JPH0768103A - Membrane deaerating method - Google Patents

Abstract

PURPOSE:To remove a dissolved gas in a solution to be treated, to decrease pressure drop and reduce a required driving power by dipping a hallow yarn deaerating membrane unit into the solution to be treated and evacuating the inside of the hollow yarn membrane by a vacuum line connected to an opening part of the hollow yarn membrane. CONSTITUTION:The deaerating membrane unit is made by joining to fix and opening one or both side of the hollow yarn deaerating membrane 2, is housed into a vessel 8 for solution to be treated, and the inside and outside of the hollow yarn membrane are divided by a partition 9. The dissolved gas in the solution to be treated which is in contact with the deaerating hollow yarn membrane is removed by evacuating an evacuating chamber 10 connected to the inside of hollow yarn membrane by an evacuating means 3. In this case, the whole solution to be treated is deaerated by circulating the solution to be treated in the vessel 8 with a circulating pump 5.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a membrane degassing apparatus which uses a hydrophobic gas permeable membrane to remove dissolved gas in raw water by flowing raw water through one side and depressurizing the other side. More specifically, it relates to a hollow fiber type membrane degassing device.

[0002]

2. Description of the Related Art Recently, a so-called degassing process for removing gases such as oxygen, nitrogen, and carbon dioxide dissolved in water by using a hydrophobic gas separation membrane has recently been put into practical use. 57-35795, JP-A-62-273095). This method uses raw materials such as silicone, which has a gas permeation function and has a property of not allowing water to permeate. Only dissolved gas is removed through the membrane and degassed. By removing the dissolved gas in the water, it is possible to prevent, for example, corrosion of the inner surface of the liquid contacting the pipe due to dissolved oxygen in the water circulation line and deterioration of the water quality of the ultrapure water due to carbon dioxide. With this method, there are no problems such as chemical residual components found in the conventional chemical addition method, the apparatus is simpler than the vacuum degassing method, etc., and the operating cost is reduced. There is.

Degassing membranes generally used at present include flat membranes and hollow fiber membranes, and flat membranes are often used in a spiral type. The hollow fiber type is a system in which raw water is caused to flow inside the hollow fiber membrane and pressure is reduced outside to remove dissolved gas in the raw water flowing inside the hollow fiber. In the case of the hollow fiber type, the membrane area per unit volume can be made large, so the dissolved gas concentration can be sufficiently reduced in a small unit, and highly efficient degassing treatment is possible. is doing.

[0004]

However, in the conventional methods of flowing raw water inside the hollow fiber and depressurizing the outside,
While it was easy to suppress the concentration film development that occurred in the raw water flow and was capable of highly efficient degassing, if the raw water contained dust, etc., clogging at the hollow fiber inlet could occur if the raw water contained dust. May occur. Further, when an attempt is made to increase the amount of treated water, an increase in pressure loss due to the flow resistance of raw water causes a significant increase in required power, making it difficult to process a large amount of water. In addition, when the outside air temperature of the unit is low, water vapor is likely to condense on the outer surface of the hollow fiber membrane and block the membrane surface, so that the membrane area effective for deaeration is reduced and the treatment efficiency is likely to be lowered. Had.

Further, when it is intended to remove a specific gas such as oxygen or carbon dioxide, it is known to flow a carrier gas other than the degassing target to the depressurization side for the purpose of improving the degassing efficiency. As described in (Japanese Patent Laid-Open No. 3-249907), this method is a technique established by a flat film stacking type or a spiral type, and it is necessary that the carrier gas flows evenly on the depressurized side. In the case of the hollow fiber type, the arrangement of the hollow fiber membrane has a slight deviation, or the condensed steam generated when the temperature is low as described above becomes an obstacle, and the effect of flowing the carrier gas cannot be sufficiently exerted.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to bundle one or both of a large number of hollow fiber degassing membranes, fix them by adhesive bonding, and open one or both of the ends of the hollow fiber membrane bundles. The hollow fiber degassing membrane unit is immersed in the liquid to be treated, and the inside of the hollow fiber membrane is decompressed by a vacuum line connected to the opening of the hollow fiber membrane, so that the hollow fiber membrane is dissolved in the liquid that contacts the outer surface of the hollow fiber membrane. It is basically achieved by a membrane degassing method characterized by removing the gas that

That is, by contacting the outside of the hollow fiber with the liquid to be treated, it is possible to prevent an increase in pressure loss due to the flow of the liquid to be treated inside the hollow fiber membrane, and the hollow fiber membrane is required to have such a high pressure resistance. It is possible to enable large-scale processing without doing so. Further, since the depressurized side is inside the hollow fiber membrane and is surrounded by the liquid to be treated, it is kept at the same temperature as the raw water, and it is possible to prevent the condensation of water vapor on the surface of the hollow fiber membrane and sufficiently maintain the treatment efficiency.

FIG. 1 is a sectional view showing the structure of an example of a degassing membrane unit used in the membrane degassing method of the present invention. Further, FIG. 2 is an example of a membrane degassing apparatus equipped with the degassing membrane unit of FIG. The degassing membrane unit shown in FIG. 1 is one in which one end of a hollow fiber degassing membrane 2 is bonded and opened, and the other end is sealed. In FIG. The inner and outer sides of the fiber membrane are divided by a partition 9, and the decompression means 3 decompresses the decompression chamber 10 that is connected to the inner side of the hollow fiber membrane, whereby It removes dissolved gas. As the depressurizing means here, it is most common to use a vacuum pump, particularly a water-sealed vacuum pump that has no problem even in the presence of water vapor, but is not particularly limited as long as it can realize depressurization such as an ejector and an aspirator. Not done. At this time, the liquid to be treated is circulated in the container 8 by the circulation pump 5, so that the entire liquid to be treated is degassed. The degassed liquid can be taken out from the use point 6 provided in the circulation line in a required amount, and is supplied from the reservoir tank 4 to the liquid chamber 11 to be treated by the amount of the taken out liquid.

The degassing membrane unit used in the membrane degassing method of the present invention basically comprises an adhesive part and a hollow fiber membrane, and the outside of the hollow fiber membrane is in contact with the liquid to be treated, and ,
It is sufficient that the inside of the hollow fiber membrane is depressurized.
There is no problem even if one or more sealing portions 23 are bonded as shown in FIG. Further, as shown in FIG. 5, the hollow fiber degassing membrane 2 may be arranged in a U shape, and both ends thereof may be bonded and opened in the same direction. Further, as shown in FIG. 6, both ends of the hollow fiber membrane 2 may be bonded and opened. In this case, as shown in FIG. 7, the decompression chambers 10 and 11 are present at both ends of the hollow fiber membrane 2, whereby the membrane surface can be decompressed more sufficiently.
There is also a method of providing a space 13 and a connecting pipe 14 to the vacuum line at one end of the hollow fiber degassing membrane 2 as shown in FIG. In this case, although the number of hollow fiber membranes decreases, the pipe also plays a role of a reinforcing material, so that it is effective when the strength and elongation of the hollow fiber membrane is not sufficient. Further, as an effective means for protecting and reinforcing the hollow fiber membrane, as shown in FIG.
It is also possible to equip the outer peripheral portion with. Examples of the reinforcing member 21 include a perforated cylindrical structure 16 and a mesh cylindrical structure 17 as shown in FIG.

By the way, a major factor that influences the degassing efficiency of the present degassing membrane unit is the circulation of the liquid to be treated. This is because if the liquid in contact with the hollow fiber membranes stays, the entire container cannot be degassed. In the example described above, the liquid is circulated by the circulation pump 5 of the apparatus, but in order to more effectively circulate the liquid, it is important to provide a liquid circulation mechanism in the container or the degassing membrane unit. Is. 11 and 12 show an example in which the liquid circulating means is provided in the degassing membrane unit. Although not necessarily as shown in these figures, it is preferable to use a system that allows sufficient liquid circulation.

In the above example, deaeration is performed only by depressurizing the inside of the hollow fiber membrane. However, when a specific gas such as oxygen or oxygen dioxide is removed, as shown in FIG. A large degassing performance can be obtained by using a unit of a type in which both ends of 2 are opened and released and a gas other than the removal target is made to flow from one side as a carrier gas. In this case, it is more effective to reduce the pressure from the end opposite to the carrier gas supply side inside the hollow fiber membrane, but it is not always necessary to reduce the pressure. Further, as the carrier gas, air or nitrogen is preferable in view of cost and safety. FIG. 13 shows an example of an apparatus when a carrier gas is used.

The deaeration membrane units exemplified so far are examples of the case where they are used alone, but when it is necessary to deaerate a larger amount of liquid in a short time, they may be installed in parallel as shown in FIG. It is possible. Considering use in series, such as when the liquid container to be treated is limited,
If a degassing membrane unit of the type in which the vacuum line leading to the inside of the hollow fiber is arranged at the lower end of the unit as described above, a plurality of units can be connected as shown in FIG. Needless to say, the connecting portion referred to here must prevent gas such as O-ring, sealant, and attachment from passing through gas as well as liquid, and must prevent leakage into the inside of the hollow fiber.

Further, when a plurality of degassing membrane units are used in the liquid container to be treated in this way, a liquid feeding means 18 as shown in FIG. It is desirable to have.

The hollow fiber membrane used in the degassing membrane unit in the present invention is not particularly limited to the shape of the hollow fiber, and is generally called tubular type (hollow fiber diameter of several mm or more), capillary type (hollow fiber). The size of the diameter and the shape of the cross section of the hollow fiber are not limited to those of the diameter such as the diameter of about 1 mm) and the hollow fiber type (hollow fiber diameter less than 1 mm), but the hollow fiber type can take a large membrane area. Also,
The state of the pores is also not particularly limited, but in order to exert degassing performance, the membrane surface on the side where the raw water flows is sufficiently dense so that the raw water does not enter the pores. Things are good. Further, in order to have sufficient gas permeability, it is desirable that the inside of the hollow fiber membrane and the surface of the pressure reducing side are sparse. This reduces the gas permeation resistance,
Further, since the pore area on the depressurization side becomes large, it becomes easy to sufficiently depressurize the film surface. By the way, the membrane material should be hydrophobic and can be formed into the shape of a hollow fiber,
Polyethylene, polypropylene, polytetrafluoroethylene, polyvinylidene fluoride, poly (4-methylpentene) and the like are preferable, but a polymer made of polyvinylidene fluoride or 4-methylpentene is particularly preferable. Further, in order to improve the hydrophobicity of the membrane, it is possible to form a hydrophobic membrane such as a cross-linking silicone-based or fluororesin-based one or both of the inner and outer surfaces of the hollow fiber to form a composite membrane. In particular, the crosslinkable silicone-based composite film is a film characterized by forming a crosslinkable silicone-based thin film on the surface of the base material film, and the surface state is so dense that it is generally called a non-porous film. There are many things we are doing. Therefore, in addition to the hydrophobic property of silicone itself,
It has an excellent property that it can suppress the adsorption of dirt components.

Of course, in the above-mentioned hydrophobic thin film, it is preferable that the surface which comes into contact with the liquid to be treated has a dense structure as described above, and therefore it is formed on the inner side when formed on the outer surface of the hollow fiber membrane. It goes without saying that the degassing efficiency is higher than that of the case.

[0016]

The present invention will be described more specifically with reference to the following examples. However, the present invention is not limited to this.

Example 1 A degassing membrane unit of the type shown in FIG. 1, which is an example of the present invention, was produced. This unit consists of 24,000 hollow fiber membranes with an inner diameter of 180 μm and an outer diameter of 225 μm, made by wet-spinning polyvinylidene fluoride (HYLAR460 manufactured by Ausimont, USA).
One side of 450 mm, effective length of 430 mm) is heat-sealed and sealed, and the other end is adhesively opened. This degassing membrane unit was loaded into a membrane degassing apparatus as shown in FIG. At this time, the volume of the liquid container to be treated is 10 liters, and the vacuum line is set to 50 Torr.
The circulation flow rate by the circulation pump was set to 2 liters / minute. The liquid to be treated has a water temperature of 25 ° C and a dissolved oxygen concentration of 8.0 ppm.
Pure water of was used. When the degassing test was performed under the above conditions, it took 12 minutes to reduce the dissolved oxygen concentration to 1.0 ppm, and the required power of the pump at this time was 260 W
Min = 187 kJ).

Comparative Example 1 Using the same number of hollow fiber membranes and the same length as in Example 1,
The liquid to be treated is flown into the hollow fiber membrane as shown in FIG.
A conventional degassing membrane unit, which is a system of depressurizing the outside, was manufactured, and a degassing test was conducted with an apparatus as shown in FIG. The volume of the liquid container to be treated, the vacuum line, and the water quality of the liquid to be treated were the same as in Example 1, and the circulation rate to the degassing membrane unit was 2 liters / minute. At this time, it takes 5 minutes to reduce the dissolved oxygen concentration to 1.0 ppm, and the required power of the pump is 980 W (power amount 980 W × 5
Min = 294 kJ).

[0019]

The membrane degassing method of the present invention enables large-scale degassing with low power.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of an example of a degassing membrane unit according to the present invention.

FIG. 2 is a circuit diagram of an example of a membrane degassing apparatus according to the present invention.

FIG. 3 is a cross-sectional view of an example of a degassing membrane unit in which a sealing portion is assembled according to the present invention.

FIG. 4 is a sectional view of an example of a degassing membrane unit having a plurality of sealing portions according to the present invention.

FIG. 5 is a cross-sectional view of an example of a degassing membrane unit in which the end portions of the hollow fiber membrane according to the present invention are collected on one side.

FIG. 6 is a cross-sectional view of an example of a degassing membrane unit in which both ends of a hollow fiber membrane are opened according to the present invention.

FIG. 7 is a circuit diagram of an example of a membrane degassing apparatus in which vacuum lines are connected to both ends of a degassing membrane unit according to the present invention.

FIG. 8 is a sectional view of an example of a degassing membrane unit having a central pipe according to the present invention.

FIG. 9 is a cross-sectional view of an example of a degassing membrane unit including a porous reinforcing material according to the present invention.

FIG. 10 is an example of a porous reinforcing material for a degassing membrane unit according to the present invention.

FIG. 11 is an example of a cross-sectional view of a degassing membrane unit including a liquid feeding means according to the present invention.

FIG. 12 is an example in which the perforated pipe of the cross-sectional view of the degassing membrane unit provided with the liquid feeding means according to the present invention is provided on one side.

FIG. 13 is a circuit diagram of an example of a membrane degassing apparatus having a carrier gas supply port according to the present invention.

FIG. 14 is a circuit diagram of an example of a membrane degassing apparatus in which a plurality of degassing membrane units are arranged in parallel according to the present invention.

FIG. 15 is a cross-sectional view of an example having a central pipe of a degassing membrane unit for series connection according to the present invention.

FIG. 16 is a cross-sectional view of an example of the degassing membrane unit for series connection without a central pipe according to the present invention.

FIG. 17 is a sectional view of an example of a state in which degassing membrane units according to the present invention are connected in series.

FIG. 18 is a circuit diagram of an example of a membrane degassing apparatus provided with a liquid circulating means, in which a plurality of degassing membrane units are arranged according to the present invention.

FIG. 19 is a cross-sectional view of an example of a conventional degassing membrane unit.

FIG. 20 is a circuit diagram of an example of a conventional membrane degassing apparatus.

[Explanation of symbols]

 1: Adhesive part 2: Hollow fiber degassing membrane 3: Decompression means 4: Reservoir tank 5: Circulation pump 6: Use point 7: Degassing membrane unit 8: Liquid container for treatment 9: Partition 10: Decompression chamber 11: Treatment Liquid chamber 12: Valve 13: Space 14: Central pipe 15: Carrier gas supply port 16: Reinforcement member with perforated cylindrical structure 17: Reinforcement member with meshed cylindrical structure 18: Liquid feeding means 19: Perforated pipe 20: End plate 21: Reinforcing material 22: Flow of liquid to be treated 23: Sealing part 24: Vacuum line 25: Supply port of liquid to be treated

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI technical display area C02F 1/20 A

Claims (11)

[Claims] 1. A hollow fiber degassing membrane unit in which one or both of a large number of hollow fiber degassing membranes are bundled and adhered and fixed, and one or both of the ends of the bundles of hollow fiber membranes are opened. It is characterized in that the gas dissolved in the liquid contacting the outer surface of the hollow fiber membrane is removed by immersing in the liquid and depressurizing the inside of the hollow fiber membrane with a vacuum line connected to the opening of the hollow fiber membrane. Membrane degassing method. 2. A hollow fiber degassing membrane unit in which one or both of a large number of hollow fiber degassing membranes are bundled, adhered and fixed, and one or both ends of the bundles of hollow fiber membranes are opened. It is installed in the liquid chamber so as to be immersed in the liquid to be treated, and a vacuum line for removing gas dissolved in the liquid contacting the outer surface of the hollow fiber membrane is connected to the inside of the hollow fiber membrane. A membrane degassing apparatus used in the membrane degassing method according to claim 1. 3. The method for degassing a membrane according to claim 1, wherein a hollow fiber degassing membrane unit having a structure in which the outer surface of the hollow fiber membrane is dense and the inner surface is sparse is used. 4. The method for degassing a membrane according to claim 1, wherein the hollow fiber membrane material is a hollow fiber degassing membrane unit which is a polymer made of polyvinylidene fluoride or 4-methylpentene. 5. A hollow fiber degassing membrane unit having a pipe fixed together with a bundle of hollow fiber degassing membranes, wherein one end or both ends of the pipe communicate with the inside of the hollow fiber degassing membrane, 2. The structure in which the inside of the hollow fiber membrane is communicated through the pipe by connecting the units to each other and can be connected to a vacuum line.
A degassing membrane unit used in the described membrane degassing method. 6. The method for operating a degassing membrane unit according to claim 5, wherein connecting pipes are connected in series or in parallel and a plurality of degassing membrane units are operated while sharing a vacuum line. 7. A degassing membrane unit for use in the membrane degassing method according to claim 1, further comprising a liquid circulating means to the hollow fiber degassing membrane. 8. The membrane degassing apparatus according to claim 2, further comprising means for circulating the liquid to be treated to the degassing membrane unit inside the liquid to be treated container outside the membrane degassing unit. 9. The membrane degassing apparatus according to claim 2, further comprising a gas supply means to the inside of the hollow fiber membrane. 10. The method for operating a degassing membrane apparatus according to claim 9, wherein a carrier gas other than a removal target is flown inside the hollow fiber membrane. 11. The method for operating a degassing membrane apparatus according to claim 10, wherein the carrier gas is nitrogen or air.