Catalytic dihydrogen recombiner

Abstract

Catalytic Dihydrogen Recombiner (1) comprising: At least one first catalytic block (30a) of a honeycomb substrate made of a low-thermal-conductivity material, bearing a first catalytic coating; at least one second catalytic block (30b) of a honeycomb substrate made of a low-thermal-conductivity material, bearing a second catalytic coating, this second substrate having the same cross-section as the first; a support structure (3, 21) for the blocks stacked one above the other, and / or side by side. Figure for the abstract: Fig. 1

Description

Title of the invention: Catalytic dihydrogen recombiner technical field

[0001] The present invention relates to devices for the catalytic recombination of dihydrogen, also called "catalytic recombiners". Previous technique

[0002] The presence of gaseous dihydrogen proves dangerous in certain situations (nuclear enclosures, batteries, fuel cells, hydrogen production, storage, transport or distribution of hydrogen, water treatment by electrolysis...) and catalytic recombiners have been proposed to reduce the concentration of dihydrogen by causing its recombination with surrounding oxygen.

[0003] Most known catalytic recombiners comprise metal plates coated with a catalytic material, arranged parallel to each other in a support frame.

[0004] Such recombiners have disadvantages.

[0005] First, the reactive surface area is relatively small compared to the volume occupied, which makes them rather bulky and impractical to install. This drawback is significant when attempting to equip existing nuclear facilities where safety improvements are required by authorities and operators, as it becomes difficult to install recombiners in the most relevant locations with regard to potential accumulations of dihydrogen pockets if these locations are already heavily congested with equipment.

[0006] Next, the plates are likely to deform in the event of an earthquake, which can modify the gas flow characteristics between the plates and make them less efficient.

[0007] Finally, such recombiners do not allow easy modification of the composition of the catalytic material, to adapt it best to the environment in which the recombiner is used.

[0008] French application FR2999442 describes a device comprising a honeycomb catalyst for the passive recombination of hydrogen. The honeycomb structure is self-supporting, being formed by a corrugated metal strip wound upon itself, this strip being coated with a catalytic material, for example platinum and palladium on alumina. In one example, two honeycomb catalysts are used, the first being arranged in a large-section conduit formed by a catalyst support frame, the second in a smaller-section chimney overhanging the first. In another example, the two catalysts are arranged concentric They are mounted on metallic supports and have different compositions in terms of catalytic materials. A heating element can be integrated into the housing containing the catalysts.

[0009] Patent KR101312857B1 describes a passive recombiner comprising a honeycomb ceramic support coated with a catalytic material, and arranged in a movable drawer relative to a support frame. The presence of the drawer allows for easy removal of the ceramic support for inspection or maintenance operations. Description of the invention

[0010] There is a need to further improve di-hydrogen catalytic recombiners, in particular to improve their performance and facilitate their adaptation to a given environment.

[0011] The invention applies equally to passive and active recombiners.

[0012] By "passive" it is meant that no external action is necessary to achieve the recombination of dihydrogen, and the entry of the gas mixture occurs without the input of external energy, the flow being obtained by natural convection, in particular under the effect of an inlet-outlet temperature gradient. In an "active" recombiner, an external action is exerted to force the gas flow at the inlet, for example the presence of a fan or a turbine. Summary of the invention

[0013] The invention aims to meet the need mentioned above, and it achieves this through a catalytic dihydrogen recombiner, comprising:

[0014] - At least one first catalytic block of an alveolar substrate, preferably made of a material with low thermal conductivity, in particular a ceramic, bearing a first catalytic coating, - at least one second catalytic block of an alveolar substrate, preferably made of a material with low thermal conductivity, in particular a ceramic, bearing a second catalytic coating, this second block advantageously having the same cross-section as the first, - a support structure for the blocks one above the other and / or one next to the other.

[0015] By "poor heat conductivity material" is meant a material with a thermal conductivity less than or equal to 20 Wm'K1 at 20°C, better less than or equal to 10 Wm'K, even better less than or equal to 7.5 Wm'K, for example between 0.5 and 7.5 Wm'K1.

[0016] The substrate ensures the block's mechanical strength and internal cohesion. For the first and / or second block, the corresponding catalytic coating may be present at least on the internal surface of the cells, or even exclusively on it. When the The catalytic coating is present only on the inner surface of the cells; the outer lateral surface of the block is devoid of catalytic coating. This helps prevent direct exposure of the block's support frame material to the reaction occurring within the catalytic material.

[0017] The support structure may have a body defining a conduit inside which the blocks are placed.

[0018] The invention has multiple advantages.

[0019] First of all, the alveolar structure of the blocks allows a high volumetric density of catalyst, thanks to a large exchange surface per unit volume.

[0020] The catalytic coating, which is preferably located inside the block, on the surface of the alveoli, is in fact protected from any risk of degradation during handling or during unexpected contact with the block.

[0021] The fact that the blocks have the same cross-section gives the whole a modular aspect which facilitates the interchangeability of the catalytic blocks according for example to the nature of the catalyst(s) present, in order to best adapt the recombiner to the conditions of use and optimize its performance, for example in order to recombine as much or as little dihydrogen as possible at the inlet, depending on the desired start-up temperature.

[0022] In particular, the arrangement of the blocks can be designed to achieve a lower inlet ignition temperature. The interchangeability of the blocks allows them to be arranged in a specific order to favor a higher or lower ignition temperature.

[0023] Moreover, it is easy to have a stock of catalytic blocks with different properties, due to the use of different catalysts and / or used in different quantities, and to make from this stock the combinations most suited to one environment or another.

[0024] The modular design also allows, where appropriate, the use of a greater or lesser number of catalytic blocks within the recombiner, and of varying thicknesses. The invention facilitates easy intervention for replacing a single block and enhances the modularity / adaptability of the recombiner to accommodate a larger release of dihydrogen in the protected volume. For example, simply increasing the frontal surface area exposed to the flow allows a greater quantity of dihydrogen to enter the recombiner while using only one type of catalytic block.

[0025] Preferably, the support structure holds the blocks one on top of the other.

[0026] Preferably, the substrate has refractory properties, which allows the recombiner to be used in a high-temperature environment. normal operating conditions (i.e., before the initiation of the catalytic reaction corresponding to the arrival of dihydrogen).

[0027] Another advantage of the refractory character is that it is possible to consider using organic materials (for example technical plastics) whose operating temperature is more limited than that of metal, to make the structure of the frame of the recombiner.

[0028] Finally, the rigidity of the substrate reduces the risk of modification of the cross-section of the flow channels in the event of an earthquake, compared to conventional plate recombiners.

[0029] Preferably, the support structure comprises chassis supporting the catalytic blocks and arranged to allow individual extraction of each chassis independently of the other chassis. Each chassis comprises, for example, a lower frame on which the blocks are placed, this frame being extended upwards by at least two opposing uprights, between which the blocks are received. At least one mounting plate can be connected to the frame to allow the chassis to be fixed to the body of the recombiner. Preferably, this plate has vertical oblong holes allowing adjustment of the vertical position of the chassis within the body of the recombiner. The support structure may also comprise an upper frame, which is fixed in the body of the recombiner above the blocks and holds them against the lower frame. This upper frame may be integral with a mounting plate on the body of the recombiner.This plate may have vertical oblong holes allowing adjustment of the height of the upper frame in the body of the recombiner.

[0030] At least one passage for an upward gas flow can be provided between the blocks and the body of the recombiner, in particular a passively generated upward gas flow, so as to create, by the Venturi effect, suction through the blocks. In this way, gas circulation can be encouraged, tending to facilitate the initiation of the reaction, for example. The Venturi effect is also particularly advantageous for so-called "active" operating conditions, i.e., with a forced flow to be treated, generated, for example, by a fan or a turbine, because the flow velocity is in this case higher and adjustable.

[0031] In one embodiment of the invention, at least two frames are fixed inside the body, on each of two opposite faces of the recombiner body, with a gap provided between the frames both between those fixed to the same face and between those on opposite faces. For example, four frames occupy substantially the entire internal cross-section of the body, while leaving a space between them and between the frames and the body faces other than the two faces to which the frames are fixed.

[0032] Each substrate preferably has a parallel channel structure, and various channel sections are possible, for example hexagonal sections, or of other shapes, for example circular or non-hexagonal polygonal, for example square.

[0033] The general shape of the blocks can be variable, for example square, rectangular, cylindrical or other, in front view, to adapt to different environmental and / or flow conditions.

[0034] The different blocks can be obtained by extrusion or by casting in a die, with the same cross-section but with thicknesses that may vary, if necessary, from one block to another. Within the recombiner, the different successive catalytic blocks arranged at different heights may or may not have the same thickness.

[0035] By way of non-limiting example, the first and second catalytic coatings may differ at least in the nature of the catalyst. Thus, one may use an inlet catalytic block that includes a catalyst allowing the reaction to begin at a lower temperature, and at least one catalytic block placed above it that includes a catalyst requiring a higher temperature to act. The first and second coatings may differ at least in the amount of catalyst, and / or in the nature of the catalyst.

[0036] The first and second blocks may have different thicknesses, as mentioned above. A thinner block may then contain a lower quantity of catalyst, for example.

[0037] The recombiner may include a heating element located near at least one of the blocks. For example, the recombiner may include at least one heating resistive track deposited on at least one of the substrates. This may, for example, make it easier or faster to reach the ignition temperature required for the recombiner to operate. This resistive track is, for example, deposited by imprinting an electrically conductive ink.

[0038] The recombiner may include at least one temperature sensor to measure the temperature near at least one of the blocks.

[0039] The recombiner may comprise a greater or lesser number of catalytic blocks, and for example at least three catalytic blocks arranged one above the other, each of them of different nature, composition and / or geometry, the number of catalytic blocks and the diversity of their characteristics within the same recombiner not being limited.

[0040] The support structure can be configured to be suspended within the enclosure to be protected, and may for this purpose include suspensions at the top. These suspensions may be height-adjustable, for example, being telescopic. Alternatively, the support structure is configured to be fixed to a wall side of the enclosure to be equipped via a bracket.

[0041] The support structure may include a hopper in the lower part, for example with a cross-section between 0.1 and 1 m². The inlet section may be rectangular in shape, for example with sides of dimensions between 0.2 and 0.4 m for one and between 0.4 and 0.6 m for the other (these dimensions are only an example and are in no way limiting).

[0042] The support structure may have a vertical chimney-forming duct, with the catalytic blocks arranged above the hopper and at the inlet of this chimney-forming duct. The latter may be held in place by the aforementioned suspensions.

[0043] The "monolithic" geometry of the substrate, combined with the nature of the material (preferably both rigid and light) has the advantage of being able to produce thin blocks of large dimensions (for example 1m by 1m, and with a thickness 1 to 20 times smaller, ranging from 5 to 10 cm for example).

[0044] This flexibility in the production of the blocks makes it possible to consider applications where the blocks are produced in the form of panels to cover the walls of large volume enclosures (for example reactor containment structures, ...) exposed to the release of dihydrogen.

[0045] The invention thus also relates, independently or in combination with the foregoing, to a monolithic panel for the catalytic recombination of dihydrogen, in particular made with a poorly thermally conductive cellular substrate, preferably ceramic, characterized in that it has a thickness of 1 to 20 times less than its longest dimension, better 5 to 20 times less, even better 10 to 20 times less, the longest dimension being, for example, greater than or equal to 0.5 m, better 0.75 m, even better 1 m. The panel may be in the form of a slab, generally square or rectangular, with a long side measuring, for example, more than 0.5 m, better more than 0.75 m, even better 1 m or more. The thickness of such a panel is preferably at least five and better at least ten times less than the side of the slab, being preferably between 5 and 10 cm.

[0046] The invention also relates to an enclosure, in particular a reactor enclosure, the wall of which is lined at least partially with such panels. Brief description of the drawings

[0047] The invention will be better understood upon reading the detailed description that follows, the non-limiting examples of its implementation, and upon examination of the accompanying drawing, in which:

[0048] [fig. 1] Figure [fig. 1] schematically represents, in perspective, an example of a catalytic recombiner according to the invention,

[0049] [fig.2] Fig.2 illustrates the operation of the recombiner,

[0050] [fig.3] the [fig.3] represents in isolation, schematically and partially, a example of means of supporting catalytic blocks inside the body of the recombiner,

[0051] [fig.4] Fig.4 represents, in perspective, an isolated example of a catalytic block,

[0052] [fig.5] [fig.5] represents the block of [fig.4] in front view,

[0053] [fig.6] the [fig.6] represents in isolation the chassis of the support means of the [fig.3],

[0054] [fig.7] [fig.7] is an exploded, schematic and partial view of a variant of re combiner,

[0055] [fig.8] Fig.8 is a schematic, perspective view of a variant of re combiner, the means for supporting the catalytic blocks appearing in transparency,

[0056] [fig.9] the [fig.9] is a cross-section of the recombiner of the [fig.8],

[0057] [fig.10] Fig.10 illustrates the dismantling of the block support means,

[0058] [fig. 11] [fig. 11] represents in a partial and schematic way an example of a track resistive material present on the substrate of a catalytic block, and

[0059] [fig. 12] Figure 12 schematically and partially represents a temperature sensor temperature mounted near a catalytic block. Detailed description

[0060] In the figures, the different constituent elements of the recombiner have not always been represented to scale and with respect to relative proportions, for the sake of clarity.

[0061] Figures 1 and 2 show a first example of a recombiner 1 according to the invention.

[0062] This recombiner 1 comprises a support structure for catalytic blocks, which can be arranged to be suspended within the enclosure to be protected, and may for this purpose include at its upper part a set of suspensions 2, as illustrated. These suspensions 2 are, for example, height-adjustable.

[0063] In variants (not illustrated), the recombiner 1 is arranged for wall mounting, for being suspended from a bracket or for being placed on the floor.

[0064] In the illustrated example, the recombiner 1 comprises a body 3 housing the catalytic blocks, as detailed later, surmounted by a conduit 4 forming a chimney, connecting at its upper end to the suspensions 2.

[0065] The body 3 can be connected below to a hopper 5, as illustrated, open downwards.

[0066] During operation, hydrogen is passively drawn in through the hopper 5 and catalytic combustion occurs with oxygen from the air, producing water vapor, which exits through the upper end of the conduit 4, as illustrated. The arrows show on [fig.2] the preferred flow direction resulting from a natural circulation caused by the temperature gradient following the exothermic nature of the catalytic reaction.

[0067] The catalytic blocks can be supported in various ways within the recombiner.

[0068] In the example of [fig.3], the body 3 houses two chassis 21 for supporting the blocks.

[0069] Each chassis 21 has upper and lower grilles 23 (the lower grille being non (as shown in [Fig. 3]), supported by respective frames 24 and 28, which are connected to each other by vertical columns 25, as illustrated in particular in [Fig. 6]. Three catalytic blocks 30a, 30b and 30c are, for example, arranged between the grids 23 and 24 of each chassis 21, as illustrated in [Fig. 3].

[0070] An example of a catalytic block 30 is shown in isolation in Figures 4 and 5.

[0071] The latter comprises a ceramic substrate 31, through which a plurality of parallel channels 32 (also called alveoli), for example each of square section, as illustrated.

[0072] All blocks 30a, 30b and 30c can be made from the extrusion of the same ceramic substrate, for example cordierite (thermal conductivity of the order of 3 Wm'K1 at 25°C), and thus have the same cross-section.

[0073] The substrate 31 of the blocks is coated with a catalyst, for example one or more metals such as Pt, Pd, Rh, ..., at the level of the channels 32.

[0074] Each frame 21 may include uprights 26, which extend over at least part of the height of the blocks 30. These uprights 26 are for example made of a single piece of metal with the frame 24 supporting the lower grid, as seen in [fig.5].

[0075] The support frame of the upper grid 23 can be connected on one edge to a fixing plate 27, allowing the chassis 21 to be hung on the body 3, for example using screws not shown.

[0076] In the variant illustrated in [fig.7], the suspensions 2 are arranged to be fixed on the side of the conduit 4, for example on two opposite sides as illustrated, and no longer at its upper end.

[0077] In the variant illustrated in figures 8 to 10, the recombiner 1 comprises a conduit body 3, which houses, for example, four support frames 21 arranged in the section in two rows of two.

[0078] Each chassis 21 comprises, for example, a lower frame 24 supporting the blocks and two opposing uprights 26 extending upwards from the frame 24, between which the blocks 30a, 30b, and 30c are housed. The height of the uprights 26 in this example is less than the combined heights of the three blocks, such that the upper block 30c is only partially housed between the uprights 26.

[0079] The frame 24 connects to a mounting plate 37, which extends downwards.

[0080] This plate 37 has vertical oblong holes 40, which allow adjustment of the height of the chassis 21 in the body 3, as illustrated by the arrows on the [fig.8].

[0081] Frames 38 held by plates 39 are fixed above the chassis 21 to hold the blocks in place between the uprights 26 against vertical shocks, for example. These plates 39 have vertical oblong holes 40, as do the plates 37, allowing their position to be adjusted in the body 3 so as to keep the blocks axially wedged between the frames 24 and 38. The latter may support grids, if necessary.

[0082] The plates 37 and 39 used to hold the same set of catalytic blocks are fixed on the same face 3a or 3b of the body 3, as can be seen in particular in [fig.9].

[0083] The dimensions of the blocks and the frames 21 can be chosen such that passages 45 remain on the three free sides of each frame 21, outside the blocks, as illustrated in [Fig. 9]. Maintaining the blocks 30a, 30b, and 30c inside the recombiner allows both gas circulation through the blocks and circulation outside the blocks, around them inside the body 3. Such circulation can promote the creation of an air intake through the blocks by the so-called "trumpet-injector" Venturi effect, and improve the initiation of the catalytic reaction, for example.

[0084] Each chassis 21 can be extracted independently of the other three, as illustrated in [fig.10], by removing the screws which hold the lower plate 37 onto the body 3.

[0085] In all the examples described above with reference to the figures, the catalytic blocks advantageously exhibit different catalytic properties; for example, the lowest inlet catalytic block 30a has a catalyst that initiates the hydrogen oxidation reaction at a lower temperature than the catalysts in the other blocks. The heat released during oxidation warms the blocks 30b and 30c located above it, thus allowing the use of catalysts for these blocks that require a higher initiation temperature but are, for example, less expensive.

[0086] The size and shape of the cavities of the catalytic blocks will be adapted to the objective sought, in particular in terms of hydraulic pressure losses, flow velocity, presence of possible instrumentation, ... In the illustrated example, the respective thicknesses ea, eb and ec of blocks 30a, 30b and 30c are equal, but blocks of different thicknesses can be used, or even blocks with thicknesses that are, for example, half that of another block can be placed in the same compartment.

[0087] Any suitable material, including ceramic, can be used to make the substrate for the blocks.

[0088] The catalyst of a given formulation can be deposited partially or totally on the internal surfaces of the substrate's alveoli.

[0089] Each block or support for this block can be equipped with dedicated instrumentation and / or a specific heating system, intended, for example, to accelerate the initiation of the catalytic reaction at a given H2 concentration. As an example, the positioning of a temperature sensor 120 near a block 30 is illustrated in [Fig. 12].

[0090] For heating a block, tracks of an electrical conductor 110 can advantageously be printed on the substrate 31 of the block, in order to create a heating resistance, as illustrated very schematically in [Fig. 11]. Alternatively, a heating resistance is, for example, pressed against the inlet face of the lower catalytic block.

[0091] In variants not illustrated, the recombiner 1 is made with a chimney-forming duct of different height, or even without such a duct.

[0092] The hopper 5 can be made with a different geometry and opening angle, and the recombiner can be made without such a hopper, if necessary.

[0093] The catalytic blocks 30 can be maintained otherwise without departing from the scope of the present invention.

[0094] The recombiner can have a totally passive character, not requiring the input of energy from an energy source, for example in electrical form, to start to operate.

[0095] In variants not illustrated, with the aim of obtaining an improvement in the flow rate, in line with the rate of catalytic recombination allowed by the high density of catalyst linked to the arrangement in alveolar cells, the recombiner is associated with an actuator such as an extractor (fan, vacuum cleaner ...) at the level of the conduit 4 forming a chimney for example.

Claims

Demands

1. Catalytic dihydrogen recombiner (1), comprising: - At least one first catalytic block (30a) of a veolar al substrate in a material with low thermal conductivity, bearing a first catalytic coating, - at least one second catalytic block (30b) of a veolar al substrate in a material with low thermal conductivity, bearing a second catalytic coating, this second substrate being of the same cross-section as the first, - a support structure (3, 21) for the blocks one above the other, and / or one next to the other.

2. Recombiner according to claim 1, the support structure holding the blocks (30a, 30b, 30c) one on top of the other.

3. Recombiner according to any one of the preceding claims, the support structure comprising chassis (21) supporting the blocks and arranged to permit individual extraction of each of the chassis independently of the other chassis or chassis.

4. Recombiner according to any one of the preceding claims, the support structure comprising a body (3) defining a conduit, at least one passage (45) for an upward gas flow being provided between the catalytic blocks and said body (3), in particular a passively generated upward gas flow, so as to create by Venturi effect an aspiration through the blocks.

5. Recombiner according to any one of the preceding claims, each substrate (31) having a parallel channel (32) structure.

6. Recombiner according to any one of the preceding claims, the first and second catalytic coatings differing at least in the nature of the catalyst.

7. Recombiner according to any one of the preceding claims, the first and second catalytic coatings differing at least in the amount of catalyst.

8. Recombiner according to any one of the preceding claims, the first and second catalytic blocks (30a, 30b) having different thicknesses (ea, eb).

9. Recombiner according to any one of claims 1 to 7, the first and second catalytic blocks (30a, 30b) having the same thickness.

10. Recombiner according to any one of the preceding claims, comprising a heating element (110) located near at least one of the blocks.

11. Recombiner according to any one of the preceding claims, comprising at least one heating resistive track (110) deposited on at least one of the substrates (31).

12. Recombiner according to any one of the preceding claims, comprising at least one temperature sensor (120) for measuring the temperature in the vicinity of at least one of the blocks.

13. Recombiner according to any one of the preceding claims, comprising at least three blocks (30a, 30b, 30c) of a ceramic honeycomb substrate bearing a catalytic coating, arranged one above the other.

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