CA1155067A - Hollow fiber assembly having selective permeability - Google Patents
Hollow fiber assembly having selective permeabilityInfo
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- CA1155067A CA1155067A CA000367137A CA367137A CA1155067A CA 1155067 A CA1155067 A CA 1155067A CA 000367137 A CA000367137 A CA 000367137A CA 367137 A CA367137 A CA 367137A CA 1155067 A CA1155067 A CA 1155067A
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Abstract
Abstract:
The present invention relates to a hollow fiber assembly having selective permeability. The assembly is comprised of a cylindrical arrangement of hollow fibers having selective permeability. A cylindrical layer of hollow fibers is formed in a crisscross arrangement. A
hollow portion is located inside the cylindrical layer of hollow fibers. A plurality of engaging members which are separated from one another are located in the hollow portion. A first resin wall is disposed at an open end of the hollow fiber and arranged to be open to the exterior.
The wall is spaced from the engaging members but not spaced from the hollow fibers. A second resin wall is disposed at the other end of the assembly to secure the end of the assembly. An elastic supporting member is provided for controlling the distance between the two resin walls.
The present invention relates to a hollow fiber assembly having selective permeability. The assembly is comprised of a cylindrical arrangement of hollow fibers having selective permeability. A cylindrical layer of hollow fibers is formed in a crisscross arrangement. A
hollow portion is located inside the cylindrical layer of hollow fibers. A plurality of engaging members which are separated from one another are located in the hollow portion. A first resin wall is disposed at an open end of the hollow fiber and arranged to be open to the exterior.
The wall is spaced from the engaging members but not spaced from the hollow fibers. A second resin wall is disposed at the other end of the assembly to secure the end of the assembly. An elastic supporting member is provided for controlling the distance between the two resin walls.
Description
llSS067 Hollow Fiber Assembly Having Selective Permeability The present invention relates to a hollow fiber assembly having selective permeability. More particularly, it relates to a membrane separation apparatus made by assembling hollow fibers, of which wall membranes have selective permeability to a fluid.
The scope of application of membrane separation apparatuses includes gas separation, liquid permeation, dialysis, ultrafiltration, reverse osmosis, etc. Examples of the practical application of the invention are: the conversion of sea water into fresh water; the desalting of brackish water; the purification of waste water; the refining of protein; the condensing of fruit juice; the separation of oil from water; blood dialysis; etc.
Many membrane separation apparatuses utilizing hollow L5 fibers having selective permeability have been proposed.
A typical structure for these apparatuses is a hollow fiber assembly comprising a number of hollow fibers arranged in layers around a supporting core and contained in a cylindrical vessel. The supporting core is usually a perforated cylindrical tube. Typical examples of such supporting cores are shown in U.S. Patent No. 3,526,001 which issued to W. G. Smith on August 25, 1970 and U.S.
Patent NQ. 3,755,034 which issued to H. I. Mahon on August 28, 1973. These supporting cores have many small .
holes, and their structure is said to be suitable for uniformly dispersing a fluid supplied to the membrane separation apparatus, but in fact they have the following defects:
(1) A part of the hollow fiber layers which are in contact with the non-perforated portions of the supporting core forms a dead space, and the fluid to be treated remains at the portion. This causes insufficient contact with the fresh fluid to be treated, leading to a lowering of the permeation flow rate and the separation efficiency of the apparatus. Also, in supplying a fluid from the supporting core to the hollow fiber layer, these dead spaces interupt the uniform, radial flow of the fluid, and produces channeling flow and concentration polarization, thus leading to drastic decreases in permeation performance and separation efficiency of the apparatus.
The scope of application of membrane separation apparatuses includes gas separation, liquid permeation, dialysis, ultrafiltration, reverse osmosis, etc. Examples of the practical application of the invention are: the conversion of sea water into fresh water; the desalting of brackish water; the purification of waste water; the refining of protein; the condensing of fruit juice; the separation of oil from water; blood dialysis; etc.
Many membrane separation apparatuses utilizing hollow L5 fibers having selective permeability have been proposed.
A typical structure for these apparatuses is a hollow fiber assembly comprising a number of hollow fibers arranged in layers around a supporting core and contained in a cylindrical vessel. The supporting core is usually a perforated cylindrical tube. Typical examples of such supporting cores are shown in U.S. Patent No. 3,526,001 which issued to W. G. Smith on August 25, 1970 and U.S.
Patent NQ. 3,755,034 which issued to H. I. Mahon on August 28, 1973. These supporting cores have many small .
holes, and their structure is said to be suitable for uniformly dispersing a fluid supplied to the membrane separation apparatus, but in fact they have the following defects:
(1) A part of the hollow fiber layers which are in contact with the non-perforated portions of the supporting core forms a dead space, and the fluid to be treated remains at the portion. This causes insufficient contact with the fresh fluid to be treated, leading to a lowering of the permeation flow rate and the separation efficiency of the apparatus. Also, in supplying a fluid from the supporting core to the hollow fiber layer, these dead spaces interupt the uniform, radial flow of the fluid, and produces channeling flow and concentration polarization, thus leading to drastic decreases in permeation performance and separation efficiency of the apparatus.
(2) A considerable pressure is required to push out the fluid to be treated from the small holes of the supporting core so that pressure loss becomes large.
(3) The small holes in the supporting core are apt to be blocked by a slight amount of solid particles contained in the fluid to be treated. Once the holes have been plugged, the dead space is increased, further causing a larger loss of separation efficiency.
(4) In pushing out the fluid to be treated into the hollow fiber layer from the small holes of the supporting core under a high pressure, the hollow fiber layer expands under the flow resistance of the fluid, and tension occurs in the individual hollow fibers. Such tension acts upon the resin wall securing the fiber with the result that the distance between the two resin walls of the assembly, i.e.
the effective length of the hollow fiber assembly, is shortened. In this case, if the strength of a piece of supporting core is smali, the assembly per se shows a large shrinkage, which eventually causes a loss of separation performance. For example, when assembly shrinkage occurs, the hollow fiber layers are locally deformed to form coarse portions of hollow fiber layers.
This may be why the fluid to be treated is involved in channeling and concentration polarization. Alternatively, a large gap in distance is formed between the conduit for supplying the fluid to the supporting core of the assembly and the assembly, leading to a problem in operation such that the connection part between the conduit and the end plate is disconnected to prevent the fluid to be treated from running into the supporting core. In either case, the separation efficiency and the permeation performance of the hollow fiber assembly are lowered.
the effective length of the hollow fiber assembly, is shortened. In this case, if the strength of a piece of supporting core is smali, the assembly per se shows a large shrinkage, which eventually causes a loss of separation performance. For example, when assembly shrinkage occurs, the hollow fiber layers are locally deformed to form coarse portions of hollow fiber layers.
This may be why the fluid to be treated is involved in channeling and concentration polarization. Alternatively, a large gap in distance is formed between the conduit for supplying the fluid to the supporting core of the assembly and the assembly, leading to a problem in operation such that the connection part between the conduit and the end plate is disconnected to prevent the fluid to be treated from running into the supporting core. In either case, the separation efficiency and the permeation performance of the hollow fiber assembly are lowered.
(5) On the other hand, in order to prevent a loss of efficiency of the apparatus attributed to the shrinkage of the assembly as in (4) above, a supporting core having high strength is used. In such a case, the entire pressure acts upon the hollow fiber so that the hollow fiber is partially stretched under the flow resistance of the fluid. As a result, some permanent stress remains, leading to a decrease in separation efficiency and permeation performance of the hollow fiber assembly.
(6) That portion near the open end of the hollow fiber is the location where the pressure of the fluid which permeates into the hollow fiber is the smallest. In the cases of ultrafiltration or reverse osmosis which causes permeation by the difference of pressures between the inside and the outside of the hollow fiber membrane, that portion nearest to this opening shows the largest amount of permeation. Should there arise any retention of flow of the fluid to be treated, such retention would have a large effect on the separation performance of the apparatus. Therefore, in forming a tube sheet portion by impregnating an adhesive agent having fluidity, if the adhesive agent plugs the small holes of the supporting core, the outflow of the fluid to be treated is interrupted and the supply of the treating fluid runs short compared with the amount of permeation into the hollow fiber, resulting in a drop of the separation efficiency or the accumulation of scale components.
It is, therefore, a main object of the present invention to provide a hollow fiber assembly having a large permeation flow rate and a high separation efficiency with good durability by improving the conventional hollow fiber assembly having a continuous supporting core.
In accordance with an aspect of the invention there is provided a hollow fiber assembly having selective permeability, said assembly being comprised of a cylindrical arrangement of hollow fibers, said fibers having selective permeability comprising: a cylindrical layer of hollow fibers formed by the crisscross winding of hollow fibers; a hollow portion located inside said cylindrical layer of hollow fibers; a plurality of engaging members which are respectively separated from one another in said hollow portion; a first resin wall which is disposed at an open end of said hollow fibers and arranged to be open to the exterior of the assembly, said first wall being spaced from said engaging means but not spaced from said hollow fibers; a second resin wall which is disposed at the other end of said assembly for securing the end of said assembly; an elastic supporting member for controlling the distance between the first and second resin walls; and a fluid supply conduit.
A hollow fiber assembly having selective permeability according to the present invention is illustrated with reference to the accompanying drawings, wherein:
Fig. 1 is a vertical sectional view of an embodiment of the present invention;
Fig. 2 is a vertical sectional view of an example of the membrane separation apparatus equipped with the assembly shown in Fig. l;
Figs. 3 and 5 (appearing on the same sheet as Fig. 3) llSS067 are vertical sectional views showing other embodiments of the invention;
Figs. 4, 6 and 7 are vertical sectional views of examples of the membrane separation apparatus made by combining plural assemblies shown in Figs. 3 and 5; and Fig. 8 is an enlarged illustrative view of the crisscross arrangement in the cylindrical layer of hollow fiber.
In Fig. 1, the cylindrical hollow fiber layers l are arranged as shown in Fig. 8, in multilayers of tape-like hollow fibers laid in a crisscross pattern in a nearly parallel relation to one another in a flat arrangement. A
hollow portion 2 is located inside the cylindrical layers of hollow fibers. Plural engaging members 3 are separated from one another. These engaging members are preferably arranged to be separated at a distance of 1 to 3 cm. A
resin wall 4 holds the hollow fibers in a manner so that they are open to the exterior. The resin wall 4 is separated from the engaging members, preferably by a distance of 1 to 5 cm. A resin wall 5 is holds the end of the cylindrical assembly. The central part of the resin wall 5 contains a conduit 8 which provides a fluid supply.
An elastic supporting member 6 regulates the distance between the resin walls 4 and 5. A flow screen 7 is comprised of a net-like cloth having a low fluid flow resistance. The screen covers the outside of the hollow fiber layers.
Fig. 2 is an embodiment of the membrane separation apparatus furnished with a hollow fiber assembly shown in Fig. 1, wherein the flow of the fluid to be treated is indicated by arrows. In Fig. 2, a case 9 accommodates the assembly. At one end of case ~ there is an end plate 10 which has an exit for the permeating fluid. At the otheL
end there is an end plate 11 which has an inlet and an outlet for the fluid to be treated. The end plates 10 and 11 are secured with C-rings 17. The hollow fiber ~155067 assembly, end plates and supply conduit are furnished with O-rings 16 so that the supplied fluid, the permeated fluid, and the concentrated fluid are prevented from being mixed with one another. The assembly includes a pressure-sustaining water collecting sheet 12. An outlet 13 is provided for the permeated fluid, an inlet 14 is provided for the fluid to be treated and an outlet 15 is provided for the concentrated fluid.
With regard to Fig. 3, a cylindrical layer 1 of hollow fiber is arranged in such a manner as shown in Fig. 8. A
hollow portion 2 is located inside the cylindrical layer of the hollow fiber. A plurality of engaging members 3 on which there is fitted a protecting net 18 comprising a net-like cloth are located in the hollow portion 2. The hollow fibers are densely arranged adjacent a resin wall 4. A hole 8 is located in the center of wall 4, communicating with the hollow portion 2, separated from the engaging members 3. A resin wall 5 secures the end of the cylindrical assembly. An elastic supporting member 6 zo controls the distance between the resin walls 4 and 5. A
flow screen 7 comprises net-like cloth having a small flow resistance.
Fig. 4 is an example of a membrane separation apparatus furnished with the hollow fiber assembly shown in Fig. 2, wherein the liquid flow is shown by arrows. In Fig. 4, a vessel 9 accommodates two units of the above assembly. A supply connector 19 is set into a cehtral hole in the resin wall and the pressure-sustaining water collecting sheet 12. The supply connector 19 and a 3~ permeating water connector 20 are secured in the vessel with an end plate 10. This unit is also located in the opposite end of the vessel 9 so that fluid to be treated is supplied from the supply connector on one side and the concentrated fluid is taken out from the other connector.
The permeated fluid is taken out by permeating water connectors on both sides.
~ 7 --In Fig. 5, a cylindrical layer 1 of hollow fibers forms a hollow portion 2. An engaging member 3 and a protecting net 18, covering the engaging members, is located in hollow portion 2. A resin wall 4 has at its central portion a supply conduit 8 communicating with the hollow portion 2. The resin wall 4 is so arranged that the hollow fibers have access to the exterior. Wall 4 is separated from the engaging means by preferably a distance of 1 to 5 cm. A resin wall 5 secures the end of the tubular assembly. A hole is provided at the center of wall 5. An elastic supporting member 6 controls the distance between the resin walls 4 and 5. A flow screen 7 is included in the assembly.
Fig. 6 is an example of a membrane separation apparatus furnished with the hollow fiber assembly of Fig.
5 wherein the flow of the liquid to be treated is shown by arrows. In Fig. 6, a vessel 9 accommodates three units of the above assembly. The permeating fluid is fed through the resin wall 4 and is gathered by the permeating liquid collecting block 21. The fluid flows to the center of the block, to the permeating water conduit 22 and is fed to the end plate. T,he supplied fluid is introduced into the vessel 9 through the end plate 10, passes through the space between the hole provided at the center of the resin wall 5 and the permeating water conduit 22 and is introduced into the hollow part of the hollow fiber assembly. The fluid is fed through the hollow fiber layer 1 and the flow screen 7 to reach the inner wall of the vessel 9. It then passes through the space between the permeating liquid collecting block 21 and the container vessel to reach the resin wall 5 of the second hollow fiber assembly. Through a course similar to that described above, the liquid passes through the second assembly, reaches the end plate 11 through the third assembly and then flows out as a concentrated liquid.
Fig. 7 shows an example of the membrane separation apparatus furnished with the hollow fiber assembly of Fig.
5, wherein the flow of the fluid to be treated is shown by arrows. In Fig. 7, a vessel 9 contains four sets of the above assembly. The permeating liquid which has been fed through the open part of the hollow fiber of the resin wall 4 passes through the pressure-sustaining water collecting sheet 12 to flow through the passage in the connecting tube 23 into the permeating water conduit 22, and is then fed into the end plate. The permeating fluid fed from the second fiber assembly flows into the permeating water conduit 22 through the pressure-sustaining water collecting sheet 12 common to the first assemblyl and the connecting pipe 23, and is fed to the end plate.
The permeating fluid coming out from the third and fourth assemblies is also fed to the end plate through the same route as the permeating fluid from the first and the second assemblies. The supplied fluid comes in from the end plate 10, is fed to the outer periphery of the first assembly, goes to the hollow portion through the flow screen 7 and the hollow fiber layer 1, and is then fed to the hollow portion of the second assembly through the path in the connecting tube 23 provided at the center of the resin wall 4. The fluid which passed through the hollow fiber layer 1 of the second assembly passes through the space between the vessel 9 and the outer periphery of the resin wall 5 of the second assembly to reach the third assembly. The fluid is fed through the third and the fourth assemblies via the same courses as in the first and second assemblies to the end plate 11 and flows out of the assembly as a concentrated fluid. U-packing is denoted by numeral 25.
In Fig. 8, a flat bundle 26 of hollow fibers have selective permeability. The fibers are of the tape form having a width in the range of 15 d to 50,000 d, wherein d is the outer diameter of the hollow fiber. The ratio of thickness to width ranges from 1/20,000 to 1/5. The 1~5S067 g nearly parallel tapes are arranged without any space between one another. In Fig 8 the hollow fibers are shown as having spaces between one another merely to facilitate understanding. The layers produced by nearly parallel t:apes are arrangéd to intersect at angles of from 5 to 60.
Typical hollow fibers used in the present invention, although not limited to such, have an outer diameter of 10 to 10,000 microns and a hollow rate of 3 to 80 %. The membrane walls have a selective permeability to fluid and may be any of the microporous, anisotropic or composite form or combinations thereof. Usually, cellulose acetate and aromatic polyamide, or the like are used.
Preferably, the hollow fiber layers are wound to make a packing density of 45 to 70 %. When the density is less than 45 %, the flow velocity of the fluid becomes too low, and the luid runs into the cylindrical layers of the hollow fibers at the inlet of the hollow portion, on the right side in Fig. 1, without reaching the deep inside part of the hollow portion. As a result, the separation efficiency of the assembly is lowered because of the failure of a uniform flow of the fluid in the hollow fiber layer. When the density exceeds 70 %, the liquid does not flow smoothly through the hollow fiber layer. In order to operate the assembly forcibly, it is necessary to elevate the liquid supply pressure, causing a large pressure loss and the possible collapse of the hollow fiber layer.
Preferably, the packing density is from 50 to 65 ~.
It is also desirable for the hollow fibers to be disposed in crisscross relation to one another at a winding angle of 5 to 60 to the axial direction of the hollow fiber layer. When the winding angle is too small, the hollow fiber layer is liable to collapsed. When the winding angle becomes too large, the length of the hollow fiber wound on the core length becomes long, resulting in a large pressure loss of the permeating fluid and a decrease in the amount of permeation.
llS50~7 The diameter of the hollow portion is preferably from l to lO cm, and the thickness of the hollow fiber layer is from 5 to 50 cm. When the diameter of the hollow portion is too small, the supply pressure of liquid must be made large. When it is too small, the liquid is not radially supplied in the whole lengthwise direction of the hollow fiber layer, and the hollow fiber layer is liable to collapse. If the thickness of the hollow fiber layer is too small, the permeation area of the hollow fiber becomes small and the fIuid treating capacity decreases. If it is too large, the pressure loss is enlarged and a channeling is liable to result.
In order to manufacture the above hollow fiber cylindrical layer, the engaging members are usually arranged on the shaft of a winding machine. If necessary, a protective net is covered thereon. Then, the hollow filaments are wound up thereon uniformly at a moderate tension while traversing the filament. Thereafter, only the shaft is takenl out to make the central part hollow.
In this case, it is of course to be understood that the hollow portion includes the engaging members and the protective net.
The engaging member to be used in the present invention is to support partially the hollow fiber layer facing the hollow portion inside the cylindrical layer of the hollow fiber. For the engaging member, it is necessary to use a material having a small resistance to fluid flow such as, for example, net-like material, ring-form material, etc. The engaging members have a function equivalent to that of the hollow portion which passes the fluid to the fiber layer. The engaging members are not formed as an integral or single member, but a plurality of preferably more than 3 members. These members are provided mutually with spaces so that, when any ~hange occurs to the distance between the resin walls 4 and 5, the difference does not concentrate at a single ~lS5067 spot. Further, the engaging members to be used in the present invention evenly disperse the shrinking force under tension which acts upon the hollow fiber layer during operation. In addition, they prevent the hollow fiber from being excessively expanded by the action of the flow resistance of fluid. The distance between the engaging members is preferably 1 to 3 cm.
The elastic supporting members to be used in the present invention prevents excessive shrinkage of the hollow fiber assembly and absorbs the shock exerted on the hollow fibers when the fluid to be treated is abruptly supplied to the hollow fiber assembly. The elastic supporting members make moderate recovery from deformation by elasticity. Preferably, when the elastic modulus of the elastic supporting members is E kg/cm2, the total sectional area of the elastic supporting members is S cm2 and the flow rate of the fluid to be supplied is Q liter/min, the following relationshp exists:
Q ~ 40.
The material of the elastic supporting member may be fiber glass reinforced plastics (FRP), stainless steel, etc.
The number of the elastic supporting members is dependent upon the type of the material, the size of the assembly, etc. and usually may be from 2 to 50.
Further, in the present invention, it is important to separate the engaging members and the resin wall 4.
Preferably, the separation is 1 to 5 cm. ~y adopting the construction as above, it is possible to avoid problems caused by the application of an adhesive agent to the supporting core as previously explained, i.e. loss of separation performance caused by a retaining of the fluid to be treated.
The resin to constitute the resin wall 4 and the resin wall 5 of the present invention is preferably a liquid which has fluidity before curing and becomes a hard solid 1l5l52o67 form when cured. Representative examples of such resins are epoxy, polyester, silicon and polyurethane resins.
The flexible hollow fiber assembly according to the present invention has, due to the construction as above, very little dead space for fluid in the hollow fiber layer and no obstacle such as a supporting core. As a result, an extremely small pressure loss is realized which permits an even flow in the hollow fiber layer, thereby providing a high separation efficiency. Moreover, when the assembly is operated repeatedly intermittently, or the liquid to be treated is at a high flow rate, the separation performance remains high and durability is good.
Practical and presently perferred embodiments of the present invention are illustratively described in the lS following Examples.
Example 1 On a 20 mm in diameter shaft of a winding machine, three net-like engaging members, each having an outer diameter of 27 mm and a length of 300 mm, were arranged at the distance of 30 mm from one another. The surface of the engaging members were covered with a soft protective net. Around it there was wound a hollow fiber of cellulose acetate for reverse osmosis purposes having an outer diameter of 230 microns and an inner diameter of 110 microns. The fibers were wound over the protecting net with a packing density of 50 %, at a winding angle of 8 to 30. The fiber was wound in a fixed number of turns to form a cylindrical layer of hollow fibers having an outer diameter of 118 mm and a length of 1260 mm. The surface of the resulting cylinder was covered with a flow screen.
Thereafter, only the shaft was removed to make a central hollow. Into the two ends of the thus formed hollow fiber layer, epoxy resin was injected to locations spaced by 20 mm from the ends of the engaging members, and the resin was cured to form the resin walls 4 and 5. Between the two resin walls 4 and 5, there were fitted three FRP
,., l~S506~7 elastic supporting members of 10 mm in width and 2 mm in thickness. The resin wall 4 was cut perpendicularly to the axis of the hollow fiber layer to make the hollow fiber open externally through said resin wall, and a hollow fiber assembly was prepared. The end of the protective net was also separated by 20 mm from the resin wall 4.
The hollow fiber assembly was incorporated into the membrane separation apparatus shown in Fig. 2, into which 1500 ppm NaCl aqueous solution was supplied as a feed and circulated at a temperature of 25C under a pressure of 30 kg/cm2 to carry out a reverse osmosis test. The results are as shown in Table 1.
Comparative Example 1 Instead of the hollow fiber assembly of Example 1, there was prepared a hollow fiber assembly having a perforated supporting core for supporting the hollow fiber layer at its center. The core was embedded in the resin wall. The hollow fiber assembly was incorporated in the membrane separation apparatus as shown in Fig. 2, with which a reverse osmosis test was carried out under the same conditions as in Example 1. The results are as shown in Table 1.
The supporting core had a diameter of 27 mm and a length of 1 m. Seventy small holes having a diameter 1.7 mm were provided on the core. The winding density of the hollow fiber layer and the winding angle were the same as those of Example 1.
11550~7 Table 1 .
Example 1Comparative . Example 1 Supply flow rate 22000 19100 (liter/day) Permeation flow rate 16500 14300 (liter/day) Pressure drop between 0.1 1.2 inlet and outlet (kg/cm2) Water recovery*l) 75 75 Salt content in permeating 120 300 water (ppm) Salt rejection rate*2) 92 80 Note: *l~ Water recovery rate (%) =
Permeation flow rate Supply flow rate x 100 *2) Salt rejection rate (%) =
(1 Salt content in permeating liquid) x 100 Salt content in supply liquid As is apparent from Table 1, the hollow fiber assembly of the present invention is remarkably superior to the product using a cotinuous supporting core in respect to the permeation flow rate, pressure loss and effect of salt separation.
Example 2 On a 30 mm in diameter shaft, three net-like engaging members having an outer diameter of 35 mm and a length of 300 mm were arranged at a distance of 30 mm from one another. A cellulose triacetate hollow fiber for reverse osmosis purposes, having an outer diameter of 165 microns and an inner diameter of 70 microns was wound in a fixed number of turns on the engaging members. The winding traversed three engaging members and had a packing density of 53 % and a winding angle of 8 to 30 to form a cylindrical layer of hollow fiber having an outer diameter of 193 mm and a length of 1260 mm. The surface of the hollow fiber layer was covered with a flow screen.
Thereafter, only the shaft was removed to make the central part hollow. Into the two ends of the formed hollow fiber layer, epoxy resin was injected to locations spaced 30 mm from the ends of the engaging members, thereby forming when cured the resin walls 4 and 5. Between the two resin walls 4 and 5, three elastic supporting members of 7 mm in width and 3.5 mm in thickness (FRP rods) were fitted in parallel with the axis of the cylindrical body. Resin wall 4 was cut to allow the hollow fiber layer to be open to the exterior.
The hollow fiber assembly was set into the membrane separation apparatus. By the use of a 1500 ppm NaCl aqueous solution, a reverse osmosis test was carried out under the conditions of 25C temperature, 30 kg/cm2 pressure and a 30 % recovery rate. A water permeation test was made with the concentrated water outlet open.
Shrinkage was evaluated, correlated with the resistance of the hollow fiber layer by circulating water only, without exerting pressure. A compression test was made by applying an external load. Shrinkage was evaluated by exerting a load between the resin walls without water circulation. The results are as shown in Table 2.
Comparative Example 2 By using a net-like supporting core of 35 mm in outer diameter instead of the engaging member of Example 2 and without fitting a FRP rod as used in Example 2, a hollow fiber assembly was prepared in the same manner as shown in Example 2. The assembly was incorporated into the membrane separation apparatus as shown in Fig. 2 to carry out a test under the same conditions as in Example 2. The results are shown in Table 2.
~S5067 Table 2 _ Example 2 Comparative Example 2 _ _ I
Su~ply flow rate 220 220 (m /day) Permeation flow rate 67 67 (m3/day) Water recovery 30 30 Salt content in permeating 75 105 water (ppm) Salt rejection rate 95 93 Shrinkage of assembly 2 8 (mm) Shrinkage of assembly in water permeation test shrinkage (mm/amount of 0.010 0.035 water circulated (m3/day) Shrinkage of assembly in compression test shrinkage (mm)/load (kg) 10.03 0.12 As is apparent from Table 2, the hollow fiber assembly of the present invention is excellent in salt separating efficiency. It exhibits a small amount of shrinkage with respect to water circulation. In Comparative Example 2, due to the large shrinkage of the assembly, a long supply conduit 8 as in Fig. 2 must be used to prevent its separation from the end plate 11, thus requiring the use of a long vessel 9. As a result, the volume efficiency (amount of water permeation per volume of vessel) was lower in actual application than in Example 2. Also, when the reverse osmosis operation of Comparative Example 2 was intermittently repeated, the supporting core repeatedly sustained a compression deformation of 8 mm to form permanent stress, by which the separation efficiency showed a further decrease.
It is, therefore, a main object of the present invention to provide a hollow fiber assembly having a large permeation flow rate and a high separation efficiency with good durability by improving the conventional hollow fiber assembly having a continuous supporting core.
In accordance with an aspect of the invention there is provided a hollow fiber assembly having selective permeability, said assembly being comprised of a cylindrical arrangement of hollow fibers, said fibers having selective permeability comprising: a cylindrical layer of hollow fibers formed by the crisscross winding of hollow fibers; a hollow portion located inside said cylindrical layer of hollow fibers; a plurality of engaging members which are respectively separated from one another in said hollow portion; a first resin wall which is disposed at an open end of said hollow fibers and arranged to be open to the exterior of the assembly, said first wall being spaced from said engaging means but not spaced from said hollow fibers; a second resin wall which is disposed at the other end of said assembly for securing the end of said assembly; an elastic supporting member for controlling the distance between the first and second resin walls; and a fluid supply conduit.
A hollow fiber assembly having selective permeability according to the present invention is illustrated with reference to the accompanying drawings, wherein:
Fig. 1 is a vertical sectional view of an embodiment of the present invention;
Fig. 2 is a vertical sectional view of an example of the membrane separation apparatus equipped with the assembly shown in Fig. l;
Figs. 3 and 5 (appearing on the same sheet as Fig. 3) llSS067 are vertical sectional views showing other embodiments of the invention;
Figs. 4, 6 and 7 are vertical sectional views of examples of the membrane separation apparatus made by combining plural assemblies shown in Figs. 3 and 5; and Fig. 8 is an enlarged illustrative view of the crisscross arrangement in the cylindrical layer of hollow fiber.
In Fig. 1, the cylindrical hollow fiber layers l are arranged as shown in Fig. 8, in multilayers of tape-like hollow fibers laid in a crisscross pattern in a nearly parallel relation to one another in a flat arrangement. A
hollow portion 2 is located inside the cylindrical layers of hollow fibers. Plural engaging members 3 are separated from one another. These engaging members are preferably arranged to be separated at a distance of 1 to 3 cm. A
resin wall 4 holds the hollow fibers in a manner so that they are open to the exterior. The resin wall 4 is separated from the engaging members, preferably by a distance of 1 to 5 cm. A resin wall 5 is holds the end of the cylindrical assembly. The central part of the resin wall 5 contains a conduit 8 which provides a fluid supply.
An elastic supporting member 6 regulates the distance between the resin walls 4 and 5. A flow screen 7 is comprised of a net-like cloth having a low fluid flow resistance. The screen covers the outside of the hollow fiber layers.
Fig. 2 is an embodiment of the membrane separation apparatus furnished with a hollow fiber assembly shown in Fig. 1, wherein the flow of the fluid to be treated is indicated by arrows. In Fig. 2, a case 9 accommodates the assembly. At one end of case ~ there is an end plate 10 which has an exit for the permeating fluid. At the otheL
end there is an end plate 11 which has an inlet and an outlet for the fluid to be treated. The end plates 10 and 11 are secured with C-rings 17. The hollow fiber ~155067 assembly, end plates and supply conduit are furnished with O-rings 16 so that the supplied fluid, the permeated fluid, and the concentrated fluid are prevented from being mixed with one another. The assembly includes a pressure-sustaining water collecting sheet 12. An outlet 13 is provided for the permeated fluid, an inlet 14 is provided for the fluid to be treated and an outlet 15 is provided for the concentrated fluid.
With regard to Fig. 3, a cylindrical layer 1 of hollow fiber is arranged in such a manner as shown in Fig. 8. A
hollow portion 2 is located inside the cylindrical layer of the hollow fiber. A plurality of engaging members 3 on which there is fitted a protecting net 18 comprising a net-like cloth are located in the hollow portion 2. The hollow fibers are densely arranged adjacent a resin wall 4. A hole 8 is located in the center of wall 4, communicating with the hollow portion 2, separated from the engaging members 3. A resin wall 5 secures the end of the cylindrical assembly. An elastic supporting member 6 zo controls the distance between the resin walls 4 and 5. A
flow screen 7 comprises net-like cloth having a small flow resistance.
Fig. 4 is an example of a membrane separation apparatus furnished with the hollow fiber assembly shown in Fig. 2, wherein the liquid flow is shown by arrows. In Fig. 4, a vessel 9 accommodates two units of the above assembly. A supply connector 19 is set into a cehtral hole in the resin wall and the pressure-sustaining water collecting sheet 12. The supply connector 19 and a 3~ permeating water connector 20 are secured in the vessel with an end plate 10. This unit is also located in the opposite end of the vessel 9 so that fluid to be treated is supplied from the supply connector on one side and the concentrated fluid is taken out from the other connector.
The permeated fluid is taken out by permeating water connectors on both sides.
~ 7 --In Fig. 5, a cylindrical layer 1 of hollow fibers forms a hollow portion 2. An engaging member 3 and a protecting net 18, covering the engaging members, is located in hollow portion 2. A resin wall 4 has at its central portion a supply conduit 8 communicating with the hollow portion 2. The resin wall 4 is so arranged that the hollow fibers have access to the exterior. Wall 4 is separated from the engaging means by preferably a distance of 1 to 5 cm. A resin wall 5 secures the end of the tubular assembly. A hole is provided at the center of wall 5. An elastic supporting member 6 controls the distance between the resin walls 4 and 5. A flow screen 7 is included in the assembly.
Fig. 6 is an example of a membrane separation apparatus furnished with the hollow fiber assembly of Fig.
5 wherein the flow of the liquid to be treated is shown by arrows. In Fig. 6, a vessel 9 accommodates three units of the above assembly. The permeating fluid is fed through the resin wall 4 and is gathered by the permeating liquid collecting block 21. The fluid flows to the center of the block, to the permeating water conduit 22 and is fed to the end plate. T,he supplied fluid is introduced into the vessel 9 through the end plate 10, passes through the space between the hole provided at the center of the resin wall 5 and the permeating water conduit 22 and is introduced into the hollow part of the hollow fiber assembly. The fluid is fed through the hollow fiber layer 1 and the flow screen 7 to reach the inner wall of the vessel 9. It then passes through the space between the permeating liquid collecting block 21 and the container vessel to reach the resin wall 5 of the second hollow fiber assembly. Through a course similar to that described above, the liquid passes through the second assembly, reaches the end plate 11 through the third assembly and then flows out as a concentrated liquid.
Fig. 7 shows an example of the membrane separation apparatus furnished with the hollow fiber assembly of Fig.
5, wherein the flow of the fluid to be treated is shown by arrows. In Fig. 7, a vessel 9 contains four sets of the above assembly. The permeating liquid which has been fed through the open part of the hollow fiber of the resin wall 4 passes through the pressure-sustaining water collecting sheet 12 to flow through the passage in the connecting tube 23 into the permeating water conduit 22, and is then fed into the end plate. The permeating fluid fed from the second fiber assembly flows into the permeating water conduit 22 through the pressure-sustaining water collecting sheet 12 common to the first assemblyl and the connecting pipe 23, and is fed to the end plate.
The permeating fluid coming out from the third and fourth assemblies is also fed to the end plate through the same route as the permeating fluid from the first and the second assemblies. The supplied fluid comes in from the end plate 10, is fed to the outer periphery of the first assembly, goes to the hollow portion through the flow screen 7 and the hollow fiber layer 1, and is then fed to the hollow portion of the second assembly through the path in the connecting tube 23 provided at the center of the resin wall 4. The fluid which passed through the hollow fiber layer 1 of the second assembly passes through the space between the vessel 9 and the outer periphery of the resin wall 5 of the second assembly to reach the third assembly. The fluid is fed through the third and the fourth assemblies via the same courses as in the first and second assemblies to the end plate 11 and flows out of the assembly as a concentrated fluid. U-packing is denoted by numeral 25.
In Fig. 8, a flat bundle 26 of hollow fibers have selective permeability. The fibers are of the tape form having a width in the range of 15 d to 50,000 d, wherein d is the outer diameter of the hollow fiber. The ratio of thickness to width ranges from 1/20,000 to 1/5. The 1~5S067 g nearly parallel tapes are arranged without any space between one another. In Fig 8 the hollow fibers are shown as having spaces between one another merely to facilitate understanding. The layers produced by nearly parallel t:apes are arrangéd to intersect at angles of from 5 to 60.
Typical hollow fibers used in the present invention, although not limited to such, have an outer diameter of 10 to 10,000 microns and a hollow rate of 3 to 80 %. The membrane walls have a selective permeability to fluid and may be any of the microporous, anisotropic or composite form or combinations thereof. Usually, cellulose acetate and aromatic polyamide, or the like are used.
Preferably, the hollow fiber layers are wound to make a packing density of 45 to 70 %. When the density is less than 45 %, the flow velocity of the fluid becomes too low, and the luid runs into the cylindrical layers of the hollow fibers at the inlet of the hollow portion, on the right side in Fig. 1, without reaching the deep inside part of the hollow portion. As a result, the separation efficiency of the assembly is lowered because of the failure of a uniform flow of the fluid in the hollow fiber layer. When the density exceeds 70 %, the liquid does not flow smoothly through the hollow fiber layer. In order to operate the assembly forcibly, it is necessary to elevate the liquid supply pressure, causing a large pressure loss and the possible collapse of the hollow fiber layer.
Preferably, the packing density is from 50 to 65 ~.
It is also desirable for the hollow fibers to be disposed in crisscross relation to one another at a winding angle of 5 to 60 to the axial direction of the hollow fiber layer. When the winding angle is too small, the hollow fiber layer is liable to collapsed. When the winding angle becomes too large, the length of the hollow fiber wound on the core length becomes long, resulting in a large pressure loss of the permeating fluid and a decrease in the amount of permeation.
llS50~7 The diameter of the hollow portion is preferably from l to lO cm, and the thickness of the hollow fiber layer is from 5 to 50 cm. When the diameter of the hollow portion is too small, the supply pressure of liquid must be made large. When it is too small, the liquid is not radially supplied in the whole lengthwise direction of the hollow fiber layer, and the hollow fiber layer is liable to collapse. If the thickness of the hollow fiber layer is too small, the permeation area of the hollow fiber becomes small and the fIuid treating capacity decreases. If it is too large, the pressure loss is enlarged and a channeling is liable to result.
In order to manufacture the above hollow fiber cylindrical layer, the engaging members are usually arranged on the shaft of a winding machine. If necessary, a protective net is covered thereon. Then, the hollow filaments are wound up thereon uniformly at a moderate tension while traversing the filament. Thereafter, only the shaft is takenl out to make the central part hollow.
In this case, it is of course to be understood that the hollow portion includes the engaging members and the protective net.
The engaging member to be used in the present invention is to support partially the hollow fiber layer facing the hollow portion inside the cylindrical layer of the hollow fiber. For the engaging member, it is necessary to use a material having a small resistance to fluid flow such as, for example, net-like material, ring-form material, etc. The engaging members have a function equivalent to that of the hollow portion which passes the fluid to the fiber layer. The engaging members are not formed as an integral or single member, but a plurality of preferably more than 3 members. These members are provided mutually with spaces so that, when any ~hange occurs to the distance between the resin walls 4 and 5, the difference does not concentrate at a single ~lS5067 spot. Further, the engaging members to be used in the present invention evenly disperse the shrinking force under tension which acts upon the hollow fiber layer during operation. In addition, they prevent the hollow fiber from being excessively expanded by the action of the flow resistance of fluid. The distance between the engaging members is preferably 1 to 3 cm.
The elastic supporting members to be used in the present invention prevents excessive shrinkage of the hollow fiber assembly and absorbs the shock exerted on the hollow fibers when the fluid to be treated is abruptly supplied to the hollow fiber assembly. The elastic supporting members make moderate recovery from deformation by elasticity. Preferably, when the elastic modulus of the elastic supporting members is E kg/cm2, the total sectional area of the elastic supporting members is S cm2 and the flow rate of the fluid to be supplied is Q liter/min, the following relationshp exists:
Q ~ 40.
The material of the elastic supporting member may be fiber glass reinforced plastics (FRP), stainless steel, etc.
The number of the elastic supporting members is dependent upon the type of the material, the size of the assembly, etc. and usually may be from 2 to 50.
Further, in the present invention, it is important to separate the engaging members and the resin wall 4.
Preferably, the separation is 1 to 5 cm. ~y adopting the construction as above, it is possible to avoid problems caused by the application of an adhesive agent to the supporting core as previously explained, i.e. loss of separation performance caused by a retaining of the fluid to be treated.
The resin to constitute the resin wall 4 and the resin wall 5 of the present invention is preferably a liquid which has fluidity before curing and becomes a hard solid 1l5l52o67 form when cured. Representative examples of such resins are epoxy, polyester, silicon and polyurethane resins.
The flexible hollow fiber assembly according to the present invention has, due to the construction as above, very little dead space for fluid in the hollow fiber layer and no obstacle such as a supporting core. As a result, an extremely small pressure loss is realized which permits an even flow in the hollow fiber layer, thereby providing a high separation efficiency. Moreover, when the assembly is operated repeatedly intermittently, or the liquid to be treated is at a high flow rate, the separation performance remains high and durability is good.
Practical and presently perferred embodiments of the present invention are illustratively described in the lS following Examples.
Example 1 On a 20 mm in diameter shaft of a winding machine, three net-like engaging members, each having an outer diameter of 27 mm and a length of 300 mm, were arranged at the distance of 30 mm from one another. The surface of the engaging members were covered with a soft protective net. Around it there was wound a hollow fiber of cellulose acetate for reverse osmosis purposes having an outer diameter of 230 microns and an inner diameter of 110 microns. The fibers were wound over the protecting net with a packing density of 50 %, at a winding angle of 8 to 30. The fiber was wound in a fixed number of turns to form a cylindrical layer of hollow fibers having an outer diameter of 118 mm and a length of 1260 mm. The surface of the resulting cylinder was covered with a flow screen.
Thereafter, only the shaft was removed to make a central hollow. Into the two ends of the thus formed hollow fiber layer, epoxy resin was injected to locations spaced by 20 mm from the ends of the engaging members, and the resin was cured to form the resin walls 4 and 5. Between the two resin walls 4 and 5, there were fitted three FRP
,., l~S506~7 elastic supporting members of 10 mm in width and 2 mm in thickness. The resin wall 4 was cut perpendicularly to the axis of the hollow fiber layer to make the hollow fiber open externally through said resin wall, and a hollow fiber assembly was prepared. The end of the protective net was also separated by 20 mm from the resin wall 4.
The hollow fiber assembly was incorporated into the membrane separation apparatus shown in Fig. 2, into which 1500 ppm NaCl aqueous solution was supplied as a feed and circulated at a temperature of 25C under a pressure of 30 kg/cm2 to carry out a reverse osmosis test. The results are as shown in Table 1.
Comparative Example 1 Instead of the hollow fiber assembly of Example 1, there was prepared a hollow fiber assembly having a perforated supporting core for supporting the hollow fiber layer at its center. The core was embedded in the resin wall. The hollow fiber assembly was incorporated in the membrane separation apparatus as shown in Fig. 2, with which a reverse osmosis test was carried out under the same conditions as in Example 1. The results are as shown in Table 1.
The supporting core had a diameter of 27 mm and a length of 1 m. Seventy small holes having a diameter 1.7 mm were provided on the core. The winding density of the hollow fiber layer and the winding angle were the same as those of Example 1.
11550~7 Table 1 .
Example 1Comparative . Example 1 Supply flow rate 22000 19100 (liter/day) Permeation flow rate 16500 14300 (liter/day) Pressure drop between 0.1 1.2 inlet and outlet (kg/cm2) Water recovery*l) 75 75 Salt content in permeating 120 300 water (ppm) Salt rejection rate*2) 92 80 Note: *l~ Water recovery rate (%) =
Permeation flow rate Supply flow rate x 100 *2) Salt rejection rate (%) =
(1 Salt content in permeating liquid) x 100 Salt content in supply liquid As is apparent from Table 1, the hollow fiber assembly of the present invention is remarkably superior to the product using a cotinuous supporting core in respect to the permeation flow rate, pressure loss and effect of salt separation.
Example 2 On a 30 mm in diameter shaft, three net-like engaging members having an outer diameter of 35 mm and a length of 300 mm were arranged at a distance of 30 mm from one another. A cellulose triacetate hollow fiber for reverse osmosis purposes, having an outer diameter of 165 microns and an inner diameter of 70 microns was wound in a fixed number of turns on the engaging members. The winding traversed three engaging members and had a packing density of 53 % and a winding angle of 8 to 30 to form a cylindrical layer of hollow fiber having an outer diameter of 193 mm and a length of 1260 mm. The surface of the hollow fiber layer was covered with a flow screen.
Thereafter, only the shaft was removed to make the central part hollow. Into the two ends of the formed hollow fiber layer, epoxy resin was injected to locations spaced 30 mm from the ends of the engaging members, thereby forming when cured the resin walls 4 and 5. Between the two resin walls 4 and 5, three elastic supporting members of 7 mm in width and 3.5 mm in thickness (FRP rods) were fitted in parallel with the axis of the cylindrical body. Resin wall 4 was cut to allow the hollow fiber layer to be open to the exterior.
The hollow fiber assembly was set into the membrane separation apparatus. By the use of a 1500 ppm NaCl aqueous solution, a reverse osmosis test was carried out under the conditions of 25C temperature, 30 kg/cm2 pressure and a 30 % recovery rate. A water permeation test was made with the concentrated water outlet open.
Shrinkage was evaluated, correlated with the resistance of the hollow fiber layer by circulating water only, without exerting pressure. A compression test was made by applying an external load. Shrinkage was evaluated by exerting a load between the resin walls without water circulation. The results are as shown in Table 2.
Comparative Example 2 By using a net-like supporting core of 35 mm in outer diameter instead of the engaging member of Example 2 and without fitting a FRP rod as used in Example 2, a hollow fiber assembly was prepared in the same manner as shown in Example 2. The assembly was incorporated into the membrane separation apparatus as shown in Fig. 2 to carry out a test under the same conditions as in Example 2. The results are shown in Table 2.
~S5067 Table 2 _ Example 2 Comparative Example 2 _ _ I
Su~ply flow rate 220 220 (m /day) Permeation flow rate 67 67 (m3/day) Water recovery 30 30 Salt content in permeating 75 105 water (ppm) Salt rejection rate 95 93 Shrinkage of assembly 2 8 (mm) Shrinkage of assembly in water permeation test shrinkage (mm/amount of 0.010 0.035 water circulated (m3/day) Shrinkage of assembly in compression test shrinkage (mm)/load (kg) 10.03 0.12 As is apparent from Table 2, the hollow fiber assembly of the present invention is excellent in salt separating efficiency. It exhibits a small amount of shrinkage with respect to water circulation. In Comparative Example 2, due to the large shrinkage of the assembly, a long supply conduit 8 as in Fig. 2 must be used to prevent its separation from the end plate 11, thus requiring the use of a long vessel 9. As a result, the volume efficiency (amount of water permeation per volume of vessel) was lower in actual application than in Example 2. Also, when the reverse osmosis operation of Comparative Example 2 was intermittently repeated, the supporting core repeatedly sustained a compression deformation of 8 mm to form permanent stress, by which the separation efficiency showed a further decrease.
Claims (5)
1. A hollow fiber assembly having selective permeability, said assembly being comprised of a cylindrical arrangement of hollow fibers, said fibers having selective permeability comprising: a cylindrical layer of hollow fibers formed by the crisscross winding of hollow fibers; a hollow portion located inside said cylindrical layer of hollow fibers; a plurality of engaging members which are respectively separated from one another in said hollow portion; a first resin wall which is disposed at an open end of said hollow fibers and arranged to be open to the exterior of the assembly, said first wall being spaced from said engaging means but not spaced from said hollow fibers; a second resin wall which is disposed at the other end of said assembly for securing the end of said assembly; an elastic supporting member for controlling the distance between the first and second resin walls; and a fluid supply conduit.
2. The assembly according to claim 1, wherein the engaging members are disposed at a distance of 1 to 3 cm from one another.
3. The assembly according to claim 1, wherein the first resin wall is disposed at a distance of 1 to 5 cm from the engaging members.
4. The assembly according to claim 1, wherein the engaging members are covered with a net-like cloth.
5. The assembly according to claim 1, wherein the elastic modulus of the elastic supporting members E kg/cm2, the total sectional area of the elastic supporting members S cm2 and the flow rate of the fluid to be supplied Q liter/min are related by the formula:
.
.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000367137A CA1155067A (en) | 1980-12-18 | 1980-12-18 | Hollow fiber assembly having selective permeability |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000367137A CA1155067A (en) | 1980-12-18 | 1980-12-18 | Hollow fiber assembly having selective permeability |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1155067A true CA1155067A (en) | 1983-10-11 |
Family
ID=4118737
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000367137A Expired CA1155067A (en) | 1980-12-18 | 1980-12-18 | Hollow fiber assembly having selective permeability |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1155067A (en) |
-
1980
- 1980-12-18 CA CA000367137A patent/CA1155067A/en not_active Expired
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