EP0225344A1

EP0225344A1 - Burner for liquid fuel boiler with combustion gas recycling circuit

Info

Publication number: EP0225344A1
Application number: EP19860903184
Authority: EP
Inventors: Rudolf Müller
Original assignee: Individual
Current assignee: Individual
Priority date: 1985-06-04
Filing date: 1986-06-03
Publication date: 1987-06-16
Also published as: WO1986007434A1; JPS62503116A; FR2582781A1

Abstract

Le brûleur se compose essentiellement d'une douille support (11), d'un manchon (12) de guidage des gaz combustibles et de combustion, et d'un gicleur (13) qui débouche dans une ouverture (27) d'une plaque d'obturation (16) de la douille support (11). Des ouvertures d'amenée d'air (18) sont ménagées dans la plaque d'obturation (16). Une douille de guidage (42) porte une plaque déflectrice composée d'ailettes (30) séparées par des fentes (31) qui engendrent un courant d'air turbulent autour de la flamme.The burner essentially consists of a support bushing (11), a sleeve (12) for guiding the combustible and combustion gases, and a nozzle (13) which opens into an opening (27) in a plate. shutter (16) of the support sleeve (11). Air supply openings (18) are provided in the shutter plate (16). A guide sleeve (42) carries a deflection plate composed of fins (30) separated by slots (31) which generate a turbulent air current around the flame.

Description

BURNER FOR LIQUID FUEL BOILER WITH COMBUSTION GAS RECYCLING CIRCUIT

The present invention relates to a burner for -heater with liquid fuel provided with means for recycling the combustion gases, this burner comprising a jet of aliTβ aration in liquid fuel and a sleeve for guiding the combustible gases coming from the vaporization of this fuel liquid, mixed with recycled combustion gases, this sleeve being arranged coaxially with respect to this nozzle which is mounted inside a support bush equipped with air supply members arranged concentrically around said nozzle.

The German patent application No 2810 193, published before examination and the French utility certificate No 80 16736 describe burners designed to ensure partial recirculation of the combustion gases inside the burner heads. The consequence is a relatively high temperature combustion resulting in a relatively high residual rate of nitrogen oxides. In both cases the combustion air is directed towards the center of the guide sleeve and the recycled gases rather towards the periphery of the sleeve, which promotes this combustion at high temperature.

The present invention proposes to overcome this drawback by producing a burner as mentioned above making it possible to obtain as complete combustion as possible with a relatively low flame temperature, which guarantees an extremely reduced rate of oxides of nitrogen in the residual combustion gases and very complete combustion of the liquid fuel.

This object, as well as others which will become apparent on reading the description below, is achieved by the burner according to the invention which ensures dynamic recycling of the partially cooled combustion gases. In addition, this burner is designed in a very simple and economical manner, so that the parts known to be delicate in conventional burners are effectively protected against high temperatures and deposits - unburnt residues. Thanks to this design, a thermal distribution is obtained such that heavy or medium oils can be burnt as completely as light fuels. The simple construction of this burner allows almost immediate adaptation for the use of combustible gas instead of liquid fuel.

The desired object is achieved by a burner according to the invention, characterized in that the sleeve of the combustible and combustion gases is open at its two ends and is mounted substantially in the extension of the support bushing, axially offset by relative to the latter, so as to provide an annular space arranged to allow penetration of the combustion gases into said sleeve, at its open upstream end, disposed opposite the support bushing.

According to an advantageous embodiment, the support bushing is closed, at its end disposed near the sleeve for guiding the combustible and combustion gases, by a closure plate provided with a central opening formed in the extension of the nozzle and d 'a first series of openings arranged in a ring concentrically around said central opening, constituting said air intake members.

This plate may also include a second series of openings arranged in a crown, concentrically between said central opening and said first series of openings.

The openings of said second series of openings are advantageously each formed by a hole in the closure plate.

According to another embodiment, the closure plate comprises, in its central part surrounding the central opening, a deflector plate composed of fins in the form of circular sectors, offset and partially superimposed relative to one another so as to provide slots arranged to generate turbulence whose axis of rotation corresponds substantially to the axis of the nozzle, these slots constituting in this case said second series of openings. The gas is guided using a cylindrical sleeve oriented along the axis of the nozzle and mounted perpendicularly on said closure plate, so as to separate said first and said second series of openings.

This socket is preferably open at one of its ends and partially closed at its other end arranged near the nozzle, by said deflector plate. It is advantageously mounted on said closure plate, the deflector plate being mounted inside this socket so that the plane of the closure plate is parallel to the plane of the deflection plate, the latter being offset from first along the axis of the nozzle in the direction of a separation from the free end of this nozzle, this end being arranged in a parallel plane intermediate between the plane of the deflector plate and the plane of the plate shutter.

According to a preferred embodiment, the guide sleeve for combustible gases mixed with combustion gases, is open at its two ends and is mounted substantially in the extension of the support sleeve, offset axially relative to the latter so as to spare an annular space arranged to allow penetration of the recycled combustion gases into said sleeve, at its upstream end disposed opposite the support sleeve, this support sleeve being closed at its end disposed near the sleeve for guiding combustible and combustion gases by a closure plate provided with a central opening and a ring of openings constituting said air intake members, said central opening being limited by a cylindrical bushing for guiding combustible gases, this bushing being mounted on said blanking plate coaxial with the support bushing and the gas guide sleeve com fuel and combustion and carrying a deflector plate mounted parallel to the closure plate, this deflector plate being constituted by fins in the form of circular sectors, offset and partially superimposed so as to form slots suitable for generating turbulence, the axis of rotation corresponds to the axis of the nozzle, the latter being arranged in look of a central opening formed in said deflector plate.

The free end of the nozzle is preferably arranged in a parallel plane intermediate between the plane of the closure plate of the support sleeve and the plane of the deflection plate mounted inside the guide sleeve of the combustible gases.

The present invention will be better understood with reference to the description of an exemplary embodiment and the attached drawing in which:

FIG. 1 represents a view in axial section of a first embodiment of the burner according to the invention,

FIG. 2 represents a view in axial section of a second embodiment of this burner,

FIG. 3 represents a perspective view of the deflector plate of the burner of FIG. 2,

The figure represents an axial section view of a third embodiment of this burner, and

FIG. 5 represents a perspective view of the deflector plate of the burner of FIG. H.

With reference to fig. 1, the burner 10 as described essentially comprises a support bushing 11, a guide sleeve 12 of the combustible gases coming from the vaporization of a liquid fuel, mixed with recycled combustion gases, and a jet of fuel 13, mounted in a manner known per se inside the support socket 11 and associated with an ignition electrode 14. The ^* douil¬ the support 11 is advantageously constituted by a cylindrical piece mounted in an appropriate opening of a wall 15 of the combustion chamber of a boiler (not shown), equipped with a closure plate 16 provided with a central opening 17, with a first ς

series of air intake openings 18 and a second series of air intake openings 19. The two series of air intake openings 18 and 19 are located on two circles concentric with the central opening 17, disposed opposite the injection orifice of the supply nozzle 13.

The guide sleeve 12 for combustible gases preferably consists of a metal cylinder, the diameter of which may be less, but is preferably equal to or greater than that of the support sleeve 11. This guide sleeve is open at its two ends. mites upstream 20 and downstream 21. It is mounted substantially coaxially and in the extension of the support sleeve, offset axially relative to the latter, so as to provide an annular space 22, suitable for permitting penetration of the combustion gases recycled into said sleeve at its upstream end, disposed opposite the support sleeve. As shown in the figure, the combustible gases coming from the vaporization of the liquid fuel injected by the nozzle 13 penetrate into the guide sleeve 12 as shown by the arrows A. Simultaneously air jets represented by the arrows B are injected through the openings 19 arranged in a circle around the central aperture 17. A curtain of air jets, injected through the openings 18, and illustrated by the arrows C, is formed in the peripheral zone of the guide sleeve 12. These air jets mix with the recycled gases along a path illustrated by the arrows D and have the effect of cooling the latter and of maintaining the combustion zone at a relatively low temperature.

The gas guide sleeve 12 is preferably linked to the support sleeve 11 by connecting rods 23 which define the actual width of the annular space separating these two components. Note, however, that this method of attachment could be replaced by another one leading to similar results. To facilitate guiding the recycled gases according to arrows D, the upstream end 20 of the guide sleeve is preferably flared.

The burner described with reference to fig. 2 constitutes a variant of the burner described above. For clarity, identical items will be designated by the same references and different references will be assigned to the new or modified elements.

As before, the burner 10 essentially consists of a support bush 11, a sleeve 12 for guiding the combustible gases and the recycled combustion gases, a supply nozzle 13 associated with an ignition electrode 11. The support sleeve is mounted in a suitable opening in a wall 15 of the combustion chamber of a boiler and is closed at its end disposed opposite the guide sleeve 12 by a closure plate 16 provided with a central opening 27, the diameter of which is substantially larger than that of the central opening 17 of the closure plate 16 corresponding to the burner illustrated in FIG. 1. A series of air intake openings 18 is formed in the closure plate 16. These openings are arranged in a circle concentric with the central opening 27.

This central opening 27 is partially closed by a deflector plate 28, provided with a central opening 29 and composed, as shown in more detail la'fig. 3, a series of fins, in the form of circular sectors 30, offset from one another and partially superimposed so as to provide slots 31 intended for the passage of air and arranged to cause rotary turbulence about an axis corresponding to the axis of the nozzle 13. The zone of formation of this turbulence is delimited inside a guide sleeve 32 having a substantially cylindrical shape, mounted on the closure plate 16, substantially in the extension of the support sleeve 11, coaxial with this sleeve and the sleeve 12 for guiding the gases.

As before, the combustible gases coming from the vaporization of the liquid fuel are injected into the zone delimited by the sleeve 12 in the direction of the arrows A. The air having passed through the slots 31 creates a rotary turbulence illustrated by the arrows B, and located around Jets of combustible gases represented by the arrows A. The cooling air having passed through the openings 18 follows a laminar trajectory along the inner wall of the guide sleeve 12. This air has the effect of cooling the combustion gases recycled illustrated by arrows D.

The variants illustrated by Figures and 5 are relatively close, from the construction point of view, to the embodiment illustrated by Figures 2 and 3. We find on this burner 10 the support bushing 11, the guide sleeve 12, the associated nozzle 13 has its ignition electrode 11, disposed inside the support socket 11, itself engaged in a suitable opening of a wall 15 of the combustion chamber of a boiler (not shown). As previously, the support sleeve 11 is closed at its end arranged opposite the upstream end of the guide sleeve by a closure plate 16 provided with a central opening 27 and equipped with supply ori air 18 arranged in a circle concentric to the central opening 27. A guide bush 12, the length of which is substantially greater than that of the guide bush 32 shown in FIG. 2, is mounted on the closure plate 16 so as to engage exactly in the central opening 27 of the latter. A deflector plate 13, illustrated in more detail in FIG. 5 and comprising a central opening 29 and fins 30 in the form of circular sectors, offset and partially superimposed to form slots 31. Which in this case are radial, is mounted on the inside the guide sleeve 12 of substantially cylindrical shape. It will be noted that in the example illustrated by FIG. 2, the deflector plate 28 is disposed substantially in the same plane as the closure plate 16. In the example illustrated in FIG. 1, the deflector plate 13 is disposed in a plane parallel to that of the closure plate 16, the first being offset axially relative to the second in the direction of the upstream end of the guide sleeve 12 of the combustible and combustion gases . It will also be noted that the end of the nozzle 13 is arranged in a parallel plane intermediate between the planes corresponding respectively to the deflector plate 13 and to the closure plate 16.

As in the example illustrated in fig. 1 the guide sleeve 12 is linked to the support sleeve 11 or to the closure plate 16 by connecting rods 22 providing a sufficient opening between the two components to allow easy circulation of the recycling gases. As before, the combustible gases coming from the vaporization of the liquid fuel are injected through the central opening 29 of the deflector plate 13 in the direction of the arrows A. The air injected through the slots 31 of this deflector plate causes turbulence illustrated by the arrows B. A curtain of cooling air injected through the openings 18 of the closure plate 16 is illustrated by the arrows C and the recycled combustion gases are represented by the arrows D.

The advantage of this variant, considered as a preferred embodiment of the burner according to the invention, is due to the fact that the addition of the relatively long guide sleeve 12 makes it possible to extend the path followed by the air-combustion gas mixture recycled. This increase in the trajectory of the mixture makes it possible to reduce the temperature and makes it possible to increase the quantity of recycled gas. The increase in the quantity of recycled gas makes it possible to ensure better combustion and the lowering of the temperature of the mixture makes it possible to significantly reduce the rate of nitrogen oxides contained in the residual combustion gases.

The burners as described above, essentially those of FIGS. 2 and 1, provide combustion in two phases. During the first phase, the liquid fuel is vaporized and the gases which thus form are mixed with the air injected through the slots in the deflector plate and burned in an oxygen-poor atmosphere. The resulting combustion produces carbon monoxide CO, carbon dioxide C02 and hydrocarbons. The thermal energy released by this combustion corresponds substantially to a third of the total thermal energy of the fuel. The heat produced is low during this first phase so that the formation of nitrogen oxides produced is also low.

Simultaneously the secondary air ejected through the openings 18 formed in the closure plate 16 is preheated by mixing with the combustion gases recycled inside the gas guide bush. This preheating takes place immediately upon the appearance of the flame in the burner at the time of ignition and not after heating o

walls or other components of the burner.

During the recycling of the combustion gases, part of the energy of the latter is transferred to the walls of the combustion chamber of the boiler before they are re-aspirated by the secondary air from the openings 18. Depending on the type of boiler, their temperature can vary between 600 and 1O00-C. However, they are hot enough to ensure excellent preheating of this air. Furthermore, the mass of gas to be heated by combustion is increased due to the existence of this mixture of secondary air and recycled combustion gases. Due to this increase in gas mass, the flame temperature is reduced proportionally.

During the second phase of combustion, the preheated air comes into contact with the recycled gases formed during the first phase and which consist of a mixture of combustion gases and hydrocarbons, and ensures complete combustion. Since the air is strongly preheated, especially in the variant illustrated in fig. 1 where its common trajectory with the recycled gases is lengthened, combustion is optimal. The gaseous mixture absorbs part of the heat of the flame when it enters the combustion zone, which makes it possible to observe in this zone a temperature below the average, which has the direct consequence of a reduction. the rate of nitrogen oxides (NOx) whose formation is favored, in a manner known per se by the high temperatures.

For example, if the ambient air at a temperature of 20'C, the recycled gases a temperature of 800 * C and the combustion zone, i.e. the flame, a temperature of 800 ^* C and if the air-gas mixture is recycled in equal proportions during the first combustion phase, the temperature of the preheated air is approximately equal to:

Ta = (20 ^* C + 800 ^* 0/2 = 410'C

If about 651 of preheated secondary air is mixed with the gases from the first combustion phase, the temperature of the preheated mixture will be of :

Tra = ïa / 0, 65 = 630 * C

The flame temperature for combustion of a stoichiometric mixture is equal to:

Tfl = (l '800-C + 800 ^* 0/2 = l' 300-C

Given that an excess of air is injected on the order of 10%, the actual flame temperature can be estimated at:

Tfl = T200-C

The design of the burner described makes it possible to obtain a temperature distribution favorable to prolonging the longevity of the components of the burner and in particular of the guide sleeve. Indeed, this sleeve is constantly swept by the air propelled through the air supply openings, which ensures effective cooling of this part. However, thanks to the recycling of the combustion gases and to the good heat exchange which takes place between these combustion gases and the fresh air injected, owing to the fact that the exchange surface, constituted essentially by the wall of the guide sleeve is relatively large, the injected air is preheated, which makes it possible to maintain a temperature close to 800 ° C. in the burner zone disposed downstream of the central opening of the shutter plate. This temperature is sufficient to ensure cracking of the heaviest molecules and to guarantee complete combustion of the injected fuel.

It is advantageous to increase the heat exchange surface between the combustion gases and the air injected through the air supply openings to increase the rate of cracking of the heavy molecules, which makes it possible to reduce the length of the sleeve. guide and proportionately reduce the risk of carbon deposits or ash on the inner wall of this sleeve. To reduce this risk, the diameter of this sleeve can also be increased somewhat, which also promotes silent operation of the burner. The distance between the shutter plate carrying the air-aperture openings and the gas guide sleeve must be large enough to allow good recycling of the combustion gases. The mixture obtained of combustible gas resulting from the vaporization of the liquid fuel, of combustion gas and of air is close to the stoichiometric mixture. The recycling of the combustion gases also causes a slowing down of the combustible gases, which promotes silent operation of the burner.

Besides the fact that this burner can use medium and heavy oils, it has the advantage of being of simple design and very economical construction.

The burner as described can have various variants and undergo different modifications obvious to those skilled in the art, without going beyond the ambit of the present invention.

Claims

claims

1. Burner for a liquid fuel boiler provided with means for recycling combustion gases, this burner comprising a nozzle for supplying liquid fuel and a sleeve for guiding the combustible gases coming from the vaporization of this liquid fuel, mixed with gases combustion rods, this sleeve being arranged coaxially with respect to this nozzle which is mounted inside a support bushing fitted with air supply members arranged con¬ centrically around said nozzle, characterized in that the sleeve (12) combustible and combustion gases is open at its two ends (20, 21) and is mounted substantially in the extension of the support sleeve (11), axially offset relative to the latter, so as to provide a annular space (22) arranged to allow combustion gases to penetrate into said sleeve, at its open upstream end (20) disposed opposite the support bushing.

2. Burner according to claim 1, characterized in that the support bushing (11) is closed at its end disposed near the guide sleeve (12) of the combustible and combustion gases by a closure plate (16) provided a central opening (17) formed in the extension of the nozzle (13) and a first series of openings (18) arranged in a crown concentrically around said central opening (17), constituting said feed members of air.

3. Burner according to claim 2, characterized in that said plate comprises a second series of openings (19) arranged in a crown, concentrically between said central opening (17) and said first series of openings (18).

. Burner according to claim 3. characterized in that the openings of said second series of openings each consist of a hole in the shutter plate (16).

5. Burner according to claim 3. characterized in that the closure plate (16) comprises, in its central part surrounding the open-

central structure (17), a deflecting plate (28, 13) composed of fins (30), in the form of circular sectors, offset and partially superimposed relative to each other so as to provide slots (3D arranged for generate turbulence whose axis of rotation corresponds substantially to the axis of the nozzle (13), these slots constituting in this case said second series of openings.

6. Burner according to claim 3, characterized in that it comprises a cylindrical guide sleeve (32, 12) of combustible gases, this sleeve being oriented along the axis of the nozzle (13) and mounted perpendicularly on said plate obturation (16), so as to separate said first and said second series of openings.

. Burner according to claims 5 and 6, characterized in that the cylindrical guide bush (32, 12) of the combustible gases is open at one of its ends and partially closed at its other end disposed near the nozzle, by said deflecting plate trice (28, 13).

8. Burner according to claims 5 and 6, characterized in that said guide sleeve (12) of combustible gases is mounted on said closure plate and in that the deflector plate (13) is mounted inside this socket in such a way that the plane of the closing plate is parallel to the plane of the deflecting plate, the latter being offset with respect to the first along the axis of the nozzle in the direction of separation from the free end of this nozzle.

9. Burner according to claim 8, characterized in that the free end of the nozzle (13) is arranged in a parallel plane intermé¬ diary between the plane of the deflector plate (13) and the plane of the sealing plate ( 16).

10. Burner for a liquid fuel boiler provided with means for recycling combustion gases, this burner comprising a nozzle for supplying liquid fuel and a sleeve for guiding combustible gases originating from the vaporization of this liquid fuel .

mixed with recycled combustion gases, this sleeve being arranged coaxially with respect to this nozzle mounted inside a douil¬ the support equipped with air supply members arranged concentrically around said nozzle, characterized in that the guide sleeve (12) for combustible gases mixed with combustion gases is open at its two ends and is mounted substantially in the extension of the support bushing (11), offset axially relative to the latter so as to provide a space annular (22) arranged to allow penetration of the recycled combustion gases into said sleeve, at its open upstream end (20), disposed opposite the support bushing (it), in that this support bushing is closed at its end mite disposed near the guide sleeve for combustible and combustion gases by a closure plate (16) provided with a central opening (27) and an opening ring s (18) constituting said air intake members, in that said central opening is limited by a cylindrical guide bush (12) for combustible gases, this bush being mounted on said shutter plate coaxially with the support sleeve and the sleeve for guiding the combustible and combustion gases, and in that this sleeve carries a deflector plate (13) mounted parallel to the closure plate, this deflector plate being constituted by fins (30) in the form of circular sectors, offset and partially superimposed so as to form slots (31) capable of generating turbulence whose axis of rotation corresponds to the axis of the nozzle, the latter being disposed opposite a central opening (29) formed in said deflector plate.

11. Burner according to claim 10, characterized in that the free end of the nozzle (13) is arranged in a parallel intermediate plane between the plane of the closure plate (16) of the support bushing and the plane of the deflector plate (13) mounted inside the guide bush (12) of combustible gases.