filter candle

Abstract

To provide a novel filter candle (10;50) for gaseous fluid, particularly hot gas filtration, comprising one or more hollow cylindrical filter elements (12;52), a support element (16), and two or more annular sealing discs (34,36;54). [Solution] In the filter candle of the present invention, the filter elements are made of a porous material, have the same inner and outer diameters, and are arranged coaxially in a row. The support element includes a metal tube (16) arranged within the filter element, the outer diameter of the metal tube being smaller than the inner diameter of the filter element, and the metal tube having a wall (24) with a plurality of through holes (26). The sealing disks have an outer diameter equal to or greater than the outer diameter of the filter element and an inner diameter smaller than the inner diameter of the filter element, and first and second end sealing disks are arranged on opposite axial end faces of the aligned filter elements. The filter elements are compressed between the end sealing disks.

Description

[Technical Field]

[0001] The present invention relates to a filter candle for the filtration of gaseous fluids, in particular hot gases. A typical application of such filter candles is the purification of industrial flue gases or exhaust gases by removing particles. [Background technology]

[0002] Prior art filter candles for hot gas applications are often based on a porous filter element in the form of a hollow cylinder closed at one end. The gaseous fluid to be purified typically passes through the filter element wall from the outside in a substantially radial direction and exits the filter element through a single axial opening. Several such filter candles may be arranged parallel to one another to form a filtration assembly.

[0003] This type of filter candle can also operate as a blowback filter, where the filter element is cleaned by a high-pressure gas stream flowing in the opposite direction to the normal filtration process.

[0004] The filter candles mentioned above, which are typically made of ceramic material, are rigid and self-supporting. However, their main drawback is that they have limited mechanical strength, especially tensile and bending strength. As a result, they can fail if subjected to mechanical stress, for example if dust builds up between the filter candles. Summary of the Invention [Problem to be solved by the invention]

[0005] It is an object of the present invention to provide a filter candle with improved mechanical strength. [Means for solving the problem]

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

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

[0008] An annular gap exists between the inner surface of one or more filter elements and the outer surface of the metal tube to allow unimpeded flow through the entire inner surface area of ​​the filter elements. When a radial force is applied to the filter elements, the filter elements move and / or bend until they abut against the metal tube. In this way, the metal tube supports and stabilizes the filter elements, improving the mechanical strength of the entire filter candle, especially its bending strength.

[0009] According to the present invention, one or more filter elements are compressed between the first and second end sealing disks, taking advantage of the relatively high compressive strength of the porous material of the filter elements. However, the compression of the filter elements is such that radial movement between the filter elements and the adjacent end sealing disks is permitted until the filter elements contact the metal tube as described above. During this movement, the axial end faces of the filter elements must be tightly covered by the sealing disks.

[0010] According to a first preferred embodiment of the present invention, the filter candle comprises only one filter element, the two axial end faces of which are provided with only two sealing disks, and 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 row, where in addition to the two end sealing disks, further internal sealing disks are provided between adjacent filter elements. Such segmentation of the filter candle provides it with greater flexibility and resilience against mechanical stresses, in particular radial forces acting on it.

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

[0013] The filter element(s) preferably have an outer diameter of about 30 mm to about 150 mm, more preferably about 60 mm to about 70 mm, and an inner diameter of about 15 mm to about 120 mm, more preferably about 40 mm to about 50 mm. The wall thickness of the hollow cylinder is typically in the range of about 7.5 mm to about 20 mm.

[0014] The radial distance between the filter element and the metal tube is preferably about 1 mm to about 5 mm, more preferably about 3 mm to about 4 mm. To ensure that the axial end face of the filter element is in complete contact with the sealing disk even when the filter element abuts against the metal tube, the outer diameter of the annular sealing disk is equal to or larger than the outer diameter of the filter element, and the inner diameter of the sealing disk is smaller than the inner diameter of the filter element.

[0015] In the present invention, each sealing disk preferably comprises an annular metal disk, preferably a steel disk, and a gasket provided on one or both sides of the metal disk in contact with the filter element, i.e., end sealing disks are provided with a gasket on one side and inner sealing disks are provided with a gasket on both sides, thus providing a substantially airtight seal between the filter element and the sealing disk while at the same time allowing radial movement of the filter element relative to the sealing disk.

[0016] Preferably, the gasket used in the sealing disk 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 already known in the prior art. The choice of a specific gasket material also depends on the intended use of the filter candle of the present invention and the respective operating conditions. For example, most polymeric gasket materials are limited in terms of their operating temperature.

[0017] The gasket used in the sealing disk preferably has a thickness of about 1 mm to about 5 mm, preferably about 1.5 mm to about 3 mm.

[0018] One or more of the sealing discs may comprise a resilient compensating element. In particular, it is preferred that one of the end sealing discs comprises a resilient compensating element. In embodiments of the invention having two or more filter elements, it is also preferred that the inner sealing disc comprises a resilient compensating element, which allows axial bending of two adjacent filter elements relative to each other. The inner sealing disc can comprise such an adjusting element in addition to or instead of the annular metal disc.

[0019] The filter element(s) of the filter candle of the present invention are typically made of a ceramic material, preferably a material comprising sintered silicon carbide. These ceramic materials exhibiting high porosity are known from the prior art. Furthermore, the filter element(s) can comprise one or more catalytic materials, in particular for the removal of nitrogen oxides.

[0020] The metal tube serving as the support element of 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, in particular about 3 mm to about 6 mm. However, in certain cases, for example, when the gaseous fluid to be filtered requires a higher corrosion or chemical resistance in the support element, the use of other metals or alloys may be preferable. This therefore also applies to the annular metal disk of the sealing disk.

[0021] Typically, the metal tube has an axial length greater than the total axial length of the filter element, the middle section of the metal tube extends within the filter element, and the two end sections of the metal tube extend outside the filter element, with the through-holes in the wall of the metal tube being uniformly distributed throughout the middle section and the walls of the two end sections being free of through-holes.

[0022] The number and size of the through holes are preferably selected so that the total area of ​​the through holes is large enough to facilitate radial flow of the gaseous fluid into the metal tube, but small enough to maintain sufficient mechanical stability of the metal tube, the wall thickness of which must also be taken into account with regard to the latter requirement.

[0023] According to a preferred embodiment of the invention, the first end section of the metal tube extends to the outside of the filter element through a first end sealing disk, which is fixed to said first end section, preferably by welding or screwing. It is further preferred that the first end section comprises an axial discharge opening for the gaseous fluid.

[0024] In the above-described embodiment, the second end section of the metal tube can also extend outside the filter element through a second end sealing disk, which is axially movable relative to the metal tube. It is further preferred that the second end section is closed at its axial end, thereby allowing evacuation of the gaseous fluid only through the first end section.

[0025] By providing a first end sealing disk fixed to the metal tube and a second end sealing disk movable relative to the metal tube, differences in thermal expansion between the metal tube and the porous material of the filter element are taken into account.

[0026] Preferably, the one or more filter elements are compressed between the first and second end sealing disks by an axial force exerted on the second end sealing disk via a flange element fixed to the second end section of the metal tube and a spring element, preferably a high temperature spring, abutting the second end sealing disk.

[0027] As explained above, the metal tube is preferably closed at the second end section and the gaseous fluid is discharged only through the first end section, so that a spring cover is preferably 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 disk.

[0028] A plurality of filter candles of the present invention may preferably be arranged parallel to one another to form a filter assembly, particularly for hot gas filtration.

[0029] The present invention also relates to the use of a filter candle according to the invention, or a filter assembly comprising a plurality of filter candles according to the invention, for hot gas filtration, in particular for cleaning industrial flue gases or exhaust gases. The present invention provides, for example, the following items. (Item 1) one or more filter elements (12; 52) in the form of a hollow cylinder; a support element (16); At least two annular sealing discs (34, 36; 54) A filter candle (10; 50) for gaseous fluids, in particular for hot gas filtration, comprising: the one or more filter elements (12; 52) are made of a porous material, and a plurality of the filter elements (12; 52) have substantially the same inner and outer diameters and are arranged coaxially in a line with one another; the support element (16) comprises a metal tube (16) disposed within the one or more filter elements (12; 52), the metal tube (16) having an outer diameter smaller than an inner diameter of the filter elements (12; 52), the metal tube (16) having a wall (24) with a plurality of through holes (26); the at least two annular sealing discs (34, 36; 54) have outer diameters equal to or greater than the outer diameters of the filter elements (12; 52) and inner diameters smaller than the inner diameters of the filter elements (12; 52), the first and second end sealing discs (34, 36) being disposed on opposite axial end faces of a single filter element (12) or on opposite axial end faces of a plurality of the filter elements (52) arranged in a row, and optionally, a further inner sealing disc (54) being disposed between two adjacent filter elements (52) of the plurality of filter elements (52); A filter candle, wherein the one or more filter elements (12, 52), and optionally the inner sealing disc (54), are compressed between the first end sealing disc (34) and the second end sealing disc (36). (Item 2) Item 1. The filter candle (10) according to item 1, comprising only one filter element (12) having an axial length of preferably about 0.5 m to about 3.0 m, more preferably about 1.0 m to about 2.5 m. (Item 3) Item 1. A filter candle (50) according to item 1, comprising a plurality of the filter elements (52) arranged in a row, each having a total axial length of preferably about 0.5 m to about 6.0 m, and preferably about 1.5 m to about 5.0 m. (Item 4) Item 4. The filter candle (50) according to item 3, comprising two to eight of the filter elements (52), preferably three to five of the filter elements (52). (Item 5) 5. The filter candle (10; 50) according to any one of items 1 to 4, wherein the one or more filter elements (12; 52) have an outer diameter of about 30 mm to about 150 mm, preferably about 60 mm to about 70 mm, and an inner diameter of about 15 mm to about 120 mm, preferably about 40 mm to about 50 mm. (Item 6) 6. The filter candle (10; 50) according to any one of items 1 to 5, wherein the radial distance between the filter element (12; 52) and the metal tube is about 1 mm to about 5 mm, preferably about 3 mm to about 4 mm. (Item 7) Each of said sealing discs (34, 36; 54) an annular metal disc (46), preferably a steel disc, for providing a substantially airtight seal between the filter element (12; 52) and the sealing disc (34, 36; 54) and for permitting radial movement of the filter element (12; 52) relative to the sealing disc (34, 36; 54); a gasket (48) provided on one or both sides of the metal disc (46) in contact with the filter element (12; 52); 7. The filter candle (10; 50) according to any one of items 1 to 6, comprising: (Item 8) 8. The filter candle (10; 50) according to item 7, wherein the gasket (48) comprises graphite, metal fibers, metal mesh, a polymeric material, or a combination thereof. (Item 9) 9. The filter candle (10; 50) according to any one of items 1 to 8, wherein one or more of the sealing discs (34, 36; 54), in particular the end sealing discs (34, 36) and / or one of the internal sealing discs (54), are provided with an elastic adjustment element (56). (Item 10) 10. The filter candle (10; 50) according to any one of items 1 to 9, wherein the one or more filter elements (12; 52) are made of a ceramic material, preferably a material comprising sintered silicon carbide. (Item 11) The filter candle (10; 50) according to any one of items 1 to 10, wherein the metal tube (16) is a steel tube, preferably having a wall thickness of about 2 mm to about 10 mm, in particular about 3 mm to about 6 mm. (Item 12) 12. The filter candle (10; 50) according to any one of claims 1 to 11, wherein the metal tube (16) has an axial length greater than the total axial length of the filter element (12; 52), and the through holes (26) are uniformly distributed throughout the entire intermediate section (18) of the metal tube (16) that extends within the filter element (12; 52). (Item 13) Item 13. The filter candle (10; 50) according to item 12, wherein a first end section (20) of the metal tube (16), preferably provided with an axial discharge opening (30) for the gaseous fluid, extends to the outside of the filter element (12; 52) through the first end sealing disk (34), and the first end sealing disk (34) is fixed to the first end section (20), preferably by welding or screwing. (Item 14) Item 14. A filter candle (10; 50) according to item 13, wherein a second end section (22) of the metal tube (16), which is preferably closed at its axial end (32), extends outside the filter element (12; 52) through the second end sealing disk (36), and the second end sealing disk (36) is axially movable relative to the metal tube (16). (Item 15) Item 15. The filter candle (10; 50) according to item 14, wherein the one or more filter elements (12; 52) are compressed between the first end sealing disk (34) and the second end sealing disk (36) by an axial force exerted on the second end sealing disk (36) via a spring element (38), preferably a high-temperature spring, abutting the second end sealing disk (36) and a flange element (40) fixed to the second end section (22) of the metal tube. (Item 16) Item 16. The filter candle (10; 50) according to item 15, wherein the compression of the one or more filter elements (12; 52) allows radial movement between the filter element (12; 52) and the adjacent sealing disc (34, 36; 54) until the filter element (12; 52) comes into contact with the metal tube (16).

[0030] The exemplary embodiments described below serve to explain the invention in further detail with reference to the drawings. [Brief explanation of the drawings]

[0031] [Figure 1] 1 is a longitudinal section of a first exemplary embodiment of a filter candle of the present invention; FIG. [Figure 2] FIG. 2 is a longitudinal section of a second exemplary embodiment of a filter candle of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0032] 1 shows a first exemplary embodiment of a filter candle 10 of the invention in longitudinal section. The depiction of the filter candle 10 is schematic and not necessarily to scale.

[0033] In this first embodiment, the filter candle 10 comprises a single hollow cylindrical filter element 12. The filter element 12 may, for example, 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, porous filter elements made of sintered silicon carbide material, also known as filter candles, are sold by the applicant under the trademark "Dia-Schumalith."

[0034] A metal tube 16 (typically a steel tube) is arranged inside the filter element 12 as a support element, extending coaxially with the filter element along the rotation axis 14. The metal tube 16 has a middle section 18 that extends within the filter element 12 and first and second end sections 20 and 22 that extend outside the filter element 12. A wall 24 of the metal tube 16 has a plurality of through holes 26 uniformly distributed throughout the middle section 18 of the metal tube 16, while the walls 24 of the first and second end sections 20, 22 are free of through holes.

[0035] The metal tube 16 may, for example, have an outer diameter of about 34 mm and a thickness of 4 mm of its wall 24. In either 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. The width of this gap 28 may, for example, be 3 mm.

[0036] For example, in a typical application of the filter candle 10 for use in hot gas filtration, the gaseous fluid to be filtered passes substantially radially from the outside through the filter element 12 into the annular gap 28 and through the through holes 26 into the metal tube 16. The gaseous fluid then exits the metal tube 16 through the axial discharge opening 30 in the first end section 20, while the second end section 22 is closed at its axial end 32.

[0037] The filter candle 10 further comprises two annular sealing disks, a first end sealing disk 34 and a second end sealing disk 36. The first end sealing disk 34, as indicated by reference numeral 37, surrounds the first end section 20 of the metal tube 16 and is fixed thereto by welding, thus hermetically closing the annular gap 28 at the first end section 20. In contrast, the second end sealing ring 36, which surrounds the second end section 22 of the metal tube 16, is axially movable relative to the metal tube 16 to allow for differential thermal expansion of the metal tube 16 and the filter element 12.

[0038] The filter element 12 is compressed between a first end sealing ring 34 and a second end sealing ring 36, the compressive force being exerted by a spring element 38, preferably a high temperature spring, which surrounds the second end section 22 of the metal tube 16 and abuts a flange element 40 secured to the second end sealing ring 34 and second end section 22, for example, by a threaded nut 42.

[0039] The second end section 22 of the metal tube 16, including the spring element 38, is covered by a spring cover 44 that abuts the second end sealing disk 36. The spring cover 44 protects the spring element 38 from external dust and dirt and also prevents gaseous fluids from passing through the small annular gap between the metal tube 16 and the second end sealing disk 36.

[0040] Each of the end sealing disks 34, 36 includes a metal disk 46 (typically a steel disk) and a gasket 48 that directly contacts the respective axial end face of the filter element 12 to provide an airtight seal while simultaneously allowing radial movement of the filter element 12. The first end sealing disk 34 may further include a resilient adjustment element.

[0041] As a result of an external force acting on the filter element 12, the filter element 12 moves 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 it from further bending and breaking. Thus, the metal tube 16 acts as a support element that increases the overall tensile and bending strength of the filter candle 10.

[0042] To provide an airtight seal against the end face of the filter element 12 at all locations, the outer diameter of the annular sealing disks 34, 36 is greater than or equal to the outer diameter of the filter element 12, and the inner diameter of the sealing disks 34, 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, 36 should be at least twice the radial distance between the filter element 12 and the metal tube 16.

[0043] 2 shows a second exemplary embodiment of a filter candle 50 of the invention in longitudinal section. The filter candle 50 of the second embodiment corresponds to the filter candle 10 of the first embodiment, except for the differences explained below. Identical or corresponding elements of the first and second embodiments are provided with the same reference numerals.

[0044] The filter candle 50 of the second embodiment includes, instead of a single filter element, a plurality of shorter filter elements 52 of porous material. In this example, four filter elements 52 are shown, but a fewer or greater number of filter elements are also possible. The individual filter elements 52 are shaped as hollow cylinders with identical inner and outer diameters and are arranged coaxially in a row along the rotational axis 14 of the filter candle 50.

[0045] The individual filter elements 52 may be of the same or different lengths, and their overall length may be the same as the overall length of a single filter element of the first embodiment (e.g., 1.5 m), although the use of multiple filter elements 52 is also particularly useful for longer overall lengths, such as lengths up to 6 m.

[0046] An inner annular sealing disk 54 is disposed between each pair of adjacent filter elements 52. The filter elements 52, together with the inner sealing disk 45, are compressed between the first end sealing disk 36 and the second end sealing disk 38, similar to the filter candle 10 of the first embodiment.

[0047] The division into a plurality of filter elements 52 makes the filter candles 50 more flexible and resilient to mechanical stresses, in particular radial forces exerted on the filter candles 50. For that purpose, the inner sealing disc 54 typically comprises an elastic adjustment element 56 that allows axial bending of two adjacent filter elements 52 relative to one another. The elastic adjustment element 56 is provided with gaskets 58 on both sides.

[0048] Bending strength measurement The bending strength of the inventive filter candle according to the first exemplary embodiment was measured in a four-point bending test. The filter element of the tested filter candle was a hollow cylinder of sintered silicon carbide (Dia-Schumalith) based ceramic material with a length of 1.5 m, an outer diameter of 60 mm and an inner diameter of 40 mm.

[0049] In a four-point bending test, the filter element of the filter candle of the present invention cracked at a force of about 4800 N.

[0050] Typically, the corresponding filter element alone, without the supporting metal tube, which is conventionally used in filter candles, cracks at bending forces in the range of 2500-3500N.

[0051] The bending strength of the filter candle of the invention is therefore increased by approximately 60% compared to the corresponding conventional filter candle. [Explanation of symbols]

[0052] 10...filter candle, 12...filter element, 16...metal tube, 18...mid-section, 20...first end section, 22...second end section, 24...wall, 26...through hole, 34...first end sealing disk, 36...second end sealing disk, 38...spring element, 50...filter candle, 52...filter element, 54...inner sealing disk.

Claims

[Claim 1] The invention described in this specification.

Images