FR2809103A1 - Preformed component for use in e.g. absorber of ammonia cycle refrigeration circuit, has a reagent dispersed through a porous substrate formed from connected stacked thin layers of carbon fibers - Google Patents

Abstract

A preformed component has a chemical reagent, that can react reversibly with a gas, is dispersed through a porous substrate formed from stacked thin layers of carbon fibers. The layers are connected together by fibers extending through them. Independent claims are included for the following: (a) the formation of the component by assembling the layered substrate, impregnating it with the a liquid composition containing the reagent and then drying the substrate. (b) the filling of a thermo-chemical reactor with the components.

Description

FIELD OF THE INVENTION The invention relates to a preformed part comprising a porous carbon substrate in which at least one reactive agent capable of chemically reversibly reacting with a gas is dispersed.

Such a part is particularly useful as a chemical energy storage reactor loading element. The reactive agent may be a salt, in particular a metal chloride, capable of reacting with respect to a gas. One application is the production of thermochemical heat exchange systems, in particular for refrigeration plants, the gas then being typically ammonia gas.

BACKGROUND OF THE INVENTION The use of a reversible chemical reaction between a reactant and a gas in thermochemical heat exchange systems is well known. For example, one can refer to the articles by Ph. Touzain et al .: "Reaction of Metal Chloride Graphite Intercalation Compounds with Ammonia" and "Thermochemical Heat Transformation: Study of the Ammonial Magnesium Chloride-GIC Pair in a Laboratory Pilot", published in Mol. Cryst. Liq. Cryst. 1994, vol. 295, pp. 231-236 and 243-248.

Such heat exchanger systems have been used in refrigeration devices having an autonomous operating capacity, for example for containers. In the refrigeration cycle, the gas, typically ammonia gas, stored in a liquid state in a pressure tank, is passed through an expansion valve in an evaporator located in an enclosure to be cooled. The ammonia gas from the evaporator is admitted into a reactor containing a reactive agent, typically a metal chloride, with which it combines chemically, the reaction being exothermic. In the regeneration cycle, an inverse chemical reaction is carried out by supplying heat to the reactor. The ammonia gas then released is fed via a condenser to the pressure vessel, where it is stored. Refrigeration devices of this type are for example described in documents WO 92/13244 and FR 2 703 763.

The practical efficiency and the efficiency of these refrigeration devices largely depend on the capacity of the reactor to absorb and return the ammonia gas during successive cycles of refrigeration and regeneration.

It has been proposed by WO 91/15292 to charge the reactor with an active composite in which the reactive agent is dispersed in a porous carbon substrate suitable for promoting the accessibility of the gas to the reactive agent and to the reactive agent. present the favorable characteristics of thermal conductivity. The porous carbon substrate is in this case formed of recompressed expanded graphite.

OBJECTS AND SUMMARY OF THE INVENTION The object of the invention is to provide a preformed part of the type comprising a reactive agent dispersed in a porous carbon substrate, and offering increased accessibility of a gas to the reactant particles dispersed in the porosity of the substrate, to optimize the use of the reagent.

The invention also aims to provide a preformed part having a mechanical strength allowing it to withstand without damage and without loss of efficiency successive cycles of absorption and release of a gas, with the resulting volume changes .

The present invention also aims to provide a preformed part which has thermal conductivity characteristics allowing, in particular, good evacuation of the heat produced by reaction with the reagent.

According to one aspect of the invention, these objects are achieved because the substrate, within which the reagent is dispersed, is a three-dimensional carbon fiber texture comprising substantially two-dimensional carbon fiber layers which are superimposed and interconnected by fibers extending transversely to the layers. The use of such a three-dimensional carbon fiber texture makes it possible to obtain a relatively homogeneous and easily accessible substrate porosity which promotes a substantially uniform dispersion of the reactive agent, an accessibility of the gases throughout the volume of the substrate and a good conduction of heat. In addition, by its mechanical properties, such a texture is not damaged by successive cycles of absorption and release of gas.

In one embodiment of the part, the layers of the three-dimensional texture are formed of superposed individual layers, in particular layers superimposed flat, which are interconnected by transversely extending fibers.

To promote the conduction of heat, particularly towards the periphery of the substrate, the layers advantageously comprise continuous filaments which extend in different directions. In particular, the layers may comprise a plurality of unidirectional layers each comprising continuous filaments extending parallel to the same direction. The plies are superposed with different directions, for example using three plies which form between them angles substantially equal to 60, and they are interconnected. The heat generated within the substrate by reaction between a gas and the reactive agent can then be transmitted almost isotropically towards the periphery of the substrate.

In another embodiment of the part, the layers of the three-dimensional texture are formed by winding a strip in superimposed turns around an axis, the turns being interconnected by fibers extending transversely, for example radially. the piece obtained is then a cylindrical piece with circular section or not.

According to another aspect of the invention, the preformed part comprises a first part comprising the reactive agent dispersed within the substrate constituted by the three-dimensional carbon fiber texture, and a second portion made of carbon fibers devoid of reactive agent, the second part being adjacent to the first, along an edge of the piece.

The presence, along an outer edge, of a portion of carbon fibers devoid of reactive agent makes it possible to have, between the substrate and a wall against which the part is arranged, a compressible interface capable of providing a good conduction of heat.

Advantageously, the second part, forming this interface, is formed by the same carbon fiber texture as the substrate of the first part.

Preferably, the preformed part has a first central part formed by the substrate in which the reagent is dispersed, and a second peripheral part devoid of reactive agent. The preformed part is advantageously of annular shape.

The reactive agent is a salt, such as a metal chloride, more particularly a nickel chloride, a manganese chloride or a mixture of both.

Passages may be formed through the substrate to promote gas diffusion therein.

According to another of its aspects, the invention also aims to provide a method of manufacturing a preformed part as defined above.

This object is achieved by a method which, in one of its aspects, comprises the steps of: - realizing a three-dimensional carbon fiber texture at least by superposition of essentially two-dimensional layers of carbon fibers and bonding the layers together by means of fibers extending transversely with respect to the layers, impregnating a substrate made in said three-dimensional carbon fiber texture with a liquid composition containing the reactive agent, and drying the impregnated substrate.

Preferably, prior to impregnation, the substrate is thermally treated at an elevated temperature, sufficient to stabilize the texture chemically and dimensionally, and to increase the thermal conductivity.

The layers of the three-dimensional texture can be formed of superposed individual strata, in particular layers superimposed flat.

Advantageously, strata are used which comprise continuous filaments extending in different directions, in particular unidirectional sheets superimposed in different directions. The unidirectional sheets are bonded together, for example by needling.

In addition to continuous filaments, the layers may comprise staple fibers.

The layers of the three-dimensional texture may alternatively be formed by winding at least one strip into superimposed turns to form a cylindrical piece.

Advantageously, the connection between them of the layers constituting the substrate is carried out by needling. This is preferably designed so that the level of fibers transferred transversely to the layers is controlled, in particular, to be substantially uniform throughout the substrate.

In another aspect of the process, a carbon fiber edge portion without a reactive agent is added to the impregnated and dried substrate.

Advantageously, a block formed by a three-dimensional carbon fiber texture is formed, the block is cut to obtain said substrate and said edge portion separated from each other, and the edge portion is assembled to the impregnated and dried substrate. . Preferably, a cylindrical block is formed and said substrate and said edge portion are obtained by cutting a ring at the periphery of the block.

According to yet another of its aspects, the invention also relates to a chemical thermal energy storage reactor loading using at least one preformed part as defined above.

Advantageously, the loading comprises a plurality of assembled preformed parts, these being preferably in the form of superimposed coaxial annular parts.

<U> Brief description of the drawings </ U> The invention will be better understood on reading the description given below, by way of indication but not limitation, with reference to the accompanying drawings, in which - Figure 1 is a view schematic top of an embodiment of a preformed part according to the invention; - Figure 2 is a sectional view along the plane II-II of Figure 1; - Figure 3, in conjunction with Figures 4A to 4D, shows successive steps of a method of manufacturing the preformed part of Figures 1 and 2; FIG. 5 is a diagrammatic sectional view of a reactor load formed of parts such as those of FIGS. 1 and 2; and FIG. 6 is a schematic perspective view showing another embodiment of a preformed part. according to the invention.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION The description which follows relates to a preformed part in which a metal chloride or a mixture of metal chlorides is dispersed so as to chemically react reversibly with a refrigerant gas. such as ammonia gas.

In a more general manner, the invention is not limited to this application, but encompasses all those that may involve a reversible chemical reaction between a gas and a reactive agent dispersed in a substrate.

FIG. 1 shows a preformed piece 10 of cylindrical shape, more particularly annular, comprising a central portion 12 and a peripheral portion 14 adjacent to the central portion and extending along the outer peripheral edge 10a of the piece 10.

The central portion 12 is formed by a substrate in a three-dimensional carbon fiber texture in which at least one metal chloride is dispersed.

The three-dimensional carbon fiber texture may be formed at least in part of substantially two-dimensional individual layers superimposed flat and interconnected by fibers extending transversely relative to each other.

Examples of essentially two-dimensional layers that can be used in the context of the present invention are: fabrics; multidirectional plies formed of several superimposed unidirectional plies with different directions and bonded together for example by stitching or by light needling; complexes formed of layers, such as fabrics or multi-directional webs, pre-sewn with a fiber web.

The three-dimensional texture is obtained from fibers, threads or cables made of carbon or carbon precursor. In the latter case, the precursor, for example a cellulose, a preoxidized polyacrylonitrile (PAN), a pitch, a phenolic compound, or the like, can be converted by heat treatment (carbonization) after completion of the texture.

Advantageously, the constituent strata of the three-dimensional texture comprise continuous filaments which extend in several directions.

The layers may also comprise discontinuous fibers (or filaments) in the form, as indicated above, of pre-needle-punched fiber webs with the strata, or in the form of free fibers deposited on the strata during the manufacture of the substrate, or by producing a part of the constituent yarns of the strata with staple fibers.

The two-dimensional strata can be bonded to one another by implantation of threads or fibers through the layers or by needling. Advantageously, in order to obtain a substantially homogeneous density of fibers transferred transversely with respect to the strata (or "Z" fibers), needling is carried out progressively, after each stratum addition, with permanent control of the penetration depth of the needles. . The presence of staple fiber promotes the removal of fibers to be transferred to Z by the needles.

Needle-bonding methods of superimposed two-dimensional layers and control of Z-fiber transport are described, for example, in US 4,790,052 and US 5,779,215.

In addition to the central passage 16 of the part 12 of the part 10, several passages 18 may be formed through the portion 12, extending axially between the opposite faces 10b and 10c of the part 10. The passages 18 are for example distributed over one or more circumferences around the axis of the part.

The metal chloride forming the reactive agent dispersed in the substrate is preferably nickel chloride NiCl 2, manganese chloride MnCl 2 or a mixture of nickel chloride and manganese.

The peripheral portion 14 is carbon fiber, preferably also a three-dimensional carbon fiber texture. Preferably, the substrate of the central portion 12 and the peripheral portion 14 are made in the same texture, and preferably from the same starting block, but it is not mandatory.

The peripheral portion 14 is, in the illustrated example, simply fitted on the central portion 12, with no other connection between them that a possible connection by friction. However, it could be envisaged a connection for example by spot bonding, if it is compatible with the intended use of the part produced.

Steps for producing a preformed part such as that of FIGS. 1 and 2 are indicated in FIG. 3 and illustrated in FIGS. 4A to 4D.

The first step 20 consists in producing a three-dimensional carbon texture block 11 (FIG. 4A), as indicated above, for example by superposing and gradually needling two-dimensional circular carbon fiber layers until it reaches a thickness corresponding to that desired for the part to be manufactured. Advantageously, the layers are formed of three superimposed unidirectional layers with their directions forming mutual angles substantially equal to 60 and linked together by light needling. Strata furthermore equipped with a pre-needle-punched staple fiber web may be used on the plies, the plies being formed at least in part of continuous filaments.

Block 11 is then heat treated at high temperature (step 22) for a relatively short time, from one to a few minutes. The heat treatment is carried out under vacuum or under an inert atmosphere, for example under nitrogen, at a temperature sufficient to increase the thermal conductivity of the carbon fiber texture and to stabilize the texture both dimensionally and chemically, vis-à-vis the reactant subsequently introduced and the gas with which the reagent is intended to react. The heat treatment temperature may vary depending on the nature of the carbon precursor of the fibers. For example, when the precursor is a polyacrylonitrile (PAN), the heat treatment is carried out at a temperature of at least 1800 C, up to 2500 C.

The block obtained is machined (step 24) to form the central passage 16, to form the additional passages 18, and to cut the peripheral portion 14 so that a substrate 12 'of the central part and the part peripheral 14 (FIG. 4B).

The machining can be done by pressurized water jet. Note that the central passage 16 can be obtained by stacking layers not in the form of solid discs and performing a subsequent machining, but directly by stacking annular strata.

Substrate 12 'is then impregnated (step 26) with a liquid composition containing the reactive agent, in this case NiCl 2, MnCl 2 or a mixture of both dissolved in a solvent, for example formed from a water-ethanol mixture. The impregnation is performed by immersing the substrate 12 'in a bath containing the liquid composition. Prior drying of the substrate 12 'is preferable. The porosity of the three-dimensional texture allows atmospheric pressure impregnation. The impregnation could also be carried out under vacuum.

After impregnation, drying is carried out to remove the solvent (step 28) and the central portion 12 (FIG. 4C) of the part to be manufactured in which the chloride is dispersed is obtained. Depending on the amount of chloride to be introduced, it may be carried out several consecutive cycles of impregnation and drying.

The three-dimensional texture, in particular when it is obtained by needling superimposed strata with control at the level of fibers transferred in Z, has a porosity distributed in a substantially homogeneous and easily accessible manner. The dispersion of the metal chloride and its accessibility by a diffusing gas through the texture are thus favored up to the heart of the central portion 12.

The final step 30 is to join the central portion 12 with the peripheral portion 14 previously cut. The latter is simply fitted on part 12.

FIG. 5 illustrates a load 32 formed of several superposed identical parts 10 housed in a chemical energy storage reactor. Only the side wall 34 of the reactor is shown. This wall is a cylindrical wall whose inner diameter is equal to or slightly less than the outer diameter of the parts 10, so that they are stacked without play in the reactor.

The aligned passages 18 form housings in which porous tubes (not shown), for example made of graphite, which receive the gas, for example ammonia gas, intended to react chemically with the metal chloride dispersed in the central portions 12 can be introduced. and through which this gas can diffuse in these central parts. The fact that several preformed parts are stacked also promotes the diffusion of gas at the interfaces between the parts. In this way, the gas can access a very large majority of active sites where metal chloride is present.

The aligned central passages 16 form a housing for a heating element (not shown) to provide the necessary calories for the release of the gas chemically trapped by the metal chloride.

The absorption reaction of the gas by the metal chloride is exothermic and can cause an increase in volume. The heat produced must be evacuated effectively. The use, for the substrate of part 12, of a structure formed of two-dimensional layers of carbon fibers facilitates the evacuation of heat towards the periphery of part 12. The conduction of heat is further favored by the use of continuous filaments. This conduction is further favored by the use of strata with filaments extending in several directions, in particular strata formed by stacking unidirectional layers forming between them equal angles, such as three plies at 60, the thermal conductivity then being substantially the same in all directions.

The peripheral portion 14 of carbon fibers free of metal chloride is not directly affected by the chemical reaction and acts as a thermal bridge to ensure efficient transfer of heat to the reactor wall. In addition, the peripheral portion 14 has a resilient deformation capacity that allows it to absorb dimensional changes in the radial direction, without disrupting the operation of the reactor. The width of the peripheral edge is chosen to allow these dimensional variations while maintaining a useful volume (i.e. the volume containing the metal chloride as large as possible). The width of the edge may be between 5% and 30% of the radius of the preformed part.

Although it has been envisaged above the embodiment of a preformed part with a peripheral portion 14 free of reactive agent, it will be noted that the presence of this peripheral part is not necessary, the preformed part possibly consisting of the only central part 12.

In addition, although it has been envisaged above the realization of the substrate by superposition and connection between them of superposed individual layers, it is possible, alternatively, to produce the substrate by winding a strip in superimposed turns which are interconnected. In the same way as for the strata, it is possible to use for the strip a substantially two-dimensional fibrous texture such as a fabric, a multidirectional sheet, or a fabric complex or multi-directional sheet precoated with a veil of fibers. The strip may be formed at least in part of continuous filaments.

The connection of the turns between them can be carried out by needling as winding progresses. A method for bonding turns of a coiled fibrous web with control of the transport of the fibers transversely to the turns, for example radially, is described in US Pat. No. 4,790,052.

It is thus possible to directly obtain an annular cylindrical piece with circular section, or not, by winding on a mandrel of appropriate shape.

<U> Example </ U> A preformed part as illustrated by FIGS. 1 and 2 has been produced using the method of FIG. 3.

Discs with a diameter of approximately 150 mm are cut from one or more two-dimensional multidirectional sheets of preoxidized polyacrylonitrile fibers (carbon precursor). Each sheet is formed by superposition, with orthogonal directions, and light needling of three unidirectional sheets forming between them angles of 60. The disks are stacked while being needled as they are stacked, as described in US 4,790,052 or US 5,792,715 already cited. A cylindrical block of three-dimensional texture is thus formed, the superposition of the discs and their needling being continued until the desired thickness is obtained.

The block is charred under nitrogen raising the temperature to about 1600 C, to convert the precursor into carbon. A final heat treatment is then performed at a temperature of about 2200 C under vacuum.

The block obtained has a volume porosity of about 80%, relatively homogeneous and uniformly distributed within it.

Pressurized waterjet machining is performed to form the central axial passage 16, to form a plurality of passages 18 with axes parallel to that of the block, and to cut off an annular peripheral edge portion 14 of equal width. at about 10 mm, which is separated from the remaining central portion of diameter approximately equal to 130 mm.

This central portion is dried at about 100 ° C. for 1 h, and is then impregnated by immersion under atmospheric pressure in a bath formed of nickel chloride concentrated to 350 μl in a solvent consisting of a mixture of water and ethanol in a volume ratio of 15: 1.

After impregnation, drying is carried out in an oven at about 120 ° C. for several hours. The solvent being removed, the central portion 12 of the part to be produced is obtained. This central portion contains a 40% nickel chloride mass content and has a residual volume porosity of 58%. The mass of nickel chloride dispersed in the carbon fiber substrate could be increased by proceeding to one or more successive impregnation / drying cycles. However, the residual porosity is then reduced and the efficiency measured by the amount of reagent reagent accessible to gas after several cycles of absorption and release reaction may be affected if the mass of nickel chloride introduced exceeds a certain threshold.

The desired preformed part is then obtained by replacing the pre-cut peripheral edge portion 14 around the central portion 12. Several preformed parts thus produced, with a single impregnation, are stacked in a reactor of an installation similar to that described in the document FR 2 703 763 cited above, the cylindrical wall of the reactor having an internal diameter such that the parts are introduced without play, preferably even with a slight compression which is exerted essentially on the edge portion 14 free of nickel chloride.

In the foregoing, it has been envisaged to produce preformed parts of generally cylindrical shape, the portion devoid of reactive agent extending all along the outer peripheral edge.

As required, generally non-cylindrical pieces, for example of prismatic shape, can of course be made.

Moreover, a part having the desired overall shape can be made by assembling several elementary parts.

Thus, FIG. 6 shows an annular sector-shaped elemental piece 50 having a first portion 52 formed by a substrate in a three-dimensional carbon fiber texture impregnated with a reactive agent and a second portion 54 into a three-dimensional carbon fiber texture. without reactive agent extending along the arcuate edge 50a of the piece 50. The piece 50 may have one or more passages 58 which extend between two opposite faces 50b and 50c.

The piece can be made by a process analogous to that described above with reference to FIG. 3. A complete annular piece is obtained by juxtaposition of several annular elementary pieces 50.

Claims (31)

1. Preformed part comprising a porous carbon substrate in which is dispersed at least one reactive agent capable of reversibly chemically reacting with a gas, characterized in that the substrate consists of a two-dimensional carbon fiber texture comprising layers essentially two-dimensional carbon fibers which are superimposed and interconnected by fibers extending transversely to the layers. 2. Part according to claim 1, characterized in that the layers are formed of superposed individual layers. 3. Part according to claim 2, characterized in that the strata comprise continuous filaments which extend in different directions. 4. Part according to claim 3, characterized in that the strata comprise a plurality of unidirectional sheets which each comprise continuous filaments extending parallel to the same direction, the layers being superimposed with different directions and interconnected. 5. Part according to claim 4, characterized in that the layers comprise three unidirectional sheets forming between them angles substantially equal to 60. 6. Part according to claim 1, characterized in that the layers are formed by winding a strip in superposed turns. 7. Part according to any one of claims 1 to 6, characterized in that it comprises a first portion comprising the reagent dispersed within the substrate consisting of the three-dimensional carbon fiber texture, and a second fiber portion of carbon without a reactive agent, the second portion being adjacent to the first, along an edge of the part. 8. Part according to claim 7, characterized in that the second part is formed by the same carbon fiber texture as the substrate of the first part. 9. Part according to any one of claims 7 and 8, characterized in that the first portion is a central portion and the second portion is a peripheral portion surrounding the central portion. 10. Part according to any one of claims 1 to 9, characterized in that it is annular. 11. Part according to any one of claims 1 to 10, characterized in that it has a plurality of passages extending through the first part between two opposite faces of the part. 12. Part according to any one of claims 1 to 11, characterized in that the reactive agent is constituted by at least one metal salt. 13. Part according to claim 12, characterized in that the reactive agent consists of at least one metal chloride. 14. Part according to claim 13, characterized in that the metal chloride is selected from nickel chloride, manganese chloride and a mixture of both. 15. A method of manufacturing a preformed part according to any one of claims 1 to 14, characterized in that it comprises the steps of - achieving a three-dimensional carbon fiber texture at least by superposition of substantially two-dimensional layers in carbon fibers and bonding the layers together by fibers extending transversely to the layers, - impregnating a substrate made in said three-dimensional carbon fiber texture with a liquid composition containing the reactive agent, and - drying the substrate impregnated. 16. The method of claim 15, characterized in that layers consisting of individual layers substantially two-dimensional are superimposed. 17. The method of claim 16, characterized in that strata are used which comprise continuous filaments extending in different directions. 18. A method according to claim 17, characterized in that the layers are formed by superposition of several unidirectional sheets each comprising continuous filaments extending parallel to the same direction and binding of the sheets together, the sheets being superimposed with different directions. . 19. The method of claim 18, characterized in that the layers are formed by superposition of at least three unidirectional sheets forming between them angles substantially equal to 60. 20. Method according to any one of claims 18 and 19, characterized in that the unidirectional sheets are bonded together by needling. 21. The method of claim 15, characterized in that the realization of the three-dimensional texture comprises the winding of a strip in superimposed turns and the connection between them of the layers formed by the turns. 22. Method according to any one of claims 15 to 20, characterized in that the layers comprise discontinuous filaments. 23. Method according to any one of claims 15 to 22, characterized in that the substantially two-dimensional layers are bonded together by needling. 24. A method according to any one of claims 15 to 23, characterized in that is added to the impregnated substrate and dried a carbon fiber edge portion free of reactive agent. 25. Process according to claim 24, characterized in that a block formed by a three-dimensional carbon fiber texture is formed, the block is cut to obtain said substrate and said edge portion separated from each other, and collecting the edge portion with the impregnated and dried substrate. 26. The method of claim 25, characterized in that one forms a cylindrical block and one obtains said substrate and said edge portion by cutting a ring at the periphery of the block. 27. Method according to any one of claims 15 to 26, characterized in that a ring-shaped substrate is produced. 28. Method according to any one of claims 15 to 27, characterized in that a plurality of passages are formed through the substrate extending between two opposite faces thereof. 29. Loading a chemical energy storage reactor, characterized in that it is formed of at least one preformed part according to any one of claims 1 to 14. 30. Loading according to claim 29, characterized in that it is formed of several preformed parts assembled. 31. Loading according to claim 30, characterized in that the preformed parts are superimposed coaxial annular pieces.