JP2020075210A - Membrane separation unit - Google Patents

Abstract

To provide a membrane separation unit having a high water-saving effect when an RO membrane module is flushed.SOLUTION: A membrane separation unit 1 of this invention comprises: a reverse osmosis membrane module 4 that separates supply water W2 including feed water W1 into permeated water W3 and concentrated water W4; a supply water line L2 that supplies the supply water W2 to the reverse osmosis membrane module 4; a permeated water line L3 that sends the permeated water W3 separated in the reverse osmosis membrane module 4; a concentrated water line L4 that sends the concentrated water W4 separated in the reverse osmosis membrane module 4; first flow rate measuring means FM1 that measures a flow rate of the permeated water W3; second flow rate measuring means FM2 that measures a flow rate of the concentrated water W4; a recovery ratio calculating section 301 that calculates a recovery ratio from the flow rate of the permeated water W3 and the flow rate of the concentrated water W4; and a flushing control section 303 that performs control of finishing a flushing step of the reverse osmosis membrane module 4, in which the flushing control section 303 finishes the flushing step based on the recovery ratio in the flushing.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a membrane separation device.

  Conventionally, high-purity pure water that does not contain impurities is used in the manufacturing process of semiconductors, the cleaning of electronic components and medical instruments, and the like. This kind of pure water is generally produced by subjecting raw water such as ground water or tap water to a reverse osmosis membrane separation treatment with a reverse osmosis membrane module (hereinafter, also referred to as “RO membrane module”).

  As pure water is produced by the reverse osmosis membrane separation process using the reverse osmosis membrane module, contaminants such as suspended substances, humic substances, and proteins adhere to the reverse osmosis membrane module. Occasionally or irregularly, it becomes necessary to wash the reverse osmosis membrane module. Such washing of the reverse osmosis membrane module is generally called flushing.

  For example, Patent Document 1 discloses a technique of performing a flushing operation after adjusting the osmotic pressure of supply water.

JP, 2017-064599, A

  However, conventionally, flushing is finished after a uniform amount of flushing water or a constant amount of flushing water is flowed. However, depending on the conditions, for example, when the flushing recovery rate is low, it is possible to save flushing water. Cases are also possible.

  It is an object of the present invention to provide a membrane separation device that has a high water-saving effect when flushing an RO membrane module.

  The present invention provides a reverse osmosis membrane module for separating feed water including feed water into permeated water and concentrated water, a feed water line for supplying feed water to the reverse osmosis membrane module, and a reverse osmosis membrane module. The permeated water line for delivering permeated water, the concentrated water line for delivering concentrated water separated by the reverse osmosis membrane module, the first flow rate measuring means for measuring the flow rate of the permeated water, and the flow rate of the concentrated water are A second flow rate measuring means for measuring, a recovery rate calculation section for calculating a recovery rate from the permeated water flow rate and the concentrated water flow rate, and a flushing control section for controlling the flushing step of the reverse osmosis membrane module. And a flushing control unit that ends the flushing process based on the recovery rate during flushing.

  In addition, the membrane separation device includes an integrated water flow rate calculation unit that calculates the integrated water flow rate of the water supply and / or an integrated drainage amount calculation unit that calculates the integrated water flow rate of the concentrated water as drainage by the first flow rate measurement means. Furthermore, it is preferable that the flushing control unit terminates the flushing step when the accumulated water flow rate or the accumulated drainage amount during flushing reaches a predetermined amount calculated based on the recovery rate.

  Further, it is preferable that the flushing control unit terminates the flushing process based on the recovery rate at the time of water supply in addition to the recovery rate at the flushing.

  Further, the flushing control unit, the smaller the ratio of the recovery rate at the time of flushing to the recovery rate at the time of water supply, or the greater the difference obtained by subtracting the recovery rate at the time of flushing from the recovery rate at the time of water supply, It is preferable to reduce the predetermined amount.

  ADVANTAGE OF THE INVENTION According to this invention, it becomes possible to provide the membrane separation apparatus with a high water-saving effect at the time of flushing of an RO membrane module.

It is the whole block diagram of the membrane separation device concerning the embodiment of the present invention. It is a figure which shows the relationship between the pressure and the flow volume which concern on the flow volume adjustment unit used by embodiment of this invention. It is a functional block diagram of a control part contained in the membrane separation device concerning a 1st embodiment of the present invention. It is an example of the graph which shows the relationship between the recovery rate at the time of flushing and the amount of water required for flushing in the embodiment of the present invention. It is a flow chart which shows operation of the membrane separation device concerning a 1st embodiment of the present invention. It is a functional block diagram of a control part contained in a membrane separation device concerning a 2nd embodiment of the present invention. It is a flow chart which shows operation of the membrane separation device concerning a 2nd embodiment of the present invention. It is a functional block diagram of a control part contained in a membrane separation device concerning a 3rd embodiment of the present invention. It is an example of the graph which shows the relationship of the ratio of the recovery rate at the time of water supply with respect to the recovery rate at the time of flushing, and the amount of water required for flushing in the embodiment of the present invention. It is a flowchart which shows operation | movement of the membrane separation apparatus which concerns on the 3rd Embodiment of this invention.

[1st Embodiment]
[1.1 Structure of Membrane Separation Device]
The membrane separation device 1 according to the first embodiment of the present invention will be described with reference to the drawings. FIG. 1 is an overall configuration diagram of a membrane separation device 1 according to this embodiment. The membrane separation device 1 according to the present embodiment is applied to, for example, a pure water production system that produces pure water from fresh water.

  As shown in FIG. 1, the membrane separation device 1 according to the present embodiment includes a pressurizing pump 2, a pressurizing side inverter 3, an RO membrane module 4 as a reverse osmosis membrane module, a flow rate adjusting unit 5, and a drainage flow rate. A drainage flow rate adjusting valve 7 (proportional control valve) as adjusting means, a water supply pump 12, a water supply side inverter 13, a water supply pressure adjusting valve 14 (proportional control valve) as water supply pressure adjusting means, and a first flow rate detecting means. The flow rate sensor FM1 as the above, the flow rate sensor FM2 as the second flow rate detecting means, and the control unit 30. Note that the illustration of the electrical connection line between the control unit 30 and the controlled device is omitted.

  The membrane separation device 1 also includes a water supply line L1, a supply water line L2, a permeate water line L3, a first concentrated water line L41, and a second concentrated water line L42. The "line" in the present specification is a general term for lines through which a fluid can flow, such as a flow path, a route, and a pipeline.

  The water supply line L1 is a line that supplies the water supply W1 to the pressurizing pump 2. The upstream end of the water supply line L1 is connected to a supply source (not shown) of the water supply W1. A water supply pump 12 is provided on the upstream side of the water supply line L1.

  The water supply pump 12 is a device that sucks in the water supply W1 flowing through the water supply line L1 and pressure-feeds (discharges) it toward the pressure pump 2. The water supply pump 12 is supplied with drive power whose frequency is converted from the water supply side inverter 13. The water supply pump 12 is driven at a rotation speed according to the frequency (hereinafter, also referred to as “drive frequency”) of the supplied (input) drive power.

  The water supply side inverter 13 is an electric circuit (or a device having the circuit) that supplies the drive power whose frequency has been converted to the water supply pump 12. The water supply side inverter 13 is electrically connected to the control unit 30. A command signal is input to the water supply side inverter 13 from the control unit 30. The water supply side inverter 13 outputs to the water supply pump 12 drive power having a drive frequency corresponding to the command signal (current value signal or voltage value signal) input by the control unit 30. In the present embodiment, the control unit 30 controls the water supply side inverter 13 so that the water supply pump 12 discharges the water supply W1 at a predetermined constant pressure value.

  The water supply pressure adjusting valve 14 is a proportional valve that adjusts the pressure of the water supply W1 supplied to the pressurizing pump 2 by adjusting the opening degree substantially steplessly. The water supply pressure adjusting valve 14 is electrically connected to the control unit 30, and the opening degree is adjusted by the control of the control unit 30.

  The supply water line L2 is a line that supplies the supply water W1 as the supply water W2 to the RO membrane module 4. The upstream end of the supply water line L2 is connected to the pressure pump 2. The downstream end of the supply water line L2 is connected to the primary inlet port of the RO membrane module 4. The supply water line L2 is provided with the pressurizing pump 2 and the RO membrane module 4 in order from the upstream side to the downstream side.

  The pressurizing pump 2 is provided in the supply water line L2. The pressurizing pump 2 is a device that sucks the feed water W1 in the feed water line L2 and feeds (discharges) it as the feed water W2 toward the RO membrane module 4. The pressurizing pump 2 is supplied with drive power whose frequency is converted from the pressurizing side inverter 3. The pressurizing pump 2 is driven at a rotation speed according to the frequency (hereinafter, also referred to as “driving frequency”) of the driving power supplied (input).

  The pressurizing side inverter 3 is an electric circuit (or a device having the circuit) that supplies the pressurizing pump 2 with drive power whose frequency has been converted. The pressure-side inverter 3 is electrically connected to the control unit 30. A command signal is input to the pressure inverter 3 from the control unit 30. The pressurizing side inverter 3 outputs to the pressurizing pump 2 drive power having a drive frequency corresponding to the command signal (current value signal or voltage value signal) input by the control unit 30.

  The RO membrane module 4 is a facility for membrane-separating the supply water W2 discharged from the pressurizing pump 2 into permeated water W3 from which dissolved salts have been removed and concentrated water W41 from which dissolved salts have been concentrated. The RO membrane module 4 includes a single or a plurality of RO membrane elements (not shown). The RO membrane module 4 membrane-separates the feed water W2 with these RO membrane elements to produce permeated water W3 and concentrated water W41.

  The permeated water line L3 is a line for sending out the permeated water W3 separated by the RO membrane module 4. The upstream end of the permeate line L3 is connected to the secondary port of the RO membrane module 4. The permeated water line L3 is provided with a flow rate sensor FM1.

  The flow rate sensor FM1 is a device that detects the flow rate of the permeated water W3 flowing through the permeated water line L3 as a detected flow rate value. The flow rate sensor FM1 is connected to the permeated water line L3. The flow rate sensor FM1 is electrically connected to the control unit 30. The detected flow rate value of the permeated water W3 detected by the flow rate sensor FM1 is transmitted to the control unit 30 as a detection signal. As the flow rate sensor FM1, for example, a pulse transmission type flow rate sensor in which an axial flow impeller or a tangential impeller (not shown) is arranged in the flow path housing can be used.

  The first concentrated water line L41 is a line for sending the concentrated water W41 separated by the RO membrane module 4. The upstream end of the first concentrated water line L41 is connected to the primary outlet port of the RO membrane module 4. Further, the downstream side of the first concentrated water line L41 is connected to the primary side of the flow rate adjusting unit 5.

  The second concentrated water line L42 is a line for sending the concentrated water W42 whose flow rate is adjusted by the flow rate adjusting unit 5. The upstream end of the second concentrated water line L42 is connected to the secondary side of the flow rate adjusting unit 5. Further, the second concentrated water line L42 is provided with a drainage flow rate adjusting valve 7 as a drainage flow rate adjusting means and a flow rate sensor FM2 in this order.

  In the following, the first concentrated water line L41 and the second concentrated water line L42 may be collectively referred to as "concentrated water line L4". Further, the concentrated water W41 and the concentrated water W42 may be collectively referred to as "concentrated water W4".

  The flow rate adjusting unit 5 concentrates in proportion to the constant pressure element that causes the concentrated water of substantially constant flow rate to flow and the pressure difference in the flow rate adjusting unit 5 substantially regardless of the pressure difference in the flow rate adjusting unit 5. And a proportional element for increasing the flow rate of water. The differential pressure in the flow rate adjusting unit 5 is specifically the differential pressure between the water pressure of the first concentrated water line L41 and the water pressure of the second concentrated water line L42. The constant flow rate element that holds a constant flow rate value without requiring auxiliary power or external operation, and may be, for example, an element called by the name of water governor. Further, as the proportional element, for example, one called by the name of an orifice may be used, and the flow rate of the concentrated water W4 flowing from the orifice is proportional to the differential pressure in the flow rate adjusting unit 5.

  FIG. 2 is a graph showing an example of the relationship between the inlet pressure of the RO membrane module 4 and the flow rate of the concentrated water flowing through the flow rate adjusting unit 5. Since the flow rate adjusting unit 5 includes the constant flow rate element, when the inlet pressure is generated, the flow rate of the concentrated water flowing through the flow rate adjusting unit 5 increases to point A at once. That is, approximately, at the same time when the inlet pressure is generated, the flow rate at the height of point A flows into the flow rate adjusting unit 5. At the same time, since the flow rate adjusting unit 5 includes the proportional element, thereafter, the flow rate of the concentrated water flowing through the flow rate adjusting unit 5 increases linearly as the inlet pressure increases.

  In addition, in the flow rate adjusting unit 5, the constant flow element and the proportional element may be integrally configured or may be separately configured. In the case of being integrally configured, for example, the flow direction of the proportional element matches the major axis direction of the flow rate adjusting unit 5, and the flow direction of the constant flow rate element is orthogonal to the major axis direction of the flow rate adjusting unit 5. It may be configured as follows. Alternatively, the flow direction of the proportional element may be orthogonal to the major axis direction of the flow rate adjusting unit 5, and the flow direction of the constant flow rate element may be aligned with the major axis direction of the flow rate adjusting unit 5. Alternatively, both the flow direction of the constant flow element and the flow direction of the proportional element may be configured to coincide with the long axis direction of the flow rate adjusting unit 5.

  The drainage flow rate adjusting valve 7 is a valve capable of adjusting the drainage flow rate of concentrated water W42 as concentrated drainage discharged from the second concentrated water line L42 to the outside of the apparatus. The drainage flow rate adjusting valve 7 is electrically connected to the control unit 30. The valve opening degree of the drainage flow rate adjusting valve 7 is controlled by a drive signal transmitted from the control unit 30. By transmitting a current value signal (for example, 4 to 20 mA) from the control unit 30 to the drainage flow rate adjusting valve 7 and controlling the valve opening degree, the drainage flow rate of the concentrated water W42 can be adjusted.

  The flow rate sensor FM2 is a device that detects, as a detected flow rate, the flow rate of the concentrated water W42 as concentrated waste water that is discharged from the second concentrated water line L42 to the outside of the apparatus after being adjusted by the drainage flow rate adjusting valve 7. The flow rate sensor FM2 is connected to the second concentrated water line L42. The flow rate sensor FM2 is electrically connected to the control unit 30. The detected flow rate value of the concentrated water W42 detected by the flow rate sensor FM2 is transmitted to the control unit 30 as a detection signal. As the flow rate sensor FM2, for example, a pulse transmission type flow rate sensor in which an axial flow impeller or a tangential impeller (not shown) is arranged in the flow path housing can be used.

[1.2 Functional Blocks of Control Unit]
The control unit 30 has a CPU, a ROM, a RAM, a CMOS memory, and the like, and these are known to those skilled in the art and configured to be able to communicate with each other via a bus.

  The CPU is a processor that controls the membrane separation device 1 as a whole. The CPU reads out various programs stored in the ROM via the bus and controls the entire membrane separation apparatus 1 in accordance with the various programs, so that the recovery rate calculation unit as shown in the functional block diagram of FIG. It is configured to realize the functions of 301, the cumulative water flow rate calculation unit 302, and the flushing control unit 303.

  The recovery rate calculation unit 301 calculates the recovery rate in the membrane separation device 1 from the flow rate value of the permeated water W3 measured by the flow rate sensor FM1 and the flow rate value of the concentrated water W42 measured by the flow rate sensor FM2. In particular, the recovery rate calculation unit 301 calculates the recovery rate both during water supply and flushing of the membrane separation device 1.

  The cumulative water flow rate calculation unit 302 calculates the cumulative water flow rate of the supply water W2 to the RO membrane module 4 during the flushing of the membrane separation device 1. More specifically, the cumulative water flow rate calculation unit 302 uses the flushing start command in the membrane separation device 1 as a trigger to measure the flow rate value of the permeated water W3 measured by the flow rate sensor FM1 thereafter and the flow rate sensor FM2. Based on the flow rate value of the concentrated water W42 that is supplied, the cumulative water flow rate of the water W2 supplied to the RO membrane module 4 is calculated.

  The flushing control unit 303 ends the flushing process based on the recovery rate calculated by the recovery rate calculation unit 301 during the flushing of the membrane separation device 1. In particular, in the present embodiment, the flushing control unit 303 calculates the cumulative water flow amount at the time of flushing calculated by the cumulative water flow amount calculation unit 302 based on the recovery rate calculated by the recovery rate calculation unit 301. When the amount of water required for the above (first predetermined amount) is reached, the flushing process is terminated.

  FIG. 4 shows the relationship between the recovery rate calculated by the recovery rate calculation unit 301 and the amount of water required for flushing. Conventionally, it has been known that the flushing effect increases as the recovery rate decreases as the amount of permeated water decreases and the amount of concentrated drainage increases. Specifically, the ratio of the amount of water that does not pass through the RO membrane from the primary side inlet and flows to the primary side outlet is larger than the amount of water that permeates from the primary side inlet to the secondary side of the RO membrane module 4, and the RO membrane surface In this case, the flow velocity is high, and the degree of removing the dirt adhering to the surface of the film is high, so that the flushing effect is high. That is, the lower the recovery rate, the smaller the amount of water required to achieve the predetermined flushing effect. Therefore, as the recovery rate increases, the amount of water required for flushing monotonically increases. In the graph of FIG. 4, when the recovery rate at flushing b is higher than the recovery rate at flushing a, when the recovery rate at flushing a is greater than the water amount Qa required for flushing at the recovery rate at flushing b The amount of water Qb required for is higher. In the graph of FIG. 4, the relationship between the recovery rate and the amount of water required for flushing is linear, but the relationship is not limited to this.

  In the membrane separation device 1 according to the present embodiment, the relationship between the recovery rate during flushing and the amount of water required for flushing, which is illustrated in FIG. 4, is theoretically derived, and the flushing control unit 303 uses the relationship based on this relationship. A predetermined amount of 1 may be calculated. Alternatively, in the membrane separation device 1, the relationship between the recovery rate during flushing and the amount of water required for flushing is derived in advance based on an empirical rule, and the flushing control unit 303 calculates the first predetermined amount based on this relationship. May be.

[1.3 Operation of Membrane Separation Device]
FIG. 5 is a flowchart showing the operation of the membrane separation device 1.
In step S1, the flushing control unit 303 calculates the first predetermined amount based on the recovery rate at the flushing time calculated by the recovery rate calculation unit 301.
In step S2, the cumulative water flow rate calculation unit 302 calculates the cumulative water flow rate to the RO membrane module 4.

  In step S3, if the cumulative water flow rate to the RO membrane module 4 is equal to or larger than the first predetermined value (S3: YES), the process proceeds to step S4. When the cumulative water flow rate to the RO membrane module 4 is less than the first predetermined value (S3: NO), the process returns to step S1.

  In step S4, the flushing control unit 303 finishes the flushing process and finishes the series of processes.

[1.4 Effects of First Embodiment]
According to the membrane separation device 1 according to the first embodiment described above, the following effects can be obtained, for example.
The membrane separation device 1 according to the first embodiment ends the flushing process based on the recovery rate calculation unit 301 that calculates the recovery rate from the flow rate of the permeated water W3 and the flow rate of the concentrated water W4, and the recovery rate during flushing. And a flushing control unit 303.
As a result, when the decrease in the concentration on the membrane surface is fast, that is, the amount of water that permeates from the primary side inlet to the secondary side of the RO membrane module 4 does not pass through the RO membrane from the primary side inlet to the primary side outlet. When the ratio of the amount of flowing water increases, the flow velocity on the surface of the RO membrane becomes faster, and the degree of removing the dirt attached to the surface of the membrane becomes higher. As a result, a small amount of water is required to achieve the predetermined flushing effect, and thus flushing with a high water saving effect can be performed.

The membrane separation device 1 further includes an integrated water flow rate calculation unit 302 that calculates the integrated water flow rate of the supply water W2, and the flushing control unit 303 determines that the integrated water flow rate during flushing is based on the recovery rate during flushing. When the calculated predetermined amount is reached, the flushing process is ended.
By determining the required amount of water at the time of flushing according to the recovery rate at the time of flushing, it becomes possible to perform flushing with a high water saving effect.

[2 Second Embodiment]
[2.1 Structure of Membrane Separation Device]
The overall configuration of the membrane separation device 1A according to the second embodiment of the present invention is basically the same as that of the membrane separation device 1 according to the first embodiment, and therefore its illustration and description are omitted. The control unit 30A included in the membrane separation apparatus 1A according to the second embodiment has a functional block different from that of the control unit 30 included in the membrane separation apparatus 1 according to the first embodiment. The membrane separation device 1A is different from the membrane separation device 1 according to the first embodiment.

[2.2 Functional Blocks of Control Unit]
FIG. 6 is a functional block diagram of the control unit 30A. Unlike the control unit 30, the control unit 30A does not have the integrated water flow rate calculation unit 302, but has an integrated drainage amount calculation unit 304 instead. Further, the control unit 30A has a flushing control unit 303A instead of the flushing control unit 303.

  The integrated drainage amount calculation unit 304 calculates the integrated drainage amount of the concentrated water W42 as the concentrated drainage water from the second concentrated water line L42 during the flushing of the membrane separation device 1A. More specifically, the integrated wastewater amount calculation unit 304 uses the flushing start command in the membrane separation device 1A as a trigger, and from the flow rate value of the concentrated water W42 measured by the flow rate sensor FM2 thereafter, from the second concentrated water line L42. The integrated amount of discharged water of the concentrated water W42 as the concentrated waste water of is calculated.

  The flushing control unit 303A ends the flushing process based on the recovery rate calculated by the recovery rate calculation unit 301 during the flushing of the membrane separation device 1A. In particular, the flushing control unit 303A determines that the integrated drainage amount at the time of flushing calculated by the integrated drainage amount calculation unit 304 is the amount of water required for flushing calculated based on the recovery rate calculated by the recovery rate calculation unit 301 (second When the predetermined amount is reached, the flushing is ended.

[2.3 Operation of Membrane Separation Device]
FIG. 7 is a flowchart showing the operation of the membrane separation device 1A.
In step S11, the flushing control unit 303A calculates the second predetermined amount based on the recovery rate at the time of flushing calculated by the recovery rate calculation unit 301.
In step S12, the integrated drainage amount calculation unit 304 calculates the integrated drainage amount from the second concentrated water line L42.

  In step S13, when the integrated drainage amount from the second concentrated water line L42 is the second predetermined value or more (S13: YES), the process proceeds to step S14. When the integrated drainage amount from the second concentrated water line L42 is less than the second predetermined value (S13: NO), the process returns to step S11.

  In step S14, the flushing control unit 303A ends the flushing process and ends the series of processes.

[2.4 Effects of Second Embodiment]
According to the membrane separation apparatus 1A according to the second embodiment described above, the same effect as that of the membrane separation apparatus 1 according to the first embodiment can be obtained.

The membrane separation device 1A further includes an integrated drainage amount calculation unit 304 that calculates the integrated drainage amount of the concentrated water W4, and the flushing control unit 303 calculates the integrated drainage amount during flushing based on the recovery rate during flushing. When the predetermined amount is reached, the flushing process is ended.
By determining the required amount of water at the time of flushing according to the recovery rate at the time of flushing, it becomes possible to perform flushing with a high water saving effect.

[3 Third Embodiment]
[3.1 Configuration of Membrane Separation Device]
The overall configuration of the membrane separation device 1B according to the third embodiment of the present invention is basically the same as that of the membrane separation device 1 according to the first embodiment, and therefore its illustration and description are omitted. The control unit 30B included in the membrane separation device 1B according to the third embodiment has a functional block different from that of the control unit 30 included in the membrane separation device 1 according to the first embodiment. The membrane separation device 1B is different from the membrane separation device 1 according to the first embodiment.

[3.2 Functional Block of Control Unit]
FIG. 8 is a functional block diagram of the control unit 30B. Unlike the control unit 30, the control unit 30B has a flushing control unit 303B instead of the flushing control unit 303.

  The flushing control unit 303 ends the flushing process based on the recovery rate calculated by the recovery rate calculation unit 301 during the flushing of the membrane separation device 1. In particular, in the present embodiment, the flushing control unit 303 calculates the cumulative water flow amount at the time of flushing calculated by the cumulative water flow amount calculation unit 302 based on the recovery rate calculated by the recovery rate calculation unit 301. When the amount of water required for the above (first predetermined amount) is reached, the flushing process is terminated.

  The flushing control unit 303B ends the flushing process based on the recovery rate calculated by the recovery rate calculation unit 301 during the flushing of the membrane separation device 1B. In particular, the flushing control unit 303B calculates the cumulative water flow amount during flushing calculated by the cumulative water flow amount calculation unit 302 based on the recovery ratio during flushing and the recovery ratio during water supply calculated by the recovery ratio calculation unit 301. When the calculated amount of water required for flushing (the third predetermined amount) is reached, flushing is terminated.

FIG. 9 shows the relationship between the ratio between the recovery rate during flushing and the recovery rate during water supply calculated by the recovery rate calculation unit 301, and the amount of water required for flushing. The concentration ratio of concentrated water is calculated by the following formula (1).
Concentration factor = 1 / (1-recovery rate / 100) (1)
Therefore, it is known that the gap between the recovery rate at the time of flushing and the recovery rate at the time of water supply has a larger difference in the degree of concentration, and the flushing effect becomes higher. That is, the smaller the recovery rate at the time of flushing compared to the recovery rate at the time of water supply, the smaller the amount of water required to achieve the predetermined flushing effect. Therefore, as the ratio of the recovery rate during flushing to the recovery rate during water supply increases, the amount of water required for flushing increases monotonically. In the graph of FIG. 9, when the ratio b of the flushing recovery rate / water supply recovery rate is higher than the flushing recovery rate / water supply recovery rate a, the flushing recovery rate / water supply recovery rate a In the case of, the water quantity Qa required for flushing is higher than the water quantity Qa required for flushing in the case of the ratio b of recovery rate during flushing / recovery rate during water supply. Note that in the graph of FIG. 9, the relationship between the ratio of the recovery rate during flushing / recovery rate during water supply and the amount of water required for flushing is linear, but the present invention is not limited to this.

  In the membrane separation apparatus 1B according to the present embodiment, the relationship between the ratio of the recovery ratio during flushing / recovery ratio during water supply and the amount of water required for flushing is theoretically derived, and the flushing control unit 303B The third predetermined amount may be calculated based on this relationship. Alternatively, in the membrane separation apparatus 1B, the relationship between the ratio of the recovery rate during flushing / recovery rate during water supply and the amount of water required for flushing is derived in advance based on an empirical rule, and the flushing control unit 303B determines the first based on this relationship. The predetermined amount of 3 may be calculated.

[2.3 Operation of Membrane Separation Device]
FIG. 10 is a flowchart showing the operation of the membrane separation device 1B.
In step S21, the flushing control unit 303B calculates the third predetermined amount based on the recovery rate during flushing and the recovery rate during water supply calculated by the recovery rate calculation unit 301.
In step S22, the cumulative water flow rate calculation unit 302 calculates the cumulative water flow rate to the RO membrane module 4.

  In step S23, when the cumulative water flow rate is the third predetermined value or more (S23: YES), the process proceeds to step S24. If the cumulative water flow rate is less than the third predetermined value (S23: NO), the process returns to step S21.

  In step S24, the flushing control unit 303B ends the flushing process and ends the series of processes.

[3.4 Effects of Third Embodiment]
According to the membrane separation apparatus 1B according to the third embodiment described above, the same effects as those of the membrane separation apparatus 1 according to the first embodiment and the membrane separation apparatus 1B according to the second embodiment can be obtained.

In addition, in the membrane separation device 1B according to the third embodiment, the flushing control unit 303B ends the flushing process based on the recovery rate during water supply in addition to the recovery rate during flushing. Further, the flushing control unit 303B decreases the third predetermined amount as the ratio of the recovery rate during flushing to the recovery rate during water supply decreases.
As a result, it is possible to execute the optimum flushing in terms of the water saving effect according to the level of the flushing efficiency.

[4 modification]
The degree of enrichment may be grasped by measuring the electrical conductivity in the membrane separators 1 to 1B, and the recovery rate calculator 301 may calculate the rate of recovery based on this degree of enrichment.
In the membrane separation devices 1 to 1B, the amount of water required for flushing and the flushing time may be adjusted based on the water temperature of the feed water W1 or the feed water W2.
In addition, in the membrane separation devices 1 to 1B, the bubbling step of supplying air from the lower portion of the RO membrane module 4 to swing the bundle of hollow fiber membranes may be performed to further enhance the water saving effect.

Further, in the membrane separation apparatus 1B according to the third embodiment, the flushing control unit 303B derives the water amount required for flushing based on the ratio of the recovery rate during flushing / recovery rate during water supply. The amount of water necessary for flushing may be derived based on the difference between the water recovery rate and the water supply recovery rate.
Further, in the membrane separation device 1B according to the third embodiment, the flushing control unit 303B ends the flushing process based on the comparison between the cumulative amount of water passing through the RO membrane module 4 and the third predetermined amount. The flushing step may be terminated based on the comparison between the cumulative amount of wastewater discharged from the second concentrated water line L42 and the third predetermined amount.

1, 1A, 1B Membrane separation device 2 Pressurizing pump 3 Pressurizing side inverter (inverter)
4 RO membrane module (reverse osmosis membrane module)
5 Flow rate adjusting unit 7 Drain flow rate adjusting valve 12 Water supply pump 13 Water supply side inverter (inverter)
14 Water supply pressure adjusting valve FM1, FM2 Flow rate sensor (flow rate detecting means)
L1 water supply line L2 supply water line L3 permeate water line L4 concentrated water line L41 first concentrated water line L42 second concentrated water line

Claims (4)

A reverse osmosis membrane module for separating feed water including feed water into permeated water and concentrated water,
A supply water line for supplying supply water to the reverse osmosis membrane module,
A permeate line for delivering permeate separated by the reverse osmosis membrane module;
A concentrated water line for delivering the concentrated water separated by the reverse osmosis membrane module,
First flow rate measuring means for measuring the flow rate of the permeated water,
Second flow rate measuring means for measuring the flow rate of the concentrated water;
A recovery rate calculation unit that calculates a recovery rate from the flow rate of the permeated water and the flow rate of the concentrated water;
A flushing control unit that controls the flushing process of the reverse osmosis membrane module,
The membrane separation device, wherein the flushing control unit ends the flushing process based on the recovery rate at the time of flushing. The membrane separation device further includes an integrated water flow rate calculation unit that calculates the integrated water flow rate of the water supply and / or an integrated drainage flow rate calculation unit that calculates the integrated drainage flow rate of the concentrated water as drainage by the first flow rate measurement means. ,
The membrane separation according to claim 1, wherein the flushing control unit terminates the flushing step when the accumulated water flow rate or the accumulated drainage amount during flushing reaches a predetermined amount calculated based on the recovery rate. apparatus.   The membrane separation device according to claim 2, wherein the flushing control unit terminates the flushing process based on the recovery rate during water supply in addition to the recovery rate during flushing.   The flushing control unit, the smaller the ratio of the recovery rate during flushing to the recovery rate during water supply, or the greater the difference between the recovery rate during water supply and the recovery rate during flushing, the greater the predetermined amount. The membrane separation device according to claim 3, wherein

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