WO2016038996A1

WO2016038996A1 - Seawater desalination system

Info

Publication number: WO2016038996A1
Application number: PCT/JP2015/069379
Authority: WO
Inventors: 聡之石井; 吉川　慎一; 浩樹宮川
Original assignee: 株式会社日立製作所
Priority date: 2014-09-11
Filing date: 2015-07-06
Publication date: 2016-03-17
Also published as: JP2016055270A

Abstract

Provided is a seawater desalination system which can sufficiently remove the flocculants together with foreign matter in a simple manner. The system is equipped with: addition devices (not shown) for adding, to seawater, an inorganic flocculant and an organic flocculant which flocculate foreign matter contained in the seawater and render the foreign matter removable; static mixers (2, 3) with which the seawater to which the flocculants were added by the addition devices is stirred and mixed; a flocculate growth device (4) which comprises a meandering pipeline configured of straight pipes (10a) each having a given length and, connected thereto, bent pipes (10b) bent at a given angle and which causes, within the pipeline, flocculates to grow in the seawater that has been stirred and mixed with the flocculants by the static mixers (2,3); a sand filter device (5) in which the flocculates yielded in the flocculate growth device (4) are removed; and a reverse osmosis membrane (7) through which the seawater from which the flocculates have been removed in the sand filter device (5) is passed to obtain fresh water.

Description

Seawater desalination system

The present invention relates to a seawater desalination system.

The technology for desalinating seawater is used on islands that are surrounded by ocean and lack fresh water. In this technique, seawater is dechlorinated using, for example, a reverse osmosis membrane (RO membrane). Thereby, fresh water is obtained. Here, the seawater usually contains foreign matters such as dust and dirt. Therefore, from the viewpoint of preventing clogging due to fouling in the reverse osmosis membrane, foreign matters in the seawater are often removed before the seawater is supplied to the reverse osmosis membrane.

As a technique for removing foreign substances from seawater, a technique is known in which a flocculant is added to seawater and the foreign substances are aggregated and removed together with the flocculant. In relation to such a technique, Patent Document 1 describes an impurity aggregation method for removing impurities such as suspended substances in raw water. Specifically, Patent Document 1 describes the use of two types of flocculant A and flocculant B, and flocculant A controls the flocculant conditions according to the concentration index of the suspended solids in raw water, It is described that the coagulant B controls the coagulation conditions according to a water quality index different from the concentration index of the suspended substance.

JP 2008-264723 A

The flocculant is, for example, an inorganic flocculant or an organic flocculant. However, when these flocculants come into contact with the reverse osmosis membrane, the deterioration of the reverse osmosis membrane may be promoted. Therefore, it is preferable that the added flocculant is sufficiently agglomerated together with the foreign substances and sufficiently removed before the reverse osmosis membrane treatment. Therefore, after adding the flocculant, it is preferable to secure a sufficient time for causing the flocculant to aggregate.

Here, as a form of adding the flocculant to the seawater, the flocculant is added to the seawater stored in the tank, and the flocculant is aggregated in the tank, or the flocculant is added to the seawater flowing through the pipe. There is an in-line method in which aggregation is performed. Among these, an inline method may be adopted from the viewpoint of space saving of installation area and reduction of equipment cost.

However, in the in-line method, depending on various conditions such as the length and thickness of the pipe and the flow rate of seawater, it may not be possible to secure sufficient residence time after the flocculant is added. As a result, the flocculant does not aggregate sufficiently, and an excessive amount of the flocculant remains in the seawater. And an unaggregated flocculant may contact a reverse osmosis membrane and a deterioration of a reverse osmosis membrane may be accelerated | stimulated.

Further, in the technique described in Patent Document 1, the aggregation conditions such as the concentration of the flocculant to be added and the stirring speed are controlled in accordance with the concentration index of the suspended matter in the raw water. However, the control of the aggregation conditions is complicated. Accordingly, there is a need for a system that can sufficiently remove the flocculant by a simple method.

The present invention has been made in view of these problems, and the problem to be solved by the present invention is to provide a seawater desalination system capable of sufficiently removing the coagulant together with foreign substances by a simple method.

The present inventors have intensively studied to solve the above problems. As a result, it has been found that the above-mentioned problem can be solved by setting the shape of the pipe through which the seawater to which the flocculant is added flows to a “current pipe” that combines a straight pipe and a curved pipe.

According to the present invention, it is possible to provide a seawater desalination system capable of sufficiently removing the coagulant together with foreign substances by a simple method.

It is a systematic diagram of the seawater desalination system of this embodiment. It is a figure which shows the piping shape of the aggregate growth apparatus with which the seawater desalination system of this embodiment is equipped. It is the shape of the unit piping which comprises the piping of the aggregate growth apparatus with which the seawater desalination system of this embodiment is equipped, (a) is the shape of a straight pipe, (b) is the shape of a curved pipe. It is the 1st modification about the shape of piping which constitutes an aggregate growth device. It is the 2nd modification about the shape of piping which constitutes an aggregate growth device. It is a 3rd modification about the shape of piping which constitutes an aggregate growth device. It is a 4th modification about the shape of piping which constitutes an aggregate growth device. It is a 5th modification about the shape of piping which constitutes an aggregate growth device. It is a 6th modification about the shape of piping which constitutes an aggregate growth device. It is a 7th modification about the shape of piping which constitutes an aggregate growth device. It is an 8th modification about the shape of piping which constitutes an aggregate growth device. It is the shape of piping which comprises the aggregate growth apparatus used by the comparative example 1. FIG. It is the shape of piping which comprises the aggregate growth apparatus used in the comparative example 2.

Hereinafter, embodiments for carrying out the present invention (this embodiment) will be described with reference to the drawings.

FIG. 1 is a system diagram of a seawater desalination system 100 of the present embodiment. In the seawater desalination system 100, foreign substances in the seawater are aggregated and removed by the inorganic flocculant and the organic flocculant added to the seawater. And the seawater after a foreign material was removed is dechlorinated by a reverse osmosis membrane (RO membrane), and fresh water is obtained.

The seawater desalination system 100 includes a pump 1, a static mixer 2, a static mixer 3, an aggregate growth device 4, a sand filtration device 5, a pump 6, and an RO membrane 7. The seawater desalination system 100 includes an inorganic flocculant tank and a supply pump (inorganic flocculant addition device) for supplying the inorganic flocculant to the seawater in the pipe, although none of them is shown. Further, the seawater desalination system 100 is provided with an organic flocculant tank and a supply pump (an organic flocculant adding device) for supplying the organic flocculant to the seawater in the pipe, although none is shown.

The pump 1 is for passing seawater through the pipe. The pump 1 is inverter controlled. In the seawater desalination system 100, the frequency of the inverter is kept constant, so that seawater flows through the pipe at a constant flow rate.

The static mixer 2 is a line mixer that does not include a drive unit. An inorganic flocculant is added to the seawater upstream of the static mixer 2. And in the static mixer 2, seawater and an inorganic flocculant are fully stirred and mixed. The inorganic flocculant used is, for example, iron (III) chloride.

The static mixer 3 is a line mixer that does not include a drive unit, like the static mixer 2. An organic flocculant is added upstream of the static mixer 3 to the seawater (including the inorganic flocculant) stirred and mixed in the static mixer 2. And in the static mixer 3, the said inorganic flocculent, seawater, and an organic flocculant are fully stirred and mixed. Thereby, aggregates, such as a foreign material contained in seawater, begin to arise. The organic flocculant used is, for example, a polycarboxylic acid polymer.

The agglomerate growth apparatus 4 promotes the growth of agglomerates that have started to be generated in the static mixer 3. That is, in the seawater desalination system 100, aggregates grow in-line. Seawater (including agglomerates) treated by the static mixer 3 flows into the agglomerate growth apparatus 4 from the inlet A in FIG. And the seawater containing the aggregate which grew up is discharged | emitted from the outflow port B in FIG.

The agglomerate growth apparatus 4 is configured by connecting a straight pipe having a predetermined length and having no bent portion and a bent pipe bent at a predetermined angle. And the seawater containing a flocculant flows through these piping, The aggregate containing a foreign material will produce | generate. In addition, the produced | generated aggregate is removed in the sand filtration apparatus 5 (after-mentioned) of a back | latter stage. A more specific configuration and the like of the aggregate growth apparatus 4 will be described later with reference to FIGS.

The sand filtration device 5 removes the agglomerates generated in the agglomerate growth device 4 from the seawater. By filtering the seawater containing agglomerates which are solids, the agglomerates remain on the sand and clear seawater is obtained.

The pump 6 is a pump for permeating the clear seawater obtained by the sand filtration device 5 through the RO membrane 7 in the subsequent stage. Moreover, the RO membrane 7 is for dechlorinating seawater to obtain fresh water. The obtained fresh water is used for purposes such as waterworks and waterworks. Moreover, the salt etc. which did not permeate | transmit the RO membrane 7 are discharged | emitted by the ocean etc. as concentrated water.

FIG. 2 is a diagram showing a pipe shape of the aggregate growth apparatus 4 provided in the seawater desalination system 100 of the present embodiment. In FIG. 2, “A” and “B” correspond to “A” and “B” in FIG. As shown in FIG. 2, the aggregate growth mechanism 4 is the same as the straight pipe 10a except that the straight pipe 10a (unit pipe), the curved pipe 10b (unit pipe), and the straight pipe 10a have different arrangement directions. A straight pipe 10c (10a) is connected. That is, in this embodiment, the straight pipe arranged in the horizontal direction is referred to as “straight pipe 10a”. On the other hand, the straight pipe arranged in the vertical direction has the same shape as the straight pipe 10a. For convenience of explanation, this straight pipe is referred to as “straight pipe 10c”.

First, the straight pipe 10a and the curved pipe 10b will be described.
FIG. 3 shows the shape of a unit pipe constituting the pipe of the agglomerate growing apparatus 4 provided in the seawater desalination system 100 of the present embodiment, where (a) shows the shape of the straight pipe 10a and (b) shows the bent pipe 10b. It is the shape. As shown in FIG. 3, the straight pipe 10a is a cylindrical pipe having a predetermined length. The curved pipe 10b is a pipe (elbow) bent at a predetermined angle (90 ° in the present embodiment). By using the curved pipe 10b, the flow direction of the seawater is changed.

Returning to FIG. 2, the aggregate growth apparatus 4 will be described.
In this embodiment, the aggregate growth apparatus 4 includes eight straight pipes 10a arranged in the horizontal direction, one straight pipe 10c arranged in the vertical direction, and fourteen bent pipes 10b connecting them. Are connected. Specifically, in the agglomerate growing apparatus 4, the straight pipe 10a (including the straight pipe 10c) and the curved pipe 10b are connected so that the horizontal flow of seawater changes every predetermined distance. Such a pipe connected so that the flow direction changes every predetermined distance may be referred to as a “current pipe”.

The flow of seawater in the aggregate growth apparatus 4 will be described. In FIG. 2, seawater that flows in from the inlet A first flows horizontally in the right direction on the paper for a predetermined distance (the horizontal length of the first straight pipe 10a). And the flowing seawater changes a flow direction by the two curved pipes 10b, and then flows horizontally in the left direction on the paper. By repeating these operations, the seawater that has flowed through the straight pipe 10a that is the lowest in the vertical direction flows in the vertical direction (upward) by the straight pipe 10c that is arranged in the vertical direction. And the seawater which flowed is discharged | emitted from the outflow port B of the aggregate growth mechanism 4 finally through the straight pipe | tube 10a arrange | positioned in the horizontal direction.

As described above, in the agglomerate growing apparatus 4, flows in different horizontal directions (the right direction on the paper surface and the left direction on the paper surface) are repeated every predetermined distance. That is, the straight pipe 10a is connected so that the flow of seawater reciprocates in the horizontal direction. In order to change the flow direction, the curved pipe 10b is connected at every predetermined distance.

In FIG. 2, the flow pipe is configured so that the flow reciprocates in the left-right direction (horizontal direction), so this pipe is a left-right flow pipe. That is, in FIG. 2, the seawater from the inlet A first flows through the straight pipe 10a in the right direction (forward direction) of the drawing. Next, the flow direction is changed by the two curved pipes 10b, and seawater flows through the second straight pipe 10a in the left direction (return direction) in the drawing. Thus, in FIG. 2, seawater reciprocates in the left-right direction.

Here, near the inner wall of the straight pipe 10a, turbulent flow is likely to occur, and pressure loss occurs not a little. In addition, a large pressure loss occurs in the bent pipe 10b because the flow direction changes and vortices are generated. Therefore, in the aggregate growth apparatus 4, compared with the case where the aggregate growth apparatus 4 is comprised only by the straight pipe 10a, or the case where the aggregate growth apparatus 4 is comprised only by the curved pipe 10b, a big pressure loss will arise. Become.

From the viewpoint of driving energy of the pump 1 (see FIG. 1), it is preferable that the pressure loss in the piping is as small as possible. However, in this embodiment, the agglomerate growing apparatus 4 is designed so that the pressure loss in the piping constituting the agglomerate growing apparatus 4 is increased. The pressure energy lost in the pipe is used for the growth of agglomerates by the aggregating agent. Therefore, the generation of aggregates from seawater is promoted by increasing the pressure loss. As a result, large agglomerates are easily generated even in-line, and the aggregating agent can be sufficiently removed easily. Further, by sufficiently removing the flocculant, it is possible to suppress the unaggregated flocculant from reaching the RO membrane 7 and to suppress the deterioration of the RO membrane 7. Note that the larger the energy used for agglomeration, the better. This point will be described later.

The magnitude of the pressure loss in the aggregate growth apparatus 4 is not particularly limited. However, the magnitude (Hf / T) of pressure loss per unit time (unit residence time) from the first curved pipe 10b in the aggregate growth apparatus 4 to the last curved pipe 10b in the aggregate growth apparatus 4 Is preferably 1 × 10 ⁻² mAq / s or more, preferably 4 × 10 ⁻¹ mAq / s or more, and the upper limit is preferably 9 × 10 ⁻¹ mAq / s or less, 7 × 10 ⁻¹ mAq / s or less is more preferable. When the magnitude of the pressure loss per unit time is in this range, the aggregate removal efficiency can be further increased. Further, fouling to the RO membrane 7 can be sufficiently suppressed.
In addition, the magnitude | size (Hf / T) [mAq / s] of the pressure loss per unit time is computable with the following formula | equation (1).

Hf / T = P / (ρ × g) (1)
However, P represents the work amount per unit time (J) by seawater per unit volume, ρ represents the density of seawater (kg / m ³ ), and g represents the acceleration of gravity (m / s ² ). Further, 1 mAq = 0.1 kgf / cm ² .

In addition, the residence time of the seawater in the pipe from the first curved pipe 10b in the aggregate growing apparatus 4 to the last curved pipe 10b in the aggregate growing apparatus 4 is not particularly limited. However, the residence time of seawater between these is preferably 13 seconds or more, more preferably 14 seconds or more, and the upper limit thereof is preferably 260 seconds or less, more preferably 25 seconds or less. When the residence time is within this range, aggregation can be promoted particularly sufficiently, and the removal efficiency of the aggregate can be further increased.
The “residence time” as used herein refers to a part of the seawater flowing through the pipe, when a part of the seawater flows through the first bent pipe 10b in the agglomerate growing apparatus 4 when the part is focused on. This is the time required to flow to the last curved pipe 10b in the growth apparatus 4.

Further, in the agglomerate growing apparatus 4, the vertical position of the seawater outlet B is higher than the position of the inlet A as shown in FIG. By doing in this way, the potential energy of the outlet B becomes larger than the potential energy of the inlet A. Accordingly, since the potential energy increases in the process from the inlet A to the outlet B, the amount of energy used for aggregation until the outlet B is reduced. Therefore, it is possible to sufficiently suppress the decomposition of the aggregate that may occur due to an excessive amount of energy used for aggregation, and to form a larger aggregate.

In particular, in the aggregate growth apparatus 4 of the present embodiment, in order to increase the position of the outlet B, a pipe 10c that generates a vertical flow is disposed in the vicinity of the outlet B (immediately in the present embodiment). ing. Therefore, there is a vertical flow at the final stage of the aggregate growth, and the sea level rises in the pipe, so that the residence time can be secured, and the aggregate growth is further promoted.

Furthermore, in the

static mixers

2 and 3 and the agglomerate growing apparatus 4, the in-line agglomeration process is performed as described above. Therefore, it is possible to simplify equipment, reduce the installation area, and reduce power by not installing the agglomeration tank. Moreover, since there is no drive part, it is possible to simplify equipment, reduce operating costs, and improve reliability.

The seawater desalination system 100 has been described above with reference to FIGS. 1 to 3, but the seawater desalination system of the present embodiment is not limited to the above example. In particular, the piping configuration of the agglomerate growing apparatus 4 is not limited to the example of FIG. For example, the piping configuration of the agglomerate growing apparatus 4 can be the configurations shown in FIGS.

FIG. 4 is a first modified example of the shape of the pipe constituting the aggregate growth apparatus 4. In the flocculant growth apparatus 4 shown in FIG. 2, the piping is configured to reciprocate the seawater three times, but in the flocculant growth apparatus 4 illustrated in FIG. 4, the piping is configured to reciprocate the seawater two times. Yes. As in FIG. 2, from the viewpoint of increasing the pressure loss as much as possible, it is preferable to perform more reciprocations, but a sufficiently good effect can be obtained even with two reciprocating pipes as shown in FIG. .

FIG. 5 is a second modified example of the shape of the pipe constituting the aggregate growth apparatus 4. In the flocculant growth apparatus 4 shown in FIG. 2, the vertical height of the outlet B is higher than the vertical height of the inlet A, but in the aggregate growth apparatus 4 shown in FIG. 5, These are the same height. As described above, the length of the pipe 10c arranged in the vertical direction is preferably long from the viewpoint of increasing the potential energy as much as possible, but is long enough for the inlet A and the outlet B to be the same height. Even with the straight pipe 10c, a sufficiently good effect can be obtained.

FIG. 6 is a third modified example of the shape of the pipe constituting the aggregate growth apparatus 4. In the flocculant growth apparatus 4 shown in FIG. 2, the vertical height of the outlet B is higher than the vertical height of the inlet A by the straight pipe 10c arranged in the vertical direction. In the aggregate growth apparatus 4 shown in FIG. 6, a plurality of straight pipes 10a arranged in the same vertical plane are connected by a curved pipe 10b. Even in such a connection mode, a sufficiently good effect can be obtained.

FIG. 7 is a fourth modified example of the shape of the pipe constituting the aggregate growth apparatus 4. In the flocculant growth apparatus 4 shown in FIG. 2, the straight pipe 10 a is arranged in the horizontal direction and is a reciprocating flow in the horizontal direction. However, in the flocculant growth apparatus 4 shown in FIG. Is arranged. That is, the up and down flow pipe is configured so that the seawater reciprocates in the up and down direction. Even in such a connection mode, a sufficiently good effect can be obtained.

FIG. 8 is a fifth modified example of the shape of the pipe constituting the aggregate growth apparatus 4. In the flocculant growth apparatus 4 shown in FIG. 2, the straight pipe 10a and the curved pipe 10b are connected in the same vertical plane (including the X axis and the Y axis), but the flocculant growth shown in FIG. In the apparatus 4, the straight pipe 10 a and the curved pipe 10 b are connected in three dimensions in the X direction, the Y direction, and the Z direction. That is, the swirl-like flow pipe is configured so as to reciprocate in the vertical and horizontal directions so that the seawater swirls. Even in such a connection mode, a sufficiently good effect can be obtained.

FIG. 9 is a sixth modified example of the shape of the pipes constituting the aggregate growth apparatus 4. In the flocculant growth apparatus 4 shown in FIG. 2, the straight pipe 10a and the curved pipe 10b are connected so that the reciprocating flow of seawater occurs in the same vertical plane, but the flocculant growth apparatus 4 shown in FIG. Then, the straight pipe 10a and the curved pipe 10b are connected so that the reciprocating flow of seawater occurs in the same horizontal plane (in the plane including the X axis and the Z axis). That is, a flow pipe that runs on the ground is configured so that seawater is parallel to the ground (not shown). Even in such a connection mode, a sufficiently good effect can be obtained.

FIG. 10 is a seventh modified example of the shape of the pipes constituting the aggregate growth apparatus 4. In the flocculant growth apparatus 4 shown in FIG. 2, the reciprocating flow of seawater in the same plane in the vertical direction is performed by connecting the pipes 10a having the same length. However, in the flocculant growth apparatus 4 shown in FIG. 10, the lengths of the straight pipes 10a arranged in the same plane in the vertical direction are different. Specifically, the length of the straight pipe 10a becomes longer as it goes downward in the vertical direction. That is, in this connection form, the length of the straight pipe 10a is non-uniform, and a non-uniform flow pipe is configured. Even in such a connection mode, a sufficiently good effect can be obtained. In particular, since the length of the straight pipe 10a arranged on the lowermost side is the longest, it is possible to generate a sufficient pressure loss and grow to a size of agglomerates that can remove minute agglomerates. .

FIG. 11 shows an eighth modification of the shape of the pipes constituting the aggregate growth apparatus 4. In the flocculant growth apparatus 4 shown in FIG. 2, the piping is configured so that the seawater reciprocates three times. However, in the flocculant growth apparatus 4 illustrated in FIG. 11, the piping is configured so that the seawater reciprocates four times. Yes. Even in such a connection mode, a sufficiently good effect can be obtained.

The modification examples of the aggregate growth apparatus 4 have been described above with reference to FIGS. 4 to 11. However, various modifications are possible in addition to this.

For example, the pipes constituting the agglomerate growing apparatus 4 have the same inner diameter in the above example, but the agglomerate growing apparatus 4 may be configured by combining pipes having different inner diameters. That is, the pipes constituting the agglomerate growing apparatus 4 do not have to have the same inner diameter in all portions, and may include portions having different inner diameters as appropriate.

Furthermore, for example, in this embodiment, two types of flocculants are used, but one type may be used, or three or more types may be used. In addition, although two

static mixers

2 and 3 are provided as stirring and mixing devices, the number may be appropriately increased or decreased depending on the type of the flocculant.

Further, as the stirring and mixing device, a static stirring and mixing device (such as a static mixer) is preferable, but it is not limited thereto. Further, the static stirring and mixing device is not limited to a static mixer, and may be any device.

Furthermore, for example, an agitation device that performs gentle agitation may be provided between the aggregate growth device 4 and the sand filtration device 5. Thereby, the further growth of the aggregate which grew in the aggregate growth mechanism 4 can be aimed at.

Moreover, although the sand filtration device 5 is provided as the aggregate filtration device, for example, a membrane filtration device such as an inexpensive microfiltration membrane or an ultrafiltration membrane may be used.

Hereinafter, the present embodiment will be described with specific examples.

<Example 1>
The seawater desalination system 100 shown in FIG. 1 and the aggregate growth apparatus 4 shown in FIG. 2 were used to remove foreign matter in seawater as aggregates. As the inorganic flocculant, a 4% by mass aqueous solution of iron (III) chloride was used. As an organic flocculant, a 0.2% by mass polycarboxylic acid polymer aqueous solution was used. The linear velocity of seawater flowing through the seawater desalination system 100 was 400 m / 1 day. Moreover, the internal diameter of piping (including piping which comprises the aggregate growth apparatus 4) which comprises the seawater desalination system 100 was 15 mm.

The seawater desalination system 100 was operated under these conditions. As a result, in FIG. 2, the magnitude of the pressure loss per unit time (Hf / T) from the first curved pipe 10b in the aggregate growth apparatus 4 to the last curved pipe 10b in the aggregate growth apparatus 4 The calculated value was 7 × 10 ⁻¹ mAq / s based on the formula (1). Furthermore, the residence time from the first curved pipe 10b in the condensate growing apparatus 4 to the last curved pipe 10b in the aggregate growing apparatus 4 was 14 seconds.

<Example 2>
A seawater desalination system 100 was configured in the same manner as in Example 1 except that the inner diameter was changed to 20 mm. As a result, the pressure loss per unit time was 4 × 10 ⁻¹ mAq / s, and the residence time was 25 seconds.

<Example 3>
A seawater desalination system 100 was configured in the same manner as in Example 1 except that the apparatus shown in FIG. 4 was used as the aggregate growth apparatus 4 and the inner diameter was changed to 25 mm. As a result, the magnitude of the pressure loss per unit time was 7 × 10 ⁻² mAq / s, and the residence time was 14 seconds.

<Example 4>
A seawater desalination system 100 was configured in the same manner as in Example 3 except that the inner diameter was changed to 40 mm. As a result, the pressure loss per unit time was 5 × 10 ⁻² mAq / s, and the residence time was 18 seconds.

<Example 5>
A seawater desalination system 100 was configured in the same manner as in Example 3 except that the inner diameter was changed to 50 mm. As a result, the magnitude of the pressure loss per unit time was 4 × 10 ⁻² mAq / s, and the residence time was 28 seconds.

<Example 6>
A seawater desalination system 100 was configured in the same manner as in Example 3 except that the inner diameter was changed to 60 mm. As a result, the magnitude of the pressure loss per unit time was 2 × 10 ⁻² mAq / s, and the residence time was 40 seconds.

<Example 7>
A seawater desalination system 100 was configured in the same manner as in Example 1 except that the apparatus shown in FIG. 5 was used as the aggregate growth apparatus 4 and the inner diameter was changed to 40 mm. As a result, the magnitude of the pressure loss per unit time was 5 × 10 ⁻² mAq / s, and the residence time was 17 seconds.

<Example 8>
A seawater desalination system 100 was configured in the same manner as in Example 1 except that the apparatus shown in FIG. 6 was used as the aggregate growth apparatus 4 and the inner diameter was changed to 40 mm. As a result, the magnitude of the pressure loss per unit time was 4 × 10 ⁻² mAq / s, and the residence time was 16 seconds.

<Example 9>
A seawater desalination system 100 was configured in the same manner as in Example 1 except that the apparatus shown in FIG. 7 was used as the aggregate growth apparatus 4 and the inner diameter was changed to 20 mm. As a result, the pressure loss per unit time was 4 × 10 ⁻¹ mAq / s, and the residence time was 25 seconds.

<Example 10>
A seawater desalination system 100 was configured in the same manner as in Example 1 except that the apparatus shown in FIG. 8 was used as the aggregate growth apparatus 4 and the inner diameter was changed to 30 mm. As a result, the magnitude of the pressure loss per unit time was 1 × 10 ⁻¹ mAq / s, and the residence time was 32 seconds.

<Example 11>
A seawater desalination system 100 was configured in the same manner as in Example 1 except that the apparatus shown in FIG. 9 was used as the aggregate growth apparatus 4 and the inner diameter was changed to 40 mm. As a result, the pressure loss per unit time was 5 × 10 ⁻² mAq / s, and the residence time was 18 seconds.

<Example 12>
A seawater desalination system 100 was configured in the same manner as in Example 1 except that the apparatus shown in FIG. 10 was used as the aggregate growth apparatus 4 and the inner diameter was changed to 40 mm. As a result, the magnitude of the pressure loss per unit time was 5 × 10 ⁻² mAq / s, and the residence time was 16 seconds.

<Example 13>
A seawater desalination system 100 was configured in the same manner as in Example 3 except that the inner diameter was changed to 90 mm. As a result, the magnitude of the pressure loss per unit time was 1 × 10 ⁻² mAq / s, and the residence time was 260 seconds.

<Example 14>
A seawater desalination system 100 was configured in the same manner as in Example 1 except that the apparatus shown in FIG. 11 was used as the aggregate growth apparatus 4 and the inner diameter was changed to 15 mm. As a result, the magnitude of the pressure loss per unit time was 9 × 10 ⁻¹ mAq / s, and the residence time was 20 seconds.

<Example 15>
A seawater desalination system 100 was configured in the same manner as in Example 3 except that the inner diameter was changed to 20 mm. As a result, the magnitude of the pressure loss per unit time was 5 × 10 ⁻² mAq / s, and the residence time was 13 seconds.

<Comparative Example 1>
A seawater desalination system was configured in the same manner as in Example 1 except that the apparatus shown in FIG. 12 (consisting only of the straight pipe 10a) was used as the aggregate growth apparatus 4 and the inner diameter was changed to 30 mm. As a result, the magnitude of the pressure loss per unit time was 5 × 10 ⁻³ mAq / s, and the residence time was 60 seconds.

<Comparative example 2>
A seawater desalination system was configured in the same manner as in Comparative Example 1 except that the inner diameter was changed to 20 mm. As a result, the magnitude of the pressure loss per unit time was 9 × 10 ⁻³ mAq / s, and the residence time was 300 seconds.

<Comparative Example 3>
A seawater desalination system was configured in the same manner as in Example 1 except that the apparatus shown in FIG. 13 (consisting only of the bent tube 10b) was used as the aggregate growth apparatus 4 and the inner diameter was changed to 40 mm. As a result, the magnitude of the pressure loss per unit time was 1 mAq / s, and the residence time was 25 seconds.

<Comparative example 4>
A seawater desalination system was configured in the same manner as in Comparative Example 3 except that the inner diameter was changed to 20 mm. As a result, the magnitude of the pressure loss per unit time was 3 mAq / s, and the residence time was 18 seconds.

<Performance evaluation method>
In each of the seawater desalination systems of Examples 1 to 15 and Comparative Examples 1 to 4, performance evaluation was performed. The performance evaluation was performed on two points: presence / absence of remaining unaggregated flocculant and foulant removal performance.

The presence / absence of unaggregated flocculant was determined for each of the inorganic flocculant and the organic flocculant. Specifically, first, the metal content and TOC (Total Organic Compound) in seawater before treatment by the seawater desalination system were measured. Furthermore, the metal content and TOC in the obtained fresh water were measured. And about each of metal content and TOC, the value measured by seawater and fresh water was compared, and it evaluated by how much metal content and TOC increased / decreased, respectively.

Also, the foulant removal performance was evaluated by calculating the removal rate of acidic sugar, which is the main factor of foulants to the ROs membrane and the like. Specifically, first, the amount of acidic sugar in seawater before treatment by the seawater desalination system was measured. Further, the amount of acidic sugar in the obtained fresh water was measured. And the value measured by seawater and fresh water was compared, and how much acid sugar decreased was calculated. And when the calculated removal rate (reduction rate) is 90% or more, ◎, when the removal rate is 70% or more and less than 90%, ○, when the removal rate is 50% or more and less than 70%, Δ, removal rate Of less than 50% was evaluated as x.

<Evaluation results>
The results of the two items evaluated are shown in the following Table 1 (Examples 1 to 15) and Table 2 (Comparative Examples 1 to 4) together with the conditions of each seawater desalination system.

As shown in Table 1, in Examples 1 to 15 (Table 1) provided with a flow pipe, the aggregation performance was good. In these Examples 1 to 15, Hf / T was in the range of 1 × 10 ⁻² mAq / s to 90 × 10 ⁻² mAq / s. On the other hand, as shown in Table 2, the flocculant remains only in the straight pipe 10a (Comparative Examples 1 and 2) or the curved pipe 10b (Comparative Examples 3 and 4). The aggregation performance was insufficient. From these facts, by using the agglomerate growing apparatus 4 provided with the flow pipe, the aggregating agent can be sufficiently agglomerated and removed, and the water quality can be improved. Thereby, it was found that the flocculant can be prevented from contacting the RO membrane.

As for the foulant removal performance, good results were obtained in all of Examples 1 to 15 (Table 1) provided with the flow pipe. In particular, when a flow pipe that reciprocates in the horizontal direction is used and the pressure loss per unit time (Hf / T) is 40 × 10 ⁻² mAq / s to 70 × 10 ⁻² mAq / s Especially good performance was shown (Examples 1 and 2). On the other hand, in Comparative Examples 1 to 4 (Table 2) that did not have a flow pipe, the pressure loss per unit time was excessively small or excessively large, and the foulant removal performance was poor. From these things, pressure loss can be made moderate by comprising the agglomerate growth apparatus 4 with a flow pipe, and favorable foulant removal performance is obtained.

Furthermore, it was also found that these results do not depend on the inner diameter of the pipe. That is, when Example 2 and Comparative Example 2 were compared, for example, the inner diameter of the pipe was the same (20 mm), but both the aggregation performance and the foulant removal performance were completely different. Therefore, it is possible to set an arbitrary inner diameter, such as a long diameter when processing seawater with a large flow rate and a short diameter when a small flow rate is sufficient.

2,3 Static mixer
4 Aggregate growth device 5 Sand filtration device (aggregate removal device)
7 RO membrane (reverse osmosis membrane)
10a Horizontal straight pipe 10b Curved pipe 10c Vertical straight pipe 10d Diagonal straight pipe 100 Seawater desalination system A Inlet B Outlet

Claims

In a seawater desalination system that obtains fresh water by passing seawater through a reverse osmosis membrane,
A flocculant addition device that adds a flocculant that aggregates and removes foreign matter in the seawater,
A stirring and mixing device for stirring and mixing the seawater to which the flocculant has been added by the flocculant adding device;
In the stirring and mixing apparatus, the aggregate is grown in-line from the seawater stirred and mixed with the flocculant, and a straight pipe having a predetermined length and a bent pipe bent at a predetermined angle are connected. An agglomerate growth apparatus provided with a flowing pipe;
An agglomerate removing device for removing the agglomerates generated in the agglomerate growing device;
A seawater desalination system comprising: a reverse osmosis membrane that obtains fresh water by transmitting seawater from which aggregates have been removed in the aggregate removal apparatus.
The seawater desalination system according to claim 1, wherein the seawater outlet from the agglomerate growing apparatus is located at a position higher in the vertical direction than the seawater inlet to the agglomerate growing apparatus.
3. The seawater desalination according to claim 1, wherein a straight pipe extending in a vertical direction is disposed in the vicinity of an outlet of seawater among pipes provided in the aggregate growth apparatus. system.
The agglomerate growing apparatus comprises at least two bent tubes,
The pressure loss per unit time from the first curved pipe in the aggregate growth apparatus to the last curved pipe in the aggregate growth apparatus is 1 × 10 −2 mAq / s or more and 9 × 10 −1 mAq. The seawater desalination system according to claim 1 or 2, characterized by being / s or less.
The agglomerate growing apparatus comprises at least two bent tubes,
The residence time of seawater in a pipe from the first curved pipe in the aggregate growing apparatus to the last curved pipe in the aggregate growing apparatus is 13 seconds or more and 260 seconds or less. The seawater desalination system according to 1 or 2.
The aggregate growth apparatus includes at least two straight pipes and at least two bent pipes,
In the aggregate growth apparatus, the at least two straight pipes and the at least two bent pipes are connected so that seawater flows in a reciprocating manner in the horizontal direction to constitute the flow pipe. The seawater desalination system according to claim 1 or 2.