Column filter using bundles of long fibers

Abstract: A colunm filter using bundles of long fibers, said filter being provided with an upright cylindrical shell and the bundles of long fibers being arranged upright inside the shell with lower end portions thereof being fixed and upper end portions thereof being free-standing, characterized in that a plurality of holders for the respective bundles of long fibers, each of said holders being formed of an upper cap member and a lower hollow member communicating to each other, said upper cap member defining openings therethrough and said lower hollow member defining at least an axially-elongated opening through a side wall thereof and opening at both upper and lower ends thereof, are provided on a perforated plate arranged transversely in a lower interior part of the shell with the upper cap member being located above the perforated plate and the lower hollow member being positioned below the perforated plate; the holders cover all perforations of the perforated plate; and the lower end portion of each of the bundles of long fibers is fixed to a lower periphery of a side wall of the associated upper cap member.

Description: BACKGROUND OF THE INVENTION a) Field of the Invention: This invention relates to a column filter which uses bundles of long fibers as a filter medium to remove at a high rate suspended solids from raw liquids such as city water, industrial water, sewage, river water, lake or pond water, supernatant waters from coagulation and settling treatments, waters discharged intermediately during the practice of various processes, recovered waters such as those from pulp- and paper-making processes, various waste waters, processing waters or valuable-material-containing liquids from biological treatment apparatus, alcoholic beverages, oils and the like. In particular, this invention is concerned with a column filter of the above sort, in which an improvement has been applied to the structure holding lower end portions of the bundles of long fibers. b) Description of the Related Art: The application is a divisional application of EP 89 109 509.3. In the parent application of this application, which was patented as EP 0344633 and was published on April 27, 1994, a column filter according to Figs. 1-3 is claimed. This divisional application concerns an improvement to the structure holding lower end portions of the bundles of long fibers in the above claimed column filter. In the above column filter, the fixing of lower end portions of bundled long fibers was conducted as shown in FIG. 9. Each bundle of long fibers 3 was folded and bound at the folded part by a ring 31. The folded part was positioned to close up each perforation 24 of the perforated plate 2. Using a bolt 32 connected to the ring 31, the bundle of long fibers 3 was fixed with a stem-like holder 33 and a nut 34. The conventional fixing method was therefore accompanied by drawbacks to be described next. In such a structure, the long fibers bundled together at the ring 31 were arranged very densely and a raw water always had to pass through the densely-bundled part of the long fibers during the filtration. The densely-bundled part of the long fibers was therefore prone to clogging with suspended solids. Once the densely-bundled part was clogged, it was difficult to remove the thus-trapped solids even when backwashing was conducted. Because, when a fluid such as compressed air or backwash water is caused to pass upwardly through each perforation 24 in such a structure as depicted in FIG. 9, the fluid passes preferentially through the point of contact between the upper surface of the perforated plate 2 and the bundled long fibers 3 and hardly passes through the fiber part through which the fluid is supposed to pass, namely, the densely-bundled part of the long fibers. When the nut 34 is tightened firmly to increase the degree of contact between each bundle of long fibers 3 and the edge of its corresponding perforation 24, the fluid preferentially passes through the perforations 24 having bundles of long fibers 3 less clogged with trapped solids. The fluid therefore does not pass through the bundles of long fibers which require washing, namely, through the perforations 24 having bundles of long fibers 3 whose densely-bundled parts are clogged with trapped solids. When the filter is operated continuously under the above conditions, more solids gradually remain in the densely-bundled part of each bundled long fibers. This causes the initial pressure drop to increase gradually in the life of column filter, and in some instances gives serious problems to the filtration plant itself. As another drawback, even when the bundle of long fibers 3 is so fixed as to squeeze itself in the corresponding perforation 24, a small clearance still remains between the peripheral edge of the perforation 24 and the bundles of long fibers 3. An increased pressure drop causes suspended solids to leak through the clearance, so that the quality of the filtered water falls toward the end of filtration. SUMMARY OF THE INVENTION An object of this invention is to solve the above-described drawbacks of the column filter which uses bundles of long fibers and to provide a column filter capable of exhibiting the advantages of bundles of long fibers to a maximum extent, so that the bundles of long fibers can be washed thoroughly by backwashing and leakage of suspended solids into a filtered liquid can be minimized. To realize the above-described object, the present invention provides a column filter using bundles of long fibers, said filter being provided with an upright cylindrical shell, and the bundles of long fibers being arranged upright inside the shell with lower end portions thereof being fixed and upper end portions thereof being free-standing, characterized in that a plurality of holders for the respective bundles of long fibers, each of said holders being formed of an upper cap member and a lower hollow member communicating to each other, said upper cap member defining openings therethrough and said lower hollow member defining at least an axially-elongated opening through a side wall thereof and opening at both uper and lower ends thereof, are provided on a perforated plate arranged transversely in a lower interior part of the shell with the upper cap member being located above the perforated plate and the lower hollow member being positioned below the perforated plate; the holders cover all perforations of the perforated plate; and the lower end portion of each of the bundles of long fibers is fixed to a lower periphery of a side wall of the associated upper cap member. The length of the long fiber bundles may preferably be longer than 1,000 mm but shorter than 3,000 mm - especially longer than 2,000 mm but shorter than 3,000 mm. As the shape of each upper cap member, a cylindrical, polygonally-cylindrical, truncated conical, polygonally-conical truncated or hemispherical shape may be chosen suitably. Similarly, the lower hollow member may be formed into a cylindrical, polygonally-cylindrical, truncated conical, polygonally-conical truncated or hemispherical shape as desired. The fixing of the lower end portions of the bundles of long fibers can be effected, for example, by pinching the lower end portions, adhering the lower end portions, or fusion-bonding the lower end portions themselves. In the column filter according to this invention, the bundles of long fibers are not merely provided at the individual perforations of the perforated plate. The plurality of holders for the respective bundles of long fibers, each of said holders being formed of the upper cap member and the lower hollow member communicating to each other, said upper cap member defining the openings therethrough and said lower hollow member defining the axially-elongated opening through the side wall thereof and opening at both upper and lower ends thereof, are provided on the perforated plate arranged transversely in the lower part of the shell with the upper cap member being located above the perforated plate and the lower hollow member being positioned below the perforated plate. The holders cover all perforations of the perforated plate. The lower end portion of each of bundles of long fibers is fixed to the lower periphery of the side wall of the associated upper cap member. The openings of each upper cap member are therefore surrounded substantially by the associated bundles of long fibers. Suspended solids are hence hardly allowed to leak into a filtered liquid. Upon backwashing, a fluid such as compressed air or back-washing water is allowed to flow out evenly through the individual openings of each upper cap member, so that dense parts of the bundles of long fibers, said parts being located in the proximity of the perforated plate, can be effectively washed to ensure sufficient backwashing. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a simplified vertical cross-section of the column filter according to the parent application in an initial stage of filtration; FIGS. 2 and 3 are simplified vertical cross-sections of the column filter according to the parent application in a final stage of filtration and under backwashing; FIG. 4 is a simplified vertical cross-section showing the overall construction of the column filter according to the present invention; FIG. 5 is an enlarged vertical cross-section of each holder for bundles of long fibers, said holder being used in the column filter of FIG. 4; FIG. 6 is a partly cut-away perspective view of the holder of FIG. 5; FIG. 7 is similar to FIG. 5 but shows a modified holder; and FIG. 9 is an enlarged fragmentary vertical cross-section illustrating the construction of a lower part of the column filter of FIG. 1. DETAILED DESCRIPTION OF THE INVENTION The present invention will hereinafter be described in detail with reference to the drawings. The column filter according to the present invention is illustrated in FIG. 4. The perforated plate 2 is arranged transversely in the lower part of the upright cylindrical shell 1 . Holders 2' for bundles of long fibers, which will be described subsequently, are attached to the perforated plate 2. The bundled long fibers 3 are fixed at lower end portions thereof by the holders 2' but are free-standing at upper end portions thereof. The bundled long fibers 3 are packed at a relatively high density within the shell 1, so that the bundled long fibers 3 extend upright in the shell 1. The raw water feed line 4 is provided in communication with the top part of the shell 1, and the backwash water discharge line 5 is communicated as a branch to the raw water feed line 4. A filtered water outlet line 6 is provided in communication with a bottom part of the shell 1. A backwash air feed line 8 is provided as a branch in communication with the water outlet line 6. A backwash water feed line 7 is also communicated as a branch to the outlet line 6. In this invention, the backwash air feed line 8 may be bifurcated to communicate with the shell 1 at antipodal points on the side wall of the shell 1. A single backwash air feed line may certainly be used without problems. Numerals 9, 10, 11, 12 and 13 indicate valves, respectively. A description will next be made of the holders 2' which are used for the bundled long fibers in the column filter of this invention. The holders 2' constitute the most important feature in this invention. As illustrated in FIGS. 5 and 6 by way of example, each of the holders 2' is formed basically of a cap 21 as an upper cap member, said cap defining many circular orifices 20 through its top wall and its side wall 42, and a tube 23 as a lower hollow member, said tube defining as axially-elongated openings slits 22 through a side wall 41 thereof and opening at both upper and lower ends thereof. Attachment of each holders 2' to its corresponding perforation 24 of the perforated plate 2 is performed in the following manner. First of all, a pair of holes (not shown) are bored in an antipodal relation through the side wall 41 of the tube 23 at points adjacent the upper end of the tube 23. The T-shaped head of a T-bolt 25 is inserted into the holes so that the tube 23 is suspended from the T-bolt 25. Incidentally, the outer diameter of the tube 23 is slightly smaller than the diameter of the perforation 24 of the perforated plate 2 so that an upper end portion of the tube 23 may be closely fitted in the the perforation 24. Thereafter, the stem of the T-bolt 25 is inserted upwardly through the perforation 24 until the upper end portion of the tube 23 is fitted in the perforation 24. A nut 27 with legs 26 is then applied on the T-bolt 25 to hold the T-bolt 25 in the perforation 24 by the legs 26. The cap 21 with the bundled long fibers 3 fixed at their low end portions on the entire peripheral side wall 42 by a band 28 is then placed over the perforation 24 with the stem of the T-bolt 25 extending through a hole 29 of the cap 21. A nut 30 is next applied on the T-bolt 25 so that the cap 21 is fixed over the perforation 24. In a manner as described above, the holders 2' for the bundled long fiber are attached to the respective perforations 24 of the perforated plate 2. Incidentally, the orifices 20 of the cap 21 permit the passage of fluids such as filtered water, compressed air and backwash water therethrough. It should however be noted that the formation of the orifices 20 in the top wall of the cap 21 is not essential. It is however necessary to form many orifices through the entire peripheral side wall 42 of the cap 21. The circular orifices 20 may be replaced by slits. The slit 22 of the tube 23 primarily serves to permits passage of compressed air therethrough. The slit 22 may be replaced by a plurality of small holes arranged vertically. The structure of the holders 2' for bundled long fibers and the manner of their attachment shown in FIGS. 5 and 6 are merely illustrative. Their detailed structures may be modified as desired, provided that described basically, the holders 2' for bundled long fibers, each of said holders 2' being composed of the cap 21 defining many orifices 20 or slits through the entire peripheral side wall 42 thereof and the tube 23 defining a slit 22 or vertically-arranged small holes through the side wall 41 thereof and opening at both upper and lower ends thereof, are attached to the respective perforations 24 of the perforated plate 2 arranged transversely within the shell 1 with the cap 21 being located above the perforated plate 2 and the tube 23 being positioned below the perforated plate 2; and the lower end portions of the bundled long fibers 3 are fixed to lower peripheries of the side walls 42 of the associated caps 21. Where the upright cylindrical shell 1 has a relatively large diameter, it is desirable, as shown in FIG. 6, to provide one or more upright partition walls 43 substantially in parallel with the bundled long fibers 3 within the shell 1 to divide the interior of the shell 1 into vertically-extending sections so that the bundled long fibers 3 may be prevented from being bent horizontally or obliquely during the feeding of the raw water. In a column filter operation of the present invention, as the filtration proceeds and more solids are trapped in the interstices among the long fibers 3 in the bundles, the pressure drop increases gradually. As the pressure drop increases, the vertically-extending long fibers in the bundles begin to be bent from the lower end portions thereof so that their vertical length decreases gradually. When the increase of the pressure drop has reached a predetermined value, backwashing is conducted in the following manner. Referring again FIGS. 4 to 6, the valves 9,13 are closed to stop the filtration and the valves 10,12 are then opened to feed compressed air through the backwash air feed line 8. Since the bottom part underneath the perforated plate 2 is filled with the filtered water, the inflow of the compressed air firstly causes the filtered water to flow out through the individual orifices 20 of each cap 21. However, a water level L is soon formed below the perforated plate 2 as depicted in FIG. 5. A layer A of the compressed air is therefore formed above the water level L . The compressed air therefore enters the tube 23 through a portion of the slit 22, said portion being located above the water level L , and then blows out through the individual orifices 20 of each cap 21. By the blow-out of the compressed air, the water inside the upright cylindrical shell 1 is agitated and the bundled long fibers 3 are shaken. The interstices which have been formed among the fibers 3 are hence broken up to disintegrate solids trapped and accumulated therein. In addition, solids deposited on the bundled long fibers 3 are also shaken off. In particular, the water which is contained underneath the perforated plate 2 at the beginning of feeding of the compressed air is lifted at once by the compressed air and jets out as high-velocity plug flows through the individual orifices 20 of each cap 21, followed by the flow-out of the compressed air. The densely-bundled part of the bundled long fibers 3 located around each cap 21 can therefore be washed effectively by the passage of the fluids therethrough. While continuing the above-described inflow of the compressed air or after closing the valve 12 to stop the feeding of the compressed air, the valve 11 is opened to feed backwash water through the backwash water feed line 7. The backwash water thus fed enters primarily through the lower opening of each tube 23 and flows out through the individual orifices 20 of each cap 21. Since the bundled long fibers 3 are fixed at the lower end portions thereof and are free-standing at the upper end portions thereof, the bundled long fibers 3 are caused to extend and are shaken like a streamer by the upflow of the backwash water. The solids released from the bundled long fibers 3 by the impact of the inflow of the compressed air are hence flushed by the backwash water, so that the backwash water containing a great deal of solids suspended therein is discharged through the backwash water discharge line 5. Different from the backwashing method described above, the backwashing can also be performed by feeding compressed air intermittently through the backwash air feed line 8 while feeding backwash water at a constant rate through the backwash water feed line 7. In this case, high-velocity plug flows are formed as described above whenever the compressed air is fed so that more effective backwashing is feasible. Another embodiment of the supports for bundles of long fibers, which are employed in this invention, is illustrated in FIG. 7. A conical diaphragm seat 37 defining many through-perforations 36 is provided in an upper interior part of each cap 21'. Provided inside the diaphragm seat 37 is a conical diaphragm 38 which can close up the through-perforations 36 when brought into close contact with the inner surface of the diaphragm seat 37. Slits 20' are formed through a top wall of the cap 21' and also through its side wall 42'. Through a side wall 41' of a tube 23', a plurality of small slit 22' are spacedly formed in an axial, namely, vertical row. The remaining structure is similar to the holder shown in FIG. 5. An upper end portion of the diaphragm 38 is secured on the inner surface of the top wall of the cap 21', while its lower end portion flares out in the form of a horn. It is made of a flexible material. The diaphragm seat 37 and diaphragm 38 function as follows. During the filtration, the filtered water passes downwardly through the slits 20' and the diaphragm 38 is pushed inwardly by the filtered water. Therefore, the diaphragm seat 37 and diaphragm 38 neither exhibit any function nor interfere with the filtration. However, they function in the following manner during backwashing. By an upflow of compressed air or backwash water fed through the tube 23', the diaphragm 38 is outwardly pushed and opened so that the diaphragm 38 is brought into close contact with the inner surface of the diaphragm seat 37. As a result, the compressed air or backwash water is allowed to pass only through the slits 20'A formed below the diaphragm seat 37. Accordingly, the compressed air or backwash water is allowed to flow out preferentially through the lower end portion of the fixed part of the bundled long fibers 3, so that the hardly-washable lower end portions of the bundled long fibers 3 can be washed effectively. The construction of FIG. 7 is particularly effective for ensuring the flushing of trapped solids from the bundled long fibers during backwashing. A description will next be made of the bundled long fibers 3 useful in the practice of this invention. The bundled long fibers 3 useful in this invention are somewhat bent or collapsed at lower parts thereof and are reduced in height at an initial stage even when a raw water of a relatively high flow velocity is fed as a downflow, and upon continuation of the feeding of the raw water, the lower parts of the bundled longer fibers 3 are progressively bent further and their height is reduced little by little. The bundled long fibers 3 are thus required to have stiffness and packing quantity or density sufficient to prevent their horizontal bending and to allow them to remain upright as a whole in the upright cylindrical shell 1 during the feeding of the raw water. Usable fibers include synthetic fibers such as acrylic fibers, polyester fibers and polyamide fibers as well as natural fibers such as cotton and wool. As these synthetic fibers or natural fibers, it is preferable to use units of non-twisted monofilaments having a diameter not greater than 80 µm, usually around 35 µm or so. However, units of twisted filaments may also be used so long as they take the form of bundled long fibers which are not bent horizontally and remain upright as a whole in the upright cylindrical shell 1 while the raw water is passed. As the packing density of the long fibers in the bundles employed in this invention becomes higher, finer suspended solids can be removed to provide filtered water of higher quality. However, the pressure drop increases. On the other hand, the quality of filtered water falls as the packing density of the long fibers becomes lower. In contrast, the pressure drop decreases. It is accordingly desirable to choose bundles of long fibers having a most suitable packing density depending on the nature or concentration of solids suspended in the raw water. When bundles of long fibers composed of units of non-twisted monofilaments 1,000-3,000 mm long are used by way of example, it is preferable to pack bundles to give a packing density of 25-110 kg in terms of their dry weight per bulk volume m³ of the bundles.

Claims: A column filter using bundles of long fibers, said filter being provided with an upright cylindrical shell (1), and the bundles of long fibers (3) being arranged upright inside the shell with lower end portions thereof being fixed and upper end portions thereof being free-standing, characterized in that a plurality of holders (2';2'') for the respective bundles of long fibers, each of said holders being formed of an upper cap member (21;21')and a lower hollow member (23;23') communicating to each other, said upper cap member (21;21') defining openings (20,20') therethrough and said lower hollow member (23;23') defining at least an axially-elongated opening (22;22') through a side wall (41;41') thereof and opening at both upper and lower ends thereof, are provided on a perforated plate (2) arranged transversely in a lower interior part of the shell (1) with the upper cap member (21;21') being located above the perforated plate (2) and the lower hollow member (23;23') being positioned below the perforated plate (2); the holders (2';2'') cover all perforations (24) of the perforated plate (2); and the lower end portion of each of the bundles of long fibers (3) is fixed to a lower periphery of a side wall (42;42') of the associated upper cap member (21;21'). The column filter as claimed in Claim 1, wherein the openings of the upper cap member (21) are holes (20). The column filter as claimed in Claim 1, wherein the openings of the upper cap member (21')are slits (20'). The column filter as claimed in Claim 1, wherein the axially-elongated opening of the lower hollow member (23) is a slit (22). The column filter as claimed in Claim 1, wherein the axially-elongated opening of the lower hollow member (23') comprises a plurality of small holes (22'). The column filter as claimed in any one of the preceding claims, wherein the long fibers in the bundles are longer than 1,000 mm, but shorter than 3,000 mm. The column filter as claimed in any one of the preceding, wherein the packing density of the bundles of long fibers is 25 - 110 kg in terms of their dry weight per bulk volume m³ of the bundles. The column filter as claimed in any one of the preceding, wherein the upper cap member is cylindrical. The column filter as claimed in any one of the preceding claims, wherein the openings (20:20') formed through the upper cap member (21;21') are distributed over the side wall (42;42') of the upper cap member. The column filter as claimed in Claim 8 or 9, wherein a conical diaphragm seat (37) defining through-perforations (36) therethrough is provided at an inner upper part of the upper cap member (21') and a conical diaphragm (38) is arranged inside the conical diaphragm seat (37) to close up the through-perforations (36) when brought into close contact with an inner surface of the conical diaphragm seat (37). The column filter as claimed in any one of the preceding claims, wherein the lower hollow member is tubular. The column filter as claimed in any one of the preceding claims, wherein at least one upright partition wall (43) is additionally provided substantially in parallel with the bundles of long fibers (3) within the shell (1) whereby the interior of the shell (1) is divided into vertically-extending sections. The column filter as claimed in any one of the preceding claims, wherein the bundles of long fibers have each been obtained by bundling units of non-twisted monofilaments having a diameter not greater than 80 µm.

Inventors: IWATSUKA TAKESHI C OJAPAN ORGA, KASAI TOSHIO JAPAN ORGANO CO L, IWATSUKA, TAKESHI C/OJAPAN ORGANO CO.,LTD., KASAI, TOSHIO JAPAN ORGANO CO.,LTD.
Applicants: ORGANO KK, JAPAN ORGANO CO., LTD.
Application year: 1989
Main classification: B01D35
IPC codes: B01D35