BACKGROUND
[0001] The present invention relates to a removing system for contaminant in air, in which the air and an absorbent are brought into gas-liquid contact to dissolve the contaminant contained in the air into the absorbent and then remove it.
[0002] These days, in a manufacture environment in a clean room of a semiconductor factory or a liquid crystal factory, it is reported that not only particulate contaminant but also airborne molecular contaminations (AMCs) contained in air has an influence on product yield and performance deterioration.
[0003] As one of techniques for removing the airborne molecular contaminations (AMCs) from the air, a gas-liquid contact type removing system for contaminant in air (an air washer) is known. The removing system (the air washer) is an equipment that the air to be treated and an absorbent are brought into gas-liquid contact to dissolve the airborne molecular contaminations (AMCs), such as sulfur dioxide (SO2) or ammonia (NH3) , contained in the air into the absorbent and then to remove it, and is installed in an outside air conditioning unit of the semiconductor factory or the liquid crystal factory.
[0004] A removal ability of such a removing system (the air washer) is largely varied depending on pH of the absorbent with which the air is brought into gas-liquid contact. As a concentration of an acid component in the air is high, pH of the absorbent is decreased to deteriorate the removal ability for the acid component, such as SO2 . In the same way, as a concentration of an alkali component in the air is high, pH of the absorbent is increased to deteriorate the removal ability for the alkali component, such as NH3. For example, when there is an emission source near the system, a content

of acid gas SO2 is varied within a range from 1 ppb or less to several 10 ppb depending on a wind direction.
[0005] As a known technique for eliminating the deterioration of the removal ability of the removing system (the air washer), a technique for supplying a constant amount of chemical liquid to keep pH of the absorbent constant is known; however, the technique has a problem of high running cost because the chemical liquid is continuously supplied.
[0006] Then, a system for controlling an amount of the chemical liquid while monitoring pH of the absorbent is proposed (for example, refer to Japanese Unexamined Patent Application Publications 2004-230385, 2002-239331 and 2000-79319).
[0007] A technique described in Japanese Unexamined Patent Application Publication 2004-230385 applies a system in which pH of the absorbent is managed within a predetermined range
(4.5 to 9.5) by employing pure water, buffering liquid, acidic■alkaline solution or water, and the water supplying is controlled by switching ON/OFF of an electromagnetic valve.
[0008] A technique described in Japanese Unexamined Patent Application Publication 2002-239331 applies a system in which pH of the absorbent is managed within a predetermined range by supplying general water (pH 6 to 8, an electric conductivity of 20 uS/cm or more), and the water supplying is controlled by switching ON/OFF of an electromagnetic valve.
[0009] A technique described in Japanese Unexamined Patent Application Publication 2000-79319 applies a water supplying system for controlling pH of the absorbent within a predetermined range (4.5 to 9.5) by an ion removing apparatus .

[0010] However, the conventional techniques of the above described Japanese Unexamined Patent Application Publications have a problem in measurement precision and responsiveness of the pH measurement device to cause low controllability, and require a periodically calibration of the electrode and a replenishment of potassium chloride (KC1) solution to cause short life and low maintenance performance, such as increased replacement frequency.
[0011] Additionally, the conventional techniques of the above described Japanese Unexamined Patent Application Publications 2004-230385 and 2002-239331 have a problem in which in a case where pH of the absorbent is maintained in a managed value, a concentration of the airborne molecular contaminations (AMCs) in the absorbent is increased and the electric conductivity continues increasing to cause a re-scattering of the airborne molecular contaminations
(AMCs) and an occurrence of scale.
[0012] Additionally, the conventional technique of the above described Japanese Unexamined Patent Application Publication 2000-79319 has a problem in which because a large amount of high concentration absorbent is supplied to the ion removing device (a device employing an ion exchange resin and electrolysis), a replacement frequency is increased to cause a problem of high running cost.
[0 013] The present invention has been made in order to solve the above problems, and to provide a removing system for contaminant in air, in which a removal performance for a water-soluble component in the air is always kept high and the maintenance performance is improved to decrease the running cost.
SUMMARY
[0014] In accordance with an aspect of the present

invention, a removing system for contaminant in air, in which the air and an absorbent are brought into gas-liquid contact to dissolve the contaminant contained in the air into the absorbent and remove it, the removing system comprises: a pre-stage air washer which employs a chemical liquid containing at least either an alkaline solution or an acidic solution as the absorbent; a chemical liquid supply device configured to supply the chemical liquid to the pre-stage air washer; a post-stage air washer which employs a pure water as the absorbent, the post-stage air washer being arranged at a downstream side of the pre-stage air washer in an air flow direction; an ion exchange resin through which the absorbent of the post-stage air washer is passed, the ion exchange resin containing at least either a cation exchange resin or an anion exchange resin; and a control unit configured to estimate a concentration of the contaminant contained in the air flowed into the pre-stage air washer based on an electric conductivity of the absorbent passed through the ion exchange resin and then to calculate an amount of the chemical liquid to be supplied from the chemical liquid supply device to the pre-stage air washer.
[0015] In the removing system for contaminant in air, the pre-stage air washer may include: a pre-stage gas-liquid contact material by which the air and the absorbent are brought into gas-liquid contact; a pre-stage water tank configured to store the absorbent passed through the pre-stage gas-liquid contact material; and a pre-stage absorbent circulation equipment configured to circulate the absorbent between the pre-stage water tank and the pre-stage gas-liquid contact material, the post-stage air washer may include: a post-stage gas-liquid contact material by which the air and the absorbent are brought into gas-liquid contact; a post-stage water tank configured to store the absorbent passed through the post-stage gas-liquid contact material; and a post-stage absorbent circulation equipment configured

to circulate the absorbent between the post-stage water tank and the post-stage gas-liquid contact material and between the post-stage water tank and the ion exchange resin, and the chemical liquid may be supplied from the chemical liquid supply device to the pre-stage circulation equipment or the pre-stage water tank.
[0016] In the removing system for contaminant in air, the pre-stage air washer may include: a pre-stage gas-liquid contact material by which the air and the absorbent are brought into gas-liquid contact; a pre-stage water tank configured to store the absorbent passed through the pre-stage gas-liquid contact material; and a pre-stage absorbent circulation equipment configured to circulate the absorbent between the pre-stage water tank and the pre-stage gas-liquid contact material, the post-stage air washer may include: a post-stage gas-liquid contact material by which the air and the absorbent are brought into gas-liquid contact; a post-stage water tank arranged below the post-stage gas-liquid contact material; a receiving part having a capacity smaller than that of the post-stage water tank and arranged between the post-stage gas-liquid contact material and the post-stage water tank such that the absorbent passed through the post-stage gas-liquid contact material is temporarily received and the absorbent overflowed from the receiving part is stored in the post-stage water tank; a water supply equipment configured to send the absorbent from the receiving part to the ion exchange resin; and a post-stage absorbent circulation equipment configured to circulate the absorbent between the post-stage water tank and the post-stage gas-liquid contact material, and the chemical liquid may be supplied from the chemical liquid supply device to the pre-stage absorbent circulation equipment or the pre-stage water tank.
[0017] A removing system for contaminant in air, in which

the air and an absorbent are brought into gas-liquid contact to dissolve the contaminant contained in the air into the absorbent and remove it, the removing system comprises: a pre-stage air washer which employs a chemical liquid containing one of an alkaline solution and an acidic solution as the absorbent; a middle-stage air washer which employs a chemical liquid containing the other of the alkaline solution and the acidic solution as the absorbent, the middle-stage air washer being arranged at a downstream side of the pre-stage air washer in an air flow direction; a chemical liquid supply device configured to supply the chemical liquid to the pre-stage air washer and the middle-stage air washer; a post-stage air washer which employs a pure water as the absorbent, the post-stage air washer being arranged at a downstream side of the middle-stage air washer in the air flow direction; a cation exchange resin and an anion exchange resin, the absorbent of the post-stage air washer being passed through the cation exchange resin and the anion exchange resin; and a control unit configured to estimate a concentration of the contaminant contained in the air flowed into the pre-stage air washer based on an electric conductivity of the absorbent passed through each of the cation exchange resin and the anion exchange resin and then to calculate an amount of the chemical liquid to be supplied from the chemical liquid supply device to each of the pre-stage air washer and the middle-stage air washer.
[0018] In the removing system for contaminant in air, the pre-stage air washer may include: a pre-stage gas-liquid contact material by which the air and the absorbent are brought into gas-liquid contact; a pre-stage water tank configured to store the absorbent passed through the pre-stage gas-liquid contact material; and a pre-stage absorbent circulation equipment configured to circulate the absorbent between the pre-stage water tank and the pre-stage gas-liquid contact material, the middle-stage air washer may include:

a middle-stage gas-liquid contact material by which the air and the absorbent are brought into gas-liquid contact; a middle-stage water tank configured to store the absorbent passed through the middle-stage gas-liquid contact material; and a middle-stage absorbent circulation equipment configured to circulate the absorbent between the middle-stage water tank and the middle-stage gas-liquid contact material, the post-stage air washer may include: a post-stage gas-liquid contact material by which the air and the absorbent are brought into gas-liquid contact; a post-stage water tank configured to store the absorbent passed through the post-stage gas-liquid contact material; and a post-stage absorbent circulation equipment configured to circulate the absorbent between the post-stage water tank and the post-stage gas-liquid contact material, between the post-stage water tank and the cation exchange resin and between the post-stage water tank and the anion exchange resin.
EFFECT OF THE INVENTION
[0019] According to the present invention, various excellent advantages can be obtained, for example, the removal performance for water-soluble component in air can be always kept high, the maintenance performance can be improved and the running cost can be decreased.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020] FIG. 1 is a system diagram showing a removing system for contaminant in air, according to one embodiment of the present invention.
[0021] FIG. 2 is a graph showing a relationship between a SO2 concentration in outside air and an electric conductivity of an absorbent after a cation exchange resin, in the removing system for contaminant in air, according to the embodiment of the present invention.

[0022] FIG. 3 is a system diagram showing a first modified example of the removing system for contaminant in air, according to the embodiment of the present invention.
[0023] FIG. 4 is a system diagram showing a second modified example of the removing system for contaminant in air, according to the embodiment of the present invention.
[0024] FIG. 5 is a system diagram showing a third modified example of the removing system for contaminant in air, according to the embodiment of the present invention.
[0025] FIG. 6 is a system diagram showing a fourth modified example of the removing system for contaminant in air, according to the embodiment of the present invention.
[0026] FIG. 7 is a system diagram showing a fifth modified example of the removing system for contaminant in air, according to the embodiment of the present invention.
DETAILED DESCRIPTION
[0027] Hereinafter, with reference to the attached drawings, a removing system for contaminant in air, according to an embodiment of the present invention will be described. The following description shows an exemplary case where the removing system for contaminant in air, according to the embodiment of the present invention is applied to an outside air conditioning unit equipped in order to introduce outside air into a clean room of a semiconductor factory or a liquid crystal factory. FIG. 1 is a system diagram showing the removing system for contaminant in air, according to the embodiment of the present invention.
[0028] As shown in FIG. 1, the removing system 10 for contaminant in air, according to the present embodiment is

configured to bring an air and an absorbent come into gas-liquid contact to dissolve a contaminant contained in the air into the absorbent and then to remove the contaminant. The removing system 10 includes a pre-stage air washer 11 which employs a chemical liquid as the absorbent, a chemical liquid supply device 12 configured to supply the chemical liquid to the pre-stage air washer 11, a post-stage air washer 13 arranged at a downstream side of the pre-stage air washer 11 in an air flow direction and which employs a pure water as the absorbent, an ion exchange resin 14 through which the absorbent of the post-stage air washer 13 is passed, an electric conductivity meter 15 configured to measure an electric conductivity of the absorbent passed through the ion exchange resin 14 and a control unit 16 configured to calculate an amount of the chemical liquid supplied from the chemical liquid supply device 12 to the pre-stage air washer 11 based on a measurement result of the electric conductivity meter 15.
[0029] The pre-stage air washer 11 includes a pre-stage gas-liquid contact material 17 by which the air and the absorbent are brought into gas-liquid contact, a pre-stage water tank 18 configured to store the absorbent passed through the pre-stage gas-liquid contact material 17, and a pre-stage absorbent circulation equipment 19 configured to circulate the absorbent between the pre-stage water tank 18 and the pre-stage gas-liquid contact material 17.
[0030] The pre-stage gas-liquid contact material 17 is provided in a chamber (not shown) through which the air is flowed, and disposed vertically so as to perpendicularly cross the air flow direction (a direction shown by an arrow directing from the left side to the right side in FIG. 1). The pre-stage gas-liquid contact material 17 is made of hydrophilic or water absorptive material, such as polyester and ceramic. By dropping the absorbent on the pre-stage

gas-liquid contact material 17, a liquid film is formed on a surface of the pre-stage gas-liquid contact material 17. The pre-stage gas-liquid contact material 17 does not always have the above configuration even if it has a configuration that the air and the absorbent are effectively brought into gas-liquid contact. For example, it may have a configuration that the absorbent is sprayed by a spray nozzle and a mist of the scattered absorbent is collected by an eliminator, or various modification may be applied.
[0031] The pre-stage water tank 18 is arranged below the pre-stage gas-liquid contact material 17. To the pre-stage water tank 18, a drain pipe 20 is connected.
[0032] The pre-stage absorbent circulation equipment 19 includes a circulation pipe 21 arranged from the pre-stage water tank 18 to an upper portion of the pre-stage gas-liquid contact material 17 and a circulation pump 22 provided at a middle of the circulation pipe 21.
[0033] Between the chemical liquid supply device 12 and the circulation pipe 21, a chemical liquid supply pipe 23 is connected, and the chemical liquid is replenished from the chemical liquid supply device 12 to the absorbent in the circulation pipe 21 through the chemical liquid supply pipe 23. In this case, the chemical liquid contains at least either an alkaline solution, such as an electrolytic water, or an acidic solution.
[0034] For example, as the alkaline solution, potassium hydroxide (KOH), sodium hydroxide (NaOH), potassium carbonate (K2CO2) and sodium carbonate (Na2CC>2) are employed. As the acidic solution, carbonic acid (H2CO2) , hydrochloric acid (HC1) , hypochlorous acid (HC10) and citric acid (CeUsOi) are employed.

[0035] The chemical liquid supply pipe 23 may be arranged from the chemical liquid supply device 12 to the pre-stage water tank 18, instead of being connected to the circulation pipe 21, such that the chemical liquid is replenished from the chemical liquid supply device 12 to the pre-stage water tank 18.
[0036] The post-stage air washer 13 includes a post-stage gas-liquid contact material 24 by which the air and the absorbent are brought into gas-liquid contact, a post-stage water tank 25 configured to store the absorbent passed through the post-stage gas-liquid contact material 24, and a post-stage absorbent circulation equipment 27 configured to circulate the absorbent between the post-stage water tank 25 and the post-stage gas-liquid contact material 24 and between the post-stage water tank 25 and the ion exchange resin 14.
[0037] The post-stage gas-liquid contact material 24 is provided in a chamber (not shown) in which the air is flowed, and vertically disposed so as to perpendicularly cross the air flow direction (the direction shown by the arrow from the left side to the right side in FIG. 1) . The post-stage gas-liquid contact material 24 has the same configuration as that of the above described pre-stage gas-liquid contact material 17, and its detail description is omitted.
[0038] The post-stage water tank 25 is arranged below the post-stage gas-liquid contact material 24. Between the post-stage water tank 25 and the pre-stage water tank 18, a communication pipe 26 is provided so as to communicate both the water tanks 18 and 25 each other.
[0039] The post-stage absorbent circulation equipment 27 includes a first circulation pipe 28 arranged from the post-stage water tank 25 to an upper portion of the post-stage gas-liquid contact material 24, a circulation pump 29

provided at a middle of the first circulation pipe 28, and a second circulation pipe 30 branched from the first circulation pipe 28 at a downstream side of the circulation pump 29 in an absorbent circulation direction and connected to the post-stage water tank 25.
[0040] From a water source (not shown) to the post-stage water tank 25, a water supply pipe 31 is disposed such that the absorbent is replenished to the post-stage water tank 25 through the water supply pipe 31. In this case, a pure water is employed as the absorbent.
[0041] The ion exchange resin 14 is at least either a cation exchange resin or an anion exchange resin. In a case where the chemical liquid supplied from the chemical liquid supply device 12 to the pre-stage air washer 11 is an alkaline solution, the cation exchange resin is provided. In a case where the chemical liquid supplied from the chemical liquid supply device 12 to the pre-stage air washer 11 is an acidic solution, the anion exchange resin is provided.
[0042] The electric conductivity meter 15 is provided at a middle of the second circulation pipe 30 at the downstream side of the ion exchange resin 14 in the absorbent circulation direction. The electric conductivity meter 15 is electrically connected to the control unit 16, and the control unit 16 is electrically connected to the chemical liquid supply device 12 .
[0043] Next, with reference to figures, an operation of the removing system 10 for contaminant in air, according to the present embodiment of the invention, having the above described description will be described.
[0044] First, in the pre-stage air washer 11, the circulation pump 22 of the pre-stage absorbent circulation

equipment 19 is driven to pump the absorbent containing the chemical liquid from the pre-stage water tank 18 . Then, the pumped absorbent containing the chemical liquid is dropped on the pre-stage gas-liquid contact material 17 through the circulation pipe 21, and a liquid film is formed on the surface of the pre-stage gas-liquid contact material 17.
[0045] As shown by a thick line arrow in FIG. 1, when an outside air to be treated is introduced into the above chamber (not shown) and then passed through the pre-stage gas-liquid contact material 17 having the liquid film formed on the surface as described above, the air and the absorbent are brought into gas-liquid contact such that airborne molecular contaminations (AMCs) contained in the air are dissolved into the absorbent and then removed. The absorbent into which the airborne molecular contaminations (AMCs) are dissolved is naturally dropped and then returned in the pre-stage water tank 18.
[0046] The air passed through the pre-stage air washer 11 as described above is flowed into the post-stage air washer 13. In the post-stage air washer 13, the circulation pump 29 of the post-stage absorbent circulation equipment 27 is driven to pump the absorbent (the pure water) from the post-stage water tank 25. The pumped absorbent (the pure water) is dropped on the post-stage gas-liquid contact material 2 4 through the first circulation pipe 28, and a liquid film is formed on the surface of the post-stage gas-liquid contact material 24.
[0047] When the air flowed into the post-stage air washer 13 is passed through the post-stage gas-liquid contact material 24 having the liquid film formed on the surface as described above, the air and the absorbent are brought into gas-liquid contact such that airborne molecular contaminations (AMCs) contained in the air are dissolved into

the absorbent and then removed. After that, a clean air which is passed through the post-stage gas-liquid contact material 24 and from which the airborne molecular contaminations (AMCs) are removed is supplied to the clean room (not shown) , as shown by the thick line in FIG. 1. Then, the absorbent into which the airborne molecular contaminations (AMCs) are dissolved is naturally dropped and then returned in the post-stage water tank 25.
[0048] The pure water as the absorbent is supplied to the post-stage water tank 25 through the water supply pipe 31, and the pure water supplied to the post-stage water tank 25 is supplied to the pre-stage water tank 18 through the communication pipe 26. Then, when a liquid level of the pre-stage water tank 18 exceeds a predetermined level, the absorbent in the pre-stage water tank 18 is discharged outside through the drain pipe 20. When a liquid level of the post-stage water tank 25 exceeds a predetermined level, the absorbent in the post-stage water tank 25 is flowed in the pre-stage water tank 18 through the communication pipe 2 6 and then discharged outside through the drain pipe 20.
[0049] On the other hand, in the post-stage air washer 13, a part of the absorbent (the pure water) pumped from the post-stage water tank 25 by driving the circulation pump 2 9 of the post-stage absorbent circulation equipment 27 is passed through the ion exchange resin 14 through the second circulation pipe 30 and then returned to the post-stage water tank 25. Then, during circulating of the absorbent through the second circulation pipe 30, the electric conductivity meter 15 measures an electric conductivity of the absorbent in the second circulation pipe 30, and a measured value is sent to the control unit 16. The control unit 16 estimates a concentration of the airborne molecular contaminations
(AMCs) contained in the outside air flowed in the pre-stage air washer 11 based on the measured value of the electric

conductivity of the absorbent by the electric conductivity meter 15, and calculates an amount of the chemical liquid to be supplied to the pre-stage air washer 11 from the chemical liquid supply device 12. Then, the chemical liquid supply device 12 supplies a predetermined amount of the chemical liquid to the absorbent of the pre-stage air washer 11 based on the calculated result.
[Example]
[0050] Next, with reference to FIG. 1, in the removing system 10 for contaminant in air, according to the embodiment of the present invention, an exemplary case to treat an outside air containing sulfur dioxide (SO2), which is an acidic substance, as the airborne molecular contaminations (AMCs) will be described.
[0051] In the example, as both the pre-stage air washer 11 and the post-stage air washer 13, a vaporizing type air washer having a saturation efficiency of 95 % or larger is employed. As the chemical liquid supply device 12, an alkali electrolytic water (potassium oxide (KOH) pH 11 to 12) supply device is employed. As the ion exchange resin 14, a cation exchange resin is employed. As the control unit 16, a programmable logic controller (PLC) is employed.
[0052] As the air to be treated, an air to which sulfur dioxide (SO2) of 10 ppb (about 40,000 ng/m3) is poured in the outside air is employed. An air volume of the air is set to 12, 500 m3/h and a face velocity is set to 2.5 m/s . The outside air contains ammonia (NH3) . A flow rate of the absorbent supplied to each of the pre-stage gas-liquid contact material 17 and the post-stage gas-liquid contact material 24 is set to 15 L/min. A flow rate of the absorbent to be passed through the cation exchange resin is set to 0 . 5 L/min (1/30 of a flow amount of the absorbent supplied to the post-stage gas-liquid contact material 24) . A flow rate of the absorbent (the pure

water) supplied to the post-stage water tank 25 through the water supply pipe 31 is set to 2 L/min. As the absorbent supplied to the pre-stage gas-liquid contact material 17, a weak alkaline solution of pH 8 to 9 is employed.
[0053] Under the above condition, as shown by the thick line arrow in FIG. 1, when the outside air to be treated is passed through the pre-stage gas-liquid contact material 17, the sulfur dioxide (SO2) contained in the outside air is removed by a neutralization reaction, a sulfate ion (S042~) is dissolved in the absorbent dropped on the pre-stage gas-liquid contact material 17, and the absorbent is naturally dropped and then returned in the pre-stage water tank 18.
[0054] The air passed through the pre-stage air washer 11 as described above is flowed into the post-stage air washer 13 and then passed through the post-stage gas-liquid contact material 24. Then, the ammonia (NH3) which is not removed by the pre-stage air washer 11 is removed, an ammonia ion (NH4+) is dissolved into the absorbent dropped on the post-stage gas-liquid contact material 24, and the absorbent is naturally dropped and then returned in the post-stage water tank 25. Then, as shown by the thick line arrow in FIG. 1, a clean air from which the airborne molecular contaminations (AMCs) are removed by passing through the post-stage gas-liquid contact material 24 is supplied to the clean room (not shown).
[0055] On the other hand, in the post-stage air washer 13, a part of the absorbent (the pure water) is passed through the ion exchange resin 14 through the second circulation pipe 30, and a cation, such as an ammonia ion (NH4+) , in the absorbent is trapped. Then, an electric conductivity of the absorbent passed through the ion exchange resin 14 is measured by the electric conductivity meter 15 . Because an anion, such

as a sulfate ion (SO42") , is not trapped and but passed through the ion exchange resin 14, when the value of the electric conductivity of the absorbent passed through the ion exchange resin 14 is increased, it is possible that a concentration of the sulfur dioxide (SO2) contained in the outside air is increased.
[0056] Then, we carried out experiments and then found a fact that between an electric conductivity of the absorbent passed through the ion exchange resin 14 in the post-stage air washer 13 and a concentration of the airborne molecular contaminations (AMCs) in the outside air before passing through the pre-stage gas-liquid contact material 17 in the pre-stage air washer 11, there is a relationship shown in FIG. 2.
[0057] From the relationship between the outside SO2
concentration y, plotted on a vertical axis, and the electric
conductivity x of the absorbent after the cation exchange
resin, plotted on a horizontal axis, obtained in FIG. 2, the
following control equation is obtained:
y = 21.023x - 21.588.
R2 (multiple correlation coefficient) = 0.999.
[0058] The control unit 16 estimates a concentration y of the sulfur dioxide (SO2) contained in the outside air flowed in the pre-stage air washer 11 based on the measured value x of the electric conductivity of the absorbent received from the electric conductivity meter 15 and the above control equation. Then, the control unit 16 employs an experiment data showing a relationship between a sulfur dioxide (SO2) concentration and a required flow rate of potassium hydroxide (KOH) , calculates a predetermined flow rate of the potassium hydroxide solution to be supplied from the chemical liquid supply device 12 to the pre-stage air washer 11, and then sends the calculated amount to the chemical liquid supply device

12. The chemical liquid supply device 12 supplies the predetermined flow rate of potassium hydroxide solution to the absorbent flowing through the circulation pipe 21 of the pre-stage absorbent circulation equipment 19 based on the calculated value by the control unit 16.
[0059] As a result, as shown in Table 1, more than 99 % high removal rate of the sulfur dioxide (SO2) in the outside air and more than 94 % high removal rate of the ammonia (NH3) in the outside air could be obtained.
[0060] [Table 1]

Substance Inlet of pre-stage air washer (ng/m3) Outlet of pre-stage air washer (ng/m3) Outlet of post-stage air washer (ng/m3) Removal
efficiency
(%)
S042" 40,000 1,000 190 99.5
NH4+ 2,100 1,400 120 94.3
[0061] The relationship between the electric conductivity of the absorbent after the cation exchange resin and the concentration of SO2 in the outside air is varied depending on various parameters, such as a passing speed of the air to be treated, a supply flow rate of the pure water to the post-stage air washer 13 and a removal efficiency of the airborne molecular contaminations (AMCs) in the air. Specifically, a value of the concentration of SO2 in the outside air with respect to the electric conductivity of the absorbent after the cation exchange resin tends to become smaller as the passing speed of the air to be treated is increased, the supply flow rate of the pure water to the post-stage air- washer 13 is decreased and the removal efficiency of the airborne molecular contaminations (AMCs) in the air is decreased. Then, when the control unit 16 calculates a flow rate of potassium hydroxide to be supplied

to the absorbent in the circulation pipe 21, the different control equations corresponding to the above parameters are employed.
[0062] According to the above described removing system 10 for contaminant in air, according to the embodiment of the present invention, a concentration of the airborne molecular contaminations (AMCs) in the outside air is estimated and a required flow rate of the chemical liquid is supplied so that it becomes possible to reduce a flow rate of the chemical liquid markedly.
In addition, the control by employing the electric conductivity meter 15 provides a high controllability so that it becomes possible to reduce a replacement frequency and a maintenance frequency of the members .
[0063] Additionally, the pure water is continuously supplied to the pre-stage air washer 11 and the post-stage air washer 13 so that it becomes possible to prevent re-scattering of the airborne molecular contaminations (AMCs) removed by the pre-stage air washer 11 and to prevent an occurrence of scale.
[0064] Additionally, a flow rate of the absorbent passed through the ion exchange resin 14 is very small (in the example, 1/30 of the amount of the absorbent supplied to the post-stage gas-liquid contact material 24) and its concentration is low so that it becomes possible to reduce a replacement frequency and a maintenance frequency of the ion exchange resin 14.
[0065] Additionally, because the pre-stage air washer 11 removes the airborne molecular contaminations (AMCs) by a neutralization reaction, it becomes possible to make the removal ability of the airborne molecular contaminations (AMCs) high and to prevent the re-scattering. As described in the example, employing the potassium dioxide (KOH) as the

chemical liquid makes it possible to improve safety because the potassium dioxide (KOH) is not acted as a contaminant source.
[0066] The above described removing system 10 for contaminant in air, according to the embodiment of the present invention may be modified in various ways. For example, as shown in FIG. 3, in the post-stage air washer 13, a receiving part 32 having a capacity smaller than that of the post-stage water tank 25 may be arranged between the post-stage gas-liquid contact material 24 and the post-stage water tank 25, and a water supply equipment 33 (a water supply pump 34 and a water supply pipe 35) configured to send the absorbent from the receiving part 32 to the ion exchange resin 14 may be provided. By such a configuration, the absorbent dropped on the post-stage gas-liquid contact material 24 is collected in the receiving part 32 before fallen in the post-stage water tank 25 and then passed through the ion exchange resin 14 so that the electric conductivity meter 15 can immediately detect an increase in electric conductivity of the absorbent after passed through the ion exchange resin 14. This makes it possible to rapidly supply a required flow rate of the chemical liquid from the chemical liquid supply device 12 to the absorbent in the circulation pipe 21 depending on the suddenly increase in electric conductivity so that the responsiveness can be improved.
[0067] In the above described removing system 10 for contaminant in air, according to the embodiment of the present invention, the pure water is supplied to the pre-stage air washer 11 and the post-stage air washer 13 through the post-stage air washer 13. However, the present invention is not limited to the above configuration.
[0068] For example, as shown in FIG. 4, without providing the communication pipe 26 between the pre-stage water tank

18 and the post-stage water tank 25, the pure water may be supplied to the water tanks 18 and 25 through the respective water supply pipes 36 and 31 separately.
[0069] Alternatively, as .shown in FIG. 5, without providing the first circulation pipe 28 around the post-stage water tank 25, the pure water may be directly supplied to the post-stage gas-liquid contact material 24 through the replenishment water pipe 37 and the pure water may be supplied from the post-stage water tank 25 to the pre-stage water tank
18 through the communication pipe 26.
[0070] Alternatively, as shown in FIG. 6, without providing the communication pipe 2 6 between the pre-stage water tank 18 and the post-stage water tank 25, the pure water may be supplied to the pre-stage gas-liquid contact material 17 and the post-stage gas-liquid contact material 24 through the respective replenishment water pipes 38 and 37 separately In this case, the pre-stage absorbent circulation equipment
19 and the first circulation pipe 28 around the post-stage
water tank 25 are not provided.
[0071] The above described removing system 10 for contaminant in air, according to the embodiment of the present invention has the two-stage air washer including the pre-stage air washer 11 and the post-stage air washer 13. However, as shown in FIG. 7, a removing system 40 may have a three-stage air washer including the pre-stage air washer 11, the post-stage air washer 13 and a middle-stage air washer 41 arranged between the pre-stage and the post-stage air washers 11 and 13.
[0072] In the above modified example, the middle-stage air washer 41 includes a middle-stage gas-liquid contact material 42, a middle-stage water tank 43 and a middle-stage absorbent circulation equipment 44. Between the middle-stage water

tank 43 and the post-stage water tank 25, a first communication pipe 45 is provided, and between the pre-stage water tank 18 and the post-stage water tank 25, a second communication pipe 46 is provided. The middle-stage absorbent circulation equipment 44 includes a circulation pipe 47 arranged from the middle-stage water tank 43 to an upper portion of the middle-stage gas-liquid contact material 42 and a circulation pump 48 provided at a middle of the circulation pipe 47.
[0073] Between the chemical liquid supply device 12 and the pre-stage circulation pipe 21, the chemical liquid supply pipe 23 is connected such that the chemical liquid of alkaline solution is replenished from the chemical liquid supply device 12 to the absorbent in the pre-stage circulation pipe 21 through the chemical liquid supply pipe 23. Between the chemical liquid supply device 12 and the middle-stage circulation pipe 47, a chemical liquid replenishment pipe 49 is connected such that the chemical liquid of acidic solution is replenished from the chemical liquid supply device 12 to the absorbent in the middle-stage circulation pipe 47 through the chemical liquid replenishment pipe 49.
[0074] The ion exchange resin 14 includes both of a cation exchange resin 14a and an anion exchange resin 14b. The electric conductivity meter 15 includes a first electric conductivity meter 15a provided at the downstream side of the cation exchange resin 14a and a second electric conductivity meter 15b provided at the downstream side of the anion exchange resin 14b. The first electric conductivity meter 15a and the second electric conductivity meter 15b are electrically connected to the control unit 16, and the control unit 16 is electrically connected to the chemical liquid supply device 12.
[0075] In the removing system 40 for contaminant in air, having the above configuration, as shown by the thick line

arrow in FIG. 7, the outside air to be treated is introduced in the above chamber (not shown) , passed through the pre-stage gas-liquid contact material 17, and then the air and the absorbent are brought into gas-liquid contact so that an acidic substance contained in the air is dissolved into the absorbent and then removed.
[0076] After passed through the pre-stage air washer 11, the air is flowed into the middle-stage air washer 41, passed through the middle-stage gas-liquid contact material 42, and then the air and the absorbent are brought into gas-liquid contact so that an alkaline substance contained the air is dissolved into the absorbent and then removed.
[0077] After passed through the middle-stage air washer 41, the air is flowed into the post-stage air washer 13, passed through the post-stage gas-liquid contact material 24, and then the air and the absorbent are brought into gas-liquid contact so that airborne molecular contaminations (AMCs) contained the air are dissolved into the absorbent and then removed. After that, a clean air passed through the post-stage gas-liquid contact material 24 and from which the airborne molecular contaminations (AMCs) are removed is supplied to the. clean room (not shown) as shown by the thick solid line arrow in FIG. 7.
[0078] The pure water as the absorbent is supplied to the post-stage water tank 25 through the water supply pipe 31, and the pure water supplied to the post-stage water tank 25 is supplied to the pre-stage water tank 18 and the middle-stage water tank 43 through the second communication pipe 46 and the first communication pipe 45, respectively.
[0079] On the other hand, in the post-stage air washer 13, a part of the absorbent (the pure water) pumped from the post-stage water tank 25 is passed through the cation exchange

resin 14a and the anion exchange resin 14b, and then their electric conductivities are measured by the first electric conductivity meter 15a and the second electric conductivity meter 15b. The measured values are sent to the control unit 16. The control unit 16 estimates a concentration of the airborne molecular contaminations (AMCs) contained in the outside air flowed into the pre-stage air washer 11 based on the measured values of the electric conductivities by the first electric conductivity meter 15a and the second electric conductivity meter 15b, and calculates an flow rate of the chemical liquid to be supplied to each of the pre-stage air washer 11 and the middle-stage air washer 41.
[0080] According to the above described removing system 40 for contaminant in air, providing the pre-stage air washer 11 and the middle-stage air washer 41 makes it possible to remove the airborne molecular contaminations (AMCs) including both the alkaline substance and the acidic substance contained in the outside air with a high efficiency and to improve the removal rate of the airborne molecular contaminations (AMCs).
[0081] The above embodiments of the present invention describe the exemplary cases where the removing system for contaminant in air, according to the embodiment of the present invention is applied to the outside air conditioner equipped in order to introduce the outside air into the clean room of the semiconductor factory or the liquid crystal factory. However, they are only exemplified, and it goes without saying that the present invention can be applied to the general air conditioner for other use in a manufacturing factory of electronic components and electronic devices.
DESCRIPTION OF NUMERALS [0082] 10 a removing system for contaminant in air

11 a pre-stage air washer
12 a chemical liquid supply device
13 a post-stage air washer
14 an ion exchange resin

16 a control unit
17 a pre-stage gas-liquid contact material
18 a pre-stage water tank
19 a pre-stage absorbent circulation equipment

24 a post-stage gas-liquid contact material
25 a post-stage water tank
27 a post-stage absorbent circulation equipment
32 a receiving part
33 a water supply equipment
38 a replenishment water pipe
41 a middle-stage air washer
42 a middle-stage gas-liquid contact material
43 a middle-stage water tank
44 a middle-stage absorbent circulation equipment

CLAIMS:
1. A removing system for contaminant in air, in which the
air and an absorbent are brought into gas-liquid contact to
dissolve the contaminant contained in the air into the
absorbent and remove it, the removing system comprising:
a pre-stage air washer which employs a chemical liquid containing at least either an alkaline solution or an acidic solution as the absorbent;
a chemical liquid supply device configured to supply the chemical liquid to the pre-stage air washer;
a post-stage air washer which employs a pure water as the absorbent, the post-stage air washer being arranged at a downstream side of the pre-stage air washer in an air flow direction;
an ion exchange resin through which the absorbent of the post-stage air washer is passed, the ion exchange resin containing at least either a cation exchange resin or an anion exchange resin; and
a control unit configured to estimate a concentration of the contaminant contained in the air flowed into the pre-stage air washer based on an electric conductivity of the absorbent passed through the ion exchange resin and then to calculate a flow rate of the chemical liquid to be supplied from the chemical liquid supply device to the pre-stage air washer.
2. The removing system for contaminant in air, according
to claim 1,
wherein the pre-stage air washer includes:
a pre-stage gas-liquid contact material by which the air and the absorbent are brought into gas-liquid contact;
a pre-stage water tank configured to store the absorbent passed through the pre-stage gas-liquid contact material; and
a pre-stage absorbent circulation equipment configured to circulate the absorbent between the pre-stage water tank and the pre-stage gas-liquid contact material,
the post-stage air washer includes:

a post-stage gas-liquid contact material by which the air and the absorbent are brought into gas-liquid contact;
a post-stage water tank configured to store the absorbent; passed through the post-stage gas-liquid contact material; and
a post-stage absorbent circulation equipment configured to circulate the absorbent between the post-stage water tank and the post-stage gas-liquid contact material and between the post-stage water tank and the ion exchange resin, and
the chemical liquid is supplied from the chemical liquid supply device to the pre-stage circulation equipment or the pre-stage water tank.
3. The removing system for contaminant in air, according to claim 1,
wherein the pre-stage air washer includes:
a pre-stage gas-liquid contact material by which the air and the absorbent are brought into gas-liquid contact;
a pre-stage water tank configured to store the absorbent passed through the pre-stage gas-liquid contact material; and
a pre-stage absorbent circulation equipment configured to circulate the absorbent between the pre-stage water tank and the pre-stage gas-liquid contact material,
the post-stage air washer includes:
a post-stage gas-liquid contact material by which the air and the absorbent are brought into gas-liquid contact;
a post-stage water tank arranged below the post-stage gas-liquid contact material;
a receiving part having a capacity smaller than that of the post-stage water tank and arranged between the post-stage gas-liquid contact material and the post-stage water tank such that the absorbent passed through the post-stage gas-liquid contact material is temporarily received and the absorbent overflowed from the receiving part is stored in the post-stage water tank;
a water supply equipment configured to send the absorbent

from the receiving part to the ion exchange resin; and
a post-stage absorbent circulation equipment configured
to circulate the absorbent between the post-stage water tank
and the post-stage gas-liquid contact material, and
the chemical liquid is supplied from the chemical liquid
supply device to the pre-stage absorbent circulation
equipment or the pre-stage water tank.
4. A removing system for contaminant in air, in which the air and an absorbent are brought into gas-liquid contact to dissolve the contaminant contained in the air into the absorbent and remove it, the removing system comprising:
a pre-stage air washer which employs a chemical liquid containing one of an alkaline solution and an acidic solution as the absorbent;
a middle-stage air washer which employs a chemical liquid containing the other of the alkaline solution and the acidic solution as the absorbent, the middle-stage air washer being arranged at a downstream side of the pre-stage air washer in an air flow direction;
a chemical liquid supply device configured to supply the chemical liquid to the pre-stage air washer and the middle-stage air washer;
a post-stage air washer which employs a pure water as the absorbent, the post-stage air washer being arranged at a downstream side of the middle-stage air washer in the air flow direction;
a cation exchange resin and an anion exchange resin, the absorbent of the post-stage air washer being passed through the cation exchange resin and the anion exchange resin; and
a control unit configured to estimate a concentration of the contaminant contained in the air flowed into the pre-stage air washer based on an electric conductivity of the absorbent passed through each of the cation exchange resin and the anion exchange resin and then to calculate a flow rate of the chemical liquid to be supplied from the chemical liquid supply

device to each of the pre-stage air washer and the middle-stage air washer.
5. The removing system for contaminant in air, according to claim 4,
wherein the pre-stage air washer includes:
a pre-stage gas-liquid contact material by which the air and the absorbent are brought into gas-liquid contact;
a pre-stage water tank configured to store the absorbent passed through the pre-stage gas-liquid contact material; and
a pre-stage absorbent circulation equipment configured to circulate the absorbent between the pre-stage water tank and the pre-stage gas-liquid contact material,
the middle-stage air washer includes:
a middle-stage gas-liquid contact material by which the air and the absorbent are brought into gas-liquid contact;
a middle-stage water tank configured to store the absorbent passed through the middle-stage gas-liquid contact material; and
a middle-stage absorbent circulation equipment configured to circulate the absorbent between the middle-stage water tank and the middle-stage gas-liquid contact material,
the post-stage air washer includes:
a post-stage gas-liquid contact material by which the air and the absorbent are brought into gas-liquid contact;
a post-stage water tank configured to store the absorbent passed through the post-stage gas-liquid contact material; and
a post-stage absorbent circulation equipment configured to circulate the absorbent between the post-stage water tank and the post-stage gas-liquid contact material, between the post-stage water tank and the cation exchange resin and between the post-stage water tank and the anion exchange resin.