Catalyst support system for ammonia oxidation burner

Abstract

The catalyst support system (1) for the ammonia oxidation burner (2) comprises a catalytic gauze for the oxidation of ammonia and a basket (14) connected to a support ring (10) for holding an inert substance and / or a catalyst for removing N2O from the gaseous effluent of this catalytic gauze (9), this basket (14) having a modular structure comprising a plurality of modules, each module comprising a gas-permeable surface (16) and a support frame (15), each module being connected to an adjacent module by a connection configured to allow limited displacement between the modules, and only the outer modules forming the periphery of the basket being connected to the support ring (10).

Description

Technical Field

[0001] The present invention relates to the field of catalyst support systems for ammonia oxidation burners.

Background Art

[0002] In the nitric acid production process, a burner causes a catalytic reaction between ammonia and an oxygen-containing gas such as air or pure oxygen at a high temperature on a catalytic gauze. Usually, the catalytic gauze is made of a noble metal such as Pt / Rh.

[0003] The oxidation product of ammonia is a gas mixture mainly composed of nitric oxide NO and nitrogen dioxide NO2, and containing a trace amount of dinitrogen monoxide (also called nitrous oxide) N2O. The ammonia oxidation gas is cooled in one or more heat exchangers to promote the conversion from NO to NO2, and finally absorbed in water in an appropriate absorption column to produce nitric acid.

[0004] Overall, the nitric acid synthesis process involves severe conditions regarding temperature and its gradient, so the equipment is subjected to severe stress. The ammonia burner is particularly stressed because it has to withstand the high temperatures generated by the oxidation of ammonia, which can rise above 900°C, for example up to 920°C.

[0005] Dinitrogen monoxide N2O is a known pollutant and is not involved in the synthesis of nitric acid. Therefore, by flowing the above gas mixture through a catalyst suitable for decomposing N2O into nitrogen and oxygen, the N2O contained in the ammonia gas can be directly removed in the ammonia burner. A catalyst configured to remove N2O before the adsorption step is called an N2O secondary abatement catalyst.

[0006] Therefore, a known design of an ammonia burner includes a basket disposed under the ammonia oxidation catalytic gauze and suitable for accommodating an N2O secondary abatement catalyst. The basket may contain an inert substance for uniformly dispersing the gas.

[0007] The ammonia burner usually includes a load-bearing structure installed on the container of the ammonia burner. The load-bearing structure includes a metal ring for supporting the catalyst gauze and a carrier plate for supporting the basket.

[0008] The basket may be realized as an integral type, or may include a beam-shaped rectangular component with both ends supported on the carrier plate. The basket has a gas-permeable floor surface for supporting the catalyst or the inert substance, and usually, this surface is in a lattice or mesh shape.

[0009] However, in the above design of the basket, some drawbacks have become apparent, especially under severe thermal stress caused by high-temperature ammonia oxidation gas. Since the metal ring and the carrier plate are subject to considerable thermal elongation, they must be able to withstand the weight and pressure drop of the catalyst gauze and the basket containing the reduction catalyst.

[0010] In particular, the drawback of the integral basket is that the circumferential thermal expansion can only be compensated at the outer edge of the basket. This problem is not solved by the known method of further dividing the basket into relatively large sections supported at both ends of the ring.

[0011] If the thermal expansions of the components connected to each other are different, it may cause deformation or failure.

[0012] In fact, it has been observed that cracks may occur in the metal ring supporting the gauze, and deformation and / or swelling may occur in the basket. The displacement between the components of the support structure due to thermal stress may cause the net of the basket to be damaged and / or the floor surface to undulate. The adverse effects may include the formation of a gas bypass path and the non-uniform distribution of the catalyst or the inert substance. In a specific region of the catalyst layer, the amount of gas received may be reduced or it may remain substantially inert.

[0013] Furthermore, when a basket containing the N2O secondary reduction catalyst is fixed by a joint welded to the carrier plate, as a result of the high-temperature cycle generated by the ammonia oxidation reaction, the catalyst may be displaced from the peripheral portion of the basket to the central region of the basket, and in some cases, the basket may rupture and the catalyst may be released outside the basket.

[0014] Therefore, there is a need for a catalyst support system for an ammonia oxidation burner that is less affected by the above-described structural integrity problems.

[0015] Patent Document 1 discloses a catalyst support system for an ammonia oxidation burner.

Prior Art Documents

Patent Documents

[0016]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0017] An object of the present invention is to overcome the above-mentioned drawbacks of the prior art. An object of the present invention is to provide a novel catalyst support system that can better withstand the thermal stress of an ammonia burner. The present invention addresses the problem of how to improve the design of a basket for supporting an N2O secondary catalyst and / or an inert material downstream of an ammonia oxidation catalyst gauze in order to avoid or reduce the above-mentioned drawbacks.

[0018] The objects of the present invention include, among other things, avoiding catalyst bypass, being able to adapt to thermal expansion, making more effective use of the secondary catalyst to reduce the inert catalyst, and simplifying the installation procedure.

Means for Solving the Problems

[0019] The above object is achieved by the catalyst support system according to claim 1. The basket for holding the N2O secondary catalyst and / or the inert substance has a modular structure, each module includes a gas-permeable floor and a support frame, and each module is connected to an adjacent module by a connection configured to allow limited displacement between the modules. The outer module forming the periphery of the basket is connected to the support ring.

[0020] In a highly preferred embodiment, these modules include an inner portion located at the center of the basket and a plurality of modules arranged to form one or more concentric annular rows.

Advantages of the Invention

[0021] The modular structure of the above basket has numerous advantages.

[0022] The main advantage is that its adaptability to thermal expansion is much better. Different from the case of an integral basket, thermal expansion is dispersed among the modules. The arrangement of multiple sets of concentric annular modules is particularly effective in adapting to radial and circumferential expansion. The modular basket has an improved ability to follow thermal expansion and to adapt to the temperature profile in the ammonia oxidation reactor.

[0023] The outer module is preferably connected to the support ring by a radial joint. The radial joint is configured to resist radial stress, but the module is configured to be able to displace freely in other directions with limited displacement relative to the ring. Therefore, the outer module can move together with the support ring to adapt to thermal expansion. The relative displacement that may occur between the outer module and the adjacent module is absorbed by each connection. Related advantages include reducing the displacement of the N2O catalyst and avoiding or reducing the gas bypass path.

[0024] By avoiding displacements that cannot be controlled by the connections between the modules, the modules are properly held. At the same time, however, they enable the absorption of thermal expansion, so that the entire module structure of the basket can adapt to thermal stress.

[0025] A further advantage is that the gas flow distribution in the basket is optimized, so that the amount of catalyst used for N2O decomposition can be reduced. The installation of joints with radial rigidity only in the outer part of the basket enables the simplification of the procedure for attaching the basket to the support ring.

[0026] Finally, the applicant has also found that incorporating the catalyst support system of the present invention into an ammonia burner is very effective in avoiding the generation of excessive thermal stress, and thus the operating life of the ammonia burner is expected to be extended.

Brief Description of the Drawings

[0027]

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Mode for Carrying Out the Invention

[0028] The present invention relates to a catalyst support system for an ammonia oxidation burner, comprising a load-bearing structure including a first support ring for supporting a catalyst gauze for ammonia oxidation and a second support ring located below the first ring, and a basket connected to the second support ring and configured to contain an inert substance and / or a catalyst for removing N2O from the gaseous effluent of the catalyst gauze. The basket has a modular structure including a plurality of modules, each module including a gas-permeable bed and a support frame, and each module is connected to an adjacent module by a connection configured to allow limited displacement between the modules, and only the outer modules forming the periphery of the basket are connected to the support ring.

[0029] The load-bearing structure generally includes a first support ring for the catalyst gauze and a second support ring for the modular basket. Since the second ring is below the first ring, the first ring may be called the upper ring and the second ring may be called the bottom ring. The second ring is vertically below the first ring.

[0030] The structure may include an outer wall, an inner wall, and an upper connecting portion welded between the outer wall and the inner wall, and the first support ring is welded to the inner wall. The load-bearing structure may also include a seal wall arranged to hermetically seal the side surface between the first support ring and the second support ring. The seal wall may be welded to the first ring and the second ring.

[0031] Overall, the modular basket has a gas-permeable floor surface such as a grid or a net and a support structure. The purpose of the support structure is to support the gas-permeable surface. In the modular structure of the present invention, each module provides a part of the gas-permeable bed and a part of the associated support structure.

[0032] Each of the outer basket modules can be connected to the second support ring by a radial joint configured to prevent the module from displacing radially with respect to the ring. Preferably, the radial joint allows for a limited vertical displacement of the module. More preferably, the radial joint also allows for a small rotation of the module with respect to the support ring.

[0033] In a preferred implementation, the radial joint comprises at least one fixing pin for each module. The fixing pin is inserted with play into a hole in the frame of the basket module and welded to the support ring.

[0034] In a highly preferred embodiment, the system includes a set of cooling tubes disposed below the basket to provide additional support means for the basket modules. Preferably, the only support means for the basket are the cooling tubes and the radial joints between the outer modules of the basket and the second ring. Thus, the weight of the basket module is substantially supported by the underlying cooling tubes. The fixing of the outer module to the support ring provides radial support. The connections between the modules hold the modules properly. Thus, it is possible to compensate for thermal expansion by relative movement while maintaining the overall configuration of the basket. The outer module can be partially supported by the cooling tubes located below it and partially supported by the second support ring.

[0035] In a preferred embodiment, the connections between the modules include segments having an overall C-shaped or U-shaped cross-section. These segments are arranged downwardly on the edge walls of adjacent modules. As a result, these segments are such that the C-shaped or U-shaped segments surround the edge walls of the two modules. The segments are held in place by pins inserted into the passages of the edge walls.

[0036] The components of the connection between modules are preferably gas-permeable and, for example, have suitable gas passages. Preferably, the gas passages are circular holes.

[0037] The modules are arranged to form a two-dimensional array. In a highly preferred embodiment, the modules are arranged in one or more concentric circular rings or rows. For example, the outer modules form an outer ring, and further modules form one or more additional circular rings. The modules can have a shape similar to a sector of an annulus. A preferred shape is substantially trapezoidal. A single inner module can form the center of the basket.

[0038] In an embodiment using modules arranged according to a plurality of circular rings, the connections between the modules preferably include radial joints and circumferential joints each configured to allow limited displacement between the connected modules.

[0039] The upper ring is preferably a circular crown. The upper ring can include notches periodically arranged along the circular crown and configured to compensate for thermal expansion. Preferably, the notches start from a point located at the center of the upper ring and are arranged radially.

[0040] The above system can include a first set of cooling tubes arranged between an outer wall and an inner wall.

[0041] The first set of cooling tubes can be attached to the outer wall or the inner wall of the catalyst support system and can be used to protect the pressure vessel of the ammonia burner from overheating. A cooling medium such as water or steam can be passed through the cooling tubes to remove heat from the load-bearing structure and the low N2O gas discharged from the basket.

[0042] The catalyst gauze can be properly held on the upper ring by one or more counterweights.

[0043] In a preferred embodiment, the upper connecting part has a curved shape. Preferably, the outer wall and the inner wall are parallel, so that the load-bearing structure functions as a radially elastic support.

[0044] The upper ring can be manufactured according to any known process or technique, but preferably, the upper ring is obtained by forging.

[0045] According to an interesting application of the present invention, a catalyst for N2O reduction / decomposition and an inert substance are filled into the basket. By using the inert substance to redistribute the flow in the basket, a uniform flow distribution at the outlet of the basket is achieved.

[0046] Preferably, the upper connecting part provided for connecting the outer wall and the inner wall of the catalyst support system has a curved shape. The curved shape is particularly effective in adapting to the thermal dilation of the catalyst support system at high temperatures.

[0047] The ammonia burner may include a reaction vessel and a catalyst support system as provided herein. The reaction vessel comprises a reactor wall, and the catalyst support system can be attached to the reactor wall by means of one or more welds.

[0048] Preferably, the outer wall and the inner wall of the catalyst support system are parallel, so that the load-bearing structure functions as a radially elastic support. By the term "elastic support", the applicant suggests that the catalyst support system may deform elastically under thermal strain and that no plastic deformation remains in the structure when thermal stress is removed from the structure.

[0049] The above-mentioned catalyst support system may include a catalyst gauze for the oxidation of ammonia. Another aspect of the present invention is an ammonia oxidation burner comprising a catalyst gauze for the oxidation of ammonia as described in the claims and a support system for this catalyst gauze. Preferably, the burner is a vertical burner, more preferably a vertical cylindrical burner.

[0050] Figure 1 shows a catalyst support system 1 for an ammonia oxidation burner 2.

[0051] The catalyst support system 1 includes a load-bearing structure 3. The load-bearing structure 3 includes an outer wall 4 facing the wall of the ammonia burner 2, an inner wall 5 facing the reaction region of the ammonia burner, a lower connecting part 6, and an upper connecting part 7.

[0052] The lower connecting part 6 is welded to the outer wall 4, connecting the load-bearing structure 3 and the ammonia burner 2. The upper connecting part 7 is welded between the outer wall 4 and the inner wall 5 and has a curved shape capable of absorbing thermal stress. In particular, the curved upper connecting part 7 forms a wave that gives some radial elasticity to the system.

[0053] In a particular embodiment, since the outer wall 4 can be directly welded to the container of the burner 2, the lower connecting part 6 is optional.

[0054] The catalyst support system 1 further includes an upper ring 8 and a bottom ring 10. The upper ring 8 is welded to the inner wall 5 and is configured to support a catalyst gauze 9 for the oxidation of ammonia. The bottom ring 10 is disposed below the upper ring 8.

[0055] The upper ring 8 and the bottom ring 10 are connected by a seal wall 11. The seal wall 11 is welded to the lower end of the upper ring 8 and also welded to the upper end of the bottom ring 10.

[0056] The catalyst gauze 9 is held in an appropriate position above the upper ring 8 by an appropriate counterweight 27.

[0057] The bottom ring 10 supports the basket 14. The basket 14 may contain an inert substance and / or a catalyst for removing N2O from the gas emissions of the catalyst gauze 9. The inert gas, if provided, is used for the purpose of dispersing the flow rate, i.e., to achieve a uniform gas flow rate dispersion at the outlet of the basket.

[0058] A set of the first cooling coils 25 is arranged between the inner wall 5 and the outer wall 4 of the catalyst support system 1. A cooling medium such as water or steam flows through the cooling coils 25 to remove the heat generated by the oxidation reaction of ammonia from the catalyst support system 1.

[0059] A set of the second cooling coils 26 is provided below the basket 14. The set of the second cooling coils 26 removes heat from the gas emissions of the basket 14, and this removed heat can be used for the purpose of steam generation or steam superheating. The set of the second cooling coils 26 may also provide a structural function and can be used, in particular, to at least partially support the weight of the basket 14 to enhance the mechanical stability of the entire support system 1.

[0060] The basket 14 has a modular structure. The modular structure includes a central module and a plurality of modules arranged to form one or more concentric annular rows. Each module preferably has a grid-like gas-permeable floor 16 and a support frame 15 (Figure 1). In other words, each module forms part of the support structure and part of the gas-permeable floor of the entire basket 14.

[0061] The basic design principle of the modular basket 14 is shown in Figure 2. The basket 14 includes a central module 20 and modules 21, 21a arranged to form one or more annular rows 17, 18. The outer module 21a forms the outer annular row 18, and the modules 21 form one or more annular rows 17.

[0062] Each module is connected to adjacent modules along a radial connection channel 23 and a circumferential connection channel 23a. The term circumferential here means a connection channel along a line perpendicular to the median radius of the module.

[0063] The central module 20 can be circular or polygonal. In the case of a polygon, the central module 20 preferably has many sides, such as at least 10 or 12 sides, in order to approximate a circle. Each module 21 is preferably delimited by straight sides and preferably has a substantially trapezoidal shape approximating an annular sector shape.

[0064] The shape and size of the modules can vary depending on their position within the basket. For example, in the scheme of FIG. 2, the inner modules have a shape close to a triangle, while the outer modules 21a have a shape close to a rectangle.

[0065] Each module 21, 21a is provided with a perforated floor, such as a grid or net with holes 33, so that each module forms part of the gas-permeable floor 16 of the basket 14.

[0066] The connection channels 23 and 23a are arranged to allow relative displacement between adjacent modules and thus function as expansion joints to compensate for thermal expansion. The connection channels 23 and 23a extend beyond the boundary line between adjacent modules. This boundary line is preferably straight.

[0067] The outermost row 18 of modules 21a is connected to the bottom ring 10 by a radial joint 22 configured to prevent radial displacement. A preferred embodiment of such a joint 22 is shown in FIG. 7.

[0068] FIG. 3 shows a portion of the basket 14 extending over 90° in accordance with an embodiment in which the modules 21, 21a form two concentric annular rows 17 and an outer row 18. This figure shows the radial connection channels 23 and the circumferential connection channels 23a.

[0069] FIG. 4 shows a preferred embodiment of the connection channels 23 and 23a. The connection channel 23 or 23a is a segment 24 having an overall C-shaped or U-shaped cross-section, and includes a segment 24 arranged to surround the side walls of two adjacent modules 21 or 21a downward. The segment 24 is held in place by one or more pins 36.

[0070] The connection channel further includes a cover piece 35 arranged at the intersection of the channels 23 and 23a to prevent catalyst particles from entering the gap between the modules. The intrusion of such catalyst particles is undesirable because it may prevent the freedom of displacement between the modules for compensating thermal stress.

[0071] FIG. 5 shows the arrangement of the fixing pins 36 in more detail. The pins 36 are inserted into the holes of the side walls 151, 152 of the modules 21, 21a and have curved ends 361 arranged on the upper surface 241 of the segment 24.

[0072] FIG. 6 shows a portion of the upper ring 8 in a preferred embodiment. The upper ring 8 is provided with notches 28 periodically arranged along the ring 8. The notches 28 are configured to compensate for thermal expansion.

[0073] FIG. 7 shows a preferred embodiment of the radial joint 22 for connecting between the frame 15 of the outer module 21a and the bottom ring 10. The joint 22 includes a pin 220 passing through the hole of the frame 15 and the hole of the bottom ring 10. The pin 220 is welded to the bottom ring 10 at the weld point 13. The pin 220 has a head 37 of an appropriate shape to prevent the basket from coming off the bottom ring 10.

[0074] The gap 38 between the head 37 and the basket 14 above the pin 220 allows the module 21a, and thus the entire basket 14, to move axially (vertically) with respect to the bottom ring 10. Providing the gap 38 is particularly effective in absorbing axial thermal expansion.

Claims

1. A catalyst support system (1) for an ammonia oxidation burner (2), comprising: A load-bearing structure (3) including a first support ring (8) for supporting a catalyst gauze (9) for the oxidation of ammonia and a second support ring (10) located below the first ring; connected to the second support ring (10) and configured to hold an inert substance and / or a catalyst for removing NO from the gaseous effluent of the catalyst gauze (9) 2 a basket (14), and The catalyst support system (1), wherein the basket (14) has a modular structure including a plurality of modules, each module includes a gas-permeable floor (16) and a support frame (15), and each module is connected to an adjacent module by a connection configured to allow limited displacement between the modules, and only the outer module (21a) forming the peripheral edge of the basket is connected to the support ring.

2. The catalyst support system (1) according to claim 1, wherein each of the outer modules (21a) of the basket is connected to the second ring (10) by a radial joint (22), the radial joint being configured to prevent radial displacement of the module with respect to the ring (10) and to allow limited vertical displacement, preferably also rotation, of the module.

3. The catalyst support system (1) according to claim 1 or 2, comprising a set of cooling tubes disposed below the basket, the modules of the basket being disposed on the cooling tubes, and the only support means of the basket being the cooling tubes and the radial joints between the outer modules of the basket and the second ring (10).

4. The catalyst support system (1) according to any one of claims 1 to 3, wherein the module includes an inner module (20) located at the center of the basket and modules (21, 21a) arranged to form one or more concentric annular rows (17, 18).

5. The catalyst support system (1) according to claim 4, wherein each module is connected to an adjacent module by a radial joint (23) and a circumferential joint (23a), the radial joint and the circumferential joint being configured to allow limited displacement between the connected modules.

6. The connection portion between the modules of the basket includes a segment (24) having a C-shaped or U-shaped cross-section as a whole, the segment is arranged downward on the side walls of two adjacent basket modules, as a result, the segment surrounds the edge wall of the module, and the segment is held in a predetermined position by pins (36) inserted into holes in the side walls. The catalyst support system (1) according to any one of claims 1 to 5.

7. The catalyst support system (1) according to any one of claims 1 to 6, including a seal wall (11) arranged to hermetically seal the side surface between the first support ring (8) and the second support ring (10).

8. The load-bearing structure (3) includes an outer wall (4), an inner wall (5), and an upper connecting portion (7) welded between the outer wall (4) and the inner wall (5), and the first support ring (8) is welded to the inner wall (5). The catalyst support system (1) according to any one of claims 1 to 7.

9. The catalyst support system (1) according to claims 7 and 8, wherein the seal wall (11) is welded to the first support ring (8) and the second support ring (10).

10. The upper connecting portion (7) has a curved shape, and the outer wall (4) and the inner wall (5) are parallel. As a result, the load-bearing structure (3) functions as a support portion having elasticity in the radial direction. The catalyst support system (1) according to claim 8 or 9.

11. The catalyst support system (1) according to any one of claims 8 to 10, having a set of cooling tubes (25) arranged between the outer wall (4) and the inner wall (5).

12. The catalyst support system (1) according to any one of claims 1 to 11, wherein the catalyst gauze (9) is held in a predetermined position on the first support ring (8) by one or more counterweights (27).

13. An ammonia oxidation burner, including a catalyst gauze (9) for the oxidation of ammonia and the support system for the catalyst gauze according to any one of claims 1 to 12.

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