WO1995031270A1

WO1995031270A1 - Device for detoxifying exhaust fumes from mobile equipments

Info

Publication number: WO1995031270A1
Application number: PCT/DE1995/000618
Authority: WO
Inventors: Jörg KIESER; Günter LINS; Robert SEEBÖCK
Original assignee: Siemens Aktiengesellschaft
Priority date: 1994-05-11
Filing date: 1995-05-10
Publication date: 1995-11-23
Also published as: DE9407861U1

Abstract

In motor vehicles for example, exhaust fumes are to flow through a plasma reactor that works according to the principle of dielectrically inhibited discharge ('silent discharge'). The plasma reactor consists of at least two electrodes and at least one dielectric body. Known plasma reactors contain several adjacent discharge section. According to the invention, several concentric discharge sections (2 to 9) follow each other in the direction of flow, two pipe systems (10, 20) being coaxially nested into each other for that purpose. At least one pipe system (10, 20), preferably the second pipe system (20), is coated on its sides exposed to the exhaust fumes with a dielectric material.

Description

description

Device for the detoxification of exhaust gases from mobile systems

The invention relates to a device for the decontamination of exhaust gases from mobile systems, in which the exhaust gas passes through a plasma reactor which works according to the principle of dielectric barrier discharge and is formed from an arrangement of flat plates in which metallic and dielectric layers alternate, whereby discharge paths arranged spatially next to one another are formed.

In the case of dielectrically disabled discharges, one also speaks of a "silent discharge". Such silent discharges are generated between electrodes, between which there is at least one dielectric layer or body, in such a way that a gas discharge is direct, i.e. from electrode to electrode, is not possible.

Devices for generating stylish discharges are known from the prior art. Such devices are often used for ozonizers and usually have a coaxial geometry here.

Other devices corresponding to the prior art for generating silent discharges have plane-parallel arrangements of electrodes and are used to generate UV radiation.

From DE-OS 37 08 508 a device is already known which serves to reduce pollutants in combustion exhaust gases, in which at least one reaction space is arranged in the exhaust gas duct, which is formed from metallic, parallel plates or concentric tubes and has a gap cross section has, wherein at least one plate or a tube of the reaction chamber is coated with an electrically insulating dielectric material. Furthermore, such a device is known from WO-A-92/19361, in which an exhaust gas is conducted into an annular space between an outer metal cylinder and an inner cylinder made of ceramic.

The prior art in particular is concerned with clarifying the functioning of the method for detoxifying exhaust gases according to the principle of dielectric barrier discharge. Power plants on the one hand and also motor vehicles on the other hand are addressed there, the construction of the devices not being specified precisely.

A compact design of the plasma reactor is imperative, particularly for use in mobile systems. At the same time, however, a large effective length and / or a large effective cross section of the reaction space should be ensured.

Starting from the known plasma reactor comprising a plurality of discharge sections arranged spatially next to one another, it is therefore an object of the invention to achieve a large effective length with a compact, space-saving design.

The object is achieved according to the invention in a device of the type mentioned at the outset in that the discharge sections are connected in series in terms of flow and are arranged concentrically to one another, for which purpose two tube systems are nested coaxially one inside the other. The first pipe system preferably consists of at least three metallic pipes arranged coaxially on a support plate and the second pipe system consists of at least two pipes arranged coaxially on a support plate. These two pipe systems are nested to build the reactor. In the invention, the second tube system, which does not form an outer wall of the plasma reactor, is advantageously covered with a dielectric layer on the entire surface. However, both pipe systems can also be dielectrically coated on their sides facing the plasma.

Further details and advantages of the invention result from the following figure description of exemplary embodiments. They show

Figure 1 shows a plasma reactor in a sectional view, Figures 2 and 3, the two pipe systems to build the

1 and FIG. 4 a section of the plasma reactor perpendicular to FIG. 1.

The figures are described together below.

In FIG. 1, 1 denotes a reactor which, according to FIGS. 2 and 3, consists of two pipe systems 10 and 20 which are nested coaxially one inside the other.

The pipe system 10 according to FIG. 2 consists, for example, of three metallic pipes 12, 13 and 14 arranged coaxially on an annular support plate 11. The inner pipe 12 breaks through the support plate 11 and serves as a gas inlet pipe. Its diameter is determined by the requirements of the exhaust gas generating system. The inside and outside diameters of the further tubes 13 and 14 are selected such that the radial distances a between the tubes 11 to 13 are equal to one another and that the tubes 11 to 13 of the tube system 10 are the same distance from those of the tube system 20 everywhere have s.

In another embodiment, which is not shown in detail, the distances between the tubes 11 to 13 can be selected such that the cross section to be flowed through remains constant as a function of the distance R from the central axis, ie d ~ R - * - is. In a further embodiment, the striking distance of the silent discharge is specifically changed as a function of the radius.

2, the outer diameter of the outer tube 14 is equal to the diameter of the support plate 11. The ends of the inner tubes 12 and 13 are at the same distance 1 from the support plate 11. The outer tube 14 extends beyond the tubes 12 and 13 so far, that the pipe system 20 takes place in the chamber 1 formed from the pipe system 10 and an end plate 30. On the one hand, the distance b between the ends of the pipe system 20 and the support plate 11, on the other hand, the distance c between the ends of the pipes 12 and 13 and the support plate 21 of the pipe system 20 and furthermore the distance d between the support plate 21 of the pipe system and the end plate 30 is equal to the lay length , so that applies

b = c = d = s.

The pipe system 20 according to FIG. 3 consists of metal parts and is covered on its entire inner and outer surface with a dielectric layer 28. It consists, for example, of two tubes 22 and 23 arranged coaxially on an annular support plate 21.

The inner and outer diameters of the tubes 21 and 22 are chosen in FIG. 3 such that the radial distances e of the dielectric coated tubes are the same among one another and that the tubes of the tube system 20 have the same radial distance s everywhere as those of the tube system 10. The outer diameter of the outer tube 23 is equal to the diameter of the support plate 21. The distances m of the ends of the tubes 21 and 23 from the support plate are the same. The pipe system 20 is introduced into the pipe system in such a way that the spacing requirements mentioned when coating the pipe system 10 are met. The radial distance a of the tubes 14 and 23 is electrically nic ^'ge it conductive spacers respects.

As already mentioned, the distances between the tubes 21 and 23 can be selected so that the cross-section to be flowed through as a function of the distance from the central axis either remains constant or that the stroke length s assumes different, particularly advantageous values.

In Figure 3, the support plate 21 is electrically conductively connected to a supply line 26 at a suitable point. The feed line is encased with a dielectric layer 28, which connects seamlessly to the dielectric sealing of the pipe system 20 and is led through the end plate 30 out of the reaction chamber. The end plate 30 has a. Gas outlet connection 31, the diameter of which is equal to the diameter of the gas inlet pipe 12.

The pipe systems 10 and 20 are therefore electrodes between which a silent discharge can be operated. For this purpose, they are connected to a generator 40, which provides an electrical voltage with a suitable time profile, amplitude, frequency and / or pulse shape, pulse / pause ratio. The plasma reactor formed by the pipe systems is used in any, e.g. Flows through the exhaust gas in the direction indicated by the arrows in FIG. 1.

The number of pipes of the pipe systems 10 and 20 given by way of example is not limited to three or two. Like the total length of the arrangement, it results from the desired degree of detoxification and from the input parameters. The pipe system not provided with a dielectric layer can be coated with a conventional catalyst material on the side facing the exhaust gas in order to achieve improved detoxification. Instead of the pipe system 20, the pipe system 10 can also have a dielectric on the side facing the exhaust gas. be coated trically. In particular, a ceramic catalyst material can take on the role of the dielectric. Such a material can consist, for example, of mixtures containing titanium oxide, vanadium oxide and tungsten oxide.

In further embodiments, both pipe systems 10 and 20 of FIG. 1 can also be completely dielectric-coated at least on their facing sides facing the plasma. In addition to the detoxification effect, this has the advantage that the metallic surfaces are largely protected against corrosion. Furthermore, the distances b, c and d of the figure, which were defined above as the pitch, can also be different from one another. The stroke distance is thus varied, in particular in the reverse region of the exhaust gas flow, which can have advantages in practice. It is also possible for the cross section of the tubes to deviate from the circular shape and for example to be elliptical or also rectangular.

Claims

1. Device for the detoxification of exhaust gases from mobile systems, in which the exhaust gas passes through a plasma reactor which works according to the principle of dielectric barrier discharge and which has an arrangement of at least two electrodes and at least one dielectric body, the plasma reactor Consists of several spatially arranged discharge paths, characterized in that the discharge paths (2 to 9) are connected in series in terms of flow and are arranged concentrically to one another, for which purpose two tube systems (10, 20) are coaxially interconnected.

2. Device according to claim 1, so that the first pipe system (10) consists of at least three metallic pipes (12 to 14) coaxially arranged on an annular support plate (11).

3. Device according to claim 1, so that the second pipe system (20) consists of metal parts (21 to 23) which are covered with a dielectric layer (28) on the entire surface.

4. Apparatus according to claim 3, so that the second pipe system (20) consists of at least two pipes (22, 23) arranged coaxially on an annular support plate (21).

5. The apparatus of claim 3, d a d u r c h g e ¬ k e n n z e i c h n e t that both pipe systems (10, 20) are dielectric coated at least on their sides facing the exhaust gas

6. Apparatus according to claim 3 or claim 5, since ¬ characterized in that the dielectric layer consists of ceramic catalyst material, in particular from mixtures containing titanium oxide, vanadium oxide and tungsten oxide.

7. The device as claimed in claim 1, so that the striking distance in the more distant discharge paths is smaller than that of the innermost discharge path.