JP2003275743A - Buffer tank - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To manufacture high-purity ultrapure water easily. <P>SOLUTION: A cylindrical buffer tank 15 arranged in an ultrapure water manufacturing apparatus 1 is formed by using polyvinyl chloride, or the like so that the tank 15 has 1/12 to 1/20 d/h ratio (wherein (d) is the diameter of a tank body 19 of the tank 15; (h) is the height from the bottom face of the tank body 19 to an overflow pipe 21). The pipe 21 is arranged in the upper part of the tank body 19, and an inlet pipe 20 and an outlet pipe 22 are arranged in the lower part of the tank body 19. Since the tank 15 of the apparatus 1 secures necessary mechanical strengths and is formed into a shape as slender as possible, the surface area of the water in the tank 15 which is to be treated and is exposed to the atmosphere can be made so small that the dissolution of oxygen gas and gaseous carbon dioxide into the water to be treated can be kept to the minimum. Therefore, high-purity ultrapure water can be manufactured easily by such a simple structure. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a buffer tank for temporarily storing a liquid, and more particularly to a buffer tank suitable for a secondary pure water system of an ultrapure water production system.

[0002]

2. Description of the Related Art Conventionally, semiconductor elements, liquid crystal displays,
Or, in the manufacturing process of pharmaceuticals, ionic substances,
Ultrapure water in which fine particles, organic substances, dissolved gas, viable bacteria and the like are reduced to the ppb order is used. Ultrapure water
Mainly, a pretreatment system that removes suspended matter in raw water,
An ultra-high performance system equipped with a primary pure water system that removes ionic substances, fine particles, organic substances, dissolved gases, and live bacteria, and a secondary pure water system that further improves the purity of the primary pure water obtained by the primary pure water system. It is manufactured by a pure water manufacturing device.

In the secondary pure water system, generally, continuous circulation operation is performed, and the secondary pure water generated in the secondary pure water system, sent to the point of use, and not used is returned to the buffer tank and again. Supplied to the secondary pure water system. The waste water of the ultrapure water used at the point of use is sent to, for example, a recovery system for reuse.

In the semiconductor industry in recent years, the demand for the purity of ultrapure water has become more and more stringent as the degree of integration of semiconductor elements is improved. Dissolved oxygen in the liquid to be processed forms a natural oxide film on the surface of a semiconductor wafer in a short time, for example, and causes deterioration of device characteristics and yield. Therefore, the concentration of dissolved oxygen in ultrapure water for wafer cleaning is as low as possible. Is required. Further, the dissolved carbon dioxide gas in the liquid to be treated is
It is required that the concentration of dissolved carbon dioxide gas in the water to be treated be as low as possible because it reacts with a slight amount of dissolved calcium ions or the like to form an insoluble scale and deteriorates the performance of the membrane treatment apparatus.

Therefore, in the ultrapure water production system, in order to suppress the rise of the dissolved oxygen concentration and the dissolved carbon dioxide concentration, nitrogen gas is enclosed (purged) in the buffer tank installed at the inlet of the secondary pure water system. Things are also being done. This suppresses the dissolution of oxygen and carbon dioxide in the secondary pure water during the circulation process described above.

[0006]

However, in the above-mentioned conventional ultrapure water production system, in order to purge the buffer tank with nitrogen and keep the tank at a positive pressure at all times, for example, a pump for supplying nitrogen and a slight pressure are used. A plurality of devices such as a meter and a breather valve are required, which complicates the overall configuration of the device and poses a problem in terms of cost.

Therefore, the present invention has been made to solve the above problems, and provides a buffer tank having a simple structure and a contact area between a stored liquid and an atmosphere being as small as possible. is there.

[0008]

To achieve the above object, a buffer tank according to the present invention comprises a tubular tank body, an inlet pipe for introducing a liquid, which is provided below the tank body, A tank body is provided with an outlet pipe for discharging liquid and a overflow pipe provided above the tank body, and the diameter (d) of the tank body is provided.
And the ratio (d / h) of the height (h) from the bottom surface of the tank body to the overflow pipe is set to d / h = 1/12 to 1/20.

That is, since the buffer tank of the present invention is formed so as to have a vertically long shape as much as possible while ensuring the required rigidity, the water level of the liquid exposed to the atmosphere (maximum Since the upper surface) has a small area, it is possible to suppress the dissolution of oxygen, carbon dioxide, etc. in the liquid as much as possible. Therefore, according to the present invention, the purity of the stored liquid is maintained with a simple device configuration without applying a complicated device configuration such as purging nitrogen gas (inert gas) into the tank body. can do.

In the present invention, the cross sectional area of the outlet pipe is preferably 1.2 to 2.8 times the cross sectional area of the overflow pipe. Further, it is preferable that the outlet pipe and the inlet pipe are formed with substantially the same cross-sectional area, and the cross-sectional area of the cross section of the tank body is 16 to 38 times the cross-sectional area of the outlet pipe. Further, it is desirable that the flow rate of the liquid overflowing from the overflow pipe is set to about 10 to 20% of the amount of the liquid flowing into the buffer tank, and the liquid is always kept in the overflow state.
With such a structure of the buffer tank, it is possible to constantly discharge the portion of the stored water in contact with the air to prevent the dissolution of oxygen or carbon dioxide into the stored water.

In the present invention, the buffer tank may be provided with a second inlet pipe for returning the liquid once discharged from the outlet pipe and introducing it again. In this case, it is possible to collect the unused liquid to be processed that has passed through the so-called use point in the buffer tank.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram functionally showing an ultrapure water production system according to an embodiment of the present invention, and FIG. 2 shows a buffer tank and an RO water tank (water storage tank) constituting the ultrapure water production system in detail. FIG.

As shown in these drawings, the ultrapure water production system 1 is used for producing ultrapure water for cleaning semiconductor elements such as wafers and liquid crystal components such as LCD substrates. It is mainly composed of a primary deionized water system 5 and a secondary deionized water system 6 which successively increase the purity of the raw water supplied from the raw water tank 2.

In this embodiment, the primary pure water system 5
Comprises a reverse osmosis membrane treatment device 7, a mixed bed ion exchange device 8 and a degassing tower 9, while the secondary pure water system 6 comprises:
An ultraviolet irradiation device 10, a mixed bed type ion exchange device 11 and an ultrafiltration membrane treatment device 12 are provided.

The mixed bed type ion exchange apparatus 8 uses anion exchange resin and cation exchange resin in a mixed state in one column, and contains cations in the water to be treated sent from the RO water tank 14. And anions are removed respectively. In the degassing tower 9, the inside of the tower is degassed via a vacuum pump or the like to remove oxygen, carbon dioxide gas, etc. dissolved in the water to be treated. The ultraviolet irradiation device 10 is mainly used for decomposing volatile organic substances, and for example, irradiates ultraviolet rays having a wavelength of 250 to 260 nm (preferably wavelength 253.7 nm) through a UV germicidal lamp to treat the treated material. Decomposes organic substances and live bacteria in water to organic acids or carbon dioxide. The mixed bed type ion exchange device 11 is a device that uses an anion exchange resin and a cation exchange resin in a mixed state in one column, and is an organic acid or carbon dioxide gas in the water to be treated decomposed by the ultraviolet irradiation device 10. Etc. are removed. The ultrafiltration membrane device 12 is a device that uses an ultrafiltration membrane (UF membrane) to sterilize and turbidize the water to be treated.

Primary pure water system 5 and secondary pure water system 6
An RO water tank 14 and a buffer tank 15 are provided between the and, via the mixed bed type ion exchange device 8 and the degassing tower 9. The RO water tank 14 includes the water to be treated that has been treated by the reverse osmosis membrane treatment device 7 and the buffer tank 15.
It has an inlet pipe 16 and an inlet pipe 17 for receiving the overflow water, respectively, and temporarily stores the supplied water to be treated. Further, the RO water tank 15 is provided with an outlet pipe 18, through which the water to be treated is supplied to the mixed bed ion exchange device 8.

The buffer tank 15 comprises a tubular tank body 19, an inlet pipe 20, an overflow pipe 21, an outlet pipe 22, and a secondary side return inlet pipe 23. The cylindrical tank body 19 is made of, for example, polyvinyl chloride, and has a diameter (d) of the tank body 19 and the tank body 19
The ratio (d / h) of the height (h) from the bottom surface to the overflow pipe 21 is d / h = 1/12 to 1/20. That is, the tank main body 19 is formed to be as long as possible while ensuring the minimum necessary mechanical strength. The tank body 19 may be made of reinforced plastic such as FRP or stainless steel such as SUS304.

The inlet pipe 20 is provided below the tank body 19 and supplies the water to be treated sent from the degassing tower 9 into the tank body 19. Overflow pipe 21,
It is provided above the tank body 19 and overflow water is stored in the RO water tank 14. RO water tank 1
The water in 4 is treated by the mixed bed ion exchange device 8 and the degassing tower 9, and is supplied to the tank body 19 again. Outlet pipe 22
Is provided below the inlet pipe 20 in the tank body 19, and the water to be treated stored in the tank body 19 is irradiated with the ultraviolet irradiation device 10 (secondary pure water system 6 side).
Supply to.

The secondary side return inlet pipe 23 is for returning unused ultrapure water that has passed through the point of use through the secondary pure water system 6 to the tank body 19. In addition,
The waste water of the ultrapure water used at the use point is sent to, for example, a recovery system (not shown) for reuse.

The cross-sectional area of the outlet pipe 22 is 1.2 to 2.8 times the cross-sectional area of the overflow pipe 21. Further, the outlet pipe 22 and the inlet pipe 20 are formed with substantially the same cross-sectional area, and the cross-sectional area of the cross section (cross section in the diameter b direction) of the tank body 19 is 16 to 38 of the cross-sectional area of the outlet pipe 22.
Is doubled. Further, the flow rate of the water to be treated overflowing from the overflow pipe 21 is at least 3 to 20%, preferably 5 to 20% of the capacity of the tank main body per hour.
More preferably, it is set to 10 to 20%. Such a buffer tank 15 can store a predetermined amount of water to be supplied to the secondary pure water system 6 side and can circulate an appropriate amount in the device.

Next, a water treatment operation using the buffer tank of this embodiment will be described. Raw water supplied from the raw water tank 2 enters the primary pure water system 5 and is treated by the reverse osmosis membrane device 7 to remove TOC (total organic carbon) in the ionic and colloidal water to be treated. Further, the water to be treated is once stored in the RO water tank 14 and then supplied to the mixed bed type ion exchange device 8 to remove cations and anions. Further, the primary pure water from which oxygen and carbon dioxide have been removed in the degassing tower 9 enters the buffer tank 15 through the inlet pipe 20 and is sent to the secondary pure water system through the outlet pipe 22. The water to be treated sent to the secondary deionized water system passes through the ultraviolet irradiation device 10 and the mixed bed type ion exchange device 11 to the T
Secondary pure water that was not used at the use point after the OC was removed and sent to the use point was returned to the secondary side return inlet pipe 2
It is returned from 3 to the buffer tank.

Thus, the ultrapure water producing system 1 of this embodiment
Between the degassing tower 9 (primary deionized water system 5) and the ultraviolet irradiation device 10 (secondary deionized water system 6), the buffer tank 15 for temporarily storing the water to be treated is the minimum necessary machine. Since it is formed to be as long as possible while ensuring its mechanical strength, the water surface of the water to be treated exposed to the atmosphere in the buffer tank 15 has a small area, which adversely affects the cleaning target such as a semiconductor element. It is possible to suppress the oxygen and carbon dioxide gas that exert the influence of being dissolved in the water to be treated as much as possible. Further, since the liquid surface in contact with air is removed by overflow, high-purity ultrapure water can be produced.

Although the present invention has been specifically described with reference to the embodiments, the present invention is not limited to the above-mentioned embodiments, and various modifications can be made without departing from the scope of the invention. That is, in the present embodiment, the buffer tank 1
Although the shape of No. 5 was formed in a tubular shape, it may be any shape as long as it is a long and slender vertically long tank, and the shape of the horizontal cross section is an ellipse or the shape of the horizontal cross section is A polygonal tank including a square may be applied to the present invention.

[0024]

EXAMPLES Next, examples of the present invention will be described. In this embodiment, the outlet pipe 22 of the buffer tank 15 is
Also, changes in the water quality (specific resistance, water temperature, dissolved oxygen) of the water to be treated flowing through the inlet pipe 20 were measured, and the applicability to the ultrapure water production system 1 was examined.

(Details of Configuration Regarding Buffer Tank and Its Surroundings) Material of Buffer Tank 15: Polyvinyl Chloride Pipe (VP) Shape of Buffer Tank 15: Box-shaped tank of the tank tank 15 in which the horizontal cross section of the internal space is elliptical Inlet pipe 20
Caliber: 50 A caliber (50.8 mm) caliber of outlet pipe 22 of buffer tank 15: caliber 50 A (50.8 mm) caliber of buffer tank 15 d: 500 A caliber (304.
8 mm) (* Cross sectional area of buffer tank 15 in the horizontal sectional direction = sectional area of inlet pipe 20 and outlet pipe 22 x about 25 times) Height of inlet pipe 17 of RO water tank 14 and overflow pipe 21 of buffer tank 15 Difference a: 350 mm Height difference between inlet pipe 20 and outlet pipe 22 c: 350 mm Height difference between mounting base of tank body 19 and outlet pipe 22 b: 3
00mm Total length of buffer tank 15 (tank body 19) e: 39
60 mm (* caliber d of buffer tank 15 x about 13 times) Height h from bottom surface of tank body 19 to overflow pipe 21: 3700 mm (* Diameter d of tank body 19 and from bottom surface of tank body 19 to overflow pipe 21 Ratio of height h d / h)

(Measuring instrument) -Resistance measuring instrument: Thornton, resistivity meter 200CR x 2
Table (calibrated) -Dissolved oxygen meter: Orbsphere Laboratores, MOCA
560D x 2 units (calibrated)

(Measurement conditions) Flow rate of treated water in the inlet pipe 20 of the buffer tank 15: 1
1m ³ / h Flow rate of treated water at the outlet pipe 22 of the buffer tank 15: 1
0.5m ³ / h Overflow amount of treated water from the overflow pipe 21: 0.5m ³ / h

(Measurement Result) Tables 1 and 2 show measured data of the specific resistance of the treated water at the inlet and outlet (the inlet pipe 20 and the outlet pipe 22) of the buffer tank 15, the water temperature, and the dissolved oxygen in the treated water, respectively.

[Table 1]

[Table 2] In addition, graphs of the measurement data of Table 1 and Table 2 are shown in FIGS. 3 and 4, respectively. These Tables 1 and 2
As is clear from FIGS. 3 and 4, the water quality of the water to be treated (pure water or ultrapure water) at the inlet and outlet of the buffer tank hardly changes, for example, as in the device configuration such as purging the buffer tank 15 with nitrogen gas. It was confirmed that there was not.

[0029]

As described above, since the buffer tank of the present invention is formed so as to be as elongated as possible while ensuring the required rigidity, it is exposed to the atmosphere in the tank body. The water surface of the liquid has a small area, and as a result, it is possible to suppress the dissolution of oxygen and carbon dioxide gas in the liquid as much as possible. Therefore, according to the present invention, the purity of the stored liquid can be maintained with a simple device configuration without applying a complicated device configuration such as filling the tank body with nitrogen gas.

[Brief description of drawings]

FIG. 1 is a block diagram functionally showing an ultrapure water production system according to an embodiment of the present invention.

FIG. 2 is a diagram showing in detail a buffer tank and an RO water tank constituting the ultrapure water production system of FIG.

FIG. 3 is a graph showing data on the specific resistance and water temperature of the water to be treated at the inlet and outlet of the buffer tank of FIG.

FIG. 4 is a graph showing data of dissolved oxygen in treated water at the inlet and outlet of the buffer tank of FIG.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Ultrapure water production apparatus, 5 ... Primary pure water system, 6 ... Secondary pure water system, 15 ... Buffer tank, 19 ... Tank body, 20 ... Inlet pipe, 21 ... Overflow pipe, 22 ... Outlet pipe, 23 ... Secondary return inlet pipe.

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) C02F 1/20 C02F 1/20 A 1/42 1/42 B (72) Inventor Hiromitsu Ota Atsugi City, Kanagawa Prefecture 2-9-8 Okada Nomura Micro Science Co., Ltd. (72) Inventor Hitoshi Kojima 2-9-8 Okada, Atsugi City, Kanagawa Nomura Micro Science Co., Ltd. F-term (reference) 3E070 AA03 AB02 GB01 GB04 GB11 4D006 GA03 GA06 JA58A JA67A JA67B JA67C JA71 KA01 KA72 KB04 KB11 KB14 PA01 PB02 PB24 PB68 PC03 PC04 4D025 AA04 AB16 AB34 BA08 BA13 BA22 BB04 DA01 DA04 DA10 4D037 AA03 AB11 BA18 BA23 BB07 CA03 CA15

Claims (5)

[Claims] 1. A cylindrical tank main body, an inlet pipe provided below the tank main body for introducing liquid, an outlet pipe provided below the tank main body for discharging liquid, and a tank main body of the tank main body. An overflow pipe provided above, and a ratio (d / h) of a diameter (d) of the tank body and a height (h) from a bottom surface of the tank body to the overflow pipe.
The buffer tank is characterized in that d / h = 1/12 to 1/20. 2. The buffer tank according to claim 1, further comprising a purification system for purifying the liquid overflowed from the overflow pipe and supplying the purified liquid again from the inlet pipe. 3. The buffer tank according to claim 1, further comprising a second inlet pipe for re-introducing the liquid discharged from the outlet pipe. 4. The buffer tank according to claim 1, wherein the liquid is pure water. 5. The outlet pipe is connected to an outflow passage of a circulation-type pure water production system, and the inlet pipe is connected to a return passage of the pure water production system. The described buffer tank.