filter candle

Abstract

The present invention relates to a filter candle for gaseous fluids, comprising: one or more filter elements in the shape of a hollow cylinder made of a porous material, wherein the plurality of filter elements have substantially the same inner and outer diameter and are arranged in-line coaxially to each other; a support element comprising a metal tube arranged within the one or more filter elements, wherein the outer diameter of the metal tube is smaller than the inner diameter of the filter elements, and wherein the metal tube has a wall with a plurality of perforations; and at least two annular sealing discs with an outer diameter equal to or larger than the outer diameter of the filter elements and with an inner diameter smaller than the inner diameter of the filter elements, wherein a first end sealing disc and a second end sealing disc are arranged at opposite axial end faces of a single filter element or of a plurality of filter elements arranged in-line, and wherein optionally further inner sealing discs are arranged between two adjacent filter elements of the plurality of filter elements.

Description

Technical Field

[0001] This invention relates to filter candles for gaseous fluids, and particularly for hot gas filtration. A typical application of such filter candles is the purification of industrial flue gases or exhaust gases by removing particulate matter. Background Technology

[0002] According to existing technology, filter candles used in hot gas applications are typically based on porous filter elements in the shape of a hollow cylinder with a closed end. The gaseous fluid to be purified typically passes through the wall of the filter element from the outside in a generally radial direction and exits the filter element through an axial opening. Multiple such filter candles can be arranged parallel to each other to form a filter assembly.

[0003] This type of filter candle can also be used as a backflush filter, where the filter element is cleaned by a high-pressure airflow flowing in the opposite direction to the normal filtration process.

[0004] The aforementioned filter candles are typically made of ceramic materials and are rigid and self-supporting. However, a major drawback is their limited mechanical strength, particularly their limited tensile and flexural strength. Therefore, if the filter candles are subjected to mechanical stress, there is a risk of failure, which may occur, for example, when dust bridging occurs between the filter candles. Summary of the Invention

[0005] One object of the present invention is to provide a filter candle with improved mechanical strength.

[0006] This problem is solved by the filter candle according to claim 1.

[0007] In the filter candle of the present invention, a support element is disposed within one or more cylindrical filter elements. The support element comprises a metal tube having significantly higher tensile and flexural strength than the porous material of the filter elements. After passing through the filter elements, the gaseous fluid enters the metal tube through multiple perforations and exits the filter candle through an opening at one end of the tube.

[0008] To provide unobstructed flow through the entire inner surface area of ​​one or more filter elements, an annular gap exists between the inner surface and the outer surface of the metal tube. If a force is applied to the filter element in the radial direction, the filter element will move and / or bend until it abuts against the metal tube. In this way, the metal tube supports and stabilizes the filter element and improves the overall mechanical strength of the filter element, particularly its flexural strength.

[0009] According to the present invention, utilizing the relatively high compressive strength of the porous material of the filter element, one or more filter elements are compressed between first and second end sealing discs. However, the compression of the filter element allows radial movement between the filter element and the adjacent end sealing disc until the filter element contacts the metal tube, as described above. During this movement, the axial end face of the filter element must be tightly covered by the sealing disc.

[0010] According to a first preferred embodiment of the invention, the filter candle comprises only one filter element. In this case, only two sealing discs are provided on the two axial end faces of the filter element. The filter element preferably has an axial length of about 0.5 m to about 3.0 m, more preferably about 1.0 m to about 2.5 m.

[0011] According to a second preferred embodiment of the invention, the filter candle comprises a plurality of filter elements arranged in a straight line. In this case, in addition to the two end sealing discs, additional internal sealing discs are provided between adjacent filter elements. This segmentation of the filter candle provides further flexibility and elasticity against mechanical stresses, particularly against radial forces applied to the filter candle.

[0012] The total axial length of the multiple filter elements in the second embodiment can preferably be within the same range as the length of a single filter element in the first embodiment. However, for larger lengths, such as from about 1.5 m to about 5.0 m, segmentation is particularly preferred. In the second embodiment, the filter candle preferably comprises two to eight filter elements, more preferably three to five filter elements. The filter elements may have the same or different lengths.

[0013] The outer diameter of the one or more filter elements is preferably from about 30 mm to about 150 mm, more preferably from about 60 mm to about 70 mm, and the inner diameter is from about 15 mm to about 120 mm, more preferably from about 40 mm to about 50 mm. The wall thickness of the hollow cylinder is typically in the range of from about 7.5 mm to about 20 mm.

[0014] The radial distance between the filter element and the metal tube is preferably from about 1 mm to about 5 mm, more preferably from about 3 mm to about 4 mm. The outer diameter of the annular sealing disc is equal to or greater than the outer diameter of the filter element, and the inner diameter of the sealing disc is smaller than the inner diameter of the filter element, so that even if the filter element abuts against the metal tube, the axial end face of the filter element can be in complete contact with the sealing disc.

[0015] In this invention, preferably, each sealing disc includes: an annular metal disc, preferably a steel disc; and gaskets disposed on one or both sides of the metal disc in contact with the filter element; that is, the end sealing disc has a gasket on one side, and the inner sealing disc has gaskets on both sides. In this way, a substantially airtight seal is provided between the filter element and the sealing disc, while allowing radial movement of the filter element relative to the sealing disc.

[0016] Preferably, the gasket for the sealing disc of the filter candle of the present invention comprises graphite, metal fibers, metal mesh, polymeric materials, or combinations thereof. These and other suitable gasket materials are known in the prior art. The selection of a particular gasket material will also depend on the intended use of the filter candle of the present invention and the corresponding operating conditions. For example, most polymeric gasket materials are limited in their operating temperature.

[0017] The thickness of the gasket used for the sealing disc is preferably from about 1 mm to about 5 mm, and more preferably from about 1.5 mm to about 3 mm.

[0018] One or more sealing discs may include a resilient compensating element. In particular, it is preferred if one of the end sealing discs includes a resilient compensating element. In embodiments of the invention having more than one filter element, it is also preferred that the inner sealing disc includes a resilient compensating element. This allows for axial bending of two adjacent filter elements relative to each other. In addition to or instead of an annular metal disc, the inner sealing disc may include such a compensating element.

[0019] The filter elements of the filter candle of the present invention are typically made of ceramic materials, preferably of materials including sintered silicon carbide. These ceramic materials with high porosity are known in the prior art. Furthermore, the filter elements may include one or more catalytic materials, particularly catalytic materials for the removal of nitrogen oxides.

[0020] The metal tube used as the support element for the filter candle of the present invention is preferably a steel tube, more preferably having a wall thickness of about 2 mm to about 10 mm, particularly about 3 mm to about 6 mm. However, in some cases, the use of other metals or alloys may also be preferred, for example, where the gaseous fluid to be filtered requires the support element to have higher corrosion resistance or chemical resistance. This applies accordingly to the annular metal disc of the sealing disc.

[0021] Typically, the axial length of the metal tube is greater than the total axial length of the filter element, with the middle section of the metal tube extending inside the filter element and the two end sections extending outside the filter element. In this case, the perforations on the metal tube wall are evenly distributed on the middle section, while the walls of the two end sections are not perforated.

[0022] The number and size of the perforations are preferably chosen such that the total area of ​​the perforations is large enough to facilitate radial flow of gaseous fluid into the metal tube, but small enough to maintain sufficient mechanical stability of the metal tube. Regarding the latter requirement, the wall thickness of the metal tube must also be considered.

[0023] According to a preferred embodiment of the invention, a first end section of the metal tube extends to the outside of the filter element and passes through a first end sealing disc, wherein the first end sealing disc is preferably fixed to the first end section by welding or threaded connection. More preferably, the first end section includes an axial discharge opening for gaseous fluid.

[0024] In the above embodiments, the second end section of the metal tube may also extend to the outside of the filter element and pass through the second end sealing disc, wherein the second end sealing disc is axially movable relative to the metal tube. More preferably, the second end section is closed at its axial end, thereby allowing gaseous fluid to exit only through the first end section.

[0025] The thermal expansion difference between the porous materials of the metal tube and the filter element is taken into account by providing a first end sealing disc fixed to the metal tube and a second end sealing disc movable relative to the metal tube.

[0026] Preferably, the one or more filter elements are compressed between the first and second end sealing discs by an axial force applied to the second end sealing disc by a spring element, preferably a high-temperature spring, against the second end sealing disc and a flange element fixed to the second end portion of the metal tube.

[0027] Since the metal tube is preferably closed at the second end section, as described above, and the gaseous fluid is discharged only through the first end section, a spring cover can preferably be provided to surround the second end section including the spring element, thereby protecting the spring element from external dust, etc. The spring cover preferably abuts against the second end sealing disc.

[0028] The plurality of filter candles of the present invention can preferably be arranged in parallel with each other to form a filter assembly, particularly for hot gas filtration.

[0029] The present invention also relates to the use of the filter candle of the present invention or a filter assembly comprising a plurality of filter candles of the present invention for hot gas filtration, particularly for purifying industrial flue gas or waste gas. Attached Figure Description

[0030] The exemplary embodiments described below are provided to illustrate further details of the invention with reference to the accompanying drawings, wherein...

[0031] Figure 1 A longitudinal cross-sectional view of a first exemplary embodiment of the filter candle of the present invention is shown; and

[0032] Figure 2 A longitudinal cross-sectional view of a second exemplary embodiment of the filter candle of the present invention is shown. Detailed Implementation

[0033] exist Figure 1 The first exemplary embodiment of the filter candle 10 of the present invention is shown in a longitudinal cross-sectional view. The illustration of the filter candle 10 is schematic and not necessarily drawn to scale.

[0034] In this first embodiment, the filter candle 10 includes a filter element 12 in the shape of a hollow cylinder. For example, the filter element 12 may have 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, a porous filter element made of sintered silicon carbide material, also known as a filter candle, is sold by the applicant under the trademark "Dia-Schumalith".

[0035] Inside the filter element 12, a metal tube 16 (typically a steel tube) is provided as a support element, extending coaxially with the filter element along the rotation axis 14. The metal tube 16 includes a middle section 18 extending within the filter element 12, and first and second end sections 20 and 22 extending outside the filter element 12. The wall 24 of the metal tube 16 has a plurality of perforations 26 evenly distributed on the middle section 18, while the walls 24 of the first and second end sections 20 and 22 are not perforated.

[0036] The metal tube 16 may have an outer diameter of, for example, about 34 mm, and its wall 24 has a thickness of 4 mm. In any case, the outer diameter of the metal tube 16 is smaller than the inner diameter of the filter element 12, such that an annular gap 28 is formed between the filter element 12 and the metal tube 16. This gap 28 may have a width of, for example, about 3 mm.

[0037] In a typical application of the filter candle 10, such as in a hot gas filtration application, the gaseous fluid to be filtered passes through the filter element 12 from the outside in a generally radial direction into the annular gap 28 and is inserted into the metal tube 16 through the perforation 26. The gaseous fluid then exits the metal tube 16 through the axial discharge opening 30 at the first end section 20, while the second end section 22 is closed at its axial end 32.

[0038] The filter element 10 also includes two annular sealing discs, namely a first end sealing disc 34 and a second end sealing disc 36. The first end sealing disc 34 surrounds the first end segment 20 of the metal tube 16 and is fixed to the first end segment by welding, as shown by reference numeral 37, thereby providing an airtight closure of the annular gap 28 at the first end segment 20. Conversely, the second end sealing disc 36 surrounds the second end segment 22 of the metal tube 16 and is axially movable relative to the metal tube 16 to allow different thermal extensions of the metal tube 16 and the filter element 12.

[0039] The filter element 12 is compressed between the first and second end sealing rings 34 and 36, wherein the compressive force is applied by a spring element 38, preferably a high-temperature spring. The spring element 38 surrounds the second end segment 22 of the metal tube 16 and abuts against the second end sealing disc 36 and the flange element 40, which is fixed to the second end segment 22, for example, by a nut 42.

[0040] The second end section 22 of the metal tube 16, including the spring element 38, is covered by a spring cap 44, which abuts against the second end sealing disc 36. The spring cap 44 protects the spring element 38 from external dust and the like, and it also inhibits gaseous fluid that may pass through the small annular gap between the metal tube 16 and the second end sealing disc 36.

[0041] Each of the end sealing discs 34 and 36 includes a metal disc 46 (typically a steel disc) and a gasket 48. The gasket is in direct contact with the corresponding axial end face of the filter element 12 to provide an airtight seal, but simultaneously allows radial movement of the filter element 12. The first end sealing disc 34 may additionally include a resilient compensating element.

[0042] Due to the external force acting on the filter element 12, the filter element 12 will move radially along the gasket until it contacts the metal tube 16. At this point, the metal tube 16 supports and stabilizes the filter element 12, ideally preventing further bending and breakage. The metal tube 16 thus serves as a support element that increases the overall tensile and bending strength of the filter element 10.

[0043] To provide an airtight seal at the end face of the filter element 12 at each location, the outer diameters of the annular sealing discs 34 and 36 are greater than or equal to the outer diameter of the filter element 12, and the inner diameters of the sealing discs 34 and 36 are less than the inner diameter of the filter element 12. Specifically, the difference between the outer and inner diameters of the sealing discs 34 and 36 should be at least twice the radial distance between the filter element 12 and the metal tube 16.

[0044] exist Figure 2The second exemplary embodiment of the filter candle 50 of the present invention is shown in longitudinal cross-sectional view. Except for the differences described below, the filter candle 50 of the second embodiment corresponds to the filter candle 10 of the first embodiment. Identical or corresponding elements in the first and second embodiments have the same reference numerals.

[0045] The filter candle 50 of the second embodiment includes a plurality of shorter porous material filter elements 52, rather than a single filter element. In this example, four filter elements 52 are shown, but fewer or more filter elements are also possible. Each filter element 52 is shaped as a hollow cylinder with the same inner and outer diameters and is arranged coaxially in a straight line along the axis of rotation 14 of the filter candle 50.

[0046] The lengths of the individual filter elements 52 can be the same or different, and their total length can be the same as the length of a single filter element in the first embodiment (e.g., 1.5 m). However, using multiple filter elements 52 is particularly advantageous for larger total lengths, such as up to 6 m.

[0047] An internal annular sealing disc 54 is provided between every two adjacent filter elements 52. The filter elements 52 and the internal sealing disc 45 are compressed together between the first and second end sealing discs 36 and 38, as in the filter candle 10 of the first embodiment.

[0048] Segmenting the filter element 52 into multiple sections provides the filter candle 50 with further flexibility and elasticity to resist mechanical stresses, particularly radial forces applied to the filter candle 50. For this purpose, the internal sealing disc 54 typically includes an elastic compensating element 56 that allows two adjacent filter elements 52 to bend axially relative to each other. The elastic compensating element 56 has gaskets 58 on both sides.

[0049] Measurement of bending strength

[0050] The bending strength of the filter candle of the present invention according to the first exemplary embodiment was determined in a 4-point bending test. The filter element of the tested filter candle is a hollow cylinder (Dia-Schumalith) based on a sintered silicon carbide ceramic material, with a length of 1.5 m, an outer diameter of 60 mm, and an inner diameter of 40 mm.

[0051] In a 4-point bending test, the filter element of the filter candle of the present invention broke under a force of approximately 4,800 N.

[0052] The corresponding filter element, which is conventionally used as a filter candle, typically breaks under bending forces in the range of 2,500 to 3,500 N when there is no supporting metal tube.

[0053] Therefore, compared with the corresponding conventional filter candle, the flexural strength of the filter candle of the present invention is increased by about 60%.

Claims

1. A filter candle (50) for use with gaseous fluids and for filtering hot gases, said filter candle comprising: Multiple filter elements (52) are in the shape of hollow cylinders and are made of porous material, wherein the multiple filter elements (52) have the same inner diameter and outer diameter and are arranged in a straight line coaxially with each other; - A support element comprising a metal tube disposed within the plurality of filter elements (52), wherein the outer diameter of the metal tube (16) is smaller than the inner diameter of the plurality of filter elements (52), and wherein the metal tube (16) has a wall (24) having a plurality of perforations (26), wherein the axial length of the metal tube (16) is greater than the total axial length of the plurality of filter elements (52), and wherein the perforations (26) are evenly distributed on the middle section (18) of the metal tube (16) extending within the plurality of filter elements (52); as well as - A first annular end sealing disc (34), a second annular end sealing disc (36), and an inner annular sealing disc (54) have an outer diameter equal to or greater than the outer diameter of the plurality of filter elements (52), and an inner diameter smaller than the inner diameter of the plurality of filter elements (52). The first annular end sealing disc (34) and the second annular end sealing disc (36) are disposed at the opposite axial end faces of the plurality of filter elements (52) arranged in a row, and the inner annular sealing disc (54) is disposed between two adjacent filter elements (52) of the plurality of filter elements (52). The plurality of filter elements (52) and the internal annular sealing disc (54) are compressed between the first annular end sealing disc (34) and the second annular end sealing disc (36). The radial distance between the plurality of filter elements (52) and the metal tube is 1 mm to 5 mm. Each of the first annular end sealing disc (34), the second annular end sealing disc (36), and the inner annular sealing disc (54) includes an annular metal disc (46) and a gasket (48). The gasket is disposed on one or both sides of the annular metal disc (46) in contact with the plurality of filter elements (52) so as to provide an airtight seal between each of the first annular end sealing disc (34), the second annular end sealing disc (36), and the inner annular sealing disc (54) and the plurality of filter elements (52), and to allow radial movement of the plurality of filter elements (52) relative to the first annular end sealing disc (34), the second annular end sealing disc (36), and the inner annular sealing disc (54).

2. The filter candle (50) according to claim 1, wherein the total axial length of the plurality of filter elements is 0.5m to 6.0m.

3. The filter candle (50) according to claim 1, wherein the total axial length of the plurality of filter elements is 1.5m to 5.0m.

4. The filter candle (50) according to claim 2 or 3, wherein the filter candle (50) comprises two to eight filter elements (52).

5. The filter candle (50) according to claim 2 or 3, wherein the filter candle (50) comprises three to five filter elements (52).

6. The filter candle (50) according to claim 1, wherein the plurality of filter elements (52) have an outer diameter of 30 mm to 150 mm and an inner diameter of 15 mm to 120 mm.

7. The filter candle (50) according to claim 6, wherein the outer diameter of the plurality of filter elements (52) is 60 mm to 70 mm.

8. The filter candle (50) according to claim 6, wherein the inner diameter of the plurality of filter elements (52) is 40 mm to 50 mm.

9. The filter candle (50) according to claim 1, wherein the radial distance between the plurality of filter elements (52) and the metal tube is 3 mm to 4 mm.

10. The filter candle (50) according to claim 1, wherein the annular metal disk is a steel disk.

11. The filter candle (50) according to claim 10, wherein the gasket (48) comprises graphite, metal fiber, metal mesh, polymer material or a combination thereof.

12. The filter candle (50) according to claim 1, wherein one or more of the first annular end sealing disc (34), the second annular end sealing disc (36) and the inner annular sealing disc (54) include an elastic compensation element (56).

13. The filter candle (50) according to claim 1, wherein the plurality of filter elements (52) are made of ceramic material.

14. The filter candle (50) according to claim 1, wherein the plurality of filter elements (52) are made of a material including sintered silicon carbide.

15. The filter candle (50) according to claim 1, wherein the metal tube (16) is a steel tube with a wall thickness of 2 mm to 10 mm.

16. The filter candle (50) according to claim 1, wherein the metal tube (16) is a steel tube with a wall thickness of 3 mm to 6 mm.

17. The filter candle (50) according to claim 1, wherein a first end section (20) of the metal tube (16) extends to the outside of the plurality of filter elements (52) and through a first annular end sealing disc (34), the first end section including an axial discharge opening (30) for gaseous fluid.

18. The filter candle (50) according to claim 17, wherein the first annular end sealing disc (34) is fixed to the first end section (20) by welding or threaded connection.

19. The filter candle (50) according to claim 17, wherein a second end section (22) of the metal tube (16) extends to the outside of the plurality of filter elements (52) and through a second annular end sealing disc (36), the second end section being closed at its axial end (32), and wherein the second annular end sealing disc (36) is axially movable relative to the metal tube (16).

20. The filter candle (50) according to claim 19, wherein the plurality of filter elements (52) are compressed between the first annular end sealing disc (34) and the second annular end sealing disc (36) by an axial force applied to the second annular end sealing disc (36) by a spring element (38), the spring element (38) abutting against the second annular end sealing disc (36) and a flange element (40) fixed to the second end section (22) of the metal tube.

21. The filter candle (50) according to claim 20, wherein the spring element (38) is a high-temperature spring.

22. The filter candle (50) according to claim 20, wherein the compression of the plurality of filter elements (52) allows each filter element (52) to move radially relative to the sealing discs adjacent to each filter element (52) in the first annular end sealing disc (34), the second annular end sealing disc (36) and the inner annular sealing disc (54) until each filter element (52) contacts the metal tube (16).

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