Method for producing pure water and apparatus for producing pure water

Abstract

The present application provides a pure water production method for producing pure water from treated water containing silicon dioxide using a mixed bed ion exchange device, comprising: a water taking step of contacting the treated water with ion exchange resin built in the mixed bed ion exchange device; a regeneration step performed after the water taking step to regenerate ion exchange performance of the ion exchange resin; and a standing step of maintaining a standing state of not supplying water to the mixed bed ion exchange device and taking water for a given standing time after the regeneration step, the standing time being 0.5 hours or more and 720 hours or less.

Description

TECHNICAL FIELD

[0001] The present application relates to a pure water production method and a pure water production apparatus for producing pure water from a treated water containing silicon dioxide using a mixed bed ion exchange device. BACKGROUND

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

[0003] The pretreatment device removes suspended substances contained in raw water such as surface water and underground water by coagulation, sedimentation, and filtration, and a primary pure water production device having a reverse osmosis membrane and an ion exchange device removes 99 to 99.99% of the raw water components to produce primary pure water. The above subsystem produces ultra pure water by removing extremely small amounts of ions and colloidal components remaining in the primary pure water.

[0004] In such a production process of ultra pure water, an ion exchange device is mainly used to remove ions from raw water to produce primary pure water. As the ion exchange device, there are known a mixed bed ion exchange device in which cation (positive ion) exchange resin and anion (negative ion) exchange resin are used as a single bed, respectively, and a mixed bed ion exchange device in which cation exchange resin and anion exchange resin are used in a mixed state. As for the mixed bed ion exchange device, for example, JP Laid-Open No. 2000-301145 is known. Further, as for the mixed bed ion exchange device, for example, JP Laid-Open No. 6-315683 is known.

[0005] In recent years, the requirements for ultrapure water have become increasingly stringent. Power plants, pharmaceutical manufacturing plants, and semiconductor manufacturing plants all require ultrapure water with high purity. Regarding the mixed-bed ion exchange units mentioned above, the regeneration process to restore the ion exchange performance of the ion exchange resins requires separating the mixed cation exchange resins from the anion exchange resins. Typically, during the separation process, backwashing is performed by injecting wash water upwards from the bottom of the ion exchange unit. Simultaneously, the density difference between the resins is used to move the anion exchange resins to the upper layer and the cation exchange resins to the lower layer, thus separating the anion and cation exchange resins. During the regeneration process, while the resins are separated, a regenerator such as an acid is injected from the bottom to regenerate the cation exchange resins, and a regenerator such as an alkali is injected from the top to regenerate them. After regeneration, the resins are washed with water, and air or nitrogen is injected into the resin bed to remix the separated cation and anion exchange resins. At this point, residual silica-type anion exchange resin that has not been fully regenerated is also present in the lower layer. Therefore, in mixed-bed ion exchange devices, there is a tendency for silica to leak towards the treated water side during water sampling. In ultrapure water requiring high purity, the silica concentration also needs to be reduced. Summary of the Invention

[0006] The present invention is proposed to solve the technical problems of the prior art as described above, and its object is to provide a method and apparatus for producing pure water that can reduce the concentration of silica leaking to the treated water side in a mixed bed ion exchange device.

[0007] To achieve the above objectives, the pure water manufacturing method of the present invention is a method for manufacturing pure water from treated water containing silica using a mixed-bed ion exchange device, comprising:

[0008] The water collection process involves bringing the water to be treated into contact with the ion exchange resin built into the mixed-bed ion exchange device.

[0009] The regeneration process, performed after the water intake process, regenerates the ion exchange performance of the ion exchange resin; and

[0010] The settling process involves maintaining the mixed-bed ion exchange device in a settling state for a given time after the regeneration process. This settling state is characterized by the absence of water flow or sampling within the device.

[0011] The settling time is more than 0.5 hours and less than 720 hours.

[0012] On the other hand, the pure water production apparatus of the present invention is a pure water production apparatus that produces pure water from treated water containing silica, and includes a mixed bed ion exchange device and a control device.

[0013] The control device performs the following procedures:

[0014] The water collection process involves bringing the water to be treated into contact with the ion exchange resin built into the mixed-bed ion exchange device.

[0015] The regeneration process, performed after the water intake process, regenerates the ion exchange performance of the ion exchange resin; and

[0016] The settling process involves maintaining the mixed-bed ion exchange device in a settling state for a given time after the regeneration process. This settling state is characterized by the absence of water flow or sampling within the device.

[0017] The settling time is more than 0.5 hours and less than 720 hours.

[0018] The above and other objects, features and advantages of the present invention will become apparent from the description of examples of the invention with reference to the accompanying drawings. Attached Figure Description

[0019] Figure 1 This is a block diagram illustrating one configuration example of a pure water manufacturing apparatus used in the pure water manufacturing method of the present invention.

[0020] Figure 2 This is a graph showing the silica concentration in the treated water under the second to sixth conditions shown in Table 3 and in the second comparative example. Detailed Implementation

[0021] The invention will now be described using the accompanying drawings.

[0022] Figure 1 This is a block diagram illustrating one configuration example of a pure water manufacturing apparatus used in the pure water manufacturing method of the present invention.

[0023] like Figure 1 As shown, the pure water production apparatus (primary pure water production apparatus) includes: a treated water tank 1, which temporarily stores the treated water after treatment by a pretreatment device (not shown); a resin tower 2, which removes ions from the treated water; a treated water tank 3, which temporarily stores the treated water after it has passed through the resin tower 2; a pump (P) 4, which is used to deliver the treated water from the treated water tank 1 to the resin tower 2; and a control device 5, which controls the operation of the primary pure water production apparatus. Additionally, Figure 1The once-through water production apparatus also has pumps (P) 6 and 7 for supplying cleaning water or a regenerant for ion exchange resin to the resin tower 2, and a compressor (C) 8 for injecting air or the like for mixing the ion exchange resin after regeneration into the resin tower 2. The control device 5 can be connected to the pumps 4, 6, and 7 for cleaning water and a regenerant, the compressor 8, and the concentration meter or the like for treated water by a known communication unit, and can control the operation of the pumps 4, 6, and 7, the compressor 8, and the like, and can receive the measurement results of the concentration meter. The communication unit can use any one of a known wired communication unit or a wireless communication unit, and the communication standard can adopt any known standard. In addition, the control device 5 has a timer for controlling the standing time in the standing process of the resin tower 2 described later. Figure 1 The once-through water production apparatus is configured to control the operation of the entire water production apparatus. The resin tower 2 is the above-described mixed bed type ion exchange apparatus in which ion exchange resin (cation exchange resin and anion exchange resin) is built in. The treated water stored in the treated water 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. For the treated water, a known concentration meter can be used to measure the concentration of silica.

[0024] From the top and the bottom of the resin tower 2, cleaning water is supplied from a tank not shown by the pumps 6 and 7. In addition, from the top and the bottom of the resin tower 2, a regenerant for ion exchange resin is supplied from a tank not shown by the pumps 6 and 7. The regeneration and water cleaning waste liquid is discharged from a water collecting pipe (intermediate header) not shown provided near the interface of the cation exchange resin and the anion resin. Furthermore, in order to mix the ion exchange resin after regeneration, air or the like is injected from the bottom of the resin tower 2 by the compressor 8. In Figure 1 In the drawing, in order to avoid the drawing becoming complicated, the resin tower 2 is supplied with cleaning water and a regenerant through the same line. However, for an actual resin tower 2, the cleaning water and the regenerant are sometimes supplied separately through different lines.

[0025] The control device 5 is connected to the pumps 4, 6, and 7 for cleaning water and a regenerant, the compressor 8, and the concentration meter or the like for treated water by a known communication unit, and can control the operation of the pumps 4, 6, and 7, the compressor 8, and the like, and can receive the measurement results of the concentration meter. The communication unit can use any one of a known wired communication unit or a wireless communication unit, and the communication standard can adopt any known standard. In addition, the control device 5 has a timer for controlling the standing time in the standing process of the resin tower 2 described later.

[0026] The control device 5 can be realized by, for example, a known PLC (Programmable Logic Controller). The control device 5 can be realized by a known information processing device (computer) having a CPU (Central Processing Unit), a storage device, an I / O interface, a communication device, and the like. The control device 5 performs processing by a processor included in the PLC or the information processing device in accordance with a program previously stored in the storage device, thereby realizing the water production method of the present application.

[0027] In such a configuration, in the present embodiment, the water taking process and the regeneration process described below are operated Figure 1 The primary water manufacturing apparatus shown, and a standing process is provided after the regeneration process, that is, a process of maintaining a standing state in which the resin tower 2 is not supplied with water or water is taken, and the like, for a given time. The water taking process, the regeneration process, and the standing process are processes described in (1) to (3) below. The water taking process, the regeneration process, and the standing process are realized by the control device 5 controlling the operation of the pump 4 for the treated water, the pumps 6 and 7 for the cleaning water and the regenerant, the compressor 8, and the like. The control device 5 manufactures the treated water (primary water) from the resin tower 2 by repeatedly executing the water taking process, the regeneration process, and the standing process.

[0028] (1) Water taking process

[0029] The water taking process is a process of generating primary water by removing ions from the treated water. In the water taking process, the pump 4 is used to supply the treated water to the resin tower 2 and to cause the ion exchange resin inside the resin tower 2 to come into contact with the treated water, thereby generating treated water (primary water) from which ions have been removed from the treated water by ion exchange.

[0030] (2) Regeneration process

[0031] The regeneration process is a process of regenerating the ion exchange performance of the ion exchange resin built into the resin tower 2. The regeneration process includes the processes described in (2-1) to (2-5) below.

[0032] (2-1) Separation process

[0033] The cleaning water is injected upward from the bottom of the resin tower 2 to separate the cation exchange resin from the anion exchange resin inside the resin tower 2. At this time, a well-known separation accelerator can be added to the cleaning water, or a medicine can be used to change the ion type of the ion exchange resin.

[0034] (2-2) Medicine passing process

[0035] After the separation process, the anion exchange resin is changed to a regenerated type (OH type, hereinafter referred to as R-OH) and the cation exchange resin is changed to a regenerated type (H type, hereinafter referred to as R-H) using a regenerant, thereby regenerating the ion exchange performance of each.

[0036] (2-3) Extrusion and cleaning process

[0037] After the medicine passing process, the cleaning water is injected from the top and the bottom of the resin tower 2 in the same direction as the direction in which the regenerant is passed, and the regenerant remaining inside the resin tower 2 is extruded and cleaned with the cleaning water.

[0038] (2-4) Mixing process

[0039] After the extruding 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. The specific gravities of the ion exchange resins differ depending on the type and ion of the resin, and therefore the cation exchange resin and the anion exchange resin are mixed in a balanced distribution.

[0040] (2-5) Purging process

[0041] After the mixing process, washing water is injected into the resin tower in a downward flow for compaction of the ion exchange resins and washing. This purging process can also be omitted.

[0042] (3) Standing process

[0043] The standing process is a process in which the state in which the resin tower 2 is not subjected to water passage, water collection, or the like is maintained for a given time (standing time) after the end of the regeneration process. The standing time differs depending on the silica load of the treated water and the silica concentration required for the treated water, but is preferably 0.5 hours or more. The standing time is more preferably 5 hours or more and further preferably 17.5 hours or more, as shown in the examples described later.

[0044] Thus, by providing the standing process after the regeneration process, the silica concentration that leaks to the treated water side from the resin tower (mixed bed type ion exchange device) 2 can be reduced. As described above, in the mixed bed type ion exchange device, if the water collection process is performed in a state in which the silica type anion exchange resin moves to the lower portion of the resin tower 2 due to mixing, there is a tendency for silica to easily leak to the treated water side. If the standing process is provided after the regeneration process, the silica type anion exchange resin in the lower portion of the resin tower 2 is reduced due to diffusion of the silica, and it is considered that the silica that leaks to the treated water side is also reduced.

[0045] The standing time can be set in advance based on experimental results or the like depending on the silica concentration required for the treated water. In the case where the silica concentration of the treated water is measured using a concentration meter, the standing time can be changed depending on the silica concentration required for the treated water.

[0046] [Examples]

[0047] Next, examples of the present application will be described.

[0048] (First Example)

[0049] In the first example, it is shown that the silica concentration of the treated water can be reduced by providing the standing process.

[0050] Table 1 shows the experimental conditions and the silica concentration of the treated water of the first condition with the standing process and the first comparative example without the standing process, respectively. Table 2 shows the regeneration conditions of the cation exchange resin and the anion exchange resin performed in the present embodiment, respectively.

[0051] The first condition and the first comparative example were experimented under the same conditions except for the presence or absence of the standing process. That is, the same model of ion exchange resin of the same manufacturer was used, and the same inner diameter column was used as the resin column 2, the same treated water was passed at the same silica load, the same elution time was performed, the cation exchange resin and the anion exchange resin were regenerated under the conditions shown in Table 2, and the ion exchange resins were mixed under the same mixing conditions and the same elution conditions. The standing time of the first condition was set to 17.5 hours (h), and the standing time of the first comparative example was set to 0 hours (h).

[0052] In addition, although the elution process, the regeneration process, and the standing process are performed in the same resin column 2 in an actual water purification device, the inner diameter of the column for elution used in the experiment of the first embodiment is small, and backwashing and mixing cannot be smoothly performed. Therefore, in the first embodiment, backwashing was performed by transferring the ion exchange resin in the column for elution to a column with a large inner diameter. In addition, in the first embodiment, mixing was performed manually before transferring the ion exchange resin after regeneration to the column for elution. Furthermore, the column for elution does not have a configuration corresponding to an intermediate header, and therefore the regeneration of the cation exchange resin and the anion exchange resin was performed using different columns. Therefore, the work sequence of the experiment shown in the first embodiment was in the order of elution, transfer of the column, backwashing and separation, extraction of the anion exchange resin (the cation exchange resin was left as it was), regeneration of the two ion exchange resins (passing of the eluent, extrusion, and washing), extraction of the two ion exchange resins, mixing, filling of the two ion exchange resins with respect to the column for elution, standing (only the first condition), elution (15-minute washing), and elution (for confirming the initial silica leakage concentration).

[0053] The meanings of the abbreviations used in Tables 1, 2, and Tables 3, 4 described later are as follows.

[0054] CER: Cation (positive ion) exchange resin.

[0055] AER: Anion (negative ion) exchange resin.

[0056] LV (m / h): Linear velocity. Characterizes the speed (flow rate) of the washing water passing through the cross section of the resin column (column).

[0057] SV (L / L-resin / h): Space velocity. Characterizes the speed (flow rate) of the eluent and the washing water per unit amount of resin.

[0058] UPW: Ultra-Pure Water

[0059] [Table 1]

[0060]

[0061] [Table 2]

[0062] Regeneration step

[0063]

[0064] (Second Example)

[0065] In the second example, the change in the silica concentration of the treated water by changing the standing time is shown.

[0066] Table 3 shows the experimental conditions and the silica concentration of the treated water of the second condition to the sixth condition having the standing step, and the second comparative example not having the standing step, respectively.

[0067] As shown in Table 3, the standing time of the second condition is 1 hour (h), the standing time of the third condition is 3.4 hours (h), the standing time of the fourth condition is 5.4 hours (h), the standing time of the fifth condition is 20 hours (h), and the standing time of the sixth condition is 24 hours (h). The standing time of the second comparative example is 0 hours (h). The other conditions are the same as those of the second condition to the sixth condition and the second comparative example. Figure 2 is a graph showing the silica concentration of the treated water in the second condition to the sixth condition and the second comparative example shown in Table 3.

[0068] From Table 3 and Figure 2 It is known that the longer the standing time, the lower the silica concentration of the treated water. In addition, if the standing time is 1 hour or more as shown in the second condition, and is 0.5 hours or more at the lowest, it is considered that the silica concentration of the treated water is lower than that of the second comparative example not having the standing step.

[0069] In addition, from Figure 2 It is known that the silica concentration of the treated water is greatly reduced until the standing time reaches 5 hours, and if the standing time is further extended, the reduction slows down, and if the standing time exceeds 17.5 hours, it tends to be stable. In addition, in the sixth condition where the standing time is 24 hours, the measurement result of the silica concentration is below the measurement limit (2 μg / L), and therefore, the silica concentration is set to "0" in the graph of Figure 2 . Therefore, the sixth condition is excluded from the data for observing the change in the silica concentration with respect to the standing time.

[0070] Therefore, the standing time is preferably 0.5 hours or more, more preferably 5 hours or more, and further preferably 17.5 hours or more. However, if the standing time is too long, the efficiency of producing the ultrapure water using the pure water production device decreases, and thus is not preferable. From Table 3 and Figure 2 It is known that if the standing time exceeds 24 hours, the silica concentration of the treated water does not change much. Therefore, the standing time is preferably, for example, 720 hours (30 days) or less.

[0071] [Table 3]

[0072]

[0073] (Third Embodiment)

[0074] In the third embodiment, the change in the silica concentration of the treated water with the temperature in the resin column 2 in the standing process is shown.

[0075] Table 4 shows the silica concentration of the treated water in the seventh condition and the eighth condition in which the temperature in the resin column 2 is changed, respectively, at the same standing time (17.5 hours). From Table 4, it is known that, in the case where the same experimental conditions and the same standing time are set, the higher the standing temperature in the resin column 2, the lower the silica concentration of the treated water. However, if the standing temperature in the resin column 2 is too high, there is a concern that the product life of the ion exchange resin decreases and the like. Therefore, the standing temperature in the resin column 2 is appropriately set in the range of 20°C to 60°C, for example, according to the silica concentration required for the treated water.

[0076] For example, a heater or the like can be installed on the outer periphery of the resin column 2, and the temperature in the resin column 2 is measured with a known thermometer while the on / off of the heater is controlled with the control device 5, thereby setting the temperature in the resin column 2.

[0077] [Table 4]

[0078]

[0079] According to the present embodiment, in the mixed bed type ion exchange device, by providing the standing process after the regeneration process, the silica concentration leaked to the treated water side can be reduced. In addition, by providing the standing process, the silica concentration leaked to the treated water side can be reduced without using a chemical or the like, and thus not only the chemical cost can be reduced, but also the treatment cost required for the treatment of the cleaning waste liquid can be reduced.

[0080] Although the present application has been described with reference to the embodiments, the present application is not limited to these embodiments. Those skilled in the art will appreciate that various modifications can be made to the form and details of the present application without departing from the spirit and scope of the application as defined by the claims.

Claims

1. A pure water production method of producing pure water from treated water containing silica using a mixed bed ion exchanger device in which a cation exchange resin and an anion exchange resin are built-in, comprising: a water taking step of bringing the treated water into contact with the cation exchange resin and the anion exchange resin built-in the mixed bed ion exchanger device; a regeneration step of regenerating ion exchange performance of the cation exchange resin and the anion exchange resin after the water taking step; and a standing step of maintaining a standing state in which water is not supplied to or taken from the mixed bed ion exchanger device for a given standing time after the regeneration step, the standing time being 0.5 hours or more and 720 hours or less, the concentration of silica leaked to a treated water side due to mixing of the cation exchange resin and the anion exchange resin being reduced by the standing step.

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

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

4. The pure water production method according to claim 1 or 2, wherein a temperature in the mixed bed ion exchanger device in the standing step is in a range of 20°C to 60°C.

5. A pure water production device of producing pure water from treated water containing silica, the pure water production device having a mixed bed ion exchanger device in which a cation exchange resin and an anion exchange resin are built-in, and a control device, the control device executing the following steps: a water taking step of bringing the treated water into contact with the cation exchange resin and the anion exchange resin built-in the mixed bed ion exchanger device; a regeneration step of regenerating ion exchange performance of the cation exchange resin and the anion exchange resin after the water taking step; and a standing step of maintaining a standing state in which water is not supplied to or taken from the mixed bed ion exchanger device for a given standing time after the regeneration step, the standing time being 0.5 hours or more and 720 hours or less, the concentration of silica leaked to a treated water side due to mixing of the cation exchange resin and the anion exchange resin being reduced by the standing step. ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​

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