Cleaning method for startup time of ultrapure water production apparatus

Abstract

To provide a cleaning method for an ultrapure water production apparatus that shortens the start-up time thereof and enables early production of high-purity ultrapure water.SOLUTION: Provided is a cleaning method for startup time of an ultrapure water production apparatus equipped with a subsystem having an ion exchange device, in which members used on a rear stage side of the ion exchange device and having a ratio (wetted surface area per unit ultrapure water flow rate) of a wetted surface area (m2) for each member to a passing water flow rate (m3 / h) of the member in the ultrapure water production apparatus of 1.0×10-6 m2 / (m3 / h) or more, are installed in the ultrapure water production apparatus after cleaned in advance with water or a chemical solution.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a cleaning method for ultrapure water production equipment when it is started up, that is, when it starts to operate. [Background technology]

[0002] The point of use (use point) of ultrapure water in a semiconductor manufacturing factory or the like is connected to an ultrapure water production system by an ultrapure water supply pipe, and any remaining ultrapure water not used at this use point is returned to the sub-tank of the ultrapure water production system via an unused ultrapure water return pipe.

[0003] Conventionally, when an ultrapure water production system is installed, expanded, modified, or maintained, dust particles in the air, other fine particles, particles contained in water such as iron rust, and even shavings generated during the manufacturing process (hereinafter collectively referred to as "fine particles") are mixed into the system and removed by cleaning when the system is started up.

[0004] Preventing initial contamination of ultrapure water production equipment depends largely on the quality of the water at start-up. In particular, contamination on the secondary side of the ion exchange unit has a significant impact on the quality of the ultrapure water produced, so cleanliness control of this part is extremely important.

[0005] Conventionally, to clean an ultrapure water production apparatus, the components that make up the ultrapure water production system are assembled to complete the ultrapure water production apparatus, and then only the areas where the components are assembled, or the entire system, is washed with ultrapure water, or ultrapure water containing TMAH (tetramethylammonium hydroxide) or hydrogen peroxide as needed (e.g., Patent Document 1).

[0006] Patent Document 2 discloses a method for starting up an ultrapure water production system in which the impurity concentration in the feedwater is specified when an ultrafiltration membrane (UF membrane) is installed, and water flow is started when the concentration falls below a reference value.

[0007] Patent Document 3 discloses a method for cleaning ultrapure water production equipment and point-of-use piping by using an alkaline solution and sterilizing water. This method is effective for removing fine particles and sterilizing the system, as well as reducing metals, but requires large-scale cleaning because it involves cleaning actual equipment, and the process takes several days. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Japanese Patent Application Laid-Open No. 2000-317413 [Patent Document 2] Japanese Patent Application Publication No. 2022-187148 [Patent Document 3] Patent No. 5287713 Summary of the Invention [Problem to be solved by the invention]

[0009] An object of the present invention is to provide a cleaning method for ultrapure water production equipment during start-up, which shortens the start-up time of the equipment and enables high-purity ultrapure water to be produced quickly. [Means for solving the problem]

[0010] The present invention is as follows.

[0011] [1] A cleaning method for ultrapure water production equipment equipped with a subsystem having an ion exchange device at the start-up stage, comprising: Regarding the components used in the downstream side of the ion exchange device, the liquid contact area (m 2 ) and the water flow rate (m 3 / h) (wetted area per unit ultrapure water flow rate) is 1.0 x 10 -6 m 2 / (m 3 1. A cleaning method for ultrapure water production equipment at the start-up of the equipment, characterized in that the components (including the parts) are previously cleaned with water or a chemical solution before being installed in the equipment.

[0012] [2] A cleaning method for the start-up of an ultrapure water production system according to [1], in which the components are cleaned by immersing or running them over for at least one hour using one or more of pure water, warm pure water, acidic chemicals, alkaline chemicals, and oxidizing chemicals.

[0013] [3] The method for cleaning the ultrapure water production system of [1] or [2] during startup, wherein the component is at least one of a treated water strainer, a resin catcher, piping, a valve, a pump, a degassing membrane, a dissolving membrane, a UF membrane, a gasket, a sampling valve, a sampling tube, and a heat exchanger of an ion exchange system. [Effects of the Invention]

[0014] In the present invention, among the components of the ultrapure water production system, the liquid contact area per unit ultrapure water flow rate is 1.0 × 10 -6 m 2 / (m 3 / h) or more, are pre-cleaned with water or chemicals before being installed in the ultrapure water production system. This allows high-purity ultrapure water to be obtained quickly, even when starting up an ultrapure water production system that requires water quality on the sub-ng / L level.

[0015] According to one aspect of the present invention, it is possible to omit the large-scale chemical cleaning process that is performed after pre-cleaned components are installed in the ultrapure water production system, thereby shortening the test run process. However, the large-scale chemical cleaning process may still be performed.

[0016] Even when an ultrapure water production system is expanded or maintained, by pre-cleaning the above components as described above before assembling them into the ultrapure water production system, it becomes possible to use high-purity ultrapure water quickly.

[0017] In one aspect of the present invention, by cleaning the components using chemical cleaning, it is possible to eliminate the chemical cleaning process for the entire ultrapure water production system and shorten the start-up period. However, a large-scale chemical cleaning process may also be performed. [Brief explanation of the drawings]

[0018] [Figure 1] FIG. 1 is a flow diagram of a subsystem of an ultrapure water production system. [Figure 2] 10 is a graph showing experimental results. DETAILED DESCRIPTION OF THE INVENTION

[0019] The ultrapure water production system that is the subject of this invention comprises a primary pure water production system and a subsystem (secondary pure water production system). In addition, a pretreatment device is usually provided upstream of the primary pure water production system.

[0020] In the pretreatment equipment, the raw water is subjected to pretreatment such as filtration, coagulation and sedimentation, and microfiltration membranes, mainly to remove suspended solids. This pretreatment usually reduces the number of particles in the water to 10 3 The number of cells / mL or less

[0021] The primary pure water production system is equipped with a reverse osmosis (RO) membrane separation device, a degassing device, a regenerative ion exchange device (mixed-bed or 4-bed 5-tower type, etc.), an electric deionization device, an oxidation device such as an ultraviolet (UV) irradiation oxidation device, etc., and removes most of the electrolytes, fine particles, live bacteria, etc. from the pretreated water. The primary pure water production system is composed of, for example, a heat exchanger, two or more RO devices, a mixed-bed ion exchange device, and a degassing device.

[0022] The subsystem consists of a water supply pump, a cooling heat exchanger, a low-pressure ultraviolet oxidation device, a non-regenerative mixed-bed ion exchange device, and a membrane filtration device such as an ultrafiltration (UF) membrane separator or a microfiltration (MF) membrane separator, and may also be equipped with a membrane degasser, an RO membrane separator, an electrodeionization device, etc. In the subsystem, the TOC components in the water are oxidized and decomposed by the low-pressure ultraviolet oxidation device, and the oxidized decomposition products are removed by the mixed-bed ion exchange device in the subsequent stage.

[0023] FIG. 1 is a system diagram showing an example of a subsystem of such an ultrapure water production system.

[0024] The primary pure water produced in the primary pure water production system is pumped from a sub-tank (primary pure water tank) 1 by a pump 2 and processed through a low-pressure ultraviolet oxidation device (UV device) 3, an ion exchange device 4, a pump 5, piping 6, a degassing device 7, piping 8, and an ultrafiltration (UF) device 9.

[0025] In the low-pressure ultraviolet oxidation device 3, TOC is decomposed into organic acids and even CO2 using 185 nm ultraviolet light emitted from a low-pressure ultraviolet lamp. The organic matter and CO2 produced by the decomposition are removed in the downstream ion exchange device 4 and degassing device 7. In the UF (ultrafiltration) device 9, fine particles are removed, as well as particles effluent from the ion exchange resin.

[0026] The ultrapure water produced in this subsystem is sent to a use point 11 via an ultrapure water supply pipe 10 , and unused ultrapure water is returned to the sub-tank 1 via a return pipe 12 .

[0027] In Fig. 1, a pipe 21 branches off from a pipe 8 that sends water from the degassing membrane device 7 to the UF device 9, and a portion of the degassed water is introduced into a preheater 22 via the pipe 21 and preheated. After that, the water is heated again through a pipe 23 and a heater 24 and sent to a use point 28 via a pipe 25, a UF device 26, and a pipe 27. Unused ultrapure water at the use point 28 is sent to the preheater 22 via a return pipe 29. Excess ultrapure water in the preheater 22 is returned to the sub-tank 1 via a return pipe 30.

[0028] A sampling valve 10a is provided in the piping 10, and sample water can be introduced into the analysis device 16 via sampling piping 15. Sample water is sampled from the piping 27 via sampling valve 27a and sampling piping 31, and after being cooled in a sampling cooler 32, can be introduced into the analysis device 16 via piping 33.

[0029] After the new construction or expansion of this subsystem is completed, the ultrapure water production equipment is operated to produce ultrapure water. Among the components incorporated into the subsystem during this new construction or expansion, there are components located at the ion exchange unit or downstream side (but up to the point of use) that have a liquid contact area of ​​1.0 x 10 per unit ultrapure water flow rate. -6 m 2 / (m 3 / h) or more must be washed in advance (hereinafter referred to as pre-washing).

[0030] Such components include the strainer and resin catcher of the ion exchange device 4, the pump 5, the degassing device 7, the UF device 9, the piping 10, the sampling valves 10a and 27a, the preheater 22, the heater 24, the UF device 26, the piping 6, 8, 10, 21, 23, 25, 27, and 31, the sampling piping 15, 31, and 33, the various valves and gaskets provided on these piping, and the sampling cooler 32.

[0031] The pre-cleaning may be one or more of the following: cleaning with pure water (resistivity of 5 MΩcm or more, preferably 18 MΩcm or more), cleaning with warm pure water (30°C or more, preferably 40 to 75°C), cleaning with an acidic chemical (nitric acid or the like, preferably at a concentration of 0.1% or more), cleaning with an alkaline chemical (choline hydroxide or the like, preferably at a pH > 10.5), cleaning with an oxidizing chemical (H2O2 or the like, preferably at a concentration of 0.1% or more).

[0032] Pre-cleaning is preferably carried out until the amount of eluted fine particles and soluble components from the component is reduced to half or less. After the initial cleaning has been performed to determine the elution process from the component and the required time, pre-cleaning can be carried out by specifying the cleaning time without checking the amount of elution. Usually, pre-cleaning by immersion or pouring for at least one hour is preferable.

[0033] Stainless steel members are particularly effective as materials for the members to be pre-cleaned, but this is not limiting and non-ferrous materials such as fluororesin members and other plastic materials may also be used. [Example]

[0034] [Example 1, Comparative Examples 1 and 2] An example of cleaning the strainer (made of SUS) of the ion exchange resin device in the subsystem will be explained.

[0035] This strainer is cylindrical, measuring φ114.3 mm and L373 mm, with numerous slits on the circumferential side. There are four slits, each 0.2 mm wide. The liquid contact area per strainer, ignoring the slits, is 0.29 m 2 The water flow rate per strainer is 14.5 m 3 / h, and the wetted area per unit ultrapure water flow rate is 2.0 × 10 -2 m 2 / (m 3 / h). This value is the reference value of 1.0 × 10 -6 m 2 / (m 3 / h).

[0036] In Example 1, this strainer was immersed in 1% H2O2 for 2 hours for cleaning, and then incorporated into an ion exchange device.

[0037] In Example 2, this strainer was washed by running ultrapure water over it at a rate of 1 L / hr for 5 days, and then incorporated into an ion exchange device.

[0038] In Comparative Example 1, the strainer was installed in the ion exchange device without being washed at all.

[0039] The ion exchange resin and other components of the ion exchange device, such as the casing, were washed with ultrapure water in the same manner as above. The ion exchange resin was a mixture of anion and cation exchange resins (1160 L).

[0040] Each ion exchanger was filled with ultrapure water for SV=50hr. -1 The water was passed through the filter and the Fe concentration in the outflow water was measured. The results are shown in Figure 1.

[0041] As shown in FIG. 1, in Comparative Example 1, it took 8 days or more for the Fe concentration to fall to 1 ng / L or less, whereas in Examples 1 and 2, it fell to 1 ng / L or less in 3 days. [Explanation of symbols]

[0042] 1 Subtank 3. UV oxidation equipment 4. Ion exchange unit 7 Degassing device 9,26 UF equipment 11,28 Use Points 16 Analyzer 22 Preheater 24 Heater 32 Sampling Cooler

Claims

1. 1. A method for cleaning an ultrapure water production system equipped with a subsystem having an ion exchange device at the time of startup, comprising: Regarding the components used in the downstream side of the ion exchange device, the liquid contact area (m ２ ) and the water flow rate (m ３ / h) (wetted area per unit ultrapure water flow rate) is 1.0 × 10 －６ m ２ / (m ３ 1. A cleaning method for ultrapure water production equipment at the start-up of the equipment, comprising the steps of: cleaning the above-mentioned components (i.e., the components of the equipment) with water or a chemical solution in advance; and then installing the components in the equipment.

2. 2. The method for cleaning the ultrapure water production system at the start-up of claim 1, wherein the components are immersed or allowed to flow for at least one hour using one or more of pure water, warm pure water, acidic chemicals, alkaline chemicals, and oxidizing chemicals.

3. 3. The method for cleaning an ultrapure water production system during startup according to claim 1 or 2, wherein the component is at least one of a treated water strainer, a resin catcher, piping, a valve, a pump, a degassing membrane, a dissolving membrane, a UF membrane, a gasket, a sampling valve, a sampling tube, and a heat exchanger of an ion exchange system.

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