JP7234793B2 - SOIL CLEANING DEVICE AND SOIL CLEANING METHOD - Google Patents

Description

The present invention relates to a soil purification device and a soil purification method.

One of the methods for cleaning contaminated soil is the electric heating method. The electric heating method desorbs contaminants from the soil and purifies the soil by heating the soil with electrical energy. According to the electric heating method, the cost is lower than the method of excavating and carrying out soil purification, and it is possible to purify even if a building or the like exists on the contaminated soil. There is an advantage that it is possible to purify even poorly permeable soil that is difficult to purify by chemical injection.

In a soil purification device that purifies soil by an electric heating method, a plurality of electrodes are inserted into the soil to be purified, and a voltage is applied between the electrodes to cause an electric current to flow through the soil between them. Joule heat is generated by the electrical resistance of . When the soil temperature rises, VOCs (Volatile Organic Compounds) such as tetrachlorethylene, trichlorethylene, dichloroethylene, and trichloroethane adsorbed to soil particles are desorbed from the soil and eluted into groundwater. It is possible to remove VOCs from the soil and purify soil contamination by performing pumping treatment for pumping up this groundwater to the ground and gas suction treatment for sucking underground gas containing VOC gasified from groundwater. .

Patent Literature 1 discloses a soil remediation apparatus that uses phase angle control to make the current between electrodes inserted in the soil to be remedied as uniform as possible, thereby improving the utilization efficiency of power supply equipment.

JP 2016-159260 A

When cleaning soil by the electric heating method, a voltage is applied to a plurality of electrodes inserted into the soil to heat the soil. At this time, due to the contact resistance between the electrode and the soil, the electrode surface generates heat, and the temperature of the electrode surface becomes higher than the temperature of the soil. The specific resistance of soil varies greatly depending on the moisture contained in the soil, but when the electrode surface becomes hot, the soil near the electrode dries up. When the soil dries, the specific resistance of the soil increases sharply, and the current flowing between the electrodes decreases. The temperature at which the soil resistivity rapidly increases due to the drying of the soil varies depending on the type of soil. If the soil is small, it is about 120 degrees Celsius.

When the current flowing between the electrodes is reduced due to drying of the soil, the inventor of the present invention finds that the electric power required to heat the soil cannot be applied to the soil. Found it.

The present invention has been made to solve the above problems, and by preventing the soil from drying out in the vicinity of the electrode surface, it is possible to stably heat the soil and efficiently purify the soil. An object of the present invention is to provide a soil remediation device and a soil remediation method that can be carried out.

A first aspect of the present invention is a soil remediation device comprising a soil warming device that heats soil by applying a voltage to a plurality of electrodes inserted into the soil, the soil warming device comprising: a temperature sensor provided on the electrode; and a voltage control section for controlling a voltage applied to the electrode. The voltage applied to the electrode is lowered, and the voltage applied to the electrode is lowered until the temperature detected by the temperature sensor drops to a predetermined value or until a predetermined time elapses, and then the voltage is increased.

According to this aspect of the invention, by measuring the temperature or the water content of the soil with the temperature sensor, it is possible to prevent drying of the soil in the vicinity of the electrode surface. Therefore, it is possible to stably heat the soil while preventing a rapid increase in the specific resistance of the soil, and to efficiently clean the soil.

BRIEF DESCRIPTION OF THE DRAWINGS It is a schematic diagram of the soil purification apparatus which concerns on embodiment of this invention. FIG. 4 is a plan view showing the arrangement of three electrodes 61, 62, 63 inserted into soil; Fig. 4 is a vertical cross-sectional view of an electrode 61 inserted into soil; FIG. 5 is a cross-sectional view taken along the line AA of FIG. 4; 4 is a graph showing changes over time in the temperature of an electrode 61, the temperature of soil in a region surrounded by electrodes 61, 62, and 63, and the current applied to the electrodes. 4 is a graph showing changes over time in the temperature of an electrode 61, the temperature of soil in a region surrounded by electrodes 61, 62, and 63, and the current applied to the electrodes. It is a schematic diagram of the soil purification apparatus based on the modification of embodiment of this invention. It is a schematic diagram of the soil purification apparatus which concerns on the other modified example of embodiment of this invention.

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic diagram of a soil purification apparatus according to an embodiment of this invention.

This soil remediation device is a soil warming device that heats the soil. 63, a temperature sensor 73 that measures the temperature of the electrode 61 out of the three electrodes 61, 62, and 63, an electrode temperature measuring instrument 17 that measures the temperature of the electrode 61 based on the signal from the temperature sensor 73, and the electrode temperature An ON/OFF control device 16 is provided as a voltage control unit according to the present invention for turning ON/OFF the three-phase AC power supply 15 based on the temperature of the electrode 61 measured by the measuring device 17 .

FIG. 2 is a plan view showing the arrangement of three electrodes 61, 62, 63 inserted into soil.

As shown in this figure, the electrodes 61, 62, 63 are arranged at equal intervals and at positions corresponding to the vertices of an equilateral triangle in plan view. The arrangement of the three electrodes 61, 62, 63 may be other than the arrangement shown in FIG. Moreover, the number of electrodes may be plural, and may be more than three.

FIG. 3 is a vertical cross-sectional view of the electrode 61 inserted into the soil, and FIG. 4 is a cross-sectional view taken along line AA. The electrodes 62 and 63 also have the same configuration as the electrode 61 shown in these figures, except that the temperature sensor 73 is omitted.

The electrode 61 includes a conductive metal pipe 71 and a cylindrical non-conductive member 72 surrounding the outer periphery of the pipe 71 near the upper end thereof. A temperature sensor 73 is suspended by a cable 74 inside the pipe 71 . The depth region of the electrode 61 surrounded by the non-conductive members 72 is a depth region where no current flows through the soil even if a voltage is applied to the electrode 61, and is surrounded by the non-conductive members 72 indicated by arrows in FIG. Depth region 76 where there is no current is the depth region where current flows through the soil when a voltage is applied to electrode 61 . For this reason, the non-conductive member 72 prevents electric current from flowing in a depth region where there is little contamination such as embankment and a depth region where a structure exists between the electrodes, thereby wasting electrical energy. can be prevented.

The temperature sensor 73 is arranged near the center of the depth region 76 of the electrode 61 that is not surrounded by the non-conductive member 72 . The temperature sensor 73 is not in contact with the inner peripheral surface of the pipe 71 at the electrode 61 , but since there is almost no gas flow in the interior space of the pipe 71 , the temperature sensor 73 senses the temperature through the internal atmosphere of the pipe 71 . can be used to measure the temperature of pipe 71 at electrode 61 . The temperature of the electrode 61 may be measured directly by bringing a temperature sensor 73 into contact with the pipe 71 of the electrode 61. Alternatively, as shown in FIG. may be measured indirectly through the internal atmosphere or the like.

Next, a description will be given of the operation of soil purification by the soil purification apparatus having the configuration described above, comparing the case where the present invention is applied and the case where it is not applied. 5 and 6 are graphs showing changes over time in the temperature of the electrode 61, the temperature of the soil in the area surrounded by the electrodes 61, 62 and 63, and the current applied to the electrode 61. FIG. 5 shows a comparative example in which the present invention is not applied, and FIG. 6 shows a case in which the present invention is applied. Here, the horizontal axis in FIGS. 5 and 6 indicates the number of days (days) of energization, and the vertical axis indicates temperature (Celsius) and current (ampere). The current shown in these figures represents the total value of the three electrodes 61,62,63. In these figures, the dashed line indicates the current value, the dashed line indicates the temperature of the electrode 61, and the solid line indicates the temperature of the soil.

When the three-phase AC power supply 15 is turned on by the action of the ON/OFF control device 16 shown in FIG. The moisture in the water is heated by Joule heat. In the case of the comparative example shown in FIG. 5, when the temperature of the electrode 61 exceeded 120 degrees Celsius and about one week passed, the current value abruptly decreased. It is presumed that this is because the soil in the vicinity of the electrodes 61, 62, and 63 has dried up, causing a rapid increase in the specific resistance of the soil, and thus the current flowing between the electrodes 61, 62, and 63 has decreased. be done. When such a phenomenon occurs, it becomes impossible to apply the electric power necessary for heating the soil, and it is found that the temperature of the soil does not rise to the temperature necessary for purification. was done.

Therefore, in the soil purification apparatus according to this embodiment, as shown in FIG. 6, when the temperature of the electrode 61 measured by the temperature sensor 73 reaches 120 degrees Celsius, the ON/OFF control device shown in FIG. 16 turns off the three-phase AC power supply 15, and the voltage applied to the electrodes 61, 62, 63 is turned off. Then, when the temperature of the electrode 61 drops to 100 degrees Celsius by turning off the three-phase AC power supply 15, the three-phase AC power supply 15 is turned on again by the action of the ON/OFF control device 16, and the electrodes 61, 62, 63 is turned on. By repeating such operations, as shown in FIG. 6, the current values flowing through the electrodes 61, 62, and 63 during energization can be kept constant, and the temperature of the soil can be raised to the temperature required for purification. becomes possible.

Thus, by raising the temperature of the soil, it becomes possible to purify the soil. In addition, in order to purify the soil more efficiently, after the temperature of the soil rises, the groundwater that has eluted the VOC desorbed from the soil is pumped up to the ground, and the underground gas containing the VOC gasified from the groundwater is used. By performing a gas suction process or the like, it is possible to more reliably remove VOCs from the soil and purify the contaminated soil.

In the embodiment described above, when the temperature of the electrode 61 detected by the temperature sensor 73 rises to 120 degrees Celsius as the first set value, the ON/OFF control device 16 as the voltage control section The voltage applied to the electrode 61 is turned off, and when the temperature of the electrode 61 detected by the temperature sensor 73 drops to 100 degrees Celsius as the second set value smaller than the first set value, the voltage applied to the electrode 61 is turned off. The voltage is turned on. However, after the voltage applied to the electrode 61 is turned off, the voltage applied to the electrode 61 may be turned on after a predetermined time has elapsed.

Also, instead of on/off control of the voltage applied to the electrode 61, the voltage may be lowered or raised. In this case, the voltage applied to the electrode 61 may continue to be lowered when the temperature of the electrode 61 rises to the set value, and the operation of raising the voltage may be omitted. Note that turning off the voltage is one mode of decreasing the voltage, and turning on the voltage is one mode of increasing the voltage.

Next, a modification of the embodiment of the invention will be described. FIG. 7 is a schematic diagram of a soil purification device according to a modification of the embodiment of the invention.

In the above-described embodiment, the temperature sensor 73 for measuring the temperature of the electrode 61 of the three electrodes 61 , 62 , 63 is arranged. In contrast, in this embodiment, temperature sensors 73 are provided for all three electrodes 61 , 62 , 63 . In this embodiment, electrodes 62 and 63 have the same configuration as electrode 61 shown in FIG.

This soil remediation apparatus measures the temperature of each electrode 61, 62, 63 with a temperature sensor 73 and individually controls the voltage applied to each electrode 61, 62, 63 using voltage phase angle control. be. This soil purification apparatus comprises a three-phase AC power source 15, a phase detector 25 connected to each phase Φ1, Φ2, and Φ3 of the three-phase AC power source 15, and the three-phase AC power source 15 through the phase detector 25. It has triacs 21, 22, and 23 connected to the phases Φ1, Φ2, and Φ3, respectively, and a current measuring device 26. A voltage from each triac 21 , 22 , 23 is applied to each electrode 61 , 62 , 63 via a current measuring device 26 .

A temperature sensor 73 arranged on the three electrodes 61 , 62 , 63 is connected to the electrode temperature measuring instrument 17 . This electrode temperature measuring instrument 17 is connected to the ON/OFF control device 16 . On the other hand, each gate of the triacs 21 , 22 , 23 is connected to the gate signal generator 31 in the voltage controller 33 . The gate signal generator 31 is connected to a timing controller 32 that receives a signal from the ON/OFF controller 16 and generates a timing signal.

In such a configuration, when the soil resistance between the electrodes 61, 62, and 63 is different, a voltage corresponding to the resistance can be applied. That is, when each phase of the three-phase AC power supply 15 is connected to each electrode 61, 62, 63 and voltages 120 degrees out of phase with each other are applied, the voltage of the same magnitude is applied between each electrode 61, 62, 63. is applied. On the other hand, the timing control unit 32 controls the gate signal transmitted from the gate signal generation unit 31 to each of the triacs 21, 22, and 23, thereby changing the phase position at which each of the triacs 21, 22, and 23 is turned on. This makes it possible to apply voltages of different magnitudes between the electrodes 61 , 62 , 63 . Therefore, when the resistance value of the soil between the electrodes 61, 62, 63 is different and the current flowing through each electrode 61, 62, 63 changes due to this, the change in the current value is detected by the current measuring device 26. By changing the voltage applied to each electrode 61 , 62 , 63 , it becomes possible to pass a current of a required magnitude to each electrode 61 , 62 , 63 .

Then, in the soil purification apparatus according to this embodiment, when the temperature of any one of the electrodes 61, 62, 63 measured by the temperature sensor 73 of each electrode 61, 62, 63 reaches 120 degrees Celsius, the temperature shown in FIG. 3 stops the gate signal to be sent to any one of the triacs 21, 22, 23 by the operation of the ON/OFF control device 16 shown in FIG. Then, when the temperature of the electrodes 61, 62, 63 to which the supply of voltage has been stopped drops to 100 degrees Celsius, the transmission of the gate signal to the triacs 21, 22, 23 is restarted, and the electrodes to which the supply of power has been stopped The supply of voltage to 61, 62, 63 is resumed.

By repeating such operations, as in the case of the embodiment shown in FIG. 1, as shown in FIG. , the soil can be raised to the temperature required for purification.

Although three electrodes 61, 62, 63 are used in the embodiment shown in FIG. 7, more electrodes may be used. In such a case, it is not necessary to provide temperature sensors 73 for all electrodes. For example, if 20 electrodes are used, only 10 of them may be provided with temperature sensors 73 . Further, when 30 electrodes are used, 10 temperature sensors 73 may be arranged for every 3 electrodes arranged close to each other.

In addition, in the embodiment shown in FIG. 7, the voltages applied to the electrodes 61, 62, 63 are controlled using voltage phase angle control. The voltage applied to the electrodes 61, 62, 63 may be controlled.

Next, still another modification of the embodiment of the invention will be described. FIG. 8 is a schematic diagram of a soil purification device according to still another modification of the embodiment of the invention. The same reference numerals are assigned to the same members as in the embodiment shown in FIG. 1, and detailed description thereof will be omitted.

The soil purification apparatus shown in FIG. 1 employs a configuration in which the three-phase AC power supply 15 is turned ON/OFF based on the temperature of the electrode 61 measured by the temperature sensor 73 . On the other hand, the soil purification apparatus according to this embodiment employs a configuration in which the three-phase AC power supply 15 is turned ON/OFF based on the moisture content of the soil measured by the moisture content sensor 79 .

Here, the moisture content in this specification indicates the percentage of moisture contained in the soil. The moisture content sensor 79 is also called a soil moisture sensor and is commercially available. It has a configuration for detecting a ratio.

In the soil purification apparatus according to this embodiment, when the moisture content of the soil measured by the moisture content sensor 79 drops to the preset first set value, the action of the ON/OFF control device 16 shown in FIG. The three-phase AC power supply 15 is turned off, and the voltages applied to the electrodes 61, 62, and 63 are turned off. Then, by turning off the three-phase AC power supply 15, water is supplied to the soil from the surrounding area, and the water content of the soil measured by the water content sensor 79 rises to a second set value that is higher than the first set value. Then, the three-phase AC power supply 15 is turned on again by the action of the ON/OFF control device 16, and the voltage applied to the electrodes 61, 62, and 63 is turned on.

By repeating such operations, drying of the soil in the vicinity of the surfaces of the electrodes 61, 62, 63 can be prevented in the same manner as in the embodiment shown in FIG. Therefore, a sudden increase in the specific resistance of the soil can be prevented, and thus the value of current flowing through the electrodes 61, 62, 63 can be kept constant during energization. Therefore, it is possible to raise the temperature of the soil to the temperature required for purification.

Note that the water content sensor 79 is preferably arranged near the surface of the electrode 61 from the viewpoint of preventing the soil near the surface of the electrode 61 from drying out. However, the water content sensor 79 may be arranged at a position separated from the electrode 61 to estimate the water content near the surface of the electrode 61 based on the water content at that position.

In the embodiment shown in FIG. 8, the temperature sensor 73 in the embodiment shown in FIG. 1 is changed to a water content sensor 79. The three temperature sensors 73 provided may be replaced with three moisture content sensors 79 .

It will be appreciated by those skilled in the art that the multiple exemplary embodiments described above are specific examples of the following aspects.

(Section 1)
A soil remediation device comprising a soil warming device that heats soil by applying a voltage to a plurality of electrodes inserted into the soil, the soil warming device comprising:
a temperature sensor provided on the electrode;
A voltage control unit that controls the voltage applied to the electrode,
The voltage control section reduces the voltage applied to the electrodes when the temperature detected by the temperature sensor rises to a set value.

According to the soil purification apparatus of the first aspect, by measuring the temperature with the temperature sensor provided on the electrode, it is possible to prevent drying of the soil in the vicinity of the surface of the electrode. Therefore, it is possible to stably heat the soil while preventing a rapid increase in the specific resistance of the soil, and to efficiently clean the soil.

(Section 2)
In the soil purification device according to paragraph 1,
The voltage control unit reduces and then increases the voltage applied to the electrode.

According to the soil purification device described in the second aspect, it is possible to continuously heat the soil.

(Section 3)
In the soil purification device according to paragraph 2,
The voltage control unit turns off the voltage applied to the electrode when the temperature detected by the temperature sensor rises to a set value, and then turns it on again.

According to the soil purification apparatus of the third aspect, it is possible to prevent drying of the soil in the vicinity of the electrode surface by turning on/off the power supply.

(Section 4)
In the soil purification device according to paragraph 3,
The voltage control unit turns off the voltage applied to the electrode when the temperature detected by the temperature sensor rises to a first set value, and after turning off the voltage applied to the electrode, the temperature sensor When the temperature detected by falls to a second set value smaller than the first set value, the voltage applied to the electrodes is turned on.

According to the soil purification apparatus of the fourth aspect, it is possible to prevent drying of the soil in the vicinity of the electrode surface by controlling the on/off of the power supply based on the temperature.

(Section 5)
A soil remediation device comprising a soil warming device that heats soil by applying a voltage to a plurality of electrodes inserted into the soil, the soil warming device comprising:
a moisture content sensor that measures the moisture content of the soil;
A voltage control unit that controls the voltage applied to the electrode,
The voltage control unit reduces the voltage applied to the electrodes when the moisture content of the soil detected by the moisture content sensor drops to a set value.

According to the soil purification apparatus of the fifth item, by measuring the moisture content of the soil, it is possible to prevent drying of the soil in the vicinity of the electrode surface. Therefore, it is possible to stably heat the soil while preventing a rapid increase in the specific resistance of the soil, and to efficiently clean the soil.

(Section 6)
In the soil purification device according to item 5,
The voltage control unit reduces and then increases the voltage applied to the electrode.

According to the soil remediation device of item 6, it is possible to continue heating the soil.

(Section 7)
In the soil purification device according to paragraph 6,
The voltage control unit turns off the voltage applied to the electrodes when the water content of the soil detected by the water content sensor drops to a set value, and then turns it on again.

According to the soil remediation device of item 7, it is possible to prevent drying of the soil near the surface of the electrode by turning on/off the power supply.

(Section 8)
In the soil purification device according to item 7,
The voltage control unit turns off the voltage applied to the electrode when the water content of the soil detected by the water content sensor drops to a first set value, and after turning off the voltage applied to the electrode and turning on the voltage applied to the electrodes when the moisture content of the soil detected by the moisture content sensor rises to a second set value larger than the first set value.

According to the soil purification apparatus of the eighth aspect, it is possible to prevent drying of the soil in the vicinity of the surface of the electrode by controlling the on/off of the power supply based on the water content.

(Section 9)
A soil remediation method comprising the step of heating soil by applying a voltage to a plurality of electrodes inserted into the soil, wherein the step of heating the soil comprises:
a temperature measurement step of measuring the temperature of the electrode;
a voltage control step of lowering the voltage applied to the electrode when the temperature of the electrode measured in the temperature measurement step rises to a set value;
including.

(Section 10)
A soil remediation method comprising the step of heating soil by applying a voltage to a plurality of electrodes inserted into the soil, wherein the step of heating the soil comprises:
a moisture content measuring step of measuring the moisture content of the soil;
a voltage control step of lowering the voltage applied to the electrodes when the moisture content of the soil measured in the moisture content measuring step drops to a set value;
including.

According to the soil remediation devices of items 9 and 10, by measuring the temperature of the electrodes or the water content of the soil, it is possible to prevent drying of the soil in the vicinity of the surface of the electrodes. Therefore, it is possible to stably heat the soil while preventing a rapid increase in the specific resistance of the soil, and to efficiently clean the soil.

It should be noted that the above description is for the description of the embodiments of the present invention, and does not limit the present invention.

15 Three-phase AC power supply 16 ON/OFF controller 17 Electrode temperature measuring instrument 21 Triac 22 Triac 23 Triac 31 Gate signal generator 32 Timing controller 33 Voltage controller 61 Electrode 62 Electrode 63 Electrode 71 Pipe 72 Non-conductive member 73 Temperature Sensor 74 Cable 79 Moisture content sensor

Claims (5)

A soil remediation device comprising a soil warming device that heats soil by applying a voltage to a plurality of electrodes inserted into the soil, the soil warming device comprising:
a temperature sensor provided on the electrode;
A voltage control unit that controls the voltage applied to the electrode,
The voltage control unit
(a) reducing the voltage applied to the electrode when the temperature detected by the temperature sensor rises to a set value;
(b) after decreasing the voltage applied to the electrode until the temperature detected by the temperature sensor drops to a predetermined value or until a predetermined time elapses,
(c) increasing the voltage ;
A soil remediation device that repeats (a) to (c) . In the soil purification device according to claim 1,
The voltage control unit, when the temperature of the electrode detected by the temperature sensor rises to a set value, turns off the voltage applied to the electrode and then turns it on again. In the soil purification device according to claim 2,
The voltage control unit turns off the voltage applied to the electrode when the temperature of the electrode detected by the temperature sensor rises to a first set value, and after turning off the voltage applied to the electrode, The soil cleaning apparatus turns on the voltage applied to the electrodes when the temperature of the electrodes detected by the temperature sensor drops to a second set value smaller than the first set value. In the soil purification device according to any one of claims 1 to 3,
The soil purification apparatus, wherein the electrode has a conductive metal pipe, and the temperature sensor is provided inside the pipe. A soil remediation method comprising the step of heating soil by applying a voltage to a plurality of electrodes inserted into the soil, wherein the step of heating the soil comprises:
a temperature measurement step of measuring the temperature of the electrode;
(a) reducing the voltage applied to the electrode when the temperature of the electrode measured in the temperature measuring step rises to a set value;
(b) after decreasing the voltage applied to the electrode until the temperature of the electrode drops to a predetermined value or until a predetermined time elapses,
(c) a voltage control step of increasing the voltage and repeating (a)-(c) ;
A soil remediation method comprising:

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