A stratified multiphase extraction method based on pollutant distribution characteristics

Abstract

The present invention relates to a stratified multiphase extraction method based on pollutant distribution characteristics. The method first determines the distribution of the main strata and the pollution distribution within a site containing pollutants. For NAPL phases, including LNAPL and DNAPL, the thickness range of the NAPL distribution in the stratum is determined. Stratified multiphase extraction wells are arranged within the site to determine the thickness of the NAPL in the wells. The stratified multiphase extraction wells are used to form isolation zones corresponding to the positions of the LNAPL layer and the DNAPL layer, respectively. The LNAPL layer and the DNAPL layer are extracted stratified by the stratified multiphase extraction wells. The advantages of the present invention are that, during the multiphase extraction process for groundwater remediation, extraction is performed in stages based on pollution stratification, and the target layer is dynamically adjusted to concentrate the vacuum degree and avoid waste. Comprehensive comparisons show that the overall energy efficiency can be improved by more than 30% to 50%.

Description

Technical Field

[0001] The present invention relates to the field of environmental geotechnical engineering technology, in particular to a layered multiphase extraction method based on pollutant distribution characteristics, and in particular to a layered extraction method applicable to multiphase extraction wells of contaminated groundwater on site. Background Art

[0002] Multiphase extraction is one of the most commonly used technologies in the field of soil and groundwater remediation. Its principle is to simultaneously extract soil gas, groundwater and non-aqueous liquid pollutants from underground contaminated areas to the ground for separation and treatment, so as to achieve the effect of rapid control and synchronous remediation of soil and groundwater pollution.

[0003] Multiphase extraction technology targets LNAPL (light non-aqueous phase liquid), DNAPL (heavy non-aqueous phase liquid), and dissolved pollutants. Traditional multiphase extraction typically uses a mixed extraction method, extracting water, gas, and NAPL together for post-processing. This approach significantly increases the wastewater and gas treatment volume required. Furthermore, the differences in the phases result in inconsistent spatial impact radii for oil, water, and gas, making coordination and unification difficult. This in turn increases the density of multiphase extraction wells and disposal costs. Furthermore, multiphase extraction is a vacuum-dependent extraction technology. The larger the target layer, the lower the vacuum level, and the poorer the results. Summary of the Invention

[0004] The purpose of the present invention is to provide a stratified multiphase extraction method based on the distribution characteristics of pollutants in response to the above-mentioned deficiencies in the prior art, adopt targeted staged extraction based on the pollutant stratification and dynamically adjust the target layer at the same time to improve the extraction effectiveness and efficiency.

[0005] The purpose of the present invention is achieved by the following technical solutions:

[0006] A stratified multiphase extraction method based on pollutant distribution characteristics, characterized in that the method comprises:

[0007] Determine the distribution of major stratigraphic layers and contamination within the site containing contaminants. For NAPL phases, including LNAPL and DNAPL, determine the thickness range of the NAPL distribution within the stratigraphic layers. Arrange stratified multiphase extraction wells within the site, with the design of the stratified multiphase extraction wells matching the contamination distribution. Determine the thickness of the NAPL within the wells based on the thickness range of the NAPL distribution.

[0008] Clay filter materials are provided at the top and bottom of the LNAPL layer in the stratified multiphase extraction well, each exceeding a certain thickness range, so that an isolation zone consisting of two layers of the clay filter materials is formed at the position of the stratified multiphase extraction well corresponding to the LNAPL layer;

[0009] The layered multiphase extraction well is provided with clay filter material beyond a certain thickness range corresponding to the top of the DNAPL layer, so that the layered multiphase extraction well corresponds to the DNAPL layer and forms an isolation zone consisting of a layer of clay filter material and a natural clay soil isolation layer;

[0010] The LNAPL layer and the DNAPL layer are extracted in separate layers using the separate multiphase extraction well.

[0011] The LNAPL free phase is directly extracted. Depending on the formation properties of the LNAPL enrichment zone, extraction is performed at different extraction locations within the layered multiphase extraction well, including:

[0012] When the LNAPL enrichment zone is located in a sandy soil layer, the extraction location is located in the oil layer;

[0013] When the LNAPL enrichment zone is located in a silty soil layer, the extraction position is located at the oil-water interface;

[0014] When the LNAPL enrichment zone is located in a clay layer, the extraction location is located below the oil layer.

[0015] When the oil thickness in the stratified multiphase extraction well is less than the critical thickness within 24 hours, the extraction of the LNAPL free phase is terminated.

[0016] The DNAPL free phase is directly extracted, and the extraction position is located at the bottom of the well pipe of the layered multiphase extraction well.

[0017] When the extraction ratio of the DNAPL free phase is less than 0.5% for 7 consecutive days, the extraction of the DNAPL free phase is completed.

[0018] After the extraction of the NAPL free phase is completed, the dissolved phase is extracted by mixed extraction.

[0019] A controllable opening and closing valve is provided in the layered multiphase extraction well corresponding to the clay filter position. The sealing of the valve realizes the sealing of the corresponding target layer, thereby realizing the separate extraction of the target layer.

[0020] The advantages of the present invention are: in the process of multiphase extraction and remediation of groundwater, based on the pollution stratification, extraction is carried out in stages, the target layer is dynamically adjusted, the vacuum degree is concentrated, waste is avoided, and comprehensive comparison can improve the overall energy efficiency by more than 30-50%. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 Schematic diagram of NAPL pollution layers in the present invention

[0022] Figure 2 This is a schematic diagram of the design of a contaminated stratified multiphase extraction well in the present invention;

[0023] Figure 3 Schematic diagram of LNAPL free phase extraction in the present invention;

[0024] Figure 4 Schematic diagram of DNAPL free phase extraction in the present invention;

[0025] Figure 5 Schematic diagram of concentrated extraction of NAPL residual phase in the present invention. DETAILED DESCRIPTION

[0026] The features of the present invention and other related features are further described in detail below through embodiments in conjunction with the accompanying drawings to facilitate understanding by those skilled in the art:

[0027] like Figure 1-5 As shown, marks 1-6 in the figure respectively represent: stratified multiphase extraction well 1, clay filter 2, LNAPL free phase 3, groundwater 4, DNAPL free phase 5, and stratified valve 6.

[0028] Example: Figures 1 to 5 As shown, in this embodiment, the stratified multiphase extraction method based on the pollutant distribution characteristics is used to perform stratified extraction of pollutants in a contaminated site, thereby achieving the purpose of pollutant treatment.

[0029] Specifically, the layered multiphase extraction method in this embodiment includes the following steps:

[0030] (1) Refined hydrogeological pollution survey:

[0031] like Figure 1 As shown, before designing a stratified multiphase extraction well, the main strata distribution and contamination distribution, as well as basic parameters such as stratum thickness and permeability, must be determined based on the specific contaminated site's Geotechnical Investigation Report, Hydrogeological Investigation Report, and Contaminated Site Survey Report. For the NAPL phase, the thickness range of the NAPL distribution in the stratum and the thickness of the NAPL in the well must be determined.

[0032] (2) Layered multiphase extraction well design:

[0033] like Figure 2As shown in the figure, based on the detailed survey results of NAPL contamination distribution, a stratified multiphase extraction well 1 for NAPL was designed. For the LNAPL layer, considering the oscillation range of LNAPL distribution, clay filter material 2 was installed at the top and bottom of the LNAPL layer (LNAPL-rich area), exceeding 10% of the thickness to isolate the LNAPL layer from other layers. For the DNAPL layer (DNAPL-rich area), which generally has a natural clay barrier layer below it, clay filter material 2 was installed at the top of the DNAPL layer, exceeding 10% of the thickness to isolate the DNAPL layer from other layers.

[0034] In this embodiment, two layers of clay filter media 2 or a combination of clay filter media 2 and a clayey soil barrier layer are used for isolation of the LNAPL layer and the DNAPL layer. This allows the vacuum pump's energy efficiency to be effectively concentrated on the corresponding target layer during extraction in the stratified multiphase extraction well, thereby increasing the actual impact radius of the multiphase extraction and improving efficiency.

[0035] (3) Contamination stratification multiphase extraction:

[0036] 1) LNAPL free phase extraction:

[0037] Direct extraction is used for LNAPL free phase. Figure 3 As shown, when the LNAPL-enriched zone is located in a sandy soil layer, the extraction location is within the oil layer; when the LNAPL-enriched zone is located in a silty soil layer, the extraction location is at the oil-water interface; and when the LNAPL-enriched zone is located in a clayey soil layer, the extraction location is below the oil layer. Through the targeted design of different extraction locations, LNAPL present in various soil layers can be effectively extracted, effectively improving pollutant treatment efficiency. Free-phase extraction terminates when the 24-hour oil thickness in the well is less than a critical thickness. The critical thickness is defined as the oil layer thickness in the well at which the amount of LNAPL extracted in separate layers equals the amount of LNAPL separated at the end of conventional extraction (related to LNAPL solubility, 30 cm in silty soil).

[0038] 2) DNAPL free phase extraction:

[0039] like Figure 4 As shown in the figure, the DNAPL free phase is directly extracted, and the extraction port is located at the bottom of the extraction well pipe. When the extraction ratio of DNAL is less than 0.5% for 7 consecutive days, the extraction is completed.

[0040] 3) Dissolved phase extraction:

[0041] After the NAPL free phase extraction is completed, the dissolved phase is extracted by mixed extraction to achieve the remediation of non-NAPL enriched layers.

[0042] 4) Extraction of NAPL residual phase:

[0043] like Figure 5 As shown, based on the design of a NAPL stratified multiphase extraction well, the installation of a stratified valve 6 allows for individual extraction of the target layer, concentrating vacuum extraction in the NAPL layer at the oil-water interface. Specifically, the stratified valve 6 is located at the location where the clay filter media 2 is placed, further enhancing the sealing effect on the basis of isolation, thereby further concentrating the efficiency of the vacuum pump. Generally speaking, under a vacuum of -0.1 MPa, the vacuum degree of the target layer can reach -0.08 to -0.09 MPa, achieving energy efficiency. For the LNAPL residual phase, extraction of the LNAPL residual phase ends when the LNAPL extraction ratio is less than 0.1% for 24 consecutive hours. For the DNAPL residual phase, extraction of the DNAPL residual phase ends when the DNAPL extraction ratio is less than 0.5% for 24 consecutive hours.

[0044] Although the above embodiments have described in detail the concepts and embodiments of the present invention with reference to the accompanying drawings, ordinary technicians in this field can recognize that various improvements and modifications can still be made to the present invention without departing from the scope of the claims, so they are not described in detail here.

Claims

1. A stratified multiphase extraction method based on pollutant distribution characteristics, characterized by: The method includes: Determine the distribution of major stratigraphic layers and contamination within the site containing contaminants. For NAPL phases, including LNAPL and DNAPL, determine the thickness range of the NAPL distribution within the stratigraphic layers. Arrange stratified multiphase extraction wells within the site, with the design of the stratified multiphase extraction wells matching the contamination distribution. Determine the thickness of the NAPL within the wells based on the thickness range of the NAPL distribution. Clay filter materials are provided at the top and bottom of the LNAPL layer in the stratified multiphase extraction well, each exceeding a certain thickness range, so that an isolation zone consisting of two layers of the clay filter materials is formed at the position of the stratified multiphase extraction well corresponding to the LNAPL layer; The layered multiphase extraction well is provided with clay filter material beyond a certain thickness range corresponding to the top of the DNAPL layer, so that the layered multiphase extraction well corresponds to the DNAPL layer and forms an isolation zone consisting of a layer of clay filter material and a natural clay soil isolation layer; Performing stratified extraction on the LNAPL layer and the DNAPL layer using the stratified multiphase extraction well; The LNAPL free phase is directly extracted. Depending on the formation properties of the LNAPL enrichment zone, extraction is performed at different extraction locations within the layered multiphase extraction well, including: When the LNAPL enrichment zone is located in a sandy soil layer, the extraction location is located in the oil layer; When the LNAPL enrichment zone is located in a silty soil layer, the extraction position is located at the oil-water interface; When the LNAPL enrichment zone is located in a clay layer, the extraction location is below the oil layer; When the oil thickness in the stratified multiphase extraction well is less than the critical thickness within 24 hours, the extraction of the LNAPL free phase is terminated.

2. The stratified multiphase extraction method based on pollutant distribution characteristics according to claim 1, characterized in that: The DNAPL free phase is directly extracted, and the extraction position is located at the bottom of the well pipe of the layered multiphase extraction well.

3. The stratified multiphase extraction method based on pollutant distribution characteristics according to claim 2, characterized in that: When the extraction ratio of the DNAPL free phase is less than 0.5% for 7 consecutive days, the extraction of the DNAPL free phase is completed.

4. The stratified multiphase extraction method based on pollutant distribution characteristics according to claim 1, characterized in that: After the extraction of the NAPL free phase is completed, the dissolved phase is extracted by mixed extraction.

5. The stratified multiphase extraction method based on pollutant distribution characteristics according to claim 1, characterized in that: A controllable opening and closing valve is provided in the layered multiphase extraction well corresponding to the clay filter position. The sealing of the valve realizes the sealing of the corresponding target layer, thereby realizing the separate extraction of the target layer.

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