METHOD AND DEVICE FOR FRAGMENTING AND/OR WEAKENING POURABLE MATERIAL BY MEANS OF HIGH-VOLTAGE DISCHARGES

Abstract

A method for fragmenting and/or weakening pourable material with high-voltage discharges includes guiding an annular or arcuate material flow past a high-voltage electrode assembly while immersed in a process liquid, by means of which high-voltage electrode assembly high-voltage punctures through the material flow are produced in that high-voltage pulses are applied to the high-voltage electrodes of the high-voltage electrode assembly by means of a high-voltage generator. Material is fed to the flow upstream of the high-voltage electrode assembly, and material is led away from the flow downstream of the high-voltage electrode assembly. This enables a continuous process, in which the speed of the material and the intensity of the high-voltage punctures can be set in wide ranges, and any insufficiently processed material can be fed back to the process zone over a short distance and practically without additional space requirement.

Claims

1. Method for fragmenting and/or weakening pourable material by means of high voltage discharges, the method comprising: a) providing a high voltage electrode arrangement which is attributed to one or more high voltage generators, by means of which it is charged with high voltage pulses; b) guiding an annular or arcuate, particularly circular or circular-segment-shaped material stream of pourable material, immersed in a process liquid, past the high voltage electrode arrangement; and c) generating high voltage punctures through the material stream while guiding the latter past the high voltage electrode arrangement by charging the high voltage electrode arrangement with high voltage pulses, wherein material is supplied to the material stream upstream of the high voltage electrode arrangement and material is guided away from the material stream downstream of the high voltage electrode arrangement (2).

2. Method according to claim 1, wherein no material is guided away in that area of the material stream, where high voltage punctures through the material stream are generated by the high voltage electrode arrangement.

3. Method according to claim 1, wherein a partial stream of the material stream or the entire material stream is guided downstream of the high voltage electrode arrangement into a central section which is surrounded by the annular or arcuate material stream.

4. Method according to claim 3, wherein at least a part of the material guided into the central section is guided out of this area.

5. Method according to claim 3, wherein at least a part of the material guided into the central section is guided back from this section into the annular or arcuate material stream.

6. Method according to claim 4, wherein the material guided into the central section is separated by means of a separation device, particularly by means of a sieve, in completely processed material and not completely processed material and the completely processed material is guided out of the central section, while the not completely processed material is guided back into the annular or arcuate material stream.

7. Method according to claim 1, wherein the material stream is formed by supplying the material onto a carousel-type device and guiding it past the high voltage electrode arrangement by rotating this device around a substantially vertical axis running through the central section.

8. Method according to claim 1, wherein a high voltage electrode arrangement is used, which comprises a matrix-type arrangement of a plurality of high voltage electrodes, each of which is charged with high voltage pulses.

9. Method according to claim 8, wherein a matrix-type electrode arrangement is used, which extends across an area larger than 180° of the annular or arcuate material stream.

10. Method according to claim 1, wherein an element is used as opposite electrode for the high voltage electrodes of the high voltage electrode arrangement, which limits the bottom side of the material stream in the area of the high voltage electrode arrangement, and particularly wherein this element is the floor of a carousel-type device by means of which the material stream is guided past the high voltage electrode arrangement.

11. Method according to claim 1, wherein each high voltage electrode is attributed to one or more own opposite electrodes, which is or are arranged laterally neighboring and/or below the respective high voltage electrode, in such a way that high voltage punctures are generated through the material of the material stream between the high voltage electrode and the opposite electrode or electrodes by charging the respective high voltage electrode with high voltage pulses.

12. Method according to claim 1, wherein the material of the outer and/or the inner edge section of the annular or arcuate material stream is not guided away, but rotates continuously as continuous annular or arcuate material stream.

13. Method according to claim 1, wherein material from the middle section of the material stream is guided away at a first position downstream of the high voltage electrode arrangement, the material of the outer and/or the inner edge section is guided at least partially into the middle section of the material stream at a second position downstream of the first position and new material is supplied in the outer and/or inner edge section of the material stream at a third position downstream of the second position, before the material stream is again guided past the high voltage electrode arrangement and is charged with high voltage punctures.

14. Method according to claim 1, wherein the inner and/or the outer edge section of the material stream is limited or are limited, respectively, by substantially unmoved sections of the same material in the area where high voltage punctures through the material of the material stream are generated.

15. Method according to claim 14, wherein the substantially unmoved sections are generated in such a way that the inner and/or outer edge section of the material stream is or are, respectively, retained downstream of the high voltage electrode arrangement.

16. Method according to claim 12, wherein the material of the outer edge section of the annular or arcuate material stream is not guided away, but rotates continuously as continuous annular or arcuate material stream, and wherein the inner edge section of the material stream is limited by substantially unmoved sections of the same material in the area where high voltage punctures through the material of the material stream are generated.

17. Method according to claim 13, wherein the material of the outer edge section of the annular or arcuate material stream is guided at the second position at least partially into the middle of the material stream and new material is supplied into the outer edge section of the material stream at the third position, before the material stream is again guided past the high voltage electrode arrangement and is charged with high voltage punctures.

18. Method according to claim 3, wherein material from the middle section of the material stream is guided away downstream from the high voltage electrode arrangement and into the central section.

19. Method according to claim 1, wherein the high voltage electrode arrangement has one or more high voltage electrodes which are shiftable independently from one another along particularly parallel, particularly vertically oriented shift axes, and wherein these high voltage electrodes, while guiding the material stream past the high voltage electrode arrangement and generating high voltage punctures through the material stream, are shifted in such a way along their shift axes that each of them follows the contour of the material stream with a certain distance or follow the contour of the material stream in contact with the surface of the material stream and are at the same time immersed into the process liquid.

20. Method according to claim 11, wherein the opposite electrode attributed to the respective high voltage electrode is shifted along the shift axis together with the respective high voltage electrode.

21. Method according to claim 1, wherein an own high voltage generator is attributed to each high voltage electrode of the high voltage electrode arrangement, by means of which it is charged with high voltage pulses independently from the other high voltage electrodes.

22. Method according to claim 21, wherein the high voltage generator in each case is firmly connected to the respective high voltage electrode.

23. Device for carrying out the method according to claim 1, the device comprising: a) a high voltage electrode arrangement which is attributed to one or more high voltage generators, by means of which it can be charged with high voltage pulses; b) a carousel-type device, by means of which pourable material is guided past the high voltage electrode arrangement as annular or arcuate, particularly circular or circular-segment-shaped, material stream, immersed into a process fluid , particularly by rotating it around a central and substantially vertical axis (Z), in such a way that high voltage punctures through the material stream can be generated while it is guided past the high voltage electrode arrangement when the high voltage electrode arrangement is charged with high voltage pulses; c) Means for supplying material upstream of the high voltage electrode arrangement to the annular or arcuate material stream generated by means of the carousel-type device during use as intended. d) means for guiding away material downstream of the high voltage electrode arrangement from the annular or arcuate material stream generated by means of the carousel-type device during use as intended.

24. Device according to claim 23, wherein the carousel-type device has sieve openings in the area in which it carries the material forming the annular or arcuate material stream, in operation as intended, as means for guiding away material, via which sieve openings material which is smaller than the sieve openings can be guided away from the material stream.

25. Device according to claim 23, wherein the carousel-type device forms a closed floor in the area in which it carries the material forming the annular or arcuate material stream, in operation as intended, and wherein the means for guiding away material are formed in such a way, particularly as one or multiple guiding installations, that with them a partial stream of the material stream or the entire material stream can be guided into a central section in the center of the carousel-type device, which is surrounded by the annular or arcuate material stream.

26. Device according to claim 25, wherein means are present for guiding at least a part of the material guided into the central section out of the central section and away from the carousel-type installation, and particularly wherein these means comprise a material slide or a funnel.

27. Device according to claim 25, wherein means are present for guiding back at least a part of the material guided into the central section into the annular or arcuate material stream, and particularly wherein these means comprise one or more guiding installations.

28. Device according to claim 26, wherein a separation installation is arranged in the central section, particularly comprising a sieve, by means of which the material guided into this section can be separated in completely processed material and not completely processed material, wherein the completely processed material can be guided out of the central section with the means for guiding away the material and the not completely processed material can be supplied into the annular or arcuate material stream with the means for guiding back the material.

29. Device according to claim 23, wherein the device has means, particularly one or more aretaining installations, by means of which it is possible to effect during use as intended that the inner edge section and/or the outer edge section of the annular or arcuate material stream is or are limited, respectively, substantially by unmoved sections of the same material in the area where high voltage punctures are generated through the material of the material stream.

30. Device according to claim 23, wherein the device is formed in such a way that the material of the inner edge section and/or of the outer edge section of the annular or arcuate material stream is not guided away from the material stream downstream of the high voltage electrode arrangement, in operation as intended, but circulates continuously as continuous annular or arcuate partial material stream.

31. Device according to claim 23, wherein the device is formed in such a way that, in operation as intended, material from the middle section of the material stream is guided away from the middle section of the material stream at a first position downstream of the high voltage electrode arrangement, the material of the outer and/or the inner edge section is guided at least partially into the middle of the material stream at a second position downstream of the first position, and new material is supplied into the outer and/or inner edge section of the material stream at a third position downstream of the second position, before the material stream is again guided past the high voltage electrode arrangement and is charged with high voltage punctures.

32. Device according to claim 29, wherein the device is formed in such a way that the material of the outer edge section of the annular or arcuate material stream is not guided away but circulates continuously as continuous annular or arcuate material stream, and wherein the inner edge section of the material stream is limited by substantially unmoved sections made of the same material in the section where high voltage punctures through the material of the material stream are generated.

33. Device according to claim 30, wherein the device is formed in such a way that the material of the outer edge section of the annular or arcuate material stream is guided at least partially into the middle of the material stream at the second position and new material is supplied into the outer edge section of the material stream at the third position, before the material stream is again guided past the high voltage electrode arrangement and is charged with high voltage punctures.

34. Device according to claim 23, wherein the section of the carousel-type installation, in which the latter, in operation as intended, carries the material forming the annular or arcuate material stream, is limited at its outer circumference by a limitation wall closed with respect to circumference, and wherein the device is formed in such a way that this limitation wall is moved together with the material of the material stream in operation as intended of the device.

35. Device according to claim 23, wherein the section of the carousel-type installation, in which the latter, in operation as intended, carries the material forming the annular or arcuate material stream, is limited at its inner circumference by a fixed limitation wall which has an interruption downstream of the high voltage electrode arrangement and wherein the means for guiding away material from the material stream are formed in such a way that material from the annular or arcuate material stream is guided through this interruption, in operation as intended, into a central section in the center of the carousel-type installation, which is surrounded by the annular or arcuate material stream.

36. Device according to claim 34, wherein the means for guiding away material from the material stream are formed or are adjustable in such a way that the entire annular or arcuate material stream is guided into the central section in operation as intended.

37. Device according to claim 34, wherein the means for guiding away material from the material stream are formed or are adjustable in such a way that material of the outer edge section of the annular or arcuate material stream is not guided into the central section in operation as intended, but circulates continuously as continuous annular or arcuate material stream.

38. Device according to claim 23, wherein the high voltage electrode arrangement comprises a matrix-type arrangement made of multiple high voltage electrodes, each of which are charged with high voltage pulses.

39. Device according to claim 38, wherein the matrix-type electrode arrangement extends across an area larger than 180° of the annular or arcuate material stream in operation as intended.

40. Device according to claim 38, wherein an own high voltage generator is attributed to each high voltage electrode (12) of the matrix-type high voltage electrode arrangement, by means of which this high voltage electrode can be charged with high voltage pulses independently from the other high voltage electrodes.

41. Device according to claim 40, wherein the high voltage generator is connected to the high voltage electrode in a fixed way.

42. Device according to claim 40, wherein the high voltage electrodes are shiftable along particularly parallel, particularly vertically oriented shifting axes independently from one another.

43. Device according to claim 42, further comprising a machine controller, by means of which, in operation as intended, during the guiding of the annular or arcuate material stream past the matrix-type arrangement of high voltage electrodes and the generation of high voltage punctures through the material of the material stream, the high voltage electrodes can be shifted along their shifting axes in such a way that each of them follows the contour of the material stream at a certain distance or each of them follows the contour of the material stream in contact with the latter.

44. Device according to claim 23, wherein the section of the carousel-type installation serves as opposite electrode for the high voltage electrodes of the high voltage electrode arrangement, on which section the latter carries the material forming the annular or arcuate material stream.

45. Device according to claim 23, wherein one or more own opposite electrodes are attributed to each high voltage electrode, which is or are arranged laterally adjacent and/or below the respective high voltage electrode, and particularly is or are carried by the latter in such a way that high voltage punctures between the high voltage electrode and the opposite electrode or electrodes through the material of the material stream can be generated in operation as intended by charging the respective high voltage electrode with high voltage pulses.

Description

SHORT DESCRIPTION OF THE DRAWINGS

[0065] Further embodiments, advantages and applications of the invention result from the dependent claims and from the now following description by the drawings. It is shown in:

[0066] FIG. 1 a top view on a first device according to the invention in a first type of operation;

[0067] FIG. 2 a vertical section through the first device along the line A-A of FIG. 1;

[0068] FIG. 3 a vertical section through the first device along the line B-B of FIG. 1;

[0069] FIG. 4 a top view on the first device according to the invention in a second type of operation;

[0070] FIG. 5 a top view on a second device according to the invention;

[0071] FIG. 6 a vertical section through the second device along the line C-C of FIG. 5;

[0072] FIG. 7 a top view on a third device according to the invention;

[0073] FIG. 7a the detail X of FIG. 7;

[0074] FIG. 8 a vertical section through the third device along the line D-D of FIG. 7;

[0075] FIG. 9 a top view on a fourth device according to the invention;

[0076] FIG. 10 a vertical section through the fourth device along the line F-F of FIG. 9;

[0077] FIG. 11 a vertical section through the fourth device along the line E-E of FIG. 9;

[0078] FIG. 12 a side view of one of the high voltage electrodes of the devices;

[0079] FIG. 13 a side view of an alternative of the high voltage electrode of FIG. 12.

WAYS OF CARRYING OUT THE INVENTION

[0080] FIG. 1 to 3 show a first device according to the invention for fragmenting pourable material 1 by means of high voltage punctures, once in a top view from above (FIG. 1), once in a vertical section along the line A-A of FIG. 1 (FIG. 2) and once in a partial vertical section along the line B-B of FIG. 1 (FIG. 3).

[0081] As can be seen, the device has a carousel-type installation 9, 10, 11, formed by an annular floor plate 10, a cylindrical outer wall 9 firmly connected to the floor plate 10 and protruding perpendicularly upward from the floor plate 10 and with a cylindrical inner wall 11 not connected to the floor plate 10 and protruding perpendicularly upward from the floor plate 10. The floor plate 10 is even and continuously closed and it is supported on a annular supporting element 25 of a fixed supporting structure by means of a roller race 24, and is rotated in operation as intended about a vertical rotation axis Z running through the center of the annular shape of the floor plate 10 in a rotation direction R by means of a drive motor 26, wherein the material 1 to be fragmented, which is lying on the floor plate 10, forms a annular or annular-segment-shaped material stream 4 in rotation direction R around the rotation axis Z.

[0082] The carousel-type installation 9, 10, 11 is arranged inside a circular pool 27 filled with water 5 (process liquid), the floor of which is penetrated by the annular supporting element 25. The carousel-type installation 9, 10, 11 is entirely immersed in the water 5 in the pool 27 except the upper limitation edges of the outer wall 9 and of the inner wall 11. In the area inside the annular supporting element 25, the floor of the pool 27 is formed by a circular funnel 19 extending downwards, the bottom end of which ends above a transport band 20 which transports obliquely upward until a level above the water level of the pool 27 (not shown entirely here due to space reasons) and which is arranged inside a housing 30, which is connected at the bottom funnel end and forms together with the pool 27 a watertight tank. The pool 27 is surrounded by an annular protecting wall 31, through which the housing of the transport band 30 and the transport band 20 protrude.

[0083] As it can further be seen, the device has a high voltage electrode arrangement 2 with a plurality of high voltage electrodes 12 arranged in a matrix-shaped manner above the carousel-type installation 9, 10, 11, wherein the high voltage electrode arrangement extends across an area of 270° of the annular shape of the carousel-type installation 9, 10, 11. Each of the high voltage electrodes 12 protrudes downward from the top up to just above the surface of the annular-segment-shaped material stream 4 transported in the carousel-type installation 9, 10, 11, wherein it dives into the water 5 and has an own high voltage generator 3 arranged directly above it, by means of which in operation it is charged with high voltage pulses. In the figures, only one of the high voltage electrodes is shown with the reference number 12 and only one of the high voltage generators are shown with the reference number 3, due to clarity reasons.

[0084] As can be seen in FIG. 12, which shows one of the high voltage electrodes 12 of the high voltage electrode arrangement 2 of this device in the side view, each of the high voltage electrodes 12 has an own opposite electrode 13 which is grounded and which is arranged in such a way with respect to the respective high voltage electrode 12 that, in operation as intended shown in the figures, high voltage punctures between the high voltage electrode 12 and the opposite electrode 13 attributed to it are generated through the material 1 of the material stream 4 by charging the respective high voltage electrode 12 with high voltage pulses.

[0085] As can further be seen, the device has a supplying transport band 15 arranged inside a closed housing 32, by means of which material 1 to be fragmented, in the present case pieces of noble metal ore 1, is delivered on the floor plate 10 of the carousel-type installation 9, 10, 11 upstream of the high voltage electrode arrangement 2.

[0086] The height of the material bed 1 passed below the high voltage electrode arrangement 2 as annular-segment-shaped material stream 4 is determined by a passage limitation sheet metal 33 before the inlet into the area (process zone) between the carousel-type installation 9, 10, 11 and the high voltage electrode arrangement 2.

[0087] A fixed first guiding sheet metal 17 is located downstream of the high voltage electrode arrangement 2, which extends from the outer wall 9 of the carousel-type installation 9, 10, 11 through a first interruption 23 into its inner wall 11 into a section 7 in the center of the carousel-type installation 9, 10, 11 and guides the material stream 4 exiting the process zone into the central section 7 substantially entirely via the first interruption 23 in the inner wall 11 in operation as intended.

[0088] The floor of the central section 7 is formed as even sieve floor 8, with a sieve opening size which is dimensioned in such a way that material fragmented to target size 1a passes through the sieve openings and falls into the funnel 19 arranged below, while material 1b which is larger than the target size remains on the sieve floor 8. The completely processed material 1a or the material fragmented to target size, respectively, is guided from the funnel 19 onto the transport band 20, by means of which it is transported out of the device.

[0089] The not completely processed material or the material not yet fragmented to target size, respectively, is pushed on the sieve floor 8 and is guided out of the central section 7 from a second fixed guiding sheet metal 21 following the first guiding sheet metal 17 via a second interruption 28 in the inner wall 11 back into the annular-segment-shaped material stream 4, by means of which it is again guided past a part of the high voltage electrode arrangement 2 and charged with high voltage punctures.

[0090] As seen in FIG. 3, which shows a vertical section through a part of the first device in the area of the process zone along the line B-B of FIG. 1, the floor plate 10 of the carousel-type installation 9, 10, 11 has a top side coated with a wear-reducing rubber layer 29, on which the material 1 to be processed is located.

[0091] FIG. 4 shows a top view on the device in another operating way. As can be seen, here the second guiding sheet metal 21 is arranged in a position where it closes the second interruption 28 in the inner wall 11 from the side of the central section 7 and frees one discharge shaft 34, into which the not completely processed material or the material not yet fragmented to target size 1b, which is pushed on the sieve floor 8 by the incoming material 1, falls and subsequently is discharged from the device with installations (not shown).

[0092] FIGS. 5 and 6 show a second device according to the invention for fragmenting pourable material 1 by means of high voltage discharges, once in a top view from above (FIG. 5) and once in a partial vertical section along the line C-C of FIG. 5 (FIG. 6).

[0093] This device differs from the device shown in FIGS. 1 to 3 substantially in that here the first guiding sheet metal 17 arranged downstream of the high voltage electrode arrangement 2 doesn't extend entirely up to the outer wall 9 of the carousel-type installation 9, 10, 11, such that between its outer end and the outer wall 9 an opening 35 is formed, through which the material 1 can pass in the outer edge section of the material stream 4, such that it is not guided by the first guiding sheet metal 17 into the central section 7 but rotates continuously as continuous annular material stream 4a. Accordingly, here not the entire material stream 4 exiting the process zone is guided into the central section 7, but only material 1 from its middle section and from its inner edge section.

[0094] As particularly visible in FIG. 6, a further difference of this device to the device shown in FIG. 1 to 4 is that here the high voltage electrodes 12 of the high voltage electrode arrangement 2 are arranged in such a way that the rotating material stream 4a is substantially not charged with high voltage punctures, in the outer edge section of the material stream 4. Accordingly, the material 1 has substantially the initial piece size in the outer edge section of the material stream 4.

[0095] For the rest, this second device has an identical structure like the first device.

[0096] FIGS. 7 and 8 show a third device for fragmenting pourable material 1 by means of high voltage discharges according to the invention, once in a top view from above (FIG. 7) and once in a partial vertical section along the line D-D of FIG. 7 (FIG. 8).

[0097] This device differs from the device shown in FIGS. 5 and 6 first in that here the matrix-shaped high voltage electrode arrangement 2 has less high voltage electrodes 12 and extends only across an area of about 170° of the annular shape of the carousel-type installation 9, 10,

[0098] As can be seen in connection with FIG. 7a, which shows the detail X of FIG. 7, a further difference is that the inner wall 11 of the carousel-type installation 9, 10, 11 has on its side facing the material stream 4, in the area where the high voltage electrode arrangement 2 extends above the carousel-type installation 9, 10, 11, multiple accumulation ribs 22 which extend radially into the material stream 4, by means of which the material 1 is accumulated in the inner edge section of the material stream 4 as unmoved material zones 14. Thereby, the high voltage electrodes 12 of the high voltage electrode arrangement 2 are arranged here in such a way that the unmoved material zones 14 are substantially not charged with high voltage punctures in the inner edge section of the material stream 4. Accordingly, the material 1 has substantially its original piece size in these zones 14.

[0099] Still a further difference is that this device has a single fixed guiding sheet metal 16 which guides the material 1, downstream of the high voltage electrode arrangement 2, from the middle section and from the inner edge section of the material stream 4 moving along the unmoved material zones 14 via the first interruption 23 in the inner wall 11 into the central section 7 and onto the sieve floor 8 and additionally also guides the material 1b which remains on the sieve floor 8 and which wasn't fragmented to target size or which is not completely processed, respectively, via a second interruption 28 arranged at a position upstream of the high voltage electrode arrangement 2, back into the material stream 4.

[0100] For the rest, this third device has an identical structure like the second device.

[0101] FIG. 9 to 11 show a fourth device for fragmenting pourable material 1 by means of high voltage discharges according to the invention, once in a top view from above (FIG. 9), once in a vertical section along the line F-F of FIG. 9 (FIG. 10) and once in a partial vertical section along the line E-E of FIG. 9 (FIG. 11).

[0102] This device differs from the devices shown in FIG. 1 to 8 in that it doesn't have installations by means of which the material stream 4 exiting the process zone or a part of it is guided into the center 7 of the carousel-type installation 9, 10, 11. The inner wall 11 has no interruptions here and is firmly connected to the floor plate 10 of the carousel-type installation 9, 10, 11, such that they rotate about the rotation axis Z together with it and with the outer wall 9. The carousel-type installation 9, 10, 11 therefore forms in this case a closed annular channel which rotates about the rotation axis Z.

[0103] In case of the device shown here, the material 1 from the middle section of the material stream 4, which exits the process zone formed between the floor plate 10 of the carousel-type installation 9, 10, 11 and the high voltage electrode arrangement 2, is removed and guided away from the device by means of a removal transport band 18 arranged inside a housing 36, which receives the material 1 from the floor plate 10 by means of a (not shown) inlet sheet metal.

[0104] The material 1 in the outer edge section and in the inner edge section of the material stream 4 remains on the floor plate 10 and rotates as continuous annular material stream 4a, 4b.

[0105] Contrary to the first device shown in FIGS. 1 to 4, here the high voltage electrodes 12 of the high voltage electrode arrangement 2 are arranged in such a way that the rotating partial material streams 4a, 4b are not charged with high voltage punctures in the outer and in the inner edge section of the material stream 4. Accordingly, the material 1 has its initial piece size in these partial material streams 4a, 4b.

[0106] New material to be fragmented 1 is delivered via the supplying transport band 18, downstream of the removal position of the removal transport band 18, into the middle section of the annular floor plate 10, such that downstream of this delivery position a closed material stream 4 of substantially unprocessed material 1 is present again, which is delivered to the process zone again.

[0107] For the rest, this fourth device has an identical structure like the first device.

[0108] FIG. 13 shows a further high voltage electrode 12 for the aforementioned devices according to the invention, which differs from the one shown in FIG. 12 substantially in that it has two identical opposite electrodes 13 arranged face to face in a mirrored way. A further difference is that this high voltage electrode 12 has a straight electrode tip.

[0109] While in the present application preferred embodiments of the invention are described, it is clearly noted that the invention is not limited thereto and may be executed in other ways within the scope of the now following claims.