Patent Application
20160271532
The present invention relates to a structure of 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 cleaning effect of a filter can be provided by ejecting a liquid toward an outer surface of a 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 water such as sewage water, human sewage, or industrial wastewater, a preliminary filtration treatment for removing foreign matter, contaminants, and microbes in the water is necessary. The inventors of the present invention 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 tends to occur.
The apparatus disclosed in PTL 2 is 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 of 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 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, the ejection of the liquid to be filtered from the nozzle needs to be maintained at a certain high flow rate level or more. However, according to the studies conducted by the inventors, it was found that, as a result of being subjected to ejection 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 pleated filter whose degradation and breakage due to use are prevented and which can be stably used for a long period of time, a ballast water treatment apparatus functioning as a filtering device using the pleated filter, and a ballast water treatment method using the pleated filter.
As a result of intensive studies on degradation of a filter, the inventors of the present invention confirmed that breakage tends to occur in folded portions corresponding to peaks and valleys of pleats of a filter that has been subjected to ejection at a high flow rate, and arrived at the following structures.
Specifically, a pleated filter includes a filter base having folds that repeatedly form peak portions and valley portions and having a shape of a cylinder whose axial direction is a ridge line direction of the folds, and a reinforcing sheet disposed in a valley portion viewed from the inside of the shape of the cylinder. In the pleated filter, the reinforcing sheet includes a first reinforcing sheet located on a back side of a fold forming a projection toward the outer circumferential side of the shape of the cylinder and a second reinforcing sheet located in a spacing between adjacent folds forming projections toward the inner circumferential side of the shape of the cylinder. The first reinforcing sheet and the second reinforcing sheet are disposed apart from each other in a depth direction of pleats of the pleated filter.
The present invention provides a ballast water treatment apparatus including the above pleated filter as a filter membrane, an upper surface of the cylinder and a bottom surface of the cylinder of the pleated filter each being sealed in a watertight manner, the pleated filter being rotatably held about a cylindrical axis; an untreated-water nozzle that ejects untreated water toward an outer circumferential surface of the pleated filter; 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.
Furthermore, a method for treating ballast water includes installing the above ballast water treatment apparatus; 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 pleated filter whose breakage due to use is prevented, thereby contributing to stable use for a long period of time, and a ballast water treatment apparatus and a ballast water treatment method using the pleated filter.
Embodiments of the present invention will now be listed and described. An embodiment of the present invention is a pleated filter including a filter base having folds that repeatedly form peak portions and valley portions and having a shape of a cylinder whose axial direction is a ridge line direction of the folds, and a reinforcing sheet disposed in a valley portion viewed from the inside of the shape of the cylinder. The reinforcing sheet includes a first reinforcing sheet located on a back side of a fold forming a projection toward the outer circumferential side of the shape of the cylinder and a second reinforcing sheet located in a spacing between adjacent folds forming projections toward the inner circumferential side of the shape of the cylinder. The first reinforcing sheet and the second reinforcing sheet are disposed apart from each other in a depth direction of pleats of the pleated filter. With this structure, breakage due to use is effectively prevented, and the pleated filter can be stably used for a long period of time.
The inventors of the present invention developed a pleated filter including a reinforcing sheet in a valley portion viewed from the inside of the shape of a cylinder and verified that an effect for preventing breakage was obtained. The inventors of the present invention found that when the spacing between pleats of a pleated filter is small, a space between pleats becomes extremely small because of the presence of the reinforcing sheet, and the volume of a feed that can be filtered may decrease. In view of this, the inventors of the present invention conceived the above structure, which is a structure suitable for ensuring a large filtering volume while effectively preventing breakage. The reinforcing sheet includes a first reinforcing sheet located on the back side of a fold forming a projection toward the outer circumferential side of the shape of the cylinder, and a second reinforcing sheet located in a spacing between adjacent folds forming a projection toward the inner circumferential side of the shape of the cylinder. The first reinforcing sheet and the second reinforcing sheet are disposed apart from each other in a depth direction of pleats of the pleated filter. This structure can effectively reinforce only a portion that is susceptible to breakage while keeping a sufficient space between pleats.
The cylindrical pleated filter is fixed by frame members provided so as to cover upper and lower openings thereof. The pleated filter has this structure in order that the frame members hermetically seal the upper and lower openings while maintaining the pleated shape and the cylindrical shape. Each of the first reinforcing sheet and the second reinforcing sheet is fixed to the frame members together with a filter base of the pleated filter. To achieve a function of preventing breakage, the first reinforcing sheet and the second reinforcing sheet may be separately provided, and each of the reinforcing sheets may be fixed to the frame members. Furthermore, considering the ease of assembly of the pleated filter, in particular, positioning and an accurate arrangement of the reinforcing sheets, the first reinforcing sheet and the second reinforcing sheet are preferably an integrally formed body including a connecting portion.
The shape and the arrangement of the connecting portion are not particularly limited. However, the pleated filter of the present invention preferably has a structure in which a separation and a space are ensured between the first reinforcing sheet and the second reinforcing sheet. For example, the pleated filter of the present invention preferably has a structure in which the two reinforcing sheets are connected to each other with a rod-like or plate-like connecting member therebetween. In the simplest structure, a single connecting member may be provided between end portions or central portions of the two reinforcing sheets. Alternatively, the two reinforcing sheets may be connected to each other with a plurality of connecting members therebetween. In this case, the resulting structure becomes strong and thus is convenient for assembly etc. A particularly preferable embodiment is a rectangular frame member. Specifically, the reinforcing sheet is preferably an integrally formed body that includes the first reinforcing sheet, the second reinforcing sheet, and connecting portions disposed on upper ends and lower ends of the reinforcing sheets, and the integrally formed body preferably has a rectangular shape as a whole. This shape is preferable from the standpoint that a large space in a central portion can be ensured, and the two reinforcing sheets are strongly connected to each other. The simplest embodiment of this shape is a rectangular frame member that is integrally formed as a whole by the first reinforcing sheet, the second reinforcing sheet, and upper and lower connecting portions, the rectangular frame member being a rectangular sheet member formed of a single plate having an opening in a central portion thereof. This embodiment is preferable from the viewpoint of, for example, a reduction in the cost because of the ease of production and handling.
One or both of the reinforcing sheets are preferably formed by using a flat sheet base having a large number of holes penetrating from a front surface to a back surface, that is, a porous sheet material. In particular, it is simple and easy to use a mesh-like sheet material as the porous sheet material. The reinforcing sheet is a member having a strength high enough to prevent a bending deformation of the filter. In addition, it is necessary to take a consideration that expansion of the pleats of the filter due to a pressure of untreated water is not excessively disturbed. Furthermore, it is preferable to consider improvement of the flow of the filtrate and a reduction in the weight of the entire filter. The simplest structure is a rectangular sheet member having a shape obtained by removing a central portion of a mesh-like sheet material. This structure is easily obtained by integral formation, and the reinforcement at a low cost can be easily realized.
A size of a hole of about 0.5 to 8 mm (a pitch of 1 to 10 mm in a case of a mesh) is preferably used from the viewpoint of the balance between permeation of the filtrate and strength of the sheet. More preferably, the size of a hole is 3 to 5 mm (the pitch is 3 to 5 mm in a case of a mesh). The thickness of the sheet is selected in consideration of the pitch of pleats (spacing between adjacent valley portions) and a desired strength. The thickness of the sheet used is preferably 0.3 to 2 mm and more preferably 0.5 to 1.5 mm.
These reinforcing sheets are preferably formed of a resin selected from the group consisting of polypropylene, polyethylene (in particular, medium to low-density polyethylene in terms of restoring force), polyamide resins such as nylon, polyester resins such as polyethylene terephthalate, and vinyl chloride. From the viewpoint of the ease of handling during production, a reduction in the weight, the cost, etc., resin members having required strength are preferably used. Polypropylene is particularly preferable from the viewpoint of having appropriate strength and restoring force. Some metallic materials and nonmetallic materials such as glass-ceramics have a performance superior to that of resins in terms of strength. However, in the present embodiment, a restoring force for deformation is also required for the reinforcing sheets. Therefore, in the case of a metal, it is necessary to use a spring material or to perform a quenching treatment. However, comprehensively considering a processing for forming a mesh-like structure and corrosiveness for seawater, the resin materials mentioned above are suitable.
The present invention also discloses a ballast water treatment apparatus using the above pleated filter as a filter membrane. Specifically, a ballast water treatment apparatus includes the cylindrical pleated filter as a filter membrane, an upper surface of the cylinder and a bottom surface of the cylinder of the pleated filter each being sealed in a watertight manner, the pleated filter being rotatably held about a cylindrical axis; an untreated-water nozzle that ejects untreated water toward an outer circumferential surface of the pleated filter; 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.
In the apparatus having this structure, untreated water is ejected from the nozzle opening outside the cylinder of the cylindrical pleated filter toward an outer surface of the pleated filter, and thus the pressure of the untreated water concentrates on a part of pleats. Consequently, the pressure is applied in directions in which the pleats open, and the filter is more likely to break in valley portions and peak portions as described above. In view of this, by employing the above-described breakage-preventing structure with the reinforcing sheets, it is possible to expect the advantages such as the suppression of the occurrence of filtration failure, a long-term operation of the apparatus due to extension of the lifetime of the pleated filter, and a reduction in the operation cost.
A method in which the above pleated filter is used in filtration may be a method for treating ballast water, the method including installing the 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.
By using the apparatus or using the method, breakage of a filter is suppressed as compared with existing techniques, and the filter can be stably used for a long period of time without causing filtration failure. 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.
The structures of a pleated filter and a ballast water treatment apparatus according to embodiments of the present invention will now be described with reference to the drawings. The scope of the present invention is not limited to these embodiments 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.
As illustrated in
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 formed 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 formed of a polyester such as polyethylene terephthalate is particularly suitably used.
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
Such a breakage of the filter base also occurs in the inner ends of the filter. Although significant improvement is achieved by providing the reinforcing sheets, further improvement is desired. The inventors of the present invention focused on the fact that the movement of the filter significantly relates to the breakage. The inventors of the present invention further focused their attention on, as means for restricting the movement, the shape of the folds of the filter and arrived at a concept of arranging pleats densely. Specifically, it is expected that the effect of suppressing deformation can be achieved by making the inner circumferential side of the cylinder of pleats be as dense as possible.
In the drawings used in the above description, for the sake of explanation, the filter shape is drawn in a state where a filter base is folded at an ideal acute angle. Regarding a practical shape of the pleated filter, it is difficult to ideally fold a base at an acute angle.
The operation when the reinforcing sheet includes a first reinforcing sheet and a second reinforcing sheet will be described with reference to
A pleated filter in
As a preferred application example of a filtering device using the pleated filter described above, a structure of a ballast water treatment apparatus will be described with reference to drawings.
In this embodiment, the untreated water ejected from the untreated-water nozzle is applied to the outer circumferential surface of pleats of the pleated filter, and an effect of cleaning the pleated filter is obtained by the pressure of the untreated water. The untreated water that is not filtered and suspensoid settled in the case are sequentially discharged from the discharge flow path on the bottom portion of the case. 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 an amount of treatment of 10 to 20 ton/hour and more than 100 ton/hour, which are required for ballast water. Although valves and the like are not illustrated in the discharge flow path 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.
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 onto the pleated filter surface, thereby generating vibrations in directions in which folds of the pleated filter open and close. As a result, a hole such as splitting is easily formed in the folds. In this embodiment, a case of a pleated filter provided with a reinforcing sheet is described as an example. Accordingly, breakage can be effectively suppressed, and a long-term stable operation of the apparatus can be more reliably realized. In this embodiment, the pleated filter 101 includes a filter base 111, a first reinforcing sheet 112, and a second reinforcing sheet 113.
In order to confirm the effect obtained by a reinforcing sheet, filtration of seawater was performed using the ballast water treatment apparatus illustrated in
Materials used are as follows.
Filter base: Polyethylene terephthalate non-woven cloth (trade name: AXTAR G2260-1S BKO, manufactured by Toray Industries, Inc.)
First reinforcing sheet and second reinforcing sheet:
Spacing between first reinforcing sheet and second reinforcing sheet: 50 mm
Standard seawater (salt concentration: 2% to 4%, turbidity: 1 to 1,000 NTU (nephelometric turbidity units)) taken in Imari city in Saga prefecture was used as seawater which was untreated water. An initial differential pressure of the filtering operation was about 5 kPa, and the rotational speed of the filter was 95 rpm. The difference in pressure between the inside and the outside of the filter was constantly measured. The time at which the differential pressure increased by 2 kPa from the start of the filtering operation was considered as the occurrence of clogging. The cumulative operating time until the occurrence of clogging was measured. Furthermore, L-sized plankton contained in the filtered seawater was monitored. The time at which plankton leakage was detected was considered as filter damage. The cumulative operating time until the damage was measured. In this Experimental Example, after 70 hours passed, clogging of the pleated filter did not occur, and damage of the pleated filter also did not occur.
An experiment was conducted using the same ballast water treatment apparatus and under the same conditions as those in Experimental Example 1 except that, as a reinforcing sheet, a single reinforcing sheet was used in each spacing between pleats. The reinforcing sheet is a single reinforcing sheet having a size of the first reinforcing sheet and the second reinforcing sheet that are continuously connected to each other, and has an effective length of 200 mm and a width of 70 mm. The material of the reinforcing sheet is the same as that in Experimental Example 1 except for the size. An experiment was conducted using the same apparatus and under the same conditions as those in Experimental Example 1. As a result, clogging of the pleated filter was observed after 20 hours. After 70 hours passed, damage of the pleated filter did not occur.
An experiment was conducted using the same ballast water treatment apparatus and under the same conditions as those in Experimental Example 1 except that no reinforcing sheet was used. After 70 hours passed, clogging of the pleated filter did not occur. However, after 50 hours passed, damage of the pleated filter was observed.
According to the pleated filter of the present invention, a decrease in the performance due to breakage does not occur, and the pleated filter has good durability. Accordingly, the pleated filter of the present invention can be suitable for use in 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, or the treatment of water such as sewage water, human sewage, industrial waste water, or the like. Furthermore, the pleated filter 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 |
|---|---|---|---|
| 2013-254004 | Dec 2013 | JP | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2014/081301 | 11/27/2014 | WO | 00 |
