EP0774620B1 - Liquid or gaseous fuel burner with very low nitric oxides emission - Google Patents

Description

The present invention relates to a liquid or gaseous fuel burner comprising a primary air supply duct, fuel injection means in a fireplace arranged inside said duct, in the axis of the latter, and comprising multiple orifices creating several divergent and independent flames in the hearth, a flame stabilizer arranged coaxially inside said duct, and several secondary air injectors, as much as flames, arranged around the axis of the burner and at the front of the fuel injection means in positions such that each injector provides additional flux to each flame after an initial combustion phase.

Such a burner, which is the subject of French patent n ° 93 07863 in the name of the applicant, reduces the emission of nitrogen oxide to a very low level without reducing the burner power or increase the unburnt content of the exhaust gases.

In the burner which is the subject of French patent n ° 93 07863, each secondary air injector is supplied by a conduit constituted by a metal tube projecting inside the foyer. Although they are cooled by the air which circulates there, these tubes subjected to the radiation of the flame and convection of the hot gases from the hearth can be brought to relatively high temperature (800 ° - 900 ° C), depending on the operating conditions. Even if they are made in refractory steel their resistance over time is problematic.

Document US-A-4 488 849 relates to a burner which comprises a combustion chamber made of refractory material.

The object of the present invention is to remedy this drawback by avoiding the use of metal parts to make the part of the burner subject to the radiation of flames.

The burner object of the present invention is defined by the features of claim 1.

To take into account the rotation of the primary air which is generated by the stabilizer flames, the orifices through which said secondary air ducts open into the hearth are angularly offset, in the direction of rotation of the primary air, with respect to the planes radials containing the axes of the corresponding orifices of the fuel injection means, and means are provided for adjusting this angular offset. The means of injection fuel generally consisting of a rod fitted at its front end (side hearth) of an injection head pierced with orifices distributed around its axis, which coincides with the axes of the burner and the primary air duct, we can, for example, mount the cane on the burner body so that it can rotate about its axis with respect to the ring made of refractory material and provide means, accessible from the rear of the burner, for control its rotation.

Incidentally, the burner can be equipped with fuel injection lances additional gaseous gases arranged in the primary air duct and the ends of which are located near the means for injecting the main fuel, around them. Others lances for injecting a gaseous fuel, the ends of which are close to the secondary air outlet ports can be placed in the primary air duct or in passages made in the ring of refractory material.

La figure 1 est une vue en coupe, par un plan diamétral, d'un brûleur réalisé conformément à l'invention ;

La figure 2 est une vue de face du brûleur de la figure 1 ;

La figure 3 est une vue en coupe, partielle, par un plan diamétral montrant une variante de réalisation de l'anneau en matériau réfractaire ;

Les figures 4a et 4b sont des vues partielles, respectivement en coupe et de face, montrant une autre variante de réalisation de l'anneau en matériau réfractaire et des injecteurs d'air secondaire.

Les figures 5a et 5b sont des vues partielles, respectivement en coupe et de face, d'un autre brûleur réalisé conformément à l'invention et permettant l'utilisation d'un combustible gazeux additionnel ; et

Les figures 6a et 6b sont des vues partielles, respectivement en coupe et de face, montrant une variante de réalisation permettant, comme le brûleur des figures 5a et 5b, l'utilisation d'un combustible gazeux additionnel.

The following description refers to the accompanying drawings which show, by way of example, two embodiments of the invention and in which:

Figure 1 is a sectional view, through a diametrical plane, of a burner produced in accordance with the invention;

Figure 2 is a front view of the burner of Figure 1;

Figure 3 is a partial sectional view through a diametral plane showing an alternative embodiment of the ring of refractory material;

Figures 4a and 4b are partial views, respectively in section and from the front, showing another alternative embodiment of the ring of refractory material and of the secondary air injectors.

Figures 5a and 5b are partial views, respectively in section and from the front, of another burner produced in accordance with the invention and allowing the use of an additional gaseous fuel; and

Figures 6a and 6b are partial views, respectively in section and from the front, showing an alternative embodiment allowing, like the burner of Figures 5a and 5b, the use of an additional gaseous fuel.

The burner shown in FIGS. 1 and 2 is mounted on a wall 10 of a hearth 12. The burner body consists of a metal base 14 used to fix it to the wall 10, by a primary air duct 16 fixed in a central opening of the base which it crosspiece and by a secondary air supply box 18 fixed on the rear face of the base around the primary air duct. The duct 16 and the box 18 are connected to a air supply and valves allow to regulate the primary and secondary air flows.

A fuel injection pipe 20 is arranged in the axis of the air duct primary 16. This rod has at its end an injection head 21 comprising several orifices or nozzles making it possible to create several independent flames and divergent in the hearth 12. A flame stabilizer 22 is arranged in the air duct primary and fixed on the rod 20. It has a hub and inclined blades 23 allowing to communicate to the primary air, at its exit from the duct 16, a rotational movement (arrow A in FIG. 2) around the axis X-X of the burner, which is also the axis of said duct and of the injection head. The blades 23 are circumscribed by a ferrule and an annular space is fitted between the latter and the primary air duct 16. The injection head 21 is located in front of the stabilizer hub plane but back from the end of the duct 16.

The burner further comprises a ring of refractory material 24 which is fixed to the front face of the base 14, around the end of the primary air duct 16. This ring can be formed of segments fixed individually on the base, for example by means of screws 26, which facilitates its replacement. A bowl-shaped cavity 25 is dug in the face front of the ring. The bottom of this cavity is flat and is flush with the front end of the conduit 16 and its side wall is frustoconical.

FIG. 3 shows an alternative embodiment in which the side wall of the cavity is rounded instead of being tapered. Other forms may be adopted for the cavity 25 the essential being that its diameter is equal to several times its depth and that its bottom either flat or almost flat, i.e. slightly concave or frustoconical with a apex angle greater than 120 °. The ring 24 fits into an opening in the wall of the fireplace provided for this purpose.

Passages 28 are provided in the ring 24; they lead, on the one hand, into the hearth 12, on the part 30 of the ring bordering the cavity 25 and, on the other hand, in the box 18, through holes drilled in the base 14. The holes 29 through which the passages 28 open into the hearth constitute secondary air injectors; they are lying in a circumferential direction and have, for example, a rectangular or oval section.

The passages 28 can be produced in different forms without departing from the scope of the invention. For example, FIGS. 4a and 4b show an alternative embodiment in which the secondary air passages 28 are replaced by an annular passage 28 'formed between the ring of refractory material, the diameter of which is reduced, and a casing sheet concentric 31. The ring 24 has a flange 30 whose diameter is equal to that of the ferrule 31 and which closes the passage 28 ′ on the hearth side. Notches 29 formed on the periphery of this rim communicate the passage 28 'with the hearth and allow the injection of air secondary in the latter. This construction method makes it possible to reduce the diameter of the ring.

Another exemplary embodiment is shown in Figures Sa and 5b: the passages 28 are produced in the form of rectilinear tubes with oval section, embedded in the refractory ring.

There are as many orifices or notches 29 as there are flames and each orifice or notch is placed in relation to one of the flames in a position such that it provides an air flow additional after the first fuel combustion phase with primary air. The FIG. 2 shows, in particular, that each orifice 29 is offset angularly, in the direction of rotation A of the primary air, of an angle α with respect to the plane P containing the axis of the burner and the axis of the corresponding orifice of the injection head 21 through which the jet of air is emitted pulverized fuel producing flame F. This angle α must be adjusted at start-up of the burner. To allow this adjustment, the fuel injection rod 20 is mounted on the body of the mill so that it can rotate around the X-X axis of the burner, and a mechanism placed at the rear of the burner allows this rotation to be controlled.

Furthermore, the ratio of the radius r of the primary air duct 16 to the distance R of the ports 29 on the burner axis must be between 0.25 and 0.75 (preferred value 0.35).

Figures 5a and 5b show an alternative embodiment fitted with lances 32 placed inside the primary air duct 16 and opening into the hearth slightly in front of the injection head 21. An annular space is provided between the flame stabilizer 22 and the conduit 16 for the passage of lances which are distributed around the axis of the burner. These lances supply the burner with combustible gas.

This burner is also equipped with a second set of combustible gas lances 34 which are housed in passages formed in the ring of refractory material 24. The lances 34 are located between the burner axis and the secondary air injection ports 29 and regularly distributed around this axis.

Figures 6a and 6b show an alternative embodiment in which lances 34 ' are arranged in the primary air duct 16 and have a bent end portion outwards and located in the cavity 25.

The burner of the invention has the advantage of not having a metal part exposed to flame radiation in the fireplace, while retaining the performance of very low emission of nitrogen oxides from the burner, subject of French patent n ° 93 07863 in the name of the applicant, and to be removable from the outside, without the need to enter the home.

Claims (10)

1. Liquid or gas fuel burner comprising a primary air feed pipe (16), fuel injection means (20) in a furnace and placed inside said pipe in the axis of the latter and comprising multiple orifices creating several divergent and independent flames in the furnace, a flame stabiliser (22) placed coaxially inside said pipe, and several secondary air feed pipes (28) placed around fuel injection means (20) and the primary air pipe (12) in positions so that each secondary air pipe provides an additional flow of air to each flame after a first combustion stage, characterised in that it comprises a ring made of refractory material (24) which surrounds the front extremity of the primary air pipe (16), in that said ring comprises on its front face a bowl-shaped cavity (25) whose bottom is virtually flat and whose diameter is equal to several times the depth, in that said primary air pipe opens onto the bottom of said cavity and in that said secondary air pipes are constituted by passages (28) formed in said ring and opening onto the front face of the portion (30) of the ring bordering said cavity.
2. Burner according to claim 1, characterised in that said flame stabiliser (22) comprises slanted blades (23) provoking a rotation of the air at the outlet of the primary air pipe (16), in that the orifices (29) via which said passages (28) open into the furnace are angularly offset by an angle α in the direction of rotation of the primary air with respect to the radial planes P containing the axes of the corresponding orifices of the fuel injection means (21) and in that means are provided to adjust the angular offsetting α.
3. Burner according to claim 1 or 2, characterised in that the fuel injection means are constituted by a cane (20) placed in the axis of the primary air pipe mounted in the body of the burner so as to be able to rotate around its axis and fitted at its front extremity with an injection head (21), and in that means are provided for making said cane rotate around its axis.
4. Burner according to claim 1, 2 or 3, characterised in that the side wall of said cavity is truncated.
5. Burner according to claim 1, 2 or 3, characterised in that the side wall of said cavity is rounded.
6. Burner according to one of claims 1 to 5, characterised in that said secondary air pipes are replaced by an annular passage (28') situated at the periphery of the refractory ring (25).
7. Burner according to one of the preceding claims, characterised in that it further comprises lances for injecting a gas fuel (32) placed in the primary air pipe (16) and whose extremities are close to the fuel injection means (21).
8. Burner according to one of the preceding claims, characterised in that it further comprises lances for injecting a gas fuel (34) placed in passages provided in said refractory ring and whose extremity located close to the secondary air orifices (29).
9. Burner according to one of claims 1 to 7, characterised in that it further comprises lances for injecting a gas fuel (34') placed in the primary air pipe (16) and including an end portion bent outwardly and situated in said cavity (25).
10. Burner according to one of the preceding claims, characterised in that said fuel injection means (21) are situated at the front of said flame stabiliser and standing back with respect to the bottom of said cavity (25) of the refractory ring.

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