Patent Application
20110062062
This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2009-212189, filed Sep. 14, 2009; the entire contents of which are incorporated herein by reference.
Embodiments described herein relate generally to a power recovery apparatus.
A desalination apparatus supplies a reverse osmosis membrane (hereinafter referred to as a RO membrane) with seawater having a higher pressure than a reverse osmosis pressure. The desalination apparatus allows seawater to permeate the reverse osmosis membrane and thereby extracts fresh water from the seawater by filtering out salt. Further, the desalination apparatus ejects remaining seawater as highly-concentrated salt water (brine). At this time, the highly-concentrated salt water is ejected maintained at a high pressure, and therefore has high pressure energy. In recent years, aiming for energy saving, power recovery apparatuses are mounted on desalination apparatuses (see, Jpn. Pat. Appln. KOKAI Publication No. 2004-81913 and No. 2001-46842, for example). Power recovery apparatuses collect highly-concentrated salt water at a high pressure, and utilize pressure energy of the highly-concentrated salt water to press seawater.
Conventional power recovery apparatuses require a boost pump to further boost a pressure of seawater which has been pressed by using pressure energy. This is because the pressure of the seawater which has been pressed by using the pressure energy need be further boosted to a pressure of seawater to be supplied to the RO membrane. However, the boost pump is a factor which causes various problems.
Firstly, since the boost pump boosts up the pressure of seawater to a very high pressure, the boost pump need be constituted by a thick member so that the pump may not break down due to its own internal pressure. A problem therefore occurs in that pump efficiency extremely decreases and power consumption of the boost pump increases accordingly.
Further, the boost pump has a high internal pressure, which often causes leakages of inner fluids. Therefore, the working ratio of the apparatus decreases and causes a problem that clear water cannot stably supplied.
Further, a large number of pumps, such as water pumps, high pressure pumps, and boost pumps are installed in desalination plants. Since pumps require periodical maintenance, a large number of pumps installed in a plant cause increase in costs and labor for maintenance services.
Further, the boost pumps each are constituted by a thick member as described above, and are therefore relatively expensive components in plants. The boost pumps are therefore factors which increase construction costs of plants.
A power recovery apparatus described in one of the foregoing publications includes two RO membranes. Proposed herein is a technique to exclude installation of a boost pump, e.g., highly-concentrated salt water ejected from a first RO membranes is filtered by a second RO membranes. However, the RO membranes are expensive components, and the configuration described above is therefore a factor which may increase plant construction costs.
In general, according to one embodiment, a power recovery apparatus is used in a desalination apparatus. The desalination apparatus boosts a first pressure of seawater to a second pressure by a high-pressure pump, and extracts fresh water from the seawater at the second pressure and ejects concentrated water at a third pressure by a reverse osmosis membrane. The concentrated water at the third pressure is supplied to the power recovery apparatus. The power recovery apparatus collects energy of the concentrated water at the third pressure. The power recovery apparatus includes a pressure conversion section and a seawater supply section. The pressure conversion section includes a movable part dividing inside of the conversion section into first and second spaces, moves the movable part by causing the first space to receive the concentrated water at the third pressure from the reverse osmosis membrane, and pushes out seawater filled in the second space, in accordance with movement of the movable part, to output the seawater at the second pressure. The pressure conversion section further includes a drive mechanism which drives the movable part so as to output the seawater at the second pressure from the second space. The seawater supply section merges the seawater from the pressure conversion section with the seawater from the high-pressure pump.
The high pressure pump 40 boosts a pressure of the supplied seawater and outputs the boosted seawater to a high-pressure RO membrane 50. At this time, a pressure P4 after the boost is representatively 6.0 MPa although the pressure P4 after the boost varies depending on the type of the high-pressure RO membrane 50.
The high-pressure RO membrane 50 filters the seawater from the high pressure pump 40. When the high-pressure RO membrane 50 has a recovery rate of 40%, 40% of seawater flowing into the high-pressure RO membrane 50 is extracted as fresh water and 60% of seawater is ejected as highly-concentrated salt water. The fresh water from the high-pressure RO membrane 50 is supplied to a low-pressure pump 80, and the highly-concentrated salt water is supplied to the power recovery apparatus 60. At this time, the pressure of the fresh water decreases to about 0.2 MPa (=P3). However, a pressure P6 of the highly-concentrated salt water is about 5.8 MPa.
The fresh water from the high-pressure RO membrane 50 is pressed again by the low-pressure pump 80, and permeates the low-pressure RO membrane 90, thereby filtering out contained boron. Further, the fresh water which has permeated the low-pressure RO membrane 90 is subjected to a chemical treatment in a clear water reservoir 100, and is then supplied as clear water from a supply pump 110 to homes, etc.
The power recovery apparatus 60 boosts and outputs seawater from the safety filter 30 by using pressure energy which the highly-concentrated salt water has internally. Seawater from the power recovery apparatus 60 is merged with seawater from the high pressure pump 40 and is supplied together to the high-pressure RO membrane 50.
An end of a valve 70 is open to air. An ejection flow rate of highly-concentrated salt water from which pressure energy has been collected by the power recovery apparatus 60 is controlled by the valve 70.
At first, the configuration of the power recovery apparatus 60 will be described with reference to
The pressure meter 61 measures a pressure of highly-concentrated salt water supplied from the high-pressure RO membrane 50, and notifies a measurement result thereof to the motor control section 67. The 4-port switch valve 62 switches directions of flow of highly-concentrated salt water into a pressure conversion section 63 and ejection from the pressure conversion section 63. The 4-port switch valve 62 switches the directions of flow-in and ejection of highly-concentrated salt water in accordance with a switch instruction from the switch control section 66. A method for switching the 4-port switch valve may be of a pneumatic type, a hydraulic water type, a hydraulic oil type, and a solenoid coil type. Available as a water pressure source is highly-concentrated salt water, seawater from the water pump 20, or high-pressure salt water from the high pressure pump 40.
The pressure conversion section 63 includes converters 631-1 and 631-2.
The cylinder 6311-1 includes three holes and forms a sealed space.
The piston 6312-1 is positioned inside the cylinder 6311-1, and divides the sealed space into first and second spaces, with a seal material provided between the piston 6312-1 and the cylinder 6311-1. The first space is supplied with highly-concentrated salt water, and the second space is supplied with seawater.
The movable member 6313-1 is constituted by a large number of magnets arrayed in a pipe. For example, the movable member 6313-1 is constituted by a coil. The movable member 6313-1 is driven in a lengthwise direction thereof when the stationary member 6314-1 is supplied with an electric current. The movable member 6313-1 and the stationary member 6314-1 make neither contact nor friction between each other.
Further, the movable member 6313-1 has an end bonded to the piston 6312-1 from the side of the second space, and another end protruding outside through a hole in the cylinder 6311-1. A seal material is attached to an edge of the hole. Since the movable member 6313-1 is bonded to the piston 6312-1 from the side of the second space, an area A1 where the piston 6312-1 faces the first space differs from an area A2 where the piston 6312-1 faces the second space. Here, a relationship between the areas A1 and A2 is preset based on the pressure P6 of highly-concentrated salt water from the high-pressure RO membrane 50, the pressure P4 of seawater from the high pressure pump 40, friction between the cylinder 6311-1 and the piston 6312-1, and friction between the cylinder 6311-1 and the movable member 6313-1.
An electric current supplied to the stationary member 6314-1 is controlled by the motor control section 67.
The seawater supply section 64 includes check valves 641-1 to 641-4. The check valves 641-1 to 641-4 each independently open/close in accordance with environmental pressure differences. In this manner, seawater is supplied from the power recovery apparatus 60 to outside or to the pressure conversion section 63.
The detection sections 65-1 and 65-2 are to detect positions of the movable member 6313-1 protruding from the converter 631-1. The detection section 65-1 is located at a position where the movable member 6313-1 can be detected when the piston 6312-1 comes close to the left end of the cylinder 6311-1. The detection section 65-2 is located at a position where the movable member 6313-1 is not detected when the piston 6312-1 comes close to the right end of the cylinder 6311-1. The detection sections 65-1 and 65-2 output detection signals to the switch control section 66 when the movable member 6313-1 is detected and when the movable member 6313-1 is not detected, respectively. In this manner, the positions of the piston 6312-1 in the cylinder 6311-1 can be grasped. Detection sections 65-3 and 65-4 have the same configurations as the detection sections 65-1 and 65-2, and detect positions of a movable member 6313-2 protruding from the converter 631-2. The detection sections 65-3 and 65-4 output detection signals to the switch control section 66 when the movable member 6313-2 is detected and is not detected, respectively. In this manner, the positions of the piston 6312-2 in the cylinder 6311-2 can be grasped. A detection method for the detection sections 65-1 to 65-4 may be of a mechanical, electric, or optical type. Although the present embodiment is configured to output the detection signals to the switch control section 66, movement of the movable members may alternatively be mechanically transmitted to the 4-port switch valve 62.
The switch control section 66 outputs a switch instruction to the 4-port switch valve 62 in accordance with detection signals from the detection sections 65-1 to 65-4. That is, when the switch control section 66 receives detection signals from the detection sections 65-1 and 65-4, the switch control section 66 determines that the piston 6312-1 is positioned close to the left end of the cylinder 6311-1 and that the piston 6312-2 is positioned close to the right end of the cylinder 6311-2. Further, the switch control section 66 outputs a switch instruction to make the converter 631-1 eject highly-concentrated salt water and to make the converter 631-2 be supplied with highly-concentrated salt water. Otherwise, when the switch control section 66 receives detection signals from the detection sections 65-2 and 65-3, the switch control section 66 determines that the piston 6312-1 is positioned close to the right end of the cylinder 6311-1 and that the piston 6312-2 is positioned close to the left end of the cylinder 6311-2. Further, the switch control section 66 outputs a switch instruction to the 4-port switch valve 62 to make the converter 631-1 be supplied with highly-concentrated salt water and to make the converter 631-2 eject highly-concentrated salt water.
The motor control section 67 controls an electric current supplied to the stationary members 6314-1 and 6314-2, based on a measurement result from the pressure meter 61. The stationary members 6314-1 and 6314-2 apply a leftward or rightward force to the movable members 6313-1 and 6313-2 based on the electric current supplied by the motor control section 67. The pistons 6312-1 and 6312-2 are applied the leftward or rightward force by the movable members 6313-1 and 6313-2. For example, when a measurement result from the pressure meter 61 decreases to be smaller than a value which has been expected beforehand, the motor control section 67 controls the electric current supplied to the stationary member 6314-1 in a manner that the movable member 6313-1 is driven to move in the same direction as the moving direction in which the piston 6312-1 is moving, in the state of
Next, operation of the power recovery apparatus 60 configured as described above will be described.
The power recovery apparatus 60 in
Seawater from the safety filter 30 is supplied to a high-pressure pump 40 at 0.2 MPa (=P3), and is supplied to the second space of the converter 631-2 through the check valve 641-4.
Seawater boosted to 6.0 MPa (=P4) by the high pressure pump 40 is merged with seawater from the power recovery apparatus 60, and is supplied together to the high-pressure RO membrane 50. At this time, the seawater from the power recovery apparatus 60 has been ejected from the second space of the converter 631-1 and passed through the check valve 641-2. The high-pressure RO membrane 50 outputs fresh water and highly-concentrated salt water.
The highly-concentrated salt water ejected from the high-pressure RO membrane 50 passes through the pressure meter 61 and 4-port switch valve 62 and flows into the first space of the converter 631-1. At this time, the second space of the converter 631-1 is filled with seawater. The highly-concentrated salt water moves the piston 6312-1 in the cylinder 6311-1 in a direction toward the second space, and ejects seawater in the second space while pressing the seawater.
A force N1 acting in a leftward direction is now assumed to be applied to the piston 6312-1 from the movable member 6313-1. An area where the piston 6312-1 faces the first space is A1, and an area where the piston 6312-1 faces the second space is A2. Hence, a pressure P8 of the seawater which is ejected from the second space of the cylinder 6311-1 is expressed as P8=(P7*A1+N1)/A2, using a pressure P7 of highly-concentrated salt water from the 4-port switch valve 62. Accordingly, the pressure P8 is substantially equal to or slightly higher than the pressure P4. The force N1 can be either a positive or negative value, depending on differences between directions of motor thrusts.
States of the check valves 641-1 to 641-4 in
Since pressure P8>pressure P3, the check valve 641-1 is closed. Since pressure P8>pressure P14, the check valve 641-2 is opened. A pressure difference between the pressure P8 and pressure P14 can be considered to be a pressure loss when seawater passes through the check valve 641-2.
Further, since pressure P14>pressure P13, the check valve 641-3 is closed. Further, as an end of the valve 70 is open to air, a gauge pressure of the second space of the cylinder 6311-2 is therefore substantially zero. That is, P13 is a small pressure. Therefore, P3>P13 is given, and the check valve 641-4 is opened.
Seawater from the safety filter 30 passes through the check valve 641-4 and flows into the second space of the converter 631-2. At this time, the first space of the converter 631-2 is filled with highly-concentrated salt water. Since an end of the valve 70 is open to air, a gauge pressure of the first space of the converter 631-2 is substantially zero. Seawater which has passed through the check valve 641-4 has a pressure of 0.2 MPa, and moves the piston 6312-2 in the cylinder 6311-2 toward the first space. The piston 6312-2 moves toward the first space, thereby ejecting highly-concentrated salt water in the first space out through the 4-port switch valve 62 and the valve 70.
When the operation as described above is continued, the piston 6312-1 moves close to the left end inside the cylinder 6311-1 and the piston 6312-2 moves close to the right end inside the cylinder 6311-2. Then, the detection sections 65-1 detects the movable member 6313-1 to come into contact, and the detection sections 65-4 detects the movable member 6313-2 to go out of contact. Accordingly, detection signals are output from the detection sections 65-1 and 65-4 to the switch control section 66. The switch control section 66 receives the detection signals from the detection sections 65-1 and 65-4, and then issues a switch instruction to the 4-port switch valve 62 so as to switch directions of flow-in and ejection of highly-concentrated salt water. When flow-in and ejection of highly-concentrated salt water are switched over, the power recovery apparatus 60 enters into the state represented in
In the power recovery apparatus 60 in
The highly-concentrated salt water ejected from the high-pressure RO membrane 50 passes through the pressure meter 61 and 4-port switch valve 62 and flows into the first space of the converter 631-2. At this time, the second space of the converter 631-2 is filled with seawater. Highly-concentrated salt water moves the piston 6312-2 in the cylinder 6311-2 toward the second space, and presses and ejects seawater in the second space.
A force N2 acting in a leftward direction is now supposed to be applied to the piston 6312-2 from the movable member 6313-2. An area where the piston 6312-2 faces the first space is A1, and an area where the piston 6312-2 faces the second space is A2. Accordingly, a pressure P13 of the seawater which is ejected from the second space of the cylinder 6311-2 is expressed as P13=(P7*A1+N2)/A2, using a pressure P7 of highly-concentrated salt water from the 4-port switch valve 62. Accordingly, the pressure P13 is substantially equal to or slightly higher than the pressure P4. The force N2 can be either a positive or negative value, depending on differences between directions of motor thrusts.
States of the check valves 641-1 to 641-4 in
Since pressure P13>pressure P3, the check valve 641-1 is closed. Since pressure P13>pressure P14, the check valve 641-2 is opened. A pressure difference between the pressure P13 and pressure P14 can be considered to be a pressure loss when seawater passes through the check valve 641-3.
Further, since pressure P14>pressure P8, the check valve 641-2 is closed. Further, as an end of the valve 70 is open to air, a gauge pressure of the second space of the cylinder 6311-1 is therefore substantially zero. That is, P8 is a small pressure. Therefore, P3>P8 is given, and the check valve 641-1 is opened.
Seawater from the safety filter 30 passes through the check valve 641-1 and flows into the second space of the converter 631-1. At this time, the first space of the converter 631-1 is filled with highly-concentrated salt water. Since an end of the valve 70 is open to air, a gauge pressure of the first space of the converter 631-1 is substantially zero. Seawater which has passed through the check valve 641-1 has a pressure of 0.2 MPa, and moves the piston 6312-1 in the cylinder 6311-1 toward the first space. The piston 6312-1 moves toward the first space, and thereby ejects highly-concentrated salt water in the first space through the 4-port switch valve 62 and the valve 70.
When the operation as described above is continued, the piston 6312-1 moves close to the right end inside the cylinder 6311-1. Then, the detection section 65-3 detects that the movable member 6313-2 comes into contact, and the detection section 65-2 detects that the movable member 6313-1 goes out of contact. Therefore, detection signals are output from the detection sections 65-2 and 65-3 to the switch control section 66. The switch control section 66 receives the detection signals from the detection sections 65-2 and 65-3, and then issues a switch instruction to the 4-port switch valve 62 so as to switch directions of flow-in and ejection of highly-concentrated salt water. When flow-in and ejection of highly-concentrated salt water are switched over, the power recovery apparatus 60 enters again into the state represented in
In the present embodiment, moving speeds of the piston 6312-1 and piston 6312-2 are made equal to each other by adjusting an opening rate of the valve 70. In this manner, a flow rate of the water pump 20 does not chronographically vary, and stable operation is achieved.
Next, power consumption or, namely, desalination costs when fresh water of 1 m3 is produced will be calculated and compared through numerical simulations between desalination apparatuses in three cases described below. The desalination apparatuses in the three cases are a desalination apparatus including no power recovery apparatus, a desalination apparatus including a conventional power recovery apparatus 120, and a desalination apparatus including a power recovery apparatus 60 according to the present embodiment.
Further,
Descriptions below will be made with reference to
The valve 70 requires fluid resistance to some extent from reasons described above. Supposing that a pressure loss occurring in the valve 70 is proportional to a square of a flow rate (m3/s), resistance coefficients as represented in
Results of numerical simulations, i.e., pressures and flow rates at respective sections in
A power W which a pump applies to a fluid is obtained by multiplying a flow rate Q by a pressure P. That is, the power of the water pump 20 in
Further, a required power W power recovery is obtained by an expression below.
Wpower recovery=ΣΔPiQi/ηi (1)
In the above expression, ΔP is a pump head (Pa), Q is a flow rate (m3/s), and η is a pump efficiency. From the expression (1), the required power in
Further, a power recovery rate ξ is calculated by an expression below.
ξ=100(W−Wpower recovery)/W (2)
In the expression above, W is a required power (W) when no power recovery apparatus is included. From the expression (2), a power recovery rate in
Further, a simple desalination cost γ is calculated by an expression below.
γ=Wpower recovery/Q (3)
In the expression above, Q is a flow rate of fresh water per hour (m3/h). From the expression (3), a simple desalination cost in
In this manner, from comparison between
Further, the desalination apparatus including the power recovery apparatus 60 according to the present embodiment requires a lower desalination cost than the desalination apparatus including the conventional power recovery apparatus 120. In this manner, the power recovery apparatus 60 according to the present embodiment is found to be capable of effectively collecting pressure energy from highly-concentrated salt water without using the boost pump 121. Further, the lower desalination cost achieved by the desalination apparatus including the power recovery apparatus 60 owes to low pump efficiency of the boost pump 121.
As has been described above, in the first embodiment, the movable members 6313-1 and 6313-2 are provided so as to penetrate the second spaces of the cylinders 6311-1 and 6311-2 to outside. The penetration to outside causes ends of the movable members 6313-1 and 6313-2 to receive a pressure equal to an atmospheric pressure. Therefore, each of areas where the pistons 6312-1 and 6312-2 respectively make contact with the second spaces is smaller than each of areas where the pistons 6312-1 and 6312-2 respectively make contact with the first spaces by each of cross-sectional areas of the movable members 6313-1 and 6313-2 vertical to their own lengthwise directions. That is, area A1>area A2. In this manner, the power recovery apparatus 60 is capable of outputting seawater from the second spaces at a pressure equal to a pressure of seawater output from the high-pressure pump 40, by using a pressure of highly-concentrated salt water supplied to the first spaces.
Also in the first embodiment, the positions of the movable members 6313-1 and 6313-2 protruding from the cylinders 6311-1 and 6311-2 are detected. Based on detection results thereof, the 4-port switch valve 62 is switched over. In this manner, the positions of the pistons 6312-1 and 6312-2 inside the cylinders 6311-1 and 6311-2 can be correctly and easily recognized.
Also in the first embodiment, the shaft motors are constituted by the movable members 6313-1 and 6313-2 and the stationary members 6314-1 and 6314-2. Further, a leftward or rightward force is applied to the pistons 6312-1 and 6312-2 by controlling a supplied electric current by using the motor control section 67. When the high-pressure RO membrane 50 is used for a long time, the RO membrane clogs and consequently decreases the pressure P6 of highly-concentrated salt water from the high-pressure RO membrane 50. The motor control section 67 maintains constantly a pressure of seawater ejected from the second spaces by controlling sizes and directions of forces generated by the shaft motors, even when a pressure of highly-concentrated salt water decreases. In this manner, the motor control section 67 is capable of constantly equalizing the pressure P14 of seawater output from the power recovery apparatus 60 to the pressure P4 of seawater output from the high-pressure pump 40.
Therefore, the power recovery apparatus 60 according to the first embodiment can collect pressure energy existing in highly-concentrated salt water, without a boost pump.
Thus, the power recovery apparatus 60 according to the first embodiment requires no boost pump, and can therefore decrease power consumption for desalination. Further, a total number of pumps installed in a plant decreases, and accordingly, maintenance costs and plant construction costs can be reduced.
In addition, the power recovery apparatus 60 can achieve effects as described above by providing the movable members in the second spaces of the converters 631-1 and 631-2. Therefore, plant construction costs can be more reduced.
In the first embodiment described above, the power recovery apparatus 60 may have a structure as represented in
Although the first embodiment has been described with reference to an example in which the power recovery apparatus 60 includes the 4-port switch valve 62, a 5-port switch valve 69 may be used in place of the 4-port switch valve 62, as represented in
Also, the first embodiment has been described with reference to an example in which two converters 631-1 and 631-2 are mounted on the power recovery apparatus 60. However, 2n converters (where n is an natural number) may be mounted.
A pressure conversion section 131 in the power recovery apparatus 130 includes converters 1311-1 and 1311-2. The converters 1311-1 and 1311-2 have the same structures as each other, and therefore, only the converter 1311-1 will be described herein.
The converter 1311-1 includes cylinders 13111-1 and 13112-1, pistons 13113-1 and 13114-1, and a shaft motor which consists of a movable member 13115-1 and a stationary member 13116-1.
The cylinder 13111-1 has an open surface, and another surface where a hole is provided. Further, an inside area of a cross-section vertical to a lengthwise direction of the cylinder 13111-1 is A1. Further, the cylinder 13112-1 has an open surface, and another surface where a hole is provided. Further, an inside area of a cross-section vertical to a lengthwise direction of the cylinder 13112-1 is A2. Open surfaces of the cylinders 13111-1 and 13112-1 are opposed to each other.
The piston 13113-1 is positioned inside the cylinder 13111-1, and forms a first space, with a seal material provided between the piston 13113-1 and the cylinder 13111-1. The piston 13113-1 has an area A1. Further, the piston 13114-1 is positioned inside the cylinder 13112-1, and forms a second space, with a seal material provided between the piston 13114-1 and the cylinder 13112-1. The piston 13114-1 has an area A2. The first space is supplied with highly-concentrated salt water, and the second space is supplied with seawater. Here, a relationship between the areas A1 and A2 is preset on the basis of a pressure of highly-concentrated salt water from a high-pressure RO membrane 50, a pressure of seawater from a high pressure pump 40, friction between the cylinder 13111-1 and the piston 13113-1, and friction between the cylinder 13112-1 and the piston 13114-1.
The movable member 13115-1 is constituted by a large number of magnets arrayed in a pipe. The movable member 13115-1 is driven in a lengthwise direction thereof when the stationary member 13116-1 is supplied with an electric current. The electric current supplied to the stationary member 13116-1 is controlled by a motor control section 67. The movable member 13115-1 and the stationary member 13116-1 make neither contact nor friction between each other. Further, the movable member 13115-1 connects the pistons 13113-1 and 13114-1. A dog is formed at a predetermined position on the movable member 13115-1.
Detection sections 132-1 and 132-2 are to detect positions of the dog. The detection section 132-1 is located at a position where contact with the dog can be detected when the piston 13114-1 comes close to the left end of the cylinder 13112-1. The detection section 132-2 is located at a position where contact with the dog can be detected when the piston 13113-1 comes close to the right end of the cylinder 13111-1. The detection sections 132-1 and 132-2 output detection signals to a switch control section 133 when the dog is detected. In this manner, the positions of the pistons 13113-1 and 13114-1 in the converter 1311-1 can be recognized. Further, detection sections 132-3 and 132-4 have the same configuration as the detection sections 132-1 and 132-2, and are to detect positions of the dog on the movable member 13115-2. When the detection sections 132-3 and 132-4 detect the dog, the detection sections 132-3 and 132-4 output detection signals to the switch control section 133. In this manner, positions of the pistons 13113-2 and 13114-2 in the converter 1311-2 can be grasped.
The switch control section 133 outputs a switch instruction to a 4-port switch valve 62 in accordance with detection signals from the detection sections 132-1 to 132-4. That is, when the control section 133 receives detection signals from the detection sections 132-1 and 132-4, the switch control section 133 determines that the piston 13114-1 is positioned close to the left end of the cylinder 13112-1 and that the piston 13113-2 is positioned close to the right end of the cylinder 13111-2. Further, the switch control section 133 outputs a switch instruction to the 4-port switch valve 62 to make the converter 1311-1 eject highly-concentrated salt water and to make the converter 1311-2 be supplied with highly-concentrated salt water.
Otherwise, when the switch control section 133 receives detection signals from the detection sections 132-2 and 132-3, the switch control section 133 determines that the piston 13113-1 is positioned close to the right end of the cylinder 13111-1 and that the piston 13114-2 is positioned close to the left end of the cylinder 13112-2. Further, the switch control section 133 outputs a switch instruction to the 4-port switch valve 62 to make the converter 1311-1 be supplied with highly-concentrated salt water and to make the converter 1311-2 eject highly-concentrated salt water.
With the configuration as described above, the power recovery apparatus 130 according to the above second embodiment can achieve the same operation and effects as the power recovery apparatus 60 according to the first embodiment.
Also, the above second embodiment has been described with reference to an example in which two converters 1311-1 and 1311-2 are mounted on the power recovery apparatus 130. However, 2n converters (where n is an natural number) may be mounted.
A pressure conversion section 141 in the power recovery apparatus 140 includes converters 1411-1, 1411-2, and 1411-3, a crankshaft 1412, and a motor 1413. The converters 1411-1, 1411-2, and 1411-3 each are connected to the crankshaft 1412. Arms of the crankshaft 1412 are designed to be arranged at angular intervals of 120 degrees between each other, as illustrated in
The converters 1411-1, 1411-2, and 1411-3 have the same structures as each other, and therefore, only the converter 1411-1 will be described herein. The converter 1411-1 includes cylinders 14111-1 and 14112-1, pistons 14113-1 and 14114-1, and connection rods 14115-1 and 14116-1.
The cylinder 14111-1 has an open surface, and another surface where a hole is provided. Further, an inside area of a cross-section vertical to a lengthwise direction of the cylinder 14111-1 is A1. Further, the cylinder 14112-1 has an open surface and another surface where a hole is provided. Further, an inside area of a cross-section vertical to a lengthwise direction of the cylinder 14112-1 is A2. Open surfaces of the cylinders 14111-1 and 14112-1 are opposed to each other.
The piston 14113-1 is positioned inside the cylinder 14111-1 and forms a first space, with a seal material provided between the piston 14113-1 and the cylinder 14111-1. The piston 14113-1 has an area A1. Further, the piston 14114-1 is positioned inside the cylinder 14112-1 and forms a second space, with a seal material provided between the piston 14114-1 and the cylinder 14112-1. The piston 13114-1 has an area A2. The first space is supplied with highly-concentrated salt water, and the second space is supplied with seawater. Here, a relationship between the areas A1 and A2 is preset on the basis of a pressure of highly-concentrated salt water from a high-pressure RO membrane 50, a pressure of seawater from a high pressure pump 40, friction between the cylinder 14111-1 and the piston 14113-1, and friction between the cylinder 14112-1 and the piston 14114-1.
The connection rod 14115-1 connects the piston 14113-1 and a pin of the crankshaft 1412. The connection rod 14116-1 connects the piston 14114-1 and a pin of the crankshaft 1412.
In a state of
The angle detection section 142 is to detect a rotation angle of the crankshaft 1412. When the rotation angle reaches a predetermined angle, the angle detection section 142 then outputs a detection signal to a switch control section 143. For example, total six angles are registered in advance in the angle detection section 142 as the predetermined angle. The six angles correspond to angles at which the pistons 14113-1 to 14113-3 come close to the right ends of the cylinders 14111-1 to 14111-3, and angles at which the pistons 14114-1 to 14114-3 come close to the left ends of the cylinders 14112-1 to 14112-3. When the rotation angle reaches any of the angles, the angle detection section 142 outputs a detection signal to the switch control section 143. In this manner, the switch control section 143 can grasp positions of the pistons in the converters.
When the switch control section 143 receives the detection signal from the angle detection section 142, the switch control section 143 issues a switch instruction to a 3-port valve among switch valves 62-1 to 62-3, which is connected to one of the converters corresponding to the detection signal.
The motor control section 144 controls an electric current supplied to the motor 1413, based on a measurement result from a pressure meter 61. The motor 1413 applies torque to the crankshaft 1412 in a clockwise or anticlockwise direction based on the electric current supplied by the motor control section 144. For example, when a measurement result from the pressure meter 61 decreases to be smaller than a value which has been expected beforehand, the motor control section 144 controls the electric current supplied to the motor 1413 so as to apply a load to the crankshaft 1412 in an anticlockwise direction.
Next, operation of the power recovery apparatus 140 configured as described above will be described.
The power recovery apparatus 140 in
Seawater from a safety filter 30 is supplied to a high-pressure pump 40 at 0.2 MPa and is also supplied to the second spaces of the converters 1411-2 and 1411-3 through check valves 641-4 and 641-6.
Seawater which has been boosted to 6.0 MPa by the high-pressure pump 40 is merged with seawater from the power recovery apparatus 140, and is introduced into the high-pressure RO membrane 50. At this time, the seawater from the power recovery apparatus 140 has been ejected from the second space of the converter 1411-1 and passed through the check valve 641-2. The high-pressure RO membrane 50 outputs fresh water and highly-concentrated salt water.
The highly-concentrated salt water ejected from the high-pressure RO membrane 50 passes through the pressure meter 61 and 3-port switch valve 62-1, and flows into the first space of the converter 1411-1. At this time, the second space of the converter 1411-1 is filled with seawater. Highly-concentrated salt water moves the piston 14113-1 in the cylinder 14111-1 in a leftward direction, and the piston 14114-1 in the cylinder 14112-1 in a leftward direction. In this manner, seawater in the second space of the converter 1411-1 is pressed and ejected. At this time, the piston 14113-1 moves in the leftward direction, thereby applying torque to the crankshaft 1412 in a direction denoted in
As torque in the clockwise direction is applied by the motor 1413, the pistons 14113-1 and 14114-1 are applied with a force which will be hereinafter referred to as N1. The piston 14113-1 has an area A1, and the piston 14114-1 has an area A2. Thus, a pressure of seawater which is ejected from the second space of the converter 1411-1 is expressed as (P*A1+N1)/A2, using a pressure P of highly-concentrated salt water from the 3-port switch valve 62-1. Accordingly, the pressure of seawater ejected from the second space of the converter 1411-1 is equal to or slightly higher than a pressure of seawater supplied to the high-pressure RO membrane 50. The force N1 can be either a positive or negative value, depending on differences between directions of motor thrusts.
When the crankshaft 1412 rotates in the arrow direction in
When the operation as described above is continued, a detection signal is output from the angle detection section 142 to the switch control section 143 each time when the rotation angle of the crankshaft 1412 reaches the predetermined angle. The switch control section 143 receives the detection signal from the angle detection section 142, and then switches the 3-port switch valves 62-1 to 62-3 successively so as to switch directions of flow-in and ejection of highly-concentrated salt water.
With the configuration as described above, the power recovery apparatus 140 according to the above third embodiment can achieve the same operation and effects as the power recovery apparatus 60 according to the first embodiment.
Further, in the third embodiment, the pistons are connected to the crankshaft 1412. Therefore, displacements in lengthwise directions of the pistons transit like a sine curve. Further, the 3-port switch valves 62-1 to 62-3 switch directions of flow-in and ejection of highly-concentrated salt water corresponding to positions of the pistons in the cylinders. In this manner, pulsation which takes place when the 3-port switch valves 62-1 to 62-3 switch directions of flow-in and ejection is reduced.
The above third embodiment has been described with reference to an example in which three converters 14111-1 to 14111-3 are mounted on the power recovery apparatus 140. However, 3n converters (where n is an natural number) may be mounted.
The areas A1 and A2 may be equal to each other.
A pressure conversion section 151 in the power recovery apparatus 150 includes vane-type rotary actuators 1511-1 and 1511-2, a rotary shaft 1512, and a motor 1513. The rotary actuators 1511-1 and 1511-2 are connected by the rotary shaft 1512. Further, the rotary shaft 1512 is connected to the motor 1513 through an angle detector 152. An electric current supplied to the motor 1513 is controlled by a motor control section 154.
The housing 15111-1 forms a sealed space and has a cylindrical shape having a radius r1. The rotary shaft 1512 is located so as to penetrate the housing 15111-1 along a center axis thereof. A screen part 15113-1 is formed to extend from an inner wall surface of the housing 15111-1 to the rotary shaft 1512. The screen part 15113-1 is fixed inside the housing 15111-1.
The vane 15112-1 is formed to be connected with the rotary shaft 1512, and makes contact with the inner wall surface of the housing 15111-1 through a sealing agent. The vane 15112-1 has an area A1.
A sealed space formed by the housing 15111-1 is divided into first and third spaces by the vane 15112-1 and the screen part 15113-1. When highly-concentrated salt water is made flow into the first space, the vane 15112-1 rotates in an arrow direction illustrated in
The rotary actuator 1511-2 includes a housing 15111-2 and a vane 15112-2. The housing 15111-2 forms a sealed space and has a cylindrical shape having a radius r2. A relationship of radius r1>radius r2 is given. The rotary shaft 1512 is located so as to penetrate the housing 15111-2 along a center axis thereof. A screen part 15113-2 is formed to extend from an inner wall surface of the housing 15111-2 to the rotary shaft 1512. The screen part 15113-2 is fixed inside the housing 15111-2.
The vane 15112-2 is formed to be connected with the rotary shaft 1512, and makes contact with the inner wall surface of the housing 15111-2 through a sealing agent. The vanes 15112-1 and 15112-2 maintain a same angle each other.
The vane 15112-2 has an area A2. Here, a relationship between the areas A1 and A2 is preset on the basis of a pressure of highly-concentrated salt water from a high-pressure RO membrane 50, a pressure of seawater from a high pressure pump 40, friction between the housings 15111-1 and 15111-2 and the vanes 15112-1 and 15112-2.
A sealed space formed by the housing 15111-2 is divided into second and fourth spaces by the vane 15112-2 and the screen part 15113-2. When seawater is made flow into the fourth space, the vane 15112-2 rotates in an arrow direction illustrated in
The angle detection section 152 is to detect a rotation angle of the rotary shaft 1512. When the rotation angle reaches a predetermined angle, the angle detection section 152 outputs a detection signal to a control section 153. For example, two angles are registered in advance in the angle detection section 152 as the predetermined angle. One is an angle at which the vane 15112-1 and 15112-2 respectively come close to the screen part 15113-1 and 15113-2 from left sides. Another one is an angle at which the vanes 15112-1 and 15112-2 respectively come close to the screen parts 15113-1 and 15113-2 from right sides. When the rotation angle reaches any of the angles, the angle detection section 152 outputs detection signals to the control section 153. In this manner, the positions of the vanes 15112-1 and 15112-2 in the rotary actuators 1511-1 and 1511-2 can be recognized.
When the control section 153 receives the detection signal from the angle detection section 152, the control section 153 issues a switch instruction to a 4-port switch valve 62 so as to switch over the spaces into and from which highly-concentrated salt water is made flow and eject, respectively.
The motor control section 154 controls an electric current supplied to the motor 1513, based on a measurement result from a pressure meter 61. The motor 1513 applies left-handed or right-handed torque to the rotary shaft 1512 based on the electric current supplied by the motor control section 154. For example, when a measurement result from a pressure meter 61 decreases to be smaller than a value which has been expected beforehand, the motor control section 154 controls the electric current supplied to the motor 1513 so as to apply torque to the rotary shaft 1512 in a same direction with a rotating direction thereof.
Next, operation of the power recovery apparatus 150 configured as described above will be described.
The power recovery apparatus 150 in
Seawater from a safety filter 30 is supplied to a high-pressure pump 40 at 0.2 MPa and is also supplied to the fourth space of the rotary actuator 1511-2 through a check valve 641-4.
Seawater which has been boosted to 6.0 MPa by the high-pressure pump 40 is merged with seawater from the power recovery apparatus 150, and is supplied to the high-pressure RO membrane 50. At this time, the seawater from the power recovery apparatus 150 has been ejected from the second space of the rotary actuator 1511-2 and passed through the check valve 641-2. The high-pressure RO membrane 50 outputs fresh water and highly-concentrated salt water.
The highly-concentrated salt water ejected from the high-pressure RO membrane 50 passes through the pressure meter 61 and 4-port switch valve 62 and flows into the first space of the rotary actuator 1511-1. At this time, the third space of the rotary actuator 1511-1 is filled with highly-concentrated salt water. Highly-concentrated salt water rotates the vane 15112-1 in the rotary actuator 1511-1 in a direction toward the third space, and ejects highly-concentrated salt water in the third space through the 4-port switch valve 62 and valve 70.
When the vane 15112-1 of the rotary actuator 1511-1 rotates, the vane 15112-2 of the rotary actuator 1511-2 connected by the rotary shaft 1512 rotates accordingly. Therefore, seawater is ejected from the second space of the rotary actuator 1511-2 through the check valve 641-2, and seawater is made flow into the fourth space of the rotary actuator 1511-2 through the check valve 641-4.
Here, the vane 15112-1 has an area A1, and the vane 15112-2 has an area A2. Thus, a pressure of seawater ejected from the second space of the rotary actuator 1511-2 is higher than that of highly-concentrated salt water from the 4-port switch valve 62.
Operation of the motor will now be described. As positive or negative torque is applied by the motor 1513, rotation torque of the vanes 15112-1 and 15112-2 increases or decreases. If a pressure measured by the pressure meter 61 is lower than a preset pressure, the motor generates torque in the presently rotating direction. Otherwise, if higher than the preset pressure, the motor generates torque in a direction opposite to the presently rotating direction. From the operation as described above, the pressure of seawater ejected from the second space of the rotary actuator 1511-2 is equal to or slightly higher than a pressure of seawater supplied to the high-pressure RO membrane 50.
When the operation as described above is continued, the vanes 15112-1 and 15112-2 respectively come close to the screen parts 15113-1 and 15113-2 from left sides. Then, the angle detection section 152 detects the predetermined angle to be reached, and outputs the detection signal to the control section 153. The control section 153 receives the detection signal from the angle detection section 152, and then issues a switch instruction to the 4-port switch valve 62 so as to switch directions of flow-in and ejection of highly-concentrated salt water.
With the configuration as described above, the power recovery apparatus 150 according to the above fourth embodiment can achieve the same operation and effects as the power recovery apparatus 60 according to the first embodiment.
The above fourth embodiment has been described with reference to an example in which the pressure converter 151 includes the vane-type rotary actuators 1511-1 and 1511-2. However, the present embodiment is not limited to this example. For example, the fourth embodiment is practicable even when a gear motor, an axial piston motor, a plunger pump, a radial piston motor, and a trochoid motor is included in place of the vane-type rotary actuators.
The areas A1 and A2 may be equal to each other.
While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Indeed, the novel embodiments described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the embodiments described herein may be made without departing from the spirit of the inventions. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the inventions.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2009-212189 | Sep 2009 | JP | national |
