JP2014000548A - Cleaning method when uplifting ultrapure water production system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a cleaning method of an ultrapure water production system capable of shortening a cleaning trial operation time until produced-supplied ultrapure water reaches a desired water quality, when newly uplifting the ultrapure water production system and when re-uplifting after resting by a periodic inspection, by surely removing particulates.SOLUTION: The method is provided for uplifting and cleaning at least a part of the ultrapure water production system composed of an ultrapure water production device, a use point of ultrapure water and a piping system for connecting the ultrapure water production device and the use point. The cleaning method of the ultrapure water production system comprises a carbon dioxide melting water circulating process and a pushing-out process.

Description

  The present invention relates to a method for cleaning an ultrapure water production system for producing and supplying ultrapure water widely used in electronic component manufacturing factories such as semiconductor devices, liquid crystal displays, silicon wafers, and printed circuit boards, nuclear power plants, and pharmaceutical manufacturing factories. In particular, the present invention relates to a cleaning method at the start-up.

  Conventionally, in the manufacturing process of electronic parts such as semiconductor devices, liquid crystal displays, silicon wafers, printed circuit boards, power generation processes of nuclear power plants, manufacturing processes of pharmaceuticals, etc., ionic substances, fine particles, organic substances, dissolved gases, viable bacteria, etc. Ultrapure water with a very low impurity content is used. In particular, the demand for purity of ultrapure water used in the manufacturing process of electronic components such as semiconductor devices has become stricter as the degree of integration of semiconductor devices increases. For example, the required water quality for the ultrapure water for cutting-edge semiconductor manufacturing is 18.2 MΩ · cm or more in specific resistance, 1 μm / mL (milliliter, the same applies hereinafter) with a particle size of 0.05 μm or more, all organic Carbon (hereinafter also referred to as TOC) 1 μg / L (liter, the same applies hereinafter) or less, metal 5 ng / L or less, and further, for example, metal 1 ng / L or less tends to be stricter.

  Such ultrapure water is produced from raw water such as industrial water, city water, and well water in an ultrapure water production system equipped with a pretreatment system, a primary pure water system, and a secondary pure water system, and is supplied to the place of use. Is done. The pretreatment system is used to clarify raw water using a coagulating sedimentation device, a sand filtration device, or the like to obtain pretreatment water. The primary pure water system is appropriately selected from activated carbon devices, reverse osmosis membrane devices, 2-bed 3-tower ion exchange devices, vacuum degassing devices, mixed bed ion exchange devices, precision filters, etc. Impurities are removed to obtain primary pure water. Secondary pure water system, also called subsystem, removes impurities such as trace amounts of fine particles and ionic substances in primary pure water, and produces ultrapure water with high purity. It can be called a device. The secondary pure water system is installed after the primary pure water tank, and is configured by combining various unit water treatment devices. The water treatment equipment that constitutes the secondary pure water system is an ultraviolet oxidizer (TOC-UV) that decomposes organic matter, a polisher that uses a non-regenerative mixed-bed ion exchange resin that adsorbs and removes ionic substances, and ultrafiltration. A membrane processing device such as a membrane device or a degassing membrane device.

  This ultrapure water production system consists of a piping system that reaches a place of use (use point) from a pure water tank that temporarily stores primary pure water through a secondary pure water system, and a pure water tank that is usually used from the place of use. It has a piping system that forms a circulation system with the return piping system.

  When a new ultrapure water production system or ultrapure water production system is started up or when it is restarted after an outage due to periodic inspections, the impurities described above that are mixed and generated in the system are removed, and super A cleaning trial run is performed until the pure water reaches the desired water quality. In recent years, for the purpose of improving the operation efficiency of factories, there is a strong demand for the start-up of a device in a short period called “vertical start-up” of the device.

  As a cleaning method for removing the impurities described above, flushing and blowing with pure water, cleaning by circulating pure water, cleaning with hot water, cleaning with hydrogen peroxide, cleaning using a basic aqueous solution, and the like, A method using so-called functional water in which ozone or hydrogen is dissolved, a method using a surfactant, and the like are known. Of these various cleaning methods, cleaning is performed according to the type and purpose of impurities to be cleaned. Is done. Further, in order to perform sufficient cleaning, there are cases where cleaning is performed in stages by combining a plurality of methods in consideration of the characteristic effects of various cleaning methods.

  Among the various impurities described above, a cleaning method including cleaning using a basic aqueous solution is known as a method for increasing the removal rate of fine particles. (See, for example, Patent Document 1, Patent Document 2, and Patent Document 3.)

JP 2007-260211 A JP 2008-221144 A Japanese Patent No. 4449080

Electrophoresis 2004, 25, 203-213

  However, conventional cleaning methods do not always remove fine particles, and ultrapure water to be manufactured and supplied is desirable when a new ultrapure water production system is started up or when it is restarted after a periodical shutdown. There was a problem that it took a long time for the cleaning trial run to reach the water quality.

  The ultrapure water production system to be cleaned of the present invention has a circulation system by a piping system that reaches a use place from a pure water tank through an ultrapure water production apparatus, and a return piping system that returns from the use place to the pure water tank. It has an established piping system. In this specification, “system circulation” refers to circulation in a piping system constituting the circulation system of the ultrapure water production system. In addition, in the middle of the pipe constituting the ultrapure water production system, equipment such as a pump, a joint, and a valve, and various water treatment devices are provided as necessary. In this specification, the “piping system (line)” refers to the entire system in which these facilities and the like are connected by piping to form a flow path. “Washing water” refers to carbon dioxide-dissolved water or pure water that is circulated in the system.

  By the way, the present inventors conducted research to solve the above-mentioned problems, and measured the number of fine particles in the circulating water by circulating a system of carbon dioxide-dissolved water instead of pure water when the piping system was newly started up. It was found that the number of fine particles increased compared with the case where pure water was circulated in the system.

  Furthermore, carbon dioxide-dissolved water with an increased number of fine particles was discharged from the circulation system, and then pure water was circulated in the system. As a result, the pure water was immediately circulated through the system when a new piping system was started up. It was found that the value was maintained lower than the case.

Although the reason why the increase in the number of fine particles due to the system circulation of the carbon dioxide-dissolved water is not always clear, it can be considered as follows.
It has been reported that the surface potential of a general material constituting a piping system of an ultrapure water production system varies depending on pH (see Non-Patent Document 1). On the other hand, the fine particles increased by the system circulation of carbon dioxide-dissolved water are considered to have been detached from the piping system. Therefore, at least one of the causes of the increase in the number of fine particles described above is the attractive force that acts between the piping system and the fine particles because the decrease in pH in the piping system due to the carbon dioxide-dissolved water changes the surface potential of the fine piping system or fine particles. This is thought to be due to the fact that the reluctance became smaller, or the repulsive force worked between them.

  It is conceivable that the fine particles once desorbed from the piping system are reattached to the piping system as soon as they are transferred to the pure water circulation and the pH value is restored. However, the present inventors have further obtained the knowledge that the reattached fine particles are easily re-detached by bringing the liquidity of the washing water close to neutral.

Carbon dioxide in the carbon dioxide-dissolved water can be easily removed by deaeration. Since the cleaning method of the present invention uses carbon dioxide-dissolved water, the components of the cleaning water remain in the ultrapure water production system as in the method of cleaning using a basic aqueous solution, and the cleaning of such residual components is performed. There is no risk of further time.
Furthermore, carbon dioxide-dissolved water has good handling properties such as safety.

  The method for cleaning an ultrapure water production system according to an embodiment of the present invention includes an ultrapure water production apparatus, a use point of ultrapure water, and an ultrapure water comprising a piping system connecting the ultrapure water production apparatus and the use point. A method of starting and cleaning at least a part of a production system, wherein carbon dioxide-dissolved water is circulated in at least a part of the ultrapure water production system, and fine particles adhering to the ultrapure water production system are dissolved in the carbon dioxide. A carbon dioxide-dissolved water circulation step for desorption in water, and an extrusion step for discharging the fine particles desorbed in the carbon dioxide-dissolved water out of the system.

  The cleaning method for an ultrapure water production system according to an embodiment of the present invention is characterized in that the carbon dioxide concentration of the carbon dioxide-dissolved water is 100 to 1,000 ppm.

  The ultrapure water production system cleaning method according to the embodiment of the present invention is characterized in that the carbon dioxide-dissolved water has a pH of 3-4.

  The cleaning method for an ultrapure water production system according to an embodiment of the present invention includes a rinsing process for cleaning at least a part of the ultrapure water production system by passing pure water.

  The cleaning method for an ultrapure water production system according to an embodiment of the present invention is characterized in that at least a part of the extrusion step is performed without passing pure water through the ultrapure water production apparatus.

  The cleaning method for an ultrapure water production system according to an embodiment of the present invention includes a carbon dioxide introduction step of introducing carbon dioxide into the pure water in a state where pure water is circulated through at least a part of the ultrapure water production system. It is characterized by having.

  In the cleaning method for an ultrapure water production system according to an embodiment of the present invention, the ultrapure water production apparatus includes a degassing membrane device having a gas introduction line, and the carbon dioxide introduction step is performed via the gas introduction line. Carbon dioxide is introduced into the pure water.

  In the cleaning method for an ultrapure water production system according to an embodiment of the present invention, the carbon dioxide concentration is such that the surface potential of at least a part of the contact surface with pure water of the ultrapure water production system is 0 to 5 mV. It is characterized by being

  The method for cleaning an ultrapure water production system according to an embodiment of the present invention is characterized by having a startup process for starting up the ultrapure water production apparatus after the extrusion process.

  Here, “extrusion” means discharging fine particles out of the system by discharging carbon dioxide-dissolved water in the ultrapure water production system. In addition, “rinsing” refers to flushing (rinsing) impurities by passing pure water through the ultrapure water production system. The “pure water” used in the extrusion process and the rinsing process may be “ultra pure water”, and it may be considered that pure water or ultra pure water is used.

  According to the present invention, by circulating the carbon dioxide-dissolved water in the system, the fine particles adhering to the inner wall surface of the piping system can be efficiently desorbed and dispersed in the carbon dioxide-dissolved water. In the extrusion process, the fine particles released in the carbon dioxide-dissolved water are discharged out of the system, so that the fine particles can be removed reliably. At the time of start-up, it is possible to shorten the cleaning trial operation time until the ultrapure water produced and supplied reaches the desired water quality.

It is a schematic block diagram of the ultrapure water manufacturing system which is the washing | cleaning object of embodiment. It is a schematic block diagram of the ultrapure water manufacturing system which is the washing | cleaning object of embodiment. It is a SEM photograph of fine particles in primary pure water. It is a SEM photograph of fine particles in carbon dioxide-dissolved water. It is a graph which shows the relationship between the number of microparticles | fine-particles, pH, and time in an Example. It is a graph which shows the relationship between the number of fine particles and time in a reference example. It is a graph which shows the number of fine particles at the time of starting in an Example and a comparative example.

  Next, the form for implementing this invention is demonstrated. The present invention is not limited to these.

FIG. 1 is a schematic configuration diagram illustrating an example of an ultrapure water production system 1 that is a cleaning target of the present embodiment. An ultrapure water production system 1 shown in FIG. 1 has a line L1 for introducing primary pure water, a pure water tank 11 connected to the line L1 for storing primary pure water, and an ultrapure water production apparatus at the subsequent stage of the pure water tank 11. A secondary pure water system 10 is provided. The secondary pure water system 10 includes a deaeration membrane device 14. The ultrapure water production system 1 also includes a line L2 that is a piping system that reaches a use point that is a place of use from the pure water tank 11 through the secondary pure water system 10, and a return that returns from the use point to the pure water tank 11. The piping system which comprises the circulation system with the line L3 which is a piping system is provided. Although not shown, a pre-treatment system and a primary pure water system are provided in the front stage of the pure water tank 11 as necessary.
A blow line L4 is connected through a valve B4 immediately before the use point of the line L2.

In the ultrapure water production system 1 shown in FIG. 1, primary pure water is introduced into a pure water tank 11 from a line L1 and stored. During normal operation for producing ultrapure water, the primary pure water stored in the pure water tank 11 is supplied to the line L2 by the pump P. A secondary pure water system 10 is configured on the line L2, and the supplied primary pure water is processed by the secondary pure water system 10 and is used as a point of use via a valve B2 interposed in the line L2. Supplied.
The remaining ultrapure water that is not used at the use point is returned and circulated to the pure water tank 11 through the line L3 connected to the line L2 via the valve B3.

  For the piping system, a material with extremely little elution of components into the produced ultrapure water is used. Specific examples of such materials include PVC (polyvinyl chloride), PTFE (polytetrafluoroethylene), PVDF (polyvinylidene fluoride), FRP (fiber reinforced plastic), PPS (polyphenylene sulfide), and PFA (tetrafluoro). Organic polymer materials such as ethylene / perfluoroalkyl vinyl ether copolymer) and stainless steel.

The cleaning method of this embodiment is characterized in that, in the ultrapure water production system, fine particles attached to the inner wall surface are desorbed by changing the surface potential of the inner wall surface of the piping system. As specific means for changing the surface potential, means for circulating the carbon dioxide-dissolved water in which carbon dioxide is dissolved in pure water for a predetermined time is used.
As the pure water, primary ultrapure water is generally used when the ultrapure water production system includes the primary pure water system in the previous stage.

The removal of the fine particles is considered to be based on the following principle. That is, the fine particles each have a unique surface potential, and it is considered that the fine particles are electrically or electrostatically attached to the inner wall surface of the piping system.
On the other hand, among the constituent materials of the ultrapure water production system, the surface potential of the organic polymer material described above has a pH of 7 and is negative. This surface potential is known to change in the positive direction through an isoelectric point where the surface potential becomes zero when the pH is reduced. In particular, organic polymer materials such as PVC, PTFE, and PVDF have a pH of It is known that the isoelectric point is about 2.0 to 3.9.

When carbon dioxide-dissolved water of a predetermined concentration is circulated in the ultrapure water production system (system circulation), the surface potential of the inner wall surface of the piping system changes from minus to plus, so that the electrical The attractive force is reduced, and the detachment of fine particles from the inner wall surface of the piping system is promoted.
Thus, by circulating the carbon dioxide-dissolved water in the system, the fine particles adhering to the inner wall surface of the piping system are desorbed and dispersed in the carbon dioxide-dissolved water. Thereafter, the fine particles detached in the carbon dioxide-dissolved water are discharged out of the ultrapure water production system.

Next, each step will be described.
[CO2 dissolved water circulation process]
The carbon dioxide dissolved water circulation step is a step of circulating the carbon dioxide dissolved water in the system. An important purpose of the carbon dioxide dissolved water circulation process is to desorb fine particles from the inner wall surface of the piping system. Therefore, in the carbon dioxide-dissolved water circulation step, in addition to the chemical cleaning effect by carbon dioxide, physical removal, peeling, and diffusion effects by the flow are also important.

In the carbon dioxide-dissolved water circulation step, the carbon dioxide concentration of the carbon dioxide-dissolved water is preferably 100 to 1,000 ppm. This is to promote the detachment of the fine particles. From the viewpoint of shortening the start-up (cleaning trial operation) period, the carbon dioxide concentration is more preferably 100 to 300 ppm.
The pH of the carbon dioxide-dissolved water is preferably 3-4. This is because the surface potential of organic polymer materials such as PVC, PTFE, and PVDF is set to 0 mV or more to promote the detachment of fine particles. From the viewpoint of shortening the start-up (cleaning trial operation) period, the pH is more preferably 3.5 to 4.
In the present embodiment, the carbon dioxide concentration is a value measured using a Sievers 900 on-line TOC Analyzer (manufactured by GE) as a TOC meter, and pH is a pH meter D-52 (manufactured by Horiba, Ltd.). Measured value.

  The carbon dioxide-dissolved water circulation step is preferably performed for about 1 to 10 hours. The first purpose of the carbon dioxide-dissolved water circulation process is to desorb the fine particles from the inner wall surface of the piping system. Therefore, in order to obtain a chemical cleaning effect with carbon dioxide-dissolved water, the carbon dioxide-dissolved water circulation step is more preferably 2 hours or more, and less than 5 hours from the viewpoint of shortening the start-up (cleaning trial operation) period. It is more preferable.

  In the carbon dioxide-dissolved water circulation process, the physical removal effect by the flow is also important. Therefore, as the flow rate (linear velocity) in the carbon dioxide dissolved water circulation process, the higher the speed, the stronger the physical force due to the flow, and the higher the cleaning effect can be expected. However, in order to flow at a high flow rate, the pump capacity increases. Therefore, in practice, the linear velocity is generally preferably in the range of the linear velocity for transferring a liquid such as an aqueous solution, for example, 0.1 to 10 m / sec, and more preferably 0.5 to 5 m / sec. In the cleaning method of the present invention, in addition to the system circulation, for example, in a state where the cleaning target portion of the ultrapure water production system is filled with carbon dioxide-dissolved water, a minute vibration is applied to the cleaning water by ultrasonic waves or the like. A method for enhancing the cleaning effect may be employed.

  The temperature of the carbon dioxide-dissolved water in the carbon dioxide-dissolved water circulation step is not particularly limited, but from the viewpoint of detergency, the temperature is preferably high as long as it does not exceed the heat resistance temperature of the constituent material of the piping system of the ultrapure water production system. . From the viewpoint of heat resistance of the constituent materials of the piping system, when polyvinyl chloride (PVC) having a heat resistant temperature of about 45 ° C. is used as the constituent material, the temperature is about 40 ° C. and the heat resistant temperature is about 80 ° C. When polyvinylidene fluoride (PVDF) is used as a constituent material, the temperature can be raised to about 75 to 80 ° C. However, the temperature of the washing water is often the result of the water temperature.

[CO2 introduction process]
In this embodiment, in order to supply carbon dioxide-dissolved water to be circulated to the ultrapure water production system, the following carbon dioxide introduction step may be included.
The ultrapure water production system to be cleaned usually includes valves and lines for introducing exhaust gas and nitrogen gas (not shown) at various places. As the carbon dioxide introduction step, carbon dioxide can be introduced into the ultrapure water production system via such a line in a state where pure water is circulated in the system and dissolved in the pure water.
For example, carbon dioxide can be introduced from a gas introduction line L5 that is normally provided in the degassing membrane device 14. Use of the gas introduction line L5 is preferable because it does not require a special valve or pump for introducing carbon dioxide. In this case, the pressure of the introduced carbon dioxide can be appropriately determined from the flow rate of the system circulation, the performance of the degassing membrane device, and the like.

[Extrusion process]
The extrusion step is a step of discharging the fine particles dispersed in the carbon dioxide-dissolved water out of the ultrapure water production system after the carbon dioxide-dissolved water circulation step. The extrusion process can be performed by supplying nitrogen gas sealed in the upper part of the pure water tank or primary pure water stored in the pure water tank to the secondary pure water system.
The temperature of carbon dioxide-dissolved water and pure water (cleaning water) in the extrusion process is not particularly limited, but as with the carbon dioxide-dissolved water circulation process, the heat resistance of the constituent materials of the piping system of the ultrapure water production system is from the viewpoint of cleaning power. The temperature is preferably high as long as the temperature is not exceeded. A preferable temperature range from the viewpoint of heat resistance is the same as in the carbon dioxide-dissolved water circulation step.

  In general, an ultrapure water production system is usually provided with piping systems for sampling and blow discharge at various places. Therefore, in the extrusion process, carbon dioxide-dissolved water can be discharged using any one of the piping systems as appropriate.

  By the way, the present inventors have found that when the carbon dioxide-dissolved water is circulated in the system at a pH of approximately 4.2, the fine particles dispersed in the carbon dioxide-dissolved water gradually decrease and reach a steady state with a certain number. I found out. This is presumably because the fine particles dispersed in the carbon dioxide-dissolved water reattach to the inner wall surface of the piping system over time. Furthermore, the present inventors have also found that the reattached fine particles are easily re-detached when the liquidity is close to neutrality.

Therefore, the extrusion process is preferably performed at once without passing the primary pure water through the secondary pure water system 10 in order to suppress the reattachment of fine particles as described above. By performing the extrusion process in this way, the fine particles can be discharged efficiently at once, and the amount of primary pure water (that is, the amount of wastewater generated) and the work time required for the subsequent rinsing process can be reduced. .
Specifically, the carbon dioxide-dissolved water in the secondary pure water system 10 is blown and discharged, and the primary pure water is passed through the secondary pure water system 10 by replacing it with nitrogen gas in the pure water tank 11. It can be done at once.

The extrusion process can also be performed by extruding carbon dioxide-dissolved water with primary pure water. For example, extrusion is performed by passing primary pure water through the secondary pure water system 10. In this case, the extrusion process time is almost the same in the same system regardless of the concentration of the carbon dioxide-dissolved water used, and ideally, pure water equivalent to the volume of the system is used.
When the extrusion process is performed by extruding with primary pure water, the carbon dioxide-dissolved water and the primary pure water may be partially mixed, the pH of the wash water changes, and the dispersed fine particles are in the piping system. There is a risk of reattachment to the inner wall. However, since the reattached fine particles are easily re-detached as described above, they can be immediately detached from the inner wall surface of the piping system and removed in the rinsing process or the startup process.

[Rinse process]
The rinsing step is a step of draining the primary pure water from the pure water tank 11 while washing the secondary pure water system 10. In the rinsing step, the cleaning time differs depending on the amount of carbon dioxide-dissolved water remaining even in the same system, and the longer the rinsing step, the longer the time required.
The rinsing step may be performed after the extrusion step is performed at once without passing the primary pure water through the secondary pure water system 10. In this case, since the washing water can be discharged in a short time, the amount of drainage in the rinsing process, that is, the amount of primary pure water used can be reduced.
After performing the extrusion process by extruding with primary pure water, the rinsing process may be performed. In this case, the extrusion process and the rinsing process are not clearly distinguished, and may be a continuous process.

  In the extrusion process and the rinsing process, the washing water is acidic due to the dispersed carbon dioxide. Therefore, the pH of the washing water can be substantially 7 by removing carbon dioxide by means such as deaeration. As a degassing method, for example, there is a method of degassing carbon dioxide by operating the degassing membrane device 14.

  By making the pH of the washing water substantially neutral by degassing, it is possible to desorb and remove the fine particles adhering to the inner wall surface of the piping system. Therefore, for example, the extrusion step may be performed after the deaeration membrane device 14 is operated in the rinsing step and the pH of the cleaning water is substantially set to 7. Also in this case, the extrusion process and the rinsing process are not clearly distinguished, and may be a continuous process.

  In the cleaning method of this embodiment, since carbon dioxide is used, waste water can be discharged without performing waste water treatment. Therefore, there is a merit that a special process and equipment for wastewater treatment are not required.

Check the quality of at least the rinse drainage from the wastewater from the extrusion process (hereinafter also referred to as extrusion wastewater) and the wastewater from the rinse process (hereinafter also referred to as rinse wastewater), and carbon dioxide in the circulation system of the ultrapure water production system. It is preferable to carry out a rinsing process until the influence of is eliminated. This water quality check is performed at the end of the circulation system of the ultrapure water production system 1, that is, near the end of the return pipe L3 (location close to the use point) or the blow line L4. It is preferable because it can be removed sufficiently.
Confirmation of water quality is preferable because it is easy to measure pH, conductivity, specific resistance, or carbon dioxide concentration. By confirming the water quality (pH, etc.) of both the extruded waste water and the rinse waste water, the fine particles dispersed in the carbon dioxide-dissolved water can be surely discharged and the fine particles can be reliably removed. In particular, it is preferable to discharge the rinse wastewater out of the system while passing the primary pure water until the pH of the rinse wastewater becomes substantially 7 neutral.

  In addition to the method of cleaning the entire ultrapure water production system as described above, individual parts of the ultrapure water production system, such as individual devices such as filtration membrane devices and UV oxidation devices, parts of piping, joints of piping, etc. May be washed. The carbon dioxide-dissolved water may be supplied immediately before the portion to be cleaned and discharged immediately thereafter, or may be cleaned by applying vibrations such as ultrasonic waves in a state where the carbon dioxide-dissolved water is filled. In addition, it can be used for cleaning filtration membrane devices and prefabricated pipes just before new construction and assembly, and can effectively shorten the new startup cleaning time.

[Start-up process]
The startup process is a process of starting up the ultrapure water production apparatus in order to start normal operation.
The start-up process is not particularly limited, and generally a method for starting up an ultrapure water production system is applicable.
The start-up process is preferably performed after confirming that the ultrapure water production system has been sufficiently cleaned in the extrusion process or the rinsing process by measuring the water quality. The operation of each water treatment device in the startup process will be described below with reference to the drawings.

FIG. 2 is a schematic configuration diagram of an ultrapure water production system 2 that is a cleaning target of the embodiment. The ultrapure water production system 2 shown in FIG. 2 is the ultrapure water production system 1 shown in FIG. 1 in which a secondary pure water system 10 that is an ultrapure water production apparatus is configured as follows. .
2, components having the same functions as those shown in FIG. 1 are denoted by the same reference numerals and description thereof is omitted.

  The secondary pure water system 20 includes a heat exchanger 12 for adjusting the water temperature, an ultraviolet oxidation device 13 for decomposing organic substances, and a degassing membrane device for removing dissolved gas as unit devices of the water treatment device. 14. A polisher 15 which is a non-regenerative mixed bed ion exchange resin tower for removing ion components, and an ultrafiltration membrane device 16 for removing fine particles are provided. Instead of the ultrafiltration membrane device 16, a microfiltration membrane device or the like can be used as the filtration membrane device. A water treatment device such as an ion adsorption membrane device, a booster pump, or the like may be further arranged in front of the ultrafiltration membrane device 16 shown in FIG.

The lamp of the ultraviolet oxidizer 13 is generally turned off in the carbon dioxide dissolved water circulation process and turned on from off in the startup process. The lamp of the ultraviolet oxidizer 13 may be turned on in the extrusion process or the rinsing process.
The deaeration membrane device 14 stops operation in the carbon dioxide dissolved water circulation step. It is preferable to start the operation in a rinsing process or a startup process.

The polisher 15 is preferably filled with the mixed bed ion exchange resin in the start-up process after confirming that the ultrapure water production system has been sufficiently cleaned in the extrusion process. This is because an ion component such as bicarbonate ion (HCO ₃ ⁻ ) derived from carbon dioxide becomes a load of the mixed bed type ion exchange resin. Therefore, in the carbon dioxide-dissolved water circulation process and the extrusion process, the polisher 15 is preferably performed without filling the mixed bed type ion exchange resin, or is preferably bypassed by a piping system connecting the front and back of the polisher 15.

  A filtration membrane such as an ultrafiltration membrane used for the ultrafiltration membrane device 16 has a large membrane area (contact area with water to be treated), and when carbon dioxide-dissolved water comes into contact with the membrane surface, carbon dioxide is present on the filtration membrane surface or inside. The specific resistance at the outlet of the filtration membrane device 16 in the start-up process may be slow. Moreover, there is a possibility that fine particles may adhere to the ultrafiltration membrane. When there is such a concern, the ultrafiltration membrane device 16 can set the filtration membrane module as a dummy module in which no membrane is contained in the module in the carbon dioxide dissolved water circulation step and the extrusion step. is there. Moreover, you may bypass by the piping system which connects the front and back of the ultrafiltration membrane apparatus 16 instead of using a dummy module. When these measures are taken, the ultrafiltration membrane device 16 allows water to pass through the ultrafiltration membrane module or the like in the startup process.

The measuring instrument 17 is a measuring instrument that measures water quality such as TOC, fine particles, pH, conductivity, specific resistance, and carbon dioxide concentration. The number of fine particles can be confirmed using a fine particle meter as the measuring instrument 17, for example.
In the embodiment, an on-line particle meter M50e (manufactured by PMS) is used as the particle meter.
Other water qualities can be confirmed with, for example, a pH meter, a pH test paper, a TOC meter, a specific resistance meter, or the like. The measuring instrument 17 may be used alone or in combination of two or more.

  In FIG. 2, the measuring instrument 17 is on the branched blow line L4, but may be on the main line such as the line L2. In the case of branching, each water quality may be measured online or offline. Further, the measuring instrument may be temporarily installed for the apparatus start-up test operation instead of being always installed. Counting the number of fine particles can be performed by interposing a filter for analysis in the blow line L4 and capturing the fine particles with the filter.

  After measuring the water quality (specific resistance, TOC, fine particles, etc.) with the measuring instrument 17 and confirming that the water quality is normal, the UV oxidizer lamp is turned on and the valve B3 is opened to switch to the circulation system. Normal operation.

Next, examples, reference examples and comparative examples of the present invention will be described.
Example 1
[Measurement of fine particles]
A simulation apparatus as shown in FIG. 1 was newly installed to measure the number of fine particles.
The simulation apparatus used in Example 1 is an apparatus that simulates the ultrapure water production system 2 shown in FIG. 2, and only the deaeration membrane apparatus 14 is used as a water treatment apparatus on a pipe constituting the secondary pure water system 10. Is a device installed.

The specifications of the equipment and apparatus used in Example 1 and the experimental conditions are shown below.
Primary pure water: specific resistance 18.2 MΩ · cm, number of fine particles having a particle diameter of 0.05 μm or more / mL or less,
Pure water tank 11: size 1,600 mm inner diameter × 1,500 mm height, material: SUS304,
Pump P: Circle pump (CRN-15, manufactured by Grundfos, material: SUS316),
Deaeration membrane device 14: Liquicel X40 (manufactured by Polypore, material: polyethylene, polypropylene),
Measuring instrument 17: Particle meter (online particle meter M50e (manufactured by PMS)), TOC meter (Sievers 900 on-line TOC Analyzer (manufactured by GE)) and pH meter (pH meter D-52 (manufactured by Horiba Seisakusho)) ,
PVDF piping: piping inner diameter 75mm, piping total length 95,000mm,
Teflon (registered trademark) coated SUS pipe: pipe inner diameter 400 mm, pipe total length 2,500 mm,
Scanning electron microscope (SEM): S-4100 type (manufactured by Hitachi High-Technologies Corporation),
Energy dispersive X-ray analyzer (EDX): Genesis (manufactured by Edax Japan).

In the simulator, primary pure water and carbon dioxide-dissolved water were sequentially circulated in the system according to the following procedure, and the number of fine particles having a particle size of 0.05 μm or more was measured.
[1] The pure water tank 11 was filled with primary pure water, and the primary pure water was circulated through the system using the pump P. At this time, the valve B2 is closed and the valves B3 and B4 are opened. The total amount (water retention amount) of primary pure water in the simulator during system circulation of primary pure water was 3,000 L, and the linear velocity during system circulation was 0.9 m / sec.
[2] Primary pure water was circulated in the system for 8 hours, and then the pH and the number of fine particles were measured.
At this time, as described later, the primary pure water was sampled and observed by SEM, and the composition of the fine particles was analyzed by EDX.
FIG. 3 shows a SEM photograph of [2].
[3] Next, carbon dioxide was introduced from the gas introduction line L5 of the degassing membrane device 14, and the number of fine particles and pH when the carbon dioxide concentration reached 1.6 ppm were measured.
Following [4] and [3], carbon dioxide gas was introduced, and when the carbon dioxide concentration reached 106 ppm, the introduction of carbon dioxide was stopped.
At this time, the number of fine particles and pH were measured, and as described later, carbon dioxide-dissolved water was sampled, the fine particles in the carbon dioxide-dissolved water were observed by SEM, and the composition of the fine particles was analyzed by EDX.
The results in [1] to [4] are shown in Table 1 below. FIG. 4 shows a photograph taken by SEM in [4].

[5] From the state of [4], the pump P is operated to introduce primary pure water from the pure water tank 11, and the valve B2 is opened to discharge the carbon dioxide-dissolved water, which is circulated in the simulator. The carbon dioxide-dissolved water was gradually replaced with primary pure water. While measuring the pH, substitution with primary pure water was performed until the pH reached 4.8, and simultaneously the change in the number of fine particles was measured.
[6] When the pH of the carbon dioxide-dissolved water in the simulation apparatus reached 4.8 in [5], the operation of the degassing membrane apparatus 14 was started and the change in the number of fine particles was measured.
Changes in pH and the number of fine particles in [5] [6] are shown in FIG. In FIG. 5, the system circulation start time of primary pure water is defined as 0 hour (h), the number of fine particles is indicated by a solid line, and pH is indicated by a broken line.
The SEM observation of the fine particles was performed as follows.

[SEM observation of fine particles]
3 L of sample water is passed through the Nuclepore membrane (NPMF, pore size 0.2 μm, manufactured by Nomura Micro Science Co., Ltd.) in 2 hours from the sampling line installed between the branch of line L2 and valve B3. The supplements were observed by SEM at a magnification of 20,000 times. At the same time, the number of fine particles having a particle diameter of 0.2 to 0.5 μm and the number of fine particles having a particle diameter exceeding 0.5 μm in 1 mL of sample water were counted.
[Analysis of fine particles]
About the supplement mentioned above, the composition was analyzed by EDX.

The fine particles observed in FIG. 3 are elliptical or indeterminate particulate materials, and it was confirmed by EDX analysis that they consist of metal elements such as iron and manganese.
In FIG. 4, a film-like substance not observed in FIG. 3 was observed, and it was confirmed by EDX analysis that the elements constituting the film-like substance were mainly carbon and oxygen. That is, it is considered that this film-like substance is derived from organic substances constituting the piping system or organic substances attached to the inner wall surface of the piping system.

From Table 1, the number of fine particles having a particle size of 0.2 to 0.5 μm is not increased when the carbon dioxide concentration is increased from 0 ppm to 1.6 ppm, but is increased by increasing the concentration to 106 ppm. I understand that. Even when the carbon dioxide concentration is increased from 0 ppm to 106 ppm, the number of fine particles having a particle size exceeding 0.5 μm is not increased among the above-mentioned elliptical and irregular particulate materials.
From this, it is presumed that fine particles of 0.2 to 0.5 μm were detached from the inner wall surface of the piping system and the like by circulating the carbon dioxide-dissolved water in the system. In addition, when the SEM observation results of FIG. 4 are combined, it is considered that the detached fine particles were observed as a film-like substance due to aggregation.

  From FIG. 5, it can be seen that the fine particles detached in the carbon dioxide-dissolved water circulation step are reduced by maintaining the pH at approximately 4.2, and are in a steady state after being reduced by a certain amount. This is considered to be a state in which the desorbed fine particles are repeatedly reattached and redetached to the inner wall surface of the piping system, and the number of adhering fine particles and desorbed fine particles is in equilibrium. Then, the operation of the degassing membrane device 14 is started, and it can be seen that the number of fine particles to be desorbed increases as the pH of the cleaning water becomes substantially neutral due to degassing. From this, it can be seen that the fine particles once detached from the inner wall surface of the piping system are easily detached even when they are reattached.

Reference example 2
FIG. 6 shows the result of measuring the number of fine particles when primary pure water was circulated in the system for 8 hours in [2] of Example 1.
Example 2

The ultrapure water production system 2 shown in FIG. 2 was newly installed, and cleaning was performed.
The ultrapure water system 2 used in Example 2 is one in which the following water treatment devices are further installed on the piping of the secondary pure water system in the simulation apparatus of Example 1. The specifications of the equipment and apparatus used in Example 2 and the experimental conditions are shown below.
Primary pure water: specific resistance 18.2 MΩ · cm, number of fine particles having a particle diameter of 0.05 μm or more / mL or less,
Heat exchanger 12: Plate type heat exchanger (manufactured by Nisaka Manufacturing Co., Ltd., material: SUS316),
UV oxidation device 13: JPW-2X2 (manufactured by Nippon Photo Science Co., Ltd., material: SUS316L),
Polisher 15: A Teflon (registered trademark) coated SUS container (inner diameter 400 mm, height 2,500 mm) filled with MBGP (manufactured by Nomura Micro Science Co., Ltd.) as a mixed bed ion exchange resin.
Ultrafiltration membrane device 16: OLT-6036H (manufactured by Asahi Kasei Corporation),
PVDF piping: piping inner diameter 75mm, piping total length 95,000mm,
The measurement instrument 17 used the following specific resistance meter and TOC meter in addition to the same measurement instrument as in Example 1.
Specific resistance meter: 200CR (made by Thornton),
TOC meter: Sievers 900 on-line TOC Analyzer (manufactured by GE).

Start-up washing was performed according to the following procedure.
[1] When installation of equipment such as a pump and each water treatment device and piping work were completed, the pure water tank 11 was prepared and received primary pure water. The temperature control by the heat exchanger 12 was not performed, and the water temperature was assumed to be good.
[2] Primary pure water is filled from the pure water tank 11 to the entire ultrapure water production system 2, and then each water treatment device and piping are vented, and then large dust and impurities are discharged by flushing. Went.
[3] Primary pure water was introduced from the pure water tank 11 and the system was circulated for 1 hour at a linear velocity of 0.9 m / sec.
At this time, the operation of the deaeration membrane device 14 was stopped, the polisher 15 was not filled with the mixed bed type ion exchange resin, and a dummy module was used for the ultrafiltration membrane device 16.
[4] Carbon dioxide is introduced from the gas introduction line L5 of the degassing membrane device 14 into the primary pure water being circulated in the system, and the carbon dioxide-dissolved water is used for 2 hours after the carbon dioxide concentration reaches 115 ppm. Circulation (carbon dioxide dissolved water circulation step).
[5] With the primary pure water of the pure water tank 11 completely discharged, the pump P and the valve B2 were opened, and the carbon dioxide-dissolved water was discharged out of the system for 15 minutes (extrusion process).
The linear velocity of the carbon dioxide-dissolved water drainage at this time was 0.9 m / sec.
[6] Next, the pure water tank 11 was filled with primary pure water, and the operation of the deaeration membrane device 14 was started, and flushing with the stored primary pure water was performed for 15 minutes at a linear velocity of 0.9 m / sec (rinse) Process).
It was confirmed that the measured value of the carbon dioxide concentration by the TOC meter installed as the measuring instrument 17 reached a specified value of less than 20 mg / L and that the cleaning was sufficient.
[7] The polisher 15 was filled with a mixed bed type ion exchange resin. The ultrafiltration membrane device 16 replaced the dummy module with an ultrafiltration membrane module.
[8] Primary pure water was passed through the polisher 15. The water was discharged (blowed) at the exit of the polisher 15, and when the quality of the blow water reached the same specified value as [6], the blow pipe was closed and sent to the subsequent stage.
[9] Blowed at the outlet of the ultrafiltration membrane device 16. The water quality of the blow water was confirmed with an appropriate measuring instrument, and when the water quality reached the same specified value as [6], the blow pipe was closed and sent to the subsequent stage.
[10] The lamp of the ultraviolet oxidizer 13 was turned on, and the primary pure water was passed through the secondary pure water system. After measuring the water quality (specific resistance, TOC, fine particles, etc.) at the outlet of the ultrafiltration membrane device 16 and confirming that the water quality can be returned to the circulation system (normal operation), turn on the lamp of the UV oxidation device 13 The valve B3 was opened and switched to the circulation line for normal operation. ([7] to [10]: Startup process.)

Within one day from the start of normal operation after the start-up process is completed, the specific resistance: 18.2 MΩ · cm or more, TOC: less than 1 ppb, the number of fine particles having a particle diameter of 0.05 μm or more: reference value of less than 1 / mL Achieved. The sampling point was the outlet of the ultrafiltration membrane device 16.
In Example 2, the number of fine particles having a particle size of 0.05 μm or more at the outlet of the ultrafiltration membrane device 16 after the start-up process is completed is shown by a solid line in FIG.

Comparative Example 1
In [2] of Example 2, the ultrapure water production system was set up and washed according to the same series of operating procedures as in Example 2 except that carbon dioxide was not introduced.

After the start-up process is completed, after 3 days from the start of normal operation, a specific value of specific resistance: 18.2 MΩ · cm or more, TOC: less than 1 ppb, number of fine particles with particle diameter of 0.05 μm or more: less than 1 standard / mL Achieved. The sampling point was the outlet of the ultrafiltration membrane device 16.
In Comparative Example 1, the number of fine particles having a particle size of 0.05 μm or more at the outlet of the ultrafiltration membrane device 16 after the start-up process is completed is shown by a broken line in FIG.
As described above, in Example 2, the water quality could be improved in a short time by using the cleaning method of the present invention. On the other hand, in Comparative Example 1, since the cleaning method of the present invention is not used, it can be seen that the startup cleaning takes time.

DESCRIPTION OF SYMBOLS 1, 2 ... Ultrapure water production system, 10 ... Secondary pure water system, 11 ... Pure water tank, 14 ... Deaeration membrane apparatus, 17 ... Measuring instrument, L5 ... Gas introduction line.

Claims (9)

A method of starting and cleaning at least a part of an ultrapure water production system, an ultrapure water use point, and a pipe system connecting the ultrapure water production system and the use point,
A carbon dioxide-dissolved water circulation step in which carbon dioxide-dissolved water is circulated in at least a part of the ultrapure water production system, and fine particles adhering in the ultrapure water production system are desorbed into the carbon dioxide-dissolved water;
A method for cleaning an ultrapure water production system, comprising: an extruding step for discharging the fine particles desorbed in the carbon dioxide-dissolved water out of the system.   The method for cleaning an ultrapure water production system according to claim 1, wherein the carbon dioxide concentration of the carbon dioxide-dissolved water is 100 to 1,000 ppm.   The method for cleaning an ultrapure water production system according to claim 1 or 2, wherein the pH of the carbon dioxide-dissolved water is 3-4.   The method for cleaning an ultrapure water production system according to any one of claims 1 to 3, further comprising a rinsing step for washing at least part of the ultrapure water production system by passing pure water through the water. .   5. The method for cleaning an ultrapure water production system according to claim 1, wherein at least a part of the extrusion step is performed without passing pure water through the ultrapure water production apparatus.   The carbon dioxide introduction step of introducing carbon dioxide into the pure water in a state where pure water is circulated in at least a part of the ultrapure water production system. 5. A method for cleaning an ultrapure water production system according to item. The ultrapure water production apparatus includes a degassing membrane apparatus having a gas introduction line,
The cleaning method for an ultrapure water production system according to claim 6, wherein the carbon dioxide introduction step introduces carbon dioxide into the pure water through the gas introduction line.   The carbon dioxide concentration is a concentration at which a surface potential of at least a part of a contact surface with pure water of the ultrapure water production system is 0 to 5 mV. A method of cleaning the described ultrapure water production system.   The method for cleaning an ultrapure water production system according to any one of claims 1 to 8, further comprising a startup step of starting up an ultrapure water production apparatus after the extrusion step.

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