EP1092846A2 - Hydrodynamically optimized catalytic body - Google Patents

Abstract

The catalytic body has an inflow surface (3) and outflow surface (4). The inflow surface is formed as a sleeve surface (8) of a conical or frusto-conical projection (7) with a concave curvature at least in some sections. The curvature of the inflow surface can be smooth. The outflow surface can be planar or can be curved. The catalytic body can be a monolith. The catalytic body can be made from several superposed layers of a structured surface material

Description

The invention relates to a catalytic molded body with an upstream and a downstream surface, as well as a peripheral surface.

In order to comply with legal regulations which require the exhaust gas flows from motor vehicles to be largely freed from environmentally harmful substances, such as nitrogen oxides or aromatic hydrocarbons, the exhaust gas is cleaned with the aid of a catalytic converter. The exhaust gas stream is passed through a catalytic molded body arranged in the exhaust gas line of the motor vehicle. Such a shaped body usually has a multiplicity of channel-like structures which are arranged parallel to the axis of the catalytic shaped body. The customary catalytic moldings are either made from ceramic materials or from metal. The material can either itself be catalytically active or the walls of the channels can be coated with a catalytically active material, usually metals such as platinum, vanadium, cobalt, nickel, chromium etc. When installed, the catalytic molded body is arranged in a housing in the exhaust line of a motor vehicle. During operation, the exhaust gas flows against the end face of the catalytic molding. The total gas flow is divided into a large number of individual gas flows which are passed through the channel-like structures and reunite on the downstream surface of the catalytic shaped body. The exchange between the individual gas flows is restricted by the at least partially, in extreme cases completely gas-tight walls of the channels.
The cross-sectional area of the catalytic shaped body is generally larger than that of the tube through which the exhaust gas stream coming from the engine is fed to the catalytic converter. The cross section of the exhaust gas flow at the entrance is drastically expanded by the housing in which the catalytic molded body is installed and reduced again at the exit. This results in a lateral pressure gradient on the upstream end face of the molded body, which lies in the order of magnitude of the pressure loss over the molded body, and thereby in a radial distribution of the gas velocities in the channel-like structures. Different flow velocities and thus different hydrodynamic dwell times occur in the channel-like structures through which flow occurs independently. In the middle of a ceramic honeycomb in an exhaust gas catalytic converter for an automobile, there are usually high flow velocities, on the other hand the gas flows through the honeycomb only slowly. This uneven distribution causes the effectiveness of the shaped body to be reduced in the catalytic purification of the exhaust gas stream. In order to obtain a better cleaning effect, a more uniform flow against the molded body is therefore desirable. Various solutions have been described to overcome this difficulty.

In T. Hauber, P. Zacke, J. Braun, D. Ueberschär, Soc. Automot. Closely. Paper # 98 04 24 describes that the flow against a molded body by the extension of the Inlet funnel and drain funnel can be improved. For the technical use of the However, this is disadvantageous because the geometric length of the honeycomb body Catalytic converter housing extended and tolerable limits are quickly exceeded.

As an alternative, it was proposed to optimize the flow against the molded body, to install additional technical devices in the inflow funnel, which by Forces deflect the gas flow and thereby the flow to the honeycomb body even.

DE 36 27 637 A1 describes a catalyst muffler with a Muffler housing and a catalytic converter arranged in it. Before the upstream side of the A plurality of exhaust manifold plates is arranged through the catalyst Exhaust gas flowing into the muffler housing evenly into the Exhaust gas passages of the catalyst distributed.

No. 3,964,875 describes a catalyst system for cleaning car exhaust gases a housing and a catalytic molded body arranged therein. On the upstream side is a deflector in the form of an impeller at the entrance to the housing arranged, through which the incoming exhaust gas gets a swirl and radially outwards is distributed. This is intended to provide a more even flow to the face of the catalytic shaped body can be achieved.

However, the disadvantage of such additional internals is the increased heat capacity of the Catalyst system. By heating the internals, the exhaust gas flow is additional Extracted heat required for heating the catalytic molded body to temperatures catalytic activity is needed. This lowers the cleaning capacity of such Catalyst systems in the warm-up phase drastically.

Another disadvantage of these internals is their low mechanical stability. The Internals are strong in the exhaust system of a vehicle due to sound waves Deformed and therefore susceptible to mechanical damage. Such damage adversely affects the life of the catalysts itself, the engine and its components.

As a further possibility, it was proposed to shape the molded body itself modify. The shaped body should be designed so that the flow resistance of the individual channel-like structures to be flowed through varies radially. This will the flow resistance in the direction of the lateral pressure drop is reduced, so that over the entire cross section of the molded body a uniform flow rate is achieved.

DE 43 39 447 A1 proposes changing the channel density Flow resistance to vary. This is a curved honeycomb body proposed that has a number of through openings that pass through this extend along a direction in which the honeycomb body is curved. The distances between the inner partitions that define the through openings are on a radially outer side of a curved section is set larger than on a radially inner side thereof. This means that the cross section of the radially outer through openings is smaller than the cross section in the radial Direction through openings. So the flow resistance, the passage openings on the outside in the radial direction with fewer Cross-sectional area larger than that of the radially inner through openings larger cross-sectional area.

The same effect can be achieved by varying the channel length. This happens preferably in that the shaped body along its axis a larger Has expansion than in the longitudinal direction along its circumferential surface.

DE 22 01 881 describes a one-piece support body through channels for catalysts described, the support body conical or at least on one side lying in the flow path of the gas is pyramid-shaped. This conical or pyramidal section of the Carrier body is preferably arranged on the upstream side.

A comparable route is followed with the teaching of DE 24 28 964. There will be a Catalytic converter system described with a housing and a longitudinally arranged therein flowable catalytic shaped body. The catalytic molded body is for Longitudinal axis longer than in the edge areas, so that in the area of the larger Flow energy by correspondingly increasing the length of the application flow in the Flow center a greater flow resistance and thus a more uniform Flow can be achieved over the entire cross-section of the application.

EP 0 818 613 also teaches a catalyst device for cleaning exhaust gases. This consists of a tubular housing that is located at both ends Tapered in the shape of a truncated cone. A catalytic molded body is provided in the housing, wherein the end face against which the exhaust gas flows has a convex curvature. Together with the frustoconical section of the housing, this is said to be a more uniform distribution of the flow velocity across the cross section can be achieved.

DE 197 49 379 describes a catalyst carrier body which is a has improved heat radiation behavior from the individual layers of the matrix. For this purpose, it is provided that the catalyst carrier body on the outflow side Has a head start. The projection can be shaped differently. It will proposed to design the projection conical or frustoconical or that the projecting shape by an essentially inward from the perimeter of the matrix extending, at least partially convex curvature is formed. Through the protruding shape increases the area that is used for heat radiation and thus for Heat transfer to the exhaust gas flowing off is available.

Although with the designs known from the prior art upstream end face of the catalytic molded body a noticeably more uniform Flow profile can be achieved across the cross section, but none can Realize homogeneous speed distribution.

The object of the invention is therefore to provide a catalytic shaped body, which enables a better homogenization of the inflow.

This task is accomplished by a catalytic molded body with an upstream and a downstream surface solved in that the upstream surface as a lateral surface a conical or frustoconical projection is formed, the outer surface has a concave curvature at least in sections.

By designing the upstream surface in such a way that the upstream surface is designed as a lateral surface of a conical or frustoconical projection, wherein the lateral surface has a concave curvature at least in sections, a compared to the designs known from the prior art on the upstream surface, much more homogeneous flow distribution can be achieved. Due to its uniform flow, the catalytic according to the invention shows Moldings have a better effectiveness and a longer shelf life because no or at least a significantly lower early deactivation of the catalyst in particular heavily used areas.

The concave curvature of the upstream surface extends from the circumference of the catalytic shaped body towards the axis lying in the flow direction. The lead ideally ends in a tip. However, because of the high mechanical loads in this area occur, the tip can also be cut. The lead then gets one frustoconical shape. The truncated cone can be rounded on the upstream side. this will achieved when the lateral surface has a convex curvature in sections.

For production reasons, the curved end face can be designed that it is when looking at a longitudinal section through the catalytic shaped body composed of linear sections, with two adjacent linear sections each form an angle with each other. Likewise, the surface on the inflow side wound catalytic shaped bodies. In this case, the Enveloping the lateral surface has a concave curvature. Particularly good results in the homogeneity distribution of the flow, however, are obtained if the Curvature of the upstream surface is smooth.

In general, it is sufficient to have the face on the inflow side with the inventive one To design curvature. In this case, the downstream surface of the catalytic shaped body be planar. This can save costs can be achieved in the production of the catalytic shaped body.

However, it is also possible for the outflow-side surface of the catalytic shaped body trained curved. This allows an even finer tuning of the Homogeneity profile can be achieved over the cross section of the catalytic molded body.

In general, the catalytic shaped body is designed in such a way that the Catalytic shaped body is designed as a monolith.

However, it is also possible to design the catalytic shaped body in such a way that the catalytic molded body from a plurality of layers one above the other structured flat material is built.

The catalytic molded body can be constructed from a catalytically active material. This is possible, for example, by designing it as a metal catalyst.

In another embodiment, the catalytic shaped body is parallel to Longitudinal axis of the catalytic shaped channels running through, the Walls are preferably coated with a catalytically active material.

Another improvement in the flow profile across the cross section of the catalytic Shaped body can be achieved if a housing for receiving the catalytic Shaped body is provided with a tubular section at the ends conical sections are formed. The frustoconical sections represent the Transition between the exhaust pipe coming from the engine, which has a low Has diameter, to the tubular section of the catalyst housing. By the slope of the truncated cone can be the flow profile over the cross section of the influence the catalytic molding. The conical sections can on the upstream or downstream side of the catalyst housing different Have slopes.

The catalytic shaped body according to the invention is particularly suitable for cleaning Material flows, especially exhaust gas flows from internal combustion engines.

Fig. 1

einen Längsschnitt durch einen erfindungsgemäßen katalytischen Formkörper, der in ein Katalysatorgehäuse eingebaut ist;

Fig. 2a - e

einen Längsschnitt durch verschiedene katalytische Formkörper, die jeweils in ein Katalysatorgehäuse eingebaut sind;

Fig. 3

ein Diagramm, in dem die Gasgeschwindigkeit im Katalysator gegen den radialen Abstand von der Achse des katalytischen Formkörper für die in den Figuren 2 a - e gezeigten Formen aufgetragen ist;

Fig. 4

einen Längsschnitt durch verschiedene gebräuchliche Formen für das Katalysatorgehäuse.

The catalytic shaped body according to the invention is explained in more detail below with reference to a drawing. The same reference numerals in the figures denote the same objects. It shows:

Fig. 1

a longitudinal section through an inventive catalytic molded body which is installed in a catalyst housing;

2a-e

a longitudinal section through various shaped catalytic bodies, which are each installed in a catalyst housing;

Fig. 3

a diagram in which the gas velocity in the catalyst is plotted against the radial distance from the axis of the catalytic molded body for the molds shown in FIGS. 2a-e;

Fig. 4

a longitudinal section through various common shapes for the catalyst housing.

FIG. 1 shows a longitudinal section through a catalytic shaped body 1 according to the invention. Exhaust gas flows through the catalytic shaped body 1 in the direction of arrow 2. It has an upstream surface 3, a downstream surface 4 and one Circumferential surface 5. The catalytic molded body can be (not shown) Channels that run in the direction of the longitudinal axis 6 of the molded body 1. The upstream surface 3 of the catalytic shaped body 1 is curved, the line which is in longitudinal section between the axis 6 of the molded body and the Circumferential surface 5 extends, has a concave curvature. The catalytic molded body 1 therefore forms a cone 7 on the inflow side, the lateral surface 8 of which is concave Has curvature. In the embodiment shown, the cone 7 runs into a tip 9 out. This is subject to high mechanical loads during the operation of the catalytic converter. It is therefore also possible to design the cone 7 as a truncated cone or the tip 9 round off to achieve increased mechanical stability. This embodiment is represented by the dashed line 15. The downstream surface 4 of the In the illustrated embodiment, the catalytic shaped body is designed to be planar. The catalytic molded body can be made of a ceramic material, or also be designed as a metal catalyst.

The catalytic molded body 1 is in a housing 10, for example made of stainless steel exists, built. The housing 10 comprises a tubular portion 11, the Inner diameter is the maximum outer diameter of the catalytic shaped body 1 corresponds, so that the inflowing exhaust gas forcibly the catalytic molded body 1 must flow through. At the two ends of the tubular section 11 close each conical sections 12a, 12b. Through these conical sections 12a, 12b, the diameter of the infeed or outfeed is widened or reduced Exhaust pipes 13a, 13b on the diameter of the catalytic shaped body 1. The slope The amount of the conical section on the upstream side is chosen to be greater than on the downstream side. The installation of the catalytic molded body 1 in the housing 10 takes place in such a way that the cone 7 of the catalytic shaped body 1 in the protrudes conical section 12a of the housing 10.

2 shows longitudinal sections through different catalytic shaped bodies 1, which are each installed in a housing 10. For the sake of simplicity, only those are shown upper halves of the catalyst device. The representation is schematic and does not correspond to a real version in scale.

The four catalytic shaped bodies shown each have a circular shape Cross section on. They differ in the design of the upstream or downstream face. The catalytic moldings correspond to Representations 2a to c embodiments from the prior art. Figure 2d shows one Embodiment of the catalytic shaped body according to the invention. Figure 2e shows one special embodiment of the lateral surface of the catalytic according to the invention Molded body.

Figure 2 a shows a catalytic molded body, the end faces both on the The upstream side is planar as on the downstream side. Figure 2b shows one Catalytic molded body, the upstream surface of which is conical, wherein the lateral surface of the cone has no curvature. The downstream face is executed planar. Figure 2c shows a catalytic molded body in which both on the upstream side and on the downstream side as a jacket of a cone. Here, too, the lateral surface has no curvature. Figure 2d corresponds to one Embodiment of the catalytic shaped body according to the invention. On the On the inflow side, the end face is designed as a lateral surface of a cone, the Lateral surface has a concave curvature in the direction of the longitudinal axis of the catalytic Has molded body.

To investigate the flow profile, a monolithic honeycomb shaped body made of copper spinel active material was installed in each case. The shaped bodies produced corresponded in their longitudinal section to the representations in FIGS. 2a to d. The maximum diameter of the monoliths was in each case 13.2 cm, and the longitudinal extent in the embodiment according to FIG. 2a was 15.2 cm. In embodiments b to d, the longitudinal extent in the section with constant diameter corresponded to the embodiment according to FIG. 2a. All four monoliths a to d were crossed by the same number of square longitudinal channels of the same lateral dimensions (400 cpsi; 7.2 mil). The monoliths were each installed in the same housing and measured in a test apparatus. For this purpose, a gas stream was applied to the monolith to be tested in such a way that a gas load of 90,000 h ^-1 resulted. Atmospheric air was used as the test gas. The temperature of the gas stream was 450 ° C, which corresponds to a value characteristic for exhaust gas temperatures. The flow velocities were measured on the outflow side.

R = MonolithradiusThe measurement results are shown in FIG. 3. The normalized tube speed (y) is plotted against the radius (x). The standardization of the tube speed was carried out in the following way:
u (r) / u = normalized empty pipe speed
in which

R = monolith radius

The curves clearly show those compared to those known from the prior art Forms (a to c) much more homogeneous distribution of the flow velocity in radial direction in the case of the catalytic molding (d) according to the invention.

Figure 2e schematically shows an embodiment of the upstream end face, as it is e.g. occurs with wound catalysts. The individual windings on the upstream end face each formed stages 16. Levels 16 are like this shaped that the envelope, the longitudinal section through the dashed line 17th is shown, has a concave curvature.

Figure 4 shows schematically cross sections through different housing shapes for catalytic moldings. In cases a, b, d, the longitudinal axis 14 of the falls supplying exhaust pipe together with the longitudinal axis 6 of the catalytic molded body. In these cases, according to the invention, the surface on the inflow side is a shell surface symmetrical cone or truncated cone. In case c, the longitudinal axis 14 falls of the supplying exhaust pipe not with the longitudinal axis 6 of the catalytic molded body together. In this case, the surface on the inflow side is a shell surface asymmetrical cone or truncated cone according to the teaching of the invention to execute.

Claims (12)

Catalytic molded body with one upstream (3) and one downstream Surface (4) and a peripheral surface (5), characterized in that the upstream surface (3) as the outer surface (8) of a truncated or frustoconical Projection (7) is formed, the lateral surface (8) at least has a concave curvature in sections. Catalytic shaped body according to claim 1, characterized in that the The lateral surface (8) has a convex curvature in sections. Catalytic shaped body according to claim 1 or 2, characterized in that the curvature of the upstream surface (3) is smooth. Catalytic shaped body according to one of claims 1 to 3, characterized characterized in that the downstream surface (4) of the catalytic shaped body (1) is planar. Catalytic shaped body according to one of claims 1 to 3, characterized characterized in that the downstream surface (4) of the catalytic shaped body (1) is curved. Catalytic shaped body according to one of claims 1 to 5, characterized characterized in that the catalytic shaped body (1) is designed as a monolith. Catalytic shaped body according to one of claims 1 to 6, characterized characterized in that the catalytic molded body (1) from a variety layers of a structured flat material arranged one above the other is. Catalytic shaped body according to one of claims 1 to 7, characterized characterized in that the catalytic molded body (1) from a catalytically active Material is built up. Catalytic shaped body according to one of claims 1 to 8, characterized characterized in that the catalytic molded body (1) from parallel to the longitudinal axis (6) of the catalytic shaped body extending channels, the Walls are preferably coated with a catalytically active material. Catalytic shaped body according to one of claims 1 to 9, characterized characterized in that a housing (10) for receiving the catalytic Shaped body is provided with a tubular section (11), on the Ends of conical sections (12a, b) are formed. Catalytic molded body according to claim 10, characterized in that the At least the lateral surface (8) of the conical or frustoconical projection (7) partially within one of the conical sections (12a, b) of the housing (10) is arranged. Use of a catalytic shaped body according to one of claims 1 to 11 for cleaning material flows, in particular exhaust gas flows from Internal combustion engines.

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