KR100492230B1 - Apparatus and Method for Purifying Polluted Soil by Using Heated Air - Google Patents

Abstract

The present invention relates to a purification apparatus and a method for purifying soil that is contaminated at high concentration with oil by purifying and restoring it within a short period of time by injecting hot air. Purification apparatus according to the present invention is embedded in the soil (1) contaminated by oil and the injection well (11) for injecting air into the soil (1), connected to the inlet of the injection well (11) 11) is installed between the air injector 12 for supplying air to the injection well 11 and the air injector 12, and heats the air flowing from the air injector 12 to the injection well 11 An air heater 13, an extraction well 21 embedded in the soil 1 and guiding oil contaminants volatilized by the heated air to the outside, and connected to an outlet of the extraction well 21. And an air extractor 23 for discharging contaminants. According to the present invention, by injecting hot air into the soil to increase the volatility of oil contaminants present in the soil, low volatility oils such as diesel oil can be easily removed within a short period of time.

Description

Apparatus and Method for Purifying Polluted Soil by Using Heated Air}

The present invention relates to a purification apparatus and a purification method for restoring soil and groundwater contaminated with high concentration by oil such as gasoline or diesel, and more particularly, to purify the purification period by injecting and extracting hot air into the contaminated soil. It relates to a purification apparatus and a purification method that can be shortened.

Recently, various environmental pollution accidents occur frequently as a side effect of the rapid economic growth.In particular, the number of oil storage facilities including gas stations is rapidly increasing as oil consumption increases with increasing industrial activity and the number of automobiles supplied. Contamination of soil or groundwater due to oil leakage is on the rise.

In order to apply the restoration technology for restoring contaminated soil and groundwater, it is necessary to first review the types and characteristics of contaminants and the hydrogeological characteristics of the contaminated site, and the cost, duration, ease of maintenance, etc. Restoration techniques should be applied by comprehensive evaluation of the items. That is, the most basic considerations for restoring soil and groundwater by oil include characteristics such as viscosity, vapor pressure and solubility of oil pollutants leaked into soil and groundwater, degree of oil pollutant leakage, pollutant concentration, contaminated soil and Hydrogeological characteristics of groundwater; and the like.

To date, various restoration techniques have been developed and applied to minimize the impact of soil and groundwater contamination due to leakage of oil pollutants. Typical restoration techniques include excavation of soil in contaminated areas, transported off site, and thermally treated to stabilize or landfill.

However, these off-site restoration methods have limitations in application due to the risk of exposure to contaminants during soil excavation and high restoration costs. Therefore, in-suit restoration methods have recently been used in which contaminants are treated directly in the site. In particular, when restoring soil contaminated by oil components in the site treatment method, soil vapor extraction (SVE) extracts volatile substances present between the pores of the soil, or by injecting air into the soil. Bio Venting (BV) has been used to enhance the activity of indigenous microorganisms or to inject and treat microorganisms, nutrients, and emulsifiers in the soil.

Soil gas extraction (SVE) has been the most widely used method for restoring contaminated soil because of its ease of operation and economic effects. However, in the case of restoring soil pollution by high concentration of oil by soil gas extraction method, it is difficult to treat to very low concentration as the volatile oil component ratio increases with time, and secondary treatment of extract gas is difficult. There is a disadvantage in that it is necessary, and there is a limit in applicability when the level of saturated soil or groundwater is high. In other words, when the soil gas extraction method is used, the concentration of gas extracted continuously decreases with time, and thus the treatment effect becomes lower as time passes. This is due to the volatilization of oil components due to the forced extraction of gas. This is because the amount of gas volatilized decreases as the kinetic limitation is maintained, and the volatile components such as BTEX are initially removed, but the proportion of low volatility components increases as the extraction time elapses. . Therefore, in the case of restoring soil contamination by high concentration of oil by the soil gas extraction method, there is a limit to the removal of low volatile contaminants despite long-term extraction. In addition, there is a problem that the recovery period is long because the dispersion rate of oil contaminants is low.

And, it is generally known that the vapor pressure of contaminants can be removed by volatilization at least 70 Pa or more, and low volatility oils such as diesel or lubricating oil are difficult to remove by conventional soil gas extraction methods because the vapor pressure is very low.

On the other hand, in the case of the bioventilation method (BV), which improves the disadvantages of the soil gas extraction method according to the pollution degree and the characteristics of the pollutants, when the appropriate amount of air is injected into the soil, oil contaminants can be removed by biodegradation without extraction process, and thus spilled to the ground. Since no gas is generated, a reprocessing process such as an extraction process and a reprocessing facility are not required. However, such a bio venting method also takes a long time to restore.

In addition, when oil contaminants are present in low-permeability soils such as clay, conventional in-situ restoration methods are not easy to remove, and are therefore costly ex-situ. Restoration method is applied. This is because the transfer rate of substances such as gas or water migration in clay is very low, and there is little opportunity for substances (chemical solvents, stabilizing substances, air, etc.) to remove pollutants to come into contact with oil components and to perform their functions. If the method is used, it may be difficult to close the injection wells, or to take a long time to recover.

On the other hand, due to these problems, recently, methods such as oxidizing agent injection or soil flushing have been developed, but until now, the proven technology has not been applied in Korea.

The present invention has been developed to solve the problems of the conventional restoration method as described above, by purifying the soil and groundwater contaminated by the high concentration of oil by injecting and extracting hot air into the soil can be quickly removed It is an object to provide an apparatus and a purification method.

It is still another object of the present invention to provide a purifying apparatus and a purifying method capable of removing the contaminants after the primary removal of the contaminants through the injection and extraction of hot air, by adjusting the temperature of the injection air. will be.

In order to achieve the above object, the purification apparatus according to the present invention, the injection well is embedded in the soil contaminated by oil and injects air into the soil, and the air connected to the inlet of the injection well to supply air to the injection well An air heater installed between the injector, the injection well and the air injector, for heating the air flowing from the air injector to the injection well, and the oil contaminant embedded in soil and volatilized by the heated air to the outside. And an air extractor connected to an outlet of the extraction well to discharge oil contaminants.

In addition, the purification apparatus is provided between the extraction well and the air extractor to separate the water from the oil contaminants discharged from the extraction well, and a gas-liquid separator is installed on the downstream side of the air extractor, The method may further include an activated carbon adsorption tower for removing total petroleum hydrocarbon (TPH) in the separated gaseous oil contaminants.

The injection well is buried to a depth reaching down to the surface of the groundwater in the soil, and the extraction well is buried to be disposed slightly above the surface of the groundwater, thereby simultaneously extracting not only gaseous oil, but also weak oil and groundwater. It is desirable to be able to.

And, it is preferable that a plurality of the injection wells and the extraction wells are installed at predetermined intervals in the contaminated site so that contaminants can be removed quickly.

On the other hand, the purifying method according to the invention, the step of heating the air with an air heater, injecting the heated air through the injection well embedded in the contaminated soil, and the oil volatilized by the heated air Extracting and removing the contaminants through the extraction well embedded in the soil. Here, the temperature of the air heated in the air heater is preferably 200 ℃ to 400 ℃.

In addition, in order to remove the contaminants remaining after the above-described steps, the air heater is heated to 100 ℃ ~ 150 ℃ in the soil and injected into the soil, the temperature of the soil suitable for the microorganisms activity (about 30 By maintaining the temperature at 50 ° C. to 50 ° C., the remaining contaminants can be removed by a biological restoration method.

After extracting the oil contaminants through the extraction well, the oil contaminant is separated into a gas component and a liquid component in a gas-liquid separator, and further, the total petroleum-based hydrocarbon (TPH) is removed from the gas component in an activated carbon adsorption tower. You may.

Hereinafter, with reference to the accompanying drawings will be described in detail a preferred embodiment of the present invention.

1 is a view showing a schematic configuration of a purification apparatus according to the present invention.

As shown in FIG. 1, the purification apparatus according to the present invention includes an injection well 11, which is embedded in soil 1 contaminated by oil and injects air into the soil 1, and the injection well 11. An air injector 12 connected to the inlet and supplying air to the injection well 11, and is installed between the injection well 11 and the air injection 12, flowing from the air injection 12 to the injection well 11. An air heater 13 for heating the air, an extraction well 21 for guiding the contaminants volatilized and embedded in the soil 1 to the outside, and an air extractor connected to the outlet of the extraction well 21 to discharge the pollutants. 23 is provided.

In this purifier, the air is introduced through the air injector 12 and then heated to a certain temperature while passing through the air heater 13. The heated hot air is continuously injected into the contaminated soil 1 through the injection well 11. As hot air is injected, the soil is heated, and oil components present in the soil are volatilized. As such, the volatilized oil component is discharged through the extraction well 21 together with moisture and air, and this discharge is made by the air extractor 23.

A gas-liquid separator 22 is installed between the extraction well 21 and the air extractor 23 to separate moisture from contaminants discharged from the extraction well 21. An activated carbon adsorption tower 7 is installed downstream of the air extractor 23 to remove total petroleum hydrocarbon (TPH) in the gaseous contaminants separated from the water in the gas-liquid separator 22.

As described above, low volatility materials such as diesel oil are not easy to remove by soil gas extraction (SVE) in the soil. However, oil contaminants increase volatility with increasing temperature. Therefore, in the present invention, in order to increase the volatility of the oil contaminants to easily remove from the soil (1) and ground water (2), the hot air heated by the air heater 13 through the injection well (11) (1) and ground water (2). According to the test result, the temperature of the air injected through the injection well 11 is preferably selected in the range of 200 ℃ to 400 ℃.

On the other hand, in order to extract the volatilized gas component after injecting hot air into the soil 1, most of the oil is saturated in the air gap of the ground water level of the groundwater 2 due to the accumulation of excessive oil leakage. That is, it exists in a free liquid state. These oils have very high concentrations in small areas and must be removed quickly. However, in the method of removing contaminants by simple extraction, only the volatilized gas components in the unsaturated layer soil can be removed, so that the applicability is limited in the case of high fluid oil or groundwater level. Therefore, in order to solve this problem, the present invention utilizes a dual phase extraction technique for simultaneously extracting liquid oil and groundwater.

To this end, as shown in Figure 1, the injection well 11 is buried to reach below the water surface of the ground water 2, the extraction well 21 is buried to be disposed slightly above the water surface of the ground water (2) At the same time, both liquid oil and groundwater are extracted. In addition, it will be possible to embed both the injection well 11 and the extraction well 21 to a depth that can reach near or below the water surface of the groundwater 2 in the soil 1.

In this way, the buried depth of the injection well 11 and the extraction well 21 is set at or near the surface of the groundwater 2 to remove free products from the unsaturated and saturated soil, and to reduce the groundwater level. Lower and increase the air permeation coefficient, it is possible to maximize the driving effect by the extraction. In addition, it is possible to facilitate the supply of air to promote the decomposition of oil contaminants by microorganisms.

2 is a plan view showing the arrangement of the injection well 11 and the extraction well 21 when the purification apparatus according to the present invention is installed in a contaminated site. As shown in Figure 2, when applying the purification apparatus according to the present invention, by installing a plurality of injection wells 11 and extraction wells 21 at predetermined intervals within the contaminated site, the injection and extraction of hot air By doing so quickly, it is desirable to quickly remove contaminants of oil components. The required number of installations of the injection well 11 and the extraction well 21 is calculated from the influence radius A derived through field experiments.

In addition, in the present invention, as described above, most oil contaminants are first removed through a gas extraction process of injecting hot air into the soil and extracting volatilized contaminants, and then adding oil contaminants remaining without being removed. In order to remove it, the bioremediation method is used as a subsequent process.

Conventional bioremediation methods for soil and groundwater restoration include bioventing applied to soil and air sparging applied to groundwater. These methods are used to decompose pollutants through engineering controls that increase the activity of indigenous microorganisms at the polluting site. They remove oils with low volatility and low Henry's constants that could not be removed in the gas extraction process. It is effective to In other words, in the case of the bio venting method, when an appropriate amount of air is injected into the soil or groundwater, oil contaminants can be removed by biodegradation without extracting wells. This is because no gas is discharged to the ground, and reprocessing such as gas-liquid separator or activated carbon adsorption tower is performed. This means no facilities and subsequent processes are required. Therefore, in the present invention, by treating the low-concentration oil contaminants that are not removed by the gas extraction process by using the bio-venting method or the air dispersion method, which is a biological restoration method that does not require a reprocessing process, the restoration period of the soil can be greatly shortened.

Specifically, the hot water of 200 ° C. to 400 ° C. is injected into the soil 1 and the ground water 2 through the injection well 11 to perform a vapor extraction process, and then the injection well 11 is used as a biorecovery process. The medium temperature air of 100 degreeC-150 degreeC is inject | poured into the soil 1 and groundwater 2 through this. By injecting mesophilic air in this range, the soil can be maintained at about 30 ° C. to 40 ° C., which is an appropriate temperature for microbial decomposition, so that the microbial activity can be promoted and the recovery time can be shortened.

Hereinafter, various experimental results performed for the application of the present invention will be described.

Experiment on the relationship between the vapor pressure and the removal effect of contaminants

In general, it is known that the evaluation of the pollutant removal effect by the soil gas extraction method (SVE) at room temperature (25 ° C.) is effective when the vapor pressure of the pollutant becomes 70 Pa or more. The experimental results of the saturated steam pressure change of diesel pollutants with temperature are summarized in Table 1 below.

Temperature ( ^oC ) Saturated vapor pressure of each pollutant (Pa) n-C10 n-C12 n-C13 n-C15 n-C16 n-C17 21 120.97 11.13 3.78 - - - 30 307.71 33.43 11.21 - - - 40 990.23 111.49 36.15 3.38 0.69 - 50 1371.55 172.08 58.45 6.73 2.04 - 60 2078.18 431.31 157.29 18.65 6.46 0.88 80 2546.62 744.86 304.43 52.48 21.85 8.86 100 3198.99 1455.45 1045.56 297.89 133.53 58.98

As can be seen from Table 1, only n-C10 among the DROs in the diesel range at 21 ° C. close to room temperature is effectively removed by soil gas extraction (SVE) with a vapor pressure of 120.97 Pa. The remaining pollutants are saturated steam pressure. Since it is 70 Pa or less, it cannot be removed by the soil gas extraction method. On the other hand, as the temperature rises, the vapor pressure of each contaminant component gradually increases. That is, when the temperature is 40 ℃, since the vapor pressure of n-C12 is increased to 111.49Pa can be easily removed by the soil gas extraction method. In addition, when the temperature is 60 ℃ can be easily removed to n-C13 (tridecane).

That is, in Table 1, contaminants in the diesel range that are not removed at room temperature by the soil gas extraction method by injecting and extracting air are removed in order of low carbon number as the temperature increases, and most of the contaminants at a temperature of about 100 ° C It is shown that the component can be removed.

On the other hand, when estimated from the above experimental results, for the contaminants (C18 ~ C22) of 18 to 22 carbon number to increase the temperature to more than 100 ℃ will be able to be removed more effectively by the soil gas extraction method.

In the present invention, after removing most of the contaminants by the soil gas extraction method, the contaminants in the C18 to C22 range having a large molecular weight remaining in the soil raise the temperature to the highest level of the activity of the microorganisms, By biologically decomposing.

Experiment on Volatilization Rate with Temperature of Diesel Oil

The preliminary experimental results for examining the removal trend by the volatilization rate of the contaminants with temperature are shown in FIGS. 3 to 5. In this experiment, 5 g of soil was put into a vial, and the soil was contaminated to have a concentration of 50,000 mg / kg of C10, C12, C14, and C15 in the diesel range, and then 25 ° C, 50 ° C, and 80 ° C. This is the result of analyzing the contaminants in the soil after leaving for a predetermined time in and then collected by time. That is, the present experiment looked at the effect of volatilization at each temperature, and in Figures 3 to 5 showed only the effect of volatilization without the effect of the dispersion (advection) by the flow of air.

Figure 3 is a graph showing the volatilization removal trend of diesel range contaminants at room temperature (25 ℃). As shown in Figure 3, it can be seen that at room temperature of 25 ℃ the removal rate of the contaminants C10, C12 in the soil is removed to some extent after 1 to 2 days (24 to 48 hours). This is because the vapor pressure of C10 and C12 at 25 ° C. is about 120.11 Pa, so that the effect of volatilization can be obtained to some extent. However, considering that the soil temperature is kept at 25 ° C in Korea, the progress of volatilization effect may be slow. On the other hand, in the case of C14 and C16 with low volatility, the removal rate by volatilization at normal temperature is very low. This shows that there are many problems in removing low-volatile materials, which occupy most of diesel, by volatilization at room temperature.

4 is a graph showing the volatilization tendency of diesel range contaminants at a temperature of 50 ° C. As shown in Figure 4, in the case of the soil having a high concentration of oil even at a temperature of 50 ℃ it can be seen that the removal rate of all components is not very high. In other words, when diesel contaminants are present as nonaqueous phase liquids (NAPL), the removal effect by volatilization can be increased by increasing the temperature, but when the temperature is about 50 ° C., the effect as expected is insufficient. will be.

5 is a graph showing the volatilization removal trend of diesel pollutants at a temperature of 80 ° C. As shown in FIG. 5, between 1 and 2 days at a temperature of 80 ° C., C10 to C14 were almost removed, and in the case of C16, the components remained but were completely removed by volatilization after 3 days.

In view of the above test results, most of the contaminants in a few days are maintained when the soil temperature of the contaminated soil at the concentration of 50,000 mg / kg is contaminated by 10 times the concentration of 5,000 mg / kg, the soil pollution prevention standard by oil. It can be seen that it can be removed. In conclusion, the volatilization effect by increasing the vapor pressure of pollutants is shown in proportion to the temperature, the soil temperature should be above 80 ℃ for the rapid removal of pollutants.

<Diesel Removal Column Experiment>

On the other hand, in order to determine the removal characteristics of oil pollutants in the soil according to the temperature was configured the following experimental apparatus. Air was introduced into each column, and a flow control valve was installed to maintain an air flow rate of 100 to 200 mL / min, which is an experimental flow rate condition, between each column and the pump. And, it was installed to be able to experiment three columns in one experiment. The soil used in each experiment was granite weathered directly from the construction site, and diesel was purchased from a gas station. Soil was treated to maintain a water content of about 10% of the sample passed through the sieve 30, and uniformly mixed 20μl of diesel in 11g of soil was filled in each column. Porosity of 0.38 and 16,000 mg / kg of total petroleum hydrocarbon (TPH) conditions were 25 ° C, 85 ° C, 105 ° C, and 125 ° C respectively (the actual soil temperatures were 25 ° C, 71 ° C, 91 ° C, and 115 ° C, respectively). ), Two days were conducted for each temperature condition on day 1 with air flow rate of 100 mL / min and day 2 on air flow rate of 200 mL / min. The experiment was conducted for 3 days. The analysis of the concentration of diesel (TPH) was carried out by sonication for 20 minutes in a total volume of soil, that is, 11 g in 40 mL of vial with 35 mL of methylene chloride, followed by filtering. After filtering, 1 μl of the sample was taken with a syringe, and subjected to Gas Chromatograph (GC) analysis. The results for this experiment are shown in FIG. 6.

As shown in FIG. 6, at room temperature (25 ° C.), the removal rate of diesel was less than 10% irrespective of time and air flow rate, but as the temperature was increased, the removal rate of diesel was increased to 80% in one day, and the air flow rate was increased. The removal rate of diesel on Day 2, which increased to 200 mL / min, was less than 10%. If the total petroleum hydrocarbon (TPH) concentration is assumed to be 10,000 mg / kg, if the soil temperature is 120 ° C or higher, the soil contamination concern standard concentration of 2,000 mg / kg, which corresponds to the 80% removal rate, may be initially satisfied. It is expected to be. On the other hand, at the maximum temperature condition 115 ℃ proceeded to the third day, at this time the diesel removal rate is 99.3%, it can be seen that most of the diesel components are removed.

When restoring the soil and ground water contaminated by oil by the present invention as described above there are a number of advantages.

First, the restoration period can be shortened and the removal rate of low volatility contaminants can be improved. As described above, low-volatile oils such as diesel oil and lubricating oil have a very low vapor pressure, and according to the conventional soil gas extraction method (SVE) and the like, the restoration period takes a long time and cannot be completely removed. However, according to the present invention, since the use of high temperature air not only promotes volatilization of volatile contaminants, but also increases the vapor pressure of low volatile contaminants, thereby increasing volatility, thereby reducing the recovery time of contaminated soil and The removal rate can also be improved.

Second, oil can be effectively removed from low permeability soils. That is, as in the present invention, when hot air is injected into the clay soil, the water content decreases due to the high temperature and the pore of the soil is increased, thereby increasing the contact opportunity with air and contaminants. In addition, since the viscosity of the non-volatile contaminants and the residual in the soil is reduced, the mobility is increased, thereby greatly increasing the efficiency of the biological restoration process, where air supply is the most important as well as physical treatment such as extraction.

 Third, it is possible to increase the microbiological decomposition of oil by increasing the temperature of the soil and ground water. Air or soil temperature is a very important factor that greatly affects the activity of microorganisms that break down oil pollutants. In general, as the temperature increases, the decomposition rate increases, but when the temperature increases by 10 ° C, the activity is known to increase more than two times. Therefore, by injecting hot air, decomposition by microorganisms can be expected in addition to the effect of volatilization. In addition, even when performing the bioremediation method using hot air by adjusting the temperature of the air or soil to be injected to the temperature of the best microbial activity, it is possible to increase the decomposition rate of oil contaminants to significantly shorten the recovery period.

As described above, according to the present invention, when the soil is contaminated at high concentration by the leaked oil, hot air is injected into the soil, thereby extracting and removing the volatilized contaminants quickly, and then If the temperature is kept below a certain level, by adjusting the temperature to medium temperature and using the biological restoration method, the soil restoration period can be greatly shortened and the pollutants can be stably removed.

In particular, according to the present invention, it is possible to increase the removal efficiency of low volatile components, such as diesel, in oil contaminants, and to remove high concentrations of free fluid at the same time.

In the above, certain preferred embodiments of the present invention have been illustrated and described. However, the present invention is not limited to the above-described embodiments, and various modifications can be made by those skilled in the art without departing from the gist of the present invention as claimed in the claims. will be.

1 is a schematic configuration diagram of a purification apparatus according to the present invention.

Figure 2 is a plan view showing the arrangement of the injection well and extraction well of the purification device of FIG.

Figure 3 is a graph showing the trend of volatilization of diesel contaminants at room temperature.

Figure 4 is a graph showing the volatilization of diesel contaminants at a temperature of 50 ℃.

5 is a graph showing the volatilization tendency of diesel contaminants at a temperature of 80 ℃.

Figure 6 is a graph showing the removal rate of diesel contaminants in soil over time and air injection temperature.

<Explanation of symbols for the main parts of the drawings>

11: injection well 12: air injector

13: air heater 21: extraction well

22: gas-liquid separator 23: air extractor

24: activated carbon adsorption tower

Claims (8)

An injection well 11 embedded in the soil 1 contaminated by oil and injecting air into the soil 1; An air injector 12 connected to the inlet of the injection well 11 and supplying air to the injection well 11; An air heater (13) installed between the injection well (11) and the air injector (12) to heat air flowing from the air injection (12) to the injection well (11); An extraction well 21 embedded in soil 1 to guide oil contaminants volatilized by the heated air to the outside; And It is connected to the outlet of the extraction well 21 includes an air extractor 23 for discharging oil contaminants, The injection well 11 is buried to a depth reaching down to the water surface of the groundwater 2 in the soil, the extraction well 21 is embedded to be disposed slightly above the water surface of the groundwater (2) Purifier made with. The method of claim 1, A gas-liquid separator 22 installed between the extraction well 21 and the air extractor 23 to separate water from oil contaminants discharged from the extraction well 21; And Installed on the downstream side of the air extractor 23, further comprises an activated carbon adsorption tower (7) for removing the total petroleum-based hydrocarbon (TPH) in the gaseous oil contaminants separated from the water by the gas-liquid separator 22 Purifier, characterized in that. delete The method according to claim 1 or 2, Purification apparatus characterized in that the injection well (11) and the extraction well (21) are provided in a plurality at predetermined intervals in the contaminated site. delete delete delete delete