AU667949B2 - Exhaust filter regeneration - Google Patents

Description

OPI DATE 12/04/94 AOJP DATE 07/07/94 APPLN. ID 46974/93 PCT NUMBER PCT/DE93/00705 1111111111111111111111111111111 111111111111111111111 AU9346974 (51) Internationale Patentklassifikation 5 :I (11) Internationale Veridffentlichungsnummer: WO 94/07008 FOI1N 3/02 Al (43) Internationales Veriffentlichungsdatum: 31. Mirz 1994 (31.03.94) (21) Internationales Aktenzeichen: PCT/DE93/00705 (74) Anwalt: BEINES, Ulrich; Berger Dorfstrale 35, D-41189 M6nchengladbach (DE).

(22) Internationales Anmeldedatum: 5. August 1993 (05.08.93) (81) Bestimmungsstaaten: AU, CA, CZ, HU, JP, KP, KR, PL, Prioritiitsdaten: RU, SK, US, europiisches Patent (AT, BE, CH, DE, P42 30 631.0 12. September 1992 (12.09.92) DE DK, ES, FR, GB, GR, IE, IT, LU, MC, NL, PT, SE).

(71) Anmelder (fir alle Bestinimungsstaaten ausser US): Veriffentlicht AMANN SOHNE GMBH CO. [DE/DE]; Postfach Mit internationalem Recherchenbericht.

9, D-74355 B6nnigheim (DE).

(72) Erfinder; und Erfinder/Anmelder (nur fir US) RAUCHLE, Eberhard [DE/DE]; RAUCHLE, Fritz, Konstantin [DE/DE]; Blumenstrage 11, D-71686 Remseck WIENECKE, Rudolf [DE/DE]; Albrecht-Diirer-Weg, D-85579 Neubiberg TRUCKENMOLLER, Kurt [DE/DE]; Karl- Wulle-Strage 42, D-74076 Heilbronn TRUCKEN- MOLLER, Roman [DE/DE]; Kilihckerstrae 23, D- 74223 Flein (DE).

667949 (54)Title: METHOD OF REMOVING ELECTRICALLY CONDUCTING PARTICLES FROM A STREAM OF GAS, AND DEVICE FOR CARRYING OUT THE METHOD (54) Bezeichnung: VERFAHREN ZUR ENTFERNUNG VON ELEKTRISCH LEITENDEN TEILCHEN AUS EINEM GASSTROM SOWIE VORRICHTUNG ZUR DRUCFOHRUNG DES VERFAHRENS (57) Abstract Described is a method for the removal of electrically conducting particles from a stream of gas, the method calling for the gas stream to be passed through a filter thus separating the particles out from the gas. The particle-contaminated filter (20) is subsequently regenerated in situ by sub- 23 jecting the particles (26) to a spark discharge and/or short arc discharge for a length of time such 4 that the particles ignite and are thus converted by combustion into gaseous compounds. The device designed to carry out the method has a filter (20) through or past which the gas stream flows, at least 2 26 two electrodes 3, 4) associated with the filter plus at least one counter-electrode 6) designed to generate the spark and/or are discharge, that at least two electrodes 3, 4) and the at least one counter-electrode 6) being connected to a suitable power source.

-27 (57) Zusammenfassung 6 Es wird ein Verfahren zur Entfernung von elektrisch leitenden Teilchen aus einem Gasstrom beschrieben, bei dem man den Gasstrom durch ein Filter (20) flihrt und hierdurch die Teilchen aus 24 dem Gasstrom abscheidet. Anschliessend regeneriert man das mit Teilchen (26) beladene Filter derart stationlir, dass man die abgeschiedenen Teilchen (26) mit elektrischcn Funken- und/oder kurzzeitigen Bogenentladungen so lange beaufschlagt, dass hierdurch die Teilchen zoinden und hiernach die geziindeten Teilchen durch Verbrennung in gasfirmige Verbindungen ilberfiihrt werden. Eine entsprechende Vorrichtung zur Druchfilhrung des Verfahrens weist ein vom Gasstrom an- bzw.

durchstr6mtes Filter mindestens zwei, dem Filter zugeordnete Elektroden 3, 4) sowie mindestens eine Gegenelektrode 6) zur Erzeugung der elektrischen Funken- und/oder Bogenentladung auf, wobei die mindestens beiden Elektroden 3, 4) sowie die mindestens eine Gegenelektrode 6) mit einer entsprechenden Spannungsquelle verbunden sind. Method of Removing Electrically Conducting Particles from a Stream of Gas, and Device for Carrying out the Method The present invention relates to a method to remove electrically conducting particles from a gas stream, as well as a device to perform the method.

It is a known method to remove particles from a gas stream, for instance from exhaust gases out of an industrial source or out of an automobile, in particular from exhaust gases out of a diesel engine, using a respective filter device. Such a filter is located in the gas stream and is perfused by the gas stream. However as soon as the filter is loaded it must be removed from the system in order to remove the filtered particles in a mechanical way or to discard of the filter completely. In automobiles supplied with a diesel engine it is therefore necessary to regenerate or remove the filter in regular intervals, for instance every 5000 to 15000 kilometres, depending on the S° service instructions.

o 4o The same holds true for filters used in industrial exhaust gas streams.

1s Said regeneration or said removal of the filter represents a major effort in particular in industrial fields.

It is an object of the present invention to overcome or substantially ameliorate the above disadvantages.

The present invention in one broad form provides a method for the removal of S 20 electrically conducting particles from a gas stream, comprising the steps of: leading said gas stream through a filter; separating said particles from said gas stream and regenerating said filter containing said particles; wherein said filter loaded with particles is regenerated by treating said filtered particles with electrical spark- and/or short-time arc discharges for such a length of time, until said particles ignite and the ignited particles are converted by combustion into gaseous products, and wherein said electrical spark and/or short-time discharges have a duration between 10 seconds and 10-1 seconds.

A

The present invention in another broad form provides a device for the performance of the method according to any of the previous claims, said device comprising: a filter which is superfused or perfused by a gas stream containing said particles; said filter being assigned at least two electrodes as well as at least two counter electrodes adapted to generate an electrical spark- and/or arc discharge having a duration of between 10-1 seconds and 10-8 seconds; said at least two counter electrodes being arranged in a parallel manner and said at least two counter electrodes being connected with the same power source, wherein ,aid at least two counter electrodes are electrically decoupled.

The inventive method for the removal of electrically conducting particles from a gas stream is based on the concept, that the gas stream is led through a filter and so the particles are separated from the gas stream. For the regeneration of the filter loaded with the electrically conducting particles it is not necessary to remove the filter o. from the system as is necessary according to the state of the art. Rather, the filter S* oloaded with the particles is regenerated at certain time intervals in a stationary manner, e whereby the separated particles are treated with an electrical spark- and/or short-time j arc discharge for a sufficient time to ignite the particles and convert them by a 20 combustion to gaseous products.

The inventive method provides a range of advantages. In contrast to the state of the art methods described before, it is not necessary to remove the filter completely from the system and to regenerate it externally or to get rid of it, which makes the inventive method very advantageous for economic reasons. Furthermore the 25 regeneration (cleaning) of the filter can be performed in particularly short intervals, o which makes it possible to regenerate the filter at any time within a short period. For that reason no significant pressure increase in the gas stream will be observed due to resistance increase by a highly loaded filter. Furthermore the inventive method does not require the use of chemicals in the gas stream to remove the particles from the filter during the regeneration, which makes the inventive method highly attractive for environmental reasons. Due to said simple regeneration of the filter it is possible in the inventive method to use particularly fine-meshed filters. For that reason the inventive method shows a particularly strong separating potency with respect to the particles to be filtered, which leads to a particularly pronounced cleaning potency with respect to the gas stream.

I At T- I; i.

A particularly advantageous embodiment of the inventive method represents the use of a direct current or an alternating current, in particular an alternating current or a high frequency current to generate the spark- and/or short-time arc discharge, In the context of the present invention spark- and/or short-time arc discharge represents such an electrical discharge, which generates an electric spark or an electrical arc with a duration between 0,0001 sec and 1 sec, preferably between 0,001 sec and 0,01 sec.

According to a further particularly advantageous embodiment of said inventive method a multitude of spark- and/or short-time arc discharges is generated, using a single power source. This embodiment is to be preferred when the electrically conducting particles, for instance soot particles are to be separated from a gas stream of an automobile, in particular an automobile driven by a diesel engine.

o In order to guarantee, that particularly energy-rich spark discharges or short-time arc S*00 I discharges are generated, a power source with a voltage of less than 50 kV is used, in particular with a voltage between 500 V and 50 kV and preferably with a voltage between 2 kV and 25 kV.

Y c The time interval which is required for the ignition of the particles separated on the filter by the spark- and/or short-time arc discharge depends on the power source used S and the type of the filtered particles. Usually the treatment interval in the inventive method is less than 2 sec and varies preferably between 0,01 sec and 1,5 sec. In particular with soot and sulphur particles it could be observed, that said treatment intervals were sufficient to ignite such particles on the filter and to convert them in the gas carbon dioxide or the gas sulphur dioxide.

I The mean pore width of the filter used in the inventive method depends generally on the particle size to be filtered. Normally this mean pore width varies between 5 nm and btge -an 2 Q s^ 4 400 nm, in particular between 150 nm and 300 nm, whereby in special cases it is possible to use filters with a larger mean pore width as well as filters with a smaller mean pore width. If the inventive method should be used, to remove soot particles from exhaust gas of a diesel engine, then usually such filters are used, of which the s pore width varies within the previously mentioned concrete values.

According to a particularly suitable embodiment the gas stream is divided in two different gas streams, with a different filter being installed in each of the different gas streams. This embodiment of the inventive method is always used in such cases where the gas stream shows a relatively high concentration of electrically conducting particles, and makes it possible to have longer intervals betwveen the different S regenerations. Furthermore it is possible, to use this embodiment in such a manner that ew S only one filter is perfused, whereas the other is being regenerated.

It si *t To speed up the conversion of the electrically conducting particles in gaseous products a particularly advantageous embodiment of the inventive method provides the addition of air and/or oxygen to the gas stream during the regeneration of the filter.

C. S *S44 As has been mentioned above repeatedly the inventive method and the device to be 99999 '20 described hereafter are in particular used to separate soot particles from the exhaust 4 9 gas of a diesel engine. This is due to the fact, that since the inventive method allows a particularly rapid and simple regeneration of the filter the use of a relatively small and therefore light filter is possible, which can be built in a space-saving way, for instance in the exhaust pipe of an automobile.

Ai The inventive device to perform the previously described iniventive method comprises a filter perfused or superfused by the gas stream. Assigned to the filter are at least two electrodes as well as at least one counter electrode to induce the electrical sparkand/or arc discharge, these at least two electrodes and the at least one counter electrode all being connected with a single power source.

Said inventive device has the decisive advantage, that when both electrodes and the counter electrode are connected with the power source, a spark- and/or short-time arc discharge is always generated between the counter electrode and the area between the electrodes, as soon as the surface of the filter is covered with the electrically conducting particles, meaning that the particles have been separated at the filter. In this t state of operation in which a regeneration is necessary, a spark- or arc discharge is I' generated as described before, due to the shortening of the distance between the counter electrode and the layer of electrically conducting particles which now 1i functions as an electrode, since the distance between the layer of electrically conducting particles and the counter electrode is shortened in the same manner. This has as a consequence, that the separated particles are ignited and burned and are so S t converted in gaseous products. With the progression of the regeneration the distance 1 between the burning particle layer and the counter electrode is continuously o increasing. When a critical distance is reached (this critical distance being dependent on the geometric configuration of both electrodes and the counter electrode) the S' electrical spark discharge or arc discharge is automatically interrupted. At that moment the filter has been regenerated completely. A further arc- or spark discharge is only started when the cleaned area of the filter is once again covered with electrically conducting particles, requiring once again a regeneration.

The distance between the counter electrode or the counter electrodes must be so chosen, that a complete filling with particles is prevented. When this would happen the f 'gap would be filled by the particles, leading to an electrical short circuit between the -O .p fT 6 counter electrode and the layer of particles or between the counter electrode and the electrode, setting an end to the generation of the arc- or spark discharge. The distance varies preferably between about 2 mm and about 10 mm.

The inventive device provides the decisive advantage, that it always generates a sparkor arc discharge when the separated electrically conducting particles have formed a layer of a certain thickness on the filter. Since the generation of the spark- or arc discharge is inevitable, it is not necessary to provide for control elements in the inventive device. The end of the generation of the spark- or arc discharge is an automatic process as well, brought about by the increase in the distance, so that neither for this event control elements are required. Thus, the inventive device allows a particularly simple and effective regeneration of the filter, without the need for any 'I additives to the gas stream, which would stimulate the burning or the dissociation of "the particle layer from the surface of the filter. Also the inventive device possesses a s very simple form and a low weight, so that the inventive device can be used in systems where weight and space are of crucial importance, in particular in automobiles in the i exhaust system of a diesel engine. It is just required to mount the filter and the I t r C 4 i previously described at least two electrodes and the at least one counter electrode in t the exhaust gases stream of a diesel engine, in particular in the exhaust pipe in the area ,20[ of the silencer. Due to the previously described independent regeneration this requires relatively little space.

The design of the filter depends on the intended use of the inventive device.

According to a first embodiment of the inventive device the. filter has the form of a filter pipe, preferably a ceramic filter pipe. Such a filter pipe is particularly suited to be mounted in a correspondingly cylindrical exhaust pipe. It is very practical to mount the filter pipe in the gas stream in such a manner, that the particles are separated on the Souter surface of the filter pipe.

L 7 It goes without saying, that it is also possible to use instead of a ceramic filter pipe a filter pipe made from other material as for instance from electrically-non-conductive steel, glass or others, whereby it is recommendable to use heat-resistant material. It is also possible to fix the filter pipe in the gas stream in such a manner, that the particles are separated on the inside of the filter pipe.

The position and the design of the at least two electrodes connected, with the filter depends on the type of filter used. In the previously described cylindrical filter pipe it lo is particularly suitable to make the at least two electrodes as ring electrodes and to apply them to the filter pipe in particular on the surface of the filter pipe and in direct contact with said filter pipe. These ring electrodes are constructed with an axial distance from each other as will be described later in detail in an example.

tttt .4 iS It is important for the design of the counter electrode required in the inventive device, that the design and position of the counter electrode is such, that the spark- or arc discharge, which was described before repeatedly, is generated between the electrically conducting particles separated on the filter and the counter electrode. It is therefore suitable in the above described embodiment with the cylindrical filter pipe, to place the counter electrode at a radial and axial distance from the at least two electrodes, and to construct the counter electrode as a row of counter electrodes S directly assigned to the filter pipe. In particular when the at least two electrodes have the form of a ring electrode, it is recommendable to give the counter electrode or the i row of counter electrodes the same form of ring electrode. The diameter of the counter electrode in the form of the ring electrode is significantly greater than the diameter of the electrodes connected to the filter pipe, thus warranting a continuous radial distance between the cylindrical filter pipe and the counter electrodes in the form of ring electrodes.

L

i 8 According to another embodiment of the inventive device the filter is not built as a pipe. Rather this embodiment provides the filter as a plate system, preferably consisting of a number of single plates constructed distanced from each other, and fixed in such a way that they are positioned in the direction of the gas stream or crosswise to it. Depending on the concentration of the particles in the gas stream the system may particularly contain two to twenty plates.

With respect to the positioning of the plates relative to the direction of the gas stream to be cleaned it is possible to fix the plates crosswise, preferably with an angle of 90 relative to the streaming direction of the gas stream.

S According to a particularly suitable variation of the previously described embodiment of the inventive device, distinguished by a particularly loig duration, the filter plates are fixed distanced from each other in such a way, that th- gas stream is split up in different smaller gas streams so forming different single gas stream canals. To obtain this effect, the filter plates are positioned in the stream direction of the gas stream, said gas stream being led once or more often through the filter plates by the use of suited blocking or diverting elements in the single gas stream canals.

According to a variation of the previously described embodiment a partition, in particular a gastight partition, is constructed between adjacent filter plates, with the consequence that as described above, the gas stream is divided in several single gas streams and each single gas stream being covered from adjacent gas streams by a gastight partition.

In order to warrant, that in the inventive device containing the filter as a plate filter, the spark- and/or arc discharge happens without any tult, each filter plate is provided with at least two separately positioned electrodes. Furthermore, the counter electrode P f,$A(4 f each of the at least two electrodes is positioned at the same distance. This enables a 9 Sreproducible and fault-free spark- and arc discharge between the counter electrode and the filter area between the two eiectrodes, when said filter area is covered with a layer of electrically conducting particles and therefore this region has to be regenerated.

In the above variation in which adjacent filter plates are connected by a partition it is recommended to fix the counter electrode at the gastight partition.

According to a further, particularly advantageous embodiment of the inventive device comprising a number of counter electrodes, each counter electrode or each electrode is connected with at least one capacitor, linked between the respective counter electrode or the electrode and the power source. Such decorpled electrodes enable a current limitation practically without any loss, whereby variation of the capacitance of the capacitor limits the performance of the discharge and keeps it on a predetermined level. Furthermore this variation prevents, that the discharge happens at only one i electrode or at some of the electrodes, so extending the discharges over the whole area to of the filter. In addition, such a device can help to generate an unlimited number of 15 discharges, each of the single counter electrodes and electrodes being linked to one single power source.

Instead of the previously described capacitor which is linked to each counter ft a .c electrode or electrode it is also possible to use a resistance. The use of such a Sresistance would however lead to a certain energy loss due to heat.

A particularly suitable variation of the previously described embodiment of the *4 0 inventive device with capacitors linked to each counter electrode or each electrode provides the use of a coaxial cable for the capacitor. This variation has the advantage that the weight is relatively low, which makes it especially simple to be built in automobiles. In addition the capacitance of such a coaxial cable capacitor can be varied in a particularly simple manner by adjusting the length of the coaxial cable. In t V this variation of the inventive device the performance of the discharge can be varied rapidly in any way as needed and adapted to changes in the working conditions.

The capacitance of the capacitor linked between each counter electrode and the power source varies &,-tween 5 pF and 5000 pF, preferably between 100 pF and 1500 pF.

In all variations which were described and in which several electrodes or counter electrodes are linked with one single power source, the respective electrodes and counter electrodes are connected in a parallel fashion.

For the material of the electrodes and the counter electrodes in general an electrically conducting material is selected, in particular such a material which does not oxidise or corrode under working conditions. This means in special cases, that the electrodes or counter electrodes are made of aluminium, iron (steel), copper, platinum, platinum alloys, tungsten or nickel. For economic reasons the use of aluminium, copper or iron is preferred.

According to another particularly suitable embodiment o .the inventive device each counter electrode is connected to a second capacitor, this second capacitor linking the electrode with its respective counter electrode. This second capacitor makes it possible, to vary the timing of the spark- or arc discharge and therefore the frequency range of the discharge.

The capacitance of this second capacitor depends on the wanted modulation, such capacitors being preferred as second capacitor which possess a capacitanco which is less than or equal with the capacitance of the first capacitor.

Concretely the capacitance of the second capacitor is 10% to 90% of the capacitance of the first capacitor.

T

11 The previously described variation in the capacitance of the second capacitor can be reached in a particularly simple way, when here also a coaxial cable is used as the second capacitor. Variation in the length of the coaxial cable provides the wanted capacitance of such a second capacitor.

As power source connected to the electrode and the counter electrode, it is preferred to use a power source adapted to produce alternating current. Usually such a power source induces an alternating current voltage with a frequency between 5 Hz and 20000 Hz, preferably 50 Hz.

The required voltage produced by the power source depends on the design and the construction of the counter electrode and its linked electrode. Usually the inventive device contains a power source which provides a counter-current voltage between 500 V and 50 kV, preferably between 2 kV and 25 kV.

Before, variations of the inventive method and of the inventive device were ao *ee described, in which the gas stream was divided in at least two single gas streams. It is preferred to adapt each single gas stream with a separate filter, which is applied in connection with the gas stream and is perfused by it. This makes it possible, to filter off larger amounts of particles from the gas stream or to regenerate the filter in unperfused state.

To accelerate the regeneration of the filter and so force the conversion of the 20 electrically conducting particles in gaseous products, a further advantageous embodiment of the inventive device provides an inlet of fresh air and/or an opening for oxygen, its position being before the filter, relative to the streaming direction of the gas stream. Said fresh air inlet and/or oxygen opening comprises a valve and a sensor, said valve being opened or closed depending on the control signal for the opening of the valve. The sensor is linked to the electrode or the counter electrode in such a manner, S ,'tW 14 b rl_; I that the control signal for the opening of the valve is produced, when a current flows between the electrode and the counter electrode, this being the case when a sparkand/or short-time arc discharge is being generated.

In the previous statements and in the statements to follow the expression "short-time" is used repeatedly in connection with the spark- and/or arc discharge.

This means, that the discharge takes place during a time interval between 10- 1 and 10-8 seconds, preferably between 10- 6 and 10- 2 seconds.

According to a particularly suited embodiment of the inventive device the filter is functioning at the same time as the silencer of a diesel engine, this embodiment being particularly economic in terms of space-saving.

The inventive device is further described by two examples in connection with the figures. They represent: figure 1 a general scheme; figure 2 a variation of the scheme from figure 1; figure 3 a schematic cross-section view of a first embodiment of the device; figure 4 a schematic cross-section view of a second embodiment of the device and figure 5 a sketch of the flow stream of the particles containing gas stream in the embodiment as depicted in figure 4.

I I I j1 NAlbRittlOOO1I BFO P~ 13 In figures 1 to 5 the same parts have the same number.

Figure 1 represents schematically a general scheme, which is used in the embodiments illustrated in figures 3 to 5. The scheme comprises a power source 1, which produces an alternating current with a voltage of 5 kV and a frequency of 50 Hz.

This power source 1 is connected with three exemplary electrodes 2, 3 and 4 as well as three exemplary counter electrodes 5, 6 and 7, electrodes 2, 3 and 4 as well as counter electrodes 5, 6 and 7 being connected in a parallel fashion. Each counter electrode 5 to 7 is connected with a capacitor 8, 9 or 10, each of the capacitors 8 to 10 possessing a capacitance of 500 pF. In other words the counter electrodes 5 to 7 are decoupled, which means that with an existing voltage between electrodes 5 and 2, electrodes 6 and 3 and electrodes 7 and 4 an electrical spark- and/or arc discharge is being generated when a certain limit voltage is reached, this limit depending on the distance between the electrodes and the capacitance of the capacitors 8 to 10. Duimi.g this spark- and/or discharge alternating current is flowing through the respective capacitors 8 to 1s The scheme depicted in. figure 2 differs from the first scheme in that it ~1 comprises a second capacitor 11. Once again the scheme contains a power source 1, a first capacitor 8, and a single illustrative electrode pair consisting of a counter electrode and an electrode 2. Parallel to the electrodes 5 and 2 a second capacitor 11 is connected, which induces a modulation in time of the spark- and/or arc discharge 2o occurring between electrodes 5 and 2. The capacitor 11 possesses a capacitance in the same range as the first capacitor. The power source 1 generates the same voltage as o described above for scheme 1.

In figure 3 a first embodiment of the device is desc:ibed, which comprises a cylindrical ceramic filter pipe 20, which is connected with cylindrical case 21 surrounding the

I

IN:\AIibtt00801:BFD 14 filter pipe. Between the filter pipe 20 and the case 21 a cylindrical ring-like space 22 is present, through which a particle-containing gas stream is flowing, for instance a diesel Sengine exhaust fume containing soot particles, in the direction of the arrow 23. Due to the fact, that the cylindrical ring-like space is closed at one end by the respective closing element 24, the gas stream is forced in the inner space of the filter pipe 20 and leaves this filter pipe in the direction of the arrow 25. This phenomenon makes it possible to separate the particles at the outside of filter pipe 20 as layer 26.

The filter pipe 20 is connected with three exemplary electrodes 2 to 4, the case 21 with two exemplary counter electrodes 5 and 6. Electrodes 2 to 4 as well as counter electrodes 5 and 6 have a ring-like shape and are connected in the way as shown in figure I. As soon as an electrically conducting layer 26 has been deposed at the outside of the filter pipe and this layer has obtained a certain thickness, thie layer 26 becomes conducting due to its connection with the electrodes 2 to 4, with the consequence, that s, as soon as a certain limit of the layer thickness is reached, an electrical spark- and/or short-time arc discharge is generated between the layer and the counter electrodes and 6, just as sketched at position 27. The consequence of the discharge is the ignition of layer 26 and the conversion of the respective layer material into a gas, which leads i Qi to the combustion of the layer material and a regeneration of the filter. In the course of :~Oq the disappearance of the layer the conductivity of the layer is interrupted, which automatically stops the burning after the complete regeneration of the filter pipe.

i s S The latter embodiment provides particularly the advantage, that it is possible to regenerate the filter pipe automatically depending on the thickness of the filter pipe without complicated control systems. The same holds true for the second embodiment described hereafter.

The embodiment depicted in the figures 4 and 5 differs from the above described embodiment by using instead of the ceramic filter pipe 20 a plate filter 30, the plates

-A

i ~PO-i-l.

being positioned at a distance from each other. Between each plate 30 there exists a gastight partitioning 31, which forces the gas stream to flow in the direction of arrow 32 (figure 5) through the filter plate 30-due to the presence of the closing element 33 at the front side. At the perfusion of filter plate 30 the electrically conducting particles contained in the gas stream are filtered, which causes the deposition of an electrically conducting layer of filtered particles on the surface of filter plate Electrodes 2, 3 and 4 are assigned to the gastight partitioning 31 and the counter i electrodes 5 and 6 to the filter plate 30, the construction being in the manner as shown in figure 1.

As soon as the particle layer 34 at the surface of filter plate 30 has reached a sufficient thickness and homogeneity it becomes electrically conducting, which upon its turn leads to a spark- and/or arc discharge between the conducting layer and the electrodes 5 when a certain limiting layer thickness is reached. Now the particles are thereby ignited and are converted in gaseous products and the filter is consequently automatically regenerated. As soon as the burning step is finished and the distance between the electrodes correspondingly increased, no further discharges are generated until once again the limiting layer thickness on the surface of the filter plate is present.

o, This embodiment provides therefo:e the same automatic start and finish of the regeneration without any need of complicated control elements, just as was the case at the first embodiment.

The previously described embodiments of the inventive device are particularly suited, to remove soot particles form exhaust fumes from diesel engines, in particular in automobiles.

Claims (41)

1. A method for the removal of electrically conducting particles from a gas stream, comprising the steps of: leading said gas stream through a filter; separating said particles from said gas stream and regenerating said filter containing said particles; wherein said filter loaded with particles is regenerated by treating said filtered particles with electrical spark- and/or short-time arc discharges for such a length of time, until said particles ignite and the ignited particles are converted by combustion into gaseous products, and wherein said electrical spark and/or short-time discharges have a duration between 10-8 seconds and 10-1 seconds.

2. The method according to claim 1, wherein said spark and/or arc discharges are generated by an alternating current or direct current voltage.

3. The method according to claim 2, wherein said spark and/or arc S 15 discharges are generated by an alternating current voltage or a high frequency voltage.

4. The method according to any one of the previous claims, wherein a multitude of spark and/or arc discharges is generated by the use of a single power source. 2 5. The method according to any one of the previous claims, wherein a 0: o power source is used with a voltage of less than 50 kV.

6. The method according to claim 5, wherein said power supply source is "used with a voltage of between 500 V and 50 kV.

7. The method according to claim 5 or 6, wherein a power source is used with a voltage between 2 kV and 25 kV.

8. The method according to any one of the previous claims, wherein said filtered particles are treated with said spark and/or arc discharge during a time interval of less than 2 seconds. 17

9. The method according to claim 8, wherein said time interval is between 0.01 and 1.5 seconds. The method according to any one of the previous claims, wherein a filter is selected with a mean pore width between 5 nm and 400 nm.

11. The method according to claim 10, wherein said filter has a mean pore width of between 150 nm and 300 nm.

12. The method according to any one of the previous claims, wherein one splits said gas stream in at least two different gas streams and one filter is applied to each of the gas streams.

13. The method according to any one of the previous claims, wherein air is added during the regeneration of said filter.

14. The method according to any one of the previous claims, wherein soot t particles from diesel engine exhaust gas are filtered.

15. A device for the performance of the method according to any of the S 15 previous claims, said device comprising: a filter which is superfused or perfused by a gas stream containing said particles; said filter being assigned at least two electrodes as well as at least two counter electrodes adapted to generate an electrical spark- and/or arc discharge having a S' 20 duration of between 10- 1 seconds and 10-8 seconds; said at least two counter electrodes being arranged in a parallel manner and said at least two counter electrodes being connected with the same power source, wherein said at least two counter electrodes are electrically decoupled.

16. The device according to claim 15, wherein said filter is built in the exhaust system of a diesel engine.

17. The device according to claim 15 or 16, wherein said filter is shaped as a filter pipe. 1 r [N:\libttlOOBOl:BFD 18

18. The device according to claim 17, wherein said filter is shaped as a ceramic filter pipe.

19. The device according to claim 17 or 18, wherein said filter pipe is fixed in the gas stream in such a manner that the particles to be separated are filtered at the outside of the filter pipe. The device according to any one of the claims 15 to 19, wherein at least two ring electrodes, which are positioned at axial distance from each other, are assigned to said filter pipe.

21. The device according to any one of the claims 17 to 20, wherein at least one counter electrode, which is positioned at radial and axial distance from said at least two electrodes, is assigned to said filter pipe.

22. The device according to claim 21, wherein said counter electrode is shaped as a ring electrode.

23. The device according to claim 15 or 16, wherein said filter is shaped as a plate filter. •i ,24. The device according to claim 23, wherein said filter comprises a .Ott plurality of single filter plates.

25. The device according to claim 24, wherein said filter comprises t between 2 and 20 filter plates. S 20 26. The device according to any one of claims 23 to 25, wherein said filter plates are fixed with such distances from each other, that gas stream canals are formed.

27. The device according to claim 26, further comprising partitioning between adjacent filter plates.

28. The device according to claim 27, wherein said partitioning is gastight partitioning.

29. The device according to any one of the claims 23 to 28, wherein at least two electrodes distanced from each other are assigned to each filter plate. [N:libtt00B01 :BFD I The device according to claim 29, wherein said counter electrode is positioned at the same distance from each of the two electrodes.

31. The device according to claim 30, wherein the counter electrodes are assigned to the partitioning.

32. The device according to any one of the claims 15 to 31, wherein each counter electrode is connected with at least one capacitor, which is linked between its corresponding counter electrode and the power source.

33. The device according to claim 32, wherein said capacitor is shaped as a coaxial cable.

34. The device according to claim 32 or 33, wherein the capacitance of said capacitor is 5 pF to 5000 pF. The device according to claim 34, wherein the capacitance of the capacitor is between 100 pF and 1500 pF.

36. The device according to any one of the claims 15 to 35, wherein said electrodes and said counter electrodes are made from a metal.

37. The device according to claim 36, wherein said electrodes and said counter electrodes are made from iron, aluminium, or copper. il, 38. The device according to any one of the claims 32 to 37, wherein a second capacitor is assigned to each counter electrode.

39. The device according to claim 38, wherein said second capacitor connects the counter electrode with the electrode. •40. The device according to claim 38 or 39. wherein said second capacitor possesses a capacitance which is less than or equal to the capacitance of the first capacitor.

41. The device according to any one of the claims 15 to 32, wherein said electrodes are connected with one alternating current power source.

42. The device according to claim 41, wherein said power source generates an alternating current voltage with a frequency between 5 Hz and 20000 Hz. ;Y .[N:\libtO0801 :B FD I

43. The device according to claim 42, wherein said power source generates an alternating current voltage with a frequency of 50 Hz.

44. The device according to any one of the claims 15 to 43, wherein the power source generates an alternating current voltage between 500 V and 50 kV.

45. The device according to claim 44, wherein the power source generates an alternating current voltage between 2 kV and 25 kV.

46. The device according to any one of the claims 15 to 45, wherein a filter is assigned to each single gas stream.

47. The device according to one of the claims 15 to 46, further comprising an inlet for fresh air upstream from the filter with respect to the streaming direction of the gas stream. c 48. The device according to claim 47, wherein said inlet for fresh air Scontains a valve and a sensor, said valve being opened or shut depending on a control 1 signal created by the sensor.

49. The device according to claim 48, wherein said sensor is assigned to said electrodes and said counter electrodes and generates the signal for the opening of said valve, when a current flows between the counter electrodes and the electrodes. The device according to any one of the claims 15 to 49, wherein said filter is arranged inside the silencer of a diesel engine.

51. A method for the removal of electrically conducting particles from a i gas stream, said method being substantially as hereinbefore described with reference to the accompanying drawings. 2,J

52. A device for the performance of the method of any one of claims 1- 14, or 51, said device being substantially as hereinbefore described with reference to the accompanying drawings. DATED this Eighteenth Day of December 1995 Amann Sohne GmbH Co. Patent Attorneys for the Applicant SPRUSON FERGUSON LU 'TA