JP2012161768A - Apparatus for cleaning contaminated soil and method for cleaning soil - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an apparatus and a method by which volatile organic compounds (VOC) can be easily removed from contaminated soil in a short period of time without addition of quicklime or the like.SOLUTION: The apparatus includes a gasifier 10 which includes: a hollow container 13 for receiving soil contaminated by VOC and superheated steam; an electric heater 14 which is disposed at the outer wall of the container 13 and heats the soil received in the container 13; and a screw 15 for agitating the soil while transporting the soil from the receiving port to the discharge port of the container 13. The gasifier 10 makes the inside of the container 13 a superheated steam atmosphere, the electric heater 14 gives heat to the superheated steam and by agitation of the soil by the screw 15, the superheated steam is infiltrated into the soil to give the soil heat. Thus the soil is heated to 80 to 200°C.

Description

  The present invention relates to a contaminated soil purification apparatus and a soil purification method used to purify soil contaminated with volatile organic compounds.

  Organic compounds that easily volatilize at room temperature, such as trichloroethylene, tetrachloroethylene, formaldehyde, toluene, benzene, and xylene, are called volatile organic compounds (VOCs), have a high ability to dissolve fats and oils, are difficult to decompose, are stable, and burn. Because of its difficult properties, it is used for cleaning of IC boards and electronic parts in electrical and semiconductor factories, pre-treatment cleaning of metal parts, solvent for paints and adhesives, dry cleaning and agricultural chemicals, etc. I came.

  At that time, since there was no law to regulate VOC, it was discarded as it was, contaminated the soil, and also contaminated the groundwater flowing through the soil. In addition, due to recent redevelopment and the like, the soil is dug and VOC is released into the atmosphere, so that oxidants and suspended particulate matter (SPM) are generated by the photochemical reaction, and the atmosphere is also polluted. VOCs have been pointed out to have an effect on the human body because they may be harmful and carcinogenic, such as headaches, dizziness and kidney injury.

  In view of these circumstances, many devices and methods for removing VOC from soil and groundwater contaminated with VOC have been proposed (see, for example, Patent Documents 1 to 5).

  In Patent Document 1, the contaminated soil containing a volatile organic compound is heated with a rotary kiln for heating to separate or decompose the volatile organic compound, and the dust in the exhaust gas derived from the rotary kiln is separated by an inertia dust collector or a bug filter. Since the trapped dust contains a high concentration of volatile organic compounds, this dust is supplied to a dust heating device and heated, and the volatile organic compounds are volatile separated or decomposed and purified. Yes.

  In Patent Documents 2 to 4, organic halogen compounds such as PCBs and dioxins are efficiently extracted from contaminated soil, and by using water vapor, the organic halogen compounds are stably decomposed into hydrogen halide and carbon dioxide and harmless. It has become. In these apparatuses and methods described in Patent Documents 2 to 4, the contaminated soil is heated indirectly, the organic halogen compound contained in the contaminated soil is volatilized, and reacted with water vapor in the indirectly heated system. Decomposes into hydrogen halide and carbon dioxide. At this time, it is indirectly heated while being controlled by the concentration of carbon monoxide in the gas that generates the amount of water vapor, and the organic halogen compound contained in the soil is reliably decomposed.

  In addition, a purification method is widely used in which quick lime or the like is added to and mixed with contaminated soil, and VOC is volatilized and removed by the heat of hydration. For example, in Patent Document 5, soil contaminated with a volatile organic compound or the like is uniformly mixed with an inorganic compound that reacts exothermically with water while being sufficiently finely divided, and then not only the surface of the mixture but also the inside. Purify by contact with air. In the apparatus and method described in Patent Document 5, a part of the mixture is lifted by a predetermined amount through the protruding portion along with the rotation of the cylindrical portion of the air contact processing unit, and then dropped, and then simply stirred. Unlike this, air can be brought into contact with the inside even more effectively, thereby increasing the purification efficiency of the contaminated soil.

JP 2002-219444 A JP 2004-057911 A JP 2004-298800 A JP 2006-035218 A JP 2008-055410 A

  In the technique described in Patent Document 1, the volatile organic compound that has been heated to the boiling point of the volatile organic compound or more and soaked in the soil is volatilized and separated or decomposed to purify the soil. The inside is set to 750 ° C., and in contact with the high temperature gas in the furnace, the volatile organic compound in the gas is completely burned, so a lot of fuel is required, and furthermore, in the dust scattered with the exhaust gas of the rotary kiln Since high-concentration volatile organic compounds are contained, it is necessary to heat the dust above the boiling point of the volatile organic compounds to separate or decompose the volatile organic compounds. Necessary. Moreover, since it burns at a high temperature with a burner, it can be processed in a short time. However, if it is to be processed at a low temperature such as 80 ° C. to 200 ° C., heat is transferred to the inside of the contaminated soil and exists in the inside. There is a problem that a considerable amount of time is required to sufficiently volatilize the VOC.

  In the apparatus and method described in Patent Documents 2 to 4, first, indirect heating is performed at a temperature of 200 to 600 ° C. to volatilize the organic halogen compound, and then the organic volatilized at a high temperature of 600 to 1300 ° C. Halogen compounds react with water vapor to decompose volatile organic compounds, but heat is not transmitted to the inside of the soil only by indirect heating, and it takes considerable time to volatilize and remove VOC. For the decomposition, a separate reactor is required, and the reactor has to be further heated, resulting in a problem that much energy is required.

  In the method of adding the above-mentioned quick lime and the like to volatilize and remove VOC by the heat of hydration, after adding and mixing quick lime etc. to the contaminated soil, a curing time of at least 12 hours or more is required. Yard) is also required. Moreover, since dust and VOC gas are generated when quicklime is mixed, a temporary tent and a large-scale ventilation facility are required. Furthermore, since dust and VOC gas are generated in the process, workers are required to have protective equipment such as dustproof and gas masks, and the working environment is not good. In addition, since a large amount of quicklime is used, if the quicklime gets wet with water such as rain during storage, there is a risk of fire due to heat generation.

  Since the addition amount of quick lime etc. is influenced by the property of contaminated soil, the addition amount of quick lime etc. varies greatly depending on the water content and soil quality of the contaminated soil. For this reason, in the planning stage, it was necessary to conduct a confirmation test of the amount of added mixture in advance. If a prior confirmation test could not be carried out at the time of planning, the plan had to take into account the risk of using an added amount that takes safety into account.

  In the technique described in Patent Document 5, it is not necessary for the operator to perform work or the like under a poor environment, and after mixing the contaminated soil and the inorganic compound, the mixture is granulated to be uniform with the inorganic compound. While mixing, air is brought into contact with the inside of the mixture, thereby promoting the volatilization of the VOC and effectively volatilizing and recovering the VOC. However, since mixing of an inorganic compound is required and the addition amount varies greatly depending on a predetermined water content, it is necessary to perform a confirmation test of the addition amount in advance. As a result of conducting a prior confirmation test, there is a problem that a considerable amount of time is required for processing.

  In shield construction, etc., which has become longer in recent years, long-distance pumping has been made possible by mixing a property improver (polymer agent) such as a fluidizing agent into the VOC-contaminated soil being pumped. In the VOC contaminated soil, it was difficult to effectively volatilize and separate the VOC by heating at about 80 ° C.

  Therefore, VOC can be sufficiently removed from the soil contaminated with VOC without requiring consumption of a large amount of fuel and energy, and without the addition of quick lime, inorganic compounds, etc., and its VOC removal treatment Therefore, it has been desired to provide an apparatus and a method that can be performed easily, in a short time, and at a relatively low temperature.

  As a result of intensive studies, the inventors of the present invention have found that a hollow container that receives soil contaminated with VOC, an electric heater that is disposed on the outer wall of the container and indirectly heats the soil in the container, and soil Using a gasifier equipped with a screw that moves the container from the inlet to the outlet of the container, superheated steam is blown into the gasifier and stirred by the screw, while being indirectly heated by an electric heater and directly heated by superheated steam. , By transferring heat sufficiently to the inside of the soil by heating for a short time and heating the whole soil to 80 ° C. or higher, for example, 80 ° C. to 200 ° C., sufficiently volatilizing the VOC contained in the soil and removing it from the soil I found out that I can.

  In addition, by blowing superheated steam into a hollow container to create a superheated steam atmosphere, the container can be in an oxygen-free state, that is, a reducing atmosphere. Under this reducing atmosphere, VOC can be made of steam, carbon dioxide, or the like. It has also been found that it can be broken down into harmless small molecules.

  This invention is made | formed by discovering these things, The said subject can be solved by providing the contaminated soil purification apparatus and soil purification method of this invention.

  The contaminated soil purification apparatus of this invention is an apparatus which purifies the soil contaminated with the volatile organic compound (VOC), Comprising: The gasification apparatus mentioned above is included. The gasifier includes a hollow container for receiving soil contaminated with VOC and superheated steam, an indirect heating means disposed on the outer wall of the container for heating the soil received in the container, A transport stirring means for stirring the soil while transporting the soil from the receiving port to the discharge port of the container; The gasifier has a superheated steam atmosphere inside the hollow container, the indirect heating means applies heat to the superheated steam, the superheated steam is permeated into the soil by stirring by the conveying stirring means, and the soil is heated to 80 ° C. Heating to a temperature of ˜200 ° C.

  In addition to electric heaters, the heat source that indirectly heats the container is a radiant that burns heavy oil or kerosene, or burns heavy oil or liquefied gas in the combustion pipe, and heats the object through the combustion pipe.・ A tube burner can be used. In this case, the indirect heating means is disposed in the container. Moreover, a kiln system can be employ | adopted as a container and conveyance stirring means to receive and heat soil.

  In addition, since the cracked gas generated by decomposing the VOC discharged from the gasifier cannot be discharged as it is, it can further include an exhaust gas treatment device for removing impurities contained in the cracked gas. . In order to reuse the treated soil after the VOC discharged from the gasifier is removed, a cooling device for cooling the treated soil can also be provided.

  This exhaust gas treatment device cools a cracked gas and separates a gas separation component contained in the cracked gas, an adsorption device for adsorbing and removing impurities contained in the gas component, and a gas component And a blower that keeps the inside of the container, the cooling / separation device, and the adsorption device in the gasification device at a negative pressure and discharges the gas component from which impurities have been removed to the atmosphere. Can do.

  The cooling separation device is configured as a container containing a liquid such as cooling water or an alkaline aqueous solution, for example, a bubbling tank, and accepts a liquid containing impurities in order to separate and remove impurities remaining in the cooling separation device. A coagulation tank for coagulating and precipitating impurities floating in the liquid can be provided.

  Further, the soil purification apparatus includes a water storage tank for storing water, a steam generation means for evaporating water, a water supply means for supplying water from the storage tank to the steam generation means, and a steam for heating the generated steam to generate superheated steam. And a superheated steam generator including a heating unit. This superheated steam can be supplied to the container.

  In the present invention, in addition to the above-described soil purification apparatus, a soil purification method performed by this apparatus can also be provided. In this method, the inside of the container is heated by an indirect heating means disposed on the outer wall of the hollow container, the step of receiving soil contaminated with VOC and superheated steam into the container, and the soil by the conveying and stirring means. And agitating while being conveyed from the inlet to the outlet of the container. In this receiving step, the inside of the container is set to a superheated steam atmosphere, and in the step of stirring, the indirect heating means gives heat to the superheated steam, the superheated steam permeates the soil by stirring by the transport stirring means, and gives heat. The soil is heated to a temperature of 80 ° C to 200 ° C.

  By providing the soil purification apparatus and the soil purification method of the present invention, VOC can be volatilized and removed from contaminated soil at a low temperature in a short time, and the VOC is decomposed and processed without using a separate reactor. be able to. In addition, since a curing yard is not required, purification work can be performed even in a narrow place if an installation space for the apparatus according to the processing capacity can be secured.

  In addition, by providing the exhaust gas treatment device, hydrogen chloride contained in the cracked gas, some carbon dioxide gas, etc. can be dissolved and removed, and fine dust can be adsorbed and removed by the adsorption device. In addition, air pollution can be prevented, and furthermore, since the inside of the apparatus can be maintained at a negative pressure, it is possible to prevent VOC, dust, and the like from leaking into the atmosphere. As a result, large-scale ventilation equipment is not required, which leads to improvement of the worker's working environment.

  In addition, since the treatment can be performed without using the medicine, a storage space for the medicine becomes unnecessary, and a risk of danger such as a fire during the storage can be eliminated. Furthermore, since the apparatus can be planned from the required processing capacity, a reliable purification plan can be established.

The figure which showed one structural example of the soil purification apparatus of this invention. The figure which showed another structural example of the soil purification apparatus of this invention. The figure which showed the structural example of the superheated steam production | generation apparatus. Sectional drawing which showed another structural example of the soil purification apparatus of this invention.

  FIG. 1 is a diagram showing one configuration example of the soil purification apparatus of the present invention. In this embodiment, the soil purification apparatus is composed of a gasifier.

  The gasifier 10 includes a soil inlet 11 for receiving soil contaminated with organic compounds that easily volatilize at room temperature, such as trichlorethylene, tetrachloroethylene, formaldehyde, toluene, benzene, and xylene, that is, volatile organic compounds (VOC), and a VOC. Soil discharge port 12 for discharging the soil that has been removed and purified, a hollow container 13 for storing the received soil, an electric heater 14 as an indirect heating means disposed on the outer wall of the container 13, and a container 13 and includes a screw 15 as a conveying and stirring means for conveying and stirring the soil received from the soil receiving port 11 to the soil discharge port 12.

  The container 13 is a hollow cylindrical container elongated in one side, and is provided with a receiving nozzle as a soil receiving port 11 protruding from one end thereof, and protruding from a side wall of the container adjacent to the other end as a soil discharge port 12. A discharge nozzle is provided. The container 13 is installed so that the opening of the receiving nozzle faces upward and the opening of the discharge nozzle faces downward. The receiving nozzle is provided with a hopper 16 through which soil is introduced.

  The hopper 16 has a steel box-like structure, and includes an openable and closable lid whose lower side is recessed like a funnel. By opening this lid, a required amount of soil can be dropped and put into the container 13 through the receiving nozzle at the bottom.

  The container 13 is further provided with a steam receiving port 17 for receiving superheated steam, for example, as a steam nozzle protruding from the container side wall adjacent to the other end. The steam nozzle is installed so that the opening faces upward, and is provided to receive steam at over 100 ° C. at normal pressure as superheated steam.

  The container 13 is heated by the electric heater 14 and the material is made of a material having good thermal conductivity in order to transfer the heat to the soil inside. Made of durable material. For example, carbon steel, nickel chrome molybdenum steel, stainless steel and the like can be mentioned. In the present invention, the soil received in the container 13 is heated to a temperature of 80 ° C. or higher, specifically 80 ° C. to 200 ° C. Since it should just be, it is comparatively low-temperature and since there is almost no condensed water, cheap carbon steel can be used.

  The electric heater 14 is installed on the outer periphery of the container 13 in close contact with the side wall thereof. Thereby, the heat generated by the electric heater 14 can be directly transmitted to the wall of the container 13, and can be transferred from the wall to the air or superheated steam to be transferred to the soil. The electric heater 14 includes a resistance heating element, and heat can be applied to the side wall of the container 13 by generating heat in the resistance heating element by supplying an electric current.

  Since the electric heater 14 gives heat to the air surrounding the electric heater 14 in addition to the side wall of the container 13, the amount of heat radiation is large, and if it is used as it is, a lot of energy is wasted. Therefore, after the electric heater 14 is disposed, it can be surrounded by a heat insulating material so as not to dissipate heat to the outside, and can be efficiently applied to the wall. As the heat insulating material, for example, fiber heat insulating materials such as glass wool and rock wool, and foam heat insulating materials such as urethane foam and polystyrene foam can be used.

  The screw 15 includes a rotary shaft that is rotatably provided so as to bridge between both ends of the hollow cylindrical container 13 that is elongated in one side, and a spiral blade that is provided around the rotary shaft. One end of the rotating shaft is connected to a motor (not shown), and the rotating shaft rotates in a certain direction by the rotation of the motor. The motor can control the rotation speed by controlling the number of rotations of the rotating shaft, and can control the soil conveyance speed by this control. The soil is interposed between blades arranged at equal intervals in the traveling direction, and moves between the blades one forward in the traveling direction while the rotation shaft rotates once. Thereby, soil can be moved toward the soil discharge port 12 from the soil receiving port 11 and can be conveyed.

  The screw 15 is made of a material having heat resistance without being corroded by moisture contained in the soil, and having a strength capable of transporting and stirring the soil in a certain direction. An example of this material is stainless steel. Stainless steel is also preferred in that it has a relatively high thermal conductivity that can efficiently provide the soil with heat received from the superheated steam in contact with the superheated steam.

  VOC exists in the state attached to the soil particle in the soil which has various particle sizes, large and small, and intervenes between soil particles. The soil particles are, in descending order of size, stones, gravel, sand, and mud (silt, clay), which are debris made from broken rocks. Stone means particles with a particle diameter of 75 mm or more, gravel means particles with a particle diameter of 2 to 75 mm, sand means 0.074 to 2 mm, and mud means 0.074 mm or less. Say.

  VOCs adhere to any size of soil particles, but large stones and gravel can be removed by washing with water. On the other hand, sand and mud having a small particle diameter have a large specific surface area and cannot be sufficiently removed even by washing with water. Moreover, it may be interposed between these particles. For this reason, sand and mud having a small particle diameter are supplied to the gasifier 10 as contaminated soil to be treated, and VOC is volatilized and separated and removed.

  When throwing soil contaminated with VOC into the gasifier 10, stones and gravel with a large particle size are separated by a classifier such as a sieve, and soil consisting of sand or mud with a small particle size is thrown into the gasifier 10. can do.

  In the present invention, it is possible to supply the soil composed of the above sand and mud. However, when the particle size of the supplied soil is large and small, the heat conduction differs depending on the particle size, and more water is contained. In addition, because it contains a powdery material such as clay or silt, a rapidly-dried soil mass is formed in the gasifier 10, heat is transferred to the interior of the soil mass, and adheres in the interior. It takes time to volatilize the VOC.

  Therefore, as a pre-treatment before putting into the gasifier 10, after removing stones and gravel with a large particle diameter in the soil, clay and silt with a small particle diameter are granulated using a granulator, and the particle diameter is reduced. Can be aligned. Thereby, since there is no powdery material such as clay and silt, even if it is put into the gasifier 10, it does not form a lump, and since the particle diameter is almost uniform, it can be heated uniformly. Heating time can be shortened and energy consumption can be reduced.

  In addition, since the clot is difficult to be formed, it is possible to prevent the spiral blade from being damaged by contacting and colliding with the clot, and a blade having a relatively thin thickness can be used. Thin blades are preferable in that the weight of the screw 15 can be reduced, and as a result, the power consumption of the motor that rotates the screw 15 can be suppressed.

  The processing using the gasifier 10 will be described. The soil contaminated with VOC is put into the hopper 16, the lid is opened, and a predetermined amount of soil is put into the container 13. The container 13 is charged through the soil receiving port 11.

  The gasifier 10 supplies the heat generated by the resistance heating element to the container 13 by energizing the electric heater 14 before the soil is put in advance to heat the air in the container 13 and rotate the motor. The rotation of the screw 15 is started. There, the soil is introduced as described above, and superheated steam is also introduced through the steam receiving port 17.

  As the screw 15 rotates, the soil is stirred and conveyed in a certain direction. Meanwhile, heat is indirectly applied through the wall of the container 13 by the electric heater 14, and heat is directly applied by contact with superheated steam. Since the inlet for superheated steam, that is, the steam inlet 17 is on the soil outlet 12 side, the soil is heated and heated by the superheated steam having a high temperature as it is conveyed to the soil outlet 12.

  The soil agitated by the rotation of the screw 15 forms a large number of voids in the soil, superheated steam enters the voids, and heat is efficiently given to the internal soil. At this time, moisture in the soil evaporates as the soil is heated, and VOCs volatilize accordingly. The VOC attached to the soil particles is stripped (peeled off) by the superheated steam and volatilized by being given heat from the superheated steam. In this way, VOCs present in the soil are also volatilized efficiently.

  The boiling point of VOC is about 50 to 260 ° C. In the present invention, the temperature of the introduced soil is set to 80 ° C. or higher by the electric heater 14 and superheated steam, specifically, the kind of the organic compound contained It was found that VOC can be reduced to a value below the soil environmental standard by raising the temperature to 80 ° C. to 200 ° C. according to the concentration. From this, it is considered that VOC is sufficiently volatilized and separated from the soil by raising the temperature of the soil to 80 ° C. or higher.

  By the way, the soil environmental standard values are shown as follows: per liter of test solution, dichloromethane is 0.02 mg or less, trichlorethylene is 0.03 mg or less, tetrachloroethylene is 0.01 mg or less, and benzene is 0.01 mg or less.

  Further, since superheated steam is supplied into the superheated steam atmosphere inside the container 13 and is in an oxygen-free state (reducing atmosphere), decomposition of the volatilized VOC proceeds, and VOC finally becomes carbon dioxide, hydrogen chloride, etc. It is decomposed into small molecules. Most of this cracked gas is composed of steam, carbon dioxide, and nitrogen, and contains trace amounts of hydrogen chloride and the like. Nitrogen is nitrogen in the air that flows in along with the soil when the soil is charged.

  On the other hand, the soil from which VOC has been volatilized and removed is treated soil in which VOC has a concentration lower than the environmental standard, but cannot be reused as it is because it is heated to 80 ° C. or higher. Therefore, it can be cooled by naturally cooling, etc., and then reused for landfill or the like.

  As the superheated steam, steam heated to, for example, 150 ° C. to 500 ° C. at normal pressure can be used. The superheated steam can be determined according to the capacity of the container 13, and an amount that can be introduced while maintaining the inside of the container 13 at a slight negative pressure or normal pressure can be introduced.

  In view of the above, the soil purification apparatus of the present invention, as described above, further includes a cooling device 20 for cooling the treated soil, and an exhaust gas treatment device for treating cracked gas, as shown in FIG. Can be provided.

  The cooling device 20 can be a heat exchanger that performs heat exchange with cooling water and cools the treated soil. In addition, it is also possible to employ a watering device that sprays cooling water directly onto the treated soil and cools the treated soil as the cooling water evaporates, or an air cooling device that blows air with a blower and air-cools. The treated soil after being cooled by the cooling device 20 is put into the treated soil storage container 21 and stored until reused. It is also possible to take it out from the treated soil storage container 21, transport it to a storage location, and store it in the storage location.

  The exhaust gas treatment device cools the cracked gas and removes the bubbling tank 22 as a cooling / separation device for separating the gas components contained in the cracked gas and the mist accompanying the gas components discharged from the bubbling tank 22. A mist removing device 23 for removing the dust, an adsorbing device 24 for adsorbing and removing fine dust contained in the gas component from which the mist has been removed, and a hollow container provided in the gasifier 10 for sucking the gas component 13, a bubbling tank 22, a mist removing device 23, and a suction device 24 are held at a negative pressure, and a blower device 25 that discharges a gas component from which dust has been removed to the atmosphere.

  The bubbling tank 22 has a predetermined volume, a sealed container in which cooling water or an alkaline aqueous solution is accommodated, a supply pipe for receiving a decomposition gas into the cooling water or the alkaline aqueous solution and bubbling gas components, and a gas It consists of a discharge pipe that discharges only the components.

For example, when an alkaline aqueous solution is stored in the bubbling tank 22, the cracked gas is rapidly cooled by the alkaline aqueous solution, and when part of hydrogen chloride or carbon dioxide contained in the cracked gas is contained, SO _x or the like is alkaline. Nitrogen, the remaining carbon dioxide, and steam, excluding these, react with and dissolve to form bubbles and move to the top of the alkaline aqueous solution and are discharged from the discharge pipe. In addition, as an alkali, potassium hydroxide, sodium hydroxide, or calcium hydroxide can be used.

  The cracked gas includes solids such as fine earth particles and dust. Most of them are deposited on the bottom of the cooling water or the aqueous alkali solution, and some of them move upward together with the bubbles, and are contained in the gas component and sent to the downstream side.

  The gas component discharged from the discharge pipe contains solids and mist in addition to the above nitrogen and carbon dioxide. When carbon dioxide dissolves in the mist to form an acid, acid corrosion occurs, and when the adsorbent filled in the adsorption device 24 is wetted by the mist, the adsorption capability is greatly reduced. 23 to remove the mist. As the mist removing device 23, a demister provided with a metal mesh inside the sealed container and capturing and separating the mist by the metal mesh can be used.

  The adsorption device 24 can be an adsorption tower in which an airtight container is filled with an adsorbent, and adsorbs and removes solid substances in the gas component from which mist has been removed. For example, when the bubbles burst in the bubbling tank 22, the solid matter is present as fine dust in the bubbles. By adsorbing and removing with the adsorption device 24, it is possible to prevent these fine dusts from being diffused into the atmosphere. In addition, when chlorine and carbon monoxide are contained in the gas component, it can be adsorbed and removed by the adsorption device 24. As an adsorbent that can be used in the adsorption device 24, activated carbon, zeolite, or the like can be used.

  The blower 25 is, for example, a blower, sucks the gas component discharged from the adsorption device 24, and releases it to the atmosphere as exhaust gas. For this reason, the suction side is set to a negative pressure, and the inside of the apparatus connected from the container 13 of the gasification apparatus 10 to the adsorption apparatus 24 through the bubbling tank 22 and the mist removing apparatus 23 can be held at a slight negative pressure. As a result, VOC and decomposition gas generated in the gasifier 10 are not released to the atmosphere, solid matter is not discharged, and a large-scale ventilation facility is not required. Can also be improved.

  By installing the bubbling tank 22, solids are deposited in the bubbling tank 22. In order to separate and remove the solids, cooling water or alkaline aqueous solution containing the solids is received, and the liquid is contained in the liquid. A coagulation tank 26 for coagulating and precipitating floating solids is further provided.

  The aggregation tank 26 is a container having a predetermined capacity capable of receiving and storing the liquid. When a flocculant is added to the stored liquid and left standing for a certain period of time, the solid substance floating in the liquid is agglomerated by the flocculant and precipitates into a large lump, which is separated into a supernatant and a precipitate. The

  As the aggregating agent, a conventionally known agent can be used. Specifically, aluminum sulfate, polyaluminum chloride (PAC), ferrous sulfate, ferric sulfate, ferric chloride, etc. are used. be able to.

  The cooling water or the alkaline aqueous solution in the bubbling tank 22 can be replenished by the amount extracted to the aggregation tank 26. The supernatant liquid of the coagulation tank 26 is drained and then used as makeup water for the bubbling tank 22 or as washing water. If the amount of water used is low and water remains, it will be drained into rivers after water quality analysis. On the other hand, if water runs short, it is replenished.

  The wastewater treatment is performed by a wastewater treatment device (not shown). The wastewater treatment apparatus can include a sand filtration tank, a fiber filtration tank, an activated carbon tank, and a reuse tank. Depending on the size of the suspended matter in the wastewater, the relatively large ones are removed by the sand filtration tank, the smaller ones are removed by the fiber filtration tank containing lint-like fibers, and finally the activated carbon tank. After the fines are adsorbed and removed, the waste water is stored in a reuse tank for reuse.

  In sites where there is no source of superheated steam, superheated steam must be generated. For this reason, the soil purification apparatus of this invention can further be equipped with a superheated steam production | generation apparatus. As the superheated steam generation device, for example, a device having a configuration shown in FIG. 3 can be used.

  The superheated steam generator shown in FIG. 3 has a water storage tank 30 as a water storage tank for storing water, a boiler 31 as a steam generating means for evaporating water and generating steam, and water from the water storage tank 30 to the boiler 31. A water supply pump 32 as water supply means for supplying water and a steam heater 33 as steam heating means for heating the steam generated in the boiler 31 to generate superheated steam.

  The water storage tank 30 is a container having a predetermined capacity made of FRP, carbon steel or the like that can store a predetermined amount of water, and the water supply pump 32 is a centrifugal pump, a diagonal flow pump, an axial flow pump, a reciprocating pump, or the like. Can be used. Moreover, the boiler 31 can employ | adopt what generate | occur | produces a vapor | steam by heating and evaporating water using a burner or an electric heater. It is also possible to employ a radial tube burner configured by a U-shaped or W-shaped tube and combustion means for supplying air to the inside and injecting and burning the fuel.

  The steam heater 33 may be based on electromagnetic induction heating in addition to the above-described burner. In electromagnetic induction heating, a strong electric current is passed through a coil to generate a strong magnetic field, and a metal such as iron or stainless steel that is easy to conduct electricity is placed on it, and an eddy current is generated by electromagnetic induction. This is a heating method using the principle of generating heat. Therefore, as a steam heater using this electromagnetic induction heating, a coil in which a conducting wire is wound around the outer periphery of a cylindrical tube made of iron or stainless steel can be used.

  The piping from the boiler 31 to the steam heater 33 and the piping from the steam heater 33 to the gasifier 10 are wound with a heat insulating material so that the temperature of the steam and superheated steam flowing inside does not decrease.

  Here, the result of actually treating the contaminated soil using the soil purification apparatus of the present invention is shown. VOC-contaminated soil containing trichlorethylene at a concentration of about 10 mg / L is supplied to the container 13 with superheated steam at about 350 ° C. using the gasifier 10 shown in FIGS. After passing through the gasifier 10 for 1 minute and raising the temperature to about 110 ° C., it was taken out as treated soil and cooled to room temperature.

  Table 1 below shows the results of the test. In Table 1, “Fluidizer” is a property improver (polymer agent) that fluidizes excavated soil in shield construction or the like, and “<0.005” indicates that it is less than the lower limit of quantification. The standard conformity judgment was made based on whether or not the designated standard in the Soil Contamination Countermeasures Law was less than 0.03 mg / L.

  When the concentration of trichlorethylene in the cooled treated soil is measured, it can be confirmed that it can be reduced to less than 0.03 mg / L of the designated standard as shown in Test Nos. 1 and 3 in Table 1. did it. In Test Nos. 2 and 4, it was shown that trichlorethylene could be sufficiently removed although it could not be reduced to less than 0.03 mg / L of the designated standard. In addition, when the temperature of the superheated steam is set to about 500 ° C., the normal temperature soil is passed through the gasifier 10 for about 9 minutes, and the temperature is increased to about 180 to 200 ° C., the results are shown in Test Nos. 5 and 6 Thus, in any case, it was possible to lower the value to below the lower limit of quantification, rather than the specified standard.

  Although only the concentration of trichlorethylene is shown here, other tetrachlorethylene and the like could be made to have a concentration lower than the same designated standard. From this result, it is found that by controlling the temperature of the soil to an appropriate temperature such as 80 ° C. to 200 ° C. in a superheated steam atmosphere, the VOC can be volatilized and removed in a very short time, and the soil can be purified. I was able to.

  INDUSTRIAL APPLICABILITY The soil purification apparatus and the soil purification method of the present invention can be applied to the treatment of excavated soil that cannot be processed in-situ with excavation and that occurs in a large amount in a short time in shield construction contaminated with VOC. . For this excavated soil, during excavation or sediment discharge, iron powder (iron powder for VOC purification), iron powder and hydrogen peroxide (Fenton method chemicals), strong oxidants such as permanganic acid are added and mixed. However, since the VOC cannot be sufficiently decomposed and removed, it is appropriate to employ the apparatus and method of the present invention.

  So far, the configuration using the electric heater 14 has been described as the heat source for indirectly heating the container 13, but is not limited to this, and combustion gas obtained by burning heavy oil or kerosene, or heavy oil or liquefied gas in the combustion pipe It is also possible to use a radiant tube burner or the like that heats the object through the combustion tube. Further, as the container 13 and the conveying and stirring means, a kiln system can be adopted instead of the container and the screw.

  Specifically, as shown in the cross-sectional view of the apparatus shown in FIG. 4, the soil inlet 40, the soil outlet 41, the container 42, the tube 43, the combustion means, and the power means 44 are configured. The container 42 is a steel container formed of a hollow cylindrical carbon steel, stainless steel or the like which is elongated on one side, and an inner part made of the same rotatable material having a smaller diameter than the steel container. A tube 45 is inserted. It is possible to use a container made of aluminum, copper or the like having a high thermal conductivity, not limited to steel, but steel is preferable in consideration of material costs. On the inner wall of the inner tube 45, a spiral plate 46 that protrudes inward and is formed in a spiral shape is disposed. Since the container 42 is installed with the longitudinal direction of the container in the horizontal direction, a spherical object 47 such as a steel sphere or a ceramic ball is arranged in the container 42, and an inner tube 45 is installed thereon, Only the inner tube 45 can be rotated. In addition, since this is an example, this invention is not limited to this structure.

  A steam soil mixing nozzle 48 to which a steam line is connected is provided at one end of the container 42, and a soil receiving port 40 is provided in the steam soil mixing nozzle 48. The soil receiving port 40 can be flange-connected and can be connected to a hopper. A soil discharge port 41 is provided on the other end side of the container 42.

  The steam soil mixing nozzle 48 may be horizontal as shown in FIG. 2, but is inclined so that the container 42 side is downward, so that the soil introduced from the soil receiving port 40 smoothly enters the container 42. It can also be put in. In the steam soil mixing nozzle 48, a guide 49 for guiding the soil into the inner pipe 45 is disposed continuously to the nozzle. For example, as the guide 49, a circular tube cut into half in the length direction thereof and formed into an arc shape can be used.

  Since the spiral plate 46 is provided on the inner wall of the inner tube 45, the soil is moved along the spiral plate 46 from the soil receiving port 40 side to the soil discharge port 41 side by the rotation of the inner tube 45. . At this time, the soil is agitated by the spiral plate 46. The inner pipe 45 is formed with a plurality of openings 50 on the side of the soil discharge port 41 so that the soil is appropriately discharged from the soil discharge port 41, the ends thereof are closed, and the power means 44 such as a motor It is connected. For this reason, the soil does not enter the power means 44, passes through the plurality of openings 50, and is discharged to the soil discharge port 41.

  The tube 43 and the combustion means wound around the outer periphery of the container 42 can be a radiant tube burner. The tube 43 has a substantially rectangular cross section in order to increase the contact area with the outer wall of the container 42. In addition, the tube 43 can be wound so that the space | interval of an adjacent tube may become as narrow as possible, as shown in FIG. Although not shown, the combustion means is provided at one end of the tube 43 and includes an injection nozzle and a spark plug. Inside the tube 43, high-temperature exhaust gas generated by burning fuel injected from the injection nozzle flows. While flowing in the tube 43, the exhaust gas is transmitted to the soil inside the inner tube 45 through the wall surface of the container 42 and the wall surface of the inner tube 45. Moreover, since the heat is transmitted also to the spiral plate 46 provided in the inner tube 45, while the soil is agitated and moved by the spiral plate 46, the soil is always given heat and can be efficiently heated.

  By using this radial tube burner, although heavy oil, city gas, or the like is used as fuel, its thermal efficiency is very good, so that the cost can be reduced to about 1/3 compared to an electric heater. Since the soil can be efficiently heated using the container 42 as described above, the diameter of the container 42 can be increased, and the amount of contaminated soil can be increased even during the same heating time. Become.

  So far, the soil purification apparatus and the soil purification method of the present invention have been described in detail with reference to the embodiments shown in the drawings, but the present invention is not limited to the above-described embodiments, and other embodiments are described. It can be modified within the range that can be conceived by those skilled in the art, such as addition, change, deletion, etc., and any embodiment is included in the scope of the present invention as long as the operation and effect of the present invention are exhibited. is there.

DESCRIPTION OF SYMBOLS 10 ... Gasifier, 11 ... Soil inlet, 12 ... Soil outlet, 13 ... Container, 14 ... Electric heater, 15 ... Screw, 16 ... Hopper, 17 ... Steam inlet, 20 ... Cooling device, 21 ... Treated soil Storage container, 22 ... bubbling tank, 23 ... mist removing device, 24 ... adsorption device, 25 ... air blower, 26 ... coagulation tank, 30 ... water storage tank, 31 ... boiler, 32 ... water supply pump, 33 ... steam heater, 40 DESCRIPTION OF SYMBOLS ... Soil acceptance port, 41 ... Soil discharge port, 42 ... Container, 43 ... Tube, 44 ... Power means, 45 ... Inner tube, 46 ... Spiral plate, 47 ... Spherical material, 48 ... Steam soil mixing nozzle, 49 ... Guide, 50 ... Opening

Claims (10)

A soil purification device for purifying soil contaminated with volatile organic compounds (VOC),
A hollow container for receiving the soil contaminated by the VOC and superheated steam, an indirect heating means disposed in the outer wall of the container or in the container, and for heating the soil received in the container; Including a gasification device comprising a transport stirring means for stirring the soil while transporting the soil from the inlet to the outlet of the container,
The gasifier makes a superheated steam atmosphere in the container, the indirect heating means applies heat to the superheated steam, and the superheated steam permeates the soil by stirring by the conveying stirring means, thereby giving heat. A soil purification apparatus, wherein the soil is heated to a temperature of 80 ° C to 200 ° C.   An exhaust gas treatment device for removing impurities contained in the cracked gas generated by decomposing the VOC discharged from the gasifier, and a treatment after the VOC discharged from the gasifier is removed The soil purification apparatus according to claim 1, further comprising a cooling device for cooling the soil.   The exhaust gas treatment device cools the cracked gas and separates a gas component contained in the cracked gas, and an adsorption device for adsorbing and removing the impurities contained in the gas component The gas component is sucked, and the inside of the container, the cooling / separating device, and the adsorption device of the gasification device are held at a negative pressure, and the gas component from which the impurities are removed is released into the atmosphere. The soil purification apparatus of Claim 2 containing an air blower.   The soil according to claim 3, further comprising a coagulation tank that receives a liquid containing the impurities and coagulates and precipitates the impurities floating in the liquid in order to separate and remove the impurities remaining in the cooling and separating apparatus. Purification equipment.   A water storage tank for storing water; steam generating means for evaporating the water; water supply means for supplying water from the water storage tank to the steam generating means; and steam heating means for heating the generated steam to generate superheated steam. The soil purification apparatus of any one of Claims 1-4 further provided with a superheated steam production | generation apparatus. A soil purification method for purifying soil contaminated with volatile organic compounds (VOC),
Heating the inside of the container by an indirect heating means disposed in the outer wall of the hollow container or in the container;
Receiving the soil contaminated with the VOC and superheated steam into the container;
Agitating while conveying the soil from the inlet to the outlet of the container by means of conveying agitation,
In the step of receiving, the inside of the container is set to a superheated steam atmosphere, and in the stirring step, the indirect heating means applies heat to the superheated steam, and the superheated steam permeates the soil by stirring by the transport stirring means. A soil purification method, wherein the soil is heated to a temperature of 80 ° C to 200 ° C by applying heat.   Removing impurities contained in the cracked gas generated by decomposing the VOC discharged from the container; and cooling the treated soil after the VOC discharged from the discharge port of the container is removed. The soil purification method according to claim 6, further comprising a step.   The step of removing the impurities includes cooling the cracked gas, separating a gas component contained in the cracked gas, adsorbing and removing the impurity contained in the gas component, and removing the gas component. The soil purification method according to claim 7, further comprising a step of sucking and maintaining the inside of the container at a negative pressure and releasing the gas component from which the impurities are removed to the atmosphere.   The soil purification method according to claim 8, further comprising a step of receiving a liquid containing the impurities remaining after the gas component is separated and aggregating and depositing the impurities floating in the liquid.   10. The method according to claim 6, comprising: evaporating water supplied from a water storage tank; heating steam to generate superheated steam; and delivering the generated superheated steam to the container. The soil purification method according to item 1.