FILTER CANDLE

Abstract

A filter candle is provided, comprising one or more filter elements shaped as hollow cylinders of porous material, the filter elements having substantially identical inner and outer diameters and are disposed coaxially with each other; a support element comprising a metal tube disposed within the filter element(s), said metal tube having an outer diameter smaller than the inner diameter of the filter element(s), said metal tube having a wall with a plurality of perforations; and at least two annular sealing disks having an outer diameter equal to or larger than that of the filter element(s) and an inner diameter smaller than that of the filter element(s), wherein first and second terminal sealing disks are disposed at opposite axial end faces of a single filter element or of a plurality of filter elements disposed in line,
wherein the filter elements are compressed between the first and second terminal sealing disks.

Claims

1. A filter candle for gaseous fluids, comprising one or more filter elements in the shape of hollow cylinders made of a porous material, wherein the filter elements have substantially identical inner and outer diameters and are disposed coaxially in line with each other; a support element comprising a metal tube which is disposed within the one or more filter elements, wherein said metal tube has an outer diameter which is smaller than the inner diameter of the filter element(s), and wherein said metal tube has a wall with a plurality of perforations; and at least two annular sealing disks having an outer diameter equal to or larger than that of the filter element(s) and an inner diameter smaller than that of the filter element(s), wherein first and second terminal sealing disks are disposed at opposite axial end faces of a single filter element or of a plurality of filter elements disposed in line, wherein the one or more filter elements, are compressed between the first and second terminal sealing disks.

2. The filter candle according to claim 1, wherein the filter candle comprises only one filter element.

3. The filter candle according to claim 1, wherein the filter candle comprises a plurality of filter elements disposed in line, wherein further internal sealing disks are disposed between two adjacent filter elements of the plurality of filter elements, and wherein the plurality of filter elements and the internal sealing disks are compressed between the first and second terminal sealing disks.

4. The filter candle according to claim 3, wherein the filter candle comprises two to eight filter elements.

5. The filter candle according to claim 1, wherein the one or more filter elements have an outer diameter of about 30 to about 150 mm.

6. The filter candle according to claim 1, wherein a radial distance between the filter element(s) and the metal tube is from about 1 to about 5 mm.

7. The filter candle according to claim 1, wherein each sealing disk comprises an annular metal disk and a gasket provided on one or both sides of the annular metal disk in contact with a filter element, so as to provide a substantially gastight seal between the filter element(s) and the sealing disks, and to allow a radial movement of the filter element(s) relative to the sealing disk.

8. The filter candle according to claim 7, wherein the gasket comprises graphite, metal fibers, a metal mesh, a polymeric material or a combination thereof.

9. The filter candle according to claim 1, wherein one or more of the sealing disks comprise a resilient compensating element.

10. The filter candle according to claim 1, wherein the one or more filter elements are made of a ceramic material.

11. The filter candle according to claim 1, wherein the metal tube is a steel tube.

12. The filter candle according to claim 1, wherein the metal tube has an axial length larger than the total axial length of the filter element(s), and wherein the plurality of perforations are distributed uniformly over a middle section of the metal tubes which extends within the filter element(s).

13. The filter candle according to claim 12, wherein a first end section of the metal tube extends outside of the filter element(s) and through the first terminal sealing disk, and wherein the first terminal sealing disk is fixed to said first end section.

14. The filter candle according to claim 13, wherein a second end section of the metal tube extends outside of the filter element(s) and through the second terminal sealing disk, and wherein the second terminal sealing disk is axially movable relative to the metal tube.

15. The filter candle according to claim 14, wherein the one or more filter elements are compressed between the first and second terminal sealing disks by an axial force exerted onto the second terminal sealing disk through a spring element which abuts against the second terminal sealing disk and a flange element fixed to the second end portion of the metal tube.

16. The filter candle according to claim 15, wherein the compression of the one or more filter elements is such that it allows for a radial movement between a filter element and an adjacent sealing disk, until the filter element comes into contact with the metal tube.

17. The filter candle of claim 2, wherein the filter element has an axial length of about 0.5 to about 3.0 m.

18. The filter candle of claim 3, wherein the plurality of filter elements have a total axial length of about 0.5 to about 6.0 m.

19. The filter candle of claim 11, wherein the metal tube has a wall thickness of about 2 to about 10 mm.

20. The filter candle of claim 13, wherein the first end section comprises an axial discharge opening for the gaseous fluid.

21. The filter candle of claim 14, wherein the second end section is closed at its axial end.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

[0031] The exemplary embodiments described hereinafter serve to illustrate further details of the invention with reference to the drawings, wherein

[0032] FIG. 1 shows a longitudinal cross section of a first exemplary embodiment of the inventive filter candle; and

[0033] FIG. 2 shows a longitudinal cross section of a second exemplary embodiment of the inventive filter candle.

DETAILED DESCRIPTION OF THE DRAWINGS

[0034] In FIG. 1, a first exemplary embodiment of the inventive filter candle 10 is shown in a longitudinal cross section. The representation of the filter candle 10 is schematic and not necessarily true to scale.

[0035] In this first embodiment, the filter candle 10 comprises one filter element 12 in the shape of a hollow cylinder. The filter element 12 can have, as an example, a length of 1.5 m, an outer diameter of 60 mm and an inner diameter of 40 mm. The filter element 12 is made of a porous material, typically a porous ceramic material. For example, porous filter elements of a sintered silicon carbide material, also known as filter candles, are sold by the applicant under the trademark “Dia-Schumalith”.

[0036] Inside of the filter element 12, and coaxially extending with the same along a rotational axis 14, is disposed a metal tube 16 (typically a steel tube) as a support element. This metal tube 16 comprises a middle section 18 extending within the filter element 12, as well as first and second end sections 20 and 22 extending outside of the filter element 12. The wall 24 of the metal tube 16 has a plurality of perforations 26 which are distributed uniformly over the middle section 18 of the metal tube 16, whereas the wall 24 in the first and second end sections 20 and 22 is not perforated.

[0037] The metal tube 16 can have, for example, an outer diameter of about 34 mm and a thickness of 4 mm of its wall 24. In any case, the outer diameter of the metal tube 16 is smaller than the inner diameter of the filter element 12, resulting in an annular gap 28 between the filter element 12 and the metal tube 16. This gap 28 can have a width of, for example, about 3 mm.

[0038] In a typical application of the filter candle 10, for example, for use in hot gas filtration, a gaseous fluid to be filtered passes through the filter element 12 in a substantially radial direction from the outside into the annular gap 28, and through the perforations 26 into the metal tube 16. The gaseous fluid then leaves the metal tube 16 through an axial discharge opening 30 at the first end section 20, whereas the second end section 22 is closed at its axial end 32.

[0039] The filter candle 10 further comprises two annular sealing disks, namely a first terminal sealing disk 34 and a second terminal sealing disk 36. The first terminal sealing disk 34 surrounds the first end section 20 of the metal tube 16 and is fixed to the same by welding, as indicated by reference numeral 37, thus providing for a gastight closure of the annular gap 28 at the first end section 20. In contrast, the second terminal sealing disk 36, which surrounds the second end section 22 of the metal tube 16, is axially movable relative to the metal tube 16, to allow different thermal extensions of the metal tube 16 and the filter element 12.

[0040] The filter element 12 is compressed between the first and second terminal sealing disks 34 and 36, wherein the compressive force is exerted by a spring element 38, preferable a high temperature spring. This spring element 38 surrounds the second end section 22 of the metal tube 16 and abuts against the second terminal sealing disk 36 and a flange element 40 fixed to the second end section 22, for example by means of screw nuts 42.

[0041] The second end section 22 of the metal tube 16 including the spring element 38 is covered by a spring cover 44 which abuts against the second terminal sealing disk 36. The spring cover 44 protects the spring element 38 against dust etc. from the outside, and it also withholds the gaseous fluid which may pass through the small annular gap between the metal tube 16 and the second terminal sealing disk 36.

[0042] Each of the terminal sealing disks 34 and 36 comprises a metal disk 46 (typically a steel disk) and a gasket 48. This gasket is in direct contact with the respective axial end face of the filter element 12, providing for a gastight seal, but at the same time allowing a radial movement of the filter element 12. The first terminal sealing disk 34 may additionally comprise a resilient compensating element.

[0043] As a result of an external force acting on the filter element 12, the filter element 12 will move radially along the gaskets, until it comes into contact with the metal tube 16. At this point, the metal tube 16 supports and stabilizes the filter element 12, ideally preventing the filter element 12 from bending further and breaking. The metal tube 16 thus acts as a support element which increases the overall tensile and bending strength of the filter candle 10.

[0044] In order to provide for a gastight seal at the end faces of the filter element 12 in every position, the outer diameter of the annular sealing disks 34 and 36 is larger than or of the same diameter as the outer diameter of the filter element 12, and the inner diameter of the sealing disks 34 and 36 is smaller than the inner diameter of the filter element 12. In particular, the difference between the outer and inner diameters of the sealing disks 34 and 36 should be at least twice as large as the radial distance between the filter element 12 and the metal tube 16.

[0045] In FIG. 2, a second exemplary embodiment of the inventive filter candle 50 is shown in a longitudinal cross section. The filter candle 50 of the second embodiment corresponds to the filter candle 10 of the first embodiment except for the differences described below. Identical or corresponding elements in the first and second embodiments are provided with the same reference numerals.

[0046] The filter candle 50 of the second embodiment comprises, instead of a single filter element, a plurality of shorter filter elements 52 of a porous material. In this example, four filter elements 52 are shown, but a smaller or larger number of filter elements is also possible. The individual filter elements 52 are shaped as hollow cylinders with identical inner and outer diameters, being disposed coaxially in line along the rotational axis 14 of the filter candle 50.

[0047] The length of the individual filter elements 52 can be the same or different, and their total length can be the same as that of the single filter element of the first embodiment (for example, 1.5 m). However, the use of a plurality of filter elements 52 is also particularly advantageous for larger total lengths, such as total lengths of up to 6 m.

[0048] Between each two adjacent filter elements 52, an internal annular sealing disk 54 is disposed. The filter elements 52, together with the internal sealing disks 54, are compressed between the first and second terminal sealing disks 36 and 38, as in the filter candle 10 of the first embodiment.

[0049] The segmentation into a plurality of filter elements 52 provides for a further flexibility and resilience of the filter candle 50 against mechanical stress, in particular against a radial force exerted onto the filter candle 50. To that effect, the internal sealing disks 54 typically comprise a resilient compensating element 56 which allows an axial bending of the two adjacent filter elements 52 relative to each other. The resilient compensating element 56 is provided with a gasket 58 on both sides.

[0050] The following example further illustrates the invention but, of course, should not be construed as in any way limiting its scope.

Example

Measurement of Bending Strength

[0051] The bending strength of an inventive filter candle in accordance with the first exemplary embodiment was determined in a 4-point bending test. The filter element of the tested filter candle was a hollow cylinder of a ceramic material based on sintered silicon carbide (Dia-Schumalith) with a length of 1.5 m, an outer diameter of 60 mm and an inner diameter of 40 mm.

[0052] In the 4-point bending test, the filter element of the inventive filter candle cracked at a force of about 4,800 N.

[0053] The corresponding filter element alone, without a supporting metal tube, which is conventionally used as a filtered candle, typically cracks at a bending force in the range from 2,500 to 3,500 N.

[0054] Accordingly, the bending strength of the inventive filter candle is increased by about 60% as compared to a corresponding conventional filter candle.