Energy Recovery Device

Abstract

To provide energy recovery equipment in which adsorption of a piston to a distance ring is suppressed, and which can be therefore smoothly operated.SOLUTION: Energy recovery equipment is provided, which is connected to membrane separation equipment and comprises: a feed-water pump feeding sea water; a high pressure pump which feeds high-pressure sea water to the membrane separation equipment; a plurality of cylinder devices; a flow channel direction regulation mechanism; and a control portion having control function performing pressure-feeding process and filling process. The cylinder device comprises: a cylinder 8 from the other end side of which concentrated sea water is introduced and from one side of which sea water is introduced; and a piston 9 which moves in the cylinder. The piston includes a piston end face 9a provided on an end side of the cylinder, and the cylinder includes a distance ring 10 provided at an end of the interior thereof. The distance ring has: a pressure balance groove 10a formed in a face facing the piston end face; and a pressure balance flow channel hole 10b which is formed by connecting an inner peripheral surface and the pressure balance groove.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, high pressure equal to or greater than the osmotic pressure of seawater (approximately 2.5 MPa) 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 membrane) to separate salts from fresh water. In this reverse osmosis 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] For example, Patent Document 1 has proposed an example of a conventional 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 water intake pump and a booster pump via a flow path direction regulating device composed of four check valves. The other end of the cylinder devices is connected to an inlet / outlet port of a flow path switching device which is a switching valve. The inlet port of the flow path switching device is connected to an outlet port of high-pressure concentrated seawater of the 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 sent from the intake pump is pressurized by a high-pressure pump and supplied to the reverse osmosis membrane module, and 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 the cylinder device and driving the piston that pushes out (discharges) the seawater at high pressure is called the pumping process. In addition, after the pumping process is completed, seawater is supplied from the water intake 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 way, 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 the pair of cylinder devices to alternately fill with seawater from the water intake pump.

[0005] This allows continuous filtration by repeatedly performing the seawater pumping and filling processes using the two cylinder devices. In this way, by using the high pressure energy of the concentrated seawater discharged from the reverse osmosis membrane module to supply high pressure seawater from the two cylinder devices to the booster pump, the energy consumption of the booster pump is reduced and the energy in the pumping process can be recovered. In such energy recovery devices, a distance ring is fixed to an end portion inside the cylinder as a positioning stopper against which the moving piston abuts. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2013-86043 A Summary of the Invention [Problem to be solved by the invention]

[0007] The above-mentioned conventional techniques have the following problems remaining. That is, in the above-mentioned conventional technology, when the switching valve is switched to the discharge start position of the pumping process (the start position of the energy recovery process: the position where the pressure of the concentrated seawater starts to be transmitted to the filled seawater), the pressure inside the flange at the end of the cylinder and the distance ring becomes high (5 to 8 MPa), but the pressure inside the cylinder separated by the piston is low. Furthermore, when the piston moves toward the check valve side, the pressure is transmitted in the space between the outer periphery of the piston and the inner periphery of the cylinder, and the pressure inside the cylinder also becomes high. At this time, when the piston contacts the distance ring, the flow rate increases in the gap between the contact surfaces, and the pressure between the contact surfaces decreases, so that the piston adheres to the distance ring, and even when the switching valve is switched to the discharge start position, it may not operate smoothly (move toward the check valve side).

[0008] The present invention has been made in consideration of the above-mentioned conventional problems, and aims to provide an energy recovery device that can prevent the piston from sticking to the distance ring and operate smoothly. [Means for solving the problem]

[0009] The present invention employs the following configuration to solve the above problems. That is, an energy recovery device according to a first aspect of the 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 feed water 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 feed water 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 pipe, a flow path direction regulating mechanism that is 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 the high-pressure concentrated seawater is discharged from the plurality of cylinder devices to the membrane separation device. and a control unit having a control function of performing a pressure-feeding process of supplying concentrated seawater to the cylinder device and pushing out the seawater inside at high pressure, and a filling process of supplying seawater from the water supply pump to the cylinder device after the pressure-feeding process, and filling the cylinder device with the seawater while discharging the concentrated seawater inside. The cylinder device comprises a cylinder having the other end connected to the concentrated water pipe and the drainage channel, into which the concentrated seawater is introduced and one end connected to the water supply pump and into which the seawater is introduced, and a piston that reciprocates within the cylinder, the piston having a piston end face facing the end side of the cylinder, the cylinder having a distance ring provided at an end of the interior and against which the reciprocating piston abuts when it reaches the end, and the distance ring has a pressure balance groove formed on a surface facing the piston end face, and a pressure balance flow path hole formed by connecting an inner circumferential surface and the pressure balance groove.

[0010] In this energy recovery device, the distance ring has a pressure balance groove formed on the surface facing the piston end face and a pressure balance flow passage hole formed by connecting the inner peripheral surface and the pressure balance groove, so that the pressure-receiving area when the piston end face abuts is increased, which makes it easier for pressure to propagate and for the piston end face to separate from the distance ring. In other words, the pressure balance groove increases the pressure-receiving area, and pressure is propagated from the inner peripheral surface of the distance ring to the opposing surface (contact surface with the piston end face) via the pressure balance groove and the pressure balance flow passage hole, so that the pressure difference between the high pressure side and the low pressure side can be instantly balanced. The pressure balance groove and the pressure balance flow passage hole form a flow passage separate from the contact surface between the distance ring and the piston end face, which reduces the increase in flow rate in the gap between the contact surfaces between the distance ring and the piston end face. This suppresses adhesion between the distance ring and the piston end face due to a pressure drop between the contact surfaces, making it possible to smoothly separate the piston end face from the distance ring.

[0011] The energy recovery device according to a second invention is the energy recovery device of the first invention, characterized in that the pressure balance groove is formed in a ring shape centered on the axis of the distance ring. That is, in this energy recovery device, the pressure balance groove is formed in a ring shape centered on the axis of the distance ring, so that the annular pressure balance groove can increase the pressure-receiving area in the circumferential direction.

[0012] The energy recovery device of the third invention is characterized in that, in the first or second invention, the pressure balance flow path hole is also connected to the outer peripheral surface of the distance ring, and the distance ring has a pressure balance recess connected to the pressure balance flow path hole and formed on the outer peripheral surface. That is, in this energy recovery device, the distance ring has a pressure balancing recess formed on its outer surface and connected to the pressure balancing flow path hole, so that pressure can be transmitted to the outer surface side of the distance ring through the pressure balancing space formed between the pressure balancing recess and the inner surface of the cylinder.

[0013] The energy recovery device according to a fourth aspect of the present invention is the energy recovery device of the third aspect, characterized in that the pressure balance recess is formed in a ring shape extending in a circumferential direction. That is, in this energy recovery device, the pressure balancing recess is formed in a ring shape extending in the circumferential direction, so that pressure can be propagated to the outer circumferential surface of the distance ring in the circumferential direction.

[0014] The energy recovery device of the fifth invention is characterized in that, in the first or second invention, the pressure balance flow path holes penetrate from the inner surface to the outer surface of the distance ring and are formed in a radial pattern centered on the axis of the distance ring with spaces between them in the circumferential direction. That is, in this energy recovery device, the pressure balance flow path holes penetrate from the inner surface to the outer surface of the distance ring, and are formed in multiple radial directions centered on the axis of the distance ring with spaced apart circumferentially, so that pressure can be further transmitted from multiple circumferential locations to the inner and outer surfaces of the distance ring via the pressure balance flow path holes.

[0015] The energy recovery device of the sixth invention is characterized in that, in the first or second invention, the cylinder has a drain passage hole capable of discharging internal seawater to the outside when the device is stopped, and an air vent passage hole capable of discharging internal air to the outside when the device is stopped, and the pressure balance passage hole is also connected to the drain passage hole and the air vent passage hole. That is, in this energy recovery device, the pressure balance passage hole is also connected to the drain passage hole and the air vent passage hole, so that seawater and air can be discharged to the outside also through the pressure balance passage hole when the device is stopped.

[0016] The energy recovery device according to a seventh aspect of the present invention is the energy recovery device according to the first or second aspect of the present invention, characterized in that the distance ring is made of resin. That is, in this energy recovery device, the distance ring is formed from resin, which is less expensive than a metal one and also makes it easier to machine the pressure balance flow passage holes and the like. Effect of the Invention

[0017] According to the present invention, the following effects are obtained. In other words, according to the energy recovery device of the present invention, the distance ring has a pressure balance groove formed on the surface facing the piston end face, and a pressure balance flow passage hole formed by connecting the inner surface and the pressure balance groove, thereby suppressing adhesion between the distance ring and the piston end face, and enabling the piston end face to be smoothly detached from the distance ring. [Brief description of the drawings]

[0018] [Figure 1] 4 is a cross-sectional view showing an end portion of a cylinder device on a switching valve side in one embodiment of the energy recovery device according to the present invention. FIG. [Diagram 2] 4 is a cross-sectional view showing an end portion of the cylinder device on the check valve side in the present embodiment. FIG. [Diagram 3] FIG. 2 is a schematic diagram showing an energy recovery device in the present embodiment. [Figure 4] 2A is an opposing surface view of a distance ring on the piston side, and FIG. 2B is a cross-sectional view taken along line AA in the embodiment. [Diagram 5] 5A is a front view showing a cylinder inner plug flange on the switching valve side in the present embodiment, and FIG. 5B is a cross-sectional view taken along line BB. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] Hereinafter, one embodiment of the energy recovery device of the present invention will be described with reference to Figs.

[0020] As shown in FIG. 3 , 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.

[0021] 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.

[0022] The cylinder devices 7A, 7B are equipped with a cylinder 8 having one end connected to the concentrated water pipe 4 and the drainage channel 19, the other end through which concentrated seawater is introduced, and one end connected to the water supply pump P1, the one end through which seawater is introduced, and a piston 9 that reciprocates within the cylinder 8.

[0023] The piston 9 has a piston end surface 9a facing the end side of the cylinder 8, as shown in FIG. As shown in Figs. 1 and 2, the cylinder 8 is provided with a distance ring 10 that is provided at an end of the inside thereof and that abuts against a reciprocating piston 9 when the piston 9 reaches the end. As shown in Figures 1, 2 and 3, the distance ring 10 has a pressure balance groove 10a formed on the surface facing the piston end face 9a, and a pressure balance flow passage hole 10b formed by connecting the inner surface and the pressure balance groove 10a.

[0024] The pressure balance groove 10 a is formed in a ring shape with the axis of the distance ring 10 as the center. The pressure balance passage hole 10b is also connected to the outer circumferential surface of the distance ring 10, and the distance ring 10 has a pressure balance recess 10c formed on the outer circumferential surface and connected to the pressure balance passage hole 10b.

[0025] The pressure balancing recess 10c is formed in a ring shape extending in the circumferential direction. The pressure balance flow passage holes 10b penetrate the distance ring 10 from its inner peripheral surface to its outer peripheral surface, and are formed in plurality at intervals in the circumferential direction radially about the axis of the distance ring 10. That is, the pressure balance flow passage hole 10b is open to the inner peripheral surface, the outer peripheral surface, and the surface of the distance ring 10 facing the piston end surface 9a.

[0026] The cylinder 8 is provided at its end with a cylinder inner plug flange 17 that abuts against the outer surface of the distance ring 10 . As shown in Figures 1, 2 and 5, the cylinder inner plug flange 17 has a drain outlet passage hole 17a that can discharge internal seawater to the outside when the device is stopped, and an air vent passage hole 17b that can discharge internal air to the outside when the device is stopped. The drain passage hole 17a is formed in the lower part of the cylinder inner plug flange 17, and the air vent passage hole 17b is formed in the upper part of the cylinder inner plug flange 17. The pressure balance passage hole 10b is also connected to a drain passage hole 17a and an air vent passage hole 17b.

[0027] Further, the distance ring 10 has a water passage hole 10d formed so as to open on a surface facing the piston end surface 9a. The water passage holes 10d are formed in a pair above and below, and are connected to the middle of the pressure balance passage hole 10b and to the drain vent passage hole 17a or the air vent passage hole 17b. That is, the pressure balance channel hole 10b is also connected to the drain vent channel hole 17a or the air vent channel hole 17b via the water passage hole 10d. The distance ring 10 is made of a resin such as nylon resin.

[0028] The distance ring 10 and the cylinder inner plug flange 17 are provided at both ends of the cylinder 8, respectively. The distance ring 10 has a plurality of bolt holes 10e formed therein, and the cylinder inner plug flange 17 has a plurality of female threaded holes 17c formed therein corresponding to the respective bolt holes 10e. That is, the distance ring 10 is fixed to the cylinder inner plug flange 17 by inserting the bolt B1 through the bolt hole 10e and screwing it into the female threaded hole 17c. The cylinder inner plug flange 17 has a plurality of fixing holes 17d formed in the outer periphery, and is fixed to the end of the cylinder 8 by bolts B2 inserted into the fixing holes 17d.

[0029] 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.

[0030] The flow path direction regulating mechanism 11 is a check valve mechanism that is set 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 set 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.

[0031] 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.

[0032] 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.

[0033] 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.

[0034] 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 which is a switching valve mechanism that switches between supplying concentrated seawater to the first cylinder device 7A or the second cylinder device 7B and stopping the supply, 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.

[0035] 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.

[0036] 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.

[0037] 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.

[0038] 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.

[0039] 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.

[0040] 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.

[0041] The flow 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 11a is provided on both sides of the connection part of the branch pipe 11c to the cylinder connecting pipe 11d. The other end of the pair of branch pipes 11c is connected to a connecting pipe 11e.

[0042] Next, the operation of the energy recovery device 1 of this embodiment will be described with reference to the drawings. 3, 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.

[0043] When the piston 9 of the first cylinder device 7A reaches the position of a predetermined position detector on the flow path direction regulating mechanism 11 side (check valve side), 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.

[0044] In the above-mentioned first and second cylinder devices 7A, 7B, when the first and second flow path switching mechanisms 6A, 6B, which are switching valve mechanisms, switch to the discharge start position (energy recovery process start position: position where the pressure of the concentrated seawater starts to be transmitted to the already filled seawater), the pressure inside the cylinder inner plug flange 17 and distance ring 10 at the end of the cylinder 8 becomes high. At this time, pressure is transmitted from the inner surface of the distance ring 10 to the opposing surface (the contact surface with the piston end face 9a) via the pressure balance groove 10a and the pressure balance flow path hole 10b, and the pressure difference between the high-pressure side and the low-pressure side can be instantly balanced. Therefore, as the pressure between the contact surfaces decreases, the piston 9 becomes less likely to be attracted to the distance ring 10, and the piston 9 can move smoothly toward the flow path direction restriction mechanism 11, which is a check valve mechanism.

[0045] In other words, the pressure balance groove 10a and the pressure balance flow path hole 10b form a flow path separate from the gap between the contact surfaces of the distance ring 10 and the piston end face 9a, thereby mitigating the increase in flow rate in the gap between the contact surfaces of the distance ring 10 and the piston end face 9a. This makes it possible to suppress adhesion between the distance ring 10 and the piston end face 9a due to a pressure drop between the contact surfaces, and to allow the piston end face 9a to be smoothly detached from the distance ring 10.

[0046] As described above, in the energy recovery device 1 of this embodiment, the distance ring 10 has a pressure balance groove 10a formed on the surface facing the piston end face 9a, and a pressure balance flow path hole 10b formed by connecting the inner surface and the pressure balance groove 10a. Therefore, by increasing the pressure-receiving area when the piston end face 9a abuts, pressure propagation becomes easier and the piston end face 9a becomes easier to separate from the distance ring 10. In other words, the pressure balance groove 10a increases the pressure-receiving area, and pressure is transmitted from the inner surface of the distance ring 10 to the opposing surface (the contact surface with the piston end face 9a) via the pressure balance groove 10a and the pressure balance flow passage hole 10b, thereby instantly balancing the pressure difference between the high-pressure side and the low-pressure side.

[0047] Furthermore, since the pressure balancing groove 10a is formed in a ring shape centered on the axis of the distance ring 10, the annular pressure balancing groove 10a can increase the pressure-receiving area in the circumferential direction. In addition, since the distance ring 10 has a pressure balancing recess 10c formed on its outer surface and connected to the pressure balancing flow passage hole 10b, pressure can be transmitted to the outer surface side of the distance ring 10 through a pressure balancing space formed between the pressure balancing recess 10c and the inner surface of the cylinder 8.

[0048] Furthermore, since the pressure balancing recess 10c is formed in a ring shape extending in the circumferential direction, pressure can be propagated to the outer circumferential surface of the distance ring 10 in the circumferential direction. Furthermore, the pressure balance flow path holes 10b penetrate from the inner surface to the outer surface of the distance ring 10 and are formed in multiple radial directions centered on the axis of the distance ring 10 with spaced intervals in the circumferential direction, so that pressure can be further transmitted from multiple locations in the circumferential direction to the inner and outer surfaces of the distance ring 10 via the pressure balance flow path holes 10b.

[0049] In addition, since the pressure balance passage hole 10b is also connected to the drain passage hole 17a and the air vent passage hole 17b, seawater and air can also be discharged to the outside through the pressure balance passage hole 10b when the device is stopped. Since the distance ring 10 is made of resin, it is less expensive than a metal one, and the pressure balance flow passage holes 10b and the like can be easily processed.

[0050] The present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the spirit of the present invention. [Explanation of symbols]

[0051] 1...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, 7A...first cylinder device, 7B...second cylinder device, 8...cylinder, 8a...concentrated seawater inlet, 9...piston, 9a...piston end face, 10...distance ring, 10a...pressure balance groove, 10b...pressure balance flow path hole, 10c...pressure balance recess, 11...flow path direction control mechanism, 17a...drain vent flow path hole, 17b...air vent flow path hole, 19...concentrated seawater drainage path, P1...feed water pump, P2...high pressure pump, C...control unit

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, The piston has a piston end surface facing an end of the cylinder, The cylinder includes a distance ring that is provided at an end of the cylinder and that abuts against the piston when the piston reaches the end of the cylinder. a pressure balance groove formed on a surface of the distance ring facing the piston end surface; an inner circumferential surface of the pressure balance groove and a pressure balance flow passage hole formed therein, the pressure balance flow passage hole connecting the inner circumferential surface of the pressure balance groove and the pressure balance flow passage hole.

2. 2. The energy recovery device according to claim 1, An energy recovery device, characterized in that the pressure balance groove is formed in a ring shape centered on the axis of the distance ring.

3. 3. The energy recovery device according to claim 1, The pressure balance flow passage hole is also connected to an outer peripheral surface of the distance ring, 2. An energy recovery device according to claim 1, wherein the distance ring has a pressure balance recess formed on an outer circumferential surface thereof and connected to the pressure balance flow passage hole.

4. 4. The energy recovery device according to claim 3, The energy recovery device according to claim 1, wherein the pressure balance recess is formed in a ring shape extending in a circumferential direction.

5. 3. The energy recovery device according to claim 1, an energy recovery device characterized in that the pressure balance flow passage holes penetrate from the inner surface to the outer surface of the distance ring and are formed in a radial pattern centered on the axis of the distance ring with spaces between them in the circumferential direction.

6. 3. The energy recovery device according to claim 1, The cylinder has a drain passage hole through which seawater inside the cylinder can be discharged to the outside when the apparatus is stopped. and an air vent hole capable of discharging internal air to the outside when the device is stopped; 2. An energy recovery device according to claim 1, wherein the pressure balance channel hole is also connected to the drain vent channel hole and the air vent channel hole.

7. 3. The energy recovery device according to claim 1, An energy recovery device, wherein the distance ring is made of resin.

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