JPH08318122A - Treatment of decomposed fluorocarbon waste gas - Google Patents

Abstract

PURPOSE: To effectively treat waste gas produced by decomposing fluorocarbon and to recover effective components by continuously and quantitatively treating decomposed fluorocarbon gas with a circulation liquid to which alkali is added, separating solid matter and dissolved salt and reusing the circulation liquid. CONSTITUTION: After air being carrier gas is heated and its flow rate is adjusted, it is mixed with fluorocarbon. This gaseous mixture is introduced into a catalyst vessel 5 and is decomposed into hydrogen chloride, hydrogen fluoride, carbon dioxide and the like. The decomposed gas is led to a scrubber 8 and is neutralized with a circulation liquid to which alkali is added to form dissolving chloride and solid matter of fluoride. The circulation liquid containing these is led to a slurry feeding tank 13 and is completely neutralized and is cooled. Then the circulation liquid is dehydrated by the 1st dehydrator 19 to separate calcium fluoride, and further, the dissolved components are separated by an electrodialysis device 19, and the calcium chloride is removed by the 2nd dehydrator 23. The circulation liquid is led to a circulation tank 10, and alkali is added from an alkali hopper to reuse the circulation liquid.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for treating exhaust gas generated when decomposing CFCs.

[0002]

2. Description of the Related Art In recent years, chlorofluorocarbons (CFCs) in the Montreal Protocol refer to chlorofluorocarbons (CFC) in the AD 19 as a substance that has depleted the ozone layer and deteriorates the global environment.
It has been decided that by 1996, hydrochlorofluorocarbons (HCFCs) will be completely abolished by 2030.

Therefore, various methods for decomposing and detoxifying chlorofluorocarbon have been studied, and catalytic decomposition method, plasma decomposition method, combustion decomposition method, cement kiln decomposition method, ultraviolet decomposition method, electron beam decomposition method, supercritical water have been studied so far. Studies on solution, radiation decomposition, detonation decomposition, etc. are underway. In any of these methods, hydrogen fluoride or fluorine, and hydrogen chloride or chlorine are simultaneously generated as a CFC decomposition product, and they are highly harmful as their emission is regulated by the Air Pollution Control Act. Therefore, it is necessary to treat the exhaust gas.

As a characteristic of the chlorofluorocarbon-decomposing exhaust gas, in addition to the simultaneous generation of hydrogen fluoride or fluorine and hydrogen chloride or chlorine, there is a large amount of exhaust gas generated as compared with the amount of chlorofluorocarbon treated. For example, in the case of CFC 113 (C ₂ Cl ₃ F ₃ ) which is one of the CFCs used most, the amount of hydrogen fluoride and hydrogen chloride generated when 1 kg of CFC 113 is treated is 0.32 kg, respectively. 0.58 kg, and when these are further neutralized with calcium hydroxide, the amounts of calcium fluoride and calcium chloride generated are 0.62 kg and 0.89 kg, respectively, and the total amount is about 1. Up to 5 times.

An example of the decomposition treatment reaction of CFC 113 is shown by the following chemical formula. C ₂ Cl ₃ F ₃ + 3H ₂ O → CO ₂ + CO + 3HF + 3HC
l If the generated HF and HCl are neutralized with calcium hydroxide, the chemical formula becomes as follows. 2HF + Ca (OH) ₂ → CaF ₂ + 2H ₂ O 2HCl + Ca (OH) ₂ → CaCl ₂ + 2H ₂ O When neutralized with sodium hydroxide, it is represented by the following formula. HF + NaOH → NaF ₂ + H ₂ O HCl + NaOH → NaCl + H ₂ O When decomposed at a high temperature, the reaction is represented by the following formula. 2C ₂ Cl ₃ F ₃ + 4O ₂ → 4CO ₂ + 3Cl ₂ + 3F ₂ Therefore, in conventional treatment methods such as washing towers and sedimentation separation of washing effluent, exhaust gas treatment equipment is much more efficient than flon decomposition equipment. It becomes a large amount, and the economical efficiency of the entire CFC decomposition treatment facility is greatly impaired.

On the other hand, the neutralized product of the CFC-decomposed exhaust gas is a highly useful substance such as calcium fluoride as described above. The mixed amount is very small, and at the same time, the chlorine compound which is neutralized and formed can be effectively reused if efficiently removed. However, even in this case, the conventional wastewater sedimentation separation method requires a large-capacity sedimentation separation equipment because it is necessary to secure a settling time and the amount of non-soluble fluorine compounds such as calcium fluoride generated is large. This will significantly impair the economic efficiency of the CFC decomposition treatment facility. In addition, since soluble chlorine compounds (calcium chloride, etc.) are mixed in the precipitated fluorine compound, multiple washings with water are required to obtain useful high-purity fluorine compounds. The large amount of wastewater generated further impairs the economical efficiency of the CFC decomposition treatment facility.

Further, the fluorine-containing wastewater is regulated by the Water Pollution Control Law to have a fluorine concentration of 15 ppm or less in the wastewater, and some local governments may also carry out voluntary regulations that are stricter than this. Contained wastewater requires advanced treatment. However, in the conventional methods such as coagulating sedimentation, a large amount of waste water is generated, and a large settling tank is required to secure the settling time. This will impair the economics of the equipment.

[0008]

As described above, when the conventional method for treating exhaust gas is applied to the exhaust gas generated when CFCs are decomposed, the exhaust gas is efficiently treated and useful neutralization of exhaust gas is produced. There are various problems in efficiently collecting and reusing materials, and no technique has been completed up to the practical stage. Therefore, the CFC decomposition treatment technology itself has not been completed, and from this viewpoint, the development of a CFC decomposition exhaust gas treatment method has been desired.

The present invention has been made in order to solve such a conventional problem, and an object thereof is to efficiently treat exhaust gas generated when decomposing CFC and to install useful components in a small-scale facility. The purpose is to provide a method of collecting.

[0010]

[Means and Actions for Solving the Problems] A first method for treating a CFC-decomposed exhaust gas according to the present invention is to treat a CFC-decomposed exhaust gas continuously and quantitatively with a circulating liquid to which an alkali is added. To continuously separate solids and dissolved salts generated by neutralization, and reuse the circulating fluid.

A second method for treating CFC-decomposed exhaust gas according to the present invention is to treat the CFC-decomposed exhaust gas continuously and quantitatively with a circulating liquid to which an alkali is added, and to solid matter generated by neutralization from the circulating liquid. And continuously separating the dissolved salts,
After the circulating liquid from which both have been removed and the separated solid matter are mixed to dissolve and remove impurities (soluble salts, etc.) in the solid matter,
The solids are separated again and the circulating liquid is reused.

A third method for treating a CFC-decomposing gas according to the present invention is to treat a chlorofluorocarbon-decomposing exhaust gas with a circulating liquid in which an alkali is quantitatively added continuously, and to solid matter generated by neutralization from the circulating liquid. Is continuously separated, and the circulating liquid is reused.

The first and second freon-decomposing exhaust gas treatment methods are intended to treat chlorofluorocarbon (CFC), hydrochlorofluorocarbon (HCFC), etc., that is, freon containing chlorine and fluorine as components. In the first method, the solid matter is separated from the circulating fluid, whereas in the second method, the solid matter is separated from the circulating fluid and then washed with purified circulating water to reduce impurities. It has a higher purity.

The third treatment method for the CFC-decomposed exhaust gas is intended for hydrofluorocarbon (HFC), that is, a CFC containing no fluorine as a component but containing fluorine, and therefore is dissolved in the first and second treatment methods. There is no step to separate the salt formed.

Next, a detailed description will be given of a second method for treating CFC-decomposed exhaust gas including the steps of the first and third processing methods. Exhaust gas containing hydrogen fluoride or fluorine generated by the decomposition of CFCs and hydrogen chloride or chlorine (hereinafter collectively referred to as harmful gas) is introduced into the cleaning tower. This washing tower is a packed tower,
Concentration and temperature of harmful gas generated by one or more of spray tower, cyclone scrubber, venturi scrubber, wet wall tower, cross flow contact device, plate tower, bubble tower, jet scrubber, leak tray tower, etc. The harmful gas components in the exhaust gas are absorbed and neutralized in the liquid by the contact between the exhaust gas and the liquid.

A liquid to which alkali is quantitatively added is circulated continuously and quantitatively in the washing tower, and harmful gas is absorbed in the circulated liquid. Calcium hydroxide as an alkali,
Sodium hydroxide, calcium carbonate, sodium carbonate and the like can be used. These alkalis undergo a neutralization reaction with harmful gases in the circulating liquid, resulting in the formation of neutralization products in the form of fluorine and chlorine compounds.

These neutralized products can be recovered in the form of solids as useful substances after being discharged from the washing tower. In order to recover these from the circulating fluid in a higher-purity form, the amount of alkali added should be the same as the amount of alkali equivalent to neutralize the decomposed exhaust gas, depending on the type of CFC to be decomposed and the amount to be treated. By continuously and quantitatively supplying, the excess alkaline component in the circulating liquid can be minimized, and the purity of the useful substance recovered as a solid form can be improved. That is, since the useful solid substance is collected in a state of containing water, the purity of the collected useful substance is lowered if impurities are contained in this moisture. Further, even if a solid substance other than the useful substance is present in the circulating fluid, the useful substance is recovered as the solid substance, so that the purity of the useful substance is lowered. In particular, if the alkali to be added is poorly water-soluble, such as calcium hydroxide or calcium carbonate, may the undissolved alkali component impair the purity of the useful solid that is separated and collected at the same time as the precipitated useful solid. This is also important in the present invention because re-neutralization operation of excess alkali is required.

Further, particularly in the case of hydrogen fluoride or fluorine, the hardly soluble neutralization product formed forms a complex hydrate near the neutralization equivalent point and becomes a colloidal form, so that it is formed on the downstream side. It may interfere with the separation of the solid matter by dehydration or the like. Therefore, the amount of alkali to be added may be added in a slightly excess amount over the equivalent amount required for neutralization of decomposed exhaust gas within a range that does not impair the purity required as a recovered useful component, and the circulating liquid may have a predetermined excess alkalinity. is necessary. This predetermined excess alkalinity depends on the alkali used.

As means for adjusting the amount of alkali added, in addition to strictly controlling the amount of alkali added, in the present invention, means for continuously adding acid to the circulating liquid can be used. Since the range of PH for the above-mentioned predetermined excess alkalinity is known in advance, the excess alkalinity is controlled within a predetermined range by detecting the PH of the circulating fluid and feedback-controlling the amount of acid added continuously based on it. can do.

Although hydrochloric acid, sulfuric acid, nitric acid, etc. can be used as the acid to be added, since calcium chloride is already contained in the circulating liquid for treating the fluorocarbon-decomposing exhaust gas, the present invention produces it by using hydrochloric acid. It becomes possible to recover the calcium chloride without impairing the purity of the calcium chloride to be recovered by converting the neutralized salt into calcium chloride already contained.

The circulating liquid which has absorbed and neutralized harmful gas in the washing tower contains, as neutralization products, hardly soluble fluorine compounds such as calcium fluoride and sodium fluoride and soluble chlorine compounds such as calcium chloride and sodium chloride. Contains.

From the circulating liquid discharged from the washing tower, first, precipitated solids of calcium fluoride or sodium fluoride having a low solubility are separated. As means for separating solids, there are means such as dehydration, evaporative concentration, and sedimentation separation, but dehydration is most suitable as means for rapidly separating only solids from the circulating liquid. The dehydration method includes centrifugal dehydration, filter press, belt press, vacuum dehydration and the like, and any of them can be used.

The circulating liquid from which the solid matter has been separated is subsequently removed of soluble salts such as calcium chloride. As means for removing soluble salts existing in an ionic state, electrodialysis,
Although there are reverse osmosis membrane treatment, ion exchange, etc., electrodialysis is the most suitable means for rapidly separating only soluble salts.

The order of carrying out the removal of the solid matter and the soluble salt from the circulating liquid is not specified in principle, but in the present invention in which the soluble salt is removed by electrodialysis. Is a high concentration of solids in the circulating fluid,
Since the life of the ion exchange membrane used in electrodialysis may be shortened, the removal of the soluble salt first followed by the removal of the soluble salt leads to the efficient implementation of the present invention.

The solid matter separated from the circulating liquid by dehydration can be recovered and reused as it is when the purity has reached the purity required for the purpose of utilizing it as a useful substance. However, in many cases, chlorine compounds are mixed in the ionic state as a soluble salt in the neutralized product of the CFC decomposition exhaust gas as described above, and the solid matter obtained by dehydration is usually 75 to 85%. Since it contains the above water, impurities (soluble salts, etc.) are present in this water and the purity is often insufficient. On the other hand, the purity can be improved by washing the dehydrated solid with water using a liquid having a low content of soluble salts and dehydrating again. However, introducing water from the outside has the drawback of increasing the amount of drainage.

In the present invention, this washing with water is carried out with the circulating liquid in which the soluble salt is removed by the electrodialysis to reduce the content of the soluble salt, and the amount of drainage is increased without introducing water from the outside. It is possible to improve the purity of the separated solid matter.

The soluble salts removed from the circulating liquid by electrodialysis are discharged from the electrodialysis device in the form of a small amount of concentrated liquid, which is high-purity calcium chloride and sodium chloride in the case of CFC-decomposing exhaust gas. And the like. Calcium chloride and sodium chloride are widely used substances in the general industry, so they may be recovered and reused.
Further operations such as concentration and drying are necessary to obtain a solid form used in general industry, and recycling is not always economically advantageous considering the cost required for it. Therefore, in some cases, these are discharged as waste water.

In general, wastewater containing fluorine or a fluorine compound requires many operations such as coagulation and sedimentation in order to satisfy the strict regulation of the Water Pollution Control Law, and requires many equipments such as neutralization equipment related thereto. . According to the present invention, most of the fluorine compounds (Ca
F ₂ , NaF, etc.) are separated from the circulating liquid as solids. Then, the circulating liquid from which the solid matter has been removed by the dehydration treatment is subjected to an electrodialysis treatment to separate the ionic components from the circulating liquid. At this time, the dissolved salts (CaCl ₂ , N
Most of the (aCl etc.) is separated from the circulating liquid, and fine solids (CaF
₂ , NaF, etc.) cannot pass through the ion exchange membrane and remain on the circulating liquid side.

Only the ionic component is present in the liquid separated by electrodialysis. Although F + ions are also present in this, since the solubility of CaF ₂ is 8 ppm, the drainage standard of 15 ppm can be sufficiently satisfied. In the case of NaF, the solubility is higher than that of CaF _2, but only the ionic component is present and F + ions can be easily lowered.

[0030]

EXAMPLES Examples will be shown below, but the present invention is not limited to these examples. (Embodiment 1) This embodiment is an embodiment for treating a CFC decomposition exhaust gas generated when CFC ₃ (CCl ₃ F) is decomposed by a CFC decomposition treatment apparatus, and the apparatus used here uses a CFC catalyst. Then, the decomposition treatment is performed at a treatment speed of 50 kg / h. A system diagram is shown in FIG.

Approximately 260 Nm as CFC carrier gas
After supplying ³ / h of air to the heater (2) by the blower (1) to heat it, the steam supplied through the flow rate adjusting valve (3) and the chlorofluorocarbon supplied through the flow rate adjusting valve (4) are mixed. By doing so, the Freon is heated to the temperature required for catalytic decomposition to about 430 ° C. The concentration of freon is about 3 mol%.

Steam is used to supply hydrogen and oxygen necessary for the decomposition of freon by a catalyst, and the equivalent of 1.0 to 1.0 is necessary for the decomposition depending on the kind and treatment amount of freon.
Supply about 3.0 times. The amount of steam supplied is controlled to fall within this range.

Since the temperature of the air before mixing is lowered by mixing with the chlorofluorocarbon, the temperature of the air before mixing is controlled so that the temperature after mixing with the chlorofluorocarbon becomes higher than the temperature required for decomposition of the chlorofluorocarbon by the catalyst. Set higher than the temperature required for decomposition by. Further, the supply amounts of air and water vapor are set so that the temperature of the air before mixing does not exceed the partial decomposition temperature of chlorofluorocarbon, and the respective supply amounts are controlled. Further, the output of the heater (2) is controlled so that the temperature of the air becomes equal to or lower than the partial decomposition temperature of the fluorocarbon and the temperature after mixing with the fluorocarbon becomes equal to or higher than the temperature required for the catalytic decomposition of the fluorocarbon.

As the heating means of the heater (2), a combustion burner using a hydrocarbon fuel is used, and since steam is produced as a combustion product, it is possible to supplement the steam necessary for the decomposition reaction.

A mixed gas of air, water vapor and chlorofluorocarbon heated to a predetermined temperature range is introduced into the catalyst container (5) and decomposed into hydrogen chloride, hydrogen fluoride, carbon dioxide and the like by a catalytic reaction. The exhaust gas after decomposition is heated at a temperature of about 430 ° C. and the decomposition reaction heat is added to the exhaust gas, and the exhaust gas is discharged at about 450 ° C. Hydrogen fluoride and hydrogen chloride are 7.3 kg / h and 39.8 kg, respectively
/ H occurs.

Since high-temperature hydrogen chloride and hydrogen fluoride generated by decomposition are extremely corrosive, in the present invention, a catalyst container is used.
Cooling the high temperature corrosive decomposition gas inside (5) mitigates the corrosive environment of the device thereafter.

As a cooling means, a method of spraying a cracked gas immediately after leaving the catalyst inside a catalyst container (5) with a liquid is used as a means for minimizing a severe range of a corrosive environment and suppressing a pressure loss. Select. As this liquid, a chemically stable liquid such as water is used, but further mitigation of the corrosive environment can be realized by mixing alkali and partially neutralizing the halogen and hydrogen halide.

When the liquid is sprayed inside the container in which the catalyst is installed, spray droplets may be mixed into the catalyst to lower the temperature of the catalyst or the activity of the catalyst. In the present invention, a baffle plate (6) is installed between the catalyst and the spray space to prevent splashes from entering the catalyst.

When the liquid is sprayed inside the container in which the catalyst is installed, the spray droplets are transferred to the pipe connecting the container in which the catalyst is installed and the washing tower (8) on the downstream side. In the present invention, since a new factor causing corrosion is created by bringing moisture into the originally dry pipe, a separate chamber (7) having a low flow rate is provided inside the container in which the catalyst is installed. As a result, the droplets in the air are allowed to settle and the droplets are prevented from moving to the downstream pipe.

The decomposed gas is cooled in the catalyst container (5) or partially neutralized, and then the hydrogen halide (HCl, HF) is completely removed in the washing tower (8) in the next step. Washing tower (8)
The decomposed gas discharged from the exhaust gas contains a small amount of undecomposed CFC, but in the present invention, it is adsorbed in the adsorption tower (9) filled with activated carbon installed on the downstream side of the washing tower (8), and then the activated carbon Fluorocarbons released during regeneration are returned to the catalyst container (5) and treated again. Further, in the present invention, two series of the adsorption towers (9) are provided, while one series is used for adsorption, the remaining one series is regenerated, and the regenerated and desorbed CFC is introduced into the operating catalyst. As a result, the CFCs that are regenerated and desorbed from the adsorption tower (9) are treated without stopping the CFCs that are the main decomposition target.

The washing tower (8) has a circulation tank (10) and a circulation pump.
The circulating liquid is supplied at a flow rate of about 1.3 m ³ / h using (11). This is introduced into the catalyst container (5),
Along with the circulating liquid of about 1.2 m ³ / h supplied as a spray liquid in (5), the whole system is circulated as a circulating liquid of about 2.5 m ³ / h in total. The circulating liquid flow rate must be set to an amount such that boiling and evaporation do not occur due to contact with the fluorocarbon-decomposing exhaust gas of about 450 ° C. introduced into the washing tower (8), and in this embodiment, about 2.5 m ³ / h.

In the circulating liquid, powdered calcium hydroxide was used in the circulation tank (10) by the alkaline hopper (12) to obtain a necessary equivalent amount of harmful components of 53.8 kg / h, which is a 1% excess of 54.3 kg / h. It is supplied and the circulating fluid is adjusted to be alkaline. This addition is carried out strictly by the microfeeder so that it is not added in excess of 1%.

In the present embodiment, the cleaning tower (8) is a spray tower because the flow rate of the circulating liquid is small, and the harmful gas in the CFC-decomposed exhaust gas is absorbed in the circulating liquid during spraying, and further the hydroxylation in the circulating liquid is carried out. Neutralized with calcium, hydrogen fluoride produces calcium fluoride and hydrogen chloride produces calcium chloride. The inner surface of the material of the cleaning tower 8 is coated with Teflon to prevent corrosion due to harmful components introduced into the cleaning tower 8.

These neutralization products (calcium fluoride,
The amount of calcium chloride generated is 14.2 kg /
h, 60.5kg / but h, and the solubility of calcium fluoride the near temperature of about 15 to 20 g / m ³ - small as solution, in the vicinity of solubility the temperature of the calcium chloride to about 400~500kg / m ³ - About 2.5 because of the large size of the solution
In the m ³ / h circulating fluid, most of calcium fluoride is present as an insoluble solid matter, and most of calcium chloride is present as a soluble salt. The concentration in each liquid is about 0.6% by weight and about 2.3% by weight.

The circulating liquid containing calcium fluoride and calcium chloride in the above amounts and concentrations is discharged from the washing tower (8) and then introduced into the slurry supply tank (13). In the slurry supply tank (13), the circulating liquid is retained for about 30 minutes or more, during which the neutralization reaction is completed and the slurry supply tank (1
A cooling coil (14) installed inside 3) cools to a temperature suitable for dehydration and electrodialysis in the subsequent step.

The circulating liquid that has been neutralized and cooled is introduced from the slurry supply tank (13) into the first dehydrator (16) by the first slurry supply pump (15). First dehydrator (16)
The circulating liquid is dehydrated by the above, and calcium fluoride in the circulating liquid is separated from the circulating liquid in the form of a dehydrated cake having a water content of about 80%. Approximately 2.3% by weight of calcium chloride is dissolved in the water in the dehydrated cake as described above, so the purity of calcium fluoride when the dehydrated cake is dried as it is is that it remains unreacted in the circulating liquid. The residual calcium hydroxide is about 89%, which does not reach 95% or more, which is widely required in general industries such as glass manufacturing.

The circulating liquid obtained by separating calcium fluoride by the first dehydrator (16) reduces the flow rate of the separated dehydrated cake, and the first dehydrator at a flow rate of about 2.4 m ³ / h.
It is discharged from (16) to the separation liquid tank (17) and further introduced into the electrodialysis device (19) by the waste liquid pump (18). In the electrodialysis device (19), dissolved components are removed from the circulating fluid by electrodialysis. Specifically, since calcium chloride has high solubility and exists in an ionic form, most (about 90%) thereof is removed. The dissolved portion of calcium fluoride is similarly removed.

From the electrodialysis device (19), the calcium chloride removed from the circulating liquid is discharged as a concentrated liquid having a concentration of about 9% by weight at a flow rate of about 0.5 m ³ / h. Since this calcium chloride concentrate has a relatively high concentration, it is collected and reused in this embodiment. It is also possible to further concentrate and dry this to recover calcium chloride as a solid. Also, the F + ion concentration is about 8 p for the solubility of CaF _2.
Since it is as small as pm and there is no solid content, drainage standard 15
ppm can be satisfied.

On the other hand, in the circulating liquid that has passed through the electrodialysis device (19), calcium chloride as a dissolved component is separated, and the concentration of calcium chloride is about 1/10 of that before the electrodialysis treatment, that is, about 0.2% by weight. And it becomes a purified clear liquid, about 1.8m
^The rinse tank (2
It is introduced in 1). The rinse tank (21) has a first dehydrator
The calcium fluoride dehydration cake separated from the circulating liquid from (16) is also introduced, and the clarifying liquid and the dehydration cake are rinse tanks.
Mixed inside (21). Concentration in dehydrated cake 2.
3% by weight of calcium chloride is diluted with a clarified liquid having a concentration of about 0.2% by weight, and the concentration is reduced to about 0.3% by weight.

A mixed fluid of the calcium fluoride dehydrated cake and the clarified liquid was used as a circulating liquid for the second slurry supply pump (22).
Is introduced into the second dehydrator (23) from the rinse tank (21). The circulating liquid is dehydrated again in the second dehydrating device (23), and lucium fluoride is separated from the circulating liquid as a dehydrated cake having a water content of about 80%. Circulating liquid is rinse tank (21)
Since the calcium chloride concentration was reduced to about 0.3% by weight, the calcium chloride in the dehydrated cake was also reduced, and the purity of calcium fluoride when dried was the same as that of the above calcium hydroxide. In some cases, it is 97%, which is sufficiently higher than the required purity of 95%.

The circulating liquid from which calcium fluoride has been separated by the second dehydrator (23) is a circulating liquid (10) as a clear liquid from which both calcium fluoride and calcium chloride have been separated and removed.
Is discharged at a flow rate of about 1.8 m ³ / h, and alkali is added again by the alkali hopper (12) to be reused as a circulating liquid.

In this embodiment, the flow rate of the circulating liquid introduced from the circulation tank (10) to the washing tower (8) is about 2.5 m ³ / h, and the circulation tank from the second dehydrator (25) is used. The flow rate of the circulating fluid introduced into (10) is about 1.8 m ³ / h and the circulating fluid is reduced to about 0.7 m ³ / h per circulation. It will make up for the shortfall.

(Embodiment 2) This embodiment occurs when Freon 12 (CCl ₂ F ₂ ) is decomposed by a Freon decomposition treatment apparatus which decomposes Freon at a treatment rate of 50 kg / h using a catalyst. It is an example which processes a Freon decomposition exhaust gas. A system diagram is shown in FIG.

Freon is mixed with heated air and steam and then introduced into the catalyst column (5) at a concentration of 1 mol%. Freon is hydrolyzed in the catalyst tower, and hydrogen fluoride and hydrogen chloride as harmful gases are 16.5 kg / h and 30.2 k, respectively.
g / h occurs.

These are carrier gases of about 800 Nm.
It is introduced into the washing tower (8) together with ³ / h of air and a small amount of steam, carbon dioxide, carbon monoxide and the like which are decomposition by-products. The temperature of the CFC decomposition exhaust gas is about 440 ° C. because the CFC decomposition heat is added to the heating temperature.

The washing tower (8) has a circulation tank (10) and a circulation pump.
Circulating liquid is supplied at a flow rate of about 6.0 m ³ / h using (11).

For the circulating liquid, powdery calcium hydroxide was used in the circulation tank (11) by the alkali hopper (12) at 1% of 61.1 kg / h, which is the equivalent amount required for neutralization of decomposed gas.
An excess (0.6 kg / h) of 61.7 kg / h is supplied and the circulating fluid is adjusted to be alkaline. In this example, since this addition is performed by an inexpensive rotary feeder, it is difficult to strictly add 1% excessively. Therefore, the addition amount is set to 1% or more, and the pH is adjusted with an acid in the subsequent steps (24, 25). To achieve a strict 1% excess state.

In the present embodiment, the washing tower (8) is of the packed tower type because the flow rate of the circulating liquid is large, and the harmful gas in the CFC decomposition exhaust gas is absorbed in the circulating liquid in the packing material, and further, in the circulating liquid. Neutralized with calcium hydroxide, hydrogen fluoride produces calcium fluoride and hydrogen chloride produces calcium chloride. As the material of the filler, a plastic material is used to prevent corrosion due to harmful components introduced into the washing tower (8). Washing tower
The material of (8) is the same as in Example 1.

These neutralization products (calcium fluoride,
The amount of generated calcium chloride is 32.2 kg / h,
It is 45.9 kg / h, and in the circulating liquid of about 6.0 m ³ / h, most of calcium fluoride exists as a solid substance, and most of calcium chloride exists as a soluble salt (ion). The concentration in each liquid is about 0.5% by weight and about 0.7% by weight.

The circulating liquid containing calcium fluoride and calcium chloride in the above amounts and concentrations is discharged from the washing tower (8) and then introduced into the slurry supply tank (13). In the slurry supply tank (13), the circulating liquid is retained for about 30 minutes or more, during which the neutralization reaction is completed and the slurry supply tank (1
It is cooled to a temperature suitable for dehydration and electrodialysis by a cooling coil (14) installed inside 3).

The circulating liquid which has been neutralized and cooled is introduced from the slurry supply tank (13) to the first dehydrator (16) by the first slurry supply pump (15). Calcium hydroxide remains in excess because the alkali is added in excess. Therefore, when the calcium fluoride is recovered as it is, calcium hydroxide is mixed with the recovered calcium fluoride, which impairs the purity of the recovered calcium fluoride. On the contrary, in this embodiment, the slurry supply tank (13)
The PH of the circulating fluid is detected by the PH meter (24) at the outlet, and the flow control valve (2
Adjust the alkalinity excess to 1% by adding hydrochloric acid through 5).

The circulating fluid whose alkalinity is adjusted is dehydrated by the first dehydrator (16), and calcium fluoride in the circulating fluid is separated from the circulating fluid in the form of a dehydrated cake having a water content of about 80%. To be done. Approximately 0.7% by weight of calcium chloride is dissolved in the water in the dehydrated cake as described above, but even if this dehydrated cake is dried as it is, the purity of calcium fluoride remains high, and dehydration and electrodialysis can be performed efficiently. 0 to do.
It is about 95% including calcium hydroxide which is added in excess of 6 kg / h and remains unreacted in the circulating fluid, and satisfies 95% or more widely required in general industries such as glass manufacturing industry. Therefore, in this embodiment, the washing operation with water is unnecessary.

First dehydrator for calcium fluoride (16)
The flow rate of the circulating liquid separated by the first dehydrator is reduced by the flow rate of about 5.8 m ³ / h by reducing the flow rate of the separated dehydrated cake.
It is discharged from (16) to the separation liquid tank (17) and further introduced into the electrodialysis device (19) by the waste liquid pump (18). In the electrodialysis device (19), calcium chloride is removed from the circulating fluid by electrodialysis.

From the electrodialyzer (19), the calcium chloride removed from the circulating liquid was concentrated in the drainage tank (27) by the concentrated liquid pump (26) as a concentrated liquid having a concentration of about 3% by weight.
It is discharged at a flow rate of 0 m ³ / h. Since this calcium chloride concentrate has a relatively low concentration, it is discharged as waste water in this embodiment. At the time of drainage, fine solid calcium fluoride is removed by the ion exchange membrane of the electrodialysis device (19), and the solubility of dissolved calcium fluoride is as low as 8 ppm. Is sufficiently smaller than the regulation value of the Water Pollution Control Law, and no special fluorine removal operation is required.

On the other hand, the circulating liquid that has passed through the electrodialysis device (19) is separated into calcium chloride, which is a dissolved component, and the concentration of calcium chloride is purified to about 0.1% by weight, which is about 1/10 that before the electrodialysis treatment. The resulting clear liquid is about 4.8 m ³ /
It is introduced into the circulation tank (10) by the clarifying liquid pump (20) at a flow rate of h, and alkali is added again by the alkali hopper (11) to be reused as a circulation liquid.

(Embodiment 3) This embodiment is based on Freon HFC.
Is an example in which a CFC decomposition exhaust gas generated when CFCs 134a is decomposed by a CFC decomposition treatment apparatus that decomposes CFCs at a treatment rate of 50 kg / h is used. Since HFC does not contain chlorine, there is no fear of ozone destruction, but HFC has a global warming effect, so it is harmful from the viewpoint of global warming prevention and needs to be rendered harmless. The decomposition formula is 2CF ₃ CH ₂ F + 2H ₂ O + 3O ₂ → 8HF + 4CO ₂ .

A system diagram is shown in FIG. About 260 Nm ³ / h of air as a CFC carrier gas is supplied to the heater (2) by the blower (1) and heated, and then steam supplied through the flow rate adjusting valve (3) and the flow rate adjusting valve (4) By mixing with the supplied freon, the freon is heated to a temperature required for catalytic decomposition of about 430 ° C. The concentration of freon is about 3 mol%.

Water vapor is used to supply hydrogen and oxygen necessary for the decomposition of freon using a catalyst, and the equivalent of 1.0 to 1.0 is necessary for the decomposition depending on the type and treatment amount of freon.
Supply about 3.0 times. The amount of steam supplied is controlled to fall within this range.

Since the temperature of the air before mixing is lowered by mixing with the chlorofluorocarbon, the temperature of the air before mixing is controlled so that the temperature after mixing with the chlorofluorocarbon becomes equal to or higher than the temperature required for decomposition of the chlorofluorocarbon by the catalyst. Set higher than the temperature required for decomposition by. Further, the supply amounts of air and water vapor are set so that the temperature of the air before mixing does not exceed the partial decomposition temperature of chlorofluorocarbon, and the respective supply amounts are controlled. Further, the output of the heater (2) is controlled so that the temperature of the air becomes equal to or lower than the partial decomposition temperature of the fluorocarbon and the temperature after mixing with the fluorocarbon becomes equal to or higher than the temperature required for the catalytic decomposition of the fluorocarbon.

As the heating means of the heater (2), a combustion burner using a hydrocarbon fuel is used, and since steam is produced as a combustion product, it is possible to supplement the steam necessary for the decomposition reaction. Further, as the heat exchanger type, a system of indirectly heating air as a carrier gas with a combustion gas may be used. In this case, since combustion gas and the like do not mix, it is convenient for maintaining the catalyst performance for a long period of time.

A mixed gas of air, water vapor and chlorofluorocarbon heated to a predetermined temperature range is introduced into the catalyst container (5) and decomposed into hydrogen fluoride, carbon dioxide and the like by a catalytic reaction. The exhaust gas after decomposition is heated at a temperature of about 430 ° C. and the decomposition reaction heat is added to the exhaust gas, and the exhaust gas is discharged at about 450 ° C. Hydrogen fluoride is 3
9.1 kg / h is generated.

Since high-temperature hydrogen fluoride generated by decomposition is extremely corrosive, in the present invention, by cooling the high-temperature corrosive decomposed gas inside the catalyst container (5), subsequent corrosion of the apparatus will be caused. Mitigates the environment.

As a cooling means, a method of spraying a decomposition gas immediately after leaving the catalyst inside the catalyst container (5) with a liquid is used as a means for minimizing the severe range of the corrosive environment and suppressing the pressure loss. Select. As this liquid, a chemically stable liquid such as water is used, but further mitigation of the corrosive environment can be realized by mixing alkali and partially neutralizing hydrogen fluoride.

When the liquid is sprayed inside the container in which the catalyst is installed, spray droplets may be mixed into the catalyst to lower the temperature of the catalyst or the activity of the catalyst. In the present invention, a baffle plate (6) is installed between the catalyst and the spray space to prevent splashes from entering the catalyst.

After the exhaust gas is cooled in the catalyst container (5) or partially neutralized, the hydrogen halide (hydrogen fluoride) is completely removed in the washing tower (8) in the next step. The decomposition gas discharged from the washing tower (8) contains a small amount of undecomposed CFC, but in the present invention, it is adsorbed by the adsorption tower (9) filled with activated carbon installed on the downstream side of the washing tower (8). , Process the replayed one again. As a result, the decomposition efficiency of the treatment facility can be improved and the amount of undecomposed CFC released can be reduced to about 1/10. This effect is due to passing the undecomposed CFCs through the catalyst layer again. At this time, the undecomposed CFC is supplied downstream of the heater and upstream of the catalyst. When this is supplied upstream of the heater, it partially exceeds the thermal decomposition start temperature of CFCs in the heater, so if undegraded CFCs are supplied upstream of the heater, some of the CFCs will be removed. Is thermally decomposed and corrosive gas (HF) is generated. Thereby, generation of corrosive gas on the upstream side of the catalyst layer can be prevented, the durability of the equipment can be improved, and the use of high-grade corrosion resistant material can be avoided.

Further, in the present invention, two series of the adsorption towers (9) are provided, and the remaining one series is regenerated while one series is used for adsorption, and the regenerated and desorbed CFC is in operation. Introduced into the column allows the treatment of the CFCs regenerated and desorbed from the adsorption tower (9) without stopping the CFCs which are the main decomposition target.

The washing tower (8) has a circulation tank (10) and a circulation pump.
The circulating liquid is supplied at a flow rate of about 1.3 m ³ / h using (11). This is introduced into the catalyst container (5),
Along with the circulating liquid of about 1.2 m ³ / h supplied as a spray liquid in (5), the whole system is circulated as a circulating liquid of about 2.5 m ³ / h in total. The circulating liquid flow rate must be set to an amount such that boiling and evaporation do not occur due to contact with the fluorocarbon-decomposing exhaust gas of about 450 ° C. introduced into the washing tower (8), and in this embodiment, about 2.5 m ³ / h.

In the circulating liquid, powdered calcium hydroxide was used in the circulation tank (10) by the alkaline hopper (12) to obtain a necessary equivalent amount of harmful components of 72.3 kg / h, which was 1% excess of 73.0 kg / h. It is supplied and the circulating fluid is adjusted to be alkaline. This addition is carried out strictly by the micro feeder, so it is not added excessively.

In this embodiment, the washing tower (8) is a spray tower because the flow rate of the circulating liquid is small, and the harmful gas in the CFC-decomposed exhaust gas is absorbed in the circulating liquid during the spraying, and further the hydroxylation in the circulating liquid is carried out. Neutralized with calcium, hydrogen fluoride produces calcium fluoride. The inner surface of the material of the cleaning tower 8 is coated with Teflon to prevent corrosion due to harmful components introduced into the cleaning tower 8.

The generation amount of these neutralization products is 14.0 k.
Although it is g / h, the solubility of calcium fluoride is as small as about 15 to 20 g / m ³ -solution in the vicinity of the temperature and is about 2.5.
In the circulating fluid of m ³ / h, most of calcium fluoride exists as a solid. Also, the concentration in the liquid is about 0.
6% by weight.

The circulating liquid containing calcium fluoride in the above amount and concentration is discharged from the washing tower (8) and then introduced into the slurry supply tank (13). The circulating liquid is retained in the slurry supply tank (13) for about 30 minutes or more, and the neutralization reaction is completed during this period, and the cooling coil (14) installed inside the slurry supply tank (13) is used for dehydration in the subsequent step. Cooled to a suitable temperature.

The circulating liquid which has been neutralized and cooled is introduced from the slurry supply tank (13) into the first dehydrator (16) by the first slurry supply pump (15). First dehydrator (16)
The circulating liquid is dehydrated by the above, and calcium fluoride in the circulating liquid is separated from the circulating liquid in the form of a dehydrated cake having a water content of about 80%. Since the moisture in the dehydrated cake has almost no impurities other than calcium fluoride, the purity of calcium fluoride when this dehydrated cake is dried as it is, is added excessively and remains unreacted in the circulating liquid. Including calcium hydroxide which is present, it is 95% or more, which is widely required in general industries such as glass manufacturing, and calcium fluoride with high purity can be recovered.

The circulation liquid obtained by separating calcium fluoride by the first dehydrator (16) reduces the flow rate of the separated dehydrated cake, and the first dehydrator (1) at a flow rate of about 2.4 m ³ / h.
6) is discharged to the separation liquid tank (17), and the waste liquid pump
It is returned to the circulation tank (10) by (18).

The circulating liquid from which calcium fluoride has been separated by the dehydrator (16) is discharged into the circulation tank (10) at a flow rate of about 2.4 m ³ / h, and alkali is added again by the alkali hopper (12). , Reused as circulating fluid.

In this example, the flow rate of the circulating liquid introduced from the circulation tank (10) into the washing tower (8) was about 2.5 m ³ / h, and the circulation tank (10) passed from the dehydrator (16). ) Is about 2.4 m ³ / h, and the circulating liquid is about 0.1 m ³ / h per circulation, so the flow rate is reduced. Will be compensated for.

(Embodiment 4) In this embodiment, the CFC-decomposing exhaust gas generated when CFCs are decomposed by a CFC decomposition treatment apparatus for decomposing CFCs at a treatment rate of 50 kg / h using a catalyst is treated with water. In this example, the treatment is performed using an aqueous sodium oxide solution. The system diagram is similar to that of the first embodiment.

Approximately 260 Nm as CFC carrier gas
After supplying ³ / h of air to the heater (2) by the blower (1) to heat it, the steam supplied through the flow rate adjusting valve (3) and the chlorofluorocarbon supplied through the flow rate adjusting valve (4) are mixed. By doing so, the Freon is heated to the temperature required for catalytic decomposition to about 430 ° C. The concentration of freon is about 3 mol%.

Steam is used to supply hydrogen and oxygen required for the decomposition of freon by a catalyst, and the equivalent of 1.0 to 1.0 is required for the decomposition depending on the kind and treatment amount of freon.
Supply about 3.0 times. The amount of steam supplied is controlled to fall within this range.

The mixed gas of air, water vapor and chlorofluorocarbon heated to a predetermined temperature range is introduced into the catalyst container (5) and decomposed into hydrogen chloride, hydrogen fluoride, carbon dioxide and the like by a catalytic reaction. The exhaust gas after decomposition is heated at a temperature of about 430 ° C. and the decomposition reaction heat is added to the exhaust gas, and the exhaust gas is discharged at about 450 ° C. Hydrogen fluoride and hydrogen chloride are 7.3 kg / h and 39.8 kg, respectively
/ H occurs.

The exhaust gas is cooled in the catalyst container (5) or partially neutralized, and then the hydrogen halide is completely removed in the washing tower (8) in the next step.

The washing tower (8) has a circulation tank (10) and a circulation pump.
The circulating liquid is supplied at a flow rate of about 1.3 m ³ / h using (11). This is introduced into the catalyst container (5),
Along with the circulating liquid of about 1.2 m ³ / h supplied as a spray liquid in (5), the whole system is circulated as a circulating liquid of about 2.5 m ³ / h in total. The circulating liquid flow rate must be set to an amount such that boiling and evaporation do not occur due to contact with the fluorocarbon-decomposing exhaust gas of about 450 ° C. introduced into the washing tower (8), and in this embodiment, about 2.5 m ³ / h.

In the circulating liquid, sodium hydroxide in a powder form was used in the circulation tank (10) by the alkali hopper (12) to obtain a 14.6 excess of 64.0 kg / h, which is the necessary equivalent amount of harmful components of 64.0 kg / h. It is supplied and the circulating fluid is adjusted to be alkaline. This addition is carried out strictly by the micro feeder, so it is not added excessively.

In this embodiment, the cleaning tower (8) is a spray tower because the flow rate of the circulating liquid is small, and the harmful gas in the CFC decomposition exhaust gas is absorbed in the circulating liquid during spraying, and further the hydroxylation in the circulating liquid is carried out. When neutralized with sodium, hydrogen fluoride produces sodium fluoride and hydrogen chloride produces sodium chloride.

These neutralization products (sodium fluoride,
The amount of sodium chloride generated is 33.6 kg /
h, 46.8 kg / h, the solubility of sodium fluoride is relatively small at about 40 kg / m ³ -solution near the temperature, and the solubility of sodium chloride is about 260 kg / m ³ -solution near the temperature. Because it is large, it is about 2.5 m ³ /
In the circulating liquid of h, most of sodium fluoride is present as a non-dissolved solid matter than the third order, and sodium chloride is present as a soluble salt due to its large solubility.
The concentration in each liquid is about 1.3% by weight and about 1.
8% by weight.

The circulating liquid containing sodium fluoride and sodium chloride in the above amounts and concentrations is discharged from the washing tower (8) and then introduced into the slurry supply tank (13). In the slurry supply tank (13), the circulating liquid is retained for about 30 minutes or more, during which the neutralization reaction is completed and the slurry supply tank (1
A cooling coil (14) installed inside 3) cools to a temperature suitable for dehydration and electrodialysis in the subsequent step.

The circulated liquid that has been neutralized and cooled is introduced from the slurry supply tank (13) into the first dehydrator (16) by the first slurry supply pump (15). First dehydrator (16)
The circulating liquid is dehydrated by the above, and sodium fluoride in the circulating liquid is separated from the circulating liquid in the form of a dehydrated cake having a water content of about 80%. As described above, about 1.8% by weight of sodium chloride was dissolved in the water in the dehydrated cake. Therefore, the purity of sodium fluoride when the dehydrated cake was dried as it was was that dehydration and electrodialysis were performed efficiently. 0.6kg to do
/ H If the amount of sodium hydroxide that is added excessively and remains unreacted in the circulating fluid is included, it is about 90%, which is less than 95% or more widely required in general industries such as the glass manufacturing industry.

The circulating fluid obtained by separating calcium fluoride by the first dehydrator (16) has its flow rate reduced by the amount of the separated dehydrated cake, and has a flow rate of about 2.4 m ³ / h.
It is discharged from 6) into the separated liquid tank (17) and further introduced into the electrodialysis device (19) by the waste liquid pump (18). In the electrodialyzer (19), about 90% of the dissolved components of sodium chloride and sodium fluoride are separated and removed from the circulating fluid by electrodialysis.

From the electrodialysis device (19), sodium fluoride and sodium chloride removed from the circulating liquid are discharged as a concentrated liquid at a flow rate of about 0.5 m ³ / h. Since the concentrated solutions of sodium fluoride and sodium chloride have a relatively high concentration, they are recovered and reused in this embodiment. It is also possible to further concentrate and dry this to recover sodium chloride and sodium fluoride as solids.

On the other hand, the circulating liquid that has passed through the electrodialysis device (19) is separated into solids deposited by dehydration treatment, and about 90% of the dissolved components are separated and removed by electrodialysis, resulting in a clear liquid. ing. This clarified circulating fluid is about 1.8 m ³
Rinse tank (2
It is introduced in 1). The rinse tank (21) has a first dehydrator (1
6) Sodium fluoride dehydrated cake separated from the circulating liquid was also introduced, and the clear liquid and dehydrated cake were rinsed in the rinse tank (2
Mixed inside 1). Sodium chloride having a concentration of about 1.3% by weight in the dehydrated cake is diluted with a clarified liquid having a concentration of about 0.1% by weight to reduce the concentration to about 0.2% by weight.

A mixed fluid of the sodium fluoride dehydrated cake and the clarified liquid was used as a circulating liquid in the second slurry supply pump (2
It is introduced into the second dehydrator (23) from the rinse tank (21) by 2). The circulating liquid is dehydrated again in the second dehydrator (23), and sodium fluoride is separated from the circulating liquid as a dehydrated cake having a water content of about 80%. Circulating liquid is a rinse tank
Since the sodium chloride concentration is reduced to about 0.2% by weight in (21), sodium chloride in the dehydrated cake is also reduced, and the purity of sodium fluoride when dried is 95% sufficiently. It is possible to obtain products with higher added value.

The circulating liquid from which sodium fluoride has been separated by the second dehydrator (23) is a circulating liquid (10) as a clear liquid from which both sodium fluoride and sodium chloride have been separated and removed.
Is discharged at a flow rate of about 1.8 m ³ / h, and alkali is added again by the alkali hopper (12) to be reused as a circulating liquid.

In the present embodiment, the flow rate of the circulating liquid introduced from the circulation tank (10) into the washing tower (8) is about 2.5 m ³ / h, and the circulation tank from the second dehydrator (25) is used. The flow rate of the circulating fluid introduced into (10) is about 1.8 m ³ / h and the circulating fluid is reduced to about 0.7 m ³ / h per circulation. It will make up for the shortfall.

[0103]

As described above, according to the present invention, the CFC decomposition exhaust gas is quantitatively and continuously neutralized with an alkali-added circulating fluid, and the neutralized product is continuously removed and recovered from the circulating fluid. Since it is a method for treating CFC-decomposed exhaust gas that uses most of the circulating fluid repeatedly, it efficiently treats CFC-decomposed exhaust gas and efficiently recovers the solid fluoride salt of useful components and, if necessary, the chloride salt. In addition, there is an effect that the present invention can be installed on a small scale.

[Brief description of drawings]

FIG. 1 is a system diagram of a CFC decomposition processing apparatus according to a first embodiment of the present invention.

FIG. 2 is a system diagram of a CFC decomposition processing apparatus according to a second embodiment of the present invention.

FIG. 3 is a system diagram of a CFC decomposition processing apparatus according to a third embodiment of the present invention.

[Explanation of symbols]

 1 Blower 2 Heater 3, 4 Flow Rate Control Valve 5 Catalyst Container 6 Baffle 7 Separate Room 8 Washing Tower 9 Adsorption Tower 10 Circulating Tank 11 Circulating Pump 12 Alkali Hopper 13 Slurry Supply Tank 14 Cooling Coil 15 Slurry Supply Pump 16 Dehydrator 17 Separation Liquid tank 18 Waste liquid pump 19 Electrodialysis device 20 Clarifying liquid pump 21 Rinse tank 22 Slurry supply pump 23 Dewatering device 24 PH meter 25 Flow rate adjusting valve 26 Concentrate pump 27 Drainage tank

Claims (9)

[Claims] 1. A method for treating exhaust gas generated when decomposing fluorocarbons containing chlorine and fluorine as components,
A neutralization step of continuously adding an alkaline aqueous solution to the exhaust gas stream to neutralize hydrogen chloride and hydrogen fluoride contained in the exhaust gas and producing a solution containing a soluble chloride salt and a solid fluoride salt, and a soluble chloride Dehydration step of dehydrating a solution containing salt and fluoride solids to extract wet fluoride solids, and removing soluble chloride from the solution after extracting fluoride solids to purify the solution The method for treating CFC-decomposing exhaust gas, which comprises: an electrodialysis step for performing the same; and an alkaline aqueous solution generating step for adding an alkali to the purified solution and supplying the solution to the neutralizing step, and circulating the solution through each step. . 2. A method for treating an exhaust gas generated when decomposing fluorocarbons containing chlorine and fluorine as components, wherein an alkaline aqueous solution is continuously added to the exhaust gas stream to obtain hydrogen chloride and hydrogen fluoride contained in the exhaust gas. A neutralization step of neutralizing and producing a solution containing a soluble chloride salt and a fluoride salt solid;
First dehydration step of extracting a wet fluoride salt solid matter by dehydrating a solution containing soluble chloride salt and fluoride salt solid matter, and removing soluble chloride salt from the solution after extracting the fluoride salt solid matter Electrolysis step to purify the solution by washing, rinse step to wash the fluoride salt solid matter extracted in the dehydration step with purified solution, and dehydration and fluorination of the solution containing the washed fluoride salt solid matter. It is composed of a second dehydration step for recovering the salt solid matter and an alkaline aqueous solution generating step for adding an alkali to the solution after the recovery of the fluoride salt solid matter and supplying it to the neutralization step, and circulating the solution through each step. A method for treating a chlorofluorocarbon-decomposed exhaust gas. 3. The method for treating CFC-decomposed exhaust gas according to claim 1, wherein the chloride salt removed in the electrodialysis step is recovered. 4. The method for treating CFC-decomposed exhaust gas according to claim 1, 2 or 3, wherein an equivalent amount of alkali necessary for neutralizing hydrogen chloride and hydrogen fluoride contained in the exhaust gas stream is added. . 5. The CFC decomposition according to claim 4, wherein the amount of the alkali to be added is set to be in excess of an equivalent amount determined by a chemical reaction formula for neutralizing hydrogen chloride and hydrogen fluoride contained in the exhaust gas stream. Exhaust gas treatment method. 6. The method for treating CFC-decomposed exhaust gas according to claim 5, wherein an acid is continuously added to the solution on the inlet side of the first dehydration step to neutralize residual alkali in the solution. 7. The method for treating CFC decomposition exhaust gas according to claim 6, wherein the acid is hydrochloric acid. 8. A method of treating an exhaust gas generated when decomposing fluorocarbons containing no fluorine and no chlorine as a component, wherein an alkaline aqueous solution is continuously added to the exhaust gas stream to contain hydrogen fluoride contained in the exhaust gas. And a dehydration step of dehydrating the solution containing the fluoride salt solids to extract a wet fluoride salt solid, and a neutralization step of forming a solution containing the fluoride salt solids. And an alkali aqueous solution generating step of supplying an alkali to the solution after the extraction and supplying the solution to the neutralization step, wherein the solution is circulated through each step. 9. The treatment of CFC-decomposed exhaust gas according to claim 8, wherein the amount of the alkali added is set to be in excess of an equivalent amount determined by a chemical reaction formula for neutralizing hydrogen fluoride contained in the exhaust gas stream. Method.