JP5562884B2 - Seawater desalination equipment - Google Patents

Description

  An embodiment of the present invention is a seawater desalination apparatus for extracting the performance of a power recovery apparatus used in a plant for desalinating seawater using a reverse osmosis membrane and controlling it to a desired operating state. About.

  With the global water problem becoming more serious, business competition on a global scale, which regards the water business as a huge market, is accelerating. In Middle Eastern countries that do not have surface water such as rivers or groundwater as a water source, or in regions with a high risk of drought in Japan, seawater desalination technology has been introduced and large-scale seawater desalination plants have been constructed to secure water sources. The conventional seawater desalination technology has been mainly an evaporation method in which seawater is condensed and recovered after heating and evaporation, but recently, reverse osmosis membranes described in, for example, Patent Document 1 and Patent Document 2 from the viewpoint of economy The method of using is expanding.

  A conventional seawater desalination apparatus using a reverse osmosis membrane includes a high pressure pump, a reverse osmosis membrane, a booster pump, a low pressure side outlet valve, and the like. The taken seawater is subjected to an appropriate pretreatment according to the water quality, and is sent to a high-pressure pump and a power recovery device. The high pressure pump boosts the pretreated water received to a high pressure state (for example, 6 MPa) and feeds it to the reverse osmosis membrane. The reverse osmosis membrane removes the salt contained in the pretreated water and generates fresh water. The removed salinity is sent to the power recovery device as concentrated seawater together with water that has not been desalinated. At this time, since the concentrated seawater has a pressure (for example, 5.8 MPa) that is the same as the reverse osmosis membrane inlet pressure, the power recovery device recovers the pressure (power) of the concentrated seawater and supplies it to the pretreated water that has been sent introduce. The pretreated water that has become high pressure (for example, 5.8 MPa) by the recovered power is boosted by a booster pump, and is fed to the reverse osmosis membrane together with the pretreated water fed by the high pressure pump.

JP 2009-279472 A JP 2009-154070 A

Of the running cost (yen / m ³ ) of seawater desalination plants using reverse osmosis membranes, electricity costs (power costs) account for more than 50%. Therefore, it is particularly important to reduce power costs in order to be competitive with running costs that can be improved by operation and control. In recent years, it has become common to install a power recovery device that recovers the power of a high-pressure pump with high efficiency. Since the efficiency of a power recovery device that can significantly improve power consumption energy (electric power consumption) varies depending on the operating point, power recovery control that always realizes a more efficient operating point is required.

  However, in the past, the operating conditions were fixed conditions determined at the beginning of operation, and the amount of power could not be reduced to the limit. At the same time, the sensors and control methods necessary to change the operating conditions were not provided. It is.

  In general, an index representing the ratio of the production fresh water amount Qa to the pretreatment water flow rate Qb entering the reverse osmosis membrane as a percentage is called a membrane recovery rate (= (Qa / Qb) × 100%). Since the flow rates of production fresh water and concentrated seawater change depending on the recovery rate of the membrane to be operated, the amount of production fresh water and the amount of motive energy recovered from the concentrated seawater change accordingly. In accordance with the change, the power consumption with respect to the unit production water amount also changes. FIG. 12 shows an example of the relationship between the power consumption per unit production water volume and the recovery rate. As shown in the figure, there is an operating point that minimizes power consumption for a certain amount of fresh water produced or pretreated water quality. However, the operating point at which the power consumption per unit production water volume is minimized varies depending on conditions such as the quality of pretreated water, the discharge pressure of the pump, and the amount of fresh water produced. For this reason, when the process conditions of the seawater desalination apparatus are unchanged under the conditions determined at the beginning of operation, the power consumption cannot be reduced to the limit.

  The present invention has been made in view of the above circumstances, and an object thereof is to provide a seawater desalination apparatus capable of reducing power consumption.

The seawater desalination apparatus according to the present invention includes a reverse osmosis membrane module having a reverse osmosis membrane that separates seawater into fresh water and concentrated seawater, a high-pressure pump that supplies seawater to the reverse osmosis membrane at high pressure, and the high-pressure pump. concentrated seawater of high pressure and high pressure line of concentrated seawater flowing through drained from more the reverse osmosis membrane module at the downstream side, and the low pressure line of seawater of low pressure seawater flowing upstream from said high pressure pump, A low-pressure line of concentrated seawater through which low-pressure concentrated seawater drained from the reverse osmosis membrane module flows downstream from the high-pressure pump, and first and second cylinders each partitioned by a movable piston, first and second cylinders have two switching valves for switching the flow paths communicating respectively, said first and second cylinder inner of partitioned one side in the cylinder Communicating the high pressure line respectively the pace, the low pressure line to said first and second cylinder inner of partitioned the other side of the cylinder space communicates respectively, said two switching valve by the first and second The flow paths communicating with the cylinders are respectively switched, whereby the moving direction of the movable piston in the first and second cylinders is alternately switched, and the concentration is performed from the high-pressure line through the flow path. A power recovery device that introduces seawater into the space in the one-side cylinder, pushes the piston with the pressure of the introduced concentrated seawater, and sends the seawater from the space in the other-side cylinder through the flow path to the low-pressure line; A first flow sensor that detects a flow rate of fresh water that has passed through the reverse osmosis membrane, and a flow rate of concentrated seawater that does not pass through the reverse osmosis membrane, Or the 2nd flow sensor which detects the flow of the seawater sent out from the power recovery device, and the flow rate of the seawater supplied to the power recovery device, or the concentrated seawater sent out from the power recovery device The flow rate detected by the second flow rate sensor provided at least one of the third flow rate sensor for detecting the flow rate of the power recovery device and the high pressure line on the high pressure inlet side and the high pressure line on the high pressure outlet side of the power recovery device A flow rate control valve for concentrated seawater for adjusting the amount of concentrated seawater to be fed to the power recovery device based on the pressure, and the high pressure line on the high pressure inlet side and the high pressure line on the high pressure outlet side of the power recovery device. Seawater drainage for adjusting the amount of seawater drained from the power recovery apparatus based on the flow rate detected by the second flow rate sensor provided at least one of them The power recovery device is provided on at least one of the flow rate control valve and the low pressure line on the low pressure inlet side and the low pressure line on the low pressure outlet side of the power recovery device, and based on the flow rate detected by the third flow sensor A drainage flow control valve for concentrated seawater for adjusting the amount of concentrated seawater drained from, and at least one of the low pressure line on the low pressure inlet side and the low pressure line on the low pressure outlet side of the power recovery device, A seawater feed flow rate control valve for adjusting the amount of seawater fed to the power recovery device based on the flow rate detected by the third flow rate sensor .

The seawater desalination apparatus according to the present invention includes a reverse osmosis membrane module having a reverse osmosis membrane that separates seawater into fresh water and concentrated seawater, a high-pressure pump that supplies seawater to the reverse osmosis membrane at high pressure, and the high-pressure pump. a high pressure line concentrated seawater of high pressure flowing drained from more the reverse osmosis membrane module at the downstream side, and the low pressure line of seawater of low pressure seawater flowing upstream from said high pressure pump, the high-pressure pump A low-pressure line of concentrated seawater through which low-pressure concentrated seawater drained from the reverse osmosis membrane module flows on the downstream side, first and second cylinders each partitioned by a movable piston, and the first and has two switching valves for switching the flow path communicating with each of the second cylinder, said first and second one side of the cylinder space partitioned internal cylinder The high pressure lines communicate with each other, the low pressure lines communicate with the other cylinder space, and the internal space of the first cylinder and the internal space of the second cylinder communicate with each other, The concentrated seawater is introduced from the high-pressure line in synchronism with the space in the one side cylinder of the first and second cylinders, and the piston is pushed by the pressure of the introduced concentrated seawater, and the other of the first and second cylinders A power recovery device that sends out the seawater from the space in the side cylinder in synchronization with the low-pressure line, a first flow rate sensor that detects the flow rate of fresh water that has passed through the reverse osmosis membrane, and seawater supplied to the power recovery device A third flow rate sensor that detects the flow rate of concentrated seawater sent from the power recovery device, or the power recovery device Provided at least one of said pressure connection of said low pressure inlet side low voltage line and a low pressure outlet, adjusting the amount of concentrated seawater is drained from the power recovery device based on the flow rate detected by the third flow rate sensor And a drain flow rate control valve.

  Important terms in this specification are defined below.

  “Power consumption per unit produced water” refers to the amount of power consumed for driving the high-pressure pump per unit produced water that has permeated through the reverse osmosis membrane.

  “Membrane recovery rate” refers to an index that expresses, as a percentage, the amount of fresh water produced through the reverse osmosis membrane relative to the amount of seawater supplied with pressure applied to the reverse osmosis membrane. The membrane recovery rate varies depending on conditions such as the quality of pretreated water, the discharge pressure of the pump, and the amount of fresh water produced, and there is an optimum membrane recovery rate that minimizes power consumption (the inflection point in FIG. 12). ). This optimum membrane recovery rate is a variable parameter that varies with process conditions and varies with aging of the reverse osmosis membrane. For example, when the seawater temperature rises, the optimum membrane recovery rate increases (the inflection point in FIG. 12 moves to the right). On the other hand, when the electrical conductivity (EC) increases, the optimum film recovery rate decreases (the inflection point in FIG. 12 moves to the left).

  The reason why such an inflection point (optimum film recovery rate) exists is as follows.

  Increasing the water recovery pressure of the high-pressure pump to increase the membrane recovery rate increases the salinity of the concentrated seawater (brine) and increases the osmotic pressure accordingly. It is necessary to push in the concentrated seawater at a higher pressure, and the energy loss in the reverse osmosis membrane module increases accordingly. On the other hand, if the pump pressure is lowered to reduce energy loss, the amount of fresh water produced is less than the amount of seawater supplied, resulting in a decrease in membrane recovery.

The block diagram which shows the seawater desalination apparatus which concerns on 1st Embodiment. The block diagram for demonstrating the basic operation | movement of the power recovery device without a booster pump. (A)-(d) is a cross-sectional block diagram explaining operation | movement of the power recovery device without a booster pump divided into each step. The block diagram for demonstrating operation | movement of the apparatus of 1st Embodiment. (A)-(c) is a timing chart which shows the cylinder position of the upper-lower stage in a power recovery device, respectively. The control block diagram of the seawater desalination apparatus of 2nd Embodiment. The block diagram which shows the seawater desalination apparatus (including the power recovery device with which the cylinder was connected) of 3rd Embodiment. FIG. 8 is a control block diagram of the apparatus of FIG. 7. The block diagram which shows the seawater desalination apparatus of 4th Embodiment. The control block diagram of the seawater desalination apparatus of 5th Embodiment. FIG. 10 is a control block diagram of a seawater desalination apparatus according to a sixth embodiment (including a plurality of power recovery apparatuses arranged in parallel). The characteristic diagram which shows the correlation with the collection | recovery rate of a film | membrane, and the electric power consumption per unit production water volume.

  Hereinafter, preferred embodiments of the present invention will be described.

(1) The seawater desalination apparatus of this embodiment includes a reverse osmosis membrane module (4) having a reverse osmosis membrane (41) for separating seawater into fresh water and concentrated seawater, and the seawater is supplied to the reverse osmosis membrane at high pressure. A high-pressure pump (P1) to be supplied, a high-pressure line (L3, L31, L5) through which high-pressure concentrated seawater drained from the reverse osmosis membrane module flows downstream from the high-pressure pump, and upstream from the high-pressure pump The low pressure line (L2, L21) of seawater through which low-pressure seawater flows and the low pressure of concentrated seawater through which low-pressure concentrated seawater drained from the reverse osmosis membrane module flows downstream from the high-pressure pump The line (L6) and the first and second cylinders (51, 53), the interior of which is partitioned by movable pistons (52, 54) and the flow paths communicating with the first and second cylinders, respectively, 2 are switched. One of a switching valve (CV1, CV2), wherein the first and second cylinders Through the high pressure line is communicated respectively partitioned by the cylinder space on one side of parts, the low pressure line to said first and second cylinder inner of partitioned the other side of the cylinder space communicates respectively, the 2 The flow paths communicating with the first and second cylinders are switched by two switching valves, respectively, whereby the moving direction of the movable piston in the first and second cylinders is switched alternately, and the high pressure through the flow path from the line introducing the concentrated seawater to said one side cylinder space, wherein the seawater by pressing the piston in the pressure of the concentrated seawater introduced from the other side cylinder space through said flow path A power recovery device (5) for sending to the low pressure line, a first flow rate sensor (Q5) for detecting the flow rate of fresh water that has passed through the reverse osmosis membrane, and the reverse osmosis membrane. A second flow rate sensor (Q1, Q3) that detects the flow rate of concentrated seawater that does not exceed or detects the flow rate of seawater sent from the power recovery device, and the flow rate of seawater supplied to the power recovery device A third flow rate sensor (Q2, Q4) for detecting or detecting a flow rate of the concentrated seawater sent from the power recovery device, and the high pressure line on the high pressure inlet side and the high pressure outlet side of the power recovery device Concentrated seawater feed flow rate control valve (V1, V1, provided in at least one of the high pressure lines, for adjusting the amount of concentrated seawater fed to the power recovery device based on the flow rate detected by the second flow rate sensor. V3,... V2n-1, V11) and at least one of the high-pressure line on the high-pressure inlet side and the high-pressure line on the high-pressure outlet side of the power recovery device, and the flow rate detected by the second flow sensor Based on before Drainage flow control valve seawater for adjusting an amount of seawater to be discharged from the power recovery device and (V12), at least one of the low pressure line of the low pressure line and the low pressure outlet side of the low pressure inlet side of the power recovery device Concentrated seawater drainage flow control valves (V2, V4,... V2n, V22) for adjusting the amount of concentrated seawater drained from the power recovery device based on the flow rate detected by the third flow sensor. ) And water supply to the power recovery device based on the flow rate detected by the third flow sensor, provided at least one of the low pressure line on the low pressure inlet side and the low pressure line on the low pressure outlet side of the power recovery device And a seawater feed flow rate control valve (V21) for adjusting the amount of seawater to be produced .

  According to this embodiment, the flow rate of each line is adjusted by the water supply flow rate control valve of the high pressure line and the drainage flow rate control valve of the low pressure line using the flow rate detection information detected by the first, second and third flow rate sensors. This makes it possible to efficiently recover pressure energy from the concentrated seawater discharged at a high pressure from the reverse osmosis membrane module without using the auxiliary power of the conventional booster pump.

(2) In the apparatus of the above (1), a target fresh water target water amount and a membrane target recovery rate are respectively set in advance, and the fresh water amount is set to the target water amount according to the flow rate detection result from the flow sensor. And controlling the drive of the high-pressure pump so that the membrane recovery rate becomes the target recovery rate, and the concentrated seawater feed flow rate control valve (V1, V3,... V2n-1, V11) and the seawater Controls the opening of at least one of the water supply flow rate control valves (V21) , and the seawater drainage flow rate control valve (V12) and the concentrated seawater drainage flow rate control valve (V2, V4,... V2n, V22) It is preferable to further have a control part which controls at least one valve opening degree.

  In this embodiment, when a flow rate detection signal is input from the first, second, and third flow sensors to the control unit, the control unit calculates the production fresh water amount and the membrane recovery rate, respectively, and the target fresh water target water amount from the memory. And the target recovery rate of the production fresh water obtained by calculation and the target water amount are compared, and the actual recovery rate of the membrane obtained by calculation and the target recovery rate are compared. In addition, the drive of the high pressure pump is controlled so as to be below the allowable value, the water supply flow rate control valve is controlled, and the drainage flow rate control valve is controlled, so that the pressure energy of the concentrated seawater can be efficiently recovered. .

(3) The seawater desalination apparatus of this embodiment includes a reverse osmosis membrane module (4) having a reverse osmosis membrane (41) for separating seawater into fresh water and concentrated seawater, and the seawater is supplied to the reverse osmosis membrane at high pressure. A high-pressure pump (P1) to be supplied, a high-pressure line (L3, L31, L5) through which high-pressure concentrated seawater drained from the reverse osmosis membrane module flows downstream from the high-pressure pump, and upstream from the high-pressure pump The low pressure line (L2, L21) of seawater through which low-pressure seawater flows and the low pressure of concentrated seawater through which low-pressure concentrated seawater drained from the reverse osmosis membrane module flows downstream from the high-pressure pump The line (L6) and the first and second cylinders (51, 53) , the interior of which is partitioned by movable pistons (52, 54) and the flow paths communicating with the first and second cylinders, respectively, 2 are switched. One of a switching valve (CV1, CV2), wherein the first and second cylinders The high pressure line communicates with the cylinder space on one side of which the section is partitioned, the low pressure line communicates with the space on the other side of the cylinder, and the internal space of the first cylinder and the second cylinder And the concentrated seawater is introduced from the high-pressure line in synchronism with the space in the one side cylinder of the first and second cylinders, and the piston is driven by the pressure of the introduced concentrated seawater. To detect the flow rate of fresh water that has passed through the reverse osmosis membrane and the power recovery device (5A, 5B) that sends the seawater from the space in the other cylinder of the first and second cylinders in synchronization with the low-pressure line A flow rate of concentrated seawater that is detected from the flow rate of seawater supplied to the first power sensor and the power recovery device or sent from the power recovery device In the third and flow sensor (Q2, Q4), provided on at least one of said pressure connection of said low pressure line and the low pressure outlet side of the low pressure inlet side of the power recovery device, the third flow rate sensor for detecting the A drainage flow rate control valve that adjusts the amount of concentrated seawater drained from the power recovery device based on the detected flow rate.

  According to the present embodiment, the flow rate detection information detected by the first and third flow rate sensors is used to adjust the flow rate of the low-pressure line by the drainage flow rate control valve, so that the auxiliary power of the conventional booster pump is not used. The pressure energy can be efficiently recovered from the concentrated seawater discharged from the reverse osmosis membrane module at a high pressure.

  (4) In the apparatus of (3), the control unit controls the rotational driving of the high-pressure pump based on the flow rate detection result from the flow rate sensor so that the amount of fresh water produced is equal to the target water amount. In addition, it is preferable to control at least one valve opening of the drainage flow rate control valve so that the membrane recovery rate becomes the target recovery rate.

  In this embodiment, when a flow rate detection signal is input from the first and third flow sensors to the control unit, the control unit calculates the production fresh water amount and the membrane recovery rate, respectively, Call the target recovery rate, compare the actual production water volume obtained by calculation with the target water volume, compare the actual recovery rate of the membrane obtained by calculation and the target recovery rate, and the difference between them is zero or acceptable. The drive of the high-pressure pump is controlled so as to be less than the value, and the drainage flow rate control valve is controlled, whereby the pressure energy of the concentrated seawater can be efficiently recovered.

(5) In the apparatus according to any one of (2) to (4) above, a water temperature meter that measures the temperature of seawater pretreated upstream of the high-pressure pump, and the electrical conductivity of the pretreated seawater. An electric conductivity meter for measuring, a hydrogen ion exponent meter for measuring the hydrogen ion concentration of the pretreated seawater, and a watt hour meter for measuring power consumption consumed by the entire seawater desalination apparatus. Preferably, thereby, the control unit is configured to perform the operation as a previous operation condition based on the measurement result from the watt hour meter and the measurement result from at least one of the water temperature meter, the electric conductivity meter, and the hydrogen ion index meter. The power consumption per unit production water volume can be displayed for each water quality and production fresh water volume of the treated seawater .

  According to this embodiment, the water quality of the pretreated seawater that affects the reverse osmosis membrane process is measured using a water temperature meter, an electric conductivity meter, a hydrogen ion exponent meter, and a watt hour meter, and the measurement results are used. Since the control unit equipped with a display device can display the power consumption per unit production water volume, the operator can know the progress of the seawater desalination process in real time and when any abnormality occurs Can also respond quickly.

(6) The device according to any one of (2) to (4), wherein the power recovery device includes a plurality of power recovery devices having different step-up ratios, and the control unit is used from among the plurality of power recovery devices. The combination of power recovery devices can be changed.

  In this embodiment, by combining a plurality of power recovery devices having different boost ratios, it is possible to operate so as to minimize the power consumption per unit production water volume according to changes in process conditions (Table 1). .

  Various embodiments will be specifically described below.

  The power recovery system of the seawater desalination plant that is the target process includes a high-pressure pump P1, a reverse osmosis membrane module 4, a power recovery device 5, and the like. Seawater taken by the seawater supply device 2 is subjected to appropriate pretreatment by the pretreatment device 3 according to the water quality, and is sent to the high-pressure pump P1 and the power recovery device 5. The high pressure pump P1 boosts the received pretreated water to a high pressure state (for example, 6 MPa) and sends the water to the reverse osmosis membrane module 4. The reverse osmosis membrane in the module 4 separates salt contained in the pretreated water and allows fresh water to permeate. The salt separated from the membrane is sent to the power recovery device 5 as concentrated seawater (brine) together with water that has not been desalinated. At this time, since the concentrated seawater has a pressure (for example, 5.8 MPa) that is approximately the same as the reverse osmosis membrane inlet pressure, the power recovery device 5 recovers the pressure (power) of the concentrated seawater and sends the pretreated water that has been sent to it. To a reverse osmosis membrane inlet pressure (for example, 6 MPa). The pretreated water that has become high pressure due to the recovered power is fed to the reverse osmosis membrane together with the pretreated water fed by the high pressure pump. The concentrated seawater that has lost its pressure is drained from the power recovery device 5.

  FIG. 2 defines names of the input / output ports of the power recovery apparatus.

  Even in a power recovery system that does not have a booster pump as in the present embodiment, the power consumption per unit production water volume varies depending on the membrane recovery rate. Therefore, in order to limit the power consumption per unit production water to the limit, it is necessary to change the amount of concentrated seawater on the high-pressure inlet side flowing from the reverse osmosis membrane module 4 to the power recovery device 5 under the condition that the production water amount is constant. There is.

  The power recovery device 5 repeats the operations of (a) → (b) → (c) → (d) → (a) in FIG. 3, and the pressure energy (power) of the concentrated seawater discharged from the reverse osmosis membrane module. It has a cylinder / piston mechanism for recovering. It is the upper piston portion 52 that collects power in the state of FIG. Concentrated seawater flows into the chamber on the right side of the cylinder 51 from the high pressure inlet side, and a high pressure is transmitted to the piston portion 52. The pressure transmitted to the piston part 52 pushes out the pretreated water in the left chamber of the cylinder 51 and raises it to the pressure at the reverse osmosis membrane inlet. The pretreated water in the left chamber is continuously pushed out by the pressure of the concentrated seawater until the upper piston portion 52 reaches the left end through the state of FIG. After the upper piston portion 52 reaches the left end, the upper piston portion 52 plays a role of drainage by the left and right switching valves CV1, CV2. As shown in FIGS. 3 (c) and 3 (d), the upper piston 52 moves to the right due to the pretreatment water flowing into the left chamber, and the power is recovered in FIGS. 3 (a) and 3 (b). Seawater is pushed out from the cylinder 51 in the right direction and drained.

  Up to now, attention has been paid to the upper piston, but in the state of FIGS. 3 (a) and 3 (b) where the upper piston portion 52 is actually transmitting pressure, the lower piston portion 54 drains, In the state of FIGS. 3C and 3D where the piston 52 is draining, the lower piston portion 54 transmits pressure, and the moving direction of the piston portions 52 and 54 is alternately switched by the switching valves CV1 and CV2. ing. In this way, while switching the operation of the two cylinder / piston mechanisms, the operations of (a) → (b) → (c) → (d) → (a) in FIG. Collect and pressurize pre-treated water.

Further, the pressure increased by the power recovery device described above is uniquely determined by the area where the piston part receives pressure. If the pressure of the concentrated seawater is P _I , the right cross-sectional area of the piston part is A _{I, the} pressure at which the pretreatment water is boosted is P _O , the left cross-sectional area of the piston part is A _O , and the force applied to the cylinder is F, The following equations (1) and (2) hold.

F = P _I × A _I (1)
F = P _O × A _O (2)
Therefore, P _I : Po = A _O : A _I. For example, when the pressure is increased to 6 MPa with respect to the pressure 5.8 MPa of concentrated seawater, the ratio of the cylinder right area A _I and the cylinder left area A _O is 6.0: 5.8 = 30: 29. That is, the boost ratio of the power recovery device is 30:29.

  Next, various preferred embodiments will be described for carrying out the present invention.

(First embodiment)
As shown in FIG. 1, the seawater desalination apparatus 1 of 1st Embodiment is the seawater supply apparatus 2 arranged in series in order from the upstream along the main lines L1, L2, L3, and L4, the pre-processing. The apparatus 3 includes a high pressure pump P1, a reverse osmosis membrane module 4, and a production fresh water tank 6. A power recovery device 5 is provided on lines L21, L31, L5, and L6 parallel to the main line.

  The power recovery device 5 introduces the concentrated seawater (brine) from the reverse osmosis membrane module 4 into the cylinder 51 (or 53), pushes the piston portion 52 (or 54), and pushes the seawater (front) from the cylinder 51 (or 53). Treated water), pressure energy is recovered from the high pressure brine, and the brine after the pressure energy recovery is finally discharged to the concentrated seawater tank 7.

  As shown in FIGS. 2 and 3, the high pressure inlet side of the power recovery device 5 is connected to the primary space of the reverse osmosis membrane module 4 via the high pressure line L5, and the high pressure outlet side of the power recovery device 5 is the high pressure line L31. To the high pressure line L3 (the line between the high pressure pump P1 and the reverse osmosis membrane module 4). The low pressure inlet side of the power recovery device 5 is connected to the low pressure line L2 communicating with the pretreatment device 3 via the low pressure branch line L21, and the low pressure outlet side of the power recovery device 5 is the concentrated seawater tank via the low pressure line L6. 7 is connected.

  The reverse osmosis membrane module 4 is internally partitioned by a reverse osmosis membrane 41, an inlet connected to the high pressure line L3 communicates with the partitioned upstream space, and an outlet connected to the production fresh water line L4 in the downstream space. Communicate.

  A first flow rate sensor Q5 is provided in the production fresh water line L4 so that the flow rate of production fresh water sent from the reverse osmosis membrane module 4 to the production fresh water tank 6 is detected.

  A second flow rate sensor Q1 is attached to the high-pressure side inlet line L5 of the power recovery device 5. A third flow rate sensor Q2 is attached to the low pressure side outlet line L6 of the power recovery device 5.

  The operation of this embodiment will be described with reference to FIGS.

  In the seawater desalination apparatus, water is fed to the reverse osmosis membrane 41 at a pressure equal to or higher than the osmotic pressure of salt in seawater in order to obtain fresh water. At that time, the amount of fresh water produced depends greatly on the rotational speed of the high-pressure pump P1. Therefore, in order to set the production fresh water amount to a desired flow rate, for example, a method of performing PID control of the rotation speed of the high-pressure pump P1 so that the measured value of the production fresh water amount matches the target value can be considered.

  Moreover, the target water amount of the concentrated seawater sent from the reverse osmosis membrane can be obtained by calculation using the target recovery rate of the membrane set in advance and the target water amount of the production fresh water. Must be controlled by the opening degree of either the high pressure inlet side valve V11 (V1) or the high pressure outlet side valve V12.

  The target concentrated seawater flow rate Qhbsv is obtained from the following equation (3) using the set target recovery rate MRsv of the membrane and the target production water volume setting value Qpsv of the production fresh water that is the setting value of the high-pressure pump control.

Qhbsv = Qpsv x (100 / MRsv-1) (3)
However, MRsv ≠ 0.

  In order to increase the efficiency of the power recovery device, it is necessary to set the difference between the high-pressure side inlet flow rate and the low-pressure side inlet flow rate in the power recovery device to a desired value.

  As a timing chart of the cylinder position of the upper and lower pistons of the power recovery device using the switching valves CV1, CV2 and cylinder / piston mechanisms 51, 52, 53, 54, the case where the flow on the high pressure side is excessive than the flow on the low pressure side FIG. 5 (a) shows the case where the flow rates of both are appropriate, and FIG. 5 (b) shows the case where the flow rate on the low pressure side is excessive than the flow rate on the high pressure side.

  Since the upper / lower cylinder / piston mechanisms 51, 52, 53, 54 are alternately responsible for either pressure transmission or drainage by the two switching valves CV1, CV2, the upper / lower piston parts 52, 54 are in the same direction. It doesn't move. When the flow rates on the high-pressure side and the low-pressure side are appropriate, as shown in FIG. 5B, the timing t1, t3 (t2, t4) when the upper piston portion 52 arrives at the left end (right end) of the cylinder and the lower piston portion 54 The timing t1, t3 (t2, t4) at which the cylinder reaches the right end (left end) of the cylinder closely matches, and the upper and lower piston portions 52, 54 can switch the roles of pressure transmission and drainage without waste.

  On the other hand, when the flow rate on the high pressure side is excessive, as shown in FIG. 5A, the timing t1, t5 (t4) when the upper piston portion 52 arrives at the cylinder left end (right end) and the lower piston portion 54 at the cylinder right end ( Deviation occurs between the timings t2 and t6 (t3) arriving at the left end), and the time during which the piston movement for pressure transmission remains at the left end occurs, resulting in the time when the pressure transmission function is not performed.

  Further, when the flow rate on the low pressure side is excessive, as shown in FIG. 5C, the timing t2, t6 (t3) when the upper piston portion 52 arrives at the cylinder left end (right end) and the lower piston portion 54 at the cylinder right end. Deviation occurs between the timings t1 and t5 (t4) arriving at the (left end), and the piston portions 52 and 54 remain at the right end and do not perform the function of draining the concentrated seawater. As a result, the inlet of the high pressure pump The flow rate will increase. In this case, the inlet flow rate of the high-pressure pump pulsates in accordance with the time during which the piston portions 52 and 54 stay at the right end and the time during movement, thereby damaging the pump.

  Therefore, in order to increase the efficiency of the power recovery device, it is necessary to control the flow rate on the low pressure side in accordance with the flow rate on the high pressure inlet side that changes according to the membrane recovery rate.

(Second Embodiment)
Next, a second embodiment of the present invention will be described with reference to FIGS. In addition, description of the part which this embodiment overlaps with said embodiment is abbreviate | omitted.

  The seawater desalination apparatus 1A of the present embodiment includes a first flow sensor Q5, two second flow sensors Q1, Q3, two third flow sensors Q2, Q4, two water supply flow control valves V11, V21, Two drainage flow control valves V12 and V22 and a control unit 8 are provided.

  The first flow rate sensor Q5 is provided in the production fresh water line L4, detects the flow rate of production fresh water sent from the reverse osmosis membrane module 4 to the production fresh water tank 6, and sends the flow rate detection signal to the control unit 8. ing.

  The two second flow rate sensors Q1 and Q3 are provided in the high pressure lines L5 and L31 of the power recovery device 5, respectively. One second flow rate sensor Q1 is attached to the high pressure side inlet line L5 of the power recovery device 5, detects the brine flow rate sent to the upper cylinder / piston mechanisms 51, 52, and sends the flow rate detection signal to the control unit 8. To send to. The other second flow rate sensor Q3 is attached to the high pressure side outlet line L31 of the power recovery device 5, detects the seawater flow rate pushed out from the lower cylinder / piston mechanisms 53, 54, and controls the flow rate detection signal. It is to be sent to part 8.

The two third flow rate sensors Q2 and Q4 are provided in the low pressure lines L6 and L21 of the power recovery apparatus 5, respectively. One third flow rate sensor Q4 is attached to the low pressure side outlet line L21 of the power recovery device 5, detects the flow rate of seawater sent to the lower cylinder / piston mechanisms 53, 54, and sends the flow rate detection signal to the control unit. 8 to send. The other third flow rate sensor Q2 is attached to the low pressure side outlet line L6 of the power recovery device 5, detects the flow rate of seawater pushed out from the lower cylinder / piston mechanisms 53, 54, and outputs the flow rate detection signal. The data is sent to the control unit 8.

  The two water supply flow control valves V11 and V21 are provided in the inlet side high pressure line L5 and the inlet side low pressure line L21 of the power recovery device 5, respectively. One water supply flow rate control valve V11 is attached to the inlet side high pressure line L5. The other water supply flow rate control valve V21 is attached to the inlet side low pressure line L21. These water supply flow control valves V11 and V21 are on / off controlled by the control unit 8.

  The two drainage flow control valves V12 and V22 are provided in the outlet side high pressure line L31 and the outlet side low pressure line L6 of the power recovery device 5, respectively. One drainage flow rate control valve V12 is attached to the outlet side high pressure line L31. The other drainage flow rate control valve V22 is attached to the outlet side low pressure line L6. The drainage flow control valves V12, V22 are controlled to be turned on / off by the control unit 8.

  The operation of this embodiment will be described.

  When the flow rate detection signal is input to the control unit 8 from the first to third flow rate sensors Q1 to Q5, the control unit 8 causes the fluid (brine or pretreated seawater to flow through the lines L4, L5, L6, L31, and L21). ) And the membrane recovery rate are calculated, the calculated actual flow rate is compared with the target flow rate, the calculated actual recovery rate is compared with the target recovery rate, and the difference between the actual measurement value and the target value is zero. Alternatively, the opening degree of each of the valves V11, V12, V21, and V22 is controlled so as to be a predetermined allowable value or less.

  Thereby, the brine flow rate flowing through the inlet-side high-pressure line L5, the seawater flow rate flowing through the outlet-side high-pressure line L31, the seawater flow rate flowing through the inlet-side low-pressure line L21, and the brine flow rate flowing through the outlet-side low-pressure line L6 are respectively controlled. Pressure energy is recovered from the high pressure brine according to 1)-(3).

(Third embodiment)
Next, a third embodiment of the present invention will be described with reference to FIG. In addition, description of the part which this embodiment overlaps with said embodiment is abbreviate | omitted.

  In order to increase the efficiency of the power recovery device, it is effective to control the flow rate on the low pressure side in accordance with the flow rate on the high pressure side and synchronize the cylinders of the upper and lower pistons.

  In the seawater desalination apparatus 1B of the present embodiment, the two cylinders of the power recovery apparatuses 5A and 5B are physically provided in addition to the method of controlling the flow rate on the low pressure side by either the low pressure inlet valve or the low pressure outlet valve. And the cycle of piston reciprocation in the cylinder is synchronized. In this case, as shown in FIG. 7, it is only necessary to install flow control valves V21 and V22 on the low pressure inlet side and the low pressure outlet side for adjusting the low pressure side flow rate, and on the high pressure inlet side and the high pressure outlet side for adjusting the high pressure side flow rate. There is no need to install a flow control valve.

  The operation of this embodiment will be described.

In the apparatus 1B of the present embodiment, input / output of signals to / from the control unit 8 is as shown in FIG. That is, when flow rate detection signals from the first flow rate sensor Q5 and the two third flow rate sensors Q2 and Q4 are input, the control unit 8 fluids (brine or pretreated seawater) flowing through the lines L4, L6, and L21. The flow rate and the membrane recovery rate are respectively calculated, the calculated actual flow rate is compared with the target flow rate, the calculated actual recovery rate is compared with the target recovery rate, and the difference between the actual measurement value and the target value is zero or The opening degrees of the valves V21 and V22 are controlled so as to be less than a predetermined allowable value.

  As a result, the flow rate of seawater flowing through the inlet-side low-pressure line L21 and the flow rate of brine flowing through the outlet-side low-pressure line L6 are respectively controlled, and pressure energy is recovered from the high-pressure brine according to the above equations (1) to (3).

(Fourth embodiment)
Next, a fourth embodiment of the present invention will be described with reference to FIG. In addition, description of the part which this embodiment overlaps with said embodiment is abbreviate | omitted.

  In the seawater desalination apparatus 1C of the present embodiment, the hydrogen ion exponent meter 11, the water temperature meter 12, the electrical conductivity meter 13, and the seawater desalination device that measure the hydrogen ion index, electrical conductivity, and water temperature of pretreated water are consumed. A watt-hour meter (not shown) for measuring the power consumption is provided. These measuring instruments 11, 12, and 13 are attached to a low pressure line L2 between the preprocessing device 3 and the high pressure pump P1, and send detection signals to the control unit 8, respectively.

  According to the present embodiment, the quality of the pretreated water can be measured by various measuring instruments. Therefore, depending on the operating conditions such as the quality of the pretreated water and the amount of fresh water produced, the efficiency and reverse of the power recovery device during operation and the pump Since the characteristics of the osmosis membrane change, the power consumption per unit production water volume changes. The change can also be visualized by a table, a two-dimensional graph, a 3D (three-dimensional) graph, or the like.

(Fifth embodiment)
Next, a fifth embodiment of the present invention will be described with reference to FIG. In addition, description of the part which this embodiment overlaps with said embodiment is abbreviate | omitted.

  The seawater desalination apparatus 1D of the present embodiment further includes an operation condition setting unit 9 that sets various operation conditions in accordance with changes in process conditions. The operation condition setting unit 9 can realize an operation function that minimizes the total amount of electric power per unit production water amount for each water quality condition of the pretreatment water.

  In addition to the measurement information related to the water quality of the pretreated seawater from the various measuring instruments 11, 12, 13, the control unit 8 further includes water supply flow rate control valves V 11, V 21 and drainage flow rate based on the operating conditions set by the operating condition setting unit 9. Control valves V12 and V22 are respectively controlled.

  According to the present embodiment, power can be recovered more efficiently according to operating conditions such as the quality of pretreated water and the amount of fresh water produced.

(Sixth embodiment)
Next, a sixth embodiment will be described with reference to FIG. 11 and Tables 1 and 2. In addition, description of the part which this embodiment overlaps with said embodiment is abbreviate | omitted.

In the power recovery device without booster pumps, high-pressure inlet pressure P _I and the high-pressure outlet pressure P _O ratio P _I: P _O is uniquely determined by the power recovery device. However, in the seawater desalination apparatus 1E of this embodiment, as shown in FIG. 11, by connecting a plurality of power recovery apparatuses 5a, 5b,..., 5n having different boost ratios P _I : P _O in parallel lines. It becomes possible to change the boost ratio of the entire power recovery device group. As an example, consider an apparatus in which three power recovery apparatuses 1 to 3 having various boosting ratios shown in Table 1 are installed.

In the seawater desalination apparatus 1E having the power recovery device groups having different boost ratios as described above, it is assumed that one power recovery device is left unused and the operation is performed with only two power recovery devices. Then, as shown in Table 2, it becomes possible to select three combinations as the step-up ratio of the entire power recovery apparatus group, and the step-up ratio of the power recovery apparatus can be controlled. As described above, it is possible to realize an operation function that minimizes the total amount of electric power per unit production water volume in accordance with the operation conditions such as the quality of pretreated water and the amount of production fresh water.

  According to the present invention, the pressure recovered at a high recovery rate can be returned to the primary side of the reverse osmosis membrane module without using a drive source such as a booster pump, and the power consumption can be greatly reduced. .

1, 1A, 1B, 1C, 1D, 1E ... seawater desalination equipment,
2 ... Seawater supply device, 3, 31, 32 ... Pretreatment device,
4 ... reverse osmosis membrane module, 41 ... reverse osmosis membrane,
5, 5A, 5B, 5a-5n ... power recovery device,
51, 53 ... Cylinder, 52, 54 ... Piston part,
6 ... Production freshwater tank, 7 ... Concentrated seawater tank,
8 ... Control unit, 9 ... Operating condition setting unit,
11 ... Hydrogen ion index meter, 12 ... Thermometer, 13 ... Electrical conductivity meter,
P1: High pressure pump,
L2, L21, L6 ... low pressure line, L3, L31, L5 ... high pressure line,
V1, V3, ..., V2n-1, V11, V12 ... Water supply flow control valve,
V2, V4, ..., V2n, V21, V22 ... Drain flow control valve,
Q1, Q3 ... second flow rate sensor,
Q2, Q4 ... third flow sensor,
Q5: First flow sensor,
CV1, CV2 ... Switching valve.

Claims (4)

A reverse osmosis membrane module having a reverse osmosis membrane for separating seawater into fresh water and concentrated seawater;
A high-pressure pump for supplying seawater to the reverse osmosis membrane at a high pressure;
A high-pressure line through which high-pressure concentrated seawater drained from the reverse osmosis membrane module flows downstream from the high-pressure pump;
A low-pressure line of seawater through which low-pressure seawater flows upstream from the high-pressure pump;
A low-pressure line of concentrated seawater through which low-pressure concentrated seawater drained from the reverse osmosis membrane module flows downstream from the high-pressure pump;
The first and second cylinders, each of which is partitioned by a movable piston, and two switching valves for switching the flow paths communicating with the first and second cylinders, respectively, are provided inside the first and second cylinders. The high pressure line communicates with the partitioned space in the cylinder on one side, and the low pressure line communicates with the partitioned space on the other side in the first and second cylinders. The flow paths communicating with the first and second cylinders are respectively switched by a switching valve, whereby the moving direction of the movable piston in the first and second cylinders is alternately switched, and the high pressure line The concentrated seawater is introduced into the space in the one-side cylinder through the flow path, and the other piston is pushed by the pressure of the introduced concentrated seawater. A power recovery apparatus for feeding the sea water into the low pressure line from the side cylinder space through said flow channel,
A first flow sensor for detecting a flow rate of fresh water that has passed through the reverse osmosis membrane;
Detecting a flow rate of concentrated seawater that does not pass through the reverse osmosis membrane, or a second flow rate sensor that detects a flow rate of seawater sent from the power recovery device;
A third flow sensor for detecting a flow rate of seawater supplied to the power recovery device or detecting a flow rate of concentrated seawater sent from the power recovery device;
The power recovery device is provided on at least one of the high-pressure line on the high-pressure inlet side and the high-pressure line on the high-pressure outlet side of the power recovery device, and is based on the flow rate of concentrated seawater or seawater detected by the second flow sensor. A high-pressure line flow control valve for adjusting the amount of concentrated seawater sent to the water and the amount of seawater drained from the power recovery device ;
The power recovery device is provided on at least one of the low-pressure line on the low-pressure inlet side and the low-pressure line on the low-pressure outlet side of the power recovery device, and is based on the flow rate of seawater or concentrated seawater detected by the third flow sensor. A low-pressure line flow control valve for adjusting the amount of concentrated seawater drained from the water and the amount of seawater sent to the power recovery device ;
A seawater desalination apparatus comprising:   A target fresh water target water amount and a membrane target recovery rate are set in advance, and the drive of the high-pressure pump is controlled in accordance with the flow rate detection result from the flow rate sensor so that the fresh water amount becomes the target water amount. And at least one valve opening degree of the concentrated seawater feed flow rate control valve and the seawater feed flow rate control valve so that the membrane recovery rate becomes the target recovery rate, and the seawater drainage flow rate The seawater desalination apparatus according to claim 1, further comprising a control unit that controls at least one valve opening degree of the control valve and the drainage flow rate control valve of the concentrated seawater. A water temperature meter that measures the temperature of seawater pretreated upstream of the high-pressure pump, an electrical conductivity meter that measures the electrical conductivity of the pretreated seawater, and a hydrogen ion concentration of the pretreated seawater A hydrogen ion index meter, and a watt-hour meter that measures power consumption consumed by the entire seawater desalination device,
The control unit, based on the measurement result from the watt-hour meter and the measurement result from at least one of the water temperature meter, the electrical conductivity meter, and the hydrogen ion exponent meter, the water quality of the pretreated seawater as the operating condition The seawater desalination apparatus according to claim 2, wherein the power consumption per unit production water is displayed for each production freshwater. A plurality of power recovery devices having different step-up ratios are connected in parallel, and the control unit controls a control valve installed in a line connected to the plurality of power recovery devices and uses the power recovery device to be used. The seawater desalination apparatus according to claim 2, wherein the combination is changed.

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