Wall assembly for the catalyst floor of a synthesis reactor

Abstract

A gas-permeable assembly (10) for holding a granular catalyst (1), comprising: a first wall (2) arranged to face the catalyst; a second wall (4) arranged at a distance from the first wall and facing the catalyst; and a catalyst-holding core (3) interposed between the first wall and the second wall.

Description

Technical Field

[0001] The present invention relates to the field of reaction apparatuses that contain granular catalysts and have a catalyst bed across which a gas stream passes. In particular, the present invention relates to the design of a gas-permeable wall assembly arranged to hold a solid catalyst.

Background Art

[0002] Some chemical conversion apparatuses that are of interest in the industry require a suitable distribution and collection of reactant or product gas streams to / from a catalyst bed where the catalyst is granular. Notable examples include reaction apparatuses for the synthesis of ammonia and methanol.

[0003] The catalyst bed typically has the shape of a cylindrical ring delimited by an outer wall and an inner wall. The inner and outer walls are typically referred to as an internal collection device and an external collection device, respectively. One of those walls acts as a gas distribution device and the other acts as a gas collection device. The gas flow through the catalyst bed can be substantially radial or axial-radial.

[0004] The collection devices need to comply with several opposing requirements. Their design is thus a difficult task. First, the collection devices need to be gas-permeable to allow the passage of reactant and product gas streams. For this purpose, the collection devices must have openings of sufficient size and number to provide the necessary passage area. Insufficient passage area increases the velocity of the gas flow, increases the pressure drop, and affects the action of the catalyst.

[0005] The collection device must also be able to hold the catalyst, meaning that the size of the gas passage opening may be determined by the size of the catalyst granules. In particular, the collection device must be designed to prevent the catalyst from moving outside the collection device and to reduce the risk of blockage of the gas passage opening caused by the catalyst itself. Blockage of the gas passage reduces the usable area and leads to an uneven distribution of the input gas in the catalyst bed, along with the aforementioned disadvantages.

[0006] In addition to the above, the collection device must also perform a structural function, particularly to withstand the pressure of the catalyst. In many notable reactors, such as industrial ammonia and methanol converters, the catalyst bed has considerable size and height in the axial direction, and thus the mechanical stress on the collection device is relevant. In particular, the inner surface in direct contact with the catalyst can be subjected to considerable tangential and radial stresses.

[0007] There is growing interest in the use of so-called microcatalysts, that is, catalysts made of small particles. Generally, catalysts made of particles with a nominal size of 1.5 mm or less are considered microcatalysts. Some microcatalysts may have a nominal size as small as 1 mm. Catalyst size refers to the characteristic dimensions of the granules, for example, the diameter of spherical particles. This size may follow a statistical distribution, and the nominal size may represent the average size.

[0008] Microcatalysts offer advantages in terms of conversion rates and are therefore attractive in terms of the economic profitability of the reactor. In particular, microcatalysts increase the contact area with the gas flow. However, containment of microcatalysts is difficult. Collection devices are susceptible to the risk of opening clogging and / or may not be able to retain the small particles of catalyst.

[0009] Simply reducing the size of the wall openings does not provide a solution to this problem. Smaller openings can lead to excessive pressure drops and deviate from the optimal gas flow distribution. The need to provide sufficient gas passage area requires a large number of such small openings, which can make the fabrication of perforated walls impractical. Furthermore, a large number of openings can weaken resistance to mechanical stress.

[0010] Patent Document 1 discloses a cylindrical wall for filtering solid particles in a fluid, such as a radial flow catalyst bed wall.

[0011] In light of these considerations, it is clear that designing a catalyst collection system is a challenging task. The ideal assembly must retain the mechanical properties necessary to ensure the integrity of the collection system, while also holding fine catalyst particles, avoiding clogging of the openings, and maintaining an optimal gas flow distribution. [Prior art documents] [Patent Documents]

[0012] [Patent Document 1] U.S. Patent Application Publication No. 2019 / 232245 [Overview of the Initiative] [Problems that the invention aims to solve]

[0013] The object of the present invention is to overcome the drawbacks of the prior art described above. In particular, the object of the present invention is to provide a collection device that can hold fine-grained catalysts and at the same time provide a structural support for granular aggregates of catalysts. [Means for solving the problem]

[0014] The above objectives are achieved by the gas-permeable assembly described in the claims.

[0015] The assembly comprises a first wall configured to hold a granular catalyst and positioned to face the catalyst; a second wall positioned at a distance from the first wall and facing the catalyst; and a catalyst-holding core interposed between the first wall and the second wall.

[0016] The first and second walls are made gas permeable by suitable openings, such as holes or slots. The catalyst holding core is also gas permeable by openings in its structure or by a suitable void pattern.

[0017] In the assembly of the present invention, the structural function of supporting the catalyst is mainly performed by the first and second walls; the function of holding the catalyst is mainly performed by the core. The term catalyst-holding core indicates that the core is designed to hold granular catalyst, and that the function of holding the catalyst is mainly, or exclusively, performed by the core, while the first and second walls provide the structural support for the assembly.

[0018] The first and second walls may be designed with a conventional pattern of openings arranged to provide desired cross-sectional passages and minimize pressure drop even with the microcatalyst. For example, the openings may be larger than the size of the catalyst granules. On the other hand, the catalyst holding core may be designed to suitably contain the microcatalyst without needing to withstand its pressure. The core has gas passages smaller than the size of the catalyst granules in order to perform its function as a catalyst holding member.

[0019] The catalyst size can be the maximum width of the granules, or it can be effectively defined by referring to the sieving process.

[0020] For example, the size of a catalyst may be determined based on the maximum square free flow area of ​​the sieve holding the catalyst. In particular, it may be assumed that the size of the catalyst is equal to the square root of the above area. The determination of the size by sieving the catalyst may be carried out preferably according to the standard test method disclosed in ASTM D4513-11, and in particular according to the standard specification of ASTM E11-17.

[0021] Another advantage of the present invention is that the core is in direct contact with the catalyst only in a small area. Direct contact with the catalyst over the entire surface would result in wear, for example, due to the displacement of catalyst particles during operation. In the assembly of the present invention, the core is effectively protected from such relative displacement and associated wear by the first wall. Thus, the core can be selected or designed primarily for catalyst retention without needing to meet stringent structural requirements.

[0022] The catalyst holding core may include at least one of the following: porous media; nets; overlapping nets; fibrous media; fine fibrous media; fabrics; metallic fiber felt; or perforated plates. In various embodiments, the core has preferred characteristic dimensions that are comparable to the size of the catalyst.

[0023] The assembly of the present invention achieves the goal of safely and reliably containing microcatalysts while simultaneously providing good stress resistance. It can be understood that the present invention provides a composite wall structure in which multiple different components cooperate to satisfy mechanical and process requirements.

[0024] The present invention includes a catalytic reactor comprising at least one catalyst bed and a gas-permeable assembly as described in any of the multiple embodiments described herein. The reactor is preferably an ammonia converter or a methanol converter. In particular, the present invention relates to a reactor comprising a cylindrical annular catalyst bed separated by an internal collector and an external collector, at least one of which comprises a gas-permeable assembly according to the present invention. The catalyst bed and collector may be part of a catalyst cartridge inserted into a pressure vessel.

[0025] Preferably, the catalyst bed of the reactor is made of a fine catalyst having a nominal size of catalyst particles of 1.5 mm or less, preferably 1.2 mm or less, more preferably 1.0 mm or less.

[0026] The core may partially or completely fill the gap between the first wall and the second wall. In one embodiment, the gap is completely filled by the core. In one embodiment, the core is sandwiched between the first wall and the second wall in contact with both. In a preferred embodiment, the assembly has a three-layer structure composed of the above-mentioned first wall, second wall, and central core that form a sandwich wall.

[0027] By filling the gap between the first wall and the second wall, the core contributes to the transmission of mechanical stress from one wall to the other, so that the two walls can structurally cooperate. Therefore, mechanical forces are borne by the first wall and the second wall; however, the core contributes to the distribution of forces from one to the other.

[0028] In order to make the entire assembly permeable to gas, the first wall, the second wall, and the catalyst holding core have gas passages. The gas passages in the walls can be holes or openings made in the walls. The gas passages in the core can be in the form of a void pattern, particularly when the core is a porous medium, a fibrous or microfibrous medium, a fabric, or a metal fiber.

[0029] The catalyst holding core has gas passages smaller than the gas passages of the first wall and the second wall. Having smaller gas passages, the core can hold fine catalysts that would not be confined by the first wall and the second wall.

[0030] The gas passages in the core can be represented by a characteristic size. The characteristic size can be the diameter of a circular opening or the maximum width of an opening of a different shape, such as an elongated shape or a slit-shaped opening.

[0031] The core may have a suitable void pattern to allow the passage of gas flow. This void pattern may be represented, for example, by passages in a porous medium, mesh openings in a net, or perforations in a plate used as a core element. The average area of ​​the passages in the core pattern may be smaller than the area of ​​the passages in the wall openings. For example, the passage area may be defined in a plane perpendicular to the radial direction of a cylindrical annular floor.

[0032] The catalyst holding core may consist of a single net or multiple nets that overlap each other. Using two or more nets for the core element is particularly cost-effective.

[0033] In embodiments using overlapping nets, an interesting feature is that the mesh openings do not need to be smaller than the minimum size of the catalyst, thanks to the net overlaps resulting in passages that are actually smaller than the mesh openings. Furthermore, in the case of these overlapping nets, the characteristic size of the openings can be defined as the maximum width of the openings created by the overlaps.

[0034] In embodiments in which the catalyst holding core includes a porous medium, the preferred porous medium is a sintered metal plate.

[0035] In embodiments in which the catalyst holding core includes a woven net, the net may be similar to the net used in a demister pad.

[0036] In embodiments in which the catalyst holding core includes a fibrous medium, the fibrous medium may be a nonwoven fibrous medium or a nonwoven fine fibrous medium.

[0037] In embodiments where the catalyst holding core includes a fabric, this may be, for example, a ceramic fabric or a fabric made of sintered metal.

[0038] In some embodiments, the core itself may have a sandwich structure comprising reinforcing perforated plates and porous elements such as a net or multi-layer net. For example, the core may have a reinforced mesh structure comprising mesh elements between the reinforcing perforated plates. The reinforcing perforated plates are preferably made of metal.

[0039] In embodiments where the core is a perforated plate, the holes in the plate are smaller than the characteristic dimensions of the catalyst particles. For example, these characteristic dimensions could be the diameter of the spherical particles.

[0040] In a preferred embodiment, the catalyst holding core is positioned such that a portion of the pressure exerted by the catalyst in contact with the first wall is transmitted to the second wall by the core. This requires that the core has sufficient rigidity to transmit the pressure to the second wall.

[0041] In a preferred embodiment, the first wall (inner wall) facing the catalyst is structurally connected to the second wall (outer wall). The interconnection between the two walls can be achieved by welding the two walls together with a connector. The connector may preferably be a set of metal pieces arranged at equal intervals.

[0042] The above connector may have various shapes, most preferably rectangular or cylindrical. The number of interconnections and the distance between them can be determined by calculations of mechanical strength. Overall, interconnections between two walls ensure higher strength of the assembly and allow for a reduction in the thickness of the wall facing the catalyst. In this way, the thickness of the wall can be optimized according to process requirements.

[0043] Depending on the catalyst bed configuration, the gas flow into or out of the assembly may follow either a substantially purely radial or axial-radial path. The radial flow may be directed inward, i.e., toward the axis of the reactor, or outward, i.e., toward away from the axis.

[0044] The gas passage openings in the first and second walls are typically slits or holes having preferred dimensions and orientations. In preferred embodiments, the gas passage openings have an elongated shape. The term elongated shape indicates that the slits primarily extend in a particular direction. Slits in the walls may extend in the same or different directions.

[0045] The openings in the first and second walls may be arranged in the same or different patterns. In one embodiment, the elongated slits in the first and second walls may be oriented in the same direction or in different directions. For example, in one embodiment, the first wall may have multiple elongated slits oriented in a first direction, and the second wall may have multiple slits oriented in a second direction different from the first direction. For example, the slits in the first and second walls may be arranged so as to intersect each other at right angles. Combinations of multiple directions are also possible.

[0046] The above-mentioned slits can be manufactured by conventional manufacturing processes such as water, laser cutting, or electrical discharge machining. Alternatively, if the gas opening is a perforated hole, a mechanical punching method may be used. The punching method may also be used for other types of openings if made possible by the manufacturing technology. Mechanical punching may be preferred due to its lower cost compared to, for example, laser cutting.

[0047] The gas-permeable assembly of the present invention is most preferably cylindrical.

[0048] An interesting application area of ​​the present invention relates to a reaction apparatus comprising a cylindrical annular catalyst bed separated by at least one collection device having the assembly of the present invention. The term collection device refers to a gas-permeable wall arranged to distribute gas flowing into the catalyst bed or to collect gas flowing out of the catalyst bed.

[0049] The above-mentioned collection device may include an external collection device and an internal collection device. One or both of the external and internal collection devices may include the assembly of the present invention. In some embodiments, the reactor may include only one collection device, for example, only an external collection device, and a catalyst bed. A particularly interesting application area of ​​the present invention relates to reactors for the synthesis of ammonia and methanol.

[0050] A further aspect of the present invention is a reactor for the synthesis of a compound, preferably ammonia or methanol, comprising at least one cylindrical annular catalyst bed separated by at least one collector, wherein the catalyst bed contains a granular catalyst, and at least one collector of the catalyst bed comprises a gas-permeable assembly, where: The above assembly includes a first wall facing the catalyst, a second wall positioned at a distance from the first wall, and a core element between the first wall and the second wall. The first and second walls have gas passage openings larger than the granular size of the granular catalyst, while the core has gas passages smaller than the granular size of the catalyst. Thus, the catalyst is held in place by the core of the assembly.

[0051] Preferably, in the above-mentioned reaction apparatus, the first and second walls serve as structural load-bearing components for the assembly. Preferably, the core is one of the following: a porous medium; a net; an overlap of multiple nets; a fibrous medium; a fine fibrous medium; a fabric; a metallic fiber felt; or a perforated plate. [Brief explanation of the drawing]

[0052] [Figure 1] This is a schematic diagram of a gas-permeable assembly according to a preferred embodiment. [Figure 2] This is a perspective view of a gas-permeable assembly according to one embodiment. [Figure 3] This is a perspective view of another embodiment of the above assembly. [Figure 4] This is a perspective view of another embodiment of the above assembly. [Figure 5]This is a cross-sectional view of another embodiment of the above assembly. [Figure 6] This is a schematic cross-sectional view of the catalyst bed. [Modes for carrying out the invention]

[0053] Figure 1 schematically shows a cross-section of the wall assembly 10 in contact with the catalyst layer 1. For example, Figure 1 shows the outer wall assembly of a radially outward flowing catalyst bed.

[0054] The assembly 10 comprises a gas-permeable inner wall 2 facing the catalyst layer 1 and a gas-permeable outer wall 4 facing the catalyst. The assembly 10 further comprises a catalyst holding core 3 interposed between the inner wall 2 and the outer wall 4.

[0055] The catalyst-holding core 3, enclosed between the two walls 2 and 4, holds catalyst particles and can be designed to properly hold micro-catalysts. Conversely, the gas-permeable walls 2 and 4 serve as structural supports for the core 3.

[0056] The opening 5 is positioned above the surfaces of the walls 2 and 4 and allows the gas flow to pass through the catalyst bed. The design of the opening 5 may be selected to allow for an optimal pressure drop and an optimal gas flow distribution across the catalyst bed.

[0057] The opening 5 may be an elongated slit as shown in Figure 2, or a hole as shown in Figure 3. The hole may be made using a less expensive method than conventional methods, namely, a punching method instead of electrical discharge machining or water jet cutting.

[0058] Figure 2 shows an embodiment in which the inner wall 2 and the outer wall 4 have openings 5 ​​having different patterns. In particular, Figure 2 shows an embodiment in which the openings are elongated slits oriented in a first direction on the inner wall 2 and in a second direction on the outer wall 4.

[0059] Walls 2 and 4 may be connected to each other by welded elements not shown in the figure. The number and dimensions of the above-mentioned connected elements are determined by the requirements of structural integrity.

[0060] Figure 4 shows an example of Core 3, which is made of a demister pad type mesh.

[0061] Figure 5 shows an example in which the core 3 has a reinforced mesh structure, including mesh elements 30 sandwiched between perforated reinforcing plates 31 and 32.

[0062] Figure 6 is a schematic diagram of a cylindrical annular catalyst bed 20 showing the positions of internal and external collection devices made of assembly 10. The bed 20 has an axis AA and a central cavity 21. In some embodiments, an inter-bed heat exchanger may be mounted within the cavity 21.

Claims

1. A gas-permeable wall assembly (10) for use in a catalytic reactor to hold a granular catalyst (1), the wall assembly (10) comprising: a first wall (2) positioned facing the catalyst; a second wall (4) positioned at a distance from the first wall and facing the catalyst; and a catalyst holding core (3) interposed between the first wall and the second wall, the catalyst holding core (3) having gas passages smaller than the gas passage openings (5) of the first wall (2) and the second wall (4), The size of the gas passage opening (5) in the first wall (2) and the second wall (4) is larger than the size of the granular catalyst. The first wall (2) and the second wall (4) perform the structural load-bearing function of the wall assembly (10), and A wall assembly (10) comprising the catalyst holding core (3) containing a porous medium.

2. The wall assembly (10) according to claim 1, wherein the catalyst holding core (3) partially or completely fills the gap between the first wall (2) and the second wall (4).

3. The wall assembly (10) according to claim 1, wherein the porous medium is a sintered metal plate.

4. The wall assembly (10) according to claim 1, wherein the porous medium is a fibrous medium.

5. The wall assembly (10) according to claim 4, wherein the fibrous medium is a nonwoven fabric.

6. The wall assembly (10) according to claim 4, wherein the fibrous medium is a ceramic fiber fabric or a sintered metal fiber fabric.

7. The wall assembly (10) according to claim 4, wherein the fibrous medium is metal fiber felt.

8. The wall assembly (10) according to any one of claims 1 to 7, wherein the catalyst holding core (3) includes a mesh element sandwiched between reinforcing perforated plates.

9. The wall assembly (10) according to any one of claims 1 to 8, wherein the catalyst holding core can hold a fine catalyst that is not sealed by the first wall and the second wall, and the fine catalyst has a nominal size of catalyst granules of 1.5 mm or less.

10. The wall assembly (10) according to claim 9, wherein the fine catalyst has a nominal size of catalyst granules of 1.2 mm or less.

11. The wall assembly (10) according to claim 10, wherein the fine catalyst has a nominal size of catalyst granules of 1.0 mm or less.

12. The catalyst holding core (3) is arranged such that a portion of the pressure exerted by the catalyst in contact with the first wall is transmitted to the second wall by the catalyst holding core, and the catalyst holding core (3) has a rigidity suitable for transmitting a portion of the pressure exerted by the catalyst from the first wall to the second wall, according to any one of claims 1 to 11, the wall assembly (10).

13. The wall assembly (10) according to any one of claims 1 to 12, wherein the first wall (2) is connected to the second wall (4).

14. The wall assembly (10) according to claim 13, wherein the first wall (2) is connected to the second wall (4) by elements arranged at equal intervals.

15. The wall assembly (10) according to any one of claims 1 to 14, wherein the first wall (2) has openings (5) arranged according to a first pattern, and the second wall (4) has openings arranged according to a second pattern different from the first pattern.

16. The wall assembly (10) according to any one of claims 1 to 15, wherein the opening in the first wall and the opening in the second wall have an elongated shape or a circular hole shape.

17. The wall assembly (10) according to any one of claims 1 to 16, wherein the wall assembly (10) comprising the first wall (2), the second wall (4), and the catalyst holding core (3) is cylindrical.

18. A reaction apparatus for the synthesis of a compound, comprising at least one cylindrical annular catalyst bed separated by at least one collection device including a wall assembly (10) according to any one of claims 1 to 17.

19. The reaction apparatus according to claim 18 for the synthesis of ammonia or methanol.

20. A reaction apparatus for the synthesis of compounds, comprising at least one cylindrical annular catalyst bed containing a granular catalyst, wherein at least one collection device for the catalyst bed includes a gas-permeable assembly: The assembly includes a first wall facing the catalyst, a second wall spaced apart from the first wall, and a core element between the first wall and the second wall. The first and second walls have gas passage openings larger than the granule size of the granular catalyst, while the core element has gas passages smaller than the granule size of the catalyst, and thus the catalyst is held in place by the core element of the assembly. A reaction apparatus in which the first wall and the second wall perform a structural load-bearing function for the assembly.

21. The reaction apparatus according to claim 20 for the synthesis of ammonia or methanol.

22. The reaction apparatus according to claim 20 or 21, wherein the core element includes a porous medium.

23. The reaction apparatus according to claim 22, wherein the porous medium is a fibrous medium.

24. The reaction apparatus according to claim 23, wherein the fibrous medium is a metal fiber felt.

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