JP3348469B2 - Operating method of vacuum degassing tower - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a vacuum degassing tower, and more particularly to an improved vacuum degassing tower suitable for use in the production of ultrapure water for VLSI production.

[0002]

2. Description of the Related Art Ultrapure water used for cleaning a wafer in a process of manufacturing an ultra LSI is required to remove dissolved oxygen to an extremely small amount of 10 μg / l or less. Conventionally, in order to remove dissolved oxygen in the process of producing ultrapure water, a vacuum degassing tower is usually used. However, a conventional vacuum degassing tower can achieve a dissolved oxygen concentration of 30 to 50 μg / l. It was a practical limit.

[0003] The inventors of the present invention have studied the reason why the conventional vacuum degassing tower can only achieve a dissolved oxygen concentration of 30 to 50 µg / l and found that there is a problem in the position of the bleeding from the vacuum degassing tower. By extracting air from the vacuum degassing tower from the lower degassing chamber below the packed bed filled with the gas-liquid contact member, treated water having a dissolved oxygen concentration of 10 μg / l or less without increasing the capacity of the vacuum source Has been proposed (Japanese Patent Application No. 3-99123).

However, in recent ultrapure water, the dissolved oxygen concentration is required to be extremely low, such as 5 μg / l or less, and further 1 μg / l or less. In response to such a demand for dissolved oxygen concentration, it is possible to obtain treated water having a dissolved oxygen concentration of about 5 μg / l by increasing the height of the packed bed and further increasing the amount of bleeding even with a conventional vacuum degassing tower. However, an increase in the amount of extracted air is accompanied by an increase in the size of the vacuum source, and the enlarged vacuum source requires delicate operation technology, so that it is extremely difficult to always obtain treated water with stable water quality.

[0005]

SUMMARY OF THE INVENTION The present inventors have made a simple improvement to a conventional vacuum degassing tower to remove the treated water whose dissolved oxygen concentration has always been reduced to an extremely low concentration of 5 μg / l or less. Intensive study was conducted for the purpose of providing a vacuum degassing tower that can be supplied stably. As a part of this, a detailed analysis of the temperature distribution inside the vacuum degassing tower revealed that a considerable temperature difference occurred between the upper and lower layers of the packed bed.

[0006] That is, in the vacuum degassing tower, a part of the water to be treated evaporates into water vapor while flowing down the packed bed. The more the pressure in the column is reduced, the more water vapor is generated in the packed bed, and the heat of vaporization at that time causes the temperature of the treated water to decrease as it goes to the lower part of the packed bed and the temperature of the lower degassing chamber. As a result, the saturated dissolved oxygen concentration of the treated water increases, so that even if the packed bed is lengthened and the amount of bleeding is further increased, the dissolved oxygen concentration of the treated water is not stabilized at 5 μg / l or less. It is considered something.

[0007]

SUMMARY OF THE INVENTION The present invention has been accomplished to achieve the above-mentioned object, and the gist of the invention is to sandwich a filling layer formed by filling a gas-liquid contact member, and to remove the upper part from above. air chamber has a treated water reservoir for storing the lower degassing chamber and the treated water downwards, the upper degassing chamber is provided with a extraction pipe communicating with the water to be treated supply means and a vacuum source, processing Water storage
Extraction of treated water from the treated water storage section between the section and the lower degassing chamber
A mechanism to spray water into the lower degassing chamber after heating
When degassing the water to be treated using a vacuum degassing tower
To prevent flash evaporation of the heated water to be treated.
Sprinkling or heating the water to be treated by 1-2 ° C
Alternatively, supply the water to be treated to the upper degassing chamber at 20 to 35 ° C.
And a method characterized by the following.

The present invention will be described in further detail. The present invention heats treated water in a treated water storage section which has been deprived of latent heat of vaporization and cooled, so that the dissolved oxygen is easily released. It is intended to stably obtain treated water containing only a very low concentration of dissolved oxygen. 1 and 2 are conceptual views for explaining a vacuum degassing tower according to the present invention, and FIG. FIG. 2 shows an example in which it is provided outside the degassing tower, and FIG.

In FIG. 1, a vacuum degassing tower 1 includes a packed layer 5 filled with a gas-liquid contact member such as a Raschig ring,
Are divided into an upper degassing chamber 4 provided above the lower layer, a lower degassing chamber 6 provided below the packed bed 5, and a treated water storage 7. The upper deaeration chamber 4 is provided with a watering mechanism 3,
Further, the bleeding tube 1 connected to a vacuum source 11 comprising a vacuum pump
0 is open. In addition, it is preferable to install a condenser 21 in the middle of the bleed pipe 10 to condense the water vapor in the bleed gas because the capacity of the vacuum source 11 can be reduced. To remove dissolved oxygen in the water to be treated using this vacuum deaerator,
The treated water introduced through the treated water introduction pipe 2 is sprinkled into the upper deaeration chamber 4 by the sprinkling mechanism 3. The sprinkled water to be treated flows down the packed bed 5, flows into the lower degassing chamber 6, and is stored in the treated water storage 7. During this time, the dissolved gas in the water to be treated is released into the gas phase, and is discharged outside the system via the bleed pipe 10 and the condenser 21. On the other hand, the treated water stored in the treated water storage section 7 is discharged out of the system through a treated water extraction pipe 8 and a treated water extraction pump 9, and a part of the treated water is heated through a recycling pipe 19. The water is heated by the heat exchanger 16 and water is sprinkled into the lower degassing chamber 6 by the recycled water sprinkling mechanism 20. How many times the temperature of the recycle water is increased depends on the flow rate of the recycle water, the capacity of the condenser and the vacuum source, and the required dissolved oxygen concentration of the treated water.
Usually, the temperature is preferably 1 to 2 ° C. Further, it is preferable that the temperature of the recycled water be as constant as possible.

In the vacuum degassing tower according to the present invention, the temperature of the recycle water sprinkled in the lower degassing chamber is set higher than the water to be treated sprinkled in the upper degassing chamber, so that the oxygen in the lower degassing chamber is reduced. It can be operated such that the partial pressure is lower than the oxygen partial pressure in the upper degassing chamber. That is, the gas phase portion in the vacuum degassing tower is occupied by water vapor and oxygen gas released from water, and the portion occupied by water vapor, that is, the partial pressure of water vapor is determined by the water vapor pressure of water. Therefore, ignoring the pressure loss of the packed bed, the lower degassing chamber and the upper degassing chamber have the same pressure, so the degassing chamber with the higher temperature of the water to be sprinkled has an oxygen partial pressure corresponding to the higher steam partial pressure. It will be lower.

The water to be introduced into the vacuum degassing tower 1 is preferably so-called pure water (resistivity of 0.2 MΩ · cm or more) which has been subjected to an ion exchange treatment or a reverse osmosis membrane treatment. The water to be treated is usually introduced at a substantially constant temperature of 20 to 35 ° C. from the viewpoint of stability of operation and prevention of precipitation of impurities. The concentration of dissolved oxygen at the time of introduction is generally 6-1 of the atmospheric saturation, that is, the equilibrium concentration with air or a slightly supersaturated concentration at that temperature.
Since the concentration is often 2 μg / l, if the concentration of dissolved oxygen is adjusted to 200 to 10 μg / l by performing simple degassing in advance using a conventionally used vacuum degassing tower, deoxygenation can be performed more efficiently. You can do it.

In the vacuum degassing tower according to the present invention, as shown in FIG. 1, instead of installing the treated water heating means outside the vacuum degassing tower, it is installed in the treated water reservoir 7 or the lower degassing chamber. It is also possible to heat the water directly. In this case, the location of the treated water heating means is preferably near the treated water surface of the treated water storage 7. FIG. 2 conceptually shows one example of such a case, in which a metal snake tube is provided as a treated water heating heater 22 on the surface layer of the treated water storage unit 7 and steam is supplied therein. This is a method of heating treated water. Heating may be performed using an electric heater instead of the steam heater.

[0013]

EXAMPLE A pole ring (plastic, size 1 inch, manufactured by Iwao Porcelain Co., Ltd.) was filled in the middle of a cylinder having an inner diameter of 208 mm and a height of 11600 mm to fill a height of 36 mm.
A 25 mm packed layer was formed. A sprinkling pipe and a bleeding pipe were opened in the upper deaeration chamber above the packed bed, and an external circulation type heat exchanger was provided in the treated water reservoir as treated water heating means (see FIG. 1). A dissolved oxygen removal test was performed using this vacuum degassing tower.

Into this vacuum degassing tower, ion-exchanged water (resistivity: 1.0 MΩ · cm, water temperature: 25 ° C., dissolved oxygen concentration: 8 mg)
/ L) as the water to be treated was supplied at 2.5 m ³ / hr. The amount of bleed air was 157 m ³ / hr, and the pressure in the upper deaeration chamber was 2
4 Torr and the temperature of the treated water storage is 27 ° C
The deoxidation was performed while heating the treated water with a heat exchanger and spraying water into the lower degassing chamber. The dissolved oxygen concentration of the obtained treated water was 0.5 μg / l.

[Comparative Example 1] Deoxygenation treatment was performed under the same operating conditions as in the example except that the treatment water was not heated by the heat exchanger. The dissolved oxygen concentration of the obtained treated water was 30 μg / l.

[Comparative Example 2] Deoxygenation treatment was performed under the same operating conditions as in the example using a vacuum degassing tower in which the piping was changed so that the bleeding pipe was opened to the lower degassing chamber. The dissolved oxygen concentration of the obtained treated water was 5 μg / l.

Comparative Example 3 A deoxygenation treatment was performed under the same operating conditions as in Comparative Example 2, except that the treated water was not heated in Comparative Example 2. The dissolved oxygen concentration of the obtained treated water was 5 μg / l as in Comparative Example 2.

[0018]

According to the present invention, the temperature of the degassing tower and the temperature of the treated water are reduced by simply improving the conventional vacuum degassing tower by generating steam in the degassing tower. Not only can prevent an increase in the oxygen partial pressure of the gaseous phase at the bottom of the tower, but also by adjusting the heating temperature of the treated water to be higher than the temperature of the water to be treated introduced into the tower. Since the pressure can be made lower than that at the top of the tower, deoxygenation can be performed efficiently.

Therefore, if the vacuum degassing tower of the present invention is used,
A very low concentration of treated water having a dissolved oxygen concentration of 1 μg / l or less, for example, 0.5 μg / l, can be stably obtained.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram of an example of a vacuum degassing tower according to the present invention in which treated water heating means is installed outside the vacuum degassing tower.

FIG. 2 is a conceptual diagram of an example of a vacuum degassing tower according to the present invention in which treated water heating means is installed inside the vacuum degassing tower.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Vacuum deaeration tower 2 To-be-treated water introduction pipe 3 Sprinkling mechanism 4 Upper deaeration chamber 5 Packing layer 6 Lower deaeration chamber 7 Treated water storage part 8 Treated water extraction pipe 9 Treated water extraction pump 10 Extraction pipe 11 Vacuum source 12 Cooling Water supply pipe 13 Cooling water discharge pipe 14 Condensed water discharge pipe (atmosphere leg) 15 Condensed water storage tank 16 Heat exchanger for heating treated water 17 Steam supply pipe 18 Steam discharge pipe 19 Treated water recycling pipe 20 Recycled water sprinkling mechanism 21 Condenser 22 Heater for heating treated water

──────────────────────────────────────────────────続 き Continuing on the front page (72) Genhisa Miyaji 1-1, Kurosaki Castle Stone, Yawatanishi-ku, Kitakyushu City Inside the Kurosaki Plant of Mitsubishi Chemical Co., Ltd. (56) References JP-A-6-246259 (JP, A) 1987-174607 (JP, U) (58) Fields investigated (Int. Cl. ⁷ , DB name) B01D 19/00-19/04

Claims (5)

(57) [Claims] An upper deaeration chamber, a lower deaeration chamber, and a treated water storage section for storing treated water above and below a filling layer formed by filling a gas-liquid contact member; to the upper degassing chamber to degas the water to be treated with a vacuum degassing tower that provided the extraction pipe communicating with the water to be treated supply means and a vacuum source
At this time, the treated water stored in the treated water storage section is extracted and heated.
After that, spray water into the lower degassing chamber (however, flash evaporation
(Except when doing so). 2. A packing layer formed by filling a gas-liquid contact member.
Above, the upper degassing chamber above, the lower degassing chamber below and
It has a treated water storage section for storing treated water, and the upper degassing chamber
Is provided with a bleed pipe that communicates with the water supply means and the vacuum source.
Degassed water using a vacuum degassing tower
At this time, extract the treated water stored in the treated water storage
After heating at 2 ° C, sprinkle water into the lower degassing chamber.
Way. 3. A filling layer formed by filling a gas-liquid contact member is provided.
Above, the upper degassing chamber above, the lower degassing chamber below and
It has a treated water storage section for storing treated water, and the upper degassing chamber
Is provided with a bleed pipe that communicates with the water supply means and the vacuum source.
Degassed water using a vacuum degassing tower
At this time, the water to be treated is supplied to the upper degassing chamber at 20 to 35 ° C,
The treated water stored in the treated water storage section is extracted and heated.
A method characterized by sprinkling water in the lower degassing chamber afterwards. 4. Extracting the treated water stored in the treated water storage section
To a higher temperature than the water to be treated supplied to the upper degassing chamber.
After heating, water is sprayed into the lower degassing chamber.
Item 4. The method according to any one of Items 1 to 3. 5. The concentration of dissolved oxygen in the treated water is 1 μg / l or less.
2. The method according to claim 1, wherein degassing is performed so that
5. The method according to any of 4.