WO2005028081A1

WO2005028081A1 - Device and method for the plasma-assisted purification of exhaust gas and treatment of exhaust air

Info

Publication number: WO2005028081A1
Application number: PCT/EP2004/010535
Authority: WO
Inventors: Jens Grundmann; Siegfried Müller; Wolfgang Reich; Rolf-Jürgen ZAHN
Original assignee: Institut Für Niedertemperatur- Plasmaphysik E.V.
Priority date: 2003-09-24
Filing date: 2004-09-20
Publication date: 2005-03-31
Also published as: DE10344489A1; EP1663454A1; DE10344489B4

Abstract

The invention relates to a device for the plasma-assisted purification of exhaust gas and treatment of exhaust air, said device comprising at least one treatment chamber for producing dielectrically impeded discharges. The inventive device is characterised in that the treatment chamber is embodied as a structured gas chamber with partial gas chambers (1) between at least one conductive structured electrode (2) and at least one insulant (3) located on the structural elevations of the structured electrode (2) and forming a boundary surface. The boundary surface consisting of an insulant (3) is either part of an insulated electrode or separates the conductive structured electrode (2) from another smooth or structured conductive electrode. Under certain conditions, it is advantageous to interchange the design of the conductive electrode and insulant or dielectric and to arrange a structured dielectric.

Description

<description id = "desc"> Description <invention-title id = "invt">

Device and method for plasma-assisted exhaust gas purification and treatment of exhaust air

</ Invention-title>

<technicai-fieid id = "tec fid"> Technical field

The invention relates to the field of exhaust gas purification, in particular a device for decomposing soot from exhaust gases from combustion processes, the soot being subjected to a plasma treatment with a device which works on the principle of dielectric barrier discharge. The invention is also suitable for decomposing toxic or environmentally harmful gaseous exhaust gas components. It can also be used for the plasma treatment of exhaust air mixed with aerosols.

</ Technical-field>

<bac ground-art id = "bart"> State of the art

Against the background of further efforts to reduce environmental pollution, limit values for the pollutant emissions from combustion processes are announced, which go far beyond the prior art. According to the current state of knowledge, further progress in reducing particle and NOx emissions can only be achieved with exhaust gas aftertreatment. This applies particularly to the soot emission from diesel engines.

Various ways are described to solve the emission problem. The use of particle filters has been proposed for a long time. While the filtration of the particles is largely uncritical, the regeneration of the filters presents various problems. Soot is deposited in the filter and has to be reacted with oxygen. Exhaust temperatures of more than 550 ° C are required for this. In vehicles, the exhaust gas in the city cycle often only reaches temperatures below 200 ° C. Various thermal methods have therefore been proposed for the subsequent heating of the exhaust gas. However, this leads to an inadequate increase in fuel consumption. Local overheating can also partially destroy the filter element.

Various other methods therefore try to lower the soot oxidation temperature, for example by additives or coating the filter with a catalyst. Additives lead to an additional irreversible ash deposition of the filter and thus severely limit the service life. In the case of coatings, sulfur causes poisoning and additional sulfate ash deposits. Despite such measures, the required oxidation temperature is often not reached.

There are also combination solutions of the methods mentioned or electrostatic filters known, but which do not fundamentally solve the problems shown.

In addition to the above traditional methods for removing toxic substances and soot from combustion processes, it has also been proposed or investigated to treat exhaust gases in a plasma. It is known that a wide variety of chemical reactions can be initiated with plasmas, which mainly take place via very reactive species, so-called radicals. This has also been investigated and used with regard to the treatment of exhaust gases or in general for plasma chemical reactors. Solutions are also proposed, which use a dielectric barrier discharge to generate suitable plasmas.

The phenomenon of dielectric barrier discharge (hereinafter also DBE), often referred to as silent discharge, glow discharge at normal pressure or alternating voltage discharge between insulated electrodes, has long been known. This form of discharge is characterized by the fact that it can be operated in a wide pressure range and ranges from a few 10 mbar to a few bar. The electrode spacing is in the range from tenths of a mm to a few mm. Dielectrically impeded discharges are characterized in that at least one of the conductive electrodes is provided with a dielectric, which then forms an insulated electrode, or that this dielectric is arranged between the conductive electrodes. The shape of such arrangements can take many forms. Depending on this form and the other parameters, specific properties of the DBE are often achieved.

In general, the DBE can be operated with sinusoidal or rectangular AC voltages in the range from a few Hz to several 100 kHz. Due to the insulation and the charge carriers deposited on it, the discharge is limited automatically after the breakdown and the discharge duration is usually only a fraction of the half-period of the applied maintenance voltage. This simplifies control. There is also no major gas heating. Various designs of the DBE in the gas space that forms the discharge space are known from the form of the discharge. Frequently with large-area electrodes, numerous small to a few tenths of a millimeter thick discharge filaments, also called filaments, are usually formed in a statistically distributed manner. The filaments form widenings in the transition area to the insulated electrodes, which often merge into surface sliding discharges with numerous other thin discharge channels.

[0009] Such sliding discharge phenomena can be dominant in special arrangements, so-called coplanar or surface discharge arrangements. It is also known that homogeneous, non-filamented discharge structures can be formed in particular in gas fillings with noble gases or their mixtures. Most of the time, the discharge tends to filament. In addition, various combinations and transitional forms of discharge training are possible. Some of the special arrangements in the literature are also given specific names in order to emphasize special discharge properties. Examples of this are the surface discharge arrangements and coplanar discharge arrangements already mentioned, but also sliding discharges or surface sliding discharges. The distance between the electrodes is then Discharge path resulting from gas. Here the term DBE is also intended to include such special arrangements or characteristic discharge properties. Regardless of the type of training, the term DBE is used here as a generic term for the various types of training.

General representations of DBE are e.g. contained in: G. J. Pietsch and M. Haacke, Some properties of different types of dielectric barrier discharges for ozone production, Int. Sympos. on High Pressure Low Temperature Plasma Chem., Greifswald / Germ., Sep. 10-13, 2000, Contributed Papers Vol. 2, pp. 299-303, and U. Kogelschatz, B. Eliasson, W. Egli, Dielectric Barrier Discharge's Principle and Applications, Invited Plenary Lecture, XXIII ICPIG, July 17-22 ., 1997, Toulouse / France, J. Phys. IV, France 7 (1997) 04-47.

A wide variety of configurations have been proposed, in particular for gaseous media, which operate on the principle of a conventionally constructed DBE arrangement. A corresponding device is e.g. described in DE-OS 37 08 508.

It has also been proposed, for example in DE-OS 195 25 754 A1 and DE-OS 195 25 749 A1, to divide the reactor volume into spatially periodic structures, so that discharge zones and discharge-free zones arise in the direction of flow. The shape has means for increasing the field in the area of the discharge zones. DE-OS 195 25 749 A1 also provides for the introduction of chemically active materials in the area of the surfaces of the structures.

DE-OS 195 34 950 A1 describes a reactor which consists of several modules with a plurality of parallel and spatially separated channels in a dielectric body with electrodes inserted therein. A similar structure results from DE 100 27 409 C1. It specifies a plasma reactor in which a Plasma is formed in a penetration section between the profiles of two components, the cores of which consist of differently shaped sheet metal layers. The penetration section for the plasma generation is located between two components, in which channels are then formed. The components also have channel structures.

A principle similar arrangement is also in the contribution by K. Muraoka et al., Treatments of Environmentally Hazardous Materials by Combinations of Barrier Discharges with Densification by Adsorption / Trapping, ICPIG XXVI, Greifswald 20003, Proc. Vol. 3, pp. 201-202. The main goal is the treatment of VOC. Wavy zeolites are arranged between insulated electrodes, so that a honeycomb structure results. The flow takes place lengthways in the channels formed.

Another version for the construction of a dielectric barrier discharge is provided in the patent DE 43 02 456 C1. At least one electrode consists of a voltage-excited plasma.

In order to influence the plasma chemical reaction processes, it has also been proposed to add certain additives to the exhaust gas to be treated. For example, in DE 42 31 581 A1 a device for exhaust gas purification is assigned a feed for admixtures.

In these reactors constructed according to the prior art, the exhaust gas stream to be treated flows longitudinally to the electrode surfaces running parallel to one another through the discharge space. It enters one end of the discharge space formed by the electrodes and exits the other end. When inflowing heavily soot-laden exhaust gas, such as diesel exhaust gas, the soot particles would largely pass the system freely because of the relatively open structure of such reactors, without the soot particles being completely converted to CO or CO2 or otherwise bound. With changing loads, Flow velocity and ultimately different loading of the exhaust gas with soot, the linear expansion in the direction of flow must be dimensioned so that even in the worst case there is a complete decomposition. Under practical conditions, an inadequate length extension of the treatment room would be necessary. This also increases energy consumption.

This also applies to an arrangement as described in Journal of Chemical Engineering of Japan, Vol. 24, No. 1 (1991) P100-105 was used to decompose sample carriers with soot that had been introduced into the gas space of a DBE.

In solutions according to DE 100 27 409 C1 there is also the fact that the component arranged on the inflow side does not contain any plasma regeneration and could also clog in narrow channels.

[0020] A somewhat modified form of an arrangement with opposing electrode surfaces is disclosed in DE 100 07 130 C1. Electrodes insulated on both sides are proposed which, in the direction of flow, consist of waves with constant electrode spacing, of waves with repetitive changes in the electrode spacing or of fold patterns. Soot is separated by inertial forces and supported by electrical fields.

The degree of separation of such an arrangement is inadequate due to the flow, in particular for small particles. Furthermore, a voltage-resistant coating of the electrodes is necessary, which is complex. Spacers between the electrodes are also required.

Another possibility of reactor construction is named in US Pat. No. 4,954,320. The device contains metallic electrodes, between which a loose bed of dielectric insulation bodies, e.g. B. ceramic balls is introduced. A comparable variant is represented by the device according to DE 44 16 676 C2. In this case, the space between plate-shaped electrodes is filled with insulating bodies, which have channels or pores along their entire cross section. In the case of beds of insulating material introduced into the discharge space, high levels of soot separation can be achieved, but there are various problems with regeneration and operation. On the one hand, beds or fiber composites in the gas space require higher voltage amplitudes to generate a plasma in the remaining gas space, which is more complex for the control. On the other hand, there is an increased back pressure and there is also the risk of clogging with soot and slag.

For an effective treatment of soot, DE 197 17 890 C1 has also already proposed collecting soot on a porous filter element and exposing it to the plasma of a DBE. A similar principle is given in DE 100 57 862 C1.

In these filter systems with plasma regeneration constructed according to the prior art, the problem of ash deposition and constipation remains. In the case of small-pore filter elements, soot is deposited primarily on the surface, which increases the back pressure due to deposited ash as the operating time increases. In the case of larger pores, a thicker wall thickness of the porous filter element must be selected for effective filtering. Then you would have a combination of surface and depth filtration. Particles deposited in depth cannot be directly exposed to the plasma, so that the soot can only be broken down there via high temperatures, stable reaction products or exhaust gas components, which limits the available work area and location.

</ Background-art>

<disciosure id = "disc"> Disclosure of the invention

<tec -probiem id = "tprob"> Technical task

The object of the invention is to provide a freely flowable filter system with regeneration by a plasma, in which the plasma is formed with a DBE, in which there is also sufficient space for the intermediate storage of soot and a reservoir for Ash deposits are present and where the filter medium is accessible and can be exposed to the plasma at all points.

Likewise, the invention should be suitable for the plasma treatment of exhaust air which is mixed with aerosols.

Furthermore, the structure of the system should be compact and technologically simple to manufacture and inexpensive.

</ Tech problem>

<tech-soiution id = "tsoi"> Technical solution

The object is achieved by the features of claims 1-3 and 15. The other claims indicate further advantageous refinements.

On the one hand, it has been shown that, under certain conditions, a plasma that almost covers the conductive electrode can be generated in the gas space in a gas space formed between an insulating material (dielectric) and a conductive electrode structured according to the invention. Compared to arrangements according to the prior art, the device according to the invention contains, as an essential element, a coherent form, structured in all spatial directions, made of an electrically conductive material, which on the one hand serves as an electrode and in this case represents an electrode structured in all spatial directions, hereinafter also structured Designated electrode.

On the elevations of the structured electrode, an insulating material is in contact with the insulating material. This insulating material forms a delimiting surface for the structured electrode. The structured electrode also acts as a spacer.

In this way, a structured gas space with partial gas spaces, hereinafter called structured gas space with partial gas spaces 1, is formed between the structured electrode and the surface of the insulating material. Another electrode is also attached to the insulating material. In this way, the structured gas space with partial gas spaces forms the gas space for discharges. The structured electrode is formed by a wire mesh, coherent bodies or structures or individual bodies lying one against the other made of an electrically conductive material, these forming an orderly filling of one or two layers. The structured electrode can also consist of a sheet of sheet metal, perforated sheet metal, porous sheet metal material or thin wire fibers (metal fleece) which forms such sheets or approximates these sheets.

The structured gas space formed by the structured electrode and the insulating material with partial gas spaces has an open structure on two opposite end faces for the inflow and outflow of exhaust gas. On the other hand, the structured electrode practically also functions as a filter element. The open structure for the lateral inflow and outflow of soot-containing exhaust gas is designed in such a way that there are numerous deflections of the gas flow between the inlet and outlet and thus good separation of particles. With this arrangement, only a small flow back pressure is generated. Furthermore, the dwell time of the exhaust gas in the discharge configuration is lengthened by the numerous deflections of the gas flow and enlargement of the flow cross section. This increases the efficiency for the deposition and direct oxidation of particles suspended in the gas space by means of a plasma.

For the overall function, the shape of the electrode structure according to the invention is essential. From the point of view of optimal plasma generation, the electrode structure is chosen in such a way that there is no concentration of the discharge at the tips or sharp edges. Rather, as flat or rounded surfaces as possible are provided for the structure of the electrodes. The shape of the electrode structure ensures that the surfaces free towards the structured gas space with partial gas spaces are included in the discharge process, provided that a suitable alternating voltage is applied for the ignition. First of all, regardless of the gas pressure, an optimal discharge path will always be set, which corresponds to the minimum in dependence of the ignition voltage on the product of gas space thickness d and gas pressure p. In other words, a discharge is initially initiated in the immediate vicinity of the contact area of the dielectric and the protruding area of the material structures or structured electrode, because the optimal electrode spacings (gas space thicknesses) are available for ignition.

After the ignition phase, further areas of the structured electrode and volume segments of the partial gas spaces are then included in the discharge process in the course of the further voltage rise.

Due to the pronounced spatio-temporal ignition sequence, the discharge current is distributed over a larger section of the half-cycle of the applied AC voltage, which represents a great relief for the control, since maximum power does not have to be delivered in the shortest possible time.

Overall, it is advantageous that an improved overall efficiency, in particular for soot cleaning, is achieved compared to the prior art. In the device according to the invention, all areas of the arrangement can be used for soot decomposition. In addition to improved reaction conditions in the gas space due to the extended residence time of the soot particles, the plasma can also directly include the surfaces of the structured electrode functioning as a filter element in the oxidation of the particles deposited there. Compared to small-pore filter media, in which some of the particles are also separated in depth and are no longer accessible to the plasma, direct contact in the plasma is always possible here. This means that you do not have to rely on reactions via stable reaction products such as ozone or nitrogen dioxide for the deeply separated particles, which also only become effective at higher temperatures. Furthermore, the structured gas space with the partial gas spaces results in a substantially increased storage capacity for soot particles and in particular for slag products resulting from the regeneration. This significantly extends the service life compared to conventional small-pore filter systems with plasma regeneration.

In general, the structured electrode can be shaped differently. It can be shaped as a mirror-symmetrical or asymmetrical structure to the insulating material boundary (s) covering it, or the electrode structure is, seen from an insulating material boundary, identical to the other viewing direction as a negative structure (i.e. spatially offset), as is the case with a structured sheet metal layer or wire mesh shape. Overall, mountain and valley structures are preferred for the structured electrode, an offset to the previous order being provided in the direction of inflow, so that the gas flow can be deflected on the way between inlet and outlet. Optimal particle separation is thus achieved, while the throughflow is largely retained. Due to the mountain and valley structure of the structured electrode, a well-distributed plasma formation is also achieved over the surface.

In order to influence chemical reaction sequences in a targeted manner, means known per se from the prior art can also be included in the embodiment of the invention. In particular, the use of catalytic materials that are applied to the structured electrode and / or insulating material plate is considered here. In this way, the oxidation of soot and the decomposition of NO, exhaust air, which is mixed with aerosols, and other gaseous components can be supported according to the known mechanisms. In this way, the oxidation of soot and the decomposition of NO and other gaseous components can be supported according to the known mechanisms. For the coping with larger exhaust gas flows under real technical conditions, an easy scalability has also been found to be advantageous. On the one hand, a stacked construction can easily be realized by simply alternating a sequence of the described elements structured electrode and insulating material. Even non-structured electrodes, as usually used in the prior art, hereinafter also referred to as smooth electrodes, can be included in the sequence, as explained in more detail in the exemplary embodiments. In the case of a stacked construction, the electrodes are alternately combined into two groups. One electrode group is preferably grounded and the other electrode group is supplied with a suitable AC voltage.

In addition to a stack arrangement, an arrangement by winding the elements forming the device according to the invention is also possible.

Overall, a compact device can be produced with simple means. This simplifies production and reduces the cost of material.

It has also been shown that under certain conditions it is possible to reverse the arrangement described above in terms of shape and sequence by interchanging the shape of the conductive electrode and dielectric.

A gas space is then formed between the conductive electrodes and an insulating material (dielectric) structured according to the invention, in which a plasma almost covering the three-dimensionally structured insulating material can be generated. Compared to arrangements according to the prior art, the device according to the invention contains, as an essential element, a coherent shape, which is structured in all spatial directions and is made of an electrically non-conductive material

As stated in the previous basic principle, the structured insulating material acts simultaneously as a dielectric and as a spacer. The functioning with regard to deposition and oxidation corresponds to the principle already described above. [0050] Further advantageous configurations, operating modes and combinations with other methods are also possible, as shown in the description of exemplary embodiments and operating modes. </tech-solution></disclosure>

<descιϊption-of-drawings id = "desd"> Brief description of the drawings [0051] In the following, devices or device parts according to the invention with further features are explained in more detail with the aid of descriptions or descriptions of figures. 1 shows schematically the principle of a device in a three-dimensional exploded view, [0054] FIG. 2a) shows a sectional view of the basic structure with a structured electrode consisting of spherical shapes, [0055] FIG. 2b) a 3-dimensional representation of a structured electrode consisting of spherical shapes corresponding to FIG. 2a), [0056] FIG. 3 a sectional representation of the basic structure with two structured electrodes consisting of spherical shapes and three smooth electrodes, [0057] FIG. 4 a 3-dimensional one 5 shows a 3-dimensional exploded view of a stacked arrangement with three electrodes made of wire mesh, [0059] FIG. 6 shows a 3-dimensional view of a structured electrode with flat sections from a formed sheet metal layer, [0060] FIG. 7 a 3-dimensional representation g of a structured electrode made of a formed sheet metal layer, [0061] FIG. 8 schematic representation of the inflow side with a porous three-dimensionally structured electrode and with a closure of one of the structured gas spaces with partial gas spaces, 9 is a 3-dimensional exploded view of a stack arrangement with three structured dielectrics.

</ Description-of-drawings>

<mode-for-invention id == "mode"> Embodiment (s) of the invention

1 schematically illustrates the basic structure of a device in a 3-dimensional exploded view. In the figure, only the elements important for the function are shown.

As an essential element, the arrangement includes a coherent form, structured in all spatial directions, made of an electrically conductive material. This element serves as an electrode in one function and in this case represents an electrode structured in all spatial directions, hereinafter always referred to as structured electrode 2. A plate made of insulating material 3 is attached to this structured electrode 2. The areas of the coherent structure made of conductive material or structured electrode 2 protruding toward the insulating material 3 are in contact with the plate of insulating material 3. This insulating material 3 forms a delimiting surface for the structured electrode 2.

In this way, a gas space structured in all spatial directions with partial gas spaces, hereinafter referred to as structured gas space with partial gas spaces 1, is formed between the structured electrode 2 and the plate made of insulating material 3. A flat, smooth electrode 4 is also attached to the insulating material 3. The structured gas space with partial gas spaces 1 now forms the gas space for discharges in the arrangement according to the invention. The embodiment variant shown does not require any spacers, since the structured electrode 2 also fulfills this function.

[0066] This initially creates an arrangement for a dielectrically impeded discharge, but with a special conductive structured electrode 2 and the correspondingly structured structured gas space with partial gas spaces 1.

The structured gas space with partial gas spaces 1 formed by the structured electrode 2 and the insulating material 3 is for the delimiting surface made of insulating material 3 open. Laterally, the arrangement according to the invention has an open structure for the inflow and outflow of exhaust gas between two opposite sides. The other two sides are each closed by a suitable side seal.

The open structure for the lateral inflow and outflow of exhaust gas is shaped so that there are numerous deflections of the gas flow between the inlet and outlet. In the arrangement as shown in FIG. 1, the shape of the structured electrode 2 and the structured Gas space with partial gas spaces 1 for the deflection of the gas flow between inlet and outlet in the inflow direction is designed such that an offset to the previous order of the conical structures is formed, so that a direct rectilinear flow is prevented.

In this way, the exhaust gas to be treated, in particular also soot-laden exhaust gas, can flow relatively freely through the structured gas space with partial gas spaces 1 between an inlet side and an outlet side, and furthermore a good separation of particles on the structured electrode 2 can be achieved.

On the other hand, the structured electrode 2 thus also functions as a filter element which can be flowed through relatively freely.

In terms of flow, only a slight back pressure is generated compared to porous filter media.

Furthermore, the dwell time of the exhaust gas and thus of the particles in the discharge configuration is extended by the numerous deflections of the gas flow and enlargement of the flow cross section. This increases the efficiency for treatment with a plasma.

Furthermore, the shapes of the structured electrode 2 and the three-dimensionally structured gas space with partial gas spaces 1 allow a substantially increased storage capacity for soot particles or slag products resulting from the plasma treatment without a noticeable increase in the exhaust gas back pressure. The shape of the structured electrode 2 is essential for the overall function. In addition to the aspects of flow, filtering and storage, optimal plasma generation also plays an important role. For this purpose, the structured electrode 2 in the embodiment according to Fig. 1 is designed in a shape in which conical structures rise from a plate.

When a suitable alternating voltage is applied between the structured electrode 2 and the smooth electrode 4, a discharge is initially initiated in the immediate vicinity of the contact area of the insulating material 3 and the conical elevation of the structured electrode 2, because here the most optimal electrode distances for ignition of the discharge ( Gas space thicknesses). This will result in an optimal discharge path, which corresponds to the minimum depending on the ignition voltage on the product of gas space thickness d and gas pressure p. After the ignition phase, further areas of the structured electrode 2, the insulating material 3 and volume segments of the structured gas space with partial gas spaces 1 are then included in the discharge process in the course of the further voltage rise. This is primarily a geometric effect. In order to include larger electrode spacings in the discharge, correspondingly high AC voltages are applied for reliable ignition over the structured gas space with partial gas spaces 1.

For the smaller gas space thicknesses resulting from the structure, there is therefore an overvoltage across its gas space. With a DBE, the discharge is reignited in every half-wave of the AC voltage applied across the gas space, which is also pulse-shaped. The time of discharge at the smaller gas space thicknesses occurs with earlier phase positions of the maintenance voltage, while the largest partial gas space sections only ignite at phase positions with the higher voltages. Due to the pronounced spatial-temporal ignition sequence, the discharge current is distributed over a larger one Section of the half period of the applied AC voltage. This relieves the control, since maximum electrical power does not have to be delivered in the shortest possible time.

Now there are areas with high exhaust gas temperature in particular in the case of exhaust gases from diesel vehicles in the driving cycle, so that the soot decomposition could either take place thermally or via nitrogen dioxide formed in a suitable manner from the nitrogen monoxide. It has also been shown that ozone is also well suited for this, especially in the problematic temperature range below 200 ° C. In this respect, on the one hand, switching the plasma on or off according to the temperature of the exhaust gas can be included as a control option in the operating mode. This reduces the electrical power required for the plasma treatment. On the other hand, plasma can convert nitrogen monoxide to nitrogen dioxide and generate ozone. Nitrogen dioxide can then i.a. for soot decomposition in the medium temperature range, ozone at temperatures below 200 ° C.

This presupposes a relatively continuous supply of nitrogen dioxide and ozone. One possibility is to choose suitable pulse-pause ratios for the maintenance voltage, the pulse trains being so long that sufficient nitrogen dioxide and ozone are provided. The proposed device now enables an additional advantageous control for the exhaust gas treatment, in particular the soot reduction. For this purpose, the voltage applied across the structured gas space with partial gas spaces 1 is selected such that only partial areas of the structured electrode 2 and also of the structured gas space with partial gas spaces 1 and the insulating material 3 are included in the discharge. The amplitude of the applied voltage thus corresponds to the minimum of the ignition voltage for this partial gas space. In this way, a discharge is ignited and a plasma is generated only in the immediate vicinity of the contact of the insulating material 3 and the conical elevation of the structured electrode 2, because here again the smallest There are electrode gaps. It is advantageous that the voltages for igniting the discharge are low because of the small gas space thicknesses. The soot deposited in this area is directly exposed to the plasma so that reactions via reactive radicals can take place. Since the lifespan of radicals generated in the plasma and flowing in the exhaust gas is relatively short, reactions via radicals will primarily take place in the immediate area of the plasma formation. For areas of deposited soot that are not directly exposed to the plasma, the mechanisms mentioned can now be included in the soot decomposition. This is, on the one hand, cleaning at high temperatures and, on the other hand, the use of relatively stable reaction products such as nitrogen dioxide and ozone from the plasma treatment in partial areas of the structured electrode 2. The partial areas of the device according to the invention, particularly the structured electrode 2, which are not included in the plasma formation, take over one Intermediate storage function for soot, which is then decomposed at the appropriate temperatures according to the mechanisms described. Because of the largely open structure of the device acting as a filter, the intermediate storage of soot is not associated with any appreciable increase in the exhaust gas back pressure.

[0079] All of the degradation mechanisms for soot can thus be used effectively, which in particular requires less electrical power.

The device according to the invention is thus also suitable, depending on the space available, to be placed at different points in the vehicle with an effective method of working. This can be close to the engine or away from the engine, since you do not have to rely on certain temperature ranges for the functionality.

Suitable materials for designing the device according to the invention are those known for conventional DBE configurations. The conductive electrodes are preferably made of metallic materials. Materials such as ceramics, glass, Mica or ferroelectrics can be used. Other materials are also possible, provided they are suitable as a dielectric.

To support the reaction processes in the decomposition of soot or degradation of NO, the structured electrode 2 or the insulating material 3 can also be constructed from a catalytically active material or be coated with it.

The geometrical dimensions of the reactor configuration are adapted to the volume to be treated and the soot loading of the exhaust gas. In the case of a high gas throughput, the devices described above can be operated in flow with several in parallel.

It is also advantageous to have a larger treatment area on the inflow side than on the outflow side, since the higher soot concentration is present on the inflow side. In such an embodiment, the inflow side is then wider than the outflow side. The device then either has a trapezoidal shape, or the shape of the elements forming the discharge configuration consists of annular disks.

In the case of a mold made of annular disks, the exhaust gas is supplied in a suitable manner on the outer ring and removed on the inner ring.

For assembly, the device is mounted in a suitable housing for holding the device elements and channeling the exhaust gas flow. However, the device elements themselves or parts thereof can also form the housing. Furthermore, the housing is provided with a corresponding voltage feedthrough.

In the event that the proportion of oxygen in the exhaust gas is too low, ambient air can also be added to it by assigning a suitable device for admixtures to the device.

The shape of the structured electrode 2 is not tied to the embodiment according to FIG. 1. In general, the electrode structure is selected in such a way that the discharge cannot concentrate at the tips or sharp edges. The surfaces are as flat or rounded as possible provided for the structured electrode 2, as is also made clear by the other exemplary embodiments.

In the exemplary embodiment according to FIG. 1, the structured electrode 2 has an asymmetrical structure, so that the gas space with partial gas spaces 1 is formed only on one side. It is now advantageously also possible to form two gas spaces with partial gas spaces 1 with a structured electrode 2. Such an example is illustrated in FIGS. 2a) and 2b).

2 a) shows a sectional view of the principle of, in FIG. 2 b) a 3-dimensional representation of the structured electrode consisting of spherical shapes.

In this case, the structured electrode 2 is designed as a coherent structured form of adjacent balls made of an electrically conductive material. This spherical structure lies between two plates made of insulating material 3, whereby two structured gas spaces with partial gas spaces 1 are now formed. Suitable flat smooth electrodes 4 are in turn attached to the plates made of insulating material 3. These can be vapor-deposited as a conductive layer or they can be designed in another way, e.g. as plates or flat lattice structures.

The structured gas spaces with partial gas spaces 1 formed by the structured electrode 2 and the two plates made of insulating material 3 are again open towards the delimiting surface made of insulating material 3. On the side, too, there is again an open structure for the inflow and outflow of exhaust gas between two opposite sides, while the other two sides are each closed by a suitable side seal 5, as shown in FIG. 2a). In this exemplary embodiment, the two gas spaces 1 formed by the structured electrode 2 also have connections to one another, so that further deflections are present for the gas to flow through. For the filter function and plasma treatment, a change of gas flows from one structured gas space to another can also take place. As a result, the flow is advantageous The duration of the exhaust gas in the plasma is extended and the degree of separation of particles is increased.

To ignite gas discharges in the two gas spaces with partial gas spaces 1, suitable alternating voltages are applied between the structured electrode 2 and the smooth electrodes 4. In this case, the two outer smooth electrodes 4 are preferably grounded, while the high-voltage side lies on the structured electrode 2. This also provides good protection against contact with the high-voltage electrode.

As already described in the first exemplary embodiment, discharges are initially initiated in the immediate vicinity of the contact area of insulating material 3 and the elevations of the structured electrode 2. The structured electrode 2 here forms hemispherical structures practically symmetrically on both sides, so that in this case discharges can be generated on both sides of the structured electrode 2 in the two gas spaces with partial gas spaces 1. With a suitably high voltage amplitude, further areas of the structured electrode 2 and volume segments of the structured gas spaces with partial gas spaces 1 can be included in the discharge process again after the ignition phase in the course of the further voltage rise. In this way, a load and operating point-dependent voltage amplitude control can also be carried out in the plasma treatment of exhaust gases from diesel engines by using differently sized partial areas of the structured electrode 2, the plates made of insulating material 3 and the structured gas space with partial gas spaces 1 for plasma formation. This in turn enables the soot to be stored appropriately.

With larger volume flows there is again the possibility for the parallel operation of several systems. A corresponding representation is given in Fig. 3) for a device previously described according to Fig. 2a) and 2b). 3) shows a sectional illustration of the basic structure with two structured electrodes consisting of spherical shapes and three smooth electrodes. It is a simple stacked construction of the elements structured electrode 2, plate made of insulating material 3 and smooth electrode 4. A smooth electrode 4 lying between two plates made of insulating material 3 forms the common electrode to two adjacent structured electrodes 2. This principle can be used for larger orders will be continued accordingly. The structured gas spaces with partial gas spaces 1 are then formed between the structured electrodes 2 and the plates made of insulating material.

The AC voltage supply is designed such that one electrode group is acted upon with one potential and the second electrode group with the other. It is preferably provided that all smooth electrodes 4 are grounded and the structured electrodes 2 form the high-voltage side. Even with larger stack arrangements, the electrodes on the outside are preferably grounded because of the high-voltage protection. For this purpose, the arrangement preferably consists of an odd number of smooth electrodes 4 and an even number of structured electrodes 2 with the plates of insulating material 3 lying between them.

Further shapes of structured electrodes as well as simple stack arrangements are now possible. The shape of a wire mesh is another example of a structured electrode 2. Such an example is shown in FIG. 4. In FIG. 4, a 3-dimensional exploded view of the basic structure of an arrangement with a structured electrode 2 consisting of wire mesh is shown schematically. The wire mesh can be realized simply and cheaply with a suitable wire mesh, for example with a wire thickness of 0.5 mm and a mesh size of 0.8 mm. Two structured gas spaces with partial gas spaces 1 are formed between two plates made of insulating material 3 and the structured electrode 2 made of wire mesh, similar to the spherical structure described above. The structure given by the wire mesh advantageously enables numerous deflections of the Gas flow, good soot separation and intermediate storage for soot and slag products with low back pressure. The surface areas of the structured electrode 2 that are free toward the structured gas spaces with partial gas spaces 1 can also be included in the discharges and plasma formations from both sides of the gas spaces with partial gas spaces 1.

In particular in the case of stack arrangements, it has been shown that in a further embodiment according to the invention, the smooth electrode 4 can also be largely dispensed with.

5, the core for the representation of the principle consists of an alternating element sequence of four plates made of insulating material 3 and three structured electrodes 2. For larger arrangements and volume flows, this sequence can be continued accordingly. Different potentials are alternately applied to the structured electrodes. In the case of larger stack arrangements, every second of the structured electrodes 2 is preferably grounded again, while the others are acted upon by the high-voltage potential. Two opposing structured electrodes 2 thus form the electrodes for DBE in the two structured gas spaces 1 formed between the two structured electrodes 2 and the plate made of insulating material 3. It is very easy to design a device according to the invention in a stacked arrangement because only one for the core area Sequence of structured electrodes 2 and plates made of insulating material 3 is required. A smooth electrode 4 is preferably used at the beginning and end of such an arrangement, so that no areas arise without the possibility of plasma formation, as would occur with a symmetrical structured electrode 2 on the respective outer sides.

In addition to the compact shapes for the structured electrode 2 shown in the previous exemplary embodiments, such shapes are layers of sheet metal which form or approximate these shapes, perforated sheet, porous sheet-like material (e.g. sintered metal sheets) or thin wire fibers possible.

Designs with these shapes have the advantage that they can be made very thin, so that weight is saved accordingly.

Fig. 6 shows a 3-dimensional representation of a structured electrode with flat sheet metal sections from a formed sheet metal layer. As in the example according to FIGS. 4 and 5, this is arranged as structured electrode 2 in the device. Again, two structured gas spaces with partial gas spaces 1 are formed with a structured electrode 2 between two plates made of insulating material 3. The structure enables numerous deflections of the gas flow, wherein it is preferably again provided that an offset to the previous order structure is formed for the deflection of the gas flow between the inlet and outlet in the direction of inflow. The discharge sequences on the conical structure are similar to those described in FIGS. 1 and 2. A special feature here is that a plasma cannot be formed on all surface areas of the structured electrode 2. This applies to flat sheet metal sections and, in particular, to the depressions formed. These surface areas can be used advantageously for temporary storage of soot and as a slag reservoir. A relatively intensive discharge can be operated in the cone region of the structure without the other sections of the structured electrode 2 being included.

This system can be used particularly close to the engine because of the higher exhaust gas temperatures that occur.

[00104] With shaped sheet metal layers as structured electrode 2, the control principles already discussed are again possible. Such an example is shown in FIG. 7. FIG. 7 shows a 3-dimensional representation of a structured electrode made of a formed sheet metal layer. Corresponding negative structures are formed on both sides of the cone-shaped sheet metal layer on the other side. The conical structure is designed so that there are mountain and valley structures alternate. The discharge can be formed as in the cone structure described above. The surface areas of the structured electrode 2 that are free toward the structured gas spaces with partial gas spaces 1 can thus be included in the discharges and plasma formations from both sides of the gas spaces with partial gas spaces 1.

With the formed sheet metal layer, a good soot separation and intermediate storage for soot as well as slag deposition is made possible with a low back pressure.

[00106] For the treatment of larger exhaust gas flows, a parallel connection of several treatment rooms from structured gas rooms with partial gas rooms 1 can again take place.

In principle, the treatment room can also be enlarged by winding the elements forming the device according to the invention.

A winding design comprises either a sequence of the device elements insulating material 3, structured electrode 2, insulating material 3 and structured electrode 2, or a sequence of insulating material 3, structured electrode 2, insulating material 3 and smooth electrode 4. The elements must be flexible or at least have this property in the assembly phase or have such shapes formed. For the structured electrode 2, the designs with wire mesh, layers of sheet metal, perforated sheet metal, porous sheet-like material (sintered metal sheets) or thin wire fibers meet this requirement in particular. For the insulating material 3, e.g. thermally stable plastic films are suitable. The smooth electrode 4 can consist of a metal foil. The insulating material 3 can also be a carrier of the smooth electrode 4, in that a metal layer has been vapor-deposited, glued on or applied in some other way.

A winding design creates a very compact device which is particularly suitable for small installation spaces. It is also advantageous that you only have two electrodes. The outside lying electrode is preferably grounded again, so that only a high voltage lead is required.

With special requirements, extensions of the device according to the invention with other principles are now advantageously possible. If a particularly high degree of purity of the treated exhaust gas is to be achieved, it can also be combined with conventional filter processes. For this purpose, an arrangement is suitable, for example, in which the exhaust gas is treated with partial gas spaces 1 in a structured gas space according to the invention and at the same time can flow through a porous, structured electrode 2. This consists, for example, of a molded layer of a porous sintered metal sheet or thin wire fiber braid. For a mode of operation according to the invention, a shape of the structured electrode 2 is used, where two structured gas spaces with partial gas spaces 1 are formed by two plates made of insulating material 3. On the inflow side, one of the structured gas spaces with partial gas spaces 1 is sealed against an inflow by a closure 6, as shown schematically in FIG. 8. 8 shows only a sectional view of the upstream side schematically. On the outflow side, the other structured gas space with partial gas spaces 1 is sealed by a closure 6, so that exhaust gas can flow into one of the structured gas spaces with partial gas spaces 1, through which porous, structured electrode 2 flows further into the other structured gas space with partial gas spaces 1, and then flows out through the gas outlet. In the structured gas space on the inlet side with partial gas spaces 1, exhaust gas treatment takes place analogously to the principle described above. In addition, particles are deposited on the structured electrode 2 when flowing through and decomposed in the plasma. Thereafter, the exhaust gas can be further treated in the downstream structured gas space with partial gas spaces 1.

A very intensive treatment of the exhaust gas, in particular the soot components, is thus possible. For larger volume flows or other modes of operation, the principles described for the other versions are again suitable.

In another variant, one of the arrangements according to the invention can advantageously be combined with a conventional particle filter connected downstream. In the arrangement according to the invention, which can be made smaller than when used alone, a large part of soot is already decomposed. The soot particles that have not decomposed are then collected in the conventionally constructed particle filter. The long-lived species such as nitrogen dioxide or ozone generated in the arrangement according to the invention can then regenerate the downstream, conventionally constructed particle filter at corresponding exhaust gas temperatures.

It is advantageous that the pre-cleaning carried out with the device according to the invention means that the downstream conventional particle filter is less loaded with soot and slag. This significantly increases the service life. Furthermore, with the proposed combination of ozone generated in the arrangement according to the invention, soot decomposition and in particular regeneration of a conventional particle filter with low electrical power is possible at low exhaust gas temperatures below 200 ° C.

[00115] In the previous exemplary embodiments, the structured gas space was generated by the structuring of the electrodes. It has now been shown that under certain conditions it is possible to reverse the previously described arrangements with regard to shape and sequence by interchanging the shape of the conductive electrode and dielectric. Such an example is illustrated in FIG. 9. A dielectric structured in all spatial directions, hereinafter referred to as structured dielectric 3a, lies between the smooth electrodes 4. Both form the structured gas space with partial gas spaces 1. This in turn forms a treatment room for the production of dielectrically impeded discharges, one being the structured dielectric 3a almost covering plasma can be generated. The structured dielectric 3a also acts as a spacer.

The functioning with regard to deposition and oxidation corresponds to the principle already described above.

With this basic principle, extensions and variants described above are also possible. If a porous structured dielectric is used, the smooth electrodes are preferably covered with an insulating material.

Claims

Expectations

1. Device for filtering out soot from exhaust gases or aerosols from exhaust air and for plasma-assisted treatment of exhaust gas or exhaust air with a dielectric barrier discharge, characterized in that a conductive electrode (2) structured in several spatial directions, this being solid, perforated, coherent and / or has a porous structure, is arranged between two flat boundaries of insulating material (3) and the insulating material (3) rests on structural elevations of the structured electrode (2), so that the structured electrode (2) forms a spacer and that in the Space between the two flat boundaries made of insulating materials (3), which forms the structured treatment room with the partial gas spaces (1), inflowing exhaust gas or inflowing exhaust air at the structured electrode (2) is redirected and / or flows through in several directions in space, soot and Aerosols separate, and that the b boundary surface made of insulating material (3) separates the conductive structured electrode (2) from another smooth or structured conductive electrode.

2. Device for filtering out soot from exhaust gases or aerosols from exhaust air and for plasma-assisted treatment of exhaust gas or exhaust air with a dielectric barrier discharge, characterized in that a dielectric (3a) structured in several spatial directions, which divides a gas space into two partial gas spaces (1 ) separates and acts electrically as a barrier, is arranged between two flat boundaries of smooth electrodes (4) and the smooth electrodes (4) each rest on structural elevations of the dielectric (3a) structured in several spatial directions, so that the structured dielectric (3a) is one Spacer forms and that in the space between the two flat boundaries of smooth electrodes (4), inflowing exhaust gas or inflowing exhaust air on the structured dielectric (3a) is deflected and / or flowed through several times in different spatial directions, soot and aerosols separating out, and that further the limiting area the structured electrode made of smooth electrode (4) Separates dielectric (3a) from another smooth or structured dielectric.

3. Device for filtering out soot from exhaust gases or aerosols from exhaust air and for plasma-assisted treatment of exhaust gas or exhaust air according to claim 1 or 2, characterized in that the conductive structured electrode (2) or the structured dielectric (3a) for the passage of the Exhaust gases have a porous design, in the case of the arrangement of a porous structured dielectric (3a) the smooth electrodes (4) lying on the structure elevations of the dielectric (3a) are covered with an insulating material.

4. Device for filtering out soot from exhaust gases or aerosols from exhaust air and for plasma-assisted treatment of exhaust gas or exhaust air according to claim 1, characterized in that the formation of the electrically conductive structured electrode (2) by a wire mesh, connected body or structure or Individual bodies lying one against the other are made of an electrically conductive material, which form an orderly filling of one or two layers, or that they consist of sheet metal, perforated sheet metal, porous sheet-like material, wire mesh made of thin, from at least one layer which forms such shapes or approximates these shapes Fibers or metal fleece.

5. Device for filtering out soot from exhaust gases or aerosols from exhaust air and for plasma-assisted treatment of exhaust gas or exhaust air according to one or more of claims 1 to 4, characterized in that the conductive structured electrode (2) or the structured dielectric (3a) has flat and rounded and / or mountain and valley structures.

6. Device for filtering out soot from exhaust gases or aerosols from exhaust air and for plasma-assisted treatment of exhaust gas or exhaust air according to claims 1 to 5, characterized in that the shape of the structured electrode (2) or the structured dielectric (3a) for the Deflection of the gas flow between inlet and outlet in the inflow direction forms an offset to the previous order of the spatial structure.

7. Device for filtering out soot from exhaust gases or aerosols from exhaust air and for plasma-assisted treatment of exhaust gas or exhaust air according to claim 4 and one or more of claims 5 and 6, characterized in that the shaped layer made of porous sheet-like material, perforated sheet metal or thin wire fibers forms at least two structured gas spaces with partial gas spaces (1) on both sides of the structured electrode (2), at least one of which serves as a treatment space for exhaust gas, and that one of the structured gas spaces with partial gas spaces has a closure (6) on the inflow side and the other outflow.

8. Device for filtering out soot from exhaust gases or aerosols from exhaust air and for plasma-assisted treatment of exhaust gas or exhaust air according to claim 1 or 2, characterized in that a conventionally constructed particle filter is connected downstream of the device.

9. A method for filtering out soot from exhaust gases or aerosols from exhaust air and for plasma-assisted treatment of exhaust gas or exhaust air, characterized in that exhaust gas or exhaust air is passed through a device according to one or more of claims 1 to 7 and on the structured electrode ( 2) is deflected several times in different spatial directions that the structured electrode (2) or the structured dielectric (3a) and / or the delimiting surface made of insulating material (3) or the smooth electrode (4) serve to separate soot in the case of a porous structured electrode (2) or porous structured insulating material (3a), this is flowed through into a second structured gas space (1) and that a plasma treatment of the gaseous components and the separated particles or aerosols takes place, this process being carried out by catalytic means can be supported.

10. A method for filtering out soot from exhaust gases or aerosols from exhaust air and for plasma-assisted treatment of exhaust gas or exhaust air, characterized in that in a device according to one or more of claims 1 to 7, by applying a suitable alternating voltage, dielectrically impeded discharges of different designs are generated and decomposed with these exhaust gas and separated soot or exhaust air and aerosols.

11. A method for filtering out soot from exhaust gases or aerosols from exhaust air and for plasma-assisted treatment of exhaust gas or exhaust air with a device according to claim 5, characterized in that the flat sections and the depressions serve as intermediate storage for soot and as a reservoir for slag.