JP6084386B2 - Treatment method of mineral oil in radioactive control area - Google Patents

Description

  The present invention relates to a method and apparatus for in-situ processing of mineral oil retained in a radioactive control area.

  As for the treatment of waste oil in the general industrial field, an incineration process or the like is performed after an industrial waste contractor collects the oil that is not toxic as waste oil. The processing of toxic oil such as PCB is carried out in a specific facility that is legally defined.

  On the other hand, oil (turbine oil, silicon oil, etc.) used for equipment and devices in nuclear facilities has no or little contamination of radioactive materials, but liquid clearance laws and regulations are not yet established. In many cases, it cannot be taken out of the facility and stored in a radiation control area. For this reason, used waste oil that has been exchanged during regular inspections is stored in the radiation control area, and the amount thereof is increasing. Non-radioactive contaminants in the radiation control area have been incinerated, but waste oil has not been incinerated.

  Since the Great East Japan Earthquake, public opinion about the restart of nuclear power plants has been negative, and it is expected that the number of plants that will soon be decided on decommissioning will increase, including nuclear plants that have been decommissioned before the earthquake. A large amount of oil is discarded in the decommissioning process. At present, waste oil generated in large quantities must be stored in the radiation control area, resulting in a shortage of storage space. It is necessary to quickly detoxify waste oil that has not been contaminated with radiation within the radiation control area. In addition, when waste oil is processed in the radiation control area, it is necessary to avoid the generation of secondary processed products.

  Examples of the detoxification treatment of waste oil include an oil-water separation method in which oil-water separation is performed and the treated water is discharged to reduce the oil content, and a method in which the oil is gelled and reused. As an oil-water separation method, a method of separating floating oil after breaking emulsion (open document 1) has been proposed. However, in this method, it is unavoidable that oil remains, so that waste oil cannot be completely detoxified. As a method of reusing, there is a method (Publication 2) of converting to chitosan gel and reusing it as feed. However, this method also produces a residue in the form of oil. Neither method is suitable for treatment in a radiation control area from the viewpoint of secondary waste. On the other hand, as a treatment method that does not generate secondary waste, there is an electrolysis treatment method using an amphiphilic solvent (Publication 3). However, this processing method is a technique for electrolyzing VOC containing volatile oil that is easily dispersed in a solvent, and is not suitable for processing low-volatile mineral oil. Since electrolysis utilizes ions in aqueous solution, water-insoluble mineral oil cannot be treated. Thus, no appropriate method for treating mineral oil in the nuclear facility management area has been proposed.

JP H06-142407 JP 2004-159624 A JP 2010-149069

  Mineral oil held in the radiation control area is currently increasing without any treatment method. Since there is an upper limit on the storage space in the radiation control area, some kind of treatment is necessary for operation management of nuclear facilities. Moreover, the detoxification of the oil is required for the decommissioning. The present invention is to provide a processing method and apparatus for solving the above problems.

  In order to solve the above-mentioned problems, the present inventors have conducted intensive research. As a result, mineral oil is added to water to maintain an emulsified state to impart conductivity, and electrolysis using a conductive diamond electrode is performed. It has been found that treated water containing no oil can be obtained by oxidatively decomposing mineral oil without separating oil and water, and the present invention has been completed. The maintenance of the emulsified state is achieved by using a special emulsifier, preferably by further applying a shearing force. Further, it is preferable to add an electrolyte in order to improve the efficiency of electrolysis. Moreover, in order to make treated water neutral, it is preferable to adjust pH of an emulsion to an alkaline region. By using an alkaline electrolyte, pH adjustment can be achieved at the same time.

  That is, according to the present invention, a method for treating mineral oil in a radiation control area, wherein the mineral oil and an emulsifier are added to water, and electrolysis is performed using a conductive diamond electrode while maintaining an emulsified state. And a treatment method is provided that includes oxidizing and decomposing the mineral oil.

  The mineral oil and the emulsifier are preferably added to water at a ratio of 1: 1 (weight ratio). If the addition ratio of mineral oil and emulsifier is significantly different, the emulsified state cannot be maintained and electrolysis cannot be performed.

The emulsifier is composed of two or more hydrocarbons having different viscosities (preferably a combination of kinematic viscosities at 40 ° C. of 5 to 30 mm ² / s and 1 to 15 mm ² / s), nonionic surfactants (preferably polyoxyethylene -It is preferable that it is an organic type emulsifier containing 2 or more types of alkyl (C8-C18) ether), a higher alcohol (C8-C18), and water, or an inorganic type emulsifier containing fine particles.

  It is preferable to further add an electrolyte to the water. Examples of the electrolyte include sodium hydroxide and sodium sulfate. Sodium chloride, which is widely used as an electrolyte, is not preferable because it becomes hypochlorous acid and remains during electrolysis.

The electrolyte is solid sodium hydroxide, more preferably added in an amount of 0.5 g or more, preferably 1 g or more and 5 g or less in 100 ml . If the addition amount is less than 0.5 g in 100 ml, the efficiency of electrolysis does not improve, and there is no point in adding an electrolyte. Adding 5 g or more in 100 ml does not further improve the electrolysis efficiency, so there is no point in adding a large amount.

  Suitably, the mineral oil is a water-insoluble mineral oil containing at least one of turbine oil, lubricating oil, light oil, phosphate ester oil (EHC oil: phosphate ester flame retardant hydraulic fluid), and silicon oil. It is.

  It is preferable to include a step of adjusting the pH to 12 or more at the start of the treatment or during the treatment. By adjusting the pH of the emulsion to 12 or more, the pH of the liquid after the treatment can be kept neutral even if the oil decomposes during the treatment and becomes partly carboxylic acid and the pH is lowered. Can be reused or released.

  Further, according to the present invention, an emulsion preparation tank for mixing and stirring mineral oil, an emulsifier and water, an electrolysis tank provided with a diamond electrode, and an emulsion prepared in the emulsion preparation tank are electrolyzed. And a processing apparatus for carrying out the above processing method, wherein the emulsion preparation tank or the piping is provided with means for maintaining the emulsified state of the emulsion.

The processing apparatus of the present invention preferably further includes a circulation pipe for returning the processing solution electrolyzed in the electrolysis tank to the emulsion preparation tank.
The means for maintaining the emulsified state is preferably at least one of stirring means, an ultrasonic generator, and a vortex pump, and more preferably two or more. The ultrasonic generator also has an action of alleviating foaming in the emulsion, and improves the stirring effect by the shearing force. In particular, it is effective to irradiate ultrasonic waves with a low frequency of 15 to 40 kHz with high mixing power by cavitation. When an organic emulsifier is used as the emulsifier, bubbles are generated in the emulsified liquid, oil-water separation is caused, and the emulsified state is broken.

  In the processing method and processing apparatus of the present invention, a diamond electrode is used for electrolysis. The diamond electrode used in the present invention is an electrode in which conductive diamond is coated in a thin film on the surface of a metal substrate by a hot filament CVD method. A diamond electrode has a large potential difference between oxygen generation and hydrogen generation in water electrolysis (a large thermodynamic window), and hardly generates oxygen. Since oxygen is difficult to generate, electrolytic reactions other than electrolysis of water are likely to proceed, and OH radicals, which are strong oxidants, are generated. Mineral oil has a high molecular weight and is difficult to be decomposed by ordinary oxidizing agents. Even if ozone, which is a strong oxidizing agent generated from a carbon electrode such as platinum, gold, or other graphite, is used, there is a concern that a plurality of intermediate products may remain, and it is difficult to completely detoxify mineral oil. On the other hand, in the Fenton method, which is a typical OH radical generation method, ferrous ions and hydrogen peroxide are allowed to act, and iron hydroxide sludge is generated due to neutralization when the liquid is released. It is unsuitable for the treatment of mineral oil in radiation controlled areas where it is necessary to avoid outbreaks.

  According to the present invention, carbon dioxide and water can be obtained by electrolyzing a new oil and a mineral oil used in a nuclear reactor facility that are held in a radioactive control area without finding a treatment method while maintaining an emulsified state. It can be oxidized and decomposed to prevent generation of oil-derived secondary waste, and can be made harmless and aqueous solution efficiently. For this reason, it is possible to reduce the volume of waste oil by avoiding an increase in the amount of mineral oil accumulated in the radioactive control area, and it is possible to solve problems in nuclear power plant operation or decommissioning.

FIG. 1 is a schematic view showing an embodiment of a treatment apparatus for carrying out treatment of mineral oil in the radioactive control area of the present invention. FIG. 2 is a graph showing the result of the first processing in the second embodiment. FIG. 3 is a graph showing the result of the second processing in the second embodiment. FIG. 4 is a graph showing the results of processing in Example 3.

Embodiment

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings, but the present invention is not limited thereto.
An embodiment of an apparatus for carrying out the processing method of the present invention is shown in FIG.

  The treatment apparatus of the present invention comprises an emulsion preparation tank 10 for mixing and stirring mineral oil, an emulsifier and water, an electrolysis tank 20 having a diamond electrode, and an emulsion prepared in the emulsion preparation tank 10. And a pipe 30 to be sent to the electrolysis tank 20. The pipe 30 is connected to the emulsion preparation tank 10 so that the emulsion prepared in the emulsion preparation tank 10 flows out from the lower part of the emulsion preparation tank 10 to the pipe 30.

  The emulsion preparation tank 10 or the pipe 30 is provided with means for maintaining the emulsion state of the emulsion. In the illustrated embodiment, the emulsion preparation tank 10 is provided with a stirring means 25 such as a stirrer and a rotor and an ultrasonic generator 26, and a spiral pump 35 is provided in the pipe 30.

  In the illustrated embodiment, a circulation pipe 40 for returning treated water from the electrolysis tank 20 to the emulsion preparation tank 10 is further provided. The circulation pipe 40 is connected to the emulsion preparation tank 10 so that treated water is added to the upper layer of the emulsion.

Although not shown, the electrolysis tank 20 may be provided with a treated water pipe for discharging treated water.
Next, the processing method of the mineral oil of this invention using the processing apparatus shown in FIG. 1 is demonstrated.

The processing apparatus of the present invention is installed in the radiation control area, and the emulsion preparation tank 10 is filled with water and the same amount of mineral oil and emulsifier are added while stirring. The emulsion at the bottom of the emulsion preparation tank 10 is sent to the electrolysis tank 20 via the pipe 30. The emulsified liquid is electrolyzed in the electrolysis tank 20 while maintaining the emulsified state, and is oxidatively decomposed into carbon dioxide gas and water. The treated water from which the oil has disappeared is returned to the emulsion preparation tank 10 through the circulation pipe 40 and used for preparation of the emulsion. The oil content and COD _Mn in the treated water are measured and used as an index of oil decomposition progress.

  Since electrolysis is an aqueous solution reaction, oil insoluble in water cannot be oxidatively decomposed alone. In the present invention, the emulsified state is maintained to provide electrical conductivity. Although it differs depending on the type of mineral oil, it is necessary to use a specific emulsifier, especially in the case of mineral oil such as silicone oil that has a short emulsified state retention time. Suitable emulsifiers include one or more hydrocarbons and nonionic surfactants, and higher alcohols. Specifically, an emulsifier composed of 60 to 70 wt% hydrocarbon, 3 to 5 wt% n-paraffin, 10 to 30 wt% POE alkyl ether, 3 to 5 wt% higher alcohol and 5 to 10 wt% water is particularly suitable. The added amount of the emulsifier is preferably about the same weight as the mineral oil from the viewpoint of emulsification and decomposition efficiency.

  In order to improve the efficiency of electrolysis, it is preferable to add an electrolyte. As the electrolyte, sodium hydroxide and sodium sulfate are preferable. Sodium chloride is commonly used as the electrolyte, but chloride ions remain as hypochlorous acid, an oxidizing substance, during electrolysis. Since this residue affects the final water quality, sodium chloride is not preferred except when processing organic substances containing nitrogen.

  In order to reuse or discharge the treated liquid after electrolysis to the water area, the treated liquid is preferably neutral. Since electrolysis of mineral oil tends to generate carboxylic acid and lower the pH of the liquid, it is preferable to set the pH of the emulsion to an alkaline region of 12 or more.

  Also, during the electrolysis of mineral oil, oil-water separation occurs due to the fact that the decomposition rate of surfactants and higher alcohols is higher than the decomposition of mineral oil, or simply due to emulsion breakage There is a case. In the former case, the emulsifier can be emulsified again by re-adding it to the same extent as the remaining amount of mineral oil. In the latter case, the emulsified state can be maintained by continuing to stir the emulsion. Examples of the stirring method include circulation by a pump, stirring by a stirrer, and ultrasonic irradiation. The pump is indispensable for supplying the liquid to the electrode part, but a spiral pump having a high mixing effect is preferable in order to exert a stirring effect. In addition to the stirring effect, the ultrasonic irradiation has an additional effect of relaxing foaming due to the generated gas. In particular, it is preferable to use a low frequency 15 to 40 kHz ultrasonic wave having a high mixing force by cavitation. The stirrer may be installed in the circulation tank, and a shear stirrer having a high mixing effect is particularly preferable.

During oil decomposition, the oil content and COD _Mn of the liquid in the circulation tank are measured and used as an index of decomposition progress.
By the treatment method of the present invention, most of the oil is oxidatively decomposed into carbon dioxide gas and water. In the case of turbine oil, the oil content is less than 1 mg / L, COD is less than 5 mg / L, and in the case of silicon oil, the oil content is less than 10 mg / L, and COD is 5 mg / L. Less than processing is possible.

Hereinafter, the present invention will be specifically described with reference to Examples and Comparative Examples.
Turbine oil and silicon oil were processed under the operating conditions shown in Table 1 using the processing apparatus shown in FIG.

[Example 1] Maintenance of emulsified state As the emulsifiers, “Leodol SP-L10”, “Leodol TW-L120”, “Emulgen 104P + 123P” (Emulsifier manufactured by Kao Corporation) and “EBAFOSE-9500” (Ebara Industrial Washing Co., Ltd.) Maintenance of the emulsified state of turbine oil, EHC oil and silicone oil was observed using a semi-aqueous detergent). The results are shown in Tables 2-5.

“Leodol” is a fatty acid ester type nonionic surfactant made mainly from natural fats and oils, “Leodol SP-L10” is sorbitan monolaurate, and “Leodol TW-L120” is POE (20) sorbitan mono Mainly laurate. “Emulgen” is an ether type nonionic surfactant, and “Emulgen 104P” and “Emulgen 123P” are both composed mainly of polyoxyethylene lauryl ether. “EBAFOSE-9500” is composed of hydrocarbon (kinematic viscosity at 40 ° C. 5-30 mm ² / s), n-paraffin (kinematic viscosity at 40 ° C. 1-15 mm ² / s), two POE alkyl ethers, higher alcohol (C8 ~ C18) and water.

  No. 2 Rheodor TW-L120 and NO. Although 3 emulgen was not completely separated from the 60th to 120th quantile, the white phase was separated at the top.

  No. Although the emulsification retention power of 3 Emulgen was high, when it exceeded 300 minutes, the milky-white phase separated into the bottom.

  All silicone oils had low emulsification and retention, and the silicone oil phase (transparent) was completely separated.

EBA-9500 is effective for all of turbine oil, EHC oil, and silicone oil, but silicone oil has a relatively small holding power.
[Example 2] Treatment of turbine oil 50 g of turbine oil (Nihon Petroleum Corporation FBK turbine 32) and 50 g of a semi-aqueous detergent EBAFOSE-9500 (manufactured by Ebara Industrial Washing Co., Ltd.) as an emulsifier were dispersed in 1 L of demineralized water. 10 g / L of sodium hydroxide was added as an electrolyte, and the mixture was passed through a diamond electrode while maintaining an emulsified state by stirring with a stirrer. In order to alleviate foaming due to the generated gas, ultrasonic waves (US CLEANER US-4R type 100V-160W 40 kHz manufactured by ASONE) were continuously irradiated.

  In the first treatment, oil-water separation occurred when about 1/3 of the oil was decomposed, and the decomposition of the mineral oil did not proceed. Therefore, as a result of adding the same weight of EBAFOSE-9500 and re-emulsifying and continuing the treatment, the turbine oil could be decomposed to an oil content of less than 1 mg / L and COD of less than 5 mg / L.

  The results are shown in Table 6 and FIGS.

[Example 3] Treatment of silicone oil 12 g of silicone oil (DMS50 manufactured by Shin-Etsu Silicone) and 12 g of semi-aqueous detergent EBAFOSE-9500 (manufactured by Ebara Industrial Washing Co., Ltd.) as an emulsifier were dispersed in 1 L of demineralized water. 10 g / L of sodium hydroxide was added as an electrolyte, and the mixture was passed through a diamond electrode while maintaining an emulsified state by stirring with a stirrer. In order to alleviate foaming due to the generated gas, ultrasonic waves (US CLEANER US-4R type 100V-160W 40 kHz manufactured by ASONE) were continuously irradiated.

Further, the treatment liquid was filtered using a membrane filter (0.45 μmφMF), and silicate ions (Si (IV)) in the treatment liquid were measured.
The results are shown in Table 7 and FIG.

  As a result of the treatment of the silicon oil-containing liquid, it was confirmed that most of the silicon oil was decomposed and made harmless, with the initial oil content of 2600 mg / L at the final 9.5 mg / L and COD at the initial 2100 mg / L of 3.5 mg / L. It was confirmed that the silicon in the silicone oil migrated as a silicate ion (260 mg / L) into the solution.

  The oil treatment method of the present invention can perform smooth processing of mineral oil that is difficult to dispose of currently held in the radioactive control area of a nuclear facility, and solves problems in facility operation management such as securing installation space. Moreover, it can be a means for solving the problem of waste residue toward the decommissioning furnace.

Claims (5)

  A method for treating mineral oil in a radiation control area, comprising organic emulsifiers including hydrocarbons, nonionic surfactants, higher alcohols and water, turbine oil, lubricating oil, light oil, phosphate ester oil, silicone oil A water-insoluble mineral oil containing at least one of the above is added to water at a 1: 1 (weight ratio) and electrolyzed using a conductive diamond electrode while maintaining the emulsified state, and the mineral oil is oxidatively decomposed. A processing method comprising:   The processing method according to claim 1, wherein an electrolyte is further added to the water.   The processing method according to claim 2, wherein the electrolyte is solid sodium hydroxide and is added so as to be 0.5 g or more in 100 ml.   The method for treating oil according to claim 1, comprising a step of adjusting the pH to 12 or more at the start of the treatment.   The processing method according to any one of claims 1 to 4, wherein the organic emulsifier and the water-insoluble mineral oil added to water are emulsified and maintained in an emulsified state by shear stirring.