulation of said gas, supplied with gas fuel and drilled with at least two holes aligned on the same generator, possibly fitted with injectors, and making it possible to emit jets of combustible gas directed downstream; a flame stabilizer formed by two divergent wings forming a deflector on the part and on the other side of said generator, is fixed on said tube and serves to divert the flow of oxidant gas to create downstream of the burner bank a protected area where the flame can develop.

According to the invention at least one of said holes is extended by tubing extending beyond the edges wings and pierced by at least one opening fuel gas ejection at its distal end.

Such tubing thus injects part of the combustible gas at for example at least 100 mm downstream other orifices not carrying tubing, allowing the staging of the injection of this gas and of the combustion flames obtained, and therefore the reduction in percentage of nitrogen oxides NOx produced: in fact, the main flame thus obtained by this injection stepped, and which is therefore further from the stabilizer deflector, is more airy; combustion occurs at stronger excess air therefore at lower temperature, this which produces a strong reduction in the formation of nitrogen oxides of mainly thermal origin, and the higher the staging, the more nitrogen oxides are reduced.

Such a method of reducing nitrogen oxides NOx by spreading gas is certainly already taught in the aforementioned patent application EP 313 469 but the tubing are only mentioned there as an option and are located outside the blocks constituting the burner, the end of these tubes being located approximately in the same plane as the front edge of the wings of the stabilizer and outside of it.

The major disadvantage of this arrangement is significant formation of carbon monoxide CO well higher than the limit allowed by the decree mentioned above. This training is due to the too large distance between the flame which develops away from stabilizer and gas injection wings secondary of which a part strongly diluted by the air does not burn or is incomplete.

The present invention makes it possible inter alia to remedy this defect: the NOx reduction principle is still the spreading of the gas but this staging is performed axially instead of radial. To avoid CO formation is enough to keep by conventional orifices without tubing sufficient flow (less than 30% of the overall fuel gas flow) for create a pilot flame ensuring ignition and stability of the main flame from staged injection.

In a preferred embodiment for improve the ventilation of the storied main flame, the distal end of the tubing has at least four different ejection ports and the gas can then be ejected through these various corner holes different instead of a single hole in the axis of the tube. In the embodiment shown and described in the attached figures, the axes of ejection of the orifices are inclined two by two on the one hand by an angle β of 20 to 50 ° on either side of the plane defined by the generator of alignment of the holes and the axis of the tube and on the other hand with an angle α of 10 to 30 ° on both sides from the plane perpendicular to the previous one and passing through the hole extended by said tubing. These angles α and β are important for the quality of the results and should be determined according to the dimensions of the burner and of the fireplace on which it is mounted.

• introduire une partie du comburant à la racine de la flamme secondaire; ce dispositif a pour avantage, en plus de l'augmentation de la stabilité de la flamme lors du fonctionnement en gaz de turbine, de permettre une réduction de l'oxyde d'azote NO contenu dans ce gaz par effet dit de "reburning" (le NO est en effet transformé en N2 par réduction chimique venant des radicaux CH⁺ présents dans la racine de la flamme) ;
• rajouter au moins un obstacle disposé en face d'au moins un jet de gaz éjecté par un de ces trous non prolongés par une tubulure, ce qui favorise leur éclatement et élargit la flamme pilote dite également primaire pour y conférer une meilleure efficacité.

In addition, in order to be able to further increase this staging effect by reducing the primary flow, it is possible to maintain the stability of the main flame, known as the secondary flame, since it achieves the staging of the combustible gas, with only 10% of the gas. in the primary orifices therefore having no tubing; for this it is possible according to the invention:

• introduce part of the oxidizer at the root of the secondary flame; this device has the advantage, in addition to increasing the stability of the flame during operation in turbine gas, to allow a reduction of the nitrogen oxide NO contained in this gas by the so-called "reburning" effect ( NO is in fact transformed into N2 by chemical reduction coming from the CH ⁺ radicals present in the root of the flame);
• add at least one obstacle disposed opposite at least one gas jet ejected by one of these holes not extended by a tube, which promotes their bursting and widens the pilot flame also called primary to give it better efficiency.

Different forms can be given to this obstacle such as preferably cylindrical but other shapes can be used with an effect similar.

The other characteristics of the burners or ramps described in the aforementioned patent EP 313 469 can also be combined with those described above and below of the present invention for obtain a burner also ensuring a ventilation rate practically constant of the combustible air mixture in despite variations in fuel flow and / or speed of the gas to be heated. Such characteristics are described below and shown in some figures.

The result is new gas burners for the heating of a gas circulating in a conduit and which include improvements to known burners because it responds to the problem posed, which is comply with regulatory oxide emission values nitrogen NOx and carbon oxides CO while ensuring good flame stability and aeration rate practically constant of the combustible air mixture which whatever the variations in the fuel flow and / or the speed of the gas to be heated.

• la figure 1 est une vue en coupe d'un exemple de réalisation d'un brûleur selon l'invention perpendiculairement à l'axe de son tube d'alimentation en gaz combustible ;
• la figure 2 est une vue en coupe suivant II-II' de la figure 3 d'un autre exemple de réalisation d'un brûleur suivant l'invention ;
• la figure 3 est une vue frontale, face à l'écoulement du gaz à chauffer, du brûleur représenté sur la figure 2 ;
• la figure 4 est une vue en coupe suivant IV-IV' de la figure 3 d'un exemple de réalisation d'un brûleur suivant l'invention;
• la figure 5 est une vue en coupe suivant II, II' de la figure 3 d'un autre exemple de réalisation, que celui des figures 1 et 2, d'un brûleur suivant l'invention.

Such results show the novelty and the interest of the present invention without it being necessary to cite other advantages. The description and the attached drawings represent exemplary embodiments of the invention having no limiting character: other embodiments are possible within the scope and scope of this invention, in particular by changing the shape of the fuel supply tube as well as that of the stabilizing deflector, as well as the number of fuel injection orifices or holes which may for example be between 2 and 10.

• Figure 1 is a sectional view of an embodiment of a burner according to the invention perpendicular to the axis of its fuel gas supply tube;
• Figure 2 is a sectional view along line II-II 'of Figure 3 of another embodiment of a burner according to the invention;
• Figure 3 is a front view, facing the flow of gas to be heated, of the burner shown in Figure 2;
• Figure 4 is a sectional view along line IV-IV 'of Figure 3 of an exemplary embodiment of a burner according to the invention;
• Figure 5 is a sectional view along II, II 'of Figure 3 of another embodiment, as that of Figures 1 and 2, of a burner according to the invention.

This concerns a type of burner intended for be placed in a pipe to heat a gas circulating in this conduit and which comprises a tube 1 of axis XX 'able to be arranged transversely by relative to the direction A of circulation of said gases; said tube may be of circular cross section of diameter D, as shown in Figure 2 but also of any section such as for example that of the Figure 1, and can carry different burner blocks arranged side by side to form a ramp.

This tube 1 is supplied with combustible gas 10 and is drilled with at least two holes 3 per burner block, aligned on the same generator 18 parallel therefore to the axis XX 'of the tube; a flame stabilizer 2 formed by two diverging wings 12 forming deflectors of on either side of said generator 18 is fixed on said tube 1.

According to the modes of representation of FIGS. 2 to 5, said deflector stabilizer 2 may include walls 13 ₁ , 13 ₂ forming reinforcing ribs at the ends, in the direction of axis XX ′, of the wings 12 of each burner block, as well as ribs 14 ₁ , 14 ₂ intermediate when the burner block has several holes 3 and therefore requires an intermediate reinforcement of the wings 2; these may include a break 22, towards their outer edges 17 downstream relative to the direction A of circulation of the oxidizing gases, to stiffen the latter and improve the aerodynamics of the burner block.

According to the invention, at least one of said holes 3 is extended by a tube 11 extending beyond the outer edges 17 of the wings 12 and pierced with at least one 9 gas ejection port 10 fuel to sound distal end.

Thus, as shown in Figure 1, at minus a so-called classic orifice 3 having no tubing makes it possible to obtain a so-called pilot flame or primary 19 ensuring ignition and stability of minus a main flame called secondary 20 coming from of the staged injection.

As we can keep the stability of this secondary flame 20 with only 10% of the gas fuel in the primary orifices 3, thanks to devices as described below, the premix by Venturi system using a nozzle converging diverging 8 as shown in the Figure 2 and described in patent application EP 313 469 is not essential for the proper functioning of the burner: the present invention thus applies to all types of “vein” burners with stabilizer deflector, but including or not including such a device Venturi.

Preferably the distal end of the tubing 11 has several divergent ejection orifices 9 whose ejection axes are inclined by an angle β by relation to plan AA 'defined by the generator 18 of alignment of the holes 3 and the axis XX ′ of the tube 1, and of a angle α with respect to the plane BB 'perpendicular to the previous and passing through hole 3 extended by said tubing 11.

The number of orifices, their ejection angle α and β and their passage diameter are a function of the oxidizer speed and duct dimensions in which one has the burner, (and therefore the distance between the ramps that compose it), in order to be able adapt and optimize the penetration of fuel in the oxidizer vein. For that said distal end 25 of tubing 11 may be interchangeable and fixed by a threading system or other.

In the case of four ejection orifices 9 per example, their axes can be tilted two by two, with an angle β of 20 to 50 ° on either side of the plane AA ' and at an angle α of 10 to 30 ° on either side of the plane BB '.

• éventuellement un obstacle 15 disposé en face d'un desdits trous 3 non prolongé par la tubulure 11 afin de favoriser l'éclatement des jets d'éjection de gaz combustible et élargir ainsi la flamme primaire pour lui conférer une meilleure efficacité;
• des ouvertures 21 au-delà des bords extérieurs 17 des ailes tels que définis précédemment et prolongés par des ailerons ou déflecteurs complémentaires 24, et réalisés dans ces dits ailerons 24 à un niveau intermédiaire par rapport à l'extrémité 23 aval de ceux-ci par rapport à la direction A de circulation des gaz comburants ; ces ouvertures 21 permettent le passage d'une partie de ce gaz comburant qui est alors introduit à la racine de la flamme secondaire 20, assurant une alimentation plus progressive de celles-ci, et permet une réduction du NO contenu dans ce gaz comburant.

To obtain the stability of the main, so-called secondary flame 20, with only 10% of the combustible gas in the primary orifices 3 and to avoid the formation of CO during operation in turbine gas, the burner according to the invention comprises:

• possibly an obstacle 15 disposed opposite one of said holes 3 not extended by the pipe 11 in order to promote the bursting of the fuel gas ejection jets and thus widen the primary flame to give it better efficiency;
• openings 21 beyond the outer edges 17 of the wings as defined above and extended by additional fins or deflectors 24, and produced in these said fins 24 at an intermediate level relative to the downstream end 23 thereof by relation to direction A of circulation of oxidizing gases; these openings 21 allow the passage of part of this oxidizing gas which is then introduced at the root of the secondary flame 20, ensuring a more gradual supply thereof, and allows a reduction of the NO contained in this oxidizing gas.

According to the embodiment of Figure 5 a burner block such as that shown in Figure 2 can be easily modified by adding parts complementary corresponding to these fins 24 and arranged beyond the break 22 of the wings 12 corresponding to edges 17: the position and dimensions of these fins 24 having a significant effect on the results it is interesting to have the possibility to change them if necessary thanks to their realization by added piece.

As shown in Figures 2 to 4, the obstacle 15 possibly placed opposite one of the said holes 3 not extended by the pipe 11 can be worn, by a collar or fixing crown 16, on the tubing 11 with regard to the holes or orifices 3 ejection placed on either side thereof. said obstacle 15 is for example cylindrical and its axis is perpendicular to that of hole 3 opposite which it is disposed.

In a given type of burner block, this one may have at least three holes 3, one of which them 3 'is associated with the tubing 11, the obstacle 15 to a another hole 3 'adjacent to that associated with tubing 11 and the last hole is free.

A burner block can have a number of holes in any fact, for example between two and ten and the tubing 11 can be arranged in a regular manner for example in every second hole, every third hole or one hole in four, etc ...

In the embodiment shown in the Figure 4, by way of example, the following burner block the invention comprises five holes 3 in which the tubing 11 is associated with the central hole, the two holes adjacent to it being associated with an obstacle 15 and the two end holes being free.

Such burners according to the invention may also include elements characteristic of the burners, as described in patent EP 313 469, and such as in particular, in front of at least one hole 3 ₂ not extended by a pipe 11 and coaxial with that here, a diverging convergent nozzle 8 capable of causing the gas jet ejected through said hole 3 _{2 to} create a vacuum at the inlet of the nozzle 8, as shown in FIG. 4. Said inlet communicates with the external face or extra back of at least one of the wings 12 of the stabilizer 2 through at least one opening 7.

The space between the nozzles 8 and the tube 1 is closed by two wall elements 4 fixed on the tube and arranged almost parallel to the plane defined by the generator 18 for aligning the holes 3 and the axis XX 'of the tube 1 and by a front wall 5 connected to said wall elements 4 and carrying the nozzles; the openings 7 are drilled in said wall elements 4.

As examples of embodiment, one can give some indications of dimensions of a burner block according to the invention in which the length L ₁₁ of the pipe 11 beyond the orifice 3 with which it is associated is of the order from 100 to 200 mm with a length L beyond the outlet of the nozzles 8, from 40 to 150 mm approximately and preferably between 50 and 80 mm for a diameter d ₁₁ from 12 to 20 mm. The obstacle 15 may be a cylindrical tube with a diameter d ₁₅ of approximately 10 mm and placed at a distance a of the order of 25 mm from the outlet of the nozzles 8; the length L ₁₅ of such obstacles fixed on the pipe 11 can be of the order of 85 to 90 mm depending on the distance separating two adjacent holes or orifices 3; the diameter D ₁ of the fuel supply tube is of the order of 85 to 90 mm.

Claims (12)

1. A burner intended to be placed in a conduit to heat a gas flowing in said conduit, and comprising a tube (1) of axis XX' adapted to be disposed transversely with respect to the direction (A) of flow of said gas, fed with fuel gas (10) and pierced by at least two holes (3) aligned on the same generatrix (18), and a flame stabiliser (2) formed by two divergent wings (12) forming a deflector on either side of the said generatrix (18), characterised in that at least one of said holes (3) is extended by a tube (11) extending beyond the outer edges (17) of the wings (12) and pierced by at least one orifice (9) for ejection of the fuel gas (10) at its distal end.
2. A burner according to claim 1, characterised in that the distal end (25) of the tube (11) can be interchangeable.
3. A burner according to claim 1 or 2, characterised in that the distal end of the tube (11) comprises a plurality of divergent ejection orifices (9).
4. A burner according to claim 3, characterised in that the distal end (25) comprises at least four ejection orifices (9), the axes of which are inclined by an angle β of 20 to 50° on either side of the plane defined by the generatrix (18) of alignment of the holes (3) and the axis XX' of the tube (11), and by an angle α of 10 to 30° on either side of the plane perpendicular to the above plane and passing through the hole (3) extended by said tube (11).
5. A burner according to any one of claims 1 to 4, characterised in that it comprises at least one obstacle (15) disposed opposite one of the holes (3) which is not extended in the form of the tube (11).
6. A burner according to claim 5, characterised in that the said obstacle (15) is carried by the tube (11).
7. A burner according to claim 5 or 6, characterised in that the said obstacle (15) is cylindrical and its axis is perpendicular to that of the hole (3) opposite which it is disposed.
8. A burner according to any one of claims 5 to 7, and comprising at least three holes (3), characterised in that the tube (11) is associated with one of the holes (3₁) and the obstacle (15) with a hole (3₂) adjacent the hole associated with the tube (11), the latter hole being free.
9. A burner according to any one of claims 5 to 8, and comprising five holes (3), characterised in that the tube (11) is associated with the central hole, the two holes adjacent the latter being associated with an obstacle (15) and the two end holes being free.
10. A burner according to any one of claims 1 to 9, characterised in that it comprises complementary ailerons (24) in continuation of the outer edges (17) of the wings and openings (21) formed in said ailerons and adapted to allow some of the gas flowing in the conduit to pass and to introduce it towards the root of the flame of the said burner.
11. A burner according to any one of claims 1 to 10, characterised in that it comprises, in front of at least one hole (3₂) which is not extended by a tube (11) and coaxially therewith, a convergent-divergent nozzle (8) adapted so that the jet of gas ejected by said hole (3₂) creates a negative pressure at the entry to the nozzle (8), the said entry communicating with the outer surface of at least one of the wings (12) of the stabiliser (2) via at least one opening (7).
12. A burner according to claim 11, characterised in that the space between the nozzles (8) and the tube (1) is closed by two wall elements (4) fixed on the tube and disposed substantially parallel to the plane defined by the generatrix (18) of alignment of the holes (3) and the axis XX' of the tube (1), and by a front wall (5) connected to the said wall elements (4) and carrying the nozzles (8), and in that the openings (7) are pierced in said wall elements (4).

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