Energy recovery device

Abstract

To provide an energy recovery device that can suppress rapid fluctuations in the flow rate and pressure of high-pressure saltwater, which is a high-pressure supply water. [Solution] The system comprises first and second cylinder devices 9A and 9B connected to a concentrated water pipe 4 via first or second flow path switching mechanisms 6A and 6B, a control unit C that controls the flow and discharge of concentrated brine to these devices, and a flow path direction regulating mechanism 11 that fills the first and second cylinder devices with low-pressure brine and returns the high-pressure brine that is pushed out to the membrane separator. The first and second flow path switching mechanisms are equipped with a switching valve device that switches between discharging and stopping concentrated brine from the cylinder devices, and the switching valve device has concentrated-side valves 14A and 14B. The control unit controls these valves to minimize the fluctuation in the total flow rate of concentrated brine supplied from the concentrated-side connecting pipe to one of the first and second cylinders and the flow rate of concentrated brine supplied to the other of the first and second cylinders.

Description

Technical Field

[0001] The present invention relates to an energy recovery device for a water treatment system by a reverse osmosis membrane method used for desalination of seawater, brackish water, groundwater, industrial water, etc.

Background Art

[0002] As one method for producing fresh water from seawater, the reverse osmosis method is known. In this reverse osmosis method, a pressure higher than the osmotic pressure of seawater is applied to seawater in the direction opposite to the direction in which the osmotic pressure acts, and filtration is performed using a semipermeable membrane (reverse osmosis membrane (RO membrane)) to separate salts and fresh water. In this reverse osmosis method, seawater (concentrated brine) from which fresh water has been separated and salts have been concentrated flows out of the reverse osmosis membrane module while retaining high pressure energy. In order to effectively utilize the high pressure energy possessed by this outflowing concentrated brine, various energy recovery devices have been put into practical use.

[0003] In a positive displacement energy recovery device, seawater pumped from a water intake pump is pressurized by a high-pressure pump and supplied to a reverse osmosis membrane module. At the same time, high-pressure concentrated brine discharged from the reverse osmosis membrane module is supplied to a cylinder device to extrude seawater at high pressure, and high-pressure seawater is also sent from the cylinder device to the reverse osmosis membrane module via a booster pump. The operation of supplying the high-pressure concentrated brine discharged from this reverse osmosis membrane module to the cylinder device to extrude seawater at high pressure is called a pressure pumping process (or energy recovery process). Also, after the pressure pumping process is completed, seawater is supplied from the water intake pump to the cylinder device via a flow path direction control device, and the operation of filling seawater while discharging concentrated brine in the direction opposite to the pressure pumping process is called a filling process (or water supply process). Thus, in this energy recovery device, when the piston of the cylinder device reaches the end of the cylinder, control is performed so that the high-pressure concentrated brine from the reverse osmosis membrane module is alternately supplied to a pair of cylinder devices and seawater is alternately filled into the pair of cylinder devices from the water intake pump.

[0004] Conventionally, for example, Patent Document 1 describes an energy recovery device in which a control unit slows down the movement speed of the drain-side piston of a switching cylinder device to gradually initiate communication when one end of the first cylinder device or the second cylinder device is connected to a drain pipe, and slows down the movement speed of the drain-side piston of the switching cylinder device to gradually disconnect communication when one end of the first cylinder device or the second cylinder device is disconnected from the drain pipe. In this device, when communication with the drain pipe is established, the residual pressure inside the cylinder device is gradually released, and when disconnection is established, the movement speed of the drain-side piston of the switching cylinder device is controlled to gradually reduce the discharge flow rate from the first cylinder device or the second cylinder device, thereby preventing the generation of impact noise due to water hammer (pressure rise phenomenon (water hammer phenomenon)). [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Patent No. 6057348 [Overview of the project] [Problems that the invention aims to solve]

[0006] The following challenges remain in the conventional technologies described above. In other words, the conventional technology described above prevents the generation of impact noise from the first or second cylinder device by controlling the movement speed of the discharge piston of a switching cylinder device having a cylinder and a piston. However, this method employs a switching cylinder device with a complex structure and high cost, resulting in high costs. As a countermeasure, the applicant is developing an energy recovery device that controls a concentrated valve provided in a concentrated-side connecting pipe connecting one end of the first cylinder device or the second cylinder device to a concentrated water pipe, and a drain-side valve provided in a drain-side connecting pipe connecting one end of the first cylinder device or the second cylinder device to a drain pipe, and which can employ inexpensive ball valves or the like with a simple structure.

[0007] However, in the case of the energy recovery device 100 using these valves, as shown in Figure 12, a position detector S0, which is provided near the end of one of the two cylinders, for example the first cylinder 107A, detects the first piston 108A and detects when the first piston 108A has reached the vicinity of the end of the first cylinder 107A. This simultaneously marks the end of the pumping process for its own first cylinder 107A (i.e., its own enrichment-side valve 114A receives a "fully closed" command and starts "closed") and the start of the pumping process for the other second cylinder 107B (i.e., the other enrichment-side valve 114B receives a "fully open" command and starts "open"). In this case, as shown in Figure 13, the characteristics of the ball valve are equal percentage characteristics (the change in the Cv value (capacity coefficient indicating ease of flow) is small when the valve opening is small, and the Cv value increases significantly as the valve opening increases). Therefore, during the operation of the concentrate valve 114A on the first cylinder 107A side and the concentrate valve 114B on the second cylinder 107B side, as shown in Figure 14, the flow rate of the high-pressure supply water (high-pressure brine) discharged from the two cylinders 107A and 107B to the RO membrane (pressure booster pump 110 side) 105 decreases significantly.

[0008] Furthermore, as shown in Figure 15, for example, a change in the operating point of the high-pressure pump 110B that supplies water to the RO membrane 105 can cause a pressure increase within the energy recovery device 100 system. That is, if the total flow rate of concentrated brine from the concentration valve to one cylinder and the flow rate of concentrated brine from the concentration valve to the other cylinder decreases, the operating point of the high-pressure pump 110B shifts from point A to point B, and the total head of the high-pressure pump 110B changes from H to H' (in the case of a centrifugal pump, the operating point shifts to the lower flow rate side, and the discharge pressure increases. In the case of a reciprocating pump, the resistance at the water supply destination increases, and the discharge pressure increases). When the operating point of the high-pressure pump 110B changes in this way and the pressure within the system increases, there is a risk of vibration, noise, and damage to the RO membrane 105.

[0009] Furthermore, as shown in Figure 12, for example, if the concentration-side valve 114A and the drain-side valve 115A of the first cylinder 107A are both slightly open at the same time, high-pressure concentrated water leaks to the low-pressure concentrated water side (so-called leaking occurs), which reduces energy recovery efficiency, increases the discharge rate of the high-pressure pump 110B, increases power consumption, and results in uneconomical operation (reduced energy-saving performance). For example, if the position detector S0 detects a piston and simultaneously initiates the "closing" operation of the concentration-side valve 114A and the "opening" operation of the drain-side valve 115A of its own cylinder, the concentration-side valve and the drain-side valve may communicate, causing high-pressure concentrated water to leak to the low-pressure concentrated water side. Furthermore, even if the opening / closing command is sent at a timing that would theoretically prevent communication, if the ball valve is pneumatic, a time lag may occur between the receipt of the opening / closing command and the actual operation of the valve body due to its structure. This time lag may also cause the concentration-side valve and the drain-side valve to communicate, resulting in high-pressure concentrated water leaking to the low-pressure concentrated water side.

[0010] This invention has been made in view of the above-mentioned conventional problems, and aims to provide an energy recovery device that can suppress rapid fluctuations in the flow rate and pressure of high-pressure saltwater, which is high-pressure supplied water. [Means for solving the problem]

[0011] The present invention employs the following configuration to solve the above problems. Specifically, the energy recovery device according to the first invention is connected to a membrane separation device which is connected to a supply pipe of high-pressure brine and separates the high-pressure brine into fresh water and concentrated brine using a reverse osmosis membrane, discharges the fresh water into a fresh water pipe and the concentrated brine into a concentrated brine pipe, and is connected to a membrane separation device which is connected to a supply pipe of high-pressure brine and separates the high-pressure brine into fresh water and concentrated brine using a reverse osmosis membrane, discharges the fresh water into a fresh water pipe and discharges the concentrated brine into a concentrated brine pipe, and is connected to a first cylinder device which has one end connected to the concentrated brine pipe and the drain pipe and moves back and forth within a first cylinder, and is connected to the concentrated brine pipe and the drain pipe via a second flow path switching mechanism which has one end connected to the concentrated brine pipe and the drain pipe and moves back and forth within a second cylinder The device comprises a cylinder device, a control unit having a control function to control the first flow path switching mechanism and the second flow path switching mechanism to switch the connections between the first cylinder device and the second cylinder device to the concentrated water pipe and the drain pipe, and to alternately supply the concentrated brine to the first cylinder device and the second cylinder device, and a control function to alternately discharge the concentrated brine from the first cylinder device and the second cylinder device, and a flow path direction restricting mechanism connected to the other end of the first cylinder device and the other end of the second cylinder device, which alternately supplies low-pressure brine to the first cylinder device and the second cylinder device, and returns the high-pressure brine that is alternately pushed out from the first cylinder device and the second cylinder device to the membrane separator via a pressure increasing means,The first flow path switching mechanism and the second flow path switching mechanism include a switching valve device for switching between supplying the concentrated brine to the first cylinder device or the second cylinder device and stopping the supply, and discharging the concentrated brine from the first cylinder device or the second cylinder device and stopping the discharge, the switching valve device includes a one-way concentrated valve provided in the concentrated water connecting pipe that connects one end of the first cylinder device and the second cylinder device to the concentrated water pipe, and a one-way drain valve provided in the drain connecting pipe that connects one end of the first cylinder device and the second cylinder device to the drain pipe, and the first The device includes a concentrated-side valve for the other side provided in a concentrated-side connecting pipe that connects the other end of the cylinder device and the second cylinder device to the concentrated water pipe, and a drain-side valve for the other side provided in a drain-side connecting pipe that connects the other end of the first cylinder device and the second cylinder device to the drain pipe, wherein the control unit controls the concentrated-side valve for the one side and the concentrated-side valve for the other side to minimize the fluctuation in the total flow rate of the concentrated brine supplied from the concentrated-side connecting pipe to one of the first cylinder and the second cylinder, and the flow rate of the concentrated brine supplied to the other of the first cylinder and the second cylinder.

[0012] In this energy recovery device, the control unit controls the one-side concentration valve and the other-side concentration valve to minimize fluctuations in the total flow rate of concentrated brine supplied from the concentration-side connecting pipe to one of the first and second cylinders, and the flow rate of concentrated brine supplied to the other of the first and second cylinders. This suppresses sudden fluctuations in the flow rate and pressure of the high-pressure brine, which is the high-pressure supply water.

[0013] The energy recovery device according to the second invention is provided near the other end of the first cylinder and the second cylinder and detects when the first piston or the second piston reaches the vicinity of the other end of the corresponding first cylinder or the second cylinder; a pair of second position detectors provided at a position further to the other end of the first cylinder and the second cylinder than the first position detectors and detects when the first piston or the second piston reaches a position further to the other end than the first position detectors; and a first piston or the second piston is provided near one end of the first cylinder and the second cylinder and detects when the first piston or the second piston reaches the vicinity of the corresponding first cylinder or the second cylinder The device is equipped with a pair of third position detectors that detect when it has reached the vicinity of one end of the cylinder, and the control unit transmits an open operation signal to the other-side concentration valve to open when the first position detector of one of the first cylinders or the second cylinder detects one of the first pistons or the second piston, and transmits a close operation signal to the one-side concentration valve to close when the second position detector of one of the first cylinders or the second cylinder detects one of the first pistons or the second piston, and the distance between the first position detector and the second position detector in one of the first cylinders or the second cylinder is set to a distance that minimizes the fluctuation amount of the total flow rate. In other words, in this energy recovery device, the distance between the first position detector and the second position detector is set to a distance that minimizes the fluctuation in the total flow rate. Therefore, by adjusting the opening and closing timing of the one-way enrichment valve and the other-way enrichment valve, the fluctuation in the total flow rate can be easily minimized by adjusting the distance between the first position detector and the second position detector.

[0014] The energy recovery device according to the third invention is characterized in that, in the first invention, it is provided with a pair of other-end position detectors located near the other ends of the first cylinder and the second cylinder, which detect when the first piston or the second piston has reached the vicinity of the corresponding other end of the first cylinder or the second cylinder, and when the other-end position detector of one of the first cylinder and the second cylinder detects one of the first piston and the second piston, the control unit transmits an open operation signal to the other-side concentration valve to open, and after a delay of a first predetermined time after transmitting the open operation signal, transmits a close operation signal to the one-side concentration valve to close, and the first predetermined time is set to minimize the fluctuation amount of the total flow rate. In other words, in this energy recovery device, after sending an open operation signal to the other enrichment valve, a close operation signal is sent to the one enrichment valve after a first predetermined time delay. Since the first predetermined time is set to the time that minimizes the fluctuation in the total flow rate, only other-end position detectors need to be installed near the other ends of the first and second cylinders, and the fluctuation in the total flow rate can be easily set to the minimum without installing another position detector at a position offset from the other-end position detector.

[0015] The energy recovery device according to the fourth invention is characterized in that, in any of the first to third inventions, it is provided with a pair of terminal position detectors located near the other end of the first cylinder and the second cylinder and detecting when the first piston or the second piston has reached the vicinity of the corresponding other end of the first cylinder or the second cylinder, and when the terminal position detector of one of the first cylinder and the second cylinder detects one of the first piston and the second piston, the control unit transmits a closing operation signal to the one-way concentration side valve to close, and after a delay of a second predetermined time after transmitting the closing operation signal, transmits an opening operation signal to the one-way drain side valve to open, the second predetermined time being set to the time until the one-way concentration side valve is fully closed. In other words, in this energy recovery device, after sending a closing operation signal to the one-way concentration side valve, an opening operation signal is sent to the one-way drain side valve after a second predetermined time delay. Since the second predetermined time is set to the time until the one-way concentration side valve is fully closed, it is possible to prevent leakage of high-pressure concentrated water to the low-pressure concentrated water side that would occur if the one-way drain side valve were to open while the one-way concentration side valve was closing.

[0016] The energy recovery device according to the fifth invention is characterized in that, in the second invention, it comprises a flow meter connected to the concentration-side connecting pipe and transmitting a flow signal measuring the flow rate of the concentrated brine to the control unit, and a detector movement mechanism that moves at least one of the first position detector and the second position detector in a direction along the axis of the corresponding first cylinder or the second cylinder, and the control unit can adjust the position of at least one of the first position detector and the second position detector by the detector movement mechanism based on the received flow signal.

[0017] If the flow rate of concentrated brine in the pumping process increases or decreases for any reason, the timing of the increase in the flow rate of concentrated brine in the other pumping process, detected by the first position detector on one side and initiated by the pumping process on the other side (i.e., the concentrated valve for the other side receives a fully open command and starts the "open" operation), and the timing of the decrease in the flow rate of concentrated brine in the other pumping process, may be out of sync. This can cause the flow rate of the pumping process to increase or decrease significantly or be interrupted when the cylinders of the pumping process switch. However, in the above-mentioned energy recovery device, the control unit can adjust the position of at least one of the first position detector and the second position detector using a detector movement mechanism based on the received flow rate signal. Therefore, even if the flow rate of concentrated brine in the pumping process increases or decreases for any reason, the position of at least one of the first position detector and the second position detector can be automatically adjusted and set to a distance that minimizes the fluctuation in the total flow rate.

[0018] The energy recovery device according to the sixth invention, in any one of the first to third inventions, includes a connecting pipe for returning the high-pressure brine alternately extruded from the first cylinder device and the second cylinder device to the membrane separation device, and a pressure gauge for measuring a pressure signal of at least one of the concentrated brine in the concentrated side connection pipe and the high-pressure brine in the connecting pipe and transmitting the pressure signal to the control unit. The control unit is characterized in that when the pressure signal exceeds a certain pressure, the opening and closing speed of at least one of the concentrated side valve for one side and the concentrated side valve for the other side can be adjusted.

[0019] When the opening and closing time of the valve is fast, the speed at which the flow rate of the concentrated brine in the pressure feeding process of one cylinder decreases and the speed at which the flow rate in the pressure feeding process of the other cylinder increases both become fast. At this time, if for some reason the timing of the decrease in the flow rate of one cylinder and the increase in the flow rate of the other cylinder is shifted, compared to the case where the opening and closing time of the valve is slow, the flow rate significantly increases and decreases, the operating point of the high-pressure pump fluctuates, and large pressure fluctuations may occur. However, in the above energy recovery device, since the control unit can adjust the opening and closing speed of at least one of the concentrated side valve for one side and the concentrated side valve for the other side when the pressure signal exceeds a certain pressure, when the pressure signal of the pressure measured when the cylinders in the pressure feeding process are switched exceeds a certain value, by automatically adjusting (for example, slowing down) the opening and closing speed of these valves, pressure fluctuations can be suppressed.

Advantages of the Invention

[0020] According to the present invention, the following effects can be obtained. That is, according to the energy recovery device of the present invention, the control unit controls the concentrated side valve for one side and the concentrated side valve for the other side to minimize the variation in the total flow rate of the supply flow rate of the concentrated brine from the concentrated side connection pipe to one of the first cylinder and the second cylinder and the supply flow rate of the concentrated brine to the other of the first cylinder and the second cylinder. Therefore, it is possible to suppress sudden fluctuations in the flow rate and pressure of the high-pressure brine, which is the high-pressure supply water. Therefore, in the energy recovery device of the present invention, it is possible to suppress the generation of vibration and noise and the damage of the reverse osmosis membrane (RO membrane).

Brief Description of the Drawings

[0021] [Figure 1] FIG. 1 is a schematic diagram showing a state in which in a first embodiment of the energy recovery device according to the present invention, the first cylinder device is in a pumping process and the second cylinder device is in a filling process. [Figure 2] FIG. 2 is a schematic diagram showing a state in which in the first embodiment, the first piston of the first cylinder device has reached the first position detector during the pumping process. [Figure 3] FIG. 3 is a graph showing the flow rate in the pumping process when the operation timings of the opening operation of the concentrated side valve of the second cylinder device and the closing operation of the concentrated side valve of the first cylinder device are controlled by the detections of the first and second position detectors in the first embodiment. [Figure 4] FIG. 4 is a graph showing the change in the total flow rate of the concentrated brine when the operation timing of the closing operation of the concentrated side valve of the first cylinder device is shifted to the slower side with respect to the opening operation of the concentrated side valve of the second cylinder device in the first embodiment. [Figure 5] FIG. 5 is a graph showing the flow rate in the pumping process when the operation timings of the opening operation of the concentrated side valve of the second cylinder device and the closing operation of the concentrated side valve of the first cylinder device are shifted and controlled in the second embodiment. [Figure 6] FIG. 6 is a graph showing the flow rates in the pumping process and the filling process when the operation timings of the full closing of the concentrated side valve of its own cylinder device and the start of the opening operation of the drain side valve of its own cylinder device are shifted and controlled in the third embodiment. [Figure 7] FIG. 7 is a schematic diagram showing a fourth embodiment of the energy recovery device according to the present invention. [Figure 8] FIG. 8 is a schematic structural diagram showing a detector moving mechanism on the cylinder in the fourth embodiment. [Figure 9] FIG. 9 is a schematic structural diagram showing another example of the detector moving mechanism on the cylinder in the fourth embodiment. [Figure 10]This is a schematic diagram showing a fifth embodiment of the energy recovery device according to the present invention. [Figure 11] In the fifth embodiment, this is a graph showing the flow rate of the pumping process against time, with respect to a steady state (a), and cases where the flow rate of the pumping process increases (b) and decreases (c). [Figure 12] This is a schematic diagram illustrating a situation in an energy recovery device using valves where the drain valve in the first cylinder unit opens before the enrichment valve is fully closed. [Figure 13] This graph shows the flow rate percentage relative to the opening percentage of a valve (ball valve). [Figure 14] This graph shows the total flow rate of high-pressure supply water discharged to the RO membrane side in relation to the opening and closing time of the valves to the two cylinders. [Figure 15] This graph shows that when the total flow rate of high-pressure supply water decreases, the operating point of the high-pressure pump supplying high-pressure supply water to the RO membrane changes. [Modes for carrying out the invention]

[0022] Hereinafter, a first embodiment of the energy recovery device according to the present invention will be described with reference to Figures 1 to 5.

[0023] As shown in Figures 1 and 2, the energy recovery device 1 in this embodiment is connected to a membrane separation device (RO membrane) 5 that is connected to a high-pressure brine supply pipe 2a and separates the high-pressure brine into fresh water and concentrated brine using a reverse osmosis membrane, discharging the fresh water into a fresh water pipe 3 and the concentrated brine into a concentrated water pipe 4.

[0024] This energy recovery device 1 includes a first cylinder device 9A having a first piston 8A that reciprocates within a first cylinder 7A, with one end connected to the concentrated water pipe 4 and the drain pipe 19 via a first flow path switching mechanism 6A that connects and disconnects the concentrated water pipe 4 and the concentrated brine drain pipe 19, and the second cylinder device 9B having a second piston 8B that reciprocates within a second cylinder 7B, with one end connected to the concentrated water pipe 4 and the drain pipe 19 via a second flow path switching mechanism 6B that connects and disconnects the concentrated water pipe 4 and the drain pipe 19, and the first cylinder device 9B controls the first flow path switching mechanism 6A and the second flow path switching mechanism 6B to control the concentrated water pipe 4 and the drain pipe 19. The device includes a control unit C which has a control function to switch the connection between the first cylinder device 9A and the second cylinder device 9B to 19 and alternately supply concentrated brine to the first cylinder device 9A and the second cylinder device 9B, and a control function to alternately discharge concentrated brine from the first cylinder device 9A and the second cylinder device 9B, and a flow path direction restricting mechanism 11 which is connected to the other end of the first cylinder device 9A and the other end of the second cylinder device 9B and alternately supplies low-pressure brine to the first cylinder device 9A and the second cylinder device 9B, and returns the high-pressure brine that is alternately pushed out from the first cylinder device 9A and the second cylinder device 9B to the membrane separation device 5 via a pressure boosting means 10.

[0025] A high-pressure pump 10B is connected to the base end of the supply pipe 2a, and a water intake pump (not shown) is connected to the base end of the water supply pipe 2b, which is connected to the supply pipe 2a. Furthermore, the concentrated water pipe 4 is branched midway and connected to the first flow path switching mechanism 6A and the second flow path switching mechanism 6B. The first flow path switching mechanism 6A and the second flow path switching mechanism 6B are equipped with a switching valve device 13 that switches between supplying concentrated brine to the first cylinder device 9A or the second cylinder device 9B and stopping the supply, and discharging concentrated brine from the first cylinder device 9A or the second cylinder device 9B and stopping the discharge.

[0026] The above-mentioned switching valve device 13 includes a one-way concentrated valve 14A provided on the concentrated-side connecting pipe 13a that connects one end of the first cylinder device 9A and the second cylinder device 9B to the concentrated water pipe 4, a one-way drain valve 15A provided on the drain-side connecting pipe 13b that connects one end of the first cylinder device 9A and the second cylinder device 9B to the drain pipe 19, a other-way concentrated valve 14B provided on the concentrated-side connecting pipe 13a that connects the other end of the first cylinder device 9A and the second cylinder device 9B to the concentrated water pipe 4, and a other-way drain valve 15B provided on the drain-side connecting pipe 13b that connects the other end of the first cylinder device 9A and the second cylinder device 9B to the drain pipe 19.

[0027] The control unit C controls the one-side concentration valve 14A and the other-side concentration valve 14B to minimize fluctuations in the total flow rate of concentrated brine supplied from the concentration-side connecting pipe 13a to one of the first cylinder 7A and the second cylinder 7B, and the total flow rate of concentrated brine supplied to the other of the first cylinder 7A and the second cylinder 7B.

[0028] Furthermore, the energy recovery device 1 of the present invention includes a pair of first position detectors S1 provided near the other ends of the first cylinder 7A and the second cylinder 7B to detect when the first piston 8A or the second piston 8B has reached the vicinity of the other end of the corresponding first cylinder 7A or the second cylinder 7B; a pair of second position detectors S2 provided at a position further to the other end of the first cylinder 7A and the second cylinder 7B than the first position detectors S1 to detect when the first piston 8A or the second piston 8B has reached a position (end) further to the other end than the first position detectors S1; and a pair of third position detectors S3 provided near one end of the first cylinder 7A and the second cylinder 7B to detect when the first piston 8A or the second piston 8B has reached the vicinity of the one end of the corresponding first cylinder 7A or the second cylinder 7B.

[0029] The control unit C is configured to transmit an open operation signal to the other-side enrichment valve 14B to open when the first position detector S1 of one of the first cylinder 7A and the second cylinder 7B detects one of the first piston 8A and the second piston 8B, and to transmit a close operation signal to the one-side enrichment valve 14A to close when the second position detector S2 of one of the first cylinder 7A and the second cylinder 7B detects one of the first piston 8A and the second piston 8B. Furthermore, the distance between the first position detector S1 and the second position detector S2 is set to the distance that minimizes the fluctuation in the total flow rate.

[0030] The above-mentioned one-way concentration valve 14A, one-way drain valve 15A, other-way concentration valve 14B, and other-way drain valve 15B are, for example, ball valves. Furthermore, if the above valves are ball valves, the cost can be further reduced by using inexpensive ball valves with a simple structure. In addition, ball valves used for air valves and the like can be used, making maintenance and inspection easier compared to conventional switching cylinder devices, and allowing for easy control simply by opening and closing the solenoid valve.

[0031] The other ends of the first cylinder device 9A and the second cylinder device 9B are connected to the water supply pipe 2b and the pressure boosting means 10 via a flow direction regulating mechanism 11 consisting of four check valves 11a. The pressure boosting means 10 is, for example, a pressure boosting pump. One end of the first cylinder device 9A is connected to the concentration-side connecting pipe 13a of the switching valve device 13 in the first flow path switching mechanism 6A, and one end of the second cylinder device 9B is connected to the discharge-side connecting pipe 13b of the switching valve device 13 in the second flow path switching mechanism 6B.

[0032] The flow direction regulating mechanism 11 has an annular pipe 11c connected to the water supply pipe 2b via a connecting pipe 11b, and the other ends of the first cylinder device 9A and the second cylinder device 9B are connected to this annular pipe 11c via cylinder connecting pipes 11d. In the annular pipe 11c, a pair of check valves 11a are provided on both sides of the connection portion of the cylinder connecting pipes 11d. Furthermore, the connection portion between the two cylinder connecting pipes 11d in the annular pipe 11c and the supply pipe 2a are connected by a connecting pipe 11e via a pressure boosting means 10. The connecting pipe 11e described above is a line that returns the high-pressure saltwater, which is alternately pushed out from the first cylinder device 9A and the second cylinder device 9B, back to the membrane separator 5. Furthermore, a high-pressure pump 10B is connected between the connection point of the water supply pipe 2b to the flow direction regulating mechanism 11 and the connection point of the supply pipe 2a to the connecting pipe 11e.

[0033] A first position detector S1 and a second position detector S2 are installed on the outer peripheral wall on the side of the flow direction regulating mechanism 11 (the other end) of the first cylinder device 9A and the second cylinder device 9B, and a third position detector S3 is installed on the outer peripheral wall on the side of the switching valve device 13 (the one end). Furthermore, in one of the first cylinder 7A and the second cylinder 7B, which is about to complete the pumping process, the distance between the first position detector S1 and the second position detector S2 is set to minimize the fluctuation in the total flow rate, along the direction of movement of the corresponding first piston 8A or second piston 8B, as described above. The distance between the first position detector S1 and the second position detector S2 is pre-set through simulation to an interval that minimizes the fluctuation in the total flow rate.

[0034] Next, the operation of the energy recovery device 1 of this embodiment will be described with reference to the drawings. In this embodiment, for the purpose of explaining the operation, we will describe an example in which one of the first cylinder device 9A and the second cylinder device 9B is the first cylinder device 9A performing the pressurizing process, and the other of the first cylinder device 9A and the second cylinder device 9B is the second cylinder device 9B performing the filling process.

[0035] First, as shown in Figure 1, when the first piston 8A of the first cylinder device 9A, which is in the pumping process, is moving toward the other end in the direction of arrow Y1, the control unit C fully opens the one-way concentration side valve 14A of the switching valve device 13 of the first flow path switching mechanism 6A and fully closes the one-way drain side valve 15A. Furthermore, as the other of the first cylinder device 9A and the second cylinder device 9B, when the first piston 8B of the first cylinder device 9B, which is in the filling process, is moving toward one end in the direction of arrow Y2, the control unit C closes the other-side concentration valve 14B of the switching valve device 13 of the second flow path switching mechanism 6B and opens the other-side drain valve 15B. At this time, concentrated brine is discharged from the second cylinder device 9B to the drain pipe 19 via the fully open other-side drain valve 15B.

[0036] Next, as shown in Figures 2 and 3, when the first piston 8A of the first cylinder device 9A reaches the position of the first position detector S1, the control unit C transmits an open operation signal to the other-side enrichment valve 14B of the second cylinder 7B based on the detection signal from the first position detector S1, causing it to open. Furthermore, when the second position detector S2 of the first cylinder 7A detects the first piston 8A, the control unit C transmits a close operation signal to the one-side enrichment valve 14A of the first cylinder 7A, causing it to close.

[0037] In this case, for example as shown in Figure 4, if the closing operation of the one-side concentration valve 14A of the first cylinder device 9A is delayed in the direction of arrow Y3 relative to the opening operation of the other-side concentration valve 14B of the second cylinder device 9B, the total flow rate of the concentrated brine supplied from the concentration-side connecting pipe to the first cylinder 7A and the concentrated brine supplied to the second cylinder 7B will fluctuate significantly in the direction of arrow Y4 during the end of the pumping process of the first cylinder device 9A and the start of the pumping process of the second cylinder device 9B. In this embodiment, the timing difference between the start of the opening operation of the other-side enrichment valve 14B controlled by the control unit C and the start of the closing operation of the one-side enrichment valve 14A is set by the distance between the first position detector S1 and the second position detector S2 of the first cylinder 7A. Therefore, in this embodiment, the distance between the first position detector S1 and the second position detector S2 of the first cylinder 7A is set to a distance that minimizes the fluctuation in the total flow rate. For example, as shown in Figure 4, the distance between the first position detector S1 and the second position detector S2 is set to correspond to the timing difference of the operation described above, so that the total flow rate is shown by the solid line, which minimizes the fluctuation in the total flow rate.

[0038] In this embodiment, the energy recovery device 1 controls the one-side concentration valve 14A and the other-side concentration valve 14B to minimize fluctuations in the total flow rate of concentrated brine supplied from the concentration-side connecting pipe 13a to one of the first cylinder 7A and the second cylinder 7B, and the flow rate of concentrated brine supplied to the other of the first cylinder 7A and the second cylinder 7B. This suppresses sudden fluctuations in the flow rate and pressure of the high-pressure brine, which is the high-pressure supply water. Furthermore, since the distance between the first position detector S1 and the second position detector S2 is set to a distance that minimizes the fluctuation in the total flow rate, the opening and closing timing of the one-way concentration valve 14A and the other-way concentration valve 14B can be easily set to minimize the fluctuation in the total flow rate by adjusting the distance between the first position detector S1 and the second position detector S2.

[0039] Next, the second to fifth embodiments of the energy recovery device according to the present invention will be described below with reference to Figures 5 to 10. In the following descriptions of each embodiment, the same reference numerals are used for the same components described in the above embodiments, and their descriptions are omitted. Also, the piston is not shown in the schematic diagram of the energy recovery device.

[0040] The difference between the second embodiment and the first embodiment is that, in the first embodiment, the distance between the first position detector S1 and the second position detector S2 is set to a distance that minimizes the fluctuation in the total flow rate, whereas in the energy recovery device of the second embodiment, as shown in Figure 5, when the other end position detector (for example, the first position detector S1) of one of the first cylinder 7A and the second cylinder 7B detects a position, the control unit C transmits an open operation signal to the other enrichment side valve 14B to open it, and after a predetermined delay after that transmission, transmits a close operation signal to the one enrichment side valve 14A to close it, thereby minimizing the fluctuation in the total flow rate.

[0041] In Figure 5, one of the first cylinder 7A and the second cylinder 7B is shown as the first cylinder 7A, and the other of the first cylinder 7A and the second cylinder 7B is shown as the second cylinder 7B. In other words, as shown in Figure 5, when the position detector on the other end of the first cylinder 7A (for example, the first position detector S1) detects the first piston 8A, the control unit C sends an open operation signal to the other-side enrichment valve 14B of the second cylinder device 9B to open it. After sending the open operation signal, the control unit C delays the transmission by a first predetermined time T1 using a built-in timer before sending a close operation signal to the one-side enrichment valve 14A to close it. In this case, since the first predetermined time T1 is set to the time that minimizes the fluctuation in the total flow rate, it is possible to suppress sudden fluctuations in the flow rate and pressure of the high-pressure saltwater.

[0042] In the energy recovery device of the second embodiment, after sending an open operation signal to the other-side enrichment valve 14B, a close operation signal is sent to the one-side enrichment valve 14A after a delay of a first predetermined time T1. Since the first predetermined time T1 is set to the time that minimizes the fluctuation in the total flow rate, only other-end position detectors need to be provided near the other ends of the first cylinder 7A and the second cylinder 7B. The fluctuation in the total flow rate can be easily minimized without installing another position detector at a position offset from the other-end position detector. For example, if the first position detector S1 is installed as the other-end position detector, the second position detector S2, which is installed further away towards the other end, becomes unnecessary.

[0043] Next, the difference between the third embodiment and the second embodiment is that, in the second embodiment, after sending an open operation signal to the other-side concentration valve 14B, a first predetermined time T1 is delayed before sending a close operation signal to the one-side concentration valve 14A, whereas in the energy recovery device of the third embodiment, as shown in Figure 6, in addition to the operation of the second embodiment, when the terminal-side position detector of one of the first cylinder 7A and the second cylinder 7B (for example, if a second position detector S2 is provided at the terminal portion in the second embodiment, this becomes the terminal-side position detector) detects a position, the control unit C sends a close operation signal to the one-side concentration valve 14A, and after sending the close operation signal, a second predetermined time T2 is delayed before sending an open operation signal to the one-side drain valve 15A, where the second predetermined time T2 is set to the time until the one-side concentration valve 14A is fully closed.

[0044] In other words, as shown in Figure 6, when the terminal position detector (for example, the second position detector S2) of the first cylinder 7A detects a position, the control unit C transmits a closing operation signal to the one-way concentration side valve 14A to close it, and after a delay of a second predetermined time T2 after transmitting the closing operation signal, transmits an opening operation signal to the one-way drain side valve 15A to open it. In this embodiment, instead of delaying by a second predetermined time T2 using a timer built into the control unit C, a fully closed limit switch (S / W) is provided to the one-way concentration valve 14A, which sends a signal when it is fully closed. When the control unit C receives this signal, it may send the above-mentioned open operation signal.

[0045] In this case, since the second predetermined time T2 is set to the time until the one-way concentration valve is fully closed, it is possible to prevent the one-way concentration valve 14A and the one-way drain valve 15A from being open at the same time. In the above description, the timing difference in operation (second predetermined time T2) was applied to either the first cylinder 7A or the second cylinder 7B, specifically to the first cylinder 7A side. However, it is also acceptable to apply the timing difference to either the first cylinder 7A or the second cylinder 7B, specifically to the second cylinder 7B side.

[0046] In this third embodiment of the energy recovery device, after sending a closing operation signal to the one-way concentration side valve 14A, an opening operation signal is sent to the one-way drain side valve 15A after a second predetermined time T2 delay. Since the second predetermined time T2 is set to the time until the one-way concentration side valve 14A is fully closed, it is possible to prevent leakage of high-pressure concentrated water to the low-pressure concentrated water side that would occur if the one-way drain side valve 15A were to open while the one-way concentration side valve 14A is closing.

[0047] Next, the difference between the fourth embodiment and the first embodiment is that in the first embodiment, the first position detector S1 and the second position detector S2 are fixed and the distance between the first position detector S1 and the second position detector S2 is constant, whereas in the energy recovery device 41 of the fourth embodiment, as shown in Figures 7 and 8, at least one of the first position detector S1 and the second position detector S2 is provided with a detector movement mechanism 42 that can move in a direction along the axis of the corresponding first cylinder 7A or second cylinder 7B.

[0048] Furthermore, the energy recovery device 41 of the fourth embodiment includes a flow meter 43 connected to the concentration-side connecting pipe 13a, which measures the flow rate of the concentrated brine and transmits a flow rate signal to the control unit C. Furthermore, the control unit C can adjust the position of at least one of the first position detector S1 and the second position detector S2 using the detector movement mechanism 42 based on the received flow rate signal. The detector movement mechanism 42, as shown in Figure 8, for example, comprises an electric operating device body 42a installed on the first cylinder 7A or the second cylinder 7B and containing a motor, and a rod portion 42b that protrudes from the electric operating device body 42a in a direction along the axis of the first cylinder 7A or the second cylinder 7B, is electrically movable, and has a second position detector S2 fixed to its tip. The second position detector S2 is movable along the axis on the first cylinder 7A or the second cylinder 7B and is not fixed. Therefore, the control unit C controls the detector movement mechanism 42 to move the rod portion 42b forward and backward from the electric operating device body 42a, thereby changing the position of the second position detector S2.

[0049] In this embodiment, the distance between the first position detector S1 and the second position detector S2 is adjusted as follows. In other words, after setting the distance between the first position detector S1 and the second position detector S2 in advance to minimize fluctuations in the total flow rate, if the flow rate of concentrated brine in the pumping process increases or decreases for any reason, the timing at which the first position detector S1 on one side detects this and starts the pumping process on the other side (i.e., the other-side concentration valve 14B receives a full-open command and starts the "open" operation), causing the flow rate of concentrated brine in the other-side pumping process to start increasing, is out of sync with the timing at which the second position detector S2 on one side detects this and ends the pumping process on one side (i.e., the one-side concentration valve 14A receives a "full-close" command and starts the "close" operation), causing the flow rate of concentrated brine in the one-side pumping process to start decreasing. In this case, when the cylinder in the pumping process switches, the flow rate in the pumping process may increase or decrease significantly or be interrupted. In this case, the distance between the pre-set first position detector S1 and the second position detector S2 deviates from the distance at which the fluctuation in the total flow rate is minimized.

[0050] In this embodiment, the control unit C adjusts the position of at least one of the first position detector S1 and the second position detector S2 using the detector movement mechanism 42 based on the flow rate signal received by the flow meter 43. In other words, the control unit C controls the detector moving mechanism 42 to move the second position detector S2 to an optimal position corresponding to the flow rate signal of the concentrated brine in the pumping process measured by the flow meter 43 (the position where the distance between the first position detector S1 and the second position detector S2 is optimal and the fluctuation of the total flow rate is minimized). In this embodiment, the position of the second position detector S2 is changed to the above-mentioned optimal position by moving the rod portion 42b forward and backward from the electric actuator body 42a.

[0051] Thus, in the energy recovery device 41 of the fourth embodiment, the control unit C can adjust the position of at least one of the first position detector S1 and the second position detector S2 using the detector movement mechanism 42 based on the received flow rate signal. Therefore, even if the flow rate of concentrated brine in the pumping process increases or decreases for any reason, the position of at least one of the first position detector S1 and the second position detector S2 can be automatically adjusted and set to a distance that minimizes the fluctuation in the total flow rate.

[0052] As another example of this embodiment, a slider-type detector movement mechanism 42C may be used, as shown in Figure 9. The detector movement mechanism 42C described above includes a rail section 42c installed on the first cylinder 7A or the second cylinder 7B and extending in a direction along the axis of the first cylinder 7A or the second cylinder 7B, and a slider section 42d provided below the rail section 42c and movable along the rail section 42c by being driven by a motor or the like. A second position detector S2 is attached to the lower part of the slider section 42d, and as the slider section 4d moves, the second position detector S2 can be moved in a direction along the axis of the first cylinder 7A or the second cylinder 7B. Thus, the control unit C may automatically adjust the distance between the first position detector S1 and the second position detector S2 by controlling the slider-type detector movement mechanism 42C based on the flow rate signal from the flow meter 43. In the fifth embodiment (including the other examples described above), the one-way concentration valve 14A, the one-way drain valve 15A, the other-way concentration valve 14B, and the other-way drain valve 15B are, for example, ball valves, but are not limited to these, and switching cylinder devices such as pressure distribution valves may be used as these valves.

[0053] Next, the difference between the fifth embodiment and the fourth embodiment is that the fourth embodiment is equipped with a flow meter 43 for measuring the flow rate of concentrated brine in the concentration-side connecting pipe 13a, whereas the energy recovery device 51 of the fifth embodiment, as shown in Figure 10, is equipped with pressure gauges 53C and 53D that transmit pressure signals to the control unit C, measuring the pressure of at least one of the concentrated brine in the concentration-side connecting pipe 13a and the high-pressure brine in the connecting pipe 11e. Furthermore, in the fifth embodiment, the control unit C can adjust the opening and closing speed of at least one of the one-side enrichment valve 14A and the other-side enrichment valve 14B when the pressure signal exceeds a predetermined pressure. Furthermore, valves with adjustable opening and closing speeds (opening and closing operation times) can be used, for example, valves that utilize valve drive mechanisms such as servo motors, pulse motors, or inverter-driven electric motors.

[0054] The fifth embodiment is effective in the following cases: For example, if the valve opening and closing time is fast, both the rate at which the flow rate of concentrated brine decreases in the pumping process of one cylinder and the rate at which the flow rate increases in the pumping process of the other cylinder become fast. In this case, if for some reason the timing of the decrease in flow rate of one cylinder and the increase in flow rate of the other cylinder are out of sync, the flow rate may increase or decrease significantly compared to when the valve opening and closing time is slow, causing the operating point of the high-pressure pump to fluctuate and potentially resulting in large pressure fluctuations.

[0055] Referring to Figure 11, if the flow rate of concentrated brine in the pumping process increases compared to the steady state shown in Figure 11(a), the timing of detection by the second position detector S2 becomes earlier by time T3, as shown in Figure 11(b). As a result, the flow rate decreases compared to the steady state. Furthermore, compared to the steady state shown in Figure 11(a), if the flow rate of concentrated brine in the pumping process decreases, the timing of detection by the second position detector S2 will be delayed by time T4, as shown in Figure 11(c). As a result, the flow rate will increase compared to the steady state.

[0056] However, in the energy recovery device 51 of the fifth embodiment, the control unit C can adjust the opening and closing speed of at least one of the one-side enrichment valve 14A and the other-side enrichment valve 14B when the pressure signals from the pressure gauges 53C and 53D exceed a predetermined pressure. In other words, if the pressure signal measured when the cylinder in the pumping process switches exceeds a certain value, the control unit C determines that the valve opening and closing time was too fast and the flow rate of concentrated brine fluctuated significantly from the steady state. By automatically adjusting the opening and closing speed of these valves (for example, by slowing them down), pressure fluctuations can be suppressed. In this embodiment, the energy recovery device 51 is equipped with both a pressure gauge 53C capable of measuring the pressure of concentrated brine in the concentration-side connecting pipe 13a and a pressure gauge 53D capable of measuring the pressure of high-pressure brine in the connecting pipe 11e. However, it is also acceptable to equip only one of these devices and perform the automatic adjustment based on its pressure signal.

[0057] It should be noted that the present invention is not limited to the embodiments described above, and various modifications can be made without departing from the spirit of the invention.

[0058] For example, although the above embodiment shows a case with two cylinder devices, it may also be applied to a case with three cylinder devices. In this case, while the first and second cylinder devices are operating, the piston of the remaining third cylinder device is stopped at the end on the switching valve device 13 side. [Explanation of symbols]

[0059] 1, 41, 51… Energy recovery device, 2a… Supply pipe, 2b… Water supply pipe, 3… Freshwater pipe, 4… Concentrated water pipe, 5… Membrane separation device, 6A… First flow path switching mechanism, 6B… Second flow path switching mechanism, 7A… First cylinder, 7B… Second cylinder, 8A… First piston, 8B… Second piston, 9A… First cylinder device, 9B… Second cylinder device, 10… Pressure boosting means, 11… Flow path direction regulating mechanism, 13… Switching valve device, 13a… Concentrated side connecting pipe, 13b… Drainage side connecting pipe, 14A… Concentrated side valve for one side, 14B… Concentrated side valve for the other side, 15A… Drainage side valve for one side, 15B… Drainage side valve for the other side, 43… Flow meter, 53C, 53D… Pressure gauge, C… Control unit, S1… First position detector, S2… Second position detector, S3… Third position detector

Claims

1. An energy recovery device connected to a membrane separation device which is connected to a supply pipe for high-pressure brine and separates the high-pressure brine into fresh water and concentrated brine using a reverse osmosis membrane, discharging the fresh water into a fresh water pipe and the concentrated brine into a concentrated brine pipe, A first cylinder device having a first piston that reciprocates within a first cylinder, one end of which is connected to the concentrated water pipe and the drain pipe via a first flow path switching mechanism that connects and disconnects the concentrated water pipe and the concentrated brine drain pipe, A second cylinder device having a second piston that reciprocates within a second cylinder, one end of which is connected to the concentrated water pipe and the drain pipe via a second flow path switching mechanism that connects and disconnects the concentrated water pipe and the drain pipe, A control unit having a control function to switch the connections between the first cylinder device and the second cylinder device to the concentrated water pipe and the drain pipe by controlling the first flow path switching mechanism and the second flow path switching mechanism, and to alternately flow the concentrated brine into the first cylinder device and the second cylinder device, and a control function to alternately discharge the concentrated brine from the first cylinder device and the second cylinder device, The system includes a flow path direction regulating mechanism connected to the other end of the first cylinder device and the other end of the second cylinder device, which alternately supplies low-pressure brine to the first cylinder device and the second cylinder device, and returns the high-pressure brine, which is alternately pushed out from the first cylinder device and the second cylinder device, to the membrane separator via a pressure boosting means, The first flow path switching mechanism and the second flow path switching mechanism are equipped with a switching valve device that switches between supplying the concentrated brine to the first cylinder device or the second cylinder device and stopping the supply, and discharging the concentrated brine from the first cylinder device or the second cylinder device and stopping the discharge, The switching valve device includes a one-way concentrate valve provided in the concentrate-side connecting pipe that connects one end of the first cylinder device and the second cylinder device to the concentrate water pipe, A one-way drain valve is provided in the drain-side connecting pipe that connects one end of the first cylinder device and the second cylinder device to the drain pipe, A concentrating valve for the other side is provided in the concentrating-side connecting pipe that connects the other end of the first cylinder device and the second cylinder device to the concentrating water pipe, The device includes a drain-side connecting pipe that connects the other end of the first cylinder device and the second cylinder device to the drain pipe, and a drain-side valve for the other end provided in the drain-side connecting pipe. An energy recovery device characterized in that the control unit controls the one-side concentration valve and the other-side concentration valve to minimize the fluctuation in the total flow rate of the concentrated brine supplied from the concentration-side connecting pipe to one of the first cylinder and the second cylinder, and the flow rate of the concentrated brine supplied to the other of the first cylinder and the second cylinder.

2. In the energy recovery device according to claim 1, A pair of first position detectors provided near the other ends of the first cylinder and the second cylinder to detect when the first piston or the second piston has reached the vicinity of the corresponding other end of the first cylinder or the second cylinder, A pair of second position detectors are provided at positions on the first cylinder and the second cylinder that are further apart from the other end of the first position detector, and detect when the first piston or the second piston has reached a position further apart from the other end of the first position detector. The system includes a pair of third position detectors provided near one end of the first cylinder and the second cylinder, which detect when the first piston or the second piston has reached the vicinity of the corresponding end of the first cylinder or the second cylinder. When the control unit detects one of the first pistons, the first position detector of either the first cylinder or the second cylinder, it transmits an open operation signal to the other concentrating valve to open it. When the second position detector of either the first cylinder or the second cylinder detects either the first piston or the second piston, a closing operation signal is transmitted to the one-side concentrating valve to cause it to close. An energy recovery device characterized in that the distance between the first position detector and the second position detector in one of the first cylinder and the second cylinder is set to a distance that minimizes the fluctuation amount of the total flow rate.

3. In the energy recovery device according to claim 1, The system includes a pair of other-end position detectors provided near the other ends of the first and second cylinders, which detect when the first piston or the second piston has reached the vicinity of the corresponding other end of the first or second cylinder. When the control unit detects one of the first pistons or the second pistons using the other end position detector of one of the first cylinders or the second cylinder, it transmits an open operation signal to the other-side enrichment valve to open it. After the transmission of the opening operation signal, a closing operation signal is transmitted to the one-way concentration valve after a delay of a first predetermined time, An energy recovery device characterized in that the first predetermined time is set to the time that minimizes the fluctuation amount of the total flow rate.

4. In the energy recovery device according to any one of claims 1 to 3, The system includes a pair of terminal position detectors provided near the other ends of the first and second cylinders, which detect when the first piston or the second piston has reached the vicinity of the corresponding other end of the first or second cylinder. When the control unit detects one of the first pistons or the second pistons using the terminal position detector of either the first cylinder or the second cylinder, it transmits a closing operation signal to the one-side concentrating valve to close it. After the transmission of the closing operation signal, an opening operation signal is transmitted to the one-way drain valve after a second predetermined time delay. An energy recovery device characterized in that the second predetermined time is set to the time until the one-way concentration valve is fully closed.

5. In the energy recovery device according to claim 2, A flow meter connected to the concentration side connecting pipe and transmitting a flow rate signal that measures the flow rate of the concentrated brine to the control unit, At least one of the first position detector and the second position detector is provided with a detector movement mechanism that can move in a direction along the axis of the corresponding first cylinder or second cylinder, An energy recovery device characterized in that the control unit can adjust the position of at least one of the first position detector and the second position detector using the detector movement mechanism based on the received flow rate signal.

6. In the energy recovery device according to any one of claims 1 to 3, The device includes a connecting pipe that returns the high-pressure saltwater, which is alternately pushed out from the first cylinder device and the second cylinder device, to the membrane separation device. The system includes a pressure gauge that transmits a pressure signal to the control unit, which measures the pressure of at least one of the concentrated brine in the concentrated brine in the connecting pipe and the high-pressure brine in the connecting pipe. An energy recovery device characterized in that the control unit can adjust the opening and closing speed of at least one of the one-side concentration valve and the other-side concentration valve when the pressure signal exceeds a certain pressure.

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