Method and apparatus for producing pure water

Abstract

To provide a pure water production method and a pure water production apparatus that can reduce a concentration of silica leaking to a treated water side in a mixed bed ion exchange device.SOLUTION: There is provided a pure water production method for producing pure water from treated water containing silica using a mixed bed ion exchange device, the method including: a water sampling process of bringing the treated water into contact with an ion exchange resin contained in the mixed bed ion exchange device; a regeneration process of regenerating an ion exchange performance of the ion exchange resin after the water sampling process; and a standing process of keeping a standing state in which water passing or water collection is not performed on the mixed-bed ion exchange device for a predetermined standing time after the regeneration process, wherein the standing time is 0.5 hours or more and within 720 hours.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a pure water production method and a pure water production apparatus for producing pure water from treated water containing silica using a mixed bed ion exchange apparatus.

Background Art

[0002] Generally, pure water (ultra-pure water) used in semiconductor manufacturing factories and the like is produced using a pure water production apparatus equipped with a pretreatment apparatus, a primary pure water production apparatus, and a subsystem for treating primary pure water.

[0003] The pretreatment apparatus removes suspended substances contained in raw water such as tap water and groundwater by coagulation, sedimentation, and filtration, and 99 to 99.99% of the raw water components are removed by a primary pure water production apparatus having a reverse osmosis membrane and an ion exchange apparatus to produce primary pure water. The above subsystem produces ultra-pure water by removing very trace amounts of ions and colloid components remaining in the primary pure water.

[0004] In such a process for producing ultra-pure water, an ion exchange apparatus is mainly used to remove ions from raw water to produce primary pure water. As the ion exchange apparatus, a multiple bed type ion exchange apparatus using a cation exchange resin and an anion exchange resin as single beds respectively, and a mixed bed type ion exchange apparatus using a cation exchange resin and an anion exchange resin in a mixed state are known. The multiple bed type ion exchange apparatus is described, for example, in Patent Document 1. Also, the mixed bed type ion exchange apparatus is described, for example, in Patent Document 2.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Summary of the Invention

[0006] In recent years, the water quality requirements for ultrapure water have tended to become stricter, and ultrapure water used in power plants, pharmaceutical manufacturing plants, semiconductor manufacturing plants, etc., requires high purity. Of the above-mentioned double-bed and mixed-bed ion exchange systems, in the mixed-bed ion exchange system, it is necessary to separate the cation exchange resin and anion exchange resin in a mixed state during the regeneration process to regenerate (restore) the ion exchange performance of the ion exchange resin. Normally, in the separation process, washing water is injected from the bottom of the ion exchange system in an upward flow to backwash the mixed resin inside, and the difference in specific gravity of the resins is used to move the anion exchange resin to the upper layer and the cation exchange resin to the lower layer, thereby separating the anion exchange resin and the cation exchange resin. In the regeneration process, while the resins are separated, a regenerating agent for the cation exchange resin, such as an acid, is injected from the bottom, and a regenerating agent for the anion exchange resin, such as an alkali, is injected from the top to perform the regeneration process. After the regeneration process is completed, the resins are washed with water, and air or nitrogen gas is injected into the resin layer to remix the separated cation exchange resin and anion exchange resin. In this process, since silica-type anion exchange resin that is not fully regenerated remains in the lower layer, mixed-bed ion exchange systems tend to leak silica into the treated water during water sampling. For ultrapure water, where high purity is required, the silica concentration also needs to be reduced.

[0007] This invention was made to solve the problems of the background technology described above, and aims to provide a method and apparatus for producing pure water that can reduce the silica concentration leaking to the treated water side in a mixed-bed ion exchange apparatus. [Means for solving the problem]

[0008] To achieve the above objective, the present invention provides a method for producing pure water, which involves producing pure water from treated water containing silica using a mixed-bed ion exchange apparatus. A water sampling step involves bringing the water to be treated into contact with the ion exchange resin contained within the mixed-bed ion exchange apparatus, A regeneration step performed after the water sampling step to regenerate the ion exchange performance of the ion exchange resin, A resting step is performed in which, after the regeneration step, a state of stillness is maintained for a predetermined resting time in which no water is passed through or collected from the mixed-bed ion exchange device. It has, The aforementioned mixed-bed ion exchange apparatus contains a mixture of cation exchange resin and anion exchange resin as the ion exchange resin. In the regeneration process, the cation exchange resin and the anion exchange resin are separated and regenerated, and then the cation exchange resin and the anion exchange resin are mixed. The aforementioned standing time is 0.5 hours or more and within 720 hours.

[0009] On the other hand, the pure water production apparatus of the present invention is a pure water production apparatus that produces pure water from water to be treated containing silica, Mixed-bed ion exchange system, A control device that performs a water sampling step of bringing the water to be treated into contact with the ion exchange resin contained within the mixed-bed ion exchange apparatus, a regeneration step performed after the water sampling step to regenerate the ion exchange performance of the ion exchange resin, and a resting step after the regeneration step to maintain a resting state for a predetermined resting time in which no water is passed through or water is sampled from the mixed-bed ion exchange apparatus, It has, The aforementioned standing time is 0.5 hours or more and within 720 hours. [Effects of the Invention]

[0010] According to the present invention, the silica concentration leaking to the treated water side in a mixed-bed ion exchange apparatus can be reduced. [Brief explanation of the drawing]

[0011] [Figure 1] This is a block diagram showing an example configuration of a pure water production apparatus used in the pure water production method of the present invention. [Figure 2] Table 3 shows a graph illustrating the silica concentration of the treated water under conditions 2 through 6 and in comparative example 2. [Modes for carrying out the invention]

[0012] Next, the present invention will be described with reference to the drawings.

[0013] Figure 1 is a block diagram showing an example configuration of a pure water production apparatus used in the pure water production method of the present invention.

[0014] As shown in Figure 1, the pure water production system (primary pure water production system) includes a treated water tank 1 for temporarily storing treated water treated by a pretreatment device (not shown), a resin tower 2 for removing ions from the treated water, a treated water tank 3 for temporarily storing treated water that has passed through the resin tower 2, a pump (P) 4 for supplying treated water from the treated water tank 1 to the resin tower 2, and a control device 5 for controlling the operation of the primary pure water production system. The primary pure water production system shown in Figure 1 further includes pumps (P) 6 and 7 for supplying washing water or a regenerating agent for the ion exchange resin to the resin tower 2, and a compressor (C) 8 for injecting air or the like into the resin tower 2 to mix the regenerated ion exchange resin. The control device 5 may be configured to control the operation of the entire pure water production system, including the primary pure water production system shown in Figure 1. The resin tower 2 is the mixed-bed ion exchange system described above, containing ion exchange resins (cation exchange resin and anion exchange resin). The water to be treated, stored in the water to be treated tank 1, is supplied from the top of the resin tower 2, and the treated water is supplied from the bottom of the resin tower 2 to the treated water tank 3. The silica concentration of the treated water may be measured using a well-known concentration meter.

[0015] Washing water is supplied to the top and bottom of the resin tower 2 from a tank (not shown) via pumps 6 and 7. A regenerating agent for the ion exchange resin is also supplied to the top and bottom of the resin tower 2 from a tank (not shown) via pumps 6 and 7. The regeneration and washing wastewater is discharged from a collection pipe (intermediate collector) (not shown) located near the interface between the cation exchange resin and the anion resin. Furthermore, air or other fluids are injected from the bottom of the resin tower 2 via compressor 8 to mix the regenerated ion exchange resin. In Figure 1, to avoid complexity in the diagram, washing water and the regenerating agent are supplied to the resin tower 2 through the same line. However, in actual resin towers 2, washing water and the regenerating agent may be supplied through separate lines.

[0016] The control device 5 is connected via well-known communication means to a pump 4 for treated water, pumps 6 and 7 for washing water and regenerant, a compressor 8, and a concentration meter, etc., and can control the operations of the pump 4, the pumps 6 and 7 for washing water and regenerant, and the compressor 8, etc., and can receive the measurement results from the concentration meter. The communication means may use either well-known wired communication means or wireless communication means, and any well-known communication standard may be used for the communication standard. Further, the control device 5 includes a timer and controls the standing time in the standing process of the resin tower 2 described later.

[0017] The control device 5 can be realized by, for example, a well-known PLC (Programmable Logic Controller). The control device 5 may also be realized by a well-known information processing device (computer) equipped with a CPU (Central Processing Unit), a storage device, an I / O interface, a communication device, etc. The control device 5 realizes the pure water production method of the present invention by a processor provided in the PLC or the information processing device executing processing according to a program stored in the storage device in advance.

[0018] In such a configuration, in the present embodiment, the primary pure water production device shown in FIG. 1 is operated in a water intake process and a regeneration process described below, and a standing process is provided in which a standing state where water is not passed through or taken in from the resin tower 2, etc. after the regeneration process is maintained for a predetermined time. The water intake process, the regeneration process, and the standing process are the processes described in (1) to (3) below. The water intake process, the regeneration process, and the standing process are realized by the control device 5 controlling the operations of the pump 4 for treated water, the pumps 6 and 7 for washing water and regenerant, the compressor 8, etc. The control device 5 repeatedly executes the water intake process, the regeneration process, and the standing process to produce treated water (primary pure water) from the treated water using the resin tower 2. (1) Water intake process The water intake process is a process of removing ions from the treated water to generate primary pure water. In the water intake process, the treated water is supplied to the resin tower 2 using the pump 4 to bring the ion exchange resin in the resin tower 2 into contact with the treated water, and treated water (primary pure water) from which ions have been removed from the treated water by ion exchange is generated. (2) Regeneration process The regeneration process is a process for regenerating the ion exchange performance of the ion exchange resin contained in the resin tower 2. The regeneration process includes the processes shown in the following (2-1) to (2-5). (2-1) Separation process Washing water is injected from the bottom of the resin tower 2 in an upward flow to separate the cation exchange resin and the anion exchange resin in the resin tower 2. At this time, a well-known separation promoter may be added to the washing water, or the ion form of the ion exchange resin may be converted using a chemical. (2-2) Chemical passing process After the separation process, the anion exchange resin is converted to a regenerated form (OH form, hereinafter referred to as R-OH), and the cation exchange resin is converted to a regenerated form (H form, hereinafter referred to as R-H) using a regenerant, thereby regenerating the respective ion exchange performances. (2-3) Extrusion and washing process After the chemical passing process, washing water is injected from the top and bottom of the resin tower 2 in the same direction as the regenerant passing direction, and the regenerant remaining in the resin tower 2 is extruded and washed with the washing water. (2-4) Mixing process After the extrusion and washing process, air or the like is injected from the bottom of the resin tower 2 to mix the cation exchange resin and the anion exchange resin in the resin tower 2. Since the ion exchange resins have a specific gravity difference depending on the type of resin and the ion form, they are mixed so that the cation exchange resin and the anion exchange resin are evenly distributed. (2-5) Blowing process After the mixing process, washing water is injected in a downward flow into the resin tower for consolidation and washing of the ion exchange resin. This blowing process may be omitted. (3) Standing process The standing process is a process of maintaining the resin tower 2 in a standing state without passing water or taking water for a predetermined time (standing time) after the completion of the regeneration process. The standing time varies depending on the silica load of the treated water and the silica concentration required for the treated water, but it is preferably 0.5 hours or more. As shown in the examples described later, the standing time is more preferably 5 hours or more, and even more preferably 17.5 hours or more.

[0019] Thus, by providing a settling process after the regeneration process, the silica concentration leaking from the resin tower (mixed-bed ion exchange device) 2 to the treated water side can be reduced. As mentioned above, in a mixed-bed ion exchange device, if the water sampling process is carried out while the silica-type anion exchange resin has moved to the lower layer of the resin tower 2 due to mixing, silica tends to leak into the treated water side. By providing a settling process after the regeneration process, silica diffuses, reducing the amount of silica-type anion exchange resin in the lower layer of the resin tower 2, and thus reducing the amount of silica leaking into the treated water side.

[0020] The standing time can be predetermined based on experimental results, etc., according to the required silica concentration in the treated water. When measuring the silica concentration of the treated water with a concentration meter, the standing time may be changed according to the required silica concentration in the treated water. [Examples]

[0021] Next, embodiments of the present invention will be described. (First embodiment) In the first embodiment, it is shown that the silica concentration of the treated water can be reduced by providing a settling process.

[0022] Table 1 shows the experimental conditions and silica concentration of the treated water for the first condition, which includes a settling step, and the first comparative example, which does not include a settling step. Table 2 shows the regeneration conditions for the cation exchange resin and anion exchange resin used in this example.

[0023] The experiment for Condition 1 and Comparative Example 1 was conducted under the same conditions except for the presence or absence of a standing process. That is, the same model ion exchange resin from the same manufacturer was used, a column with the same inner diameter was used as resin column 2, water to be treated with the same silica load was passed through for the same sampling time, and the cation exchange resin and anion exchange resin were regenerated under the conditions shown in Table 2. After that, the ion exchange resins were mixed under the same mixing conditions and blowdown conditions. The standing time for Condition 1 was 17.5 hours (h), and the standing time for Comparative Example 1 was 0 hours (h).

[0024] In actual primary pure water production systems, the water sampling, regeneration, and standing processes are carried out within the same resin column 2. However, the water sampling column used in the experiment of the first embodiment has a small inner diameter, making it difficult to perform backwashing and mixing effectively. Therefore, in the first embodiment, the ion exchange resin in the water sampling column is transferred to a column with a larger inner diameter for backwashing. Also, in the first embodiment, the regenerated ion exchange resin is mixed manually before being transferred to the water sampling column. Furthermore, since the water sampling column does not have a component equivalent to an intermediate collector, the regeneration of the cation exchange resin and anion exchange resin is carried out in separate columns. Therefore, the experimental procedure shown in the first embodiment is as follows: water sampling, column transfer, removal of the anion exchange resin (the cation exchange resin is left as is), regeneration of both ion exchange resins (chemical passage, extrusion, washing), removal of both ion exchange resins, mixing, loading of both ion exchange resins into the water sampling column, standing (first condition only), blowing (washing for 15 minutes), and water sampling (to confirm the initial silica leak concentration).

[0025] The meanings of the abbreviations used in Tables 1 and 2, and in Tables 3 and 4 described later, are as follows.

[0026] CER: Cation (positive ion) exchange resin.

[0027] AER: Anion exchange resin.

[0028] LV (m / h): Linear velocity. Represents the velocity (flow rate) of the washing water passing through the cross-section of the resin column.

[0029] SV (L / L - resin / h): Space velocity. Represents the speed (flow rate) of chemicals or cleaning water passing through a unit amount of resin.

[0030] UPW: Ultra-Pure Water.

[0031] [Table 1]

[0032] [Table 2] (Second example) In the second embodiment, it is shown that the silica concentration of the treated water changes by changing the standing time.

[0033] Table 3 shows the experimental conditions and silica concentration of the treated water for conditions 2 to 6, which include a settling step, and for comparative example 2, which does not include a settling step.

[0034] As shown in Table 3, the standing time for condition 2 was 1 hour (h), for condition 3 it was 3.4 hours (h), for condition 4 it was 5.4 hours (h), for condition 5 it was 20 hours (h), and for condition 6 it was 24 hours (h). The standing time for comparative example 2 was 0 hours (h). All other conditions were the same for conditions 2 to 6 and comparative example 2. Figure 2 is a graph showing the silica concentration of the treated water for conditions 2 to 6 and comparative example 2, as shown in Table 3.

[0035] As can be seen from Table 3 and Figure 2, the silica concentration in the treated water decreases as the standing time increases. Furthermore, if the standing time is 1 hour or more, as shown in the second condition, and at least 0.5 hours or more, it is considered that the silica concentration in the treated water will be lower than in the second comparative example, which does not have a standing process.

[0036] Furthermore, as can be seen from Figure 2, the silica concentration in the treated water decreases significantly until the standing time reaches about 5 hours. As the standing time increases further, the decrease slows down, and the concentration stabilizes after 17.5 hours. In condition 6, where the standing time is 24 hours, the measured silica concentration is below the detection limit (2 μg / L), so the silica concentration is set to "0" in the graph in Figure 2. For this reason, condition 6 is excluded from the data used to observe the change in silica concentration with respect to standing time.

[0037] Therefore, a standing time of 0.5 hours or more is desirable, 5 hours or more is more desirable, and 17.5 hours or more is even more desirable. However, if the standing time is too long, it is undesirable because it reduces the efficiency of ultrapure water production using a pure water production device. As can be seen from Table 3 and Figure 2, the silica concentration of the treated water is not considered to change much if the standing time exceeds 24 hours. Therefore, it is desirable that the standing time be, for example, within 720 hours (30 days).

[0038] [Table 3] (Third embodiment) In the third embodiment, it is shown that the silica concentration of the treated water changes depending on the temperature inside the resin tower 2 during the standing process.

[0039] Table 4 shows the silica concentration of the treated water under conditions 7 and 8, where the temperature inside the resin column 2 was varied during the same standing time (17.5 hours). As can be seen from Table 4, when the experimental conditions and standing time are set to the same level, a higher standing temperature inside the resin column 2 can reduce the silica concentration of the treated water. However, if the standing temperature inside the resin column 2 is too high, problems such as a decrease in the product life of the ion exchange resin may occur. Therefore, the standing temperature inside the resin column 2 should be set appropriately within the range of 20°C to 60°C, for example, according to the silica concentration required for the treated water.

[0040] The temperature inside the resin tower 2 can be set, for example, by attaching heaters to the outer circumference of the resin tower 2, measuring the temperature inside the resin tower 2 with a well-known thermometer, and controlling the on / off state of the heaters with the control device 5.

[0041] [Table 4] According to this embodiment, in a mixed-bed ion exchange system, the silica concentration leaking into the treated water can be reduced by providing a settling step after the regeneration step. Furthermore, by providing a settling step, the silica concentration leaking into the treated water can be reduced without using chemicals, thus reducing chemical costs as well as the treatment costs required for treating the washing wastewater. [Explanation of Symbols]

[0042] 1. Water tank to be treated 2. Resin tower 3. Treated water tank 4, 6, 7 Pumps 5 Control device 8 Compressors

Claims

1. A method for producing pure water from treated water containing silica using a mixed-bed ion exchange apparatus, A water sampling step involves bringing the water to be treated into contact with the ion exchange resin contained within the mixed-bed ion exchange apparatus, A regeneration step performed after the water sampling step to regenerate the ion exchange performance of the ion exchange resin, A resting step is performed in which, after the regeneration step, a state of stillness is maintained for a predetermined resting time in which no water is passed through or collected from the mixed-bed ion exchange device. It has, The aforementioned mixed-bed ion exchange apparatus contains a mixture of cation exchange resin and anion exchange resin as the ion exchange resin. In the regeneration process, the cation exchange resin and the anion exchange resin are separated and regenerated, and then the cation exchange resin and the anion exchange resin are mixed. A method for producing pure water, wherein the aforementioned standing time is 0.5 hours or more and within 720 hours.

2. The method for producing pure water according to claim 1, wherein the standing time is 5 hours or more.

3. The method for producing pure water according to claim 1 or 2, wherein the standing time is 17.5 hours or more.

4. The method for producing pure water according to claim 1 or 2, wherein the temperature inside the mixed-bed ion exchange apparatus during the standing step is in the range of 20°C to 60°C.

5. A pure water production apparatus that produces pure water from treated water containing silica, Mixed-bed ion exchange system, A control device that performs a water sampling step of bringing the water to be treated into contact with the ion exchange resin contained within the mixed-bed ion exchange apparatus, a regeneration step performed after the water sampling step to regenerate the ion exchange performance of the ion exchange resin, and a resting step after the regeneration step to maintain a resting state for a predetermined resting time in which no water is passed through or water is sampled from the mixed-bed ion exchange apparatus, It has, A pure water production apparatus in which the aforementioned standing time is 0.5 hours or more and within 720 hours.

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