JP2002079255A - Electrodialytic method and apparatus therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance the separation and recovery effect of HCl to obtain high purity HCl in electrodialysis using a proton permselective cation exchange membrane. SOLUTION: HCl gas in an acidic gas component contained in exhaust gas is once absorbed by a washing liquid and HCl is separated and recovered from the washing liquid after the absorption of the HCl gas by electrolysis using the proton permselective cation exchange membrane C1 and an anion exchange membrane A. In this case, a plurality of the proton permselective cation exchange membranes C1 are inserted in the gap between the anion exchange membranes A mutually forming a pair.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a combustion facility including a refuse incineration facility, an electrodialysis method for deoxidizing acidic gas components in exhaust gas discharged from a chemical plant, and an apparatus therefor.

[0002]

2. Description of the Related Art Conventionally, as a method of deoxidizing acidic gas components such as HCl and SOx contained in exhaust gas discharged from waste incineration facilities (general waste or industrial waste incineration plant, etc.). Most commonly adopted is a method in which these acidic gas components are washed with water and adjusted to a pH of 6 to 7 by neutralization of an alkaline agent such as caustic soda to convert them into salts.

This conventional method will be described with reference to a system configuration diagram shown in FIG. The conventional system shown in FIG. 3 is configured to include a first washing tower 51 and a second washing tower 52. Exhaust gas from a refuse incinerator (not shown) is introduced into the top of the first cleaning tower 51 through a flue 53, and a cleaning liquid 54 stored in a lower portion of the first cleaning tower 51.
Is sprayed from a spray nozzle 56 disposed above the first cleaning tower 51 by a circulation pump 55, whereby acid gas components (HCl, SOx, etc.) in the exhaust gas introduced into the first cleaning tower 51 are removed. It is absorbed by the cleaning liquid 54. Since the pH of the cleaning liquid 54 becomes small with the absorption of the acidic gas component, caustic soda is replenished from the caustic soda head tank 57 into the circulating cleaning liquid 54, and the pH of the cleaning liquid 54 is maintained at 6 to 7. The first washing tower 5
Excess cleaning liquid 54 in 1 is discharged out of the system by a discharge pump 58.

[0004] The exhaust gas leaving the first washing tower 51 is discharged from the flue 5
9 to the second washing tower 52. The exhaust gas introduced into the second cleaning tower 52 still contains an acidic gas component, and the cleaning liquid 60 stored in the lower part of the second cleaning tower 52 is circulated by a circulation pump 61 to the second cleaning tower 52. Is introduced from above, so that it is brought into gas-liquid contact with the exhaust gas and the acidic gas component in the exhaust gas is absorbed by the cleaning liquid 60. Since the pH of the cleaning liquid 60 also becomes small with the absorption of the acidic gas component, the circulating cleaning liquid 60 is replenished with caustic soda from the caustic soda head tank 57 similarly to the first cleaning tower 51, and the pH of the cleaning liquid 60 is increased. Are held at 6 to 7. Then, the exhaust gas that has exited from the second washing tower 52 is discharged from the flue 63 to the atmosphere through a chimney via a gas reheater (not shown) and the like. Note that the first washing tower 51 and the second washing tower 52 are not limited to spray towers, and various other systems such as a system filled with a filler such as Raschig rings can be used.

However, the conventional method shown in FIG. 3 has the following problems. (1) Caustic soda is required to neutralize acidic gas components. (2) Salt is generated by neutralization with caustic soda, but this salt cannot be removed by conventional wastewater treatment equipment, and when the treated water is discharged into rivers, etc., a problem of salt damage occurs in some areas. Might be. (3) As a method for recycling the generated salt, there is an evaporation to dryness technique. However, when this technique is applied, enormous energy is required. (4) As a method of decomposing the generated salt into acid and alkali and reusing the same, there is a bipolar membrane electrodialysis method. However, this method is expensive because a bipolar membrane is used, and the decomposition of acid and alkali is also required. There are also problems with purity and concentration, and utilization has not progressed. (5) It is conceivable to use a desalination technique using an RO (Reverse Osmosis) membrane, but this method not only requires a running cost but also leaves a problem of disposal of the concentrated salt.

[0006] In order to solve such a problem, the applicant of the present invention temporarily absorbs HCl gas in an acid gas into a cleaning solution, and forms a proton-selective cation exchange membrane from the cleaning solution after the absorption of HCl. HCl using electrodialysis
An exhaust gas treatment method that separates and recovers the same has already been proposed (Japanese Patent Application No. 11-138257). According to the exhaust gas treatment method according to the invention of the prior application, the amount of alkaline agent such as caustic soda for neutralization can be extremely reduced, the discharge of salt can be reduced, and a highly pure acid is recovered. It has the advantage of being able to be recycled.

[0007]

However, in the above-mentioned prior application, the electrodialysis apparatus has a structure in which proton-selective cation exchange membranes and anion exchange membranes are alternately arranged and the HCl gas component absorption membrane is used. Since the subsequent washing solution is introduced into every other compartment, the proton-selective cation exchange membrane can block cations other than protons (heavy metal ions) to a certain level. There was a problem that leakage of a very small amount of cations was inevitable. For this reason, further improvement for obtaining a concentrated hydrochloric acid with higher purity while suppressing the leak rate is being demanded.

The present invention has been made in view of such circumstances, and in a device in which electrodialysis is performed using a proton-selective cation exchange membrane, the efficiency of separation and recovery of HCl is increased to achieve a higher level. It is an object of the present invention to provide an electrodialysis method and an apparatus capable of obtaining HCl having a purity.

[0009]

In order to achieve the above object, an electrodialysis method according to a first aspect of the present invention comprises:
After the HCl gas in the acidic gas component contained in the exhaust gas is once absorbed into the cleaning solution, HCl is removed from the cleaning solution after the absorption of the HCl gas by electrodialysis using a proton-selective cation exchange membrane and an anion exchange membrane. In the electrodialysis method for separating and recovering, a plurality of proton-selective cation exchange membranes are interposed between anion exchange membranes forming a pair.

[0010] In the present invention, in the first stage, HC of acid gas components such as HCl and SOx contained in exhaust gas is used.
1 gas is selectively absorbed by the cleaning solution, and in the second step, the proton is selectively absorbed by the proton-permeable cation exchange membrane through the proton-permeable cation exchange membrane. HCl is recovered and concentrated by combining hydrogen ions that have passed through the permselective cation exchange membrane with chloride ions that have passed through the anion exchange membrane. Thus, the deoxidizing treatment can be performed without neutralizing the HCl gas in the exhaust gas. In this case, since a plurality of proton selectively permeable cation exchange membranes are interposed between the anion exchange membranes forming a pair with each other,
It is possible to more reliably suppress the passage of a trace amount of heavy metal ions through the proton-selective cation exchange membrane, thereby increasing the efficiency of separating and recovering HCl and recovering high-purity concentrated hydrochloric acid.

Next, an electrodialysis apparatus according to a second aspect of the present invention relates to an apparatus for specifically performing the electrodialysis method according to the first aspect of the present invention, wherein HCl contained in an acidic gas component contained in exhaust gas. An electrodialysis apparatus comprising: an exhaust gas cleaning unit that absorbs gas into a cleaning solution; and an electrodialysis unit that introduces a cleaning solution after absorbing the HCl gas extracted from the exhaust gas cleaning unit, wherein the electrodialysis units are paired with each other. A plurality of units comprising a plurality of proton selectively permeable cation exchange membranes disposed between the anion exchange membranes formed are connected in series to form a compartment, and the exhaust gas is provided to each unit of the electrodialysis unit. The cleaning liquid extracted from the cleaning unit is introduced.

In the present invention, the exhaust gas is supplied to an exhaust gas cleaning section.
When introduced into the exhaust gas, HCl, SO contained in the exhaust gas
HCl gas of acid gas components such as x is exhaust gas cleaning
Is selectively absorbed in the part. Next, this exhaust gas cleaning unit
Cleaning solution that has absorbed HCl gas by
It is. In this electrodialysis unit, a pair of shaded
Multiple proton permselective cations between on-exchange membranes
Multiple units with exchange membranes are connected in series.
Cleaning chamber after absorption of HCl gas
When hydrogen is introduced into each of these units, hydrogen
On passes through proton-selective cation exchange membranes
Does not pass through the anion exchange membrane, and ⁺, K⁺, M
g²⁺, Ca²⁺Cations are proton-selective permeable cations
Each unit does not pass through the ion exchange membrane
Hydrogen ions passed through a proton-permeable cation exchange membrane
And chlorine ions that have passed through the anion exchange membrane
By doing so, HCl is recovered and concentrated. Thus,
Deoxidizing process without neutralizing HCl gas in exhaust gas
It is possible to do. In this case, in each unit
Is a multi-layer process between anion exchange membranes that are paired with each other.
Ton permselective cation exchange membrane is interposed,
Trace amounts through this proton-selective cation exchange membrane
More reliably prevent heavy metal ions from passing through
High concentration of high-purity concentrated salt
The acid can be recovered.

According to a third aspect of the present invention, in the second aspect, the intermediate liquid is circulated in a compartment interposed between the proton-permeable cation exchange membranes, and concentrated HCl is supplied to the intermediate liquid. It was done. By doing so, concentrated hydrochloric acid with higher purity can be obtained.

Next, a fourth invention uses the electrodialysis apparatus according to the second invention or the third invention in an exhaust gas treatment device in a refuse incineration plant. By using the waste gas incinerator as described above, the deoxidizing treatment of the acidic gas component in the exhaust gas discharged from the waste incinerator can be effectively performed.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, specific embodiments of the electrodialysis method and apparatus according to the present invention will be described with reference to the drawings.

FIG. 1 shows a system configuration diagram of an exhaust gas treatment apparatus according to one embodiment of the present invention, and FIG. 2 shows a detailed structure of an electrodialysis tank.

The exhaust gas treatment apparatus of this embodiment includes a first cleaning tower (exhaust gas cleaning section) 11, a second cleaning tower 12, and an electrodialysis tank (electrodialysis section) 13. Exhaust gas sent from a refuse incineration facility (not shown) via a flue 14 flows from the top of the first cleaning tower 11 to the first cleaning tower 1.
The washing liquid 15 introduced into the first washing tower 11 and stored in the lower part of the first washing tower 11 is circulated upward by a circulation pump 16 and sprayed into the tower from an upper spray nozzle 17, whereby the first washing tower 11 It absorbs HCl gas in the exhaust gas introduced therein. Since the concentration of HCl in the cleaning solution 15 increases with the absorption of the HCl gas, the concentration is controlled to be in a range of, for example, 0.04 to 10% by weight by treating with an electrodialysis tank 13 described later.
Here, the reason why the HCl concentration was defined in the above range was 0.0%.
When the amount is less than 4% by weight, protons for performing electrodialysis are insufficient, and stable operation of the electrodialysis cannot be performed. When the amount is 10% by weight or more, a decrease in the HCl gas absorption rate becomes large. As the pH of the washing solution becomes more acidic, the SO ₂ component is hardly absorbed by the washing solution, so that only the HCl component can be recovered.

The cleaning liquid 15 after the absorption of the HCl gas is sent by a pump 18 and solid matter (S
After removing harmful substances for stable operation of the electrodialysis tank 13 such as S) and heavy metals, the temperature of the water cooler 20 is reduced to 60%.
The temperature is lowered to not more than ° C. and sent to the electrodialysis tank 13. It goes without saying that there is no problem even if the pretreatment device 19 and the water cooler 20 are installed in reverse order.

In the electrodialysis tank 13, an anode 21 and a cathode 22 are disposed at both ends, respectively, and a proton-selective cation exchange membrane C1 and an anion exchange membrane A described later are interposed between the electrodes 21 and 22. Are provided. Note that at least one cation exchange membrane C2 adjacent to the anode 21 and the cathode 22 is provided. In this way, the cleaning liquid sent through the pretreatment device 19 and the water cooler 20 flows into the stock solution chamber 23, and the cleaning liquid having a low HCl concentration due to the processing in the electrodialysis tank 13 is passed through the pipe 24. 1 Returned to the washing tower 11.

On the other hand, the permeation chamber 25 of the electrodialysis tank 13 is supplied with a lean HC from a HCl tank 26 by a pump 27.
1 solution is supplied. The diluted HCl solution is concentrated by H ⁺ ions and Cl ⁻ ions that pass through the ion exchange membrane from the stock solution chamber 23, and the concentrated HCl solution is returned from the pipe 28 to the HCl tank 26, and a part of the concentrated HCl solution is product HCl. Is drawn out of the pipe 29 from the system.

Various electrolytes are circulated through the liquid contact channel between the anode 21 and the cathode 22 according to the purpose of use. These electrolytes are stored in the circulation tank 31, are sent to the anode 21 side and the cathode 22 side by the pump 32, and return to the circulation tank 31 after exiting the electrodialysis tank 13. The circulation tank 31 and the pump 32 may be provided separately for the anode 21 and the cathode 22 respectively.

In order to absorb acid gas components mainly including SOx and acid gas components such as HCl gas not absorbed in the first cleaning tower 11, the exhaust gas leaving the first cleaning tower 11 is subjected to a flue 33 Is introduced into the second washing tower 12. In the second washing tower 12, the washing liquid 34 stored in the lower part is circulated upward by the circulation pump 35 and is injected, whereby the exhaust gas introduced into the second washing tower 12 is brought into gas-liquid contact, The SO ₂ gas in the exhaust gas and the acidic gas components such as HCl gas not absorbed in the first cleaning tower 11 are absorbed. In order to maintain the pH of the cleaning liquid 34 in the second cleaning tower 12 at 6 to 7, an alkaline agent such as caustic soda is supplied from the head tank 36 to the cleaning liquid 34. Note that this second
The exhaust gas that has exited the washing tower 12 is discharged from a pipe 37 through a gas reheater and the like to a atmosphere from a chimney (neither is shown).

Next, the processing in the electrodialysis tank 13 will be described in more detail with reference to FIG.

In the electrodialysis tank 13, the anode 21
A large number of proton-selective cation exchange membranes C1 and anion exchange membranes A are arranged between the anode and the cathode 22;
A cation exchange membrane C2 is provided on the side close to each of the electrodes 21 and 22.
Are stacked one on another, and a plurality of (two in this embodiment) proton-permeable cation exchange membranes C1, C1 are arranged between the anion exchange membranes A, A forming a pair. ,
A large number of compartments are formed by these ion exchange membranes C1, C2, A.

The washing liquid (aqueous HCl solution) extracted from the first washing tower 11 and sent through the pretreatment device 19 and the water cooler 20 is exchanged with the proton-selective cation exchange membrane C1 by anion exchange. It is supplied into the compartment defined by the membrane A or into the compartment defined by the cation exchange membrane C2 and the anion exchange membrane A (indicated by solid arrows in the figure). By electrodialysis, hydrogen ions H ⁺ in the HCl aqueous solution pass through the proton-selective cation exchange membranes C1 and C1, but do not pass through the anion exchange membrane A. Therefore, in the compartment defined by the proton-selective cation exchange membrane C1 and the anion exchange membrane A or in the compartment defined by the cation exchange membrane C2 and the anion exchange membrane A, two sheets are provided. Hydrogen ions H ⁺ sequentially passing through the proton-selective cation exchange membranes C1 and C1 and chlorine ions Cl passing through the anion exchange membrane A
^- and the HCl is recovered and concentrated tied. The recovered and concentrated HCl is returned from the pipe 28 to the HCl tank 26 as a concentrated HCl solution as described above (indicated by a dashed line arrow in the figure).

An intermediate liquid is circulated in the compartment interposed between the two proton-permeable cation exchange membranes C1 and C1, and only hydrogen ions H ⁺ are selectively moved (two points in the figure). (Shown by a chain line). This intermediate solution is supplied with concentrated HCl from the HCl tank 26 as appropriate, and is blown to the desalination side according to the cation concentration.

Further, although not shown in FIG. 2, the electrode solution is circulated from the circulation tank 31 to the liquid contact channel between the anode 21 and the cathode 22 as described above. As the electrode solution, sulfuric acid is generally used on the anode 21 side, and demineralized water is used on the cathode 22 side.

In this embodiment, as an example of the proton-selective cation exchange membrane C1, a thin layer of an anion exchange membrane is laminated on a cation exchange membrane.
In order to significantly reduce the thickness of the anion exchange membrane as compared with the conventional one, a solvent-soluble polymer capable of forming a thin film is used, and as the anion exchange layer, an anion exchange of a solvent-soluble polysulfone skeleton is used. It is preferable to use a polymer ("Sulfuric acid and industry", April 1996, p. 51).
-P58).

According to the electrodialysis tank 13 of this embodiment, high-purity HCl can be recovered and recycled, and the consumption of alkaline agents such as caustic soda during the treatment can be extremely reduced. It is effective. In addition, the amount of discharged salt can be suppressed to a minimum, and it is possible to eliminate various problems at the time of salt damage and salt recycling. Since a plurality of proton-selective cation exchange membranes C1 are interposed between the anion-exchange membranes A, A forming a pair, a very small amount is passed through the proton-selective cation exchange membrane C1. It is possible to more reliably suppress the passage of heavy metal ions,
By increasing the separation and recovery efficiency of HCl, high-purity concentrated hydrochloric acid can be recovered.

In this embodiment, the anion exchange membranes A,
A description has been given of the case where two proton-selective cation exchange membranes C1 are provided between A. However, the number of the proton-selective cation exchange membranes C1 provided may be three or more. Needless to say.

[Brief description of the drawings]

FIG. 1 is a system configuration diagram of an exhaust gas treatment apparatus according to one embodiment of the present invention.

FIG. 2 is a diagram showing a detailed structure of an electrodialysis tank in the present embodiment.

FIG. 3 is a system configuration diagram of a conventional exhaust gas treatment apparatus.

[Explanation of symbols]

 Reference Signs List 11 first washing tower 12 second washing tower 13 electrodialysis tank 15 washing liquid 19 pretreatment device 20 water cooler 21 anode 22 cathode 23 stock solution chamber 25 permeation chamber 26 HCl tank

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification FI FI Theme Court II (Reference) B01D 61/46 ZAB (71) Applicant 500418152 Makoto Watanabe 2-1-1, Miyakojima Nantori, Miyakojima-ku, Osaka-shi, Osaka- No. 1005 (71) Applicant 500417775 Tadayoshi Matsuda 2-4-15-607 Takaida Motomachi, Higashiosaka-shi, Osaka (71) Applicant 000133032 TAKUMA CORPORATION 1-323 Dojimahama, Kita-ku, Osaka-shi, Osaka (72) Inventor Eiji Tashiro 3-9-1, Tsukamoto-dori, Hyogo-ku, Kobe-shi, Hyogo (72) Inventor Tadao Soejima 3-3-13-306, Nishiiwata, Higashi-Osaka-shi, Osaka (72) Inventor Akira Nakajima Osaka, Osaka, Osaka (72) Inventor Makoto Watanabe 2-1-1-1005 Miyakojima Minamidori, Miyakojima-ku, Osaka-shi, Osaka (72) Inventor Tadayoshi Matsuda Gen Takaida, Higashi-Osaka-shi, Osaka 2-45, 607-cho (72) Inventor Kazuo Osumi 2-2-233, Kinrakuji-cho, Amagasaki City, Hyogo Prefecture Inside of Takuma Co., Ltd. (72) Inventor Tomohisa Ota 1-2-1, Niihama, Araimachi, Takasago City, Hyogo Prefecture No. 1 Inside Takuma Central Research Laboratory (72) Inventor Hideyuki Nishizawa 2-33 Kingara-cho, Amagasaki-shi, Hyogo F-term inside Takuma Co., Ltd. GA17 HA47 JA30A JA43A JA45A KA01 KB30 MA13 MA14 MA40 PA04 PB20 PC80 4D061 DA08 DB20 DC13 EA09 EB13

Claims (4)

[Claims] 1. H in an acid gas component contained in exhaust gas
In the electrodialysis method in which Cl gas is once absorbed by the cleaning solution, and then the HCl is separated and recovered from the cleaning solution after the absorption of HCl gas by electrodialysis using a proton-selective cation exchange membrane and an anion exchange membrane. An electrodialysis method comprising interposing a plurality of proton-selective cation exchange membranes between a pair of anion exchange membranes. 2. H in an acidic gas component contained in an exhaust gas.
An electrodialysis apparatus comprising: an exhaust gas cleaning unit that absorbs Cl gas into a cleaning liquid; and an electrodialysis unit that introduces a cleaning liquid after absorbing the HCl gas extracted from the exhaust gas cleaning unit. A plurality of units comprising a plurality of proton-selective cation exchange membranes disposed between the anion exchange membranes are formed in series to form a compartment, and the compartments are formed in each unit of the electrodialysis unit. An electrodialysis apparatus characterized in that a cleaning liquid extracted from an exhaust gas cleaning section is introduced. 3. The electrodialysis apparatus according to claim 2, wherein an intermediate liquid is circulated in the compartment sandwiched between the proton-selective cation exchange membranes, and the intermediate liquid is supplied with concentrated HCl. 4. The electrodialysis device according to claim 2, which is used for an exhaust gas treatment device in a refuse incineration plant.