JP4740445B2 - In-situ purification of soil contaminated with volatile organic compounds - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention is an environmental problem of soil contamination due to soil contaminated with artificial chemical substances, that is, organic compound fuels such as heavy oil, gasoline and kerosene, synthetic organic chlorine compounds such as dioxin and PCB, volatile organic chlorine compounds such as trichlorethylene and tetrachloroethylene, etc. In particular, the present invention relates to a method for safely purifying soil contaminated with volatile organic compounds such as trichlorethylene in situ.
[0002]
[Prior art]
Recently, pollution by artificial chemical substances has been increasing due to increased industrial activities and higher living standards. In particular, trichlorethylene and other volatile organic compounds are used as cleaning agents for semiconductor manufacturing and dry cleaning.
When washing wastewater containing the volatile organic compound leaks out for some reason, trichlorethylene easily penetrates into the ground, causing wide-area groundwater contamination.
[0003]
Moreover, since trichlorethylene etc. are highly volatile substances, if these substances exist underground, they will volatilize in the air in the soil, and will diffuse and rise to the ground surface, causing environmental pollution problems.
For this reason, Japanese Patent No. 2589002 has been proposed as a method for purifying soil contaminated with this volatile organic compound. The present invention is a method of spraying and mixing an inorganic compound (such as quicklime) on soil contaminated with a volatile organic compound, and causing an exothermic reaction with water in the soil to volatilize and remove harmful gases of the volatile organic compound in the soil.
[0004]
However, in this purification method, it is difficult to sufficiently stir and mix soil and quicklime when the amount of treated soil increases, and the temperature of the entire soil cannot be sufficiently raised. Therefore, there is a problem that the volatilization efficiency of volatile organic compounds in the soil is low.
Furthermore, this method is effective only when the contaminated soil depth is shallow (up to about 1 to 2 m from the ground surface), but the processing becomes impossible when the contaminated depth is deeper than the above depth.
[0005]
In addition, when the soil contaminated with volatile compounds on the surface is stirred and mixed, volatile harmful gases are scattered in the air, which may cause air pollution.
In addition, in said method, there also exists a problem which cannot process a contaminated groundwater simultaneously.
[0006]
In addition to the above methods, methods for purifying soil contaminated with volatile organic compounds include the following methods.
1) Method of sucking polluted gas in soil 2) Method of pumping up contaminated groundwater and vaporizing it Currently, the above method is the main method. There is a problem whether it can be purified.
[0007]
Next, in-situ purification methods include the following methods.
3) Vitrification 4) In-situ oxidative decomposition method injecting an oxidizer such as potassium permanganate 5) A method in which quick lime and contaminated soil are stirred and mixed by a powder jet stirring method, and water absorption is generated and purified. 3) The purification method of 4) is not economical and expensive, and the method of 5) pumps quick lime into the soil with air, so that polluted gas is scattered in the atmosphere, or the compressed air is used. Contaminated gas may diffuse into the soil.
[0008]
[Problems to be solved by the invention]
Such conventional purification techniques have the following main problems.
1) Not economical and very expensive.
2) It takes time to clean up the contamination.
3) There is a risk that polluted gas will be scattered in the atmosphere.
[0009]
[Means for Solving the Problems]
In the present invention, quick lime piles made of quick lime in a pile shape are placed in a soil contaminated with a volatile organic compound at intervals of 0.8 to 2.0 m, and the vicinity of the quick lime piles by a water absorption action by a chemical reaction of quick lime. Inhalation of soil water from the intermediate ground of the limestone, as well as heat generated by the chemical reaction of quicklime and the harmful gas of volatile organic compounds volatilized by the temperature rise of the intermediate ground derived from heat conduction, and contaminated groundwater and, wherein the purifying contaminated with volatile organic compounds soil and the ground water at the same time.
[0010]
In addition, the volatile organic compound is volatilized by the chemical reaction of quicklime without mixing the soil contaminated with the volatile organic compound with quicklime, and contaminated with the volatile organic compound without scattering the volatilized harmful gas. It is a method of purifying soil contaminated with volatile organic compounds that improve the soft ground together with the purification of soil in place.
[0011]
Furthermore, the reaction heat of quicklime piles placed in soil contaminated with volatile organic compounds raises the soil temperature of the contaminated soil and, in combination with the soil gas suction method, increases the purification rate, The soil was contaminated with organic organic compounds.
[0012]
Furthermore, the contaminated soil is characterized by raising the soil temperature of soil contaminated with semi-volatile organic compounds by the reaction heat of quicklime piles, volatilizing harmful gases of semi-volatile organic compounds and absorbing and purifying them. This is a method of purifying in situ.
[0013]
This invention pays attention to the problems of the prior art as described above, uses a quick lime pile method with a proven track record for improving soft ground, raises the soil temperature with reaction heat, and volatilizes volatile organic compounds. By doing so, the pollutant gas can be easily sucked and the purification rate can be increased.
In addition, this method does not stir and mix the contaminated soil, so that the contaminated gas can be safely purified without being scattered into the atmosphere.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
In the embodiment of the present invention, thermal behavior in soil when quicklime stakes are placed will be described based on calculated values and actually measured values.
The quicklime pile placed in the ground generates heat at the time of water-absorbing reaction of soil water, reaches a maximum of about 400 ° C at the quicklime pile body part, and the soil temperature also depends on the ground conditions, but 50 ° C-70 ° C is 5-10 It turns out to continue for a week.
[0015]
In the heat calculation, the water permeability from the soil block shared by the quicklime pile is heated, but it is held in the quicklime pile in a hot water state at a boiling temperature of 100 ° C under 1 atm. If the temperature of the lime pile is gradually decreased under the condition that it is used to heat the soil by heat exchange with the soil, the heat retained inside the pile until the surface temperature reaches 100 ° C. Calculated as being transferred to the soil by the temperature gradient between the center and outer part of the quicklime pile, and after the quicklime pile temperature reaches 100 ° C, the retained heat of the soil mass including the quicklime pile moves within the system Thus, when heat transfer is estimated based on the idea that moderate cooling and heating continue in equilibrium until the temperature converges to a constant value, a conceptual diagram of this heat transfer process is shown in FIG. The temperature rises up to the theoretical maximum temperature of 320 ° C. , Lime piles and soil mass temperature is Da設 the soil is converged to about 70 ° C. in equilibrium.
[0016]
Next, thermal behavior in the soil when quicklime stakes are placed will be described in terms of calculated values and actual values.
The range of influence of quicklime piles in a square layout with a pitch of 1.2 m is determined as an equivalent circle, and there is one quicklime pile in the columnar soil, and the inside of the pile is an axial target model with uniform temperature. As shown in FIG. 2, the calculation result analyzed by the finite element method analysis is compared with the actual measurement value, and the calculation result and the measurement value (FIG. 3) are very similar.
From the above, it has been found that placing quicklime stakes on contaminated soil maintains the soil mass temperature as a heat source for soil heating at a temperature of about 50 ° C to 70 ° C over a long period of time.
[0017]
In addition, in the soil gas suction method, it is very effective to use soil heating together, and the following effectiveness is widely known.
1) The purification speed can be increased.
2) Effective for removing semi-volatile substances that are relatively difficult to vaporize at room temperature.
Next, the quantitative proof of effectiveness is publicly known (Obayashi Institute of Technology No. 60, 2000), and the outline of the test is as follows.
[0018]
In a small column experimental apparatus, the soil is filled with contaminated soil (kerosene) and sucked with a vacuum pump, and in an experiment in which air heated at a constant speed is passed through the column, the soil temperature is 50 ° C, 35 ° C. The removal rate and removal rate were confirmed at three types of 20 ° C.
[0019]
The test result at that time was that the soil temperature was 50 ° C. and 20 ° C. were compared, and the removal rate was 100%.
In addition, in a comparative test of the removal rate of contaminated soil of trichlorethylene, which is a representative of volatile organic compounds, and contaminated soil of semivolatile kerosene, at a soil temperature of 50 ° C, the removal rate is 100%. Was about 100 times faster.
[0020]
From the above, it was found that heating soil contaminated with volatile organic compounds is very effective in increasing the purification rate and removing semi-volatile organic compounds that are difficult to volatilize.
[0021]
Next, one embodiment of the present invention will be described with reference to FIGS. 4 and 5. FIG. 4 is a schematic view of a method for purifying soil contaminated with volatile organic compounds, and FIG. 5 is a plan view of lime pile driving. It is.
In the quick lime pile construction method, quick lime piles 5 are placed in the soil 1 contaminated with volatile organic compounds at intervals of 0.8 m to 2.0 m, and the suction well 4 is set up in the ground. A vacuum pump 2, a contaminated gas and groundwater purification device 3 are attached to the suction well 4.
[0022]
The quick lime pile 5 which is contaminated with a volatile organic compound such as trichlorethylene and placed in the soil 1 sucks the soil water of the intermediate ground 6 by the water absorption action by the chemical reaction of the quick lime pile 5, and the quick lime by the chemical reaction. The pile body generates heat up to a maximum of 400 ° C. After that, depending on the ground conditions, the quicklime pile placed in the soil and the mass of the lump are converged to about 70 ° C and maintain an equilibrium state. Volatilizes and generates harmful gases.
Volatilized harmful gas and contaminated groundwater are sucked by the suction well 4, and the contaminated gas and the contaminated groundwater are purified by the purification device 3, and quick lime piles are built in the ground, so soft ground is improved. Can be done.
[0023]
【The invention's effect】
According to the present invention, polluted gas can be purified without being scattered in the atmosphere, and the contaminated groundwater can be purified at the same time, and the soft ground can be improved as a secondary effect.
[0024]
In this invention, quick lime stakes are placed in the soil at a distance of 0.8m to 2.0m in the contaminated soil to absorb the water in the soil. It can volatilize, make it easy to suck pollutant gas, increase the purification rate, purify polluted gas without scattering into the atmosphere, and purify contaminated groundwater at the same time. Moreover, soft ground can be improved as a secondary effect.
[0025]
Moreover, since it is the placement of quicklime piles as a heat source for heating soil contaminated with volatile organic compounds, it is economical, extremely effective and reliable, and can also improve the ground.
[Brief description of the drawings]
FIG. 1 is a conceptual diagram of a heat transfer process of quicklime piles.
FIG. 2 is a comparison diagram between a calculated value and an actual measurement value of a temporal change in underground temperature of quicklime piles.
FIG. 3 is a diagram showing measurement results of underground temperature of quicklime piles.
FIG. 4 is a schematic diagram of a method for purifying soil contaminated with volatile organic compounds.
FIG. 5 is a plan view of quicklime pile driving.
[Explanation of symbols]
1 Soil contaminated with volatile organic compounds 2 Vacuum pump 3 Contaminated gas and groundwater purification device 4 Suction well 5 Quicklime pile 6 Intermediate ground (soil contaminated with volatile organic compounds)

Claims (4)

Quick lime piles made of quick lime in a pile shape are placed in the soil contaminated with volatile organic compounds at intervals of 0.8 to 2.0 m, and the intermediate ground around the quick lime piles is absorbed by the water absorption by the chemical reaction of quick lime. Volatile by absorbing soil water and sucking harmful gas of volatile organic compounds volatilized due to heat generated by quick lime chemical reaction and temperature rise of intermediate ground derived from heat conduction and contaminated groundwater A method for purifying soil contaminated with a volatile organic compound in situ, comprising purifying soil contaminated with an organic compound and groundwater at the same time. Volatile organic compounds were volatilized by the chemical reaction of quicklime without stirring and mixing the soil contaminated with volatile organic compounds with quicklime, and contaminated with the volatile organic compounds without causing volatilization of harmful gases. The method for purifying soil contaminated with a volatile organic compound according to claim 1, wherein the soil is purified. The reaction heat of quick lime piles placed in soil contaminated with volatile organic compounds raises the soil temperature of contaminated soil and increases the purification rate by suctioning with the soil gas suction method. A method for purifying soil contaminated with the volatile organic compound according to claim 1 or 2 in situ. Claim raising the soil temperature of the soil contaminated with semi-volatile organic compounds by the reaction heat of quick lime pile, characterized in that it absorbs purifying evaporate the harmful gases semi-volatile organic compounds 1, 2, 3 A method for purifying soil contaminated with the volatile organic compound according to any one of the above .

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