JP2004141840A - Method and apparatus for reducing dissolved oxygen - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method and apparatus capable of efficiently reducing dissolved oxygen in a raw water at a low cost by effectively utilizing the partial pressure difference of an inert gas to lower the consumption of the inert gas. <P>SOLUTION: The raw water is introduced into the upper part of a stripping tower 1 wherein multiple stages of gas-liquid contact sections 2 are disposed, and the inert gas is also introduced into the lower part of the stripping tower 1. The raw water flowing down and the inert gas rising up are repeatedly subjected to countercurrent contact to each other in the gas-liquid contact sections 2 in the stripping tower 1 to strip the dissolved oxygen from the raw water into the inert gas by a mass transfer, thus the dissolved oxygen in the raw water being efficiently reduced. Moreover, the maintenance cost can be reduced by its simple construction. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method and an apparatus for reducing dissolved oxygen in raw water used for boiler water supply, drinking water production, semiconductor ultrapure water production, various kinds of test research, and the like. More specifically, the present invention relates to a method and apparatus for reducing dissolved oxygen in raw water by bringing dissolved oxygen in raw water into gas-liquid contact with an inert gas to mass-transfer dissolved oxygen to the inert gas, that is, stripping the dissolved oxygen. .
[0002]
[Prior art]
As a method of reducing dissolved oxygen in raw water using inert gas, water and nitrogen gas are mainly brought into gas-liquid contact, and the gas partial pressure difference of nitrogen gas is used to efficiently dissipate oxygen dissolved in water. A method is known in which the mass is reduced by mass transfer to the nitrogen gas side.
[0003]
As a gas-liquid contacting device for bringing a liquid and a gas into gas-liquid contact, raw water is pumped into a static mixer via a liquid feed pump, and the gas and the raw water are mixed to remove the substance to be removed from the raw water in the gas. A stationary mixer is placed in the water in the tank where raw water is stored, or a static mixer is placed in the lower part of the stationary mixer, and the static mixer is placed through the gas pipe. There is known a device that supplies gas into the inside, raises the raw water together with the gas in the mixer to generate a circulating flow of water, and mixes the gas and the raw water in the mixer to move oxygen to the gas side. I have.
[0004]
A stationary type in which a spiral blade portion is disposed in the tube wall portion and a plurality of fluid passages through which a fluid flows in the tube axis direction are formed by the blade portion and the tube axis direction is arranged vertically. A fluid mixer, liquid supply means for supplying a liquid from a position higher than the fluid mixer to the fluid mixer by a difference in hydrostatic pressure, and gas supply means for flowing gas into the fluid mixer. A gas-liquid contact device (JP-A-5-15753) is known.
[0005]
In addition, there is also a device that utilizes the negative pressure generated on the back of the rotating impeller to continuously introduce gas into the processing liquid, generate fine bubbles, and react the harmful components in the fine bubbles with the processing liquid. It is known.
[0006]
Furthermore, there is known an oxygen reducing apparatus (Japanese Patent Laid-Open No. 6-190360) for removing dissolved oxygen in a liquid by bubbling an inert gas into the liquid.
[0007]
[Problems to be solved by the invention]
A device for pumping the raw water into a static mixer through a liquid feed pump, mixing compressed air and raw water and mass-transferring harmful substances in the raw water into the air, removes the harmful substances from the air and the raw water. The volume ratio is 2 to 30, and it is difficult to increase the ratio of air more than this. The harmful substance removal efficiency is as low as 30 to 50% by passing through the mixer only once, and the harmful substance in raw water is low. In order to remove 90% or more, it is necessary to use 4 to 8 mixers, the same number of liquid feed pumps is required, and the equipment cost is increased. Further, since the volume ratio of gas-liquid is large, there is a disadvantage that the amount of gas used increases.
[0008]
In addition, a device that supplies gas into a static mixer through an air pipe and raises raw water together with the gas in the mixer to generate a circulating flow of water is used for gas-liquid contact in a co-current flow. Low volume ratio of liquid.
[0009]
The gas-liquid contact device disclosed in Japanese Patent Application Laid-Open No. HEI 5-15753 makes a liquid and a gas co-currently contact with each other, has a high volume ratio of the gas and the liquid, uses a large amount of inert gas, and reduces dissolved oxygen. It is not enough as a device. Further, a device that continuously introduces gas into the processing liquid by using a negative pressure generated on the back surface of the rotating impeller to generate fine bubbles requires a long processing time and a large device.
[0010]
The dissolved oxygen reducing device disclosed in Japanese Patent Application Laid-Open No. 6-190360 utilizes the bubbling effect for gas-liquid contact, and therefore has low gas-liquid contact efficiency. For this reason, the tower height of the bubbling tank is increased, and the number of towers is increased. In addition, the installation area increases.
[0011]
An object of the present invention is to solve the above-mentioned drawbacks of the prior art, to effectively utilize the gas partial pressure difference of the inert gas, to reduce the dissolved oxygen in the raw water at a low cost and to reduce the dissolved oxygen efficiently. To provide.
[0012]
[Means for Solving the Problems]
The feature of the dissolved oxygen reducing method of the present invention is that in the dissolved oxygen reducing method, a stripping tower comprising a plurality of gas-liquid contact portions and a gas-liquid separation portion disposed between the gas-liquid contact portions in a substantially vertical direction. The raw water is supplied to the upper part of the stripping tower, an inert gas is introduced from the lower part of the stripping tower, and the raw water flowing down in the gas-liquid contact portion and the rising inert gas are brought into countercurrent contact to repeat dissolved oxygen in the raw water. It is to dissipate to the inert gas side for mass transfer. Further, a high-performance static mixer is disposed at the gas-liquid contact portion.
[0013]
Raw water is supplied to the upper part of the stripping tower in which a plurality of gas-liquid contact parts are arranged in multiple stages as described above, and inert gas is introduced from the lower part of the stripping tower, and the raw water flowing down in the gas-liquid contact part rises. By repeating the countercurrent contact of the inert gas, and by repeating the mass transfer of the dissolved oxygen in the raw water to the inert gas side, the raw water flowing downward through the gas-liquid contact part The inert gas that rises in the raw water as fine bubbles becomes inert with the raw water while continuously rotating and dividing right and left, merging, reversing and shearing in the static mixer. The gas is contacted and agitated, and the dissolved oxygen in the raw water is diffused and mass-transferred to the inert gas side, so that the dissolved oxygen is reduced.
[0014]
Further, the dissolved oxygen reducing apparatus of the present invention is characterized in that a plurality of gas-liquid contact portions are arranged in multiple stages substantially vertically, and a gas-liquid separation portion is arranged between the gas-liquid contact portions. The water supply pipe and the inert gas discharge pipe are located in the lower part of the stripping tower, and the inert gas supply pipe is connected to the upper part of the water storage section and the treated water discharge pipe is connected to the bottom of the water storage section. .
[0015]
As described above, the gas-liquid contact section is combined in multiple stages, and the raw water supply pipe and the inert gas discharge pipe are provided at the upper part of the stripping tower in which the gas-liquid separating section is disposed between the gas-liquid contact sections, and the water is stored at the lower part of the stripping tower. The raw water and inert gas rotate while flowing through the gas-liquid contact part by arranging the inert gas supply pipe at the top of the water storage section and the treated water discharge pipe at the bottom of the water storage section. In addition, the contact and stirring are performed while continuously repeating the splitting, merging, inversion, and shearing stress actions, and the dissolved oxygen in the raw water is released to the inert gas side. In addition, after the inert gas is separated from the water in the gas-liquid separation section, the water and the inert gas sequentially rotate and divide right and left, merge, reverse, and shear stress action successively at the lower gas-liquid contact section. When the inert gas is separated from the water in the gas-liquid separation unit or the water storage unit, the dissolved oxygen in the water is diffused to the inert gas side to perform mass transfer, and the dissolved oxygen is reduced.
[0016]
The feature of the gas-liquid contact part in the present invention is that a high-performance static mixer is arranged. This static mixer is composed of right-handed and left-handed mixing elements. A mixing element having a plurality of right-handed and left-handed spiral blades provided with a large number of holes is alternately arranged vertically. Such raw water flowing downward while flowing through the gas-liquid contact portion and inert gas rising in the raw water as fine bubbles are rotated and divided in the right and left directions, merge, invert, and While the shear stress action is continuously repeated, the raw water and the inert gas come into contact with each other and are stirred, and the dissolved oxygen in the raw water is diffused to the inert gas side to perform mass transfer, and the dissolved oxygen is reduced. Note that the static mixer is not limited to the mixing element system, and various static mixers can be selectively used.
[0017]
The feature of the gas-liquid separation unit in the present invention is, for example, that a plurality of holes are provided in the thickness direction of the disk, and the holes have a diameter such that water temporarily stays at a predetermined depth on the upper surface of the disk according to the raw water treatment amount. In this case, a hole in which raw water is temporarily retained is provided on the upper surface of the disk. Thus, by disposing a disk having a large number of holes, and providing a temporary stagnation portion of water on the upper surface of the disk in accordance with the raw water processing amount, the disk is intensely contacted by the gas-liquid contact portion, and the raw water is stirred. The inert gas mixture is separated from the raw water together with the dissolved oxygen from the raw water during the temporary residence in the temporary residence part on the upper surface of the disk.
[0018]
For example, as shown in FIG. 1, the dissolved oxygen reducing apparatus according to the present invention includes a tubular stripping tower 1 in which gas-liquid contact sections 2 are combined in multiple stages and a gas-liquid separation section is provided between the gas-liquid contact sections 2a and 2b. 3 is disposed, and a water storage unit 4 is disposed below the stripping tower 1. A raw water supply pipe 5 is disposed above the stripping tower 1, and an exhaust pipe 6 is disposed at the top. An inert gas supply pipe 7 is provided below the gas-liquid contact section 2b, and a treated water discharge pipe 8 is provided at the bottom of the water storage section 4.
[0019]
As shown in FIG. 2, the gas-liquid contact portion in the present invention includes a mixing element 11 having a plurality of spiral right-handed wings 10 having a large number of holes 9 and a plurality of spiral elements having a large number of holes 12. As shown in FIG. 3, the basic structure is such that two mixing elements 14 each having the left twisted blade 13 are alternately arranged as shown in FIG. The mixing elements 11 and 14 have four fluid passages in which a plurality of, for example, four, right-handed or left-handed spiral blades 10 and 13 having a large number of holes 9 and 12 formed therein are provided. . While the raw water and the inert gas flow through the plurality of mixing elements 11 and 14, the right-handed and left-handed rotating blades 10 and 13 continuously rotate and divide, merge, reverse, and shear stress action. While contacting and stirring the inert gas rising through the four fluid passages and the holes 9 and 12 formed in the blades 10 and 13 to form fine bubbles and rising in the raw water, the dissolved oxygen in the raw water is It is released to the inert gas side and performs mass transfer. The number of blades of the mixing element, the size of the holes, the aperture ratio of the holes, and the like can be appropriately selected.
[0020]
Further, as shown in FIG. 4, as the gas-liquid separation unit 3 arranged between the gas-liquid contact units combined in multiple stages, a large number of holes are provided in a disk 15 having the same outer diameter as the inner diameter of the stripping tower 1. Five holes 16 whose diameters are adjusted so that the raw water temporarily stays at a predetermined depth, for example, 100 mm, on the disk according to the raw water treatment amount and a hole 17 smaller in diameter than the holes 16 are punched, and the upper surface of the disk 15 is formed. Is provided with a temporary stagnation section 18 for water. After the inert gas of microbubbles mixed in water is separated in the temporary stagnation section 18 for raw water, the gas is temporarily connected to the lower gas-liquid contact section via the holes 16 and 17. It is a structure that flows down.
[0021]
Further, as the gas-liquid separation section, as shown in FIG. 5, a cylindrical body 21 in which a static mixer 20 is provided in the center of a disk 19 having the same diameter as the inner diameter of the stripping tower 1 is disposed. A structure in which a stagnant portion 22 of the treated water is provided above the disk 19 may be used. In this case, the amount of treated water flowing through the static mixer 20 from above to below and the amount of inert gas flowing from below to above can be appropriately changed depending on the use conditions, but the falling speed of the treated water amount is 0.05. It is preferable that the inert gas is used at a rate of 0.5 to 10 m / sec.
[0022]
Further, as the gas-liquid separation unit, as shown in FIG. 6, an inverted truncated conical disk 23 having the same diameter as the inner diameter of the stripping tower 1 is arranged, and a plurality of disks 23 are provided in the thickness direction of the disk 23. A hole 24 may be formed, and a retaining portion 25 for temporarily retaining treated water may be provided above the disk 23 to perform gas-liquid separation. Also in this case, the rising speed of the inert gas and the falling speed of the treated water are preferably in the range of 0.5 to 10 m / sec and 0.05 to 1.5 m / sec. The dimensions and aperture ratio of the hole at the center and the hole 24 of the disk 23 and the installation angle of the disk 23 in the axial direction can be appropriately changed according to the use conditions.
[0023]
For example, as shown in FIG. 1, the dissolved oxygen reducing apparatus of the present invention includes a plurality of stripping towers 1 in which gas-liquid contact sections 2 are combined in a two-stage arrangement, or a required dissolved water treatment. Depending on the amount of oxygen, the number of stages and the number of elements of the gas-liquid contact section 2 and the number of towers of the stripping tower can be appropriately changed.
[0024]
【Example】
As shown in FIG. 7, six stages of gas-liquid contact portions 27 in which mixing elements 11 and 14 having four spiral blades are alternately arranged in the vertical direction are combined, and between each gas-liquid contact portion 27. Raw water having a dissolved oxygen content of 9 mg / l and a water temperature of 20 ° C. is supplied from a raw water supply pipe 29 at a flow rate of 75 m ³ / m ² · Hr to the upper part of the diffusion tower 26 in which the gas-liquid separation section 28 is arranged in five stages. Nitrogen gas having a purity of 99.9% is introduced at 500 m ³ / m ² · Hr from the lower inert gas supply pipe 30 at 500 m ³ / m ² · Hr, and the nitrogen and oxygen mixed gas is exhausted from the discharge pipe 31 at the top of the stripping tower 26. The dissolved oxygen in the treated water discharged from the treated water discharge pipe 33 at the bottom of the water storage part 32 at the lower part of 26 was measured using a dissolved oxygen meter (DO-32A) manufactured by TOA DK KK. The result was 0.16 mg / l. The amount of the raw water flowing through the stripping tower 26 and the amount of the inert gas are not limited to those in the above embodiment, and the raw water is 200 to 2000 m ³ / m ² · Hr, and the amount of the inert gas is 20 to 200 m ^3. / M ² · Hr within a preferred range. Further, the inert gas used is not limited to nitrogen gas, and one type such as argon and helium gas or a composite type of these gases can be appropriately selected depending on the purpose of use. Further, as the material of the stripping tower, one kind of metal, glass, ceramics, plastics or the like or a composite material thereof can be appropriately selected.
[0025]
【The invention's effect】
The method and apparatus for reducing dissolved oxygen of the present invention provide a gas-liquid contact portion capable of gas-liquid contact with high efficiency in multiple stages, and contacting the raw water and the inert gas in countercurrent to obtain a gas partial pressure difference of the inert gas. Can be effectively used to reduce the amount of inert gas consumed, to efficiently reduce dissolved oxygen in water, and to produce low-dissolved oxygen water at low cost depending on the application.
[Brief description of the drawings]
FIG. 1 is a schematic system diagram showing an example of a dissolved oxygen reducing device of the present invention.
FIGS. 2A and 2B show an embodiment of a gas-liquid contact portion used in the present invention. FIG. 2A is a perspective view of a right-handed mixing element, and FIG. 2B is a perspective view of a left-handed mixing element.
FIG. 3 is a basic structural diagram showing one embodiment of a gas-liquid contact portion used in the present invention.
4A and 4B show a first embodiment of a gas-liquid separation unit used in the present invention, wherein FIG. 4A is a plan view and FIG. 4B is a cross-sectional view.
5A and 5B show a second embodiment of the gas-liquid separation unit used in the present invention, wherein FIG. 5A is a plan view and FIG. 5B is a cross-sectional view.
6 (a) is a plan view and FIG. 6 (b) is a sectional view showing a third embodiment of the gas-liquid separation section used in the present invention.
FIG. 7 is a schematic system diagram of a dissolved oxygen reducing apparatus showing one embodiment of the present invention.
[Explanation of symbols]
1,26: stripping towers 2, 2a, 2b, 27a, 27b, 27c, 27d, 27e, 27f: gas-liquid contact parts 3, 28a, 28b, 28c, 28d, 28e: gas-liquid separation parts 4, 32: water storage parts 5, 29: raw water supply pipe 6, 31: discharge pipe 7, 30: inert gas supply pipe 8, 33: treated water discharge pipe 11, 14: mixing element

Claims (4)

In the method for reducing dissolved oxygen in raw water, raw water is placed on the upper part of a cylindrical stripping tower having a plurality of gas-liquid contact sections and a gas-liquid separation section between the gas-liquid contact sections in a substantially vertical direction. And introducing an inert gas from the lower part of the stripping tower, and repeatedly contacting the raw water flowing down in the gas-liquid contact portion with the rising inert gas in a countercurrent manner, to dissolve dissolved oxygen in the raw water into the inert gas side. A method for reducing dissolved oxygen, comprising: 2. The method for reducing dissolved oxygen according to claim 1, wherein the inert gas is one of nitrogen, argon, helium, and krypton gas or a combination of these gases. A device for reducing dissolved oxygen in raw water, comprising a plurality of gas-liquid contact portions in a substantially vertical direction and a gas-liquid separation portion disposed between the plurality of gas-liquid contact portions. A dissolved oxygen reducing device, wherein a supply pipe and an inert gas discharge pipe are disposed at a lower portion of the stripping tower, and an inert gas supply pipe and a water storage section are disposed at a bottom of the stripping tower. 4. The dissolved oxygen reducing device according to claim 3, wherein a static mixer is arranged at the gas-liquid contact portion.

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