1. A reverse osmosis treatment apparatus comprising: a first pressure vessel in which primary treatment is performed on water to be treated; a second pressure vessel in which secondary-treatment is performed on the water to be treated that has been subjected to the primary treatment; and one or more reverse osmosis membrane elements respectively including reverse osmosis membranes and water collecting pipes through which permeated water to be treated flows, the one or more reverse osmosis membrane elements which are connected in series by the water collecting pipes, and are provided in each of the first pressure vessel and the second pressure vessel, wherein the first pressure vessel includes at a first end part thereof, an introducing pipe through which the water to be treated is supplied; and at a second end part thereof, a first concentrated water discharging pipe through which the water to be treated that has been subjected to the primary treatment is discharged, and a first discharging pipe through which the permeated water is discharged, the second pressure vessel includes at a first end part thereof, an introducing pipe through which the water to be treated that has been subjected to the primary treatment is introduced; and at a second end part thereof, a second concentrated water discharging pipe through which the water to be treated that has been subjected to the secondary treatment is discharged, and a second discharging pipe through which the permeated water is discharged, a number of the reverse osmosis membrane elements that are connected in the first pressure vessel is equal to or less than the number of the reverse osmosis membrane elements that are connected in the second pressure vessel.

2. The reverse osmosis treatment apparatus according to Claim 1, comprising a plurality of the first pressure vessels.

3. The reverse osmosis treatment apparatus according to Claim 1 or 2, further comprising a first valve provided to the first discharging pipe of the first pressure vessel, wherein a flow rate of the permeated water generated in the first pressure vessel is adjusted by-adjusting the first valve.

TECHNICAL FIELD

[0001] The present invention relates to a reverse osmosis treatment apparatus, and more particularly, to a reverse osmosis treatment apparatus that enables easy replacement of elements.

BACKGROUND ART

[0002] In desalination apparatuses including reverse osmosis membranes (hereinafter, RO membranes), in order to utilize a reverse osmotic pressure, as illustrated in Fig. 8, a plurality of RO membrane elements 222 are arranged in series in a cylindrical pressurization vessel 224, and the RO membrane elements 222 are connected to one another by a water collecting pipe 234 provided at the respective centers of the RO membrane elements 222. Feed water is supplied by a high-pressure pump from one side of the desalination apparatus, and the inside of the pressurization vessel 224 is pressurized according to the opening degree of a valve provided on a concentrated water side. When the applied pressure exceeds the osmotic pressure of the feed water, the feed water passes through the RO membranes, and resultant desalinated water (permeated water) flows into the water collecting pipe 234 at the centers.

[0003] The salt concentration of the feed water supplied into the pressurization vessel 224 becomes higher from the feed water side toward the concentrated water side, and hence the pressure to be applied to the inside of the pressurization vessel 224 is finally determined according to the salt concentration, the amount of permeated water, and the feed water flow rate of the membrane plane at the last stage. Accordingly, a pressure more than necessary is applied on the feed water side inside of the pressurization vessel 224, and hence the amount of permeated water increases. For example, Fig. 9 shows a relation between RO membrane element positions and relative fluxes when seven RO membrane elements 222 are arranged in series. The element position in Fig. 9 represents a number of RO membrane elements 222 counted from the feed water side. As is apparent from Fig. 9, the amount of permeated water is larger on the feed water side, and the amount of permeated water decreases toward the concentrated water side. The reason for this is as follows. Because the salt concentration of water to be treated is higher toward the concentrated water side, a higher pressure is necessary on the concentrated water side. However, since the same pressure is applied also on the feed water side, a larger amount of permeated water is generated on the feed water side. In this fashion, the amount of permeated water inside of the pressurization vessel 224 is non-uniform as shown in Fig. 9, resulting in an increase in necessary power and a progress in contamination of the RO membrane elements on the feed water side.

[0004] In order to solve such a problem, for example, Patent Document 1 describes a seawater desalination apparatus including a plug for blocking a water collecting pipe, the plug being provided in a connection portion between RO membrane elements at the center of a pressurization vessel; and permeated water lines for respectively discharging permeated water separated forward and backward from the water collecting pipe to the outside. Conventional Art

Documents Patent Documents

[0005] Patent Document 1: Japanese Patent Application Laid-open No. 2010-179264 DISCLOSURE OF INVENTION PROBLEMS TO BE SOLVED BY THE INVENTION

[0006] In general, the RO membrane elements are replaced in the following manner. That is, an RO membrane element on the feed water side that is most easily contaminated is detached; and an RO membrane element is newly added on the concentrated water side. However, because in the apparatus described in Patent Document 1, the plug for blocking the water collecting pipe is provided in the connection portion between the RO membrane elements, the replacement in such a manner unfavorably changes the position of the plug, and thus cannot be adopted. Accordingly, it is necessary to disassemble the RO membrane elements once and attach the plug again, which requires time and effort.

[0007] The present invention has been made in view of the above-mentioned circumstances, and therefore has an object to provide a reverse osmosis treatment apparatus that enables easy replacement of RO membrane elements.

MEANS FOR SOLVING PROBLEM

[0008] In order to achieve the above-mentioned object, a first aspect of the present invention provides a reverse osmosis treatment apparatus including a first pressure vessel in which primary treatment is performed on water to be treated; a second pressure vessel in which secondary treatment is performed on the water to be treated that has been subjected to the primary treatment; and one or more reverse osmosis membrane elements respectively including reverse osmosis membranes and water collecting pipes through which permeated water to be treated flows, the one or more reverse osmosis membrane elements which are connected in series by the water collecting pipes, and are provided in each of the first pressure vessel and the second pressure vessel. The first pressure vessel includes at a first end part thereof, an introducing pipe through which the water to be treated is supplied; and at a second end part thereof, a first concentrated water discharging pipe through which the water to be treated that has been subjected to the primary treatment is discharged, and a first discharging pipe through which the permeated water is discharged, the second pressure vessel includes at a first end part thereof, an introducing pipe through which the water to be treated that has been subjected to the primary treatment is introduced; and at a second end part thereof, a second concentrated water discharging pipe through which the water to be treated that has been subjected to the secondary treatment is discharged, and a second discharging pipe through which the permeated water is discharged, a number of the reverse osmosis membrane elements that are connected in the first pressure vessel is equal to or less than the number of the reverse osmosis membrane elements that are connected in the second pressure vessel.

[0009] In the case where reverse osmosis treatment is performed with a plurality of reverse osmosis membrane elements being connected in series, the reverse osmosis membranes on the supply side of the water to be treated are more easily contaminated, and hence the reverse osmosis membrane elements on the feed water side need to be replaced more frequently. According to the first aspect, the pressure vessel is divided into the first pressure vessel and the second pressure vessel, and hence replacement of the reverse osmosis membrane elements in the first pressure vessel that are more easily contaminated is made easier. Further, since the number of the reverse osmosis membrane elements that are connected in the first pressure vessel is equal to or less than the number of the reverse osmosis membrane elements that are connected in the second pressure vessel, easy replacement of the reverse osmosis membrane elements can be achieved. In addition, since it is not required to replace the reverse osmosis membrane elements in the second pressure vessel that are less easily contaminated, the reverse osmosis membrane elements in the second pressure vessel can be used over a long period of time.

[0010] According to a second aspect of the present invention, the reverse osmosis treatment apparatus according to the first aspect includes a plurality of the first pressure vessels.

[0011] The amount of permeated water is larger on the feed water side of the reverse osmosis membrane elements. Accordingly, because the amount of the water to be treated that is supplied into the second pressure vessel is smaller than the amount of the water to be treated that is introduced into the first pressure vessel, the water to be treated that is discharged from a plurality of first pressure vessels can be treated in a single second pressure vessel, leading to efficient treatment.

[0012] According to a third aspect of the present invention, the reverse osmosis treatment apparatus according to the first or second aspect further comprises a first valve provided to the first discharging pipe of the first pressure vessel, wherein a flow rate of the permeated water generated in the first pressure vessel is adjusted by adjusting the first valve.

[0013] In the reverse osmosis treatment apparatus according to the third aspect, the flow rate of the permeated water can be adjusted by adjusting a pressure inside of the first pressure vessel by means of the first valve. By reducing the amount of permeated water in the first pressure vessel, the salt concentration of the water to be treated that has been subjected to the primary treatment can be made lower. Accordingly, in the secondary treatment, even if a small pressure is applied, the amount of permeated water can be larger, and hence the amount of permeated water in the overall apparatus can be increased.

ADVANTAGES OF THE INVENTION

[0014] According to the present invention, the pressure vessel is divided into two vessels. In the first pressure vessel, the primary treatment is performed, and in the second pressure vessel, the secondary treatment is performed. Thus, since only the first pressure vessel that is more easily contaminated can be disassembled and the reverse osmosis membrane elements in the first pressure vessel can be replaced, easy replacement can be achieved. In addition, as for the reverse osmosis membrane elements in the second pressure vessel which are less easily contaminated, the frequency of the replacement thereof can be reduced, thus enabling long-term usage.

BRIEF DESCRIPTION OF DRAWINGS

[0015]

Fig. 1 is a block diagram of a desalination system including a reverse osmosis treatment apparatus according to an embodiment of the present invention;

Fig. 2 is a perspective view illustrating a configuration of an element of the reverse osmosis treatment apparatus according to the embodiment;

Fig. 3 is a front view of the element illustrated in Fig. 2, illustrating a state before RO membranes of the element are wound around;

Fig. 4 is a front view of the element illustrated in Fig. 2;

Fig. 5 is a cross-sectional view illustrating a schematic configuration of the reverse osmosis treatment apparatus according to the embodiment;

Fig. 6 is a graph showing a relation between RO membrane element positions and relative fluxes of permeated water in the reverse osmosis treatment apparatus according to the embodiment;

Fig. 7 is a cross-sectional view illustrating a schematic configuration of a reverse osmosis treatment apparatus according to another embodiment of the present invention;

Fig. 8 is a cross-sectional view illustrating a schematic configuration of a conventional reverse osmosis treatment apparatus; and

Fig. 9 is a graph showing a relation between RO membrane element positions and relative fluxes of permeated water in the conventional reverse osmosis treatment apparatus.

DETAILED DESCRIPTION

[0016] Hereinafter, exemplary embodiments of the present invention are described with reference to the accompanying drawings. The present invention is described by way of the following embodiments, but the present invention can be modified according to a large number of techniques without departing from the scope of the present invention, and embodiments other than the following embodiments can be utilized. Accordingly, all modifications that fall within the scope of the present invention can be covered by the scope of claims.

[0017] Fig. 1 is a block diagram of a desalination system 20 including a reverse osmosis treatment apparatus 10 according to an embodiment of the present invention. Note that the desalination system according to the present invention can be used for a system that performs reverse osmosis treatment on water to be treated, for example, waste water recycle, pure water production, brine desalination, and seawater desalination.

[0018] The desalination system 20 illustrated in Fig. 1 includes a tank 12 in which water to be treated is reserved, a high-pressure pump 14, and the reverse osmosis treatment apparatus 10. The water to be treated in the tank 12 is supplied at high pressure to the reverse osmosis treatment apparatus 10 by the high-pressure pump 14, and is subjected to reverse osmosis treatment (desalination treatment) by RO membranes (treatment membranes) of the reverse osmosis treatment apparatus 10, to be thereby separated into desalinated water (permeated water) 16 and concentrated water (treated water) 18 having a concentrated salt content. The permeated water 16 thus obtained is discharged to the outside of the reverse osmosis treatment apparatus 10 via a discharging pipe. Similarly, the concentrated water 18 is discharged to the outside of the reverse osmosis treatment apparatus 10 via a discharging pipe that is different from the discharging pipe for discharging the permeated water. Note that, in the desalination system 20 according to the embodiment, in which the water to be treated is supplied at high pressure to the reverse osmosis treatment apparatus 10 by the high-pressure pump 14, a valve is provided on the concentrated water exit side of the reverse osmosis treatment apparatus 10, and the pressure inside of the reverse osmosis treatment apparatus 10 is set according to the opening degree of the valve.

[0019] With regard to the water to be treated in the tank 12, raw water may be used without any change, but it is preferable to use water to be treated from which suspended components and the like contained in raw water have been removed by pretreatment. In the pretreatment, a filter is utilized, or raw water is introduced into a sedimentation tank, and a disinfecting agent of chlorine or other substances is added thereto, whereby particles contained in the raw water are precipitated and removed, and microorganisms are sterilized. Alternatively, an aggregating agent of iron chloride or other substances is added to raw water to aggregate suspended components, the suspended components are filtered out, and the pretreated water may be used.

[0020] The reverse osmosis treatment apparatus 10 is configured by packing one element 22 illustrated in Fig. 2 or a plurality of elements 22 connected in series in each of a cylindrical first vessel 80 and a cylindrical second vessel 82 illustrated in Fig. 5 to form a first module 84 and a second module 86/ and connecting the first module 84 and the second module 86, as one unit; and using this unit alone or further connecting the units in parallel.

[0021] As illustrated in Fig. 2, each element 22 is configured by arranging a membrane unit 32 including RO membranes 28 and a discharging pipe 30, around a water collecting pipe 34. The membrane unit 32 is configured by connecting four bag-like RO membranes 28, 28... in a radial pattern to the outer periphery of the water collecting pipe 34 as illustrated in Fig. 3; and winding these RO membranes 28, 28... to have a spiral form around the water collecting pipe 34 as illustrated in Fig. 4. One end of each bag-like RO membrane 28 is opened, and each RO membrane 28 is bonded to the water collecting pipe 34 such that this opening is communicated with through-holes 36 of the water collecting pipe 34 illustrated in Fig. 3. The water to be treated flows through an outer surface of the RO membranes 28, and passes through the RO membranes 28 to be thereby desalinated. Then, the permeated water that has passed through the RO membranes 28 and been desalinated is collected from the inside of the RO membranes 28 into the water collecting pipe 34 via the openings of the RO membranes 28 and the through-holes 36 of the water collecting pipe 34, and the permeated water is then discharged from the element 22 via the water collecting pipe 34 and the discharging pipe 30. Note that the reference numeral 38 in Fig. 3 designates a mesh-like spacer arranged inside of the RO membrane 28. The spacer 38 serves to prevent internal space of the RO membrane 28 from being crushed even when the RO membrane 28 is wound to have a spiral form. In addition, the reference numeral 40 designates a mesh¬like spacer arranged between adjacent RO membranes 28 and 28. The spacer 40 is bonded in a radial pattern to the outer periphery of the water collecting pipe 34, similarly to the RO membrane 28.

[0022] Fig. 5 is a cross-sectional view illustrating the reverse osmosis treatment apparatus 10 according to the embodiment. In the present embodiment, the first module 84 for primary treatment, in which two elements 22 are connected in series, is illustrated as the first vessel 80, and the second module 8 6 for secondary treatment, in which five elements 22 are connected in series, is illustrated as the second vessel 82. The end parts (two end parts) of the first vessel 80 are opened such that the water to be treated can be introduced and first concentrated water (the water to be treated that has been subjected to the primary treatment) that remains without being treated in the first vessel 80 can be discharged. Similarly, the end parts (two end parts) of the second vessel 82 are opened such that the concentrated water (the water to be treated that has been subjected to the primary treatment) discharged from the first vessel 80 can be introduced and second concentrated water (the water to be treated that has been subjected to the secondary treatment) that remains without being treated in the second vessel 82 can be discharged. A predetermined operation pressure is applied to the introduction-side opening of the first vessel 80 by the high-pressure pump 14. In addition, the first vessel 80 and the second vessel 82 may be formed of FRP (fiber-reinforced plastic) or other materials in order to enable the first vessel 80 and the second vessel 82 to resist a high pressure (5 MPa or more). In addition, it is preferable that the first vessel 80 and the second vessel 82 are connected to each other by a pipe formed of a material that can resist high pressure.

[0023] As illustrated in Fig. 5, the first vessel 80 is provided with an introducing pipe 56 for introducing the water to be treated into the first vessel 80; and a first concentrated water discharging pipe 62 for discharging the first concentrated water corresponding to the water to be treated that remains without passing through to enter the water collecting pipes 34. The permeated water which has passed through the RO membranes 28 and been collected into the water collecting pipes 34 is discharged from the first vessel 80 via a first discharging pipe 58 provided on the first concentrated water discharging pipe 62 side. A measuring instrument 66 and a first valve 64 are provided at an exit of the first discharging pipe 58.

[0024] The second vessel 82 is provided with an introducing pipe 68 for introducing the first concentrated water discharged from the first vessel 80 into the second vessel 82; and a second concentrated water discharging pipe 70 for discharging the second concentrated water that remains without passing through to enter the water collecting pipes 34. A concentrated water discharging valve 74 for adjusting the pressure inside of the second vessel 82 is provided at an exit of the second concentrated water discharging pipe 70. The permeated water which has passed through the RO membranes 28 and been collected into the water collecting pipes 34 is discharged from the second vessel 82 via a second discharging pipe 72 provided on the second concentrated water discharging pipe 70 side. A measuring instrument 76 is provided at the exit of the second discharging pipe 72.

[0025] In the reverse osmosis treatment apparatus 10 thus configured, the water to be treated that is supplied from the tank 12 in Fig. 1 via the introducing pipe 56 is introduced into the element 22 via a flow channel 57, and the water to be treated sequentially passes through the RO membranes 28 of the elements 22, and then is collected into the water collecting pipes 34. In the present embodiment, the reverse osmosis treatment is performed at two stages through the first vessel 80 and the second vessel 82, and the permeated water generated in the first vessel 80 is discharged from the first vessel 80 via the first discharging pipe 58. The first concentrated water that remains without passing through to enter the water collecting pipes 34 is discharged from the first concentrated water discharging pipe 62 and supplied into the second vessel 82 via the introducing pipe 68. Then, the first concentrated water is introduced into the element 22 via a flow channel 69, sequentially passes through the RO membranes 28, and then is collected into the water collecting pipes 34. The permeated water generated in the second vessel 82 is discharged from the second vessel 82 via the second discharging pipe 72. The second concentrated water that remains without passing through to enter the water collecting pipes 34 is discharged from the second concentrated water discharging pipe 70.

[0026] Fig. 6 is a graph showing a relation between RO membrane element positions (horizontal axis) and relative fluxes (vertical axis) of the permeated water in the reverse osmosis treatment apparatus according to the embodiment. Note that, data of the present invention given here is based on an experiment carried out under the conditions that two elements are provided in the first vessel (element positions No. 1 and No. 2 in the horizontal axis in Fig. 6); and five elements are provided in the second vessel (element positions No. 3 to No. 7 in the horizontal axis in Fig. 6). In the conventional case, a larger amount of permeated water is generated on the feed water side, and the amount of permeated water gradually decreases toward the concentrated water side. This is because the pressure applied to the inside of the vessel is determined by the pressure applied to the element at the last stage. In contrast to this, in the present invention, the pressure inside of the first vessel 80 can be adjusted by the first valve 64, and hence the relative fluxes can be set to a desired value as shown in Fig. 6, so that the amount of permeated water can be reduced (controllable). The salt concentration of the first concentrated water can be made lower by reducing the amount of permeated water generated in the first vessel 80, and hence the amount of permeated water can be increased in the second vessel 82 as indicated by the element positions 3 to 7 in Fig. 6. Accordingly, the non-uniformity of the amount of permeated water among the RO membrane elements can be resolved, whereby the amount of permeated water in the overall apparatus can be increased.

[0027] Note that the flow rate in the first vessel 80 can be controlled by adjusting the opening degree of the first valve 64 on the basis of a value measured by the measuring instrument 66. Similarly, the flow rate in the second vessel 82 can be controlled by adjusting the opening degree of the concentrated water discharging valve 74 on the basis of a value measured by the measuring instrument 76. In addition, the flow rate of the permeated water can also be controlled by providing a pressure meter between the high-pressure pump 14 and the reverse osmosis treatment apparatus 10 and adjusting the high-pressure pump 14 on the basis of a value measured by the pressure meter. A flow rate meter, a pressure meter, and a conductance meter can be used as the measuring instruments 66 and 76. Measuring the electrical conductance enables to monitor the salt rejection ratio, and hence the amount of permeated water can be checked.

[0028] Note that, in Fig. 5, the first vessel 80 is provided with two elements 22 and the second vessel 82 is provided with five elements 22, but the numbers of elements are not limited thereto. It is preferable, however, that the number of elements 22 in the first vessel 80 be equal to or less than the number of the elements 22 in the second vessel 82. With regard to contamination of the elements 22, the feed water-side elements 22 are more easily contaminated, and hence if the elements 22 in the first vessel 80 are replaced, the permeated water can be efficiently generated in the overall apparatus. Accordingly, if the number of elements 22 in the first vessel 80 is reduced, easy replacement of the elements 22 in the first vessel 80 can be achieved. With reference to Fig. 6, considering that the permeated water is discharged from the first vessel 80, it is preferable to provide two elements in the first vessel 80, but it can be sufficient to provide one element, in terms of the contamination. The number of elements in the first vessel 80 is preferably 1 to 4 and more preferably 2 to 3.

[0029] Fig. 7 is a cross-sectional view illustrating a reverse osmosis treatment apparatus 110 according to another embodiment of the present invention. The reverse osmosis treatment apparatus 110 illustrated in Fig. 7 is different from the reverse osmosis treatment apparatus 10 illustrated in Fig. 5 in that two first vessels 80a and 80b are provided. A larger amount of permeated water is generated in the first vessels 80a and 80b, whereas a smaller amount of the first concentrated water remains without being treated in the first vessels 80a and 80b. As illustrated in Fig. 7, the first concentrated water from the plurality of first vessels is supplied to the second vessel 82, leading to efficient treatment. Also in the reverse osmosis treatment apparatus 110 illustrated in Fig. 7, the first vessels 80a and 80b are respectively provided with measuring instruments 66a and 66b and first valves 64a and 64b, and the pressures inside of the first vessels 80a and 80b are respectively adjusted by the first valves 64a and 64b, whereby the amount of permeated water can be adjusted.

[0030] According to the present invention, the non-uniformity of the amount of permeated water among the elements 22, 22... can be resolved, and a large amount of permeated water can be obtained with a low pressure. In addition, the pressure vessel is divided into two, and the number of the RO membrane elements in the pressure vessel at the first stage, at which the RO membranes are more easily contaminated, is reduced. As a result, easy replacement of the RO membrane elements can be achieved, and the pressure vessel at the second stage, at which the RO membranes are less easily contaminated, can be used over a long period of time.
EXPLANATIONS OF LETTERS OR NUMERALS

[0031] 10, 110: reverse osmosis treatment apparatus

12: tank

14: high-pressure pump

16: permeated water

18: concentrated water

20: desalination system

22: element

24: vessel

28: RO membrane

30: discharging pipe

32: membrane unit

34: water collecting pipe

36: through-holes

38, 40: spacer

56: introducing pipe

57: flow channel

58: first discharging pipe

62: first concentrated water discharging pipe

64: first valve

66, 76: measuring instrument

68: introducing pipe

69: flow channel

70: second concentrated water discharging pipe

72: second discharging pipe

74: concentrated water discharging valve

80: first vessel

82: second vessel

84: first module

86: second module

We claim:

1. A reverse osmosis treatment apparatus comprising: a first pressure vessel in which primary treatment is performed on water to be treated; a second pressure vessel in which secondary-treatment is performed on the water to be treated that has been subjected to the primary treatment; and one or more reverse osmosis membrane elements respectively including reverse osmosis membranes and water collecting pipes through which permeated water to be treated flows, the one or more reverse osmosis membrane elements which are connected in series by the water collecting pipes, and are provided in each of the first pressure vessel and the second pressure vessel, wherein the first pressure vessel includes at a first end part thereof, an introducing pipe through which the water to be treated is supplied; and at a second end part thereof, a first concentrated water discharging pipe through which the water to be treated that has been subjected to the primary treatment is discharged, and a first discharging pipe through which the permeated water is discharged, the second pressure vessel includes at a first end part thereof, an introducing pipe through which the water to be treated that has been subjected to the primary treatment is introduced; and at a second end part thereof, a second concentrated water discharging pipe through which the water to be treated that has been subjected to the secondary treatment is discharged, and a second discharging pipe through which the permeated water is discharged, a number of the reverse osmosis membrane elements that are connected in the first pressure vessel is equal to or less than the number of the reverse osmosis membrane elements that are connected in the second pressure vessel.

2. The reverse osmosis treatment apparatus according to Claim 1, comprising a plurality of the first pressure vessels.

3. The reverse osmosis treatment apparatus according to Claim 1 or 2, further comprising a first valve provided to the first discharging pipe of the first pressure vessel, wherein a flow rate of the permeated water generated in the first pressure vessel is adjusted by-adjusting the first valve.