TWI699245B - Cleaning method of ultrapure water production system - Google Patents

Abstract

The present invention provides a cleaning method for an ultrapure water production system, which can efficiently remove impurities such as organic matter, fine particles, ionic substances, etc., mixed or generated in the ultrapure water production system. By supplying ultrapure water at high pressure to at least a part of an ultrapure water production system equipped with an ultrapure water production device, a point of use, and a piping connecting the ultrapure water production device and the point of use, it is attached to the ultrapure water production The fine particles or organic matter in the system, especially on the inner wall of the piping, etc., will be physically cleaned and removed.

Description

Cleaning method of ultrapure water production system

The present invention relates to a cleaning method of an ultrapure water production system, and particularly relates to the cleaning of the piping of an ultrapure water production system when the ultrapure water production system is newly started or restarted after stopping for a certain period of time. Net method.

Previously, in the field of electronic equipment manufacturing such as semiconductors and liquid crystal panels, ultrapure water with extremely small contents of impurities such as organic matter, fine particles, and ionic substances was used to clean the system. Among them, in the semiconductor manufacturing process, with the miniaturization and larger capacity of semiconductors, very high purity is required for the ultrapure water used. For example, the latest water quality requirements for ultrapure water used in semiconductor manufacturing are electrical resistivity: 18.2MΩ‧cm or more, particles: 1/mL or less, viable bacteria: 1/L or less, TOC (Total Organic Carbon: total Organic carbon): 1ppb or less, silicon dioxide: 1ppb or less, metals: 1ppt or less, ions: 10ppt or less.

The ultrapure water used in the semiconductor manufacturing process as described above is manufactured in an ultrapure water manufacturing device mainly equipped with a pretreatment system, a primary pure water system, and a secondary pure water system (subsystem), and is supplied to use point. The pretreatment system is used to use purification treatment equipment such as coagulation filtration, micro-filtration membrane (Micro-Filtration Membrane, MF membrane), ultrafiltration membrane (Ultrafiltration Membrane, UF membrane), or dechlorination treatment equipment using activated carbon, etc. Those who come to purify raw water. The primary pure water system is used to use reverse osmosis membrane (Reverse Osmosis Membrane, RO membrane) device, Degassing membrane devices, ion exchange towers, etc., which remove impurities such as ion components or TOC components contained in pretreated water. The subsystems mainly include: a sub-tank for temporarily storing pure water, a heat exchanger, an ultraviolet oxidation device (ultraviolet (UV) device), a catalytic oxidizing substance decomposition device, a degassing device, and a mixed bed ion Exchange devices and ultrafiltration membrane devices (UF devices) are used to remove very small particles or trace ions, especially low-molecular trace organic matter and other impurities in the primary pure water to produce ultrapure water with higher purity. An ultrapure water production system equipped with such an ultrapure water production device includes: water delivery piping to circulate ultrapure water from the subsystem to the point of use; and return piping to deliver the ultrapure water not used at the point of use to the subsystem Circulate in the sub-tank.

Normally, when the ultrapure water production system as described above is newly started or restarted after stopping operation for a certain period of time, impurities such as organic matter, fine particles, and ionic substances are mixed or generated in the system, so these impurities are removed. The system is cleaned until the ultrapure water at the point of use meets the required water quality. Among them, with the new construction of the factory, when the ultrapure water production system is newly launched, since particles or organic matter adhere to the inner wall of the piping during the implementation, the cleaning of the system takes a lot of time, and the operating efficiency of the industry decreases. .

As a method for cleaning impurities mixed or generated in the system as described above, for example, Patent Document 1 proposes a method of cleaning the inner wall of the pipe by alternately supplying compressed gas and ultrapure water, as an ultrapure method. The cleaning method when starting up the water production device.

[Prior Art Literature] [Patent Literature]

[Patent Document 1] Japanese Patent Laid-Open No. 2004-050048

It is known that fine particles adhering to the inner wall of the pipe of an ultrapure water production device will peel off from the inner wall of the pipe due to sudden pressure fluctuations. In Patent Document 1, in order to accelerate the peeling of the fine particles, Compressed gas and ultrapure water are used for cleaning. However, gas is used in order to fluctuate the pressure received by the piping. Therefore, the dissolved gas remains in the dead space in the piping, and therefore, the purity of the ultrapure water produced may be reduced. Therefore, it takes more time to remove the dissolved gas, and therefore there is a problem that it is difficult to clean the ultrapure water production system in a short time.

The present invention is formed based on the above-mentioned situation, and its purpose is to provide a cleaning system for ultrapure water production system that can efficiently remove particles caused by impurities mixed in or generated in an ultrapure water production system. method.

In order to solve the above-mentioned problems, firstly, the present invention provides a cleaning method of an ultrapure water production system, which is to provide an ultrapure water production device, a point of use, and connect the ultrapure water production device to the point of use The method of cleaning at least a part of the ultrapure water production system of the piping includes a high-pressure cleaning step of cleaning by supplying ultrapure water at high pressure (Invention 1).

According to the aforementioned invention (Invention 1), by supplying ultrapure water at high pressure, the particles adhering to the ultrapure water production system, especially the inner wall of the piping, etc., can be peeled and removed efficiently, so that it can be removed in a short time. Cleaning operations are carried out inside.

In the invention (Invention 1), it is preferable to continuously or intermittently perform the supply of ultrapure water in the high-pressure cleaning step at a pressure higher than the applied pressure at the point of use, or to gradually increase it to a higher pressure. The supply of ultrapure water in the high-pressure washing step is performed by applying a higher pressure at the point of use (Invention 2).

According to the invention (Invention 2), it is performed by continuously or intermittently supplying ultrapure water at a pressure higher than the applied pressure at the point of use, or by gradually increasing to a pressure higher than the applied pressure at the point of use In the supply of ultrapure water, the generated turbulence can be used to effectively remove particles attached to the inner wall of the piping of the ultrapure water production system. In addition, the term "continuously" in the present invention refers to cleaning at a pressure higher than the applied pressure at the point of use and a flow rate of 0.5 m/sec or more for 0.5 hours or more, so that the total flow rate becomes 10% of the piping water volume. The so-called "intermittently" refers to the intermittent comprehensive cleaning for 0.5 hours or more at a higher pressure than the applied pressure at the point of use and a flow rate of 0.5m/sec or more, so that the overall flow rate becomes the amount of water retained in the piping 10 times or more; the so-called "gradually" means: washing at a flow rate of 0.5m/sec or more, and finally a pressure higher than the applied pressure at the point of use, at a pressure rise rate of 0.5×△necessary pressure rise/ h. The pressure rise rate is above 10% to make the pressure rise gradually.

In the aforementioned inventions (Invention 1, Invention 2), it is preferable that at least a part of the pipe contains polyvinylidene fluoride (PVDF) (Invention 3).

As the piping material of the ultrapure water production system, polyvinyl chloride (polyvinyl chloride) is used in consideration of the eluted substances in the ultrapure water and less dirt during construction. chloride, PVC) or polyvinylidene fluoride (PVDF), etc. Among them, PVDF is suitable as a piping material due to its excellent corrosion resistance or heat resistance, but sometimes deformation such as heat wrinkles during processing or transportation wrinkles during construction may occur, and such wrinkles are easy to enter fine particles. And other impurities. According to the invention (Invention 3), when the ultrapure water production system is cleaned, the wrinkles of the PVDF piping can be stretched by high-pressure washing, so that the fine particles etc. entering the wrinkles can be effectively removed.

In the invention (Inventions 1 to 3), it is preferable to add alkali, hydrogen peroxide (H ₂ O ₂ ), ozone or gas to the ultrapure water in the high-pressure cleaning step, or the ultrapure water It is hot water (Invention 4).

According to the invention (Invention 4), in addition to the physical cleaning effect of the high-pressure cleaning step, a chemical cleaning effect brought by alkali, hydrogen peroxide (H ₂ O ₂ ) or ozone, and gas The physical cleaning effect, the sterilization effect brought by hot water, etc., can make the cleaning effect more excellent.

In the above inventions (Inventions 1 to 4), it is preferable to include a discharge step (Invention 5) of extruding the ultrapure water remaining in the system after the high-pressure washing step to the outside of the system.

According to the invention (Invention 5), since the ultrapure water remaining in the system after the high-pressure washing step is squeezed out of the system, it is possible to prevent the particles dispersed in the ultrapure water after the high-pressure washing step from reattaching On the inner wall of the piping, etc.

In the above inventions (Inventions 1 to 5), it is preferable that the ultrapure water production device includes an ultrafiltration membrane device (UF device), and the ultrapure water production system replaces the ultrafiltration membrane device (UF device). Membrane device (UF device) is provided with a dummy tube or a dummy UF device without UF function to pass water (Invention 6).

According to the invention (Invention 6), by replacing the UF device with a dummy tube or a dummy UF device during the cleaning of the ultrapure water production system, it is possible to prevent the UF device from peeling off particles from the piping during the cleaning stage. It is blocked, so the cost of 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, especially the inner wall of the pipe, etc. can be peeled and removed efficiently, so that the cleaning can be performed in a short time. Net operation.

1: Ultrapure water manufacturing system

2: Pretreatment system

3: Primary pure water system

4: Secondary pure water system (subsystem)

41: Sub-tank

42: heat exchanger

43: Ultraviolet oxidation device (UV device)

44: Catalytic oxidizing substance decomposition device

45: degassing device

46: Mixed bed ion exchange device

47: Ultrafiltration membrane device (UF device)

5: point of use

L1, L2, L31~L36, L4: water supply piping

R1, R2: return piping

P: Pump

W: Raw water

Fig. 1 is a block diagram showing an ultrapure water production system used in a cleaning method of an ultrapure water production system according to an embodiment of the present invention.

2 is a graph showing the relationship between the number of fine particles and the elapsed time after washing when the piping pressure of Example 1 is changed from 0.4 MPa to 0.7 MPa.

3 is a graph showing the relationship between the number of fine particles in Example 2 and the elapsed time after washing.

Fig. 4 is a graph showing the relationship between the number of fine particles and the elapsed time after washing in a comparative example.

Hereinafter, the embodiment of the cleaning method of the ultrapure water production system of the present invention will be described with reference to the drawings as appropriate. The embodiments described below are for making the present invention easy to understand and do not limit the present invention in any way.

[Ultra pure water manufacturing system]

Fig. 1 is a block diagram showing an ultrapure water production system used in a cleaning method of an ultrapure water production system according to an embodiment of the present invention. The ultrapure water production system 1 shown in Fig. 1 is composed of an ultrapure water production device sequentially equipped with a pretreatment system 2, a primary pure water system 3, and a secondary pure water system (subsystem) 4, and supplies ultrapure water to the point of use 5. water. The raw water W supplied to the pretreatment system 2 undergoes purification treatment using coalescing filtration, MF membrane (microfiltration membrane), UF membrane (ultrafiltration membrane), etc., or dechlorination treatment using activated carbon, etc., and then passes through the water supply piping L1. Supply to the primary pure water system 3. The treated water supplied to the primary pure water system 3 is supplied to the subsystem 4 through the water supply pipe L2 after impurities such as ion components or TOC components are removed by RO membrane (reverse osmosis membrane), degassing membrane, ion exchange tower, etc. Subsystem 4 removes impurities such as very small particles or trace ions, especially low-molecular trace organic matter, in the treated water, thereby producing ultrapure water with higher purity. The ultrapure water produced in the subsystem 4 is delivered to the point of use 5 through the water delivery pipe L4.

Subsystem 4 includes in order: sub-tank 41, heat exchanger 42, ultraviolet oxidation device (UV device) 43, catalytic oxidizing substance decomposition device 44, degassing device 45, mixed bed ion exchange device 46, ultrafiltration Membrane device (UF device) 47. The sub-tank 41 is used to temporarily store the treated water supplied by the primary pure water system 3. The heat exchanger 42 is used to adjust the temperature of the treated water. The ultraviolet oxidizing device (UV device) 43 is used for oxidatively decomposing organic matter (TOC component) in water by oxidation treatment by ultraviolet irradiation. The catalytic oxidizing substance decomposition device 44 uses palladium (Pd) compounds such as metal palladium, palladium oxide, palladium hydroxide, or precious metal catalysts such as platinum (Pt) to oxidize the H generated in the ultraviolet ray oxidation device (UV device) 43 ₂ O ₂ , and other oxidizing substances are decomposed and removed. The degassing device 45 is used to reduce the amount of dissolved oxygen in the treated water. The mixed bed ion exchange device 46 is used to remove cations and anions in the treated water to improve the purity of the treated water. The ultrafiltration membrane device (UF device) 47 is used to remove particles of ion exchange resin and the like flowing out from the mixed bed ion exchange device 46. The devices constituting the subsystem 4 are connected by pipes L31 to L36, respectively.

In the present embodiment, the water supply pipe L31 connecting the sub tank 41 and the heat exchanger 42 is provided with a pump P for changing the pressure of the supplied ultrapure water. The pump P is also installed in the water supply pipe L35 connecting the degassing device 45 and the mixed bed ion exchange device 46.

The ultrapure water production system of this embodiment includes, in addition to the water delivery pipes L1, L2, L31~L36, and L4, the return pipe R1 is used to transfer the unused ultrapure water at the point of use 5 to the sub-storage of the subsystem 4. Circulate in the tank 41; and the return pipe R2, which is used to circulate the ultrapure water that passes through the dummy pipe or the dummy UF device without UF function during washing from the water supply pipe L4 to the sub-tank 41 directly.

There are requirements for the purity of the treated water sent from the subsystem 4 to the point of use 5. Therefore, the mixed bed ion exchange device 46 and the ultrafiltration membrane device (UF device) 47 are connected to the water supply pipe L36, and the subsystem 4 is connected to The material of the water supply pipe L4 and the return pipe R1 connected to use point 5 is polyvinylidene fluoride (PVDF). PVDF has excellent chemical resistance to chemical solutions such as alkalis, corrosion resistance to sterilization cleaning or sterilization using ultraviolet rays, and heat resistance to sterilization cleaning using hot water. Therefore, it has the ability to inhibit the elution of impurities in the treated water. effect. On the other hand, in mixed bed ion exchange Since the purity of the treated water required in the front stage of the device 46 is not so high, the material of the pipes other than the above is not necessarily PVDF.

[How to clean the ultrapure water production system]

Next, the cleaning method using the ultrapure water manufacturing system of the above-mentioned embodiment is demonstrated. The cleaning method of the ultrapure water production system of this embodiment is targeted for: the devices 41 to 47 of the subsystem 4, the water supply pipes L31 to L36 connecting the devices of the subsystem 4, and the connection between the subsystem 4 and the point of use 5. Connected water supply pipe L4, return pipe R1, and return pipe R2. In this embodiment, the particle size of the fine particles to be washed is 10 nm to 200 nm, and the ultrapure water used for washing refers to pure water having a specific resistance value of 15 MΩcm or more.

<High-pressure cleaning step>

The high-pressure cleaning step is a step of physically removing fine particles or organic matter adhering to the ultrapure water production system, particularly on the inner wall of the pipe, etc., using ultrapure water supplied at a high pressure. The pressure of the supplied ultrapure water is changed by changing the inverter of the pump P arranged in the subsystem 4, or by opening and closing a valve (not shown) provided in the piping in the subsystem 4 To adjust.

It is preferable that the supplied ultrapure water has a temperature of 20°C to 85°C, a flow rate of 0.5m/sec to 4.0m/sec, and a flow rate of 10 times the pipe volume. By supplying ultrapure water under these conditions, fine particles and the like can be efficiently removed. In addition, the time to end the cleaning is measured by an online particle monitor (not shown) installed in the return pipe R1, and it is determined whether the number of particles of 20nm or more in the treated water reaches 1/mL or less ( Hereinafter, there is a case called "constant state") to determine.

The supply of ultrapure water in the high-pressure washing step can be continuously performed at a higher pressure than the applied pressure at the point of use 5. The so-called "continuously" here is a pressure higher than the applied pressure at the point of use 5, and the washing is performed at a flow rate of 0.5 m/sec or more for 0.5 hours or more, so that the total flow rate becomes 10 times or more of the water volume of the piping. In this case, the applied pressure at the point of use 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 attached to the inner wall of the piping of the ultrapure water production system, etc., which are difficult to peel off in normal water flow, can be easily peeled and removed.

The supply of ultrapure water in the high-pressure washing step may also be performed intermittently at a higher pressure than the applied pressure at the point of use 5. The so-called "intermittently" here means that the pressure is higher than the applied pressure at point 5, and the comprehensive cleaning is performed intermittently for 0.5 hours or more at a flow rate of 0.5 m/sec or more, so that the overall flow rate becomes more than 10 times the amount of water retained in the piping. . In this case, the applied pressure at the point of use 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-mentioned conditions, the generated turbulence and the like can be used to effectively remove fine particles attached to the inner wall of the pipe of the ultrapure water production system.

The intermittent high-pressure cleaning is preferably performed after a predetermined time has elapsed, after a predetermined flow of water is passed, or after confirming that the measured number of fine particles becomes a constant state. By performing the intermittent high-pressure cleaning in this manner, the piping of the subsystem 4 and the like are easily subjected to sudden pressure fluctuations, and therefore the removal efficiency of fine particles attached to the piping and the like is improved.

The supply of ultrapure water in the high-pressure washing step can be performed by gradually increasing the pressure to a pressure higher than the applied pressure at the point of use 5. The so-called "Gradually" is to wash for 0.5 hours or longer with a flow rate of 0.5m/sec or more, and the total flow rate is 10 times or more of the water volume in the piping. In this case, the applied pressure at the point of use 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-mentioned conditions, the generated turbulence and the like can be used to effectively remove fine particles attached to the inner wall of the pipe of the ultrapure water production system.

The high-pressure cleaning performed gradually is preferably performed by continuously or stepwise increasing the pressure. In the case of continuously increasing the pressure, it is preferably performed at a predetermined rate of increase, and in the case of increasing the pressure in stages, it is preferable to perform a predetermined flow of water after a predetermined period of time, or to confirm The number of fine particles is measured after it becomes a constant state. By gradually performing high-pressure cleaning as described above, the piping of the subsystem 4 and the like are easily subjected to sudden pressure fluctuations, and therefore the removal efficiency of fine particles attached to the piping and the like is improved.

The cleaning method of the ultrapure water production system of the present invention is not limited to the above-mentioned embodiment. The ultrapure water in the high-pressure cleaning step may be added with alkali, hydrogen peroxide (H ₂ O ₂ ), ozone or gas , Or the ultrapure water is hot water. By combining ultrapure water with alkalis, etc. to perform cleaning as described above, in addition to the physical cleaning effect of the high-pressure cleaning step brought by ultrapure water, chemical cleanings caused by alkalis are also added. The cleaning effect or the physical cleaning effect caused by the gas can make the cleaning effect of the cleaning method of the ultrapure water production system of the present invention more excellent. Hereinafter, the cleaning effect when the high-pressure cleaning step is performed using the alkali or the like will be described.

[Alkali]

By using an alkali, it is possible to chemically peel off and disperse the fine particles attached to the piping of the subsystem 4 and the like. The ultrapure water to which alkali is added 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. In addition, the washing time with alkali-added ultrapure water is preferably in the range of 0.5 hour to 2 hours.

[hydrogen peroxide]

By using hydrogen peroxide (H ₂ O _2), hydrogen peroxide can be used (H ₂ O ₂₎ foaming force chemically microorganisms on pipe and other subsystems attached to the 4 removed. The concentration of ultrapure water to which hydrogen peroxide (H ₂ O ₂ ) is added is preferably 0.1% or more. In addition, the washing time with ultrapure water added with hydrogen peroxide (H ₂ O ₂ ) is preferably in the range of 0.5 hour to 2 hours.

[ozone]

By using ozone, the oxidative decomposition power of ozone can be used to chemically remove particles attached to the piping of the subsystem 4, etc. The concentration of ozone-added ultrapure water is preferably 0.1 mg/L or more. In addition, the washing time with the ultrapure water added with ozone is preferably in the range of 0.5 hour to 2 hours.

[gas]

By continuously or intermittently introducing gases such as air or nitrogen into ultrapure water, the bubbles of air or nitrogen are used to vigorously agitate the washing water. Therefore, the particles attached to the piping of subsystem 4 can be physically Sexually peel and disperse.

[Hot water]

By using the ultrapure water in the high-pressure cleaning step as hot water, the piping of subsystem 4 can be Wait for sterilization and washing. The temperature of the hot water is preferably 60°C or higher. In the case of sterilizing and washing with hot water, the piping of the subsystem 4 is preferably made of PVDF, which is excellent in heat resistance.

<Discharge Step>

In addition, in the present embodiment, the cleaning method of the ultrapure water production system of the present invention includes a discharge step of extruding the ultrapure water remaining in the system after the high-pressure cleaning step to the outside of the system. The water passing time in the discharge step is preferably in the range of 0.5 hour to 24 hours.

The combination of the high-pressure cleaning step, the alkali, etc., and the discharge step in the cleaning method of the ultrapure water production system of this embodiment is preferably performed sequentially: high-pressure cleaning with alkali-added ultrapure water The cleaning step is a cleaning and discharging step using ultrapure water added with hydrogen peroxide (H ₂ O ₂ ). By combining as described above, two effects of chemical cleaning by alkali and hydrogen peroxide (H ₂ O ₂ ) and physical cleaning by high-pressure supply of ultrapure water can be expected. In the combination, the high-pressure washing step using alkali-added ultrapure water and the washing using hydrogen peroxide (H ₂ O ₂ )-added ultrapure water may be sequentially repeated twice. By repeating the washing with alkali and hydrogen peroxide (H ₂ O ₂ ) twice, the effect of chemical washing is further improved.

In the combination, the high-pressure washing step using ultrapure water added with alkali may be divided into a washing step using ultrapure water added with alkali and a high pressure washing step using ultrapure water. In this case, the high-pressure cleaning step using ultrapure water is preferably performed after alkaline cleaning. Here, the so-called after alkaline cleaning means that after a predetermined time has elapsed during alkaline cleaning, after a predetermined flow of water is passed, or the number of particles measured is confirmed to be constant. After setting the state.

In addition, in the combination, a high-pressure washing step may be further performed in the discharge step, or a high-pressure washing step may be performed after the discharge step. Here, the term "after the discharge step" refers to after a predetermined time has passed in the discharge step, after a predetermined flow rate of water has been passed, or after confirming that the number of measured particles has become a constant state. By performing a high-pressure washing step during or after the discharge step, the treated water that cannot be completely extruded or not completely extruded only by the discharge step is squeezed out of the system, so it can be expected to prevent fine particles dispersed in the treated water The effect of attaching to the inner wall of the pipe.

The time required for washing with the above-mentioned combination is 2 hours to 7 days. The time to complete the cleaning is measured by an online particle monitor (not shown) installed in the return pipe R1. It is determined whether the number of particles of 20nm or more in the treated water becomes 1/mL or less (constant state). ) To judge.

In addition, when cleaning the ultrapure water production system, instead of the ultrafiltration membrane device (UF device) 47, a dummy pipe made of polyvinyl chloride (PVC) (not shown) or a dummy UF device (not shown) without UF function is installed. Icon). By using a dummy tube or a dummy UF device, clogging of the UF device can be prevented during the cleaning phase, so the cost of the UF device can be reduced. In addition, in the case of using a dummy tube or dummy UF device, the cleaning time is 12 hours to 7 days.

Above, the present invention has been described with reference to the drawings, but the present invention is not limited to the above-mentioned embodiment, and various modifications can be implemented.

[Example]

Hereinafter, the present invention will be further described in detail based on examples, but The present invention is not limited to the following examples.

[Example 1]

The ultrapure water production system shown in FIG. 1 is used to clean the subsystem 4. An online particle monitor (manufactured by Particle Measuring Systems, trade name: UDI-20) is installed in the return pipe R2, and the piping pressure of the return pipe R1 is changed from 0.4 MPa to 0.7 MPa.

[result]

The relationship between the pressure and the number of fine particles and the elapsed time after washing is shown in FIG. 2. From this result, it can be seen that when the pressure becomes higher, fine particles will raise dust. From this, it can be seen that there is a certain effect for cleaning the piping of the subsystem 4 under high pressure conditions.

[Example 2, Comparative Example]

Use a pipe made of PVDF with a pipe diameter of 25A as the return pipe R2, and install two pipes with a pipe length of 50m. One of them was subjected to continuous high-pressure washing with ultrapure water added with alkali. As a comparative example, the other one was washed with only ultrapure water added with alkali. The water flow rate was set to 0.5m/sec, and the flow rate was set to 3m ³ . Regarding the pressure of the return pipe R2, it was set to 0.4 MPa for alkaline cleaning + continuous high-pressure cleaning (Example 2), and 0.3 MPa for only alkaline cleaning (comparative example). The pressure during normal water flow is 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]

In the case of continuous high-pressure washing with ultrapure water added with alkali (actual The relationship between the number of fine particles and the elapsed time after washing in Example 2) is shown in Fig. 3. The number of fine particles and the elapsed time after washing in the case of washing with only alkali-added ultrapure water (comparative example) The relationship is shown in Figure 4. From this result, it can be seen that if continuous high-pressure washing is performed using ultrapure water added with alkali, the number of fine particles of 20 nm or more stabilizes after 30 hours. From this, it can be seen that if alkaline washing is combined with continuous high-pressure washing, the washing time is shortened.

As explained above, according to the cleaning method of the ultrapure water production system of the present invention, by supplying ultrapure water at high pressure, it is possible to efficiently remove the particles attached to the ultrapure water production system, especially the inner wall of the pipe, etc. The ground is peeled and removed, so it can be cleaned in a short time. In addition, in the case of the high-pressure cleaning step using ultrapure water added with alkali, in addition to the physical cleaning effect brought by the high-pressure supply of ultrapure water, a chemical cleaning effect by alkali is also added. Therefore, cleaning in the ultrapure water production system can be performed more effectively.

[Industrial availability]

The present invention is useful as a method for removing impurities mixed or generated in the system when the ultrapure water production system is newly started or when it is restarted after stopping the operation for a certain period of time to clean the system to the point of use The ultrapure water meets the required water quality.

1‧‧‧Ultra pure water manufacturing system

2‧‧‧Pretreatment system

3‧‧‧Pure water system

4‧‧‧Secondary pure water system (subsystem)

41‧‧‧Sub-tank

42‧‧‧Heat exchanger

43‧‧‧Ultraviolet oxidation device (UV device)

44‧‧‧Catalyst-type oxidizing substance decomposition device

45‧‧‧Degassing device

46‧‧‧Mixed bed ion exchange device

47‧‧‧Ultrafiltration membrane device (UF device)

5‧‧‧Use point

L1, L2, L31~L36, L4‧‧‧Water supply pipe

R1, R2‧‧‧Return piping

P‧‧‧Pump

W‧‧‧raw water

Claims (5)

A cleaning method of an ultrapure water production system, which is a method for the piping of an ultrapure water production system that includes an ultrapure water production device, a point of use, and a piping connecting the ultrapure water production device and the point of use A method for cleaning, wherein the cleaning method of the ultrapure water production system includes a high-pressure cleaning step of cleaning by supplying ultrapure water at high pressure, and the cleaning in the high-pressure cleaning step is intermittent high-pressure cleaning Cleaning or gradual high-pressure cleaning, the intermittent high-pressure cleaning is to intermittently supply ultrapure water at a higher pressure than the applied pressure at the point of use, and the gradual high-pressure cleaning gradually rises to The ultrapure water is supplied at a pressure higher than the applied pressure at the point of use. The cleaning method of the ultrapure water production system described in the first item of the scope of patent application, wherein at least a part of the pipe contains polyvinylidene fluoride. The cleaning method of the ultrapure water production system described in the first item of the scope of patent application, wherein alkali, hydrogen peroxide, ozone or gas is added to the ultrapure water in the high-pressure cleaning step, or the ultrapure The water is hot water. The cleaning method of the ultrapure water production system described in the first item of the patent application includes a discharge step of squeezing the ultrapure water remaining in the system after the high-pressure cleaning step to the outside of the system. The cleaning method of the ultrapure water production system as described in the first item of the scope of patent application, wherein the ultrapure water production device is equipped with an ultrafiltration membrane device, and when the ultrapure water production system is cleaned, it replaces all Designed for the ultrafiltration membrane device Install a dummy tube or a dummy ultrafiltration device without ultrafiltration function to pass water.

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