Pure water production method and production equipment

Abstract

To start up a regenerative ion exchange apparatus quickly with low elution.SOLUTION: A method for producing pure water involves alternating between an operating state in which treated water is treated in an ion exchange apparatus 2A filled with regenerable ion exchangers and a regeneration standby state in which a supply of treated water is stopped, ion exchangers 21 and 22 are regenerated, and the apparatus waits until the next operating state. In the regeneration standby state, after the regeneration of the ion exchangers 21 and 22 is completed, wash water is made to pass through the ion exchangers until the next operating state.SELECTED DRAWING: Figure 1D

Description

[Technical field]

[0001] The present invention relates to a method and apparatus for producing pure water. [Background technology]

[0002] Conventionally, ultrapure water with extremely low impurity content such as ionic substances, fine particles, organic matter, dissolved gas, and live bacteria has been used in the manufacturing process of electronic parts such as semiconductor devices, liquid crystal displays, silicon wafers, and printed circuit boards, as well as in the manufacturing process of pharmaceuticals. In particular, a large amount of ultrapure water is used in the manufacturing process of electronic parts, including semiconductor devices, and the requirements for the purity of ultrapure water are becoming increasingly strict as the integration density of semiconductor devices increases. For example, ultrapure water for semiconductor manufacturing requires specifications such as a resistivity of 18.2 MΩ·cm or more, less than 1 particle / mL of particles 0.05 μm or more, less than 1 μg / L of total organic carbon (TOC), and less than 1 ng / L of metal components, and the required water quality tends to become even stricter.

[0003] In particular, in recent years, there has been a demand for the reduction of trace impurities such as boron and TOC. In general, it is difficult to completely remove boron using ultrapure water production equipment (subsystems) that only have non-regenerative ion exchange devices, and removal of boron using primary pure water systems has been considered. Regenerative ion exchange devices that use acids and alkalis as regenerants are widely used as a method for removing boron and TOC in primary pure water systems. On the other hand, regenerative ion exchange devices are isolated from the primary pure water system and are placed on standby for a certain period of time after the regeneration operation is performed before starting operation. During this standby period, some of the organic parent material may dissolve from the ion exchanger, which may affect the quality of the treated water.

[0004] Patent Document 1 discloses a method for storing a demineralization tower after regeneration in a condensate demineralization unit of a thermal power plant. After the regeneration of the cation layer and anion layer is completed, they are separated by backwashing, and then washing water is passed through the cation layer and anion layer continuously or intermittently. This prevents organic components eluted from the cation resin from contaminating the anion resin. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 7-116526 Summary of the Invention [Problem to be solved by the invention]

[0006] The storage method after regeneration of a demineralization tower described in Patent Document 1 aims to quickly stabilize the water quality of the condensate, and is not related to a method for producing pure water.

[0007] An object of the present invention is to provide a method for producing pure water which can start up a regenerative ion exchange device quickly and with low elution. [Means for solving the problem]

[0008] The method for producing pure water of the present invention is carried out by using a device filled with a renewable ion exchanger. Arranged in parallel Ta Multiple In the ion exchange device, an operating state in which the water to be treated is treated and a regeneration standby state in which the supply of the water to be treated is stopped, the ion exchanger is regenerated, and the device is on standby until the next operating state. Between multiple ion exchange units having alternating repeating Each of the plurality of ion exchange devices In the regeneration standby state, wash water is passed through the ion exchanger continuously from the time when the regeneration of the ion exchanger is completed until the time when the next operating state starts. Effect of the Invention

[0009] According to the present invention, there is provided a method for producing pure water, which can start up a regenerative ion exchange device quickly and with low elution. [Brief description of the drawings]

[0010] [Figure 1A] FIG. 1 is a schematic diagram of a pure water production system according to one embodiment of the present invention (when tower A is in operation). [Figure 1B] FIG. 1 is a schematic diagram of a pure water production system according to one embodiment of the present invention (when tower A cation resin is being regenerated). [Figure 1C] FIG. 1 is a schematic diagram of a pure water production system according to one embodiment of the present invention (when tower A anion resin is being regenerated). [Figure 1D] FIG. 1 is a schematic diagram of a pure water production system according to one embodiment of the present invention (when tower A is on standby). [Figure 1E] FIG. 1 is a schematic diagram of a pure water production system according to one embodiment of the present invention (when tower A is operated again). [Diagram 2] FIG. 2 is a schematic diagram of a test device in the examples and comparative examples. [Diagram 3] 1 is a graph showing the relationship between the amount of water passing and the TOC of treated water in an example and a comparative example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] Hereinafter, an embodiment of the pure water production method and the pure water production apparatus of the present invention will be described with reference to the drawings. FIGS. 1A to 1E show a schematic configuration of the pure water production apparatus 1 and a regeneration method of the regenerative ion exchange apparatus 2. In each figure, the thick lines indicate the lines through which the water to be treated, the treated water, or the washing water flows. The pure water production apparatus (primary system) constitutes an ultrapure water production apparatus together with an upstream pretreatment system and a downstream subsystem (secondary system). The regenerative ion exchange apparatus 2 requires periodic regeneration, but ultrapure water used in semiconductor manufacturing processes and the like needs to be continuously produced. For this reason, in this embodiment, three resin towers (hereinafter referred to as A tower 2A, B tower 2B, and C tower 2C) are provided in parallel, and an operating state and a regeneration standby state are alternately repeated among the three towers so that two towers are operating and one tower is isolated from the pure water production apparatus 1. In the following explanation, a method of switching A tower 2A from an operating state to a regeneration standby state, waiting for a predetermined time after regeneration, and then switching it to an operating state will be described.

[0012] 1A shows a pure water production system 1 in which A tower 2A and B tower 2B are in operation and C tower 2C is in a standby state for regeneration. The pure water production system 1 of this embodiment includes a raw water tank 3, a raw water pump 4, a filter 5, an activated carbon tower 6, a cation resin tower 7, a decarbonation device 8, an anion resin tower 9, a reverse osmosis membrane device 10, a reverse osmosis membrane device treated water tank (hereinafter referred to as RO treated water tank) 11, a reverse osmosis membrane device treated water transfer pump (hereinafter referred to as RO treated water pump) 12, and an ultraviolet oxidation device 13, which are arranged in series along a line L1 from upstream to downstream with respect to the flow direction D of the water to be treated. The raw water (hereinafter referred to as water to be treated) produced in the pretreatment system and stored in the raw water tank 3 is pressurized by the raw water pump 4, and then the filter 5 removes relatively large particle size dust and the like, and the activated carbon tower 6 removes impurities such as hydrogen peroxide, chlorine, and organic matter. The water to be treated has its cation components removed in a cation resin tower 7, its carbon dioxide removed in a decarbonation device 8, and its anion components removed in an anion resin tower 9, and ion components are further removed in a reverse osmosis membrane device 10. The treated water from the reverse osmosis membrane device 10 is then sent to an RO treated water tank 11, where it is pressurized by an RO treated water pump 12, after which organic components are decomposed by an ultraviolet oxidizer 13 and the water is then sent to the regenerative ion exchange device 2.

[0013] The A tower 2A, B tower 2B, and C tower 2C of the regenerative ion exchange device 2 are filled with a regenerative ion exchanger, which in this embodiment is an ion exchange resin. The ion exchange resin removes organic components and ionic components from the water to be treated. In particular, boron has a weak adsorption force to the resin, so it is easily released from the resin. The ion exchange device installed in the subsystem is usually a cartridge-type non-regenerative type, partly because the ion load of the water to be treated is small. The non-regenerative ion exchange device is used for a long time until the ion exchange performance deteriorates and it is time to replace it, so the captured boron is likely to flow into the water to be treated. In contrast, the regenerative ion exchange device 2 is effective as a means for removing boron, because the boron captured in the resin can be removed by regeneration before it breaks through the resin.

[0014] Since all three resin towers (A tower 2A, B tower 2B, C tower 2C) have the same configuration, the following mainly describes A tower 2A. Although the explanation is omitted, lines L6 to L9 and valves V3 to V8 are also provided in B tower 2B and C tower 2C. A tower 2A, B tower 2B, and C tower 2C are connected to lines L2A, L2B, and L2C branching from line L1 on the inlet side, respectively, and are connected to lines L3A, L3B, and L3C merging with line L4 on the outlet side, respectively. Line L4 is connected to line L5 connecting to the subsystem. Valves V1A, V1B, and V1C are provided on lines L2A, L2B, and L2C, respectively, and valves V2A, V2B, and V2C are provided on lines L3A, L3B, and L3C, respectively. Valves V1A, V1B and V2A, V2B are open, and valves V1C, V2C are closed. Therefore, towers A 2A and B 2B are in operation to treat the water to be treated, and tower C 2C is isolated from the pure water production system 1 and is in a standby state for regeneration.

[0015] The A tower 2A is a double-bed ion exchange resin tower in which the lower part is filled with an anion layer 21 made of anion exchange resin, and the upper part is filled with a cation layer 22 made of cation exchange resin. The anion layer 21 and the cation layer 22 may be formed of ion exchange fibers, monolithic ion exchangers, etc. Between the anion layer 21 and the cation layer 22, a header 23 is provided for supplying a regenerant for the anion layer 21. The line L2A is connected to the bottom of the A tower 2A, and the line L3A is connected to the top of the A tower 2A. Thus, the water to be treated is introduced into the A tower 2A as an upward flow, anion components are removed in the anion layer 21, then cation components are removed in the cation layer 22, and then the water is discharged from the line L3A. The regenerative ion exchange device 2 may be a mixed bed type in which a cation exchange resin and an anion exchange resin are mixed and packed in one resin tower, or a two-bed, two-tower type in which a cation exchange resin and an anion exchange resin are packed in different resin towers and these resin towers are connected in series. Alternatively, the cation layer 22 may be packed in the lower portion and the anion layer 21 may be packed in the upper portion, and the water to be treated may be supplied as a downward flow.

[0016] A line L6 is provided that branches off from the line L2A at a position between the valve V1A and the A tower 2A. The line L6 joins the line L1 via the RO treated water tank 11. The position where the line L6 joins the line L1 may be the inlet side of the reverse osmosis membrane device 10 (between the anion resin tower 9 and the reverse osmosis membrane device 10), the inlet side of the cation resin tower 7 (between the activated carbon tower 6 and the cation resin tower 7), or the inlet side of the ultraviolet oxidation device 13 (between the RO treated water pump 12 and the ultraviolet oxidation device 13). It is desirable to return the eluted components from at least the A tower 2A (regenerative ion exchange device 2) to a stage preceding the device that has one or more functions for removing the eluted components. During the operation of the A tower 2A, the valves V6 and V8 on the line L6 are closed.

[0017] A line L7 for supplying hydrochloric acid merges with line L3A. When A-tower 2A is in operation, valve V3 on line L7 is closed. A line L8 for supplying caustic soda is provided on the side wall of A-tower 2A and connected to header 23. When A-tower 2A is in operation, valve V4 on line L8 is closed. Line L9, which is a drainage line, branches off from line L8, and valve V5 on line L9 is closed. Line L10, which is a drainage line, branches off from line L6, and valve V7 on line L10 is closed.

[0018] Next, a method for regenerating the A tower 2A will be described. As shown in FIG. 1B, the valves V1A and V2A are closed to isolate the A tower 2A, and the valves V1C and V2C are opened to operate the C tower 2C. The valves V3 and V5 are opened, and hydrochloric acid is supplied to the A tower 2A through the line L7 to regenerate the cation exchange resin with the hydrochloric acid. The hydrochloric acid supplied through the line L7 is supplied to the top of the A tower 2A, flows through the inside of the cation layer 22 as a downward flow, and is recovered in a wastewater tank (not shown) through the header 23, line L8, and line L9. By flowing the hydrochloric acid in the opposite direction to the water to be treated, the cationic components captured by the cation exchange resin can be removed more effectively. That is, since the lower part of the cation layer 22 is the inlet side of the water to be treated, more cationic components are captured than in the upper part which is the outlet side. By flowing the hydrochloric acid from top to bottom, the cationic components are prevented from flowing back to the upper side and contaminating the upper part of the cation layer 22. When the cation layer 22 is regenerated with hydrochloric acid, water from the RO treated water tank 11 is supplied in an upward flow manner from the bottom of the anion layer 21 in order to prevent the hydrochloric acid from coming into contact with the anion layer 21. Subsequently, the remaining hydrochloric acid is washed out with water from the RO treated water tank 11 using the same line as that for the hydrochloric acid (not shown).

[0019] Next, as shown in FIG. 1C, valves V3 and V5 are closed, valves V4, V7, and V8 are opened, and caustic soda is supplied to A tower 2A through line L8 to regenerate the anion exchange resin with caustic soda. The caustic soda supplied from line L8 is supplied to the top of the anion layer 21 of A tower 2A through header 23, flows through the anion layer 21 as a downward flow, passes through line L10, and is recovered in a wastewater tank (not shown). The reason for flowing caustic soda in the opposite direction to the water to be treated is the same as in the case of hydrochloric acid described above. When regenerating the anion layer 21 with caustic soda, water from the RO treated water tank 11 is supplied in a downward flow from the top of the cationic layer 22 to prevent caustic soda from contacting the cationic layer 22. Next, the remaining caustic soda is washed using the water from the RO treated water tank 11 using a similar line (not shown).

[0020] Next, as shown in FIG. 1D, the valves V4 and V7 are closed, the valves V2A and V6 are opened, and the wash water is supplied to the A tower 2A from the lines L4 and L3A. At this time, the lines L3B, L3C, L4, and L3A function as wash water supply lines that supply the wash water to the A tower 2A. The wash water is the outlet water of the B tower 2B and the C tower 2C, that is, pure water, so it has high purity. The flow rate of the wash water is preferably between 0.5 and 5% of the total flow rate of the pure water discharged from the B tower 2B and the C tower 2C. The pure water used as the wash water flows through the cation layer 22 and the anion layer 21 in this order, and is returned to the RO treated water tank 11 through the return line, line L6. At this time, the lines L2A and L6 function as wash water recovery lines that recover the wash water. Since the wash water is reused in this way, the water recovery rate is hardly reduced. The wash water may be returned to a position other than the RO treated water tank 11 as long as it is upstream of the regenerative ion exchange device 2. However, since the wash water may contain organic matter that has eluted from the resin in Tower A 2A, as mentioned above, it is desirable to return the water to the upstream stage of a device that has at least one function for removing the eluted components from Tower A 2A.

[0021] Usually, the switching between the A tower 2A, the B tower 2B, and the C tower 2C is performed on a weekly or monthly basis, but the regeneration is completed in a few hours. Conventionally, after the regeneration is completed, the resin tower is filled with pure water (i.e., the resin is immersed in the resin) and waits until the next operation starts until the timing of switching. However, if the waiting time is long, the resin matrix peels off, and the peeled organic matter and fine particles are likely to flow into the immersion water in the resin tower. The leaked organic matter and fine particles may not only remain in the resin tower, but also adhere to the inner wall and resin of the resin tower. For this reason, the water quality of the treated water (TOC, resistivity, number of fine particles, etc.) may become unstable for a while after the resin tower is connected to the pure water production device and the supply of the water to be treated is started. As a result, the load in the downstream subsystem may increase and the water quality at the point of use may fluctuate. In this embodiment, after the regeneration is completed, the washing water is circulated in the standby state until the next operation state, so that the organic matter and fine particles peeled off from the resin are washed away by the washing water and are less likely to accumulate in the resin tower. Therefore, when the resin tower is connected to the pure water production system 1, the amount of organic matter and fine particles present in the resin tower is reduced, and the quality of the treated water is stabilized quickly after the supply of the water to be treated begins.

[0022] Next, as shown in Fig. 1E, valves V6 and V8 are closed, valve V1A is opened, and operation of tower A 2A is resumed. At the same time, valves V1B and V2B are closed to isolate tower B 2B from the pure water production system 1. While tower A 2A and tower C 2C are operating, tower B 2B is regenerated and put into standby according to the above-mentioned procedure.

[0023] This embodiment can be implemented simply by changing the operation method of the existing equipment, so there is no need to add new lines or valves. The wash water is pressurized by the upstream raw water pump 4 and the RO treated water pump 12, so there is no need to install a new pump. The most convenient wash water is the outlet water of the resin towers in operation (tower B 2B and tower C 2C in this embodiment), but there are no particular limitations as long as it is wash water that does not contaminate the resin of the regenerative ion exchange device 2 in standby and has a certain purity. The wash water may be water that has a resistivity equal to or higher than that of the treated water produced by the regenerative ion exchange device 2.

[0024] (Example) The effect of the present invention was confirmed using the device shown in FIG. 2. A cation tower was prepared by filling 300 mL of a strong acid cation resin in an acrylic column having a diameter of 25 mm. Similarly, an anion tower was prepared by filling 300 mL of a strong basic anion resin in an acrylic column having a diameter of 25 mm. An anion tower and a cation tower were connected in series to prepare two such two-bed, two-tower ion exchange devices. Hydrochloric acid was previously supplied to each cation tower in a downward flow to regenerate the strong acid cation resin. Similarly, caustic soda was previously supplied to each anion tower in a downward flow to regenerate the strong basic anion resin. Next, the water to be treated, which was treated in the same manner as in the embodiment, through a filter, an activated carbon device, an ion exchange device (a two-bed, three-tower device in which a cation exchange resin tower, a decarbonation device, and an anion exchange resin tower are connected in series), and a reverse osmosis membrane device, was passed through the anion tower and the cation tower in that order. In order to obtain treated water continuously, lines 1 and 2 were operated alternately at a constant yield (operation → regeneration → standby while passing wash water → operation).

[0025] In the embodiment, the water to be treated was passed through the ion exchange device of the line 1 at a space velocity of SV90. That is, the water to be treated was passed from the bottom to the top of the anion tower in an upward flow, and further passed from the bottom to the top of the cation tower in an upward flow. During the operation of the line 1, washing water was passed through the ion exchange device of the line 2 in a standby state at a space velocity of SV1. That is, a part of the treated water of the line 1 was passed through the washing line in a downward flow from the top of the cation tower, and further passed through the top of the anion tower in a downward flow (the flow of washing water is shown by a broken line). The water to be treated was passed through the line 1 for 65 hours, and then the line 2 was switched to an operating state for alternate operation, and the TOC of the treated water of the line 2 was measured. The TOC was measured using a TOC meter SIEVERS M9e manufactured by Suez. The comparative example was the same as the embodiment except that water passing washing was not performed when the line 2 was in a standby state. The results are shown in FIG. 3. The horizontal axis indicates the amount of water passing per unit volume of resin, and the vertical axis indicates the TOC of the treated water. In the Example, since line 2 was washed by passing water through it during standby, the TOC of the treated water stabilized when about 500 times the volume of the resin was passed through it. In the Comparative Example, it was necessary to pass about 1000 times the volume of the resin through it until the TOC of the treated water stabilized, and it was confirmed that the TOC stabilized in a shorter time in the Example. [Explanation of symbols]

[0026] 1 Pure water production equipment 2. Regenerative ion exchange device 2A, 2B, 2C Ion exchange resin tower (A tower, B tower, C tower) 21 Ion exchanger (anion layer) 22 Ion exchanger (cation layer)

Claims

1. In a plurality of ion exchange devices filled with regenerative ion exchangers and arranged in parallel, an operating state in which water to be treated is treated and a regeneration standby state in which the supply of the water to be treated is stopped, the ion exchangers are regenerated, and the system is on standby until the next operating state are alternately repeated between the plurality of ion exchange devices, In the regeneration standby state, washing water is continuously passed through the ion exchanger until a next operating state is started after the regeneration of the ion exchanger is completed.

2. 2. The method for producing pure water according to claim 1, wherein the cleaning water and the regenerant supplied for regenerating the ion exchanger are passed in a direction opposite to a direction in which the water to be treated is passed.

3. 3. The method for producing pure water according to claim 1, wherein the cleaning water has a resistivity equal to or higher than that of the treated water produced by the ion exchange device.

4. 2. The method for producing pure water according to claim 1, wherein the cleaning water is treated water produced by the ion exchange device in operation.

5. 5. The method for producing pure water according to claim 1, wherein the water used as the cleaning water is returned to a stage upstream of a device having one or more functions for removing components eluted from the ion exchange device.

6. 6. The method for producing pure water according to claim 1, wherein the space velocity of the wash water in the ion exchange device is lower than the space velocity of the water to be treated in the ion exchange device.

7. a plurality of ion exchange devices filled with regenerative ion exchangers and arranged in parallel, the plurality of ion exchange devices being capable of alternately repeating between an operating state in which the water to be treated is treated and a regeneration standby state in which the supply of the water to be treated is stopped, the ion exchangers are regenerated, and the plurality of ion exchange devices are on standby until the next operating state; a cleaning water supply line for continuously supplying cleaning water to the ion exchanger during the regeneration standby state until a next operating state is started after the regeneration of the ion exchanger is completed; A pure water production apparatus having the above structure.

8. The water purifying apparatus according to claim 7, a pretreatment system provided upstream of the pure water production apparatus; a subsystem provided downstream of the water purifying apparatus; An ultrapure water production apparatus comprising:

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