DE8901773U1 - Catalyst moldings with spacers - Google Patents

Description

89 G 3 O 5 1 OE

Siemens AG

Catalyst moldings with spacers 5

The invention relates to a catalyst molded body for a flowing, liquid or gaseous medium, in particular for the catalytic removal of nitrogen oxide from an exhaust gas by means of ammonia gas, with a number of catalyst plates arranged parallel to one another, which are provided with openings on which tabs are located.

For example ^{, DE} -PS 26 58 539 discloses a process for removing nitrogen oxides from exhaust gases by selective contact reduction using a catalyst provided with flow channels with the addition of ammonia gas. This catalyst has a honeycomb structure, i.e. it is designed as a cell-like, channel-shaped body. The individual flow channels, which are parallel to one another, have a hexagonal cross-section. There is no connection between these flow channels.

In contrast, a catalyst molded body of the type mentioned above with a plate-shaped structure is known from DE-PS 28 53 023. This molded body has a large number of plate-shaped catalysts that are arranged parallel to the gas flow containing nitrogen oxide. Each plate-shaped catalyst consists of a metal plate on both sides of which a catalytically active substance is applied. The metal plate can be perforated, i.e. provided with openings or windows. When these openings are made, tongue-shaped elevations or tabs are created, which in the known construction are all on one and the same side of the respective metal plate.

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In the brochure "NOx Reduction with Plate-Type and Honeycomb-Type Catalytic Converters", Siemens AG, Berlin and Munich, order number A19100-U311-A106-X-7600, April 1988, there is a description of industrially manufactured plate and honeycomb catalysts for nitrogen oxide reduction. The ceramic or metallic catalyst moldings are combined into modules and - depending on requirements - stacked on top of each other if necessary. The plate catalysts are designed to have continuous beads running in the direction of flow, which contribute to the formation of the individual flow channels and at the same time serve as spacers between the neighboring plate catalysts.

^ The invention is based on the observation that in a plate-shaped catalyst body with flow channels that are sealed off from one another, the flowing medium slides past the catalyst walls in a predominantly laminar flow and only comes into inadequate contact with the inner surfaces. The invention is also based on the consideration that catalytic utilization can be improved if a certain turbulence of the flowing medium is ensured within the catalyst body. It is also based on the observation that the tabs and openings on the catalyst plates of a catalyst body of the type mentioned at the beginning cause a certain turbulence, but that this can be improved even further .

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L The present invention is based on the object of

/L- Catalyst moldings of the type mentioned above are to be designed in such a way that the catalytic effect is increased due to increased turbulence, while at the same time spacers are to be provided in a simple manner.

This object is achieved according to the invention in that the tabs are bent away from the relevant catalyst plate in opposite directions and that the tabs have such a length that

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They also serve as spacers to adjacent catalyst plates.

In contrast to the known catalyst moldings according to 5 OE-PS 28 53 023, in this case the two tabs at each opening are bent away from the catalyst plate in opposite directions. This has the advantage that the liquid or gaseous medium can pass through the openings, which creates particularly good turbulence. The medium can, so to speak, pass from one flow channel into the neighboring flow channels. The catalyst molding thus consists of a large number of long parallel channels, all of which are cross - connected to one another. This enables liquid or gas exchange between the channels; turbulence occurs at the same time. Both improve the contact of the medium with the inner catalyst walls.

A preferred embodiment is characterized in that the tabs are each designed as S-shaped leaves. These S-shaped leaves, which act as spacers, have the advantage that damage is avoided when assembling a stack of parallel catalyst plates.

Further advantageous embodiments are described in the subclaims.

Embodiments of the invention are explained in more detail below using nine figures. They show:

FIG 1 to 4 Top views of various catalyst plates before

the bending of tabs as spacers; FIG 5 shows a section of a catalyst plate shown in perspective before the formation of tabs; FIG 6 shows the catalyst plate of Figure 5 after the formation of the tabs;

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FIG 7 a section along the line VIl-VII of Figure 6} FIG 8 a number of catalyst plates arranged parallel to each other with S-shaped tabs to illustrate the stacking principle j and

FIG 9 shows a cubic frame with a number of inserted catalyst plates with oppositely bent tabs.

Figure 1 shows a view of a catalyst plate 2 for the catalytic removal of nitrogen oxide from an exhaust gas using ammonia gas. This catalyst plate 2 is square. It consists of a metal plate that is coated on both sides with a catalytically active substance. After cutting and drying, a number of rows of offset incisions 4 in an I- or double-T shape are arranged in the catalyst plate 2. The individual rows are spaced apart by a distance a from one another. The incisions 4 are placed in a gap.

From Figure 2 it is clear that the individual incisions A do not need to be double-T-shaped. It is only important that they can be bent into tabs 6 (see

e.g. Figure 6). The double V-shaped incisions 4 shown in Figure 2 allow the forward

tapered tabs 6.
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Figure 3 shows that the individual rows of incisions

can have a distance d not equal to 0 from each other; d can be chosen, for example, as d = a.

Figure 4 shows that the incisions 4 can be arranged in rows, each of which is offset from one another by a fraction of the distance ρ between adjacent incisions 4. In the present case, the mutual offset has been chosen to be p/3.

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' 1 Regarding the embodiments of Figures 1 to A, it should be noted that further arrangements of the incisions A can be selected as required. It should also be noted that each catalyst plate 2 can contain more incisions A than shown.

Figure 5 shows once again a section of a catalyst plate 2 according to Figure 1 in a perspective view.

From Figures 6 and 7 it is clear that at each incision A

by bending in opposite directions, two lips or tabs 6 were created. By bending the tabs 6 away from the / ^ catalyst plate 2 in opposite directions, an opening 8 is created between them. These openings 8 are important because the gas flow between two adjacent catalyst plates 2 can exchange with the adjacent gas flows via these openings 8. The arrangement of the tabs 6 itself already causes a certain amount of turbulence. However, this is significantly increased by the said openings 8. As a result of the turbulence thus generated in the catalyst molding, there is good catalytic utilization of the inner catalyst surfaces within the catalyst molding.

In Figures 6 and 7 it is indicated that the tabs 6 are round, specifically quarter-circle-shaped. Their length and shape ( ) are dimensioned such that they simultaneously serve as spacers to adjacent catalyst plates 2 in the catalyst molding.

This spacer principle is clear from Figure 8. Here the parallel arrangement of a number of catalyst plates 2 is shown looking upwards, i.e. in the direction of flow. The individual tabs 6 are each designed as S-shaped leaves. This prevents damage to the catalytically active surface of the adjacent plates 2. From Figure 8 it is clear that the length and shape of the tabs 6

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Determine the distance between the individual catalyst plates 2 within the stack. Special spacers are therefore not required. In Figure 8, the openings 8 of adjacent plates 2 are set exactly on the gap. It can thus be seen that all flow channels 10 are connected to one another transversely via these openings 8. This results in a three-dimensional, sieve-shaped catalyst body which has good turbulence properties and thus ensures good catalytic utilization.

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Finally, in Fig. 9, it is shown in perspective how the individual catalyst plates 2 are inserted parallel into a cubic frame 12 of edge length A to form a catalyst molding 14. According to the length of the individual incisions 4, the openings 8 each extend over only a fraction of the height A of the catalyst molding 14 measured in the direction of flow. The individual catalyst plates 2 can be inserted into the frame 12 without great difficulty. There is no need to fear mechanical instabilities due to the temperature differences that occur during operation, because the individual tabs 6 simultaneously act as spring elements. The medium flowing through the catalyst molding is designated M.

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Claims (5)

•i I"' :":·": ·::■:".· 89 63 05 I DE / I · Protection claims 1. Catalyst molding (14) for a flowing liquid or gaseous medium (M), in particular for the catalytic removal of nitrogen oxide from an exhaust gas using ammonia gas, with a number of catalyst plates (2) arranged parallel to one another, which are provided with openings (8) on which tabs (6) are located, characterized in that the tabs (6) are bent in opposite directions away from the relevant catalyst plate (2), and that the tabs (6) have such a length that they simultaneously serve as spacers to adjacent catalyst plates (2). 2. Catalyst molding according to claim 1, characterized in that the tabs (6) are each designed as S-shaped leaves (Fig. 8 and 9). 3. Catalyst molding according to claim 1 or 2, characterized in that the tabs (6) are each formed from a double-T-shaped incision (4) in the catalyst plate (2). 4. Catalyst molding according to one of claims 1 to 3, characterized in that the uff- C openings (8) are offset sideways from each other - seen in the direction of the flow. 5. Catalyst molding according to one of claims 1 to 4, characterized in that it is three-dimensionally sieve-shaped. 02 01