EP0099828B1 - Apparatus for the combustion of combustible fluids with air induction - Google Patents

Abstract

1. A device for the combustion of a mixture of fluids, comprising an injector for motive fluid, at the outlet of which is disposed a burner body forming a venturi (1, 2, 3, 4), characterized in that the injector is formed by one or more injectors (6) of annular cross-section arranged coaxially to the centre axis, at the outlet of which injector or injectors is disposed a burner boby forming a venturi (1, 2, 3, 4), then a flame arrester (5) of aerodynamic type with a tunnel arranged at the end of said body opposite to the injection end (1), the tunnel (11) of said flame arrester (5) having either a frustoconical profile with an angle at the apex of between 108 and 358 or an evolutive profile with an angle at the apex of 908 relative to the axis.

Description

The present invention relates to a fluid mixture combustion device, which makes it possible to obtain a high dilution ratio between an inducing fluid and one or more induced fluids; this device is particularly suitable as industrial torch burners that can burn fuels or residual gases under the best conditions, and burners that can work with a high discharge pressure (combustion in the submerged position of the burner, for example).

Various types of industrial gas burners are known in the art with induction of atmospheric air. In these burners, a jet of gas under high pressure is directed by an injector towards a burner head, a venturi portion of which is open at its two ends, so that the gas entering at one end drives itself the air necessary for its combustion, without the need for auxiliary ventilation, and mixes intimately with this air in the venturi, the mixture burning at the other end of the burner head (see FR-A-2 137761) .

A detailed study of such burners, both theoretically and technically, is given in the following reference: "Industrial gas burners" by Pierre HOSTALIER, Eyrolles Edition.

The invention aims to improve such induction burners in order to allow in particular their application in large dimensions such as torch burners intended to burn combustible fluids such as coal or finely atomized fuel oil in air or l oxygen, or residual gases in industrial units - petroleum refineries, steel factories (blast furnace gas) - or in order to burn gases from the gasification of coal.

In such uses in industrial torch burners, the combustion device must be capable of operating efficiently, that is to say ensuring complete combustion of combustible materials, with a wide variety of gases, ranging from the heaviest ( butane) to the lighter (methane, refinery gas with a high hydrogen content) or ranging from the poorest gases (poor or medium gas from the gasification of coal) to the richest gases.

In the application as a burner, the ratio between the induced air flow and the flow of gas to be burned, acting as the working gas, must at all times be greater than or equal to the stoichiometric ratio, so that the burner can operate fully. autonomous, without additional external air supply, even if the flow and pressure of the engine gas vary suddenly in large proportions, as occurs frequently in industry.

The burner must, moreover, be able to work efficiently with a discharge overpressure, which, naturally, reduces the induction of atmospheric air. However, this remains sufficient to ensure combustion with excess air in many operating cases. The burner can therefore find application when one wants to carry out a submerged combustion, in which it is necessary to overcome a significant pressure drop.

Finally, the flame must be stabilized for a wide range of excess air and a wide variety of combustible gases, without additional excessive pressure drops at the burner nose.

The device according to the invention aims to meet these requirements and to be able to be used also with steam as the working fluid, the induced fluids then being in principle atmospheric air, and the gas to be burned. This device can then operate as a particularly efficient torch burner insofar as the introduction of pressurized steam makes it possible to considerably increase the air induction, and to catalyze the combustion reaction.

The device according to the invention finally aims to allow the use of air or oxygen as the working fluid, the induced fluid or fluids then being combustible fluids. The device can then operate in a manner known per se as a gasifier.

FR-A-1 491 215 describes an ejector-mixer -or trunk- intended to be installed in a pipe for mixing different fluids with a view to their combustion. This tube includes an annular section nozzle, imparting a high speed to an inducing fluid, a convergent in which the acceleration of an induced fluid takes place, and a divergent or diffuser in which the mixing of the two fluids is completed.

FR-A-1 451 539 describes a similar horn, but with a plurality of annular nozzles.

These devices are used to make gas mixtures.

The present invention provides a device for the combustion of a mixture of fluids, comprising a driving fluid injector at the outlet of which is a burner body forming a venturi, characterized in that the injector consists of one or more injectors with annular cross section arranged coaxially to the central axis, at the outlet of which or which is placed a burner body forming a venturi, then an aerodynamic type flame holder with a sheath disposed at the end of said body opposite the end of the injection, the flue-pipe of said flame catcher having either a frustoconical profile with an angle at the apex between 10 ° and 35 °, or an evolving profile with an apex angle equal to 90 ° relative to the axis.

The Applicant has, in fact, established:

- On the one hand, that an injection of gaseous fluid, in the form of at least one ply or a veil with an annular section, has the effect of considerably increasing the contact surface with the induced fluid, which results in a rate very high training;

- on the other hand, that a flame holder of the aerodynamic type with shovel of the type mentioned ensures perfect stabilization of the flame, despite the variations in the speed of the gas mixture inherent in this mode of injection, even when the speed of the gas mixture at the combustion head becomes lower than that of the flame front.

Advantageously, the induced fluid will be entrained not only at the periphery of the ply of annular cross section, but also along its internal surface, at least one inlet being provided for this purpose in the central part of the injection ring, which will double the exchange surface between fluids.

When it is technologically possible, it is advantageous to use two, three or even more annular webs, so that each of them produces its own training effect.

To do this, the sheets or webs of fluids with annular section will preferably be arranged along the same injection axis, the injection orifices of the sheets with increasing annular section being offset from upstream to downstream in the direction of the combustion body: each annular injector is dimensioned, positioned and profiled so as to constitute a body of the tube for the injection nozzle which is located upstream in the flow. Thus, the successive effects of each of the tubes induce a fluid flow greater than that which would be obtained with annular injectors placed concentrically in the same zone.

The profiled body of the device according to the invention may comprise, in a manner known per se, an inlet for induced gaseous fluid, preferably circular, but which may be a simple frustoconical cone converging in the direction of flow of the gas flow , a cylindrical mixer co-axial with said inlet and connected to it, a truncated cone diverging in the direction of flow in gas flow, this diverging being coaxial with said mixer and connected to it.

Advantageously, when it is economically and technologically possible, the diverging part can end in a flared profile, which makes it possible to reduce the size of the burner and to further increase the efficiency. The exit angle of the divergent, in this case, is at most 20 °.

In this divergence, the pressure increases by converting the kinetic energy of the fluid into regular deceleration. It has been found that the addition of a cylindrical section at the outlet of the divergent diffuser ensures an additional increase in pressure, since the flow is regulated and further slowed down.

The means for injecting the pressurized gaseous fluid will comprise one or more annular injectors disposed at the upstream end of the body of the burner. In the case where the device comprises several annular injectors with different sections, these injectors will be arranged along the axis of said body and the injectors of increasing section will be offset from upstream to downstream along said axis.

The annular injector or injectors preferably have a restriction or neck upstream of their orifice and their dimensions are such that the speed of the working fluid at the neck is equal to that of the sound in this fluid. If it is desired to obtain high dilution rates and if there is fluid under high pressure, this is injected into the body of the device with a largely supersonic expansion rate. The annular section of the injector will thus have a convergent-divergent profile and the Applicant has established that it is desirable that the exit angle of the divergent from the injector is equal to approximately 24 °. On the other hand, if the pressure of the available working fluid is too low, the critical expansion rate of the fluid not being reached, it is desirable to reduce the length of the divergent as much as possible so as to obtain a better adaptation. The outlet section of the injector is then equal to its section at the neck.

For the same purpose, an additional induced fluid inlet will be present in the central part of each injector, in order to double the exchange surfaces.

In order to stabilize the flame at the end of the combustion head, it will be fitted with a flame holder. In order to limit the pressure drops due to this flame catch, this should not produce a narrowing of the cross section of the mixture of fluids at the outlet of the diffuser. The flame catcher is therefore of the aerodynamic type with opening and it preferably comprises for this purpose two coaxial cylinders of unequal length joined by an annular part, the shortest cylinder, open at its two ends, being connected to the end of the diffuser, preferably by means of a cylindrical element forming a stabilizer of the speed of the fluids, the annular part joining the two cylinders being perpendicular to the axis of the burners. The longer outer cylinder promotes the establishment of a stable flow regime.

It can be connected to a tapered angle angle aperture between 10 and 35 °, in which the flow speed of the mixture decreases at the same time as the section increases and the flame front stabilizes in an area where there is has equal flow and flame propagation velocities. It has been noted that the wider the apex angle, the greater the flexibility of the burner.

Optionally, for particular applications such as radiant burners for example, the profile of the flue can be scalable with a cylindrical radius of curvature, so that the angle at the final apex of the flue is equal to 180 °. In this case, the flame adheres to the wall of the refractory pipe, by Coanda effect. This workpiece, heated at high temperature, radiates towards the charge to be heated.

With a flame arrestor with two coaxial cylinders, the fluids are ignited at the end of the internal cylinder, while a recirculation of fumes occurs between the two cylinders and brings the combustible mixture to a temperature higher than its ignition temperature. Two or more passages may advantageously be provided in the internal cylinder of the flame holder, so as to supply the combustible recirculation zone with combustible mixture. Likewise, optionally, one or more fresh air intake orifices may be provided in the external cylinder.

Tests carried out by the Applicant and which will be reported below, it appears that with very different working fluids, the quantity of fluid induced in such a burner is such that the dilution rate, that is to say the ratio of the mass flow of induced fluid to the mass flow of working fluid, is clearly greater than unity and can reach values greater than 50, whatever the supply pressure, while obtaining a perfectly stable flame.

According to a variant of the present invention, the injectors of annular sections can be produced in a manner known per se: they can also be advantageously replaced for reasons of simplicity of construction by one or more bundles of cylindrical tubes arranged in rings on the outer surface a metallic or refractory skirt which fulfills the function of the pump body described above.

The device according to the invention can be advantageously used in industry in all techniques using industrial burners or gasifiers, for example in heat treatment furnaces, in refinery furnaces or flares, glassworks, furnaces ceramic, in processes with submerged combustion or when the burnt gases must overcome a high pressure drop, as well as in the gasification processes of coal or petroleum residues.

Its performance also remains when it works with a wide variety of fluids, which allows it to be used as a flare for burning residual gases in industry, and in particular with steam injection as the working fluid.

• - la figure 1 est une vue schématique en coupe d'un brûleur conforme à l'invention;
• - la figure 2 illustre schématiquement une variante de réalisation du corps du brûleur, de l'accroche-flamme et de l'ouvreau;
• - la figure 3 est une coupe partielle, à plus grande échelle, d'une buse d'injection;
• - la figure 4 est une vue de détail illustrant la section d'injection;
• - les figures 5 à 9 représentent, en application brûleur à gaz, pour différents gaz, des courbes indiquant les débits d'air induit en fonction du débit de gaz combustible, à diverses pressions d'injection, dans le cas d'un brûleur équipé d'un unique injecteur annulaire;
• - la figure 10 représente deux courbes donnant les taux de dilution soit à partir d'un injecteur annulaire, soit à partir d'un injecteur à faisceau annulaire.

The invention will be described more fully below, with reference to the accompanying drawings, in which:

• - Figure 1 is a schematic sectional view of a burner according to the invention;
• - Figure 2 schematically illustrates an alternative embodiment of the burner body, the flame holder and the burner;
• - Figure 3 is a partial section, on a larger scale, of an injection nozzle;
• - Figure 4 is a detail view illustrating the injection section;
• - Figures 5 to 9 show, in gas burner application, for different gases, curves indicating the induced air flow rates as a function of the fuel gas flow rate, at various injection pressures, in the case of a burner equipped a single annular injector;
• - Figure 10 shows two curves giving the dilution rates either from an annular injector, or from an annular beam injector.

The burner shown in FIG. 1 comprises two induced fluid inlets 1, arranged upstream in the direction of flow of the gas and delimited by a converging profile, which may possibly be frustoconical. Each profile is connected to a cylindrical portion 2, forming a mixer, extending by a divergent 3, in the form of a truncated cone forming a diffuser.

As a variant (FIG. 2), the diverging portion of the burner body may have a profile 3a which widens regularly downstream in the manner of a trumpet, which increases the efficiency of the diffuser. In this case, the exit angle a of the divergent 3a is at most equal to 20 °.

At the end of the divergent 3 of the burner body is fixed a cylindrical chamber 4, serve as a stabilizer intended to homogenize the speed of the gases. The chamber 4 is provided, at its downstream end, with an aerodynamic type flame catcher, which will be described in more detail below.

The inlet of the working fluid is effected by a nozzle 6 with annular section.

The nozzles 6 are pierced along the axis of a conduit 8, open at their two ends and which communicate with the atmosphere through their downstream end.

In a gas burner application,

the air supply is carried out in the usual way by entrainment by combustible gas, which acts as a driving agent, but, the gas being injected under pressure and at high speed in the form of a cylindrical or conical sheet, in contact with air both from its external part and from its internal part, diffusion and mixing with the air occurs very quickly, with a minimum pressure drop in contact with the walls. The energy exchange between the two gas flows, the motor flow of combustible gas, on the one hand, and the induced air flow, on the other hand, first in the mixers 2, then in the diverging lines 3 , leads to an extremely homogeneous mixture at the inlet of the stabilizer 4. In addition, due to the high speed of the injection gas, the multiple air induction, at the periphery and at the center of the layers of the combustible gas, and the importance of the gas-air contact surfaces, a very large dilution of the combustible gas is obtained in all cases, greater than the stoichiometric mixture.

A variant of this gas burner type application consists in supplying the device shown in FIG. 1 with a working fluid - consisting of pressurized steam instead of combustible gas. The induced fluids are then the combustible fluid and the atmospheric air which can be introduced as a mixture or separately.

The flame catch 5 disposed at the downstream end of the stabilizer 4 is of the aerodynamic type and comprises two coaxial cylinders 5a, 5b, joined by an annular part 9 perpendicular to the axis of the stabilizer 4. The cylinder 5a, open at its two ends, is arranged in the extension of the stabilizer 4. Its walls are pierced with orifices 10, allowing the passage of the combustible mixture in the interval separating the cylinder 5a from the cylinder 5b. The latter is longer than the cylinder 5a. It is extended by a frustoconical opening 11 which diverges in the direction of flow, with an apex angle p of between 10 and 35 °. In some cases, the profile of the opening 12 can be evolving cylindrical with an angle at the final vertex of 90 ° relative to the axis.

The initial ignition of the air-gas mixture arriving through the stabilizer 4 and the continuous re-ignition of the flame are ensured by the recirculation, in the space separating the two cylinders, of high temperature fumes, which bring the combustible mixture to a temperature higher than its ignition temperature. Because no material obstacle is placed on the path of the gas mixture, it does not undergo significant pressure drops.

A preferred embodiment of an annular injection nozzle appears in FIG. 3. The wall of each injector closest to the axis X'X, is substantially cylindrical and ends in a diverging angle of angle α ₁ substantially equal to 7 °. The other wall has a protuberance defining with the adjacent wall a neck 7 separating a convergent from a diverging angle a ₂ of between 0 and 24 ° (0 ° in the case where the gas pressure is low, and the flow is subsonic, and 24 ° in the case of a sonic flow at the neck and largely supersonic in the divergent).

Figure 4 shows a detailed view of the entire fluid injection section here comprising three injectors.

Example 1 below illustrates the dilution effect which can be obtained on gas burners fitted with injectors described above.

Example 1

• - longueur de mélangeur 2a = 66 mm;
• - diamètre du mélangeur 2a = 30 mm;
• - angle au sommet du cône divergent du diffuseur: 7° ;
• - diamètre de sortie du divergent: 70 mm;
• - diamètre du stabilisateur 4: 70 mm;
• - longueur du stabilisateur 4: 145 mm;
• - diamètre interne du cylindre 5a de l'accroche-flamme: 70 mm;
• - Longueur du cylindre 5a de l'accroche-flamme: 50 mm;
• - diamètre interne du cylindre 5b de l'accroche-flamme: 120 mm;
• - longueur du cylindre 5b de l'accroche-flamme: 60 mm;
• - angle de révolution du cône de l'ouvreau 11: 11 = 30°;
• - longueur de l'ouvreau divergent 11: 50 mm;
• - diamètre de sortie du brûleur: 145 mm;
• - largeur des fentes annulaires des injecteurs successivement utilisés: 0,1; 0,2; et 0,4 mm.

A burner with a single annular injector was used, having the following dimensional characteristics:

• - mixer length 2a = 66 mm;
• - diameter of the mixer 2a = 30 mm;
• - angle at the top of the divergent cone of the diffuser: 7 °;
• - outlet diameter of the divergent: 70 mm;
• - diameter of stabilizer 4: 70 mm;
• - length of stabilizer 4: 145 mm;
• - internal diameter of cylinder 5a of the flame holder: 70 mm;
• - Length of cylinder 5a of the flame holder: 50 mm;
• - internal diameter of cylinder 5b of the flame holder: 120 mm;
• - length of cylinder 5b of the flame holder: 60 mm;
• - angle of revolution of the cone of the opening 11: 11 = 30 °;
• - length of the divergent opening 11: 50 mm;
• - burner outlet diameter: 145 mm;
• - width of the annular slots of the successively used injectors: 0.1; 0.2; and 0.4 mm.

With this burner, a systematic series of tests was carried out with methane, ethane, propane and butane, at different supply pressures, using the various ring injectors.

The measurements related each time to the flow rate Q ′ of combustible gas serving as engine gas, the flow rate Q ″ of induced air and the stability of the flame.

The results obtained in five of these tests appear in Figures 5, 6, 7, 8 and 9 of the accompanying drawings.

FIG. 5 relates to the injection of methane with an annular injector having a slit width of 0.1 mm. The 0 "/ Q 'dilution rate is very high and significantly higher than the stoichiometric ratio. It is however necessary to operate under an injection pressure of at least 3 bar relative, because, at lower pressure, the quantity of induced air is too high, which results in mixing conditions between methane and air, such that one is outside the flammable boundary conditions, in which case the latter must be artificially reduced the induced air flow by means of an adjustable intake window.

FIG. 6 reports tests carried out with ethane and an annular injector with a slit width equal to 0.1 mm. The% dilution rate is equal to or greater than the stoichiometric ratio and there is an excellent adaptation of this ratio to the injection pressure. The flame is perfectly stable throughout the pressure range.

FIG. 7 relates to propane tests with an annular injection slit of 0.1 mm. of width. In this case, too, the dilution ratio 1 is generally higher than the stoichiometric ratio, although it tends to decrease at high pressures.

FIG. 8 relates to similar tests carried out with butane and an annular injector with a slit width equal to 0.1 mm. These tests show that the dilution ratio% is very close to the stoichiometric ratio.

FIG. 9 relates to other tests carried out with methane and an annular injector with a slit width equal to 0.2 mm. This figure is therefore to be compared with FIG. 5, which relates to similar tests carried out with an injection slot of width equal to 0.1 mm. In this case, too, the% ratio adapts well to pressure variations and remains close to the stoichiometric ratio. The flame is perfectly stable throughout the supply pressure range.

Advantageous tests carried out with annular injectors of larger cross section have confirmed these excellent performances of the burner according to the invention.

Surprisingly, these performances are maintained even when the burner has very large dimensions, which can reach diameters greater than 200 mm. at the burner outlet (outlet diameter of the divergent). It can therefore be used with advantage as a torch burner for burning residual gases whose composition, flow rate and pressure are subject to frequent variations.

Example 2 below illustrates the advantage of the device according to the present invention when using a working fluid consisting of steam under pressure.

Example 2

The same device was used as that described in Example 1. Curve A in FIG. 10 relates to the injection of steam as a working fluid with an annular injector having a slit width of 0.1 mm.

The combustible gas is induced in the axis of the device, and the induced air arrives at the periphery of the annular injector.

This curve A shows that the dilution rate obtained Ù is very high and can commonly reach values of 30 to 50.

Example 3

As a variant, the annular injection of example 2 was replaced by a bundle of 8 tubes of 2 mm diameter at the neck arranged in a ring on a metal skirt of diameter equivalent to that of example 2.

Curve 8 in FIG. 10 relates to the results obtained with this type of injector by annular bundles of tubes. These results show the equivalence of the results with those of the previous example.

Claims (9)

1. A device for the combustion of a mixture of fluids, comprising an injector for motive fluid, at the outlet of which is disposed a burner body forming a venturi (1, 2, 3, 4), characterised in that the injector is formed by one or more injectors (6) of annular cross-section arranged coaxially to the centre axis, at the outlet of which injector or injectors is disposed a burner body forming a venturi (1, 2, 3, 4), then a flame arrester (5) of aerodynamic type with a tunnel arranged at the end of said body opposite to the injection end (1), the tunnel (11) of said flame arrester (5) having either a frustoconical profile with an angle at the apex of between 10° and 35° or an evolutive profile with an angle at the apex of 90 relative to the axis.

2. A device according to claim 1, comprising a plurality of annular injectors (6) of different sections, characterised in that the dimensions of each injector are such that per se it forms an aspirator body for the injection nozzle situated upstream in the fluid flow.

3. A device according to either of claims 1 and 2, characterised in that the injector or injectors (6) have a constriction defining a neck (7) of a convergent-divergent, upstream of their injection orifice, the divergent following said neck (7) having an angle at the apex (a₂) of between 0 and 24⁰.

4. A device according to any of claims 1 to 3, characterised in that the wall of each injector (6) nearest to its axis X'-X comprises a portion parallel to this axis terminating in a divergent of angle (a₁) substantially equal to 7°.

5. A device according to any of claims 1 to 4, characterised in that each injector of annular section comprises a group of cylindrical tubes arranged in a ring relative to the outer surface of a metallic or refractory skirt acting as the aspirator body.

6. A device according to any of claims 1 to 5, characterised in that an additional air inlet (8) is provided following the axis of said injection means (6).

7. A device according to any of claims 1 to 6, characterised in that said burner body comprises, from upstream to downstream, an air inlet (1), preferably convergent in the direction of gas flow, a cylindrically shaped mixer (2) coaxial to said air inlet (1) and connected thereto, and a divergent forming a gas diffuser (3) coaxial to said mixer and connected thereto, and in that said burner body has a continuous profile which is flared downstream in the shape of a trumpet, the angle (a) at the end of the divergent (3a) being at most equal to 20°.

8. A device according to any of claims 1 to 7, characterised in that said flame arrester (5) comprises two coaxial cylindrical portions (5a, 5b) of unequal length and joined by an annular portion, the shorter cylinder (5a), which is open at both ends, being joined to the downstream end of the diffuser (3), preferably by means of a cylindrical member (4) serving to stabilise the velocity of the gases, the annular portion (9), which joins the two cylinders (5a, 5b), being perpendicular to the axis of the diffuser (3) on the periphery of the end thereof or of the cylindrical stabiliser which extends it.

9. A device according to claims 8, characterised in that said cylindrical portion (5a) of the flame arrester (5) is perforated with openings (10) for the passage of the combustible gaseous mixture, and in that said cylindrical portion (5b) is optionally perforated with openings for the passage of air when the burner operates without excessive discharge pressure.

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