Device comprising catalyst modules and method for catalytically reducing nitrogen oxides

Abstract

The invention relates to a device (1), in particular for the catalytic reduction of nitrogen oxides, comprising - a container (2) extending along a longitudinal axis (L), - a first catalyst module (10), - a first support device (12) arranged on an inner wall of the container (2) for supporting the first catalyst module (10), wherein the first support device (12) extends along the inner wall of the container (2) at least partially circumferentially about the longitudinal axis (L) and has an inner contour facing the longitudinal axis (L) and having a first opening width, in particular a first opening diameter, - and a second catalyst module (20) which is arranged in the container (2) below the first support device (12) in the direction of the longitudinal axis (L) and has an outer contour facing the inner wall of the container (2) and having an outer width, in particular an outer diameter, which is smaller than the first opening width of the first support device (12), wherein the first catalyst module (10) is configured to be flowed through substantially perpendicular to the longitudinal axis (L) and the second catalyst module (20) is configured to be flowed through substantially parallel to the longitudinal axis (L). The invention also relates to a method for catalytically reducing nitrogen oxides using a device of this type.

Description

Device with catalyst modules and Processes for the catalytic reduction of nitrogen oxides

[0001] The invention relates to a device particularly suitable for the catalytic reduction of nitrogen oxides and to a method for the catalytic reduction of nitrogen oxides. Furthermore, the invention relates to a system in which a device containing nitrogen oxides, preferably NOₓ, is used. X and N2O, a polluted exhaust gas stream is produced, and a process for the production of nitric acid by catalytic oxidation of ammonia on a primary catalyst and conversion of the NO produced in the process X - Nitrogen oxides in an absorption tower to nitric acid with the formation of exhaust gases leaving the absorption tower.

[0002] Many processes, such as combustion processes, especially the combustion of nitrogen-containing fuels like ammonia (NH3)-containing fuels, or many chemical-industrial processes, such as the production of nitric acid or caprolactam, produce flue gases or exhaust gases containing various types of nitrogen oxides, such as nitric oxide (NO) and nitrogen dioxide (NO2) (collectively referred to as NO). X They contain nitrogen oxides (NOx) and / or nitrous oxide (N2O). NO and NO2 can cause acid rain and / or smog and are therefore ecotoxicologically relevant. N2O is a greenhouse gas whose global warming potential (GWP) is currently estimated at a factor of 273 compared to CO2, and it also contributes significantly to the depletion of stratospheric ozone. For this reason, global limits have been set for the maximum permissible emissions of NO. Xand N2O, or political mechanisms and monetary incentives for their reduction have been established. There is an urgent need for technical solutions that reduce nitrous oxide emissions along with NO. x -eliminate or at least reduce emissions.

[0003] To eliminate nitrogen oxide emissions in gas streams, methods for catalytic reduction are known, among others, whereby the nitrogen oxides (NOx) are reduced. Xand / or N₂O) are chemically reduced in the presence of suitable catalysts using reducing agents. Of particular technical importance here are catalysts for the selective chemical reduction of nitrogen oxides, so-called SCR catalysts, which catalyze the reaction of the reducing agent with the nitrogen oxides as selectively as possible, but not with O₂ present in the exhaust gas. The achievable degree of nitrogen oxide reduction depends, among other things, on the amount of reducing agent added. Especially when high reduction rates are desired, i.e., when the residual concentrations of nitrogen oxides become very low, it is advantageous to dose the reducing agents or the chemical reducing equivalents they contain in equimolar or nearly equimolar amounts, or even a molar excess, relative to the nitrogen oxide components.However, this can lead to an undesirable slippage of the reducing agent or its not yet fully oxidized reaction products.

[0004] One solution to this problem, known in the prior art, e.g., from EP 1 229 994 Bl, is the doping of the catalysts with an oxidative catalytic component, which oxidizes the excess reducing agent or its not yet fully oxidized reaction products to harmless products. The problem here, however, is that the reducing agent is already oxidized by the oxidative component before it reacts with the nitrogen oxides to be reduced. For each specific application, the catalytic oxidation and reduction activity of the catalyst must be precisely matched. This significantly complicates the universal application of such catalysts and prevents their practical commercial use. The same applies to physical mixtures of SCR catalysts with selected oxidation catalysts, as proposed, for example, in JP 09000884.

[0005] A more universal solution to the slip problem is the separate post-oxidation of the slip products with suitable oxidation catalysts. Such a two-stage process is described, for example, in EP 3 741 449 A1. Both the catalyst for the catalytic reduction of the nitrogen oxides (here N₂O) and the catalyst for post-oxidation are designed as axially flowed beds with monolithic catalysts, i.e., honeycomb bodies. However, since the flow in the channels of the honeycomb bodies is generally laminar, the achievable conversion of the reducing agents is limited by the mass transport of the reactant. This leads, particularly in the catalyst bed for N₂O reduction, especially with a desired small catalyst volume, to a greater likelihood of slip formation of reducing agents.

[0006] A further disadvantage of honeycomb catalysts is the limited spatial extent of the actual catalytically active mass compared to particulate catalysts. Honeycomb bodies coated with catalytically active material, in particular, typically exhibit only a very thin layer of this material. Under certain reaction conditions, i.e., at slow reaction rates, for example, due to low concentrations of reactants or low temperatures, this can become a limiting factor for the achievable conversion. This is especially true for reactions that proceed relatively slowly due to high activation energies, such as the reduction of N₂O.

[0007] Finally, coated honeycomb catalysts, compared to particulate catalysts, have a lower mass of catalytically active material relative to their filling volume, and therefore a lower intrinsic catalyst reserve. When the catalyst ages or is deactivated by continuous thermal stress or progressive poisoning of the catalyst surface, the reaction—unlike with particulate catalysts—can only shift to the interior of the catalyst to a limited extent. Due to these lower internal reserves, honeycomb catalysts are therefore exhausted more quickly than particulate catalysts and must be replaced more frequently.

[0008] US Patent 2,475,855 A describes a catalytic reactor in which the reactants are fed from bottom to top through a reactor vessel that contains several stacked reactors. The system comprises ordered catalyst beds. The support plate of the lowest catalyst bed has the smallest diameter, and the diameters of the support plates of the catalyst beds arranged above it increase upwards.

[0009] Furthermore, WO 2013 / 087181 A2 specifies a method and a device for the removal of NO. X and N2O from gases known, wherein the gas to be purified is first passed through a first catalyst bed (DeNO₂) x -stage) for selective catalytic NO xThe process involves a reduction reaction (with the addition of NH3 as a reducing agent) and subsequent catalytic decomposition of N2O to N2 and O2 in a second catalyst bed (DeN2O stage). The first catalyst bed of the DeNOx stage, like the second catalyst bed of the DeN2O stage, can be configured as an axially or laterally flowed bed. The DeNOx and DeN2O catalysts used can be shaped bodies of any size and geometry, e.g., cylinders, rings, trilobes, or even honeycomb structures. Several advantageous combinations, i.e., sequential arrangements of catalyst beds, are disclosed. These include the lateral flow through two sequentially arranged catalyst beds, the axial flow through two sequentially arranged catalyst beds, and the axial flow through a first catalyst bed followed by a laterally flowed second catalyst bed.

[0010] EP 2 2286 897 Al describes a device for N2O and NO x -Elimination with two catalyst beds, wherein at least one catalyst bed is designed in the form of a radially flowing hollow cylinder. According to Figure 6, the second catalyst bed can be designed as an axially flowing bed.

[0011] US Patent 3,733,181 A describes a device for cleaning engine exhaust gases comprising a combination of two concentrically arranged radial baskets filled with particulate catalyst, wherein catalytic reduction of nitrogen oxides takes place in the first, inner catalyst bed and catalytic oxidation of hydrocarbons and carbon monoxide takes place in the second catalyst bed. Air is supplied to the exhaust gas to be treated between the two packings.

[0012] WO 2021 / 198150 Al discloses a two-stage catalytic process for the removal of NO X and N2O, with the exhaust gas containing a reducing agent for NO Xadded and then this in a first DeNOx stage to catalytic NO x The reduction process is carried out, and the effluent from this stage, which contains not only N₂O but also unreacted reducing agent, is then passed into a second stage for the decomposition of N₂O and oxidation of the unreacted reducing agent by a cobalt-containing catalyst. The catalyst of the first stage is preferably an Fe-zeolite of the Fe-BEA type. The first stage and / or the second stage can be designed in the form of monolithic structures, in particular honeycomb structures.

[0013] Against this background, the object of the present invention is to enable the catalytic reduction of nitrogen oxides from exhaust gases by means of reducing agents with the smallest possible catalyst volume and a high degradation rate, whereby the amount of catalyst used is as minimal as possible or even zero. Slip occurs at reducing agents or from their not fully oxidized reaction products.

[0014] The invention relates to a device, in particular for the catalytic reduction of nitrogen oxides, comprising a container extending along a longitudinal axis, a first catalyst module, a first support device arranged on an inner wall of the container for supporting the first catalyst module, wherein the first support device extends at least partially around the longitudinal axis along the inner wall of the container and has an inner contour facing the longitudinal axis with a first opening width, in particular a first opening diameter, and a second catalyst module arranged in the container in the direction of the longitudinal axis below the first support device, which has an outer contour facing the inner wall of the container with an outer width, in particular an outer diameter, which is smaller than the first opening width of the first support device, wherein the first catalyst module is configured toThe first catalyst module is configured to be flowed through essentially perpendicular to the longitudinal axis, and the second catalyst module is configured to be flowed through essentially parallel to the longitudinal axis.

[0015] The inner contour is defined as an outline perpendicular to the longitudinal axis of the container, which, viewed along the longitudinal axis of the container, is formed by one or more internally enclosed surfaces of the support structure, facing an operating space enclosed by the first support structure. The outer contour is defined as an outline perpendicular to the longitudinal axis of the container, which, viewed along the longitudinal axis of the container, is formed by one or more externally enclosed surfaces of the catalyst module.

[0016] According to a further aspect of the invention, a system is proposed in which a system containing nitrogen oxides, preferably NOX and N2O, a contaminated exhaust gas stream is generated, with a device described above, which is designed as a device for the catalytic reduction of nitrogen oxides and to which the exhaust gas stream containing the nitrogen oxides can be fed, in particular wherein the exhaust gas stream containing the nitrogen oxides has a pressure of 1 bara to 15 bara, preferably 3 bara to 12 bara, upon entering the container and / or a temperature of 200°C to 650°C, preferably 300°C to 600°C, particularly preferably 300°C to 550°C. Such a plant can, for example, be designed as a plant for the production or processing of chemical or other products or as an energy generation plant, for example for heating or propulsion purposes or for electricity generation.

[0017] The invention further relates to a method for the catalytic reduction of nitrogen oxides in an exhaust gas stream using a previously described device, in particular for the catalytic reduction of nitrogen oxides, wherein nitrogen oxides introduced into the container with the exhaust gas stream are catalytically reduced in the first catalyst module in the presence of a reducing agent, and wherein the unreacted reducing agent and / or the reaction products not completely oxidized in the first catalyst module are catalytically reduced in the second catalyst module. The catalytic reduction of nitrogen oxides is referred to as the first reaction stage, and the catalytic oxidation of the unreacted reducing agent and / or the reaction products not completely oxidized in the first reaction stage is referred to as the second reaction stage. The first reaction stage comprises the first catalyst module and can optionally include further catalyst modules, for example, for N₂O degradation by catalytic decomposition or by catalytic reduction with a reducing agent, or for the catalytic reduction of NO. x The second reaction stage includes the reduction step. The second reaction stage includes the second catalyst module.

[0018] Finally, the invention also relates to a process for the production of nitric acid by catalytic oxidation of ammonia over a primary catalyst and conversion of the NO produced in the process. x-Nitrogen oxides in an absorption tower to nitric acid with the formation of exhaust gases leaving the absorption tower, wherein nitrogen oxides contained in the exhaust gases are catalytically reduced according to a process mentioned above.

[0019] The arrangement of the catalyst modules in the container according to the invention enables a compact design with small catalyst volumes. Because the second catalyst module has an outer width (outer contour) that is smaller than the opening width (inner contour) of the first support structure, not only the first catalyst module but also the second catalyst module can be removed upwards from the container. In this respect, the device according to the invention offers improved accessibility to both catalyst modules for installation, inspection, or catalyst replacement. The compact arrangement of two catalyst modules enables exhaust gas purification processes with a high degradation rate and small catalyst volumes.

[0020] The container is preferably essentially cylindrical in shape.

[0021] According to the invention, the first catalyst module is configured to allow flow essentially perpendicular to the longitudinal axis, and the second catalyst module is configured to allow flow essentially parallel to the longitudinal axis. Such a flow pattern enables a particularly compact design. Preferred embodiments of the first catalyst module

[0022] The first catalyst module can comprise a catalyst basket and a catalyst bed arranged within the catalyst basket, in particular a packed bed of particulate catalyst. The packed bed of particulate catalyst can result in more intimate mixing of the reaction components and, compared to honeycomb catalysts with axial channels, can lead to lower slip of reducing agent at the same catalyst volume and degradation rates.

[0023] The particulate catalyst can be in the form of a shaped body of a predetermined size and geometry, preferably with a geometry that has a large surface area to volume ratio and at the flow through which generates the lowest possible pressure loss. Preferably, the particulate catalyst, or the individual catalyst particles, have the geometry of a cylinder, hollow cylinder, multi-hole cylinder, ring, or in particular a trilobe or star-shaped strand.

[0024] Preferably, the particulate catalyst has an equivalent diameter of the catalyst particles in the range of 1 to 10 mm, particularly preferably from 1 to 5 mm. The equivalent diameter is the diameter of a sphere of the same volume.

[0025] Preferably, the particulate catalyst is a particulate total catalyst.

[0026] Preferably, the first catalyst module comprises a catalyst which facilitates the chemical conversion of NOx or N2O, particularly preferably of NO X and N2O, with reducing agent. Such catalysts are, for example, SCR catalysts known to those skilled in the art, such as those described in Han, L., Cai, S., Gao, M., Hasegawa, J., Wang, P., Zhang, J., Shi, L., Zhang, D., (2019) Selective Catalytic Reduction of NO X with NH3by Using Novel Catalysts: State of the Art and Future Prospects. Chem. Rev., 119 (19), 10916-10976, or in Janssen, F. Handbook of heterogeneous Catalysis, Vol. 4, chap. 1.2 Environmental Catalysis - Stationary Sources, p. 1633-1668, Wiley-VCH, Weinheim, 1997 are listed.

[0027] Preferably, the first catalyst module comprises a V2O5-TiO2-based SCR catalyst, wherein the reducing agent for NO X preferably gaseous NH3 is used.

[0028] Particularly preferably, the first catalyst module comprises the catalytic chemical reduction of N2O or the preferred joint chemical reduction of N2O and NO. XA zeolite catalyst loaded with transition metals or transition metal ions. Preferably selected as transition metals are cobalt, particularly copper, and most preferably iron. Other possible transition metals, which preferably occur together with cobalt, copper, and / or iron in the zeolite, are manganese, vanadium, chromium, or nickel. The zeolites are preferably SiO2-rich so-called "high silica" zeolites with high hydrothermal resistance, exhibiting a molar ratio of [SiO2] to [AlO2] units, and thus a molar Si / Al ratio, of at least 8, preferably at least 9, more preferably at least 10, even more preferably at least 11, most preferably at least 12, and particularly at least 13. Preferably, the zeolites are selected from the group of types MFI, BEA, FER, MOR and MEL or mixtures thereof, preferably of type BEA or MFI, and particularly preferably a BEA zeolite.

[0029] Particularly preferably, the first catalyst module comprises an iron-loaded zeolite catalyst, for example, containing substantially, preferably > 50 wt%, and in particular > 70 wt%, one or more iron-loaded zeolites. For example, in addition to an Fe-BEA zeolite, another iron-containing zeolite, such as an iron-containing zeolite of the MOR type, may be included in the catalyst used according to the invention. For example, the first catalyst bed may comprise a catalyst such as that specified in the Atlas of Zeolite Structure Types, Elsevier, 4th revised Edition 1996, to which explicit reference is made herein.

[0030] Furthermore, the catalyst in the first catalyst module may contain other additives known to those skilled in the art, such as binders.

[0031] The content of transition metals in the zeolites can vary widely, based on the mass of zeolite, for example up to 25%, but preferably from 0.1 to 10%.

[0032] The doping of zeolites with transition metals can be carried out, for example, starting from the H- or, preferably, NH4-form of the zeolites by ion exchange (in aqueous phase or by solid-state reaction) with corresponding salts of the transition metals. The resulting catalyst powders are typically calcined in a chamber furnace in air at temperatures in the range of 400 to 650°C. After calcination, the transition-metal-containing zeolites are washed intensively in distilled water and dried after filtration. These and other relevant methods for loading or doping zeolites with transition metals are known to those skilled in the art. Finally, the transition-metal-containing zeolites obtained in this way are mixed with suitable additives for plasticizing and binders, such as aluminosilicates or boehmite, and extruded, for example, into cylindrical catalyst bodies.

[0033] According to an advantageous embodiment of the invention, the first catalyst module is arranged in the container in a replaceable manner. This offers the advantage that the first catalyst module can be filled either inside the container or, preferably, outside the container by removing the catalyst module. Furthermore, the accessibility of the second catalyst module for installation, inspection, or catalyst replacement can be improved.

[0034] According to an advantageous embodiment of the invention, a holding device of the first catalyst module, in particular a retaining ring of the first catalyst module, rests on the first support device, in particular on a first support ring of the first support device. This allows the first catalyst module to be held on the support device.

[0035] According to an advantageous embodiment of the invention, the holding device is arranged in an upper region of the first catalyst module, so that the first catalyst module, in particular suspended, is arranged essentially below the first support device. In this context, it is advantageous if the first catalyst module has a hollow cylindrical shape and allows flow from the inside to the outside essentially perpendicular to the longitudinal axis, i.e., essentially radially or laterally.

[0036] According to an alternative, advantageous embodiment of the invention, the holding device is arranged in a lower region of the first catalyst module, so that the first catalyst module, in particular in a standing position, is arranged essentially above the first support device. In this context, it is advantageous if the first catalyst module has a hollow cylindrical shape and allows flow from the outside to the inside essentially perpendicular to the longitudinal axis, i.e., essentially radially or laterally.

[0037] Preferably, the holding device of the first catalyst module rests on the first support device such that there is an overlap between the holding device and the support device in a direction perpendicular to the longitudinal axis, preferably in the range of 30 mm to 200 mm, particularly preferably in the range of 50 mm to 150 mm, and most preferably in the range of 80 mm to 120 mm. Such an overlap provides a sufficient surface area and thus ensures safety for supporting the first catalyst module, as well as a sufficient sealing surface.

[0038] The width of the support device, in particular of the first support ring, in a direction perpendicular to the longitudinal axis is preferably 20 mm to 300 mm, particularly preferably 40 mm to 250 mm, and most preferably 60 mm to 200 mm. The width of the retaining device, in particular of a first retaining ring projecting over the outer edge of the first catalyst basket, in a direction perpendicular to the longitudinal axis is preferably 30 mm to 500 mm, particularly preferably 50 mm to 300 mm, and most preferably 80 mm to 200 mm.

[0039] According to an advantageous embodiment, the first support structure is welded to the inner wall of the container. Preferably, the first catalyst module is bolted to the first support structure, and particularly preferably bolted in such a way that bolts connected to the support structure, which are distributed as evenly as possible around the circumference of the first support structure, are inserted into bores in the first support structure. The bolts can be formed or arranged, in particular, on a flange. The bores of the first support structure can be formed on the first support ring. Bolt-bore pairings can, in particular, facilitate the positioning and assembly of the first catalyst module.

[0040] The first support structure can have one or more support ribs to increase strength and load-bearing capacity. The support ribs are preferably arranged on the inner wall of the container, and in particular welded to it. The support ribs can be evenly spaced along the circumference and, in particular, support the bearing ring.

[0041] Preferably, a first sealing element, in particular a seal that is either mounted or inserted, is arranged between the first support device and the first holding device. The sealing element largely reduces or prevents bypass or leakage flows. This is not only important for the effectiveness of the first reaction stage with regard to achieving the highest possible degradation rates of nitrogen oxides, especially NOₓ. X, but above all for the effectiveness of the second catalyst module. Even the smallest bypass flows around the first catalyst module, which necessarily contain the full amount or concentration of added reducing agent, can lead to a significant additional load of reducing agent on the downstream, second catalyst module.

[0042] To further prevent bypass flow through the first catalyst module, which is preferably filled with particulate catalyst, this module is mounted on the inner and outer walls in the upper area. The catalyst bed is provided with a gas-impermeable cover, e.g., in the form of welded-on sheets, so that horizontal or radial flow through the catalyst bed in the upper covered portion is impossible. The height of the cover in the horizontal or axial direction is preferably 0.1 to 5 times the catalyst bed thickness (distance between the inner and outer edges of the first catalyst module, measured on the side facing the catalyst charge). The gas-impermeable cover in the upper region of the first catalyst module, particularly the first catalyst basket, prevents flow over the catalyst bed if it has not settled down to the axially upper cover ("lid") of the first catalyst basket. This can occur, for example, if the catalyst bed settles during the operation of the process.Otherwise, a bypass flow caused by overflow could lead to an undesirable overload of the downstream, second catalyst module with reducing agent. Preferred embodiments of the second catalyst module

[0043] Preferably, the second catalyst module is designed to allow flow essentially parallel to the longitudinal axis of the container, i.e., to allow flow essentially axially.

[0044] Preferably, the second catalyst module comprises an oxidation catalyst, for example, an oxidation catalyst for the oxidation of volatile organic or inorganic compounds (VOCs or VICs). The oxidation catalyst can consist of noble metals (Pt, Pd, Rh) supported on surface-rich oxides and / or ceramic or metallic substrates, transition metal oxides (e.g., of Fe, Mn, Cu, Cr, Co, Ni, etc.), or metal-loaded zeolites. Such catalysts are described, for example, in "Handbook of Heterogeneous Catalysis," Wiley-VCH, edited by Ertl, Knötzinger, Schüth, Weitkamp, ​​2nd ed. 2008, Volume 5, Chapter 11.5 "Solid Catalysts for the Oxidation of Volatile Organic Compounds."

[0045] The second catalyst module can be provided with a particulate catalyst or preferably with a packing of monolithic catalyst elements, e.g. containing monolithic honeycomb bodies or coated with catalytically active materials.

[0046] According to an advantageous embodiment of the invention, the second catalyst module comprises one or more monolithic catalyst elements, preferably honeycomb bodies, which preferably have channels and are arranged such that the channels are aligned in the direction of the longitudinal axis of the container and are subjected to a substantially axial flow, preferably both axially and through which the fluid flows. This enables high efficiency of the second catalyst module at low pressure.

[0047] In an advantageous embodiment, the second catalyst module comprises only one, appropriately sized honeycomb structure, which preferably has a metallic base (substrate).

[0048] According to an advantageous embodiment of the invention, several honeycomb bodies are combined to form a honeycomb module, and the second catalyst module comprises several individually replaceable honeycomb modules. This allows bypass flows to be effectively suppressed. The individual (monolithic) honeycomb bodies are also referred to as bricks, and the honeycomb modules as cans. The honeycomb modules can have metal frames. Preferably, two, four, or six honeycomb bodies are combined in one honeycomb module. The honeycomb bodies can have different cross-sectional or end faces, e.g., with triangular, hexagonal, or preferably rectangular, in particular square, geometries.For a rectangular cross-section, the first edge length is, for example, in the range of 5 to 20 cm and the second edge length is also in the range of 5 to 20 cm; preferably, the first edge length is in the range of 10 to 15 cm and the second edge length is also in the range of 10 to 15 cm. The height of a honeycomb structure is preferably in the range of 5 to 25 cm, more preferably in the range of 7.5 to 15 cm. The cell density of the catalyst honeycombs (expressed as channels per square inch) is preferably 120 to 500 cpsi, more preferably 180 to 420 cpsi.

[0049] Preferably, the individual honeycomb modules within the second catalyst module are placed on a support structure, for example, a grating, and are pressed down and fixed onto it by clamps, clips, brackets, or similar devices, which are, for example, fixed to the underside of the grating by threaded rods. In this way, a virtually complete seal between the end faces of the honeycomb modules and the grating can be achieved.

[0050] According to an advantageous embodiment of the invention, the honeycomb bodies or honeycomb body modules in the second catalyst module are arranged in several layers offset along the longitudinal axis. Preferably, the honeycomb body modules are arranged in 2 to 5 layers, particularly preferably in 2 to 3 layers. A gap can be provided between the layers, i.e., between the end faces of the honeycomb bodies, which is preferably in the range of 3 to 30 mm, particularly preferably in the range of 4 to 20 mm. This gap allows for intermediate, and in particular radial, mixing of the gas stream exiting a first layer of honeycomb bodies. Furthermore, it prevents any potential slippage of unreacted reducing agent and / or its not yet fully oxidized reaction products from the first layer of honeycomb bodies into a subsequent, second layer of honeycomb bodies.

[0051] Preferably, the honeycomb bodies or honeycomb body modules are arranged such that they occupy a usable flow area of ​​the cross-sectional area of ​​the second catalyst module, which is greater than 60% of the cross-sectional area of ​​the second catalyst module, preferably greater than 75% of the cross-sectional area of ​​the second catalyst module.

[0052] The gaps that arise in the edge area of ​​the second catalyst module are preferably covered with rectangular honeycomb body modules if they cannot be easily covered. The cells are not filled with specially cut honeycomb cores, but sealed with blanking plates. This has the advantage that when replacing worn honeycomb cores, only standardized honeycomb core modules need to be exchanged, and no special adjustments are necessary.

[0053] According to an advantageous embodiment of the invention, the second catalyst module is arranged in the container in an interchangeable manner. The second catalyst module can therefore be easily removed from the container.

[0054] According to an advantageous embodiment of the device according to the invention, it has a second support device arranged on an inner wall of the container, by which the second catalyst module is supported. The second support device extends at least partially around the longitudinal axis along the inner wall of the container and has an inner contour facing the longitudinal axis with a second opening width, in particular a second opening diameter, which is smaller than the first opening width of the first support device. This dimensioning makes it possible for a second catalyst module, which is inserted from above through an opening in the first support device, to be supported by the second support device. The second support device may have a second bearing ring.

[0055] According to an advantageous embodiment of the invention, the second support device preferably prevents undesired lateral flow around the second catalyst module. The width of the second support device, in particular of the second support ring, in a direction perpendicular to the longitudinal axis is preferably 30 mm to 300 mm, more preferably 50 mm to 250 mm, and most preferably 80 mm to 200 mm.

[0056] According to an advantageous embodiment of the invention, a holding device for the second catalyst module, in particular a retaining ring of the second catalyst module, rests on the second support device, specifically on a second support ring of the second support device. This allows the second catalyst module to be held on the second support device. The width of the holding device, in particular a second retaining ring projecting beyond the outer edge of the second catalyst basket, in a direction perpendicular to the longitudinal axis, can have a radial dimension of 30 mm to 300 mm, preferably 30 mm to 300 mm, more preferably 50 mm to 150 mm, and particularly preferably 80 mm to 120 mm.

[0057] According to an advantageous embodiment of the invention, the holding device is arranged in an upper region of the second catalyst module, so that the second catalyst module, in particular suspended, is arranged essentially below the second support device.

[0058] Preferably, the holding device, in particular the retaining ring of the second catalyst module, rests on the second support device, in particular the second support ring, in such a way that an overlap of the catalyst module with the support device is present in a direction perpendicular to the longitudinal axis. The overlap is preferably in the range of 30 mm to 250 mm, particularly preferably in the range of 50 mm to 150 mm, and most preferably in the range of 80 mm to 120 mm. Such an overlap provides a sufficient surface area and thus safety for supporting the second catalyst module.

[0059] According to an advantageous embodiment, the second support structure is welded to the inner wall of the container. The second catalyst module can be bolted to the second support structure, preferably such that bolts connected to the second support structure, which are distributed as evenly as possible around its circumference, are inserted into bores in the second support structure. The bolts can be formed or arranged, in particular, on a flange. The bores in the second support structure can be formed on the second support ring. The positioning and assembly of the second catalyst module can be facilitated, in particular, by means of a bolt-bore pairing.

[0060] Preferably, the second support ring is supported by radially oriented support ribs welded perpendicular to the container wall and to the second support ring.

[0061] The outer diameter of the second catalyst module is preferably at least 10 mm, particularly preferably at least 20 mm, and most preferably at least 40 mm smaller than the inner diameter of the first support ring for the first catalyst basket.

[0062] Preferably, a second sealing element, in particular a seal that is either mounted or inserted, is arranged between the second support device and the second holding device. This sealing element largely reduces or prevents bypass or leakage flows.

[0063] According to an advantageous embodiment of the invention, it is provided that a downwardly projecting outer wall of the second catalyst module rests on the second support device, in particular on a second support ring of the second support device.

[0064] Preferably, the outer wall of the second catalyst module on the gas-outflowing side preferably projects more than 10 mm, in particular more than 20 mm, and most preferably more than 40 mm beyond the lower end (outlet surface) of the catalyst module.

[0065] Preferably, a circumferential second sealing element, in particular a seal placed on top or inserted into the wall, is arranged between the second support structure and the downwardly projecting outer wall. This sealing element largely reduces or prevents bypass or leakage flows.

[0066] According to a preferred embodiment of the invention, the second catalyst module, which in particular rests on the second support structure via its outer wall, is clamped relative to the second support structure by a clamping device arranged on the inner wall of the container. The clamping device can consist of a retaining ring or several retaining elements. The clamping device comprises clamping plates, each with a radial dimension in the range of 30 mm to 250 mm, preferably in the range of 40 mm to 200 mm, and particularly preferably in the range of 50 mm to 150 mm. The clamping device may include, in particular, S-shaped clamping plates that serve as hold-downs. A sufficiently high contact pressure can be generated to stabilize the second catalyst bed by means of the clamping plates, preferably 4 to 36, more preferably 8 to 24. Furthermore, the clamping plates enable quick, easy, and non-destructive assembly and disassembly of the second catalyst module. In addition, the clamping plates can be used to center and / or variably position the second catalyst module.

[0067] Alternatively or additionally to the clamping device and / or the attachment of a second sealing element and / or the bolting of the second catalyst module to the second support structure, the second catalyst module can be welded to the second support structure. Welding provides a combination of fastening, positioning, and sealing, with the weld seam acting as a sealing element. Furthermore, it offers the advantage of partially or completely preventing any deterioration of flow conditions caused by clamping plates positioned in the flow lines (e.g., due to turbulence and friction losses), and increasing the frontal area of ​​the second catalyst module.

[0068] According to an advantageous embodiment of the invention, the distance between the first catalyst module and the second catalyst module is in the range of 0.2 m to 3 m, preferably in the range of 0.5 m to 1.5 m, and more preferably in the range of 0.5 m to 0.8 m. The ratio of this distance to the width of the second catalyst module in a direction perpendicular to the longitudinal axis is preferably in the range of 0.1 to 1.2, and more preferably in the range of 0.15 to 0.8. If the second catalyst module has a non-circular wall, for example, a rectangular, polygonal, or angled shape, the diameter value to be applied in the aforementioned ratio corresponds to the diameter of a circle with the same area (relative to the frontal area of ​​the module in the axial direction).By selecting such a distance between the first and second catalyst modules, it can be ensured that the second catalyst module is subjected to a uniform flow. This results in a uniform stress on the catalyst of the second catalyst module. Local or point-like overloads caused by flow strands can be avoided. Local or point-like breakthrough of reducing agent and / or its not yet fully oxidized reaction products can be counteracted. Optional third catalyst module

[0069] According to an advantageous embodiment, the device comprises a third catalyst module and a third support device arranged on an inner wall of the container for supporting the third catalyst module, wherein the third support device extends at least partially around the longitudinal axis along the inner wall of the container and one of the The first catalyst module has an inner contour facing the longitudinal axis with a third opening width, in particular a third opening diameter, which is larger than the first opening width of the first support device. Preferably, the first catalyst module has an outer contour facing the inner wall of the container with an outer width, in particular an outer diameter, which is smaller than the third opening width of the third support device. If the first catalyst module has a retaining device, for example a retaining ring, this preferably has an outer diameter which is smaller than the third opening width of the third support device.

[0070] The third catalyst module can be part of a first reaction stage for the catalytic degradation of nitrogen oxides, i.e., for example, for the degradation of N2O by catalytic decomposition or by catalytic reduction with a reducing agent, or also for the catalytic reduction of NO. x -Reduction in an exhaust gas stream.

[0071] Preferably, the third catalyst module is configured to be flowed through substantially perpendicular to its longitudinal axis. Particularly preferably, the third catalyst module is configured to be flowed through substantially in a direction opposite to the direction in which the first catalyst bed is substantially flowed through. For example, the third catalyst bed can be flowed through radially from the outside inwards, and the first catalyst bed radially from the inside outwards.

[0072] According to an advantageous embodiment, a holding device of the third catalyst module, in particular a retaining ring of the third catalyst module, rests on the third support device, specifically on a third support ring of the third support device. Preferably, the holding device of the third catalyst module is arranged in a lower region of the third catalyst module, so that the third catalyst module, in particular in a standing position, is arranged substantially above the third support device.

[0073] The advantageous configurations described in connection with the first catalyst module can also be applied, alone or in combination, to the third catalyst module. Preferred design of the container

[0074] According to an advantageous embodiment, the container has an upper container part and a lower container part arranged in the direction of the longitudinal axis below the upper container part, which are preferably connected to each other by a container flange, wherein the first support device and the second support device and / or the third support device, if present, are arranged in the lower container part. Preferred procedural configurations

[0075] According to the invention, the first catalyst module is configured for the catalytic reduction of nitrogen oxides introduced into the container and contained in an exhaust gas stream in the presence of a reducing agent, and the second catalyst module is configured for the catalytic oxidation- is configured for the removal of reducing agent that is not converted in the first catalyst module and / or reaction products that are not fully oxidized in the first catalyst module.

[0076] According to an advantageous embodiment, the reducing agent for the reduction of nitrogen oxides is selected from the group comprising: - NH3, - Urea - Hydrocarbons, especially methane, ethane, propane, butane, - LPG, - Natural gas, - CO, - H2.

[0077] The reducing agent may comprise one or preferably several components of the above group.

[0078] According to an advantageous embodiment, it is provided that the reducing agent is dosed at least stoichiometrically, preferably superstoichiometrically, i.e., that an equimolar amount, preferably a molar excess, of reducing equivalents contained in the reducing agent, relative to the nitrogen oxide to be chemically reduced, is present in or dosed into the exhaust gas stream entering the device according to the invention.

[0079] The reducing agent for the reduction of NO X preferably comprises NH3 and / or urea, in particular NH3.

[0080] In preferred embodiments, NH3 is converted to NO. x -Reduction in an amount of 0.9 to 2.5 molar proportions, preferably 1.0 to 1.6 molar proportions, more preferably 1.0 to 1.4 molar proportions, and even more preferably 1.0 to 1.2 molar proportions, based on a molar proportion of NO to be chemically reduced X .

[0081] The reducing agent for the reduction of N2O includes in particular NH3 and / or hydrocarbons.

[0082] In preferred embodiments, the reducing agent for N2O is NH3, which is preferably used in an amount of 0.5 to 3.0 molar proportions, more preferably in an amount of 0.7 to 2.5 molar proportions, and even more preferably in an amount of 0.8 to 2.0 molar proportions, based on a molar proportion of chemically reduced N2O, i.e., based on the amount of N2O contained in the exhaust gas at the entry into the first reaction stage.

[0083] In other preferred embodiments, the reducing agent for N2O is a hydrocarbon or a mixture of several hydrocarbons, preferably in an amount of 0.2 to 1.0 molar proportions, more preferably in an amount of 0.2 to 0.7 molar proportions, based on the molar amount of N2O in the exhaust gas at the entry into the first reaction stage.

[0084] This amount of reducing agent for N2O is additive to any amount of reducing agent that may be required for NO. x -Reduction.

[0085] In the chemical reduction of nitrogen oxides, the reducing agent used is oxidized. Depending on the type of reducing agent used, several oxidized reaction products may be formed, differing in their degree of oxidation. For example, in the particularly favored reduction of N₂O with hydrocarbons according to the following reaction equations, not only CO₂ but also a significant amount of CO can be formed: (2n+l) N2O + C n H 2n+2 (2n+l) N2+ n CO + (n+1) H2O 4n N2O + C n H 2n+2 4n N2+ n CO2+ 2n H2O

[0086] When using NH3 as a reducing agent for NO according to the invention Xand / or N2O, the exhaust gas exiting the first reaction stage has an NH3 concentration of preferably at most 20 ppmv, more preferably at most 10 ppmv, even more preferably at most 5 ppmv and particularly preferably at most 3 ppmv.

[0087] In the use of hydrocarbons as a reducing agent for N2O according to the invention, the exhaust gas exiting the first reaction stage has a CO concentration of preferably at most 200 ppmv, more preferably at most 150 ppmv, even more preferably at most 100 ppmv and particularly preferably at most 50 ppmv.

[0088] The second reaction stage, as described in the invention, serves to oxidize reducing agents that did not react at all in the first catalyst module during the chemical reduction of the nitrogen oxide. Furthermore, the second catalyst module serves to further oxidize any oxidation products formed from the reducing agent in the first catalyst module that are not yet completely oxidized. Complete oxidation here means the oxidation of the reducing agent or its not yet completely oxidized reaction products to an oxidation state that allows release to the environment; however, the oxidation state achieved does not necessarily have to be the highest theoretically possible oxidation state. If the reducing agent is, for example, methane (CH4), then carbon monoxide (CO) is a reaction product that is not yet completely oxidized and, according to the invention, is preferentially further oxidized to carbon dioxide (CO2) in the second reaction stage.If, on the other hand, the reducing agent is ammonia (NH3), then nitrogen (N2) is already a completely oxidized reaction product and further oxidation, e.g. to NO or NO2, is not desired.

[0089] According to an advantageous embodiment of the second reaction stage, tailored to the performance data of the first reaction stage, the exhaust gas exiting the second reaction stage has an NH3 concentration of preferably at most 5 ppmv, more preferably at most 3 ppmv, even more preferably at most 2 ppmv and particularly preferably at most 1 ppmv and a CO- Concentration preferably of at most 90 ppmv, more preferably of at most 60 ppmv, even more preferably of at most 40 ppmv and particularly preferably of at most 20 ppmv.

[0090] Furthermore, the residual concentration of NO is XThe residual NOx concentration in the exhaust gas at the outlet of the second reaction stage is preferably at most 20 ppmv, more preferably at most 10 ppmv, even more preferably at most 5 ppmv, and particularly preferably at most 2 ppmv. A residual NOx concentration of nearly 0 ppm, i.e., less than 1 ppm, is especially preferred. The residual N₂O concentration in the exhaust gas at the outlet of the second reaction stage is preferably at most 50 ppmv, more preferably at most 30 ppmv, even more preferably at most 10 ppmv, and particularly preferably at most 5 ppmv. According to an advantageous embodiment, the exhaust gas stream containing the nitrogen oxides has a temperature in the range of 200 °C to 650 °C, preferably 300 °C to 600 °C, particularly preferably 300 °C to 550 °C, upon entering the container.

[0091] According to an advantageous embodiment, it is provided that a first space velocity of the first reaction stage is in the range of 2,000 h⁻¹. -1 up to 50,000 h 1preferably 3,000 h -1 up to 30,000 h 1 , especially preferred 5,000 h -1 up to 25,000 h -1 is being discontinued.

[0092] According to an advantageous embodiment, it is provided that a second space velocity of the second reaction stage is in the range of 20,000 h⁻¹. -1 up to 300,000 h 1 preferably 30,000 h -1 up to 250,000 h 1 especially preferred 30,000 h -1 up to 200,000 h 1 , is being discontinued.

[0093] The aforementioned space velocities are defined as the quotient of the exhaust gas volume flow rate, based on its standard conditions, and the volume of the catalyst bed through which the exhaust gas flows, i.e., the volume of the catalyst bed or catalyst packing through which the exhaust gas flows. This means that the space velocity can be adjusted according to the invention by adjusting the exhaust gas volume flow rate and / or by adjusting the catalyst volume. The standard conditions correspond to the standard conditions defined in DIN 1343 at temperature = 273.15 K and pressure = 1.01325 bara.

[0094] According to an advantageous embodiment, it is provided that a first space velocity of the first catalyst module and a second space velocity of the second catalyst module are set such that the ratio of the first space velocity to the second space velocity is in the range of 1 / 2 to 1 / 20, preferably in the range of 1 / 3 to 1 / 10.

[0095] According to an advantageous embodiment, the exhaust gas stream containing the nitrogen oxides is provided that, upon entering the container, it has a pressure of 1 bara to 15 bara, preferably 3 bara to 12 bara and / or a temperature of 200°C to 650°C, preferably 300°C to 600°C, particularly preferably 300°C to 550°C. Preferred applications

[0096] The device and method according to the invention are preferably used in plants in which nitrogen oxides, preferably NOₓ, are used. X and N2O-laden exhaust gases These can include, for example, production facilities for the manufacture or processing of chemical or other products, or energy generation facilities, for example for heating or propulsion purposes or for electricity generation.

[0097] The device and method according to the invention are particularly advantageous in plants in which the exhaust gases loaded with nitrogen oxides are present at elevated pressures of 1.0 bara to 15 bara, preferably 1.2 bara to 12 bara, more preferably 1.5 bara to 12 bara, most preferably 2 bara to 12 bara, and particularly preferably 3.0 bara to 12 bara.

[0098] The device and method according to the invention are particularly advantageous in plants for the production of chemical products, such as nitric acid, caprolactam, adipic acid or glyoxalic acid.

[0099] The device and method according to the invention can be used particularly advantageously in a plant or process for the production of nitric acid.

[0100] The industrial-scale production of nitric acid generally involves the catalytic oxidation of ammonia over a primary catalyst, typically a precious metal catalyst based on platinum / rhine (the Ostwald process). In this process, NH3 is very selectively oxidized to NO, which is then further oxidized to NO2 and finally reacted with water in an absorption tower to produce nitric acid. The platinum / rhine catalysts are formed as thin meshes and spread over a wide area in a burner. A gas mixture consisting of approximately 8–12 vol% ammonia and air flows through the meshes, resulting in a temperature of approximately 850–950°C at the meshes due to the exothermic nature of the reaction. Typically, both the catalytic oxidation of NH3 and the absorption of the NOx formed in the absorption tower are carried out at elevated pressures.If catalytic oxidation and absorption occur at the same pressure, the system is called a single-pressure system. If absorption occurs at higher pressures than catalytic oxidation, which is particularly common with high product capacities, the system is called a dual-pressure system. The pressure is usually generated by compressors that compress the required combustion air to the desired operating pressure, typically 3–12 bara, before vaporized NH3 is added to it prior to entering the catalytic burner. In the dual-pressure process, an additional second compression stage or compressor is present, located between the NH3 burner and the absorption tower. The NOx-containing process gas is gradually cooled after leaving the NH3 burner via various heat exchangers before entering the absorption tower.After the product acid is washed out in the absorption tower, the residual gas leaving the absorption tower is gradually reheated via various heat exchangers, depending on the process variant, to temperatures between approximately 300°C and 600°C, before the residual gas is then expanded again via an expander (residual gas turbine) and released into the atmosphere. An overview of the process of nitric acid production and its associated processes... Various process variants are given, for example, in Ullmann's Encyclopedia of Industrial Chemistry, Vol. A 17, VCH Weinheim (1991).

[0101] Depending on the design of the absorption tower, i.e., its size, operating pressure, and cooling water temperature, the residual gas leaving the absorption tower typically exhibits residual concentrations of NO. XThe residual gas contains approximately 100–800 ppmv, and in some cases even more than 1000 ppmv. Furthermore, the residual gas also contains N₂O, depending on the plant type and operating mode, in the range of approximately 500–2500 ppmv, unless this has been reduced beforehand by separate measures, e.g., secondary measures. The N₂O is produced during the catalytic oxidation of NH₃ in the NH₃ burner, where it does not burn completely selectively to NO. No significant absorption of the formed N₂O occurs in the absorption tower.

[0102] A common technical measure for N₂O reduction is the use of catalysts for N₂O decomposition, so-called secondary catalysts, which are installed directly below, i.e., downstream in the process gas direction, the Pt / Rh network catalysts and operated at the high temperatures prevailing there, approximately 850–950°C. A general overview of the fundamental possibilities for N₂O reduction in plants for industrial HNO₃ production, which also describes the so-called secondary measures and secondary catalysts, can be found in Perez-Ramirez, J., Kapteijn, F., Schöffel, K., Moulijn, JA, (2003) Formation and control of N₂O in nitric acid production: Where do we stand today? Appl. Catal. B. 44 (2), 117–151.

[0103] Preferably, the device according to the invention is integrated into a plant for the production of nitric acid (HNO3). In particular, the device according to the invention is arranged in the residual gas stream of the HNO3 production plant downstream of the absorption tower and upstream of the residual gas turbine, preferably downstream of the last heat exchanger before the residual gas enters the residual gas turbine. With the aforementioned integration of the device according to the invention for nitrogen oxide reduction into the residual gas stream of HNO3 production, it is hereinafter referred to as a tertiary denitrification device.

[0104] According to an advantageous embodiment, the plant for the production of nitric acid comprises, in addition to the aforementioned tertiary denitrification device, a secondary catalyst for N2O degradation, i.e., for the catalytic decomposition of N2O into N2 and O2. The secondary catalyst is preferably arranged directly below, i.e., directly downstream of, the catalyst for NH3 oxidation (primary catalyst), and preferably directly below the precious metal-containing mesh catalysts.

[0105] The secondary catalyst preferably contains transition metal (mixed) oxides such as Co, Fe, Mn, or Cu oxides combined with refractory oxides such as Al₂O₃, MgO, ZnO, ZrO₂, or CeO₂ as catalytic active components. The catalytically active components preferably exhibit a perovskite structure, perovskite-like structures, or spinel structures, as described, for example, in (N. Gunasekaran et al., Catal. Lett. (1995), 34 (3,4), pp. 373-382). The use of cobalt-containing oxides or mixed oxides, such as Co3O4 or LaCoO3, is particularly advantageous.

[0106] Secondary catalysts are preferably used as bulk materials with a high geometric surface area, e.g., as star-shaped extrudates, multi-hole cylinders or trilobes, or even as honeycomb structures. The use of 3D-printed shapes as secondary catalysts is particularly preferred, as these are characterized not only by a high geometric surface area but also by particularly low pressure losses.

[0107] Preferably, the ratio of the geometric surface area to the bulk volume of the secondary catalysts that can be used according to the invention is 500 m³. 2 / m 3 up to 2000 m 2 / m 3 , preferably 700 m 2 / m 3 up to 1500 m 2 / m 3 , even more preferred 800 m 2 / m 3 up to 1200 m 2 / m 3 .

[0108] Due to the aforementioned surface-to-volume ratios, high N₂O degradation rates can be achieved with relatively small amounts of catalyst and the associated low pressure losses. To limit the pressure losses caused by the secondary catalysts, the N₂O degradation by the secondary catalysts is, according to the invention, limited to a maximum of 95%, preferably a maximum of 90%, and particularly a maximum of 85%.

[0109] This results in optimal synergy with the tertiary denitrification device. Here, if necessary, in addition to the NOₓ xFurther reduction of N₂O allows for a complete reduction of N₂O to values ​​exceeding 95%, preferably more than 98%, and particularly more than 99%. This is possible because the excess dosage of reducing agent in the tertiary denitrification device is not limited by its specific two-stage design, especially by the second reaction stage for the oxidation of unreacted reducing agent and / or its reaction products that were not completely oxidized in the first reaction stage. This is particularly true when, in the especially preferred combination of secondary measure or secondary catalyst and tertiary denitrification device, a pre-reduction of N₂O takes place at the secondary catalyst, so that the absolute amount of N₂O, and thus also the absolute amount of reducing agent required for N₂O in the tertiary denitrification device, is drastically reduced, i.e., to approximately 1 / 5 to 1 / 20.

[0110] Consequently, a preferred embodiment of the process for the production of nitric acid comprises a secondary catalyst for N₂O decomposition, which is arranged downstream of the primary catalyst for the oxidation of ammonia. Particularly preferably, the N₂O reduction effected by the secondary catalyst for N₂O decomposition is a maximum of 95%, more preferably a maximum of 90%, and more particularly a maximum of 85%.

[0111] Further details, features, and advantages of the invention will become apparent from the drawings and from the following description of preferred embodiments with reference to the drawings. The drawings merely illustrate exemplary embodiments of the invention, which do not limit the scope of the invention. Brief description of the characters

[0112] Fig. 1 schematically shows a first embodiment of a device according to the invention.

[0113] Fig. 2 schematically shows a second embodiment of a device according to the invention.

[0114] Fig. 3 schematically shows a third embodiment of a device according to the invention.

[0115] Fig. 4 schematically shows a fourth embodiment of a device according to the invention.

[0116] Fig. 5 schematically shows a fifth embodiment of a device according to the invention. Embodiments of the invention

[0117] Figure 1 schematically shows a first embodiment of a device 1 according to the invention for the catalytic reduction of nitrogen oxides, which can be used, for example, for exhaust gas aftertreatment in a system for the production of nitric acid, generating exhaust gases. The device 1 is particularly suitable for cleaning an exhaust gas stream containing nitrogen oxides, which, upon entering a container 2 of the device 1, has a pressure of 1 bar to 15 bar, preferably 3 bar to 12 bar, and / or a temperature of 200°C to 650°C, preferably 300°C to 600°C, and most preferably 300°C to 550°C.

[0118] The device 1 comprises a container 2 extending along a longitudinal axis L. According to the exemplary embodiment, the container has a circular cross-section, i.e., is essentially cylindrical. The container 2 comprises a container wall 7 and an inlet 3 for introducing the exhaust gas from the combustion. The inlet 3 is located at the top of the container 2. At the bottom of the container 2 is an outlet 5 through which the exhaust gas, purified of nitrogen oxides in the device 1, can be discharged. Between the inlet 3 and the outlet 5 are two catalyst modules 10, 20, through which the exhaust gas flows sequentially. In the first catalyst module 10, introduced nitrogen oxides are reduced in the presence of a reducing agent, for example, NH3.In the second catalyst module 20, the reducing agent and / or its reaction products that were not fully oxidized in the first catalyst module 10 are oxidized.

[0119] The first catalyst module 10 comprises a first catalyst bed 11 through which flow is essentially perpendicular to the longitudinal axis L, and the second catalyst module 20 comprises a second catalyst bed 21 through which flow is essentially parallel to the longitudinal axis L.

[0120] The first catalyst bed 11 is designed as a radial basket and is essentially permeated by the exhaust gas to be processed, flowing from the radial outside to the radial inside. The flux F of the exhaust gas is indicated by arrows in Fig. 1.

[0121] The first catalyst bed 11 has a gas-impermeable cover 9 on one side facing the inlet 3. The cover 9 prevents axial flow through the first catalyst bed 11 and deflects the exhaust gas to be cleaned towards the container wall 7. The cover 9 also extends from the top of the catalyst bed 11, at least partially, along an inner wall 13 and an outer wall 15 of the first catalyst bed 11. A particulate catalyst 17 is arranged as bulk material between the inner wall 13 and the outer wall 15. The particulate catalyst is a catalyst that facilitates the chemical conversion of NO. X or N2O, especially preferably NO X and N2O, with reducing agent, here NH3, promotes.

[0122] Furthermore, the first catalyst bed 11 has a first retaining ring 19 on a side facing the outlet 5. The first catalyst bed 11 is supported by a first support device 12 and is bolted to it. The first support device 12 comprises a first support ring 12.1 and several first support ribs 12.2. The first support ribs 12.2 are spaced uniformly along a circumferential direction of the device 1 and are welded to the inner side of the container wall 7. A first sealing element, not visible in Figure 1, is arranged between the retaining ring 19 and the first support ring 12.1. In the first embodiment shown in Figure 1, the first catalyst bed 11 can be described as having a vertical arrangement in the container 2.

[0123] The second catalyst bed 21 comprises an oxidation catalyst. According to the exemplary embodiment, the second catalyst bed 21 has several honeycomb bodies with honeycomb channels oriented along the longitudinal axis E of the housing 2. Several honeycomb bodies, for example two, four, or six, are grouped together to form a honeycomb body module and arranged in a layer on a grid. The second catalyst bed 21 comprises several layers of honeycomb body modules offset along the longitudinal axis and spaced apart from one another. The second catalyst module 20 has an outer contour facing the inner wall of the container 2 with an outer width, in particular an outer diameter, that is smaller than the first opening width of the first support device.

[0124] The second catalyst bed 21 is supported from below by a second support structure 22, which is arranged on the inside of the container wall 7. The second support structure 22 comprises a second support disc 22.1 and several second support ribs 22.2. The second catalyst bed 21 is welded to the second support structure 22 or alternatively connected via a sealing element.

[0125] Furthermore, a clamping device 23 is provided on the upper side of the second catalyst bed 21, which fixes and centers the catalyst bed 21 relative to the support device 21. The clamping device- Direction 23 comprises retaining elements designed as S-shaped clamping plates. These clamping plates allow pressure to be applied to the second catalyst bed 21. In the first embodiment shown in Figure 1, the second catalyst bed 21 can be described as being arranged vertically in the container 2.

[0126] The container 2 has an upper container part 2.1 and a lower container part 2.2 arranged below the upper container part 2.1 in the direction of the longitudinal axis L. The two container parts 2.1, 2.2 are connected to each other via a container flange 50. The first support device 12 and the second support device (22) are both arranged in the lower container part 2.2.

[0127] Figure 2 schematically illustrates a second embodiment of a device 1 according to the invention. The device 1 according to the second embodiment essentially corresponds to the device according to the first embodiment. In contrast to the first embodiment, the second catalyst module 20 is suspended in the device 1 according to the second embodiment. A second retaining ring 29, located on the upper side of the second catalyst module 20, rests on the second support ring 22.1. A sealing element (not shown) may be arranged between the second retaining ring 29 and the second support ring 22.1. The retaining ring 29 and the support ring 22.1 are preferably screwed together.

[0128] Figure 3 schematically illustrates a third embodiment of a device 1 according to the invention. The device 1 according to the third embodiment essentially corresponds to the device according to the first embodiment. In contrast to the first embodiment, the first catalyst module 10 is suspended in the device 1 according to the second embodiment. A first retaining ring 19, located on the upper side of the first catalyst module 10, rests on the first support ring 12.1. A sealing element (not shown) may be arranged between the first retaining ring 19 and the first support ring 12.1. The retaining ring 19 and the support ring 12.1 are preferably screwed together.

[0129] Figure 4 schematically shows a fourth embodiment of a device 1 according to the invention. The device 1 according to the fourth embodiment essentially corresponds to the device according to the first embodiment. In contrast to the first embodiment, both the first catalyst module 10 and the second catalyst module 20 are arranged suspended.

[0130] The exemplary embodiments of devices for the catalytic reduction of nitrogen oxides described above enable a compact design. High reduction rates of nitrogen oxides can be achieved.

[0131] Figure 5 schematically shows a fifth embodiment of a device 1 according to the invention. The device 1 according to the fifth embodiment essentially corresponds to the device according to the third embodiment. In contrast to the third embodiment, a third catalyst module 30 is additionally provided. The third catalyst module 30 can be part of the first reaction stage, for example for the catalytic degradation of nitrogen oxides, i.e. for example for the degradation of N2O by catalytic decomposition or by catalytic reduction with reducing agents or also for the catalytic NO x -Reduction in an exhaust gas stream.

[0132] The third catalyst module 30 is arranged above the first catalyst module 10. The third catalyst module 30 comprises a third catalyst bed 31 through which the exhaust gas to be processed flows substantially perpendicular to the longitudinal axis L. The third catalyst bed 31 is designed as a radial basket and is flowed through substantially from radially outside to radially inside. The exhaust gas flow rate F is indicated by arrows in Fig. 5.

[0133] The third catalyst bed 31 has a gas-impermeable cover 38 on a side facing the inlet 3. The cover 38 prevents axial flow through the third catalyst bed 31 and deflects the exhaust gas to be cleaned towards the container wall 7. The cover 38 also extends from the top of the catalyst bed 31, at least partially, along an inner wall 33 and an outer wall 35 of the third catalyst bed 31. A particulate catalyst is arranged as bulk material between the inner wall 33 and the outer wall 35. Furthermore, the third catalyst bed 31 has a retaining ring 39 on a side facing the outlet 5.

[0134] A third support device 32 for supporting the third catalyst module 30 is arranged on an inner wall of the container 2. The third support device 32 extends at least partially around the longitudinal axis L along the inner wall of the container 2 and has an inner contour facing the longitudinal axis L with a third opening width, in particular a third opening diameter, which is larger than the first opening width of the first support device 12. The third catalyst bed 31 is supported by the third support device 32 and is bolted to it. The third support device 32 comprises a third support ring 32.1 and several third support ribs 32.2. The third support ribs 32.2 are evenly spaced along a circumferential direction of the device 1 and welded to the inner side of the container wall 7. Between the retaining ring 39 and the third support ring 32.1 is a first sealing element, not visible in Figure 5. In the fifth embodiment shown in Figure 5, the third catalyst bed 31 can be described as being arranged vertically in the container 2.

[0135] The container 2 has an upper container part 2.1 and a lower container part 2.2 arranged below the upper container part 2.1 in the direction of the longitudinal axis L. As can be seen in Fig. 5, the first support device 12, the second support device 22, and the third support device 32 are arranged in the lower container part 2.2. The opening widths, in particular the opening diameters, of the support devices 12, 22, 32 decrease from top to bottom along the longitudinal axis L. This means that the opening width of the third support device 32 is larger than the opening width of the first support device 12, which in turn is larger than the opening width of the second support device 22. This design allows the first catalyst module 10, the second catalyst module 22, and the third support device 32 to be located in the lower container part 2.2. The third catalyst module 30 and the third catalyst module 20 can be removed upwards from container 2. In this respect, the device 1 offers improved accessibility to all three catalyst modules 10, 20, 30 for installation, inspection, or catalyst replacement. Reference symbol list 1 Device for the catalytic reduction of nitrogen oxides 2 containers 2.1 upper part of the container 2.2 lower part of the container 3 Entrance 5 outlets 7 Container wall 9 Cover 10 first catalyst module 11 first catalyst bed 12 first support device 12.1 first support ring 12.2 first supporting rib 13 Inner wall of the first catalyst bed 15 Outer wall of the first catalyst bed 17 particulate catalyst 19 first retaining ring 20 second catalyst module 21 second catalyst bed 22 second support device 22.1 second support ring 22.2 second supporting rib 23 Clamping device 29 second retaining ring 30 third catalyst module 31 third catalyst bed 32 third support device 32.1 third support ring 32.2 third supporting rib 33 Inner wall of the third catalyst bed 35 Outer wall of the third catalyst bed 38 Cover 39 third retaining ring 50 Container flange F Flow of the exhaust gas to be cleaned L Longitudinal axis

Claims

Patent claims:

1. Device (1), in particular for the catalytic reduction of nitrogen oxides, comprising a container (2) extending along a longitudinal axis (L), a first catalyst module (10), a first support device (12) arranged on an inner wall of the container (2) for supporting the first catalyst module (10), wherein the first support device (12) extends at least partially around the longitudinal axis (L) along the inner wall of the container (2) and has an inner contour facing the longitudinal axis (L) with a first opening width, in particular a first opening diameter, and a second catalyst module (20) arranged in the container (2) in the direction of the longitudinal axis (L) below the first support device (12), which has an outer contour facing the inner wall of the container (2) with an outer width, in particular an outer diameter, which is smaller than the first opening width of the first support device (12), characterized in thatthat the first catalyst module (10) is configured to be flowed through substantially perpendicular to the longitudinal axis (L) and the second catalyst module (20) is configured to be flowed through substantially parallel to the longitudinal axis (L).

2. Device according to claim 1, characterized in that the first catalyst module (10) comprises an iron-loaded zeolite catalyst.

3. Device according to one of the preceding claims, characterized in that a holding device (19) of the first catalyst module (10), in particular a retaining ring of the first catalyst module (10), rests on the first support device (12), in particular on a first support ring (12.1) of the first support device (12).

4. Device according to claim 3, characterized in that the holding device (19) is arranged in an upper region of the first catalyst module (10), so that the first catalyst module (10), in particular suspended, is arranged substantially below the first support device (12).

5. Device according to claim 3, characterized in that the holding device (19) is arranged in a lower region of the first catalyst module (10), so that the first catalyst module (10), in particular in a standing position, is arranged substantially above the first support device (12).

6. Device according to one of the preceding claims, characterized in that the second catalyst module (20) has one or more monolithic catalyst elements, preferably one or more honeycomb bodies, which preferably have channels and are arranged such that the channels are aligned in the direction of the longitudinal axis (L) of the container (2) and are supplied with flow substantially axially, preferably supplied with flow substantially axially and flowed through substantially axially.

7. Device according to claim 6, characterized in that several monolithic catalyst elements, preferably honeycomb bodies, are combined to form a honeycomb body module and the second catalyst module (20) comprises several individually replaceable honeycomb body modules.

8. Device according to claim 6 or 7, characterized in that the honeycomb bodies or honeycomb body modules are arranged in several layers offset along the longitudinal axis (L).

9. Device according to one of claims 6 to 8, characterized in that the honeycomb bodies or the honeycomb body modules are arranged such that they cover a usable flow area of ​​the cross-sectional area of ​​the second catalyst module (20) which is greater than 60% of the cross-sectional area of ​​the second catalyst module (20), preferably greater than 75% of the cross-sectional area of ​​the second catalyst module (20).

10. Device according to one of the preceding claims, characterized by a second support device (22) arranged on an inner wall of the container (2), by which the second catalyst module (20) is supported, wherein the second support device (12) extends at least partially around the longitudinal axis (L) along the inner wall of the container (2) and has an inner contour facing the longitudinal axis (L) with a second opening width, in particular a second opening diameter, which is smaller than the first opening width of the first support device (12).

11. Device according to claim 10, characterized in that a holding device (29) of the second catalyst module (20), in particular a retaining ring of the second catalyst module (20), or a downwardly projecting outer wall of the second catalyst module (20) rests on the second support device (22), in particular on a second support ring (22.1) of the second support device (22).

12. Device according to claim 10, characterized in that the second catalyst module (20) is clamped relative to the second support device (22) by a clamping device (23) arranged on the inner wall (7) of the container (3).

13. Device according to one of the preceding claims, characterized in that a distance between the first catalyst module (10) and the second catalyst module (20) is in the range of 0.2 m to 3 m, preferably in the range of 0.5 m to 1.5 m, more preferably in the range of 0.5 m to 0.8 m, wherein preferably a ratio of the distance and a width of the second catalyst module (20) in a direction perpendicular to the longitudinal axis (L) is in the range of 0.1 to 1.2, preferably in the range of 0.15 to 0.

8.

14. Device according to one of the preceding claims, characterized in that the device (1) comprises a third catalyst module (30) and a third support device (32) arranged on an inner wall of the container (2) for supporting the third catalyst module (30), wherein the third support device (32) extends at least partially around the longitudinal axis (L) along the inner wall of the container (2) and has an inner contour facing the longitudinal axis (L) with a third opening width, in particular a third opening diameter, which is larger than the first opening width of the first support device (12).

15. Device according to one of the preceding claims, characterized in that the container (2) has an upper container part (2.1) and a lower container part (2.2) arranged in the direction of the longitudinal axis (L) below the upper container part (2.1), wherein the first support device (12) and the second support device (22) and the third support device (32) that may be present are arranged in the lower container part (2.2).

16. Device according to one of the preceding claims, characterized in that the first catalyst module (10) is configured for the catalytic reduction of nitrogen oxides introduced into the container (2) and contained in an exhaust gas stream in the presence of a reducing agent, and the second catalyst module (20) is configured for the catalytic oxidation of reducing agent not reacted in the first catalyst module (10) and / or reaction products not fully oxidized in the first catalyst module (10).

17. Plant in which a device containing nitrogen oxides, preferably NO X and N2O, a contaminated exhaust gas stream is generated, with a device (1) according to one of the preceding claims, which is designed as a device for the catalytic reduction of nitrogen oxides and to which the exhaust gas stream containing the nitrogen oxides can be directed, in particular wherein the exhaust gas stream containing the nitrogen oxides- The gas flow upon entering the container (2) has a pressure of 1 bara to 15 bara, preferably 3 bara to 12 bara and / or a temperature of 200°C to 650°C, preferably 300°C to 600°C, particularly preferably 300°C to 550°C.

18. Plant according to claim 17, characterized in that the plant is a plant for the production or processing of chemical or other products, in particular a plant for the production of nitric acid or caprolactam or adipic acid or glyoxalic acid.

19. Plant according to claim 17, characterized in that the plant is an energy generation plant, in particular for heating or propulsion purposes or for electricity generation.

20. Method for the catalytic reduction of nitrogen oxides in an exhaust gas stream with a device according to one of claims 1 to 16, wherein nitrogen oxides introduced into the container (2) with the exhaust gas stream are catalytically reduced in the first catalyst module (10) in the presence of a reducing agent and wherein unreacted reducing agent and / or not completely oxidized reaction products in the first catalyst module (10) are catalytically oxidized in the second catalyst module (20).

21. Method according to claim 20, characterized in that a first spatial velocity of the first reaction stage (10) and a second spatial velocity of the second reaction stage (20) are set such that the ratio of the first spatial velocity to the second spatial velocity is in the range of up to 1 / 20, preferably in the range of 1 / 3 to 1 / 10, cherishes.

22. Method according to claim 20 or 21, wherein the exhaust gas stream containing the nitrogen oxides has a pressure of 1 bara to 15 bara, preferably 3 bara to 12 bara and / or a temperature of 200°C to 650°C, preferably 300°C to 600°C, particularly preferably 300°C to 550°C upon entry into the container.

23. Process for the production of nitric acid by catalytic oxidation of ammonia over a primary catalyst and conversion of the NO produced in the process x -Nitrogen oxides in an absorption tower to nitric acid with the formation of exhaust gases leaving the absorption tower, wherein nitrogen oxides contained in the exhaust gases are catalytically reduced according to a process according to one of claims 20 to 22.

24. A process for the production of nitric acid with the generation of exhaust gases according to claim 23, wherein the process comprises a secondary catalyst for N2O decomposition, which is arranged downstream of the primary catalyst for the oxidation of ammonia.

25. Process for the production of nitric acid with the formation of exhaust gases according to claim 24, wherein the N2O degradation caused by the secondary catalyst for N2O decomposition is a maximum of 95%, preferably a maximum of 90%, in particular a maximum of 85%.

Images