Concentration system

Abstract

Provided is a concentration system in which a solvent is separated from a target solution containing a target component to obtain a concentrated liquid in which the target component is concentrated. The concentration system comprises a plurality of semipermeable membrane modules. Each of the plurality of semipermeable membrane modules has a semipermeable membrane, and a first chamber and a second chamber partitioned by the semipermeable membrane. The first chambers of the plurality of semipermeable membrane modules are connected to provide a concentration channel, and the second chambers of the plurality of semipermeable membrane modules are connected to provide a dilution channel. The target solution is caused to flow through the concentration channel, and an auxiliary solution having an osmotic pressure is caused to flow through the dilution channel. The concentration system is provided with: a concentrated liquid flow meter downstream of the concentration channel to measure the flow rate of the concentrated liquid; and, downstream of the concentrated liquid flow meter, a concentrated liquid recovery channel for recovering the concentrated liquid, a concentrated liquid return channel for returning the concentrated liquid to the upstream of the concentration channel, and a concentrated liquid regulator for adjusting the flow rate of the concentrated liquid flowing through the concentrated liquid recovery channel and the concentrated liquid return channel so that the measured value of the concentrated liquid flow meter is within a predetermined range .

Description

Concentration System

[0001] The present invention relates to a concentration system.

[0002] With the aim of reducing the energy required for desalination using reverse osmosis (RO), etc., studies have been conducted on an osmotically assisted reverse osmosis (OARO) method or a brine concentration (BC) method, which is a membrane separation method in which a high-pressure target solution is passed through the first chamber of a semipermeable membrane module having a semipermeable membrane and a first and second chamber separated by the semipermeable membrane, and a low-pressure target solution is passed through the second chamber, causing the solvent (water, etc.) contained in the target solution in the first chamber to migrate through the semipermeable membrane to the target solution in the second chamber, thereby discharging a concentrated target solution (concentrate) from the first chamber and a diluted target solution (diluted solution) from the second chamber.

[0003] For example, Patent Document 1 (WO 2018 / 084246), Patent Document 2 (JP 2019-188330 A), and Patent Document 3 (JP 2018-515340 A) disclose the use of a multistage membrane separation system in which a plurality of semipermeable membrane modules are connected in series in a brine concentration method.

[0004] International Publication No. 2018 / 084246 Japanese Patent Application Laid-Open No. 2019-188330 Japanese Patent Application Laid-Open No. 2018-515340

[0005] In such a multistage membrane separation (concentration) system including a plurality of semipermeable membrane modules, the target solution is sequentially concentrated in a flow path (concentration flow path) formed by connecting the first chambers of a plurality of semipermeable membrane modules.

[0006] The concentration system is designed to obtain a concentrated solution of a desired concentration according to the concentration, flow rate, pressure, temperature, etc. of the target solution. However, if the concentration, flow rate, pressure, temperature, etc. of the target solution differ from or fluctuate from the designed values, it is not possible to obtain a concentrated solution of the desired concentration. Furthermore, the design of such a concentration system is complex, and when actually operated, a concentrated solution of the desired concentration is not necessarily obtained as designed.

[0007] Therefore, an object of the present invention is to stably obtain a concentrated solution of a predetermined concentration when a solvent is separated from a target solution and concentrated by osmotic pressure-assisted reverse osmosis or brine concentration using a multistage concentration system (membrane separation system) including a plurality of semipermeable membrane modules.

[0008] As a result of extensive research, the present inventors have found that the above problems can be solved by the following means, and have arrived at the present invention. That is, the present invention has the following configuration.

[0009] [1] A concentration system for obtaining a concentrated solution in which a target component is concentrated by separating a solvent from a target solution containing the target component, the concentration system comprising: a plurality of semipermeable membrane modules, each of the plurality of semipermeable membrane modules having a semipermeable membrane and a first chamber and a second chamber separated by the semipermeable membrane; a concentration flow path connected to the first chambers of the plurality of semipermeable membrane modules; a dilution flow path connected to the second chambers of the plurality of semipermeable membrane modules; the target solution flows through the concentration flow path; and an auxiliary solution having an osmotic pressure flows through the dilution flow path. The concentration system comprises: a concentrate flow meter downstream of the concentration flow path for measuring the flow rate of the concentrate; and a concentrate recovery flow path downstream of the concentrate flow meter for recovering the concentrate, a concentrate return flow path for returning the concentrate to the upstream of the concentration flow path, and a concentrate adjuster for adjusting the flow rates of the concentrate flowed through the concentrate recovery flow path and the concentrate return flow path so that the measured value of the concentrate flow meter is within a predetermined range.

[0010] [2] A reverse osmosis module is provided upstream of the plurality of semipermeable membrane modules, the reverse osmosis module having a reverse osmosis membrane and a first upstream chamber and a second upstream chamber separated by the reverse osmosis membrane, the first upstream chamber is connected to the first chamber of the semipermeable membrane module located most upstream of the plurality of semipermeable membrane modules to form the concentration flow path, a solvent contained in the target solution supplied to the first upstream chamber at a pressure higher than that of the second upstream chamber migrates through the semipermeable membrane into the second upstream chamber, and the target solution is diluted to obtain a permeate, a permeate flow path is provided for discharging the permeate, and a permeate flow meter is provided downstream of the permeate flow path for measuring the flow rate of the permeate, The concentration system according to [1], further comprising: a permeate recovery flow path downstream of the permeate flow meter for recovering the permeate; a permeate return flow path for returning the permeate to the upstream of the concentration flow path; and a permeate adjuster for adjusting the flow rate of the permeate flowing through the permeate recovery flow path and the permeate return flow path so that the measured value of the permeate flow meter falls within a predetermined range.

[0011] [3] The concentration system according to [2], comprising a plurality of reverse osmosis modules.

[0012] [4] The concentration system according to any one of [1] to [3], wherein the semipermeable membrane is a hollow fiber membrane.

[0013] [5] The concentration system according to either [2] or [3], wherein the reverse osmosis membrane is a hollow fiber membrane.

[0014] [6] A concentration system for separating a solvent from a target solution containing a target component to obtain a concentrated solution in which the target component is concentrated, comprising: a reverse osmosis module and a plurality of semipermeable membrane modules; the reverse osmosis module has a reverse osmosis membrane and a first and a second upstream chamber separated by the reverse osmosis membrane; each of the plurality of semipermeable membrane modules has a semipermeable membrane and a first and a second chamber separated by the semipermeable membrane; a concentration flow path is provided connecting the first upstream chamber of the reverse osmosis module to the first chambers of the plurality of semipermeable membrane modules; and a dilution flow path is provided connecting the second chambers of the plurality of semipermeable membrane modules; the target solution is flowed through the concentration flow path; an auxiliary solution having an osmotic pressure is flowed through the dilution flow path; the solvent contained in the target solution supplied to the first upstream chamber at a pressure higher than that of the second upstream chamber migrates through the semipermeable membrane into the second upstream chamber, and the target solution is diluted to obtain a permeate; a permeate flow path through which the permeate flows, a permeate recovery flow path for recovering the permeate, and a permeate return flow path for returning the permeate to the upstream of the concentration flow path; a permeate flow meter downstream of the permeate flow path for measuring the flow rate of the permeate; and a permeate adjuster downstream of the permeate flow meter for adjusting the flow rate of the permeate flowing in the permeate recovery flow path and the permeate return flow path so that the measured value of the permeate flow meter falls within a predetermined range.

[0015] [7] The concentration system according to claim 6, further comprising: a concentrate flow meter downstream of the concentration flow path for measuring the flow rate of the concentrate; a concentrate recovery flow path downstream of the concentrate flow meter for recovering the concentrate; a concentrate return flow path for returning the concentrate upstream of the concentration flow path; and a concentrate adjuster for adjusting the flow rate of the concentrate flowing through the concentrate recovery flow path and the concentrate return flow path so that the measurement value of the concentrate flow meter falls within a predetermined range.

[0016] [8] The concentration system according to [6] or [7], comprising a plurality of reverse osmosis modules.

[0017] [9] The concentration system according to any one of [6] to [9], wherein the semipermeable membrane and the reverse osmosis membrane are hollow fiber membranes.

[0018]

[10] The concentration system according to any one of [1] to [9], wherein a part of the concentrated solution is used as the auxiliary solution.

[0019]

[11] The concentration system according to any one of [1] to

[10] , further comprising a pressurizing device for pressurizing the target solution to a pressure higher than that of the auxiliary solution.

[0020] According to the present invention, a concentrated solution of a predetermined concentration can be stably obtained when a solvent is separated from a target solution and concentrated by osmotic pressure-assisted reverse osmosis or brine concentration using a multistage concentration system (membrane separation system) including a plurality of semipermeable membrane modules.

[0021] Fig. 1 is a schematic diagram showing an example of a concentration system according to embodiment 1. Fig. 2 is a schematic diagram showing an example of a concentration system according to embodiment 2. Fig. 3 is a schematic diagram showing an example of a concentration system according to embodiment 3. Fig. 4 is a schematic diagram showing an example of a concentration system according to embodiment 4.

[0022] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the drawings, the same reference numerals denote the same or corresponding parts.

[0023] <Concentration System> The concentration system of this embodiment is a system for obtaining a concentrated solution in which the target component is concentrated by separating the solvent from a target solution containing the target component.

[0024] (Embodiment 1) Fig. 1 is a diagram schematically showing the configuration of a concentration system 100A according to one embodiment of the present invention. The concentration system 100A is a multistage concentration system (membrane separation system). Note that, although Fig. 1 depicts three semipermeable membrane modules 1, 2, and 3 as the multiple semipermeable membrane modules, the multiple semipermeable membrane modules may be, for example, any number of semipermeable membrane modules greater than or equal to two.

[0025] Each of the plurality of semipermeable membrane modules 1, 2, 3 has a semipermeable membrane 1A, 2A, 3A, and a first chamber 11, 21, 31 and a second chamber 12, 22, 32 separated by the semipermeable membrane.

[0026] A concentration flow path 5 is provided in which the first chambers 11, 21, and 31 of multiple semipermeable membrane modules 1, 2, and 3 are connected. That is, the concentration flow path 5 is composed of the first chambers 11, 21, and 31 and a flow path connecting them. In at least some of the multiple semipermeable membrane modules, the first chambers are preferably connected in series. In some of the multiple semipermeable membrane modules, the first chambers may be connected in parallel.

[0027] A dilution flow path 6 is provided, which is formed by connecting the second chambers 12, 22, and 32 of multiple semipermeable membrane modules 1, 2, and 3. That is, the dilution flow path 6 is composed of the second chambers 12, 22, and 32 and a flow path connecting them. In at least some of the multiple semipermeable membrane modules, the second chambers are preferably connected in series. In some of the multiple semipermeable membrane modules, the second chambers may be connected in parallel.

[0028] The target solution is caused to flow through the concentration flow path 5. The target solution is caused to flow through the first chamber 11 of the semipermeable membrane module 1, the first chamber 21 of the semipermeable membrane module 2, and the first chamber 31 of the semipermeable membrane module 3 in this order.

[0029] An auxiliary solution having osmotic pressure is flowed through the dilution flow path 6. The auxiliary solution is flowed in the order of the second chamber 32 of the semipermeable membrane module 3, the second chamber 22 of the semipermeable membrane module 2, and the second chamber 12 of the semipermeable membrane module 1. That is, the auxiliary solution is flowed in the reverse order of the target solution when the semipermeable membrane modules are connected. However, the auxiliary solution is not limited to the embodiment shown in Fig. 1, and may be flowed in the order of the second chamber 12 of the semipermeable membrane module 1, the second chamber 22 of the semipermeable membrane module 2, and the second chamber 32 of the semipermeable membrane module 3.

[0030] In each semipermeable membrane module, the flow directions on both sides of the semipermeable membrane (in the first and second chambers) may be in any direction, and may be opposite directions (counterflow system) or parallel directions (parallel flow system).

[0031] In multiple semipermeable membrane modules, the flow directions on both sides of the semipermeable membrane (in the first and second chambers) may be in any direction, and may be opposite directions (counterflow method) or parallel directions (parallel flow method).

[0032] The target solution has a higher pressure (hydrostatic pressure) than the auxiliary solution, i.e., in each of the multiple semipermeable membrane modules, the liquid in the first chamber (target solution) has a higher pressure than the liquid in the second chamber (auxiliary solution).

[0033] Here, the pressure of the target solution is increased by a pressurizing device or the like. An example of the pressurizing device is a high-pressure pump (not shown) that can pressurize the target solution while feeding it into the first chamber. Note that the pressurizing device may be a device other than a pump, and may be, for example, a device that pressurizes the liquid in the first chamber from outside the semipermeable membrane module.

[0034] Because the target solution has a higher pressure than the auxiliary solution, in each of the multiple semipermeable membrane modules, the solvent (water, etc.) contained in the target solution in the first chamber migrates through the semipermeable membrane to the auxiliary solution in the second chamber, and the concentrated solution is discharged from the first chamber and the diluted solution is discharged from the second chamber.

[0035] The concentration system 100A includes a concentrate flow meter 71 for measuring the flow rate of the concentrate downstream of the concentration flow path 5. The concentration system 100A also includes, downstream of the concentrate flow meter 71, a concentrate recovery flow path 51 for recovering the concentrate, a concentrate return flow path 61 for returning a portion of the concentrate upstream of the concentration flow path 5, and a concentrate regulator 81 for adjusting the flow rate of the concentrate.

[0036] The concentrate flow meter 71 is provided on the most upstream side of the concentration flow path 5 (downstream of the first chamber 31 of the semipermeable membrane module 3). The concentrate adjuster 81 is provided downstream of the concentrate flow meter 71 and connected to the concentrate recovery flow path 51 and the concentrate return flow path 61. The concentrate recovery flow path 51 and the concentrate return flow path 61 are connected in such a way that the downstream side of the concentration flow path 5 branches. The downstream side of the concentrate return flow path 61 (to which a portion of the concentrate is returned) is not particularly limited, and may be configured to be connected to the most upstream side of the concentration flow path 5 (i.e., upstream of the first chamber 11 of the semipermeable membrane module 1), as shown in FIG. 1, for example, or may be configured to be connected to a connection portion of the concentration flow path 5 that connects multiple semipermeable membrane modules together. In addition, the concentrate return flow path 61 may be further branched and configured to be adjusted so that a desired amount is distributed to the concentration flow path 5 of each semipermeable membrane module.

[0037] Here, the concentrated liquid adjuster 81 adjusts the amount of concentrated liquid discharged into the concentrated liquid recovery channel 51 and the amount of concentrated liquid supplied to the concentrated liquid return channel 61 so that the measured value of the concentrated liquid flow meter 71 falls within a predetermined range, thereby adjusting the flow rate of the target solution (liquid flowing in the concentration channel 5). For example, if the measured value of the concentrated liquid flow meter 71 is lower than the predetermined range (lower limit flow rate), it is determined that the target solution is sufficiently concentrated, and the concentrated liquid adjuster 81 increases the amount of concentrated liquid discharged into the concentrated liquid recovery channel 51 and decreases the amount of concentrated liquid supplied to the concentrated liquid return channel 61.

[0038] On the other hand, if the measured value of the concentrated liquid flow meter 71 is higher than the predetermined range (upper flow rate), it is determined that the target solution is not sufficiently concentrated, and the concentrated liquid adjuster 81 reduces the amount of concentrated liquid discharged to the concentrated liquid recovery line 51 and increases the amount of concentrated liquid supplied to the concentrated liquid return line 61. This allows the flow rate of the concentrated liquid to be returned to the predetermined range. For example, if the concentrated liquid adjuster 81 is a switching valve, the switching valve may be switched so that the concentrated liquid is supplied only to the concentrated liquid return line 61 or only to the concentrated liquid recovery line 51.

[0039] Here, the concentrated liquid adjuster 81 may be a switch such as a selector valve or a flow rate adjuster such as a flow rate control valve. The adjustment by such concentrated liquid adjuster 81 may be automated by a control device or the like. In this case, the concentrated liquid adjuster 81 is electrically connected to, for example, the concentrated liquid flow meter 71 and a control device (not shown).

[0040] (Embodiment 2) Fig. 2 is a diagram schematically illustrating the configuration of a concentration system 100B according to another embodiment of the present invention. The concentration system 100B is a multistage concentration system (membrane separation system). Note that Fig. 2 illustrates one reverse osmosis module 4 as the reverse osmosis module and three semipermeable membrane modules 1, 2, and 3 as the multiple semipermeable membrane modules. The multiple semipermeable membrane modules may be any number of semipermeable membrane modules, for example, two or more. Furthermore, although Fig. 2 illustrates one reverse osmosis module (reverse osmosis module 4), multiple (n) reverse osmosis modules may be provided.

[0041] Each of the semipermeable membrane modules 1, 2, 3 has a semipermeable membrane 1A, 2A, 3A, and a first chamber 11, 21, 31 and a second chamber 12, 22, 32 separated by the semipermeable membrane. The reverse osmosis module 4 has a reverse osmosis membrane 4A, and a first front-stage chamber 41 and a second front-stage chamber 42 separated by the reverse osmosis membrane 4A.

[0042] A concentration flow path 5 is provided, which connects the upstream first chamber 41 of the reverse osmosis module 4 and the first chambers 11, 21, and 31 of the multiple semipermeable membrane modules 1, 2, and 3. That is, the concentration flow path 5 consists of the upstream first chamber 41, the first chambers 11, 21, and 31, and a flow path connecting them. In at least some of the reverse osmosis module 4 and the multiple semipermeable membrane modules 1, 2, and 3, the upstream first chamber 41 and the first chambers 11, 21, and 31 are preferably connected in series. In some of the reverse osmosis module 4 and the multiple semipermeable membrane modules 1, 2, and 3, the upstream first chamber 41 and the first chambers 11, 21, and 31 may be connected in parallel.

[0043] A permeate flow path 7 is provided, which is connected to the upstream second chamber 42 of the reverse osmosis module 4. A dilution flow path 6 is also provided, which is connected to the second chambers 12, 22, and 32 of the multiple semipermeable membrane modules 1, 2, and 3. That is, the dilution flow path 6 is composed of the second chambers 12, 22, and 32 and a flow path connecting them. In at least some of the multiple semipermeable membrane modules 1, 2, and 3, the second chambers are preferably connected in series. In some of the multiple semipermeable membrane modules, the second chambers may be connected in parallel.

[0044] The target solution is passed through the concentration flow path 5. The target solution passes through the upstream first chamber 41 of the reverse osmosis module 4, the first chamber 11 of the semipermeable membrane module 1, the first chamber 21 of the semipermeable membrane module 2, and the first chamber 31 of the semipermeable membrane module 3, in this order.

[0045] In the reverse osmosis module 4, the target solution is pressurized at high pressure, causing the solvent (water, etc.) contained in the target solution in the first upstream chamber 41 to migrate through the reverse osmosis membrane 4A into the second upstream chamber 42, and the concentrated target solution is discharged from the first upstream chamber 41, and the permeated liquid is discharged from the second upstream chamber 42.

[0046] An auxiliary solution having osmotic pressure is flowed through the dilution flow path 6. The auxiliary solution is flowed in the order of the second chamber 32 of the semipermeable membrane module 3, the second chamber 22 of the semipermeable membrane module 2, and the second chamber 12 of the semipermeable membrane module 1. That is, the auxiliary solution is flowed in the reverse order of the target solution when the semipermeable membrane modules are connected. However, the auxiliary solution is not limited to the embodiment shown in Fig. 2, and may be flowed in the order of the second chamber 12 of the semipermeable membrane module 1, the second chamber 22 of the semipermeable membrane module 2, and the second chamber 32 of the semipermeable membrane module 3.

[0047] In each semipermeable membrane module, the flow directions on both sides of the semipermeable membrane (in the first and second chambers) may be in any direction, and may be opposite directions (counterflow system) or parallel directions (parallel flow system).

[0048] In each of the multiple semipermeable membrane modules, the target solution has a higher pressure than the auxiliary solution, so that in each of the multiple semipermeable membrane modules, the solvent (water, etc.) contained in the target solution in the first chamber migrates through the semipermeable membrane to the auxiliary solution in the second chamber, and the concentrated solution is discharged from the first chamber and the diluted solution is discharged from the second chamber.

[0049] The target solution has a higher pressure (hydrostatic pressure) than the auxiliary solution, i.e., in each of the multiple semipermeable membrane modules, the liquid in the first chamber (target solution) has a higher pressure than the liquid in the second chamber (auxiliary solution).

[0050] The pressure of the target solution is increased by a pressurizing device or the like. An example of the pressurizing device is a high-pressure pump (not shown) that can pressurize the target solution while feeding it into the first chamber. The pressurizing device may be a device other than a pump, and may be, for example, a device that pressurizes the liquid in the first chamber from outside the semipermeable membrane module.

[0051] The concentration system 100B is equipped with a concentrate flow meter 71 downstream of the concentration flow path 5 for measuring the flow rate of the concentrate. The concentration system 100B is equipped with a concentrate recovery flow path 51 for recovering the concentrate, a concentrate return flow path 61 for returning a portion of the concentrate to the upstream of the concentration flow path 5, and a concentrate regulator 81 for adjusting the flow rate of the concentrate, downstream of the concentrate flow meter 71. The concentration system 100B is equipped with a permeate flow meter 72 downstream of the permeate flow path 7 for measuring the flow rate of the permeate. The concentration system 100B is equipped with a permeate recovery flow path 52 for recovering the permeate, a permeate return flow path 62 for returning a portion of the permeate to the upstream of the concentration flow path, and a permeate regulator 82 for adjusting the flow rates of the permeate flowed through the permeate recovery flow path 52 and the permeate return flow path 62 so that the measurement value of the permeate flow meter 72 falls within a predetermined range.

[0052] The concentrate flow meter 71 is provided on the most upstream side of the concentration flow path 5 (downstream of the first chamber 31 of the semipermeable membrane module 3). The concentrate adjuster 81 is provided downstream of the concentrate flow meter 71 and connected to the concentrate recovery flow path 51 and the concentrate return flow path 61. The concentrate recovery flow path 51 and the concentrate return flow path 61 are connected in such a way that the downstream side of the concentration flow path 5 branches. The downstream side of the concentrate return flow path 61 (to which a portion of the concentrate is returned) is not particularly limited, and may be configured to be connected to the most upstream side of the concentration flow path 5 (i.e., upstream of the first chamber 11 of the semipermeable membrane module 1), as shown in FIG. 2, for example, or may be configured to be connected to a connection portion of the concentration flow paths 5 that connect multiple semipermeable membrane modules together. In addition, the concentrate return flow path 61 may be further branched and configured to be adjusted so that a desired amount is distributed to the concentration flow paths 5 of each semipermeable membrane module.

[0053] The permeate flow meter 72 is provided on the most upstream side of the permeate flow channel 7 (downstream of the first-stage second chamber 42 of the reverse osmosis module 4). The permeate adjuster 82 is provided downstream of the permeate flow meter 72 and is connected to the permeate recovery channel 52 and the permeate return channel 62. The permeate recovery channel 52 and the permeate return channel 62 are connected in such a way that the downstream side of the permeate flow channel 7 branches. The downstream side of the permeate return channel 62 (to which a portion of the concentrate is returned) is not particularly limited, and may be connected to the most upstream side of the concentration channel 5 (i.e., upstream of the first-stage first chamber 41 of the reverse osmosis module 4) as shown in FIG. 2, for example, or may be connected to a connection portion of the concentration channels 5 that connect multiple semipermeable membrane modules. The permeate return channel 62 may also be further branched and adjusted so that a desired amount is distributed to the concentration channels 5 of each semipermeable membrane module.

[0054] Here, the concentrated liquid adjuster 81 adjusts the amount of concentrated liquid discharged into the concentrated liquid recovery channel 51 and the amount of concentrated liquid supplied to the concentrated liquid return channel 61 so that the measured value of the concentrated liquid flow meter 71 falls within a predetermined range, thereby adjusting the flow rate of the target solution (liquid flowing in the concentration channel 5). For example, if the measured value of the concentrated liquid flow meter 71 is lower than the predetermined range (lower limit flow rate), it is determined that the target solution is sufficiently concentrated, and the concentrated liquid adjuster 81 increases the amount of concentrated liquid discharged into the concentrated liquid recovery channel 51 and decreases the amount of concentrated liquid supplied to the concentrated liquid return channel 61.

[0055] On the other hand, if the measured value of the concentrated liquid flow meter 71 is higher than the predetermined range (upper flow rate), it is determined that the target solution is not sufficiently concentrated, and the concentrated liquid adjuster 81 reduces the amount of concentrated liquid discharged to the concentrated liquid recovery line 51 and increases the amount of concentrated liquid supplied to the concentrated liquid return line 61. This allows the flow rate of the concentrated liquid to be returned to the predetermined range. For example, if the concentrated liquid adjuster 81 is a switching valve, the switching valve may be switched so that the concentrated liquid is supplied only to the concentrated liquid return line 61 or only to the concentrated liquid recovery line 51.

[0056] Furthermore, the permeate adjuster 82 adjusts the amount of permeate discharged to the permeate recovery channel 52 and the amount of permeate supplied to the permeate return channel 62 so that the measured value of the permeate flow meter 72 falls within a predetermined range, thereby adjusting the flow rate of the target solution (the liquid flowing in the permeate channel 7). For example, if the measured value of the permeate flow meter 72 is lower than the predetermined range (lower limit flow rate), it is determined that the target solution is not sufficiently concentrated, and the permeate adjuster 82 reduces the amount of permeate discharged to the permeate recovery channel 52 and increases the amount of permeate supplied to the permeate return channel 62.

[0057] On the other hand, if the measured value of the permeate flow meter 72 is higher than the predetermined range (upper flow rate), it is determined that the target solution is sufficiently concentrated, and the permeate regulator 82 increases the amount of permeate discharged to the permeate recovery channel 52 and decreases the amount of permeate supplied to the permeate return channel 62. This allows the flow rate of the permeate to be returned to within the predetermined range. For example, if the permeate regulator 82 is a switching valve, the switching valve may be switched so that the permeate is supplied only to the permeate return channel 62 or only to the permeate recovery channel 52.

[0058] Here, the concentrated liquid regulator 81 and the permeate liquid regulator 82 may be a switch such as a selector valve or a flow rate regulator such as a flow rate control valve. The adjustments by the concentrated liquid regulator 81 and the permeate liquid regulator 82 may be automated by a control device or the like. In this case, the concentrated liquid regulator 81 and the permeate liquid regulator 82 are electrically connected to, for example, the concentrated liquid flow meter 71 and the permeate liquid flow meter 72 and a control device (not shown).

[0059] (Embodiment 3) Fig. 3 is a diagram schematically illustrating the configuration of a concentration system 100C according to one embodiment of the present invention. The concentration system 100C according to this embodiment is a multistage concentration system (membrane separation system). Note that Fig. 3 illustrates one reverse osmosis module 4 as the reverse osmosis module and three semipermeable membrane modules 1, 2, and 3 as the multiple semipermeable membrane modules. The multiple semipermeable membrane modules may be any number of semipermeable membrane modules, for example, two or more. Furthermore, although Fig. 3 illustrates one reverse osmosis module (reverse osmosis module 4), multiple reverse osmosis modules may be provided.

[0060] Each of the semipermeable membrane modules 1, 2, 3 has a semipermeable membrane 1A, 2A, 3A, and a first chamber 11, 21, 31 and a second chamber 12, 22, 32 separated by the semipermeable membrane. The reverse osmosis module 4 has a reverse osmosis membrane 4A, and a first front-stage chamber 41 and a second front-stage chamber 42 separated by the reverse osmosis membrane 4A.

[0061] A concentration flow path 5 is provided, which connects the upstream first chamber 41 of the reverse osmosis module 4 and the first chambers 11, 21, and 31 of the multiple semipermeable membrane modules 1, 2, and 3. That is, the concentration flow path 5 consists of the upstream first chamber 41, the first chambers 11, 21, and 31, and a flow path connecting them. In at least some of the reverse osmosis module 4 and the multiple semipermeable membrane modules 1, 2, and 3, the upstream first chamber 41 and the first chambers 11, 21, and 31 are preferably connected in series. In some of the reverse osmosis module 4 and the multiple semipermeable membrane modules 1, 2, and 3, the upstream first chamber 41 and the first chambers 11, 21, and 31 may be connected in parallel.

[0062] A permeate flow path 7 is provided, which is connected to the upstream second chamber 42 of the reverse osmosis module 4. A dilution flow path 6 is also provided, which is connected to the second chambers 12, 22, and 32 of the multiple semipermeable membrane modules 1, 2, and 3. That is, the dilution flow path 6 is composed of the second chambers 12, 22, and 32 and a flow path connecting them. In at least some of the multiple semipermeable membrane modules 1, 2, and 3, the second chambers are preferably connected in series. In some of the multiple semipermeable membrane modules, the second chambers may be connected in parallel.

[0063] The target solution is passed through the concentration flow path 5. The target solution passes through the upstream first chamber 41 of the reverse osmosis module 4, the first chamber 11 of the semipermeable membrane module 1, the first chamber 21 of the semipermeable membrane module 2, and the first chamber 31 of the semipermeable membrane module 3, in this order.

[0064] In the reverse osmosis module 4, the target solution is pressurized at high pressure, causing the solvent (water, etc.) contained in the target solution in the first upstream chamber 41 to migrate through the reverse osmosis membrane 4A into the second upstream chamber 42, and the concentrated target solution is discharged from the first upstream chamber 41, and the permeated liquid is discharged from the second upstream chamber 42.

[0065] An auxiliary solution having osmotic pressure is flowed through the dilution flow path 6. The auxiliary solution is flowed in the order of the second chamber 32 of the semipermeable membrane module 3, the second chamber 22 of the semipermeable membrane module 2, and the second chamber 12 of the semipermeable membrane module 1. That is, the auxiliary solution is flowed in the reverse order of the target solution when the semipermeable membrane modules are connected. However, the auxiliary solution is not limited to the embodiment shown in Fig. 3, and may be flowed in the order of the second chamber 12 of the semipermeable membrane module 1, the second chamber 22 of the semipermeable membrane module 2, and the second chamber 32 of the semipermeable membrane module 3.

[0066] In each semipermeable membrane module, the flow directions on both sides of the semipermeable membrane (in the first and second chambers) may be in any direction, and may be opposite directions (counterflow system) or parallel directions (parallel flow system).

[0067] In each of the multiple semipermeable membrane modules, the target solution has a higher pressure than the auxiliary solution, so that in each of the multiple semipermeable membrane modules, the solvent (water, etc.) contained in the target solution in the first chamber migrates through the semipermeable membrane to the auxiliary solution in the second chamber, and the concentrated solution is discharged from the first chamber and the diluted solution is discharged from the second chamber.

[0068] The target solution has a higher pressure (hydrostatic pressure) than the auxiliary solution, i.e., in each of the multiple semipermeable membrane modules, the liquid in the first chamber (target solution) has a higher pressure than the liquid in the second chamber (auxiliary solution).

[0069] The pressure of the target solution is increased by a pressurizing device or the like. An example of the pressurizing device is a high-pressure pump (not shown) that can pressurize the target solution while feeding it into the first chamber. The pressurizing device may be a device other than a pump, and may be, for example, a device that pressurizes the liquid in the first chamber from outside the semipermeable membrane module.

[0070] The concentration system 100C is provided with a permeate flow meter 72 for measuring the flow rate of the permeate downstream of the permeate flow channel 7. The concentration system 100C is provided with a permeate recovery flow channel 52 for recovering the permeate, a permeate return flow channel 62 for returning a portion of the permeate to the upstream of the concentration flow channel, and a permeate adjuster 82 for adjusting the flow rates of the permeate flowing through the permeate recovery flow channel 52 and the permeate return flow channel 62 so that the measured value of the permeate flow meter 72 falls within a predetermined range.

[0071] The permeate flow meter 72 is provided on the most upstream side of the permeate flow channel 7 (downstream of the first-stage second chamber 42 of the reverse osmosis module 4). The permeate adjuster 82 is provided downstream of the permeate flow meter 72 and is connected to the permeate recovery channel 52 and the permeate return channel 62. The permeate recovery channel 52 and the permeate return channel 62 are connected in such a way that the downstream side of the permeate flow channel 7 branches. The downstream side of the permeate return channel 62 (to which a portion of the concentrate is returned) is not particularly limited, and may be connected to the most upstream side of the concentration channel 5 (i.e., upstream of the first-stage first chamber 41 of the reverse osmosis module 4) as shown in FIG. 3, for example, or may be connected to a connection portion of the concentration channels 5 that connect multiple semipermeable membrane modules. The permeate return channel 62 may also be further branched and adjusted so that a desired amount is distributed to the concentration channels 5 of each semipermeable membrane module.

[0072] Here, the permeate adjuster 82 adjusts the amount of permeate discharged to the permeate recovery channel 52 and the amount of permeate supplied to the permeate return channel 62 so that the measured value of the permeate flow meter 72 falls within a predetermined range, thereby adjusting the flow rate of the target solution (the liquid flowing in the permeate channel 7). For example, if the measured value of the permeate flow meter 72 is lower than the predetermined range (lower limit flow rate), it is determined that the target solution is not sufficiently concentrated, and the permeate adjuster 82 reduces the amount of permeate discharged to the permeate recovery channel 52 and increases the amount of permeate supplied to the permeate return channel 62.

[0073] On the other hand, if the measured value of the permeate flow meter 72 is higher than the predetermined range (upper flow rate), it is determined that the target solution is sufficiently concentrated, and the permeate regulator 82 increases the amount of permeate discharged to the permeate recovery channel 52 and decreases the amount of permeate supplied to the permeate return channel 62. This allows the flow rate of the permeate to be returned to within the predetermined range. For example, if the permeate regulator 82 is a switching valve, the switching valve may be switched so that the permeate is supplied only to the permeate return channel 62 or only to the permeate recovery channel 52.

[0074] Here, the concentrated liquid regulator 81 and the permeate liquid regulator 82 may be a switch such as a selector valve or a flow rate regulator such as a flow rate control valve. The adjustments by the concentrated liquid regulator 81 and the permeate liquid regulator 82 may be automated by a control device or the like. In this case, the concentrated liquid regulator 81 and the permeate liquid regulator 82 are electrically connected to, for example, the concentrated liquid flow meter 71 and the permeate liquid flow meter 72 and a control device (not shown).

[0075] (Embodiment 4) Fig. 4 is a diagram schematically illustrating the configuration of a concentration system 100D according to another embodiment of the present invention. The concentration system 100D is a multistage concentration system (membrane separation system). Note that Fig. 4 illustrates one reverse osmosis module 4 as the reverse osmosis module and three semipermeable membrane modules 1, 2, and 3 as the multiple semipermeable membrane modules. The multiple semipermeable membrane modules may be any number of semipermeable membrane modules, for example, two or more. Furthermore, although Fig. 4 illustrates one reverse osmosis module (reverse osmosis module 4), multiple (n) reverse osmosis modules may be provided.

[0076] Each of the semipermeable membrane modules 1, 2, 3 has a semipermeable membrane 1A, 2A, 3A, and a first chamber 11, 21, 31 and a second chamber 12, 22, 32 separated by the semipermeable membrane. The reverse osmosis module 4 has a reverse osmosis membrane 4A, and a first front-stage chamber 41 and a second front-stage chamber 42 separated by the reverse osmosis membrane 4A.

[0077] A concentration flow path 5 is provided, which connects the upstream first chamber 41 of the reverse osmosis module 4 and the first chambers 11, 21, and 31 of the multiple semipermeable membrane modules 1, 2, and 3. That is, the concentration flow path 5 consists of the upstream first chamber 41, the first chambers 11, 21, and 31, and a flow path connecting them. In at least some of the reverse osmosis module 4 and the multiple semipermeable membrane modules 1, 2, and 3, the upstream first chamber 41 and the first chambers 11, 21, and 31 are preferably connected in series. In some of the reverse osmosis module 4 and the multiple semipermeable membrane modules 1, 2, and 3, the upstream first chamber 41 and the first chambers 11, 21, and 31 may be connected in parallel.

[0078] A permeate flow path 7 is provided, which is connected to the upstream second chamber 42 of the reverse osmosis module 4. A dilution flow path 6 is also provided, which is connected to the second chambers 12, 22, and 32 of the multiple semipermeable membrane modules 1, 2, and 3. That is, the dilution flow path 6 is composed of the second chambers 12, 22, and 32 and a flow path connecting them. In at least some of the multiple semipermeable membrane modules 1, 2, and 3, the second chambers are preferably connected in series. In some of the multiple semipermeable membrane modules, the second chambers may be connected in parallel.

[0079] The target solution is passed through the concentration flow path 5. The target solution passes through the upstream first chamber 41 of the reverse osmosis module 4, the first chamber 11 of the semipermeable membrane module 1, the first chamber 21 of the semipermeable membrane module 2, and the first chamber 31 of the semipermeable membrane module 3, in this order.

[0080] In the reverse osmosis module 4, the target solution is pressurized at high pressure, causing the solvent (water, etc.) contained in the target solution in the first upstream chamber 41 to migrate through the reverse osmosis membrane 4A into the second upstream chamber 42, and the concentrated target solution is discharged from the first upstream chamber 41, and the permeated liquid is discharged from the second upstream chamber 42.

[0081] An auxiliary solution having osmotic pressure is flowed through the dilution flow path 6. The auxiliary solution is flowed in the order of the second chamber 32 of the semipermeable membrane module 3, the second chamber 22 of the semipermeable membrane module 2, and the second chamber 12 of the semipermeable membrane module 1. That is, the auxiliary solution is flowed in the reverse order of the target solution when the semipermeable membrane modules are connected. However, the auxiliary solution is not limited to the embodiment shown in Fig. 4, and may be flowed in the order of the second chamber 12 of the semipermeable membrane module 1, the second chamber 22 of the semipermeable membrane module 2, and the second chamber 32 of the semipermeable membrane module 3.

[0082] In each semipermeable membrane module, the flow directions on both sides of the semipermeable membrane (in the first and second chambers) may be in any direction, and may be opposite directions (counterflow system) or parallel directions (parallel flow system).

[0083] In each of the multiple semipermeable membrane modules, the target solution has a higher pressure than the auxiliary solution, so that in each of the multiple semipermeable membrane modules, the solvent (water, etc.) contained in the target solution in the first chamber migrates through the semipermeable membrane to the auxiliary solution in the second chamber, and the concentrated solution is discharged from the first chamber and the diluted solution is discharged from the second chamber.

[0084] The target solution has a higher pressure (hydrostatic pressure) than the auxiliary solution, i.e., in each of the multiple semipermeable membrane modules, the liquid in the first chamber (target solution) has a higher pressure than the liquid in the second chamber (auxiliary solution).

[0085] The pressure of the target solution is increased by a pressurizing device or the like. An example of the pressurizing device is a high-pressure pump (not shown) that can pressurize the target solution while feeding it into the first chamber. The pressurizing device may be a device other than a pump, and may be, for example, a device that pressurizes the liquid in the first chamber from outside the semipermeable membrane module.

[0086] The concentration system 100D is equipped with a concentrate flow meter 71 downstream of the concentration flow path 5 for measuring the flow rate of the concentrate. The concentration system 100B is equipped with a concentrate recovery flow path 51 for recovering the concentrate, a concentrate return flow path 61 for returning a portion of the concentrate to the upstream of the concentration flow path 5, and a concentrate regulator 81 for adjusting the flow rate of the concentrate, downstream of the concentrate flow meter 71. The concentration system 100B is equipped with a permeate flow meter 72 downstream of the permeate flow path 7 for measuring the flow rate of the permeate. The concentration system 100B is equipped with a permeate recovery flow path 52 for recovering the permeate, a permeate return flow path 62 for returning a portion of the permeate to the upstream of the concentration flow path, downstream of the permeate flow meter 72, and a permeate regulator 82 for adjusting the flow rates of the permeate flowed through the permeate recovery flow path 52 and the permeate return flow path 62 so that the measurement value of the permeate flow meter 72 falls within a predetermined range.

[0087] The concentrate flow meter 71 is provided on the most upstream side of the concentration flow path 5 (downstream of the first chamber 31 of the semipermeable membrane module 3). The concentrate adjuster 81 is provided downstream of the concentrate flow meter 71 and connected to the concentrate recovery flow path 51 and the concentrate return flow path 61. The concentrate recovery flow path 51 and the concentrate return flow path 61 are connected in a manner such that the downstream side of the concentration flow path 5 branches. The downstream side of the concentrate return flow path 61 (to which a portion of the concentrate is returned) is not particularly limited, and may be configured to be connected to the most upstream side of the concentration flow path 5 (i.e., upstream of the first chamber 11 of the semipermeable membrane module 1), as shown in FIG. 4, for example, or may be configured to be connected to a connection portion of the concentration flow paths 5 that connect multiple semipermeable membrane modules together. In addition, the concentrate return flow path 61 may be further branched and configured to be adjusted so that a desired amount is distributed to the concentration flow paths 5 of each semipermeable membrane module.

[0088] The permeate flow meter 72 is provided on the most upstream side of the permeate flow channel 7 (downstream of the first-stage second chamber 42 of the reverse osmosis module 4). The permeate adjuster 82 is provided downstream of the permeate flow meter 72 and is connected to the permeate recovery channel 52 and the permeate return channel 62. The permeate recovery channel 52 and the permeate return channel 62 are connected in such a way that the downstream side of the permeate flow channel 7 branches. The downstream side of the permeate return channel 62 (to which a portion of the concentrate is returned) is not particularly limited, and may be connected to the most upstream side of the concentration channel 5 (i.e., upstream of the first-stage first chamber 41 of the reverse osmosis module 4) as shown in FIG. 4, for example, or may be connected to a connection portion of the concentration channels 5 that connect multiple semipermeable membrane modules. The permeate return channel 62 may also be further branched and adjusted so that a desired amount is distributed to the concentration channels 5 of each semipermeable membrane module.

[0089] Here, the concentrated liquid adjuster 81 adjusts the amount of concentrated liquid discharged into the concentrated liquid recovery channel 51 and the amount of concentrated liquid supplied to the concentrated liquid return channel 61 so that the measured value of the concentrated liquid flow meter 71 falls within a predetermined range, thereby adjusting the flow rate of the target solution (liquid flowing in the concentration channel 5). For example, if the measured value of the concentrated liquid flow meter 71 is lower than the predetermined range (lower limit flow rate), it is determined that the target solution is sufficiently concentrated, and the concentrated liquid adjuster 81 increases the amount of concentrated liquid discharged into the concentrated liquid recovery channel 51 and decreases the amount of concentrated liquid supplied to the concentrated liquid return channel 61.

[0090] On the other hand, if the measured value of the concentrated liquid flow meter 71 is higher than the predetermined range (upper flow rate), it is determined that the target solution is not sufficiently concentrated, and the concentrated liquid adjuster 81 reduces the amount of concentrated liquid discharged to the concentrated liquid recovery line 51 and increases the amount of concentrated liquid supplied to the concentrated liquid return line 61. This allows the flow rate of the concentrated liquid to be returned to the predetermined range. For example, if the concentrated liquid adjuster 81 is a switching valve, the switching valve may be switched so that the concentrated liquid is supplied only to the concentrated liquid return line 61 or only to the concentrated liquid recovery line 51.

[0091] Furthermore, the permeate adjuster 82 adjusts the amount of permeate discharged to the permeate recovery channel 52 and the amount of permeate supplied to the permeate return channel 62 so that the measured value of the permeate flow meter 72 falls within a predetermined range, thereby adjusting the flow rate of the target solution (the liquid flowing in the permeate channel 7). For example, if the measured value of the permeate flow meter 72 is lower than the predetermined range (lower limit flow rate), it is determined that the target solution is not sufficiently concentrated, and the permeate adjuster 82 reduces the amount of permeate discharged to the permeate recovery channel 52 and increases the amount of permeate supplied to the permeate return channel 62.

[0092] On the other hand, if the measured value of the permeate flow meter 72 is higher than the predetermined range (upper flow rate), it is determined that the target solution is sufficiently concentrated, and the permeate regulator 82 increases the amount of permeate discharged to the permeate recovery channel 52 and decreases the amount of permeate supplied to the permeate return channel 62. This allows the flow rate of the permeate to be returned to within the predetermined range. For example, if the permeate regulator 82 is a switching valve, the switching valve may be switched so that the permeate is supplied only to the permeate return channel 62 or only to the permeate recovery channel 52.

[0093] Here, the concentrated liquid regulator 81 and the permeate liquid regulator 82 may be a switch such as a selector valve or a flow rate regulator such as a flow rate control valve. The adjustments by the concentrated liquid regulator 81 and the permeate liquid regulator 82 may be automated by a control device or the like. In this case, the concentrated liquid regulator 81 and the permeate liquid regulator 82 are electrically connected to, for example, the concentrated liquid flow meter 71 and the permeate liquid flow meter 72 and a control device (not shown).

[0094] In the first to fourth embodiments, from the viewpoint of ease of control and accuracy, flow meters such as the concentrate flow meter 71 and the permeate flow meter 72 are used. However, a concentration meter or a pressure meter may be used instead of the flow meters to perform similar control.

[0095] According to the concentration system of the present embodiment shown in FIGS. 1 to 4, a predetermined amount of concentrated liquid can be stably obtained when a solvent is separated from a target solution and concentrated by the OARO method or the BC method using a multistage concentration system (membrane separation system) including a plurality of semipermeable membrane modules.

[0096] (Target Solution and Auxiliary Solution) The target solution and auxiliary solution are not particularly limited, and examples thereof include salt water (brine, seawater, brackish water, etc.), industrial wastewater, etc. The concentration system described above can be suitably used to further concentrate a target solution, particularly when the target solution is a highly concentrated (high osmotic pressure) solution such as brine.

[0097] The target solution or the like may be subjected to pretreatment to remove fine particles, microorganisms, scale components, etc. contained in the solution. As the pretreatment, various known pretreatments used in seawater desalination technology or the like can be carried out, and examples thereof include filtration using an NF membrane, UF membrane, MF membrane, etc., addition of sodium hypochlorite, addition of a coagulant, activated carbon adsorption treatment, ion exchange resin treatment, etc. Such pretreatment is preferably carried out before the target solution and auxiliary solution are supplied to the semipermeable membrane module.

[0098] Theoretically, membrane separation by the BC method is possible if the osmotic pressure difference (absolute value) between the target solution (liquid to be concentrated) flowing through the first chamber (high-pressure side) and the auxiliary solution (liquid to be diluted) flowing through the second chamber (low-pressure side) is smaller than the pressure of the target solution. In this case, it is preferable that the difference between the osmotic pressures of the target solution and the auxiliary solution be 30% or less of the pressure of the target solution.

[0099] The auxiliary solution is not particularly limited as long as it is a liquid having osmotic pressure. However, a portion of the target solution (concentrate) concentrated in the concentration flow paths of multiple semipermeable membrane modules may be used as the auxiliary solution in multiple semipermeable membrane modules. For example, in FIG. 1 , a portion of the target solution discharged from at least one of the first chambers 11, 21, and 31 of multiple semipermeable membrane modules 1, 2, and 3 may be used as the auxiliary solution. Also, in FIG. 2 , a portion of the target solution discharged from at least one of the first chambers 11, 21, and 31 of multiple semipermeable membrane modules 1, 2, and 3 and the first chamber 41 of the reverse osmosis module 4 may be used as the auxiliary solution. It is preferable that a mechanism (not shown) for reducing the pressure of the liquid be provided in the flow path for supplying a portion of the concentrate as the auxiliary solution to the dilution flow path (the second chamber of the semipermeable membrane module). Examples of such a mechanism include a device, such as an automatic control valve, that maintains high pressure upstream and reduces pressure downstream, and an energy recovery device that has a mechanism for converting energy recovered from a pressurized supply liquid into auxiliary energy for driving a pump or the like.

[0100] Alternatively, a dilute solution may be supplied to the concentration flow path together with the target solution. The target solution may then be concentrated to obtain a concentrate, which may then be used as an auxiliary solution, and the auxiliary solution may be diluted to obtain a dilute solution, which may then be supplied to the concentration flow path together with the target solution.

[0101] In this way, when the target solution is circulated in the concentration system, the recovery rate of the concentrated liquid (target component) from the target solution can be increased.

[0102] In addition, when the diluent and the target solution are combined in a tank and the resulting combined solution is supplied to the concentration flow path, the liquids of different concentrations mix together in the tank, creating a concentration gradient in the tank, which can cause the concentration of the liquid supplied to the concentration flow path to become unstable. For this reason, it is preferable that the diluent and the target solution are thoroughly mixed in the tank. Here, for example, by returning a portion of the liquid sent from the pump to the tank to stir the liquid in the tank, the diluent and the target solution can be thoroughly mixed without the need for a separate stirring device.

[0103] Furthermore, a temperature regulator such as a heat exchanger may be provided to ensure a stable temperature when the temperature of the target solution rises due to heat generated by the pump or when the temperature of the target solution itself becomes high or low. In particular, when the target solution circulates through a concentration system, the liquid temperature may gradually rise and exceed the heat resistance temperature of the semipermeable membrane, or in the case of a target solution whose viscosity changes significantly depending on the liquid temperature, the amount of permeate water and the amount of auxiliary solution passing through may be affected, and the desired concentration performance may not be achieved. For this reason, it is particularly important to provide a temperature regulator in a concentration system in which the target solution circulates.

[0104] (Multiple Semipermeable Membrane Modules) In a concentration process (membrane separation process) by the OARO method or the BC method using multiple semipermeable membrane modules, osmotic pressure acting in the opposite direction to the direction in which the solvent moves from the first chamber to the second chamber is unlikely to occur, so concentration can be carried out at a lower pressure (pump pressure) than in the RO method. Therefore, in the concentration system of this embodiment, which mainly performs concentration by the OARO method, the power consumption of pumps, etc. can be reduced, and the energy efficiency of concentration can be improved.

[0105] In RO concentration, the osmotic pressure of the concentrated target solution on one side of the semipermeable membrane is generated in the opposite direction to the pump pressure. Therefore, when the osmotic pressure of the concentrated target solution reaches the pump pressure, the pump pressure and the osmotic pressure of the target solution acting in the opposite direction are balanced, preventing further water from passing through the semipermeable membrane and preventing concentration.

[0106] In contrast, in membrane separation treatment (concentration method) using the OARO method or the BC method, the difference in concentration (osmotic pressure difference) between the liquids supplied to the first and second compartments in each semipermeable membrane module is small, and the osmotic pressure that inhibits concentration treatment as in the RO method is unlikely to occur. Therefore, in a concentration system using the OARO method or the BC method, the final concentration of the target solution can be increased more than in a concentration system using only the RO method. In principle, it is thought that the target solution can be concentrated to a saturated concentration.

[0107] In this embodiment, as in the multistage concentration systems shown in FIG. 2 of Patent Document 1 (WO 2018 / 084246) and FIG. 4 of Patent Document 2 (JP 2019-188330 A), one or more other semipermeable membrane modules may be further connected in parallel to each of a plurality of semipermeable membrane modules 1a, 1b, 1x, and 1y connected in series.

[0108] As shown in FIG. 2 of Patent Document 1 and FIG. 4 of Patent Document 2, it is preferable to have a larger number of semipermeable membrane modules connected in parallel toward the upstream side of the concentration flow path (downstream side of the dilution flow path). In this case, it is thought that the cross-sectional area of ​​the flow path increases downstream of the dilution flow path, reducing the flow resistance. Because water migrates from the first chamber (concentration flow path side) to the second chamber (dilution flow path side) through a semipermeable membrane, the amount of flow increases toward the downstream side of the dilution flow path, and the flow resistance tends to increase. Therefore, reducing the flow resistance downstream of the dilution flow path is effective in reducing the flow resistance of the dilution flow path throughout the entire concentration system.

[0109] Furthermore, in a multistage concentration system such as that of this embodiment, the target solution flowing through the first chamber (concentration flow path) is sequentially concentrated, and as the concentration progresses, the flow rate of the target solution decreases. If the flow rate per semipermeable membrane module decreases, the concentration efficiency decreases. In order to suppress such a decrease in the flow rate of the target solution downstream of the concentration flow path, it is preferable that the number of semipermeable membrane modules connected in parallel is greater upstream of the concentration flow path.

[0110] Furthermore, in the concentration system of this embodiment, the configuration disclosed in Japanese Patent No. 7020512 can be applied.

[0111] (Semipermeable Membrane) Examples of the semipermeable membrane used in this embodiment include semipermeable membranes called reverse osmosis membranes (RO membranes), forward osmosis membranes (FO membranes), nanofiltration membranes (NF membranes), and ultrafiltration membranes (UF membranes). The semipermeable membrane is preferably a reverse osmosis membrane, a forward osmosis membrane, or a nanofiltration membrane. When a reverse osmosis membrane, a forward osmosis membrane, or a nanofiltration membrane is used as the semipermeable membrane, the pressure of the liquid (target solution) in the first chamber is preferably 0.5 to 10.0 MPa.

[0112] Typically, RO membranes and FO membranes have pore sizes of approximately 2 nm or less, and UF membranes have pore sizes of approximately 2 to 100 nm. NF membranes have a relatively low rejection rate for ions and salts compared to RO membranes, and typically have pore sizes of approximately 1 to 2 nm. When an RO membrane, FO membrane, or NF membrane is used as the semipermeable membrane, the salt rejection rate of the RO membrane, FO membrane, or NF membrane is preferably 90% or higher.

[0113] The material constituting the semipermeable membrane is not particularly limited, but examples thereof include cellulose-based resins, polysulfone-based resins, polyamide-based resins, etc. The semipermeable membrane is preferably made of a material containing at least one of a cellulose-based resin and a polysulfone-based resin.

[0114] The cellulose-based resin is preferably a cellulose acetate-based resin. Cellulose acetate-based resins are resistant to chlorine, a disinfectant, and have the characteristic of being able to inhibit the growth of microorganisms. The cellulose acetate-based resin is preferably cellulose acetate, and from the viewpoint of durability, more preferably cellulose triacetate.

[0115] The polysulfone-based resin is preferably a polyethersulfone-based resin. The polyethersulfone-based resin is preferably a sulfonated polyethersulfone.

[0116] 1 to 4, the semipermeable membranes of the semipermeable membrane modules are depicted as flat membranes for simplification, but the shape of the semipermeable membrane is not particularly limited. The semipermeable membrane may be, for example, a flat membrane such as a spiral membrane (spiral-type semipermeable membrane) or a hollow fiber membrane (hollow fiber-type semipermeable membrane), but is preferably a hollow fiber membrane. Hollow fiber membranes are advantageous in that they have a smaller membrane thickness than flat membranes and can further increase the membrane area per module, thereby increasing the permeation efficiency.

[0117] In each of the multiple semipermeable membrane modules, it is preferable that the first chamber is outside the hollow fiber membrane and the second chamber is inside (hollow portion) of the hollow fiber membrane, because even if the solution flowing inside the hollow fiber membrane is pressurized, the pressure loss may become large and it may be difficult to apply pressure sufficiently, and further, although hollow fiber membranes generally easily maintain their structure against external pressure, high internal pressure may damage the hollow fiber membrane.

[0118] A specific example of a hollow fiber membrane is a membrane with a single layer structure composed entirely of a cellulose-based resin. However, the single layer structure referred to here does not necessarily mean a membrane with a uniform layer throughout; for example, it may be a membrane that is non-uniform in the thickness direction. Specifically, the membrane may have a dense layer on the outer surface, which serves as a separation active layer that essentially determines the pore size of the hollow fiber membrane, and the inner surface side may have a lower density than the dense layer. Since the dense layer essentially serves as a separation active layer that determines the pore size of the hollow fiber membrane, when the solution outside the hollow fiber membrane is pressurized, having a dense layer on the outer surface of the hollow fiber membrane allows for more accurate control of the movement of molecules from the outside to the inside of the hollow fiber membrane.

[0119] Another specific example of a hollow fiber membrane is a two-layer membrane having a dense layer of a polyphenylene resin (e.g., sulfonated polyethersulfone) on the outer surface of a support layer (e.g., a layer made of polyphenylene oxide). Another example is a two-layer membrane having a dense layer of a polyamide resin on the outer surface of a support layer (e.g., a layer made of polysulfone or polyethersulfone).

[0120] The above-disclosed embodiments, modifications, and examples are all illustrative and not restrictive. Furthermore, appropriate combinations of the embodiments, modifications, and examples are also included within the scope of the present invention. In other words, the technical scope of the present invention is defined by the claims, and includes all changes, modifications, substitutions, etc. within the meaning and scope of the claims.

[0121] The present invention achieves stable production of a concentrated solution of a predetermined concentration when separating and concentrating a solvent from a target solution by the OARO method or the BC method using a multistage concentration system (membrane separation system) including multiple semipermeable membrane modules, thereby making a significant contribution to the industrial world.

[0122] 1, 2, 3 Semipermeable membrane module, 1A, 2A, 3A Semipermeable membrane, 4 Reverse osmosis module, 4A Reverse osmosis membrane, 5 Concentration flow path, 6 Dilution flow path, 7 Permeation flow path, 11, 21, 31 First chamber, 12, 22, 32 Second chamber, 41 Pre-stage first chamber, 42 Pre-stage second chamber, 51 Concentrate recovery flow path, 52 Permeate recovery flow path, 61 Concentrate return flow path, 62 Permeate return flow path, 71 Concentrate flow meter, 72 Permeate flow meter, 81 Concentrate regulator, 82 Permeate regulator, 100A, 100B, 100C, 100D Concentration system.

Claims

1. A concentration system for obtaining a concentrated solution in which a target component is concentrated by separating a solvent from a target solution containing the target component, the concentration system comprising a plurality of semipermeable membrane modules, each of the plurality of semipermeable membrane modules having a semipermeable membrane and a first chamber and a second chamber separated by the semipermeable membrane, a concentration flow path connected to the first chambers of the plurality of semipermeable membrane modules, and a dilution flow path connected to the second chambers of the plurality of semipermeable membrane modules, the target solution is flowed through the concentration flow path, and an auxiliary solution having osmotic pressure is flowed through the dilution flow path, a concentrate flow meter for measuring the flow rate of the concentrate is provided downstream of the concentration flow path, and a concentrate recovery flow path for recovering the concentrate, and a concentrate return flow path for returning the concentrate to the upstream of the concentration flow path, all downstream of the concentrate flow meter, and a concentrate adjuster for adjusting the flow rates of the concentrate flowed through the concentrate recovery flow path and the concentrate return flow path so that the measured value of the concentrate flow meter is within a predetermined range.

2. A reverse osmosis module is provided upstream of the plurality of semipermeable membrane modules, the reverse osmosis module having a reverse osmosis membrane and a first and second upstream chambers separated by the reverse osmosis membrane, the first upstream chamber is connected to the first chamber of the semipermeable membrane module located most upstream of the plurality of semipermeable membrane modules to form the concentration flow path, the solvent contained in the target solution supplied to the first upstream chamber at a pressure higher than that of the second upstream chamber migrates through the semipermeable membrane into the second upstream chamber, and the target solution is diluted to obtain a permeate, a permeate flow path is provided for discharging the permeate, and a permeate flow meter is provided downstream of the permeate flow path for measuring the flow rate of the permeate, 2. The concentration system according to claim 1, further comprising: a permeate recovery flow path downstream of the permeate flow meter for recovering the permeate; a permeate return flow path for returning the permeate to the upstream of the concentration flow path; and a permeate adjuster for adjusting the flow rate of the permeate flowing through the permeate recovery flow path and the permeate return flow path so that the measurement value of the permeate flow meter falls within a predetermined range.

3. The concentration system of claim 2, comprising a plurality of reverse osmosis modules.

4. The concentration system according to any one of claims 1 to 3, wherein the semipermeable membrane is a hollow fiber membrane.

5. The concentration system according to claim 2 or 3, wherein the reverse osmosis membrane is a hollow fiber membrane.

6. A concentration system for separating a solvent from a target solution containing a target component to obtain a concentrated solution in which the target component is concentrated, comprising: a reverse osmosis module and a plurality of semipermeable membrane modules; the reverse osmosis module has a reverse osmosis membrane and a first and a second upstream chamber separated by the reverse osmosis membrane; each of the plurality of semipermeable membrane modules has a semipermeable membrane and a first and a second chamber separated by the semipermeable membrane; a concentration flow path is provided connecting the first upstream chamber of the reverse osmosis module to the first chambers of the plurality of semipermeable membrane modules; and a dilution flow path is provided connecting the second chambers of the plurality of semipermeable membrane modules; the target solution is flowed through the concentration flow path; an auxiliary solution having an osmotic pressure is flowed through the dilution flow path; the solvent contained in the target solution, which is supplied to the first upstream chamber at a pressure higher than that of the second upstream chamber, migrates through the semipermeable membrane into the second upstream chamber, and the target solution is diluted to obtain a permeate; a permeate flow path through which the permeate flows, a permeate recovery flow path for recovering the permeate, and a permeate return flow path for returning the permeate to the upstream of the concentration flow path; a permeate flow meter downstream of the permeate flow path for measuring the flow rate of the permeate; and a permeate adjuster downstream of the permeate flow meter for adjusting the flow rate of the permeate flowing in the permeate recovery flow path and the permeate return flow path so that the measured value of the permeate flow meter falls within a predetermined range.

7. The concentration system according to claim 6, further comprising: a concentrate flow meter downstream of the concentration flow path for measuring the flow rate of the concentrate; a concentrate recovery flow path downstream of the concentrate flow meter for recovering the concentrate; a concentrate return flow path for returning the concentrate upstream of the concentration flow path; and a concentrate adjuster for adjusting the flow rate of the concentrate flowing through the concentrate recovery flow path and the concentrate return flow path so that the measurement value of the concentrate flow meter falls within a predetermined range.

8. The concentration system of claim 6 or 7, comprising a plurality of reverse osmosis modules.

9. The concentration system according to any one of claims 6 to 8, wherein the semipermeable membrane and the reverse osmosis membrane are hollow fiber membranes.

10. A concentration system according to any one of claims 1 to 9, wherein a portion of the concentrate is used as the auxiliary solution.

11. The concentration system of any one of claims 1 to 10, comprising a pressurizing device for pressurizing the target solution to a higher pressure than the auxiliary solution.

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