JP7626580B2 - Energy Recovery Device - Google Patents

Description

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.

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 the seawater in the direction opposite to 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, the seawater from which the fresh water has been separated and the 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 into practical use.

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 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 the 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.

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 the 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.

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 a booster pump, reducing the energy consumption of the high-pressure pump.

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 paths using two pressurizing pumps, making the system complicated and increasing the costs of the system.
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 differs from the cross-sectional area of the other end side of the piston 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 a desired pressure and flow rate, which requires only one pressurizing pump and simplifies the equipment.

JP 2013-86043 A JP 2020-110736 A

The above-mentioned conventional techniques have the following problems remaining.
That is, in the above-mentioned conventional technology, 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.

The present invention was made in consideration of the above-mentioned conventional problems, and aims to provide an energy recovery device that can prevent seawater in front of and behind the piston in the cylinder from mixing.

The present invention employs the following configuration to solve the above problems. That is, the energy recovery device according to the 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 drainage channel, a flow path direction control 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 the connection of the plurality of cylinder devices to the concentrated water pipe and the drainage channel. The device is equipped with a control unit having a control function for performing a pumping process in which the concentrated seawater is supplied to the cylinder device at high pressure to push out the seawater inside at high pressure, and a filling process in which the seawater from the water supply pump is supplied to the cylinder device after the pumping process to fill the cylinder device with the seawater while discharging the concentrated seawater inside. The cylinder device is equipped with a cylinder having one end connected to the concentrated water pipe and the drainage channel, the other end of which is connected to the concentrated seawater pipe and the drainage channel, and one end of which is connected to the water supply pump and 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 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 apart from the tip portion in the axial direction and separated from the tip portion by a space between the tip portion and the cylinder.

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 circumferential surface of the piston rod, spaced axially from the tip portion and with a space between the tip portion and the piston. This prevents seawater that leaks beyond the tip or rear end portion from collecting in the space inside the piston, preventing the seawater in front of the piston and the seawater behind the piston in the cylinder from mixing before and after the piston beyond the piston.

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.

The energy recovery device according to a third invention is characterized in that, in the first or second invention, the front end portion and the rear end portion each have 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.

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.

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.

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, thereby making it possible to efficiently obtain fresh water.

1 is a schematic diagram showing a first embodiment of an energy recovery device according to the present invention; 3A is a schematic diagram showing a state in which the piston has moved to an end on one end side of the cylinder, and FIG. 3B is a schematic diagram showing a state in which the piston has moved to an end on the other end side of the cylinder in the first embodiment. FIG. FIG. 5 is a schematic diagram showing a main part of a second embodiment of an energy recovery device according to the present invention.

The first embodiment of the energy recovery device of the present invention will be described below with reference to Figures 1 and 2.

As shown in FIG. 1, the energy recovery device 1 in this embodiment is an energy recovery device that is 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.

This energy recovery device 1 includes a feedwater pump P1 that supplies seawater, a high-pressure pump P2 that pressurizes seawater and supplies high-pressure seawater to a membrane separation device 5, and a number 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 a flow path switching mechanism 6A, 6B that connects and cuts communication with the concentrated seawater drainage channel 19, and a flow path switching mechanism 6B that connects and cuts communication with the concentrated seawater drainage channel 19 ... the other end connected to the concentrated water pipe 4 and the drainage channel 19, and a flow path switching mechanism 6B that connects and cuts communication with the concentrated seawater drainage channel 19 and the other end connected to one end of the multiple cylinder devices 7A, 7B and alternately supplies seawater to the multiple cylinder devices 7A, 7B and alternately supplies seawater to the multiple cylinder devices 7A, 7B. It is equipped with a flow path direction control 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 with a control function that performs a pressure transfer process in which the concentrated seawater is supplied to the cylinder devices 7A, 7B 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 by supplying high-pressure concentrated seawater to the cylinder devices 7A, 7B, and a filling process in which seawater is supplied from the water supply 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.

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 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 9 a and the rear end 9 b. The front end 9 a and the rear end 9 b are provided to have the same central axis as the piston rod 12.

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 locations on the upper and lower surfaces of the piston rod 12 facing the space S.
The other end of the rod internal flow passage 12 b opens at the other end of the piston rod 12 .
In addition, a drain receiver 12c is provided below the other end of the piston rod 12 to receive seawater discharged from the rod internal flow passage 12b.

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 of a combination of 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 has moved to the end on 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 has moved 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 an on-off valve 8e is connected to each of them.

A concentrated seawater inlet 8a, which is connected to the concentrated water pipe 4 and the drainage channel 19 and through which concentrated seawater is introduced and discharged, is provided on the circumferential surface at the other end of the cylinder 8 or in the vicinity of the other end.
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 the concentrated seawater from leaking to the outside.

The flow direction regulation mechanism 11 is configured to supply the seawater pushed out from each cylinder device 7A, 7B to the suction side of the high-pressure pump P2. In other words, the flow direction regulation mechanism 11 is configured to send the seawater pushed out from each cylinder device 7A, 7B to the connecting pipe 11e connected to the suction side of the high-pressure pump P2.

The cylinder devices 7A and 7B include a first cylinder device 7A, one end of which is 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 drain pipe 19 for concentrated seawater, and a second cylinder device 7B, one end of which is 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.

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

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.

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 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.

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, the drain pipe 19, and the concentrated water pipe 4, a drain side piston 20a that reciprocates 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 reciprocates together with the drain side piston 20a within the switching cylinder 20, and a switching piston rod 22 that has the drain side piston 20a at one end and the supply side piston 20b in the middle, and the other end protruding from the other end of the switching cylinder 20 to the outside and connected to the drive device 14.

The switching cylinder 20 has an outlet port 13a connected to the concentrated seawater discharge 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 7A or the second cylinder device 7B and provided between the outlet port 13a and the inlet port 13b.

The control unit C is equipped with position detectors (not shown) that are provided at multiple locations, including, for example, near the other end of the cylinder 8 of each cylinder device 7A, 7B, at positions where the position of the piston 9, in particular, when the piston 9 has reached the vicinity of the other end of the cylinder 8, can be detected, 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 at a location on the cylinder 8 other than the above.

In addition, in this embodiment, even if a position detector is not provided 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 adopted 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.

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 drive 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 .

The other ends of the first cylinder device 7A and the second cylinder device 7B are connected to the water supply pump P1 via a flow 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.

The inlet port 13b of the switching cylinder device 13 is connected to the concentrated water pipe 4. One end of the switching cylinder device 13 is provided with an outlet port 13a connected to a drain pipe 19. The drain side piston 20a and the supply side piston 20b arranged in the switching cylinder 20 are connected to a switching piston rod 22. 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.

The flow direction control 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 connection pipe 11d. In the branch pipes 11c, a pair of check valves 11 are provided on both sides of the connection part of the cylinder connection pipe 11d. The other ends of the pair of branch pipes 11c are connected to a connecting pipe 11e.

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 into the drain pipe 19 via the concentrated seawater inlet 8a and the inlet/outlet port 13c.

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 outflow/inflow 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 outflow/inflow port 13c and the outflow port 13a is cut off, and the pressure transfer process of the second cylinder device 7B is started.
In this manner, the flow path is 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.

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 : Flow rate of concentrated seawater sent from the piston inside the cylinder to the other end side. _Q2 : Flow rate of seawater sent from one end side of the piston inside the cylinder. _A1 : Cross-sectional area of the cylinder from the piston on the other end side (the area obtained by subtracting the cross-sectional area of the piston rod from the cross-sectional area inside the cylinder, i.e., the ring-shaped area around the piston rod)
_A2 : Cross-sectional area of the cylinder on one end 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 = Q ₂ /Q ₁ :A ₂ /A ₁

For example, a case where the ratio of a cross-sectional area _A1 on the other end side of the piston 9 in the cylinder 8 to a 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 of the pumping process, if the inlet flow rate of concentrated seawater at the other end side of the piston 9 in the cylinder 8 is 5,000 ^m3 /d and the pressure is 4.0 MPa, the outlet flow rate of seawater at one end side of the piston 9 in the cylinder 8 is 10,000 ^m3 /d and the pressure is 2.0 MPa.

At this time, seawater with a flow rate of 10,000 ^m3 /d and a pressure of 2.0 MPa is sent from the first cylinder device 7A to the high-pressure pump P2, so if it is desired to send seawater with a flow rate of 10,000 ^m3 /d and a pressure of 4.0 MPa to the membrane separation device 5, it is sufficient to increase the pressure in the high-pressure pump P2 by 2.0 MPa.
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 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 compensated for by the booster pump, is taken into account in the total head of the high-pressure pump, making the booster pump unnecessary.

In the membrane separation device 5, concentrated seawater is sent to the first cylinder device 7A at a flow rate of 5,000 m ³ /d and a pressure of 4.0 MPa, and fresh water (permeate) is sent to the fresh water pipe 3 at a flow rate of 5,000 m ³ /d.
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 rate of concentrated seawater from the other end of the cylinder 8 is 5,000 m ³ /d.

In this way, the cylinder devices 7A and 7B are equipped with a piston 9 that reciprocates within the cylinder 8, and a piston rod 12 that has one end connected to the piston 9 and the other end protruding 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 the seawater pumped out from the cylinder devices 7A and 7B.

In addition, 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 will also flow into the space S.
Furthermore, seawater that has leaked into the space S is discharged from the piston side opening 12a through the rod internal flow passage 12b and from the other end of the piston rod 12 to an external drain receiver 12c.

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 rear end portion 9b accumulates in the space S within the piston 9, making it possible to prevent 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.

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

In addition, since the tip end 9a and the rear end 9b are each provided with a seal portion 9c extending annularly around the outer periphery, the double seal portion 9c can separately suppress leakage of seawater from both the front of the tip end 9a and the rear of 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.

Furthermore, the cylinder 8 is provided with a one-end drain 8c capable of discharging seawater to the outside in the portion facing the space S when the piston 9 has moved to the one-end end. Therefore, when the piston 9 is in a stopped state in which it has moved to the one-end end, 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 that can discharge 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 that has accumulated in the space S can be discharged to the outside from the other-end drain 8d.

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 will be denoted by the same reference numerals, and the description thereof will be omitted.

The difference between the second embodiment and the first embodiment is that the first embodiment has two cylinder devices 7A and 7B, whereas the energy recovery device 21 of the second embodiment has three cylinder devices 7A, 7B, and 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.

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.

In the second embodiment, for example, when the first cylinder device 7A of the three cylinder devices 7A, 7B, and 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, and 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, and 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.

In this way, even in the energy recovery device 21 of the second embodiment, the three cylinder devices 7A, 7B, and 7C are equipped with a piston 9 that reciprocates within the cylinder 8, and a piston rod 12 that has one end connected to the piston 9 and the other end protruding 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, and 7C.

In addition, 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 circumferential surface of the piston rod 12 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, and it is possible to prevent 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.

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.

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...seal, 11...flow path direction control mechanism, 12...piston rod, 12a...piston side opening, 12b...rod internal flow path, 19...concentrated seawater drainage path, P1...water supply pump, P2...high pressure pump, C...control unit, S...space

Claims (4)

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 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. 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. 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 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. 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 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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