Method and apparatus for membrane treatment of solution

Abstract

To provide a solution membrane treatment device which can increase the concentration of a solution with good efficiency.SOLUTION: A solution membrane treatment device 1-1 comprises a membrane concentrator 20 that brings a first solution into contact with a second solution with a pressure lower than the first solution via a semi-permeable membrane 21 to concentrate the same, and further comprises a second solution heater 30 for heating the second solution. The solution membrane treatment device 1-1 uses at least a part of the first solution before concentration or after concentration by the membrane concentrator 20 as the second solution, makes a temperature of the second solution higher than a temperature of the first solution by the second solution heater 30, and performs membrane treatment by the membrane concentrator 20.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method and apparatus for membrane treatment of a solution. [Background technology]

[0002] As an apparatus for membrane treatment of a solution such as seawater, Patent Document 1 discloses a fresh water production system in which seawater is supplied to a first reverse osmosis membrane module to separate fresh water and discharge concentrated salt water, while low osmotic pressure water is supplied to a second reverse osmosis membrane module to separate fresh water and discharge concentrated low osmotic pressure water, and the discharged concentrated salt water and concentrated low osmotic pressure water are supplied to a forward osmosis membrane module, where the concentrated salt water is diluted with water supplied from the concentrated low osmotic pressure water via the forward osmosis membrane. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2017-176929 Summary of the Invention [Problem to be solved by the invention]

[0004] The main purpose of the above-mentioned freshwater production system is to increase the amount of freshwater produced, and since it is configured to dilute concentrated seawater produced in the first reverse osmosis membrane module in the forward osmosis membrane module, there was room for consideration in increasing the concentration rate when concentrating the solution.

[0005] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a method and apparatus for membrane treatment of a solution that can efficiently achieve high concentration of the solution. [Means for solving the problem]

[0006] The object of the present invention is achieved by a membrane treatment method for a solution, which includes a membrane concentration step of concentrating a first solution by contacting the first solution with a second solution at a lower pressure than the first solution via a semipermeable membrane, and further includes a second solution heating step of heating the second solution, in which at least a part of the first solution before or after concentration in the membrane concentration step is used as the second solution, and the second solution heating step is used to raise the temperature of the second solution higher than the temperature of the first solution to perform the membrane concentration step.

[0007] It is preferable that this membrane treatment method for a solution further includes an RO membrane water passing step in which the first solution is pressurized and passed through a reverse osmosis membrane to concentrate it, and it is preferable that the membrane concentration step further concentrates the first solution concentrated in the RO membrane water passing step.

[0008] In the membrane treatment method for a solution including the RO membrane water passing step, the membrane concentration step can heat at least a portion of the first solution concentrated in the membrane concentration step as the second solution in the second solution heating step. In this case, the method can further include an NF membrane water passing step in which the first solution is passed through a nanofiltration membrane, and the RO membrane water passing step can concentrate at least a portion of the first solution that has permeated the nanofiltration membrane in the NF membrane water passing step. Alternatively, the membrane concentration step can heat at least a portion of the first solution before the RO membrane water passing step as the second solution in the second solution heating step.

[0009] In addition, the membrane concentration step can be performed by arranging a plurality of membrane concentration devices each equipped with the semipermeable membrane, supplying the first solution to each of the membrane concentration devices in series, and supplying the second solution in series or in parallel, and the second solution heating step can be performed by heating the second solution supplied to at least any of the membrane concentration devices.

[0010] The method may further include an NF membrane water passing step of passing the first solution through a nanofiltration membrane, and at least a portion of the first solution that has permeated the nanofiltration membrane in the NF membrane water passing step can be used as the second solution and heated in the second solution heating step.

[0011] In the membrane concentration step, the first solution from which the second solution is branched can be cooled before concentration, and brought into contact with the second solution via a semipermeable membrane.

[0012] The above-mentioned object of the present invention can also be achieved by a membrane treatment device for a solution, which includes a membrane concentration device that concentrates a first solution by contacting it with a second solution having a lower pressure than the first solution via a semipermeable membrane, and further includes a second solution heating device that heats the second solution, and at least a part of the first solution before or after concentration by the membrane concentration device is used as the second solution, and the temperature of the second solution is raised by the second solution heating device to a temperature higher than the temperature of the first solution, thereby performing membrane concentration by the membrane concentration device. [Effects of the Invention]

[0013] According to the present invention, it is possible to provide a membrane treatment method and apparatus for a solution that can efficiently perform high concentration of the solution. [Brief explanation of the drawings]

[0014] [Figure 1] 1 is a diagram illustrating the principle of a film treatment device for a solution according to the present invention. [Figure 2] FIG. 2 is another principle diagram of the film treatment device for a solution according to the present invention. [Figure 3] 1 is a schematic configuration diagram of a film treatment apparatus for a solution according to an embodiment of the present invention. [Figure 4] FIG. 10 is a schematic configuration diagram of a film treatment apparatus for a solution according to another embodiment of the present invention. [Figure 5] FIG. 10 is a schematic configuration diagram of a film treatment apparatus for a solution according to still another embodiment of the present invention. [Figure 6] FIG. 10 is a schematic configuration diagram of a film treatment apparatus for a solution according to still another embodiment of the present invention. [Figure 7] FIG. 10 is a schematic configuration diagram of a film treatment apparatus for a solution according to still another embodiment of the present invention. [Figure 8] FIG. 10 is a schematic configuration diagram of a film treatment apparatus for a solution according to still another embodiment of the present invention. [Figure 9] FIG. 10 is a schematic configuration diagram of a film treatment apparatus for a solution according to still another embodiment of the present invention. [Figure 10] FIG. 10 is a schematic configuration diagram of a film treatment apparatus for a solution according to still another embodiment of the present invention. [Figure 11] FIG. 10 is a schematic configuration diagram of a film treatment apparatus for a solution according to still another embodiment of the present invention. [Figure 12] FIG. 10 is a schematic configuration diagram of a film treatment apparatus for a solution according to still another embodiment of the present invention. [Figure 13] FIG. 10 is a schematic configuration diagram of a film treatment apparatus for a solution according to still another embodiment of the present invention. [Figure 14] FIG. 10 is a schematic configuration diagram of a film treatment apparatus for a solution according to still another embodiment of the present invention. [Figure 15] FIG. 10 is a schematic configuration diagram of a film treatment apparatus for a solution according to still another embodiment of the present invention. [Figure 16] FIG. 10 is a schematic configuration diagram of a film treatment apparatus for a solution according to still another embodiment of the present invention. [Figure 17] FIG. 10 is a schematic configuration diagram of a film treatment apparatus for a solution according to still another embodiment of the present invention. [Figure 18] FIG. 10 is a schematic configuration diagram of a film treatment apparatus for a solution according to still another embodiment of the present invention. [Figure 19] FIG. 10 is a schematic configuration diagram of a film treatment apparatus for a solution according to still another embodiment of the present invention. [Figure 20] FIG. 10 is a schematic configuration diagram of a film treatment apparatus for a solution according to still another embodiment of the present invention. [Figure 21] FIG. 10 is a schematic configuration diagram of a film treatment apparatus for a solution according to still another embodiment of the present invention. [Figure 22] FIG. 10 is a schematic configuration diagram of a film treatment apparatus for a solution according to still another embodiment of the present invention. [Figure 23] FIG. 10 is a schematic configuration diagram of a film treatment apparatus for a solution according to still another embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0015] 1 is a diagram illustrating the principle of a membrane treatment device for a solution according to the present invention (hereinafter simply referred to as "membrane treatment device"). The membrane treatment device 1-1 shown in FIG. 1 includes a membrane concentration device 20 and a second solution heating device 30.

[0016] In the membrane concentration device 20, a high-pressure chamber 22 and a low-pressure chamber 23 are formed by dividing the interior of the chamber with a semipermeable membrane 21. A first solution is introduced into the high-pressure chamber 22, while a second solution having a lower pressure than the first solution is introduced into the low-pressure chamber 23. The first solution and the second solution introduced into the high-pressure chamber 22 and the low-pressure chamber 23, respectively, come into contact with each other via the semipermeable membrane 21 and are then discharged to the outside. At least a portion of the first solution that has passed through the membrane concentration device 20 is used as the second solution. The second solution heating device 30 heats the second solution. The heated second solution is supplied to the low-pressure chamber 23 at a temperature higher than that of the first solution supplied to the high-pressure chamber 22.

[0017] In the membrane concentration device 20, a membrane concentration step is performed in which the pressure in the high-pressure chamber 22 is made higher than the pressure in the low-pressure chamber 23, thereby moving water from the high-pressure chamber 22 to the low-pressure chamber 23 through the semipermeable membrane 21 and concentrating the first solution passing through the high-pressure chamber 22. In this membrane concentration step, if the first solution supplied to the high-pressure chamber 22 becomes highly concentrated, concentration polarization increases, which may result in a decrease in water flux.

[0018] The membrane treatment method for a solution of the present invention (hereinafter simply referred to as the "membrane treatment method") includes a second solution heating step in which the second solution supplied to the low-pressure chamber 23 is heated. This allows the temperature of the second solution to be higher than the temperature of the first solution in the membrane concentration step. This increases the osmotic pressure of the second solution, thereby improving the membrane permeation flux of the semipermeable membrane 21. Furthermore, when the density of the second solution decreases due to an increase in the temperature of the second solution, the flow rate on the membrane surface of the semipermeable membrane 21 increases, thereby reducing concentration polarization, which also improves the membrane flux. For these reasons, by increasing the temperature of the second solution within a range that does not adversely affect the durability of the semipermeable membrane 21, the permeability of the semipermeable membrane 21 from the high-pressure chamber 22 to the low-pressure chamber 23 can be improved, allowing for efficient high concentration of the first solution passing through the high-pressure chamber 22.

[0019] The membrane treatment device 1-1 shown in FIG. 1 uses a portion of the first solution after concentration in the membrane concentration step as the second solution. However, as in the membrane treatment device 1-2 shown in FIG. 2, a portion of the first solution before being introduced into the high-pressure chamber 22 (i.e., before being concentrated in the membrane concentration step) may be used as the second solution, and this second solution may be heated in the second solution heating device 30 to a temperature higher than that of the first solution introduced into the high-pressure chamber 22. In this case, too, the first solution can be efficiently highly concentrated by increasing the pressure of the first solution using a pressure increasing means such as a high-pressure pump 2a and maintaining the low-pressure chamber 23 at a lower pressure than the high-pressure chamber 22. Furthermore, when the temperature of the first solution is high, a cooling means may be provided to cool the first solution after the second solution has branched off by heat exchange with cooling water, for example. This makes it easier to ensure a temperature difference between the first solution and the second solution in the membrane concentration step.

[0020] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. FIG. 3 is a schematic diagram of a membrane treatment device according to one embodiment of the present invention. As shown in FIG. 3, a membrane treatment device 1-3 includes an RO membrane unit 10, a membrane concentration device 20, and a recovered liquid heating device 30. In the following embodiments, the first solution shown in FIGS. 1 and 2 will be described as the liquid to be treated, and the second solution will be described as the recovered liquid from which water is recovered. However, the present invention is not limited to these specific examples. A preferred example of the liquid to be treated is a solution of inorganic salts such as seawater, but it may also be an organic solution, etc.

[0021] The RO membrane unit 10 is composed of an RO membrane module equipped with an RO membrane (reverse osmosis membrane) 11 inside a casing, and generates produced water (fresh water) by passing the liquid to be treated through the RO membrane 11. The RO membrane 11 may be shaped as a flat membrane or a hollow fiber membrane, for example. The liquid to be treated that has not passed through the RO membrane 11 of the RO membrane unit 10 and has been concentrated is supplied to a membrane concentration device 20. The RO membrane unit 10 shown in FIG. 3 has a single stage, but can also have a multi-stage structure.

[0022] In the membrane concentration device 20, a high-pressure chamber 22 and a low-pressure chamber 23 are formed by dividing the inside of a casing with a semipermeable membrane 21. The liquid to be treated that has been concentrated in the RO membrane unit 10 without passing through the RO membrane 11 is introduced into the high-pressure chamber 22, while the recovered liquid described below is introduced into the low-pressure chamber 23. The liquid to be treated and the recovered liquid introduced into the high-pressure chamber 22 and the low-pressure chamber 23, respectively, come into contact with each other via the semipermeable membrane 21 and are then discharged to the outside. The semipermeable membrane 21 may be a hollow fiber membrane instead of a flat membrane. An RO membrane (reverse osmosis membrane) can be suitably used as the semipermeable membrane 21, but other semipermeable membranes such as an FO membrane (forward osmosis membrane) may also be used.

[0023] The recovered liquid heating device 30 is composed of a heat exchanger that heats the recovered liquid by exchanging heat with exhaust heat, and corresponds to the second solution heating device in Figures 1 and 2. The heat source of the recovered liquid heating device 30 is not particularly limited, and in addition to exhaust heat, natural energy such as sunlight or other heat sources may be used.

[0024] Next, a membrane treatment method using the membrane treatment device 1-3 having the above configuration will be described. First, an RO membrane water passing step is performed in which the liquid to be treated, such as seawater, is pressurized by a high-pressure pump 2a and supplied to an RO membrane unit 10, and then the liquid to be treated is passed through an RO membrane 11 to be concentrated. The high-pressure pump 2a can be, for example, an inverter-controlled pump, thereby achieving energy savings.

[0025] The liquid to be treated that has been concentrated in the RO membrane water passing step is supplied to the high-pressure chamber 22 of the membrane concentrator 20, where it is concentrated, and then discharged from the membrane concentrator 20. A portion of the liquid to be treated that has been discharged from the membrane concentrator 20 is branched off and used as the recovered liquid. The recovered liquid is heated in a recovered liquid heating step using a recovered liquid heating device 30, and then supplied to the low-pressure chamber 23 of the membrane concentrator 20. The recovered liquid that is supplied to the low-pressure chamber 23 is reduced in pressure by passing through the membrane concentrator 20, and therefore has a lower pressure than the liquid to be treated that is supplied to the high-pressure chamber 22, and a higher temperature than the liquid to be treated. This promotes the movement of water from the high-pressure chamber 22 to the low-pressure chamber 23 via the semipermeable membrane 21, and the liquid to be treated that passes through the high-pressure chamber 22 can be concentrated to a high concentration.

[0026] The remaining portion of the liquid to be treated concentrated by the membrane concentrator 20 that is not used as the recovered liquid can be used as the concentrated liquid in other processes, such as forward osmosis power generation and desalination by evaporation and concentration for salt production. The recovered liquid recovered by the membrane concentrator 20 is combined with the liquid to be treated upstream of the high-pressure pump 2a and supplied again to the RO membrane unit 10. This improves the production efficiency of the produced water in the RO membrane unit 10. Furthermore, the liquid to be treated is diluted and its osmotic pressure is reduced, allowing it to be supplied to the RO membrane unit 10 at low pressure, thereby saving energy required for the high-pressure pump 2a. Furthermore, because the recovered liquid combined with the liquid to be treated is heated by the recovered liquid heating device 30, the temperature of the liquid to be treated supplied to the high-pressure chamber 22 of the membrane concentrator 20 can be raised within a range that does not exceed the temperature of the recovered liquid supplied to the low-pressure chamber 23. This reduces the viscosity of the liquid to be treated in the high-pressure chamber 22, allowing the liquid to be concentrated at low pressure.

[0027] The membrane treatment device 1-4 shown in Figure 4 is different from the membrane treatment device 1-3 shown in Figure 3 in that all of the recovered liquid introduced into the low-pressure chamber 23 is not heated by the recovered liquid heating device 30, but rather a portion of the recovered liquid is bypassed through a bypass flow path 3 without being supplied to the recovered liquid heating device 30. The flow rate of the recovered liquid bypassed through the bypass flow path 3 can be controlled by adjusting the opening of the flow control valve 4. With this configuration, the temperature rise of the recovered liquid can be easily controlled to the minimum necessary, thereby achieving energy savings. Note that in Figure 4, the same components as those in Figure 3 are denoted by the same reference numerals (the same applies to the following drawings).

[0028] The membrane treatment device 1-5 shown in Figure 5 is the membrane treatment device 1-3 shown in Figure 3, to which an NF membrane unit 40 has been added. The NF membrane unit 40 is composed of an NF membrane module equipped with an NF membrane (nanofiltration membrane) 41 inside a casing, and generates a permeate by passing the liquid to be treated through the NF membrane 41. Examples of the shape of the NF membrane include a flat membrane and a hollow fiber membrane. The NF membrane unit 40 may be configured in multiple stages instead of in a single stage.

[0029] According to the membrane treatment device 1-5 shown in Fig. 5, an NF membrane water passing step is performed in which a liquid to be treated, such as seawater, is supplied to an NF membrane unit 40 by a medium-pressure pump 2b, and the liquid to be treated is passed through an NF membrane 41. A portion of the liquid to be treated that has permeated the NF membrane 41 is pressurized by a high-pressure pump 2a and supplied to an RO membrane unit 10. The subsequent steps are the same as those in the membrane treatment method using the membrane treatment device 1-4 shown in Fig. 4.

[0030] 3, the membrane treatment device 1-6 shown in Fig. 6 is configured such that, instead of using the liquid to be treated after concentration by the membrane concentrator 20 as the recovered liquid, a portion of the liquid to be treated before concentration by the membrane concentrator 20 is branched off and used as the recovered liquid. The recovered liquid is supplied to the recovered liquid heating device 30 by the supply pump 2c and heated, and then supplied to the low-pressure chamber 23 of the membrane concentrator 20. The recovered liquid discharged from the low-pressure chamber 23 is merged with the liquid to be treated, used as the liquid to be treated, and supplied to the RO membrane unit 10 by the high-pressure pump 2a.

[0031] The membrane treatment device 1-7 shown in Figure 7 is the same as the membrane treatment device 1-5 shown in Figure 5, except that it is equipped with an energy recovery device 60 that performs pressure exchange between the liquid to be treated before and after the membrane concentration step, and the membrane concentration device 20 is composed of three stages of membrane concentration devices 20-1, 20-2, and 20-3. The configuration of each membrane concentration device 20-1, 20-2, and 20-3 is the same as the membrane concentration device 20 shown in Figure 5, and the liquid to be treated concentrated in the RO membrane unit 10 is supplied in series to each high-pressure chamber 22. The liquid to be treated that is concentrated without passing through the NF membrane 41 of the NF membrane unit 40 is used as a recovered liquid, and is supplied in parallel to the low-pressure chambers 23 of the membrane concentration devices 20-1, 20-2, and 20-3 via the recovered liquid heating device 30 by operation of the supply pump 2c. The liquid to be treated that does not permeate the NF membrane 41 has a high osmotic pressure due to an increase in solute concentration, so by using this as the recovered liquid, the osmotic pressure difference with the liquid to be treated can be maintained small in the membrane concentration devices 20-1, 20-2, and 20-3.

[0032] The membrane treatment device 1-7 shown in Figure 7 reduces pressure loss of the low-pressure recovered liquid, allowing it to be reliably supplied to each membrane concentrator 20-1, 20-2, 20-3, and can increase the concentration rate of the liquid to be treated by maintaining the recovered liquid at a higher temperature than the liquid to be treated. The flow rate of the recovered liquid supplied to the low-pressure chamber 23 of each membrane concentrator 20-1, 20-2, 20-3 can be individually controlled by adjusting the opening of the flow control valves 4-1, 4-2, 4-3, thereby allowing the recovered liquid to be supplied to each membrane concentrator 20-1, 20-2, 20-3 at an appropriate flow rate. The number of stages in each membrane concentrator 20-1, 20-2, 20-3 is not particularly limited. The recovered liquid heating device 30 only needs to heat the recovered liquid supplied to at least one of the multiple-stage membrane concentrators 20-1, 20-2, and 20-3, and may be configured, for example, to heat only the recovered liquid supplied to the membrane concentrator 20-1 in the first stage or the membrane concentrator 20-3 in the last stage.

[0033] In the membrane concentrators 20-1, 20-2, and 20-3 shown in FIG. 7, the recovered liquid obtained by recovering water from the liquid to be treated is merged, and then a portion of the recovered liquid is circulated individually to each membrane concentrator 20-1, 20-2, and 20-3 by the circulation pump 2e. This allows the recovered liquid discharged outside the system to be further diluted. The circulation flow rate to each membrane concentrator 20-1, 20-2, and 20-3 can be individually controlled by adjusting the opening of the flow control valves 4-4, 4-5, and 4-6. The configuration for circulating the recovered liquid by the circulation pump 2e may be any configuration in which the recovered liquid discharged from at least one of the membrane concentrators 20-1, 20-2, and 20-3 in each stage is merged with the recovered liquid supplied to at least one of the membrane concentrators 20-1, 20-2, and 20-3 in each stage.

[0034] In the membrane treatment device 1-7 shown in Figure 7, the energy recovery device 60 is composed of a turbocharger, and rotates a turbine using concentrated liquid discharged from the membrane concentrator 20-3 in the second stage. This power is used to pressurize the liquid to be treated, which is supplied to the membrane concentrator 20-1 in the first stage. The configuration of the energy recovery device 60 is not particularly limited as long as it can recover the energy of the concentrated liquid and pressurize the liquid to be treated. For example, other energy recovery devices such as a rotor type or a piston type may be used in addition to a turbine type. The liquid to be treated concentrated in the membrane concentrators 20-1, 20-2, and 20-3 is reduced in pressure by passing through the energy recovery device 60, and the pressure of the liquid to be treated supplied to the membrane concentrators 20-1, 20-2, and 20-3 is increased, thereby enabling high concentration.

[0035] The membrane treatment device 1-8 shown in Fig. 8 is configured in such a way that a portion of the concentrated liquid, which is discharged outside the system after the liquid to be treated is concentrated by the membrane concentrators 20-1, 20-2, and 20-3 in the membrane treatment device 1-7 shown in Fig. 7, is merged with the concentrated liquid to be treated without passing through the NF membrane 41 of the NF membrane unit 40 and used as a recovered liquid, and the other configurations are the same as those of the membrane treatment device 1-7 shown in Fig. 7. Specific examples of membrane treatment devices that use at least a portion of the concentrated liquid concentrated by the membrane concentrators 20-1, 20-2, and 20-3 as a recovered liquid in this way are shown in Figs. 9 to 12.

[0036] A membrane treatment device 1-9 shown in Fig. 9 is configured such that the NF membrane unit 40 is not included in the membrane treatment device 1-7 shown in Fig. 7. The liquid to be treated that has been concentrated in the RO membrane unit 10 is pressurized by a booster pump 2d and an energy recovery device 60 and supplied to two-stage membrane concentrators 20-1 and 20-2. On the other hand, a portion of the recovered liquid that has passed through the two-stage membrane concentrators 20-1 and 20-2 in parallel is merged with the liquid to be treated upstream of the high-pressure pump 2a, while the remainder is circulated by a circulation pump 2e.

[0037] 10 is configured to include three-stage membrane concentrators 20-1, 20-2, and 20-3, in which recovered liquid supplied in parallel to the two membrane concentrators 20-2 and 20-3 on the rear stage is joined together, and then the pressure is increased by operating a boost pump 2d and the liquid is supplied to the membrane concentrator 20-1 on the front stage. If the pressure of the recovered liquid joined after passing through the membrane concentrators 20-2 and 20-3 is sufficient, the configuration may not include the boost pump 2d.

[0038] The membrane treatment device 1-11 shown in Figure 11 is configured to have three stages of membrane treatment devices 20-1, 20-2, and 20-3, and the recovery liquid supplied to the membrane treatment device 20-3 on the rear stage is supplied in parallel to the two membrane treatment devices 20-1 and 20-2 on the front stage by operating the boost pump 2d.

[0039] The membrane treatment device 1-12 shown in Figure 12 is configured to have four stages of membrane treatment devices 20-1, 20-2, 20-3, and 20-4, in which recovery liquid supplied in parallel to the two membrane treatment devices 20-3 and 20-4 on the rear stage is merged and supplied in parallel to the two membrane treatment devices 20-1 and 20-2 on the front stage by operating the boost pump 2d.

[0040] As shown in Figures 9 to 12, the concentration and flow rate of the recovered liquid supplied to each membrane treatment device can be easily adjusted by appropriately combining parallel supply with serial supply for the supply of the recovered liquid to each membrane treatment device. As a result, the number of pumps required can be reduced, and the pump efficiency can be improved by increasing the capacity, and the membrane flux in each membrane treatment device can be equalized. In the configurations shown in Figures 9 to 12, the recovered liquid heating device 30 only needs to be configured to heat the recovered liquid supplied to at least one of the multiple membrane concentration devices.

[0041] The membrane treatment devices 1-13 to 1-19 shown in Figures 13 to 19 are configured to include multiple stages of membrane treatment devices, and are provided with an NF membrane unit 40, where at least a portion of the treated liquid that has permeated the NF membrane 41 is used as a recovered liquid and heated by a recovered liquid heating device 30.

[0042] The membrane treatment device 1-13 shown in Figure 13 is the membrane treatment device 1-9 shown in Figure 9, in which the liquid to be treated that has passed through membrane concentration devices 20-1 and 20-2 is depressurized by a pressure reducing valve 5 and then supplied to an NF membrane unit 40, and the liquid to be treated that has permeated the NF membrane 41 is used as a recovered liquid.

[0043] 14 is configured to include two-stage membrane concentrators 20-1 and 20-2 and an NF membrane unit 40, in which the liquid to be treated that is supplied to the NF membrane unit 40 and permeates the NF membrane 41 is used as the recovered liquid, heated in a recovered liquid heating device 30-1, and then merged with the recovered liquid passing between the two-stage membrane concentrators 20-1 and 20-2. The liquid to be treated that is concentrated without permeating the NF membrane 41 is pressurized by a booster pump 2d and concentrated in the membrane concentrators 20-1 and 20-2, and a portion of the concentrated liquid to be treated is heated by the recovered liquid heating device 30-2 as the recovered liquid.

[0044] The membrane treatment device 1-15 shown in FIG. 15 is the same as the membrane treatment device 1-13 shown in FIG. 13, except that it includes multiple NF membrane units 40-1 and 40-2 instead of the single NF membrane unit 40. The liquid to be treated concentrated in the membrane concentrators 20-1 and 20-2 is supplied to the NF membrane unit 40-1 via a pressure reducing valve 5-1 and concentrated there. The liquid to be treated is then supplied to the membrane concentrator 20-3 and the NF membrane unit 40-2 and further concentrated there. A portion of the liquid to be treated concentrated in the NF membrane unit 40-2 is used as a recovered liquid via a pressure reducing valve 5-2. The liquid to be treated that permeates the NF membrane unit 40-1 is heated as a recovered liquid by a recovered liquid heating device 30-1, and a portion of the liquid is supplied to the membrane concentrator 20-1 under the control of the flow control valve 4-1. The liquid to be treated that permeates the NF membrane unit 40-2 is heated as a recovered liquid by a recovered liquid heating device 30-2 and then supplied to the membrane concentrators 20-2 and 20-3 under the control of the flow control valve 4-2.

[0045] 15, the liquid to be treated that has permeated the NF membrane unit 40-1 may be supplied to the membrane concentrators 20-1 and 20-2 as a recovered liquid, and the liquid to be treated that has permeated the NF membrane unit 40-2 may be supplied to the membrane concentrator 20-3 as a recovered liquid. Alternatively, the liquid to be treated that has permeated the NF membrane unit 40-2 may be supplied to the membrane concentrators 20-1 and 20-2 and the membrane concentrator 20-3 as a recovered liquid. The recovered liquid heating device 30 may be configured to heat the recovered liquid of at least one of the membrane concentrators 20-1, 20-2, and 20-3.

[0046] The membrane treatment device 1-16 shown in FIG. 16 includes two NF membrane units 40-1 and 40-2 and two membrane concentrators 20-1 and 20-2. The liquid to be treated, concentrated in the NF membrane unit 40-1, is pressurized by a booster pump 2d-1 and concentrated in the membrane concentrator 20-1. The liquid then passes through a pressure reducing valve 5 and is further concentrated in the NF membrane unit 40-2. The liquid then passes through a booster pump 2d-2 and is further concentrated in the membrane concentrator 20-2, where it is recovered as a concentrated liquid. Because the recovered concentrated liquid is under high pressure, it can be suitably used for applications such as osmotic power generation. A portion of the liquid to be treated that has permeated the NF membrane units 40-1 and 40-2 is heated by recovered liquid heating devices 30-1 and 30-2 and supplied to the membrane concentrators 20-1 and 20-2 as a recovered liquid.

[0047] A membrane treatment device 1-17 shown in FIG. 17 is the membrane treatment device 1-16 shown in FIG. 16, except that, instead of the pressure reducing valve 5 and the booster pump 2d-2, an energy recovery device 60 is provided to exchange pressure between them.

[0048] 18 is a membrane treatment device 1-18 in which the pressure is reduced by an energy recovery device 60 instead of the pressure reducing valve 5 in the membrane treatment device 1-13 shown in FIG. The liquid to be treated supplied to the high-pressure chamber 22 of the membrane concentration devices 20-1 and 20-2 is pressurized by the energy recovery device 60.

[0049] A membrane treatment device 1-19 shown in Fig. 19 is configured such that the pressure is increased by energy recovery devices 60-1 and 60-2 instead of the two booster pump units 2d-1 and 2d-2 in the membrane treatment device 1-16 shown in Fig. 16. The liquid to be treated concentrated in the membrane concentration devices 20-1 and 20-2 is depressurized by the energy recovery devices 60-1 and 60-2.

[0050] The membrane treatment device 1-20 shown in Figure 20 is configured to include a membrane concentration device 20 and an NF membrane unit 40. The liquid to be treated that has permeated the NF membrane 41 of the NF membrane unit 40 is heated by a recovered liquid heating device 30 and supplied to the low-pressure chamber 23 of the membrane concentration device 20 as a recovered liquid. Meanwhile, the liquid to be treated that has not permeated the NF membrane 41 of the NF membrane unit 40 but is concentrated is pressurized by a booster pump 2d and supplied to the high-pressure chamber 22 of the membrane concentration device 20. The NF membrane 41 inhibits the permeation of divalent and higher ions contained in the liquid to be treated, such as seawater, while allowing monovalent ions to easily permeate. Therefore, the recovered liquid, which is made up of the liquid to be treated that has permeated the NF membrane 41, is particularly inhibited from decreasing in concentration of monovalent ions. This reduces the osmotic pressure difference between the liquid to be treated and the recovered liquid supplied to the high-pressure chamber 22 and low-pressure chamber 23 of the membrane concentration device 20, thereby ensuring the concentration of the liquid to be treated without excessively increasing the pressure in the high-pressure chamber 22. In the membrane treatment device 1-20 shown in FIG. 20, the membrane concentration devices 20 may be arranged in multiple stages, similarly to the membrane treatment device 1-13 shown in FIG. 13 and the like.

[0051] 20, a bypass flow path 3 is branched off from the flow path that supplies the liquid to be treated that has permeated the NF membrane unit 40 to the recovered liquid heating device 30, and the flow rate of the permeated liquid bypassed to the bypass flow path 3 can be controlled by changing the opening of a flow control valve 4. If a desired pressure difference occurs between the high-pressure chamber 22 and the low-pressure chamber 23 even when the flow control valve 4 is fully closed, the bypass flow path 3 may not be provided and the entire amount of the liquid to be treated that has permeated the NF membrane unit 40 may be supplied to the membrane concentration device 20.

[0052] 6, the membrane treatment device 1-21 shown in Fig. 21 is provided with a treated liquid heating device 70 that heats the treated liquid before the recovery liquid is branched, in addition to a recovered liquid heating device 30 that heats the recovered liquid branched off from the treated liquid before concentration by the membrane concentrator 20. By providing the treated liquid heating device 70, the treated liquid and the recovered liquid that are supplied to the high-pressure chamber 22 and the low-pressure chamber 23 of the membrane concentrator 20, respectively, are both heated, so that the temperature difference between the two in the membrane concentrator 20 is maintained, and the viscosity of the treated liquid in the high-pressure chamber 22 is reduced, allowing the treated liquid to be concentrated at low pressure.

[0053] The membrane treatment device 1-22 shown in FIG. 22 is the membrane treatment device 1-21 shown in FIG. 21 , except that instead of the liquid heating device 70, a liquid cooling device 80 is provided that cools the liquid to be treated after the branched recovered liquid by heat exchange with cooling water or a refrigerant. The provision of the liquid cooling device 80 reduces the temperature of the liquid to be treated supplied to the high-pressure chamber 22 of the membrane concentration device 20, easily ensuring a temperature difference with the recovered liquid supplied to the low-pressure chamber 23. This is effective, for example, when the temperature of the liquid to be treated is higher than expected or when it is desired to increase the salt rejection rate in the RO membrane unit 10. The recovered liquid supplied to the low-pressure chamber 23 may be bypassed via the bypass flow path 3 without being heated in part or entirely by the recovered liquid heating device 30. The liquid cooling device 80 shown in FIG. 22 may be arranged to cool the liquid to be treated after the branched recovered liquid rejoins, as shown in FIG. 23. This is also effective when the temperature of the liquid to be treated is higher than expected or when it is desired to increase the salt rejection rate in the RO membrane unit 10. [Explanation of symbols]

[0054] 1. Membrane treatment equipment 2a high pressure pump 2b Medium pressure pump 2c Supply Pump 2d Booster Pump 2e Circulation Pump 3 Bypass flow path 4 Flow control valve 5. Pressure reducing valve 10 RO membrane units 20 Membrane concentrator 21 Semi-permeable membrane 22 Hyperbaric Chamber 23 Low-pressure chamber 30 Recovery liquid heating device (second solution heating device) 40 NF membrane unit 60 Energy Recovery Device

Claims

1. A membrane treatment method for a solution, comprising a membrane concentration step of concentrating a first solution by contacting the first solution with a second solution having a lower pressure than the second solution via a semipermeable membrane, The method further includes a second solution heating step of heating the second solution, A membrane treatment method for a solution, in which at least a portion of the first solution before or after concentration by the membrane concentration step is used as the second solution, and the temperature of the second solution is made higher than the temperature of the first solution by the second solution heating step, thereby performing the membrane concentration step.

2. The method further includes a reverse osmosis membrane water passing step of increasing the pressure of the first solution and passing it through a reverse osmosis membrane to concentrate the first solution, 2. The membrane treatment method for a solution according to claim 1, wherein the membrane concentration step further concentrates the first solution concentrated in the RO membrane water passing step.

3. 3. The membrane treatment method for a solution according to claim 2, wherein the membrane concentration step comprises heating the second solution by heating at least a part of the first solution concentrated by the membrane concentration step as the second solution.

4. The method further includes a NF membrane water passing step of passing the first solution through a nanofiltration membrane, The membrane treatment method for a solution according to claim 3 , wherein the RO membrane water passing step concentrates at least a portion of the first solution that has permeated the nanofiltration membrane in the NF membrane water passing step.

5. 3. The membrane treatment method for a solution according to claim 2, wherein the membrane concentration step comprises heating the second solution by heating at least a part of the first solution before the RO membrane water passing step.

6. The membrane concentration step includes disposing a plurality of membrane concentration devices each having the semipermeable membrane, supplying the first solution to each of the membrane concentration devices in series, and supplying the second solution to each of the membrane concentration devices in series or in parallel, The membrane treatment method for a solution according to claim 1 , wherein the second solution heating step heats the second solution supplied to at least one of the membrane concentration devices.

7. The method further includes a NF membrane water passing step of passing the first solution through a nanofiltration membrane, 7. The membrane treatment method for a solution according to claim 1, wherein at least a portion of the first solution that has permeated the nanofiltration membrane in the NF membrane water passing step is used as the second solution and is heated in the second solution heating step.

8. 8. The membrane treatment method for a solution according to claim 1, wherein the membrane concentration step comprises cooling the first solution from which the second solution has been branched before concentration and contacting the first solution with the second solution via a semipermeable membrane.

9. A membrane treatment device for a solution, comprising a membrane concentration device that brings a first solution into contact with a second solution having a lower pressure than the first solution via a semipermeable membrane to concentrate the first solution, a second solution heating device for heating the second solution; A membrane treatment device for a solution, in which at least a portion of the first solution before or after concentration by the membrane concentration device is used as the second solution, and the temperature of the second solution is made higher than the temperature of the first solution by the second solution heating device, thereby performing membrane concentration by the membrane concentration device.

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