Energy recovery device
The energy recovery device stabilizes flow rates through feedback-controlled valves and pumps, addressing flow rate fluctuations and piston position issues to prevent blockages and ensure continuous water supply in reverse osmosis systems.
Patent Information
- Authority / Receiving Office
- JP · JP
- Patent Type
- Applications
- Current Assignee / Owner
- DMW
- Filing Date
- 2024-11-27
- Publication Date
- 2026-06-08
Smart Images
Figure 2026093035000001_ABST
Abstract
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 of producing fresh water from seawater, the reverse osmosis method is known. In this reverse osmosis method, seawater is filtered through a semipermeable membrane (reverse osmosis membrane (RO membrane)) by applying a pressure higher than the osmotic pressure of seawater in the direction opposite to the direction in which the osmotic pressure acts, separating 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 referred to as a pressure pumping process (or energy recovery process). Further, after the pressure pumping process is completed, seawater is supplied from the water intake pump to the cylinder device via a flow path direction regulating device, and the operation of filling seawater while discharging concentrated brine in the direction opposite to the pressure pumping process is referred to as 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 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 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 freshwater pipe, and discharges the high-pressure concentrated seawater into a concentrated water pipe, comprising: an intake pump for supplying seawater; a pressurizing pump that pressurizes the seawater from the intake pump and supplies the high-pressure seawater to the membrane separation device; three cylinder devices, each having a piston that moves back and forth within a cylinder, with one end communicating with the intake pump and the other end connected to the concentrated water pipe and the drainage channel via a flow path switching mechanism that connects and disconnects the concentrated seawater pipe and the drainage channel; and controlling the flow path switching mechanism to switch the connection of the three cylinder devices to the concentrated water pipe and the drainage channel. The present invention describes an energy recovery device comprising a control unit having a control function that sequentially alternates and repeats the following steps in each cylinder device: a pumping step of supplying the concentrated seawater at high pressure to the cylinder device to push out the seawater inside at high pressure; a filling step of supplying seawater from the intake pump to the cylinder device after the pumping step to fill it with seawater while discharging the concentrated seawater inside; and a standby step of not supplying either the concentrated seawater or the seawater to the cylinder device. The control unit performs each of the above steps differently in the three cylinder devices, except immediately before and after switching between each step, and performs the pumping step or the filling step simultaneously in two of the cylinder devices immediately before and after switching between each step.
[0005] In this device, the control unit performs the pumping process, filling process, and standby process using three cylinder devices that are different from each other, except immediately before and after switching between each of the aforementioned processes. By using one of the three cylinder devices for the pumping process, one for the filling process, and one for the standby process, seawater is constantly supplied from the intake pump, which suppresses the pulsation of the high-pressure pump (booster pump). [Prior art documents] [Patent Documents]
[0006] [Patent Document 1] Patent No. 6412233 [Overview of the Initiative] [Problems that the invention aims to solve]
[0007] The following challenges remain in the conventional technologies described above. In other words, in 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 operation. 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 and filling processes 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 with the first cylinder is equal to the rate at which the flow rate of the cylinder device increases when the filling process is started with the second cylinder. In other words, if the flow rate is properly adjusted, as shown in Figure 5(a), the piston 8 reaches the switching valve side end 7a of the cylinder 7, and after a waiting period, the process switches to the pumping process.
[0008] However, if the flow rate control malfunctions in the 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, and eventually the system stops working. Furthermore, if the flow rate adjustment malfunctions in the 3-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, then, similar to the 2-cylinder system, the system will switch to the pumping process before the piston reaches the end on the switching valve side, rendering 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 will move further away from the end 7a on the switching valve side with each reciprocating cycle, and eventually the system will stop working. If the system (water desalination equipment) continues to operate in the above condition (where the piston stops midway through the cylinder), the concentrated brine side of the RO membrane becomes blocked, preventing water from being 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. [Means for solving the problem]
[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 device comprises 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 supplies the low-pressure brine from the flow path direction regulating mechanism to the cylinder devices after the filling process to fill them with the low-pressure brine while discharging the concentrated brine inside, and repeats 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 filling process.
[0011] In this energy recovery device, 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, thereby 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, which would prevent 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 device, 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 (a two-cylinder device), it is preferable to set the piston movement speed in the filling process to be faster than the piston movement speed in the pumping process, and to automatically adjust the booster pump and flow control valve so that an appropriate waiting time is secured between the completion 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 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 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 systems, multiple cylinders, including two-cylinder systems, are used, resulting in intermittent flow rates during the filling process, as described above. When the opening of the flow control valve is controlled by feedback, the system attempts to increase the opening of the flow control valve when it determines that the discharge flow rate has decreased significantly while the piston is waiting (when the filling flow rate is zero). Conversely, when the filling process restarts, it attempts to decrease the opening of the flow control valve. This can lead to large fluctuations in the valve opening, causing a hunting phenomenon and preventing the opening from remaining constant. In contrast, in the present invention described above, the control unit holds a second flow rate signal during the filling process as a retained 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 control unit then controls the flow control valve based on the retained flow rate value until the rapid increase in the filling flow rate of the next filling process ends. At the end of the rapid increase in the filling flow rate of the next filling process, the hold on the retained flow rate value is released, and the flow control valve is controlled based on the current second flow rate signal instead of the retained flow rate value until the start of the next rapid decrease in the filling flow rate. This reduces fluctuations in the opening degree of the flow control valve and makes it easier to keep the opening degree constant. In other words, the second flow rate 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 rate 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, in the fourth invention, provided near the other end of the cylinder and includes an other-end side position detector for detecting that the piston has reached near the other end of the cylinder, and an one-end side position detector provided near one end of the cylinder for detecting that the piston has reached near one end of the cylinder. The control unit sets the time when the other-end side position detector detects the piston during the filling process as the end time of the rapid increase in the filling flow rate, and sets the time when the one-end side position detector detects the piston during the filling process as the start time of the rapid decrease in the filling flow rate, and controls the flow rate adjustment valve.
[0021] The energy recovery device according to the seventh invention is, in the sixth invention, when the measured value of the filling flow rate of the low-pressure brine based on the second flow signal by the control unit is lower than the target value, the difference between the filling amount at the measured value from the end time of the rapid increase in the filling flow rate to the start time of the rapid decrease in the filling flow rate and the filling amount at the target value is integrated. When the integrated value becomes equal to or greater than a preset alarm set value, an alarm for insufficient water supply is issued and the operation is stopped.
[0022] That is, in this energy recovery device, when the measured value of the filling flow rate of the low-pressure brine based on the second flow signal by the control unit is lower than the target value, the difference between the filling amount at the measured value from the end time of the rapid increase in the filling flow rate to the start time of the rapid decrease in the filling flow rate and the filling amount at the target value is integrated. When the integrated value becomes equal to or greater than a preset alarm set value, an alarm for insufficient water supply is issued and the operation is stopped. Therefore, it is possible to prevent in advance the clogging of the concentrated brine side of the RO membrane and the inability to supply water from the booster pump. That is, even if the above flow rate control is performed, if the water supply during the filling process is insufficient due to some reason and exceeds the alarm set value, and the control unit determines that if the operation is continued further, the cylinder will be in a clogged state, the operation of the system can be automatically stopped by closing each valve, etc., ensuring safety.
[0023] The energy recovery device according to the eighth invention is characterized in that, in the sixth invention, 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, the control unit issues an alarm of insufficient water supply and stops the operation.
[0024] That is, in this energy recovery device, 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, the control unit issues an alarm of insufficient water supply and stops the operation. Therefore, the cylinder device during the filling process does not switch to the pumping process, and an alarm of insufficient water supply is issued to automatically stop, ensuring safety. That is, if the cylinder device during the filling process switches to the pumping process with insufficient water supply, the position where the pumping process switches moves away from the cylinder end as the number of reciprocations of the piston increases, and finally the operation stops. However, the control unit can detect the piston position in advance and prevent this.
Advantages of the Invention
[0025] According to the present invention, the following effects can be achieved. That is, according to the energy recovery device according to the present invention, the control unit controls the booster pump (feedback) based on the first flow signal in the concentrated-side connection pipe (controls the rotational speed of the booster pump) to adjust the flow rate of the concentrated brine to the cylinder device during the pumping process. Therefore, even if the flow rate of the concentrated brine in the concentrated-side connection 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, and it is possible to prevent a state of insufficient water supply to the cylinder device during the filling process. Therefore, the energy recovery device of the present invention can prevent the concentrated brine side of the RO membrane from becoming blocked, which would prevent water from being supplied from the booster pump. [Brief explanation of the drawing]
[0026] [Figure 1] This is a schematic diagram showing an embodiment of the energy recovery device according to the present invention, in which the first cylinder device is in the pumping process and the second cylinder device is in the filling process. [Figure 2] This embodiment is a schematic diagram showing a flow path switching mechanism equipped with a switching cylinder device. [Figure 3] This is a graph showing the change in the normal filling flow rate during the filling process in this embodiment. [Figure 4] 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 during the filling process. [Figure 5] This is an explanatory diagram illustrating the sequential movement of the piston inside the cylinder during the filling process when a state of insufficient water supply occurs. [Modes for carrying out the invention]
[0027] Hereinafter, an 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. , a second cylinder device 9B having 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 that, after the pumping process, supplies low-pressure brine from the flow path direction regulating mechanism 11 to the first cylinder device 9A and the second cylinder device 9B to fill with low-pressure brine while discharging the concentrated brine inside, and repeats these processes sequentially 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. 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.
[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 that is connected to the concentrated water pipe 4 and transmits a first flow signal to the control unit C, which measures the flow rate of the concentrated brine. The control unit C has the function of controlling the booster pump 10 (by feedback) based on the first flow rate signal in the concentration-side connecting pipe (controlling the rotational speed of the booster pump 10) 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 measures the flow rate of low-pressure brine and transmits a second flow signal to the control unit C. The control unit C also has the function of adjusting the discharge flow rate of concentrated brine by controlling the flow control valve 19a based on the second flow rate signal. Furthermore, 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 rate signal and the second flow rate 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 retained 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, and controlling the flow control valve 19a based on the retained flow rate value until the rapid increase in the filling flow rate of the next filling process ends, releasing the retention of the retained 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 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 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.
[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 the supply, and discharging concentrated brine from the first cylinder device 7A or the second cylinder device 7B and stopping the 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 at which the flow path for the discharge of concentrated brine in the switching valve device 13 is fully opened during the filling process being the end of the rapid increase in filling flow rate P1, and the point at which the flow path on the discharge side of the concentrated brine in the switching valve device 13 is closed being the start of the rapid decrease in filling flow rate P2. The point at which the discharge flow path becomes fully open may be the point at which the control unit C receives a signal from the drive unit 14 indicating that it is fully open, or it may be the point at which the time elapsed after the drive unit 14 receives the fully open signal from the control unit C until the discharge flow rate becomes fully open is estimated in advance and set 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 together with the drain side piston 21a within the switching cylinder 20, and a switching piston rod 22 which has the drain side piston 21a at one end, the supply side piston 21b at the middle section, and the other end protruding to the outside from the other end of the switching cylinder 20. The switching cylinder 20 has an outlet port 13a connected to the concentrated seawater drain pipe 19 and provided at one end, an inlet port 13b connected to the concentrated water pipe 4 and provided in the middle, and an inlet / outlet port 13c connected to the first cylinder device 9A or the second cylinder device 9B and provided between the outlet port 13a and the inlet port 13b. The above-mentioned drive device 14 is a switching valve drive actuator in which the tip of a movable operating shaft is connected to a switching piston rod 22.
[0036] The control unit C described above has the function of operating the drive unit 14. In other words, the control unit C determines that the moment when the drive unit 14 fully opens the inlet / outlet port 13c in the first cylinder device 9A or the second cylinder device 9B in the filling process is the end of the rapid increase in filling flow rate P1. Furthermore, the control unit C 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 manipulating 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 and detecting 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 and detecting 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 and detecting 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, When the target value Q2 > measured value Q1 (part L2 in Figure 4), the flow control valve 19a is opened. When the target value Q2 < the measured value Q1 (part L1 in Figure 4), feedback control is performed to close the opening of the flow control valve 19a. Furthermore, if the measured value Q1 falls below the target value Q2 (part L2 in Figure 4), the control unit C accumulates the difference in volume (hatched area in Figure 4), and when this 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 low water supply alarm and stop operation when the first position detector S1 (other end position detector S1) in the first cylinder unit 9A or second cylinder unit 9B during the pumping process detects the first and second pistons 8A and 8B before the one end position detector S3 in the first cylinder unit 9A or second cylinder unit 9B during the filling process detects the first and second pistons 8A and 8B or the second first and second pistons 8A and 8B, or when the one end position detector S3 in the first cylinder unit 9A or second cylinder unit 9B during the filling process and the first position detector S1 (other end position detector S1) in the first cylinder unit 9A or second cylinder unit 9B during the pumping process simultaneously detect the first and second pistons 8A and 8B or the second first and second pistons 8A and 8B.
[0041] In this embodiment, the energy recovery device 1 has a control unit C that performs feedback control (controls the rotational speed of the pressure booster pump) of the 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. As a result, 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, which would prevent water from being supplied from the booster pump.
[0042] Furthermore, in addition to controlling the booster pump 10, the control unit C controls the flow control valve 19a based on a second flow 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 control valve 19a, it becomes easier to keep the flow rate of low-pressure brine flowing into the energy recovery device on the water supply side and the discharge flow rate from the energy recovery device on the wastewater side constant, enabling smooth operation. For example, if the control unit C determines from the second flow rate signal that the flow rate of low-pressure brine has decreased and the flow rate in the filling process has decreased, it increases the flow rate of concentrated brine discharged from the flow control valve 19a to adjust the flow rate on the discharge side and allow the filling process to proceed smoothly.
[0043] Furthermore, based on the first flow rate signal and the second flow rate signal, the control unit C increases the flow rate of low-pressure brine to the cylinder device 9A or 9B during the filling process compared to the flow rate of concentrated brine to the cylinder device 9A or 9B 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 9A or 9B during the filling process. In particular, in the case of a two-cylinder energy recovery system (a two-cylinder device), the piston movement speed in the filling process is set to be faster than the piston movement speed in the pumping process, and the booster pump 10 and flow control valve 19a are automatically adjusted so that an appropriate waiting time is secured between the completion of the filling process and the start of the pumping process.
[0044] Furthermore, the control unit C holds the second flow rate signal during the filling process as a retained 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 high-pressure salt water rapidly decreases immediately before the end of the filling process. The control unit C controls the flow control valve 19a based on the retained flow rate value until the end of the rapid increase in the filling flow rate of the next filling process P1. At the end of the rapid increase in the filling flow rate of the next filling process P1, the control unit C releases the retention of the retained flow rate value and controls the flow control valve 19a based on the current second flow rate signal instead of the retained flow rate value until the start of the next rapid decrease in the filling flow rate P2. This reduces fluctuations in the opening degree of the flow control valve 19a and makes hunting less likely.
[0045] In other words, the second flow rate signal, which is small and nearly constant when the filling flow rate fluctuations are small, is held and fixed as the retained flow rate value, and the flow control valve 19a is controlled using this retained flow rate value until P1, when the rapid increase in filling flow rate at the start of the next filling process ends. However, from P1, when the rapid increase in filling flow rate at the start of the next filling process ends, until P2, when the rapid decrease in the filling flow rate at the next filling process begins, the flow control valve 19a is controlled by switching from the retained flow rate value to the actual current second flow rate signal, thereby suppressing fluctuations in the opening degree of the flow control valve 19a due to feedback control associated with rapid increases and decreases in filling flow rate.
[0046] In addition, the second flow rate signal during the filling process, excluding the period immediately after the start of the filling process when the filling flow rate of low-pressure brine increases sharply and the period immediately before the end of the filling process when the filling flow rate of low-pressure brine decreases sharply, may be used as the retained flow rate value. However, the second flow rate signal at any point during the filling process (hereinafter referred to as the "period of approximately constant flow rate"), excluding the period when the filling flow rate increases sharply and the period immediately before the end of the filling process, may be used as the retained flow rate value. However, it is preferable to use the average value of the second flow rate signal during the period of approximately constant flow rate as the retained flow rate value. By using the average value of the second flow rate signal as the retained flow rate value in this way, stability against flow rate measurement noise is improved. In addition, it is preferable to use the average value of the second flow rate as the retained flow rate value, but the second flow rate signal at the midpoint of the period of approximately constant flow rate may also be used as the retained flow rate value.
[0047] Furthermore, the control unit C controls the flow rate adjustment valve 19a, defining the point at which the flow path for the discharge of concentrated brine in the switching valve device 13 becomes fully open as the end of the rapid increase in the filling flow rate P1, and the point at which the flow path on the discharge side of the concentrated brine in the switching valve device 13 is closed as the start of the rapid decrease in the filling flow rate P2. Therefore, the end of the rapid increase in the filling flow rate P1 and the start of the rapid decrease in the filling flow rate P2 can be easily determined according to the valve opening state of the drainage side flow path.
[0048] Alternatively, the control unit C may control the flow rate adjustment valve 19a by defining the point in time when 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 in time when 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. In this case as well, the end of the rapid increase in the filling flow rate of low-pressure saltwater P1 and the start of the rapid decrease in filling flow rate P2 can be easily determined in response to the detection of the first and second pistons 8A and 8B by the one-end position detector S3 and the other-end position detector S2.
[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 signal is lower than the target value Q2, it calculates the difference between the amount of brine filled at the measured value Q1 and the amount of brine filled at the target value Q2 from the end of the rapid increase in the filling flow rate P1 to the start of the rapid decrease in the 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 to the filling process is insufficient and exceeds the alarm setting value, and if operation continues any further, the cylinder will become congested, the concentrated brine side of the RO membrane will become blocked, and water will no longer be supplied from the booster pump. In response, the control unit C determines this and automatically stops the operation of the system (energy recovery device) by closing each valve, 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, although the above embodiment shows a case with two cylinders (two-cylinder system), 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. In other words, in the case of a three-cylinder system, while the first and second cylinder systems are operating, the remaining third cylinder system is in a state where the piston is stopped at the end of the flow path switching mechanism (standby process). Furthermore, even when the present invention is applied to this three-cylinder system, the control unit repeatedly alternates between 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 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 becomes 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 end on the switching valve side 7a with each reciprocating cycle, and eventually the operation stops, so the above control of the present invention is effective. Furthermore, although the above-described 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. [Explanation of Symbols]
[0053] 1…Energy recovery device, 2a…Supply pipe, 2b…Water delivery 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 rate adjustment 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, Multiple cylinder devices, each having a piston that moves back and forth within a cylinder, are connected at one end to the concentrated water pipe and the drain pipe via a flow path switching mechanism that connects and disconnects the concentrated water pipe and the concentrated brine drain pipe, respectively. 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 saltwater to the high-pressure pump, A water supply side connecting pipe connected to the water supply pipe and sending the low-pressure saltwater to the plurality of cylinder devices, A flow direction restricting mechanism connected to the water supply side connecting pipe, which is capable of alternately supplying the low-pressure brine to the plurality of cylinder devices, and which returns the high-pressure brine, alternately pushed out from the plurality of cylinder devices, to the membrane separator via a booster pump, The control unit has 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 and the energy-transferred high-pressure brine is pushed out 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, and the low-pressure brine is filled while the concentrated brine inside is discharged, in each of the cylinder devices in sequence. The flow path switching mechanism includes a first flow meter connected to the concentrated water pipe and which transmits a first flow signal measuring the flow rate of the concentrated brine to the control unit. An energy recovery device characterized in that 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 process.
2. In the energy recovery device according to claim 1, A flow control valve provided in the drain pipe, which can adjust the flow rate of the concentrated brine being drained, The system includes a second flow meter connected to the water supply side connecting pipe, which measures the flow rate of the low-pressure saltwater and transmits a second flow signal to the control unit, An energy recovery device characterized in that the control unit controls the flow control valve based on the second flow signal to adjust the wastewater flow rate.
3. In the energy recovery device according to claim 2, An energy recovery device 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. In the energy recovery device according to claim 2 or 3, 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 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, and controls the flow rate adjustment valve based on the retained flow rate value until the rapid increase in the filling flow rate of the next filling process ends. An energy recovery device characterized by releasing the holding of the held flow rate value at the end of the rapid increase in the filling flow rate in the next filling step, and controlling 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. In the energy recovery device according to claim 4, The flow path switching mechanism includes 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, The system includes a drive device for driving the aforementioned switching valve device, An energy recovery device characterized in that the control unit controls the flow rate adjustment valve, with the point at which the flow path for the discharge of the concentrated brine in the switching valve device is fully opened during the filling process being considered the end of the rapid increase in the filling flow rate, and the point at which the flow path on the discharge side of the concentrated brine in the switching valve device is closed being considered the start of the rapid decrease in the filling flow rate.
6. In the energy recovery device according to claim 4, A position detector located near the other end of the cylinder is provided to detect when the piston has reached the vicinity of the other end of the cylinder. The cylinder is provided near one end and includes a one-end position detector that detects when the piston has reached the vicinity of one end of the cylinder. An energy recovery device characterized in that the control unit controls the flow rate adjustment valve, with the point in time when the other end position detector detects the piston during the filling process being considered the end of the rapid increase in filling flow rate, and the point in time when the one end position detector detects the piston during the filling process being considered the start of the rapid decrease in filling flow rate.
7. In the energy recovery device according to claim 6, The energy recovery device is characterized in that, when the control unit, based on the second flow signal, measures the measured filling flow rate of the low-pressure saltwater based on the second flow signal and the measured value, it 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 filling flow rate to the start of the rapid decrease in 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. In the energy recovery device according to claim 6, An energy recovery device 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.