JP5508741B2 - Treatment equipment for persistent liquids containing organochlorine compounds - Google Patents

Description

  The present invention relates to a decomposition treatment of a hardly decomposable waste liquid by non-equilibrium plasma, and relates to a detoxification treatment apparatus suitable for decomposition of an organic chlorine compound.

  Conventionally, insulation oil containing PCB (polychlorinated biphenyl) having excellent electrical insulation characteristics and flame retardancy has been used for transformers. However, since the PCB is a harmful substance that adversely affects the human body and the environment as a sustainable environmentally destructive substance due to its toxicity and accumulation, the country prohibits its use today. Therefore, when disposing the insulating oil in a used transformer, it is necessary to remove the PCB from the transformer and detoxify it.

  Various proposals have been made for the above-mentioned detoxification processing technology. As the simplest and well-known method, disposal by combustion is generally used. However, since chloride compounds such as PCB are concerned about the generation of dioxins, in recent years, more advanced treatment techniques have been demanded instead.

  As an alternative processing technique, a decomposition processing technique using plasma is known. As an example, there is a plasma decomposition treatment technique described in Patent Document 1 below.

  In the plasma decomposition processing technique described in Patent Document 1, after generating water vapor plasma, the CFC liquid is supplied into the water vapor plasma in a liquid state via a probe using argon gas. As a result, chlorofluorocarbon and water vapor are decomposed into atomic and molecular forms by thermal plasma of 10,000 degrees, and are converted into carbon dioxide gas or acidic gas in the subsequent cooling process. Then, the carbon dioxide gas is discharged as it is, and the acidic gas is neutralized with an alkaline aqueous solution to be changed into a non-polluting substance such as salt and drained.

Japanese Patent Laid-Open No. 7-80286

  This technology is a type in which chlorofluorocarbons and the like are supplied from the upper side of the thermal plasma in the previous technology, but by supplying water vapor or chlorofluorocarbon to be decomposed from the lower side of the thermal plasma, It is possible to reliably prevent the chlorofluorocarbon from dropping downward and to prevent it from being accidentally discharged to the outside.

  However, since the technique described in Patent Document 1 is a processing technique using thermal plasma (thermal equilibrium plasma), the following drawbacks exist. That is, in thermal plasma (thermal equilibrium plasma), ionized nuclei and electrons need to be in a high temperature thermal equilibrium state, and so much energy is required to create this state. Therefore, there is a problem that the running cost required for the decomposition process is inevitably increased.

  In addition, the high-frequency induction thermal plasma makes it difficult to reduce the size of the apparatus, and the use of argon gas has caused the cost of decomposition treatment to increase further.

  In order to solve the above problem, a decomposition treatment technique using non-equilibrium plasma instead of the thermal equilibrium plasma has been proposed. As a decomposition processing technique using non-equilibrium plasma, a technique using corona discharge is generally known (Japanese Patent Laid-Open No. 2000-325735).

  According to this method, it is possible not only to generate plasma with much less energy than the decomposition treatment technique using thermal equilibrium plasma described in Patent Document 1, but also between plate-like electrodes, or between line-to-plate and line-pair. There is an advantage that discharge can be generated even with an electrode having a relatively simple structure such as a cylinder.

  However, corona discharge generally has an unstable discharge state and has a drawback that it easily shifts to spark discharge. That is, as the corona discharge shifts to the spark discharge, the once generated plasma disappears, and it is difficult to continue the target decomposition process stably.

  Therefore, the present invention relates to an apparatus for decomposing a difficult-to-decompose waste liquid containing an organic chlorine compound such as PCB (polychlorinated biphenyl) in order to solve such a problem, and has an energy higher than that of a conventional thermal equilibrium plasma. An object of the present invention is to provide a processing apparatus for difficult-to-decompose waste liquid that improves efficiency and realizes stable discharge as compared with the case of corona discharge and can efficiently decompose waste liquid. .

According to the first aspect of the present invention, a reaction gas supply unit that supplies a reaction gas to the reaction unit, a microwave generator that causes microwaves to enter the reaction unit and converts the reaction gas into plasma, and a waste solution are charged. In the processing apparatus for the hardly decomposable waste liquid configured to include a waste liquid input section and a thin tube for dropping the waste liquid input from the waste liquid input section into the plasma, the lower end of the thin pipe is extended to the upper position of the reaction section , And the said reaction part was comprised with the sample stand which hold | maintains the waste liquid dripped from a thin tube in a plasma generation position, It is characterized by the above-mentioned.

According to the first aspect of the present invention, since the lower end portion of the thin tube for dropping the waste liquid to the reaction portion is extended to the upper position of the reaction portion , the waste liquid can be continuously dropped at the plasma generation position, and Even if the waste liquid is directly put into the plasma generated by the discharge, the waste liquid and the organic chlorine compound can be decomposed continuously and stably without the plasma disappearing.

According to the first aspect of the present invention, the waste liquid dropped from the probe can be held in the plasma for a long time on the sample stage, so that the decomposition rate of the waste liquid and the organic chlorine compound can be improved.

1 is an overall configuration diagram of a waste liquid treatment apparatus containing an organochlorine compound according to the present invention. It is a principal part expansion longitudinal cross-sectional view which expands and shows only the plasma reaction part of the said waste-liquid processing apparatus.

  Hereinafter, embodiments of the present invention will be described with reference to FIGS. 1 and 2. FIG. 1 shows an embodiment of a waste liquid treatment apparatus containing an organochlorine compound according to the present invention. As shown in FIG. 1, the waste liquid treatment apparatus A of the present invention includes a microwave generator 1, a microwave waveguide 2, a waste liquid input section 3, a reaction gas supply section 4, a plasma reaction tube 5, and a vacuum pump 6. And the collection part 7 which collects the product after the decomposition process of a waste liquid, and decomposes the hard-to-decompose waste liquid containing an organic chlorine compound.

  8 is an isolator provided to absorb the reflected microwave in order to prevent the microwave oscillated from the microwave generator 1 from being reflected and entering the apparatus 1, and 9 is a microwave. It is a power monitor to check the strength of the.

  Reference numeral 10 denotes a stub tuner that resonates the microwave and focuses the plasma generation position. Reference numeral 11 denotes a pressure gauge that measures the atmospheric pressure in the plasma reaction tube 5 whose pressure is adjusted by the vacuum pump 6.

  In addition, the collection unit 7 includes a cold trap 12 that cools and collects water out of products generated as a result of decomposing the waste liquid, and a gas cleaning bottle 13 that collects hydrogen chloride. In addition, the gas cleaning bottle 13 is configured to include a bottle in which water is enclosed (in FIG. 1, two bottles are provided, but the number is not limited).

  Reference numeral 14 denotes an observation window for viewing the plasma generation status, and the status of the plasma reaction part shown in FIG. 2 can be confirmed. In the plasma reaction part X, a plasma reaction tube 5 is installed perpendicularly to the microwave waveguide 2, and the upper part is connected to the waste liquid input part 3 and the reaction gas supply part 4, and the lower part is the collecting part. 7 and a vacuum pump 6.

  In the plasma reaction tube 5, the lower end of a narrow tube (hereinafter referred to as a probe) 15 whose upper end is connected to the waste liquid input unit 3 extends above the generation position of the plasma generated by the microwave. In the lower part, a sample stage 16 is provided for retaining the waste liquid supplied from the waste liquid input part 3 via the probe 15 at the plasma generation position for a long time.

  The plasma reaction tube 5 is formed of, for example, a transparent quartz tube, and microwaves oscillated from the plasma generator 1 shown in FIG. 5 can pass through well.

  Next, the waste liquid processing operation by the waste liquid processing apparatus A of the present invention will be described in detail. Since the waste liquid treatment apparatus A of the present invention is used for decomposing a hardly decomposable waste liquid containing an organic chlorine compound, first, an insulating oil containing PCB (polychlorinated biphenyl) as a treatment target is decomposed. The case where it does is demonstrated.

  As the insulating oil, for example, an electric insulating oil for a pole transformer is used. When this elemental analysis of the insulating oil was conducted this time, it was a pure hydrocarbon composed of carbon and hydrogen and not containing other elements.

  In decomposing the insulating oil, first, oxygen is supplied as a reaction gas from the reaction gas supply unit 4 shown in FIG. 1 (for example, 3 L / min). The oxygen passes through the plasma reaction tube 5 downward as shown in FIG. 1, and is supplied to the plasma reaction part X shown in FIG.

  Next, the inside of the plasma reaction tube 5 is depressurized and fixed to a predetermined pressure (for example, 1.5 kPa) by using the vacuum pump 6 and the pressure gauge 11, and the microwave generated by the microwave generator 1 in this state is predetermined. Oscillates at an output of 670 W (such as 670 W).

  The microwave output from the microwave generator 1 propagates to the power monitor 9 via the microwave waveguide 2 and the isolator 8, and incident power is detected by the power monitor 9. At this time, the isolator 8 protects the microwave generator 1 by absorbing the reflected microwave. The power monitor 9 detects the power of the reflected microwave.

  The microwave that has passed through the waveguide 2 is resonated by the stub tuner 10, focused on the plasma generation position shown in FIG.

  The microwaves incident on the plasma reaction part X pass through the plasma reaction tube 5 made of a transparent quartz tube or the like satisfactorily. At this time, oxygen is supplied as a reaction gas from the reaction gas supply unit 4 shown in FIG. 1 into the plasma reaction tube 5, and the oxygen is ionized by incident microwaves to be turned into plasma.

  Note that the plasma generated at this time is generated by glow discharge because the inside of the plasma reaction tube 5 is decompressed to a constant pressure (for example, 1.5 kPa) as described above. Glow discharge is a discharge that is more stable and wider than corona discharge, and has the advantage that it can be generated with lower energy than arc discharge.

  When glow discharge plasma is generated in the plasma reaction part X, insulating oil containing PCB (polychlorinated biphenyl) to be treated is introduced into the waste oil supply part 3 in a liquid state (for example, 21.2 mg / s). The introduced waste oil descends in the probe 15 shown in FIG. 1 or FIG. 2, but the insulating oil has a high viscosity at room temperature, so that there is a problem that it stays in the probe 15.

  Therefore, when the insulating oil is introduced into the waste oil supply unit 3, a gas such as oxygen (for example, 50 ml / s) is introduced into the probe 15. The introduced insulating oil is pushed downward in the probe 15 by the introduction of the gas, and continuously dropped from the lower end (tip) shown in FIG.

  At this time, since glow discharge plasma is generated in the plasma reaction part X, the insulating oil dropped from the lower end of the probe 15 is decomposed by the plasma. Here, as described above, since the insulating oil is a pure hydrocarbon composed of carbon and hydrogen, the insulating oil is decomposed into carbon dioxide, carbon (soot) and water.

  Further, since the insulating oil dropped from the probe 15 stays on the sample stage 16 installed at the lower part of the plasma generating part X, it can stay in the plasma for a long time, improving the decomposition rate of the insulating oil by the plasma. Can be made.

  The soot (carbon) generated by the decomposition is combined with oxygen supplied from the reaction gas supply unit 4 and descends in the plasma reaction tube 5 to the lower side of the plasma reaction unit X as carbon dioxide. Therefore, by attaching soot (carbon) in the plasma reaction tube 5, it is possible to prevent the microwave from passing through the reaction tube 5 and reliably prevent the generation of plasma.

  Similarly, water and carbon dioxide generated by the decomposition of the insulating oil descend in the plasma reaction tube 5, and water or ice is collected through a cooling process by the cold trap 12, and the carbon dioxide is collected in the subsequent gas cleaning bottle 13. It passes through and is discharged to the outside environment as a harmless gas.

  Since undecomposed insulating oil stays in the apparatus below the plasma discharge tube 5, the plasma discharge tube 5 and other piping may be recovered by washing with an organic solvent such as hexane. The mixed solution of undecomposed insulating oil and hexane obtained by washing the apparatus can be subjected to weight measurement as undecomposed insulating oil by removing hexane using a rotary evaporator after filtration. As a result, the decomposition rate of the insulating oil can be calculated, and at the same time, the relationship between the input rate of the insulating oil and the decomposition rate can be examined.

  As a result, according to the hardly decomposable waste liquid treatment apparatus A of the present invention, the compound could be almost completely decomposed by subjecting the insulating oil introduced as the hardly decomposable waste liquid to plasma decomposition. As a result of our investigation, when the input speed of the insulating oil is 5 mg / s or less, the amount of the injected insulating oil can be decomposed, and the input speed is equivalent reaction with oxygen as the reaction gas. Even when it exceeded 21.2 mg / s, decomposition of about 80% was possible.

  Further, since the generated plasma is a glow discharge, a stable discharge can be realized as compared with the corona discharge plasma, and the insulating oil is dropped into the plasma reaction part X via the probe 15 so that the plasma is generated. There was no problem of disappearance during the decomposition process, and the decomposition efficiency of the insulating oil could be improved.

  Next, the dechlorination ability of the microwave plasma by this apparatus (treatment apparatus for persistent liquid waste) A will be examined. Here, trichlorobenzene was used as a substitute for PCB (polychlorinated biphenyl). This is a measure for minimizing the amount of PCB used since PCBs are concerned about adverse effects on the human body, such as carcinogenicity, and are currently strictly restricted in use and discharge by law.

  First, since the melting point of trichlorobenzene is 17 ° C. and becomes a solid due to a temperature change near room temperature, when it passes through the probe 15 from the waste liquid input part 3 shown in FIG. There is a possibility. Therefore, the trichlorobenzene was diluted to 10% with tetradecane to prepare a sample.

  In the case described above, it is possible to prevent the sample from being blocked in the probe 15 by introducing the gas such as oxygen into the probe 15 by pushing the diluted sample into the probe 15 downward. It is the same.

  The diluted sample pushed out of the probe 15 is continuously dropped into the plasma reaction part X from the lower end of the probe 15 shown in FIG. At this time, the inside of the plasma reaction tube 5 generates glow discharge plasma by the microwave output from the microwave generator 1 through the microwave waveguide 2 reacting with the reaction gas (oxygen). The sample is dechlorinated by the plasma to generate hydrogen chloride. At the same time, carbon dioxide and water are generated.

  Moreover, the said sample can raise a decomposition rate more by staying on the sample stand 14 installed in the plasma reaction part X for a long time.

  Hydrogen chloride, carbon dioxide and water generated by the decomposition descend in the plasma reaction tube 5 shown in FIG. 2, and the water is collected as water or ice by the cold trap 8 shown in FIG. On the other hand, hydrogen chloride can be collected by the cold trap 8, but can be completely collected by dissolving it in water sealed in the gas washing bottle 9 installed in the subsequent stage. It is.

  Carbon dioxide passes through the gas cleaning bottle 9 and is discharged to the outside environment as a harmless gas. On the other hand, undecomposed trichlorobenzene stays in the apparatus below the plasma reaction tube 5 and may be recovered.

  As a result of our investigation, a mixed solution of 10% trichlorobenzene and 90% tetradecane by weight ratio has an equivalent reaction with an input rate of about 21 mg / s, and there is no significant change in the amount of chlorine recovered before and after the equivalent reaction. The amount of chlorine contained in the decomposed trichlorobenzene was 13 to 22%, the amount of chlorine collected by the cold trap 12 was 51 to 67%, and the amount of chlorine contained in the exhaust gas was 3% or less.

  Similar to the decomposition rate of the insulating oil described above, a decomposition rate of about 80% was obtained in the vicinity of the equivalent reaction. In other words, according to the decomposition by microwave plasma, there is no big difference between hydrocarbon decomposition and chloride dechlorination, and even when a trace amount of PCB-containing insulating oil is decomposed, there is no big difference in the decomposition rate of insulating oil and PCB. There wasn't.

  In addition, as a result of examining the undecomposed sample with a gas chromatograph mass spectrometer, only trichlorobenzene and tetradecane were detected, but biphenyl, furan and polycyclic aromatics were not detected. Was not produced, and even when PCB was used, it was not mutated into more toxic dioxins or the like.

  As described above, the processing device for the hardly decomposable waste liquid containing the organic compound of the present invention can decompose the insulating oil and the organic chlorine compound contained therein at a high decomposition rate, and in the decomposition, It is possible to provide a safe and effective decomposition treatment technique that does not generate a new cyclic organic compound and does not generate a more toxic compound.

  Further, according to the present invention, since the waste liquid is decomposed by glow discharge plasma, more stable discharge can be realized as compared with the case of corona discharge plasma, and the decomposition rate can be improved. In addition, decomposition processing with low energy is possible even compared with arc discharge.

  Furthermore, according to the present invention, it is possible to satisfactorily prevent the disappearance of the glow discharge by dropping the waste liquid into the plasma reaction section using a probe, and the decomposition process of the waste liquid is interrupted in the middle. This can be reliably prevented and the decomposition rate of the waste liquid can be improved.

  Moreover, according to the present invention, the waste liquid can be retained in the plasma for a long time by retaining the waste liquid on the sample stage, so that the decomposition rate of the waste liquid can be further improved.

  In the above embodiment, the example of the insulating oil and the decomposition treatment of the organic chlorine compound contained in the insulating oil has been described as an example. Is also applicable.

  The present invention provides a detoxification treatment apparatus capable of directly decomposing a hardly decomposable waste liquid in a liquid state using microwave non-equilibrium plasma.

DESCRIPTION OF SYMBOLS 1 Microwave generator 2 Microwave waveguide 3 Waste liquid injection part 4 Reaction gas supply part 5 Plasma reaction tube 6 Vacuum pump 7 Collection part 8 Isolator 9 Power monitor 10 Stub tuner 11 Pressure gauge 12 Cold trap 13 Gas cleaning bottle 14 Plasma Observation window 15 Capillary (probe)
16 Sample stage A Treatment equipment for flame retardant waste liquid containing organochlorine compounds X Plasma reaction section

Claims (1)

A reaction gas supply unit that supplies a reaction gas to the reaction unit, a microwave generator that causes microwaves to enter the reaction unit to convert the reaction gas into plasma, a waste solution input unit that inputs a waste solution, and the waste solution input In the processing apparatus for persistent liquid waste comprising a thin tube for dropping the waste liquid charged from the section into the plasma, the lower end of the thin tube is extended to the upper position of the reaction section, and the reaction section Is a processing apparatus for a hardly decomposable waste liquid containing an organic chlorine compound, characterized in that it comprises a sample stage for holding the waste liquid dropped from the narrow tube at the plasma generation position.

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