Electrically regeneratable filter element

Abstract

An electrically regeneratable filter element comprises at least two flanks, each of these flanks comprising a stiff material layer. Each of these flanks has at least one thermally and electrically insulated side. The filter element comprises further a metal fiber fleece being pleated according to pleating lines providing an edge with pleat openings. The metal fiber fleece is mounted between the flanks, in such a way that the thermally and electrically insulated sides make contact with the edge, meanwhile these sides closing the pleat openings.

Claims

1. An electrically regeneratable filter element, comprising at least two flanks comprising a stiff material layer and at least one thermally and electrically insulated side, said filter element comprising a metal fiber fleece being pleated according to pleating lines providing an edge with pleat openings, such that said metal fiber fleece is mounted between said flanks, said thermally and electrically insulated sides making contact with said edge, said thermally and electrically insulated sides closing said pleat openings, said metal fiber fleece comprising at least one metal fiber strip, each metal fiber strip having two ends, a contact body being fixed to each of said ends of said metal fiber strip, said contact bodies being brought together and being electrically insulated one from the other by an electrically insulating plate, said electrically insulating plate being inserted between said contact bodies.

2. An electrically regeneratable filter element as in claim 1, at least one of said flanks having an aperture, said metal fiber fleece and flanks providing a hollow filter volume, said aperture providing entrance for gasses to to the inside of said hollow filter volume.

3. An electrically regeneratable filter element as in claim 2, all of said flanks having an aperture.

4. An electrically regeneratable filter element as in claim 1, wherein said flanks exercise a clamping force to said metal fiber fleece in a direction essentially parallel to said pleating lines.

5. An electrically regeneratable filter element as in claim 1, wherein each of said flanks comprises a thermally and electrically insulating fabric and a stiff material layer, said thermally and electrically insulating fabric being present at one side of said stiff material layer, providing a thermally and electrically insulated side to said flank.

6. An electrically regeneratable filter element as in claim 1, wherein each of said flanks comprises a ceramic plate, said metal fiber fleece being mounted between said ceramic plates of both flanks.

7. An electrically regeneratable filter element as in claim 1, each of said flanks comprising a stiff material layer, said stiff material layer and said metal fiber fleece being connected using a layer of ceramic adhesive, said layer of ceramic adhesive preventing direct contact of said metal fiber fleece over the length of said edge of said metal fiber fleece with said flank.

8. A filter unit comprising electrically regeneratable filter elements as in claim 1, said filter unit comprising a permeable core member extending through apertures of said flanks of said filter elements.

9. A filter unit as in claim 8, said filter elements being thermally insulated from each other.

10. A filter unit as in claim 8, said permeable core member being a perforated metal tube.

11. A filter system comprising at least one filter unit as in claim 8, said filter system comprising a valve system and an electronic control system, said electronic control system controlling opening and closing of said valve system and said electronic control system controlling the provision of electric current to said filter elements of said filter units of said filter system.

12. A filter system as in claim 11, said filter system comprising at least two filter units, said valve system putting one filter unit off-line, said electric current being provided to at least one filter element of said filter unit which is put off-line.

13. A filter element as in claim 1, wherein said contact bodies are fixed to said electrically insulating plate.

14. A filter element as in claim 13, wherein said contact bodies are fixed to said electrically insulating plate by means of bolts and nuts.

15. A filter element as in claim 14, wherein mica sheets are provided for avoiding electrical contact between contact bodies and bolts.

16. A filter element as in claim 1, wherein the contact bodies are nickel sheets.

17. A filter element as in claim 1, wherein nickel sheets are sintered to the ends of the metal fiber fleeces for providing the contact bodies.

18. A filter element as in claim 1, wherein said electrically insulating plate is a mica plate.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention will now be described into more detail with reference to the accompanying drawings wherein

(2) FIG. 1 shows schematically a general view of a filter unit as subject of the invention

(3) FIG. 2 shows schematically an enlarged view of part AA of the filter unit of FIG. 1.

(4) FIG. 3 shows schematically a section according to the plane BB of the filter unit of FIG. 1.

(5) FIG. 4, FIG. 5a and FIG. 5c show a detail AA of an alternative filter element as subject of the invention;

(6) FIG. 5b shows a section according to CC of the filter element of FIG. 5a;

(7) FIG. 5d shows a section according to CC of the filter element of FIG. 5c;

(8) FIG. 6 shows schematically a side view of the contact bodies from a filter element as subject of the invention.

(9) FIG. 7 shows schematically a view of alternative contact bodies from a filter element as subject of the invention.

(10) FIG. 8, FIG. 9 and FIG. 10 show schematically a section according to the plane BB of an alternative embodiment of a filter unit as subject of the invention.

(11) FIG. 11 shows a diesel exhaust filter system in a muffler-like shape, comprising different filter units as subject of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION

(12) A preferred filter unit as subject of the invention is shown in FIGS. 1, 2 and 3.

(13) The filter unit comprises a number of filter elements 11, which are stacked one on top of the other. They all have a ring-like shape. A perforated metal tube 12 is positioned inside the inner opening 13 of the filter element. Between each filter element, a disc-like SiO.sub.2 felt material 14 is positioned to thermally insulate the different filter elements from each other. At both ends of the filter unit, a metal plate 15 is fixed against the upper and lower filter element e.g. as shown in FIG. 1 by means of a screw 16, which pushes the plate towards the filter element. Between this plate 15 and the upper or lower filter element, another disc-like SiO.sub.2 felt material 14 is positioned.

(14) When this filter unit is used, preferably the gas to be filtered flows in from the outer side of the filter elements (indicated with arrow 17), through the filter medium 18 through the perforations of the metal tube 12, to the further exhaust system as indicated with arrow 19.

(15) Taking each filter element of the present embodiment into consideration, a metal fiber fleece is used as filter medium 18. The dirty gas flows in via the inflow side 20, through the metal fiber fleece, via the outflow side 21 of the metal fiber fleece to the exhaust system. The metal fiber fleece is connected via two contact bodies 22 and 23 to an electric circuit 24, providing electrical current to the metal fiber fleece in order to regenerate the dirt, e.g. soot, trapped in and on the filter medium. The metal fiber fleece is preferably pleated in such a way that the thermal radiation heat, generated by the pleats 25 during regeneration, radiates to the adjacent pleats, as indicated by arrows 26. An important reduction of electrical power is obtained using this radiation heat to propagate and support the combustion of the filtered particles

(16) The set-up of a preferred embodiment of the filter element is shown in FIG. 2. A flank 28 of the filter element comprises a metal rim 29, to which a wire mesh 30 is spot welded on several spots 31. A fine layer of ceramic material Al2O3 32 was sprayed on the electrical and thermal insulating side 33 of the flank. A relatively thick layer of ceramic adhesive 34 was applied on this mesh and the electrical and thermal insulating side 33, before the metal fiber fleece 18 was adhered to this ceramic adhesive 34, which comprises more than 10% of weight of short metal fibers.

(17) The thickness of the adhesive layer was 2 mm and an adhesive based on ZrO2-MgO compound was used. The edge of the metal fiber fleece was sunken in the adhesive layer over a depth of 1.5 mm.

(18) Metal plate and metal mesh were provided out of stainless steel AISI 304. Alternatively stainless steel AISI 430 was used.

(19) The set-up of a detail AA of an alternative embodiment of the filter element is shown in FIG. 4. A flank 401 of the filter element comprises a stiff material layer 402, being a metal rim, in which an electrically and thermally insulating fabric 403 is located. This fabric 403 preferably is a SiO.sub.2-feltlike material (e.g. non-woven), having a thickness of approximately 3 mm. The pleated edge of the metal fiber fleece 18 is squeezed between two electrically and thermally insulating sided of the flanks.

(20) When mounted, the metal fiber fleece 18 is pressed in the fabric 403 over a depth 404 of approximately 1 mm. This recess avoids the blow-through of the metal fiber fleece once the filter element is in use.

(21) The set-up of a detail AA of alternative embodiments of the filter element is shown in FIGS. 5a and 5c.

(22) A detail AA of a fist alternative embodiment is shown in FIG. 5a. A section according to the plane CC of this embodiment is shown schematically in FIG. 5b. A flank 501 of the filter element comprises a metal rim 502, in which a ceramic plate 503 is provided. This ceramic plate is based on Al.sub.2O.sub.3-ceramic material or SiO.sub.2-material and has a thickness of approximately 6 mm. The ceramic plate 503 is provided with a recess 504 having a depth 505 of 2 mm. The edge of metal fiber fleece 18 is sunken into the recess 504, so providing a sunken part 506 to the edge of metal fiber fleece 18 having a height 507 of approximately 1.5 mm.

(23) A detail AA of a second alternative embodiment is shown in FIG. 5c.

(24) A section according to the plane CC of this embodiment is shown schematically in FIG. 5d.

(25) A flank 510 of the filter element comprises a metal rim 511, in which a ceramic plate 512 is provided. This ceramic plate is based on Al2O3-ceramic material or SiO.sub.2-material and has a thickness of approximately 6 mm. At the inner side of the ceramic plate 512, which is to make contact with the metal fiber fleece 18, ceramic glue 513 is provided. The edge of metal fiber fleece 18 is sunken into the glue 513. This relatively thick layer of ceramic adhesive 513 based on ZrO.sub.2-MgO compound, comprises more than 10% of weight of short metal fibers, preferably being stainless steel fibers having an equivalent diameter of 22 m.

(26) To improve the resistance to the mechanical tension, due to the fixation of the different elements on top of each other by screw 16, several studs 35 may be welded to the upper and lower rim of each filter element. As shown in FIG. 1, FIG. 2, FIG. 4, FIG. 5a, FIG. 5b, FIG. 5c and FIG. 5d, around the filter element 11, a perforated metal plate 39 may be present (as only shown partially in the Figures for the sake of clarity).

(27) Turning now to the contact bodies 22 and 23 of the preferred embodiment as shown in FIG. 6 and FIG. 7, a fine Ni-sheet 36 was sintered to the ends of the metal fiber fleece. Both contact bodies were brought together and fixed to an insulating plate 37, e.g. a mica-plate by means of two bolts 38 and 39. In order to avoid electrical contact between contact body 22 and bolt 38, and between contact body 23 and bolt 39, two mica sheets 40 were inserted between the insulating plate 37 and the contact bodies 22 and 23.

(28) An alternative set-up is shown in FIG. 7. An identical set-up as in FIG. 6 is used, but the contact body 22 is shaped in such a way that no material of this contact body 22 is present at behind bolt 38, fixing the contact body 23 to the insulating plate 37. Identically, the contact body 23 is shaped in such a way that no material of this contact body 23 is present at behind bolt 39, fixing the contact body 22 to the insulating plate 37. Using such contact bodies, the use of two mica plates 40 may be avoided, which may simplify the construction of the filter element.

(29) An alternative cut according to BB is shown in FIG. 8. The perforated tube in this embodiment has an elliptic section. Also here, the metal fiber fleece is pleated according to pleating lines, which enables radiation from one pleat to another during regeneration.

(30) Another alternative cross section of a filter element as subject of the invention is shown in FIG. 9. The filter element in this embodiment comprises two metal fiber fleece strips, which together form the whole filter media of the filter element. Both metal fiber fleece strips have two contact bodies (22 and 23), at one end each, which are connected to an appropriate electric circuit 24.

(31) Another alternative cross section of a filter element as subject of the invention is shown in FIG. 10. The filter element comprises a set of metal fiber fleece strips, each being pleated over one pleating line 81. All strips are mounted side by side. Each metal fiber fleece strip has two contact bodies (22 and 23), one at each end of the strip. The contact bodies are lined up and connected to an appropriate electric circuit 24.

(32) As shown in FIG. 11, gas to be filtered may enter into a muffler system, via inlet 91. Several filter units 92, each comprising several filter elements 93 are present in the muffler-like system. The gas to be filtered goes, as indicated with arrow 94, through the filter media of each filter element and leaves the filter unit 92 via the perforated tube 95 in a collecting chamber 96. Via an outlet 97, the filtered exhaust gas flows further through the exhaust system as indicated with arrow 98.

(33) As filter medium, a sintered metal fiber fleece comprising three layers of stainless steel fibers is used. A first layer comprises 600 g/m.sup.2 of Fecralloy fibers with equivalent diameter of 17 m. A second layer of Fecralloy fibers is applied on top of the first layer. This layer comprises 250 g/m.sup.2 of fibers with equivalent diameter of 22 m. A third layer of Fecralloy fibers is applied on top of the second layer, having fibers with equivalent diameter of 35 m. This third layer comprises 600 g/m.sup.2 fibers.

(34) A soot retention of 91% was obtained, using a stainless steel fleece, having a porosity of 85%.

(35) The length of the metal fiber fleece in the above described embodiments is preferably 1200 mm, while the hight of the metal fiber fleece strip is preferably between 30 and 35 mm, e.g. 33.75 mm.

(36) The soot was so-called depth filtered. This is to be understood as the fact that soot particles were trapped through the whole depth of the filter.

(37) Only 1 minute per element was needed to regenerate the filter unit, while consuming only 750 W to 1500 W The pressure drop over the filter element was set to 100 mbar before regeneration.