CANDLE FILTER ELEMENT

Abstract

The invention relates to a candle filter element for installation in a pressure vessel or for implementation in a tank or basin open to atmosphere. Main parts of the candle filter element are a fixing device for the connection to the housing, a coupling part to connect the support body with the fixing device, a support body for the filter material with integrated dip channel and a bottom part.

Claims

1. Filter element comprising a support body and a filter cloth that is laid around the support body, wherein the support body comprises a centrally positioned dip channel and outer longitudinal flow channels.

2. Filter element according to claim 1, wherein the support body is formed of a continuous profile, preferably a continuous extruded profile, even more preferably comprising a thermoplastic material, a ceramic material or a metal.

3. Filter element according to claim 1, wherein the outer contour of the support body is circular, star-shaped, cricket bat-shaped or elliptical.

4. Filter element according to claim 1, wherein a central tube forms the dip channel and longitudinal bars are mounted on that central tube.

5. Filter element according to claim 1, wherein the outer longitudinal flow channels are formed by longitudinal walls within the material of the support body with rounded outer edges and covered by the filter cloth.

6. Filter element according to claim 1, wherein the dip channel volume is at least 1% larger than the total differential volume of all outer longitudinal flow channels.

7. Filter element according to claim 1, wherein the filter cloth is fixed on the filter element by cloth-fixing elements, in particular one cloth-fixing element on the bottom end of the longitudinal channel area and one cloth-fixing element on the top end of the longitudinal channel area of the candle filter element, wherein the cloth-fixing elements are also sealing the filtrate room against the feed room.

8. Filter element according to claim 1, wherein the filter element is further equipped with a coupling part between the support body and the fixing device and with a pin for an optimum alignment of the filter element in a filter device.

9. Filter element according to claim 8, wherein the filter cloth is fixed above the coupling part to cover the pin and the coupling.

10. Filter element according to claim 2, wherein the thermoplastic material is a compound material containing stability-enhancing additives such as carbon fibers or glass fibers.

11. Use of the filter element of claim 1 in a filter device, wherein the filter device is a vessel wherein the unfiltered fluid is separated from the filtered fluid by a head plate.

12. Use of the filter element of claim 1 in a filter device, wherein the filter elements are mounted on one or more common filtrate headers as collector tubes.

13. Use of the filter element of claim 1, wherein the filter element is preferably used in a system configuration where the filter elements are mounted on tube headers and are submerged in the feed contained in an open basin and the differential pressure needed to drive filtration is created by vacuum inside such tube headers.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0031] FIG. 1 shows a longitudinal section of a candle filter element according to the invention.

[0032] FIG. 2 shows a detail of the extruded support body with a filter cloth and a filter cake that includes the particles filtered from the feed suspension.

[0033] FIG. 3 shows a preferred design of a filter candle element for wet cake discharge according to the invention.

[0034] FIG. 4 shows the cross section of an alternative embodiment where the continuously extruded profile resembles a star shape.

[0035] FIG. 5 shows the cross section of an alternative embodiment where the continuously extruded profile resembles a cricket bat.

[0036] FIG. 6 shows the cross section of an alternative embodiment where the longitudinal bars are mounted on the main body.

DETAILED DESCRIPTION

[0037] It is an object of the present invention to provide a filter element comprising a support body and a filter cloth that is laid around the support body, wherein the support body comprises a centrally positioned dip channel and outer longitudinal flow channels. The filter cloth may be wrapped around the support body. During operation of the filter element that filter cloth supports a filter cake when flowed through from the outside to the inside by a suspension. The dip channel may have a circular or a non-circular, e.g. square, hexagonal etc. cross-section. “Channels” in the context of the present invention shall mean longitudinal free spaces that are formed by the material of the support body, but shall explicitly exclude tubes like, e.g., in U.S. Pat. No. 4,473,472. The simplest embodiment of the dip channel may be a longitudinal free space of circular cross-section in the center of the profile. The outer longitudinal flow channels are essentially completely open radially towards the outside of the filter element—and not only perforated to a certain extent like in U.S. Pat. No. 4,473,472-, as can be seen in FIGS. 2, 3, 4, 5 and 6. This feature of the flow channels provides for a lower resistance against the liquid flow or respective gas flow during filtration operation and backwashing and thereby results in a more efficient backwashing.

[0038] Preferably the support body of the filter element according to the invention is formed of a continuous profile, even more preferably a continuous extruded profile, preferably comprising a thermoplastic material. Instead, the extruded profile may be made of another extruded material, e.g., a metal (like aluminum, steel, etc.) or glass. In principle, even a ceramic material may be suitable.

[0039] “Continuous” in the context of the present invention means that the cross-section of the body is identical over the whole length of the support body. “Extruded” in the context of the present invention means that the support body over its whole length as well as all longitudinal bars are continuously formed in an extrusion process.

[0040] Continuous, extruded profiles generally have the advantage that they usually show no dead zones like edges, corners and the like, where filter fluid or particles could stay for long residence time and undergo changes like decomposition, ageing, bacterial growth etc. that could have negative effects.

[0041] However, for some applications where dead zones are less dangerous, also continuous profiles comprising a central tube that forms the dip channel and longitudinal bars mounted on that central tube by known methods (like welding, screwing, riveting, etc.) are suitable. Such bodies could for example be longitudinal finned tubes, like e.g., used for liquid-air heat exchangers.

[0042] Preferably the outer contour of the support body of the filter element according to the invention may be circular, star-shaped, cricket bat-shaped or elliptical. “Elliptical” shall mean a rounded, non-edged, non-circular outer contour with two axes of symmetry showing a relation of the long and short axes of symmetry of the cross-section of the support body of between 1,1:1 and 20:1. A cricket bat shape will also be possible for the purposes of the present invention. Some suitable outer contour forms, i.e. profile shapes, can be derived from FIGS. 3 (round), 4 (star-shaped) and 5 (cricket bat-shaped).

[0043] In a preferred embodiment of the invention the outer longitudinal flow channels are formed by longitudinal walls within the material of the support body with rounded outer edges and are covered by the filter cloth. During the filtration operation the filter cloth lays on these rounded outer edges and therefore is essentially supported by the longitudinal walls.

[0044] Preferably the dip channel volume is at least equal to or greater than 1%, larger than the total differential volume of all outer longitudinal flow channels of the same filter element, preferably between 1% and 5% larger. The total differential volume shall mean the total volume (accessible for the filtrate) in the filter cloth in backwashing position minus the volume (accessible for the filtrate) of the channels covered by the filter cloth in the filtration position.

[0045] In a preferred embodiment of the invention the filter cloth is a substantially cylindrical filter cloth. Preferably it is fixed on the filter element by cloth-fixing elements, in particular by one cloth-fixing element at the bottom end of the longitudinal channel area and one cloth-fixing element at the top end of the longitudinal channel area of the candle filter element. In this embodiment of the present invention the cloth-fixing elements are also sealing the filtrate room against the feed room. Cloth-fixing elements may be e.g., clamps, tension rings or other suitable devices that are principally known to the skilled in the art.

[0046] Preferably the filter element is further equipped with a coupling part between the support body and the fixing device and with a pin for an optimum alignment of the filter element in a filter device.

[0047] Preferably the filter cloth is fixed above the coupling part to cover the pin and the bottom part of the coupling part, as can be seen in FIG. 1.

[0048] The thermoplastic material of the filter element according to the invention may be a compound material containing stability-enhancing additives such as carbon fibers or glass fibers. Such materials as well as the methods to shape them in an appropriate way are in principle known by the skilled in the art.

[0049] It is another object of the present invention to provide a use of the filter element according to the invention in a filter device, wherein the filter device is a vessel wherein the unfiltered fluid is separated from the filtered fluid by a head plate.

[0050] In a preferred embodiment of the invention the filter elements in this filter device are mounted on one or more common filtrate headers as collector tubes. Such filtrate headers are described e.g., in U.S. Pat. No. 4,604,201 under the term “outlet channels”.

[0051] In another preferred embodiment of the invention the filter element is preferably used in a system configuration where the filter elements are mounted on tube work headers (i.e., not within a closed filter vessel) and are instead submerged in the feed contained in an open basin and the differential pressure needed to drive filtration is created by vacuum inside such tube work headers.

[0052] FIG. 1 shows the main parts of the candle filter element 100. The support body 1 includes an extrusion profile with integrated dip tube 2, a bottom part 3 for collecting the filtrate and redirecting the flow and a support area 4 for the clamp 5 to fasten the filter cloth 6, a coupling part 7 to connect the filter element via a pin 8 with the fixing device 9. On the fixing device 9, there is another support area 4 for the clamp 5 to fasten the filter cloth. One clamp on the bottom side and one on the top side of the filter element. On the top side, the filter element is equipped with a means to connect the same to the filtrate room.

[0053] According to the invention, unfiltered fluid passes the candle filter element from outside in. The fluid passes the filter cloth and a certain differential pressure is built from the outside to the inside. Driven by this differential pressure, the filter cloth 6 will lay down on the surface of the support body 1. This happens very evenly around the circumference. The particles of the unfiltered fluid separated on the surface of the filter cloth, build particle bridges and a filter cake 11 is thereby formed. The clean filtered fluid passes the filter cloth and is collected in the outer longitudinal flow channels 10 of the support body. These channels 10 are closed on the top side of the support body 1, so the filtered fluid is forced to flow downwards, to the bottom part 3, is redirected there to flow upwards through the dip tube 2 of the support body 1 and to exit the candle filter element at the top side. After finishing building up a filter cake 11, the filter candle will be cleaned where after filtration starts again. Cleaning can be done in two different ways. Depending whether the filter cake is desired to be discharged in a dry manner or whether a filter cake discharge as a slurry is desired for the process.

[0054] Backwash and cake discharge happens by reversing the flow of fluid by means of a pump or of introducing a gas from filtrate side. Cake discharge can be done in a dry manner, by firstly removing all the liquid from the system and dropping the filter cake through a bottom valve, or, in a slurry form by backwashing into the filled feed room and afterward draining the slurry from the same.

[0055] FIG. 3 shows a preferred design of a filter candle element for wet cake discharge according to the invention. The support body 1 for the filter cake including the outer flow channels for the filtrate and the dip tube are all made of one continuously extruded profile. Thus, the element only needs to be completed by top and bottom parts, preferably made of simple machined or injection molded parts and therefore the material used as well as the time needed to fabricate the element is kept at a minimum. The diameter of the dip tube is thereby designed to accommodate enough fluid to compensate for the volume change caused by the movement of the filter cloth during backwash.

[0056] FIG. 4 shows the cross section of an alternative embodiment where the continuously extruded profile resembles a star shape and thereby allows for a higher movement of the filter cloth when being inflated during the application of compressed gas from the inside thus having an improved filter cake release.

[0057] FIG. 5 shows the cross section of an alternative embodiment where the continuously extruded profile resembles a cricket bat that again allows for a high movement of the filter cloth when being inflated during the application of compressed gas from the inside. This embodiment has an additional advantage of allowing for accommodating a higher total volume of filter cake in a given vessel dimension.

[0058] FIG. 6 shows the cross section of an alternative embodiment where the longitudinal bars are mounted on the main body by welding (e.g., resistance welding) U-shaped metal profiles 13 onto a central tube 12.