Concealed NAPL phase extraction device and extraction method

Abstract

The invention discloses a concealed NAPL phase extraction device and method, and the device comprises a relay tank and a vacuum pump which is used for adjusting the vacuum degree in the relay tank; the oil-water separation head is connected to the middle of the relay tank through an oil pumping connecting pipe and pumps the NAPL phase into the relay tank; the oil receiving tank is connected to the bottom of the relay tank through an oil discharge pipe and an oil discharge pump and is used for storing the NAPL phase moved out by the relay tank; and the remote control system is respectively connected with the vacuum pump, the oil drain pump and the liquid level switch through electric signals, can receive the liquid level information in the relay tank detected by the liquid level switch, and sends a control instruction for starting or closing the vacuum pump and the oil drain pump. According to the extraction device and the extraction method, the problem that the local underground water level is lowered when an NAPL phase is removed by a common device is solved, so that more soil pollution is avoided, and the artificial increase of the remediation work amount is avoided. And the device is less in number of equipment, low in fault rate and more suitable for extracting the NAPL phase in the difficult-to-migrate stratum by being matched with oil film thickness measuring equipment.

Description

Technical Field

[0001] The present invention relates to the technical field of groundwater pollution prevention and control, and particularly relates to a concealed NAPL phase extraction device and an extraction method. Background Art

[0002] Petroleum and / or other water-insoluble organic liquids can be collectively referred to as non-aqueous phase liquids (NAPL). Accidents during production, transportation, sales or use may cause NAPL leakage. Severe leakage or accidents may cause a large amount of NAPL phase to enter the soil environment. These NAPL phases will migrate downward along soil gaps into groundwater and form NAPL phases on the surface or below the groundwater. For example, petroleum hydrocarbons with a lower density will form LNAPL phases floating above the groundwater surface; for example, halogenated hydrocarbons with a density greater than that of water will form DNAPL phases by aggregating above the impermeable floor below the groundwater. Although the migration rate of NAPL phase in the plot is slow along with the flow of groundwater in the plot, it will continuously diffuse into the groundwater in a dissolved state, polluting the groundwater body for a long time, or invading the human living environment in the form of gas. This not only destroys the microbial community structure in this area, but also harms the human body living in this area. With the increasing improvement of domestic environmental protection laws and regulations, the above-mentioned polluted sites urgently need to be effectively treated in an environmentally friendly and relatively concealed manner.

[0003] Currently, the main method for treating LNAPL phase in the plot is to extract it through groundwater wells. As described in Patent Reference 1,

[0004] Reference 1: Chinese patent document with patent publication number CN211027493U.

[0005] Reference 1 discloses a device for accurately extracting NAPL pollutants in groundwater, including a locator that can move up and down along the well pipe; a density meter probe or a viscometer probe fixed on the locator; an extraction pipe, the lower pipe orifice of which is fixed on the locator and is on the same horizontal plane as the density meter probe or the viscometer probe, and the upper pipe orifice of the extraction pipe is connected to the inlet of a water pump. By relying on the data returned by the density meter probe or the viscometer probe, the boundary between the NAPL phase and the water phase can be accurately found, so as to accurately extract the NAPL phase pollutants in the groundwater. A temporary storage tank and a separation and precipitation tank can be connected downstream of the water pump. A small amount of water in the extracted liquid can be separated through the separation and precipitation phase, and the NAPL phase pollutants can be recycled.

[0006] However, this method can indeed quickly extract the NAPL phase in groundwater wells. However, the NAPL phase often exists in areas, and the migration rate of the NAPL phase around groundwater wells is relatively slow, and it takes time to migrate towards the groundwater wells. Therefore, when this method extracts the NAPL phase, it often indiscriminately extracts the groundwater as well, resulting in a significant drop in the groundwater level, causing the NAPL phase to infiltrate the underlying soil, thereby polluting more soil; or because the groundwater level drops too low and the impervious floor is uneven, the NAPL phase will be discontinuous, affecting the migration of the NAPL phase towards the NAPL extraction well, thus requiring an increase in the number of NAPL extraction wells, and more seriously, it will affect the NAPL extraction evaluation results. All of the above situations will increase the repair workload.

[0007] How to effectively remove the regional NAPL phase without causing a large change in the groundwater level, thereby avoiding artificially expanding the project volume has become an urgent technical problem to be solved. To overcome the above technical problems, the applicant previously applied for a utility model patent (Reference 2).

[0008] Reference 2: Chinese patent document with patent publication number CN216911507U.

[0009] Reference 2 discloses a device for removing the NAPL phase in a contaminated plot and a contaminated plot repair system, which relates to the field of organic contaminated plot repair devices. The device includes a conveying mechanism and a regeneration mechanism. The conveying mechanism includes a driving member and a conveying member. The driving member is connected to the conveying member, and an absorbent material that can absorb the NAPL phase and can release the absorbed NAPL phase under external force is installed on the conveying member. The conveying member is used to drive the absorbent material to extend from the wellhead of the groundwater well below the NAPL phase to absorb the NAPL phase, and drive the absorbent material absorbing the NAPL phase to extend out of the wellhead. The regeneration mechanism is used to apply an external force to the absorbent material extending out of the wellhead so that the NAPL phase absorbed by the absorbent material is released. It can effectively remove the NAPL phase in the contaminated plot, and at the same time avoid the downward diffusion of the NAPL phase caused by the local groundwater level drop, thereby causing more soil pollution, and further avoid artificially increasing the repair workload.

[0010] However, the above device has more dynamic equipment and a slightly higher failure rate, and its volume is large and it cannot be operated in a concealed manner. Based on this, the applicant has re-developed a set of NAPL extraction device and its use method on this research basis. Summary of the Invention

[0011] The purpose of the present invention is to solve the technical problems that the existing NAPL extraction device has a slightly higher failure rate and its volume is large and it cannot be operated in a concealed manner, and to provide a concealed NAPL phase extraction device and extraction method.

[0012] To solve the above technical problems, the technical solution adopted by the present invention is: a concealed NAPL phase extraction device, which has:

[0013] A relay tank for temporarily storing the NAPL phase, with a liquid level switch installed inside, and

[0014] A vacuum pump, which is connected to the top of the relay tank through a pressure-reducing connecting pipe to adjust the vacuum degree inside the relay tank; and

[0015] An oil-water separation head, which is connected to the middle part of the relay tank through an oil extraction connecting pipe to pump the NAPL phase into the relay tank; and

[0016] An oil receiving tank, which is connected to the bottom of the relay tank through an oil discharge pipe and an oil discharge pump for storing the NAPL phase removed from the relay tank; and

[0017] A remote control system, which is electrically connected to the vacuum pump, the oil discharge pump and the liquid level switch respectively, can receive the liquid level information inside the relay tank detected by the liquid level switch, and issue control instructions to start or stop the vacuum pump and the oil discharge pump.

[0018] As a further optimization of a concealed NAPL phase extraction device of the present invention: the relay tank can withstand a vacuum degree of at least one atmospheric pressure.

[0019] As a further optimization of a concealed NAPL phase extraction device of the present invention: the gas extraction volume per minute of the vacuum pump is 1-10 times the volume of the relay tank, and the relay tank can be evacuated to an absolute pressure of 0.05-90 kPa. A tail gas purification device is connected to the outlet of the vacuum pump.

[0020] As a further optimization of a concealed NAPL phase extraction device of the present invention: the liquid level switch is a float switch that can sense 5% and 95% of the liquid level in the relay tank.

[0021] As a further optimization of a concealed NAPL phase extraction device of the present invention: the oil-water separation head is prepared from an oil-loving and water-repellent material.

[0022] The present invention also provides a method for extracting a concealed NAPL phase, which uses the above extraction device to complete the extraction of the NAPL phase. Specifically:

[0023] Detect the thickness of the NAPL phase, place the relay tank above the NAPL phase in the extraction well, select an appropriate length of the oil-water separation head according to the thickness of the NAPL phase, adjust the length of the oil extraction connecting pipe connecting the oil-water separation head and the relay tank, and keep a part of the oil-water separation head in the air;

[0024] Start the vacuum pump, adjust the absolute pressure inside the relay tank to 0-90 kPa, and make the NAPL phase enter the relay tank through the oil-water separation head;

[0025] When there is a relatively large amount of NAPL phase in the relay tank and the liquid level reaches the upper limit set by the liquid level switch, the remote control system receives the signal from the liquid level switch and sends a shutdown command to the vacuum pump and a startup command to the oil drain pump. After the oil drain pump starts, it discharges the NAPL phase in the relay tank to the oil receiving tank;

[0026] When there is a relatively small amount of NAPL phase in the relay tank and the liquid level reaches the lower limit set by the liquid level switch, the remote control system receives the signal from the liquid level switch and sends a shutdown command to the oil drain pump. The vacuum pump continues to maintain the vacuum in the relay tank, and the NAPL phase continues to enter the relay tank through the oil-water separator head, realizing the extraction of the NAPL phase.

[0027] As a further optimization of a concealed NAPL phase extraction method of the present invention: when the NAPL phase thickness > 10 cm, the length of the oil-water separator head < 30 cm; when the NAPL phase thickness ≤ 10 cm, the length of the oil-water separator head is less than 2 times the thickness of the NAPL layer.

[0028] As a further optimization of a concealed NAPL phase extraction method of the present invention: when the NAPL phase thickness ≤ 2 cm, keep not less than 30% of the oil-water separator head part in the air.

[0029] As a further optimization of a concealed NAPL phase extraction method of the present invention: detect the NAPL phase thickness through a water surface NAPL phase thickness detection device, and the detection device has:

[0030] A light source, placed in the aqueous phase and emitting light towards the outside at a non-vertical angle; and

[0031] A light receiver, placed above the water surface and receiving the light emitted by the light source; and

[0032] A laser rangefinder, placed above the water surface, used to measure the distance between the light receiver and the upper surface of the oil layer; and

[0033] A bracket, used to carry the light source, light receiver and laser rangefinder; and

[0034] A data processing device, used to receive the data detected by the light receiver and laser rangefinder and perform calculations, and output the LNAPL layer thickness value;

[0035] The specific NAPL phase thickness detection method includes the following steps:

[0036] S1. Roughly detect the thickness of the oil layer in the well, and measure the refractive index no of the upper oil layer of the groundwater;

[0037] S2. Adjust the length of the fixed-distance rod to be greater than the roughly measured oil layer thickness, and then lower the device into the groundwater monitoring well using the rope fixed to the traction hole of the device. Ensure that the light source is placed in the water phase, and the laser rangefinder and the optical receiver are kept in the gas phase above the oil layer. Make sure that the fixed-distance rod of the detection device is perpendicular to the underground water level, and then turn on the light source, the optical receiver, and the laser rangefinder.

[0038] S3. The data processing device receives the data from the optical receiver and the laser rangefinder and calculates the real-time thickness H of the LNAPL layer through the following formula o :

[0039] L 测 - (H L tanα + H A tany) = H o (tanβ - tanα)

[0040] Wherein, L 测 is the lateral propagation distance of the light measured by the optical receiver;

[0041] H A is the distance from the optical receiver to the upper surface of the oil layer measured by the laser rangefinder;

[0042] α is the incident angle set by the light source;

[0043] β is the exit angle of the light entering the oil layer;

[0044] γ is the exit angle of the light emerging from the water surface into the air.

[0045] β and γ are calculated through the following formula:

[0046]

[0047]

[0048] Wherein, n o is the refractive index of the oil, n W is the refractive index of the water, n A is the refractive index of the air.

[0049] As a further optimization of a concealed NAPL phase extraction method of the present invention: the vertical interception method is used to sample the liquid in the monitoring well to roughly detect the thickness of the oil layer in the groundwater monitoring well.

[0050] The present invention has the following beneficial effects: The extraction device and method of the present invention overcome the problem of local groundwater level decline caused by general devices when removing the NAPL phase, thereby avoiding more soil pollution and further avoiding artificially increasing the restoration workload. Moreover, the device has fewer moving parts and low failure rate, and is more suitable for extracting the NAPL phase in difficult-to-migrate strata when combined with the oil film thickness measuring instrument. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] Figure 1 It is a schematic structural diagram of the extraction device of the present invention;

[0052] Figure 2 It is a schematic structural diagram of the on - line monitoring device of the present invention;

[0053] Figure 3 It is a schematic principle diagram in the monitoring method of the present invention;

[0054] Markings in the figure: 102, relay tank; 103, step - down connecting pipe; 104, oil pumping connecting pipe; 105, drain pipe; 106, liquid level switch; 107, oil - water separation head; 108, oil drain pump; 109, vacuum pump; 110, tail gas purification device; 111, oil receiving tank; 112, remote control system; 202, rope; 203, laser rangefinder; 204, optical receiver; 205, upper support; 206, lower support; 207, lower support; 208, light source; 209, wire; 210, data processing unit; 211, output transmission unit. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0055] In order to better understand the present invention, the content of the present invention will be further clarified below in conjunction with embodiments, but the content of the present invention is not limited to the following embodiments.

[0056] <Embodiment 1>

[0057] As Figure 1 shown, a concealed NAPL - phase extraction device has a relay tank 102, a vacuum pump 109, an oil - water separation head 107, an oil receiving tank 111, and a remote control system 112.

[0058] Among them, the relay tank 102 is used to temporarily store the NAPL phase. A liquid level switch 106 is arranged inside it. The relay tank 102 can withstand a vacuum degree of at least one atmospheric pressure. The liquid level switch 106 is a float switch that can sense the liquid levels of 5% and 95% in the relay tank 102 or a float switch that can sense the liquid levels of 0% and 100% in the relay tank.

[0059] Among them, the vacuum pump 109 is connected to the top of the relay tank 102 through a pressure-reducing connecting pipe 103 to adjust the vacuum degree inside the relay tank 102. The air extraction volume per minute of the vacuum pump 109 is 1 - 10 times the volume of the relay tank, and it can evacuate the relay tank to an absolute pressure of 0.05 - 90 kPa. The outlet of the vacuum pump 109 is connected with an exhaust gas purification device 110. The exhaust gas purifier 110 has an outer diameter slightly smaller than the inner diameter of the NAPL phase extraction well, is filled with an adsorption material that can adsorb the NAPL phase, and its length is determined through a breakthrough curve test. It is connected in a quick-insertion manner for easy replacement.

[0060] Among them, the oil-water separation head 107 is connected to the middle of the relay tank 102 through an oil extraction connecting pipe 104 to pump the NAPL phase into the relay tank 102. The oil-water separation head 107 is made of an oil-loving and water-repellent material and is an existing technology, so it will not be elaborated here.

[0061] Among them, the oil receiving tank 111 is connected to the bottom of the relay tank 102 through an oil discharge pipe 105 and an oil discharge pump 108 and is used to store the NAPL phase removed from the relay tank 102.

[0062] Among them, the remote control system 112 is electrically connected to the vacuum pump 109, the oil discharge pump 108, and the liquid level switch 106 respectively. It can receive the liquid level information inside the relay tank 102 detected by the liquid level switch 106 and issue control instructions to start or stop the vacuum pump 109 and the oil discharge pump 108.

[0063] There are three connecting pipes and a liquid level switch on the relay tank 102, namely the pressure-reducing connecting pipe 103, the oil extraction connecting pipe 104, the oil discharge pipe 105, and the float switch 106. The pressure-reducing connecting pipe 103 is connected to the vacuum pump 109 through a pipeline, and the outlet of the vacuum pump is connected to the exhaust gas purification device 110. The oil extraction connecting pipe 104 is connected to the oil-water separation head 107 through a pipeline. The oil-water separation head can allow air and oil to pass through while water cannot pass through. When the pressure in the relay tank becomes lower, the oil-water separation head 107 at the NAPL phase and water phase interface starts to transport the NAPL phase liquid into the relay tank. The oil discharge pipe 105 is connected to the oil discharge pump 108 through a pipeline. When the oil discharge pump 108 starts, it can discharge the NAPL phase in the relay tank 102 into the oil receiving tank 111. The float switch 106 monitors the liquid level in the relay tank 102 and sends signals to start and stop oil discharge to the oil discharge pump 108 through the device remote control system 112.

[0064] The remote control system 112 can set the start and stop frequency of the device, and can also transmit information such as the device power information and instrument status in real time, so as to realize the real-time management of the device status. Through the remote control system 112, remote control and the viewing of the device operation status can be realized. The pumps and tail gas treatment devices used in the whole device are all small-volume and high-power equipment. Therefore, the NAPL phase extraction device can be placed in the NAPL phase extraction well, and only the wires and the outlet hose of the drain pump protrude from the NAPL phase extraction well. Therefore, the function of concealed extraction of the NAPL phase without equipment on the ground can be realized.

[0065] <Example 2>

[0066] A concealed NAPL phase extraction method uses the extraction device in <Example 1> to complete the extraction of the NAPL phase. The specific method is as follows:

[0067] Select a relay tank with an outer diameter slightly smaller than the inner diameter of the NAPL phase extraction well. Determine the hanging depth of the device according to the groundwater depth, and place the device above the NAPL phase in the NAPL phase extraction well. Select an appropriate length of the oil-water separator head according to the NAPL phase thickness. When the NAPL phase is relatively thick, the length of the oil-water separator head should not be selected too long, generally within 30 cm. When the NAPL phase thickness is relatively thin (within 10 cm), the length of the oil-water separator head should not be greater than 2 times the NAPL layer thickness. Adjust the length of the hose connecting the oil-water separator head to the relay tank to keep part of the oil-water separator head in the air. When the NAPL phase thickness is relatively thin (0-2 cm), keep no less than 30% of the oil-water separator head in the air.

[0068] Start the vacuum pump and adjust the absolute pressure in the relay tank to 0-90 kPa. Then the NAPL phase will enter the relay tank through the oil-water separator head. When there is more NAPL phase in the relay tank, the float switch is turned on. The float switch controls the vacuum pump to turn off and controls the drain pump to start. After the drain pump starts, it discharges the NAPL phase in the relay tank to the oil receiving tank. When the NAPL phase liquid level in the relay tank is lower than the lower float of the float switch, the float switch is turned off. The float switch controls the drain pump to turn off, and the vacuum pump continues to maintain the vacuum in the relay tank, and the NAPL phase continues to enter the relay tank through the oil-water separator head, realizing the extraction of the NAPL phase. The device remote control system can set the start and stop frequency of the device, and can also transmit information such as the device power information and instrument status in real time, so as to realize the real-time management of the device status.

[0069] Among them, the NAPL phase thickness can be detected by a water surface NAPL layer thickness detection device based on the principle of light refraction. The detection device has a light source 208, a light receiver 204, a laser rangefinder 203, a bracket and a data processing device.

[0070] Among them, the bracket is used to carry the light source 208, the optical receiver 204, and the laser rangefinder 203. The bracket includes a fixed-distance rod 206, an upper bracket 205, and a lower bracket 207. The upper bracket 205 and the lower bracket 207 are parallel to each other and are respectively perpendicular to the fixed-distance rod 206 and are arranged at its upper and lower ends. The laser rangefinder 203 and the optical receiver 204 are arranged on the upper bracket 205, and the light source 208 is arranged on the lower bracket 207. The above structural design can ensure that the longitudinal distance between the light source 208 and the fixed-distance rod 206 does not change with the change of the lateral distance. The light source 208 can rotate at any angle or be installed at a fixed angle on the lower bracket 207. And it ensures that the longitudinal distance between the laser rangefinder 203 and the fixed-distance rod 206 does not change with the change of the lateral distance.

[0071] The fixed-distance rod 206 is a telescopic straight rod. After the fixed-distance rod is telescoped, it can bear a weight of 10 kg without bending and its length remains unchanged.

[0072] The upper bracket 205 is provided with a traction hole. The connection line between the center of the traction hole and the center of gravity of the device is parallel to the fixed-distance rod 206. A suspension rope 202 is installed on the traction hole. The device is put into the groundwater monitoring well or other places where it is needed through the rope 202 fixed on the traction hole.

[0073] Among them, the light source 208 is placed in the aqueous phase and emits light towards the outside at a non-vertical angle. The light source can emit direct light, and the thickness of the light is not greater than 0.01 mm.

[0074] Among them, the optical receiver 204 is placed above the water surface and receives the light emitted by the light source 208. The resolution of the optical receiver is higher than 0.01 mm.

[0075] Among them, the laser rangefinder 203 is placed above the water surface and is used to measure the distance between the optical receiver 204 and the upper surface of the oil layer. The test accuracy of the optical rangefinder is 0.01 mm. The laser rangefinder 203 is a small-volume laser rangefinder that can be placed in the groundwater monitoring well

[0076] Among them, the data processing device is used to receive the data detected by the optical receiver 204 and the laser rangefinder 203 and perform calculations, and output the NAPL layer thickness value.

[0077] The data processing device includes a data processing unit 210 and a data transmission unit 211. The data processing unit 210 has functions of data display, input, and editing calculation. The data transmission unit 211 has components for transmitting the data on the data processor to the remote memory, components for an app to call the data from the remote memory, and components for running the app. The data transmitted by the data transmission unit 111 includes input data, measured data, test time, calculated oil layer thickness data, and instrument status.

[0078] Method for detecting the thickness of the NAPL layer using the above detection device: Adjust the length of the fixed-distance rod to be greater than the estimated thickness of the oil layer. Lower the device into the groundwater monitoring well through the rope fixed to the traction hole of the device, place the light source in the water phase, keep the laser rangefinder in the gas phase above the oil layer, ensure that the fixed-distance rod of the detection device is perpendicular to the underground water level, turn on all components of the oil layer thickness measuring instrument, and direct the light source towards the oil-water phase interface at an incident angle of α. Calculate the thickness of the oil layer above the groundwater surface through the data processor.

[0079] The light source is directed towards the oil-water phase interface at an incident angle of α. Assuming there is no water on the water surface, the exit angle of the light emerging from the water surface into the air is γ. The relationship between α and β is shown in Equation 1. If there is an oil layer on the water surface, the exit angle β of the light entering the oil layer is related to the refractive index of the oil layer. The relationship between β and α is shown in Equation 2. The light is directed towards the oil-air phase interface at an incident angle of β. From Equations 1, 2, and 3, it can be seen that the exit angle is still γ. The length (L) of the fixed-distance rod is a set value, and the distance H measured by the laser rangefinder from the upper bracket to the upper surface of the oil layer A , H L is the depth of the fixed-distance rod immersed in the NAPL phase and the water phase, and the lateral distance L measured by the photosensitive material receiver from the light source to the photosensitive point on the light source receiving surface 测 The value of H of the oil layer thickness above the groundwater surface can be calculated according to Equation 4 o value. L 测 -(H L tanα + H A tanγ) = H o (tanβ - tanα) Equation 4

[0080] <Example 3>

[0081] The experiment used a sandbox to simulate the actual pollution scenario. The size of the sandbox was 150×150×100 cm in length, width, and depth. A sieve tube with an inner diameter of 10 cm was installed as the NAPL phase extraction well, and the original soil was placed in it. 30 cm of water was added to the sandbox, and a 10-cm-thick NAPL phase was placed. The composition of the NAPL phase was diesel. The appropriate device size and model were selected using the device described in the patent: the outer diameter of the relay tank was 9.5 cm and the length was 25 cm; the length of the float switch was 23 cm, a double-ball switch; the length of the oil-water separator head was 15 cm; the suspended depth of the relay tank was set to 10 cm; the oil-water separator head was adjusted to be vertically placed in the NAPL phase, with the upper 2 cm placed in the air; the vacuum pump and the oil drain pump were commercially available micro pumps. The main power supply of the device was started, and the pressure in the relay tank was adjusted to an absolute pressure value of 80 kPa. After 10 minutes, the float switch automatically turned on, the float switch controlled the vacuum pump to stop, and the oil drain pump was started. After 1.4 L of oil was collected in the oil receiving bottle within 1 minute, the float switch automatically turned off, and the float switch controlled the oil drain pump to close and the vacuum pump to start. After 35 hours, the thickness of the NAPL layer in the sandbox was 1 cm. The depth of the oil-water separator head immersed in water was adjusted to 7 cm. The power information and instrument status of the device were viewed through the remote control system, and the start frequency of the device was adjusted to 2 hours / once through the remote control system, 30 minutes each time. After 24 hours, the thickness of the NAPL phase in the sandbox was 0.2 cm.

[0082] The specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the above specific embodiments, and those skilled in the art can make various deformations or modifications within the scope of the claims, which do not affect the essence of the present invention.

Claims

1. A concealed NAPL phase extraction device, characterized in that, It has: A relay tank (102) for temporarily storing the NAPL phase, with a liquid level switch (106) installed inside it, and A vacuum pump (109) which is connected to the top of the relay tank (102) through a pressure-reducing connecting pipe (103) to adjust the vacuum degree inside the relay tank (102); and An oil-water separation head (107) which is connected to the middle part of the relay tank (102) through an oil extraction connecting pipe (104) to pump the NAPL phase into the relay tank (102); and An oil receiving tank (111) which is connected to the bottom of the relay tank (102) through an oil discharge pipe (105) and an oil discharge pump (108) for storing the NAPL phase removed from the relay tank (102); and A remote control system (112) which is electrically connected to the vacuum pump (109), the oil discharge pump (108) and the liquid level switch (106) respectively, can receive the liquid level information inside the relay tank (102) detected by the liquid level switch (106), and issue control instructions to start or stop the vacuum pump (109) and the oil discharge pump (108).

2. The concealed NAPL phase extraction device according to claim 1, characterized in that The relay tank (102) can withstand a vacuum degree of at least one atmospheric pressure, and its outer diameter is selected to be smaller than the inner diameter of the monitoring well to be treated.

3. The concealed NAPL phase extraction device according to claim 2, characterized in that The gas extraction volume per minute of the vacuum pump (109) is 1-10 times the volume of the relay tank (102), and it can evacuate the relay tank (102) to an absolute pressure of 0.05-90 kPa. The outlet of the vacuum pump (109) is connected with an exhaust gas purification device (110).

4. The concealed NAPL phase extraction device according to claim 1, characterized in that The liquid level switch (106) is a float switch that can sense the liquid levels of 5% and 95% in the relay tank (102).

5. The concealed NAPL phase extraction device according to claim 4, characterized in that The oil-water separation head (107) is prepared from an oil-loving and water-repellent material.

6. A concealed NAPL phase extraction method, which uses the extraction device according to claim 1 to complete the extraction of the NAPL phase, characterized in that Detect the thickness of the NAPL phase, place the relay tank above the NAPL phase in the extraction well, select an appropriate length of the oil-water separation head according to the thickness of the NAPL phase, adjust the length of the oil extraction connecting pipe connecting the oil-water separation head and the relay tank, and keep a part of the oil-water separation head in the air; Start the vacuum pump, adjust the absolute pressure inside the relay tank to 0-90 kPa, and make the NAPL phase enter the relay tank through the oil-water separation head; When the NAPL phase in the relay tank reaches the upper liquid level set by the liquid level switch, the remote control system receives the signal from the liquid level switch and issues a shutdown instruction to the vacuum pump, and issues a start instruction to the oil discharge pump. After the oil discharge pump starts, it discharges the NAPL phase in the relay tank to the oil receiving tank; When the NAPL phase in the relay tank reaches the lower limit of the liquid level set by the liquid level switch, the remote control system receives the signal from the liquid level switch and sends a shutdown command to the drain oil pump. The vacuum pump continues to maintain the vacuum in the relay tank, and the NAPL phase continues to enter the relay tank through the oil-water separator head to achieve the extraction of the NAPL phase.

7. The method for extracting the concealed NAPL phase according to claim 6, wherein When the thickness of the NAPL phase > 10 cm, the length of the oil-water separator head < 30 cm. When the thickness of the NAPL phase ≤ 10 cm, the length of the oil-water separator head is less than 2 times the thickness of the NAPL layer.

8. The method for extracting the concealed NAPL phase according to claim 6, wherein When the thickness of the NAPL phase ≤ 2 cm, keep not less than 30% of the oil-water separator head above the air.

9. The method for extracting the concealed NAPL phase according to claim 6, wherein The thickness of the NAPL phase on the water surface is detected by a thickness detection device for the NAPL phase on the water surface. The detection device has: A light source (208) placed in the water phase and emitting light toward the outside at a non-vertical angle; And A light receiver (204) placed above the water surface and receiving the light emitted by the light source (208); And A laser rangefinder (203) placed above the water surface for measuring the distance between the light receiver (204) and the upper surface of the oil layer; and A bracket for carrying the light source (208), the light receiver (204), and the laser rangefinder (203); and A data processing device for receiving the data detected by the light receiver (204) and the laser rangefinder (203) and performing calculations to output the thickness value of the NAPL layer; The specific method for detecting the thickness of the NAPL phase includes the following steps: S1. Roughly detect the thickness of the oil layer in the well, and measure the refractive index n of the oil layer above the groundwater o ; S2. Adjust the length of the fixed-distance rod to be greater than the roughly measured thickness of the oil layer. Then, use the rope fixed to the traction hole of the device to lower the device into the groundwater monitoring well. The light source is placed in the water phase, and the laser rangefinder and the light receiver are kept in the gas phase above the oil layer. Ensure that the fixed-distance rod of the detection device is perpendicular to the underground water level. Turn on the light source, the light receiver, and the laser rangefinder; S3. The data processing device receives the data from the optical receiver and the laser rangefinder and calculates the real-time thickness H of the NAPL layer through the following formula o :[[]]END]] L 测 -(H L tan α + H A tan γ) = H o (tan β - tan α), where L 测 is the lateral propagation distance of the light measured by the optical receiver; H A is the distance from the optical receiver to the upper surface of the oil layer measured by the laser rangefinder; H L is the depth at which the fixed-distance rod is immersed in the oil phase and the water phase; α is the incident angle set by the light source; β is the exit angle of the light entering the oil layer; γ is the exit angle of the light exiting the water surface and entering the air. β and γ are calculated by the following formula: where n o is the refractive index of oil, n W is the refractive index of water, and n A is the refractive index of air.

10. The method for extracting the concealed NAPL phase according to claim 6, wherein The thickness of the oil layer in the groundwater monitoring well is roughly detected by using the vertical intercept method to sample the liquid in the monitoring well.

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