JP2012206073A - Deionized water production system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a deionized water production system, capable of efficiently recovering water as the whole without discharging clear water out of the system.SOLUTION: The system includes: a condensed water return pipe (6) for circulating part of condensed water from a reverse osmosis membrane device (23) to a tank (21); a condensed water discharge pipe (7) for discharging the residue out of the system; a water quality measuring means (11) which measures the quality of condensed water; and circulation amount control means (8, 30) which adjusts, based on a measurement value of the quality of condensed water by the water quality measuring means, the circulation amount of condensed water to the condensed water return pipe and the discharge amount thereof to the condensed water discharge pipe.

Description

  The present invention relates to a deionized water production system using a reverse osmosis membrane device, and more particularly to a technique for improving the recovery rate.

  In a deionized water production system that produces pure water, ultrapure water, or the like, when water is accumulated, the water quality deteriorates due to elution of impurities from constituent members (piping, each water treatment device) and the generation of microorganisms. Therefore, deionized water is produced more than the amount actually used, and surplus water that has not been used may be returned to the previous stage of the deionization production system and circulated. The amount of water to be circulated varies depending on the amount of deionized water used (the amount used at the point of use). If the amount used is large, the amount of circulating water decreases, and if the amount used is small, the amount of circulating water increases. In order to keep the deionized water at a constant water quality, it is necessary to continuously circulate and operate the deionized water production system even when the deionized water is not used.

On the other hand, the applicant has developed a simple ultrapure water production system as shown in Patent Document 1. In the reverse osmosis membrane device (see FIG. 1) as shown in Patent Document 1, although not particularly illustrated, if the concentration of concentrated water becomes too high, a scale component may be generated on the concentrated water side. In general, a concentrated water discharge path for discharging concentrated water out of the system is provided.
In general, the reverse osmosis membrane apparatus is configured in multiple stages so as to treat the concentrated water of the reverse osmosis membrane module in the previous stage as the feed water in the subsequent stage, and the water to be treated is treated in a transient manner.

Japanese Patent No. 4250922

By the way, the deionization production system using the reverse osmosis membrane used in the conventional ultrapure water production system is usually operated so that the recovery rate (= treatment water amount / raw water amount) is constant.
However, if the recovery rate is constant, a large amount of unused deionized water is returned to the tank when the amount used at the point of use is small, so even if the concentrated water is relatively clear. It is discharged out of the system, and as a whole, water is not efficiently recovered, which is not preferable.

  The present invention has been made in order to solve the above-described problems, and the object of the present invention is not to discharge clear water out of the system but to collect and use water efficiently as a whole. It is to provide a deionized water production system.

  In order to achieve the above object, a deionized water production system according to claim 1 includes a pretreatment unit into which raw water is introduced, and a deionized water production unit into which pretreatment water treated in the pretreatment unit is introduced. A deionized water production unit comprising a terminal pipe for feeding deionized water produced in the deionized water production unit to a point of use and returning surplus deionized water to the deionized water production unit. A deionized water production system having a tank into which pretreated water is introduced, and a reverse osmosis membrane device for treating water from the tank, wherein excess deionized water is returned from the terminal pipe to the tank; Concentrated water return pipe for circulating a part of the concentrated water from the reverse osmosis membrane device to the tank, a concentrated water discharge pipe for discharging the remainder out of the system, and water quality measurement for measuring the quality of the concentrated water And a measured value of the water quality of the concentrated water by the water quality measuring means. Characterized in that a circulation quantity control means for adjusting the circulation rate of the concentrated water return pipe of concentrated water and the emission of the the concentrated water discharge pipe based.

  Further, in the deionized water production system according to claim 2, in claim 1, the circulation amount control unit is configured to increase the concentration of the concentrated water by the water quality measurement unit within a range in which no scale component is deposited. The circulation amount to the water return pipe and the discharge amount to the concentrated water discharge pipe are adjusted.

The deionized water production system according to claim 3 is the deionized water production system according to claim 1 or 2, wherein the circulation amount control means includes an automatic valve, and the automatic valve according to a measured value of the quality of the concentrated water by the water quality measurement means. Is controlled to adjust the circulation amount to the concentrated water return pipe and the discharge amount to the concentrated water discharge pipe.
Further, in the deionized water production system according to a fourth aspect, in any one of the first to third aspects, the water quality measuring means measures the conductivity of the concentrated water.

According to the deionized water production system of claim 1, the concentrated water is efficiently recovered by circulating the concentrated water based on the measured value of the quality of the concentrated water by the water quality measuring means and filtered again by the reverse osmosis membrane device. In the case where a large amount of unused deionized water is circulated, the amount of concentrated deionized water that contains a large amount of unused deionized water is reduced and the recovery rate is improved. Can be made.
According to the deionized water production system of the second aspect, it is possible to maintain a high recovery rate within the range of the concentration of the concentrated water in which the scale component does not precipitate in the reverse osmosis membrane apparatus, and the water quality.

According to the deionized water production system of claim 3, the optimum recovery rate is always obtained by controlling the automatic valve according to the fluctuation of the measured value of the concentrated water quality and adjusting the circulation amount and discharge amount of the concentrated water. Can be maintained.
According to the deionized water production system of the fourth aspect, by measuring the conductivity of the concentrated water, it is possible to measure the concentration of the concentrated water and thus the water quality with a simple configuration.

1 is a system diagram of a deionized water production system according to the present invention. It is an example of the systematic diagram of the deionized water manufacturing system which concerns on this invention. 1 is a system diagram of a deionized water production system according to Example 1. FIG. It is a figure which shows transition of the collection | recovery rate in Example 1, and concentrated water electrical conductivity. It is a systematic diagram of the deionized water manufacturing system which concerns on Example 2. FIG. It is a figure which shows transition of the collection | recovery rate in Example 2, and concentrated water electrical conductivity.

Hereinafter, embodiments of a deionized water production system according to the present invention will be described in detail with reference to the drawings.
FIG. 1 shows a system diagram of a deionized water production system according to the present invention.
The deionized water production system shown in FIG. 1 mainly includes a pretreatment unit 1 into which raw water such as city water, industrial water, river water, and well water is introduced, and pretreatment water treated by the pretreatment unit 1 is introduced. Deionized water production unit 2, deionized water produced in deionized water production unit 2 is sent to use point (POU) 4, and terminal pipe 3 for returning surplus water to deionized water production unit 2, deionized A part of the concentrated water (concentrated water of the reverse osmosis membrane device 23) other than the deionized water produced in the water production unit 2 is returned to the deionized water production unit 2 and the remaining concentrated water is discharged out of the system. Concentrated water treatment unit 5.

The pretreatment unit 1 includes, for example, a turbidity device and an activated carbon adsorption device, and thereby pretreatment water is generated.
The deionized water production unit 2 includes, for example, a tank 21, a pump P 1, a safety filter 22, a pump P 2, and a reverse osmosis membrane device 23, so that pretreated water is supplied to the tank 21. The pretreated water is passed through the safety filter 22 by the pump P1, filtered, boosted by the pump P2, and then processed by the reverse osmosis membrane device 23 to obtain deionized water.

The security filter 22 is a filter for the purpose of removing foreign substances. The reverse osmosis membrane device 23 is a membrane filtration device capable of removing ionic species. In the present invention, the reverse osmosis membrane includes those capable of removing ionic species such as a reverse osmosis membrane, a loose RO membrane, and a nanofiltration membrane. . Although there is no restriction | limiting in particular as a shape of a membrane module, A spiral type and a hollow fiber type are preferable. Then, water is passed through the reverse osmosis membrane device 23 in a pressurized state by a cross flow method.
The terminal pipe 3 includes a water supply pipe 31 for supplying deionized water to the use point 4 and a return pipe 32 for returning surplus water to the tank 21, whereby excess water not used at the use point 4 is appropriately removed. It is returned to the tank 21 of the ionized water production unit 2.

  The concentrated water treatment unit 5 includes a concentrated water return pipe 6 that returns a part of the concentrated water to the deionized water production unit 2, a concentrated water discharge pipe 7 that discharges the remainder of the concentrated water to the outside of the system, and a branching device 8. Yes. The concentrated water return pipe 6 is provided with a water quality measuring device (water quality measuring means) 11 for measuring the quality (concentration, etc.) of the concentrated water. As the water quality measuring device 11, a conductivity meter, a TOC meter, a silica meter, an ion concentration meter or the like can be used. However, since the component concentration of the scale component and the conductivity can be considered to be proportional, it is easy to determine by the conductivity. The conductivity meter is preferable in that the water quality can be easily measured. The water quality measuring device 11 is electrically connected to the input side of the controller 30, and the diversion device 8 is electrically connected to the output side of the controller 30 (circulation amount control means).

And in the deionized water manufacturing system based on this invention comprised in this way, while deionized water is manufactured by the deionized water manufacturing part 2 as mentioned above, surplus water is the tank 21 of the deionized water manufacturing part 2. In accordance with the diversion degree of the diversion device 8, a part of the concentrated water other than the deionized water is returned to the tank 21 of the deionized water production unit 2 and the remaining part of the concentrated water is discharged out of the system. Is done.
In this embodiment, the membrane separation water of the reverse osmosis membrane device 23 is sent to the use point 4 as it is, but depending on the required water quality at the use point, the treated water (membrane separation water) of the reverse osmosis membrane device 23 is It is processed by one or more of an electrodeionization apparatus, an ion exchange resin tower, an ultraviolet oxidation apparatus, an ultraviolet sterilization apparatus, a degassing membrane, a reverse osmosis membrane apparatus, or a membrane filtration apparatus having ultrafiltration or microfiltration.

Hereinafter, the circulation amount control of the concentrated water by the controller 30 in the deionized water production system according to the present invention will be described.
First, the relationship between the raw water quality and the quality of the concentrated water according to the recovery rate and the relationship between the water quality measurement items (conductivity, ion concentration, etc.) are determined in advance, and the concentration according to the water quality is within the concentration range where the scale components do not precipitate. Set control values for water circulation and discharge.

Then, the quality of the concentrated water flowing through the concentrated water return pipe 6 is measured by the water quality measuring device 11, and the flow rate of the flow dividing device 8 is adjusted by the controller 30 so that the discharge amount and the circulation amount become the above control values according to the quality of the concentrated water. Variable operation of diversion degree. At this time, the measurement method using the water quality measuring device 11 may be a continuous measurement method, an intermittent measurement method, an online method or a sampling method. However, it is preferable to measure continuously by an on-line method. Further, it is preferable that the flow rate of the concentrated water is maintained at a certain amount or more, and 1.5 m ³ / h / vessel (for example, in the case of an 8-inch RO membrane) or more is secured in the vessel at the end of the concentrated water.

Any method may be used as a method of adjusting the discharge amount of the concentrated water. For example, the flow dividing device 8 may be configured by an adjustment valve, and the valve opening degree may be adjusted. In addition, a plurality of open / close valves may be provided as the diversion device 8 to change the number of open / close valves. In this case, it is preferable to install open / close valves in both the concentrated water return pipe 6 and the concentrated water discharge pipe 7.
As a water quality control method, for example, the opening / closing of the valve may be always controlled so as to maintain the control value of the circulation amount, or the control value of the circulation amount or the water quality measurement item (conductivity, ion concentration, etc.) ), The valve opening is increased so that the flow rate on the concentrated water discharge pipe 7 side increases when the upper limit value is exceeded, and the flow rate on the concentrated water discharge pipe 7 side decreases when the value falls below the lower limit value. The opening of the valve may be reduced so that The lower limit value is preferably set to be about 1 to 20% smaller than the upper limit value.

Except for the concentrated water from the reverse osmosis membrane device 23, it is not preferable that water having a lower quality than the raw water or water having a higher scale component concentration than the raw water flows into the reverse osmosis membrane device 23 as treated water. . When such poor quality water flows into the reverse osmosis membrane device 23, it is preferable to directly measure the scale component and variably operate the diversion degree of the diversion device 8.
In order to stably operate the reverse osmosis membrane device 23, the pH may be adjusted, or a scale inhibitor or a slime control agent may be added separately. Any commercially available scale inhibitor or slime control agent can be used.

Thus, by controlling the flow dividing device 8 so that the discharge amount and the circulation amount become control values, the discharge amount of clear concentrated water containing a large amount of unused deionized water is suppressed, and the reverse osmosis membrane The recovery rate can be increased and the optimum recovery rate can be maintained at all times within the concentration range where the scale component does not precipitate in the apparatus 23 and thus within the water quality range.
As an example of the diversion device 8, as shown in FIG. 2, an automatic valve 9 such as an electromagnetic valve is interposed in the concentrated water return pipe 6, and an automatic valve 10 such as an electromagnetic valve is interposed in the concentrated water discharge pipe 7. Further, the automatic valves 9 and 10 can be electrically connected to the controller 30 or those shown in Examples 1 and 2 to be described later.

[Example 1]
As shown in FIG. 3, a deionized water production system in which an automatic three-way control valve 12 such as an electromagnetic valve is interposed between a concentrated water return pipe 6 and a concentrated water discharge pipe 7 as the flow dividing device 8 in FIG. Prepared. The automatic three-way control valve 12 is electrically connected to the controller 30.

This deionized water production system is configured to obtain treated water and concentrated water using the reverse osmosis membrane in the deionized water production unit 2 using water from which the turbidity has been removed by filtering the industrial water as feed water. ing. Reverse osmosis membrane treated water is sent to the point of use as deionized water. Deionized water that has not been used flows into the tank 21 of the deionized water production unit 2 while fluctuating.
In addition, 3 ppm of Kurita Kogyo Co., Ltd. Krivator EC-503 was injected as a slime control agent before the safety filter.

The operating conditions are as follows, and the water quality is as shown in Table 1.
<Operating conditions>
・ Reverse osmosis membrane: One SUL-G20 8 inch manufactured by Toray Industries, Inc. ・ Amount of treated water: 1 m ³ / h
・ Total concentrated water volume: 4 m ³ / h or more (circulated water volume: 3.3-3.9 m ³ / h, drainage volume: 0.1-0.7 m ³ / h)
・ Recovery rate: 59-91%
・ POU recovered water: irregularly flowing at a maximum of 1 m ³ / h

  Actually, when the total amount of concentrated water is to be controlled by the automatic three-way control valve 12, it is necessary to finely adjust the opening degree of the automatic three-way control valve 12, and this fine adjustment is difficult. Therefore, as shown in FIG. 3, a concentrated water return bypass pipe 6 ′ and a concentrated water discharge bypass pipe 7 ′ are provided upstream of the automatic three-way control valve 12, and a part of the circulating water and the discharged water is branched in advance. The automatic three-way control valve 12 reduces the flow rate to be adjusted. Further, manual valves 13, 14, 15, and 16 are provided in the concentrated water return pipe 6, the concentrated water discharge pipe 7, the concentrated water return bypass pipe 6 ′, and the concentrated water discharge bypass pipe 7 ′, respectively. In this way, the size of the automatic three-way control valve 12 can be reduced, the opening degree can be easily adjusted, and the cost can be reduced.

Then, based on the value measured by the water quality measuring instrument 11, the concentrated water is converted into circulating water and discharged water by PID control using the three-way automatic control valve 12 so that the recovery rate does not cause precipitation of scale components. Distribute.
In other words, the problem in setting the recovery rate is the precipitation of scale components. The recovery rate is set so that scale components are not generated from the raw water quality, and the three-way automatic control valve 12 is set so as to achieve this recovery rate. Control. Here, as the component forming the scale _{Ba, Ca,} Mg, etc. _{SiO 2, SO 4, HCO 3} , CO 3, PO 4, F is considered, the water quality analysis of these components of concentration and temperature, pH and the like in advance The recovery rate is set so that CaCO ₃ , CaSO ₄ , Mg (OH) ₂ , CaPO ₄ , CaF ₂ , BaSO ₄ , SiO _2, etc. do not exceed the solubility product and saturation concentration. Note that the recovery rate may be set using an index such as the Langerian index, or a recovery rate that allows stable operation may be determined separately from a flat membrane test or the like.

Here, one module is loaded into one vessel using an 8-inch reverse osmosis membrane as described above, and the production water volume is set to 1.0 m ³ / h. Therefore, the above-mentioned 1.5 m ³ / h / vessel is used. In order to ensure, the amount of concentrated water will be 1.5 m ³ / h. For example, if the recovery rate is 75%, the amount of discharged water is 0.33 m ³ / h, and 1.17 m ³ / h is circulating water. If this recovery rate can be increased to 90% by measuring the quality of concentrated water, the amount of discharged water will be 0.11 m ³ / h, and the amount of circulating water will be 1.39 m ³ / h.

Therefore, the manual valve 16 of the concentrated water discharge bypass pipe 7 ′ is operated to secure 0.1 m ³ / h as a partial branch flow rate on the discharge side in advance, and the manual valve 15 of the concentrated water return bypass pipe 6 ′ is operated. to advance to ensure 1.0 m ^{3 /} h as partially branched flow of pre-circulation side, the range of the flow rate of the discharge side of 0.1 to 0.2M ^{3 /} h by an automatic three-way control valve 12, the circulation side The flow rate is controlled in the range of 0.3 to 0.39 m ³ / h. In this way, the automatic three-way control valve 12 only needs to pass a maximum of 0.59 m ³ / h. When the concentrated water return bypass pipe 6 ′ and the concentrated water discharge bypass pipe 7 ′ are not provided, a control valve capable of passing 1.5 m ³ / h is required as the automatic three-way control valve 12.

In this way, the concentrated water of the reverse osmosis membrane in the reverse osmosis membrane device 23 was measured by the electrical conductivity, and the automatic three-way control valve 12 was controlled so that the circulating water amount and the drainage amount became control values according to the electrical conductivity. Table 1 shows water quality analysis values when pretreatment water quality, POU recovered water quality, and recovery rate of reverse osmosis membrane device 23 are set. Danger of scale component generation from water quality analysis values in Table 1 The recovery rate having no property was calculated to be 60%, and the conductivity at that time was 47.5 mS / m. Therefore, the set value of conductivity was set to 47.5 mS / m.
Then, PID control was performed by the automatic three-way control valve 12 on the set value of the conductivity of the concentrated water, and the recovery rate was continuously and automatically changed in the range of 59% to 91%.
Fig. 4 shows changes in the recovery rate and concentrated water conductivity during short-term operation. Table 3 shows the amount of treated water and the amount of discharged water after 720 hours.

[Example 2]
As shown in FIG. 5, without using the automatic three-way control valve 12 of the first embodiment, the concentrated water return pipe 6 and the concentrated water discharge pipe 7 are connected to the concentrated water return bypass pipe 6 ″ and the concentrated water discharge bypass pipe 7 respectively. ”, The concentrated water return pipe 6, the concentrated water discharge pipe 7, the concentrated water return bypass pipe 6 ″ and the concentrated water discharge bypass pipe 7 ″ are installed with manual valves 13, 14, 15 and 16, respectively. Automatic valves 9 and 10 such as electromagnetic valves were installed on either the pipe 6 or the concentrated water return bypass pipe 6 "and either the concentrated water discharge pipe 7 or the concentrated water discharge bypass pipe 7". The automatic valves 9 and 10 are electrically connected to the controller 30.

When the control is performed by setting the recovery rate so that the scale component does not precipitate, the measured value of the conductivity of the recovery rate which can be operated efficiently without causing the problem of the precipitation of the scale component is set as the upper limit value. By setting the measured value of conductivity at the set recovery rate as the upper limit, it is possible to prevent the recovery rate from becoming higher and avoid the risk of scale component precipitation. Any value can be used as the lower limit value of the measured value, but if the value is too low, efficient operation cannot be performed. Therefore, the value is preferably 1 to 20% lower than the measured value set as the upper limit value. .
Note that if a recovery rate greater than 98% is set, the concentration rises rapidly, and the risk of scale component formation may increase. Therefore, the recovery rate set value is preferably 98% or less.
As described above, when the recovery rate without the risk of scale component generation was calculated from the water quality analysis values in Table 1, it was 60%, and the conductivity at that time was 47.5 mS / m. Therefore, the upper limit value of the conductivity was set to 45 mS / m, and the lower limit value was set to 40 mS / m.
When the measured value of the conductivity of the concentrated water falls below the lower limit, the automatic valve 9 on the circulation side opens and the automatic valve 10 on the discharge side closes (water passing method 1). Control was performed so that the automatic valve 9 on the circulation side was closed and the automatic valve 10 on the discharge side was opened (water flow method 2). Moreover, the opening degree of the manual valves 13, 14, 15, and 16 was adjusted so that the flow rate was as shown in Table 2, and water flow was performed. The amount of chemicals injected was the same as in Example 1.

Fig. 6 shows changes in the recovery rate and concentrated water conductivity during short-term operation. Table 3 also shows the amount of treated water and the amount of discharged water after 720 hours.
[Comparative Example 1]
The same treatment as in Example 1 was carried out except that the flow rate of the concentrated water was not controlled, and the discharged water amount was fixed at 0.7 m ³ / h and the recovery rate was 59%. The amount of treated water and the amount of discharged water are shown in Table 3 together.

[Comparative Example 2]
The same treatment as in Example 1 was performed except that the circulation amount control of the concentrated water was not performed, the drainage device was fixed at 0.33 m ³ / h, and the recovery rate was 75%. In addition, since the amount of water decreased with water flow, the pressure was increased every 100 hours, and water flow was performed while adjusting the water amount to 1 m ³ / h. Since the pump head reached its limit after 500 hours of water flow, water flow was performed while reducing the water flow rate thereafter. The amount of treated water and the amount of discharged water are shown in Table 3 together.

  Thus, compared with Comparative Examples 1 and 2, in Examples 1 and 2 of the present invention that controls the circulation amount of concentrated water, the amount of waste water is reduced and the recovery rate is improved while preventing the scale components from precipitating. I was able to.

1 Pretreatment Department 2 Deionized Water Production Department 3 Terminal Piping 4 Use Point (POU)
5 Concentrated water treatment section 6 Concentrated water return pipe 6 ', 6 "Concentrated water return bypass pipe 7 Concentrated water discharge pipe 7', 7" Concentrated water discharge bypass pipe 8 Splitting device 9, 10 Automatic valve 11 Water quality measuring instrument 12 Automatic three-way Control valve 13-16 Manual valve 21 Tank 22 Security filter 23 Reverse osmosis membrane device 30 Controller

Claims (4)

A pre-treatment unit into which raw water is introduced, a deionized water production unit into which pre-treatment water treated in the pre-treatment unit is introduced, and deionized water produced in the deionized water production unit is sent to a use point And terminal piping for returning surplus deionized water to the deionized water production unit, the deionized water production unit comprising at least a tank into which pretreated water is introduced, and reverse osmosis for treating water from the tank A deionized water production system in which surplus deionized water is returned to the tank from the terminal pipe,
A concentrated water return pipe for circulating a part of the concentrated water from the reverse osmosis membrane device to the tank, a concentrated water discharge pipe for discharging the remainder out of the system,
Water quality measuring means for measuring the quality of the concentrated water;
A circulation amount control means for adjusting a circulation amount of the concentrated water to the concentrated water return pipe and a discharge amount to the concentrated water discharge pipe based on a measured value of the water quality of the concentrated water by the water quality measurement means;
A deionized water production system comprising:   The circulating amount control means includes a circulating amount to the concentrated water return pipe and a discharged amount to the concentrated water discharge pipe so that the measured value of the concentrated water quality by the water quality measuring means is within a range in which no scale component is deposited. The deionized water production system according to claim 1, wherein the deionized water is adjusted.   The circulation amount control means includes an automatic valve, and controls the automatic valve in accordance with a measured value of the water quality of the concentrated water by the water quality measurement means to return the circulation amount to the concentrated water return pipe and the concentrated water discharge pipe. The deionized water production system according to claim 1 or 2, wherein the amount of discharge is adjusted.   The deionized water production system according to any one of claims 1 to 3, wherein the water quality measuring means measures the conductivity of the concentrated water.

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