JP2014172010A - Water treatment system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a water treatment system which can easily control recovery rates of pressure containers at the same level.SOLUTION: A water treatment system includes: a membrane module 22 for filtration of water; a pressure container 21 which accommodates the membrane module 22; permeate piping 23 which discharges a permeate obtained by the filtration in the membrane module 22; supply water piping 21h which is provided with a plurality of pressure containers 21 each accommodating the membrane module 22 and connects the pressure containers 21 in parallel so that supply water to be filtered is supplied to the membrane modules 22 respectively accommodated in the plurality of pressure containers 21; and flow control means 25 which is provided in the permeate piping 23 and controls the flow rate of the permeate flowing through the permeate piping 23 based on the ion concentration in the remainder of the supply water, discharged without filtration, in the supply water supplied to the pressure container 21.

Description

  The present invention relates to a water treatment system.

  A technique for obtaining fresh water by filtering seawater or the like using a membrane module including a membrane such as a reverse osmosis membrane is known. Such a membrane module is used, for example, housed in a pressure vessel. In the technology for obtaining fresh water from seawater, fresh water (permeated water) is obtained by supplying seawater (feed water) to a pressure vessel equipped with a reverse osmosis membrane and subjecting it to membrane treatment (permeating the reverse osmosis membrane). On the other hand, the remainder of the seawater that was not membrane-treated (that is, did not permeate the reverse osmosis membrane) is discharged to the outside as concentrated water containing ions.

  In a water treatment system to which a plurality of pressure vessels are connected, there is a desire to increase the recovery rate of the entire water treatment system (ratio of the amount of permeated water to the amount of supplied water) as much as possible. However, the recovery rate of the entire system (hereinafter referred to as “system recovery rate”) and the recovery rate of each pressure vessel are not normally correlated, and the recovery rate usually varies from pressure vessel to pressure vessel. . Therefore, if the system recovery rate is simply increased, a pressure vessel in which the recovery rate becomes extremely large may occur. In such a pressure vessel, the concentration of ions in the concentrated water increases as the amount of permeated water increases, and an inorganic substance such as metal may precipitate on the membrane surface and inhibit flow. This phenomenon is called so-called scaling.

  Thus, attempts have been made to suppress the generation of pressure vessels whose recovery rate is extremely increased when the recovery rate of each pressure vessel is set to the same level and the system recovery rate is increased. For example, Non-Patent Document 1 describes that the pipe connecting the pressure vessels has a smaller diameter on the supply water side and a larger diameter on the concentrated water side. Thereby, the dispersion | variation in the recovery rate between pressure vessels is suppressed.

Desalination and Water Treatment, Vol.5 (2009), pp.192-197.

  When the recovery rates in the respective pressure vessels are approximately the same, the system recovery rates substantially coincide with the recovery rates of the pressure vessels. Therefore, in the technique described in Non-Patent Document 1, the diameter of the pipe that connects the pressure vessels is usually determined by the system recovery rate.

  However, in a system with piping set to achieve a certain system recovery rate, if the system recovery rate is changed to a new set value, the recovery rate in each pressure vessel usually simply follows. It does not change. Therefore, when the system recovery rate is changed, the recovery rate may vary among the pressure vessels. If the recovery rate varies, scaling as described above may occur and the film processing may stop.

  If the pipe diameter is reset every time the system recovery rate is changed and the pipe is newly connected, the recovery rate in each pressure vessel can be made similar. Takes time and effort. Further, the system must be stopped while the connection is reestablished, resulting in a large loss of processing time.

  Therefore, the problem to be solved by the present invention is to provide a water treatment system capable of easily controlling the recovery rate in each pressure vessel to the same extent.

  The present inventors have intensively studied to solve the above problems. As a result, it has been found that the above problem can be solved by controlling the flow rate of the permeated water that has been subjected to the membrane treatment based on the ion concentration in the remaining portion of the feed water that has not been subjected to the membrane treatment.

  ADVANTAGE OF THE INVENTION According to this invention, the water treatment system which can control the recovery rate in each pressure vessel to the same extent easily can be provided.

It is a systematic diagram of the seawater desalination plant concerning this embodiment. It is a figure which shows the internal structure of the reverse osmosis unit with which the seawater desalination plant which concerns on this embodiment is equipped. It is a graph which shows (a) flow volume in each pressure vessel, (b) ion concentration of concentrated water, and (c) recovery rate in the reverse osmosis unit with which the seawater desalination plant concerning this embodiment is equipped. It is a modification of the reverse osmosis unit with which the seawater desalination plant concerning this embodiment is equipped. It is a figure which shows the modification of the reverse osmosis unit with which the seawater desalination plant which concerns on this embodiment is equipped, (a) Front view, (b) Side view, (c) It is a rear view.

  Hereinafter, the water treatment system according to the present embodiment will be described with reference to the drawings as appropriate. In addition, the following description is an example for implementing this invention, and this invention is not restrict | limited at all to the following content.

<Problems of conventional technology>
In order to describe the water treatment system according to the present embodiment, first, the problem to be solved by the water treatment system according to the present embodiment will be described in more detail.

  As a water treatment technique, there is a technique called crossflow filtration in which supply water (untreated water) supplied to the membrane module is partially permeated through the membrane. Water that has permeated through the membrane and has a lower solute relative to the feed water is called permeate (filtered water, treated water). Moreover, the water that has not permeated the membrane (remaining portion of the feed water) is called concentrated water because it has a higher solute concentration than the feed water.

  In particular, in a water treatment system for cross-flow filtration, there is a demand to increase the recovery rate as much as possible. This is because, when a predetermined permeate flow rate is obtained, if the recovery rate is high, the supply water flow rate is small, and the equipment scale of the pretreatment for purifying the feed water before flowing into the membrane module is reduced, resulting in a reduction in equipment cost. This is because it becomes smaller. However, as described above, if the recovery rate is large, the ion concentration (inorganic substance or the like) of the concentrated water increases, and scaling tends to occur. When scaling occurs, the membrane is blocked and permeated water cannot be obtained, so it is difficult to increase the recovery rate beyond the value at which scaling occurs.

  In designing a water treatment system, the recovery rate of the entire system is usually determined based on the ion concentration of the feed water. However, in a system in which a plurality of pressure vessels in which membrane modules are accommodated are connected in parallel, as described above, the recovery rates for each pressure vessel vary and do not match the system recovery rates.

For example, the reason for the variation in the recovery rate for each pressure vessel will be described by taking the case of a seawater desalination system using a reverse osmosis membrane as an example.
The flow rate Qp of the permeated water that passes through the reverse osmosis membrane is expressed by the following formula (1).

  In the formula (1), A is a proportional constant inherent to the reverse osmosis membrane, Pf is the pressure of the feed water, dP is the differential pressure between the feed water and the concentrated water, Pp is the pressure of the permeate, dΠ is the osmotic pressure of the feed water, S is the area of the reverse osmosis membrane. As an example of operating conditions of a general seawater desalination system, the supply water pressure Pf is about 6 MPa, the differential pressure dP of the supply water and the concentrated water is about 0.1 MPa, and the permeated water pressure Pp is about 0.1 MPa. The osmotic pressure dΠ of water is about 2 MPa.

  In the side port connection method in which piping is installed on the side of the pressure vessel and each pressure vessel is connected, the pressure loss due to the piping connecting the pressure vessels (hereinafter referred to as "side port piping") There is a difference of about 0.01 MPa. However, this pressure difference is negligibly small with respect to the absolute value of the supply water pressure Pf. Therefore, from equation (1), the permeate flow rate of each pressure vessel can be considered to be approximately the same.

  On the other hand, the flow rate of the supply water to each pressure vessel is determined by the differential pressure between the supply water and the concentrated water of each membrane module and the pressure difference between the pressure vessels by the side port piping. The differential pressure dP between the supply water and concentrated water in each pressure vessel is 0.1 MPa, and the pressure difference between the pressure vessels by the side port piping is about 0.01 MPa, so the pressure difference cannot be ignored with respect to the differential pressure dP. It is so big. Therefore, the supply water flow rate to each pressure vessel often varies by several percent to several tens percent.

  In this way, although the amount of permeate is the same, there is a variation in the flow rate of the supply water, so the recovery rate, which is the ratio between the permeate and the supply water, varies from pressure vessel to pressure vessel, causing the problems described above. It will be.

  Therefore, in this embodiment, the flow rate of the permeated water is controlled. As an index at this time, the ion concentration (conductivity) contained in the concentrated water is used. Thereby, a recovery rate can be made substantially the same in each pressure vessel. Hereinafter, the water treatment system according to the present embodiment will be described with reference to the drawings, taking a seawater desalination system as an example.

<Configuration>
FIG. 1 is a system diagram of a seawater desalination plant P according to this embodiment. The seawater desalination plant P passes through a water intake unit 1A that pumps seawater from the sea, a pretreatment unit 1B that removes particles (foreign matter, etc.) in the pumped seawater and organic substances having a relatively large molecular weight, and a pretreatment unit 1B. 1C for removing mainly ions and the like from the seawater.

  The intake section 1A is for pumping seawater from the sea. The pumped seawater is sent to a pretreatment unit 1B described later. The intake section 1A includes an intake pump 111 that pumps seawater from the sea, and an intake tank 112 that stores the pumped seawater.

  The pretreatment unit 1B removes particles (such as foreign matter) and organic matter having a relatively large molecular weight from the pumped seawater. The seawater from which these have been removed is sent to a desalting unit 1C described later. The pre-processing unit 1B includes a multi-layer filtration module pump 121 that supplies pumped seawater, a multi-layer filtration module 122 that filters the supplied seawater in two or more layers, and a multi-layer filtered seawater that is supplied to the subsequent stage. And an outer filtration membrane module pump 123. Furthermore, the pretreatment unit 1B includes an ultrafiltration membrane module 124 that filters the seawater after the multi-layer filtration with an ultrafiltration membrane, and a desalting salt that stores the pretreated seawater that has passed through the ultrafiltration membrane module 124. Part supply water tank 125.

  The desalting unit 1C removes ions (sodium ions, magnesium ions, chloride ions, etc.) from the seawater that has been treated in the pretreatment unit 1B. Fresh water is obtained by processing the pumped seawater in the desalination unit 1C. The desalination unit 1C includes a high-pressure pump 131 that supplies the pretreated seawater (feed water w1) to the reverse osmosis unit U1 (the specific structure will be described later with reference to FIG. 2) at a high pressure, and the pretreatment A reverse osmosis unit U1 having a plurality of reverse osmosis membrane modules (membrane modules) for reverse osmosis and desalination of later high-pressure seawater, and a permeate for storing permeate w2 having a reduced ion concentration through the reverse osmosis unit U1. And a water tank 135. In addition, the desalting unit 1C recovers the energy of the concentrated water tank 134 that stores the concentrated water w3 that does not pass through the reverse osmosis unit U1 and the ion concentration has increased, and the concentrated water that flows into the concentrated water tank 134 and reverses the energy. And a power recovery device 133 that uses energy for boosting the supply water w1 to the infiltration unit U1.

  FIG. 2 is a diagram showing an internal structure of the reverse osmosis unit U1 provided in the seawater desalination plant P according to the present embodiment. In FIG. 2, for convenience of illustration, the thickness and size of the members are modified and shown without departing from the gist of the present invention. The reverse osmosis unit U1 shown in FIG. 2 includes so-called side port type pressure vessels 21a, 21b, and 21c (21) in which the supply water w1 is supplied from a port provided on the side surface of the pressure vessel. It is.

  Seawater processed in the pretreatment unit 1B (see FIG. 1) flows through the supply water pipe 29 as supply water w1 and is supplied to the pressure vessel 21a of the reverse osmosis unit U1. Then, a part of the supplied supply water w1 (supply water w1a) flows through the pressure vessel 21a, and the permeated water (fresh water) w2a and the concentrated water (the remaining supply water; that is, without membrane treatment) The remaining feed water, which is water containing concentrated ions, is separated into w3a. Further, the remaining portion of the supply water w1a flows through the supply water side port pipe 21h (supply water pipe) and is supplied to the pressure vessels 21b and 21c. In each of the pressure vessels 21b and 21c, the permeated water is also supplied. Separated into w2b and w2c and concentrated water w3b and w3c.

  That is, in summary, the supply water side port pipe 21h and the supply water pipe 29 are provided with a plurality of pressure vessels 21 containing the reverse osmosis membrane module 22, and are accommodated in each of the plurality of pressure vessels 21. In addition, the pressure vessel 21 is connected in parallel so that the water to be filtered is supplied to the reverse osmosis membrane module 22.

  In the present embodiment, the pressure vessels 21a, 21b, and 21c include the same members and have the same performance. Therefore, in the following description, the pressure vessel 21 will be mainly described by taking the pressure vessel 21a as an example.

  The pressure vessel 21a includes a substantially cylindrical reverse osmosis membrane module 22a (22) (membrane module) for water filtration, and a water collecting pipe 23a (23) (permeated water) formed in the reverse osmosis membrane module 22a. Piping) is housed and provided. The supply water w1 supplied to the pressure vessel 21a is first supplied to the reverse osmosis membrane module 22a. In the reverse osmosis membrane module 22a, seawater as the supply water w1a is subjected to membrane treatment and desalted, and the obtained fresh water as the permeated water w2a flows through the water collection pipe 23a and is discharged from the pressure vessels 21b and 21c. The permeated water w2b and w2c are combined with the permeated water pipe 24 and discharged to the outside as permeated water w2. That is, the water collection pipe 23 and the permeated water pipe 24 discharge the permeated water obtained by filtration in the reverse credit membrane module 22a.

  On the other hand, the ions in the supply water w1a supplied to the reverse osmosis membrane module 22a are concentrated as the permeated water w2a is generated. Then, the concentrated ion-containing water (concentrated water w3a) is used as the concentrated water w3 together with the concentrated water w3b and w3c discharged from the pressure vessels 21b and 21c as the concentrated water side port pipe 28a and the concentrated water pipe 28b. It is discharged to the outside through.

  Although description is omitted in the present specification, as described above, the pressure vessels 21b and 21c have the same configuration as the pressure vessel 21a. However, in the present embodiment, a conductivity sensor 26a (26) (first measuring means) that measures the ion concentration in the concentrated water discharged from the pressure vessel 21a is provided. That is, the conductivity sensor 26a measures the conductivity of the remaining portion of the supply water (that is, the concentrated water w3a) discharged from the most upstream pressure vessel 21a among the plurality of pressure vessels 21 provided, and based on the measured conductivity. To measure the ion concentration.

  The conductivity sensor 26a is fixed to the side surface of the pressure vessel 21a by an attachment jig 28c so as to face the opening of the concentrated water side port pipe 28a. Thereby, it can attach easily to the pressure vessel 21a, without performing a special process.

  Moreover, the electrical conductivity sensor 26b (2nd measurement means) which measures the ion concentration in the concentrated water w3 discharged | emitted from each of the pressure vessels 21a, 21b, and 21c and joined is provided. Specifically, a conductivity sensor 26b (26) is provided in the middle of the concentrated water pipe 28b. In other words, the conductivity sensor 26b measures the conductivity of the remaining supply water (concentrated water w3) obtained by joining the remaining supply water (concentrated water w3a, w3b, w3c) discharged from each of the plurality of pressure vessels 21. The ion concentration is measured based on the measured conductivity.

  Further, a flow rate adjusting valve 25a (25) for controlling the flow rate for controlling the flow rate of the permeated water flowing through the water collecting pipe 23a is located downstream of the water collecting pipe 23a and before joining the permeated water pipe 24. (Flow rate adjusting means) is provided. Further, a flow rate adjusting valve 25b (25) (flow rate adjusting means) is provided downstream of the water collecting pipe 23b, and a flow rate adjusting valve 25c (25) (flow rate adjusting means) is provided downstream of the water collecting pipe 23c. These flow rate adjusting valves 25a are controlled according to the conductivity (that is, the ion concentration) measured by the conductivity sensors 26a and 26b. A specific control method will be described later in <Operation>.

  In summary, the flow rate adjusting valve 25 is provided in the permeated water pipe (the water collecting pipe 23 in the present embodiment), and is discharged without being filtered out of the supply water supplied to the pressure vessel 21. Further, the flow rate of the permeated water flowing through the permeated water pipe (the water collecting pipe 23 in the present embodiment), which is controlled based on the ion concentration of the remaining portion of the supplied water (that is, the concentrated water), is controlled.

  The flow rate adjustment valve 25 is controlled by the arithmetic control unit 50. That is, the arithmetic control unit 50 measures the ion concentration via the conductivity measured by the conductivity sensor 26a and the conductivity sensor 26b, and controls the flow rate adjustment valve 25 based on the measured ion concentration. is there.

  Although not shown, the arithmetic control unit 50 includes a central processing unit (CPU), a random access memory (RAM), a read only memory (ROM), and a hard disk drive (HDD). The arithmetic control unit 50 is connected to the flow rate adjustment valve 25 and the conductivity sensor 26.

<Action>
Next, a method for controlling the flow rate adjusting valves 25a, 25b, and 25c in the reverse osmosis unit U1 described with reference to FIG. 2 will be described.

  In the present embodiment, the arithmetic control unit 50 determines the permeate flow rate based on the conductivity measured by the conductivity sensor 26, and the flow rate adjustment valve 25 is controlled so as to be the flow rate. By controlling the flow rate adjusting valve 25 in this way, the recovery rate in each pressure vessel 21 can be easily controlled to the same level, and variation in the recovery rate for each pressure vessel 21 can be suppressed.

  Note that the ion concentration and the electrical conductivity are in a proportional relationship. Accordingly, the ion concentration can be calculated based on the conductivity. Therefore, “determining the permeate flow rate based on conductivity” can also be read as “determining the permeate flow rate based on ion concentration”. The same applies hereinafter.

  First, derivation of the relational expression between the ion concentration and the system recovery rate will be described.

Let Qf be the flow rate of the supply water w1 supplied to the reverse osmosis unit U1, Qp be the flow rate of the permeate water w2 discharged from the reverse osmosis unit U1, and Qb be the flow rate of the concentrated water w3 discharged from the reverse osmosis unit U1. Further, the ion concentration in the supply water w1 is Cf, the ion concentration in the permeated water w2 is Cp, and the ion concentration in the concentrated water w3 is Cb. Then, in the reverse osmosis unit U1, the flow rate and the ion mass flow rate (the product of the ion concentration and the flow rate) are stored on the supply side and the discharge side, so the following equations (2) and (3) are established. .

From the equation (3), the ion concentration Cb of the concentrated water w3 is represented by the following equation (4).

Here, the ion concentration Cp of the permeated water w2 is sufficiently smaller than the ion concentration Cf of the supply water w1. Therefore, the equation (4) can be approximated as the following equation (5).

On the other hand, assuming that the system recovery rate is R, since R = Qp / Qf, the following formula (6) is obtained in consideration of the above formula (2).

Therefore, the ion concentration Cb about the concentrated water w3 is represented by the following formula | equation (7) by said Formula (3) and Formula (6).

Then, the system recovery rate R is expressed by the following formula (8) by modifying the formula (7).

  As shown in Expression (8), it can be seen that the system recovery rate R is determined by the ion concentration Cf of the supply water w1 and the ion concentration Cb of the concentrated water w3 regardless of the number of pressure vessels 21. Further, the above derivation relates to the relationship between the system recovery rate R and the ion concentration, but the formula (8) can also be applied to the recovery rate in each pressure vessel 21.

  In each pressure vessel 21, the supply waters w1a, w1b, and w1c (that is, the supply water w1) having the same ion concentration are supplied, so that they are constant. Accordingly, when the ion concentrations of the concentrated waters w3a, w3b, and w3c discharged from the pressure vessels 21a, 21b, and 21c are equal, the recovery rates in the pressure vessels 21a, 21b, and 21c are approximately the same. Here, the concentrated water w3a, w3b, and w3c join together and are discharged to the outside as the concentrated water w3. Therefore, if the ionic concentrations of the concentrated water w3a, w3b, and w3c are equal, the ionic concentration of the concentrated water w3 discharged to the outside is also equal to these. That is, the recovery rate of each pressure vessel 21 is comparable when the ion concentration of the concentrated water w3 discharged to the outside is equal to, for example, the ion concentration of the concentrated water w3a.

  In other words, if the conductivity of the concentrated water w3a measured by the conductivity sensor 26a and the conductivity in the concentrated water w3 measured by the conductivity sensor 26b are approximately the same, the pressure vessels 21a, 21b, It can be considered that the recovery rate at 21c is comparable. At this time, the system recovery rate can be considered to be the same as the recovery rates of the pressure vessels 21a, 21b, and 21c. According to this knowledge, even when the system recovery rate is arbitrarily changed, the recovery rate of each pressure vessel 21a, 21b, 21c can be maintained at the same level by following the change.

  As described above, since the conductivity of water is proportional to the ion concentration, the ion concentration can be indirectly measured by measuring the conductivity. Therefore, instead of actually calculating the recovery rates in the pressure vessels 21a, 21b, and 21c, if only the difference in the recovery rates is determined as in the present embodiment, the ion concentrations Cf, Cp, and Cb are replaced. Thus, the conductivity can be used as it is. Therefore, in this embodiment, each pressure vessel 21a, 21b, 21c is controlled by controlling the flow rate adjusting valves 25a, 25b, 25c so that the measured value of the conductivity sensor 26a is equal to the measured value of the conductivity sensor 26b. The recovery rate can be made comparable.

  The flow rate adjusting valves 25a, 25b, and 25c may be adjusted in any way. For example, when the conductivity measured by the conductivity sensor 26a is larger than the conductivity measured by the conductivity sensor 26b, it can be considered that the ion concentration of the concentrated water w3a discharged from the pressure vessel 21a is high. Therefore, in such a case, the flow rate of the permeated water w2b, w2c is increased by increasing the opening degree of the flow rate adjusting valves 25b, 25c. Thereby, the water content contained in the concentrated water w3b and w3c can be decreased, respectively, and the ion concentration of the concentrated water w3b and w3c can be increased. As a result, the conductivity measured by the conductivity sensor 26b can be increased, and the conductivity measured by the conductivity sensor 26b can be made comparable to the conductivity measured by the conductivity sensor 26a. .

  On the other hand, when the conductivity measured by the conductivity sensor 26a is smaller than the conductivity measured by the conductivity sensor 26b, it can be considered that the ion concentration of the concentrated water w3a discharged from the pressure vessel 21a is low. . Therefore, in such a case, the flow rate of the permeated water w2a is increased by increasing the opening degree of the flow rate adjustment valve 25a. Thereby, the water content contained in the concentrated water w3a can be reduced, and the ion concentration of the concentrated water w3a can be increased. As a result, the conductivity measured by the conductivity sensor 26a can be increased, and the conductivity measured by the conductivity sensor 26a can be made comparable to the conductivity measured by the conductivity sensor 26b. .

  The opening degree of the flow rate adjusting valves 25a, 25b, and 25c may be set based on, for example, a graph or a table that can be determined by a trial operation or the like, or may be a value calculated based on design values such as piping and supply water. May be based on. Further, the opening degree of the flow rate adjusting valves 25a, 25b, and 25c may be gradually adjusted while monitoring the conductivity values measured by the conductivity sensors 26a and 26b.

<Effect>
According to the water treatment system according to the present embodiment, it is possible to provide a water treatment system capable of easily controlling the recovery rate in each pressure vessel to the same extent. This point will be described more specifically with reference to FIG. 3 obtained by the study of the present inventors.

  FIG. 3 is a graph showing (a) flow rate, (b) concentrated water ion concentration, and (c) recovery rate in each pressure vessel in the reverse osmosis unit provided in the seawater desalination plant according to the present embodiment. In FIG. 3, the black symbols are the results before the flow rate adjustment, and the white symbols are the results after the flow rate adjustment. The flow rate is controlled in the reverse osmosis unit U1 shown in FIG. 2 so that the conductivity measured by the conductivity sensor 26a and the conductivity measured by the conductivity sensor 26b are approximately the same.

  As shown by the black symbols in FIG. 3 (a), before the permeate flow rate adjustment, as described above, the supply water w1a in each pressure vessel 23a, 23b, 23c due to the pressure loss in the side port pipe 21h, etc. The flow rates of w1b and w1c are not the same, and there are variations (see (3) in FIG. 3 (a)). Similarly, the flow rates of the concentrated waters w3a, w3b, and w3c in the pressure vessels 23a, 23b, and 23c do not become the same level, and there are variations (see ▲ in FIG. 3 (a)). However, as described above, unless the permeate flow rate is particularly adjusted, the flow rates of the permeate water w2a, w2b, and w2c in the pressure vessels 23a, 23b, and 23c are approximately the same (see ◆ in FIG. 3A). .

  Further, as indicated by the black symbols in FIG. 3B, the ion concentrations of the concentrated waters w3a, w3b, and w3c are also different in the pressure vessels 21a, 21b, and 21c (FIG. 3B). (See ■). Further, as described above, since the flow rates of the supply waters w1a, w1b, and w1c are not the same, as shown by the black symbols in FIG. 3 (c), the recovery rate is also the pressure vessels 21a, 21b. , 21c (see (3) in FIG. 3C).

  On the other hand, as shown by the white symbols in FIG. 3A, the flow rates of the permeated waters w2a, w2b, and w2c, which are comparable, are measured by the conductivity sensor 26a and the conductivity. Control is performed so that the conductivity measured by the sensor 26b is approximately the same (see ◇ in FIG. 3A). As a result, the ion concentration is comparable (see □ in FIG. 3B) and the recovery rate is comparable (see □ in FIG. 3C).

  Thus, the recovery rate is controlled by controlling the permeate flow rate so that the conductivity of the concentrated water w3a from the pressure vessel 21a and the conductivity of the concentrated water w3 discharged from the reverse osmosis unit U1 are approximately the same. Can be made comparable in each pressure vessel 21a, 21b, 21c. Thereby, the dispersion | variation in the recovery rate in each pressure vessel 21a, 21b, 21c mainly resulting from the side port piping 21h can be corrected.

  And if dispersion | variation in the recovery rate of each pressure vessel 21 can be suppressed irrespective of a system recovery rate, a system recovery rate can be arbitrarily set with the same piping structure. This enables flexible operation of the water treatment plant such that the system recovery rate can be changed according to changes in water temperature, supply water concentration, membrane permeation performance, and the like.

  Moreover, in this embodiment, the flow volume adjustment valve 25 is provided in the middle of the water collection pipe | tube 23 which is a flow path of the permeated water w2a, w2b, w2c. Since the concentration of ions contained in the permeated water w2a, w2b, and w2c is low, the material of the flow rate adjustment valve 25 does not necessarily require high corrosion resistance. Therefore, it is not necessary to provide a flow rate adjusting valve having high corrosion resistance, and providing a normal flow rate adjusting valve can improve the reliability and maintainability of the water treatment system.

<Modification>
As mentioned above, although the form for implementing the water treatment system which concerns on this embodiment was demonstrated, this embodiment is not limited to the said example at all. Some examples will be described below, but the same components as those described above will be described with the same reference numerals.

  For example, the reverse osmosis unit provided in the seawater desalination system P as the water treatment system according to the present embodiment is not limited to the structure shown in FIG. 2, and may be a reverse osmosis unit U2 as shown in FIG. 4, for example. .

  FIG. 4 is a modification of the reverse osmosis unit provided in the seawater desalination plant according to the present embodiment. As shown in FIG. 2, when the conductivity sensor 26 is provided, the conductivity can be constantly measured, so that the flow control valve 25 can be appropriately adjusted when desired. However, normally, the control frequency of the flow control valve 25 is low. Therefore, the conductivity sensor 26 is not provided, and the conductivity may be appropriately measured when controlling the flow rate of the permeated water w2a, w2b, w2c.

  Specifically, the reverse osmosis unit U2 shown in FIG. 4 replaces the conductivity sensors 26a and 26b in the reverse osmosis unit U1 shown in FIG. One intake port) and an intake port 27b (27) (second intake port) capable of taking concentrated water w3 are provided. That is, in the reverse osmosis unit U2, a water intake 27a capable of taking the remaining portion of the supply water (concentrated water w3a) discharged from the most upstream pressure vessel 21a among the plurality of pressure vessels 21 provided, and a plurality of pressures And a water intake 27b capable of taking outside the feed water remaining portion (concentrated water w3) obtained by joining the feed water remaining portions (concentrated water w3a, w3b, w3c) discharged from each of the containers 21. . Since the diameters of the water intakes 27a and 27b are very small and the amounts of water taken from the water intakes 27a and 27b are very small, the amounts of water taken such as the concentrated water w3a and the concentrated water w3 do not affect the recovery rate.

  In the reverse osmosis unit U2 shown in FIG. 4, the conductivity of the concentrated water w3a and the conductivity of the concentrated water w3 are measured externally after the concentrated water w3a and w3 are taken through the intake ports 27a and 27b. It has become. Thereby, installation of a conductivity sensor can be omitted and equipment costs can be reduced. Moreover, since it is not necessary to always keep the conductivity sensor in contact with the concentrated water w3a and w3 having a high salt concentration, the durability of the conductivity sensor can be improved.

  In addition, instead of the reverse osmosis unit U1 shown in FIG. 2, a reverse osmosis unit U3 shown in FIG. 5 may be used.

  Drawing 5 is a figure showing the modification of the reverse osmosis unit with which the seawater desalination plant concerning this embodiment is equipped, (a) front view, (b) side view, and (c) back view. In FIG. 5, a part of the members is omitted for simplification of illustration.

  As shown in FIG. 5A, the reverse osmosis unit U3 includes pressure vessel groups 31a, 31b, 31c (31) in which three pressure vessels 21 are connected in parallel. Among these, the pressure vessel group 31a is constituted by pressure vessels 21a, 21b, 21c, the pressure vessel group 31b is constituted by pressure vessels 21d, 21e, 21f, and the pressure vessel group 31c is constituted by pressure vessels 21g, 21h, 21i. That is, in the reverse osmosis unit U3, among the pressure vessels 21 provided, a plurality of pressure vessels 21 are connected in parallel by a feed water pipe (a feed water side port pipe 21h in the present embodiment), and a pressure vessel group is provided. 31a, 31b, and 31c are configured, and a plurality of pressure vessel groups 31 (three in this embodiment) are provided.

  These pressure vessel groups 31 are connected in parallel to the feed water header pipe 32 (feed water pipe) through which the feed water w1 flows. Specifically, the pressure vessel group 31a is connected to the feed water header pipe 32 via the feed water pipe 29a. The pressure vessel group 31b is connected to the feed water header pipe 32 through the feed water pipe 29b. Further, the pressure vessel group 31c is connected to the feed water header pipe 32 via the feed water pipe 29c.

  Further, as shown in FIGS. 5B and 5C, the concentrated water header pipe is formed so that the concentrated water from the pressure vessel groups 31a, 31b, 31c can be merged in the concentrated water header pipe 33. 33 is connected. Further, the pressure vessels 21a to 21i are connected to the permeate header pipe 34 (permeate through the permeate pipes 24a, 24b and 24c (24) through which the permeate discharged from the pressure vessels 21a to 21i flows. Connected to the water pipe).

  However, unlike the supply water w <b> 1 side branched in each pressure vessel group 31, the permeated water pipe 24 is connected across each pressure vessel group 31. Specifically, for example, the pressure vessels 21a, 21d, and 21g are connected to the permeated water pipe 24a, and the permeated water discharged from these pressure vessels 21a, 21d, and 21g is merged to form a permeated water header tube 34. To be supplied.

In summary, the number of pressure vessels 21 constituting each of the plurality of pressure vessel groups 31 is the same (three in this embodiment), and the permeation of the pressure vessels 21 constituting the adjacent pressure vessel groups 31 is performed. On the water discharge side, adjacent pressure vessels 21 (for example, pressure vessels 21g, 21d, 21a) are connected by a permeated water pipe 24a across a plurality of pressure vessel groups 31.
The same applies to the other pressure vessels 21.

  A flow rate adjusting valve 25 that controls the flow rate of the permeated water flowing through each permeate water pipe 24 is provided downstream of the permeate water pipe 24 and immediately before joining the permeate water pipe 34. ing. That is, the permeated water pipe 24 that connects adjacent pressure vessels 21 is provided with a flow rate adjusting valve 25. In this embodiment, since the permeated water piping 24 is connected to each of the three pressure vessels 21 constituting the pressure vessel group 31, three flow rate adjustment valves 25 are also provided.

  Regarding the supply water w1 side, the inner diameter of the supply water header pipe 32 is large and the pressure loss is sufficiently small. Therefore, it can be considered that the flow states (pressure loss, flow rate, etc.) are the same in the pressure vessel groups 31a, 31b, 31c. That is, for example, in FIG. 5A, the pressure loss when supply water is supplied from the pressure vessel 21g constituting the pressure vessel group 31c to the pressure vessel 21h, and the pressure vessel 21d constituting the pressure vessel group 31b to the pressure vessel The pressure loss when the supply water is supplied to 21e can be considered to be the same level.

  Then, for example, the conductivity of the concentrated water discharged from the pressure vessel 21g arranged in the uppermost stream of the pressure vessel group 31c and the concentrated water discharged from the pressure vessel 21a arranged in the uppermost stream of the pressure vessel group 31a. It can be considered that the conductivity is comparable. Further, for example, it can be considered that the flow rate of the permeated water discharged from the pressure vessel 21g and the flow rate of the permeated water discharged from the pressure vessel 21a are approximately the same.

  Therefore, similarly to the reverse osmosis unit U1, the reverse osmosis unit U3 is adjusted by adjusting the flow rate adjustment valves 25a, 25b, 25c so that the measured values of the conductivity sensors 26a, 26b installed in the pressure vessel group 31a are equal. The recovery rates of the nine pressure vessels 21 provided in the can be made comparable. Furthermore, since it is not necessary to provide the flow rate adjusting valve 25 in all nine pressure vessels 21, the equipment cost can be reduced and the durability of the reverse osmosis unit U3 can be improved. Further, since only three flow rate adjusting valves 25 are required, control becomes easy.

  In addition to the modifications shown in FIGS. 4 and 5, for example, the following modifications may be mentioned.

  For example, in the reverse osmosis unit U1 of FIG. 2, the flow rate control is performed for each of the permeated waters w2a, w2b, and w2c discharged from the three pressure vessels 21a, 21b, and 21c. Only w2c may be controlled. Specifically, the flow rate adjustment valves 25b and 25c may be controlled based on the conductivity measured by the conductivity sensors 26a and 26b without providing the flow rate adjustment valve 25a shown in FIG. That is, the recovery rates in the pressure vessels 21b and 21c may be controlled so as to match the recovery rates in the pressure vessel 21a. If the flow rate adjusting valve 25a is not provided, the water pressure of the permeated water w3a is reduced. Therefore, the portion of the water collecting pipe 23a that connects the membrane module 22a and the permeated water pipe 24 is made of a resin material such as vinyl chloride. be able to. Thereby, equipment costs can be reduced.

  Further, the supply water side port pipe 21h and the concentrated water side port pipe 28a may have the same diameter regardless of the position, or may have different diameters depending on the position where they are arranged. When all the side port pipes have the same shape, there is an advantage that the cost for construction is small because the labor of parts management is small. Furthermore, when the diameter of the side port pipe is unified to a small diameter, there is an advantage that the quantity cost of the pipe is small.

  In the illustrated example, as the form of the pressure vessel 21, a side port type pressure vessel that supplies the supply water w1 from the side surface side of the pressure vessel 21 is illustrated, but an end port type that supplies from the axial direction of the pressure vessel is illustrated. It may be a pressure vessel. However, in the side port type pressure vessel, as described above, the pressure loss tends to increase in the supply water side port piping 21h for connecting the pressure vessels 21 to each other. Therefore, a side port type pressure vessel is suitable for the water treatment system of the present embodiment.

  Furthermore, in the above-described embodiment, the flow rate adjustment valve 25 is controlled by the arithmetic control unit 50, but may be controlled manually.

  Moreover, in this embodiment, although the valve was used as the flow rate control means of the permeated water w2a, w2b, w2c, the flow rate control means of the permeated water w2a, w2b, w2c is not limited to the valve at all. It may be used.

  Furthermore, in this embodiment, the ion concentration is measured based on the conductivity measured by the conductivity sensor as a method for measuring the ion concentration. However, an ion concentration meter that can directly measure the ion concentration may be used. .

  Moreover, in the seawater desalination plant shown in FIG. 1, means other than the reverse osmosis unit U1 are arbitrary and may be configured in any manner.

  Furthermore, in the said embodiment, although the seawater desalination system which desalinates seawater and obtains drinking water, industrial water, etc. was illustrated as a specific example of a water treatment system, a water treatment system is not limited to this. Absent. That is, the water treatment system according to the present embodiment includes, for example, a drinking water treatment plant for obtaining drinking water, a sewage treatment plant for purifying sewage sewage, an industrial wastewater treatment plant for treating industrial wastewater so as to suit the environment, and the like. It can be applied to various water treatment systems using membrane modules.

  The present invention is not limited to the embodiments described above, and includes various modifications. For example, the above-described embodiments have been described in detail for easy understanding of the present invention, and are not necessarily limited to those having all the configurations described. Further, a part of the configuration of one embodiment can be replaced with the configuration of another embodiment, and the configuration of another embodiment can be added to the configuration of one embodiment. Further, it is possible to add, delete, and replace other configurations for a part of the configuration of each embodiment.

21, 21a, 21b, 21c Pressure vessel 21h Side port piping for supply water (pipe for supply water)
22, 22a, 22b, 22c Reverse osmosis membrane module (membrane module)
23, 23a, 23b, 23c Water collection pipe (pipe for permeate)
24 Permeated water piping 25, 25a, 25b, 25c Flow rate adjusting valve (flow rate adjusting means)
26, 26a, 26b Conductivity sensor (first measuring means, second measuring means)
27, 27a, 27b Water intake (first water intake, second water intake)
28a Concentrated water side port piping 28b Concentrated water piping 29, 29a, 29b, 29c Supply water piping 31, 31a, 31b, 31c Pressure vessel group 34 Permeated water header tube (permeated water piping)
32 Header pipe for feed water (pipe for feed water)
50 Arithmetic Control Unit P Seawater Desalination Plant U1 Reverse Osmosis Unit U2 Reverse Osmosis Unit U3 Reverse Osmosis Unit w1 Supply Water w2 Permeated Water w3 Concentrated Water (Remaining Supply Water)

Claims (5)

A membrane module for water filtration,
A pressure vessel in which the membrane module is accommodated;
A permeate pipe for discharging permeate obtained by filtration in the membrane module;
A plurality of the pressure vessels containing the membrane modules are provided, and the pressure vessels are connected in parallel so that feed water to be filtered is supplied to the membrane modules accommodated in each of the plurality of pressure vessels. Supply water piping,
Flowing through the permeated water pipe, which is provided on the permeated water pipe and is controlled based on the ion concentration of the remaining portion of the feed water that is discharged without being subjected to the filtration treatment among the supplied water supplied to the pressure vessel. And a flow rate adjusting means for controlling the flow rate of the permeated water. First measuring means for measuring an ion concentration of the remaining portion of the supply water discharged from the most upstream pressure vessel among the plurality of pressure vessels provided;
The second measuring means for measuring the ion concentration of the remaining portion of the feed water obtained by joining the remaining portions of the feed water discharged from each of the plurality of pressure vessels, Water treatment system. A first intake port capable of taking outside the supply water remaining discharged from the most upstream pressure vessel of the plurality of pressure vessels provided;
The second water intake port capable of taking water to the outside of the water supply remaining portion obtained by joining the water supply remaining portions discharged from each of the plurality of pressure vessels. The described water treatment system.   The apparatus according to claim 2, further comprising an arithmetic control unit that measures the ion concentration by the first measurement unit and the second measurement unit and controls the flow rate control unit based on the measured ion concentration. Water treatment system. The plurality of pressure vessels are connected in parallel by the supply water pipe to constitute a pressure vessel group, and a plurality of the pressure vessel groups are provided,
The plurality of pressure vessel groups are connected in parallel to another supply water pipe through which the supply water flows,
The number of the pressure vessels constituting each of the plurality of pressure vessel groups is the same. On the permeate discharge side of the pressure vessel constituting the adjacent pressure vessel group, the adjacent pressure vessels are the plurality of pressure vessels. Connected by the permeated water pipe across the pressure vessel group,
The water treatment system according to claim 1 or 2, wherein the flow rate adjusting means is provided in a permeated water pipe connecting the adjacent pressure vessels.

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