JP4973853B2 - Pure water production system - Google Patents

Description

  The present invention relates to a pure water production system including a reverse osmosis membrane module and an electrodeionization device, and in particular, scale failure of the electrodeionization device is suppressed and a predetermined level of pure water is supplied even if the raw water quality fluctuates. It is related with the pure water manufacturing system which can be performed.

  In recent years, in the electronics industry field and research and development field such as a semiconductor manufacturing factory and a liquid crystal manufacturing factory, an electrodeionization apparatus has been established as a means for manufacturing ultrapure water. In this electrodeionization apparatus, the silica concentration of water supplied to the electrodeionization apparatus is limited. If the silica concentration in the water supplied to the electrodeionization device is high, silica scale is generated and the electric resistance increases, so that the voltage when operating the electrodeionization device rises and the quality of the treated water is lowered. It will be.

  Conventionally, a pretreatment device constituted by a two-stage reverse osmosis membrane module has been provided and silica has been removed, but the pretreatment device having the above configuration is very large, However, if there is no problem if the installation space is limited, there is a problem that it cannot be applied when the installation space is limited. It was.

  Therefore, as shown in FIG. 2, the ultrapure water production apparatus using the reverse osmosis membrane is used. This ultrapure water production apparatus is composed of a raw water tank T, a pretreatment apparatus, a pure water production system and a subsystem, and the pretreatment apparatus has a simple structure comprising a membrane pretreatment apparatus 21 and an activated carbon tower 22. The pure water production system includes a filtered water tank 23, a reverse osmosis membrane module (RO device) 24, a membrane deaeration device 25, and an electrodeionization device 26 that are provided in series. The sub system includes a sub tank 27, a deminer (non-regenerative ion exchange resin tower) 28, an ultraviolet treatment device 29, and a filter device (UF) 30.

  In the ultrapure water production apparatus as described above, silica is supplied to the RO raw water W1 obtained by pretreating the raw water W0 supplied from the raw water tank T by the membrane pretreatment device 21 and the activated carbon tower 22 by the RO device 24. The RO treated water W <b> 2 is removed to a condition value or less and deaerated in the membrane deaerator 25, and then introduced into the electrodeionization device 26. The treated water W3 from which ionic impurities have been sufficiently removed by the electrodeionization device 26 is supplied as ultrapure water to the use point 31 via the deminer 28, the ultraviolet treatment device 29 and the UF30. With such a configuration, the pretreatment apparatus can be simplified and a compact ultrapure water production apparatus can be obtained.

  However, in the above ultrapure water production apparatus, the electrodeionization device 26 can be operated without any problem during steady operation, but the water supply to the electrodeionization device 26 exceeds the reference value during the steady operation, and the prediction is greatly increased. This is a non-stationary operation such as when raw water W0 having a calcium concentration, silica concentration or carbonate ion concentration exceeding the above is supplied, or when the RO device 24 deteriorates over time. Since the above ultrapure water production apparatus cannot sufficiently cope with such a case, if the unsteady operation is continued for a long period of time, there is a problem that scale may be generated in the concentration chamber of the electrodeionization apparatus 26. there were.

  The present invention has been made in view of the above problems, and maintains a minimum pre-treatment device configuration, and does not cause a scale failure of the electrodeionization device even during unsteady operation. An object is to provide a pure water production system capable of supplying water.

In order to solve the above-mentioned problems, the present invention provides a pure water production system in which an electrodeionization apparatus is provided in a treated water line from a reverse osmosis membrane module, and the electrodesorption of the treated water line of the reverse osmosis membrane module. A water quality measuring device is provided upstream from the ion device, and a flow dividing mechanism is provided in the treated water line of the reverse osmosis membrane module or the treated water line of the electrodeionization device. Provided is a pure water production system characterized in that a circulation line to a raw water tank is connected and a control mechanism for the diversion mechanism is provided ( invention 1).

According to the above invention ( Invention 1), when the quality of the water supplied from the reverse osmosis membrane module to the electrodeionization device exceeds the set value (reference value) during non-steady operation, the treated water or electrodeionization of the reverse osmosis membrane module A part of the treated water of the equipment is returned to the raw water tank (filtered water tank) of the reverse osmosis membrane module, and the water with low silica concentration is merged with the raw water side to improve the quality of the raw water. As a result, the electrodeionization equipment Can improve the quality of the water supply.

In the above invention ( Invention 1), the control mechanism reverses a part of the treated water of the reverse osmosis membrane module or a part of the electrodeionization device when the measured value of the water quality measuring instrument exceeds a set value. It is preferable to control the diversion mechanism so that a predetermined flow rate is returned from the circulation line to the raw water tank of the osmosis membrane module ( Invention 2).

According to the above invention ( Invention 2), the reverse osmosis membrane is obtained by returning the necessary fixed amount of treated water to the filtered water tank only when the concentration of silica or the like measured by the water quality measuring instrument exceeds the set value (reference value). The quality of the treated water in the module can be improved, and as a result, the quality of the water supplied to the electrodeionization device can be improved. Furthermore, since a necessary fixed amount of circulating water can be quickly returned to the filtered water tank based on the measurement result of the water quality measuring instrument, the electrodeionization apparatus can be operated safely.

In the said invention ( invention 1 and 2), it is preferable that the said water quality measuring device measures a silica, calcium, or carbonic acid density | concentration ( invention 3). According to this invention ( invention 3), the electrodeionization apparatus can be safely operated by measuring the water quality that is likely to fluctuate in the raw water that is the treated water such as silica, calcium, or carbonic acid.

In the said invention ( invention 1-3), it is preferable that the said diversion mechanism is a three-way valve ( invention 4). According to this invention ( invention 4), the treated water in the treated water line of the reverse osmosis membrane module or the treated water line of the electrodeionization device can be removed from the raw water tank (filtered water tank) of the reverse osmosis membrane module simply by switching the three-way valve with the control mechanism ).

  According to the present invention, the reverse osmosis membrane module or the electrodeionized water is treated when the water quality measured by the water quality meter for the water supplied from the reverse osmosis membrane module to the electrodeionization device during the unsteady operation exceeds a set value (reference value). A part of the water is returned to the raw water tank (filtered water tank) of the reverse osmosis membrane module, and water of low silica concentration is merged with the raw water side to improve the quality of the raw water, thereby maintaining the minimum pretreatment device configuration. Thus, it is possible to provide a pure water production system capable of supplying a predetermined level of pure water to the electrodeionization device without causing a scale failure of the electrodeionization device even during non-steady operation.

  Hereinafter, a pure water production system according to an embodiment of the present invention will be described in detail based on the drawings. FIG. 1 shows a flow chart of an ultrapure water production apparatus having a pure water production system according to this embodiment.

  As shown in FIG. 1, the ultrapure water production apparatus includes a raw water tank T, a pretreatment device, a pure water production system, and a subsystem. The pretreatment device is composed of only the membrane pretreatment device 1 and the activated carbon tower 2.

  The pure water production system continuously treats the treated water of the activated carbon tower 2, and includes a filtered water tank 3 that is a raw water tank of a reverse osmosis membrane module, an RO device 4 that is a reverse osmosis membrane module, and a membrane deaeration device 5. And a silica sensor 7 as a water quality measuring device is provided upstream of the electrodeionization device 6 in the treated water line L1 of the RO device 4. The treated water line L2 of the electrodeionization apparatus 6 is provided with a three-way valve 8 having a flow rate control function as a branching mechanism. A water supply line L3 to the subsystem and a circulation line L4 to the filtered water tank 3 are provided. And branching.

  The silica sensor 7 and the three-way valve 8 are connected to a control mechanism (not shown) such as a personal computer. This control mechanism is based on the silica concentration data of the silica sensor 7 and the flow rate of the three-way valve 8. The amount of circulating water to the filtered water tank 3 can be controlled by controlling the control function.

  Further, the sub system includes a sub tank 9 in which deionized water of the electrodeionization device 6 is stored, a deminer (non-regenerative ion exchange resin tower) 10, an ultraviolet treatment device (UV) 11, and a filter device (UF) 12. The treated water W is supplied to the use point 13 as ultrapure water.

  In FIG. 1, L5 is a circulation line for returning unused ultrapure water to the sub tank 9 at the use point 13. Q1, Q2, Q3, Q4, Q5, Q6 and Q7 are respectively the amount of raw water, the amount of water supplied by the RO device 3, the amount of discharged water of the RO device 3, the amount of water supplied by the electrodeionization device 6, and the electrodeionization device 6. The amount of discharged water, the amount of water circulated to the filtered water tank 3, and the amount of water supplied to the subsystem, and the respective flow rates in Example 1 described later are described.

The effect | action is demonstrated about the ultrapure water manufacturing apparatus which has such a structure.
First, turbid components are removed from the raw water W0 supplied from the raw water tank T by the membrane pretreatment device 1, and then organic substances are removed by the activated carbon tower 2. Subsequently, the pretreated water to be treated is introduced into the pure water production system.

In the pure water production system, the RO raw water W1 is temporarily stored in the filtered water tank 3 and then processed by the RO device 3 to remove ions, silica, and the like from the RO raw water W1. Then, the permeated water of the RO device 4 is supplied to the electrodeionization device 6 after the carbonate ion and dissolved oxygen are removed by the membrane deaeration device 5. At this time, the silica concentration of the RO permeated water W2 is measured by the silica sensor 7 provided in the treated water line L1 of the RO device 4, and this is monitored by a control mechanism (not shown). Specifically, a reference value of the silica concentration (for example, a silica concentration of 0.7 mg / L (as SiO ₂ ), the same shall apply hereinafter) is set as a set value, and whether or not this value is exceeded is monitored.

  The control mechanism controls the three-way valve 8 in accordance with the output of the silica sensor 7 as will be described in detail below, whereby the flow rate of the water supply line L3 to the subsystem and the circulation line L4 to the filtered water tank 3 is controlled. Is controlled by the three-way valve 8. That is, when the output of the silica sensor 7 (water quality of the permeated water W2 of the RO device 4) exceeds the reference value (0.7 mg / L), the control mechanism is Control is performed so that the amount of circulating water from the three-way valve 8 of the treated water line L2 to the filtered water tank 3 is increased.

  In this electrodeionization apparatus 6, ionic impurities are sufficiently removed and the silica concentration is very low (usually 10 ppb or less), so that the quality of the raw water W1 in the filtered water tank 3 is improved. By performing this continuously, the silica concentration of the RO treated water W2, that is, the treated water supplied to the electrodeionization device 6 is 0.7 mg / L or less, and the electrodeionization device 6 is also in an unsteady operation. The operation of the electrodeionization device 6 can be continued without causing a scale failure.

Specifically, the relationship between the silica concentration of the RO raw water W1 and the silica concentration of the RO treated water W2 is input to the control mechanism in advance, and the silica concentration of the RO treated water W2 becomes 0.7 mg / L or less. The dilution rate of the electrodeionization apparatus 6 with the treated water W3 may be calculated, and the treated water W3 may be returned by the calculated amount. For example, in this embodiment, the dilution rate is 0.75 according to the following formula.
Q1 / (Q1 + Q6) = Q1 / Q2

  However, considering that the flow rate to the subsystem cannot be zero, the concentrated water (Q3) of the RO device 4 and the concentrated water (Q5) of the electrodeionization device 6 are inevitable, the dilution rate is It is preferably 0.5 or more.

  On the other hand, when the output of the silica sensor 7 (water quality of the permeated water W2 of the RO device 4) is in a steady operation at the reference value (0.7 mg / L or less), the control mechanism ensures a sufficient amount of water in the water supply line L3. The three-way valve 8 is controlled so that the amount of water in the circulation line L4 becomes a surplus of the necessary amount at the use point 13, or 0, so that it is not circulated more than necessary.

  Thus, by controlling the amount of the treated water of the electrodeionization device 6 returned to the filtered water tank 3 based on the output of the silica sensor 7 (water quality of the permeated water W2 of the RO device 4), the electrodeionization during unsteady operation is performed. The water quality of the raw water (RO treated water) W2 itself of the ion device 6 can be improved, and the water supply condition to the electrodeionization device 6 can be reduced below the reference value. Thereby, the water quality of the treated water W3 of the electrodeionization apparatus 6 can be maintained at a predetermined level.

  The RO treated water W2 supplied to the electrodeionization device 6 is once stored in the sub tank 9 and supplied as ultrapure water W to the use point 13 via the deminer 10, the ultraviolet treatment device 11, and the filter device 12. The The surplus water at the use point 13 is returned to the sub tank 9 from the circulation line L5.

  As mentioned above, although the pure water manufacturing system which concerns on this embodiment has been demonstrated based on drawing, this invention is not limited to the said embodiment, A various change implementation is possible.

  For example, in the present embodiment, the treated water of the electrodeionization device 6 is diluted water of the filtered water tank 3, but water having a lower silica concentration than the RO raw water W1 of the filtered water tank 3 may be returned. By providing a three-way valve with a flow rate control function between the device 4 and the electrodeionization device 6 and controlling the amount of water circulated to the filtered water tank 3, the quality of the RO raw water W1 during non-steady operation is also improved. And the water supply conditions to the electrodeionization apparatus 6 can be made below a reference value.

  In addition, the present invention has its characteristics in a pure water production system, and there are no particular restrictions on the configuration of the pretreatment device and the subsystem in the above embodiment, and it may not be provided depending on circumstances.

  Furthermore, although the silica concentration is monitored in this embodiment, the three-way valve 8 may be controlled based on the carbonate ion or calcium concentration using a carbonate ion sensor, a calcium sensor, or the like instead of the silica sensor 7.

[Reference example]
In the ultrapure water production apparatus shown in FIG. 1, when the amount of treated water in the electrodeionization apparatus 6 is 25 m ³ / h and raw water treatment with a silica concentration of 24 mg / L shown in Table 1 is performed, RO treatment by the silica sensor 7 is performed. Since the silica concentration of water W2 was 0.7 mg / L, the three-way valve 8 was controlled to close the circulation line L4 and perform steady operation.

  The raw water, the silica concentration at the RO inlet (RO raw water) and the RO outlet (RO treated water), the silica removal rate and recovery rate of the RO device 4, the water supply amount (Q 7) and the circulation amount ( Q6), raw water replenishment water amount (treatment amount), raw water dilution rate, voltage change of electrodeionization device 6 (CDI) after 30 days treatment, silica concentration of CDI treated water, and specific resistance value of CDI treated water The results are shown in Table 1.

[Example 1]
In the above reference example, when the raw water having a silica concentration of 32 mg / L was treated, the silica concentration of the RO treated water W2 by the silica sensor 7 was 1.0 mg / L, which exceeded the reference value. And the amount of water (Q6) in the circulation line L4 was set to 10 m ³ / h (the amount of water (Q7) in the water supply line L3 was set to 15 m ³ / h), and the treatment was continuously performed.

  During this operation, the raw water, the silica concentration at the RO inlet (RO raw water) and the RO outlet (RO treated water), the silica removal rate and recovery rate of the RO device 4, the water supply amount (Q7) and the circulation rate of the electrodeionization device 6 ( Q6), raw water replenishment water amount (treatment amount), raw water dilution rate, voltage change of electrodeionization device 6 (CDI) after 30 days treatment, silica concentration of CDI treated water, and specific resistance value of CDI treated water The results are shown in Table 1 respectively.

[Comparative Example 1]
In Example 1, the treated water W3 of the electrodeionization apparatus 6 is not returned to the filtered water tank 3 (Q6 = 0), so that the raw water having a silica concentration of 32 mg / L is similarly simulated as a conventional pure water production system. Processed.

  During this operation, the raw water, the silica concentration at the RO inlet (RO raw water) and the RO outlet (RO treated water), the silica removal rate and recovery rate of the RO device 4, the water supply amount (Q7) and the circulation rate of the electrodeionization device 6 ( Q6), raw water replenishment water amount (treatment amount), raw water dilution rate, voltage change of electrodeionization device 6 (CDI) after 30 days treatment, silica concentration of CDI treated water, and specific resistance value of CDI treated water The results are shown in Table 1 respectively.

  As is apparent from Table 1, in the apparatus of Example 1, the voltage of the electrodeionization apparatus 6 did not change even after 30 days of operation, and the silica concentration of the RO-treated water W2 was 0.7 mg / L, which is below the reference value. In addition, the specific resistance value was large and the purity of the treated water was high, and it was possible to operate with the same water quality as in the steady operation as a reference example. This is considered to be because the silica concentration of the RO raw water W1 is low. On the other hand, in the comparative example 1 which did not return the treated water of the electrodeionization apparatus 6 to the filtration water tank 3, the silica concentration of RO treated water W2 exceeds 1.0 mg / L and a reference value, and it operates for 30 days. A voltage increase, a silica concentration increase, and a specific resistance value of the subsequent electrodeionization apparatus 6 were observed.

It is a flowchart which shows the ultrapure water manufacturing apparatus containing the pure water manufacturing system by one Embodiment of this invention. It is a flowchart which shows the ultrapure water manufacturing apparatus containing the conventional pure water manufacturing system.

Explanation of symbols

3 ... Filtration water tank (raw water tank)
4. RO device (reverse osmosis membrane module)
6 ... Electrodeionization device 7 ... Silica sensor (water quality measuring device)
8 ... Three-way valve (diversion mechanism)
L2 ... treated water line L3 ... water supply line L4 ... circulation line W1 ... RO raw water W2 ... RO treated water (electric deionizer raw water)
W ... Pure water

Claims (3)

A pure water production system provided with an electrodeionization device in a treated water line from a reverse osmosis membrane module
A water quality measuring device for measuring silica, calcium or carbonic acid concentration is provided upstream of the electrodeionization device in the treated water line of the reverse osmosis membrane module, and the treated water line or electrodeionization device of the reverse osmosis membrane module A diversion mechanism capable of adjusting the flow rate is provided in the treated water line, and a circulation line to the raw water tank of the reverse osmosis membrane module is connected to this diversion mechanism, and a control mechanism for the diversion mechanism is provided ,
When the measured value of the water quality measuring instrument exceeds a set value, the control mechanism converts a part of the treated water of the reverse osmosis membrane module or a part of the treated water of the electrodeionization device to the original of the reverse osmosis membrane module. A predetermined flow rate is returned from the circulation line to the water tank, and the raw water supplied to the raw water tank is diluted with treated water returned from the circulation line, and the diversion mechanism is controlled so that the measured value does not exceed the set value. A pure water production system characterized by: 2. The pure water production system according to claim 1, wherein a dilution rate when the raw water supplied to the raw water tank is diluted with treated water returned from the circulation line is 0.5 or more. Water purification system according to claim 1 or 2 wherein the diverter mechanism, characterized in that it is a three-way valve.

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