Fuel fluidizing nozzle assembly

Description

BACKGROUND

[0001] This disclosure relates to a fuel fluidizing nozzle assembly for a fluidized bed reactor.

[0002] The use of fluidized bed reactors for the incineration of waste fuels, such as municipal refuse and high alkali fuels is generally known and involves the burning of these fuels with air while fluidizing it in a fluidized bed. The upper section of the reactor is typically equipped with a waste fuel feeding unit, and the waste fuel is burned while it is fluidized by primary air, which is blown through nozzle assemblies in a lower section of the reactor body.

[0003] The fuels are generally of low calorie content and contain a high percentage of tramp material that does not bum. As the fuels are fed to the fluidized bed, the volatile organic compounds are burned and coarse material, such as tramp material, spent bed make-up material, and ash, remain in the fluidized bed. Therefore, a fluidized bed reactor for the incineration of waste and high alkali fuels is typically equipped with a means in the lower section of the reactor body which is designed to provide fluidizing air to the fluidized bed while allowing coarse material to be removed from the reactor.

[0004] One example of a means for removing coarse material is depicted in Fig. 1, which is a top plan view of an open-floor grate assembly 10 disposed in the lower portion of a fluidized bed reactor 12. The grate assembly 10 includes a number of parallel, spaced apart air ducts 14 (also known as air pipes or bars, sparge pipes, and hydro tubes) extending side-by-side in a substantially horizontal plane. Air nozzle assemblies 16 are attached to the air ducts 14 for supplying fluidizing air from within the air ducts 14 into the fluidized bed of fuel, which is located above the grate assembly. As the organic compounds are decomposed and burned within the fluidized bed, the coarse material descends downwardly through spaces 18 between the air ducts 14. The coarse material is then discharged to external equipment and a portion of the bed make-up material may be separated from the coarse material and returned to the fluidized bed. Examples of such grate assemblies are described in US Pat. No. 5,966,839 and US Pat. No. 5,425,331.

[0005] US Patent 6,571,746 B1 Kinni, issued June 3, 2003 shows a general fluidized bed boiler using similar parts.

[0006] Fig. 2 depicts a cross-sectional elevation view of a portion of an air duct 14 including nozzle assemblies 16. Each nozzle assembly 16 is formed from a hollow tube 30 having an end cap 33 welded thereon and a plurality of nozzle holes 34 disposed therein proximate the end cap 33. The nozzle assemblies 16 are attached through an upper wall 32 of the air duct 14, and air from the air duct 14 passes through the hollow tube 30, and out the nozzle holes 34 into the fluidized bed of fuel. The air duct 14 may include pipes 36 through which a cooling medium, such as water, flows.

[0007] While such an arrangement works well when the nozzle assemblies 16 are newly installed, over time the nozzle holes 34, which are typically ¼ inch in diameter or less, will become plugged due to the presence of alkali materials. More specifically, alkali material gets into the nozzle assembly due to gas recirculation to the reactor and solids back flow from the bed. These alkalis cause a sticky build up on the nozzle assemblies, particularly at the nozzle holes and at any bends in the tube, which result in plugging of the nozzle assemblies. The quick plugging results in much less than the desired operating time between reactor outages for maintenance. Furthermore, repair of the nozzle assemblies typically requires cutting the top portion of the nozzle assembly, and welding a new top portion in its place, which is a time-consuming process that can extend the duration of reactor outages.

[0008] US Patent 5,145,559 A Toth, issued April 21, 1992 shows and describes a fluidized bed arrangement with nozzles that blow air in a horizontal direction.

[0009] EP 0 028 458 A2 World Energy Resources Consultancy Services (PTY) Limited, published May 13, 1991 describes a fluidized bed boiler system having burners that are constructed from several pieces.

[0010] Thus, there is a need for a nozzle assembly for use in a grate assembly of a fluidized bed reactor that reduces the likelihood of plugging and, therefore, reduces the frequency of reactor outages. Furthermore, there is a need for an easily replaceable nozzle assembly to help reduce the duration of such outages.

SUMMARY

[0011] According to the aspects illustrated herein, there is provided a grate assembly for a fluidized bed reactor. The grate assembly includes a plurality of parallel air ducts extending side-by-side in a substantially horizontal plane and defining spaces therebetween through which coarse material from the fluidized bed descends. A plurality of nozzle assemblies is attached to each air duct for supplying fluidizing air from within the air duct into the fluidized bed. Each of the nozzle assemblies includes a nozzle formed from a tube having an inlet end in fluid communication with the air duct, and an outlet end in fluid communication with the inlet end. An orifice is disposed at the outlet end of the nozzle, and the nozzle is bent proximate the outlet end to direct a primary direction of a stream of fluidizing air flowing from the orifice toward the air duct such that an angle θ between the primary direction and the substantially horizontal plane formed by the air ducts is between about 30 to about 90 degrees. The nozzle assembly may further include a connector pipe disposed between the air duct and the nozzle, and a sleeve disposed around the nozzle and the connector pipe to secure the nozzle to the connector pipe. The nozzle may be welded and/or threaded to the sleeve.

[0012] In one aspect, an inside diameter of an inlet end of the orifice is chamfered to prevent a build-up of alkali material at the inlet end. In another aspect, an inside diameter of the connector pipe is equal to an inside diameter of the nozzle to prevent build-up of material at an interface between the connector pipe and the nozzle.

[0013] Each air duct may also include a plurality of capped nozzle assemblies attached thereto for supplying fluidizing air from within the air ducts into the fluidized bed. Each of the capped nozzle assemblies includes a tube having an inlet end in fluid communication with the air duct, and an outlet end in fluid communication with the inlet end. A cap is disposed at the outlet end, and a plurality of nozzle holes disposed radially through the tube at the outlet end, through which the fluidizing air passes.

[0014] In various aspects the plurality of nozzle assemblies are arranged in groups of three along the length of the air duct, each group of three including a first nozzle assembly disposed substantially at the centerline of the air duct and second and third nozzle assemblies flanking the first nozzle assembly. The primary direction of the streams of fluidizing air flowing from the orifices of the first, second, and third nozzle assemblies may be substantially parallel. Alternatively, the primary direction of the streams of fluidizing air flowing from the orifices of the second, and third nozzle assemblies are directed at an angle away from the stream of fluidizing air flowing from the orifice of the first nozzle assembly.

[0015] The above described and other features are exemplified by the following figures and detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Referring now to the figures, which are exemplary embodiments, and wherein the like elements are numbered alike:

[0017] Fig. 1 is a top plan view of a prior art grate assembly disposed in a fluidized bed reactor;

[0018] Fig. 2 is a cross-sectional elevation view of a portion of an air duct of Fig. 1 including prior art nozzle assemblies;

[0019] Fig. 3 is a cross-sectional elevation view of a nozzle assembly in accordance with an embodiment of the present invention;

[0020] Fig. 4 is a cross-sectional elevation view of an air duct of a grate assembly including a group of nozzle assemblies of Fig. 3 in a first arrangement, as taken along section 4-4 of Fig. 5;

[0021] Fig. 5 is a top plan view of the group of nozzle assemblies in Fig. 4;

[0022] Fig. 6 is a cross-sectional elevation view of an air duct of a grate assembly including a group of nozzle assemblies of Fig. 3 in a second arrangement, as taken along section 6-6 of Fig. 7;

[0023] Fig. 7 is a top plan view of the group of nozzle assemblies in Fig. 6;

[0024] Fig. 8 is a cross-sectional elevation view of an air duct of a grate assembly including a group of nozzle assemblies of Fig. 3 in a third arrangement; and

[0025] Fig. 9 is a cross-sectional elevation view of an air duct of a grate assembly including nozzle assemblies of Fig. 3 and Fig. 2.

DETAILED DESCRIPTION

[0026] Fig. 3 is a cross-sectional elevation view of a nozzle assembly 50 in accordance with an embodiment of the present invention. The nozzle assembly 50 includes a nozzle 52, a pipe extension 54, an orifice 56, and a connector sleeve 58. The nozzle assembly 50 is attached to the top of an air duct 14 for supplying fluidizing air from within the air duct 14 into a fluidized bed of fuel. As will be described in further detail hereinafter, the nozzle assembly 50 may be used in place of, or in addition to, the prior art nozzle assembly 16 shown in Fig. 2.

[0027] The nozzle 52 is formed from a tube having an inlet end 60 and an outlet end 62, and is bent proximate the outlet end 62 to form a J-shape. The nozzle 52 directs a stream of fluidizing air, which has a primary direction of flow along a longitudinal axis 64 of the nozzle 52, toward the air duct 14 at an angle θ, which is the angle between the longitudinal axis 64 of the nozzle 52 and the substantially horizontal plane formed by the top walls 32 of the air ducts 14. It has been determined that, for use with open floor grate assemblies such as those depicted in Fig. 1, the angle θ is preferably between about 30 to about 90 degrees, and more preferably between about 30 to about 50 degrees. Within this range, the stream of fluidizing air has been found to sufficiently fluidize the bed, while avoiding excessive movement of the bed and coarse materials in a horizontal direction. This is important for an open floor grate assembly, where coarse material moves downward through the floor and further mixing of the coarse material into the bed is undesirable.

[0028] To accomplish the desired angle θ, the nozzle 52 is bent to an angle between about 120 degrees to about 180 degrees, and more preferably between about 120 degrees to about 140 degrees. The nozzle 52 may be made from metal or other rigid material that is suitable for the high temperature conditions within a fluidized bed reactor.

[0029] The orifice 56 is disposed at an outlet end 62 of the nozzle 52. In the example shown, the orifice 56 is welded into the inside diameter of the outlet end 62; it is, however, contemplated that the orifice may be disposed around the outside diameter of the nozzle 52, or formed from the nozzle 52 itself. The orifice 56 preferably has a single aperture 66, which is preferably greater than or equal to 3/8 inch in diameter. Advantageously, because the nozzle assembly 50 uses a single, relatively larger aperture 66 through which air flows, the nozzle assembly 50 plugs less frequently than prior art nozzles. An inlet end 68 of the orifice 56 is chamfered (beveled) to orifice prevent build-up of alkali materials and to make the airflow into the orifice more aerodynamic.

[0030] The pipe extension 54 includes an inlet end 70, which is attached to the top 32 of the air duct 14, by welding or the like, and an outlet end 72, which abuts the inlet end 60 of the nozzle 52. The pipe extension 54 and nozzle 52 have the same inside diameter to provide a smooth interface between the two components and thus prevent any build-up of alkali material at the interface. While the pipe extension 54 is shown as being substantially straight, it is contemplated that the pipe extension 54 may include one or more bends as may be needed for a particular application. It is noted, however, that minimizing the number of bends in the pipe extension 54 is believed to help reduce the build-up of alkali materials within the nozzle assembly 50.

[0031] The sleeve 58 is disposed around the inlet end 60 of the nozzle 52 and the outlet end 72 of the pipe extension 54 to facilitate connection of the nozzle 52 and pipe extension 54. The sleeve 58 and inlet end 60 of the nozzle 52 may be secured together using a threaded interface 74. The sleeve 58 is also secured to the nozzle 52 and to the pipe extension 54 by welds 76. Preferably, tack welds are used between the sleeve 58 and the nozzle 52 so that the nozzle 52 may be quickly removed and replaced during a reactor outage. To remove or replace the nozzle 52, the tack welds 76 on the sleeve 58 are cut and then the nozzle 52 can be turned or twisted out of the sleeve 58. Advantageously, because the nozzle 52 can be quickly removed and replaced, reactor maintenance outage time can be reduced compared to that required for prior art nozzles, which require the nozzle to be cut free.

[0032] In designing an open-floor grate assembly, nozzle assemblies 50 are laid out in a pattern to fluidize the bed and insure that they do not have the exit of airflow pointed from one nozzle assembly 50 directly at another nozzle assembly 50. For example, Fig. 4 is a cross-sectional elevation view of an air duct 14 of a grate assembly 10 including a group of nozzle assemblies 50 (indicated as 50, 50', and 50" in a first arrangement; and Fig. 5 is a top plan view of the group of nozzle assemblies 50 in Fig. 4. Each air duct 14 includes a plurality of nozzle assemblies 50 arranged in groups of three along the length of the air duct 14. Each group of three includes a first nozzle assembly 50 disposed substantially at the centerline of the air duct 14 and second and third nozzles 50' and 50" flanking the first nozzle 50. While the three nozzle assemblies 50, 50', and 50" are shown as being aligned side-by-side, it is contemplated that one or more of the nozzle assemblies in the group may be offset from the other nozzle assemblies in the group. For example, the center nozzle assembly 50 may be offset from the flanking nozzle assemblies 50' and 50".

[0033] As shown in Figs. 4 and 5, the longitudinal axes 64, 64' and 64" of the nozzles 52, 52' and 52" may be parallel to each other. As a result, the primary directions of the streams of fluidizing air flowing from the orifices 56, 56' and 56" are substantially parallel. Alternatively, the longitudinal axes 64, 64' and 64" of the nozzles 52, 52' and 52" may be arranged at an angle to each other, as shown in Figs. 6 and 7. In the example shown, the center nozzle 52 is aligned with the centerline of the air duct 14, while the outer nozzles 52' and 52" are directed toward the sides of the air duct 14. As a result, the primary direction of the streams of fluidizing air flowing from the orifices 56' and 56" of the outer nozzle assemblies 50' and 50" are directed at an angle away from the stream of fluidizing air flowing from the orifice 56 of the center nozzle assembly 50. With this arrangement, the air streams provided by the outer nozzle assemblies 50' and 50" help direct coarse material downward into the spaces 18 between the air ducts 14. Advantageously, the direction of the air stream from a nozzle assembly 50 can be changed simply by rotating the nozzle 52 within the sleeve 58.

[0034] As shown in Figure 8, one or more of the pipe extensions 50 may be angled to adjust the position of the air stream provided by the nozzles 52. In the example shown, the pipe extensions 54' and 54" of the outer nozzle assemblies 50' and 50" are angled outward from the center nozzle assembly 50. Furthermore, as shown in Figure 9, one or more nozzle assemblies 50 may be used in conjunction with a prior art nozzle assembly 16. As previously noted, such prior art nozzle assemblies 16 are typically formed from a hollow tube 30 having an end cap 33 welded thereon and a plurality of nozzle holes 34 disposed therein proximate the end cap 33.

Claims

1. A grate assembly (10) for a fluidized bed reactor (12), the grate assembly (10) comprising:

a plurality of parallel air ducts (14) extending side-by-side in a substantially horizontal plane and defining spaces (18) therebetween through which coarse material from the fluidized bed descends;

a plurality of nozzle assemblies (50) attached to each air duct (14) for supplying fluidizing air from within the air duct (14 into the fluidized bed, each of the nozzle assemblies (50) including:

a nozzle (52) formed from a tube (51) having an inlet end (60) in fluid communication with the air duct (14), and an outlet end (62) in fluid communication with the inlet end 60,

an orifice (56) disposed at the outlet end (62),

characterized in that the nozzle (52) is bent proximate the outlet end (62) to direct a stream of fluidizing air flowing from the orifice (56) in a primary direction toward the air duct (14) such that an angle θ between the primary direction and the substantially horizontal plane formed by the air ducts (14) is between about 30 to about 90 degrees.

2. The grate assembly (10) of claim 1, wherein the angle θ is between about 30 to about 50 degrees.

3. The grate assembly (10) of claim 1, wherein the nozzle (52) is bent to an angle of between about 120 degrees to about 180 degrees.

4. The grate assembly (10) of claim 1, wherein an inside diameter of an inlet end (68) of the orifice (56) is chamfered to prevent a build-up of alkali material at the inlet end (68).

5. The grate assembly (10) of claim 1, wherein the nozzle assembly (50) further includes a connector pipe (54) disposed between the air duct (14) and the nozzle (52).

6. The grate assembly (10) of claim 5, wherein an inside diameter of the connector pipe (54) is equal to an inside diameter of the nozzle (52) to prevent build-up of material at an interface between the connector pipe (54) and the nozzle (52).

7. The grate assembly (10) of claim 5, further comprising:

a sleeve (58) disposed around the nozzle (52) and the connector pipe (54) to secure the nozzle (52) to the connector pipe (54).

8. The grate assembly (10) of claim 7, wherein the nozzle (52) is threaded to the sleeve (58).

9. The grate assembly (10) of claim 7, wherein the nozzle is welded to the sleeve (58).

10. The grate assembly (10) of claim 1, further comprising:

a plurality of capped nozzle assemblies (16) attached to each air duct (14) for supplying fluidizing air from within the air ducts (14) into the fluidized bed, each of the capped nozzle assemblies (16) including:

a tube (30) having an inlet end in fluid communication with the air duct (14), and an outlet end in fluid communication with the inlet end,

a cap (33) disposed at the outlet end; and

a plurality of nozzle holes (34) disposed radially through the tube at the outlet end, through which the fluidizing air passes.

11. The grate assembly (10) of claim 10, wherein each capped nozzle assembly (16) is disposed between two nozzle assemblies (50).

12. The grate assembly (10) of claim 1, wherein the plurality of nozzle assemblies are arranged in groups of three along the length of the air duct (14), each group of three including a first nozzle assembly (50) disposed substantially at the centerline of the air duct (14) and second (50') and third nozzle assemblies (50") flanking the first nozzle assembly (50).

13. The grate assembly (10) of claim 12, wherein the primary direction (64, 64', 64") of the streams of fluidizing air flowing from the orifices (56, 56', 56") of the first (50), second (50'), and third nozzle assemblies (50") are substantially parallel.

14. The grate assembly (10) of claim 12, wherein the primary direction (64, 64', 64") of the streams of fluidizing air flowing from the orifices (56', 56") of the second (50'), and third nozzle assemblies (50") are directed at an angle away from the stream of fluidizing air flowing from the orifice (56) of the first nozzle assembly (50).

Ansprüche

1. Gitteranordnung (10) für einen Wirbelbettreaktor (12), wobei die Gitteranordnung (10) Folgendes umfasst:

mehrere parallele Luftleitungen (14), die sich Seite an Seite auf einer im Wesentlichen horizontalen Ebene erstrecken und Räume (18) dazwischen definieren, durch die grobes Material aus dem Wirbelbett absinkt;

mehrere Düsenanordnungen (50), die an jeder Luftleitung (14) zum Zuführen von fluidisierender Luft aus dem Innenraum der Luftleitung (14) in das Wirbelbett befestigt sind, wobei jede der Düsenanordnungen (50) Folgendes aufweist:

eine Düse (52), die aus einem Rohr (51) gebildet ist, das ein Einlassende (60) in Fluidverbindung mit der Luftleitung (14) und ein Auslassende (62) in Fluidverbindung mit dem Einlassende (60), eine Öffnung (56), die an dem Auslassende (62) angeordnet ist, aufweist,

dadurch gekennzeichnet, dass
die Düse (52) in der Nähe des Auslassendes (62) gekrümmt ist, um einen Strom fluidisierender Luft, die von der Öffnung (56) in eine primäre Richtung zu der Luftleitung (14) strömt, zu lenken, sodass ein Winkel θ zwischen der primären Richtung und der im Wesentlichen horizontalen Ebene, der durch die Luftleitungen (14) gebildet wird, zwischen etwa 30 bis etwa 90 Grad beträgt.

2. Gitteranordnung (10) nach Anspruch 1, wobei der Winkel e zwischen etwa 30 bis etwa 50 Grad beträgt.

3. Gitteranordnung (10) nach Anspruch 1, wobei die Düse (52) zu einem Winkel zwischen etwa 120 Grad bis etwa 180 Grad gekrümmt ist.

4. Gitteranordnung (10) nach Anspruch 1, wobei ein Innendurchmesser eines Einlassendes (68) der Öffnung (56) abgeschrägt ist, um die Ansammlung von Alkalimaterial an dem Einlassende (68) zu verhindern.

5. Gitteranordnung (10) nach Anspruch 1, wobei die Düsenanordnung (50) ferner eine Anschlussrohrleitung (54) aufweist, die zwischen der Luftleitung (14) und der Düse (52) angeordnet ist.

6. Gitteranordnung (10) nach Anspruch 5, wobei ein Innendurchmesser der Anschlussrohrleitung (54) gleich einem Innendurchmesser der Düse (52) ist, um die Ansammlung von Material an einer Schnittstelle zwischen der Anschlussrohrleitung (54) und der Düse (52) zu verhindern.

7. Gitteranordnung (10) nach Anspruch 5, ferner umfassend:

eine Hülse (58), die um die Düse (52) und die Anschlussrohrleitung (54) angeordnet ist, um die Düse (52) an der Anschlussrohrleitung (54) anzubringen.

8. Gitteranordnung (10) nach Anspruch 7, wobei die Düse (52) auf die Hülse (58) aufgeschraubt ist.

9. Gitteranordnung (10) nach Anspruch 7, wobei die Düse (52) an die Hülse (58) geschweißt ist.

10. Gitteranordnung (10) nach Anspruch 1, ferner umfassend:

mehrere Düsenanordnungen (16) mit Kappen, die an jeder Luftleitung (14) zum Abgeben von fluidisierender Luft aus dem Innenraum der Luftleitungen (14) in das Wirbelbett angeordnet sind, wobei jede der Düsenanordnungen (16) mit Kappe Folgendes aufweist:

ein Rohr (30) mit einem Einlassende in Fluidverbindung mit der Luftleitung (14) und einem Auslassende in Fluidverbindung mit dem Einlassende, einer Kappe (33), die an dem Auslassende angeordnet ist; und

mehrere Düsenlöcher (34), die radial durch das Rohr an dem Auslassende angeordnet sind, durch das die fluidisierende Luft dringt.

11. Gitteranordnung (10) nach Anspruch 10, wobei jede Düsenanordnung (16) mit Kappe zwischen zwei Düsenanordnungen (50) angeordnet ist.

12. Gitteranordnung (10) nach Anspruch 1, wobei die mehreren Düsenanordnungen in Dreiergruppen entlang der Länge der Luftleitung (14) angeordnet sind, wobei jede Dreiergruppe eine erste Düsenanordnung (50), die im Wesentlichen an der Mittellinie der Luftleitung (14) angeordnet ist, und eine zweite (50') und dritte Düsenanordnung (50'') aufweist, die seitlich an die erste Düsenanordnung (50) angrenzt.

13. Gitteranordnung (10) nach Anspruch 12, wobei die primäre Richtung (64, 64', 64") der Ströme von fluidisierender Luft, die aus den Öffnungen (56, 56', 56") der ersten (50), zweiten (50') und dritten (50") Düsenanordnung strömt, im Wesentlichen parallel ist.

14. Gitteranordnung (10) nach Anspruch 12, wobei die primäre Richtung (64, 64', 64") der Ströme von fluidisierender Luft, die aus den Öffnungen (56', 56") der zweiten (50') und dritten (50") Düsenanordnung strömt, in einem Winkel gelenkt werden, der von dem Strom der fluidisierenden Luft, die durch die Öffnung (56) der ersten Düsenanordnung (50) strömt, weg zeigt.

Revendications

1. Ensemble de grille (10) pour réacteur (12) à lit fluidisé, l'ensemble de grille (10) comportant :

plusieurs conduits d'air (14) parallèles qui s'étendent côte à côte dans un plan essentiellement horizontal et qui définissent entre eux des espaces (18) par lesquels descend le matériau grossier qui provient du lit fluidisé,

plusieurs ensembles d'ajutage (50) attachés à chaque conduit d'air (14) pour délivrer de l'air de fluidisation depuis l'intérieur du conduit d'air (14) jusque dans le lit fluidisé, chacun des ensembles d'ajutage (50) comprenant :

un ajutage (52) formé d'un tube (51) doté d'une extrémité d'entrée (60) en communication d'écoulement avec le conduit d'air (14) et d'une extrémité de sortie (62) en communication d'écoulement avec l'extrémité d'entrée (60) et

un orifice (56) disposé à l'extrémité de sortie (62),

caractérisé en ce que

l'ajutage (52) est cintré à proximité de l'extrémité de sortie (62) de manière à envoyer un écoulement d'air de fluidisation provenant de l'orifice (56) dans une direction primaire en direction du conduit d'air (14) de telle sorte que l'angle θ formé entre la direction primaire et le plan essentiellement horizontal formé par les conduits d'air (14) soit compris entre environ 30 et environ 90 degrés.

2. Ensemble de grille (10) selon la revendication 1, dans lequel l'angle θ est compris entre environ 30 et environ 50 degrés.

3. Ensemble de grille (10) selon la revendication 1, dans lequel l'ajutage (52) est cintré à un angle compris entre environ 120 degrés et environ 180 degrés.

4. Ensemble de grille (10) selon la revendication 1, dans lequel le diamètre intérieur de l'extrémité d'entrée (68) de l'orifice (56) est chanfreiné pour empêcher une accumulation de matériau alcalin à l'extrémité d'entrée (68).

5. Ensemble de grille (10) selon la revendication 1, dans lequel l'ensemble d'ajutage (50) comprend en outre un conduit de raccordement (54) disposé entre le conduit d'air (14) et l'ajutage (52).

6. Ensemble de grille (10) selon la revendication 5, dans lequel le diamètre intérieur du conduit de raccordement (54) est égal au diamètre intérieur de l'ajutage (52) de manière à empêcher l'accumulation de matériau à l'interface entre le conduit de raccordement (54) et l'ajutage (52).

7. Ensemble de grille (10) selon la revendication 5, comportant en outre un manchon (58) disposé autour de l'ajutage (52) et du conduit de raccordement (54) pour fixer l'ajutage (52) sur le conduit de raccordement (54).

8. Ensemble de grille (10) selon la revendication 7, dans lequel l'ajutage (52) est fileté sur le manchon (58).

9. Ensemble de grille (10) selon la revendication 7, dans lequel l'ajutage (52) est soudé sur le manchon (58).

10. Ensemble de grille (10) selon la revendication 1, comportant en outre :

plusieurs ensembles d'ajutage (16) recouverts d'un capuchon et fixés à chaque conduit d'air (14) pour délivrer de l'air de fluidisation de l'intérieur des conduits d'air (14) jusque dans le lit fluidisé, chacun des ensembles d'ajutage (16) recouvert d'un capuchon comprenant :

un tube (30) doté d'une extrémité d'entrée en communication d'écoulement avec le conduit d'air (14) et d'une extrémité de sortie en communication d'écoulement avec l'extrémité d'entrée,

un capuchon (33) disposé sur l'extrémité de sortie et

plusieurs trous d'ajutage (34) disposés radialement à travers le tube à l'extrémité de sortie et par lesquels l'air de fluidisation passe.

11. Ensemble de grille (10) selon la revendication 10, dans lequel chaque ensemble d'ajutage (16) recouvert d'un capuchon est disposé entre deux ensembles d'ajutage (50).

12. Ensemble de grille (10) selon la revendication 1, dans lequel les différents ensembles d'ajutage sont agencés en groupes de trois suivant la longueur du conduit d'air (14), chaque groupe de trois comprenant un premier ensemble d'ajutage (50) disposé essentiellement le long de la ligne centrale du conduit d'air (14), le second ensemble d'ajutage (50') et le troisième ensemble d'ajutage (50") étant disposés sur les flancs du premier ensemble d'ajutage (50).

13. Ensemble de grille (10) selon la revendication 12, dans lequel les directions primaires (64, 64', 64") des écoulements d'air de fluidisation qui s'écoulent des orifices (56, 56', 56") du premier ensemble d'ajutage (50), du deuxième ensemble d'ajutage (50') et du troisième ensemble d'ajutage (50") sont essentiellement parallèles.

14. Ensemble de grille (10) selon la revendication 12, dans lequel les directions primaires (64, 64', 64") des écoulements d'air de fluidisation qui s'écoulent des orifices (56', 56") du deuxième ensemble d'ajutage (50') et du troisième ensemble d'ajutage (50") s'éloignent obliquement de l'écoulement d'air de fluidisation qui s'écoule de l'orifice (56) du premier ensemble d'ajutage (50).

Drawing