In-situ permeation-enhancing thermal evaporation repairing method for low-permeability organic pollution site

Abstract

The invention discloses an in-situ permeation-enhancing thermal evaporation repair method for a low-permeability organic pollution site, which comprises the following steps of: acquiring information, identifying a low-permeability layer section with high montmorillonite content, and arranging a steam injection well, an extraction well and a temperature / pressure monitoring well network in a target area; the installation of equipment including a steam generator, a steam injection pipeline, a vacuum pump, a gas-liquid separator and a condenser is completed, and the real-time monitoring and automatic control of temperature and pressure are realized; injecting the lithium ion modified liquid into a target area through a steam injection well, opening an extraction well at the same time to collect part of original organic pollutants in a displaced stratum in the injection process, sealing for 12-48 hours after completion, and performing cation exchange reaction on lithium ions and montmorillonite clay minerals to form lithium-based montmorillonite; hot steam is injected into a target area through the steam injection well, meanwhile, the extraction well is started to collect the lithium ion modified liquid displaced by the hot steam, sealing is conducted for 8-24 hours after completion, and organic pollutants are converted into a gas phase under the pyrolysis effect and are synchronously extracted through the extraction well.

Description

Technical Field

[0001] The present invention belongs to the technical field of soil remediation, and in particular relates to an in-situ infiltration-enhancing hot steam remediation method for low-permeability organic contaminated sites. Background Art

[0002] Organically contaminated soils are widely present in environmental geotechnical engineering, particularly in industrial sites, petrochemical spill areas, and urban renewal sites, where they often contain pollutants such as benzene, chlorinated hydrocarbons, and petroleum hydrocarbons. These pollutants often exist in the soil in adsorbed, dissolved, or free forms, and are characterized by poor mobility, high toxicity, and difficulty in degradation. This complicates remediation, especially in low-permeability strata with high clay content.

[0003] Currently, mainstream technologies used for remediation of organically contaminated sites include chemical oxidation, soil leaching, and thermal treatment. Thermal treatment, in particular, uses heat to increase the vapor pressure of pollutants in the soil, causing them to volatilize and be extracted from the soil via an extraction system, ultimately achieving desorption and removal. This method offers advantages such as high treatment efficiency, short cycle times, strong adaptability, minimal soil disturbance, and the absence of harmful substances introduced to the site, making it widely applicable to the remediation of volatile and semi-volatile organic compounds.

[0004] Based on the difference in remediation temperature, thermal treatment can be divided into low-temperature thermal treatment (100-350°C) and high-temperature thermal treatment (350-600°C): the former can meet the pollutant removal target while less damaging the soil structure and has better sustainability; the latter requires a large heat input, high energy consumption and is prone to secondary damage to the soil structure. At the same time, according to different construction methods, thermal treatment can be divided into ex situ and in situ. Ex situ thermal desorption requires the contaminated soil to be excavated and transported to a dedicated device for treatment. Although the temperature control accuracy is high, there are high transportation costs and the risk of secondary pollution. In contrast, in situ thermal desorption directly heats and extracts at the contaminated site, avoiding the need for soil disturbance and transportation. It is particularly suitable for situations where the contamination is deep, the site is limited, or there are high requirements for soil structural stability.

[0005] Among in-situ heat treatment methods, resistance heating and hot steam injection are the most common. Resistance heating is suitable for low-permeability soils (such as clay), but it consumes a lot of energy and has high operating costs. Maintaining an effective current in high-resistivity soils can be difficult, reducing treatment efficiency. Furthermore, equipment layout is complex, requiring high initial investment, and the construction process is susceptible to constraints from underground pipelines and the urban built environment. During the heating process, electrolytic reactions can cause pH changes, posing a potential risk of secondary contamination.

[0006] Hot steam injection is a typical low-temperature thermal treatment method that removes pollutants through three main mechanisms: first, using steam and its condensate to replace pollutants; second, converting pollutants into the gas phase through heating and stripping; and third, using steam flow to sweep gaseous pollutants into the extraction system. However, this technology is mainly suitable for silt soil areas and faces great challenges in its application in low-permeability formations such as clay. The permeability of such formations is extremely low (usually less than 10 - 7 cm / s), steam has difficulty penetrating evenly, often forming "preferential pathways" in hyperpermeable channels, leading to uneven heating and reduced remediation efficiency. Furthermore, clay, due to its high specific surface area and high cation exchange capacity, has a strong adsorption capacity for organic pollutants, requiring continuous heating at relatively high temperatures for effective desorption.

[0007] Therefore, there is an urgent need to develop an in-situ hot steam remediation method specifically suitable for low-permeability, high-adsorption organic contaminated sites with high clay content. By combining micro-interface modification and permeability enhancement methods with hot steam remediation technology, the mobility of pollutants can be enhanced to achieve efficient, low-consumption, and safe desorption, migration, and extraction of pollutants, while maximizing the protection of soil structure and ecological functions. Summary of the Invention

[0008] The purpose of the present invention is to provide an in-situ permeability enhancement and thermal steam remediation method suitable for low-permeability organic contaminated sites. By utilizing the lithium ion fixation method to enhance the in-situ permeability of montmorillonite-rich clay layers, and combining it with hot steam injection, the migration-release synergistic enhancement of organic pollutants is achieved, thereby improving the remediation efficiency and depth. The method is particularly suitable for the enhanced migration and thermal treatment of organic pollutants in low-permeability soil layers with a high montmorillonite content.

[0009] In order to achieve the above purpose, the technical solutions adopted are as follows: The in-situ infiltration and thermal steam remediation method for low-permeability organic contaminated sites includes the following steps: (1) Obtain information on soil permeability, types of organic pollutants, and their spatial distribution, identify low-permeability intervals with high montmorillonite content, and deploy a network of steam injection wells, extraction wells, and temperature / pressure monitoring wells within the target area; (2) Complete the installation of equipment including steam generator, steam injection pipeline, vacuum pump, gas-liquid separator, and condenser, and establish a remote monitoring system to achieve real-time monitoring and automatic control of temperature and pressure; (3) Lithium ion modified liquid is injected into the target area through the steam injection well, and the extraction well is opened at the same time to collect some of the original organic pollutants in the formation that were displaced during the injection process. After completion, the well is sealed for 12-48 hours, and the lithium ions react with the montmorillonite clay minerals to form lithium-based montmorillonite; (4) Inject hot steam into the target area through the steam injection well, and at the same time open the extraction well to collect the lithium ion modified liquid displaced by the hot steam. After completion, the well is closed for 8-24 hours. The organic pollutants are converted into gas phase under the action of pyrolysis and extracted synchronously through the extraction well.

[0010] According to the above scheme, in step (1), relevant information is obtained through geological drilling, hydrological testing and pollution investigation.

[0011] According to the above scheme, the spacing between the steam injection wells in step (1) is controlled at 5-8 meters; the extraction wells are staggered to form an effective heat-gas migration path; and the temperature / pressure monitoring wells cover 1-2 meters below the bottom of the contaminated layer.

[0012] According to the above scheme, in step (2), the pipeline adopts a high-temperature corrosion-resistant casing (such as stainless steel or double-layer PVC), and the well wall filler adopts a combination of quartz sand and bentonite water stop ring.

[0013] According to the above scheme, the lithium ion modification solution in step (3) is a 0.5-2.0 mol / L soluble lithium salt aqueous solution. In an optimized scheme, a cationic surfactant (such as a polyquaternary ammonium salt) is added to the lithium ion modification solution to improve the wetting and penetration properties. In a more optimized scheme, the lithium ion modification solution is heated to 40-70°C to increase the ion activity and diffusion rate.

[0014] According to the above scheme, the injection pressure of the steam injection well in step (3) is controlled at 0.2-1.0 MPa.

[0015] According to the above scheme, in step (4), the steam injection wells are injected with hot steam at 150-200°C, with a controlled steam injection pressure of 0.5-1.5 MPa and a flow rate of 0.1-0.5 t / h / well. In the optimized scheme, intermittent low-pressure injection (e.g., 8 hours of injection + 4 hours of maintenance) is used to avoid the formation of preferential channels.

[0016] According to the above plan, the collected materials in the extraction well are also removed from the gas, condensed water and free phase through a vacuum system, and the extracted products flow through the condensation and oil-water separation device to achieve standard discharge or resource reuse.

[0017] According to the above plan, it also includes comparative analysis of permeability after repair, analysis of soil residual pollution and long-term monitoring of groundwater for 3-6 months to confirm that the standards are met; otherwise, the in-situ permeability enhancement and hot steam repair treatment will be repeated.

[0018] This method utilizes lithium ions (Li + ) on the ion exchange capacity of montmorillonite, combined with the hot steam enhanced reaction kinetics, to achieve the structural modification and permeability improvement of the low permeability stratum rich in montmorillonite clay layer, which belongs to the in-situ chemical modification and permeability enhancement technology. In the layered structure of montmorillonite, Na + , Ca 2+The cations such as NaCl exist between the crystal layers and are easily hydrated, resulting in water absorption and expansion and pore closure. This method injects a highly active lithium ion solution (such as LiCl solution) and converts the interlayer cations (Na + / Ca 2+ ) is replaced by lithium ions (Li + ), forming Li-montmorillonite; under the action of steam heat (150-200 ℃), lithium ions can pass through the interlayer space due to their small size and high mobility and migrate to the octahedral vacancies in the montmorillonite structure. + The fixing mechanism is shown in Figure 1 When heated to a certain temperature, some of the Li adsorbed between the layers or on the surface + It can enter the interior of montmorillonite crystals and be fixed in the negatively charged Al-OH octahedral cavity. + There is a strong electrostatic attraction between the negative potential points in the octahedron, which prevents it from returning to the interlayer position after cooling, thus achieving Li + The key to this structural transformation is that Li + They no longer exist as exchangeable cations, resulting in a decrease in the total charge density between the layers, thereby reducing the interlayer hydration expansion capacity. The ultimate manifestation is a decrease in the expansibility of montmorillonite and a significant increase in permeability. After the permeability enhancement treatment, the soil body has a significantly reduced specific surface area and cation exchange capacity due to the reduction in layer charge, resulting in a decrease in its adsorption capacity for pollutants, making it easier for organic pollutants to be discharged. The high temperature of the steam and the heat released by the condensation of the steam cause the organic pollutants to undergo a phase change and be vaporized. At the same time, the high temperature destroys the adsorption force between the pollutants and the soil particles, reduces their viscosity and interfacial tension, and promotes their desorption and migration. These gaseous pollutants are "entrained" by the steam and migrate, and are eventually removed from the soil through the extraction system.

[0019] Compared with the prior art, the present invention has the following beneficial effects: 1) By combining with the in-situ permeability enhancement method, the thermal steam remediation technology was extended to low-permeability organic-contaminated soil layers with high montmorillonite content, broadening the scope of application of the technology.

[0020] 2) Through chemical permeability enhancement, the permeability of the formation is significantly improved, while simultaneously reducing the soil's adsorption of organic pollutants, improving heat transfer efficiency and pollutant release. Field measurements show that the permeability coefficient of montmorillonite-rich clay layers treated with this method can increase by 5-6 orders of magnitude, far exceeding traditional methods (which typically increase by 1-3 orders of magnitude). This improved permeability is also maintained for a longer period within the formation.

[0021] 3) The temperature required for permeability enhancement and thermal steam remediation of organic pollutants is relatively low (150-200°C), resulting in low energy consumption. Temperature control and intermittent steam injection strategies are used to avoid formation fractures and channeling effects. Combined with extraction technology, efficient removal of pollutants is achieved.

[0022] 4) No acidic or corrosive components are introduced during the entire treatment process, and no harmful side reaction products are generated. It is environmentally friendly and has no obvious pollution risk to the pipe column, soil layer and groundwater, making it suitable for on-site application and promotion.

[0023] 5) Protecting soil structure and subsequent land use potential, it offers excellent ecological and economic benefits. The process is controllable and highly adaptable, making it suitable for deep remediation of various organically contaminated sites. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 :Li in montmorillonite + Schematic diagram of the fixation mechanism.

[0025] Figure 2 : The relationship between heating temperature and permeability coefficient. DETAILED DESCRIPTION

[0026] The following examples further illustrate the technical solutions of the present invention but are not intended to limit the scope of protection of the present invention.

[0027] The specific embodiment provides an in-situ permeability enhancement and steam remediation method for a high-montmorillonite content and low-permeability organic contaminated site: 1) Target Area Identification and Site Preparation: Site Investigation: Through geological drilling, hydrological testing, and contamination surveys, determine soil permeability, the types of organic pollutants, and their spatial distribution, identify low-permeability layers with high montmorillonite content, and define the target remediation area. System Deployment: Within the target area, a network of steam injection wells, extraction wells, and temperature monitoring wells will be deployed. Injection wells should be spaced 5-8 meters apart, and extraction wells should be staggered to create an effective heat-gas migration path. The well depth should reach 1-2 meters below the bottom of the contaminated layer. Temperature and pressure monitoring devices should be deployed to complete the site preparation for the remediation system.

[0028] 2) Wellbore Construction and System Installation: Wellbore drilling: Mud drilling or air drilling is used to the target depth. High-temperature, corrosion-resistant casing (such as stainless steel or double-layer PVC) is installed. The wellbore filler uses a combination of quartz sand and bentonite waterstop rings to ensure sealing and stability. System Integration: The steam generator, steam injection pipeline, vacuum pump, gas-liquid separator, condenser, and other equipment are installed. A remote monitoring system is established to achieve real-time temperature and pressure monitoring and automatic control.

[0029] 3) Lithium ion modification solution preparation: Use lithium chloride (LiCl) or other soluble lithium salts to prepare a lithium ion permeation-enhancing solution at a concentration of 0.5-2.0 mol / L, preferably 1.0 mol / L. Heat the solution to 40-70°C under heating conditions to increase ion activity and diffusion rate. Add cationic surfactants (such as polyquaternium salts) to improve wetting and permeability.

[0030] 4) Lithium ion modification fluid injection and modification reaction: The lithium ion modification fluid is injected into the target layer through the steam injection well. The injection pressure is controlled at 0.2-1.0 MPa to prevent soil disturbance. The injection volume is designed based on the soil porosity, layer thickness and pollution load to ensure uniform diffusion of the modification fluid. During the injection of the lithium ion modification fluid, extraction wells are opened to collect some of the original organic pollutants in the formation that were displaced during the injection process. After the injection is completed, the area is closed for 12-48 hours to promote the cation exchange reaction between lithium ions and montmorillonite clay minerals to form lithium-based montmorillonite.

[0031] 5) Hot steam injection and permeability treatment: A steam generation system is used to generate hot steam at a temperature of 150-200°C. The relationship between heating temperature and permeability coefficient is shown in the attached Figure 2 As shown in the figure, the steam injection pressure (0.5-1.5 MPa) and flow rate (0.1-0.5 t / h / well) are controlled based on the thermal stability of the site and the vapor diffusion radius. Hot steam is injected into the target area through the steam injection well. Intermittent low-pressure injection is used (e.g., 8 hours of injection followed by 4 hours of maintenance) to avoid the formation of preferential pathways. During the steam injection process, extraction wells are simultaneously opened to collect lithium ion-modified liquid displaced by the hot steam. After steam injection, the remediation area is sealed for 8-24 hours to enhance permeability and vaporize organic contaminants.

[0032] 6) Pollutant migration and extraction: Organic pollutants are converted into gas phase under pyrolysis and extracted simultaneously through extraction wells; gas, condensed water and free phase are removed through a vacuum system, and the extracted products flow through condensation, oil-water separation and other treatment devices to achieve standard discharge or resource reuse.

[0033] 7) Flowback and Remediation Assessment: Residual solution, condensate, and unreacted lithium ions are recovered through an extraction system. Comparative permeability analysis confirms improved permeability in the remediation area (typically 5-6 orders of magnitude above the original permeability). Soil residual contamination analysis and long-term groundwater monitoring for 3-6 months are conducted to confirm compliance with standards. If permeability improvement or contamination removal is insufficient, repeated permeability enhancement / steam injection treatment may be performed.

[0034] The above method was applied to a typical organic pollution site in East China, where the key process parameters are as follows: (1) The soil type of the site is mainly clay, with a montmorillonite content of 32-38%. The average permeability before remediation was 1.5 × 10 -8 cm / s. The main pollutant is petroleum hydrocarbon, with a content of 5600 mg / kg.

[0035] (2) Construction well pattern design Steam Injection Well Layout: 25 steam injection wells (approximately 6 meters apart) will be deployed throughout the contaminated area, covering a depth of 3-10 meters. Extraction Well Layout: 10 extraction wells (approximately 12-15 meters apart) will be installed, located around the injection wells and downwind of the contaminated area. Monitoring Wells: 6 monitoring wells will be installed to track changes in temperature, pressure, and other parameters.

[0036] (3) Lithium ion modified solution formula and injection parameters A 1 mol / L lithium chloride solution was used as the lithium ion modifier. Intermittent injection was used, with 300-500 L of the modifier injected into each steam injection well in three batches, 12 hours apart. Twenty-four hours after completion, the cations between the montmorillonite layers were fully exchanged, resulting in the formation of lithium-based bentonite. Injection was performed through the gas injection wells, while extraction wells were simultaneously opened to collect some of the organic contaminants displaced from the formation during the injection process.

[0037] (4) Hot steam injection stage The steam temperature was 200°C, the injection pressure was 0.5 MPa, and the flow rate was 0.5 t / h / well. Intermittent injection was employed, with an 8-hour injection period followed by a 4-hour hold period to prevent the formation of preferential pathways. During the hot steam injection process, the exchangeable lithium ions of the lithium-based bentonite, under the influence of temperature, were incorporated into the lattice, rapidly reducing interlayer expansion forces and increasing permeability. Injection was performed through gas injection wells, while extraction wells were simultaneously opened to collect some of the organic contaminants originally displaced from the formation during the injection process.

[0038] (5) Evaluation of post-repair effects Improved permeability: The permeability of the target layer is increased to 1.2 × 10 -5 cm / s, significantly improving soil permeability and successfully breaking down the low-permeability "barrier" of montmorillonite, ensuring efficient contaminant migration in subsequent thermal flooding. Organic pollutant concentrations decreased: total petroleum hydrocarbons dropped to <150 mg / kg, with a contaminant removal rate of approximately 97.3%. Groundwater monitoring results showed no contaminants exceeding the standard, indicating no lateral migration of volatile pollutants.

Claims

1. In-situ permeability enhancement and thermal steam remediation method for low permeability organic contaminated sites, characterized by The following steps are involved: (1) Obtain information on soil permeability, types of organic pollutants, and their spatial distribution, identify low-permeability intervals with high montmorillonite content, and deploy a network of steam injection wells, extraction wells, and temperature / pressure monitoring wells within the target area; (2) Complete the installation of equipment including steam generator, steam injection pipeline, vacuum pump, gas-liquid separator, and condenser, and establish a remote monitoring system to achieve real-time monitoring and automatic control of temperature and pressure; (3) Lithium ion modified liquid is injected into the target area through the steam injection well, and the extraction well is opened at the same time to collect some of the original organic pollutants in the formation that were displaced during the injection process. After completion, the well is sealed for 12-48 hours, and the lithium ions react with the montmorillonite clay minerals to form lithium-based montmorillonite; (4) Inject hot steam into the target area through the steam injection well, and at the same time open the extraction well to collect the lithium ion modified liquid displaced by the hot steam. After completion, the well is closed for 8-24 hours. The organic pollutants are converted into gas phase under the action of pyrolysis and extracted synchronously through the extraction well.

2. The in-situ permeability enhancement and steam remediation method for low-permeability organic contaminated sites according to claim 1, characterized in that In step (1), relevant information is obtained through geological drilling, hydrological testing and pollution investigation.

3. The in-situ infiltration and steam remediation method for low-permeability organic contaminated sites according to claim 1, characterized in that In step (1), the distance between the steam injection wells is controlled at 5-8 meters.

4. The in-situ infiltration and steam remediation method for low-permeability organic contaminated sites according to claim 1, characterized in that In step (1), the extraction wells are staggered to form an effective heat-gas migration path.

5. The in-situ permeability enhancement and steam remediation method for low-permeability organic contaminated sites according to claim 1, characterized in that The temperature / pressure monitoring well in step (1) covers 1-2 meters below the bottom of the contaminated layer.

6. The in-situ permeability enhancement and steam remediation method for low-permeability organic contaminated sites according to claim 1, characterized in that In step (2), the pipeline adopts high-temperature corrosion-resistant casing, and the well wall filler adopts a combination of quartz sand and bentonite water stop ring.

7. The in-situ permeability enhancement and steam remediation method for low-permeability organic contaminated sites according to claim 1, characterized in that In step (3), the lithium ion modification solution adopts a 0.5-2.0 mol / L soluble lithium salt aqueous solution.

8. The in-situ permeability enhancement and steam remediation method for low-permeability organic contaminated sites according to claim 1, characterized in that In step (3), the lithium ion modification solution is heated to 40-70°C before injection.

9. The in-situ permeability enhancement and steam remediation method for low-permeability organic contaminated sites according to claim 1, characterized in that Step (3) adding a cationic surfactant to the lithium ion modified solution.

10. The in-situ permeability enhancement and steam remediation method for low-permeability organic contaminated sites according to claim 1, characterized in that In step (3), the injection pressure of the steam injection well is controlled at 0.2-1.0 MPa.

11. The in-situ permeability enhancement and steam remediation method for low-permeability organic contaminated sites according to claim 1, characterized in that In step (4), the steam injection well uses hot steam at 150-200°C, and the steam injection pressure is controlled to 0.5-1.5 MPa and the flow rate is 0.1-0.5 t / h / well.

12. The in-situ permeability enhancement and steam remediation method for low-permeability organic contaminated sites according to claim 1, characterized in that It also includes removing gas, condensed water and free phase from the collected materials in the extraction well through a vacuum system, and the extracted products flow through condensation and oil-water separation devices to achieve standard discharge or resource reuse.

13. The in-situ permeability enhancement and steam remediation method for low-permeability organic contaminated sites according to claim 1, characterized in that It also includes comparative analysis of permeability after repair, analysis of residual soil pollution and long-term monitoring of groundwater for 3-6 months to confirm that the standards are met; otherwise, the in-situ permeability enhancement and thermal steam repair treatment will be repeated.

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