JP3811705B2 - Exhaust gas treatment method and equipment - Google Patents

Description

  The present invention relates to an exhaust gas treatment method and equipment for carrying out the method. In particular, the present invention relates to a method for treating exhaust gas discharged from a heating apparatus that heats an object to be treated contaminated with an organic halogen compound, which is an object of the treatment method of the present invention.

  Conventionally, various methods have been proposed for detoxifying solids contaminated with organic chlorine compounds such as dioxin and polychlorinated biphenyl (PCB) (for example, Patent Document 1).

  According to the method described in Patent Document 1, exhaust gas, that is, exhausted by heat treatment of an object to be treated (for example, soil) contaminated with an organic halogen compound (for example, dioxin or polychlorinated biphenyl (PCB)). The exhaust gas is cleaned by an oil cleaning type gas cleaning processing apparatus, and then activated carbon processing is performed.

In this oil cleaning type gas cleaning processing apparatus, high temperature exhaust gas is cleaned with liquid hydrocarbon oil, and organic halogen compounds in the exhaust gas are dispersed / dissolved in hydrocarbon oil. As a cleaning method by the oil cleaning type gas cleaning processing apparatus, an oil spray type gas cleaning method and an aeration in oil cleaning method are adopted.
In the former cleaning method, hydrocarbon oil is sprayed from a thin spray nozzle, and the sprayed hydrocarbon oil and exhaust gas are brought into countercurrent gas-liquid contact. In the latter cleaning method, the same applies to the hydrocarbon oil. The exhaust gas is aerated from a thin nozzle and is brought into gas-liquid contact.

However, in such a known processing method, when the oil spray type gas cleaning method is adopted, the oil after spraying is collected at the lower part of the apparatus and circulated to the upper part of the apparatus to reuse the oil. was there.
That is, in the exhaust gas to be cleaned, dust (fine dust) such as soil is present in addition to organic halogen compound gas components such as PCB, so this dust is mixed into the circulating oil and oil-cleaning gas There was a problem of blocking the nozzle of the cleaning apparatus.
When such a nozzle blockage occurred, the operation of the plant was interrupted, the nozzle was backwashed, and if this problem was not solved even by this reverse cleaning, it was necessary to replace the nozzle. Further, even if a filter or the like is provided in the oil circulation line or the washing machine, the filter is blocked by dust, and similarly, the filter needs to be replaced.

In the above-described aeration-in-oil cleaning method, there is a problem that a nozzle that aerates exhaust gas is blocked by dust in the exhaust gas.
The interruption of operation in a large-scale plant due to such a nozzle blockage of dust is a very big problem from the viewpoint of running costs. On the other hand, dust is simply collected in a conventional manner before gas cleaning treatment. However, the vaporized organic halogen compound is liquefied in the dust collection process and adheres to the dust, so that the dust is contaminated and the dust needs to be reheated, and the dust collector is blocked. Occur.

Japanese Patent Laid-Open No. 2003-225643

  In view of the above problems, an object of the present invention is to provide an exhaust gas treatment method capable of continuously performing the detoxification process of the exhaust gas without clogging the nozzle during the oil cleaning gas cleaning process of the exhaust gas. That is, an object of the present invention is to provide a method for treating exhaust gas that renders exhaust gas discharged from a heating device that heats an object contaminated with an organic halogen compound harmless.

  As a result of intensive studies to solve the above problems, the present inventors have replaced the exhaust gas discharged from the heating device with an oil cleaning gas instead of the conventional method in which the oil cleaning gas cleaning treatment is directly performed. Before performing the cleaning treatment, it is found that the above problem can be achieved by collecting dust at a temperature at which the exhaust gas can be kept in a gaseous state and removing dust in the exhaust gas. The invention has been completed.

That is, the present invention is an exhaust gas treatment method for detoxifying exhaust gas discharged from a heating apparatus that heat-treats an object contaminated with an organic halogen compound, and the dust in the exhaust gas at a temperature of 350 to 600 ° C. Is collected by filtration and dust collection (except when a catalyst bag filter is used), a dust collection treatment step to remove, exhaust gas from which dust has been removed and cooled to 100 to 250 ° C., and cleaning oil of 50 ° C. or less And an oil cleaning type gas cleaning treatment step of removing an organic halogen compound in the exhaust gas by contacting the exhaust gas.

  According to the present invention, the nozzle clogging during the oil cleaning type gas cleaning process is performed by collecting dust from the exhaust gas and removing dust in the exhaust gas prior to the above-mentioned requirements, in particular, the oil cleaning type gas cleaning process. By carrying out the dust treatment at a temperature of 100 ° C. or higher, it is possible to prevent the moisture in the exhaust gas from being liquefied in the dust collection process and to prevent the dust collector from being blocked. Thus, it was possible to achieve the technical effect that the exhaust gas detoxification process can be continuously performed without blocking the nozzle during the oil cleaning gas cleaning process.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
First, an exhaust gas treatment apparatus as one embodiment will be described.
FIG. 1 is a process flow diagram showing an embodiment of the processing method of the present invention.
FIG. 2 is a flow diagram showing a schematic configuration of an embodiment of an exhaust gas treatment facility and related facilities suitable for carrying out the method of the present invention.
FIG. 3 is a process flow diagram showing another embodiment of the processing method of the present invention.
FIG. 4 is a flow diagram showing a schematic configuration of an embodiment of an exhaust gas treatment facility and related facilities suitable for performing the method of the present invention on contaminants containing water.
FIG. 5 is a process flow diagram showing another embodiment of the processing method of the present invention.
FIG. 6 is a flow diagram showing a schematic configuration of another embodiment of an exhaust gas treatment facility and related facilities suitable for carrying out the method of the present invention on contaminants containing water.
FIG. 7 is a schematic diagram showing a heating device that generates exhaust gas.
As shown in FIGS. 1 and 2, the treatment facility according to an embodiment of the present invention includes a crushing unit 1 that is a pretreatment device for contaminated solid matter (contaminated object to be treated) containing moisture, and the crushed contamination. Heat treatment unit 2 (heat treatment step) that heats and processes solid matter, and dust in the exhaust gas discharged from the heat treatment unit 2 is collected and removed, and the organic halogen compound in the exhaust gas is absorbed by the cleaning oil. After removing moisture by vacuum distillation from the exhaust gas treatment unit 3 (dust collection process, oil cleaning gas cleaning process) and cleaning oil that has absorbed the organic halogen compound, the organic halogen compound in the cleaning oil is decomposed with an alkali metal. And an alkali metal processing unit 4 (alkali metal processing step).

  The crushing unit 1 is provided with a crusher 11 for crushing contaminated solids such as concrete waste.

The crushed contaminated solid is sent to the heat treatment unit 2. The heat treatment unit 2 (heat treatment step) includes a heating device 13 and a quenching device 14.
As shown in FIG. 7, the heating device 13 includes a heating furnace 106 that heats an object to be processed inside, and a jacket 105 that includes a heating medium supply port 107 and a heating medium discharge port 108 arranged on the peripheral wall of the heating furnace. And a heat medium supply unit 12 for supplying a heat medium to the heat medium supply port 107.

  The heating device 13 is provided with a nitrogen generator 15 for supplying nitrogen gas. The heat medium supply unit 12 is configured to be supplied with kerosene and LPG (liquefied petroleum gas) as fuel. The solid component processed by the heating device 13 is cooled in the quenching device 14 and is collected as a processed solid. As shown in FIG. 7, the heating device 13 (heating furnace 106) has a passage formed in a cylindrical shape for supplying air and nitrogen gas, and the inside of the heating furnace is substantially along the center. A rotating shaft 102 is rotatably provided. A plurality of paddle blades 103 are attached to the rotating shaft 102. A storage unit (jacket) 105 that stores a heat medium made of combustion gas fed by the blower 104 of the heat medium supply unit 12 is formed outside the heating device 13.

The heating device 13 includes a heating furnace 106 that heats an object to be processed inside, a jacket 105 that includes a heat medium supply port 107 and a heat medium discharge port 108 disposed on a peripheral wall of the heating furnace, and the heat A heat medium supply unit 12 that supplies a heat medium to the medium supply port, and further includes a path 25 that returns the heat medium discharged from the heat medium discharge port 105 to the heat medium supply unit 12. . By providing the path 25, there is an advantage that energy efficiency is improved.
Furthermore, the heating device 13 may include a heating furnace that heats an object to be processed inside, and an electric heater that heats the peripheral wall of the heating furnace.
Further, the heating furnace is not limited to the one described above, and may have a structure in which the container rotates (outer cylinder rotation type).

The exhaust gas treatment unit 3 (dust collection process, oil cleaning type gas cleaning process) collects and removes dust in the exhaust gas by centrifugal force in order from the exhaust gas supply side in order to process the exhaust gas generated by the heating device 13. Dust is removed by the high-temperature cyclone 16, the high-temperature bag filter 17 that collects and removes dust in the exhaust gas that has passed through the high-temperature cyclone 16, and the high-temperature cyclone 16 and the high-temperature bag filter 17. A dusting-type oil scrubber (a dusting-type gas scrubber) 18 for removing organic halogen compounds in the exhaust gas by bringing the exhaust gas into contact with the cleaning oil is provided. In the oil-sprayed oil scrubber 18, the gas component, the oil component, and the aqueous component are separated. The oil component and the aqueous component are separated by stationary separation. When the concentration of the organic halogen compound in the oil component to be treated reaches a predetermined concentration, the oil component is sent to an alkali metal treatment step described later. It is done.
In the present embodiment, when the organic halogen compound in the oil component reaches a predetermined concentration, the oil is extracted and sent to the alkali metal treatment step. As the method for extracting the oil component, almost the entire amount of oil is used. A method of extracting and adding new oil may be used, or a part of the oil may be extracted and new oil may be added according to the extracted amount. Moreover, you may make it the structure which extracts a part of oil and sends it to an alkali metal treatment process at any time, without measuring the density | concentration of the organic halogen compound in an oil component.

In order to treat the exhaust gas generated by the heating device 13, the high-temperature cyclone 16 that collects and removes dust in the exhaust gas by centrifugal force at a temperature of 100 ° C. or higher, and the dust in the exhaust gas that has passed through the high-temperature cyclone 16 are removed. A high-temperature bag filter 17 that collects dust by filtration at a temperature of 100 ° C. or higher is used.
In particular, by collecting and removing the dust in the exhaust gas containing moisture at a temperature of 100 ° C. or higher, it is possible to prevent moisture from aggregating in the dust collection treatment step and to prevent the dust collection treatment apparatus from being blocked.

A cooler 30 for lowering the temperature of the exhaust gas is provided in a path for supplying the exhaust gas from which dust is collected and removed by the high-temperature bag filter 17 to the oil-sprinkling oil scrubber 18.
The temperature of the gas entering the oil scrubber can be lowered by interposing the cooler 30 in the path for supplying the exhaust gas from which dust has been collected and removed by the high-temperature bag filter 17 to the oil-sprinkling oil scrubber 18. For this reason, it is possible to use oil having a low boiling point as the oil used in the oil scrubber, and it is possible to prevent a large amount of oil from being mixed into the exhaust gas after the oil scrubber treatment.
The temperature of the exhaust gas is preferably cooled to 100 to 250 ° C, preferably 100 to 150 ° C by the cooler 30.
When the temperature of the exhaust gas is less than 100 ° C., moisture is condensed before the organic halogen compound is absorbed in the oil component by the oil scrubber, so it is necessary to drain the condensed water, and a system for removing the contaminated water is provided separately. The necessity arises and the processing system becomes complicated. In addition, there is a problem that the risk of recontamination increases.

Further, the exhaust gas treatment unit 3 includes an oil circulation path 23 for returning the cleaning oil that has absorbed the organic halogen compound by the oil-sprayed oil scrubber 18 to the oil-sprayed oil scrubber 18, and an alkali metal treatment unit (alkali metal treatment) described later. In the step), an oil extraction path 24 for extracting cleaning oil, an activated carbon treatment device 19a for gas component treatment, and an activated carbon treatment device 19b for aqueous component treatment are provided. After the separation treatment by the oil spray type oil scrubber 18, the gas component is treated by the activated carbon treatment device 19a and discharged out of the system as a clean gas. Similarly, the aqueous component is treated by the activated carbon treatment device 19b and discharged as waste water to the outside of the system. Released.
The oil component is recycled and reused as exhaust gas cleaning oil, and is sent to the alkali metal treatment step when the concentration of the organic halogen compound, which is the target treatment product, exceeds a predetermined concentration.

In addition, a cooler 31 for lowering the temperature of the exhaust gas is interposed in a path for sending the exhaust gas emitted from the oil spray type oil scrubber 18 to a gas discharge unit that discharges the exhaust gas through the activated carbon treatment device 19a. By installing the cooler 31 in a path for sending the exhaust gas from the oil-sprayed oil scrubber 18 to the gas discharge section, oil droplets and moisture scattered along with the exhaust gas flow can be condensed and returned to the scrubber. There is an effect of reducing the load on the processing device 19a and extending the life.
In addition, it is good to cool the temperature of waste gas to 5-30 degreeC by the said cooler 31, Preferably it is 5-10 degreeC.
If the temperature of the exhaust gas that has passed through the cooler 31 is 30 ° C. or higher, the frequency of replacement of the activated carbon used in the activated carbon treatment device 19a increases, which is not preferable.

In addition, the oil spray type oil scrubber 18 brings the exhaust gas into contact with the cleaning oil, causes the cleaning oil to absorb the organic halogen compound in the exhaust gas, and discharges the cleaning oil from the contact portion. A path 23 returning to the oil-type oil scrubber 18 and a cooler 32 interposed between the paths 23 are provided.
By providing the cooler 32, there is an effect of preventing the temperature of the cleaning oil from rising.
The temperature of the cleaning oil is preferably cooled to 50 ° C. or lower, preferably 30 ° C. or lower, more preferably 15 ° C. or lower by the cooler 32.
When the temperature of the cleaning oil that has passed through the cooler 32 exceeds 50 ° C., the load on the cooler 31 increases, and there is a problem that oil droplets or water droplets that cannot be condensed increase the load on the activated carbon treatment device 19a.

The oil-sprayed oil scrubber 18 can also be used in combination with an aeration-in-oil type oil scrubber (an aeration-in-oil cleaning device). When it is desired to prevent the mist from scattering due to aeration, a wet wall type cleaning device can be used.
Of course, these cleaning devices can be used alone without being combined with the oil-sprayed oil scrubber 18. As shown in FIG. 2, the oil-sprinkling oil scrubber 18 includes a spray nozzle 18a (not shown), and the cleaning oil supplied from a cleaning oil storage tank (not shown) is directed vertically downward by the spray nozzle. Sprayed on. If the dust-removed exhaust gas is supplied into the oil-sprayed oil scrubber 18, the organic halogen compound in the exhaust gas can be absorbed in the cleaning oil by gas-liquid contact. Further, in the oil-sprayed oil scrubber 18, the cleaning oil collected at the lower part is circulated to the upper part and again sprayed from the spray nozzle.

  On the other hand, an aeration-in-oil oil scrubber is filled with cleaning oil and is usually provided with a spray nozzle facing upward in the vertical direction. The exhaust gas is aerated into the cleaning oil from the spray nozzle, and thus, the organic halogen compound in the exhaust gas can be absorbed into the cleaning oil in the same manner as described above.

The alkali metal treatment unit 4 (alkali metal treatment step) sequentially decomposes the organic halogen compounds in the cleaning oil that has passed through the oil-sprayed oil scrubber 18 with an alkali metal (for example, sodium metal) from the exhaust gas cleaning oil supply side. A vacuum distillation tank 20 that removes moisture in the cleaning oil before performing, a reaction tank (dehalogenation reaction tank) 21 that decomposes the organic halogen compound in the cleaning oil from which moisture has been removed with an alkali metal, and the reaction tank 21. A neutralization / stationary separation tank 22 for hydrating an unconsumed alkali metal (for example, metallic sodium, etc.), neutralizing an aqueous layer showing alkalinity by the hydration, and separating the aqueous layer and the oil layer It has.
Furthermore, an activated carbon treatment device 19a for treating the gas generated from the reaction vessel 21 is provided. Process oil and process waste water are formed by the neutralization / stationary separation tank 22. In this embodiment, neutralization and oil / water separation are performed in the same apparatus, but neutralization and oil / water separation may be performed in separate tanks.

The treated oil is returned to the oil-sprayed oil scrubber 18 and used to absorb the organic halogen compound in the exhaust gas.
Further, the water separated by the distillation treatment in the vacuum distillation tank 20 is subjected to activated carbon treatment and discharged as treated waste water, but can also be used as hydration water for hydration.
In this embodiment, the cleaning oil that has absorbed the organic halogen compound has been dehalogenated with an alkali metal (for example, metallic sodium). Alternatively, supercritical water oxidation treatment may be used. .

In this embodiment, the crushed contaminated solid has been processed in the heat treatment unit 2 by reduction heating that heats the organic halogen compound in an inert gas, but in the present invention, the crushed contaminated solid is treated. Alternatively, heat treatment may be used in which the temperature is higher than the evaporation temperature of the organic halogen compound to be removed.
By using a heat treatment for heating to a temperature higher than the evaporation temperature of the organic halogen compound to be removed, the organic halogen compound in the contaminated solid can be decomposed or evaporated, and the organic halogen compound can be more reliably removed from the contaminated solid.

In this embodiment, it is not necessary to add an additive specially when heating the workpiece, but the present invention is not limited to this, and an additive may be added. In the case where the concentration of the organic halogen compound in the object to be treated is high, particularly in the case of chlorinated pesticides, hydrogen chloride is generated by the treatment in the heat treatment unit 2 and the problem of equipment corrosion occurs. It is preferable to add a similar metal or an iron group metal.
Among these, a calcium compound (for example, lime) is preferable in terms of ease of handling and cost. By adding the calcium compound in this manner, chlorine in the object to be treated can be combined with calcium to fix the chlorine (for example, CaCl ₂ ) and prevent hydrogen chloride from being generated in the exhaust gas.

As another embodiment, as shown in FIGS. 3 and 4, an organic halogen compound in the exhaust gas is absorbed into the cleaning oil by the oil-sprayed oil scrubber 18, and the gas component and the oil component (including the aqueous component) are absorbed. The oil component (including the aqueous component) may be separated into the following, and the configuration leading to the next alkali metal treatment step may be employed without static separation.
This is because when pollutants containing water are processed, if the amount of water is large, it is difficult to separate the oil component and the aqueous component by stationary separation, and the separation process takes time, and the separation itself In addition, since the oil component is mixed into the separated aqueous component, a load is imposed on the subsequent activated carbon treatment, and the activated carbon needs to be frequently replaced. For this reason, it is not preferable in terms of cost, and when the allowable amount of the activated carbon is exceeded, the concentration of the organic halogen compound in the treated water when the aqueous component is treated exceeds the environmental standard. For this reason, in the case of processing contaminants containing moisture, a configuration may be adopted in which oil components (including aqueous components) extracted without standing and separating with an oil-sprinkling oil scrubber are directly led to the alkali metal treatment step. .

Further, in the alkali metal treatment step, the water in the cleaning oil is decompressed before decomposing the cleaning oil in which the organic halogen compound in the exhaust gas is absorbed with the alkali oil (for example, sodium metal) by the oil spray type oil scrubber 18. You may employ | adopt the structure which decomposes | disassembles the organic halogen compound in the washing | cleaning oil from which the water | moisture content was removed using the distillation tank 20 with an alkali metal.
If contaminated solids containing moisture are treated, a large amount of moisture will be contained in the cleaning oil. If reacted with an alkali metal (for example, sodium metal) added later, the alkali metal reacts with moisture. Since wasteful alkali metal (for example, metallic sodium) is consumed, wasteful consumption of alkali metal (for example, metallic sodium) can be suppressed by removing water in advance by vacuum distillation. Moreover, since an aqueous component evaporates by a vacuum distillation process, it can prevent that the washing oil containing the organic halogen compound in the stationary separation as described above is mixed into the treated water. Without performing this stationary separation, a method of subjecting an oil component mixed with an aqueous component to distillation under reduced pressure and treating an oil component containing a separated organic halogen compound is used when the above-mentioned oil spray type scrubber is used. It is not limited, For example, it can apply also when using an aeration-in-oil type oil scrubber.
Furthermore, an organic compound having higher volatility than an organic halogen compound decomposed with an alkali metal can be removed by distillation under reduced pressure. Examples of the highly volatile organic compound include volatile organic substances (VOC) such as trichloroethylene, tetrachloroethylene, and chlorobenzene. These volatile organic substances (VOC) can be treated with activated carbon together with water removed by vacuum distillation.

  Next, an embodiment of a method for treating an organic halogen compound using the above-described exhaust gas treatment facility will be described with reference to FIG.

The object to be treated used in this embodiment refers to a liquid or solid substance containing an organic halogen compound. For example, leachate generated in a waste treatment plant, incineration facility, factory, etc., smoke washing drainage, waste, washing Wastewater, contaminated soil, etc., and sludge deposited on the bottom of rivers, lakes, ponds, bays (sediment sludge, sludge, etc.) and soil contaminated with agricultural chemicals. In the case of contaminated soil containing concrete debris, crushing with a crusher may be necessary.
Examples of the organic halogen compound include dioxin, polychlorinated biphenyl (PCB), benzhexachloride, and aldrin.

A gas of 600 ° C. is passed from the heat medium supply unit 12 to the heating device 13, and when the temperature in the device reaches 350 to 600 ° C., the object to be processed is introduced. Since a temperature drop occurs due to the latent heat of vaporization of moisture in the object to be processed, a gas of 600 ° C. is continuously passed from the heat medium supply unit 12 so that the temperature in the heating device 13 is maintained at 350 to 600 ° C.
In the heating device 13, an object to be processed is oxidized to mainly oxidize and decompose organic compounds.

Next, an inert gas such as nitrogen gas or argon gas is introduced into the heating device 13 to bring the inside of the device into an inert gas atmosphere, and the temperature is 350 to 600 ° C., preferably 400 to 600 ° C., more preferably 450. The object to be treated is heated at a temperature of ˜550 ° C.
It is also possible to introduce hydrogen gas instead of the inert gas.
That is, the inert gas or hydrogen gas is introduced into the heating device 13, the inside of the device is placed in a low oxygen atmosphere, and the object to be processed is heated under the temperature condition. The low oxygen atmosphere means an atmosphere having an oxygen concentration of 3% or less, preferably 1% or less.
Dioxins are mainly decomposed by reducing the object to be treated at the temperature.
Further, the organic halogen compound is evaporated by heating at a temperature equal to or higher than the evaporation temperature of the organic halogen compound to be removed.
By thus heating the object to be treated, exhaust gas containing an organic halogen compound is generated. The exhaust gas contains an organic volatile substance such as an organic halogen compound or an organic halogen decomposition product, water vapor, and the like as a gas, and further includes dust in the form of fine particles. The solid component from which the organic halogen compound has been removed is supplied to the quenching device 14 and recovered.

The exhaust gas containing the organic halogen compound and fine particle dust discharged from the heating device 13 is introduced into the dust collection process.
During the dust collection process, the exhaust gas needs to be heated to a temperature of 100 ° C. or higher in order to prevent its liquefaction. If the temperature is maintained at a high temperature in the plant, it takes a lot of cost, so 600 ° C. or less is preferable. The temperature is preferably maintained at 350 to 600 ° C, more preferably 450 to 550 ° C. By preventing liquefaction of exhaust gas due to high temperature dust collection treatment, it is possible to prevent organic halogen compounds in the exhaust gas once volatilized from adhering to the dust surface during dust collection treatment, and accumulate in the pipe together with dust. This can also be prevented.
Further, since the organic halogen compound can be prevented from adhering to the dust surface, it is not necessary to heat-treat the collected dust again. In particular, it is effective when processing contaminated solids containing a large amount of moisture.

The dust collection treatment step is preferably performed in two steps.
In the first step, centrifugal dust collection processing is performed in the temperature range to remove dust having a relatively large particle size (particle size of 2 to 300 μm), and then in the second step, filtration dust collection processing is performed in the temperature range and the remaining dust is collected. Remove dust.

The device used for the centrifugal dust collection processing is not particularly limited as long as it is a centrifugal dust collection device that uses centrifugal force for dust collection and removal. In addition, a gravity dust collector (for example, a gravity settling chamber), an inertia dust collector, or the like can be used together with or instead of the centrifugal dust collector.
In the first step, for example, dust having a relatively large particle size (particle size of 2 to 300 μm) is removed using the high-temperature cyclone 16. The high-temperature cyclone 16 includes a device for heating to the above temperature range, and is generally used for the treatment of radioactive materials.

  In the second step, the remaining dust is removed from the exhaust gas after removing the dust having a relatively large particle size (particle size of 2 to 300 μm) in the first step using the high-temperature bag filter 17. The high-temperature bag filter 17 is provided with a device for heating to the above temperature range, and is used for processing radioactive substances. A bag filter is a type of filtration dust collector that generally captures dust mixed in exhaust gas with a cloth bag, etc. Examples of the hydraulic type or backwash type bag filter that are alternately used, and a pulse jet type bag filter that injects compressed air for wiping off the upper part of the filter. Preferably, a pulse jet bag filter using a sintered body made of metal fiber or ceramic can be used as the filter medium.

The exhaust gas from which the dust has been removed is introduced into the oil cleaning type gas cleaning process.
As described above, this step comprises removing the dust-removed exhaust gas by oil cleaning gas cleaning treatment to remove the organic halogen compound. Preferably, the dust-removed exhaust gas is subjected to oil cleaning gas cleaning treatment. And separating into a gas component, an oil component, and an aqueous component. This process has a function of cooling high-temperature exhaust gas in addition to a function of purifying exhaust gas.

  Examples of the oil cleaning type gas cleaning processing method include a sprayed gas cleaning method (packed tower method) and a hydrocarbon in which hydrocarbon oil is sprayed from a thin shower nozzle and the sprayed hydrocarbon oil and exhaust gas are brought into countercurrent gas-liquid contact. In addition to an aeration-in-oil cleaning method in which exhaust gas is aerated in the oil from a similarly thin nozzle and brought into gas-liquid contact, a rotoclon method, an ejector method, a rotary spray tower method, a venturi method, and the like can be exemplified. A suitable cleaning method is an oil spray type gas cleaning system. As an apparatus used for the oil spray type gas cleaning system, there is an oil spray type gas cleaning apparatus 18. Any hydrocarbon oil may be used as long as it can dissolve the organic halogen compound in the exhaust gas. Examples thereof include trans oil, kerosene, and normal paraffin oil. Further, in the spraying system such as the oil spray type gas cleaning system and the rotary spray tower system, the sprayed oil is collected in the lower part of the apparatus and circulated in the apparatus for reuse.

  In this oil cleaning type gas cleaning treatment step, as described above, the gas component, the oil component, and the aqueous component are separated, but the gas component mainly contains air, and the oil component is mainly in the exhaust gas. For example, it contains an organic halogen compound or an organic halogen compound / decomposition product, and the aqueous component mainly contains liquefied water vapor.

  The exhaust gas from which the dust has been removed by the high-temperature bag filter 17 is introduced into the oil-sprayed oil scrubber 18, and the organic halogen compound or the like is absorbed into the cleaning oil by the cleaning oil sprayed from the spray of the oil-sprayed oil scrubber 18. Is done.

  The exhaust gas as a gas component from which the organic halogen compound has been removed by the oil-spray type gas cleaning device 18 is discharged out of the system from a gas discharge unit that discharges the exhaust gas as a clean gas through the activated carbon treatment device 19a. The activated carbon treatment device 19a is provided because even if the exhaust gas from which the organic halogen compound is removed contains a trace amount of the organic halogen compound, the activated carbon treatment device 19a is adsorbed on the activated carbon of the activated carbon treatment device 19a. This is so that only the exhaust gas that does not contain is discharged outside the system.

The cleaning oil that has absorbed the organic halogen compound is supplied to the alkali metal treatment unit 4 and is first supplied to the vacuum distillation tank 20 in the alkali metal treatment step.
The vacuum distillation tank 20 is supplied with cleaning oil that has absorbed an organic halogen compound and water that has been cooled and liquefied by the oil spray type gas cleaning device 18 contained in the exhaust gas.
In addition, after leaving washing oil and water still and isolate | separating completely, only washing oil may be supplied to the following vacuum distillation tank 20, and the mixture of washing oil and water is directly distilled to the next vacuum distillation. You may supply to the tank 20. FIG.

In the vacuum distillation tank 20, moisture in the cleaning oil is removed by vacuum distillation. This is because, if the washing oil contains a large amount of water, metal sodium added later reacts with the water and wastes the metal sodium, so the water is removed beforehand by vacuum distillation.
The water recovered by distillation under reduced pressure may be supplied to an activated carbon treatment device (not shown) and discharged out of the system as treated water, or metal sodium that has not been consumed in the dehalogenation reaction described below. It may be used to process the dispersion.

The cleaning oil from which moisture has been removed by distillation under reduced pressure is supplied to a reaction tank (dehalogenation tank) 21. The washing oil is charged into a reaction vessel (dehalogenation vessel) 21 and then stirred, alkali metal (for example, a metal sodium dispersion in which sodium metal is dispersed in a hydrocarbon) and preferably dehydrated. A halogenation accelerator (for example, isopropyl alcohol) is added to cause a dehalogenation reaction. By this dehalogenation reaction, organic halogen compounds such as dioxins and polysalt biphenyls are dehalogenated (for example, dechlorinated) to become harmless organic oils, and alkali metal halides (for example, chloride) as a by-product. Sodium) is formed.
In this case, the reaction temperature for dehalogenation with the metal sodium dispersion is not particularly limited, but it is preferably performed at 30 to 100 ° C. Moreover, it is preferable that the addition ratio (Na / Cl ratio) of the alkali metal with respect to chlorine shall be 0.2-50.

Excess metal sodium not consumed in the reaction tank (dehalogenation tank) 21 is supplied to the neutralization / stationary separation tank 22. Water is supplied to the neutralization / stationary separation tank 22 to hydrate the unconsumed metallic sodium.
In this neutralization / stationary separation tank 22, since alkali is generated by the hydration reaction of metallic sodium, it is necessary to neutralize the treated water after hydration.
Carbon dioxide gas is supplied to the neutralization / stationary separation tank 22 and the carbon dioxide gas reacts with the alkali to be neutralized.
The treated water neutralized in the neutralization / stationary separation tank 22 is left to stand for oil-water separation.

The oil after the oil / water separation is recovered as treated oil. The treated oil can be reused as the cleaning oil for the oil spray type gas cleaning device 18.
The water after oil-water separation may be supplied to an activated carbon treatment device (not shown) and discharged out of the system as treated water, or excess metal sodium water in the neutralization / stationary separation tank 22 It can also be used for sums.

  In the present embodiment, the above-described apparatus is employed, and the exhaust gas treatment method for treatment as described above is employed. However, in the present invention, as shown in FIG. From the vacuum distillation tank 20a for removing components having higher volatility than the cleaning oil by vacuum distillation, and the cleaning oil from which components having high volatility have been removed by the vacuum distillation tank 20a, at least one of the cleaning oils by vacuum distillation is further added. A vacuum distillation tank 20b for removing a portion, a reaction tank (dehalogenation tank) 21 for decomposing the remaining organic halogen compound with an alkali metal, and excess alkali not consumed in the reaction tank (dehalogenation tank) 21 You may employ | adopt the apparatus provided with the neutralization / stationary separation tank 22 which processes a metal.

  In order to treat exhaust gas using such an apparatus, as shown in FIG. 5 and FIG. 6, in the alkali metal treatment step, the cleaning oil in which the organic halogen compound in the exhaust gas is absorbed by the oil-dispersed oil scrubber 18 is used as the alkali metal. Before being decomposed by (for example, metallic sodium), water and organic compounds having higher volatility than the cleaning oil are removed using the vacuum distillation tank 20a, and a part of the cleaning oil from which the moisture and the like have been removed is further removed. You may employ | adopt the method of removing using the vacuum distillation tank 20b, and decomposing | disassembling the remaining organic halogen compound with an alkali metal.

  After removing moisture and the like, by removing a part of the cleaning oil from the cleaning oil containing the organic halogen compound by distillation under reduced pressure, the concentration of the organic halogen compound can be increased, and can be efficiently reacted with the alkali metal, Treatment time with alkali metal can be shortened. Moreover, the amount of oil to be processed in the alkali metal processing step can be reduced. Furthermore, the cleaning oil that can be recovered and reused only after the alkali metal treatment can be recovered as a distilled oil, and can be reused as a cleaning oil by returning the distilled oil to the oil scrubber at an early stage.

In the vacuum distillation tank 20a, moisture and the like in the cleaning oil are removed by vacuum distillation. As a result, if the cleaning oil contains a large amount of water or the like, it is possible to prevent the sodium metal added later from reacting with the water or the like and consuming the sodium metal wastefully.
The water recovered by distillation under reduced pressure may be supplied to an activated carbon treatment device (not shown) and discharged out of the system as treated water, or metal sodium that has not been consumed in the dehalogenation reaction described below. It may be used to process the dispersion.

  The cleaning oil that has absorbed the organic halogen compound from which moisture and the like have been removed in the vacuum distillation tank 20a is then sent to the vacuum distillation tank 20b. In the vacuum distillation tank 20b, part of the cleaning oil is distilled off by vacuum distillation.

The amount of the cleaning oil distilled off in the vacuum distillation tank 20b is appropriately adjusted according to the concentration of the organic halogen compound in the cleaning oil.
For example, when the concentration of the organic halogen compound in the cleaning oil is 1 ppm, the concentration is reduced to about 10 ppm, or when the concentration of the organic halogen compound in the cleaning oil is several tens of ppm, the concentration is about 100 ppm. It is possible to perform distillation under reduced pressure so that
In this embodiment, the type of cleaning oil used is a hydrocarbon oil that is lower in volatility than water and higher in volatility than an organic halogen compound, and can dissolve the organic halogen compound in the exhaust gas. Any of them may be used, and examples thereof include kerosene and normal paraffin oil. That is, as the cleaning oil, one having a boiling point lower than that of the organic halogen compound is used.

  At least a part of the washing oil is removed by distillation under reduced pressure in the vacuum distillation tank 20b, and the remaining organic halogen compound is as described above in the reaction tank (dehalogenation tank) 21 and the neutralization / stationary separation tank 22. The same process is performed.

  Next, although an Example is given and this invention is demonstrated in more detail, this invention is not limited to this.

(Adjustment example 1)
In a horizontal rotating cylindrical reduction heating apparatus (dimensions: diameter 700 mm × length 1,000 mm, apparatus capacity 385 L) maintained at a temperature of 450 to 550 ° C. by a hot air furnace, contaminated soil 70 kg / hour (water content 23) %, PCB concentration of 1,000 mg / kg), heat treatment was performed to generate exhaust gas 60 Nm ³ / hour, and treated soil 50 kg / hour as a solid component was discharged to the quenching device.

Example 1
The exhaust gas prepared in Preparation Example 1 was supplied to a high-temperature bag filter maintained at a temperature of 550 ° C. with a heating device at a rate of 60 Nm ³ / hour to collect dust, thereby removing dust in the exhaust gas. Thereafter, the dust-removed exhaust gas was introduced into an oil-sprayed oil scrubber and washed, and thereby separated into a gas component, an oil component, and an aqueous component. Trans oil was used as the cleaning hydrocarbon oil. The oil-sprayed oil scrubber operated normally for 24 hours or more continuously without the nozzle clogging. The obtained results are shown in Table 1.

(Example 2)
The exhaust gas was washed by the same method as in Example 1.
However, before introducing the exhaust gas into the high-temperature bag filter, it is supplied to the high-temperature cyclone as a high-temperature centrifugal dust collector maintained at a temperature of 550 ° C. by a heating device and collected at a rate of 60 Nm ³ / hour, Then, it introduced into the high temperature type bag filter similar to Example 1. The oil-spraying gas absorption device operated normally for 48 hours or more continuously without the nozzle being clogged. The obtained results are shown in Table 1.

(Comparative Example 1)
The exhaust gas was washed by the same method as in Example 1. However, the exhaust gas prepared in Preparation Example 1 was directly supplied to the oil-sprinkling oil scrubber without going through the high-temperature bag filter.
In the oil-sprayed oil scrubber, the nozzles were blocked 4 hours after the start of operation, and the operation was interrupted. The results are shown in Table 1 below.

(Comparative Example 2)
The exhaust gas was washed by the same method as in Example 1. However, a room temperature bag filter was used instead of the high temperature bag filter. During the dust collection process of the exhaust gas, liquefaction of moisture in the exhaust gas was observed, and the room temperature type bag filter was blocked after 1 hour from the start of operation and the operation was interrupted.

(Evaluation)
As shown in Table 1 above, Examples 1 and 2 which are treatment methods of the present invention can achieve the prevention of liquefaction of moisture in the exhaust gas before being supplied to the cleaning apparatus, and at the same time, compared with Comparative Example 1, It has been demonstrated that an extension of time (Example 1: extension of operating period of at least 6 times, Example 2: extension of operating period of at least 12 times) can be achieved. Further, comparing the results of Examples 1 and 2 with the result of Comparative Example 2, it was proved that it is essential to perform the exhaust gas dust collection treatment at a predetermined temperature or higher.

  The treatment method and treatment facility of the present invention can employ exhaust gas discharged from a heating device that heat-treats an object contaminated with an organic halogen compound for detoxification.

FIG. 1 is a process flow diagram showing an embodiment of the processing method of the present invention. FIG. 2 is a schematic diagram showing a preferred embodiment of the treatment facility of the present invention. FIG. 3 is a process flow diagram showing another embodiment of the processing method of the present invention. FIG. 4 is a schematic view showing another preferred embodiment of the processing facility of the present invention. FIG. 5 is a process flow diagram showing another embodiment of the processing method of the present invention. FIG. 6 is a schematic view showing another preferred embodiment of the processing facility of the present invention. FIG. 7 is a schematic diagram showing a heating device that generates exhaust gas, which is a processing target of the present invention.

Explanation of symbols

13: Heating device 16: High-temperature type cyclone 17: High-temperature type bag filter 18: Oil spray type gas cleaning device 20: Vacuum distillation tank 21: Reaction tank (dehalogenation tank)
22: Neutralization / stationary separation tank 30, 31, 32: Cooler

Claims (14)

An exhaust gas treatment method for detoxifying exhaust gas discharged from a heating apparatus that heat-treats an object contaminated with an organic halogen compound,
The dust in the exhaust gas is collected by filtering and collecting at a temperature of 350 to 600 ° C. (except when a catalyst bag filter is used) and removed, and the dust is removed and cooled to 100 to 250 ° C. A method for treating exhaust gas, comprising: an oil cleaning type gas cleaning treatment step in which the exhaust gas is brought into contact with a cleaning oil of 50 ° C. or less to remove an organic halogen compound in the exhaust gas.   After the oil cleaning gas cleaning treatment step, components having higher volatility than the cleaning oil in the cleaning oil are removed by distillation under reduced pressure, and cleaning oil from which components having higher volatility than the cleaning oil are removed by the vacuum distillation. The exhaust gas treatment method according to claim 1, further comprising an alkali metal treatment step of decomposing the organic halogen compound therein with alkali metal.   As the cleaning oil, an oil having lower volatility than water and higher volatility than the organic halogen compound is used, and after the oil cleaning gas cleaning processing step, higher volatility than the cleaning oil in the cleaning oil. The exhaust gas treatment method according to claim 1, further comprising an alkali metal treatment step of removing components by vacuum distillation, further removing at least part of the washing oil by vacuum distillation, and decomposing the remaining organic halogen compound with an alkali metal. .   The exhaust gas treatment method according to claim 2 or 3, wherein the component having higher volatility than the cleaning oil is water.   The exhaust gas treatment method according to claim 2 or 3, wherein the component having higher volatility than the cleaning oil is an organic compound having higher volatility than an organic halogen compound decomposed by an alkali metal.   The heat treatment is a reduction heat treatment for heating an object contaminated with an organic halogen compound in an inert gas or a heat treatment for heating to an evaporation temperature of an organic halogen compound to be removed or higher. An exhaust gas treatment method according to claim 1. An exhaust gas treatment facility for detoxifying exhaust gas discharged from a heating device for heat-treating an object contaminated with an organic halogen compound,
Dust is removed by the dust collection processing device that collects dust in the exhaust gas at a temperature of 350 to 600 ° C. by filtration dust collection processing (except when a catalyst bag filter is used) and removes the dust, and the dust collection processing device. And an exhaust gas cleaning treatment device for removing an organic halogen compound in the exhaust gas by bringing the exhaust gas cooled to 100 to 250 ° C. into contact with a cleaning oil of 50 ° C. or less. Processing equipment. In the cleaning oil in which the components having higher volatility than the cleaning oil in the cleaning oil that has passed through the oil cleaning type gas cleaning processing device are removed by vacuum distillation, and the components having higher volatility than the cleaning oil are removed by the vacuum distillation. The exhaust gas treatment facility according to claim 7 , further comprising an alkali metal treatment device that decomposes the organic halogen compound with an alkali metal. The cleaning oil is an oil having lower volatility than water and higher volatility than the organic halogen compound, and a component having higher volatility than the cleaning oil in the cleaning oil that has passed through the oil cleaning type gas cleaning processing device. The exhaust gas treatment facility according to claim 7 , further comprising an alkali metal treatment device that removes at least a part of the washing oil by vacuum distillation and decomposes the remaining organic halogen compound with an alkali metal. The heating device includes: a heating furnace that heats an object to be processed; a jacket that includes a heating medium supply port and a heating medium discharge port that are disposed on a peripheral wall of the heating furnace; and a heating medium to the heating medium supply port The exhaust gas according to any one of claims 7 to 9 , further comprising a path for returning the heat medium discharged from the heat medium discharge port to the heat medium supply part. Processing equipment. The exhaust gas treatment facility according to any one of claims 7 to 9 , wherein the heating device includes a heating furnace for heating an object to be processed inside and an electric heater for heating a peripheral wall of the heating furnace. The exhaust gas which is to dust collecting dust removed by the dust collecting apparatus, one cooler to lower the temperature of the exhaust gas path for supplying the oil-cleaning gas cleaning apparatus according to claim 7 to 11, which is interposed The exhaust gas treatment facility described in Crab. The oil cleaning type gas cleaning processing apparatus is configured to contact exhaust gas and cleaning oil, to allow the cleaning oil to absorb the organic halogen compound in the exhaust gas, and to discharge the cleaning oil from the contact portion and return the cleaning oil again. The exhaust gas treatment facility according to any one of claims 7 to 12 , further comprising a cooler interposed between the paths. A gas discharger that discharges exhaust gas discharged from the oil cleaning gas cleaning treatment device through activated carbon; and a cooler that cools the exhaust gas discharged from the oil cleaning gas cleaning processing device and sends the exhaust gas to the gas discharge unit. The exhaust gas treatment facility according to any one of claims 7 to 13 .

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