DE10003090A1 - SCR catalyst apparatus for reducing nitrogen oxides, comprises two sections made from catalyst-coated grooved plates in stacked assemblies - Google Patents

Abstract

A catalyst apparatus (1) comprises two sections (2, 3) in succession. The first (2) includes plates (6) coated with active mass. A periodically-repeating structure (8) is introduced into the plates, running in a principal direction (11, 12). Plates are stacked such that directions (11, 12) associated with adjacent plates, intersect. The second section (3) includes a number of parallel flow channels (14). Preferred Features: The second section is constructed as a flow-permeable honeycomb or plate stack. The plate stacks incorporate two substacks (9, 10). Structures in each, extend in the same principal direction. In one substack, principal orientation of the structures is parallel to the main direction (5) of through-flow. The same structure is introduced into all plates. It is a V-shaped gutter. The two sections share a common casing (4).

Description

The invention relates to a flow-through catalyst arrangement with a first catalyst body and with one downstream second catalyst body and the use formation of the catalyst arrangement. The invention is suitable especially for the catalysis of a reaction of at least two Reactants, with at least one reactant distributed inhomogeneously is in a gaseous or liquid medium.

Such an inhomogeneous distribution is then, for example before if a required for the reaction to be catalyzed The reactant must first be added to the medium. This is for example in the known method of selective ka talytical reduction to reduce nitrogen oxides in the exhaust gas an incinerator the case. This turns the exhaust gas into additionally a reducing agent, such as ammonia, added. The reducing agent reacts on a so-called DeNOx catalyst also in the presence of oxygen Nitrogen oxides contained in the exhaust gas to nitrogen and water. The nitrogen oxides effectively become harmless nitrogen implemented. Instead of ammonia, ammonia can also be used releasing substance, such as urea, the Ab gas can be added.

One for catalysing a reaction of reactants with inho mogeneous distribution of suitable catalyst bodies is known for example from WO 94/26411 A1. There is under other proposed a plate catalyst in which the individual plates spaced apart from one another extending along a main direction and periodically repeating structure. These are so in arranged in a stack that the main directions of the Structures of immediately adjacent slabs at an angle  to cut. Due to the crossed arrangement of the plates the reaction space of the plate catalyst is not caused by cont limited structures, but extends across the total cross-sectional area of a plate. The reaction space is limited by two neighboring plates and by the Side surfaces of a possibly existing holding frame or Element box in which the plates are stacked. By the structure running in different main directions Ren of neighboring plates is the flowing medium or Flow medium at least partially from the main flow direction distracted. The comm components of the flow medium both locally and via the achieved entire reaction space.

Disadvantageously, such shows for a good through mixing the components or reactants in the flow medium designed catalytic converter compared to one ago conventional plate catalyst with parallel alignment Plates or structures have a higher pressure drop. The Pressure loss depends on a. from the angle which the Main directions of the "rotated" structures of the plates with form the main flow direction of the flow medium. On Plate catalyst according to WO 94/26411 A1 therefore tends to Constipation from particles contained in the flow medium, such as e.g. B. soot or ash particles in the exhaust gas from combustion plant due to the low flow rate can easily sell off. For these reasons in spite of the good catalytic conversion such plate catata Analyzers are not used commercially today.

The invention is therefore based on the object of a catalyze satoranordnung specify that an acceptable Druckver lust and shows a high turnover rate. It is another task of the invention, a use of this catalyst arrangement specify.  

The first-mentioned object is achieved according to the invention by a catalyst arrangement with a first catalyst body and with a downstream of the first catalyst body second catalyst body, the first catalyst body a number of plates coated with an active composition includes, in which plates each one in a respective Main direction and periodically repeating Structure is introduced, and what plates in a stack are stacked such that the main directions of the Cut structures of at least two adjacent panels, and wherein the second catalyst body is a number of paral lel extending flow channels.

The invention is based on the consideration that in egg nem conventional from parallel and through Structures spaced apart plates built Plate catalyst or a honeycomb body as a flow-through formed with a number of parallel longitudinal channels Honeycomb catalyst usually due to lack of space between the introduction site for the for the catalysis reactants in the flow medium and the catalyst a so-called static mixer is installed. This static mixer has a number transverse to it Flow direction extending mixing elements that to a turbulence increase in the medium and thus a through mix the components of the medium.

As is known, a catalyst body with an An can now number of plates, their structures compared to the structures of the remaining plates are rotated, the previously used replace static mixer.

The catalyst arrangement has an arrangement a static mixer and with a static mixer downstream catalyst body of a conventional type comparable pressure loss at one due to the catalyti activity of the first catalyst body used as a mixer  increased catalytic conversion. The second Ka Talysator body is advantageously a flowable Honeycomb or plate catalyst.

The plates are advantageously in the first catalyst body per stacked in two sub-stacks in such a way that the structure doors of the plates of each supstack into the same che main direction.

It has proven to be an advantageous arrangement of the plates shown when the main direction of the structures of the plates of the one sub-stack parallel to the main flow direction of the flow medium is aligned. With such an out design of the first catalyst body will be a good one Mixing of the flow medium at a relatively low pressure loss achieved.

In terms of an inexpensive manufacturing process, it is advantageous if the same structure is inserted in all plates is brought. The structure is introduced in the case a metallic carrier of the plate, for example Punching before or after the application of the catalytic Be layering. The metallic carrier can be, for example Expanded metal or a metal mesh. In particular, can Steel are used. Alternatively, as a carrier material ceramics can also be used.

In principle, any peri is suitable as the structure of the plates odd structure like a sine wave or a sawtooth or Triangular shape. However, it is advantageous if the structure is a bead. This allows a good spacing of the plat ten with each other, with the be limited reaction spaces with regard to the mixing of the Flow medium are well suited.

In an advantageous embodiment, both are catalysts body arranged in a common housing. For use  for example in exhaust gas ducts of large power plants, wel che channels have a large cross section, can this way whole layers, each consisting of first or second catalyst bodies, combined in a housing become. The housing then fills the entire cross section; one speaks of so-called catalyst modules.

The second task is inventively by the Ver application of the catalyst arrangement for the degradation of nitrogen oxides Exhaust gases from incinerators using the selek tive catalytic reduction (SCR process) solved.

This procedure is also carried out in the presence of acid Nitrogen oxides using a reducing agent on the catalyst sator body converted to nitrogen and water. As a reducti Onsmittel can reduce hydrocarbons or other connections are used. In particular has the use of ammonia as a reducing agent. Because of the easier handling, an aqueous one is used Urea solution introduced into the exhaust gas to be treated. On decomposes due to the relatively high temperatures in the exhaust gas Urea in ammonia.

The process can be advantageous in fumes from one with fos silem fuel operated large power plant, such. B. one Coal-fired power plant or a waste incineration plant, and esp special also in exhaust gases from an internal combustion engine, such as. B. a diesel engine or a lean engine.

Exemplary embodiments of the invention are described below a drawing explained in more detail. In it show:

Fig. 1 in a partially cut-out perspective perspecti vically a catalytic converter arrangement with a second catalyst body designed as a honeycomb catalyst, and

Fig. 2 in a representation according to FIG. 1, a catalyst arrangement with a trained as a plate catalyst th second catalyst body.

The same parts are in both figures with the same reference characters.

In Fig. 1, a flow-through catalyst arrangement 1 with a first catalyst body 2 and with a second catalyst body 3 is shown in perspective and partially broken away. Both catalyst bodies 2 , 3 are held in a common housing 4 . The housing 4 is designed in such a way that it can accommodate a large number of the first and second catalyst bodies 2 and 3 in a plane next to each other. In such a housing 4 equipped with catalyst bodies, one also speaks of a so-called catalyst module, which is placed in a flow channel. The dimensions of the housing 4 are specifically tailored to the cross-section of the flow channel.

The housing 4 and the catalyst body 2 and 3 are flowed through by the medium to be treated in the main flow direction 5 shown. In this case, an introduction point for the reactants necessary for the catalytic reaction is arranged in front of the first catalyst body 2, viewed in the main flow direction. In the case of the application of the catalyst arrangement 1 for the reduction of nitrogen oxides according to the SCR method in the exhaust gas of an incineration plant, this can be, for example, an injection device for an aqueous urea solution.

The first catalyst body 1 comprises a number of plates 6 , which are stacked in an element box 7 . The rectangular 6 plates 6 are each made of a carrier made of metal, plastic or ceramic, which is coated on both sides with a catalytically active active material. For reasons of clarity, neither the carrier nor the active composition is shown in the figure.

For the use of the catalyst arrangement 1 for reducing nitrogen oxides according to the SCR process, the active composition comprises titanium dioxide as the main component and admixtures of vanadium pentoxide, tungsten trioxide and / or molybdenum trioxide. The plates 6 are each provided with a ver running in a main direction and periodically repeating structure 8 in the form of a bead. The structure 8 can, depending on the material of the support, be punched into the finished support or be formed when the support is shaped.

The element box 7 is an open at the end faces of the metal, in particular stainless steel. The perpendicular to the plat tenebenen side surfaces of the element box 7 are provided on the inside with guide rails for fastening and easy installation of the plates 6 . The stacking of the plates 6 is subdivided into a first sub-stack 9 and a two-th sub-stack 10 , the structures 8 of all of the plates depending on a sub-stack 9 and 10 each running along a main direction. The main direction 11 of the structures of the plates of the first sub-stack 9 runs parallel to the main flow direction 5 . The main direction of the structure 8 of the plates of the second sub-stack 10 includes an angle with the main flow direction 5 .

The sub-stacks 9 and 10 are arranged such that the main directions 11 , 12 of the structures 8 of adjacent plates intersect. In this way, a reaction space is created between adjacent plates, which is not limited by the structures 8 , but extends over the entire cross section of the plates 6 . Part of the medium is deflected from the main flow direction 5 by the structures 8 of the plates of the second sub-stack 10 which run obliquely with respect to the main flow direction 5 . This leads to a thorough mixing of the medium and thus to a homogeneous distribution of the reactants in the medium.

The second catalyst body 3 is designed as a honeycomb body with a number of parallel flow channels 14 . The honeycomb body consists entirely of a catalytically active composition or active composition and is manufactured as a full extrudate. For the application of the catalyst arrangement 1 for the reduction of nitrogen oxides according to the SCR process, the active composition in turn comprises titanium dioxide as the main constituent and additions of vanadium pentoxide, tungsten trioxide and / or Mo lybdäntrioxid.

In the housing 4 , a number of holding elements 15 are arranged, on which the first catalyst body 2 are held. The underside of the housing 4 is provided with a flow-through grid 16 to protect the system from parts of the catalyst arrangement 1 .

In FIG. 2, a flow-through catalyst arrangement 17 with a first catalyst body 2 and a second catalyst body 18 is shown in perspective and partially broken away. Compared to FIG. 1, the catalytic converter arrangement 17 shown in FIG. 2 differs only in the construction of the second catalytic converter body 18 .

The second catalyst body 18 is constructed similarly to the first catalyst body 2 . It also comprises a number of plates 19 which are stacked in an element box 20 . In contrast to the catalyst body 2 , however, the main directions of the structures 21 of all plates of the catalyst body 18 point in a single direction, namely parallel to the main flow direction 5 of the medium flowing through. This corresponds to the structure of a conventional plate catalyst. The parallel stacked plates 19 are beabstan det by the structures 21 introduced into the plates 19 . A plurality of individual reaction spaces 22 are created between two adjacent plates 19 , each of which is formed by two structures of adjacent plates and by the plates 19 themselves.

Claims (9)

1. Flow-through catalyst arrangement ( 1 , 17 ) with a most catalyst body ( 2 ) and with a second catalyst body ( 3 , 18 ) connected downstream thereof, the first catalyst body ( 2 ) having a number of plates coated with an active material ( 6 ) into which plates ( 6 ) each have a structure ( 8 ) that runs in a respective main direction ( 11 , 12 ) and is repeated periodically, and which plates ( 6 ) are stacked in a stack in such a way that the main directions ( 11 , 12 ) of the structures ( 8 ) cut at least two adjacent plates ( 6 ), and the second catalyst body ( 3 , 18 ) comprises a number of parallel flow channels ( 14 , 22 ). 2. Catalyst arrangement ( 1 , 17 ) according to claim 1, wherein the second catalyst body ( 3 ) is designed as a flowable honeycomb body. 3. Catalyst arrangement ( 1 , 17 ) according to claim 1, wherein the second catalyst body ( 18 ) is designed as a flow-through plate body. 4. A catalyst arrangement ( 1 , 17 ) according to any one of the preceding claims, wherein the plates ( 6 ) in two sub-stacks ( 9 , 10 ) are stacked such that the structures ( 8 ) of the plat ten ( 6 ) of each sub-stack ( 9 , 10 ) each extend in a main direction ( 11 , 12 ). 5. A catalyst arrangement ( 1 , 17 ) according to claim 4, wherein the main direction ( 11 ) of the structures ( 8 ) of the plates ( 6 ) of the egg NEN sub-stack ( 9 ) are aligned parallel to the main flow direction ( 5 ). 6. Catalyst arrangement ( 1 , 17 ) according to one of the preceding claims, wherein the same structure ( 8 ) is introduced in all plates ( 6 ). 7. catalyst arrangement ( 1 , 17 ) according to any one of the preceding claims, wherein the structure ( 8 ) is a bead. 8. Catalyst arrangement ( 1 , 17 ) according to one of the preceding claims, wherein the first ( 2 ) and the second catalyst body are arranged by ( 3 , 18 ) in a common housing ( 4 ). 9. Use of the catalyst arrangement ( 1 , 17 ) according to one of the preceding claims for the decomposition of nitrogen oxides according to the method of selective catalytic reduction.