Energy recovery device

Abstract

Provided is an energy recovery device capable of preventing malfunction due to a reduction in the flow rate of low-pressure salt water in a filling step. An energy recovery device according to the present invention comprises first and second cylinder devices 9A, 9B that are connected to a concentrated water pipe 4 via first or second flow path switching mechanisms 6A, 6B, a control unit C that performs control for causing concentrated salt water to flow into and discharge from the first and second cylinder devices, a flow path direction regulating mechanism 11 that fills the first and second cylinder devices with low-pressure salt water and returns, to a membrane separation device via a booster pump 10, high-pressure salt water pushed out from the first and second cylinder devices, and a first flowmeter 18a that is connected to the concentrated water pipe and transmits, to the control unit, a first flow rate signal obtained by measuring the flow rate of the concentrated salt water, wherein the control unit controls the booster pump on the basis of the first flow rate signal to adjust the flow rate of the concentrated salt water supplied to the cylinder devices during a pressure-feeding step.

Description

Energy recovery device

[0001] This invention relates to an energy recovery device for a water treatment system using the reverse osmosis membrane method, which is used for desalination of seawater, brackish water, groundwater, industrial water, etc.

[0002] One method for producing fresh water from seawater is reverse osmosis. This method involves applying a pressure higher than the osmotic pressure of seawater in the opposite direction to the direction of osmosis, filtering it through a semipermeable membrane (reverse osmosis membrane (RO membrane)), and separating salts from fresh water. In this reverse osmosis method, the seawater with concentrated salts (concentrated brine), after the fresh water has been separated, flows out of the reverse osmosis membrane module while retaining high pressure energy. Various energy recovery devices have been put into practical use to effectively utilize the high pressure energy of this flowing concentrated brine.

[0003] In a positive displacement energy recovery system, seawater is supplied from an intake pump to a reverse osmosis membrane module under pressure by a high-pressure pump. Simultaneously, high-pressure concentrated brine discharged from the reverse osmosis membrane module is supplied to a cylinder device to push out seawater under high pressure. High-pressure seawater is also sent from the cylinder device to the reverse osmosis membrane module via a pressure booster pump. This operation of supplying high-pressure concentrated brine discharged from the reverse osmosis membrane module to the cylinder device to push out seawater under high pressure is called the pumping process (or energy recovery process). After the pumping process is completed, seawater is supplied from the intake pump to the cylinder device via a flow direction restricting device, and the operation of filling the cylinder with seawater while discharging concentrated brine in the opposite direction to the pumping process is called the filling process (or water supply process). Thus, in this energy recovery system, when the piston of the cylinder device reaches the end of the cylinder, a flow direction switching device alternately supplies high-pressure concentrated brine from the reverse osmosis membrane module to a pair of cylinder devices, and the intake pump alternately fills the pair of cylinder devices with seawater.

[0004] Conventionally, for example, Patent Document 1 discloses an energy recovery device connected to a membrane separation device that separates high-pressure seawater into fresh water and concentrated seawater using a reverse osmosis membrane, discharges the fresh water into a fresh water pipe, and discharges the high-pressure concentrated seawater into a concentrated water pipe. The energy recovery device includes a water intake pump for supplying seawater, a pressurizing pump for pressurizing the seawater from the water intake pump and supplying the high-pressure seawater to the membrane separation device, a flow path switching mechanism having one end communicating with the water intake pump and capable of switching between communication and cutoff with the concentrated water pipe and between communication and cutoff with the drainage path of the concentrated seawater, and the other ends are respectively connected to the concentrated water pipe and the drainage path via the flow path switching mechanism. The device also includes three cylinder devices each having a piston that reciprocates within a cylinder, a control unit having a control function for sequentially repeating the following operations in each of the three cylinder devices in this order: controlling the flow path switching mechanism to switch the connection of the three cylinder devices to the concentrated water pipe and the drainage path, supplying the high-pressure concentrated seawater to the cylinder device to extrude the internal seawater at high pressure in a pumping step, supplying the seawater from the water intake pump to the cylinder device after the pumping step to fill the cylinder device with the seawater while discharging the internal concentrated seawater in a filling step, and a standby step in which neither the concentrated seawater nor the seawater is supplied to the cylinder device. The control unit performs different operations in the three cylinder devices except immediately before and after the switching of each of the pumping step, filling step, and standby step, and performs the pumping step or the filling step simultaneously in two of the cylinder devices immediately before and after the switching of each step.

[0005] In this device, since the control unit performs different operations in the three cylinder devices except immediately before and after the switching of each of the pumping step, filling step, and standby step, by using one of the three cylinder devices for the pumping step, one for the filling step, and one for the standby step, seawater can always be supplied from the water intake pump to suppress the pulsation of the high-pressure pump (pressurizing pump).

[0006] Japanese Patent No. 6412233

[0007] The conventional technology described above has the following remaining challenges. In the case of a two-cylinder system (using two cylinder devices), the filling process must be completed earlier than the pumping process to prevent switching to the pumping process before the filling process is finished, resulting in an intermittent filling process. Therefore, the piston movement speed in the filling process must be set to be faster than the piston movement speed in the pumping process. In addition, an appropriate waiting time is required between the completion of the filling process and the start of the pumping process. Thus, in a two-cylinder energy recovery system that alternately repeats the pumping process and the filling process using a pair of cylinder devices, a waiting time after the completion of the filling process is always necessary. Furthermore, in the case of a three-cylinder system (using three cylinder devices), the rate at which the flow rate of the cylinder device decreases when the filling process is completed in the first cylinder is equal to the rate at which the flow rate of the cylinder device increases when the filling process is started in the second cylinder. That is, if the flow rate is properly adjusted, as shown in Figure 5(a), the piston 8 reaches the switching valve side end 7a of cylinder 7, and after a waiting time, the system switches to the pumping process.

[0008] However, if the flow rate adjustment malfunctions in a two-cylinder system, for example, if the flow rate of the fluid supplied from the intake pump to the cylinder device decreases for some reason and the system switches to the pumping process before the filling process is completed, as shown in Figure 5(b), the system switches to the pumping process before the piston 8 reaches the switching valve side end 7a of the cylinder 7, making the entire effective length of the cylinder 7 unusable. If operation continues in this state, as shown in Figures 5(c-g), the piston position R when switching from the filling process to the pumping process moves further away from the switching valve side end 7a with each reciprocating cycle, eventually causing the system to stop working. Similarly, if the flow rate adjustment malfunctions in a three-cylinder system, for example, if the flow rate of the fluid supplied from the intake pump to the cylinder device decreases for some reason and the system switches to the pumping process before the filling process of any of the cylinders is completed, the system switches to the pumping process before the piston reaches the switching valve side end, making the entire effective length of the cylinder unusable. If operation continues in this state, the point where the system switches from the filling process to the pumping process moves further away from the switching valve end 7a with each reciprocating cycle, and eventually the system stops working. If the system (water production equipment) continues to operate in this state (where the piston stops midway through the cylinder), the concentrated brine side of the RO membrane becomes blocked, and water cannot be supplied from the booster pump.

[0009] The present invention has been made in view of the above-mentioned conventional problems, and aims to provide an energy recovery device that can prevent malfunction due to a reduced flow rate of low-pressure brine in the filling process.

[0010] To solve the above problems, the present invention employs the following configuration. That is, the energy recovery device according to the first invention is 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, discharges the fresh water into a fresh water pipe and the concentrated brine into a concentrated brine pipe, and is connected to a plurality of cylinder devices having pistons that move back and forth inside a cylinder, one end of which is connected to the concentrated brine pipe and the drain pipe via a flow path switching mechanism that connects and disconnects to the concentrated brine pipe and also connects and disconnects to the drain pipe for concentrated brine, a high-pressure pump connected to the base end of the supply pipe, a water supply pipe connected to the high-pressure pump and supplies low-pressure brine to the high-pressure pump, a water supply side connecting pipe connected to the water supply pipe and sending the low-pressure brine to the plurality of cylinder devices, and the high-pressure brine that is connected to the water supply side connecting pipe and can alternately supply the low-pressure brine to the plurality of cylinder devices and alternately push out from the plurality of cylinder devices The present invention relates to a device comprising: a flow path direction regulating mechanism that returns brine to the membrane separator via a booster pump; a control unit having a control function that controls the flow path switching mechanism to switch the connections of the plurality of cylinder devices to the concentrated water pipe and the drain pipe, and supplies the high-pressure concentrated brine to the cylinder devices to push out the energy-transferred high-pressure brine at high pressure; and a filling process that, after the pumping process, supplies the low-pressure brine from the flow path direction regulating mechanism to the cylinder devices to fill them with the low-pressure brine while discharging the concentrated brine inside, repeating these processes sequentially in each of the cylinder devices, wherein the flow path switching mechanism includes a first flow meter connected to the concentrated water pipe that transmits a first flow rate signal measuring the flow rate of the concentrated brine to the control unit, and the control unit controls the booster pump based on the first flow rate signal to adjust the flow rate of the concentrated brine to the cylinder devices during the pumping process.

[0011] In this energy recovery system, the control unit controls the booster pump (by feedback) based on the first flow rate signal (controlling the rotational speed of the booster pump) to adjust the flow rate of high-pressure concentrated brine to the cylinder device during the pumping process. Therefore, even if the flow rate of concentrated brine fluctuates, the supply of low-pressure brine to the cylinder device during the filling process can be terminated earlier than the supply of high-pressure concentrated brine to the cylinder device during the pumping process, preventing insufficient water supply to the cylinder device during the filling process. This prevents the concentrated brine side of the RO membrane from becoming blocked and preventing water from being supplied from the booster pump.

[0012] The energy recovery device according to the second invention is characterized in that, in the first invention, it comprises a flow control valve provided in the drain pipe and capable of adjusting the flow rate of the concentrated brine to be drained, and a second flow meter connected to the water supply side connecting pipe and transmitting a second flow signal that measures the flow rate of the low-pressure brine to the control unit, wherein the control unit controls the flow control valve based on the second flow signal to adjust the drain flow rate.

[0013] In other words, in this energy recovery device, the control unit, in addition to controlling the booster pump, controls the flow control valve based on a second flow signal of low-pressure brine in the supply-side connecting pipe to adjust the discharge flow rate of concentrated brine. By feedback-controlling the opening degree of the flow control valve, it becomes easier to keep the flow rate of low-pressure brine flowing into the energy recovery device on the supply side and the flow rate of concentrated brine discharged from the energy recovery device constant, enabling smooth operation.

[0014] The energy recovery device according to the third invention is characterized in that, in the second invention, the control unit makes the flow rate of the low-pressure brine to the cylinder device during the filling process greater than the flow rate of the concentrated brine to the cylinder device during the pumping process, based on the first flow rate signal and the second flow rate signal.

[0015] In this energy recovery system, the control unit, based on a first flow rate signal and a second flow rate signal, sets the flow rate of low-pressure brine to the cylinder device during the filling process to be greater than the flow rate of concentrated brine to the cylinder device during the pumping process. This increases the filling flow rate of low-pressure brine during the filling process, further preventing insufficient water supply to the cylinder device during the filling process. In particular, in the case of a two-cylinder energy recovery system (two cylinder devices), it is preferable to set the piston movement speed during the filling process to be faster than the piston movement speed during the pumping process, and to automatically adjust the booster pump and flow control valve so that an appropriate waiting time is secured between the end of the filling process and the start of the pumping process.

[0016] The energy recovery device according to the fourth invention is characterized in that, in the second or third invention, the control unit holds the second flow rate signal during the filling process as a retained flow rate value, except when the filling flow rate of the low-pressure salt water rapidly increases immediately after the start of the filling process and when the filling flow rate of the low-pressure salt water rapidly decreases immediately before the end of the filling process, controls the flow rate control valve based on the retained flow rate value until the rapid increase in the filling flow rate of the next filling process ends, releases the retention of the retained flow rate value when the rapid increase in the filling flow rate of the next filling process ends, and controls the flow rate control valve based on the current second flow rate signal until the start of the next rapid decrease in the filling flow rate.

[0017] In energy recovery devices, since multiple cylinders, including two or more cylinders, are used, the flow rate during the intermittent filling process is as described above. In this case, if the opening degree of the flow control valve is controlled by feedback control, that is, if it is determined that the discharge flow rate has decreased significantly while the piston is waiting (while the filling flow rate is zero), the flow control valve will try to open wider, and conversely, when the filling process starts again, it will try to open narrower, causing large fluctuations in the valve opening degree and leading to a hunting phenomenon, where the opening degree does not remain constant. In contrast to this, in the present invention described above, the control unit holds the second flow rate signal during the filling process as a held flow rate value, except when the filling flow rate of low-pressure brine rapidly increases immediately after the start of the filling process and when the filling flow rate of low-pressure brine rapidly decreases immediately before the end of the filling process. The flow control valve is controlled based on the held flow rate value until the rapid increase in the filling flow rate of the next filling process ends. When the rapid increase in the filling flow rate of the next filling process ends, the holding of the held flow rate value is released, and the flow control valve is controlled based on the current second flow rate signal instead of the held flow rate value until the start of the next rapid decrease in the filling flow rate. As a result, fluctuations in the opening degree of the flow control valve can be reduced, and it becomes easier to keep the opening degree constant. In other words, the second flow signal, which is small and nearly constant when the filling flow rate fluctuation is small, is held and fixed as the retained flow rate value, and the flow control valve is controlled using this retained flow rate value until the rapid increase in filling flow rate at the start of the next filling process ends. However, after the rapid increase in filling flow rate at the start of the next filling process, until the start of the next rapid decrease in filling flow rate, the flow control valve is controlled by switching from the retained flow rate value to the actual current second flow signal, thereby suppressing fluctuations in the opening degree of the flow control valve due to feedback control associated with rapid increases and decreases in filling flow rate.

[0018] The energy recovery device according to the fifth invention is characterized in that, in the fourth invention, the flow path switching mechanism comprises a switching valve device that switches between supplying the concentrated brine to the cylinder device and stopping its supply and discharging the concentrated brine from the cylinder device and stopping its discharge, and a drive device that drives the switching valve device, and the control unit controls the flow rate adjustment valve, with the point in time when the flow path for discharging the concentrated brine in the switching valve device is fully opened in the filling process being the end of the rapid increase in filling flow rate, and the point in time when the flow path on the discharge side of the concentrated brine in the switching valve device is closed being the start of the rapid decrease in filling flow rate.

[0019] In other words, in this energy recovery device, the control unit controls the flow rate adjustment valve by determining the point at which the other end position detector detects the piston during the filling process as the end of the rapid increase in filling flow rate, and the point at which the one end position detector detects the piston during the filling process as the start of the rapid decrease in filling flow rate. Therefore, the end of the rapid increase in the filling flow rate of low-pressure saltwater and the start of the rapid decrease in filling flow rate can be easily determined in response to the detection of the piston by the one end position detector and the other end position detector.

[0020] The energy recovery device according to the sixth invention is characterized in that, in the fourth invention, it comprises a position detector on the other end side provided near the other end of the cylinder for detecting when the piston has reached the other end of the cylinder, and a position detector on the one end side provided near the one end of the cylinder for detecting when the piston has reached the one end of the cylinder, and the control unit controls the flow rate adjustment valve, with the point in time when the position detector on the other end side detects the piston during the filling process being the end of the rapid increase in the filling flow rate, and the point in time when the position detector on the one end side detects the piston during the filling process being the start of the rapid decrease in the filling flow rate.

[0021] The energy recovery device according to the seventh invention is characterized in that, in the sixth invention, when the measured value of the filling flow rate of the low-pressure salt water based on the second flow rate signal is lower than the target value, the control unit accumulates the difference between the amount of filling at the measured value and the amount of filling at the target value from the end of the rapid increase in the filling flow rate to the start of the rapid decrease in the filling flow rate, and when the accumulated value exceeds a preset alarm setting value, it issues a water supply shortage alarm and stops operation.

[0022] In other words, in this energy recovery device, when the control unit detects that the measured filling flow rate of low-pressure brine based on the second flow signal is lower than the target value, it calculates the difference between the measured filling amount and the target filling amount from the end of the rapid increase in filling flow rate to the start of the rapid decrease in filling flow rate. When the calculated value exceeds a preset alarm value, it issues a water supply shortage alarm and stops operation, thereby preventing the concentrated brine side of the RO membrane from becoming blocked and preventing water from being supplied from the booster pump. In other words, even with the above flow rate control, if the water supply in the filling process is insufficient for some reason and exceeds the alarm value, the control unit can determine that continuing operation would result in cylinder congestion and automatically stop the system operation by closing valves, etc., thereby ensuring safety.

[0023] The energy recovery device according to the eighth invention is characterized in that, in the sixth invention, the control unit issues a water supply shortage alarm and stops operation when the other end position detector in the cylinder device during the pumping process detects the piston before the one end position detector in the cylinder device during the filling process detects the piston, or when the one end position detector in the cylinder device during the filling process and the other end position detector in the cylinder device during the pumping process simultaneously detect the piston.

[0024] In other words, in this energy recovery device, the control unit issues a low water supply alarm and stops operation when the position detector at the other end of the cylinder device during the pumping process detects the piston before the position detector at one end of the cylinder device during the filling process detects the piston, or when both the position detector at one end of the cylinder device during the filling process and the position detector at the other end of the cylinder device during the pumping process simultaneously detect the piston. As a result, the cylinder device during the filling process does not switch to the pumping process, and safety can be ensured by issuing a low water supply alarm and automatically stopping. In other words, if the cylinder device during the filling process switches to the pumping process while the water supply is still low, the position where the pumping process switches will move further away from the cylinder end with each reciprocating motion of the piston, eventually causing the operation to stop. However, the control unit can detect the piston position and make a decision in advance to prevent this.

[0025] The present invention provides the following effects. Specifically, in the energy recovery device according to the present invention, the control unit controls the booster pump (by feedback) based on the first flow rate signal in the concentration-side connecting pipe (controlling the rotational speed of the booster pump) to adjust the flow rate of concentrated brine to the cylinder device during the pumping process. Therefore, even if the flow rate of concentrated brine in the concentration-side connecting pipe fluctuates, the supply of low-pressure brine to the cylinder device during the filling process can be terminated earlier than the supply of high-pressure concentrated brine to the cylinder device during the pumping process, thereby preventing insufficient water supply to the cylinder device during the filling process. Consequently, the energy recovery device of the present invention can suppress blockage of the concentrated brine side of the RO membrane, which prevents water from being supplied from the booster pump.

[0026] This is a schematic diagram showing an embodiment of the energy recovery device according to the present invention, where the first cylinder device is in the pumping process and the second cylinder device is in the filling process. This is a schematic diagram showing a flow path switching mechanism equipped with a switching cylinder device in this embodiment. This is a graph showing the change in normal filling flow rate in the filling process in this embodiment. This is a graph showing the change in filling flow rate when the measured value of the filling flow rate differs from the target value in the filling process in this embodiment. This is an explanatory diagram showing the sequential movement of the piston inside the cylinder during the process of becoming underwater in the filling process.

[0027] Hereinafter, one embodiment of the energy recovery device according to the present invention will be described with reference to Figures 1 to 4.

[0028] As shown in Figure 1, the energy recovery device 1 in this embodiment is a two-cylinder system using, for example, two cylinder devices 9A and 9B, and is connected to a membrane separation device 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 (RO membrane), discharging the fresh water into a fresh water pipe 3 and the concentrated brine into a concentrated water pipe 4.

[0029] This energy recovery device 1 has a first cylinder device 9A having a first piston 8A that moves back and forth 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 other 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. The second cylinder device 9B has a second piston 8B that moves back and forth within the second cylinder 7B, a high-pressure pump 10B connected to the base end of the supply pipe 2a, the water supply pipe 2b connected to the high-pressure pump 10B and supplying low-pressure saltwater to the high-pressure pump 10B, a water supply side connecting pipe 11b connected to the water supply pipe 2b and supplying low-pressure saltwater to the first cylinder device 9A and the second cylinder device 9B, and a water supply side connecting pipe 11b connected to the other end of the first cylinder device 9A and the second cylinder The device includes a flow path direction regulating mechanism 11 connected to the other end of the device 9B, which alternately supplies low-pressure brine to the first cylinder device 9A and the second cylinder device 9B, and returns the high-pressure brine alternately pushed out from the first cylinder device 9A and the second cylinder device 9B to the membrane separation device 5 via a booster pump 10, and a control unit C having a control function that controls the first flow path switching mechanism 6A and the second flow path switching mechanism 6B to switch the connections of the first cylinder device 9A and the second cylinder device 9B to the concentrated water pipe 4 and the drain pipe 19, supplying high-pressure concentrated brine to the first cylinder device 9A and the second cylinder device 9B to push out the energy-transferred high-pressure brine at high pressure, and a filling process in which low-pressure brine from the flow path direction regulating mechanism 11 is supplied to the first cylinder device 9A and the second cylinder device 9B after the pumping process to fill with low-pressure brine while discharging the concentrated brine inside, and repeats these processes in a sequential alternation manner in the first cylinder device 9A and the second cylinder device 9B. Furthermore, the high-pressure pump 10B is connected to the base end of the supply pipe 2a, and the intake pump (not shown) is connected to the base end of the water supply pipe 2b which is connected to the supply pipe 2a. In addition, 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.

[0030] The first flow path switching mechanism 6A and the second flow path switching mechanism 6B are each equipped with a first flow meter 18a connected to the concentrated water pipe 4, which transmits a first flow rate signal to the control unit C that measures the flow rate of the concentrated brine. The control unit C has the function of (feedback) controlling the booster pump 10 (controlling the rotational speed of the booster pump 10) based on the first flow rate signal in the concentrated side connecting pipe, and adjusting the flow rate of concentrated brine to the first cylinder device 9A or the second cylinder device 9B during the pumping process.

[0031] Furthermore, the energy recovery device 1 of this embodiment includes a flow control valve 19a provided in the drain pipe 19 that can adjust the flow rate of concentrated brine discharged, and a second flow meter 18b connected to the water supply side connecting pipe 11b that transmits a second flow signal to the control unit C, which measures the flow rate of low-pressure brine supplied. The control unit C also has the function of adjusting the flow control valve 19a based on the second flow signal to adjust the flow rate of concentrated brine discharged. In addition, the control unit C also has the function of making the flow rate of low-pressure brine to the first cylinder device 9A or the second cylinder device 9B during the filling process greater than the flow rate of concentrated brine to the first cylinder device 9A or the second cylinder device 9B during the pumping process, based on the first flow signal and the second flow signal.

[0032] Furthermore, as shown in Figure 3, the control unit C has the function of holding the second flow rate signal during the filling process as a held flow rate value, except when the filling flow rate of low-pressure salt water rapidly increases immediately after the start of the filling process and when the filling flow rate of low-pressure salt water rapidly decreases immediately before the end of the filling process, and controlling the flow rate control valve 19a based on the held flow rate value until the rapid increase in the filling flow rate of the next filling process ends, releasing the hold of the held flow rate value at the end of the rapid increase in the filling flow rate of the next filling process P1, and controlling the flow rate control valve 19a based on the current second flow rate signal until the start of the next rapid decrease in the filling flow rate P2.

[0033] 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 pump 10, which is a pressure boosting means. The connecting pipe 11e is a line that 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 separator 5. A high-pressure pump 10B is connected between the connection portion of the water supply pipe 2b to the flow direction regulating mechanism 11 and the connection portion of the supply pipe 2a to the connecting pipe 11e.

[0034] The first flow path switching mechanism 6A and the second flow path switching mechanism 6B, as shown in Figure 2 for example, employ a switching valve device 13 that switches between supplying concentrated brine to the first cylinder device 7A or the second cylinder device 7B and stopping its supply, and discharging concentrated brine from the first cylinder device 7A or the second cylinder device 7B and stopping its discharge, and a drive device 14 that drives the switching valve device 13. The control unit C has the function of controlling the flow rate adjustment valve 19a, with the point in the filling process when the flow path for discharging concentrated brine in the switching valve device 13 is fully opened being the end of the rapid increase in filling flow rate P1, and the point in the switching valve device 13 when the flow path on the discharge side of concentrated brine is closed being the start of the rapid decrease in filling flow rate P2. The point in time when the discharge flow path is fully opened may be the point in time when the control unit C receives the signal from the drive device 14 that it is fully open, or it may be the point in time when the time from when the drive device 14 receives the fully open signal from the control unit C until the discharge flow rate is fully open is estimated in advance and that time has elapsed, and this is set in advance in the control unit C.

[0035] The above-mentioned switching valve device 13 is a switching cylinder device consisting of a pressure distribution valve, and includes a supply-side piston 21b that reciprocates integrally with the drain-side piston 21a within the switching cylinder 20, and a switching piston rod 22 having the drain-side piston 21a at one end, the supply-side piston 21b in the middle, and the other end protruding to the outside from the other end of the switching cylinder 20. The above-mentioned switching cylinder 20 has an outlet port 13a provided at one end and connected to the concentrated seawater drain pipe 19, an inlet port 13b provided in the middle and connected to the concentrated water pipe 4, and an inlet / outlet port 13c provided between the outlet port 13a and the inlet port 13b and connected to the first cylinder device 9A or the second cylinder device 9B. The above-mentioned drive device 14 is a switching valve drive actuator in which the tip of a movable operating shaft is connected to the switching piston rod 22.

[0036] The control unit C has the function of operating the drive unit 14. Specifically, in the first cylinder device 9A or the second cylinder device 9B in the filling process, the control unit C determines that the moment when the drive unit 14 fully opens the inlet / outlet port 13c is the end of the rapid increase in filling flow rate P1. The control unit C also determines that the moment when the drive unit 14 begins to close the inlet / outlet port 13c is the start of the rapid decrease in filling flow rate P2. In this embodiment, the control unit C controls the opening amount of the inlet / outlet port 13c by operating the stroke amount (extension of the operating shaft) of the actuator of the drive unit 14 based on a command (signal transmission), thereby determining the end of the rapid increase in filling flow rate P1 and the start of the rapid decrease in filling flow rate P2.

[0037] Furthermore, the energy recovery device 1 of this embodiment includes a first position detector S1 (other end side position detector S1) provided near the other end of the first and second cylinders 7A and 7B to detect when the first and second pistons 8A and 8B have reached the vicinity of the other end of the corresponding first and second cylinders 7A and 7B; a second position detector S2 provided at a position further to the other end of the first and second cylinders 7A and 7B than the first position detector S1 to detect when the first and second pistons 8A and 8B have reached a position (end) further to the other end than the first position detector S1; and a third position detector S3 (one end side position detector S3) provided near one end of the first and second cylinders 7A and 7B to detect when the first and second pistons 8A and 8B have reached the vicinity of one end of the first and second cylinders 7A and 7B. Furthermore, the control unit C may control the flow rate adjustment valve 19a by setting the point at which the other end position detector S2 detects the first and second pistons 8A and 8B during the filling process as the end of the rapid increase in filling flow rate P1, and the point at which the one end position detector S3 detects the first and second pistons 8A and 8B during the filling process as the start of the rapid decrease in filling flow rate P2.

[0038] Furthermore, as shown in Figure 4, the control unit C has a function that, when the measured value Q1 of the low-pressure saltwater filling flow rate based on the second flow rate signal is lower than the target value Q2, it accumulates the difference between the amount of filling at the measured value Q1 from the end of the rapid increase in filling flow rate P1 to the start of the rapid decrease in filling flow rate P2 and the amount of filling at the target value Q2. If the accumulated value exceeds a preset alarm setting value, it issues a water supply shortage alarm and stops the operation of the system (operation of the energy recovery device 1).

[0039] In other words, as shown in Figure 4, if there is a difference between the target value Q2 of the filling flow rate and the measured value Q1, feedback control is performed to open the flow control valve 19a if the target value Q2 > measured value Q1 (part L2 in Figure 4), and to close the flow control valve 19a if the target value Q2 < measured value Q1 (part L1 in Figure 4). Also, if the measured value Q1 is less than the target value Q2 (part L2 in Figure 4), the control unit C accumulates the difference in volume (hatched part in Figure 4), and when the accumulated value exceeds the alarm setting value, it issues a water supply shortage alarm and automatically stops the system operation.

[0040] Furthermore, the control unit C has a function to issue a water supply shortage alarm and stop operation when the first position detector S1 (other end position detector S1) in the first cylinder device 9A or the second cylinder device 9B during the pumping process detects the first piston 8A or the second piston 8B before the one end position detector S3 in the first cylinder device 9A or the second cylinder device 9B during the filling process detects the first piston 8A or the second piston 8B, or when the one end position detector S3 in the first cylinder device 9A or the second cylinder device 9B during the filling process and the first position detector S1 (other end position detector S1) in the first cylinder device 9A or the second cylinder device 9B during the pumping process simultaneously detect the first piston 8A or the second piston 8B.

[0041] As described above, in the energy recovery device 1 of this embodiment, the control unit C provides feedback control (controls the rotational speed of the pressure booster pump) to the pressure booster pump 10 based on the first flow rate signal to adjust the flow rate of concentrated brine to the cylinder device 9A or 9B during the pumping process. Therefore, even if the flow rate of concentrated brine fluctuates, the supply of low-pressure brine to the cylinder device 9A or 9B during the filling process can be terminated earlier than the supply of high-pressure concentrated brine to the cylinder device 9A or 9B during the pumping process, thereby preventing insufficient water supply to the cylinder device 9A or 9B during the filling process. This prevents the concentrated brine side of the RO membrane from becoming blocked and preventing water from being supplied from the pressure booster pump.

[0042] Furthermore, in addition to controlling the booster pump 10, the control unit C controls the flow rate adjustment valve 19a based on a second flow rate signal of low-pressure brine in the water supply side connecting pipe 11b to adjust the discharge flow rate of concentrated brine. By feedback-controlling the opening degree of the flow rate adjustment valve 19a, it becomes easier to control the flow rate of low-pressure brine flowing into the energy recovery device and the discharge flow rate from the energy recovery device to a constant level, enabling smooth operation. For example, if the control unit C determines from the second flow rate signal that the supply flow rate of low-pressure brine has decreased and the flow rate in the filling process has decreased, it increases the discharge flow rate of concentrated brine from the flow rate adjustment valve 19a to adjust the discharge flow rate and allow the filling process to proceed smoothly.

[0043] Furthermore, since the control unit C makes the flow rate of the low-pressure brine to the cylinder device 9A or 9B during the filling process larger than the flow rate of the concentrated brine to the cylinder device 9A or 9B during the pumping process based on the first flow rate signal and the second flow rate signal, the filling flow rate of the low-pressure brine in the filling process increases, and the state of insufficient water supply to the cylinder device 9A or 9B in the filling process can be further prevented. In particular, in the case of an energy recovery device of a two-cylinder system (two cylinder devices), the moving speed of the piston in the filling process is set to be faster than the moving speed of the piston in the pumping process, and after the filling process is completed, the booster pump 10 and the flow rate adjustment valve 19a are automatically adjusted so that an appropriate standby time can be ensured until the pumping process is started.

[0044] Furthermore, the control unit C holds the second flow rate signal during the filling process, excluding the time when the filling flow rate of the low-pressure brine rapidly increases immediately after the start of the filling process and the time when the filling flow rate of the high-pressure brine rapidly decreases immediately before the end, as a held flow rate value, controls the flow rate adjustment valve 19a based on the held flow rate value until the end P1 of the rapid increase in the filling flow rate of the next filling process, releases the holding of the held flow rate value at the end P1 of the rapid increase in the filling flow rate of the next filling process, and controls the flow rate adjustment valve 19a based on the second flow rate signal at the current time instead of the held flow rate value until the start P2 of the next rapid decrease in the filling flow rate. Therefore, the variation in the opening degree of the flow rate adjustment valve 19a can be reduced, and the occurrence of the hunting phenomenon can be made less likely.

[0045] That is, the second flow rate signal when the variation in the filling flow rate is small and almost constant is held and fixed as the held flow rate value, and the flow rate adjustment valve 19a is controlled while maintaining the held flow rate value until the end P1 of the rapid increase in the filling flow rate at the start of the next filling process. However, after the end P1 of the rapid increase in the filling flow rate of the next filling process and until the start P2 of the next rapid decrease in the filling flow rate, the flow rate adjustment valve 19a is controlled by switching to the second flow rate signal at the actual current time instead of the held flow rate value. By doing so, the variation in the opening degree of the flow rate adjustment valve 19a due to the feedback control accompanying the rapid increase and rapid decrease in the filling flow rate can be suppressed.

[0046] In addition, the second flow rate signal during the filling process, excluding the time when the filling flow rate of the low-pressure brine suddenly increases immediately after the start of the filling process and the time when the filling flow rate of the low-pressure brine suddenly decreases immediately before the end, is used as the holding flow rate value. However, any time point during the filling process (hereinafter referred to as the substantially constant flow rate period) excluding the time when the filling flow rate of the low-pressure brine suddenly increases and the time when the filling flow rate of the low-pressure brine suddenly decreases immediately before the end may be used as the holding flow rate value of the second flow rate signal. Preferably, the average value of the second flow rate signal during the substantially constant flow rate period is used as the holding flow rate value. In this way, if the average value of the second flow rate signal is used as the holding flow rate value, the stability is improved against the flow rate measurement noise. In addition, although it is preferable to use the average value of the second flow rate as the holding flow rate value, the second flow rate signal at the midpoint of the substantially constant flow rate period may be used as the holding flow rate value.

[0047] Further, when the flow path for discharging the concentrated brine in the switching valve device 13 is fully opened during the filling process, the control unit C sets the end time P1 of the sudden increase in the filling flow rate, and when the flow path on the discharge side of the concentrated brine in the switching valve device 13 is closed, the control unit C sets the start time P2 of the sudden decrease in the filling flow rate and controls the flow rate adjustment valve 19a. Therefore, according to the valve opening state of the drain side flow path, the end time P1 of the sudden increase in the filling flow rate of the low-pressure brine and the start time P2 of the sudden decrease in the filling flow rate can be easily determined.

[0048] In addition, during the filling process, when the other end side position detector S2 detects the first and second pistons 8A and 8B, the control unit C may set the end time P1 of the sudden increase in the filling flow rate, and when the one end side position detector S3 detects the first and second pistons 8A and 8B during the filling process, the control unit C may set the start time P2 of the sudden decrease in the filling flow rate and control the flow rate adjustment valve 19a. Also in this case, according to the detection of the first and second pistons 8A and 8B by the one end side position detector S3 and the other end side position detector S2, the end time P1 of the sudden increase in the filling flow rate of the low-pressure brine and the start time P2 of the sudden decrease in the filling flow rate can be easily determined.

[0049] Furthermore, when the control unit C detects that the measured value Q1 of the low-pressure brine filling flow rate based on the second flow rate signal is lower than the target value Q2, it calculates the difference between the amount filled at the measured value Q1 and the amount filled at the target value Q2 from the end of the rapid increase in filling flow rate P1 to the start of the rapid decrease in filling flow rate P2. If the calculated value exceeds a preset alarm value, the control unit C issues a water supply shortage alarm and stops operation, thereby preventing the concentrated brine side of the RO membrane from becoming blocked and preventing water from being supplied from the booster pump. In other words, even with the above flow rate control, if the water supply in the filling process is insufficient and exceeds the alarm value, and operation continues further, the control unit C will determine that cylinder congestion will occur, the concentrated brine side of the RO membrane will become blocked, and water from being supplied from the booster pump will become impossible. In response, the control unit C will automatically stop the operation of the system (energy recovery device) by closing each valve, etc., thereby ensuring safety.

[0050] Furthermore, when the control unit C detects the first and second pistons 8A and 8B before the one-end position detector S3 in the cylinder device 9A or 9B during the filling process detects them, or when the one-end position detector S3 in the cylinder device 9A or 9B during the filling process and the first position detector S1 (other-end position detector S1) in the cylinder device 9A or 9B during the pumping process simultaneously detect the first and second pistons 8A and 8B, the control unit C issues a low water supply alarm and stops operation. As a result, the cylinder device 9A or 9B during the filling process does not switch to the pumping process, and a cylinder congestion alarm is issued, automatically stopping the system and ensuring safety. In other words, if the cylinder device 9A or 9B in the filling process switches to the pumping process while the water supply is insufficient, the position where the pumping process switches will move further away from the ends of the first and second cylinders 7A and 7B with each reciprocating motion of the first and second pistons 8A and 8B, eventually causing the operation to stop. However, the control unit C can detect the piston position and make a decision in advance to prevent this.

[0051] 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.

[0052] For example, the above embodiment shows a case with two cylinder devices (two-cylinder system), but the present invention can be applied not only to the two-cylinder system but also to cases using more cylinders, such as a three-cylinder system. That is, in the case of three cylinder devices (three-cylinder system), while the first and second cylinder devices are operating, the remaining third cylinder device is in a state where the piston is stopped at the end on the flow path switching mechanism side (standby process). Even when the present invention is applied to this three-cylinder system, the control unit repeatedly performs the pumping process, the filling process, and the standby process, in which neither concentrated brine nor low-pressure brine is supplied to the cylinder device, in this order, alternating sequentially for each cylinder device. In this three-cylinder system as well, if the flow rate of the filling process exceeds the flow rate of the pumping process, the flow rate of the filling process becomes intermittent, similar to the two-cylinder system. Also, if the flow rate of the filling process falls below the flow rate of the pumping process, the system switches to the pumping process before the piston reaches the end on the switching valve side, so the entire effective length of the cylinder cannot be used. If operation continues as is, the point where the process switches from the filling process to the pumping process will move further away from the switching valve side end 7a with each reciprocating cycle, and eventually the operation will stop. Therefore, the control described above in the present invention is effective. In addition, although the above switching valve device employs a switching cylinder device consisting of a pressure distribution valve, a switching valve device consisting of multiple switching valves such as ball valves may also be employed.

[0053] This application claims priority based on Japanese Patent Application No. 2024-206374, filed on November 27, 2024, and incorporates all the contents contained in said Japanese application.

[0054] 1...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...Increasing pressure pump, 11...Flow path direction regulating mechanism, 13...Switching valve device, 14...Drive device, 18a...First flow meter, 18b...Second flow meter, 19a...Flow control valve, C...Control unit, S1...First position detector (other end position detector), S2...Second position detector, S3...Third position detector (one end position detector), P1...End of rapid increase in filling flow rate, P2...Start of rapid decrease in filling flow rate, Q1...Measured value, Q2...Target value

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, comprising: a plurality of cylinder devices having pistons that reciprocate within a cylinder, one end of which is connected to the concentrated brine pipe and the drain pipe via a flow path switching mechanism that connects and disconnects the concentrated brine pipe and the concentrated brine drain pipe; a high-pressure pump connected to the base end of the supply pipe; a water supply pipe connected to the high-pressure pump and supplying low-pressure brine to the high-pressure pump; a water supply side connecting pipe connected to the water supply pipe and sending the low-pressure brine to the plurality of cylinder devices; and a flow path direction regulating mechanism connected to the water supply side connecting pipe that can alternately supply the low-pressure brine to the plurality of cylinder devices and return the high-pressure brine, which is alternately pushed out from the plurality of cylinder devices, to the membrane separation device via a pressure boosting pump. An energy recovery device comprising: a control unit having a control function that controls the flow path switching mechanism to switch the connection of the plurality of cylinder devices to the concentrated water pipe and the drain pipe, and repeatedly performs a pumping step in which high-pressure concentrated brine is supplied to the cylinder device to push out the energy-transferred high-pressure brine at high pressure, and a filling step in which low-pressure brine is supplied to the cylinder device from the flow path direction restricting mechanism after the pumping step to fill the cylinder device with the low-pressure brine while discharging the concentrated brine inside, while sequentially alternating between each of the cylinder devices, wherein the flow path switching mechanism includes a first flow meter connected to the concentrated water pipe that measures the flow rate of the concentrated brine and transmits a first flow rate signal to the control unit, and the control unit controls the booster pump based on the first flow rate signal to adjust the flow rate of the concentrated brine to the cylinder device during the pumping step.

2. An energy recovery device according to claim 1, comprising: a flow control valve provided in the drain pipe and capable of adjusting the flow rate of the concentrated brine to be drained; and a second flow meter connected to the water supply side connecting pipe and transmitting a second flow signal to the control unit for measuring the flow rate of the low-pressure brine, wherein the control unit controls the flow control valve based on the second flow signal to adjust the flow rate of the drained brine.

3. An energy recovery apparatus according to claim 2, characterized in that the control unit makes the flow rate of the low-pressure brine to the cylinder device during the filling process greater than the flow rate of the concentrated brine to the cylinder device during the pumping process, based on the first flow rate signal and the second flow rate signal.

4. An energy recovery device according to claim 2 or 3, wherein the control unit holds the second flow rate signal during the filling process as a held flow rate value, except when the filling flow rate of the low-pressure brine rapidly increases immediately after the start of the filling process and when the filling flow rate of the low-pressure brine rapidly decreases immediately before the end of the filling process, controls the flow rate control valve based on the held flow rate value until the rapid increase in the filling flow rate of the next filling process ends, releases the holding of the held flow rate value when the rapid increase in the filling flow rate of the next filling process ends, and controls the flow rate control valve based on the current second flow rate signal until the start of the next rapid decrease in the filling flow rate.

5. An energy recovery device according to claim 4, wherein the flow path switching mechanism comprises a switching valve device that switches between supplying the concentrated brine to the cylinder device and stopping its supply and discharging the concentrated brine from the cylinder device and stopping its discharge, and a drive device that drives the switching valve device, wherein the control unit controls the flow rate adjustment valve, with the point in time when the flow path for discharging the concentrated brine in the switching valve device is fully opened in the filling process being the end of the rapid increase in filling flow rate, and the point in time when the flow path on the discharge side of the concentrated brine in the switching valve device is closed being the start of the rapid decrease in filling flow rate.

6. An energy recovery device according to claim 4, comprising: a position detector on the other end of the cylinder provided near the other end for detecting when the piston has reached the other end of the cylinder; and a position detector on the one end of the cylinder provided near the one end for detecting when the piston has reached the one end of the cylinder, wherein the control unit controls the flow rate adjustment valve, with the point in time when the position detector on the other end detects the piston during the filling process being the end of the rapid increase in filling flow rate, and the point in time when the position detector on the one end detects the piston during the filling process being the start of the rapid decrease in filling flow rate.

7. An energy recovery device according to claim 6, wherein when the measured value of the filling flow rate of the low-pressure salt water based on the second flow rate signal is lower than the target value, the control unit accumulates the difference between the amount of filling at the measured value and the amount of filling at the target value from the end of the rapid increase in the filling flow rate to the start of the rapid decrease in the filling flow rate, and when the accumulated value exceeds a preset alarm setting value, it issues a water supply shortage alarm and stops operation.

8. An energy recovery device according to claim 6, characterized in that the control unit issues a water supply shortage alarm and stops operation when the other end position detector in the cylinder device during the pumping process detects the piston before the one end position detector in the cylinder device during the filling process detects the piston, or when the one end position detector in the cylinder device during the filling process and the other end position detector in the cylinder device during the pumping process simultaneously detect the piston.

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