JP3225571B2 - Vacuum degassing of dissolved oxygen in water - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for vacuum degassing of dissolved oxygen in water. In particular, the present invention relates to a method for removing dissolved oxygen, which is suitable for use as a part of a process for producing ultrapure water required in the semiconductor industry and the like.

[0002]

2. Description of the Related Art Removal of dissolved oxygen in water has long been performed by treating boiler water. Removal of dissolved oxygen is often performed by a so-called vacuum degassing method in which the water to be treated is exposed to a reduced pressure. However, in the recent semiconductor industry, ultrapure water having a remarkably low dissolved oxygen concentration has been required, and it is becoming difficult to satisfy this requirement by the conventional simple vacuum degassing method.

[0003]

One of the problems of the conventional vacuum degassing method is that when the degree of decompression in the apparatus is increased to reduce the oxygen concentration in the deoxygenated water, the amount of bleeding increases, and the vacuum source That is, the capacity must be significantly increased. In particular, when the concentration of dissolved oxygen is reduced to a low concentration of 50 ppb or less, which is required in the production process of ultrapure water required in the state-of-the-art semiconductor industry, the amount of bleeding increases remarkably, and the vacuum source is increased. Will be unable to respond to this in effect. Therefore, the present invention proposes a vacuum degassing method capable of reducing the dissolved oxygen concentration to an extremely low concentration of 50 ppb or less, particularly 10 ppb or less without increasing the capacity of the vacuum source.

[0004]

According to the present invention, when removing dissolved oxygen from water to be treated by vacuum degassing, the internal
Has a container with a packed bed, and the water to be treated
Dissolved gas is released while flowing down the bed.
Generated gas is open below the packed bed
Reach vacuum source via bleed tube with condenser inside
Gas generated using a vacuum deaerator
Most of the water vapor contained is condensed and removed, and the remaining gas is discharged out of the system via a vacuum source to reduce the dissolved oxygen concentration in the deoxygenated water to a low concentration of 50 ppb or less with a small vacuum source. Can be done.

The present invention will be described in further detail. In the present invention, the dissolved oxygen in the water to be treated is removed using a vacuum deaerator having a packed layer inside. The water to be treated is introduced into the apparatus via a water supply means such as a sprinkler provided above the packed bed. The water to be treated flows down along the surface of the packing while releasing the dissolved gas, and reaches the deoxygenated water storage section below the packed bed. The water to be introduced into the apparatus is so-called pure water that has been subjected to ion exchange treatment, reverse osmosis membrane treatment, etc.
2 MΩcm or more). The water to be treated is usually 20 to 35 from the viewpoint of operational stability and elution of impurities.
It is introduced at a nearly constant temperature of ° C. The concentration of dissolved oxygen at the time of introduction is generally atmospheric saturation, that is, an equilibrium concentration with air at that temperature or a slightly supersaturated concentration in many cases. However, if desired, a simple deaeration is performed in advance. Is also good.

The released dissolved gas is discharged out of the system through a bleed tube opened in the space below the packed bed, as previously proposed by the present applicant (see Japanese Patent Application No. 3-99123). Sa
It is. It is further preferable that the packed layer is at least vertically divided in the space, and a vacuum degassing device of a type in which air is also extracted from this space.

[0007] The oxygen concentration in the resulting deoxygenated water is regulated by the oxygen partial pressure of the gas phase and does not fall below the equilibrium concentration with the gas phase. Therefore, it is necessary to set the bleed amount and thus the degree of pressure reduction so that the oxygen partial pressure in the gas phase above the deoxygenated water storage part is equal to or lower than the equilibrium partial pressure with the oxygen concentration required for the deoxygenated water. In the method of the present invention, it is not necessary to increase the capacity of the vacuum source even if the bleeding amount is increased.
orr, or less, or 30 Torr or less.

A vacuum pump is usually used as a vacuum source. In the present invention, a condenser is provided in the middle of the extraction tube connecting the vacuum deaerator and the vacuum source, and condenses at least 70% of the water vapor in the gas to be extracted. Since the capacity of the vacuum source can be reduced as the condensing rate increases, it is preferable that the condensing rate be 80% or more, particularly 90% or more, using cooling water of 10 ° C. or less. The above-mentioned filling layer is divided into at least two in the vertical direction in the space portion, and air is extracted from a plurality of locations along the height direction of the filling layer, for example, from the space portion dividing the filling layer vertically and from below the filling layer. when the vacuum degassing apparatus mode that includes a first extraction pipe to bleed from the space portion
A condenser is provided in each of the bleeding tubes with the second bleeding tube that bleeds from below the packed bed, and the gas flowing in each of the condensers
Condensed more than 50% of the water vapor in the water and 70% in total
Preferably. When gas is extracted from a plurality of locations in the vertical direction, even if the gas extracted from the upper extraction tube contains a considerable amount of oxygen or other non-condensable gas, the gas extracted from the lower extraction tube These non-condensable gases are hardly contained. Therefore, in order to increase the condensation rate of water vapor in the gas extracted from the upper extraction pipe, it is necessary to use cooling water having a remarkably low water temperature. Easily over 95% without low cooling water, 98% if desired
The above can be condensed. Therefore, when air is extracted from a plurality of locations in this manner, the condensation rate of water vapor in the gas in the upper extraction pipe is set to 50% or more and that of the gas in the lower extraction pipe is set to 90% or more according to the ease of condensation. % Is preferable.

As the condenser, it is preferable to use an indirect heat exchanger such as a double tube heat exchanger or a multi-tube heat exchanger. Water is used as the refrigerant. Usually, water cooled to 15 ° C. or lower, particularly 10 ° C. or lower by a refrigerator is used. Specifically, the water is selected according to a target condensation rate in a condenser. An example of the removal of dissolved oxygen in water according to the present invention is as follows.
Using a vacuum deaerator (see FIG. 1) provided with a packed bed of 0 mm and a bed height of 5000 mm and an extraction tube opened below the packed bed, water to be treated (25 ° C., atmospheric saturation) was supplied at 50 m ³ / Hr.
In the case of deoxidizing to a dissolved oxygen concentration of 5 ppb in
By providing a condenser as shown in (1), the capacity of the vacuum source is about 1/30 of that without the condenser.

[0010] Further, the filling layer is divided into an upper part (layer height of 2700 mm) and a lower part (layer height of 3600 mm) having a diameter of 1000 mm, and the bleeding tubes are opened at two places, that is, the intermediate part and the lower part of the filling layer. Using a vacuum deaerator (see FIG. 2), the water to be treated (25 ° C.
In the case of deoxygenation at m ³ / Hr to a dissolved oxygen concentration of 5 ppb, by providing a condenser as shown in Table 2, it is possible to use a vacuum source having a capacity of about 1/3 as compared with a case without a condenser. . In addition, as is clear when comparing Table 1 and Table 2,
When air is extracted from two locations in the height direction of the packed bed, there is an advantage that the capacity of the vacuum source can be small and the amount of cooling water can be small.

[0011]

[Table 1] * 1 Pressure at the opening of the bleed tube * 2 Calculated assuming that the cooling water enters at 10 ° C and is discharged at 15 ° C * 3 Ignored because the pressure loss in the bleed tube and condenser is small

[0012]

[Table 2] * 1 Pressure at the opening of the bleed tube * 2 Calculated assuming that the cooling water enters at 10 ° C and is discharged at 15 ° C * 3 Ignored because the pressure loss in the bleed tube and condenser is small

[0013]

According to the present invention, water vapor occupying most of the gas extracted from the apparatus is condensed and removed in advance, and only the remaining gas is discharged out of the system via the vacuum source. Can be degassed at a high degree of vacuum without increasing the capacity. Therefore, according to the present invention, it is easy to obtain deoxygenated water having a dissolved oxygen concentration of 50 ppb or less and a dissolved oxygen concentration of 10 ppb or less.
It is not so difficult to obtain deoxygenated water having an extremely low concentration of ppb or less, for example, about 5 ppb.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram of an example of an apparatus for implementing the present invention.

FIG. 2 is a conceptual diagram of another example of an apparatus for implementing the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Treatment-water supply means 2 Vacuum deaerator 3 Packing layer 4 Extraction pipe 5 Condenser 6 Cooling water supply pipe 7 Cooling water discharge pipe 8 Condensed water discharge pipe (atmosphere leg) 9 Condensed water storage tank 10 Vacuum pump 11 Deoxygenated water Storage unit 12 Deoxygenated water extraction pipe

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-61-200818 (JP, A) JP-A-58-20209 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B01D 19/00 101 C02F 1/20 C02F 1/58

Claims (5)

(57) [Claims] 1. A container having a packed layer inside,
Means for supplying treated water provided above the packed bed and
Deoxygenated water storage section provided below the
Has a bleed tube to communicate the inside of the container and the vacuum source,
In addition, the bleed tube opens below the packed bed so that the opening and vacuum
To the vacuum deaerator equipped with a condenser in the middle of the source, the treated water is supplied from the treated water supply means to release the dissolved gas, and the packed bed is allowed to flow down. in by discharged out of the system through the vacuum source After condensing more than 70% of the water vapor contained therein, in water and recovering the dissolved oxygen concentration 50ppb following deoxygenated water from the savings distillation unit Vacuum degassing of dissolved oxygen. 2. A container having a packed layer inside, and a container inside the container.
Means for supplying treated water provided above the packed bed and
Deoxygenated water storage section provided below the
Bleed tube group that communicates between the inside of the container and the vacuum source
And the bleed tube group is open in the middle of the packed bed
First bleed with a condenser midway between the section and the vacuum source
Tube and an opening below the packed bed, between the opening and the vacuum source.
At least with a second bleed tube with a condenser on the way
Is also processed by a vacuum deaerator consisting of two extraction tubes.
Water to be treated is supplied from the water supply means and the packed bed flows down while releasing dissolved gas, and the generated gas passes through the bleed tube group.
By discharged from the system through the vacuum source After condensed in the condenser 70% or more of water vapor contained therein, and recovering the dissolved oxygen concentration 50ppb following deoxygenated water from the savings distillation unit Vacuum degassing of dissolved oxygen in water. 3. The condenser of the first bleed pipe and the second bleed pipe,
5 of the water vapor contained in the gas flowing into each condenser
3. The method according to claim 2, wherein 0% or more is condensed.
Vacuum degassing of dissolved oxygen in water. 4. The gas in the condenser of the second bleed pipe is
4. The method according to claim 3, wherein 95% or more of the contained water vapor is condensed. 5. A dissolved oxygen concentration of 10 ppb or less from the storage section.
The deoxygenated water of claim 1 is recovered.
4. Vacuum degassing of dissolved oxygen in water according to any of 4. Law.