JP4506093B2 - Exhaust gas treatment method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an exhaust gas treatment method in which an exhaust gas containing an acidic gas is brought into contact with an alkaline aqueous solution.
[0002]
[Prior art]
In general, a glass body optical fiber is manufactured by drawing a glass base material that is heated (transparent) by sintering a glass particulate deposit. VAD method (Vapor phase Axial Deposition), OVD method (Outer Vapor phase Deposition), MCVD method (Modified Chemical Vapor phase Deposition), etc. The gas phase synthesis method is known.
[0003]
In such a gas phase synthesis method, oxygen, hydrogen, and glass source gas are introduced into a burner having a plurality of ports, glass fine particles are generated by a hydrolysis reaction, and deposited on the outside of the glass rod. A fine particle deposit is formed, or oxygen and a raw material gas are introduced into a glass tube, and the glass tube is heated to generate glass fine particles by an oxidation reaction and is laminated on the inner surface of the glass tube.
[0004]
Silicon tetrachloride (SiCl ₄ ), germanium tetrachloride (GeCl ₄ ), or the like is used as a raw material gas for generating glass fine particles, and silicon dioxide (SiO ₂ ), germanium dioxide (GeO ₂ ) is obtained by hydrolysis or oxidation of the raw material gas. ) And the like are produced.
Therefore, the exhaust gas discharged from such a gas phase synthesis method or a device that has made glass particle deposits transparent, includes glass particles such as silicon dioxide and germanium dioxide, hydrogen chloride (HCl), chlorine Chlorine compounds such as (Cl ₂ ) are included.
[0005]
In order to treat the exhaust gas as described above, a particulate water droplet is entrained in the exhaust gas, and a dust collection process is performed to charge and collect the solid particulate accompanied by the particulate water droplet. There has been proposed a treatment method for performing a neutralization step of supplying an alkaline liquid to remove a chlorine compound (see, for example, Patent Document 1).
[0006]
[Patent Document 1]
Japanese Examined Patent Publication No. 6-85889 [0007]
[Problems to be solved by the invention]
By the way, in the conventional exhaust gas processing method as described above, in order to suppress the corrosion of the dust collector that charges and collects solid particulates, before the dust collection process in the dust collector, for example, chloride contained in the exhaust gas It is desirable to neutralize acidic gases such as hydrogen (HCl), chlorine (Cl ₂ ), hydrogen fluoride (HF) to some extent.
For this reason, it is conceivable that the exhaust gas is washed with an alkaline solution such as sodium hydroxide (NaOH) to neutralize the acidic gas as much as possible before the dust collection step.
However, in this case, SiO ₂ in the exhaust gas reacts with sodium hydroxide to form an insoluble solid such as sodium silicate (Na ₂ SiO ₃ ) that is difficult to precipitate or filter in the cleaning exhaust liquid. Is done.
Thus, when an insoluble solid is generated, it becomes difficult to treat the waste liquid, and it may cause clogging of a flow path such as a pipe or a pump.
[0008]
The present invention provides an exhaust gas treatment method capable of treating exhaust gas while preventing corrosion of the apparatus due to acidic gas contained in the exhaust gas and preventing blockage of the flow path due to generation of solids that are difficult to treat. It is intended to provide.
[0009]
[Means for Solving the Problems]
Method of processing an exhaust gas according to the present invention for achieving the above object, is discharged by a gas phase synthetic method for generating a glass soot in the optical fiber manufacturing process, glass particles and hydrogen chloride or chlorine containing silicon dioxide After the acidic exhaust gas containing benzene is brought into contact with an alkaline aqueous solution of sodium hydroxide having a pH value of 10.0 or more and 13.0 or less, fine particles contained in the exhaust gas are captured by Coulomb force. It is said.
[0010]
As the alkaline aqueous solution, sodium hydroxide is preferably used from the viewpoint of cost and the like. By selecting the use conditions, the exhaust gas containing silicon dioxide can be treated without any problem.
[0012]
Further, in the processing method of the exhaust gas, after capturing the fine particles, it is preferable to neutralize by contacting the exhaust gas to the alkaline aqueous solution.
[0013]
In the above exhaust gas treatment method, at least one of the group consisting of the density, viscosity, electrical conductivity, turbidity, and pH of the alkaline aqueous solution is measured, and the measured value becomes a predetermined value or less. In addition, it is preferable to exchange all or part of the alkaline aqueous solution.
This replacement operation is preferably performed on the alkaline aqueous solution used before capturing the fine particles, but may be performed on the alkaline aqueous solution used after capturing the fine particles. You can go.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment of an exhaust gas treatment method according to the present invention will be described with reference to FIG.
In the exhaust gas treatment method of the present embodiment, an alkaline aqueous solution having a pH value of 10.0 or more and 13.0 or less is brought into contact with an exhaust gas containing an acidic gas generated by a gas phase synthesis method or the like. It is characterized by raising the pH value of the gas.
[0015]
FIG. 1 is a configuration diagram of an exhaust gas processing apparatus for carrying out the exhaust gas processing method of the present embodiment.
As shown in FIG. 1, the exhaust gas treatment device includes a pretreatment device 100, a dust collector 200, and a neutralization device 300.
The pretreatment apparatus 100 has a container 101, and the container 101 stores an alkaline aqueous solution 102. The container 101 has an exhaust gas supply port 103, and a first pipe 104 is connected to the exhaust gas supply port 103. Exhaust gas 1 from an apparatus (not shown) used when performing a gas phase synthesis method such as the MCVD method is fed into the first pipe 104. Then, the exhaust gas 1 sent into the first pipe 104 is supplied into the container 101 through the first pipe 104.
[0016]
The alkaline aqueous solution 102 stored in the container 101 of the pretreatment device 100 is made of a sodium hydroxide aqueous solution, and the pH value thereof is 11.5 or more and 12.5 or less.
In addition, one end of a pipe line 108 having a pump 105 is connected to the container 101 at a storage portion of the alkaline aqueous solution 102. The other end of the pipe 108 is disposed in the upper space of the container 101, and the alkaline aqueous solution 102 pumped up by the pump 105 is ejected from the upper part of the container 101. By this ejection, the exhaust gas 1 and the alkaline aqueous solution 102 are positively brought into contact with each other.
[0017]
One end of a second pipe 107 is connected to the upper end of the container 101 of the pretreatment device 100. The second pipe 107 has a valve 113, and the other end is connected to the container 201 of the dust collector 200.
Then, the exhaust gas 1 processed in the container 101 of the pretreatment device 100 is sent into the container 201 of the dust collector 200 through the second pipe 107.
[0018]
The dust collector 200 has a plurality of dust collecting electrodes 202 arranged in a container 201.
The dust collector 200 captures particulates (for example, silicon dioxide and germanium dioxide) in the exhaust gas 1 sent from the pretreatment device 100 by the dust collecting electrode 202 in the container 201 by Coulomb force.
[0019]
One end of a third pipe 207 having a valve 114 is connected to the container 201 of the dust collector 200.
The other end of the third pipe 207 is connected to the container 301 of the neutralizer 300, and the exhaust gas 1 from which fine particles have been removed by the dust collector 200 is contained in the container. 301 is led.
[0020]
The container 301 of the neutralizer 300 stores an alkaline aqueous solution 302. As the alkaline aqueous solution 302, a sodium hydroxide aqueous solution is used. The pH value of the sodium hydroxide aqueous solution used as the alkaline aqueous solution 302 is approximately 13.0 or more.
One end of a pipe line 304 having a pump 303 is connected to the container 301 of the neutralization apparatus 300 at a storage portion of the alkaline aqueous solution 302. The other end of the conduit 304 is disposed in the upper space of the container 301, and the alkaline aqueous solution 302 pumped up by the pump 303 is ejected from the upper part of the container 301. By this ejection, the exhaust gas 1 and the alkaline aqueous solution 302 are positively brought into contact with each other.
[0021]
Then, the exhaust gas 1 sent from the third pipe 207 is completely neutralized with the acidic gas component by the alkaline aqueous solution 302 in the container 301.
Further, a fourth pipe 307 having an exhaust fan 306 is connected to the neutralizer 300 near the upper end of the container 301.
[0022]
Next, an exhaust gas processing method using the above-described exhaust gas processing apparatus will be described.
The exhaust gas 1 discharged from the apparatus that performs the gas phase synthesis method is sent into the container 101 of the pretreatment apparatus 100 through the first pipe 104. The exhaust gas 1 contains fine particles such as silicon dioxide and germanium dioxide, and acidic gases such as hydrogen chloride, hydrogen fluoride, and chlorine.
[0023]
The exhaust gas 1 sent into the container 101 comes into contact with the alkaline aqueous solution 102 stored in the container 101, so that the acidic gas is neutralized to some extent.
At that time, by maintaining the pH value of the alkaline aqueous solution 102 made of an aqueous sodium hydroxide solution at 10.0 or more and 13.0 or less (sodium hydroxide concentration is about 4 × 10 ⁻⁴ % to 0.4%), The acid gas can be removed while preventing the formation of an insoluble solid (for example, sodium silicate).
When the pH value of the alkaline aqueous solution 102 is larger than 13.0, sodium silicate is generated, and the first pipe 104 and the second pipe 107 are likely to be blocked at a place where the container 101 is connected. If the pH value of the alkaline aqueous solution 102 is smaller than 10.0, the neutralization effect is small, and corrosion of the second piping 107 and the dust collecting electrode 202 in the dust collecting device 200 cannot be prevented. Moreover, the amount of waste liquid of the alkaline aqueous solution 102 increases.
[0024]
The exhaust gas 1 cleaned by the pretreatment device 100 is sent into the container 201 of the dust collector 200 through the second pipe 107.
The exhaust gas 1 sent into the container 201 is captured by the dust collection electrode 202 arranged in the container 201 by the Coulomb force in the fine particles contained in the gas.
[0025]
At that time, since the pH value of the exhaust gas 1 fed into the container 201 of the dust collector 200 is changed to the alkali side in the pretreatment device 100, the exhaust gas 1 of the container 201 and the dust collection electrode 202 inside thereof is changed. Corrosion due to the exhaust gas 1 is suppressed.
The exhaust gas 1 from which the fine particles have been removed by the dust collector 200 is sent into the container 301 of the neutralizer 300 via the third pipe 207.
[0026]
The exhaust gas 1 sent into the container 301 of the neutralization apparatus 300 is sufficiently neutralized by the alkaline aqueous solution 302 in the container 301.
The neutralized exhaust gas 1 is then exhausted through the fourth pipe 307 by the exhaust fan 306.
[0027]
Thus, according to the exhaust gas treatment method described above, an insoluble solid is generated by bringing the exhaust gas 1 containing an acidic gas into contact with an alkaline aqueous solution having a pH value of 10.0 to 13.0. The exhaust gas 1 can be neutralized to some extent without causing it.
Thereby, it is possible to reliably prevent problems such as blockage or corrosion in the flow path for guiding the exhaust gas 1 to the subsequent processing apparatus and the dust collecting apparatus 200 that is the subsequent processing apparatus.
[0028]
Moreover, it is desirable to replace the alkaline aqueous solutions 102 and 302 stored in the respective containers 101 and 301 of the pretreatment apparatus 100 and the neutralization apparatus 300 before the salt concentration becomes 5 to 7%. For example, when the salt concentration of the alkaline aqueous solution 102 increases to exceed 7%, the vicinity of the connection point between the first pipe 107 and the container 101 is likely to be blocked due to the precipitation of the salt.
[0029]
For this reason, it is desirable to measure the concentration of all the salts that may be precipitated in both or either one of the respective containers 101 and 301 of the pretreatment apparatus 100 and the neutralization apparatus 300. However, it is difficult to grasp all of the salts, and the cost for that is greatly increased. Therefore, a numerical value correlated with the salt concentration of the alkaline aqueous solutions 102 and 302 is measured. The numerical value correlated with the salt concentration is the density, viscosity, electrical conductivity, turbidity, and pH value of the aqueous solution, and at least one of these groups is appropriately measured.
Then, the alkaline aqueous solutions 102 and 302 are observed and exchanged as appropriate so that the measured value becomes a predetermined value or less. As an exchange method, all may be exchanged at once, or a part may be exchanged by extracting and replenishing a predetermined amount.
[0030]
The measurement method may be online or offline. When performing on-line, for example, an electric conductivity meter is placed in the alkaline aqueous solutions 102 and 302, and the electric conductivities of the alkaline aqueous solutions 102 and 302 are constantly measured. Moreover, when performing off-line, for example, appropriate amount of alkaline aqueous solution 102,302 is taken out every predetermined time, and the turbidity of this taken-out alkaline aqueous solution 102,302 is measured with a turbidimeter.
[0031]
In addition, it is good for the predetermined value used as the threshold value of each measured value to obtain | require beforehand each value in salt concentration of the grade which does not obstruct | occlude piping beforehand by experiment.
[0032]
Thus, by observing the salt concentration, the alkaline aqueous solution can be exchanged at an appropriate timing. Therefore, it is effective to dispose of alkaline aqueous solution with neutralization ability remaining, or to continue to use alkaline aqueous solution that has lost proper neutralization ability to cause clogging of piping and equipment. Can be prevented.
[0033]
Further, when the dust collecting electrode 202 and the like in the dust collecting apparatus 200 are washed with an alkaline aqueous solution, the alkaline aqueous solution can be exchanged at an appropriate timing by observing the salt concentration as described above.
[0034]
【The invention's effect】
According to the exhaust gas processing method of the present invention, the exhaust gas is processed while preventing the device from being corroded by the acidic gas contained in the exhaust gas and preventing the blockage of the flow path due to the generation of solids that are difficult to process Can do.
[Brief description of the drawings]
FIG. 1 is a configuration diagram showing an example of an exhaust gas treatment apparatus for carrying out an exhaust gas treatment method according to the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Exhaust gas 100 Pretreatment apparatus 104 1st piping 107 2nd piping 200 Dust collector 207 3rd piping 300 Neutralization device 307 4th piping 102,302 Alkaline aqueous solution

Claims (1)

Is discharged by a gas phase synthetic method for generating a glass soot in the optical fiber manufacturing process, and glass particles comprising silicon dioxide, the exhaust gas of acidic containing hydrogen chloride or chlorine, pH value of 10.0 or more and 13 A method for treating exhaust gas, comprising: contacting fine particles contained in the exhaust gas with Coulomb force after contacting with an alkaline aqueous solution of 0.0 or less sodium hydroxide.

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