Patent Application
20160114269
The present invention relates to a structure of a filtering device including, as a filter membrane, a pleated filter that is mainly used for filtration of a liquid. In particular, the present invention relates to a pleated filter used in a treatment system of ballast water stored in ships and used for filtration of a large amount of water, and an apparatus using the same.
A wide variety of filters are used for the purpose of separating and removing a solid which is a contaminant from a gas or a liquid. Pleated filters whose filtration areas are increased by folding a filter so as to have a pleated shape are also used mainly in applications involving a gas, for example, in an air purification system. PTL 1 discloses an example of use of a cylindrically shaped pleated filter as a filter device for removing sludge from a cutting fluid of a machine tool. Regarding this device, it is described that a filter device having a high filter-cleaning effect can be provided by ejecting a liquid toward an outer surface of the cylindrical filter while rotating the filter.
Meanwhile, treatment of ballast water carried in ships has become an issue in recent years. Ballast water is seawater carried in a ship to provide safe voyage even when the ship is empty of cargo. Various methods for removing, killing, or inactivating microbes by purifying ballast water have been developed. Methods using filtration for the purpose of removing relatively large microbes have also been developed. For example, PTL 2 describes a ballast water treatment apparatus using a filter membrane, the apparatus being filed by the applicant of the present invention.
In the case of seawater desalination, the use of brackish water/seawater for purposes such as ballast water, or the treatment of sewage water, human sewage, industrial wastewater, or the like, a preliminary filtration treatment for removing foreign matter, contaminants, and microbes in water is necessary. The inventors of the present application have been examining the application of a pleated filter to such filtration. In this case, it is necessary to filter a large amount of water in the shortest possible time. However, in general, the operation at a large scale/high flow rate causes a technical problem in that a decrease in the amount of treatment or the filtration function due to clogging at an early stage is easily caused.
The apparatus disclosed in PTL 2 includes a filtering device in which a cylindrical filter is installed in a tubular case and a liquid flowing from the outside to the inside of the cylindrical filter is collected as a filtrate. In the filtering device disclosed in PTL 2, a liquid to be filtered is ejected from a nozzle provided on a side face of the tubular case onto a part of a filtering surface of the filter, thereby cleaning filtered products deposited on a surface of the filter to recover the permeation flux, and the filtered products that have been washed out are discharged from a filtration front chamber. With this structure, a stable filtration state is continuously maintained. An important factor for stably maintaining continuous filtration of such a system is the cleaning effect obtained by ejecting, onto the filtering surface of the filter, the liquid to be filtered. In the filtering device disclosed in PTL 2, in order to efficiently and effectively clean the entire filter by changing a cleaning region of the filter with time, the cylindrical filter is rotated during filtration by driving a motor or the like, thus continuously and periodically changing the position to which the ejection from the ejection nozzle is applied.
In order to reliably perform this rotation cleaning and to stably maintain a high filtration flow rate, it is necessary to maintain the ejection of the liquid to be filtered from the nozzle at a certain degree of flow rate level or higher. According to the studies conducted by the inventors, it was found that, as a result of being subjected to an ejection of the liquid to be filtered at such a high flow rate, the cylindrical filter degrades with time and breaks, and part of the liquid to be filtered may be mixed directly with the filtrate without passing through the filter.
In view of this, an object of the present invention is to provide a filtering device that can be operated stably for a long period of time while maintaining a high cleaning effect, and a ballast water treatment apparatus using the filtering device.
A filtering device according to the present invention includes, as a filter membrane, a pleated filter formed of a filter base having folds so as to repeat peak portions and valley portions, the pleated filter having a shape of a cylinder whose axial direction is a ridge line direction of the folds. In the filtering device, the pleated filter is rotatable about a cylindrical axis of the shape of the cylinder. The filtering device includes a nozzle that is provided so as to face an outer circumferential surface of the pleated filter and that ejects a liquid toward the outer circumferential surface. The relationships 4p≦W, and h/5≦L≦h/2 are satisfied, where p represents a spacing between pleats and h represents a length in the ridge line direction, the length being effective for filtration, in the folds on the outer circumferential side of the pleated filter, and W represents an opening width in a direction perpendicular to the ridge line direction and L represents an opening length in the ridge line direction in an opening portion of the nozzle.
The present invention also provides a ballast water treatment apparatus including, as a filter membrane, a pleated filter formed of a filter base having folds so as to repeat peak portions and valley portions, the pleated filter having a shape of a cylinder whose axial direction is a ridge line direction of the folds. In the ballast water treatment apparatus, the pleated filter is rotatable about a cylindrical axis of the shape of the cylinder. The ballast water treatment apparatus includes an untreated-water nozzle that is provided so as to face an outer circumferential surface of the pleated filter and that ejects a liquid toward the outer circumferential surface. The relationships 4p≦W, and h/5≦L≦h/2 are satisfied, where p represents a spacing between pleats and h represents a length in the ridge line direction, the length being effective for filtration, in the folds on the outer circumferential side of the pleated filter, and W represents an opening width in a direction perpendicular to the ridge line direction and L represents an opening length in the ridge line direction in an opening portion of the untreated-water nozzle. A top surface of the cylinder and a bottom surface of the cylinder of the pleated filter are each sealed in a watertight manner. The ballast water treatment apparatus includes a case that includes an outer cylindrical portion provided so as to surround the pleated filter and including a nozzle opening of the untreated-water nozzle therein, a filtered water flow path that leads filtered water having passed through the pleated filter from the inside of the cylinder of the pleated filter to the outside of the case, and a discharge flow path that discharges discharge water that is not filtered by the pleated filter to the outside of the case.
The present invention also provides a method for treating ballast water, the method including installing the above ballast water treatment apparatus in a hull, using, as untreated water, seawater taken from the outside of the hull, further applying a sterilization treatment to filtered water treated by the ballast water treatment apparatus, and subsequently storing the resulting water in the hull as ballast water.
According to the above, it is possible to provide a filtering device that can be operated stably for a long period of time while maintaining a high cleaning effect, a ballast water treatment method, and a ballast water treatment apparatus using the filtering device.
The inventors of the present invention conducted intensive studies on degradation of a pleated filter and confirmed that breakage easily occurs in folded portions corresponding to peaks and valleys of pleats. As measures against this, the inventors of the present invention have been examining a reinforced structure in which the folded portions of pleats do not easily break. With the reinforcement of a pleated filter, while the occurrence of breakage is suppressed, clogging may easily occur. In view of this, the inventors of the present invention developed a structure in which clogging can be suppressed by increasing a cleaning effect even in the case of a reinforced filter.
Embodiments of the present invention will be listed and described.
(1) An embodiment of the present invention provides a filtering device including, as a filter membrane, a pleated filter formed of a filter base having folds so as to repeat peak portions and valley portions, the pleated filter having a shape of a cylinder whose axial direction is a ridge line direction of the folds. In the filtering device, the pleated filter is rotatable about a cylindrical axis of the shape of the cylinder. The filtering device includes a nozzle that is provided so as to face an outer circumferential surface of the pleated filter and that ejects a liquid toward the outer circumferential surface. The relationships 4p≦W, and h/5≦L≦h/2 are satisfied, where p represents a spacing between pleats and h represents a length in the ridge line direction, the length being effective for filtration, in the folds on the outer circumferential side of the pleated filter, and W represents an opening width in a direction perpendicular to the ridge line direction and L represents an opening length in the ridge line direction in an opening portion of the nozzle.
In the structure in which a pleated filter is cleaned by ejecting a cleaning liquid toward an outer circumferential surface of the rotating pleated filter, the above embodiment provides a structure for obtaining a higher cleaning effect. In the filtering device, a nozzle for supplying a liquid to be filtered and a nozzle for supplying a cleaning liquid may be separately provided. Alternatively, a nozzle for supplying a liquid to be filtered may also have a function of cleaning. In the description below, any nozzle in each of the above cases may be used as long as the nozzle has a cleaning function. The superiority of this cleaning effect was obtained on the basis of the finding regarding a cleaning mechanism examined by the inventors as described below. By increasing the opening width W of the nozzle with respect to the spacing p between pleats in folds on the outer circumferential side of a pleated filter, the cleaning liquid can flow into a plurality of valley portions of pleats at the same time instead of flowing into a single valley portion of a pleat. Satisfying the condition of 4p≦W means that, in any state of the rotating pleated filter, a cleaning liquid flows in at least three adjacent valley portions of pleats at the same time. In this state, a high cleaning effect is obtained. Furthermore, satisfying the relationship h/5≦L≦h/2 where h represents a length of the pleated filter in the ridge line direction, the length being effective for filtration, and L represents an opening length of the nozzle means that the cleaning liquid from the nozzle does not flow in an entire valley portion of a pleat but flows only in a part of the valley portion. Since the cleaning liquid that has flowed in flows out from a portion that does not face the nozzle, the portion being a part of the valley portion of a pleat, the cleaning effect can be enhanced.
(2) A central portion of the nozzle in the direction of the opening length is preferably disposed at a position facing a central portion of the pleated filter in the ridge line direction. This is because the cleaning liquid flows from the central portion of the pleated filter, and flows to both end sides and thus easily flows out. A high cleaning effect can be obtained compared with the case where the nozzle is allowed to face an end of the pleated filter.
(3) The nozzle is preferably a rectangular nozzle having the opening width represented by W and the opening length represented by L. In the description above, the shape of the nozzle is not particularly limited, and various shapes can be used. Examples thereof include a rectangle, a substantially rectangular shape formed by rounding angles of a rectangle, an athletic track field-like shape formed by replacing ends of a rectangle with circular arcs, an ellipse, and a shape formed by connecting a plurality of circles. In any case, the opening width W is defined as a maximum width of the opening in a direction orthogonal to the ridge lines of folds of pleats, and the opening length is defined as a maximum length of the opening in a direction of folds of pleats. A rectangular nozzle that covers a substantially rectangular shape formed by rounding angles of a rectangle is preferable. The reason for this is as follows. Herein, the term “rectangular nozzle” covers a nozzle having a rectangular shape and a nozzle having a substantially rectangular shape. Specifically, the rectangular nozzle has a width that is substantially uniform over the entire length of the nozzle. Accordingly, when a cleaning liquid is ejected onto the pleats, uneven deformation of the pleats does not easily occur, and a stable cleaning effect is obtained. Furthermore, a rectangle is suitable for the shape of the nozzle also from the viewpoint of the ease of the device production.
(4) The present invention further provides a ballast water treatment apparatus using the filtering device described above. More specifically, the ballast water treatment apparatus includes, as a filter membrane, a pleated filter formed of a filter base having folds so as to repeat peak portions and valley portions, the pleated filter having a shape of a cylinder whose axial direction is a ridge line direction of the folds. In the ballast water treatment apparatus, the pleated filter is rotatable about a cylindrical axis of the shape of the cylinder. The ballast water treatment apparatus includes an untreated-water nozzle that is provided so as to face an outer circumferential surface of the pleated filter and that ejects a liquid toward the outer circumferential surface. The relationships 4p≦W, and h/5≦L≦h/2 are satisfied, where p represents a spacing between pleats and h represents a length in the ridge line direction, the length being effective for filtration, in the folds on the outer circumferential side of the pleated filter, and W represents an opening width in a direction perpendicular to the ridge line direction and L represents an opening length in the ridge line direction in an opening portion of the untreated-water nozzle. A top surface of the cylinder and a bottom surface of the cylinder of the pleated filter are each sealed in a watertight manner. The ballast water treatment apparatus includes a case that includes an outer cylindrical portion provided so as to surround the pleated filter and including a nozzle opening of the untreated-water nozzle therein, a filtered water flow path that leads filtered water having passed through the pleated filter from the inside of the cylinder of the pleated filter to the outside of the case, and a discharge flow path that discharges discharge water that is not filtered by the pleated filter to the outside of the case. According to this ballast water treatment apparatus, even when a filtration treatment of a large amount of seawater is performed, the apparatus can be stably operated for a long period of time while maintaining a high cleaning effect.
(5) The present invention further provides, as a method for using the filtering device, a method for treating ballast water, the method including installing the above ballast water treatment apparatus in a hull, using, as untreated water, seawater taken from the outside of the hull, further applying a sterilization treatment to filtered water treated by the ballast water treatment apparatus, and subsequently storing the resulting water in the hull as ballast water. A filtration treatment can be stably performed for a long period of time while suppressing the occurrence of clogging as compared with existing methods. Consequently, the labor cost of maintenance and the cost of materials to be exchanged can be reduced, and the production of ballast water can be further facilitated.
Embodiments of the present invention will now be described in detail with reference to the drawings. The scope of the present invention is not limited to these exemplifications but is defined by the claims described below. It is intended that the scope of the present invention includes equivalents of the claims and all modifications within the scope of the claims.
A porous resin sheet is used as the base of the filter. Examples of the base that can be used include porous structures such as a stretched porous body, a porous body by phase separation, and a non-woven cloth that are composed of a material such as polyester, nylon, polyethylene, polypropylene, polyurethane, polytetrafluoroethylene (PTFE), or polyvinylidene fluoride (PVdF). For the purpose of a treatment at a high flow rate, a non-woven cloth composed of a polyester such as polyethylene terephthalate is particularly suitably used as the base of the filter.
A structure is assumed in which a liquid to be filtered is supplied from the outer circumferential side of the cylinder of the pleated filter 10 having the shape illustrated in
Opening (bending) of central portions of the filter in the directions illustrated in
The reinforcing sheet 2 is a sheet composed of a resin selected from the group consisting of polypropylene, polyethylene, polyamide, polyester, and vinyl chloride, and preferably has a large number of holes penetrating from a surface of the sheet to another surface thereof. Polypropylene is particularly preferable from the viewpoint of having a suitable strength and a suitable restoring force.
When the folds of the pleats are densely arranged, a flow of a filtered objective fluid to the inside of a cylindrical body is easily blocked. In the case where the reinforcing sheet 2 is a sheet that does not have holes or the like, the flow is significantly blocked, and the filtration performance may be impaired. Therefore, the reinforcing sheet 2 is preferably a so-called porous or mesh-like sheet. A size of the holes of about 0.5 to 8 mm (in the case of a mesh, a pitch of 1 to 10 mm) is preferably used from the viewpoint of the balance between permeation of the filtrate and the strength of the sheet. The size of the hole is more preferably 3 to 5 mm (in the case of a mesh, a pitch of 3 to 5 mm). The sheet thickness is selected in consideration of the pitch (spacing between adjacent folds) of the pleats and a desired strength. A sheet thickness of 0.3 to 2 mm is preferably used. The sheet thickness is more preferably 0.5 to 1.5 mm.
As a typical example of a member used as the reinforcing member, a mesh sheet is illustrated in
As a preferred application example of a filtering device including the pleated filter described above, a structure of a ballast water treatment apparatus will be specifically described with reference to drawings. A description will now be made using seawater as a typical example of a filtrate and a cleaning liquid, and thus the names such as filtered water, cleaning water, untreated water, etc. are used below. Not only in the case where the filtering device is used as a ballast water treatment apparatus, but also in other cases, a cleaning effect described below is similarly achieved.
In this embodiment, the untreated water ejected from the untreated-water nozzle 102 is applied to the outer circumferential surface of the pleats of the pleated filter 101, and an effect of cleaning the pleated filter 101 is obtained by the pressure of the untreated water. The untreated water that is not filtered and suspensoid settled in the case 103 are sequentially discharged from the discharge flow path 108 on the bottom portion 133 of the case 103. This point that filtration is performed while continuously and constantly discharging suspensoid and residual untreated water in this manner is also a feature of this apparatus. This feature is advantageous for reliably achieving a large amount of treatment of more than 100 ton/hour, which is required for ballast water. Although valves and the like are not illustrated in the discharge flow path 108 in the figure, devices necessary for maintenance and flow rate control are provided. The filtered water filtered by the pleated filter 101 is guided to a filtered water flow path 107 through a water intake hole 141 provided in the central pipe 140 in the filter, and is discharged to the outside of the case 103.
The nozzle opening 121 of the untreated-water nozzle 102 may have a rectangular opening. A large amount of water is ejected from the untreated-water nozzle 102 onto the pleated filter surface, thereby generating vibrations in directions in which folds of the pleated filter 101 are opened and closed. As a result, holes such as tearing are easily formed in the folds. In this embodiment, a case where a pleated filter includes a reinforcing sheet is described as an example. In order to obtain the cleaning effect described below, the reinforcing sheet is not essential.
The relationship between a nozzle and a pleated filter in the embodiment described above will be described with reference to drawings.
The principle of cleaning will be described with reference to
The state of cleaning different from that in
In order to obtain this effect, the nozzle opening portion is preferably located at a position facing a central portion in the height direction (that is, in the ridge line direction of the folds) of the pleated filler 51. The central portion of the pleats is apart from the upper and lower fixed ends, and thus the pleats can be effectively expanded. Furthermore, the flow of the cleaning water disperses in the vertical direction, and a flow of cleaning is efficiently formed.
In order to obtain the cleaning effect described above, the relationships 4p≦W, and h/5≦L≦h/2 are preferably satisfied where p represents a spacing between pleats, h represents a length in the ridge line direction, the length being effective for filtration, W represents an opening width of a nozzle, and L represents an opening length of the nozzle in the ridge line direction. The space between pleats is expanded to 2 to 3 times the original width p at a maximum. Accordingly, in order to receive a jet flow of cleaning water at a height of the center of the pleats even in a state where the adjacent pleats are expanded, the width of the nozzle opening portion is preferably at least 4 times the spacing between pleats or more. The width cannot be uselessly increased and is preferably 4 times or more and 5 times or less. The length of the nozzle opening portion is shorter than the length of pleats because paths through which cleaning water exits are necessary in the upper and lower portions of the opening. In order to efficiently discharge cleaning water, spaces each having a dimension of about ¼ of the length of the pleats are preferably present in the upper and lower portions. Therefore, the length of the nozzle opening portion is preferably ½ or less of the length of the pleated filter. On the other hand, in order to introduce cleaning water in the pleats with a jet flow from the center, and to prevent the cleaning water introduced from the central portion from discharging from the center so that the cleaning water is discharged from the upper and lower portions, a length of about ⅕ of the length of the pleated filter is necessary. The length of the nozzle opening portion is preferably ½ or less and ¼ or more.
In order to confirm the effect obtained by a reinforcing sheet, filtration was performed using the ballast water treatment apparatus illustrated in
Filter base: Polyethylene terephthalate non-woven cloth (trade name: AXTAR™ G2260-1S BK0, manufactured by Toray Industries, Inc.)
Reinforcing sheet: Polypropylene mesh sheet (trade name: TRICAL NET SN-598, manufactured by Takiron Co., Ltd.)
In the apparatus, filtering operations were performed under the same conditions. The operation time until a differential pressure between the inside and the outside of the pleated filter was increased by 10 kPa compared with that at the beginning of the operation was compared. Filtration was performed using two types of rectangular nozzles. According to the results, in the nozzle having dimensions of width W×length L of 8×200 (mm), the operation time was 14 hours. On the other hand, in the nozzle having dimensions of width W×length L of 32×50 (mm), the operation time was longer, namely, 50 hours, and it was confirmed that the clogging did not easily occur.
In order to confirm the effect obtained by a reinforcing sheet, filtration was performed using the ballast water treatment apparatus illustrated in
Filter base: Polyethylene terephthalate non-woven cloth (trade name: AXTAR™ G2260-1S BK0, manufactured by Toray Industries, Inc.)
Reinforcing sheet: Polypropylene mesh sheet (trade name: TRICAL NET SN-598, manufactured by Takiron Co., Ltd.)
In the apparatus, filtering operations were performed under the same conditions. The operation time until a differential pressure between the inside and the outside of the pleated filter was increased by 10 kPa compared with that at the beginning of the operation was compared. Filtration was performed using two types of rectangular nozzles. According to the results, in the nozzle having dimensions of width W×length L of 8×300 (mm), the operation time was 47 hours. On the other hand, in the nozzle having dimensions of width W×length L of 28×123 (mm), the operation time was longer, namely, 99 hours, and it was confirmed that the clogging did not easily occur.
The filtering device of the present invention can be suitably used for preliminary filtration treatment for removing foreign matter, contaminants, and microbes in water in the cases of seawater desalination, the use of brackish water/seawater for purposes such as ballast water, and the treatment of sewage water, human sewage, industrial waste water, or the like. Furthermore, the filtering device is suitable for the treatment of water having a high suspensoid/high SS content and a concentration treatment, and thus can also be used in the field of collection of valuable recyclable materials, for example, in the field of food.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2013-270607 | Dec 2013 | JP | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2014/083855 | 12/22/2014 | WO | 00 |
