Energy Recovery Device

Abstract

To provide an energy recovery device in which mixing of seawater before and behind a piston in a cylinder can be suppressed.SOLUTION: An energy recovery device is provided which is connected to a membrane separation device 5, the energy recovery device comprises: a feed water pump P1 feeding seawater; a high pressure pump P2 feeding high pressure seawater to the membrane separation device 5; a plurality of cylinder devices 7A, 7B; a flow passage direction regulation mechanism 11; and a control unit C having a control function performing a pressure feeding step and a filling step. Each cylinder device comprises: a cylinder 8 to which seawater is introduced from one end side and concentrated seawater is introduced from the other end side; a piston 9 moving in the cylinder; and a piston rod 12 in which one end thereof is connected to the piston and the other end is projected to the outside from the other end of the cylinder, the piston includes a tip portion 9a provided at a tip of the piston rod, and a rear end portion 9b provided separately from the tip portion and provided on an outer periphery of the piston rod through a space portion S.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to an energy recovery device for a water treatment system using a reverse osmosis membrane method used for desalinating seawater, etc. [Background technology]

[0002] Reverse osmosis is known as one method for producing fresh water from seawater. In this method, a high pressure equal to or greater than the osmotic pressure of seawater is applied to seawater in the direction opposite to the direction of the osmotic pressure, and the seawater is filtered through a semipermeable membrane (reverse osmosis: RO membrane) to separate salts from fresh water. In this method, seawater from which fresh water has been separated and salts have been concentrated (concentrated seawater) flows out of the reverse osmosis membrane module while still retaining the high pressure energy. In order to effectively utilize the high pressure energy of this outflowing concentrated seawater, various energy recovery devices have been put to practical use.

[0003] Conventionally, for example, Patent Document 1 has proposed an example of an energy recovery device in a seawater desalination system using reverse osmosis. In Patent Document 1, one end of each of a pair of cylinder devices is connected to a feed water pump and a booster pump via a flow path direction regulating device composed of two check valves. The other end of the cylinder devices is connected to an inlet / outlet port of a flow path switching device. The inlet port of the flow path switching device is connected to an outlet port of high-pressure concentrated seawater of a reverse osmosis membrane module. Furthermore, an outlet port is provided at one end of the flow path switching device.

[0004] In this energy recovery system, seawater delivered from a water supply pump is pressurized by a high-pressure pump and supplied to a reverse osmosis membrane module, while high-pressure concentrated seawater discharged from the reverse osmosis membrane module is supplied to a cylinder device to drive a piston that pushes out the 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. This operation of supplying high-pressure concentrated seawater discharged from the reverse osmosis membrane module to a cylinder device to drive a piston that pushes out the seawater at high pressure is called the pumping process. In addition, after the pumping process is completed, seawater is supplied from the water supply pump to the cylinder device via the flow path direction regulating device, and the piston is driven in the direction opposite to the pumping process to fill the cylinder with seawater while discharging concentrated seawater. This operation is called the filling process. In this manner, in this energy recovery device, when the piston of the cylinder device reaches the end of the cylinder, the flow path switching device alternately supplies high-pressure concentrated seawater from the reverse osmosis membrane module to a pair of cylinder devices, and controls so that seawater is alternately filled into the pair of cylinder devices from the water supply pump.

[0005] This allows the two cylinder devices to repeatedly perform the seawater pumping and filling processes, enabling continuous filtration. In this way, the high pressure energy of the concentrated seawater discharged from the reverse osmosis membrane module is used to supply high pressure seawater from the two cylinder devices to the reverse osmosis module via the booster pump, reducing the energy consumption of the high pressure pump.

[0006] In this type of energy recovery system, high-pressure seawater is sent to the membrane separation device using a high-pressure pump that directly pressurizes the seawater sent from the feed pump, and a booster pump that increases the pressure of the seawater sent out from the cylinder device. However, this requires two booster routes using two pressurizing pumps, making the system complicated and increasing costs. As a countermeasure, Patent Document 2 describes an energy recovery device in which a cylinder device has a piston rod with one end connected to a piston that reciprocates inside the cylinder and the other end protruding from the other end of the cylinder. In this energy recovery device, the cross-sectional area of ​​one end side of the piston in the cylinder and the cross-sectional area of ​​the other end side of the piston differ depending on the thickness (cross-sectional area) of the piston rod, making it possible to set the seawater pumped out of the cylinder device to the desired pressure and flow rate, which requires only one pressurizing pump and simplifies the equipment. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] JP 2013-86043 A [Patent Document 2] JP 2020-110736 A Summary of the Invention [Problem to be solved by the invention]

[0008] The above-mentioned conventional techniques have the following problems remaining. That is, in the conventional technology described above, seawater in front of the piston in the cylinder would leak over the piston to the rear of the piston, or seawater behind the piston would leak over the piston to the front of the piston, resulting in the inconvenience of the seawater in front of and behind the piston in the cylinder mixing together.

[0009] The present invention has been made in consideration of the above-mentioned conventional problems, and has an object to provide an energy recovery device that can prevent seawater before and after a piston in a cylinder from mixing with each other. [Means for solving the problem]

[0010] The present invention employs the following configuration to solve the above problems. That is, an energy recovery device according to a first invention is 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 concentrated seawater at high pressure into a concentrated water pipe, and includes a feedwater pump that supplies seawater, a high-pressure pump that pressurizes the seawater and supplies the high-pressure seawater to the membrane separation device, a plurality of cylinder devices each having one end connected to the feedwater 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 from the concentrated seawater drainage channel, a flow path direction regulating mechanism connected to one end of the plurality of cylinder devices and alternately supplies the seawater to the plurality of cylinder devices and sends the seawater alternately pushed out from the plurality of cylinder devices at high pressure to the membrane separation device, and a flow path switching mechanism that controls the flow path switching mechanism to switch connections of the plurality of cylinder devices to the concentrated water pipe and the drainage channel. and a control unit having a control function of performing a pumping process of supplying the concentrated seawater at high pressure to the cylinder device to push out the seawater inside at high pressure, and a filling process of supplying the seawater from the water supply pump to the cylinder device after the pumping process, and filling the cylinder device with the seawater while discharging the concentrated seawater inside, wherein the cylinder device comprises a cylinder having the other end connected to the concentrated seawater pipe and the drainage channel, into which the concentrated seawater is introduced and one end connected to the water supply pump, into which the seawater is introduced from one end, a piston that reciprocates within the cylinder, and a piston rod having one end connected to the piston and the other end protruding to the outside from the other end of the cylinder, and the piston has a disk-shaped or cylindrical tip portion provided at the tip of the piston rod, and an annular or cylindrical rear end portion provided on the outer circumferential surface of the piston rod, spaced axially from the tip portion and with a space between the tip portion and the rear end.

[0011] In this energy recovery device, the piston has a disk-shaped or cylindrical tip portion provided at the tip of the piston rod, and an annular or cylindrical rear end portion provided on the outer surface of the piston rod, axially spaced from the tip portion and with a space between the tip portion and the piston. Therefore, seawater that leaks beyond the tip or rear end portion collects in the space within the piston, thereby preventing seawater in front of the piston and seawater behind the piston in the cylinder from crossing the piston and mixing before and after the piston.

[0012] The energy recovery device according to a second aspect of the present invention is characterized in that, in the first aspect, the piston rod has a piston-side opening that opens into the space at a tip side, and an internal rod flow passage having one end connected to the piston-side opening and the other end opening to the outside. That is, in this energy recovery device, the piston rod has a piston-side opening that opens into the space at the tip side, and an internal flow passage having one end connected to the piston-side opening and the other end opening to the outside, so that seawater accumulated in the space can be discharged from the piston-side opening to the outside via the internal flow passage in the rod. In particular, since the seawater in the space is at a higher pressure than the outside atmospheric pressure, it is easy to discharge it to the outside through the internal flow passage in the rod.

[0013] The energy recovery device according to a third invention is characterized in that, in the first or second invention, the front end and the rear end are each provided with a seal portion extending annularly on the outer periphery. In other words, in this energy recovery device, the front and rear end portions are each provided with a sealing portion extending annularly around the outer periphery, so that the double sealing portion can separately suppress leakage of seawater from both the front of the front end portion and the rear of the rear end portion.

[0014] The energy recovery device of the fourth invention is characterized in that, in any of the first to third inventions, the cylinder is provided with a one-end drain capable of discharging the seawater to the outside in a portion facing the space when the piston moves to the end on the one end side. That is, in this energy recovery device, the cylinder is provided with a one-end drain that can discharge seawater to the outside in the portion facing the space when the piston moves to the one-end end, so that when the piston is in a stopped state after moving to the one-end end, the seawater that has accumulated in the space can be discharged to the outside from the one-end drain.

[0015] The energy recovery device of the fifth invention is characterized in that, in any of the first to fourth inventions, the cylinder is provided with an other-end drain capable of discharging the seawater to the outside in a portion facing the space when the piston moves to the end on the other end side. In other words, in this energy recovery device, the cylinder is provided with an other-end drain that can discharge seawater to the outside in the portion facing the space when the piston moves to the other end, so that when the piston is in a stopped state after moving to the other end, the seawater that has accumulated in the space can be discharged to the outside from the other-end drain. Effect of the Invention

[0016] According to the present invention, the following effects are obtained. That is, in the energy recovery device according to the present invention, the piston has a disk-shaped or cylindrical tip portion provided at the tip of the piston rod, and an annular or cylindrical rear end portion provided on the outer circumferential surface of the piston rod, spaced axially from the tip portion with a space between the tip portion and the piston, so that seawater that leaks beyond the tip or rear end portion collects in the space within the piston, thereby preventing seawater in front of the piston and seawater behind the piston in the cylinder from crossing the piston and mixing before and after the piston. Therefore, the energy recovery device of the present invention makes it possible to simplify the equipment and, in a configuration that aims to reduce equipment costs, can prevent seawater before and after concentration from mixing together, thereby enabling fresh water to be obtained efficiently. [Brief description of the drawings]

[0017] [Figure 1]1 is a schematic diagram showing a first embodiment of an energy recovery device according to the present invention. [Diagram 2] FIG. 2 is a schematic diagram showing a state in which the piston has moved to one end of the cylinder (a) and a state in which the piston has moved to the other end of the cylinder (b) in the first embodiment. [Diagram 3] FIG. 4 is a schematic diagram showing a main part of a second embodiment of an energy recovery device according to the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] Hereinafter, a first embodiment of an energy recovery device according to the present invention will be described with reference to FIGS.

[0019] As shown in FIG. 1, the energy recovery device 1 in this embodiment is an energy recovery device connected to a membrane separation device 5 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 3, and discharges the high-pressure concentrated seawater into a concentrated water pipe 4.

[0020] The energy recovery device 1 includes a feedwater pump P1 that supplies seawater, a high-pressure pump P2 that pressurizes seawater and supplies the high-pressure seawater to a membrane separation device 5, and a plurality of cylinder devices 7A, 7B each having one end connected to the feedwater pump P1 and connected and cut off communication with the concentrated water pipe 4 and the other end connected to the concentrated water pipe 4 and the drainage channel 19 via flow path switching mechanisms 6A, 6B that connect and cut off communication with the concentrated seawater drainage channel 19, and a plurality of cylinder devices 7A, 7B each having one end connected to the plurality of cylinder devices 7A, 7B and alternately supplying seawater to the plurality of cylinder devices 7A, 7B and alternately connecting and cutting off communication with the plurality of cylinder devices 7A, 7B. The apparatus is equipped with a flow path direction regulating mechanism 11 that returns seawater alternately pushed out at high pressure from the cylinder devices 7A, 7B to the membrane separation device 5, a control unit C having a control function that performs a pressure transfer process in which seawater is supplied to the cylinder devices 7A, 7B at high pressure by controlling the flow path switching mechanisms 6A, 6B to switch the connection of the multiple cylinder devices 7A, 7B to the concentrated water pipe 4 and the drainage channel 19, and the concentrated seawater inside is pushed out at high pressure, and a filling process in which seawater is supplied from the feed water pump P1 to the cylinder devices 7A, 7B after the pressure transfer process, and the concentrated seawater inside is discharged while the seawater is filled.

[0021] The cylinder devices 7A, 7B each include a cylinder 8 having one end connected to the concentrated water pipe 4 and the drainage channel 19, through which concentrated seawater is introduced, and one end connected to the water supply pump P1, through which seawater is introduced, a piston 9 that reciprocates within the cylinder 8, and a piston rod 12 having one end connected to the piston 9 and the other end protruding outside from the other end of the cylinder 8. The piston 9 includes a disk-shaped or cylindrical tip portion 9a provided at the tip of the piston rod 12, and an annular or cylindrical rear end portion 9b provided on the outer circumferential surface of the piston rod 12, spaced axially from the tip portion 9a with a space S interposed between the tip portion 9a and the rear end portion 9b. That is, the space S is an annular space formed between the front end 9a and the rear end 9b. The front end 9a and the rear end 9b are provided to have the same central axis as the piston rod 12.

[0022] The piston rod 12 has a piston side opening 12a that opens into the space S at the tip side, and an internal rod flow passage 12b whose one end is connected to the piston side opening 12a and whose other end is open to the outside. The piston-side opening 12a is open at least at two places on the upper and lower surfaces of the piston rod 12 facing the space S. The other end of the rod internal flow passage 12b opens at the other end of the piston rod 12. In addition, below the other end of the piston rod 12, a drain receiver 12c is provided for receiving seawater discharged from the rod internal flow passage 12b.

[0023] The front end 9a and the rear end 9b of the piston 9 are provided with annular seal portions 9c extending from the outer periphery of the piston 9. The seal portions 9c are piston seals for preventing leakage, which are made by combining a leaf spring and resin. As shown in FIG. 2, the cylinder 8 is provided with a one-end drain 8c capable of discharging seawater to the outside in a portion facing the space S when the piston 9 moves to the end on the one end side, and a other-end drain 8d capable of discharging seawater to the outside in a portion facing the space S when the piston 9 moves to the end on the other end side. The one end drain 8c and the other end drain 8d are connected to the lower side of the cylinder 8, and each is connected to an on-off valve 8e.

[0024] The cylinder 8 is provided at the other end or on the peripheral surface near the other end with a concentrated seawater inlet 8a connected to the concentrated water pipe 4 and the drainage channel 19 for introducing and discharging concentrated seawater. The concentrated seawater inlet 8a is connected to one end of a connecting pipe 13e, and the other end of the connecting pipe 13e is connected to the inlet / outlet port 13c. That is, the cylinder 8 is connected to the inlet / outlet port 13c via the concentrated seawater inlet 8a and the connecting pipe 13e. In addition, a through hole 8b through which the piston rod 12 passes is formed at the other end of the cylinder 8, and a rod seal (not shown) is provided on the inner surface of the through hole 8b to prevent concentrated seawater from leaking to the outside.

[0025] The flow path direction regulating mechanism 11 is configured to supply the seawater pushed out from each of the cylinder devices 7A and 7B to the suction side of the high-pressure pump P2. That is, the flow path direction regulating mechanism 11 is configured to send the seawater pushed out from each of the cylinder devices 7A and 7B to a connecting pipe 11e connected to the suction side of the high-pressure pump P2.

[0026] The cylinder devices 7A, 7B include a first cylinder device 7A having 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 also connects and disconnects the concentrated seawater drain pipe 19, and a second cylinder device 7B having one end connected to the concentrated water pipe 4 and the drain pipe 19 via a second flow path switching mechanism 6B that connects and disconnects the concentrated water pipe 4 and also connects and disconnects the drain pipe 19.

[0027] That is, the control unit C has a control function of controlling the first flow path switching mechanism 6A and the second flow path switching mechanism 6B to switch the connection between the first cylinder device 7A and the second cylinder device 7B to the concentrated water pipe 4 and the drain pipe 19, and a control function of alternately flowing high-pressure concentrated seawater into the first cylinder device 7A and the second cylinder device 7B, and alternately discharging concentrated seawater from the first cylinder device 7A and the second cylinder device 7B.

[0028] A feedwater pump P1 is connected to the seawater supply pipe 2a, and the seawater is sent from the supply pipe 2a to the flow path direction regulating mechanism 11 by the feedwater pump P1. The flow path direction regulating mechanism 11 is configured to alternately supply seawater to the first cylinder device 7A and the second cylinder device 7B, and to return the seawater alternately pushed out at high pressure from the first cylinder device 7A and the second cylinder device 7B to the membrane separation device 5 via the connecting pipe 11e.

[0029] The concentrated water pipe 4 is branched midway and connected to a first flow path switching mechanism 6A and a second flow path switching mechanism 6B. The first flow path switching mechanism 6A and the second flow path switching mechanism 6B are equipped with a switching cylinder device 13 that switches between supplying and stopping concentrated seawater to the first cylinder device 7A or the second cylinder device 7B and discharging concentrated seawater 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 cylinder device 13.

[0030] The switching cylinder device 13 includes a switching cylinder 20 connected to one end of the first cylinder device 7A or the second cylinder device 7B, a drain pipe 19, and a concentrated water pipe 4, a drain side piston 20a that moves back and forth within the switching cylinder 20 and can connect and block one end of the first cylinder device 7A or the second cylinder device 7B to the drain pipe 19 and the concentrated water pipe 4, a supply side piston 20b that moves back and forth together with the drain side piston 20a within the switching cylinder 20, and a switching piston rod 22 having the drain side piston 20a at one end and the supply side piston 20b in the middle, and the other end protruding outside from the other end of the switching cylinder 20 and connected to the drive device 14.

[0031] The switching cylinder 20 has an outlet port 13a provided at one end side and connected to a concentrated seawater discharge pipe 19, an inlet port 13b provided in the middle part and connected to the concentrated water pipe 4, and an inlet / outlet port 13c connected to the first cylinder device 7A or the second cylinder device 7B and provided between the outlet port 13a and the inlet port 13b.

[0032] The control unit C is equipped with position detectors (not shown) provided at multiple locations including, for example, near the other end of the cylinder 8 of each cylinder device 7A, 7B at positions capable of detecting the position of the piston 9, in particular, when the piston 9 has reached the vicinity of the other end of the cylinder 8, and has the function of controlling the first flow path switching mechanism 6A and the second flow path switching mechanism 6B based on the detection signals of these position detectors. The position detector may be installed on the cylinder 8 at a location other than the above.

[0033] Furthermore, in this embodiment, even if a position detector is not provided to be attached to the cylinder 8, the piston rod 12 protrudes from the cylinder 8, and the position of the piston 9 can be determined from the amount of protrusion. Therefore, a function may be employed that issues a signal to control the first flow path switching mechanism 6A and the second flow path switching mechanism 6B when the piston rod 12 reaches a predetermined amount of protrusion.

[0034] The first flow path switching mechanism 6A and the second flow path switching mechanism 6B are provided with the drive device 14 that drives the switching cylinder device 13. The driving device 14 is configured using, for example, a hydraulic piston connected to a hydraulic pump, an electric actuator, and the like. The control section C has a function of controlling a hydraulic servo valve or a servo motor (not shown) based on the detection signal to operate the drive device 14.

[0035] The other end of each of the first cylinder device 7A and the second cylinder device 7B is connected to the water supply pump P1 via a flow path direction regulating mechanism 11 constituted by a pair of check valves 11a. One end of the first cylinder device 7A is connected to the inflow / outflow port 13c of the switching cylinder device 13 in the first flow path switching mechanism 6A, and one end of the second cylinder device 7B is connected to the inflow / outflow port 13c of the switching cylinder device 13 in the second flow path switching mechanism 6B.

[0036] Moreover, the inlet port 13b of the switching cylinder device 13 is connected to the concentrated water pipe 4. Furthermore, one end of the switching cylinder device 13 is provided with an outlet port 13a connected to a drain pipe 19. A drain side piston 20a and a supply side piston 20b disposed in the switching cylinder 20 are connected to a switching piston rod 22. Moreover, one end of the switching piston rod 22 is connected to the drive device 14 and reciprocates within the switching cylinder 20 in conjunction with the drive device 14.

[0037] The flow path direction regulating mechanism 11 has a pair of branch pipes 11c connected to the supply pipe 2a, and one end of the corresponding first cylinder device 7A and second cylinder device 7B is connected to the middle of these branch pipes 11c via a cylinder connecting pipe 11d. A pair of check valves 11 is provided on both sides of the connection part of the cylinder connecting pipe 11d in the branch pipes 11c. The other end of the pair of branch pipes 11c is connected to a connecting pipe 11e.

[0038] Next, the operation of the energy recovery device 1 of this embodiment will be described with reference to the drawings. 1, when the piston 9 of the first cylinder device 7A in the pumping process moves in the direction of the arrow Y1, the seawater in the cylinder 8 is pushed out toward the branch pipe 11c. The seawater pushed out to the branch pipe 11c is supplied to the high-pressure pump P2 via the connecting pipe 11e. On the other hand, when the piston 9 of the second cylinder device 7B in the filling process moves in the direction of the arrow Y2, the concentrated seawater in the cylinder 8 is discharged to the drain pipe 19 via the concentrated seawater inlet 8a and the inlet / outlet port 13c.

[0039] When the piston 9 of the first cylinder device 7A reaches a predetermined position of the position detector, a detection signal is sent from the position detector to the control unit C, and when the control unit C receives this detection signal, the control unit C controls the drive device 14 of the second flow path switching mechanism 6B to switch the flow path. At this time, the inlet port 13b and the outlet port 13c of the switching cylinder device 13 in the second flow path switching mechanism 6B are connected, and high-pressure concentrated seawater is supplied from the membrane separation device 5 to the second cylinder device 7B, and the connection between the outlet port 13c and the outlet port 13a is cut off, and the pressure transfer process of the second cylinder device 7B is started. In this manner, the flow paths are switched, and the pressure-feeding process and the filling process are repeatedly performed alternately in the first cylinder device 7A and the second cylinder device 7B.

[0040] In this embodiment, the flow rate of seawater sent to the high-pressure pump P2 by the cylinder devices 7A and 7B is as follows: Q1: The flow rate of concentrated seawater sent to the other end of the cylinder through the piston Q2: Flow rate of seawater sent out from one end of the piston in the cylinder A1: Cross-sectional area of ​​the cylinder from the piston to the other end (the area obtained by subtracting the cross-sectional area of ​​the piston rod from the cross-sectional area of ​​the inside of the cylinder, i.e., the ring-shaped area of ​​the outer circumference of the piston rod) A2: Cross-sectional area of ​​the cylinder on one side of the piston (cross-sectional area inside the cylinder), Then, the relationship between flow rate and area is determined by the following equation. Flow rate ratio:Area ratio=Q2 / Q1:A2 / A1

[0041] For example, a case where the ratio of the cross-sectional area A1 on the other end side of the piston 9 in the cylinder 8 to the cross-sectional area A2 on one end side of the piston 9 in the cylinder 8 is A1:A2=1:2 will be described below. In this case, in the first cylinder device 7A in the pressure-feeding process, the flow rate of concentrated seawater introduced at the other end side of the piston 9 in the cylinder 8 is 5,000 m 3 / d, and the pressure is 4.0 MPa. The discharge flow rate of seawater at one end side of the piston 9 in the cylinder 8 is 10,000 m3 / d, the pressure is 2.0MPa.

[0042] At this time, the high pressure pump P2 is supplied with a flow rate of 10,000 m from the first cylinder device 7A. 3 Since seawater with a pressure of 2.0 MPa is sent to the membrane separation device 5 at 10,000 m 3 If you want to pump seawater with a pressure of 4.0 MPa at / d, you only need to increase the pressure by 2.0 MPa in the high-pressure pump P2. Therefore, in the conventional technology, high-pressure seawater was sent to the membrane separation device using a high-pressure pump that directly pressurizes the seawater sent from the feedwater pump, and a booster pump that boosts the pressure of the seawater sent from the cylinder device, and two booster paths using two pressurizing pumps were required.In contrast, in this embodiment, the entire amount of seawater sent from the cylinder device is sent to the suction side of the high-pressure pump, and the head loss of each part, such as the RO membrane and each pipe, which was previously compensated for by the booster pump, is included in the total head of the high-pressure pump, making the booster pump unnecessary.

[0043] In addition, in the membrane separation device 5, concentrated seawater is 3 / d, and the pressure is 4.0 MPa to the first cylinder device 7A, and fresh water (permeate) is sent to the first cylinder device 7A at a flow rate of 5,000 m 3 / d sends it to fresh water pipe 3. At this time, in the second cylinder device 7B, which is the filling process, the flow rate of seawater from one end of the cylinder 8 is 10,000 m 3 / d, and the discharge volume of concentrated seawater from the other end of cylinder 8 is 5,000 m 3 / d.

[0044] In this way, the cylinder devices 7A, 7B are equipped with a piston 9 that reciprocates within the cylinder 8, and a piston rod 12 having one end connected to the piston 9 and the other end protruding outside from the other end of the cylinder 8. Therefore, the cross-sectional area of ​​the one end side of the piston 9 in the cylinder 8 differs from the cross-sectional area of ​​the other end side of the piston 9 depending on the thickness (cross-sectional area) of the piston rod 12, making it possible to set the pressure and flow rate of seawater pumped out from the cylinder devices 7A, 7B.

[0045] In this embodiment, when the piston 9 moves forward (toward one end), if seawater leaks out from behind the piston 9 over the seal portion 9c, the seawater will flow into the space S. Furthermore, when the piston 9 moves rearward (toward the other end), if seawater leaks out from the front of the piston 9 over the seal portion 9c, the seawater also flows into the space S. Furthermore, seawater that has leaked into the space S is discharged from the piston side opening 12a through the rod inner flow passage 12b and from the other end of the piston rod 12 to an external drain receiver 12c.

[0046] In this manner, in the energy recovery device 1 of this embodiment, the piston 9 has a disk-shaped or cylindrical tip portion 9a provided at the tip of the piston rod 12, and an annular or cylindrical rear end portion 9b provided on the outer circumferential surface of the piston rod 12, spaced axially from the tip portion with a space S between the tip portion 9a and the rear end portion 9b. Therefore, seawater that leaks beyond the tip portion 9a or the rear end portion 9b accumulates in the space S within the piston 9, thereby preventing the seawater in front of the piston 9 and the seawater behind the piston 9 in the cylinder 8 from mixing before and after the piston 9 beyond the piston 9.

[0047] In addition, the piston rod 12 has a piston-side opening 12a that opens into the space S at the tip side, and an in-rod flow passage 12b that has one end connected to the piston-side opening 12a and the other end open to the outside, so that seawater accumulated in the space S can be discharged from the piston-side opening 12a to the outside via the in-rod flow passage 12b. In particular, since the seawater in the space S is at a higher pressure than the outside atmospheric pressure, it is easy to discharge it to the outside via the in-rod flow passage 12b.

[0048] In addition, since the front end 9a and the rear end 9b each have a seal portion 9c extending annularly around the outer periphery, the double seal portion 9c can separately prevent leakage of seawater from both the front end 9a and the rear end 9b. It is also possible to detect the wear and deterioration state of the seal portion 9c according to the amount of seawater discharged to the outside through the rod internal flow passage 12b.

[0049] Furthermore, the cylinder 8 is provided with a one-end drain 8c capable of discharging seawater to the outside in a portion facing the space S when the piston 9 has moved to the end on the one end side, so that when the piston 9 is in a stopped state with the piston 9 having moved to the end on the one end side, the seawater accumulated in the space S can be discharged to the outside through the one-end drain 8c. In addition, the cylinder 8 is provided with an other-end drain 8d capable of discharging seawater to the outside in the portion facing the space S when the piston 9 has moved to the other end. Therefore, when the piston 9 is in a stopped state in which it has moved to the other end, the seawater accumulated in the space S can be discharged to the outside from the other-end drain 8d.

[0050] Next, a second embodiment of the energy recovery device of the present invention will be described with reference to Fig. 3. In the following description of the embodiment, the same components as those described in the above embodiment are denoted by the same reference numerals, and the description thereof will be omitted.

[0051] The difference between the second embodiment and the first embodiment is that the first embodiment has two cylinder devices 7A, 7B, whereas the energy recovery device 21 of the second embodiment has three cylinder devices 7A, 7B, 7C, as shown in FIG. 3. That is, in the second embodiment, the cylinder device is made up of a first cylinder device 7A, a second cylinder device 7B, and a third cylinder device 7C.

[0052] In the second embodiment, the branch pipe 11c branches into three pipes corresponding to the three cylinder devices, and each pipe is connected to a first cylinder device 7A, a second cylinder device 7B, and a third cylinder device 7C via a check valve 11a. The flow path switching mechanism is also made up of three mechanisms, a first flow path switching mechanism 6A, a second flow path switching mechanism 6B, and a third flow path switching mechanism 6C, corresponding to the three cylinder devices. The third cylinder device 7C also has a cylinder structure similar to that of the first cylinder device 7A and the second cylinder device 7B.

[0053] In the second embodiment, for example, when the first cylinder device 7A of the three cylinder devices 7A, 7B, 7C is in the pumping process and the third cylinder device 7C is in the filling process, the piston 9 of the second cylinder device 7B reaches the other end of the second cylinder device 7B, and the process switching of the cylinder devices 7A, 7B, 7C is set so that the second cylinder device 7B is in the standby process. In other words, by using one of the three cylinder devices 7A, 7B, 7C for the pumping process, one for the filling process, and one for the standby process, seawater is constantly supplied from the feedwater pump P1, and pulsation of the feedwater pump P1 can be suppressed. In addition, the drain receiver is not shown in FIG.

[0054] In this way, in the energy recovery device 21 of the second embodiment, the three cylinder devices 7A, 7B, 7C are equipped with a piston 9 that moves back and forth within the cylinder 8, and a piston rod 12 having one end connected to the piston 9 and the other end protruding outside from the other end of the cylinder 8. Therefore, depending on the thickness (cross-sectional area) of the piston rod 12, the cross-sectional area of ​​the one end side of the piston 9 in the cylinder 8 differs from the cross-sectional area of ​​the other end side of the piston 9, making it possible to set the pressure and flow rate of seawater pumped out from the cylinder devices 7A, 7B, 7C.

[0055] Furthermore, in cylinder devices 7A, 7B, and 7C, each piston 9 has a tip portion 9a provided at the tip of the piston rod 12 and a rear end portion 9b provided on the outer peripheral surface of the piston rod 12 with a space portion S between the tip portion 9a and the rear end portion 9b. Therefore, seawater that leaks beyond the tip portion 9a or the rear end portion 9b accumulates in the space portion S within the piston 9, thereby preventing the seawater in front of the piston 9 and the seawater behind the piston 9 in the cylinder 8 from mixing before and after the piston 9 beyond the piston 9.

[0056] The present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the spirit of the present invention. [Explanation of symbols]

[0057] Reference Signs List 1, 21...energy recovery device, 2a...supply pipe, 3...fresh water pipe, 4...concentrated water pipe, 5...membrane separation device, 6A...first flow path switching mechanism, 6B...second flow path switching mechanism, 6C...third flow path switching mechanism, 7A...first cylinder device, 7B...second cylinder device, 7C...third cylinder device, 8...cylinder, 8a...concentrated seawater inlet, 8b...through hole, 8c...one end drain, 8d...other end drain, 9...piston, 9a...tip, 9b...rear end, 9c...sealing portion, 11...flow path direction control mechanism, 12...piston rod, 12a...piston side opening, 12b...rod internal flow passage, 19...concentrated seawater drainage path, P1...feed pump, P2...high pressure pump, C...control portion, S...space portion

Claims

1. 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, A water supply pump for supplying seawater; a high-pressure pump for pressurizing the seawater and supplying the high-pressure seawater to the membrane separation device; a plurality of cylinder devices each having one end connected to the water supply 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 water pipe and the drainage channel for the concentrated seawater; a flow path direction regulating mechanism connected to one end of the plurality of cylinder devices, alternately supplying the seawater to the plurality of cylinder devices, and alternately sending the seawater extruded from the plurality of cylinder devices at high pressure to the membrane separation device; a control unit having a control function for controlling the flow path switching mechanism to switch the connection of the plurality of cylinder devices to the concentrated water pipes and the drainage channels, and performing a pressure-feeding process of supplying the concentrated seawater at high pressure to the cylinder devices and pushing out the seawater inside at high pressure, and a filling process of supplying the seawater from the water supply pump to the cylinder devices after the pressure-feeding process and filling the cylinder devices with the seawater while discharging the concentrated seawater inside, the cylinder device is a cylinder having one end connected to the concentrated water pipe and the other end into which the concentrated seawater is introduced and one end connected to the water supply pump into which the seawater is introduced; A piston that reciprocates within the cylinder; a piston rod having one end connected to the piston and the other end protruding from the other end of the cylinder to the outside, The piston has a disk-shaped or cylindrical tip portion provided at the tip of the piston rod; a rear end portion having an annular or cylindrical shape and provided on an outer circumferential surface of the piston rod, the rear end portion being spaced apart from the front end portion in the axial direction and having a space between the rear end portion and the front end portion, The piston rod has a piston side opening that opens into the space at a tip side thereof; an energy recovery device comprising: a rod internal flow passage, one end of which is connected to the piston side opening and the other end of which is open to the outside.

2. 2. The energy recovery device according to claim 1, An energy recovery device, characterized in that the front end portion and the rear end portion each have a seal portion extending annularly on the outer periphery.

3. An energy recovery device connected to a membrane separation device which 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, A water supply pump for supplying seawater; a high-pressure pump for pressurizing the seawater and supplying the high-pressure seawater to the membrane separation device; a plurality of cylinder devices each having one end connected to the water supply 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 water pipe and the drainage channel for the concentrated seawater; a flow path direction regulating mechanism connected to one end of the plurality of cylinder devices, alternately supplying the seawater to the plurality of cylinder devices, and alternately sending the seawater extruded from the plurality of cylinder devices at high pressure to the membrane separation device; a control unit having a control function for controlling the flow path switching mechanism to switch the connection of the plurality of cylinder devices to the concentrated water pipes and the drainage channels, and performing a pressure-feeding process of supplying the concentrated seawater at high pressure to the cylinder devices and pushing out the seawater inside at high pressure, and a filling process of supplying the seawater from the water supply pump to the cylinder devices after the pressure-feeding process and filling the cylinder devices with the seawater while discharging the concentrated seawater inside, the cylinder device is a cylinder having one end connected to the concentrated water pipe and the other end into which the concentrated seawater is introduced and one end connected to the water supply pump into which the seawater is introduced; A piston that reciprocates within the cylinder; a piston rod having one end connected to the piston and the other end protruding from the other end of the cylinder to the outside, The piston has a disk-shaped or cylindrical tip portion provided at the tip of the piston rod; a rear end portion having an annular or cylindrical shape and provided on an outer circumferential surface of the piston rod, the rear end portion being spaced apart from the front end portion in the axial direction and having a space between the rear end portion and the front end portion, An energy recovery device characterized in that the cylinder is provided with a one-end drain capable of discharging the seawater to the outside in a portion facing the space when the piston moves to the end of the one end.

4. An energy recovery device connected to a membrane separation device which 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, A water supply pump for supplying seawater; a high-pressure pump for pressurizing the seawater and supplying the high-pressure seawater to the membrane separation device; a plurality of cylinder devices each having one end connected to the water supply 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 water pipe and the drainage channel for the concentrated seawater; a flow path direction regulating mechanism connected to one end of the plurality of cylinder devices, alternately supplying the seawater to the plurality of cylinder devices, and alternately sending the seawater extruded from the plurality of cylinder devices at high pressure to the membrane separation device; a control unit having a control function for controlling the flow path switching mechanism to switch the connection of the plurality of cylinder devices to the concentrated water pipes and the drainage channels, and performing a pressure-feeding process of supplying the concentrated seawater at high pressure to the cylinder devices and pushing out the seawater inside at high pressure, and a filling process of supplying the seawater from the water supply pump to the cylinder devices after the pressure-feeding process and filling the cylinder devices with the seawater while discharging the concentrated seawater inside, the cylinder device is a cylinder having one end connected to the concentrated water pipe and the other end into which the concentrated seawater is introduced and one end connected to the water supply pump into which the seawater is introduced; A piston that reciprocates within the cylinder; a piston rod having one end connected to the piston and the other end protruding from the other end of the cylinder to the outside, The piston has a disk-shaped or cylindrical tip portion provided at the tip of the piston rod; a rear end portion having an annular or cylindrical shape and provided on an outer circumferential surface of the piston rod, the rear end portion being spaced apart from the front end portion in the axial direction and having a space between the rear end portion and the front end portion, An energy recovery device characterized in that the cylinder is provided with an other-end drain capable of discharging the seawater to the outside in a portion facing the space when the piston moves to the end on the other end side.

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