JP5052027B2 - Method for separating and treating PCB contaminants - Google Patents

Description

  The present invention relates to a method for separating PCB contaminants, and more particularly to a method for removing PCBs by heating PCB contaminants under reduced pressure.

  PCB (polychlorinated biphenyl) is a compound obtained by substituting one or more hydrogens of biphenyl with chlorine, and there are 10 types of homologues and 209 types of isomers depending on the number and position of chlorine to be substituted. PCB has high chemical stability and has characteristics such as high insulation, incombustibility, heat decomposability, poor water solubility, etc., so conventionally used as insulating oil and heat medium for electrical equipment such as capacitors and transformers. Although it has been used, the production has been stopped because it is harmful to the human body and the environment, and a method for treating and disassembling the electrical equipment that contains the already produced PCB and the contaminants to which the PCB has adhered has been proposed.

Patent Document 1 proposes a vacuum heating method for cleaning a member to which contaminants are attached by supplying a cleaning gas under reduced pressure. However, this vacuum heating cleaning method is effective for the treatment of PCB attached to electrical equipment and the like, but there is a problem in applying it to the treatment of sludge and soil contaminated with PCB. That is, muddy and powdery PCB contaminants have low heat transfer performance and take a long time to heat to the inside, and it is difficult to perform uniform heat treatment especially in the vacuum heating separation method of heating by radiant heat transfer, The temperature difference between the surface of the contaminant and the inside becomes large, and the PCB in the low temperature portion cannot be evaporated and separated and removed, so that the processing efficiency cannot be improved. For this reason, it is necessary to lengthen the time for the vacuum heat treatment, and if rapid heating, vibration, and stirring are added to make the heat transfer uniform, PCB contaminants are scattered as fine powder and diffused to the downstream device. Recovery has become difficult.
JP 2004-99646 A

  An object of the present invention is to provide a separation method for PCB contaminants that increases the processing efficiency for separating and removing PCBs from powdered PCB contaminants such as sludge and soil by a vacuum heating separation method.

  In the method for separating PCB contaminants of the present invention that achieves the above object, after adding a separation aid to the PCB contaminants, the PCB contaminants are heated under reduced pressure to evaporate and separate the PCBs from the PCB contaminants. Then, the PCB is brought into contact with oil and condensed and absorbed.

  The method for separating PCB contaminants of the present invention improves the heat transfer performance during vacuum heating by adding a separation aid to the PCB contaminants, and heats the PCB contaminants under reduced pressure. The time required for raising the temperature to a temperature equal to or higher than the boiling point of the PCB can be shortened, and the temperature can be uniformly raised without any low temperature portion remaining inside while preventing overheating of the surface of the PCB contaminant. For this reason, the process efficiency which evaporates and isolate | separates PCB from a PCB contaminant can be improved.

  Furthermore, since the surface of the PCB contaminant is prevented from being overheated, particles such as soil can be prevented from scattering from the surface of the PCB contaminant and being diffused to the downstream device.

  The present invention is described in detail below.

  FIG. 1 is an explanatory view schematically showing an example of a vacuum heating separation apparatus used in the PCB contaminant separation method of the present invention. In FIG. 1, the vacuum heating separation apparatus includes a vacuum heating separation furnace 1, an oil shower tower 2, a vacuum condenser 8, and a vacuum pump 9.

  The PCB contaminant p is charged into the vacuum heating separation furnace 1 directly or in a state of being put in the processing vessel 21, and the atmosphere in the furnace is replaced with an inert gas. The vacuum heating separation furnace 1 can heat the PCB contaminant p to a temperature equal to or higher than the boiling point of the PCB by a heating means (not shown), and is brought into a reduced pressure state by a communicating vacuum pump 9. In the vacuum heating separation furnace 1, the PCB contaminant p is heated under reduced pressure, and the contained PCB is evaporated and separated and removed for decontamination.

  Steam and inert gas such as PCB evaporated and separated from PCB contaminants are sucked by the vacuum pump 9 and introduced into the oil shower tower 2. In the oil shower tower 2, oil is sprayed from the nozzle 7, PCB contacts the oil and is condensed and absorbed, and the gas phase component from which the PCB has been removed is introduced into the vacuum condenser 8 and further condensed. The oil that has absorbed the PCB flows down and is stored in the oil tank 3 and is circulated to the nozzle 7 through the cooler 6 by the circulation pump 5 and repeatedly contacts the PCB. For this reason, the PCB concentration contained in the oil gradually increases. The oil circulation line 14 is provided with an oil discharge pipe 13, and a part or all of the PCB-containing oil is extracted and transferred to a PCB decomposition treatment apparatus (not shown) for PCB decomposition. Further, new oil corresponding to the extracted oil amount or oil containing almost no PCB is supplied from the oil supply pipe 15.

  In the method for separating PCB contaminants of the present invention, after adding the separation aid d to the PCB contaminant p, the PCB contaminant p is heated under reduced pressure to evaporate and separate the PCB, and the separated PCB is brought into contact with oil. And condensed and absorbed. The PCB contaminant p to be treated in the present invention may be in the form of a slurry such as sludge or soil, in the form of powder or fine particles, and may contain moisture or other liquid matter. Specific examples include sludge contaminated with PCB, soil, and activated carbon containing PCB, crushed waste or heat-sensitive copying paper, rubble, and wood chips.

  The separation aid d is not particularly limited as long as it makes the temperature rise of the PCB contaminant p uniform. However, a heat transfer promoter such as an organic solvent, a water-soluble solvent, or a metal can be preferably exemplified. . The organic solvent is an oil having a high boiling point and preferably has a boiling point close to that of PCB (about 350 ° C.). Preferable examples of such oils include paraffinic hydrocarbon compounds having 12 to 14 carbon atoms and light oil. The water-soluble solvent is preferably water or an aqueous solution in which an organic compound or an inorganic compound is dissolved. It is preferable to dissolve the organic compound or the inorganic compound and this because the heat transfer coefficient can be increased. As such an organic compound, glycerol, sorbitol, etc. can be mentioned preferably, and as an inorganic compound, a sodium salt etc. can be mentioned preferably.

  The boiling point of water under reduced pressure (7 kPa) is 38.2 ° C. When heated to a temperature higher than this temperature, moisture contained in the PCB contaminants evaporates and voids are generated inside the PCB contaminants. Since the thermal conductivity of the gas phase, particularly the thermal conductivity under reduced pressure, is very low, the thermal conductivity of PCB contaminants with voids is determined by the contact rate between the solid phase particles. For example, the thermal conductivity of sludge is 0.45 to 1.0 kcal / mhr ° C., and the porosity between soil particles is 20 to 80%. When the water present in the voids evaporates, the thermal conductivity of the dried soil decreases to 0.1 to 0.5 kcal / mhr ° C. The thermal conductivities of water and oils are 0.5 and 1.0 kcal / mhr ° C., respectively, and the thermal conductivity is 0.5 to 1.2 kcal when water or oil fills the voids between the soil particles. Increase to / mhr ° C. That is, when water or oil is present as a separation aid in the voids of the PCB contaminant, the thermal conductivity of the PCB contaminant is maintained without decreasing until the separation aid evaporates. be able to.

  FIG. 2 schematically illustrates the change over time in the temperature rise during heating, with and without the addition of a separation aid comprising an organic solvent or a water-soluble solvent to PCB contaminants. When the separation aid is added, the temperature rise rate is fast because the thermal conductivity of the PCB contaminant is kept high until the boiling point of the separation aid is reached. Evaporation heat is consumed at the boiling point, and the subsequent thermal conductivity is the same as when no separation aid is added, but the time required to reach a predetermined processing temperature is compared to when no separation aid is added. It can be greatly shortened.

  The addition amount of the separation aid composed of an organic solvent or a water-soluble solvent is preferably 10 to 90 parts by weight, more preferably 20 to 40 parts by weight with respect to 100 parts by weight of the PCB contaminant. If the amount added is less than 10 parts by weight, the effect of increasing the thermal conductivity during vacuum heating and shortening the heating time cannot be sufficiently obtained. If the amount added exceeds 90 parts by weight, the sensible heat and latent heat of evaporation during temperature rise This is not preferable because the amount of heat consumed in the process increases.

  The separation aid d evaporated and separated from the PCB contaminant p is sucked by the vacuum pump 9 together with the PCB, introduced into the oil shower tower 4, and absorbed in contact with the oil. When the separation aid is an organic solvent, it can be circulated and used as it is in the oil. The oil used for the oil shower tower 4 is preferably the same as the organic solvent used for the separation aid, and specifically, a paraffinic hydrocarbon compound having 12 to 14 carbon atoms, light oil or the like is used. Good.

  When a water-soluble solvent is used as the separation aid d, when oil containing the water-soluble solvent circulates through the oil pumping line 5 and the cooler 6 through the oil circulation line 14 and the reduced pressure oil shower tower 4, the influence of moisture and the like Since the circulation pump 5 causes cavitation, the oil circulation becomes unstable, and there is a concern that the efficiency of contact with the supplied PCB and the separation aid may be reduced. For this reason, it is preferable to arrange the oil / water separation tank 4 downstream of the oil tank 3 as shown in FIG. A well-known thing can be used for the oil-water separation tank 4, and it is good to circulate the isolate | separated oil through the circulation pump 5, and to discharge | emit the isolate | separated water | moisture content with the drain pipe 11. FIG. An oil level gauge 12 for overflowing oil in the oil / water separation tank 4 may be provided to adjust the amount of oil discharged from the oil discharge pipe 13. Further, an interface meter 10 may be provided to adjust the amount of water discharged from the drain pipe 11. By providing the oil / water separation tank 4, not only the water-soluble solvent but also the water contained in the case where the PCB contaminant p is sludge or the like can be removed.

  On the other hand, when a heat transfer accelerator such as metal is used as a separation aid, heat transfer is conducted between the sludge and soil particles by mixing the heat transfer accelerator with sludge and soil and uniformly dispersing it. It becomes the form which a promoter fills, heat transfer through particle | grains and a heat-transfer promoter can be accelerated | stimulated, and the thermal conductivity of the whole PCB contaminant can be made high. In addition, the heat transfer accelerator such as metal does not require the amount of heat required for evaporation heat unlike the case of using an organic solvent or a water-soluble solvent, and the heat transfer accelerator is not added until the predetermined processing temperature is reached. In comparison, a high thermal conductivity can always be maintained. For this reason, the time required for heating can be significantly shortened.

  The heat transfer accelerator is not particularly limited, but a metal heat transfer accelerator is preferable, and a metal piece, a metal rod, a metal net, a metal ball, or the like is more preferable. By using such a metal heat transfer accelerator, it can be uniformly mixed and dispersed with the PCB contaminant p, and in particular, it can be effectively dispersed between particles such as sludge and soil.

  The amount of the heat transfer accelerator added as a separation aid is preferably 10 to 90 parts by weight, more preferably 20 to 40 parts by weight with respect to 100 parts by weight of the PCB contaminant p. If the amount added is less than 10 parts by weight, the effect of increasing the thermal conductivity during vacuum heating cannot be sufficiently obtained. If the amount added exceeds 90 parts by weight, the proportion of PCB contaminants p decreases, and the heat transfer accelerator. The energy required to separate and recover is increased, which is not preferable. As a method for separating the heat transfer promoter from the PCB contaminant p after the treatment, a known method can be used, which can be separated and recovered by centrifugation, separation with a magnet, separation with a sieve, or the like.

  In the method for separating a PCB contaminant according to the present invention, it is preferable that the PCB contaminant p to which the separation aid d is added is placed in the processing vessel 21 and charged into the vacuum heating separation furnace 1. The processing container 21 is not particularly limited, but a metal container having high heat transfer efficiency may be used. By storing the PCB contaminant p in the processing vessel 21, the heating efficiency from the vacuum heating separation furnace 1 can be improved, and particles such as sludge and soil are scattered from the PCB contaminant p to the downstream apparatus. Diffusion can be prevented.

  The processing container 21 is preferably configured to transmit the PCB without scattering the powder or particles contained in the PCB contaminant p. For example, the opening of the processing vessel 21 may be covered with a scattering prevention film 22 such as a film, a film, a net, or a filter that is permeable to PCB, moisture, an organic solvent, or a water-soluble solvent and does not allow powder to pass therethrough. Separation aids are added to PCB contaminants, placed in a processing vessel, and the openings are covered with a scattering prevention film and placed in a vacuum heating separation furnace, so that PCBs, moisture and separation aids from PCB contaminants can be removed during vacuum heating. The scattering of particles can be prevented without hindering the evaporative separation of the agent.

  The heating means of the vacuum heating separation furnace is preferably an external heating means such as an electric heater, a heat exchanger, a heating gas, an indirect heating burner, etc., and conducts heat transfer through a shelf or a processing vessel where PCB contaminants are left stationary. And / or heating by radiation. The conditions for vacuum heat separation vary depending on the size of the equipment and the form of the object to be treated, but the rate of temperature rise is preferably 1 to 50 ° C./min, more preferably 3 to 30 ° C./min, preferably the treatment temperature. Is 180 to 600 ° C., more preferably 250 to 450 ° C., the degree of vacuum is preferably 0.01 to 60 kPa, more preferably 0.1 to 10 kPa, and the treatment time is set to a predetermined treatment temperature. Preferably it is 0 hour or more and 24 hours or less, more preferably 1 to 6 hours after reaching. By adding a separation aid, it becomes possible to achieve such processing conditions, and the PCB contaminants are heated uniformly and uniformly to perform the process of evaporating and separating the PCB, and by efficient heating. The time required for heating can be shortened by increasing the heating rate. Moreover, since the surface of the PCB contaminant is not overheated, scattering of particles and the like can be reduced.

It is explanatory drawing which shows typically an example of embodiment of the apparatus used for the separation processing method of the PCB contaminant of this invention. It is explanatory drawing which shows typically the temperature change at the time of the heating in the separation processing method of the PCB contaminant of this invention. It is explanatory drawing which shows typically an example of other embodiment of the apparatus used for the separation processing method of the PCB contaminant of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Vacuum heating separation furnace 2 Oil shower tower 9 Vacuum pump 21 Processing container 22 Anti-scattering film d Separation aid p PCB contamination

Claims (4)

A method for separating PCB contaminants by heating PCB contaminants containing powder under reduced pressure, evaporating and separating PCBs from the PCB contaminants, and condensing and absorbing the PCBs in contact with oil,
Before heating, a separation aid consisting of an organic solvent or a water-soluble solvent is added to the PCB contaminant, and it is generated inside the PCB contaminant by evaporation of water contained in the PCB contaminant during heating under reduced pressure. A method of separating PCB contaminants by filling the voids with the separation aid and maintaining the thermal conductivity of the PCB contaminants. A step of heating PCB contaminants in a vacuum heating separation furnace under reduced pressure; a step of evaporating and separating PCBs from the PCB contaminants in the vacuum heating separation furnace; and contacting the PCB with the sprayed oil in an oil shower tower. A PCB separation treatment method including an absorption step of condensing and absorbing,
Prior to the step of the heating, the evaporation of water contained in the PCB contaminants to fill voids that occur inside of the PCB contaminants, maintaining the thermal conductivity of the PCB contaminants in the process of the heating A method for separating PCB contaminants, comprising the step of adding to the PCB contaminants a separation aid comprising an organic solvent absorbed in the oil together with the PCB, or a water-soluble solvent . The separation aid is added to the PCB contaminant and placed in a processing container, and the PCB, moisture contained in the PCB contamination, and the separation aid are permeated through the opening of the processing container. The method for separating a PCB contaminant according to claim 2, wherein the powder containing powder is coated with an anti-scattering film that does not permeate and is charged into the vacuum heating separation furnace. The method for separating PCB contaminants according to claim 1, wherein 10 to 90 parts by weight of a separation aid is added to 100 parts by weight of the PCB contaminants.

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