EP0025980B1 - A static monolithic cylindrical honeycomb structure with large contact surface - Google Patents

Description

The present invention relates to a static monolithic honeycomb cylindrical structure with a large contact surface of ceramic material, comprising a plurality of parallel channels defined by walls of the radial type and walls of the circular type, in which the channels form two groups each traversed by a fluid, the channels of one of the two groups being nested between the channels of the other group at an angular offset; the cross section of said structure comprising an annular zone composed of parallel channels and a central channel allowing the admission and / or the evacuation of fluids by selective communications with one or the other of the two groups of channels, said channel being closed by a watertight cap. It applies more particularly to heat exchangers at high temperature (of the order of 1200 ° C.), but is also suitable for other applications, such as gas treatment by catalysis, material exchange by diffusion at through a wall.

Document FR-A-2417074 discloses a cylindrical honeycomb structure of this kind. The channel groups are offset radially there and the channels have an elongated section extending almost over the entire width of the annular zone in the radial direction. Therefore the extrusion nozzle for the manufacture of these structures is relatively difficult to make and fragile, its radial cores being fixed only at one of their ends. Consequently, such cylindrical structures can only be produced with a relatively large diameter.

The object of the present invention is to remedy this drawback, and to provide a cylindrical honeycomb structure of ceramic material which is easy to manufacture, using an extrusion nozzle of robust structure, which has a large surface area. exchange per unit of volume, and which may be of small diameter while having a large number of channels.

The cylindrical structure according to the invention is characterized in that at each end an end piece closes off the annular zone, and that the circular type walls of the two groups of parallel channels are inscribed in several cylinders coaxial with said structure.

• la figure 1 est une vue partielle en perspective, avec arrachement, illustrant un type de structure alvéolaire de section rectangulaire, conformément à une technique connue,
• la figure 2 est une vue partielle en perspective d'une structure alvéolaire conforme à l'invention, destinée à être traversée par deux flux distincts dont l'un est admis par un canal central,
• les figures 3A et 3B illustrent chacune une cartouche complète, comportant une structure selon la figure 2,
• la figure 4 est une coupe schématique de la cartouche illustrée en figure 3B, illustrant les trajets empruntés par les deux flux,
• les figures 5A et 5B sont des coupes schématiques pour des variantes à un seul flux d'entrée, et deux flux de sortie dont l'un est une partie filtrée du flux d'entrée, la structure selon l'invention constituant alors un filtre, respectivement à flux total et à flux dérivé, par exemple pour l'épuration des gaz émis par des moteurs diesels,
• les figures 6A, 6B, 6C illustrent en vue partielle arrachée et à échelle agrandie différentes variantes de réalisation des parois de la structure selon l'invention,
• les figures 7 et 8 illustrent, respectivement en vue partielle arrachée et en perspective, une variante conforme à l'invention de structure pour laquelle l'un des deux flux est introduit et extrait par les faces d'extrémité,
• la figure 9 illustre un maillage à cellules proches du carré, ce maillage convenant tout particulièrement à une structure traversée par un seul flux en vue d'une grande accumulation d'énergie thermique.

The advantages of the invention will appear in the light of the description which follows, given by way of illustration but in no way limiting, with reference to the figures of the appended drawing, where:

• FIG. 1 is a partial perspective view, with cutaway, illustrating a type of honeycomb structure of rectangular section, in accordance with a known technique,
• FIG. 2 is a partial perspective view of a honeycomb structure according to the invention, intended to be crossed by two separate flows, one of which is admitted by a central channel,
• FIGS. 3A and 3B each illustrate a complete cartridge, comprising a structure according to FIG. 2,
• FIG. 4 is a diagrammatic section of the cartridge illustrated in FIG. 3B, illustrating the paths taken by the two flows,
• FIGS. 5A and 5B are schematic sections for variants with a single input flow, and two output flows, one of which is a filtered part of the input flow, the structure according to the invention then constituting a filter, total flow and derivative flow respectively, for example for the purification of gases emitted by diesel engines,
• FIGS. 6A, 6B, 6C illustrate in cutaway view and on an enlarged scale different alternative embodiments of the walls of the structure according to the invention,
• FIGS. 7 and 8 illustrate, respectively in partial cutaway view and in perspective, a variant in accordance with the invention of structure for which one of the two flows is introduced and extracted by the end faces,
• FIG. 9 illustrates a mesh with cells close to the square, this mesh being particularly suitable for a structure crossed by a single flow with a view to a large accumulation of thermal energy.

Figure 1, the end of the honeycomb structure 1 according to a known technique is of rectangular section and rectangular mesh. The end face 2 is selectively closed, according to an alternation of parallel rows: a first flow is admitted (arrow 3) by the face 2 in parallel channels such as 4, and is discharged by the other face (not visible) , while a second flow is admitted (arrow 5) through lateral orifices 6 in parallel channels such as 7 (the ends of which are therefore closed), and discharged laterally in the vicinity of the other face: the heat exchange takes place made by walls such as 8 separating two adjacent sets of channels. Such a structure is obtained by extrusion, then drying and heat treatment when it is made of ceramic material, and the selective sealing of its end faces is generally carried out by dipping in a slip.

It is well understood, in addition to the difficulties of realization when the dimensions are small, that the edges, and there are twelve of them, are sources of drawbacks as well as for the treatment which is necessarily heterogeneous, as for the mechanical rigidity of the structure.

In FIG. 2, in an example of a structure 9 in accordance with the invention, the channels are defined by walls 10 of radial type and walls 11 of circular type, said channels defining assemblies with essentially radiating arrangement traversed by the same flow. Here, the general organization is cylindrical, as well as for the section, the cylindrical external surface allowing a drying and a heat treatment much more uniform and offering a mechanical rigidity much higher compared to the structures with rectangular section, that as for the arrangement of the channels traversed by the same flow, whose essentially radiating arrangement, alternating according to an angular offset, is clearly illustrated.

According to a particularly advantageous arrangement, the structure 9 is produced according to a hollow cylinder whose annular section, forming the useful cellular part, consists of sets of parallel channels, and whose central housing 12 is a channel allowing the admission and / or the evacuation of one of the two flows, said channel being closed in the vicinity of one of its ends (not visible here, but subsequently shown in the sections of Figures 4 and 5) to distribute the flow in the cells of said structure. At each end, the structure comprises an end piece 13 making it possible to close simultaneously by its circular face 14 all the channels opening onto the annular end face, while leaving free access through an orifice 15 to the central channel 12. This end piece, made of any waterproof material (metallic or ceramic) will, as the case may be, be fixed by metallization of the ceramic at high temperature, or by bonding, or by brazing with glasses, depending on the operating temperature ranges.

It is necessary to insist somewhat on the use of such a central channel, the communication of which with a set of channels is not always necessary, because this use is quite remarkable: indeed, we had not used until then a central channel as a hub passage in the case of cellular honeycomb wheels forming rotary exchangers, regenerators for example. However here, the role of the channel is infinitely more active, since it makes it possible to introduce and extract one of the flows, with the non-negligible advantage of being able to completely seal the end faces.

In addition, the central recess, in the annular arrangement, whether or not it is used for the routing of a flow, makes it possible to reduce the stresses due to dimensional variations of the structure, during its preparation and / or its use.

Here therefore, in FIG. 2, a group of channels communicates with the central channel, the end fitting simultaneously closing said channels, while the other group of channels, associated with the second flow, has lateral orifices 16 of admission and / or evacuation of the associated flow.

FIGS. 3A and 3B illustrate a complete structure, in the form of a cartridge, with a partition wall 17 fixed on the external surface to separate the two flows, and having respectively lateral inlet and outlet orifices d 'A flow 16A opening directly against the plane of the annular end faces, and 16B formed at a certain distance from said faces, which slightly complicates the machining in the latter case, but above all makes it possible to significantly increase the stiffness of the ends of the structure. The openings are generally obtained by conventional machining of the partitions by means of grinding wheels, cutters or by any other process (ultrasound, laser, etc.); machining will preferably be carried out on the raw extruded ceramic element, while on a precooked (biscuit) or even baked element, it will be preferable to use ultrasound or diamond discs, the structure provided with its openings being able to be of any type. way subjected to cooking giving it the desired mechanical strength.

FIG. 4 illustrates well the paths taken by the two flows passing through the structure 9B, and shows the tight plug 18 closing the central channel 12: the lower part of the section concerns the circulation of the flow admitted by the central channel, in channels successive parallels, while the upper part concerns the circulation of the other flow which is admitted and expelled laterally by the orifices 16B. The circular cutting of the orifices shows schematically a machining of the walls by a circular grinding wheel, but it goes without saying that one can choose any other type of cutting.

FIGS. 5A and 5B illustrate variants constituting a filter, for example for purifying the gases emitted by diesel engines, variants according to which the partitioning between the two groups of channels is such that the evacuated flow is a filtered part of the flow admitted by the central channel 12, after passing through said partitioning: a material presenting the desired porosity as a function of the particular gas to be purified will naturally be used to produce the structure; FIG. 5A, it is a total flow filter, in which case the structure 9C has no lateral orifice, while FIG. 5B, it is a derivative flow filter, in which case the structure 9'C has a lateral opening 16B for the derived portion.

FIGS. 6A to 6C represent examples of variants for the walls of the radial type and of the circular type. Figure 6A, the walls 10A are. rectilinear and inscribed in radial planes, while the walls 11A are inscribed in cylinders coaxial with said structure. Figure 6B, the walls 10B are rectilinear and inscribed in parallel planes two by two, while the walls 11B are rectilinear between two adjacent walls 10B, defining contours in broken line. Figure 6C, the walls 10C are wavy, while the walls 11C are inscribed in coaxial cylinders, but staggered at each pair of walls 10C and connecting them to the tops of the corrugations.

We have previously seen that the channels can be closed simultaneously with the annular end faces, with an end nozzle allowing a flow to pass through the central channel. It may prove to be advantageous in certain cases to introduce and extract this flow by the annular faces: in this case, each annular end face has a radial selective obturation, obturation which can be obtained by a set of radiating annular sectors: these sectors have been shown, with parts broken away, in FIGS. 6A, 6B, 6C, with the respective references 19A, 19B, 19C. If these sectors are wide enough, we can even, as shown in FIG. 7, take advantage of these wide parts to increase the useful inter-flow surface: for this purpose, a cut portion 20 opening onto other channels can be provided in their wide area by the flow admitted and discharged by the annular end faces; the walls 10D are here rectilinear, parallel for the cut portion, radial for the others, while the walls 11 D are circular. There may be provided, Figure 8, a tip 21 at each end, whose circular flange 22 bears against the periphery of the annular end faces, or more precisely sectors 19D, and whose surface defines an interior chamber opening towards the outside by a narrower orifice 23.

FIG. 9 illustrates yet another example where the walls 10E and 11 E define for each channel a cell profile close to the square.

It goes without saying that the relative spacing between the different walls will be chosen so as to be perfectly adapted to the stresses undergone under the effect of the differential pressure of the two flows. The radial type walls are arranged so as to distribute, according to the aerodynamic criteria desired. the surface offered to each of the two flows: in particular, the spacing between said walls will be chosen according to the flow rates and speeds of each of the flows.

Two additional advantages will be indicated by the structure of the invention: first, the annular design, by its rigidity of shape, makes it possible to design cartridges longer than with any other architecture of given useful section; then, the cylindrical section allows incidentally to provide a rotation of the structure around its axis during the stages of manufacture, which greatly promotes the homogeneity of drying.

Claims (16)

1. A static monolithic ceramical cylindrical honeycomb structure with large contact surface comprising a plurality of parallel channels defined by walls of the radial type (10) and walls of the circular type (11), in which the channels constitute two groups, each traversed by a fluid, the channels of one of the groups being fitted between the channels of the other group according to an angular shift, the section of the structure comprising an annular zone composed of parallel channels, and a central channel (12), which is obturated by a plug (18) and which permits the admission and/or evacuation of the fluids via selective communications with one or the other of the two groups of channels, characterized in that at each end an end piece (13) obturates the annular zone, and that the walls of circular type (11) of the two groups of parallel channels are inscribed into several cylinders coaxial to said structure.

2. A structure according to claim 1, characterized in that a group of channels presents lateral openings (16, fig. 2) for admission and/or evacuation of the associated flux.

3. A structure according to claim 2, characterized in that the lateral openings open directly against the plane of the end piece (13, fig. 3A).

4. A structure according to claim 2, characterized in that the lateral openings (16B, fig. 4) are situated at a certain distance of the end piece. (13, fig. 3B).

5. A structure according to one of the claims 2 to 4, characterized in that the partitioning between the two groups of channels is such that the flux evacuated by the associated lateral openings (16B) is a filtered part of the flux admitted by the central channel (12), after having traversed said partitioning (fig. 5B).

6. A structure according to claim 1, characterized in that one of the two flux is admitted and evacuated by the central channel, whereas the group of channels associated to the other flux presents lateral openings (16B) for admission and evacuation of said flux (fig. 4).

7. A structure according to claim 6, characterized in that the selective obturation is obtained by a group of radiating annular sectors (19A, 19B, 19C).

8. A structure according to claim 7, characterized in that the annular sectors present in their large zone a cut out portion (20, fig. 7) opening on other channels concerned by the flux which is admitted and evacuated by the annular end faces.

9. A structure according to one of the claims 6 to 8, characterized in that it comprises at each end an end piece (21, fig. 8) the circular rim (22) of which leans on the periphery of the annular end faces, and the surface of which defines an inner chamber opening to the outside via a smaller opening (23).

10. A structure according to one of the preceding claims, characterized in that the walls of radial type of the parallel channels are rectilinear (10A, fig. 6A).

11. A structure according to claim 10, characterized in that the radial walls form radial planes.

12. A structure according to claim 10, characterized in that the walls form planes which are parallel in pairs (10B, fig. 6B).

13. A structure according to one of the claims 1 to 9, characterized in that the radial walls of the parallel channels are corrugated (10C, fig. 6C).

14. A structure according to one of the claims 1 to 13, characterized in that the circular walls (11 B, fig. 6B) of the parallel channels are rectilinear between two adjacent radial walls (10B) and define contours in broken lines.

15. A structure according to the preceding claims, characterized in that the circular walls (11C, fig. 6C) are arranged in a staggered position at each couple of radial walls (10C).

16. A structure according to the claims 13 and 15, characterized in that the circular walls are joined to the radial corrugated walls at the crests of the corrugations.

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