EP0435735B1 - Industrial, liquid-fuel burner with low nitrogen oxide emissions, said burner generating several individual flames, and its use - Google Patents

Description

The present invention relates to a parallel flow liquid fuel burner according to the preamble of claim 1.

• les brûleurs à turbulence (ou à ventelles de turbulence),
• les brûleurs à écoulement parallèle.

The set of industrial burners for boilers and cooled (or hot-walled) fireplaces corresponds substantially to two essential types of technology:

• turbulence burners (or turbulence louvers),
• parallel flow burners.

The present invention relates to the latter type of burners, which comprise an air flow parallel to the axis of a cylindrical or conical body, and a flame trap, generally composed of a rosette with inclined blades serving to give a rotational movement to a part of the supply air, and taking a part of the outlet section of the cylindrical or conical body.

The prior art can be illustrated by patent FR-2,122,820 in the name of the Pillard Company and patent FR-2,564,182 in the name of the French Petroleum Institute.

The need to reduce the nitrogen oxides (NOx) generated in the flames has long demonstrated the advantage of reducing the content of free oxygen (0₂) which combines with the nitrogen in the fuel, of staging combustion to reduce peak temperatures, and to increase the rate of burnt gases recycled in the flame for the same purpose.

The present invention provides a device which enables nitrogen oxides to be reduced appreciably while maintaining good quality combustion.

In addition, the device according to the invention is easy to implement.

• brûleur à écoulement parallèle comportant un stabilisateur de flamme à rosace unique à pales inclinées,
• brûleur à écoulement parallèle dont la rosace à pales inclinées comprend un moyeu central ou disque ou cône de dimension relative suffisante en diamètre, et
• injecteur à pulvérisation, par fluide auxiliaire, ayant plusieurs orifices de sortie mais en un nombre n suffisamment faible relativement à l'angle du cône sur lequel sont situés les axes des orifices d'injection de telle façon que le brûleur génère n flammes séparées sur sa plage de fonctionnement ou sur toute la plage de fonctionnement (jusqu'à sa marche nominale).

The main idea of the present invention lies in the combination of the following characteristics:

• parallel flow burner comprising a flame stabilizer with single rosette with inclined blades,
• parallel flow burner, the rosette of inclined blades comprising a central hub or disc or cone of sufficient relative size in diameter, and
• spray injector, by auxiliary fluid, having several outlet orifices but in a number n sufficiently small relative to the angle of the cone on which the axes of the injection orifices are located so that the burner generates n separate flames on its operating range or over the entire operating range (up to its nominal run).

As has been said, such a combination makes it possible, from a liquid fuel injector, to create several independent flames which achieve staged combustion because an amount of air penetrates further into the combustion zone before meet the fuel. This quantity of air corresponds to that which is passed between neighboring fuel jets.

This combination also makes it possible to limit the peak temperature of the different flames thanks to a high rate of gas recirculation resulting from combustion in the different flames, while maintaining stabilization of the flame and avoiding the deposition of drops of unburnt fuel on the stabilizer.

All other things being equal, the burner used according to the invention makes it possible to reduce the NO emissions of the flame by approximately 30% or more.

More generally, the present invention relates to a liquid fuel parallel flow burner with the features of claim 1.

The diameter of the hub relative to the diameter of the stabilizer may be greater than 45% and preferably between 45% and 60%.

The fuel injection means can be adapted to produce a number of elementary flames at most equal to 6. Similarly, they can be adapted to generate a number of elementary flames greater than or equal to 4.

The injection means may comprise several injection orifices, the axes of which may be distributed over at least one conical surface whose angle at the top may be between 70 ° and 110 °.

The injection means may include several orifices, the axes of which may be distributed over two coaxial conical surfaces of angle with different vertices, and the orifices may be angularly offset.

The auxiliary fluid may be steam or a compressed gas forming a mixture or an emulsion between the auxiliary fluid and the fuel.

The hub may include a disc-shaped part comprising radial slots supplied with combustion air, these slots delivering a jet of combustion air substantially parallel to the surface of the disc.

The possibly multiphasic fluid, such as an emulsion leaving the injection means, may have an average speed of between 40 and 100 m / s.

The burner according to the invention can be used in an industrial application, in particular for powers between 3 and 75 MW per burner.

• la figure 1 illustre schématiquement en coupe un brûleur selon l'invention,
• la figure 2 montre une variante de brûleur selon l'invention, comportant notamment un moyeu ayant une partie tronconique,
• la figure 3 représente le stabilisateur de la figure 2, vu de face, et
• la figure 4 représente un mode de répartition des orifices d'injection du combustible sur les moyens d'injection du combustible.

The present invention will be better understood and its advantages will appear more clearly on the following description of particular examples, in no way limiting, illustrated by the appended figures, among which:

• FIG. 1 schematically illustrates in section a burner according to the invention,
• FIG. 2 shows a variant of a burner according to the invention, comprising in particular a hub having a frustoconical part,
• FIG. 3 represents the stabilizer of FIG. 2, seen from the front, and
• FIG. 4 shows a method of distributing the fuel injection orifices on the fuel injection means.

In FIG. 1, the reference 1 designates a hearth supplied by a burner 2 of the parallel flow type comprising a cylinder 3 which can optionally be replaced by a cone. This cylinder 3, of axis 4, is conventionally supplied with air. The overall direction of the air is substantially axial and is represented by the arrows 5.

Reference 6 designates the stabilizer as a whole which is centered substantially around the end of the injection nozzle 7 for liquid fuel. The axis of the injection rod coincides with the axis 4 of the cylinder 3. The fuel injection rod may preferably be of the fluid spray type auxiliary, such as steam, compressed air, or compressed gas.

The auxiliary fluid sprays or atomizes the liquid fuel, mixes with it and can form an emulsion with the latter.

To improve the injection and achieve an ultra-fine atomization of fuel, the system described in the French patent application in the name of the Société Pillard EN can be used. 88 / 17.591. This system performs a double atomization which eliminates the large diameter droplets generally formed in contact with the liquid film with solid walls, such as those of the outlet orifice.

The injection pipe 7 has, at the terminal part 8 of its end 9, several orifices 10, 11 serving for the introduction of the auxiliary fluid / fuel mixture into the hearth 1.

The injection ports have injection axes 12, 13. Preferably, according to the present invention, the axes of the injection ports are located on a conical surface with an apex angle α (Alpha) of between 60 ° and 110 °.

The stabilizer 6 comprises a rosette 14 comprising inclined blades 15, 16 relative to the axial plane. These blades which surround the central hub 17 can be flat or curvilinear.

The stabilizer further comprises an outer shroud 15a and an inner shroud 15b.

The hub 17 has a central opening 18 providing passage to the injection rod 7.

In FIG. 1, the hub 17 has the shape of a disc having radial slots. The hub can be manufactured by foundry or stamping. The radial slots 19 (FIG. 3) are supplied with combustion air and make it possible to cool and sweep the surface of the hub in order to avoid deposits therein. Air comes out of the slots substantially tangentially to the surface of the disc.

In FIG. 1, the blades 15, 16 have a leading edge included in a radial plane.

The hub 17 shown in Figure 1 is set back by relative to the radial plane comprising the leading edge of the blades 15 and 16.

In FIG. 1, the reference 39 designates an opening which may be conical (case of the figure) or cylindrical.

It will not depart from the scope of the present invention if the central hub has a conical shape or has a conical portion 20 (Fig. 2).

It can be seen in FIG. 1 that the stabilizer occupies only part of the passage section delivered to the air 5 by the cylinder 3. There is a free annular space 21 around the stabilizer 15, this space serving for the passage of part combustion air. The section of this annular space can be equal to or greater than 10% of the total passage section of the cylinder 3 and it can be preferably between 10 and 50%. Good results can be obtained for sections of passage of the annular space between 10 and 35% of the total section of passage of the passage of cylinder 3 and in particular for a value close to 25%.

In FIG. 2 which illustrates a variant of FIG. 2, the air supplying the stabilizer is guided upstream of the latter by a skirt 22, possibly pierced with passages 23.

The elements common or similar to the different figures bear the same references.

In FIG. 2, the space 21 between the stabilizer 14 and the cylinder 3 is supplied by the annular cylinder 24 delimited by the cylindrical skirt 22 and the cylinder 3.

The blades 25 shown in FIGS. 2 and 3 have a leading edge 26 inclined rearward relative to a radial plane and inclined relative to an axial plane.

When the blades of the stabilizer rosette have a leading edge inclined towards the rear, the central hub, or the disc which it comprises, may be set back from the radial plane comprising the most advanced point of the edge d attack directed towards the hearth 1. In FIG. 2, this point bears the reference 27.

In FIG. 2, the disc of the hub 28 is situated in the radial plane carrying this point 27.

FIG. 4 represents the end part 29 of an injection rod viewed from the front. This terminal part has six injection holes, 3 of which referenced 30, 31, 32 have injection axes distributed over a conical surface making an apex angle of 70 °, and three others 33, 34, 35, surrounding the previous ones , have injection axes distributed over a conical surface having an apex angle of 110 °.

The orifices 30, 31, 32 are angularly offset relative to the orifices 33, 34, 35.

In FIG. 4, the orifices whose axes are placed on the same cone successively have an angular difference of 120 ° between them. The angular difference between the successive orifices whether they are on one cone or on the other is 60 °.

These angular deviations are considered by rotating a plane on the axis 36 of the injection rod. Such an arrangement makes it possible to promote the separation of the elementary flames.

The end portion 29 of the injection rod may have a frustoconical shape (case of Figure 2) or partially spherical.

In FIG. 1, the diameter of the stabilizer is designated by the letter D and the diameter of the central hub by the letter d.

est supérieur ou égal à 35 %,
$\frac{\text{d}}{\text{D}}$

pourra être compris entre 45 % et 60 %.According to the present invention:
$\frac{\text{d}}{\text{D}}$

is greater than or equal to 35%,
$\frac{\text{d}}{\text{D}}$

may be between 45% and 60%.

In FIG. 1, two elementary flames 37 and 38 have been represented diagrammatically and in FIG. 2, 5 elementary flames 39, 40, 41, 42 and 43 have been represented diagrammatically.

According to the present invention, the "flame" generated by the burner is a multi-flame composed of several flames independent elementaries 37, 38 (Fig. 1) or 39 to 43 (Fig. 2) separated by small diameters that do not combine into a single large flame.

Between the elementary flames 39 to 43, which do not touch, passes part of the combustion air A which therefore participates in combustion at the end of the flame. Thus the separation of separate elementary flames makes it possible, in fact, to carry out a staged combustion due to the staging of the air, part of the air avoiding the fuel at the start. Conversely, the elementary flames are not very oxygenated at the start.

The rosette with inclined blades is designed to achieve a high rate of recirculation "R" of burnt gases to the elementary flames. Each flame being of small size, in lack of air at the start with a strong axial recirculation, is therefore at a limited peak temperature.

The presence of the hub 28 (disc, cone) makes it possible to produce and ignite a "pilot" eddy for stabilizing the flame, which makes it possible to avoid the unhooking of the elementary flames, to ensure their stabilization.

Claims (9)

1. A liquid fuel parallel flow burner comprising injection means (7, 8) for the fuel and a cylindrical central flame stabiliser (6) occupying a portion of the outlet section of the burner and comprising a rose (14) with inclined blades (15, 16, 25) located around a central boss (17, 28) itself positioned around the injection means (7, 8), the outlet plane of the boss being located in the outlet plane of the blades (figure 2) or set back from it (figure 1) and the diameter of the boss being greater than or equal to 35% of the diameter of the stabiliser, characterised in that the injection means comprise several injection orifices (10, 11; 30 to 35) for the fuel designed to produce separate elementary flames (37, 38; 39 to 43), in that the boss (17, 28) is disc- or cone-shaped, having radial slits (19) and in that the injection means (7, 8) are of the auxiliary fluid spray type, this combination forming a multi-flame burner operating staggered combustion.
2. A burner in accordance with claim 1, characterised in that the diameter d of the boss in relation to the diameter D of the stabiliser is in the range between 45% and 60%.
3. A burner in accordance with one of claims 1 or 2, characterised in that the fuel injection means are designed to produce a number of elementary flames equal at most to 6.
4. A burner in accordance with one of claims 1 to 3, characterised in that the injection means comprise several injection orifices whose axes are distributed over at least one conical surface having an angle at the vertex in the range between 60° and 110°.
5. A burner in accordance with one of claims 1 to 4, characterised in that the injection means have several orifices whose axes are distributed over two conical surfaces coaxial with different vertex angles and in that these orifices are offset at an angle.
6. A burner in accordance with one of the previous claims, characterised in that the auxiliary fluid is water vapour or a compressed gas forming a mixture or an emulsion of the auxiliary fluid and the fuel.
7. A burner in accordance with one of the previous claims, characterised in that the boss has a disc-shaped section and in that this section has radial slits (19) supplied with oxidising air parallel to the surface of the disc.
8. A burner in accordance with one of claims 1 to 7, characterised in that the multi-phase fluid leaves the injection means at an average speed of between 40 and 100 m/s.
9. The use of a burner in accordance with one of claims 1 to 8 in an industrial application where power levels of between 3 and 75 MW per burner are required.

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