JP3925890B2 - Method and apparatus for treating PCB-contaminated waste cleaning exhaust gas - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method and apparatus for treating exhaust gas for cleaning polychlorinated biphenyls (hereinafter referred to as “PCB”), and more particularly to a method and apparatus for treating exhaust gas generated by solvent cleaning of PCBs. .
[0002]
[Prior art]
PCBs have been produced and used as useful materials for heat transfer media, insulating oils for electrical equipment such as transformers and capacitors, carbonless paper, lubricating oils, various plasticizers, paints, sealant agents, and the like. PCBs are a concept including PCB and its derivatives. PCBs were affected by living things and the environment after the Kanemi oil affairs incident, etc., and production was discontinued by 1972. Manufacturing, importing, use for open systems, and new use by 1979 Forbidden. For closed-system applications, most of the PCBs for heat transfer media have been recovered since then, but PCBs for electrical equipment are still being used or stored by operators.
However, as the storage of used PCB electrical equipment has been prolonged, the risk of equipment loss / missing, PCB leakage, accidental leakage, etc. has increased. Already, according to a survey by the Ministry of Health and Welfare in 1993, about 7% are missing. PCBs are widely detected in the environment or in the living body, and it is suggested that they may enter the environment through various routes.
Therefore, early treatment of PCB waste is demanded globally. In Japan, high temperature pyrolysis treatment of liquid waste PCBs at Takasago Works, Kaneka Chemical Industry Co., Ltd. for about two years from November 1987 is required. The only exception is that no “PCB waste disposal” has been approved, and many other treatment facilities planned throughout the country have not been realized due to location problems.
In order to completely dispose of electrical equipment using PCBs, it is necessary to purify not only the filled insulating oil but also contaminants such as containers in which PCBs are adhered and impregnated. As a method for disposal or recycling of PCBs contaminants (waste plastics or metal scrap), a method for sufficiently removing PCBs using incineration and cleaning equipment is defined. As a criterion, 0.1 μg / 100 cm ² is determined as the surface adhesion amount, or 0.01 mg / kg as the content, and this criterion is 100 times stricter than that in North America and the like.
[0003]
[Problems to be solved by the invention]
When “Method to sufficiently remove PCB using cleaning equipment” is used as the “disposal or recycling method for PCB contaminants”, waste cleaning agent is generated and heat drying or distillation cleaning of waste cleaning agent is performed. In addition, exhaust gas containing cleaning agent vapor is also generated. Normally, activated carbon is used for this exhaust gas treatment.
In this case, since the criteria for purification are strict in Japan, the amount of solvent used is inevitably increased, and the amount of exhaust gas generated and the amount of activated carbon used are also increased. At present, spent activated carbon containing PCBs must be stored because there are no authorized treatment / disposal methods and judgment criteria.
[0004]
In the case of using a solvent as a cleaning agent, in order to recover the solvent and reduce the amount of activated carbon used, in the exhaust gas treatment, a cooling condensation treatment is generally performed before the activated carbon treatment. Since the boiling point of the cleaning solvent is usually lower than that of PCBs, most of the non-condensed components contained in the gas after cooling and condensation are solvents, and the amount of PCBs is small. However, in many cases, since the cleaning solvent itself is also harmful, the activated carbon that has been broken through with the cleaning solvent must be replaced. Therefore, a large amount of used activated carbon with a slight amount of PCBs adsorbed under conventional use conditions.
Accordingly, the present invention provides a method and apparatus for treating PCB pollutant cleaning exhaust gas, which can regenerate the activated carbon at any time when the exhaust gas at the time of solvent cleaning of PCB pollutants is treated, and thereby extend the life as much as possible. The purpose is to provide.
[0005]
[Means for Solving the Problems]
(1) In a method for treating polychlorinated biphenyl pollutant cleaning exhaust gas having an activated carbon adsorption step in which polychlorinated biphenyl contaminants are washed with a solvent and the resulting polychlorinated biphenyls and the exhaust gas containing the solvent are guided to the activated carbon layer and adsorbed. The polychlorinated biphenyl adsorbed in the activated carbon adsorption step by stopping the supply of the exhaust gas to the activated carbon layer that was previously in the adsorption step among the two or more activated carbon layers arranged in parallel and depressurizing and / or heating the activated carbon layer A desorption step of desorbing the solvent out of the solvent and the solvent, and a step of cooling and condensing the desorbed gas containing the desorbed solvent and introducing the non-condensable substance to another activated carbon layer having adsorption ability Recycled polychlorinated biphenyl pollutant cleaning exhaust gas, which has an activated carbon layer that has been previously in the adsorption process, and regenerates the exhaust gas adsorption capacity Method of processing.
(2) The method for treating polychlorinated biphenyl pollutant cleaning exhaust gas according to (1), wherein the heating temperature of the activated carbon layer is 200 ° C. or less.
(3) Two or more activated carbon layers arranged in parallel for adsorbing the cleaning exhaust gas containing polychlorinated biphenyls and the solvent generated by washing the polychlorinated biphenyls with a solvent , and the activated carbon layer adsorbing the cleaning exhaust gas Of polychlorinated biphenyls adsorbed by heating and / or depressurizing and desorbing means for desorbing the solvent, and in the desorbed gas of the solvent desorbed from the activated carbon layer, a condensable substance The apparatus for treating exhaust gas for cleaning polychlorinated biphenyl pollutants, comprising: a cooling means for cooling and condensing; a separating means for separating the cooling condensate; and an activated carbon layer on which non-condensable substances are re-adsorbed.
(4) On the inlet side of each activated carbon layer, it is possible to switch between an inlet for cleaning exhaust gas of polychlorinated biphenyl contaminants and an inlet for gas containing uncooled condensate from the cooling means. The apparatus for treating exhaust gas for cleaning polychlorinated biphenyls contaminants according to (3), wherein the activated carbon layer is disposed so that an outlet of the activated carbon layer communicates with a cooling means.
[0006]
DETAILED DESCRIPTION OF THE INVENTION
When the activated carbon is depressurized or heated, the adsorption capacity decreases, so that the adsorbed material is desorbed. The desorption efficiency depends on the boiling point, vapor pressure, molecular weight, hydrophobicity, etc. of the adsorbed material. In order to completely desorb the adsorbed material and completely regenerate the activated carbon, a high temperature state of several hundred degrees or more and steam supply are required, but a low boiling point material such as a cleaning solvent is relatively easily desorbed. In carrying out the present invention, for example, the following apparatus may be used. 1 and 2 are diagrams showing examples of embodiments of the present invention. During cleaning and activated carbon regeneration, the piping connecting the plant equipment is switched by a valve and driven.
FIG. 1 shows an example of an exhaust gas treatment channel in a drying process at the time of cleaning. The cleaning tank 11 is supplied with the gas heated by the heater 12, and the exhaust gas from the cleaning tank 11 is cooled and condensed by the cooling condenser 13, treated with activated carbon 1, and then supplied to the heater 12 again. A hot gas is circulated and supplied to the cleaning tank 11 to dry the object to be cleaned.
FIG. 2 shows a gas flow path when the activated carbon layer 1 is regenerated. A gas heated by a heater 12 is supplied to the activated carbon layer 1 from the opposite direction to that during cleaning. The exhaust gas from the activated carbon layer 1 is cooled and condensed to recover a solvent and the like, and then the activated carbon layer 2 is subjected to an adsorption treatment. The component gas that has not been adsorbed by the activated carbon layer 2 is heated again by the heater 12 and circulated and supplied to the activated carbon layer 1.
Here, although the vacuum pump 14 is shown on the downstream side of the cooling condenser 13 in the figure, the vacuum pump 14 can be changed to the upstream side of the cooling condenser 13 in the latter half of each processing step in which the solvent concentration in the exhaust gas becomes low. It is desirable to install piping and valves.
[0007]
If it does in this way, the adsorption substance of activated carbon layer 1 can be desorbed, and it can collect as a condensed liquid. The collected condensate is sent to the solvent regeneration device 15 for regeneration. In order to prevent thermal transformation of cleaning solvents or PCBs, and to prevent ignition of activated carbon, the heating temperature of activated carbon is about 200 ° C. even when an inert gas is used as a heated gas, so that the adsorbed substance to be desorbed Is mainly composed of a solvent having a low boiling point.
Since the remaining non-condensable components that cannot be removed by cooling condensation are removed by the activated carbon layer 2, the activated carbon regeneration process does not release adsorbed substances into the environment.
The regeneration of the activated carbon layer 2 is performed in the same manner.
The gas used for the circulation may be air, but it is desirable to use an inert gas such as nitrogen in order to prevent the activated carbon from igniting and to prevent the adsorbed material from changing. There is no problem even if it is released into the atmosphere after completion of the cleaning process or the regeneration process, but it is more desirable to store it in a pressurized tank and reuse it when an inert gas is used.
Since the load applied to the activated carbon tank in the exhaust gas treatment process is desirably as small as possible, the cooling temperature is desirably as low as possible, specifically 0 ° C. or lower, more preferably −10 ° C. or lower.
In the above form, the cooling condenser and activated carbon of the cleaning exhaust gas treatment facility are diverted, but the cooling condenser and activated carbon that are set as a part of the process for treating the exhaust gas generated during the solvent cleaning treatment are new. A refrigerated condenser and activated carbon may be used. When diverting, it is not necessary to provide a new device separately, and there is an advantage that the number of devices can be reduced accordingly. This is particularly effective when performing solvent cleaning intermittently. When it is newly provided, there is an advantage that the activated carbon can be sucked and regenerated without being limited to the solvent cleaning situation.
[0008]
In order to prevent alteration / deterioration of the adsorbed low-boiling solvent, ignition of the activated carbon, etc., the heating temperature is preferably about 200 ° C. or lower when an additive gas is supplied as a carrier gas. When general air containing oxygen is present, it is desirable to keep the temperature at about 100 ° C. or lower.
Regeneration by vacuum suction in this embodiment does not completely regenerate the activated carbon, but eventually PCBs accumulate and are replaced. Nevertheless, the amount of used activated carbon can be significantly reduced.
The above-mentioned form employs the idea of sequentially regenerating two or more series of activated carbons on the spot. Such a method is used to purify groundwater contaminated with a volatile solvent such as TCE (trichloroethylene) PCE (tetraethylene). Two or more series of fibrous activated carbon is periodically regenerated with heated steam. Exhaust gas containing heated steam and volatile solvent during regeneration is cooled and condensed, and the volatile solvent and water are separated by a specific gravity difference. The water separated by the difference in specific gravity is discharged as water that does not contain harmful substances after further processing.
However, if the activated carbon containing PCBs is treated with heated steam, the heated PCB may be partially detached from the activated carbon, so that it is difficult to treat the water after condensation. Activated carbon needs to be used for wastewater treatment, and liquid phase adsorption has low adsorption efficiency.
[0009]
【The invention's effect】
Since the present invention is configured as described above, the activated carbon adsorbed with the gas containing the cleaning solvent and PCBs is regenerated as much as possible to independently recover the adsorption capacity, and the activated carbon can be efficiently extended in life. Can be planned. That is, it becomes easy to repeatedly use activated carbon.
[Brief description of the drawings]
FIG. 1 is a conceptual diagram showing exhaust gas treatment in a cleaning process.
FIG. 2 is a conceptual diagram showing gas treatment in an activated carbon layer regeneration step.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Activated carbon layer 2 Activated carbon layer 11 Washing tank 12 Heater 13 Cooling condenser 14 Vacuum pump 15 Solvent reproduction | regeneration apparatus

Claims (4)

The polychlorinated biphenyls contaminants are washed with a solvent, and the resulting polychlorinated biphenyls and the exhaust gas containing the solvent are guided to the activated carbon layer and adsorbed to the activated carbon layer . of the two or more activated carbon bed, to stop the exhaust gas supply to the active carbon layer was in previously adsorption step, polychlorinated biphenyls adsorbed by the activated carbon adsorption step the activated carbon layer reduced pressure and / or heated to a solvent a desorption step in which the solvent elimination, non-condensable species in the desorption gas is cooled and condensed containing solvents released dehydration has a step of adsorbing led to another activated carbon layer with adsorption capacity of, Treatment of polychlorinated biphenyl pollutant cleaning exhaust gas, which regenerates the ability of the activated carbon layer previously adsorbed to adsorb the polluted exhaust gas of polychlorinated biphenyls. Method. The method of treating exhaust gas for cleaning polychlorinated biphenyl contaminants according to claim 1, wherein the heating temperature of the activated carbon layer is 200 ° C or lower. Two or more activated carbon layers arranged in parallel to adsorb the cleaning exhaust gas containing the polychlorinated biphenyls and the solvent generated by washing the polychlorinated biphenyl contaminants with the solvent, and warming the activated carbon layer adsorbing the cleaning exhaust gas And / or desorbing means for desorbing the solvent among the polychlorinated biphenyls adsorbed by depressurization and the solvent , and the desorbed gas from the solvent desorbed from the activated carbon layer, the condensable substance is cooled and condensed. An apparatus for treating exhaust gas for cleaning polychlorinated biphenyls pollutants, comprising: a cooling means for separating; a separating means for separating the cooling condensate; and an activated carbon layer on which non-condensable substances are re-adsorbed. On the inlet side of each activated carbon layer of the plurality of activated carbon layers, an introduction port for cleaning exhaust gas of polychlorinated biphenyl contaminants and an introduction port for gas containing uncooled condensate from the cooling means are arranged to be switchable, 4. The apparatus for treating exhaust gas for cleaning polychlorinated biphenyl contaminants according to claim 3, wherein the outlet of the activated carbon layer is arranged to communicate with a cooling means.

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