JP7736288B2 - Method and apparatus for membrane treatment of solution - Google Patents

Description

The present invention relates to a method and apparatus for membrane treatment of a solution.

As an apparatus for membrane treatment of solutions such as seawater, Patent Document 1 discloses a freshwater 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. 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.

Japanese Patent Application Laid-Open No. 2017-176929

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.

The present invention aims to provide a membrane treatment method and apparatus for a solution that can efficiently concentrate the solution to a high concentration.

The above-mentioned object of the present invention is achieved by a membrane treatment method for a solution, which includes a membrane concentration step in which a first solution is concentrated by contacting a second solution having a lower pressure than the first solution via a semipermeable membrane, and further includes a second solution heating step in which the second solution is heated, in which at least a portion 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 raises the temperature of the second solution to a temperature higher than that of the first solution, thereby performing the membrane concentration step.

This solution membrane treatment method preferably 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 the membrane concentration step preferably further concentrates the first solution concentrated in the RO membrane water passing step.

In the membrane treatment method for a solution that includes the RO membrane water passing step, the membrane concentration step can heat at least a portion of the first solution after concentration 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 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.

Furthermore, the membrane concentration step can be performed by disposing 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 one of the membrane concentration devices.

The method can further include an NF membrane water passing step in which the first solution is passed 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.

The membrane concentration step can involve cooling the first solution after the second solution has been branched off before concentration, and bringing it into contact with the second solution via a semipermeable membrane.

The above-mentioned object of the present invention is also achieved by a membrane treatment device for a solution that includes a membrane concentration device that concentrates a first solution by contacting it with a second solution at 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 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 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.

The present invention provides a membrane treatment method and apparatus for a solution that can efficiently concentrate the solution to a high concentration.

1 is a diagram illustrating the principle of a film treatment device for a solution according to the present invention. FIG. 2 is another principle diagram of the film treatment device for a solution according to the present invention. 1 is a schematic configuration diagram of a film treatment apparatus for a solution according to an embodiment of the present invention. FIG. 10 is a schematic configuration diagram of a film treatment apparatus for a solution according to another embodiment of the present invention. FIG. 10 is a schematic configuration diagram of a film treatment apparatus for a solution according to still another embodiment of the present invention. FIG. 10 is a schematic configuration diagram of a film treatment apparatus for a solution according to still another embodiment of the present invention. FIG. 10 is a schematic configuration diagram of a film treatment apparatus for a solution according to still another embodiment of the present invention. FIG. 10 is a schematic configuration diagram of a film treatment apparatus for a solution according to still another embodiment of the present invention. FIG. 10 is a schematic configuration diagram of a film treatment apparatus for a solution according to still another embodiment of the present invention. FIG. 10 is a schematic configuration diagram of a film treatment apparatus for a solution according to still another embodiment of the present invention. FIG. 10 is a schematic configuration diagram of a film treatment apparatus for a solution according to still another embodiment of the present invention. FIG. 10 is a schematic configuration diagram of a film treatment apparatus for a solution according to still another embodiment of the present invention. FIG. 10 is a schematic configuration diagram of a film treatment apparatus for a solution according to still another embodiment of the present invention. FIG. 10 is a schematic configuration diagram of a film treatment apparatus for a solution according to still another embodiment of the present invention. FIG. 10 is a schematic configuration diagram of a film treatment apparatus for a solution according to still another embodiment of the present invention. FIG. 10 is a schematic configuration diagram of a film treatment apparatus for a solution according to still another embodiment of the present invention. FIG. 10 is a schematic configuration diagram of a film treatment apparatus for a solution according to still another embodiment of the present invention. FIG. 10 is a schematic configuration diagram of a film treatment apparatus for a solution according to still another embodiment of the present invention. FIG. 10 is a schematic configuration diagram of a film treatment apparatus for a solution according to still another embodiment of the present invention. FIG. 10 is a schematic configuration diagram of a film treatment apparatus for a solution according to still another embodiment of the present invention. FIG. 10 is a schematic configuration diagram of a film treatment apparatus for a solution according to still another embodiment of the present invention. FIG. 10 is a schematic configuration diagram of a film treatment apparatus for a solution according to still another embodiment of the present invention. 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 1 is a diagram illustrating the principle of a membrane treatment device for a solution (hereinafter simply referred to as "membrane treatment device") according to the present invention. The membrane treatment device 1-1 shown in Figure 1 includes a membrane concentration device 20 and a second solution heating device 30.

The membrane concentration device 20 has a chamber separated by a semipermeable membrane 21, forming a high-pressure chamber 22 and a low-pressure chamber 23. A first solution is introduced into the high-pressure chamber 22, while a second solution at a lower pressure than the first solution is introduced into the low-pressure chamber 23. The first and second solutions introduced into the high-pressure chamber 22 and the low-pressure chamber 23, respectively, come into contact 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 higher temperature than the first solution supplied to the high-pressure chamber 22.

In the membrane concentration device 20, the pressure in the high-pressure chamber 22 is made higher than the pressure in the low-pressure chamber 23, causing water to move from the high-pressure chamber 22 to the low-pressure chamber 23 via the semipermeable membrane 21, and a membrane concentration process is carried out to concentrate the first solution passing through the high-pressure chamber 22. In this membrane concentration process, if the first solution supplied to the high-pressure chamber 22 becomes highly concentrated, concentration polarization may increase, resulting in a decrease in water flux.

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 described above. 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 and improving 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 is improved, allowing for efficient high concentration of the first solution passing through the high-pressure chamber 22.

The membrane treatment device 1-1 shown in FIG. 1 uses a portion of the first solution after concentration in the membrane concentration process 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 process) 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 pressurizing the first solution using a pressure-boosting device 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, if the temperature of the first solution is high, a cooling device may be provided to cool the first solution after branching off from the second solution by heat exchange with cooling water, for example. This makes it easier to maintain a temperature difference between the first and second solutions in the membrane concentration process.

Embodiments of the present invention will be described below with reference to the accompanying drawings. Figure 3 is a schematic diagram of a membrane treatment device according to one embodiment of the present invention. As shown in Figure 3, membrane treatment devices 1-3 include 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 Figures 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 organic solutions, etc., may also be used.

The RO membrane unit 10 consists of an RO membrane module equipped with an RO membrane (reverse osmosis membrane) 11 inside a casing, and generates produced water (freshwater) 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 is concentrated is supplied to the membrane concentrator 20. While the RO membrane unit 10 shown in Figure 3 has a single stage, it can also have a multi-stage structure.

In the membrane concentration device 20, a high-pressure chamber 22 and a low-pressure chamber 23 are formed by dividing the inside of the casing with a semipermeable membrane 21. The high-pressure chamber 22 receives the concentrated liquid to be treated that does not pass through the RO membrane 11 in the RO membrane unit 10, while the recovered liquid (described below) is received in 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 before being 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) is preferably used as the semipermeable membrane 21, but other semipermeable membranes such as an FO membrane (forward osmosis membrane) may also be used.

The recovered liquid heating device 30 consists 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 for 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.

Next, we will explain the membrane treatment method using the membrane treatment device 1-3 with the above configuration. First, the liquid to be treated, such as seawater, is pressurized by the high-pressure pump 2a and supplied to the RO membrane unit 10, and an RO membrane water passing process is performed in which the liquid to be treated is passed through the RO membrane 11 and concentrated. The high-pressure pump 2a can be, for example, an inverter-controlled pump, to achieve energy savings.

The treated liquid concentrated in the RO membrane water flow process 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 treated liquid discharged from the membrane concentrator 20 is branched off and used as recovered liquid. The recovered liquid is heated in a recovered liquid heating process using the recovered liquid heating device 30, and then supplied to the low-pressure chamber 23 of the membrane concentrator 20. The recovered liquid supplied to the low-pressure chamber 23 is reduced in pressure by passing through the membrane concentrator 20, and is therefore at a lower pressure and a higher temperature than the treated liquid supplied to the high-pressure chamber 22. This promotes the movement of water from the high-pressure chamber 22 to the low-pressure chamber 23 via the semipermeable membrane 21, allowing the treated liquid passing through the high-pressure chamber 22 to be highly concentrated.

The remaining portion of the treated liquid 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 treated liquid upstream of the high-pressure pump 2a and supplied back to the RO membrane unit 10. This improves the production efficiency of the produced water in the RO membrane unit 10. Furthermore, the diluted treated liquid reduces its osmotic pressure, allowing it to be supplied to the RO membrane unit 10 at low pressure, thereby reducing the energy required for the high-pressure pump 2a. Furthermore, because the recovered liquid combined with the treated liquid is heated by the recovered liquid heating device 30, the treated liquid supplied to the high-pressure chamber 22 of the membrane concentrator 20 can be heated within a temperature range that does not exceed the temperature of the recovered liquid supplied to the low-pressure chamber 23. This reduces the viscosity of the treated liquid in the high-pressure chamber 22, allowing the treated liquid to be concentrated at low pressure.

The membrane treatment device 1-4 shown in Figure 4 differs from the membrane treatment device 1-3 shown in Figure 3 in that, rather than heating all of the recovered liquid introduced into the low-pressure chamber 23 by the recovered liquid heating device 30, some of the recovered liquid is bypassed via the bypass flow path 3 without being supplied to the recovered liquid heating device 30. The flow rate of the recovered liquid bypassed by the bypass flow path 3 can be controlled by adjusting the opening of the flow control valve 4. This configuration allows for easy control to minimize the temperature rise of the recovered liquid, thereby achieving energy savings. Note that in Figure 4, components similar to those in Figure 3 are designated by the same reference numerals (the same applies to the following figures).

The membrane treatment device 1-5 shown in Figure 5 is the membrane treatment device 1-3 shown in Figure 3, with the addition of an NF membrane unit 40. The NF membrane unit 40 consists of an NF membrane module equipped with an NF membrane (nanofiltration membrane) 41 inside a casing, and generates 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 a single stage.

In the membrane treatment device 1-5 shown in Figure 5, the liquid to be treated, such as seawater, is supplied to the NF membrane unit 40 by the medium-pressure pump 2b, and an NF membrane water passing process is performed in which the liquid to be treated passes through the NF membrane 41. A portion of the liquid to be treated that has permeated the NF membrane 41 is pressurized by the high-pressure pump 2a and supplied to the RO membrane unit 10. The subsequent processes are the same as the membrane treatment method using the membrane treatment device 1-4 shown in Figure 4.

In the membrane treatment device 1-6 shown in Figure 6, instead of using the liquid to be treated after concentration by the membrane concentrator 20 as the recovered liquid in the membrane treatment device 1-3 shown in Figure 3, 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 and used as the liquid to be treated, and is then supplied to the RO membrane unit 10 by the high-pressure pump 2a.

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 exchanges pressure between the treated liquid before and after the membrane concentration process, 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 treated liquid concentrated in the RO membrane unit 10 is supplied in series to each high-pressure chamber 22. The treated liquid that is concentrated without passing through the NF membrane 41 of the NF membrane unit 40 is used as recovered liquid, and is supplied in parallel to the low-pressure chambers 23 of each membrane concentration device 20-1, 20-2, and 20-3 via the recovered liquid heating device 30 by operating the supply pump 2c. The liquid to be treated that does not pass through the NF membrane 41 has a higher 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.

The membrane treatment device 1-7 shown in Figure 7 reduces pressure loss of the low-pressure recovered liquid, enabling it to be reliably supplied to each membrane concentrator 20-1, 20-2, 20-3, and can increase the concentration rate of the treated liquid by heating the recovered liquid to a higher temperature than the liquid being 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 at an appropriate flow rate to each membrane concentrator 20-1, 20-2, 20-3. 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. For example, it may be configured to heat only the recovered liquid supplied to the first-stage membrane concentrator 20-1 or the last-stage membrane concentrator 20-3.

In the membrane concentrators 20-1, 20-2, and 20-3 shown in Figure 7, the recovered liquid obtained by recovering water from the liquid being treated is merged, and then a portion 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 using the circulation pump 2e may be any configuration that merges the recovered liquid discharged from at least one of the membrane concentrators 20-1, 20-2, and 20-3 in each stage with the recovered liquid supplied to at least one of the membrane concentrators 20-1, 20-2, and 20-3 in each stage.

In the membrane treatment device 1-7 shown in Figure 7, the energy recovery device 60 consists of a turbocharger, which rotates a turbine using concentrated liquid discharged from the membrane concentrator 20-3 in the second stage, and uses this power to pressurize the liquid being treated that 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 is capable of recovering the energy of the concentrated liquid and pressurizing the liquid being treated. For example, other energy recovery devices such as rotor or piston types may be used in addition to turbine types. The liquid being treated that has been concentrated in the membrane concentrators 20-1, 20-2, and 20-3 is depressurized by passing through the energy recovery device 60, and the pressure of the liquid being treated that is supplied to the membrane concentrators 20-1, 20-2, and 20-3 is increased by increasing the pressure difference between the high-pressure chamber 22 and the low-pressure chamber 23, enabling high concentration.

The membrane treatment device 1-8 shown in Figure 8 is a membrane treatment device 1-7 shown in Figure 7 in which a portion of the concentrated liquid discharged from the system after the liquid to be treated is concentrated by the membrane concentrators 20-1, 20-2, and 20-3 is merged with the concentrated liquid to be treated that has not passed through the NF membrane 41 of the NF membrane unit 40 and used as the recovered liquid. Other configurations are the same as those of the membrane treatment device 1-7 shown in Figure 7. Specific examples of membrane treatment devices in which at least a portion of the concentrated liquid concentrated by the membrane concentrators 20-1, 20-2, and 20-3 is used as the recovered liquid are shown in Figures 9 to 12.

The membrane treatment device 1-9 shown in Figure 9 is a configuration of the membrane treatment device 1-7 shown in Figure 7, but without the NF membrane unit 40. The liquid to be treated, concentrated in the RO membrane unit 10, is pressurized by the boost pump 2d and the energy recovery device 60 and supplied to the two-stage membrane concentrators 20-1 and 20-2. Meanwhile, the recovered liquid that passes through the two-stage membrane concentrators 20-1 and 20-2 in parallel is partially merged with the liquid to be treated upstream of the high-pressure pump 2a, while the remainder is circulated by the circulation pump 2e.

The membrane treatment device 1-10 shown in Figure 10 is configured with three membrane concentrators 20-1, 20-2, and 20-3. The recovered liquid supplied in parallel to the two membrane concentrators 20-2 and 20-3 on the downstream side is combined, then the pressure is increased by operating the boost pump 2d and supplied to the membrane concentrator 20-1 on the upstream side. If the pressure of the combined recovered liquid after passing through the membrane concentrators 20-2 and 20-3 is sufficient, the configuration may not include the boost pump 2d.

The membrane treatment device 1-11 shown in Figure 11 is configured with three membrane treatment devices 20-1, 20-2, and 20-3, and the recovery liquid supplied to the membrane treatment device 20-3 on the downstream side is supplied in parallel to the two membrane treatment devices 20-1 and 20-2 on the upstream side by operating the boost pump 2d.

The membrane treatment device 1-12 shown in Figure 12 is configured with four membrane treatment devices 20-1, 20-2, 20-3, and 20-4. The 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.

As shown in membrane treatment devices 1-9 to 1-12 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 recovered liquid to each stage of membrane treatment device. As a result, the number of pumps required can be reduced, improving pump efficiency through increased capacity, and also achieving equalization of membrane flux in each membrane treatment device. 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 stages of membrane concentration devices.

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

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

The membrane treatment device 1-14 shown in Figure 14 is configured with two-stage membrane concentrators 20-1 and 20-2 and an NF membrane unit 40. 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 the 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 concentrated liquid to be treated that does not permeate the NF membrane 41 is pressurized by the boost 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.

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

In the membrane treatment device 1-15 shown in FIG. 15, the liquid to be treated that has permeated the NF membrane unit 40-1 may be supplied as a recovered liquid to the membrane concentrators 20-1 and 20-2, and the liquid to be treated that has permeated the NF membrane unit 40-2 may be supplied as a recovered liquid to the membrane concentrator 20-3. Alternatively, the liquid to be treated that has permeated the NF membrane unit 40-2 may be supplied as a recovered liquid to the membrane concentrators 20-1, 20-2, and 20-3, respectively. The recovered liquid heating device 30 may be configured to heat the recovered liquid from at least one of the membrane concentrators 20-1, 20-2, and 20-3.

The membrane treatment device 1-16 shown in Figure 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 the boost pump 2d-1 and concentrated in the membrane concentrator 20-1. After passing through the pressure reducing valve 5, it is further concentrated in the NF membrane unit 40-2, and then passed through the boost pump 2d-2 and 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 the recovered liquid heating devices 30-1 and 30-2 and supplied to the membrane concentrators 20-1 and 20-2 as the recovered liquid.

The membrane treatment device 1-17 shown in Figure 17 is the membrane treatment device 1-16 shown in Figure 16, except that instead of the pressure reducing valve 5 and booster pump 2d-2, it is equipped with an energy recovery device 60 that exchanges pressure between them.

The membrane treatment device 1-18 shown in Figure 18 is a device 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 Figure 13. 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.

The membrane treatment device 1-19 shown in Figure 19 is the same as the membrane treatment device 1-16 shown in Figure 16, except that instead of the two booster pumps 2d-1 and 2d-2, the pressure is increased by energy recovery devices 60-1 and 60-2. The liquid to be treated that has been concentrated in the membrane concentrators 20-1 and 20-2 is depressurized by the energy recovery devices 60-1 and 60-2.

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 treated liquid 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 treated liquid that has not permeated the NF membrane 41 of the NF membrane unit 40 and is concentrated is pressurized by a boost 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 treated liquid, such as seawater, while readily permeating monovalent ions. Therefore, the recovered liquid, consisting of the treated liquid 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 treated liquid 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 treated liquid without excessively increasing the pressure in the high-pressure chamber 22. In the membrane treatment device 1-20 shown in Figure 20, the membrane concentration devices 20 may be arranged in multiple stages, similar to the membrane treatment device 1-13 shown in Figure 13, etc.

In the membrane treatment device 1-20 shown in Figure 20, a bypass flow path 3 is branched off from the flow path that supplies the treated liquid that has permeated the NF membrane unit 40 to the recovered liquid heating device 30, and the flow rate of the permeated liquid bypassed through the bypass flow path 3 can be controlled by changing the opening of the 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 treated liquid that has permeated the NF membrane unit 40 may be supplied to the membrane concentration device 20.

The membrane treatment device 1-21 shown in Figure 21 is the membrane treatment device 1-6 shown in Figure 6, and includes a recovered liquid heating device 30 that heats the recovered liquid branched off from the treated liquid before it is concentrated by the membrane concentration device 20, as well as a treated liquid heating device 70 that heats the treated liquid before it is branched off from the recovered liquid. By including the treated liquid heating device 70, both the treated liquid and the recovered liquid supplied to the high-pressure chamber 22 and low-pressure chamber 23 of the membrane concentration device 20 are heated, so the temperature difference between the two is maintained in the membrane concentration device 20, and the reduced viscosity of the treated liquid in the high-pressure chamber 22 allows the treated liquid to be concentrated at low pressure.

The membrane treatment device 1-22 shown in Figure 22 is the membrane treatment device 1-21 shown in Figure 21, except that instead of the treated liquid heating device 70, it is equipped with a treated liquid cooling device 80 that cools the treated liquid after branching the recovered liquid by heat exchange with cooling water or refrigerant. By providing the treated liquid cooling device 80, the temperature of the treated liquid supplied to the high-pressure chamber 22 of the membrane concentration device 20 can be lowered, 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 treated liquid is higher than expected or when it is desired to increase the desalination 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 in its entirety by the recovered liquid heating device 30. The treated liquid cooling device 80 shown in Figure 22 may also be configured to cool the treated liquid after the branched recovery liquid rejoins, as shown in Figure 23. This is also effective when the temperature of the treated liquid is higher than expected or when it is desired to increase the salt rejection rate in the RO membrane unit 10.

REFERENCE SIGNS LIST 1 Membrane treatment device 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 unit 20 Membrane concentration device 21 Semipermeable membrane 22 High-pressure chamber 23 Low-pressure chamber 30 Recovered liquid heating device (second solution heating device)
40 NF membrane unit 60 Energy recovery device

Claims (9)

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. 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. The membrane treatment method for a solution described in claim 2, wherein the membrane concentration step involves heating at least a portion of the first solution concentrated in the membrane concentration step as the second solution in the second solution heating step. 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. The membrane treatment method for a solution described in claim 2, wherein the membrane concentration step involves heating 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. 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. 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. The membrane treatment method for a solution described in any one of claims 1 to 7, wherein the membrane concentration step involves cooling the first solution after the second solution has been branched off before concentration and bringing the first solution into contact with the second solution via a semipermeable membrane. 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.