CN114425559A - In-situ thermal desorption remediation method for soil - Google Patents
In-situ thermal desorption remediation method for soil Download PDFInfo
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- CN114425559A CN114425559A CN202111650275.6A CN202111650275A CN114425559A CN 114425559 A CN114425559 A CN 114425559A CN 202111650275 A CN202111650275 A CN 202111650275A CN 114425559 A CN114425559 A CN 114425559A
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B09—DISPOSAL OF SOLID WASTE; RECLAMATION OF CONTAMINATED SOIL
- B09C—RECLAMATION OF CONTAMINATED SOIL
- B09C1/00—Reclamation of contaminated soil
- B09C1/005—Extraction of vapours or gases using vacuum or venting
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
- B01D53/002—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols by condensation
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
- B01D53/02—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols by adsorption, e.g. preparative gas chromatography
- B01D53/04—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols by adsorption, e.g. preparative gas chromatography with stationary adsorbents
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B09—DISPOSAL OF SOLID WASTE; RECLAMATION OF CONTAMINATED SOIL
- B09C—RECLAMATION OF CONTAMINATED SOIL
- B09C1/00—Reclamation of contaminated soil
- B09C1/06—Reclamation of contaminated soil thermally
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D2253/00—Adsorbents used in seperation treatment of gases and vapours
- B01D2253/10—Inorganic adsorbents
- B01D2253/102—Carbon
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D2258/00—Sources of waste gases
- B01D2258/02—Other waste gases
Abstract
The invention discloses an in-situ thermal desorption remediation method for soil, and relates to the technical field of soil remediation. During working, the extraction well is in a negative pressure state by utilizing a tail gas treatment system on the ground for vacuumizing, the injection well, the extraction well and the heater which are buried in a soil area to be repaired are utilized to work in a combined mode, the injection well introduces oxygen-expelling gas into the soil, the oxygen-expelling gas carries oxygen in the soil and organic pollutants desorbed in a heating state under the action of pressure difference to enter the extraction well, and then the extraction well enters the tail gas treatment system for treatment. The remediation method provided by the embodiment of the invention can remove free oxygen in soil, can reduce direct oxidation reaction of organic pollutants in the heat treatment process, and can reduce generation of carbon dioxide; meanwhile, the tail gas treatment system is provided with a deep condensation device for condensing organic gas in the tail gas; the carbon dioxide catcher is arranged to absorb/adsorb carbon dioxide in the tail gas. And multiple means are coupled and applied, so that the carbon emission in the in-situ thermal desorption process can be effectively reduced.
Description
Technical Field
The invention relates to the technical field of soil remediation, in particular to a soil in-situ thermal desorption remediation method.
Background
The soil pollution in the production processes of petrochemical industry and the like is mainly organic pollutants, such as petroleum hydrocarbon, polycyclic aromatic hydrocarbon, chlorohydrocarbon and the like. The in-situ thermal desorption technology is one of important technologies for restoring organic contaminated soil, and the in-situ thermal desorption technology enables organic pollutants in the soil to volatilize and be discharged after being treated by an extraction system and a tail gas treatment system by heating a contaminated land to a certain temperature in situ.
At present, although the in-situ thermal desorption technology is widely applied and has various realization forms, the problem of high carbon emission still exists, and the in-situ thermal desorption technology does not meet the current low-carbon requirement. The main expression is in the following two aspects: (1) because oxygen and dissolved oxygen exist in soil, after organic pollutants are heated to a certain temperature, a part of the organic pollutants are heated and volatilized to enter an extraction system, a part of the organic pollutants are directly oxidized into carbon oxides by the oxygen and the dissolved oxygen in the soil and enter a tail gas system to be finally discharged into the atmosphere, and the rest of the organic pollutants possibly undergo a cracking reaction to generate organic matters with higher molecular weight and even carbon. (2) At present, organic pollutants entering an extraction system are mainly directly combusted in a secondary combustion chamber to generate carbon dioxide to be discharged into the atmosphere, or are adsorbed by an adsorbent to become hazardous waste for further treatment. In the process, no matter the organic pollutants in the soil are directly heated and oxidized, or the tail gas is directly combusted to generate carbon dioxide, the soil pollutants are converted into greenhouse gases to be discharged into the atmosphere, secondary pollution is caused to the atmospheric environment, and the low-carbon target is not facilitated to be realized.
In view of this, the invention is particularly proposed.
Disclosure of Invention
The invention aims to provide an in-situ thermal desorption remediation method for soil, aiming at effectively reducing carbon emission in the in-situ thermal desorption process.
The invention is realized in the following way:
in a first aspect, the invention provides an in-situ thermal desorption remediation method for soil, comprising the following steps:
an injection well, an extraction well and a heater are buried in a soil area to be repaired, the soil is heated by the heater, the extraction well is kept in a negative pressure state in the repairing process by utilizing a tail gas treatment system on the ground, an oxygen-driving gas is introduced into the soil through the injection well, the oxygen-driving gas carries oxygen in the soil and organic pollutants desorbed in a heating state under the action of pressure difference, enters the extraction well and then enters the tail gas treatment system for treatment.
In an alternative embodiment, the treatment process of the exhaust treatment system comprises: the gas output by the extraction well is condensed and subjected to gas-liquid separation to obtain a gas phase and a liquid phase, and the gas phase is subjected to carbon adsorption.
In an alternative embodiment, carbon adsorption comprises adsorption with activated carbon followed by treatment with a carbon dioxide trap;
wherein, the carbon dioxide catcher is treated by adopting an absorbent or an adsorbent;
preferably, the absorbent is selected from the group consisting of aqueous NaOH, aqueous KOH, aqueous CaO, KCO3At least one of an aqueous solution and an organic amine;
preferably, the adsorbent is selected from at least one of activated carbon, molecular sieves, solid bases and activated alumina.
In an alternative embodiment, the liquid phase is separated into a sewage phase and an organic phase after being separated by the oil-water separator, the sewage phase enters the sewage treatment system for treatment, and the organic phase enters the oil storage tank.
In an alternative embodiment, the temperature of the material after condensation is controlled to be below 70 ℃, preferably below 50 ℃;
preferably, in the condensation process, the condensation temperature is controlled to be-40 to 40 ℃, and preferably 0 to 20 ℃.
In an optional embodiment, the heaters, the extraction wells and the injection wells are all multiple, the heaters are arranged according to the vertexes of a triangle and are distributed in an array, and the injection wells and the extraction wells are all arranged in the middle of the triangle formed by the three heaters.
In an optional embodiment, the heaters are columnar, and the distance between every two adjacent heaters is 0.5-10 m, preferably 1-8 m, and more preferably 1.5-6 m;
preferably, the bottoms of the heater, injection well and extraction well are located 3-10 m below the ground.
In an optional embodiment, the heating temperature of the heater is 50-800 ℃, preferably 100-800 ℃; more preferably 300 to 700 ℃.
In an alternative embodiment, the relative vacuum degree of the wellhead of the extraction well is-100 to 0KPa, preferably-70 to 0KPa, and more preferably-50 to-10 KPa.
In an alternative embodiment, the oxygen scavenging gas is an inert gas or a reducing gas;
preferably, the oxygen-driving gas is pressurized to 0.1-3 MPa and then enters an injection well;
more preferably, the pressure of the oxygen-scavenging gas is 0.15-2 MPa; more preferably 0.2 to 1 MPa.
The invention has the following beneficial effects: during working, the extraction well is in a negative pressure state by utilizing a tail gas treatment system on the ground for vacuumizing, the injection well, the extraction well and the heater which are buried in a soil area to be repaired are utilized to work in a combined mode, the injection well introduces oxygen-expelling gas into the soil, the oxygen-expelling gas carries oxygen in the soil and organic pollutants desorbed in a heating state under the action of pressure difference and enters the extraction well, and then the oxygen-expelling gas enters the tail gas treatment system for treatment. The remediation method provided by the embodiment of the invention can remove free oxygen in soil, can reduce direct oxidation reaction of organic pollutants in the heat treatment process, and can reduce generation of carbon dioxide.
In a preferred embodiment, the tail gas treatment system is provided with a deep condensation device for condensing organic gas components in the tail gas; and a carbon dioxide catcher is arranged to further absorb/adsorb the carbon dioxide in the tail gas. The carbon emission in the in-situ thermal desorption process can be effectively reduced by coupling and applying the various means.
Drawings
In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings needed to be used in the embodiments will be briefly described below, it should be understood that the following drawings only illustrate some embodiments of the present invention and therefore should not be considered as limiting the scope, and for those skilled in the art, other related drawings can be obtained according to the drawings without inventive efforts.
Fig. 1 is a structural diagram of a device during repair according to a repair method provided in an embodiment of the present invention;
fig. 2 is a profile of a heater, extraction well, injection well and monitoring well buried in the soil.
Icon: 1-nitrogen making machine; 2-an injection well; 3-a heater; 4-an extraction well; 5-a heat exchanger; 6-gas-liquid separator; 7-a vacuum pump; 8-an activated carbon box; 9-a carbon dioxide trap; 10-a fan; 11-standard tail gas discharge pipeline; 12-oil water separator; 13-a sewage treatment system; 14-an oil storage tank; 15-contaminated land.
Detailed Description
In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. The examples, in which specific conditions are not specified, were carried out according to conventional conditions or conditions recommended by the manufacturer. The reagents or instruments used are conventional products which are not indicated by manufacturers and are commercially available.
Referring to fig. 1, an embodiment of the present invention provides an in-situ thermal desorption remediation method for soil, including the following steps:
s1 equipment construction
An injection well 2, an extraction well 4 and a heater 3 are buried on the soil area to be remediated (i.e., contaminated land 15), and a nitrogen generator 1 is connected to the top end of the injection well 2 for supplying hydrogen gas as an oxygen-scavenging gas.
In other embodiments, nitrogen generator 1 may be other gas generating devices, such as a device for storing an inert gas, or a device for generating a reducing gas.
Specifically, the injection well 2 and the extraction well 4 are generally tubular structures with meshes, and are conventional structures.
In some embodiments, referring to fig. 2, the heaters 3, the extraction wells 4 and the injection wells 2 are all multiple, the heaters 3 are arranged according to the vertex of a triangle and are distributed in an array, the injection wells 2 and the extraction wells 4 are all arranged at the middle position of the triangle surrounded by the three heaters 3, and the monitoring wells can be buried for better monitoring. As shown in fig. 2, one of the two adjacent triangles is provided with an extraction well 4, and the other is provided with an injection well 2.
Further, the distance between the heaters 3 is determined according to the texture of soil and the repair period, the heaters are columnar, the distance between two adjacent heaters 3 is 0.5-10 m, preferably 1-8 m, and more preferably 1.5-6 m; the bottoms of the heater 3, the injection well 2 and the extraction well 4 are located 3-10 m below the ground. The heating is more uniform by controlling the distribution density of the heater 3, and the extraction well 4 and the injection well 2 are more reasonably distributed, which is favorable for further improving the soil remediation effect.
The method comprises the steps of building a tail gas treatment system on the ground, and sequentially comprising a heat exchanger 5, a gas-liquid separator 6, a vacuum pump 7, an activated carbon box 8, a carbon dioxide catcher 9, a fan 10, a standard tail gas discharge pipeline 11, an oil-water separator 12, a sewage treatment system 13 and an oil storage tank 14. The extraction well 4 is kept in a negative pressure state by using a vacuum pump 7 and a fan 10, the top of the extraction well 4 is condensed by a heat exchanger 5 and then enters a gas-liquid separator 6 for gas-liquid separation, the gas phase enters an activated carbon box 8 after passing through the vacuum pump 7 to adsorb organic matters and carbon dioxide, then the carbon dioxide is further removed by using a carbon dioxide catcher 9, and the gas is discharged through a tail gas discharge pipeline 11 which reaches the standard after being pumped out by the fan 10.
S2, gas stripping
The soil is heated by the heater 3, the extraction well 4 is kept in a negative pressure state in the repairing process by utilizing a tail gas treatment system on the ground, the oxygen-driving gas is introduced into the soil through the injection well 2, and the oxygen-driving gas carries oxygen in the soil under the action of pressure difference and organic pollutants desorbed in a heating state to enter the extraction well 4. The oxygen-expelling gas can expel oxygen in the region, so that direct oxidation reaction of organic pollutants in the heat treatment process can be reduced, the generation of carbon dioxide is reduced, and the carbon emission in the in-situ thermal desorption process is effectively reduced.
Specifically, the oxygen-scavenging gas may be an inert gas or a reducing gas, and may be an inert gas such as nitrogen or a reducing gas such as hydrogen. Preferably, nitrogen is adopted, the nitrogen raw material is easy to obtain, and the cost is lower.
In some embodiments, the oxygen scavenging gas is pressurized to 0.1 to 3MPa and then enters the injection well 2; preferably, the pressure of the oxygen-scavenging gas is 0.15-2 MPa; more preferably 0.2 to 1 MPa. Specifically, the pressure of the oxygen-scavenging gas may be 0.1MPa, 0.15MPa, 0.20MPa, 0.50MPa, 1.00MPa, 1.50MPa, 2.00MPa, 2.50MPa, 3.00MPa, or the like, or may be any value between the above adjacent pressure values.
In some embodiments, the heating temperature of the heater 3 is 50 to 800 ℃, preferably 100 to 800 ℃; more preferably 300 to 700 ℃. The temperature of the heater 3 is optimized so that the organic matters are better desorbed from the soil. Specifically, the heating temperature may be 50 ℃, 100 ℃, 150 ℃, 200 ℃, 250 ℃, 300 ℃, 350 ℃, 400 ℃, 450 ℃, 500 ℃, 550 ℃, 600 ℃, 650 ℃, 700 ℃, 750 ℃, 800 ℃ or the like, or may be any value between the above adjacent temperature values.
In some embodiments, the relative vacuum of the wellhead of the extraction well 4 is-100 to 0KPa, preferably-70 to 0KPa, more preferably-50 to-10 KPa. Specifically, the values may be-100 KPa, -90KPa, -80KPa, -70KPa, -60KPa, -50KPa, -40KPa, -30KPa, -20KPa, -10KPa, 0KPa, etc., or may be any values between the above adjacent vacuum degrees.
S3, tail gas treatment
The pollutants are desorbed from the surface of the soil particles by heating, and are pumped out along with the nitrogen through the extraction well 4 to enter a tail gas treatment system for separation and adsorption treatment. In practical operation, the treatment process of the tail gas treatment system comprises the following steps: the gas output by the extraction well 4 is condensed and subjected to gas-liquid separation to obtain a gas phase and a liquid phase, and the gas phase is subjected to carbon adsorption.
In some embodiments, the temperature of the material after condensation is controlled to be below 70 ℃, preferably below 50 ℃ to lower the gas temperature for subsequent gas-liquid separation. In practical operation, in the condensation process, the condensation temperature is controlled to be-40 ℃, and preferably 0-20 ℃. The specific condensation time is determined according to the temperature requirement of the condensed material.
Specifically, the heat exchanger 5 is selected according to the type of the pollutant and the temperature of the tail gas, and can be a refrigerator with air cooling, water cooling, ultralow temperature deep cooling and the like, and can also be realized by heat exchange of other refrigerants on site.
In some embodiments, carbon adsorption comprises adsorption with activated carbon (in activated carbon box 8) followed by treatment with carbon dioxide trap 9; the organic matter and carbon dioxide are fully absorbed by the two-step treatment. Activated carbon to CO2The adsorption capacity is weaker than that of organic pollutants, a small amount of residual carbon dioxide in the gas phase enters the carbon dioxide catcher 9 under the action of the fan 10, and carbon dioxide in tail gas is further removed.
Specifically, the carbon dioxide trap 9 is treated with an absorbent or adsorbent; the absorbent is selected from NaOH aqueous solution, KOH aqueous solution, CaO aqueous solution, and KCO3At least one of an aqueous solution and an organic amine; the adsorbent is selected from at least one of activated carbon, molecular sieve, solid alkali and activated alumina. According to the concentration difference of carbon dioxide, the above reagents can be adopted for treatment, so as to ensure that the removal rate of carbon dioxide in the tail gas passing through the carbon dioxide catcher 9 is more than 70 percent, and the concentration is lower than 0.5 percent.
Further, the liquid phase is separated into a sewage phase and an organic phase after passing through the oil-water separator 12, the sewage phase enters the sewage treatment system 13 for treatment, and the organic phase enters the oil storage tank 14.
The repairing method provided by the embodiment of the invention is specifically described with reference to fig. 1:
the high-purity nitrogen generated by the nitrogen making machine 1 is pressurized and then injected into soil of a target area through a sieve hole of the injection well 2 to remove oxygen in the area. Meanwhile, the vacuum pump 7 and the fan 10 work to keep negative pressure around the extraction well 4, so that pressure difference is formed between the injection well 2 and the extraction well 4, the high-purity nitrogen carrying gas such as oxygen in soil continuously diffuses and migrates towards the extraction well 4 under the action of the pressure difference, and enters the extraction well 4 through a sieve hole to be pumped into the heat exchanger 5 and a tail gas treatment system.
Under the condition that the nitrogen generator 1 continuously injects nitrogen, free oxygen in the soil is continuously expelled, so that an oxygen-free environment is formed in the target area. The high temperature generated by the heater 3 raises the ambient temperature of the surrounding soil through heat conduction, organic pollutants are desorbed from the surface of the soil under the conditions of high temperature and no oxygen, enter a tail gas treatment system along with nitrogen through the extraction well 4 and are condensed by the heat exchanger 5, and are separated into a gas phase and a liquid phase through the gas-liquid separator 6.
The gas phase enters an active carbon box 8 under the action of a vacuum pump 7 and a fan 10, organic pollutants, partial carbon dioxide and other gases in the gas phase are adsorbed by active carbon, but the active carbon is used for CO2The adsorption capacity is weaker than that of organic pollutants, a small amount of residual carbon dioxide in the gas phase enters the carbon dioxide catcher 9 under the action of the fan 10, and carbon dioxide in tail gas is further removed. The treated tail gas is discharged through a chimney under the action of the fan 10.
The liquid phase components separated by the gas-liquid separator enter an oil-water separator 12 for separation, wherein the sewage enters an on-site sewage treatment system 13 for further treatment, and the organic phase enters an oil storage tank 14 for storage and further treatment or recycling.
The features and properties of the present invention are described in further detail below with reference to examples.
Example 1
The embodiment provides an in-situ thermal desorption remediation method for soil, which specifically comprises the following steps:
and (3) the condition of polluted soil: when a polluted land block in a petrochemical plant area is dismantled, the soil is silt, the pollutant is petroleum hydrocarbon, the average content is 1 percent, and the pollution depth is 6 m.
Equipment construction: as shown in figure 2, the well arrangement of the heater 3 is arranged according to the vertex of the triangle, the interval of the heater 3 is 2.5m, and the injection well 2, the extraction well 4 and the monitoring well are arranged at the center of the triangle formed by the three heaters. The depths of the heater 3, the injection well 2, the extraction well 4 and the monitoring well are all 6.5m below the ground, and the temperature of the heater is controlled to be 600 ℃. The heat exchanger adopts water cooling heat exchange, and the inlet water temperature of the cooling water is 20 ℃. Carbon dioxide adsorption uses 10% lime water as an absorbent.
Gas extraction: high-purity nitrogen generated by the nitrogen generator 1 is pressurized to 0.7mPa and then is injected into soil in a target area through a mesh of an injection well 2 to drive oxygen in the area. Meanwhile, the vacuum pump 7 and the fan 10 work to enable the wellhead pressure of the extraction well 4 to be-30 kPa, so that a pressure difference is formed between the injection well 2 and the extraction well 4, the high-purity nitrogen carrying gases such as oxygen in soil continuously diffuse and migrate towards the extraction well under the action of the pressure difference, and the gases enter the extraction well 4 through a sieve hole and then are pumped out to enter the heat exchanger 5 and a tail gas treatment system.
Tail gas treatment: organic pollutants are desorbed from the surface of soil under high temperature and anaerobic conditions, enter a tail gas treatment system along with nitrogen through an extraction well 4, are condensed by a heat exchanger 5, and are separated into a gas phase and a liquid phase through a gas-liquid separator 6. The gas phase enters an activated carbon box 8 under the action of a vacuum pump 7 and a fan 10, organic pollutants, partial carbon dioxide and other gases in the gas phase are adsorbed by activated carbon, and the tail gas still containing a certain amount of carbon dioxide enters a carbon dioxide catcher 9 under the action of the fan 10 to further remove the carbon dioxide in the tail gas.
Before entering the active carbon box 8 through detection, CO in the tail gas2Has a concentration of 7200mg/L, and CO in the tail gas enters a carbon dioxide catcher 92The concentration is 6580mg/L, and CO in the tail gas after passing through the carbon dioxide catcher 92The concentration was 1299 mg/L. The treated tail gas is discharged through a chimney under the action of the fan 10. The liquid phase component separated by the gas-liquid separator enters an oil-water separator 12 for separation, and the volume ratio of the oil phase to the water phase obtained by separation is 1: 4. Wherein the sewage entersThe on-site sewage treatment system 13 is further treated, and the organic phase enters the oil storage tank 14 to be sealed for further treatment or recycling.
The results show that: after sampling and detecting, the TPH content of the treated soil is lower than 400mg/kg, and the screening value of the residential land meeting the standard requirements is obtained.
Example 2
The embodiment provides an in-situ thermal desorption remediation method for soil, which specifically comprises the following steps:
contaminated soil conditions: in a polluted land block of a certain petrochemical plant area, the soil is silt, the pollutant is petroleum hydrocarbon, the average content is 23500mg/kg, and the pollution depth is 4 m.
Equipment construction: as shown in fig. 2, the heaters 3 are spaced at intervals of 3m, and the injection well 2 and the extraction well 4 and the monitoring well are disposed at the center of a triangle formed by three heaters. The heater 3, injection well 2 and extraction well 4 and monitoring well depths were all 4.5m below the surface, with the heater temperature controlled at 500 ℃. The heat exchanger adopts water cooling heat exchange, and the inlet water temperature of the cooling water is 10 ℃. Carbon dioxide adsorption adopts 30% of binary organic amine as an absorbent.
Gas extraction and tail gas treatment: high-purity nitrogen generated by the nitrogen generator 1 is pressurized to 0.4mPa and then is injected into soil in a target area through a mesh of an injection well 2 to drive oxygen in the area. Meanwhile, the vacuum pump 7 and the fan 10 work to ensure that the well head pressure of the extraction well 4 is-40 kPa, and CO in tail gas enters the activated carbon adsorption tank 82Has a concentration of 15200mg/L, and CO in the tail gas before entering a carbon dioxide catcher 92The concentration is 12580mg/L, and CO in the tail gas after passing through the carbon dioxide catcher 92The concentration was 139 mg/L. The treated tail gas is discharged through a chimney under the action of the fan 10. The liquid phase component separated by the gas-liquid separator enters an oil-water separator 12 for separation, and the volume ratio of the oil phase to the water phase obtained by separation is 1: 3.
The results show that: after sampling and detection, the TPH content of the treated soil is lower than 400mg/kg, and the screening value of the residential land meeting the standard requirement is obtained.
It should be noted that the principle of the present embodiment is the same as that of embodiment 1, and redundant description is not repeated.
Example 3
The embodiment provides an in-situ thermal desorption remediation method for soil, which specifically comprises the following steps:
and (3) the condition of polluted soil: the oil tank area pollutes the plot, the soil quality is sandy soil, the pollutants are 8900mg/kg of petroleum hydrocarbon and 48mg/kg of benzopyrene, and the pollution depth is 8 m.
Equipment construction: as shown in fig. 2, the heaters 3 are spaced at intervals of 3m, and the injection well 2 and the extraction well 4 and the monitoring well are disposed at the center of a triangle formed by three heaters. The heater 3, injection well 2 and extraction well 4 and monitoring well depths were all 4.5m below the surface, with the heater temperature controlled at 500 ℃. The heat exchanger adopts water cooling heat exchange, and the inlet water temperature of the cooling water is 0 ℃. The carbon dioxide adsorption adopts solid alkali as an adsorbent.
Gas extraction and tail gas treatment: high-purity nitrogen generated by the nitrogen generator 1 is pressurized to 0.2mPa and then is injected into soil in a target area through a mesh of an injection well 2 to drive oxygen in the area. Meanwhile, the vacuum pump 7 and the fan 10 work to ensure that the well head pressure of the extraction well 4 is-20 kPa, and CO in tail gas2Is 3200mg/L, and CO in tail gas before entering a carbon dioxide catcher 92The concentration is 2080mg/L, and CO in the tail gas after passing through the carbon dioxide catcher 92The concentration was 390 mg/L. The treated tail gas is discharged through a chimney under the action of the fan 10. The liquid phase component separated by the gas-liquid separator enters an oil-water separator 12 for separation, and the volume ratio of the oil phase to the water phase obtained by separation is 1: 5.
The results show that: after sampling and detection, the TPH content of the treated soil is lower than 400mg/kg, and the screening value of the residential land meeting the standard requirement is obtained.
It should be noted that the principle of the present embodiment is the same as that of embodiment 1, and redundant description is not repeated.
Comparative example 1
The comparative example 1 provides an in-situ thermal desorption remediation method for soil, which is different from the method in example 1 only in that: the nitrogen gas was replaced with air, and normal temperature air was injected into the injection well 2 using an air compressor, and the pressure of the injected air was the same as in example 1, and other process parameters were the same as in example 1.
After detection, the mixture enters an activated carbon adsorption box8, CO in tail gas2Has a concentration of 12800mg/L, and CO in the tail gas enters a carbon dioxide catcher 92CO in tail gas with concentration of 9600mg/L after passing through a carbon dioxide catcher 92The concentration was 1433 mg/L.
Comparative example 2
The comparative example provides an in-situ thermal desorption remediation method for soil, which is different from the method in example 1 only in that: the heat exchanger 5 is not arranged in front of the gas-liquid separator 6, the temperature of the tail gas discharged out of the extraction well 4 reaches 110 ℃, the volume ratio of the oil phase to the water phase obtained by the gas-liquid separator is about 1:7, and the condensation amount of the organic phase is obviously reduced. Before the tail gas enters the activated carbon adsorption tank 8, CO in the tail gas2The concentration of the tail gas is slightly increased to 7430mg/L, and CO in the tail gas enters a carbon dioxide catcher 92The concentration is 7080mg/L, and CO in the tail gas after passing through a carbon dioxide catcher 92The concentration is 1639mg/L, and the absorption efficiency of the activated carbon and the absorption efficiency of the carbon dioxide are reduced due to overhigh temperature of the tail gas.
Comparative example 3
The comparative example 1 provides an in-situ thermal desorption remediation method for soil, which is different from the method in example 1 only in that: the tail gas treatment system does not contain a carbon dioxide catcher, and the tail gas is directly discharged to the atmosphere after passing through the activated carbon adsorption tank 8.
After detection, before entering the activated carbon adsorption box 8, CO in the tail gas2Has a concentration of 11960mg/L, and CO in the exhaust gas discharged into the atmosphere after passing through the activated carbon adsorption tank 82The concentration was 8790 mg/L.
In summary, the embodiments of the present invention provide an in-situ thermal desorption remediation method for soil, which has the following advantages:
(1) the process can remove free oxygen in the soil by injecting nitrogen into the target area, can reduce direct oxidation reaction of organic pollutants in the heat treatment process, can reduce the generation of carbon dioxide, and can effectively reduce carbon emission in the in-situ thermal desorption process.
(2) In the process, after the extracted tail gas is cooled by air cooling, water cooling or deep cooling heat exchange, organic pollutant components in the tail gas are condensed and separated to enter a liquid phase, so that the process is convenient to recycle and can effectively reduce the emission of organic pollutants in the tail gas.
(3) In the process, the tail gas treatment system is provided with the carbon dioxide catcher behind the activated carbon adsorption box, so that carbon dioxide in the tail gas is further caught and fixed, and near zero emission of organic pollutants and carbon oxides in the tail gas is finally realized.
The above is only a preferred embodiment of the present invention, and is not intended to limit the present invention, and various modifications and changes will occur to those skilled in the art. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Claims (10)
1. An in-situ thermal desorption soil remediation method is characterized by comprising the following steps:
an injection well, an extraction well and a heater are buried in a soil area to be repaired, the soil is heated through the heater, the extraction well is kept in a negative pressure state in the repairing process by utilizing a tail gas treatment system on the ground, an oxygen-driving gas is introduced into the soil through the injection well, the oxygen-driving gas carries oxygen in the soil and organic pollutants desorbed in the heating state under the action of pressure difference, enters the extraction well and then enters the tail gas treatment system for treatment.
2. The in-situ thermal desorption soil remediation method of claim 1, wherein the treatment process of the tail gas treatment system comprises: the method comprises the steps of firstly condensing gas output by the extraction well, carrying out gas-liquid separation to obtain a gas phase and a liquid phase, and carrying out carbon adsorption on the gas phase.
3. The in-situ soil thermal desorption remediation method of claim 2, wherein the carbon adsorption comprises adsorption with activated carbon and treatment with a carbon dioxide trap;
wherein the carbon dioxide catcher is treated by an absorbent or an adsorbent;
preferably, the absorbent is selected from the group consisting of aqueous NaOH solution, aqueous KOH solution, and aqueous CaO solutionSolution, KCO3At least one of an aqueous solution and an organic amine;
preferably, the adsorbent is selected from at least one of activated carbon, molecular sieves, solid bases and activated alumina.
4. The in-situ thermal desorption soil remediation method of claim 2, wherein the liquid phase is separated by an oil-water separator into a sewage phase and an organic phase, the sewage phase is treated by a sewage treatment system, and the organic phase is fed into an oil storage tank.
5. The in-situ thermal desorption soil remediation method of claim 2, wherein the temperature of the condensed material is controlled to be less than 70 ℃, preferably less than 50 ℃;
preferably, in the condensation process, the condensation temperature is controlled to be-40 ℃, and preferably 0-20 ℃.
6. The in-situ soil thermal desorption remediation method of claim 1, wherein the heaters, the extraction wells and the injection wells are all provided in a plurality, the heaters are arranged at the vertices of a triangle and are distributed in an array, and the injection wells and the extraction wells are all arranged at the middle positions of the three heaters which enclose the triangle.
7. The in-situ soil thermal desorption remediation method according to claim 6, wherein the heaters are columnar, the distance between every two adjacent heaters is 0.5-10 m, preferably 1-8 m, and more preferably 1.5-6 m;
preferably, the bottoms of the heater, the injection well and the extraction well are located 3-10 m below the ground.
8. The in-situ soil thermal desorption remediation method according to claim 6, wherein the heating temperature of the heater is 50-800 ℃, preferably 100-800 ℃; more preferably 300 to 700 ℃.
9. The in-situ soil thermal desorption remediation method of claim 6, wherein the relative vacuum degree of the head of the extraction well is-100 to 0KPa, preferably-70 to 0KPa, and more preferably-50 to-10 KPa.
10. The in-situ soil thermal desorption remediation method of claim 1, wherein the oxygen scavenging gas is an inert gas or a reducing gas;
preferably, the oxygen-displacing gas is pressurized to 0.1-3 MPa and then enters the injection well;
more preferably, the pressure of the oxygen-driving gas is 0.15-2 MPa; more preferably 0.2 to 1 MPa.
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