JP2014231050A - Soil cleaning apparatus utilizing electrical warming means - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a soil cleaning apparatus utilizing electrical warming means that can minimize the number of wells to be drilled and that can efficiently pump up the collected underground water to the ground.SOLUTION: A well structure 10 installed into each well is provided with: a) a well frame 11 having water permeability for taking in the underground water contained in the soil; b) an electrode 14 inserted into the well frame and electrically insulated from the well frame; c) a lifting pipe 15 inserted into the well frame such that one end thereof is positioned beneath the water surface of the pooled water taken into the well frame; and d) an air sending pipe 16 inserted into the well frame, for sending in air into the lifting pipe 15 at the position beneath the water surface. By having the well frame 11 of a) as conductive, it can serve as substitution for the electrode 14 of b). VOC and the like in the soil enters the underground water because of the Joule heating by the electric current flowing between the electrodes and taken in into the well frame 11. The underground water is pumped up to the ground by the lifting pipe 15 on the principle of air lift pump.

Description

  The present invention relates to a soil purification apparatus, and more particularly to a soil purification apparatus using an electric heating method.

  As a method of purifying soil contaminated with pollutants, after classifying the contaminated soil by excavation, it is replaced with non-contaminated soil, and the excavated contaminated soil is transported and landfilled to a final disposal site outside the site ( (Excavation and off-site transport), excavating contaminated soil at a treatment facility that has been brought into the site and refilling it (on-site purification), and purifying the soil as it is without being excavated (in-situ purification) ) On-site purification and in-situ purification do not require soil transportation work, and there is an advantage in that the cost and labor of that amount are not required, and the contamination is not taken out of the field, thereby preventing the spread of contamination. The electric heating method is one of in-situ purification technologies.

  The classification by pollutants is broadly divided into heavy metal pollution and VOC (Volatile Organic Compounds) pollution. In addition, oil pollution has recently become a problem.

  One of the in-situ VOC soil purification methods is to increase the temperature of the soil by heating (heating method). The heating method is suitable for purification of soil contaminated with VOC including tetrachloroethylene, trichloroethylene, dichloroethylene, and trichloroethane. Most VOCs are low in viscosity and have a higher specific gravity than water, so they easily penetrate deep into the ground and cause groundwater contamination. Moreover, it adsorbs in the particle | grain space | gap of viscous soil, and causes soil contamination. Therefore, in the heating method, by increasing the temperature of the soil, the VOC adsorbed in the gap between the soil particles is desorbed and its fluidity is increased and vaporized or mixed into the surrounding ground water. And VOC is collect | recovered by pumping up the gas and groundwater which contain such VOC much, and this purifies contaminated groundwater and contaminated soil.

  In addition to the method of blowing high temperature steam (steam) into the soil or sending hot water to the soil, there are methods of inserting a heater into the soil and heating the soil and groundwater around the heater by heat conduction ( For example, Patent Document 2 and Patent Document 3), an electric heating method is a method excellent in energy efficiency and controllability. In the electric heating method, a plurality of electrodes are buried in the soil, a current is passed through the soil between the electrodes, and Joule heat is generated by the electrical resistance of the soil itself. Thereby, much of the electric power used can be utilized for the heating of soil (for example, patent document 1).

  In the electric heating method, as shown in FIG. 9, a well (collection well) 51 for collecting pollutants in the contaminated soil and a well (electrode well) 52 for electric heating are excavated (boring) around the well. To do. The electrode wells 52 are respectively provided at the apexes of a hexagon surrounding the contaminated soil, for example ("region 1" in FIG. 9), and the voltage of each phase of the three-phase AC power supply is applied to the electrodes of each electrode well 52. As a result, a current flows through the soil in the region surrounded by the electrode wells 52, the temperature of the soil rises due to Joule heat, and the contaminants are detached from the soil. Contaminants detached from the soil are mixed into the groundwater, and the groundwater is pumped from the recovery well 51. Depending on the result, the purification area is expanded by drilling further recovery wells and electrode wells outside the area ("area 2", "area 3").

  The groundwater containing the pollutant pumped up from the recovery well 51 removes the pollutant by performing aeration treatment or the like on the ground (Non-patent Document 1).

JP 05-10083 A Japanese Patent Laid-Open No. 11-57685 JP 2006-272273 A

Soil Environmental Technology Study Group "Soil Contamination Control Technology", Nikka Techen Publishers, Inc., September 24, 2003

  The conventional electric heating method has a problem that the number of wells to be excavated is large because it is necessary to provide the recovery well 51 in addition to the electrode well 52 at a place where soil purification work is performed. When the area to be purified is large, as shown in FIG. 9, the number of recovery wells increases, and the cost of excavation increases.

  In addition, as mentioned above, contaminated water containing VOCs is often deep underground, but a vacuum pump placed on the ground cannot pump up contaminated water with a depth exceeding 10 m, which is a lift of 1 atm. On the other hand, if the vacuum pump is to be installed at the bottom of the well, it is necessary to excavate a well having a large diameter in order to install the pump, and the cost of excavating the well is greatly increased. In addition, there are problems that the magnetic flux of the motor is disturbed by the influence of the electric field from the electrode well, or the metal parts are corroded (electric corrosion), so that they do not operate normally.

  The problem to be solved by the present invention is to provide a soil purification apparatus by an electric heating method that can reduce the number of wells to be excavated and can efficiently pump the recovered groundwater to the ground.

The thing of the 1st aspect of this invention made in order to solve the said subject is a well structure provided in each well used for soil purification using an electric heating method,
a) a well frame having water permeability for taking in groundwater contained in the soil;
b) an electrode inserted into the well frame and electrically insulated from the well frame;
c) a pumping pipe inserted into the well frame such that one end thereof is located below the surface of the water stored in the well frame;
d) An air supply pipe inserted into the well frame and for sending air into the pumping pipe under the water surface.

Moreover, the thing of the 2nd aspect of this invention is a well structure provided in each well used for the soil purification using an electric heating method,
a) a well frame having electrical conductivity and permeability to take in groundwater contained in the soil;
b) a pumping pipe inserted into the well frame such that one end thereof is located below the surface of the water stored in the well frame;
and c) an air supply pipe inserted into the well frame for sending air into the pumping pipe under the water surface.

  In both the first and second aspects, the air supply pipe may be provided outside the pumping pipe, or may be provided inside the pumping pipe (that is, a double pipe structure may be used).

  The well structure according to the present invention is provided in each of a plurality of wells surrounding a soil region in which contaminants such as oil and VOC are held. In the first embodiment, the plurality of well structures are provided by applying a voltage to the electrodes in each well structure, and in the second embodiment, a voltage is applied to the well frame. An electric current is passed through the soil area surrounded by the well, generating Joule heat and heating. As a result, the temperature of the contaminated soil is raised, the pollutant retained in the soil is desorbed from the soil, and its fluidity is increased and mixed into the groundwater. Since the well frame of the well structure according to the present invention has water permeability, the groundwater enters the well frame by the water pressure and is stored therein.

  Thus, the groundwater (contained water) containing the contaminants taken into the well frame is drawn up to the ground by the principle of an air lift pump using a pumping pipe and an air supply pipe. That is, the water whose average gravity is lightened on average by mixing air into the pumped pipe below the surface of the stored water is fed into the pumped pipe by the water pressure from below (the head pressure of the stored water). Will be pushed up. When the water level of the stored water in the well frame decreases, the groundwater penetrates the well frame by water pressure and enters the well frame, and the water level of the stored water is recovered. By continuously sending air from the air supply pipe to the pumping pipe in this way, the stored water (contaminated water) can be continuously pumped up.

  In the well structure according to the present invention, since the electrode well also serves as the recovery well, the number of wells for purifying the same area can be reduced as compared with the conventional structure. As the area of land to be cleaned increases, this difference in number increases and the cost is greatly reduced. In other words, since the number of recovery wells is larger than before, the contaminated water can be more efficiently lifted to the ground.

  The well structure according to the present invention pumps the contaminated water to the ground by using the principle of the air lift pump, so that it is not necessary to place the pump underground. For this reason, the diameter of each well can be made small, and this also contributes to decontamination cost reduction. And since there is no limit of 10 m, which is a lift of 1 atm, contaminated water can be pumped from any depth. Furthermore, even if small earth and sand are mixed in the groundwater to be pumped up, it can be pumped up. In the conventional soil purification device that pumps up with the pump (above ground / underground), it is necessary to provide a filter or the like because the pump will be damaged if soil or sand is mixed in the pumped-up groundwater. It is possible to save the cost of the filter itself and the cost and labor for the replacement.

  Since the well structure according to the present invention applies the principle of the air lift pump, the following incidental effects can also be obtained. Since groundwater containing pollutants continues to be mixed with the air from the air pipe while going up in the pumping pipe by the principle of the air lift pump, pollutants that are easily vaporized such as VOC easily desorb from the groundwater. . For this reason, in the soil purification process using the well structure according to the present invention, an aeration process on the ground becomes unnecessary.

  In the well structure according to the first aspect of the present invention, the current between the electrodes flows in the stored water in the well frame, like the soil, and is joule-heated by this current. Since the stored water is in the immediate vicinity of the electrode, the current density is large, and since water generally has a higher specific resistance value than the soil, it reaches a higher temperature earlier than the soil. The heating of the contaminated soil is also promoted by the heat of the high-temperature stored water being given to the surrounding soil by heat conduction. Furthermore, the detachment of contaminants from the ground water during the airlift is also promoted.

  In order to utilize such a principle, in the well structure according to the first aspect, the well frame needs to be insulated from the electrode. However, the well frame itself may be an insulator or a conductive layer. The body (for example, metal) may be sufficient.

  Since the well structure of the second aspect does not use an electrode, the well diameter can be reduced, and soil contamination can be removed at low cost.

The schematic block diagram of one Example of the well structure by this invention. The perspective view which shows two types of slits provided in the well frame of the well structure of the Example. The figure of the example of arrangement | positioning of the well using the well structure by this invention. The figure which shows schematic structure of the well structure by another Example of this invention. The figure which shows schematic structure of the well structure by another Example of this invention. It is experimental data of a soil purification apparatus using the well structure of the present invention, (a) is a plan view showing the position of each well on the ground surface and the measurement position of the soil temperature, (b) is the temperature time at each measurement position The graph which shows transition. The figure of the well arrangement | positioning of another experiment using the well structure of this invention. The graph which shows transition of the elapsed days from the start of electricity supply, and the accumulation amount of VOC collection by the said experiment. The schematic block diagram which shows arrangement | positioning of the collection | recovery well and electrode well by the conventional electric heating method.

An embodiment of the well structure of the present invention will be described with reference to FIGS.
FIG. 1 is a cross-sectional view showing a schematic configuration of a well structure 10 of this example. The well structure 10 includes a well frame 11, a well lid 12 and a well bottom 13 provided above and below the well frame 11, an electrode 14 inserted in the well frame 11 from the well lid 12, a pumping pipe 15, and an air pipe. 16 and a suction tube 17 or the like. The tip of the air pipe 16 is connected to the side surface of the water pump 15 near the lower end of the water pump 15 so that air is fed into the water pump 15. In this embodiment, since the well frame 11 is made of steel, an insulating member 18 is interposed between the well lid 12 and the electrode 14 so that the electrode 14 is not in electrical contact with the well frame 11. .

  As shown in FIGS. 2 (a) and 2 (b), a number of slits 19 are formed on the lower side surface of the well frame 11 so that the groundwater contained in the soil can permeate. The width of the slit 19 is set to a size that prevents soil particles from passing (for example, about 3 mm). The length and arrangement of the slits are arbitrary as long as the strength of the well frame 11 is maintained, and is not limited to the mode shown in FIGS. 2 (a) and 2 (b).

  An air supply pump 20 for sending air is connected to the ground side of the air supply pipe 16. A suction pump 21 for sucking air (gas) from the suction pipe 17 is connected to the ground side of the suction pipe 17.

  Such a well structure 10 is installed in a well excavated around the soil to be decontaminated, as shown in FIG. In the example of FIG. 3, three wells 10-1 to 10-3 are provided at the vertices of an equilateral triangle, and the electrodes of each well are connected to terminals (Φ1 to Φ3) of each phase of the three-phase AC power supply 23. The size of this triangle is set as appropriate according to the voltage and power capacity of the three-phase AC power source 23 and the electrical resistance of the soil. The output voltage of the three-phase AC power source 23 is 80 to 250 V and the output current is 10 to 100 A. In general, the length of each side is preferably about 3 to 10 m. The depth of each well is set according to the depth of the pollutant and groundwater, but is often excavated to about 10 to 30 m underground, for example. The diameter of the well needs to be 50 mm or more because electrodes, pumping pipes, air supply pipes, etc. must be inserted as described above, but if it is too large, the cost of drilling the well will be very high. Therefore, it should be about 200 mm or less.

  In a well that has been excavated to a depth where soil containing groundwater exists, groundwater contained in the soil enters the well frame by water pressure and becomes stored water (FIG. 1). By investigating the state of this groundwater in advance, the electrode 14, the pumping pipe 15, and the air supply pipe 16 are inserted to a depth located below the surface of the stored water. There is no particular problem when the well frame 11 is made of metal, but when the well frame 11 is made of non-metal (insulator), the current between the electrodes of the adjacent wells flows only through the slits 19. The slit 19 provided in the frame 11 is also provided at a depth where it is desired to be heated after investigation.

  When the power of the three-phase AC power supply 23 is turned on and a voltage is applied to the electrode 14 of each well structure 10, the voltage of the three-phase AC power supply 23 is stored water in the well frame 11, contaminated soil between wells, adjacent wells. Applied between the stored water in the well frame 11 of the structure 10. Thereby, first, the stored water in the well frame 11 having a high current density is heated by Joule heat. The heat of the stored water heats the surrounding contaminated soil, and the contaminated soil also generates Joule heat by itself between the electrodes.

  When the soil is heated in this manner, the VOC adsorbed on the soil particles is desorbed and its fluidity is increased, and is mixed into the groundwater contained in the soil. This groundwater enters the well frame 11 as described above. Groundwater (reserved water) that has entered the well frame 11 is pumped to the ground by the principle of an air lift pump as follows.

  First, air is sent to the air supply pipe 16 by the air supply pump 20. Since the lower end of the air supply pipe 16 is connected to the pumping pipe 15 below the surface of the stored water, the air is fed into the pumping pipe 15. The air sent in is mixed into the stored water in the pumping pipe 15, so that the stored water whose average specific gravity is lightened on average stands in the well frame 11 due to the water pressure from below (the head pressure of the stored water). The inside of the pumped water pipe 15 is pushed up and floats. The amount of stored water to be pumped can be adjusted by the output of the air pump 20.

  When the stored water inside the well frame 11 is pumped up, the water level temporarily decreases. However, since the groundwater in the soil enters through the slit 19 of the well frame 11 by the water pressure, the water level is stored in the well frame 11. The stored water level is restored. In this manner, the groundwater (reserved water) mixed with VOC can be continuously collected while the air pump 20 supplies air.

  As described above, in the soil purification apparatus of the present embodiment, each well has functions of both an electrode well for heating soil (and stored water) and a recovery well for collecting VOC-contaminated water. Therefore, unlike the conventional case, there is no need to provide a recovery well different from the electrode well, the number of wells can be reduced, and the cost for drilling the well and thus the total cost for soil purification can be reduced.

  Furthermore, in the soil purification apparatus of this invention, the following effects are acquired by using an air lift pump for pumping up stored water. That is, by sending air to the stored water, the stored water is aerated, and a part of the VOC mixed in the inside is vaporized. The vaporized VOC is lifted to the ground together with the pumping pipe 15 and is also released to the outside of the pumping pipe 15. The VOC gas pulled up together with the stored water in the pumping pipe 15 is separated from the water on the ground, sent to an exhaust gas treatment device such as activated carbon adsorption, and rendered harmless. Further, the VOC gas released into the well frame 11 outside the pumping pipe 15 is sucked through the suction pipe 17 by the suction pump 21, and is similarly sent to the exhaust gas treatment apparatus to be rendered harmless. Thus, it becomes possible to improve the recovery efficiency of VOC. In addition, since the higher the temperature of the stored water, the more VOCs are vaporized by the explosion, there is an advantage of warming the stored water for this reason. In addition, since the exhaust gas treatment device is less expensive than a water treatment facility that treats the pumped VOC-contaminated water, the promotion of gasification by the air lift pump has the advantage of reducing the cost of treatment.

  In the above embodiment, the electrode 14 is provided in the well frame 11, but the well frame 11 may be made of metal and the well frame 11 may be used as an electrode. An example of this well structure 30 according to the second aspect of the present invention is shown in FIG. The well structure 30 is substantially the same as the well structure 10 of the first embodiment except that no electrode is provided. However, since no electrode is inserted, the thickness of the well frame 31 (that is, the well to be drilled) can be reduced.

  Yet another embodiment of the present invention is shown in FIG. In the well structure 40 of this embodiment, the air supply pipe 46 is arranged inside the pumped water pipe 45 to form a double pipe structure. In the well structure 40 in FIG. 5 (a), air is discharged from the lower end of the air supply pipe 46 into the pumping pipe 45. However, as shown in FIG. 5 (b), the lower end of the air supply pipe 48 is closed. The air may be discharged from the side surface. Thereby, invasion of soil particles or the like into the air pipe 48 can be prevented.

  Since the heating effect of the soil when using such three electrode wells was confirmed by experiments, the data is shown in FIG. FIG. 6 (a) shows the position of each electrode well and the measurement position of soil temperature on the ground surface. In this experiment, three electrode wells A to C were provided at the apex of an equilateral triangle with a side length of 3.5 m, and the depth of each electrode was 25 m underground. The soil was Kanto Loam, and a three-phase AC power source with an output voltage of 110 V, an output current of 20 A, and a frequency of 50 Hz was used for voltage application to each electrode. Fig. 6 (b) plots the measured soil temperature at 24 m underground at each measurement position (1) to (3) with the elapsed time (days) on the horizontal axis and the soil temperature (° C) on the vertical axis. It is. The soil temperature was measured by drilling holes at a depth of 24 m underground at measurement positions (1) to (3) and placing a thermometer at the bottom of each hole.

  As shown in the graph of FIG. 6 (b), the soil temperature, which was about 20 ° C. on the first day, increased with the passage of days, and increased to nearly 40 ° C. after 90 days. This value is consistent with the tendency indicated by the simulation results, and it was confirmed that the electrode well used in the soil purification apparatus according to the present invention has a sufficient soil heating effect. During that time, the water level was about 18 m underground.

Next, the results of experiments conducted with different well arrangements will be described with reference to FIGS. At the actual VOC contamination site, six wells were provided as shown in FIG. 7, and the well structure shown in FIG. 1 was installed in each well to verify the heating function and the VOC recovery function. The site conditions are as follows.
Contaminant: VOC (perchlorethylene (PCE), trichlorethylene (TCE), dichloroethylene (DCE), vinyl chloride monomer (VCM; where VCM is the decomposition product of DCE))
Soil quality: sandy silt (cohesive soil)
Groundwater level: 2 m from the surface
Electrode depth: 10 m
Number of electrodes: 6 Output voltage: Three-phase AC 110 V
Output current: 30-40A

  Since the soil temperature reached 50 ° C. 50 days after the start of energization, gas suction and air lift pumping were started at that time. The graph of FIG. 8 is the total of the amount of VOC recovered by vaporization by air lift pumping aeration. The increase in soil temperature is as planned, and it has been shown that the recovery of VOCs from this soil is also being carried out effectively. Thus, it was proved that the functions of both the electrode well and the recovery well can be effectively obtained by the well structure according to the present invention.

DESCRIPTION OF SYMBOLS 10, 30, 40 ... Well structure 11, 31 ... Well frame 12 ... Well lid 13 ... Well bottom 14 ... Electrode 15, 45 ... Pumping pipe 16, 46, 48 ... Air supply pipe 17 ... Suction pipe 18 ... Insulating member 19 ... Slit 20 ... Air supply pump 21 ... Suction pump 23 ... Three-phase AC power supply 51 ... Recovery well 52 ... Electrode well

Claims (5)

It is a well structure provided in each well used for soil purification using the electric heating method,
a) a well frame having water permeability for taking in groundwater contained in the soil;
b) an electrode inserted into the well frame and electrically insulated from the well frame;
c) a pumping pipe inserted into the well frame such that one end thereof is located below the surface of the water stored in the well frame;
d) a well structure having an air supply pipe inserted into the well frame for sending air into the pumping pipe below the water surface. It is a well structure provided in each well used for soil purification using the electric heating method,
a) a well frame having electrical conductivity and permeability to take in groundwater contained in the soil;
b) a pumping pipe inserted into the well frame such that one end thereof is located below the surface of the water stored in the well frame;
c) a well structure having an air supply pipe inserted into the well frame for sending air into the pumping pipe under the water surface.   The well structure according to claim 1 or 2, wherein the air supply pipe is provided outside the pumping pipe.   The well structure according to claim 1 or 2, wherein the air supply pipe is provided in the pumping pipe, and the water pumping pipe and the air supply pipe have a double pipe structure.   The well structure according to claim 4, wherein a lower end of the air pipe is sealed and an opening is provided on a side surface.

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