In-situ dehydration method and system for stock garbage based on air foam displacement

Abstract

The present invention provides an in-situ dehydration method and system for stock garbage based on air foam displacement. The method is used to dehydrate garbage piles in landfills. The method comprises: driving a vertical shaft into the garbage pile, with a plurality of infiltration holes provided on the peripheral wall of the vertical shaft; injecting air foam into the vertical shaft, the air foam moving along the vertical shaft and displacing leachate in the garbage pile through the infiltration holes; detecting whether the moisture content of the garbage pile within a preset depth is less than a preset moisture content threshold; if so, stopping injecting air foam into the vertical shaft and injecting air into the vertical shaft; and detecting whether the gas concentration reaches a preset standard threshold; if so, stopping injecting air into the vertical shaft. The in-situ dehydration method and system for stock garbage based on air foam displacement provided by the present invention can further reduce the moisture content of the garbage pile, and can effectively improve the dehydration effect of heterogeneous garbage piles and simultaneously treat harmful gases.

Description

Technical Field

[0001] The present invention relates to the technical field of garbage disposal, and in particular to an in-situ dehydration method and system for stock garbage based on air foam displacement. Background Art

[0002] Before excavation and screening of existing landfills, liquids and gases present within them are typically treated in situ to reduce the waste's moisture content and odor concentration, ensuring safety during subsequent construction. Traditional in-situ dewatering technology involves drilling vertical shafts and using submersible pumps. The shafts cause leachate within a certain area to migrate laterally into the wells, where they are rapidly pumped out by submersible pumps, thereby reducing the leachate level and moisture content within the affected area. However, through years of field application, it has been found that this technology has the following problems: (1) The moisture content of garbage after treatment with traditional in-situ dehydration technology is still high, about 45%, which greatly limits the subsequent screening efficiency; (2) Affected by the preferential flow effect in garbage, the moisture content of garbage after treatment with traditional in-situ dehydration technology has significant unevenness in spatial distribution, which is manifested as the inability to effectively discharge water in small pore areas; (3) The efficiency of traditional in-situ dehydration technology is low, especially for garbage in the unsaturated area above the water level line. The impact is very small; (4) Traditional dehydration technology does not intervene in toxic gases such as NH3 and H2S, resulting in high emission concentrations during subsequent excavation (H2S is about 3~5 mg / m 3 ), which affects the health of construction workers and surrounding residents.

[0003] To this end, the applicant has proposed a method for further reducing the moisture content by injecting air, as described in Chinese invention patent application publication number CN114700342A. The method disclosed in this patent application further reduces the moisture content and odor concentration of the treated garbage, improving its stabilization, creating favorable conditions for garbage excavation and screening. While this method offers some improvements over traditional methods, it still faces bottlenecks in dehydration efficiency and the moisture content of the treated garbage. To achieve even better dehydration efficiency and further reduce the moisture content of the treated garbage, new breakthroughs in in-situ dehydration technology for stock garbage are needed.

[0004] In view of this, it is necessary to propose a new technical solution to overcome the problems existing in the prior art. Summary of the Invention

[0005] The present invention provides an in-situ dehydration method and system for stock garbage based on air foam displacement, which can further reduce the moisture content of the garbage pile, effectively improve the dehydration effect of heterogeneous garbage piles, and simultaneously treat harmful gases.

[0006] To achieve the above-mentioned object, the present invention adopts the following technical solution: an in-situ dehydration method for stock garbage based on air foam displacement, which is used to dehydrate garbage piles in landfills, wherein the method comprises:

[0007] A vertical shaft is driven into the garbage pile, wherein a plurality of infiltration holes are provided on the peripheral wall of the vertical shaft;

[0008] Injecting air foam into the vertical shaft, the air foam moves along the vertical shaft and displaces the leachate in the garbage pile through the infiltration holes;

[0009] detecting whether the moisture content of the garbage pile within a preset depth is less than a preset moisture content threshold; if so, stopping the injection of air foam into the shaft and injecting air into the shaft; and

[0010] Detect whether the gas concentration reaches a preset standard threshold; if so, stop injecting air into the shaft.

[0011] Optionally, injecting air foam into the vertical shaft specifically includes:

[0012] disposing a foam generator connected to the vertical shaft; and

[0013] An air compressor and a foaming agent storage tank are configured to inject air and foaming agent into the foam generator respectively, so that the air and the foaming agent are mixed in the foam generator to generate the air foam.

[0014] Optionally, the foaming agent is SDS surfactant.

[0015] Optionally, the concentration of the SDS surfactant is 0.05% to 0.2%.

[0016] Optionally, a porous sponge foaming layer and a porous baffle for supporting the porous sponge foaming layer are provided in the foam generator.

[0017] Optionally, the foam generator is provided with a transparent observation window to facilitate observation of the air foam therein.

[0018] Optionally, the method further comprises performing a sealing and covering treatment on the surface of the garbage pile.

[0019] Optionally, the sealing and covering treatment includes covering the surface of the garbage dump with a geomembrane and covering the geomembrane with a soil layer.

[0020] Optionally, the water content threshold is set between 25% and 35%, and the standard thresholds include: CH4 volume fraction <5%, O2 volume fraction >15%, H2S mass concentration <0.1 mg / m 3 .

[0021] Optionally, the method further comprises providing a gas-liquid separation device on a drainage pipeline for discharging the gas-liquid mixture from the garbage dump, so as to separate the leachate and the gas.

[0022] The present invention also adopts the following technical solution: an in-situ dehydration system for stock garbage based on air foam displacement, wherein the system uses the above-mentioned method to dehydrate the garbage pile in the landfill.

[0023] By adopting the above technical solution, the present invention has the following technical effects.

[0024] On the one hand, the surfactant in the air foam can reduce the surface tension of the leachate and promote the stripping and migration of residual leachate. On the other hand, due to the large plugging pressure difference formed by the foam drive, it can displace the water in some small pores, thereby achieving a lower residual saturation, so that the moisture content can be further reduced on the basis of the field water holding rate.

[0025] Air foam forms viscoelastic fluid in high permeability areas, selectively blocks large pores or cracks, and forces subsequent injected fluids to turn to low permeability areas, which can effectively improve the dehydration effect of heterogeneous garbage piles.

[0026] Air foaming is a displacement process that creates a high pressure differential between the two ends. The foam propels forward through the waste pile like a piston, rather than simply flowing under gravity. This results in higher dewatering efficiency. It effectively displaces waste within the vertical shaft opening, regardless of the water level.

[0027] During the movement of air bubbles, the leachate and harmful gases in large and small pores are driven to the outlet together. By adding a liquid-gas separation device at the outlet, the leachate and toxic gases can be treated separately, solving potential safety hazards in the subsequent construction process. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings of the embodiments will be briefly introduced below. Obviously, the drawings in the following description only relate to some embodiments of the present invention, but are not intended to limit the present invention.

[0029] Figure 1 It is a schematic diagram of an embodiment of the in-situ dehydration system for stock garbage based on air foam displacement of the present invention.

[0030] Figure 2 The present invention is a flow chart of an embodiment of an in-situ dehydration method for stock garbage based on air foam displacement.

[0031] Figure 3It is a three-dimensional combination diagram of a foam generator in an embodiment of the in-situ dehydration system for stock garbage based on air foam displacement of the present invention.

[0032] Figure 4 It is a cross-sectional view of a foam generator in one embodiment of the in-situ dehydration system for stock garbage based on air foam displacement according to the present invention.

[0033] Figure 5 This is a schematic diagram of the distribution of injection wells and monitoring wells in a test model of the in-situ dehydration method for stock garbage based on air foam displacement of the present invention.

[0034] Figure 6 This is a real shot of foams with different SDS concentrations in a garbage pile in a test model of the in-situ dehydration method for stock garbage based on air foam displacement of the present invention.

[0035] Figure 7 This is a drainage curve diagram at different SDS concentrations in a test model of the in-situ dehydration method for stock garbage based on air foam displacement of the present invention.

[0036] Figure 8 It is a comparison diagram of the volume moisture content distribution of the in-situ dehydration method of stock garbage based on air foam displacement and the air displacement test of the present invention.

[0037] Explanation of the accompanying symbols: 1-air compressor; 2-pressure regulating valve; 3-gas flow meter; 4-foaming agent storage tank; 5-foam generator; 501-air inlet; 502-liquid inlet; 503-foam outlet; 504-transparent observation window; 505-foam cavity; 51-porous sponge foaming layer; 52-porous baffle; 6-data acquisition terminal; 7-pressure sensor; 8-water content sensor; 9-liquid flow meter; 10-gas-liquid separation device; 11-garbage pile; 12-guide layer; 13-covering layer; 15-shaft. DETAILED DESCRIPTION

[0038] To make the objectives, technical solutions, and advantages of the embodiments of the present invention more apparent, the present invention will be further described in detail below with reference to the accompanying drawings. The components of the embodiments of the present invention generally described and illustrated in the accompanying drawings can be arranged and designed in a variety of different configurations. All other embodiments derived by persons of ordinary skill in the art based on the embodiments of the present invention without inventive effort are intended to fall within the scope of protection of the present invention.

[0039] It should be noted that similar reference numerals and letters denote similar items in the following drawings, and therefore, once an item is defined in one drawing, it does not need to be further defined or explained in subsequent drawings.

[0040] Unless otherwise defined, technical or scientific terms used in this patent document shall have the ordinary meanings understood by persons of ordinary skill in the art to which this invention belongs. The terms "first," "second," and similar expressions used in the specification and claims of this invention do not denote any order, quantity, or importance, but are merely used to distinguish one component from another. Similarly, terms such as "a," "an," or "the" do not denote a limitation of quantity, but rather denote the presence of at least one. Terms such as "include" or "comprising" mean that the elements or objects preceding the phrase "include" or "comprising" include the elements or objects listed after the phrase and their equivalents, and do not exclude other elements or objects. Terms such as "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer" are used solely to indicate relative positional relationships. When the absolute position of the described object changes, the relative positional relationship may also change accordingly. These terms are used solely to facilitate the description of the invention and to simplify the description. They are not intended to indicate or imply that the device or component referred to must have, be constructed, or operate in a specific orientation, and are not to be construed as limitations on the invention.

[0041] In the description of the present invention, it should be noted that, unless otherwise expressly specified or limited, the terms "mounted," "connected," and "connected" should be understood broadly. For example, they may refer to fixed, detachable, or integral connections; mechanical or electrical connections; direct or indirect connections through an intermediary; and internal communication between two components. Those skilled in the art will understand the specific meanings of these terms in the present invention based on the specific circumstances.

[0042] The following describes some embodiments of the present invention in detail with reference to the accompanying drawings. In the absence of conflict, the features of the following embodiments can be combined with each other.

[0043] Traditional in-situ dewatering technology involves drilling vertical shafts and using submersible pumps. When the shafts are operating, leachate within the affected area migrates laterally into the shafts, where it is rapidly pumped out by the submersible pumps, thereby reducing the leachate level and moisture content within the affected area. However, traditional in-situ dewatering technology still has the following shortcomings.

[0044] Because traditional in-situ dewatering technology drains waste solely by gravity, the treated waste has a high moisture content. Specifically, traditional in-situ dewatering technology allows leachate from the waste pile to migrate laterally under gravity into a vertical shaft, where it is extracted by a submersible pump at the bottom of the shaft. Theoretically, the moisture content of the treated waste can only be reduced to the field capacity (approximately 45%). This is still high for waste pile excavation and subsequent waste screening. Previous studies have shown that screening efficiency is negatively correlated with the moisture content of the material. Screening tests on 10- to 14-year-old waste have shown that when the moisture content is reduced from 45% to 30%, the separation efficiency increases from an average of 72.29% to 92.28%.

[0045] Traditional in-situ dewatering technologies, affected by the preferential flow effect, are unable to effectively drain water from small pore areas, resulting in significant spatial heterogeneity in the moisture content after treatment. Previous studies have shown that garbage is a typical bi-porous medium, consisting of large pore regions (fracture domains) and small pore regions (matrix domains). During traditional vertical shaft pumping, water in the large pore regions migrates laterally into the shaft under the influence of gravity and is pumped out, while water in the small pore regions remains largely unaffected. This results in significant spatial heterogeneity in the moisture content after treatment.

[0046] Traditional in-situ dewatering technologies are inefficient, particularly for waste in the unsaturated zone above the waterline. Conventional vertical shaft pumping has little impact on the moisture content of waste above the waterline, making further dewatering of this area difficult. Furthermore, vertical shaft pumping projects at landfills typically last from several weeks to several months, resulting in high disposal costs.

[0047] Traditional in-situ dehydration technology is unable to simultaneously treat toxic gases, posing a safety hazard during excavation. While its primary purpose is to extract water, it may also extract a small amount of toxic gases. However, it cannot effectively capture the larger portion of toxic gases, creating the risk of toxic gas escape during subsequent excavation.

[0048] To address the above shortcomings, the present invention proposes an in-situ dehydration method and system for stock waste based on air foam displacement. Figure 1 and Figure 2 As shown, the present invention provides an in-situ dehydration method for stock garbage based on air foam displacement, which is used to dehydrate a garbage pile 11 in a landfill. The method comprises:

[0049] A vertical shaft 15 is driven into the garbage pile 11, and a plurality of infiltration holes are provided on the peripheral wall of the vertical shaft 15;

[0050] Injecting air foam into the vertical shaft 15, the air foam moves along the vertical shaft 15 and displaces the leachate in the garbage pile 11 through the leachate holes;

[0051] Detecting whether the moisture content of the garbage pile 11 within a preset depth is less than a preset moisture content threshold; if so, stopping injecting air foam into the shaft 15 and injecting air into the shaft 15; and

[0052] Check whether the gas concentration reaches a preset standard threshold; if so, stop injecting air into the shaft 15.

[0053] The surfactants in the air foam reduce the surface tension of the leachate, promoting the stripping and migration of residual leachate. Furthermore, because the foam flooding creates a significant plugging pressure differential, it displaces some water from small pores, thereby achieving a lower residual saturation and further reducing the water content based on the field water holding capacity. The air foam forms a viscoelastic fluid in highly permeable areas, selectively plugging large pores or cracks and forcing subsequent injected fluids to divert to low-permeability areas, effectively improving the dewatering of the heterogeneous waste pile 11. The movement of the air foam is a displacement behavior that generates a high pressure differential. The foam propels forward through the waste pile 11 in a piston-like manner, rather than simply flowing under gravity, resulting in higher dewatering efficiency. It effectively displaces waste within the wellbore opening of the vertical shaft 15, unrestricted by the water level. During the movement of the air foam, leachate and hazardous gases in both large and small pores are simultaneously displaced to the outlet. By adding a liquid-gas separation device at the outlet, the leachate and toxic gases can be separated and treated, resolving potential safety hazards during subsequent construction.

[0054] like Figure 1 As shown, a system for dehydrating a garbage pile 11 in a landfill using the method described above includes an air compressor 1, a pressure regulating valve 2, a gas flow meter 3, a foaming agent storage tank 4, a foam generator 5, a data acquisition terminal 6, a pressure sensor 7, a moisture content sensor 8, a liquid flow meter 9, a gas-liquid separation device 10, and a vertical shaft 15 driven into the garbage pile 11.

[0055] The air compressor 1 is connected to the foam generator 5 via an air inlet line to supply air to the foam generator 5. The pressure regulating valve 2 and the gas flow meter 3 are provided on the air inlet line to regulate and monitor the flow of air entering the foam generator 5. The foaming agent storage tank 4 is connected to the foam generator 5 via a liquid inlet line to supply the foaming agent to the foam generator 5.

[0056] Please also refer to Figure 3 and Figure 4As shown, accordingly, the foam generator 5 has an air inlet 501 for connection to the air inlet pipeline and a liquid inlet 502 for connection to the liquid inlet pipeline. The foam generator 5 is provided with a porous sponge foaming layer 51 and a porous baffle 52 for supporting the porous sponge foaming layer 51. The gas and the foaming agent solution are shear-mixed through the porous sponge foaming layer 51 to form a uniform and stable air foam. The porous baffle 52 prevents the foaming layer from shifting and promotes turbulence, thereby improving the foaming efficiency. A foam cavity 505 is provided in the foam generator 5. The foam cavity 505 is located downstream of the porous sponge foaming layer 51 and the porous baffle 52, and is used for allowing the air foam formed by the air and foaming agent passing through the porous sponge foaming layer 51 to pass through. The foam generator 5 is provided with a transparent observation window 504 to facilitate observation of the air foam therein. In this embodiment, the peripheral wall of the foam cavity 505 is made of a transparent material to form the transparent observation window 504. The lower end of the foam generator 5 has a foam outlet 503 connected to the vertical shaft 15 for injecting the air foam generated by the foam generator 5 into the vertical shaft 15 .

[0057] The vertical shaft 15, also known as the injection well, has multiple infiltration holes on its peripheral wall, allowing leachate seeping from the surrounding garbage pile 11 to enter the vertical shaft 15 through the infiltration holes. The garbage pile 11 is also equipped with multiple monitoring wells, each equipped with sensors to monitor the amount of gas and liquid within the garbage pile 11. In this embodiment, the sensors in the monitoring wells include a pressure sensor 7 and a moisture sensor 8. The pressure sensor 7 is used to collect the air pressure at its location, and the moisture sensor 8 is used to collect the moisture content at its location. The pressure sensor 7 and moisture sensor 8 are connected to the data acquisition terminal 6 to transmit the collected air pressure and moisture content data to the data acquisition terminal 6 for monitoring and controlling the dehydration process. The gas-liquid separation device 10 is connected to the drainage layer 12 within the garbage pile 11 via a drainage pipeline to separate the discharged gas and leachate. The drainage pipeline is equipped with a liquid flowmeter 9 to monitor the discharge flow of the leachate.

[0058] The in-situ dehydration system for stock garbage based on air foam displacement provided by the present invention has complete functions, fast splicing, strong mobility, is applicable to various types of domestic garbage landfills, and has high promotion value.

[0059] In some embodiments, a surfactant is used as the foaming agent. Surfactants are key to foam generation. They reduce the surface tension of the liquid, allowing air to more easily enter the liquid and become encapsulated by the liquid film, forming bubbles that then aggregate into foam. Surfactants can specifically include anionic surfactants such as sodium lauryl sulfate, sodium lauryl polyoxyethylene ether sulfate, sodium α-olefin sulfonate, fatty acid soaps, and ammonium lauryl polyether sulfate. Surfactants can also include zwitterionic surfactants, nonionic surfactants, and cationic surfactants. In this embodiment, the foaming agent is sodium dodecyl sulfate (SDS), a surfactant whose molecular structure effectively reduces the surface tension of the leachate. The mass concentration of the SDS surfactant is between 0.05% and 0.2%. Concentrations below 0.05% result in insufficient foam stability and poor displacement efficiency. Concentrations above 0.2% result in excessively high viscosity and dense foam, hindering foam migration and leachate drainage. Figure 6 The figure shows the morphology of the foam produced by solutions with SDS concentrations of 0.1%, 0.2% and 0.5%. As can be seen from the figure, the foam of the 0.5% SDS solution is finer. The SDS concentration determines the size distribution and stability of the generated foam by regulating the liquid film properties and solution viscosity. The optimal concentration range is 0.05%-0.2%. The size and stability of the foam produced are well matched to the pore structure of the garbage pile, ensuring that the foam has good generation ability, moderate effective blocking and driving effects, and key migration ability, thereby maximizing the net drainage efficiency. Too low a concentration will result in ineffective foam; too high a concentration will seriously damage its fluidity due to the generation of overly fine and high-viscosity foam, resulting in a decrease in displacement efficiency and even hindering drainage. Figure 7 The highest net drainage volume and short drainage time at 0.1% concentration are direct manifestations of this optimal matching and efficient displacement-migration process.

[0060] Please also refer to Figure 7 As shown in the figure, it shows the drainage volume generated by treating the garbage pile 11 with different SDS concentration solutions. It can be seen from the figure that using 0.1% concentration SDS solution, the drainage is completed in about 2 hours, and about 14.96m 3 , in which the SDS solution introduced is about 2.43m 3 The net displacement is about 12.53 m 3 The net drainage volume increased by 29.7% compared with the case of air displacement only. With 0.2% concentration of SDS solution, drainage was completed in about 4 hours, discharging about 10.47m 3 , in which the SDS solution introduced is about 3.98m 3 , the net displacement can be calculated by subtracting the two to be approximately 6.89 m 3, the time to complete drainage was increased by 33.3% compared to the case of air displacement alone. However, the 0.5% SDS solution performed poorly in both treatment time and drainage volume. Compared to air displacement alone, the 0.1% SDS solution had better drainage time and drainage volume. The 0.2% SDS solution shortened drainage time compared to air displacement alone, but the drainage volume was reduced.

[0061] In one embodiment, the concentration of the SDS surfactant is preferably 0.1%. The prepared SDS surfactant of appropriate concentration is stored in the foaming agent storage tank 4. When air foam needs to be injected into the vertical shaft 15, the air compressor 1 and the foaming agent storage tank 4 respectively inject air and foaming agent into the foam generator 5, so that the air and foaming agent mix in the foam generator 5 to generate the air foam. The foam generator 5 is connected to the vertical shaft 15 to inject the air foam into the vertical shaft 15.

[0062] Please continue reading Figure 1 As shown, the method further includes sealing and covering the surface of the garbage dump 11. Specifically, the sealing and covering process includes covering the surface of the garbage dump 11 with a geomembrane and covering the geomembrane with a soil layer. The geomembrane and the soil layer covering the geomembrane constitute a covering layer 13. The covering layer 13 forms a physical seal, preventing gas escape and rainwater infiltration.

[0063] ‌See also Figure 2 As shown, in a specific embodiment, before dehydration treatment, a geomembrane and 0.2 m thick compacted clay are first used to seal the surface of the garbage pile 11; the garbage pile 11 is layered with a length of 10 m as a layer, and a porous well pipe with a length of 15 m and a diameter of 110 mm is quickly inserted into the garbage pile 11 through a rapid vibration construction process to form a vertical shaft 15; the foaming function module mainly composed of an air compressor 1 and a foaming agent storage tank 4, the monitoring function module mainly composed of a flow meter and a sensor, and the post-processing function module mainly composed of a gas-liquid separation device 10 are connected.

[0064] In a specific embodiment, the specific process of the dehydration method is as follows. First, a SDS surfactant solution of a specific concentration is prepared in the foaming agent storage tank 4; then, the air compressor 1 is turned on, and the injection pressure is adjusted by the pressure regulating valve 2. At the same time, the valve of the foaming agent storage tank 4 is opened, and the injection flow rate of the SDS surfactant solution is adjusted by the degree of opening and closing of the valve; the foam generated by the foam generator 5 is injected into the garbage pile 11 through the infiltration hole of the vertical shaft 15. During the air foam displacement process, the wellhead air pressure is measured by the pressure gauge at the wellhead of the vertical shaft 15, and the changes in air pressure and water content during the air foam displacement process are monitored in real time by the pore air pressure sensor 7 and the volume water content sensor 8 in the garbage pile 11. The air injection flow rate and the liquid drainage flow rate are measured respectively by the gas flow meter 3 and the liquid flow meter 9, and the outflowing leachate and toxic gas are separated and treated by the gas-liquid separation device 10 at the drainage port. When the moisture content is less than the moisture content threshold, the valve of the foaming agent storage tank 4 is closed, and only the air compressor 1 is turned on for gas injection. When the gas concentration meets the standard, the 10 m layer of garbage is excavated. Among them, only the gas injection stage has the effect of diluting the gas concentration on the one hand, and on the other hand, it has the effect of further discharging the leachate to further reduce the moisture content. In one embodiment, the moisture content threshold is taken from 25% to 35%, and specifically 30%. The standards for the gas concentration to meet the standard are, for example: CH4 volume fraction <5%, O2 volume fraction >15%, H2S mass concentration <0.1 mg / m 3 The above process can be used to continue processing the garbage in the lower 10 m layer.

[0065] ‌‌See also Figure 1 as well as Figures 5 to 8 As shown in the figure, it is the relevant test data of the air foam displacement test conducted by the applicant in the large-scale model test system independently developed by the applicant. The model tank is 5 m long, 3.8 m wide and 7.5 m high. The landfill structure is as follows from bottom to top: a 10 cm thick insulation layer, a 40 cm thick bottom drainage layer and 11 layers of 320 cm thick garbage pile. Figure 5As shown, the model tank contains one vertical gas injection well, designated IW, and eight monitoring wells, designated M1 through M8. The vertical injection well is constructed of galvanized stainless steel, with an inner diameter of 100 mm and a length of 3.3 m. A 3-meter-long hole with an 8 mm diameter is drilled at the bottom. Monitoring wells are spaced 1 m apart along the transverse lines and 0.7 m apart perpendicular to the transverse lines. No well casing is lowered into any of the monitoring wells; instead, sensors are buried at designated depths. Specifically, along the transverse lines (i.e., M1, M2, M7, and M8), pore pressure sensors 7 and volumetric water content sensors 8 are buried in a double layer, at depths of 1.6 m and 2.4 m, respectively. Vertically along the transverse lines (i.e., M3, M4, M5, and M6), pore pressure sensors 7 and volumetric water content sensors 8 are buried in a single layer, at a depth of 1.6 m. A total of nine pore pressure sensors and twelve water content sensors are buried. After all sensors were embedded, the surface of the garbage pile 11 was sealed to ensure airtightness during subsequent testing. This involved first laying a 1.5 mm thick layer of HDPE (High Density Polyethylene) geomembrane and welding it to the geomembranes on the model's walls. This was then covered with a 0.3 cm layer of compacted sandy soil. Furthermore, to prevent the cover from lifting during subsequent high-pressure gas injection, a top layer of at least 20 kPa was added.

[0066] The large-scale model test system uses a screw air compressor 1 with specifications of 45 kW power, 0.8 MPa pressure, and 7.1 m3 flow rate. 3 / min, used in conjunction with a distribution box and pressure regulating valve 2 as the power supply for air. A movable water tank serves as the water source for reinjection and also helps control the liquid level after reinjection. Two liquid flow meters installed at the east and west openings record liquid flow during the injection and free drainage phases. A digital pressure gauge installed at the IW wellhead monitors gas pressure at the wellhead during high-pressure gas injection. A computer also collects data from various sensors in real time.

[0067] The air-foam flooding test first refilled the model trough with clean water through the west bottom opening of the water tank to a depth of 0.2 m below the surface of the landfill. The water inlet on this side was then closed. The trough was then left to stand for 8 hours to allow the pores within the landfill to open up and the previously stagnant water to connect and form a series of connected sheets. The east and west openings were then opened simultaneously, allowing the water in the model trough to drain freely under gravity until no more water escaped. This completed the pretreatment phase of the experiment, providing the conditions for conducting the air-foam flooding test at an initial field capacity.

[0068] On this basis, high-pressure foam injection is performed into the waste pile through a vertical shaft in the center of the model tank to further displace the water. First, a 0.1% SDS surfactant solution is prepared in a storage tank. Then, air compressor 1 is turned on, and the injection pressure is adjusted to 10 kPa using pressure regulating valve 2. Simultaneously, the valve of foaming agent storage tank 4 is opened, and the injection flow rate of the SDS surfactant solution is adjusted by the degree of opening and closing of the valve. Foam generated by foam generator 5 is injected into waste pile 11 through the opening section of vertical shaft 15. During the air foam displacement process, the air pressure at the wellhead of vertical shaft 15 is measured by a pressure gauge. The changes in air pressure and water content during the air foam displacement process are monitored in real time using pore air pressure sensor 7 and volumetric water content sensor 8 within waste pile 11. The air injection flow rate and liquid discharge flow rate are measured using gas flowmeter 3 and liquid flowmeter 9, respectively. The outflowing leachate and toxic gases are separated and treated using a gas-liquid separation device 10 at the discharge outlet. When the moisture content of the garbage pile 11 drops to a preset target or no water flows out under the current gas injection pressure, the air compressor 1 and the storage tank valve are closed to end the dehydration.

[0069] Please refer to Figure 8, where Figure 8 Figure (a) shows the volumetric water content distribution after air foam flooding treatment with an injection pressure of 10 kPa and a 0.1% mass concentration of SDS surfactant solution. Figure 8 Figure (b) shows the volumetric moisture content distribution after air displacement alone. This comparison shows that the air foam displacement solution of the present invention further reduces the volumetric moisture content of the garbage pile 11 and achieves more uniform dehydration across the entire pile, effectively improving the dehydration of the heterogeneous garbage pile 11.

[0070] It can be seen from the above description of the specific embodiments that the above technical solution has the following technical effects.

[0071] On the one hand, the surfactant in the air foam can reduce the surface tension of the leachate and promote the stripping and migration of residual leachate. On the other hand, due to the large plugging pressure difference formed by the foam drive, it can displace the water in some small pores, thereby achieving a lower residual saturation, so that the moisture content can be further reduced on the basis of the field water holding rate.

[0072] Air foam forms viscoelastic fluid in high permeability areas, selectively blocks large pores or cracks, and forces subsequent injected fluids to turn to low permeability areas, which can effectively improve the dehydration effect of heterogeneous garbage piles.

[0073] Air foaming is a displacement process that creates a high pressure differential between the two ends. The foam propels forward through the waste pile like a piston, rather than simply flowing under gravity. This results in higher dewatering efficiency. It effectively displaces waste within the vertical shaft opening, regardless of the water level.

[0074] During the movement of air bubbles, the leachate and harmful gases in large and small pores are driven to the outlet together. By adding a liquid-gas separation device at the outlet, the leachate and toxic gases can be treated separately, solving potential safety hazards in the subsequent construction process.

[0075] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in the present invention should be included in the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be based on the scope of protection of the claims.

Claims

1. An in-situ dehydration method for stock garbage based on air foam displacement, used for dehydrating garbage piles in landfills, characterized in that: The method comprises: A vertical shaft is driven into the garbage pile, wherein a plurality of infiltration holes are provided on the peripheral wall of the vertical shaft; Injecting air foam into the vertical shaft, the air foam moves along the vertical shaft and displaces the leachate in the garbage pile through the infiltration holes; detecting whether the water content of the garbage pile within a preset depth is less than a preset water content threshold; if so, stopping the injection of air foam into the shaft and injecting air into the shaft to dilute the gas concentration and force the leachate to be further discharged; and Detect whether the gas concentration reaches a preset standard threshold; if so, stop injecting air into the shaft.

2. The method for in-situ dehydration of stock garbage based on air foam displacement according to claim 1, characterized in that: Injecting air foam into the shaft specifically includes: disposing a foam generator connected to the vertical shaft; and An air compressor and a foaming agent storage tank are configured to inject air and foaming agent into the foam generator respectively, so that the air and the foaming agent are mixed in the foam generator to generate the air foam.

3. The method for in-situ dehydration of stock garbage based on air foam displacement according to claim 2, characterized in that: The foaming agent is SDS surfactant.

4. The method for in-situ dehydration of stock garbage based on air foam displacement according to claim 3, characterized in that: The concentration of the SDS surfactant is 0.05% to 0.2%.

5. The method for in-situ dehydration of stock garbage based on air foam displacement according to claim 2 or 3, characterized in that: A porous sponge foaming layer and a porous baffle for supporting the porous sponge foaming layer are arranged in the foam generator.

6. The method for in-situ dehydration of stock garbage based on air foam displacement according to claim 5, characterized in that: The foam generator is provided with a transparent observation window to facilitate observation of the air foam therein.

7. The method for in-situ dehydration of stock garbage based on air foam displacement according to claim 1, characterized in that: The method further comprises performing a sealing and covering treatment on the surface of the garbage pile.

8. The method for in-situ dehydration of stock garbage based on air foam displacement according to claim 7, characterized in that: The sealing and covering treatment includes covering the surface of the garbage dump with a geomembrane and covering the geomembrane with a soil layer.

9. The method for in-situ dehydration of stock garbage based on air foam displacement according to claim 1, characterized in that: The water content threshold is set between 25% and 35%, and the standard thresholds include: CH4 volume fraction <5%, O2 volume fraction >15%, and H2S mass concentration <0.1 mg / m 3 .

10. The method for in-situ dehydration of stock garbage based on air foam displacement according to claim 1, characterized in that: The method further comprises arranging a gas-liquid separation device on a drainage pipeline for discharging the gas-liquid mixture from the garbage dump to separate the leachate and the gas.

11. An in-situ dehydration system for stock waste based on air foam displacement, characterized in that: The system uses the method described in any one of claims 1 to 10 to dehydrate the garbage pile in the landfill.

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