JPH05261368A - Method and apparatus for producing pure water - Google Patents

Abstract

(57) [Summary] [Purpose] To provide a pure water production method and apparatus capable of producing pure water without increasing fine particles and impurity ions in the liquid and removing dissolved oxygen in the pure water to an extremely low concentration. To do. [Structure] A cation exchange resin tower 2, a decarbonation tower 3 and an anion exchange resin tower 6 are included, and an inert gas supply device 5 is connected to the bottom of the decarbonation tower 3 for aeration with an inert gas or an anion. The dissolved oxygen removing tower 8 is connected to the subsequent stage of the ion exchange resin tower 6, the inert gas supply device 5 is connected to the bottom thereof, and the gas discharged from the upper portion of the dissolved oxygen removing tower 8 is passed through the inert gas pipe 10. Is supplied to the bottom of the decarbonation tower 3.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for producing pure water which does not contain impurities in the air, and particularly to 2B3T.
Type and 4B5T type ion exchange resin towers and decarbonation towers in combination, and a pure water manufacturing method using the same.

[0002]

2. Description of the Related Art Ion exchange method is widely used to remove various ions in water. In particular, when producing a large volume of pure water, a decarbonation tower is installed between the cation exchange resin tower and the anion exchange resin tower for the purpose of removing carbonate ions in water. In this decarboxylation tower, the effluent water from the cation exchange resin tower has a low pH, and the carbonate ions that load the anion exchange resin in the subsequent stage can be easily discharged to the outside of the system as carbon dioxide gas. Air is aerated between the resin tower and the anion exchange resin tower to remove carbon dioxide gas in the liquid.

The content of carbonate ions in water varies depending on the raw water used for producing pure water, for example, city water, well water, etc., and is 10 to 30 ppm in city water and 20 to 50 in well water.
Contains ppm carbonate ions. Therefore, the removal of the carbonate ion is important for increasing the efficiency of the anion exchange resin in the latter stage, and the role of the decarbonation tower is great.

However, the decarbonation method by air aeration has not caused a big problem in the past when only carbon dioxide gas in pure water was targeted, but recently, organic matter contained in pure water has been produced. Or, the problem of fine particles has become apparent. For this reason, improvements in the apparatus have been made, such as filtering the air blown into the decarbonation tower to remove the fine particles in the air. However, it is difficult to sufficiently remove fine particles of 0.1 to 0.5 μm in the air with a filter. Further, by aerating the decarbonation tower with air, impurities other than fine particles in the air, such as ions,
A lot of organic substances and bacteria are mixed. These impurities are
This adversely affects the anion exchange resin column and the mixed bed column in the subsequent stage of the decarbonation column, and causes problems such as an increase in the frequency of resin regeneration and an increase in fine particles in pure water.

Further, dissolved gases in pure water and ultrapure water for cleaning semiconductors, particularly dissolved oxygen, have been removed from the viewpoint of preventing oxidation of ion exchange resins and corrosion of various metal members. Recently, it has been pointed out that if dissolved oxygen is present in the liquid during Si wafer cleaning in the manufacture of semiconductor devices, a natural oxide film is formed on the surface of the Si wafer, which causes problems in manufacturing high-performance devices. Technology has been developed to reduce the dissolved oxygen concentration in ultrapure water to several ppb or less.

Conventionally, a vacuum degassing method has been widely adopted for removing dissolved oxygen. In this method, the water to be treated is sprayed from the upper part of a vacuum tower having a tower height of about 10 m, and the dissolved oxygen is removed in the process of bringing the droplets into contact with the gas phase having a low oxygen partial pressure. However, in this method, the concentration of dissolved oxygen remaining in the liquid becomes a limit due to the vacuum level in the vacuum tower,
At the normal limit vacuum level of 20 to 30 Torr, 50 to 100 ppb of dissolved oxygen remains in the liquid. Therefore, this vacuum degassing method has a performance problem.

On the other hand, a method of making dissolved oxygen in various liquids to an extremely low concentration is currently being studied, and one of them is an inert gas aeration method in which an inert gas such as nitrogen gas is passed through the liquid. There is. This method is capable of removing dissolved oxygen by passing an inert gas such as nitrogen gas into the liquid and removing dissolved oxygen up to a concentration of 1 ppb.
There is a drawback that the amount of inert gas to be ventilated is relatively large.

On the other hand, in the primary pure water system, as described above, in order to reduce the amount of ions in the anion exchange column, the operation of removing carbonate ions in the liquid flowing out from the cation exchange column is performed. This is the role of the decarbonation tower, and normally, air is aerated from the lower part of the tower to remove carbonate ions in the liquid. Therefore, the dissolved oxygen in pure water becomes 8000 to 9000 ppb which is saturated with the atmosphere at the outlet of this decarbonation tower,
It is a heavy burden on the dissolved oxygen removal tower in the latter stage. In addition, as described above, the presence of dissolved oxygen has a negative effect of promoting the deterioration of the anion exchange resin.

[0009]

DISCLOSURE OF THE INVENTION The present invention solves the above-mentioned problems of the prior art, and performs ventilation for removing carbonate ions as carbon dioxide gas without using a filter at the ventilation port of the decarbonation tower. By this, it is possible to produce pure water without increasing the number of fine particles and the number of impurity ions in the liquid, and a method for producing pure water capable of removing dissolved oxygen in pure water to an extremely low concentration, and The purpose is to provide a device.

[0010]

The present invention has achieved the above object by aeration with an inert gas instead of air aeration in a decarbonation tower. That is, in the method for producing pure water according to the present invention, when pure water is produced by sequentially passing water through a cation exchange resin tower, a decarbonation tower and an anion exchange resin tower, an inert gas is supplied from the bottom of the decarbonation tower. It is characterized by introducing. The pure water producing apparatus according to the present invention is a pure water producing apparatus including a cation exchange resin tower, a decarboxylation tower and an anion exchange resin tower, and an inert gas supply device is connected to the bottom of the decarbonation tower. Characterize.

In the present invention, a dissolved oxygen removing tower is provided at the latter stage of the anion exchange resin tower, an inert gas supply device is connected to the bottom of the dissolved oxygen removing tower, and the dissolved oxygen removing tower is discharged from the upper portion thereof. It is also possible to introduce a part or all of the generated inert gas into the bottom of the decarbonation tower through an inert gas pipe.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a system diagram of a pure water producing apparatus showing an embodiment of the present invention. In FIG. 1, the water to be treated flows into the cation exchange resin tower 2 through the pretreatment device 1. here,
Of the various ions present in the water to be treated, cations such as Na and K react with the exchange groups of the ion exchange resin and are removed. Further, at this time, since H ions are released into water, the pH of the liquid is lowered. The decarbonation tower 3 is provided with a treated water introduction pipe 4 for spraying treated water having a low pH from the upper part of the tower and an inert gas supply device 5, and an inert gas such as nitrogen gas is supplied to the stored water in the lower part of the tower. Blow in and remove carbonate ions in water out of the system by this aeration effect. Next, in the anion exchange resin tower 6, anions other than carbonate ions are removed, and further various ions remaining in the mixed bed tower 7 are removed,
Pure water is produced by passing through this series of systems.

FIG. 2 is a graph showing changes over time in the water quality of the decarbonation tower outlet water of the method of the present invention and the conventional method when city water is used as raw water. The conventional method of aerating the decarbonation tower is
Although the effect of removing carbonic acid is sufficient, the number of fine particles having a particle size of 0.2 μm or more in the treatment liquid is as large as 1 × 10 ^{5 to} 5 × 10 ⁵ particles / ml. On the other hand, when an inert gas (for example, nitrogen gas) is blown by the method of the present invention at a rate of 80 liters / minute (gas aeration rate: about 60 m / hour), the carbon dioxide removal performance is the same. However, the number of fine particles in the treatment liquid was 1 × 10 ⁴ particles / ml or less. That is, the number of fine particles in the treatment liquid is 90% by the method of the present invention.
It is possible to reduce the above. This difference in the effect of removing fine particles has a great influence on the outlet water of the anion exchange resin tower, which is the next step of the decarbonation tower.

FIG. 3 is a graph showing changes with time in the concentration of fine particles in the outlet water of the anion exchange resin when the conventional method and the method of the present invention are adopted. In the conventional method, the fine particles of water in the outlet of the anion exchange resin tower rapidly increase from the water passage time of about 12 hours, but in the method of the present invention, the outflow of the fine particles hardly occurs even at the water passage time of 20 hours which is a normal regeneration cycle. Absent. In addition, Table 1 shows the amount of organic matter, the total amount of cations and the total amount of anions in the effluent water of the conventional method and the method of the present invention. From these results, it can be seen that the method of the present invention is effective for reducing other impurities in the fine particles.

[0015]

[Table 1]

FIG. 4 is a graph showing the transition of dissolved oxygen in a pure water producing apparatus having a conventional decarbonation tower through which air is passed. It can be seen that the dissolved oxygen in the liquid sharply rises when passing through the decarbonation tower for removing carbonate ions, which imposes a heavy burden on the dissolved oxygen removing device in the subsequent stage.

FIG. 5 is a system diagram of an apparatus for producing pure water and ultrapure water showing an embodiment of the present invention. The apparatus shown in FIG. 5 mainly comprises a pretreatment apparatus 1 for coagulation and the like, activated carbon towers 11 and 2B.
From a cation exchange resin tower 2, a decarbonation tower 3, an anion exchange resin tower 6 called 3T, a mixed bed tower 7, a dissolved oxygen removal tower 8, an ultrapure water production system 9 and an inert gas supply device 5. It is configured. City water, which is raw water, is highly purified in the process of sequentially passing through this device. In this apparatus, the inert gas supply device 5 is connected to the bottom of the dissolved oxygen removal tower 8, and the gas discharged from the upper part of the dissolved oxygen removal tower 8 is passed through the inert gas pipe 10 to the decarbonation tower of the preceding stage. The carbon dioxide ion and the dissolved oxygen contained in the water are simultaneously removed in the decarbonation tower 3.

Dissolved oxygen concentration in water when the apparatus shown in FIG. 5 was used is also shown in FIG. As can be seen from FIG. 4, by carrying out decarboxylation according to the conventional method, it is possible to remove dissolved oxygen from 600 to 600 without deteriorating the removal performance of carbonate ions.
It can be reduced to 800 ppb.

Further, FIG. 6 shows a summary of the amount of gas required for the dissolved oxygen in the inlet liquid of the dissolved oxygen removing tower 8, but it is possible to remove the dissolved oxygen in the liquid to be treated up to 1 to 3 ppb. The required nitrogen gas amount was 0.8 Nl / l with respect to the supply liquid amount in the conventional method, while it was 0.4 Nl / l in the method of the present invention, and the blown nitrogen gas amount was about 1 / l
It could be reduced to 2.

[0020]

According to the present invention, various impurities such as fine particles in the decarbonation tower can be effectively reduced, and the water quality of the outlet water of the anion exchange resin tower at the latter stage can be greatly improved. In addition, by blowing an inert gas such as nitrogen gas, it is possible to simultaneously remove dissolved oxygen in the liquid that causes deterioration of the ion-exchange resin. There is also an additional effect that the exchange frequency can be increased and bacterial growth in the system can be prevented. Furthermore, by using a system in which an inert gas is blown into the dissolved oxygen removal tower and the exhaust gas is introduced into the decarbonation tower, the amount of inert gas used can be greatly reduced.

[Brief description of drawings]

FIG. 1 is a system diagram of a pure water production apparatus showing an embodiment of the present invention.

FIG. 2 is a graph showing changes over time in the water quality of the water discharged from the decarbonation tower when the conventional method and the method of the present invention are carried out.

FIG. 3 is a graph showing the change over time in the number of fine particles in the outflow water from the anion exchange resin tower when the conventional method and the method of the present invention are carried out.

FIG. 4 is a graph showing changes in dissolved oxygen in pure water and ultrapure water production apparatuses when the conventional method and the method of the present invention are carried out.

FIG. 5 is a system diagram of an ultrapure water production system showing another embodiment of the present invention.

FIG. 6 is a graph showing the relationship between the dissolved oxygen at the inlet of the dissolved oxygen removing column and the required amount of nitrogen gas blown in when the conventional method and the method of the present invention are carried out.

[Explanation of symbols]

1 ... Pretreatment device, 2 ... Cation exchange resin tower, 3
... Decarbonation tower, 4 ... Treatment liquid inflow pipe, 5 ... Inert gas supply device, 6 ... Anion exchange resin tower, 7 ...
・ Mixed bed tower, 8 ・ ・ ・ Dissolved oxygen removal tower, 9 ・ ・ ・ Ultrapure water production system, 10 ・ ・ ・ Inert gas piping, 11 ・ ・ ・ Active carbon tower

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Office reference number FI technical display location C02F 1/42 A

Claims (4)

[Claims] 1. When producing pure water by sequentially passing water through a cation exchange resin tower, a decarbonation tower and an anion exchange resin tower, an inert gas is introduced from the bottom of the decarbonation tower. A method for producing pure water. 2. A pure water production apparatus including a cation exchange resin tower, a decarbonation tower and an anion exchange resin tower, wherein an inert gas supply device is connected to the bottom of the decarbonation tower. Manufacturing equipment. 3. When producing pure water by sequentially passing water through a cation exchange resin tower, a decarbonation tower, an anion exchange resin tower and a dissolved oxygen removal tower, an inert gas is added to the bottom of the dissolved oxygen removal tower. A method for producing pure water, characterized in that a part or all of the inert gas introduced and discharged from the upper portion of the dissolved oxygen removing tower is introduced into the bottom portion of the decarbonation tower. 4. A pure water production apparatus including a cation exchange resin tower, a decarboxylation tower, an anion exchange resin tower and a dissolved oxygen removal tower, wherein an inert gas supply device is connected to the bottom of the dissolved oxygen removal tower, 1. An apparatus for producing pure water, comprising an inert gas pipe for introducing a part or all of the inert gas discharged from the upper part of the dissolved oxygen removing tower to the bottom part of the decarbonation tower.