JPH03278805A - Removal of dissolved gas from liquid - Google Patents

Abstract

PURPOSE:To provide the change of a liq. coming in contact with a deaerating membrane as many as possible by merely allowing the passage of the liq. through a spiral deaerating membrane module by using said membrane module having the inside of a bag-like deaerating module and the inside of a center shaft communicating with each other. CONSTITUTION:A spiral deaerating membrane module 9 wherein a bag-like deaerating membrane 5 provided with spacers 6 therein and turbulence accelerating materials 7 laid one upon the other are wound around a central shaft 3 and the inside of the bag-like deaerating membrane 5 and the inside of the center shaft 3 communicate with each other is used for the removal of dissolved gas by passing the liq. containing such gas through the turbulence accelerating materials 7 existing between the center shaft 3 and the outer surface of the bag-like deaerating membrane 5. Moreover, the inner pressure of the center shaft 3 is reduced from the one end 1 thereof or the other end thereof to remove the dissolved gas from the liq.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention relates to a method for removing dissolved gas in a liquid using a degassing membrane. remove oxygen and or dissolved carbon dioxide,
It can also be used for purposes such as removing ammonia gas from wastewater. <Conventional technology> Conventional methods for removing dissolved gases in liquids include two methods: heating deaeration and vacuum deaeration. There are two ways.

The former involves applying heat to a liquid containing dissolved gas, and in some cases boiling it to remove dissolved gas from the liquid, but the equipment is complex and requires thermal energy, making the equipment expensive to install. Additionally, running costs are relatively high.

On the other hand, the vacuum degassing method is a method in which dissolved gas is removed from the liquid by applying a vacuum to the liquid to place the liquid under reduced pressure, and the energy cost is lower than the former method. However, when a vacuum is applied directly to a liquid, a structure of 10 m or more is usually required to prevent the liquid from being sucked into the vacuum side. Although the installation of such a structure is subject to restrictions on the installation location of the device, in recent years a technique has been proposed in which the liquid is degassed via a degassing membrane between the liquid and the vacuum side.

This method applies a vacuum to one side separated by a degassing membrane to reduce the pressure, brings the liquid into contact with the other side, and moves the dissolved gas in the liquid to one side through the degassing membrane. Therefore, the liquid itself is not sucked into the vacuum side, and the device can be made more compact compared to a device in which a vacuum is applied directly to the liquid.

The following methods have been conventionally proposed using the degassing membrane.

That is, this method uses a bundle of hollow fiber degassing membranes with a relatively small diameter, and the liquid is allowed to flow inside each of the degassing membranes, and the pressure is reduced on the outside. This method attempts to improve the efficiency of the degassing membrane by surrounding the liquid with a hollow fiber degassing membrane with a relatively small diameter and reducing the pressure on the outside of the membrane to improve the contact between the liquid and the degassing membrane. The disadvantage is that the pressure loss of the liquid within the degassing membrane is large, and therefore a pump with a large lift is required.

Note that if the inside of the degassing membrane is depressurized and the liquid is allowed to flow outside of it, a pump with such a large lift is not required, but in this case, the contact between the liquid and the degassing membrane is not good, resulting in poor degassing efficiency. .

<Problem to be solved by the invention> When removing gas dissolved in a liquid using a degassing membrane, in order to increase its efficiency, it is necessary to increase the chances of contact between the liquid and the degassing membrane as much as possible. At the same time, it is an important issue to improve the movement of dissolved gas in the liquid by bringing the liquid into contact with the degassing membrane in an agitated state, and it is said that no extra energy is required to achieve the above objective. This is also an important issue.

The present invention uses a degassing membrane to remove dissolved gas in a liquid.
In order to increase the chances of contact between the liquid and the degassing membrane simply by passing the liquid through the membrane without requiring extra energy, and in which the liquid comes into contact with the degassing membrane in an agitated state, degassing is possible. The purpose of this invention is to provide a method for more effectively removing dissolved gas from a liquid by using a gas that does not substantially contain the dissolved gas to be removed from the liquid. The object of the present invention is to provide a structure of a degassing membrane module used in the method.

<Means for Solving the Problems> The method for removing dissolved gas in a liquid according to claim 1 of the present invention, which has been made to achieve the above object, includes reducing the pressure on one side partitioned by a degassing membrane. In a method of removing dissolved gas in a liquid by bringing the liquid into contact with the other side, a bag-shaped degassing membrane having a spacer inside and a turbulence promoting material are overlapped and wrapped around a center shaft, and the bag is Using a spiral degassing membrane module in which the inside of the bag-shaped degassing membrane is in communication with the inside of the center shaft, the turbulence promoting material is applied to the part of the turbulence promoting material that exists between the outer surfaces of the bag-shaped degassing membrane along the center shaft. The degassing membrane according to claim 2 of the present invention is specially designed to allow a liquid containing dissolved gas to be removed to pass therethrough and to reduce the pressure inside the center shaft from one side and/or the other side. The module has a spiral shape in which a bag-shaped degassing membrane with a spacer inside and a turbulence promoting material are overlapped and wound around a center shaft, and the inside of the bag-shaped degassing membrane and the center shaft are in communication. The deaeration membrane module has two communication parts on the left and right sides between the inside of the bag-shaped deaeration membrane and the inside of the center shaft, a non-circulation part between the two communication parts, and a bag-shaped part in the non-communication part. The method for removing dissolved gas according to claim 3 of the present invention is characterized in that the interior of the degassing membrane is incompletely partitioned to form a detour in the bag-like degassing membrane. The liquid containing the dissolved gas to be removed is passed along the center shaft of the spiral degassing membrane module according to claim 2 through the turbulence promoting material present between the outer surfaces of the bag-shaped degassing membrane. At the same time, while continuously or intermittently supplying gas substantially free of the dissolved gas to be removed from one side of the center shaft to the inside thereof, the inside of the center shaft is depressurized from the other side of the center shaft. This is a characteristic feature.

Effect〉 The present invention will be explained in detail below.

An example of the spiral degassing membrane module used in the method for removing dissolved gas according to claim 1 of the present invention has the following structure.

That is, three sides as shown in FIG. 2 are joined to a center shaft 3 having a hollow part 1 as shown in FIG. A bag-shaped deaeration membrane 5 having an opening 4 is joined to the center shaft 3 at one end by aligning the slit 2 with the opening 4 as shown in FIG. By arranging a spacer 6 inside the bag-shaped deaeration membrane 5 as shown in FIG. As shown by the arrow, a turbulence promoting material 7 such as a net is placed on the outside of the membrane surface (on the side B in FIG. 3) in the direction in which the bag-shaped degassing membrane is wound around the center shaft 3.

The bag-shaped deaeration membrane 5 and the turbulence promoting material 7 shown in FIG.
If they are wound around the center shaft 3 in the direction of the arrow in FIG. 3, the turbulence promoting material 7 and the bag-shaped deaeration membrane 5 will be wound alternately around the center shaft 3 as shown in FIG. A spiral degassing membrane element 8 is formed in which the interior of the bag-shaped degassing membrane 5 and the interior of the center shaft 3 are in communication.

In the embodiment shown in FIGS. 1 to 3, one slit is provided in the center shaft 3, and the two bag-shaped deaeration membranes 5 are joined.
It is also possible to provide a plurality of slits 2, join a plurality of bag-shaped deaeration membranes 5 corresponding to the plurality of slits 2, and similarly wind them in a spiral shape.

FIG. 5 shows a spiral degassing membrane module 9, in which a center shaft 3 on which a spiral degassing membrane element 8 is formed is communicated with a connector 10, and an end cap 11 is attached to one end of the center shaft 3. one end of the center shaft 3 is closed, and the end connector 12 is attached to the other end of the center shaft 3.

The plurality of elements 8 are arranged in a housing 15 formed by a side body part 13 and two left and right end plates 14, one end plate 14 is provided with a liquid inlet 16, and the other end plate 14 is provided with a liquid inlet 16. Outlet 17
and a decompression port 18 are provided, and the center shaft 3 and the decompression port 18 are communicated via the end connector 12 described above. Note that 19 is an exterior body, 20 is a telescope stopper for preventing the spiral degassing membrane element 8 from protruding, and 21 is a telescope stopper for preventing liquid from flowing through the gap between the exterior body and the side body 13. This is a sealing material to prevent this.

Next, a degassing method of the present invention using the spiral degassing membrane module 9 shown in FIG. 5 will be explained.

A vacuum pump (not shown) is connected to the decompression port 18 via piping to reduce the pressure inside the center shaft 3, and at the same time, a liquid containing dissolved gas flows in from the liquid inlet 16. The liquid passes through the turbulence promoting material 7 that exists in the gap between the outer surfaces of the bag-shaped degassing membranes 5 shown in FIG. Dissolved gas in the liquid moves into the bag-shaped degassing membrane 5 one after another, and the dissolved gas is discharged from the decompression port 18 via the center shaft 3. Further, the liquid from which dissolved gas has been removed by passing through each spiral degassing membrane element 8 is taken out from the liquid outlet 17 to the outside. Note that since there is a spacer 6 inside the bag-shaped degassing membrane 5, even if the pressure inside the bag-shaped degassing membrane is reduced, the membrane surfaces do not come into close contact with each other. will always be ensured. Although FIG. 5 shows an example in which only one side of the center shaft 3 is depressurized, both ends of the center shaft may be connected to a vacuum pump to depressurize both ends of the center shaft.

As described above, according to the deaeration method of the present invention, compared to the conventional method using a hollow fiber deaeration membrane, the contact area between the membrane surface and the liquid is wider, and therefore the opportunity for contact between the liquid and the deaeration membrane is increased. In addition, the turbulence promoting material 7 allows the liquid to contact the membrane surface in a constantly agitated state, which improves the movement of dissolved gas in the liquid. Dissolved gas can be effectively removed. Further, since the liquid is stirred by the turbulence promoting material 7 simply by passing the liquid through it, there is a great advantage that no extra energy is required to stir the liquid.

As described above, the method for removing dissolved gas using the spiral degassing membrane of the present invention has various advantages compared to the conventional method using a hollow fiber degassing membrane, but as described below, the method for removing dissolved gas in the liquid By using a gas that does not substantially contain the dissolved gas to be removed, the dissolved gas in the liquid can be removed more effectively.

FIG. 6 is a developed view showing a main part of an embodiment of an element constituting a spiral degassing membrane module according to claim 2 of the present invention.

That is, it has slits 2 in two places, and has left and right hollow parts 1 that communicate with the two slits 2, and is joined on three sides to a center shaft 3 with which the two left and right hollow parts 1 do not communicate. A bag-shaped deaeration membrane 5 having an opening 4 on one side is joined.

As shown in FIG. 6, inside the bag-shaped deaeration membrane 5,
The upper and lower surfaces of the bag-shaped deaeration membrane 5 (
The upper and lower surfaces of the bag-shaped deaeration membrane 5 are joined between the two joint parts 22 that join the surfaces A and B in FIG. 3, and the two liquid joining parts 22, leaving only the lower part. It has one joint 23. With such a structure, a detour can be formed within the bag-shaped degassing membrane as shown by the dashed line in FIG. The bag-shaped degassing membrane 5 is wound around the center shaft 3 and the spiral degassing membrane element 8 is constructed in the same manner as shown in FIG. Spacer 6 inside the membrane
(not shown) and a turbulence promoting material 7 (not shown)
It is the same as that shown in FIG. In the embodiment shown in FIG. 6, two joint parts 22 are provided in the non-communicating part between the two left and right hollow parts 1, and one joint part 23 is provided between them to detour into the bag-shaped degassing membrane. Although the number of joints is not limited to this, any number of joints may be used as long as the inside of the bag-shaped degassing membrane is incompletely partitioned to form a detour. Further, as described above, a plurality of pairs of slits 2 are provided in one center shaft, and a plurality of bag-shaped deaeration membranes 5 corresponding to the plurality of pairs of slits 2 are joined and similarly wound in a spiral shape. There is no problem.

By arranging a plurality of spiral degassing membrane elements 8 in the housing 15 by communicating the center shafts 3 of each of the spiral degassing membrane elements 8, a spiral degassing membrane module 9 can be formed as shown in FIG.
Configure. Note that the center shaft 3 at one end of the degassing membrane module 9 has a supply port 24 for supplying gas substantially free of dissolved gas to be removed from the liquid via the end connector 12; The structure of the bag-shaped degassing membrane 5 is the same as that of the spiral degassing membrane module 9 shown in FIG. 5, except that the structure is as shown in FIG. 6, so the explanation of the other parts will be omitted. .

Next, a degassing method of the present invention using the spiral degassing membrane module 9 shown in FIG. 7 will be explained.

A vacuum pump (not shown) is connected to the decompression port 18 via piping to reduce the pressure inside the center shaft 3, and at the same time continuously or intermittently inflows the gas described below from the supply port 24, and a liquid inlet. A liquid containing dissolved gas flows in from 16. Note that the gas flowing in from the supply port 24 is a gas that does not substantially contain the dissolved gas to be removed from the liquid. For example, when removing dissolved oxygen and/or dissolved carbon dioxide from the liquid, nitrogen gas or the like may be used. used. For example, when only dissolved carbon dioxide is to be removed from a liquid, reformed air from which carbon dioxide in the air has been removed using an adsorbent, a gas separation membrane, etc. can be used.

When gas flows in from the supply port 24 in this way, the gas flows into the center shaft 3 on the side of the supply port 24, and then into the bag-shaped degassing membrane 5 as shown by the dashed line in FIG. It detours between the joints 22 and 23, flows into the center shaft 3 again, flows into the next bag-shaped deaeration membrane 5 in the same way, flows into the bag-shaped deaeration membrane 5 one after another, and then flows into the bag-shaped deaeration membrane 5 one after another. It is discharged from the pressure reducing port 18 shown in FIG.

On the other hand, the liquid flowing in from the liquid inlet 16 passes through the turbulence promoting material 7 that exists in the gap between the outer surfaces of the bag-shaped degassing membrane 5.
While the liquid is sufficiently stirred, dissolved gases in the liquid move into the bag-like degassing membrane 5 one after another through the adjacent bag-shaped degassing membranes 5, and are then transferred from the above-mentioned supply port 24 through the center shaft 3. It merges with the inflowing gas and is discharged from the pressure reduction port 18.

Further, the liquid from which dissolved gas has been removed by passing through each spiral degassing membrane element 8 is taken out from the liquid inlet 17 to the outside.

In the invention described in claim 3, in addition to simply reducing the pressure inside the bag-shaped degassing membrane, as shown in FIG. The area between the two communicating parts is a non-circulating part, and the inside of the bag-like deaeration membrane in the non-communicating part is incompletely partitioned to form a detour in the bag-like deaeration membrane. Using a degassing membrane module, a gas that does not substantially contain the dissolved gas to be removed in the liquid is introduced from one side of the center shaft, and the other side of the center shaft is depressurized to cause the gas to flow through the detour. However, by supplying gas from the outside into the bag-shaped degassing membrane, the removal efficiency of dissolved gas is much greater than simply reducing the pressure inside the bag-shaped degassing membrane. to rise.

One of the reasons for this is presumed to be that the partial pressure of the dissolved gas to be removed on the decompression side decreases, and the gas that does not substantially contain the dissolved gas to be removed is depressurized within the bag-shaped degassing membrane. This is also because the volume expands, and as a result, the flow velocity on the degassing membrane surface increases, and the concentration polarized layer generated on the membrane surface becomes substantially thinner, reducing the influence of the concentration polarized layer. This is considered to be a factor.

In any case, as shown in the examples, the former is more reliable than the latter when the pressure is reduced from the other center shaft while gas is flowing in from one side of the center shaft, and when the pressure inside the center shaft is simply reduced without gas flowing in. The concentration of dissolved gas in the processing liquid is small.

Effect> As explained above, the degassing method using the spiral degassing membrane module of the present invention has a higher degassing effect than the conventional hollow fiber degassing membrane because the module used is suitable for degassing. High energy efficiency.

In other words, since a spacer is provided inside the bag-shaped degassing membrane,
Even if the inside of the bag-shaped degassing membrane is reduced in pressure, the two degassing membranes forming the bag do not come into close contact with each other, thus ensuring a wide degassing surface. In addition, when winding the bag-shaped deaeration membrane in a spiral shape around the center shaft, the turbulence promoting material is overlapped and wound, and the liquid containing the dissolved gas to be removed is passed through the turbulence promoting material. is constantly in contact with the membrane surface in an agitated state, which improves the movement of the dissolved gas to be removed in the liquid, increasing the effect of removing the dissolved gas.

In addition, a spiral degassing membrane module is provided in which a non-communicating part is provided in the center of the center shaft of one spiral degassing membrane element, and a bag-shaped degassing membrane with a detour provided around the center shaft is wound in a spiral shape. In the method of reducing the pressure of the other center shaft while supplying a gas that does not contain the dissolved gas to be removed from the liquid from one side of the center shaft, the spacer provided inside the bag has an effect of preventing the film surface from adhering to the other, and In addition to the agitation effect of the liquid by the turbulence promoting material, the gas flows throughout the bag-shaped degassing membrane due to the detour path inside the bag-shaped degassing membrane, which reduces the partial pressure of the dissolved gas to be removed in the bag-shaped degassing membrane. Dissolved gas can be effectively removed from the liquid by thinning the concentration polarized layer generated on the membrane surface.

Examples will be described below to make the effects of the present invention more clear.

Example 1 Using pure water with a dissolved oxygen concentration of 8 mg/2, oxygen was removed using a conventional hollow fiber degassing membrane and the spiral degassing membrane module of the present invention shown in Figures 1 to 5. The removal ability of the two was compared.

Conventional method: Inner diameter 200μm1 Outer diameter 250μm1
By bundling multiple hollow fiber degassing membranes with a length of 260 mm,
Total degassing membrane area 20rr? Then, the bundle of degassing membranes was filled into a container, and the pure water was poured into each degassing membrane at a rate of 5502/h.
While flowing at a flow rate of r, the pressure inside the container was reduced to 80 torr using a vacuum pump. As a result, the dissolved oxygen concentration of the treated water was 1/2.

- As an invented method for strength wood, a spacer is provided inside the bag-shaped deaeration membrane, and three spiral deaeration membrane elements made by overlapping turbulence promoting materials and wrapped around the center shaft are connected in series, and the entire deaeration membrane is Using a spiral degassing membrane module with an area of 20 m as shown in Fig. 5, 1.0% of the pure water was applied to the turbulence promoting material along the center shaft.
Flow at a flow rate of OOj/hr, and use a vacuum pump in the same way from one side of the center shaft to
The pressure was reduced to r. As a result, the dissolved oxygen concentration in the treated water was 1/1, the same as in the conventional method.

As is clear from the above examples, the method of the present invention has a flow rate approximately twice that of the conventional method when reducing the same dissolved oxygen concentration from the same treated water despite the same membrane area and the same reduced pressure conditions. was obtained, and the superiority of the dissolved gas removal ability of the method of the present invention was confirmed.Example 2 As shown in Figure 6, a detour was formed inside the bag-shaped degassing membrane, and A spiral degassing membrane element with a spacer inside and a turbulence promoting material layered over the center shaft is connected in series in 3 or 6 stages to make the total degassing membrane area 20rrl' or 40M. Using a spiral degassing membrane module as shown in Figure 7, the turbulence promoting material is placed along the center shaft.
1,000 liters of pure water containing 8 ■/fl of dissolved oxygen, respectively.
6N1/hr/rrr membrane area, 3ONff/h from one side of the center shaft.
Nitrogen gas having a membrane area of r/rrr was continuously supplied, and the pressure was reduced to 8 ptor from the other side of the center shaft using a vacuum pump. The dissolved oxygen concentration of each treated water at this time was measured, and the results are shown in FIG. For comparison, we also measured the dissolved oxygen concentration of the treated water under the same conditions when no nitrogen gas was supplied from one side of the center shaft, and the results are shown in Figure 8. It was confirmed that when nitrogen gas was supplied from one side of the center shaft, the dissolved oxygen concentration in the treated water decreased dramatically.

[Brief explanation of the drawing]

1 to 4 are drawings showing an example of a degassing membrane module used in the method for removing dissolved gas according to claim 1 of the present invention, in which FIG. 1 shows a center shaft, and FIG. 2 shows a bag-like degassing membrane module. Figure 3 shows a cross-sectional view of a bag-shaped degassing membrane joined to a center shaft, and Figure 4 shows a cross-sectional view of a bag-shaped degassing membrane joined to a center shaft and wound into a spiral shape. FIG. 5 is a drawing showing the flow of a spiral degassing membrane module used in the method for removing dissolved gas according to claim 1. Further, FIG. 6 is a developed view of the main part showing a state in which the bag-shaped degassing membrane has a detour, and FIG. 7 is a spiral-shaped degassing membrane used in the method for removing dissolved gas according to claim 3. It is a drawing showing the flow of a module. FIG. 8 is a graph showing the dissolved oxygen removal effect in Example 2, with the vertical axis showing the dissolved oxygen concentration of the treated water and the horizontal axis showing the membrane area. 1...Hollow part 2...Slit 3...
・Center shaft 4...Opening 5...Bag-shaped degassing membrane 6...Spacer 7...Turbulence promoting material 8...Spiral-shaped degassing membrane element 9...Spiral-shaped sharp air membrane module 10... Connector
11... End cap 12... End connector 13... Side body part 14... End plate 1
5...Housing 16...Liquid inlet 17
...Liquid outflow port 18...Decompression port 19.
...Exterior body 20...Telescope stop 21...Sealing material 22.23...Joint portion 24...Supply port Figure 1 Figure 2 Figure 3 Figure 4 Figure 8 Membrane area [m2 )

Claims (1)

[Claims] 1. In a method for removing dissolved gas in a liquid by reducing the pressure on one side partitioned by a degassing membrane and bringing the liquid into contact with the other side, a bag-shaped degassing membrane having a spacer inside is used. A spiral degassing membrane module is used, in which a gas membrane and a turbulence promoting material are overlapped and wrapped around the center shaft, and the inside of the bag-shaped degassing membrane is in communication with the inside of the center shaft. A liquid containing a dissolved gas to be removed is allowed to pass through the turbulence promoting material existing between the outer surfaces of the bag-shaped degassing membrane, and the interior thereof is depressurized from one and/or the other of the center shaft. A method for removing dissolved gas in a liquid. 2. A spiral degassing membrane in which a bag-shaped degassing membrane with a spacer inside and a turbulence promoting material are overlapped and wrapped around a center shaft, and the inside of the bag-shaped degassing membrane and the center shaft are communicated. The air membrane module has two communication parts on the left and right sides between the inside of the bag-shaped deaeration membrane and the inside of the center shaft, a non-communication part between the two communication parts, and a bag-like deaeration part in the non-communication part. The inside of the membrane is incompletely partitioned,
A spiral degassing membrane module characterized by forming a detour in a bag-shaped degassing membrane. 3. Passing the liquid containing the dissolved gas to be removed along the center shaft of the spiral degassing membrane module described in claim 2 through the turbulence promoting material existing between the outer surfaces of the bag-shaped degassing membrane. At the same time, while continuously or intermittently supplying gas that does not substantially contain the dissolved gas to be removed from one side of the center shaft, the inside of the center shaft is depressurized from the other side of the center shaft. A method for removing dissolved gas in a liquid, characterized by: