Concentration System

Abstract

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. The concentration system includes a plurality of semipermeable membrane modules. A concentration flow path is provided by connecting the first chambers of the plurality of semipermeable membrane modules, and a dilution flow path is provided by connecting 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 an osmotic pressure is flowed through the dilution flow path. The target solution is concentrated by having a higher pressure than the auxiliary solution. The concentration system further includes, in the dilution flow path, an auxiliary solution booster pump that boosts the pressure of the auxiliary solution, and an auxiliary solution booster pump suction pressure gauge installed on the suction side of the auxiliary solution booster pump that measures the pressure of the auxiliary solution, and further includes a control device connected to the auxiliary solution booster pump suction pressure gauge and the auxiliary solution booster pump.

Description

[Technical Field]

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

[0002] With the aim of reducing the energy required for reverse osmosis (RO) desalination, a membrane separation method (brine concentration (BC): osmotically assisted reverse osmosis (OARO)) has been investigated. The method involves passing a high-pressure target solution through the first chamber of a semipermeable membrane module, which has a first chamber and a second chamber separated by the semipermeable membrane, and passing a low-pressure auxiliary solution (such as the target solution) through the second chamber. This causes the solvent (such as water) contained in the target solution in the first chamber to migrate through the semipermeable membrane into the auxiliary solution in the second chamber, thereby discharging a concentrated target solution (concentrate) from the first chamber and a diluted auxiliary solution (diluted solution) from the second chamber.

[0003] For example, Patent Document 1 (International Publication No. 2018 / 084246), Patent Document 2 (Japanese Patent Laid-Open No. 2019-188330), and Patent Document 3 (Japanese Patent Laid-Open No. 2018-515340) disclose the use of a multistage membrane separation system consisting of multiple semipermeable membrane modules connected in series for brine concentration (BC). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] International Publication No. 2018 / 084246 [Patent Document 2] Japanese Patent Application Publication No. 2019-188330 [Patent Document 3] Special Publication No. 2018-515340 Summary of the Invention [Problem to be solved by the invention]

[0005] When concentrating a target solution by brine concentration (BC) using such a multistage membrane separation (concentration) system including multiple semipermeable membrane modules, the target solution to be concentrated as it flows through the first chambers (concentration flow paths) of the multiple semipermeable membrane modules is pressurized by a high-pressure pump or the like, and can therefore pass through the first chambers of each of the multiple semipermeable membrane modules at the required flow rate.

[0006] On the other hand, the auxiliary solution flowing through the second chambers (dilution flow paths) of multiple semipermeable membrane modules has a relatively low pressure. Therefore, as the number of passing semipermeable membrane modules increases and the flow resistance of the auxiliary solution increases, the flow rate of the auxiliary solution decreases, especially downstream of the dilution flow path, making it difficult to pass the auxiliary solution through all the second chambers of multiple semipermeable membrane modules at the required flow rate. Furthermore, if the pressure of the auxiliary solution supplied to the dilution flow path is increased, the pressure difference between the first and second chambers decreases, resulting in a decrease in the membrane separation efficiency (concentration efficiency) of the target solution.

[0007] Therefore, in order to increase the flow rate of the auxiliary solution in the second chamber downstream of the dilution flow path where the flow rate of the auxiliary solution is likely to decrease, it is conceivable to provide an auxiliary solution booster pump midway through the dilution flow path.

[0008] Here, when an auxiliary solution booster pump is provided in the flow path, if the pressure of the liquid supplied to the upstream side (suction side) of the auxiliary solution booster pump is too high, the auxiliary solution booster pump may break down. Furthermore, semipermeable membranes may have high strength against pressure from the first chamber side, but relatively low strength against pressure from the second chamber side. For example, when a hollow fiber membrane (hollow fiber type semipermeable membrane) is used as the semipermeable membrane to concentrate by BC, the outside of the hollow fiber membrane usually becomes the first chamber (high pressure side), and the inside of the hollow fiber membrane becomes the second chamber (low pressure side). This is because hollow fiber membranes have high strength against pressure from the outside, but relatively low strength against pressure from the inside. In this case, if the pressure of the liquid (auxiliary solution) supplied to the second chamber becomes high, the semipermeable membrane may be damaged. For this reason, the inventors considered that in a multistage concentration system including multiple semipermeable membrane modules, it is necessary to appropriately control the pressure of the auxiliary solution flowing through the dilution flow path (the second chamber of the multiple semipermeable membrane modules).

[0009] Therefore, an object of the present invention is to prevent damage, failure, etc. of the semipermeable membrane modules and auxiliary solution booster pump by appropriately controlling the pressure of the auxiliary solution flowing through the dilution flow path when separating and concentrating water from a target solution by brine concentration (BC) using a multistage concentration system (membrane separation system) including multiple semipermeable membrane modules. [Means for solving the problem]

[0010] [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, A plurality of semipermeable membrane modules are provided, Each of the plurality of semipermeable membrane modules has a semipermeable membrane and a first chamber and a second chamber separated by the semipermeable membrane, a concentration flow path is provided in which the first chambers of the plurality of semipermeable membrane modules are connected, a dilution flow path is provided in which the second chambers of the plurality of semipermeable membrane modules are connected; The target solution is flowed through the concentration flow path, An auxiliary solution having an osmotic pressure is flowed through the dilution flow path, Since the target solution has a higher pressure than the auxiliary solution, in each of the plurality of semipermeable membrane modules, the solvent contained in the target solution in the first chamber migrates through the semipermeable membrane to the auxiliary solution in the second chamber, and the target solution is concentrated, thereby obtaining the concentrated liquid; The concentration system comprises: an auxiliary solution booster pump in the dilution flow path for boosting the pressure of the auxiliary solution; an auxiliary solution booster pump suction pressure gauge that is installed on the suction side of the auxiliary solution booster pump and that measures the pressure of the auxiliary solution; a control device connected to the auxiliary solution booster pump suction pressure gauge and the auxiliary solution booster pump; Concentration system.

[0011] [2] The concentration system described in [1], wherein the control device controls the discharge capacity of the auxiliary solution booster pump so that the measurement value of the auxiliary solution booster pump suction pressure gauge becomes a target value.

[0012] [3] The concentration system described in [1], wherein the control device starts controlling the start-up and discharge capacity of the auxiliary solution booster pump when the measurement value of the auxiliary solution booster pump suction pressure gauge reaches or exceeds a predetermined value.

[0013] [4] The apparatus further includes a concentrated liquid concentration meter that is installed in the concentration flow path and that measures the concentration of the target component in the concentrated liquid connected to the control device; When the measurement value of the concentrated solution concentration meter also reaches a predetermined value or more, the auxiliary solution booster pump is started to be activated and its discharge capacity is controlled. The concentration system according to any one of [1] to [3].

[0014] [5] The concentration system according to any one of [1] to [4], wherein a part of the concentrated solution is used as the auxiliary solution.

[0015] [6] The concentration system according to any one of [1] to [5], further comprising a pressurizing device for pressurizing the target solution to a pressure higher than that of the auxiliary solution.

[0016] [7] The concentration system according to any one of [1] to [6], wherein the semipermeable membrane is a hollow fiber membrane. [Effects of the Invention]

[0017] According to the present invention, when water is separated from a target solution and concentrated by brine concentration (BC) using a multistage concentration system (membrane separation system) including multiple semipermeable membrane modules, damage, failure, etc. of the semipermeable membrane modules and the auxiliary solution booster pump can be prevented by appropriately controlling the pressure of the auxiliary solution flowing through the dilution flow path. [Brief explanation of the drawings]

[0018] [Figure 1] FIG. 1 is a schematic diagram illustrating an example of a concentration system according to an embodiment. [Figure 2] FIG. 10 is a schematic diagram showing another example of the concentration system of the embodiment. [Figure 3] FIG. 10 is a schematic diagram showing another example of the concentration system of the embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0019] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the drawings, the same reference numerals denote the same or corresponding parts.

[0020] <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.

[0021] Referring to FIG. 1, the concentration system of this embodiment is a multistage concentration system (membrane separation system) equipped with a plurality of semipermeable membrane modules 1, 2, and 3. In FIG. 1, three semipermeable membrane modules 1, 2, and 3 are depicted as "plurality of semipermeable membrane modules," but the "plurality of semipermeable membrane modules" may be, for example, any number of semipermeable membrane modules greater than or equal to two.

[0022] Each of the plurality of semipermeable membrane modules 1, 2, 3 has a semipermeable membrane 10, 20, 30, and a first chamber 11, 21, 31 and a second chamber 12, 22, 32 separated by the semipermeable membrane.

[0023] A concentration flow path 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 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.

[0024] In addition, a dilution flow path is provided in which the second chambers 12, 22, and 32 of the multiple semipermeable membrane modules 1, 2, and 3 are connected. That is, the dilution flow path 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.

[0025] The target solution flows through the concentration flow path described above. The target solution flows 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.

[0026] 1, an auxiliary solution having an osmotic pressure is passed through the dilution flow path. The auxiliary solution flows 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. In other words, the auxiliary solution flows in the reverse order of the target solution in the connection of the semipermeable membrane modules. However, the auxiliary solution is not limited to the embodiment shown in FIG. 1, and may flow through 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 in this order.

[0027] In each semipermeable membrane module, the flow direction of the liquid on both sides of the semipermeable membrane (in the first and second chambers) may be any direction, and may be opposite directions (counterflow system) or parallel directions (parallel flow system).

[0028] 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).

[0029] The target solution is pressurized 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.

[0030] Because the target solution has a higher pressure than the auxiliary solution, in each of the multiple semipermeable membrane modules, the solvent (such as water) 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.

[0031] The concentration system of this embodiment includes: an auxiliary solution booster pump in the dilution flow path for boosting the pressure of the auxiliary solution; an auxiliary solution booster pump suction pressure gauge that is installed on the suction side of the auxiliary solution booster pump and that measures the pressure of the auxiliary solution; The system further includes a control device connected to the auxiliary solution booster pump suction pressure gauge and the auxiliary solution booster pump. The discharge capacity (motor rotation speed, etc.) of the auxiliary solution booster pump is controlled by a control device so that the pressure measured by the auxiliary solution booster pump suction pressure gauge reaches a target value.

[0032] It is also possible to control the discharge capacity of the auxiliary solution booster pump so as to achieve a predetermined differential pressure, flow rate, or temperature using a pressure gauge that measures the discharge side of the auxiliary solution booster pump, a differential pressure gauge that measures the differential pressure between the inlet and outlet of the second chamber of the semipermeable membrane module, a flow meter that measures the flow rate at the inlet and outlet of the second chamber of the semipermeable membrane module, or a thermometer that measures the temperature upstream and downstream of the auxiliary solution booster pump, but it is preferable to control so that the pressure measured by the auxiliary solution booster pump suction pressure gauge becomes a target value.

[0033] According to the concentration system of this embodiment having the above-mentioned features, when the concentration system (membrane separation system) of this embodiment is used to separate and concentrate water from a target solution by brine concentration (BC) (i.e., osmotically assisted reverse osmosis (OARO)), the pressure of the auxiliary solution flowing through the dilution flow path can be appropriately controlled.

[0034] The concentration system of this embodiment may be provided with a concentrated liquid pressure gauge (target solution pressure gauge) in the concentration flow path that measures the pressure of the concentrated liquid (target solution), and a concentrated liquid concentration meter that measures the concentration of the target component in the concentrated liquid and is connected to a control device. As described below, by using the concentrate pressure gauge and concentrate concentration meter in combination to start the auxiliary solution booster pump and control the discharge capacity, appropriate pressure control of the dilution path can be used to prevent damage, malfunction, etc. to the semipermeable membrane module and the auxiliary solution booster pump. A specific example of control will be described below.

[0035] As an example of this embodiment, the concentration system shown in Figure 1 includes a first auxiliary solution booster pump 41 provided upstream of the dilution flow path, an auxiliary solution booster pump suction pressure meter 51 installed on the suction side thereof, a control device 61 for the first auxiliary solution booster pump 41, a second auxiliary solution booster pump 42 provided downstream of the dilution flow path, an auxiliary solution booster pump suction pressure meter 52 installed on the suction side thereof, and a control device 62 for the second auxiliary solution booster pump 42.

[0036] The first auxiliary solution booster pump 41 and the second auxiliary solution booster pump 42 each have a pump body 41a, 42a and a motor 41b, 42b connected to a drive section of the pump body. Each of the control devices 61 and 62 includes a regulator 61a, 62a and an inverter 61b, 62b that controls the rotation speed of the motor 41b, 42b so that the measurement value of the auxiliary solution booster pump suction pressure gauge 51, 52 becomes a predetermined target pressure value. Although not shown, the control devices 61 and 62 also include control devices such as PLCs (Programmable Logic Controllers) that input signals from each regulator and inverter and output instructions to each regulator and inverter to start and stop control (starting and stopping a pump, etc.).

[0037] An example of this embodiment is a basic control method for the concentration system shown in FIG. 1, which will be described below. Input signals (such as analog signals) of the measured pressures of the auxiliary solution booster pump suction pressure gauges 51 and 52 are input to the regulators 61a and 62a, and manipulated values ​​(MVs) calculated to achieve the target pressure values ​​(target values) set by the regulators are input to the inverters 61b and 62b. The inverters 61b and 62b output inverter frequencies corresponding to the manipulated values ​​(MVs) to the motors 41b and 42b. The motors then operate at rotational speeds corresponding to the inverter frequencies, thereby determining the rotational speeds (discharge capacities) of the pump bodies 41a and 42a.

[0038] Examples of control methods for the manipulated variable (MV) of the controllers 61a and 62a include ON-OFF control, proportional control, feedback control, PID (Proportional-Integral-Differential) control, and cascade control. Furthermore, upper and lower limits for the outputtable manipulated variable (MV) may be set. The acceleration and deceleration times (speeds) of the inverter frequency may also be set appropriately. Furthermore, the target values ​​may be set appropriately, taking into consideration the pressure resistance of the auxiliary solution booster pump and the semipermeable membrane module, etc.

[0039] Furthermore, the following control methods (a to h) can also be used based on the above basic control method. Any of these control methods may be used, or they may be combined as appropriate.

[0040] (Method for controlling the discharge capacity of the auxiliary solution booster pump) a) The discharge capacities of the auxiliary solution booster pumps 41 and 42 are controlled independently (by dedicated control devices 61 and 62 for each auxiliary solution booster pump). b) The discharge capacity of each auxiliary solution booster pump 41, 42 is controlled in sequence (e.g., sequentially from the upstream side of the dilution flow path) every fixed time (control cycle time). At this time, the rotation speed of the auxiliary solution booster pump that is not controlled is maintained based on the manipulated variable (MV) calculated within the control cycle time. c) The manipulated variable (MV) of the controller 62a is a value obtained by multiplying the manipulated variable (MV) of the controller 61a (upstream of the dilution flow path) by a predetermined coefficient. The coefficient may be automatically changed (corrected) to an appropriate value.

[0041] (Method for controlling the start and control of the auxiliary solution booster pump) d) When the measurement value of each auxiliary solution booster pump suction pressure gauge 51, 52 reaches a predetermined pressure, start each auxiliary solution booster pump 41, 42. At this time, the above-mentioned control (control of the discharge capacity of the auxiliary solution booster pump) may be started immediately, or the pumps may be started (run-in) for a certain period of time at a predetermined operation amount (inverter frequency) before transitioning to the above-mentioned control. e) When the measured values ​​of all the auxiliary solution booster pump suction pressure gauges 51, 52 reach a predetermined pressure, start all the auxiliary solution booster pumps 41, 42. At this time, the above-mentioned control may be started immediately, or the pumps may be started (run-in) for a certain period of time at a predetermined operation amount (inverter frequency) before transitioning to the above-mentioned control.

[0042] (Control methods for monitoring and other aspects of concentration systems) f) High-pressure and low-pressure alarm values ​​are set on the auxiliary solution booster pump suction pressure gauges 51 and 52, and the concentration system is stopped when the measurement value of the auxiliary solution booster pump suction pressure gauge falls outside the range of these high-pressure and low-pressure alarm values. A certain delay time may be set after the high-pressure and low-pressure alarm values ​​fall outside the range. These alarm values ​​may be set appropriately taking into consideration the pressure resistance of the auxiliary solution booster pump and the semipermeable membrane module, etc. g) High-pressure and low-pressure control monitor values ​​(preliminary alarm values) are set between the high-pressure and low-pressure alarm values ​​and the target values, and an alarm is issued when the measurement value of the auxiliary solution booster pump suction pressure gauge is outside the range of the high-pressure and low-pressure control monitor values ​​for a predetermined time. These control monitor values ​​may be set appropriately taking into consideration the withstand pressure of the auxiliary solution booster pumps 41, 42 and the semipermeable membrane modules 1, 2, 3, etc. h) Although not shown, a pressure gauge is provided on the discharge side of the auxiliary solution booster pumps 41 and 42 to set an alarm value on the high pressure side, and if this value is exceeded, the concentration system is stopped. This alarm value may be set appropriately taking into consideration the withstand pressure of the auxiliary solution booster pumps 41 and 42 and the semipermeable membrane modules 1, 2, and 3, etc.

[0043] When the system is stopped, it is preferable to stop the pressurizing equipment (equipment for feeding the target solution into the first chamber while pressurizing it) such as a high-pressure pump after stopping the auxiliary solution booster pumps 41 and 42. As mentioned above, this is to avoid applying pressure only to the second chambers 12, 22, 32 in consideration of the case where application of pressure only to the second chambers 12, 22, 32 is undesirable in terms of the pressure resistance of the semipermeable membrane modules 1, 2, 3. More preferably, a pressure gauge (not shown) is provided on the discharge side of each of the auxiliary solution booster pumps 41 and 42, and the high-pressure pump is stopped after the pressure measured by the pressure gauge drops to a predetermined pressure. The order in which the pumps are stopped may be set so that the time until each pump is stopped (frequency=0 Hz) is graded according to the deceleration time of the inverter.

[0044] A specific example of the above control method is as follows. The auxiliary solution is supplied to the second chamber 32 of the semipermeable membrane module 3 at a predetermined pressure, and is discharged from the second chamber 32 as a diluted auxiliary solution mixed with the solvent that has permeated through the semipermeable membrane 30 . The pressure of the diluted auxiliary solution is measured by the auxiliary solution booster pump suction pressure gauge 51, and if the measured value is higher than the target value of the regulator 61a, the discharge capacity of the auxiliary solution booster pump 41 is adjusted to be lower, and if the measured value is lower than the target value, the discharge capacity is adjusted to be higher. The diluted auxiliary solution is sent to the second chamber 22 of the semipermeable membrane module 2 at the discharge pressure adjusted in this manner. The pressure of the auxiliary solution, which is further diluted by mixing with the solvent that has permeated through the semipermeable membrane 20 and reduced in pressure due to pressure loss when passing through the second chamber 22 of the semipermeable membrane module 2, is measured again by the auxiliary solution booster pump suction pressure gauge 52, and the discharge capacity of the auxiliary solution booster pump 42 is adjusted in the same manner as in the above-mentioned specific example (in the case of the auxiliary solution booster pump 41). Then, the auxiliary solution is sent to the second chamber 12 of the semipermeable membrane module 1 at the adjusted discharge pressure. The auxiliary solution that has been further diluted by mixing with the permeated water that has permeated through the semipermeable membrane 10 is discharged as a dilute solution from the second chamber 12 of the semipermeable membrane module 1.

[0045] With this example of the present embodiment described in Figure 1, the dilution flow path can maintain an appropriate pressure, and the concentration system can be operated stably while avoiding damage or failure of each semipermeable membrane module and auxiliary solution booster pump.

[0046] As another example of this embodiment, the concentration system shown in Fig. 2 is different from the system shown in Fig. 1 in that it is equipped with a concentrated liquid pressure meter 70 (target solution pressure meter) and a concentrated liquid concentration meter 80. This system differs from the example of this embodiment shown in Fig. 1 in that the concentrated liquid pressure meter 70 and the concentrated liquid concentration meter 80 are used before control starts. The concentration system shown in FIG. 2 is particularly effective when the pressure resistance of the semipermeable membrane module is lower in the second chamber than in the first chamber, or when it is not desirable to apply pressure only to the second chamber.

[0047] Specifically, it is as follows: After the concentration system is started, the target solution is first supplied to the first chamber of each semipermeable membrane module with almost no pressure. Next, when the concentration of the target component measured by the concentrated solution concentration meter 80 reaches a predetermined concentration (target solution concentration, etc.), pressure is applied to the target solution up to a required value. Next, when the pressure measured by the concentrated liquid pressure gauge 70 reaches a predetermined pressure, the auxiliary solution is supplied at a predetermined flow rate and pressure. The above-described sequence of auxiliary solution booster pump activation and control then begins.

[0048] When the concentration system is started with the semipermeable membrane module filled with an aqueous solution with a low osmotic pressure, such as a storage solution, and the target solution is applied at the required pressure immediately after start-up, the solvent in the storage solution will easily permeate through the semipermeable membranes 10, 20, and 30 to the second chambers 12, 22, and 32 before the storage solution in each first chamber 11, 21, and 31 is discharged. In other words, pressure equivalent to the solvent in the dilution flow path is likely to be applied to each second chamber. Therefore, this problem can be alleviated by filling each first chamber with a target solution with a relatively high osmotic pressure and then applying the required pressure to each first chamber.

[0049] (target solution and auxiliary solution) The target solution and auxiliary solution are not particularly limited as long as the target component is dissolved in a solvent. Examples of solvents include water, and the target component can be any component that dissolves in the solvent. For example, salt water (brine, seawater, brackish water, etc.) and industrial wastewater (aqueous solutions containing inorganic salts, aqueous solutions containing water-soluble organic solvents, etc.) can be used. The concentration system described above is particularly suitable for further concentrating a target solution that is highly concentrated (high osmotic pressure), such as brine.

[0050] 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.

[0051] Theoretically, membrane separation using BC 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, the difference in osmotic pressure between the target solution and the auxiliary solution is preferably 30% or less of the pressure of the target solution.

[0052] The auxiliary solution is not particularly limited as long as it is a liquid having osmotic pressure, but as shown in Figure 3, 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. It is preferable that a mechanism for reducing the pressure of the liquid is provided in the flow path for supplying a portion of the concentrated liquid as an auxiliary solution to the dilution flow path (the second chamber of the semipermeable membrane module). Examples of such a mechanism include devices such as automatic adjustment valves 90a and 90b that maintain high pressure on the upstream side and reduce pressure on the downstream side, and energy recovery devices that have a mechanism for converting energy recovered from pressurized supply liquid into auxiliary energy for driving a pump or the like.

[0053] Alternatively, a dilute solution may be supplied to the concentration flow path together with the target solution, and the target solution may 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.

[0054] 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.

[0055] (Multiple semipermeable membrane modules) In a concentration process (membrane separation process) using BC with multiple semipermeable membrane modules, osmotic pressure acting in the opposite direction to the direction in which the solvent moves from the first compartment to the second compartment is unlikely to occur, so concentration can proceed at a lower pressure (pump pressure) than in reverse osmosis (RO). Therefore, in the concentration system of this embodiment, which mainly performs concentration using BC, the power consumption of pumps, etc. can be reduced, and the energy efficiency of concentration can be improved.

[0056] Furthermore, 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 any further water from passing through the semipermeable membrane and preventing concentration from proceeding. In contrast, in membrane separation treatment (concentration method) using 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, a concentration system using the BC method can increase the final concentration of the target solution more than a concentration system using only the RO method. In principle, it is thought that the target solution can be concentrated to its saturated concentration.

[0057] In this embodiment, as in the multistage concentration systems shown in Figure 2 of Patent Document 1 (WO 2018 / 084246) and Figure 4 of Patent Document 2 (JP 2019-188330 A), one or more additional semipermeable membrane modules may be connected in parallel to each of multiple semipermeable membrane modules 1a, 1b, 1x, and 1y connected in series.

[0058] As shown in Figure 2 of Patent Document 1 and Figure 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) via a semipermeable membrane, the amount of flow increases toward the downstream side of the dilution flow path, and the flow resistance tends to increase. For this reason, 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.

[0059] Furthermore, in a multistage concentration system such as that of this embodiment, the target solution flowing in the first chamber (concentration flow path) is sequentially concentrated from semipermeable membrane module 1 to semipermeable membrane module 3, and the flow rate of the target solution decreases as the concentration progresses. 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.

[0060] The dilution flow path may be partially discontinuous. As an example, as shown in Figure 5, a part of the target solution may be supplied as an auxiliary solution to the second chamber 12 of the semipermeable membrane module 1. In this way, by making the dilution flow path partially discontinuous, the length of the continuous dilution flow path (flow path length) is reduced compared to when all second chambers of multiple semipermeable membrane modules are connected in series. Here, since the flow resistance (pressure loss) of the dilution flow path is proportional to the flow path length, the flow resistance of the dilution flow path is reduced. Therefore, it becomes easier to control the pressure of the auxiliary solution in the dilution flow path within an appropriate range. In addition, the number of auxiliary solution booster pumps installed midway through the dilution flow path can be reduced, resulting in reduced equipment costs, energy consumption, etc.

[0061] Furthermore, in the concentration system of this embodiment, the configuration disclosed in Japanese Patent No. 7020512 can be applied.

[0062] The semipermeable membrane used in this embodiment may be, for example, a semipermeable membrane called a reverse osmosis membrane (RO membrane), a forward osmosis membrane (FO membrane), a nanofiltration membrane (NF membrane), or an ultrafiltration membrane (UF membrane). 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.

[0063] Typically, RO 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 other 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.

[0064] 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.

[0065] 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.

[0066] The polysulfone-based resin is preferably a polyethersulfone-based resin. The polyethersulfone-based resin is preferably a sulfonated polyethersulfone.

[0067] In the drawings, the semipermeable membranes of the semipermeable membrane module 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.

[0068] 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. This is 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 also because, although hollow fiber membranes generally easily maintain their structure against external pressure, the hollow fiber membranes may be damaged if the internal pressure becomes too high.

[0069] 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.

[0070] Another specific example of a hollow fiber membrane is a two-layer membrane having a dense layer of 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 polyamide resin on the outer surface of a support layer (e.g., a layer made of polysulfone or polyethersulfone). [Explanation of symbols]

[0071] 1, 2, 3 semipermeable membrane module, 10, 20, 30 semipermeable membrane, 11, 21, 31 first chamber, 12, 22, 32 second chamber, 41 (first) auxiliary solution booster pump, 42 (second) auxiliary solution booster pump, 41a, 42a pump body, 41b, 42b motor, 51, 52 auxiliary solution booster pump suction pressure gauge, 61, 62 control equipment, 61a, 62a regulator, 61b, 62b inverter, 70 concentrated liquid pressure gauge, 80 concentrated liquid concentration meter, 90a, 90b automatic adjustment valve.

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, comprising: A plurality of semipermeable membrane modules are provided, Each of the plurality of semipermeable membrane modules has a semipermeable membrane and a first chamber and a second chamber separated by the semipermeable membrane, a concentration flow path is provided in which the first chambers of the plurality of semipermeable membrane modules are connected, a dilution flow path is provided in which the second chambers of the plurality of semipermeable membrane modules are connected; The target solution is flowed through the concentration flow path, An auxiliary solution having an osmotic pressure is flowed through the dilution flow path, When the target solution has a higher pressure than the auxiliary solution, in each of the plurality of semipermeable membrane modules, the solvent contained in the target solution in the first chamber migrates through the semipermeable membrane to the auxiliary solution in the second chamber, and the target solution is concentrated, thereby obtaining the concentrated liquid; The concentration system comprises: an auxiliary solution booster pump in the dilution flow path for boosting the pressure of the auxiliary solution; an auxiliary solution booster pump suction pressure gauge that is installed on the suction side of the auxiliary solution booster pump and that measures the pressure of the auxiliary solution; a control device connected to the auxiliary solution booster pump suction pressure gauge and the auxiliary solution booster pump; Concentration system.

2. 2. The concentration system according to claim 1, wherein the control device controls the discharge capacity of the auxiliary solution booster pump so that the measurement value of the auxiliary solution booster pump suction pressure gauge reaches a target value.

3. 3. The concentration system according to claim 1, wherein the control device starts controlling activation and discharge capacity of the auxiliary solution booster pump when the measurement value of the auxiliary solution booster pump suction pressure gauge reaches or exceeds a predetermined value.

4. a concentrate concentration meter that is installed in the concentration flow path and is connected to the control device and that measures the concentration of the target component in the concentrate; When the measurement value of the concentrated solution concentration meter also reaches a predetermined value or more, the auxiliary solution booster pump is started to be activated and its discharge capacity is controlled. The concentration system according to claim 1 or 2.

5. The concentration system according to claim 1 or 2, wherein a part of the concentrate is used as the auxiliary solution.

6. The concentration system according to claim 1 or 2, further comprising a pressurizing device for pressurizing the target solution to a pressure higher than that of the auxiliary solution.

7. The concentration system according to claim 1 or 2, wherein the semipermeable membrane is a hollow fiber membrane.