JP2017148698A - Cleansing method for ultrapure water production system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an ultrapure water production system cleansing method capable of efficiently eliminating an impurity such as an organic material, fine particles or an ionic material mixed into or produced in an ultrapure water production system.SOLUTION: Ultrapure water is fed under a high pressure to at least a portion of an ultrapure water manufacturing system which comprises an ultrapure water production apparatus, a use point, and a pipe line connecting the ultrapure water production apparatus with the use point, so that fine particles and an organic material adhered in the ultrapure water manufacturing system especially in an inner wall or the like of the pipeline are produced and are physically cleared and removed.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a cleaning method for an ultrapure water production system, and more particularly, to a pipe for an ultrapure water production system when a new ultrapure water production system is started up or when it is restarted after a certain period of inactivity. The present invention relates to a cleaning method.

  Conventionally, in the field of manufacturing electronic devices such as semiconductors and liquid crystal panels, ultrapure water having a very small content of impurities such as organic substances, fine particles, and ionic substances has been used to clean the system. In particular, in the semiconductor manufacturing process, the ultrapure water to be used is required to have a very high purity as the semiconductor is miniaturized and the capacity is increased. For example, the required water quality for ultrapure water used in the latest semiconductor manufacturing is: resistivity: 18.2 MΩ · cm or more, fine particles: 1 piece / mL or less, viable bacteria: 1 piece / L or less, TOC (Total Organic Carbon: Total organic carbon): 1 ppb or less, silica: 1 ppb or less, metals: 1 ppt or less, ions: 10 ppt or less.

  Ultrapure water used in such semiconductor manufacturing processes is mainly manufactured in an ultrapure water production apparatus equipped with a pretreatment system, a primary pure water system, and a secondary pure water system (subsystem). To be supplied. The pretreatment system is for turbidizing raw water using a turbidity treatment device such as coagulation filtration, microfiltration membrane (MF membrane), ultrafiltration membrane (UF membrane), etc., or a dechlorination treatment device such as activated carbon. is there. The primary pure water system is for removing impurities such as ion components and TOC components contained in pretreated water by a reverse osmosis membrane (RO membrane) device, a degassing membrane device, an ion exchange tower, and the like. Sub-systems mainly include sub-tanks that temporarily store primary pure water, heat exchangers, UV oxidation devices (UV devices), catalytic oxidant decomposition devices, deaeration devices, mixed-bed ion exchange devices, and limit Equipped with a filtration membrane device (UF device) to remove ultra-fine particles and trace ions in primary pure water, especially impurities such as low-molecular trace organics, and to produce ultrapure water with higher purity It is. An ultrapure water production system equipped with such an ultrapure water production system circulates ultrapure water that has not been used at a point of use and a water supply pipe that circulates ultrapure water from the subsystem to the point of use. And a return pipe for carrying out.

  In general, when a new ultrapure water production system such as the one described above is started up or when it is restarted after being suspended for a certain period of time, impurities such as organic substances, fine particles, and ionic substances are mixed in the system. Therefore, the system is cleaned until these impurities are removed and the ultrapure water at the use point satisfies the required water quality. In particular, when a new ultrapure water production system is started up due to the establishment of a new factory, fine particles and organic substances adhere to the inner wall of the pipe during the operation, so it takes a lot of time to clean the system. Operating efficiency is reduced.

  As a cleaning method for impurities mixed in or generated in the system as described above, for example, in Patent Document 1, compressed gas and ultrapure water are alternately supplied as a cleaning method when the ultrapure water production apparatus is started up. Thus, a method for cleaning the inner wall of the pipe has been proposed.

JP 2004-050048 A

  It is known that the fine particles adhering to the inner wall of the pipe of the ultrapure water production apparatus are peeled off from the inner wall of the pipe due to a sudden pressure fluctuation. For this purpose, cleaning is performed using compressed gas and ultrapure water in combination. However, since gas is used to fluctuate the pressure received by the piping, the dissolved gas may remain in the dead space in the piping, which may lead to a decrease in the purity of the manufactured ultrapure water. . Therefore, since it takes more time to remove the dissolved gas, there is a problem that it is difficult to clean the ultrapure water production system in a short time.

  The present invention has been made based on the above circumstances, and an ultrapure water production system capable of efficiently removing fine particles caused by impurities mixed in or generated in the ultrapure water production system. The purpose is to provide a cleaning method.

  In order to solve the above problems, firstly, the present invention provides at least a part of an ultrapure water production system including an ultrapure water production apparatus, a use point, and a pipe connecting the ultrapure water production apparatus and the use point. A method of cleaning an ultrapure water production system having a high-pressure cleaning step of cleaning by supplying ultrapure water at a high pressure is provided (Invention 1).

  According to this invention (Invention 1), by supplying ultrapure water at a high pressure, fine particles adhering to the inside of the ultrapure water production system, particularly the inner wall of the pipe can be efficiently peeled and removed. The cleaning operation can be performed in a short time.

  In the said invention (invention 1), supply of the ultrapure water in the said high pressure washing process is performed continuously or intermittently at a pressure higher than the pressure applied at the use point, or higher than the pressure applied at the use point. It is preferable to carry out by gradually increasing the pressure (Invention 2).

  According to this invention (Invention 2), the ultrapure water is supplied continuously or intermittently at a pressure higher than the arrival pressure at the use point, or gradually rises to a pressure higher than the arrival pressure at the use point. By supplying ultrapure water in this way, it is possible to effectively remove the fine particles adhering to the inner wall of the pipe of the ultrapure water production system due to the generated turbulent flow or the like. In the present invention, “continuous” means that the pressure is higher than the pressure at the point of use, the flow rate is 0.5 m / sec or more, the washing is carried out for 0.5 hours or more, and the total flow rate is 10 times or more of the amount of water retained in the pipe. “Intermittent” means that the pressure is higher than the pressure applied at the point of use, and is washed intermittently at a flow rate of 0.5 m / sec or more for a total of 0.5 hours or more. Being more than 10 times the amount of water, “gradually” means cleaning at a flow rate of 0.5 m / sec or more and gradually increasing the pressure so that the final pressure is higher than the pressure at the point of use. It means to increase at a speed of 0.5 × Δrequired increasing pressure / h and a pressure increasing rate of 10% or more.

  In the said invention (invention 1 and 2), it is preferable that at least one part of the said piping consists of polyvinylidene fluoride (PVDF) (invention 3).

  As the piping material of the ultrapure water production system, polyvinyl chloride (PVC), polyvinylidene fluoride (PVDF), or the like is used in consideration of the eluent in ultrapure water and the small amount of dirt brought in during construction. Among them, PVDF is suitably used as a piping material because of its excellent corrosion resistance and heat resistance, but distortion such as heat wrinkles in the processing process and conveyance wrinkles in the construction process may occur. Impurities such as fine particles easily enter. According to this invention (Invention 3), when cleaning the ultrapure water production system, such PVDF piping wrinkles can be stretched by high-pressure cleaning, so that fine particles and the like that have entered the wrinkles can be effectively removed. it can.

In the above invention (Invention 1-3), ultra-pure water in the high pressure washing step, alkali, hydrogen peroxide (H 2 _{O 2),} comprising ozone or gas, or preferably a hydrothermal (invention 4 ).

According to this invention (Invention 4), the physical cleaning effect of the high-pressure cleaning step includes a chemical cleaning effect with alkali, hydrogen peroxide (H ₂ O ₂ ) or ozone, a physical cleaning effect with gas, and hot water. Since a sterilizing effect and the like are further added, the cleaning effect can be further improved.

  In the said invention (invention 1-4), it is preferable to have the discharge process which pushes out the ultrapure water which has stayed in the system after the said high-pressure washing process out of the system (invention 5).

  According to this invention (invention 5), since the ultrapure water staying in the system after the high pressure cleaning step is pushed out of the system, the fine particles dispersed in the ultrapure water after the high pressure cleaning step are removed from the pipe. It is possible to prevent reattachment to the inner wall or the like.

  In the said invention (invention 1-5), the said ultrapure water manufacturing apparatus is equipped with the ultrafiltration membrane apparatus (UF apparatus), and the said ultrafiltration membrane apparatus (UF apparatus) is at the time of washing | cleaning of the said ultrapure water manufacturing system. Instead, it is preferable to install a dummy pipe or a dummy UF device having no UF function to allow water to pass through (Invention 6).

  According to this invention (invention 6), when the ultrapure water production system is cleaned, the dummy tube or the dummy UF device is used instead of the UF device, so that the UF device is clogged at the cleaning stage due to fine particles peeled off from the piping. Therefore, the cost for the UF device can be reduced.

  According to the cleaning method of the ultrapure water production system of the present invention, the fine particles adhering to the ultrapure water production system, in particular, the inner wall of the pipe can be efficiently peeled and removed, so that the cleaning operation is shortened. Can be done in time.

FIG. 1 is a block diagram showing an ultrapure water production system used in a cleaning method for an ultrapure water production system according to an embodiment of the present invention. FIG. 2 is a graph showing the relationship between the number of fine particles and the elapsed time after cleaning when the piping pressure of Example 1 is changed from 0.4 MPa to 0.7 MPa. FIG. 3 is a graph showing the relationship between the number of fine particles and the elapsed time after cleaning in Example 2. FIG. 4 is a graph showing the relationship between the number of fine particles and the elapsed time after cleaning in the comparative example.

  Hereinafter, an embodiment of a cleaning method for an ultrapure water production system of the present invention will be described with reference to the drawings as appropriate. The embodiment described below is for facilitating the understanding of the present invention, and does not limit the present invention.

[Ultrapure water production system]
FIG. 1 is a block diagram showing an ultrapure water production system used in a cleaning method for an ultrapure water production system according to an embodiment of the present invention. The ultrapure water production system 1 shown in FIG. 1 is ultrapure from an ultrapure water production apparatus having a pretreatment system 2, a primary pure water system 3, and a secondary pure water system (subsystem) 4 in this order to a use point 5. It supplies water. The raw water supplied to the pretreatment system 2 passes through the water supply pipe L1 after turbidity treatment by coagulation filtration, MF membrane (microfiltration membrane), UF membrane (ultrafiltration membrane) or dechlorination treatment by activated carbon. , Supplied to the primary pure water system 3. The treated water supplied to the primary pure water system 3 is subjected to removal of impurities such as ion components and TOC components by an RO membrane (reverse osmosis membrane), a degassing membrane, an ion exchange tower, etc., and then passes through a water supply pipe L2. , Supplied to the subsystem 4. In the subsystem 4, impurities such as trace amounts of fine particles and trace ions in the treated water, particularly low molecular weight trace organic substances, are removed, and ultrapure water with higher purity is produced. The ultrapure water produced by the subsystem 4 is sent to the use point 5 through the water supply pipe L4.

The sub-system 4 includes a sub-tank 41, a heat exchanger 42, an ultraviolet oxidizer (UV device) 43, a catalytic oxidizer decomposition device 44, a deaerator 45, a mixed bed ion exchanger 46, an ultrafiltration membrane device ( UF device) 47 in this order. The sub tank 41 is for temporarily storing treated water supplied from the primary pure water system 3. The heat exchanger 42 is for adjusting the temperature of the treated water. The ultraviolet oxidation device (UV device) 43 is for oxidizing and decomposing organic matter (TOC component) in water by oxidation treatment by ultraviolet irradiation. The catalytic oxidant decomposition apparatus 44 is formed of H ₂ generated in the ultraviolet oxidation apparatus (UV apparatus) 43 by a palladium (Pd) compound such as metal palladium, palladium oxide, palladium hydroxide, or a noble metal catalyst such as platinum (Pt). This is for decomposing and removing O ₂ and other oxidizing substances. The deaeration device 45 is for reducing the amount of dissolved oxygen in the treated water. The mixed bed type ion exchange device 46 is for removing cations and anions in the treated water and increasing the purity of the treated water. The ultrafiltration membrane device (UF device) 47 is for removing fine particles and the like of the ion exchange resin flowing out from the mixed bed type ion exchange device 46. The devices constituting these subsystems 4 are connected by pipes L31-36, respectively.

  In this embodiment, a pump P for changing the pressure of the supplied ultrapure water is provided in the water supply pipe L31 that connects the sub tank 41 and the heat exchanger 42. The pump P is also provided in a water supply pipe L <b> 35 that connects the deaeration device 45 and the mixed bed ion exchange device 46.

  The ultrapure water production system according to the present embodiment returns the ultrapure water that has not been used at the use point 5 to the subtank 41 of the subsystem 4 in addition to the water supply pipes L1, L2, L31-36, and L4. A pipe R1 and a return pipe R2 for circulating ultrapure water after passing through a dummy pipe or a dummy UF device having no UF function at the time of cleaning directly from the water supply pipe L4 to the sub tank 41 are provided.

  Since the purity of the treated water sent from the subsystem 4 to the use point 5 is required, the water supply pipe L36 connecting the mixed bed type ion exchange device 46 and the ultrafiltration membrane device (UF device) 47, the subsystem 4 and The material of the water supply pipe L4 and the return pipe R1 that connect the use point 5 is polyvinylidene fluoride (PVDF). Since PVDF is excellent in chemical resistance against chemicals such as alkali, corrosion resistance against sterilization washing and ultraviolet light sterilization, heat resistance against sterilization washing with hot water, etc., it has the effect of suppressing the elution of impurities into the treated water. On the other hand, since the purity of the treated water required before the mixed bed type ion exchanger 46 is not so high, the piping material other than the above does not need to be PVDF.

[Cleaning method of ultrapure water production system]
Next, a cleaning method using the ultrapure water production system of the embodiment as described above will be described. The target of the cleaning method of the ultrapure water production system according to the present embodiment is the devices 41-47 of the subsystem 4, the water supply pipe L31-36 connecting the devices of the subsystem 4, the subsystem 4 and the use point 5 Are water supply pipe L4 and return pipes R1 and R2. In this embodiment, the particle diameter of the fine particles to be cleaned is 10 to 200 nm, and the ultrapure water used for cleaning refers to pure water having a specific resistance value of 15 MΩcm or more.

<High pressure cleaning process>
The high-pressure cleaning process is a process of physically removing fine particles and organic substances adhering to the inside of the ultrapure water production system, particularly the inner wall of the pipe, etc., with ultrapure water supplied at high pressure. The pressure of the supplied ultrapure water is adjusted by changing the inverter of the pump P arranged in the subsystem 4 or by opening / closing a valve (not shown) installed in the piping in the subsystem 4.

  The supplied ultrapure water preferably has a temperature of 20 to 85 ° C., a flow rate of 0.5 to 4.0 m / sec, and a flow rate of 10 times the pipe volume. By supplying ultrapure water under the above-described conditions, fine particles and the like can be efficiently removed. The timing for ending the cleaning is measured by an on-line particle monitor (not shown) installed in the return pipe R1, so that the number of particles of 20 nm or more present in the treated water is 1 / mL or less (hereinafter referred to as “steady state”). It may be called “state”.).

  The supply of ultrapure water in the high-pressure washing step may be continuously performed at a pressure higher than the landing pressure at the use point 5. The term “continuous” as used herein refers to a pressure higher than the landing pressure at the use point 5, with a flow rate of 0.5 m / sec or more, and washing for 0.5 hours or more, so that the total flow rate is at least 10 times the amount of water retained in the pipe. It is to become. In this case, the landing pressure at the use point 5 is preferably 0.7 MPa or less, and the pressure of the supplied ultrapure water is preferably in the range of 0.15 MPa to 0.8 MPa. By supplying ultrapure water under the above-mentioned conditions, the fine particles adhering to the inner wall of the pipe of the ultrapure water production system that is difficult to be peeled off by normal water flow can be easily peeled and removed.

  The supply of ultrapure water in the high-pressure cleaning step may be intermittently performed at a pressure higher than the landing pressure at the use point 5. The term “intermittent” as used herein is a pressure higher than the pressure applied at the use point 5 and is washed intermittently at a flow rate of 0.5 m / sec or more for a total of 0.5 hours or more. The amount of water is 10 times or more. In this case, the landing pressure at the use point 5 is preferably 0.7 MPa or less, and the normal pressure of the supplied ultrapure water is preferably in the range of 0.15 MPa to 0.8 MPa. By supplying ultrapure water under the above-described conditions, it is possible to effectively remove fine particles adhering to the inner wall of the pipe of the ultrapure water production system due to the generated turbulent flow or the like.

  The intermittent high-pressure cleaning is preferably performed after the passage of a predetermined time, after passing water at a predetermined flow rate, or after confirming that the number of fine particles measured has reached a steady state. By performing intermittent high-pressure cleaning in this manner, the piping of the subsystem 4 is susceptible to sudden pressure fluctuations, so that the removal efficiency of fine particles adhering to the piping and the like is increased.

  The supply of ultrapure water in the high-pressure cleaning step may be performed by gradually increasing the pressure to a pressure higher than the landing pressure at the use point 5. Here, “gradual” means that the flow rate is 0.5 m / sec or more and the washing is performed for 0.5 hours or more, and the total flow rate is 10 times or more of the amount of water retained in the pipe. In this case, the landing pressure at the use point 5 is preferably 0.7 MPa or less, and the normal pressure of the supplied ultrapure water is preferably in the range of 0.15 MPa to 0.8 MPa. By supplying ultrapure water under the above-described conditions, it is possible to effectively remove fine particles adhering to the inner wall of the pipe of the ultrapure water production system due to the generated turbulent flow or the like.

  The gradual high-pressure washing is preferably performed by increasing the pressure continuously or stepwise. When the pressure is continuously increased, it is preferably performed at a predetermined rate of increase, and when the pressure is increased stepwise, after a predetermined time has elapsed, after a predetermined flow rate of water has passed, or the number of particles measured is in a steady state. It is preferable to carry out after confirming that it has become. By performing the gradual high-pressure cleaning in this manner, the piping of the subsystem 4 is susceptible to sudden pressure fluctuations, so that the removal efficiency of the fine particles adhering to the piping is increased.

The cleaning method of the ultrapure water production system according to the present invention is not limited to the above embodiment, and the ultrapure water in the high pressure cleaning step includes alkali, hydrogen peroxide (H ₂ O ₂ ), ozone or gas, or Hot water may be used. In this way, by performing cleaning by combining ultrapure water and alkali or the like, chemical cleaning effect by alkali or the like and physical cleaning effect by gas are further added to the physical cleaning effect of the high pressure cleaning process by ultrapure water. Therefore, the cleaning effect by the cleaning method of the ultrapure water production system according to the present invention can be further improved. Hereinafter, the cleaning effect when the high pressure cleaning process is performed using the alkali or the like will be described.

[alkali]
By using alkali, fine particles adhering to the piping of the subsystem 4 can be chemically peeled and dispersed. The ultrapure water containing alkali is preferably a tetramethylammonium hydroxide aqueous solution or a solution containing any of choline, caustic soda and ammonia, and preferably has a pH of 10 or more. Moreover, it is preferable that the washing | cleaning time by the ultrapure water containing an alkali is the range of 0.5 to 2 hours.

[hydrogen peroxide]
The use of hydrogen peroxide (H 2 _{O 2),} the foaming power of hydrogen peroxide (H 2 _{O 2),} it is possible to chemically remove the microorganisms adhering to the piping of the subsystem 4. The concentration of ultrapure water containing hydrogen peroxide (H ₂ O ₂ ) is preferably 0.1% or more. Also, hydrogen peroxide _(H 2 _{O 2)} cleaning time with ultrapure water containing is preferably in the range of 0.5 to 2 hours.

[ozone]
By using ozone, the fine particles adhering to the piping of the subsystem 4 can be chemically removed by the oxidative decomposition power of ozone. The concentration of ultrapure water containing ozone is preferably 0.1 mg / L or more. Moreover, it is preferable that the washing | cleaning time by the ultrapure water containing ozone is the range of 0.5 to 2 hours.

[gas]
By introducing a gas such as air or nitrogen continuously or intermittently into the ultrapure water, the washing water is strongly stirred by bubbles such as air or nitrogen, so that it adheres to the piping of the subsystem 4 or the like. Fine particles can be physically peeled and dispersed.

[hot water]
Since the ultrapure water in the high-pressure washing process is hot water, the piping of the subsystem 4 can be sterilized and washed. The temperature of hot water is preferably 60 ° C. or higher. When performing sterilization washing with hot water, the piping of the subsystem 4 is preferably made of PVDF having excellent heat resistance.

<Discharge process>
Moreover, in this embodiment, the washing | cleaning method of the ultrapure water manufacturing system which concerns on this invention has the discharge process which pushes out the ultrapure water which retains in a system after the said high pressure washing process out of the system. The water passing time in the discharging step is preferably in the range of 0.5 to 24 hours.

The combination of the high-pressure cleaning step, the alkali and the like and the discharge step in the cleaning method of the ultrapure water production system according to the present embodiment includes a high-pressure cleaning step using ultrapure water containing alkali, hydrogen peroxide (H ₂ O _It is preferable to perform the washing and discharging steps with ultrapure water containing ₂ ) in this order. By combining in this way, the effects of both chemical cleaning with alkali and hydrogen peroxide (H ₂ O ₂ ) and physical cleaning with high-pressure supply of ultrapure water can be expected. In the above combination, the high-pressure cleaning step using ultrapure water containing alkali and the cleaning using ultrapure water containing hydrogen peroxide (H ₂ O ₂ ) may be repeated twice in this order. By repeating the cleaning with alkali and hydrogen peroxide (H ₂ O ₂ ) twice, the effect of chemical cleaning is further enhanced.

  In the above combination, the high-pressure cleaning process using ultrapure water containing alkali may be performed separately in the cleaning using ultrapure water containing alkali and the high-pressure cleaning process using ultrapure water. In this case, it is preferable to perform the high-pressure washing process with ultrapure water after alkali washing. Here, “after alkali cleaning” refers to after the passage of a predetermined time in cleaning with alkali, after passing water at a predetermined flow rate, or after confirming that the number of fine particle measurement is in a steady state.

  Moreover, in the said combination, you may perform a high pressure washing | cleaning process further during a discharge process, and may be performed after a discharge process. Here, “after the discharge process” refers to after the passage of a predetermined time in the discharge process, after passing water at a predetermined flow rate, or after confirming that the number of fine particle measurement has reached a steady state. By carrying out the high-pressure washing process during or after the discharge process, the treated water that could not be pushed out or could not be pushed out by the discharge process alone was pushed out of the system. The effect of preventing reattachment to the inner wall can be expected.

  The time required for cleaning by the combination as described above is 2 hours to 7 days. The timing for ending the cleaning is measured by an on-line particle monitor (not shown) installed in the return pipe R1, so that the number of particles of 20 nm or more present in the treated water is 1 / mL or less (steady state). It is judged by whether or not.

  When cleaning the ultrapure water production system, instead of the ultrafiltration membrane device (UF device) 47, a polyvinyl chloride (PVC) dummy tube (not shown) or a dummy UF device having no UF function (not shown) Not) is installed. By using the dummy tube or the dummy UF device, it is possible to prevent the UF device from being clogged at the cleaning stage, so that the cost of the UF device can be reduced. In addition, when using a dummy pipe | tube or a dummy UF apparatus, the time which washing | cleaning requires is 12 hours-7 days.

  The present invention has been described above with reference to the drawings. However, the present invention is not limited to the above-described embodiment, and various modifications can be made.

  EXAMPLES Hereinafter, although this invention is demonstrated further in detail based on an Example, this invention is not limited to a following example.

[Example 1]
Subsystem 4 was cleaned using the ultrapure water production system shown in FIG. An on-line particulate monitor (manufactured by Particle Measuring Systems, trade name: UDI-20) was installed in the return pipe R2, and the pipe pressure of the return pipe R1 was changed from 0.4 MPa to 0.7 MPa.

[result]
FIG. 2 shows the relationship between the pressure and the number of fine particles and the elapsed time after cleaning. As can be seen from this result, when the pressure increases, fine particles are generated. Thus, it can be seen that there is a certain effect in performing the pipe cleaning of the subsystem 4 under a high pressure condition.

[Example 2, comparative example]
Two PVDF pipes with a pipe diameter of 25A were used as the return pipe R2, and two pipes were installed with a pipe length of 50 m. One was subjected to continuous high-pressure washing using ultrapure water containing alkali, and as another comparative example, the other was washed only with ultrapure water containing alkali. In each case, the water flow rate was 0.5 m / sec, and the flow rate was 3 m ³ . The pressure of the return pipe R2 was 0.4 MPa for alkali cleaning + continuous high pressure cleaning (Example 2), and 0.3 MPa for only alkali cleaning (Comparative Example). The normal pressure was 0.3 MPa. The number of fine particles was measured using an online fine particle monitor (UDI-20: manufactured by Particle Measuring Systems) installed in the return pipe R2.

[result]
FIG. 3 shows the relationship between the number of fine particles and the elapsed time after cleaning when performing continuous high-pressure cleaning using ultrapure water containing alkali (Example 2), and cleaning only with ultrapure water containing alkali. The relationship between the number of fine particles and the elapsed time after cleaning is shown in FIG. As can be seen from this result, when continuous high-pressure cleaning is performed using ultrapure water containing alkali, the number of fine particles of 20 nm or more is stabilized after 30 hours. This shows that the cleaning time is shortened when alkaline cleaning is combined with continuous high-pressure cleaning.

  As described above, according to the cleaning method of the ultrapure water production system of the present invention, by supplying ultrapure water at a high pressure, fine particles adhering to the inside of the ultrapure water production system, in particular, the inner wall of the pipe are removed. Since it can peel and remove efficiently, a cleaning operation can be performed in a short time. In addition, when the high-pressure cleaning process is performed with ultrapure water containing alkali, the chemical cleaning effect due to alkali is added to the physical cleaning effect of supplying ultrapure water at a high pressure, so that ultrapure water is more effective. Cleaning in the water production system can be performed.

  The present invention eliminates impurities mixed or generated in the system when the ultrapure water production system is newly started up or when it is restarted after a certain period of operation stoppage. It is useful as a method for cleaning the system until it meets the required water quality.

DESCRIPTION OF SYMBOLS 1 ... Ultrapure water production system 2 ... Pretreatment system 3 ... Primary pure water system 4 ... Ultrapure water production apparatus (subsystem)
41 ... Sub tank 42 ... Heat exchanger 43 ... UV oxidation device (UV device)
44 ... Catalytic oxidizing substance decomposition device 45 ... Deaeration device 46 ... Mixed bed type ion exchange device 47 ... Ultrafiltration membrane device (UF device)
5 ... Use points L1, L2, L31-36, L4 ... Water supply piping R1, R2 ... Return piping P ... Pump W ... Raw water

Claims (6)

A method for cleaning at least a part of an ultrapure water production system, a use point, and an ultrapure water production system comprising a pipe connecting the ultrapure water production device and the use point,
A cleaning method for an ultrapure water production system having a high pressure cleaning process for cleaning by supplying ultrapure water at a high pressure.   Supplying ultrapure water in the high-pressure washing step is performed continuously or intermittently at a pressure higher than the arrival pressure at the use point, or gradually increased to a pressure higher than the arrival pressure at the use point. The cleaning method of the ultrapure water production system according to claim 1.   The method for cleaning an ultrapure water production system according to claim 1 or 2, wherein at least a part of the pipe is made of polyvinylidene fluoride (PVDF). The ultrapure water according to any one of claims 1 to 3, wherein the ultrapure water in the high-pressure washing step contains alkali, hydrogen peroxide (H ₂ O ₂ ), ozone or gas, or is hot water. Cleaning method for water production system.   The cleaning method for an ultrapure water production system according to any one of claims 1 to 4, further comprising a discharge step of pushing out ultrapure water staying in the system after the high pressure cleaning step. The ultrapure water production apparatus comprises an ultrafiltration membrane device (UF device),
6. In cleaning the ultrapure water production system, instead of the ultrafiltration membrane device (UF device), a dummy tube or a dummy UF device having no UF function is installed and water is passed. The method for cleaning an ultrapure water production system according to any one of the above.

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