Stock garbage in-situ dehydration method and system based on air foam displacement

Abstract

The invention provides a stock garbage in-situ dehydration method and system based on air foam displacement. The method is used for carrying out dehydration treatment on the refuse heap of the refuse landfill. The method comprises the steps that a vertical shaft is hit into a garbage heap, and a plurality of percolation holes are formed in the peripheral wall of the vertical shaft; air foam is injected into the vertical shaft, and the air foam moves along the vertical shaft and displaces percolate in the garbage heap through the percolation holes; detecting whether the water content of the garbage heap in the preset depth is smaller than a preset water content threshold value or not; if yes, air foam injection into the vertical shaft is stopped, and air is injected into the vertical shaft; detecting whether the gas concentration reaches a preset standard threshold value or not; if yes, air injection into the vertical shaft is stopped. According to the stored garbage in-situ dehydration method and system based on air foam displacement, the water content of the garbage heap can be further reduced, the dehydration effect of the heterogeneous garbage heap can be effectively improved, and meanwhile harmful gas can be treated.

Description

Technical Field

[0001] The present invention relates to the technical field of garbage treatment, and particularly to a method and system for in-situ dehydration of stockpiled garbage based on air foam displacement. Background Art

[0002] Before the excavation and screening of a stockpiled garbage landfill, it is usually necessary to perform in-situ treatment on the liquid and gas stored therein to reduce the moisture content of the garbage and the odor concentration, and to ensure the safety during the subsequent construction process. The traditional in-situ dehydration technology uses vertical shafts in combination with submersible pumps. The operation of the vertical shafts affects the lateral migration of leachate within a certain range to the wells, and the submersible pumps are used to achieve rapid drainage, so as to reduce the leachate level and moisture content within the affected range. However, through years of on-site application, it has been found that this technology has the following problems: (1) The moisture content of the garbage after being treated by the traditional in-situ dehydration technology is still relatively high, about 45% or so, which greatly limits the subsequent screening efficiency; (2) Affected by the preferential flow effect in the garbage, the moisture content of the garbage after being treated by the traditional in-situ dehydration technology is significantly uneven in spatial distribution, manifested as the water in the small pore areas cannot be effectively discharged; (3) The efficiency of the traditional in-situ dehydration technology is low, especially it has little effect on the garbage in the unsaturated zone above the water level line; (4) The traditional dehydration technology does not intervene in toxic gases such as NH3 and H2S, resulting in a relatively high emission concentration (about 3 - 5 mg / m 3 ) during the subsequent excavation process, which affects the health of construction workers and surrounding residents.

[0003] For this reason, the applicant has proposed a solution to further reduce the moisture content by injecting air, as disclosed in the Chinese patent application for invention with the publication number CN114700342A. The moisture content of the garbage treated by the solution disclosed in the above patent application is further reduced, the odor concentration is further reduced, and the degree of stabilization is improved, creating favorable conditions for the excavation and screening of the garbage. Although the above solution has certain improvements compared with the traditional solution, there are still bottlenecks in its dehydration efficiency and the moisture content of the treated garbage. To obtain better dehydration efficiency and further reduce the moisture content of the treated garbage, it is necessary to seek new breakthroughs in the in-situ dehydration technology of stockpiled garbage.

[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 a method and system for in-situ dehydration of stockpiled garbage based on air foam displacement, which can further reduce the moisture content of the garbage heap body, effectively improve the dehydration effect of the heterogeneous garbage heap body, and simultaneously treat harmful gases.

[0006] To achieve the above object, the present invention adopts the following technical solutions: An in-situ dehydration method for stockpiled waste based on air foam displacement, which is used for dehydrating the waste heap body in a landfill. Wherein, the method includes: Driving vertical wells into the waste heap body, and a plurality of percolation holes are provided on the peripheral wall of the vertical wells; Injecting air foam into the vertical wells, and the air foam moves along the vertical wells and displaces the leachate in the waste heap body through the percolation holes; Detecting whether the moisture content of the waste heap body within a preset depth is less than a preset moisture content threshold; if so, stopping injecting air foam into the vertical wells and injecting air into the vertical wells; and Detecting whether the gas concentration reaches a preset standard threshold; if so, stopping injecting air into the vertical wells.

[0007] Optionally, injecting air foam into the vertical wells specifically includes: Configuring a foam generator connected to the vertical wells; and Configuring an air compressor and a foaming agent storage tank to respectively inject air and foaming agent into the foam generator, so that the air and the foaming agent are mixed in the foam generator to generate the air foam.

[0008] Optionally, the foaming agent is an SDS surfactant.

[0009] Optionally, the concentration of the SDS surfactant is taken from 0.05% to 0.2%.

[0010] Optionally, a porous sponge foaming layer and a porous baffle for supporting the porous sponge foaming layer are arranged in the foam generator.

[0011] Optionally, the foam generator is provided with a transparent observation window to facilitate observing the air foam therein.

[0012] Optionally, the method further includes performing a sealing and covering treatment on the surface of the waste heap body.

[0013] Optionally, the sealing and covering treatment includes covering a geomembrane on the surface of the waste heap body and covering a soil layer on the geomembrane.

[0014] Optionally, the moisture content threshold is taken from 25% to 35%, and the standard threshold includes: CH4 volume fraction < 5%, O2 volume fraction > 15%, H2S mass concentration < 0.1 mg / m 3 .

[0015] Optionally, the method further includes arranging a gas-liquid separation device on the drainage pipeline for discharging the gas-liquid mixture from the waste heap body to separate the leachate and the gas.

[0016] The present invention also adopts the following technical solution: a system for in-situ dewatering of stockpiled waste based on air foam displacement, and the system dehydrates the waste heap in a landfill by using the method described above.

[0017] By adopting the above technical solution, the present invention has the following technical effects.

[0018] On the one hand, the surfactant in the air foam can reduce the surface tension of the leachate, promote the stripping and migration of the residual leachate. On the other hand, due to the large plugging pressure difference formed by foam displacement, part of the water in small pores can be displaced, thus achieving a lower residual saturation, and enabling the water content to be further reduced on the basis of the field water holding capacity.

[0019] The air foam forms a viscoelastic fluid in the high-permeability area, selectively plugs large pores or fractures, and forces the subsequent injected fluid to turn to the low-permeability area, which can effectively improve the dewatering effect of the heterogeneous waste heap.

[0020] Air foam displacement is a displacement behavior with a large pressure difference at both ends. The foam will advance in a piston-like manner in the waste heap, rather than just flowing by gravity. Therefore, there will be a higher dewatering efficiency. It can effectively displace the waste within the open-hole section of the shaft well pipe and is not restricted by the water level line.

[0021] During the movement of the air foam, the leachate and harmful gases in both large and small pores are displaced to the outlet position together. By adding a liquid-gas separation device at the outlet, the separate treatment of leachate and toxic gases can be realized, solving the potential safety hazards in the subsequent construction process. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] 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 described below only relate to some embodiments of the present invention and do not limit the present invention.

[0023] Figure 1 It is a schematic diagram of an embodiment of the system for in-situ dewatering of stockpiled waste based on air foam displacement of the present invention.

[0024] Figure 2 It is a flowchart of an embodiment of the method for in-situ dewatering of stockpiled waste based on air foam displacement of the present invention.

[0025] Figure 3 It is a three-dimensional combination diagram of a foam generator in an embodiment of the system for in-situ dewatering of stockpiled waste based on air foam displacement of the present invention.

[0026] Figure 4It is a cross-sectional view of a foam generator in an embodiment of the in-situ dewatering system for stockpiled waste based on air foam displacement of the present invention.

[0027] Figure 5 It is a schematic diagram of the distribution of injection wells and monitoring wells in a test model of the in-situ dewatering method for stockpiled waste based on air foam displacement of the present invention.

[0028] Figure 6 It is a real-shot picture of foams with different SDS concentrations in a refuse heap body in a test model of the in-situ dewatering method for stockpiled waste based on air foam displacement of the present invention.

[0029] Figure 7 It is a drainage volume curve graph at different SDS concentrations in a test model of the in-situ dewatering method for stockpiled waste based on air foam displacement of the present invention.

[0030] Figure 8 It is a comparative graph of the volume moisture content distribution between the test of the in-situ dewatering method for stockpiled waste based on air foam displacement of the present invention and the air displacement test.

[0031] Explanation of reference numerals: 1 - air compressor; 2 - pressure regulating valve; 3 - gas flowmeter; 4 - foaming agent storage tank; 5 - foam generator; 501 - air inlet; 502 - liquid inlet; 503 - foam outlet; 504 - transparent observation window; 505 - foam chamber; 51 - porous sponge foaming layer; 52 - porous baffle; 6 - data acquisition terminal; 7 - pressure sensor; 8 - moisture content sensor; 9 - liquid flowmeter; 10 - gas-liquid separation device; 11 - refuse heap body; 12 - drainage layer; 13 - covering layer; 15 - shaft. Detailed implementation manners

[0032] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the present invention will be further described in detail below with reference to the drawings. Components of the embodiments of the present invention described and illustrated in the drawings here can be arranged and designed in various different configurations. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the scope of protection of the present invention.

[0033] It should be noted that similar reference numerals and letters denote similar items in the following drawings. Therefore, once an item is defined in one drawing, it does not need to be further defined and explained in subsequent drawings.

[0034] Unless otherwise defined, the technical terms or scientific terms used in this patent document shall have the ordinary meanings as understood by those of ordinary skill in the art to which this invention pertains. The terms "first", "second" and similar terms used in the description of the present invention and the claims do not denote any order, quantity or importance, but are only used to distinguish different components. Similarly, the terms "a", "an" or "the" and similar terms do not denote a quantity limitation, but mean that there is at least one. The terms "comprising" or "including" and similar terms mean that the elements or objects appearing before "comprising" or "including" cover the elements or objects listed after "comprising" or "including" and their equivalents, and do not exclude other elements or objects. The terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc. are only used to indicate relative positional relationships. When the absolute position of the object being described changes, the relative positional relationship may also change accordingly. They are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and thus should not be construed as a limitation on the present invention.

[0035] In the description of the present invention, it should be noted that unless otherwise clearly specified and defined, the terms "mounted", "connected" and "coupled" shall be construed in a broad sense. For example, it may be a fixed connection, a detachable connection, or an integral connection; it may be a mechanical connection or an electrical connection; it may be directly connected or indirectly connected through an intermediate medium, and it may be the communication inside two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0036] The following will describe in detail some embodiments of the present invention with reference to the accompanying drawings. Without conflict, the features in the following embodiments may be combined with each other.

[0037] Traditional in-situ dewatering technology uses vertical shafts in combination with submersible pumps. When the vertical shafts are in operation, the leachate within the affected range laterally migrates into the shafts, and is rapidly pumped out through the submersible pumps, so as to achieve the purpose of reducing the leachate level and water content within the affected range. However, the traditional in-situ dewatering technology still has the following deficiencies.

[0038] Due to the fact that traditional in-situ dehydration technology only drains under gravity, the water content of the treated garbage is high. Specifically, traditional in-situ dehydration technology allows the leachate in the landfill body to laterally migrate to the vertical shaft under the action of gravity and be pumped out by the submersible pump at the bottom of the shaft. The water content of the treated garbage can only be reduced to the field water holding capacity (about 45%) theoretically. This is still relatively high for the implementation of landfill body excavation and subsequent garbage screening. Existing research shows that the screening efficiency is negatively correlated with the water content of the material. Some research through screening tests on aged garbage with an age of 10 to 14 years shows that when the water content is reduced from 45% to 30%, the separation efficiency increases from an average of 72.29% to an average of 92.28%.

[0039] Affected by the preferential flow effect, traditional in-situ dehydration technology cannot effectively drain the water in the small pore area, resulting in significant non-uniformity in the spatial distribution of the water content after treatment. Existing research shows that garbage is a typical dual-porosity medium, which contains large pore areas (fracture domains) and small pore areas (matrix domains). During the traditional vertical shaft pumping process, the water in the large pore area will laterally migrate to the vertical shaft under the action of gravity and be pumped out, while the water in the small pore area is hardly affected. This will lead to significant non-uniformity in the spatial distribution of the water content after treatment.

[0040] The efficiency of traditional in-situ dehydration technology is low, especially having little impact on the garbage in the unsaturated zone above the water level line. Traditional vertical shaft pumping has little effect on the water content of the garbage above the water level line, and it is very difficult to further dehydrate this part of the garbage. In addition, the vertical shaft pumping project carried out in the landfill usually lasts for several weeks to several months, resulting in high treatment costs.

[0041] Traditional in-situ dehydration technology cannot handle toxic gases simultaneously, posing safety hazards during the excavation process. The main purpose of traditional in-situ dehydration technology is to pump water, and at the same time, it may also draw out a small part of toxic gases incidentally, but it cannot effectively collect a larger part of toxic gases, which poses a risk of toxic gas dispersion during the subsequent excavation process.

[0042] To address the above deficiencies, the present invention proposes an in-situ dehydration method and system for stockpiled garbage based on air foam displacement. Please refer to Figure 1 and Figure 2 As shown, the in-situ dehydration method for stockpiled garbage based on air foam displacement provided by the present invention is used to dehydrate the garbage landfill body 11, and the method includes: Driving a vertical shaft 15 into the garbage landfill body 11, and a plurality of percolation holes are provided on the peripheral wall of the vertical shaft 15; Injecting air foam into the vertical shaft 15, and the air foam moves along the vertical shaft 15 and displaces the leachate in the garbage landfill body 11 through the percolation holes; Detect whether the water content of the landfill body 11 within a preset depth is less than a preset water content threshold; if so, stop injecting air foam into the shaft 15 and inject air into the shaft 15; and Detect whether the gas concentration reaches a preset standard threshold; if so, stop injecting air into the shaft 15.

[0043] On the one hand, the surfactant in the air foam can reduce the surface tension of the leachate, promote the stripping and migration of the residual leachate. On the other hand, due to the large plugging pressure difference formed by foam flooding, it can displace the water in some small pores, thus achieving a lower residual saturation, enabling the water content to be further reduced on the basis of the field water holding capacity. The air foam forms a viscoelastic fluid in the high-permeability area, selectively plugs the large pores or fractures, forcing the subsequent injected fluid to turn to the low-permeability area, which can effectively improve the dehydration effect of the heterogeneous landfill body 11. The movement of the air foam is a displacement behavior that will form a relatively high pressure difference. The foam will advance in a piston-like manner in the landfill body 11, rather than just flowing by itself under the action of gravity, so there will be a higher dehydration efficiency. It can effectively displace the garbage within the range of the open-hole section of the shaft 15 of the shaft 15 without being restricted by the water level line. During the movement of the air foam, the leachate and harmful gases in both large and small pores are displaced to the outlet position together. By adding a liquid-gas separation device at the outlet, the separate treatment of the leachate and toxic gases can be realized, solving the potential safety hazards in the subsequent construction process.

[0044] As Figure 1 shown, a system for dehydrating the landfill body 11 of 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 water content sensor 8, a liquid flow meter 9, a liquid-gas separation device 10, and a shaft 15 driven into the landfill body 11.

[0045] The air compressor 1 is connected to the foam generator 5 through an air inlet pipeline to supply air to the foam generator 5. The pressure regulating valve 2 and the gas flow meter 3 are arranged on the air inlet pipeline to regulate and monitor the flow rate of the air input into the foam generator 5. The foaming agent storage tank 4 is connected to the foam generator 5 through a liquid inlet pipeline to supply foaming agent to the foam generator 5.

[0046] Please refer to Figure 3 and Figure 4As shown, correspondingly, the foam generator 5 has an air inlet 501 for connecting the air inlet pipeline and a liquid inlet 502 for connecting the liquid inlet pipeline. A porous sponge foaming layer 51 and a porous baffle 52 for supporting the porous sponge foaming layer 51 are arranged in the foam generator 5. The gas and the foaming agent solution are sheared and mixed through the porous sponge foaming layer 51 to form uniform and stable air foam. The porous baffle 52 prevents the displacement of the foaming layer and promotes turbulence, thereby improving the foaming efficiency. A foam chamber 505 is arranged in the foam generator 5. The foam chamber 505 is located downstream of the porous sponge foaming layer 51 and the porous baffle 52 for the air foam formed by the air and the 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 the observation of the air foam therein. In this embodiment, the peripheral wall of the foam chamber 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 connecting to the vertical shaft 15 for injecting the air foam generated by the foam generator 5 into the vertical shaft 15.

[0047] The vertical shaft 15, that is, the injection well, is provided with a plurality of percolation holes on its peripheral wall to enable the leachate seeping out from the surrounding landfill body 11 to enter the vertical shaft 15 through the percolation holes. A plurality of monitoring wells are also arranged in the landfill body 11, and sensors are arranged in the monitoring wells to monitor the gas and liquid amounts in the landfill body 11. In this embodiment, the sensors in the monitoring wells include a pressure sensor 7 and a moisture content sensor 8. The pressure sensor 7 is used to collect the air pressure at its location, and the moisture content sensor 8 is used to collect the moisture content at its location. The pressure sensor 7 and the moisture content sensor 8 are connected to a data acquisition terminal 6 to transmit the collected air pressure and moisture content data to the data acquisition terminal 6 for facilitating the monitoring and control of the dehydration process. The gas-liquid separation device 10 is connected to a drainage layer 12 in the landfill body 11 through a drainage pipeline for separating the discharged gas and leachate. A liquid flowmeter 9 is arranged on the drainage pipeline to monitor the discharge flow rate of the leachate.

[0048] The in-situ dehydration system for stockpiled waste based on air foam displacement provided by the present invention has complete functions, fast splicing, strong mobility, is applicable to various domestic landfill sites, and has high popularization value.

[0049] In some embodiments, the foaming agent is a surfactant. Surfactants are key substances for generating foam. By reducing the surface tension of the liquid, they enable air to more easily enter the liquid and be wrapped by the liquid film to form bubbles, which then aggregate into foam. Surfactants can specifically include anionic surfactants such as sodium dodecyl sulfate, sodium dodecyl polyoxyethylene ether sulfate, α-olefin sulfonate, fatty acid soap, ammonium lauryl polyether sulfate, etc.; surfactants can also include zwitterionic surfactants, nonionic surfactants, cationic surfactants, etc. In this embodiment, the foaming agent uses SDS (sodium dodecyl sulfate) surfactant, and its molecular structure can effectively reduce the surface tension of the leachate. The mass concentration of the SDS surfactant is taken from 0.05% to 0.2%. When the concentration is lower than 0.05%, the foam stability is insufficient and the displacement effect is poor. When the concentration is higher than 0.2%, due to the too high viscosity and the dense foam generated, it hinders the foam migration and the discharge of the leachate. Figure 6 The morphologies of the foams generated by the solutions with SDS concentrations of 0.1%, 0.2% and 0.5% are shown. It can be seen from the figure that for the SDS solution with a concentration of 0.5%, the foam is finer. The SDS concentration determines the size distribution and stability of the generated foam by regulating the properties of the liquid film and the solution viscosity. The optimal concentration range is 0.05% - 0.2%, and the generated foam achieves a better match with the pore structure of the landfill body in terms of size and stability, ensuring that the foam has good generation ability, moderate effective plugging and driving effects, and key migration ability, thus maximizing the net drainage efficiency. Too low a concentration results in ineffective foam; too high a concentration seriously damages its fluidity due to the generation of overly fine and high-viscosity foam, leading to a decrease in displacement efficiency and even hindering drainage. Figure 7 The highest net drainage volume and shorter drainage time at a concentration of 0.1% are a direct manifestation of this optimal matching and efficient displacement-migration process.

[0050] Please refer to Figure 7 as shown, which shows the drainage volumes of the landfill body 11 treated with SDS solutions of different concentrations. It can be seen from the figure that when using the SDS solution with a concentration of 0.1%, the drainage is completed in about 2 hours, and about 14.96 m 3 is discharged, and about 2.43 m 3 of the SDS solution is introduced. Subtracting the two can calculate the net drainage volume to be about 12.53 m 3 . The net drainage volume increases by 29.7% compared to the case of only air displacement; when using the SDS solution with a concentration of 0.2%, the drainage is completed in about 4 hours, and about 10.47 m 3 is discharged, and about 3.98 m 3 of the SDS solution is introduced. Subtracting the two can calculate the net drainage volume to be about 6.89 m 3The time to complete drainage increased by 33.3% compared to the case of only using air displacement. Using an SDS solution with a concentration of 0.5% showed poorer performance in terms of treatment time and drainage volume. Compared to the case of only using air displacement, using an SDS solution with a concentration of 0.1% had better drainage time and drainage volume; using an SDS solution with a concentration of 0.2% shortened the drainage time compared to the case of only using air displacement, but the drainage volume decreased.

[0051] In one embodiment, preferably, the concentration of the SDS surfactant is 0.1%. The properly configured SDS surfactant with the appropriate concentration is stored in the foaming agent storage tank 4. When air foam needs to be injected into the shaft 15, air and the foaming agent are respectively injected into the foam generator 5 by the air compressor 1 and the foaming agent storage tank 4, so that the air and the foaming agent are mixed in the foam generator 5 to generate the air foam. The foam generator 5 is connected to the shaft 15 to inject the air foam into the shaft 15.

[0052] Please continue to refer to Figure 1 As shown, the method further includes performing a sealing and covering treatment on the surface of the garbage heap body 11. Specifically, the sealing and covering treatment includes covering a geomembrane on the surface of the garbage heap body 11 and covering a soil layer on the geomembrane. The geomembrane and the soil layer covered thereon form a covering layer 13. Setting the covering layer 13 can form a physical seal, playing roles such as blocking gas dissipation and preventing rainwater from infiltrating.

[0053] Please refer to Figure 2 As shown, in a specific embodiment, before the dehydration treatment, first, the surface of the garbage heap body 11 is sealed with a geomembrane and 0.2 m thick compacted clay; the garbage heap body 11 is stratified with 10 m as one layer, and a porous well pipe with a length of 15 m and a diameter of 110 mm is quickly inserted into the garbage heap body 11 through a rapid vibroflotation construction process to form a shaft 15; the injection foam functional module mainly composed of the air compressor 1 and the foaming agent storage tank 4, etc., the monitoring functional module mainly composed of a flow meter and sensors, etc., and the post-treatment functional module mainly composed of the gas-liquid separation device 10, etc. are connected.

[0054] In a specific embodiment, the specific process of the dehydration method is as follows. First, prepare an SDS surfactant solution with a specific concentration in the foaming agent storage tank 4; then, turn on the air compressor 1, adjust the injection pressure through the pressure regulating valve 2, and at the same time open the valve of the foaming agent storage tank 4, and adjust the injection flow rate of the SDS surfactant solution by the degree of valve opening and closing; the foam generated by the foam generator 5 is injected into the landfill body 11 through the percolation holes of the vertical shaft 15. During the air foam displacement process, measure the wellhead air pressure through the pressure gauge at the wellhead of the vertical shaft 15, and monitor the changes in air pressure and moisture content during the air foam displacement process in real time through the pore gas pressure sensor 7 and the volumetric moisture content sensor 8 in the landfill body 11. Measure the air injection flow rate and the liquid drainage flow rate through the gas flow meter 3 and the liquid flow meter 9 respectively, and perform separate treatment of the outflowing leachate and toxic gas through the gas-liquid separation device 10 at the drainage port. When the moisture content is less than the moisture content threshold, close the valve of the foaming agent storage tank 4 and only turn on the air compressor 1 for air injection. When the gas concentration reaches the standard, excavate 10 m of garbage in this layer. Among them, only during the air injection stage, on the one hand, it has the effect of diluting the gas concentration, 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%, for example, 30%. The standard for the gas concentration to reach the standard is, for example: the volume fraction of CH4 < 5%, the volume fraction of O2 > 15%, and the mass concentration of H2S < 0.1 mg / m 3 . The following 10 m of garbage can be processed continuously according to the above process.

[0055] Please refer to Figure 1 and Figures 5 to 8 as shown. These are the relevant test data of the air foam displacement test carried out by the applicant in the large-scale model test system independently developed by it. The model tank is 5 m long, 3.8 m wide, and 7.5 m high. The landfill structure from bottom to top is successively: a 10-cm-thick insulation layer, a 40-cm-thick bottom drainage layer, and a 320-cm-thick landfill body 11 layer. As Figure 5As shown in the figure, a total of 1 vertical gas injection well is drilled in the model tank, denoted as IW, and 8 monitoring wells, denoted as M1 to M8 respectively. Among them, the vertical gas injection well is made of galvanized stainless steel, with an inner diameter of 100 mm, a length of 3.3 m, and the bottom 3 m is perforated with a pore diameter of 8 mm. The interval of the monitoring wells along the transverse survey line is 1 m, and the interval perpendicular to the transverse survey line is 0.7 m. No well pipes are lowered in all the monitoring wells, and only corresponding sensors are buried at the specified depths. Specifically: the pore air pressure sensors 7 and volumetric water content sensors 8 on the transverse survey line (i.e., M1, M2, M7, and M8) are buried in two layers, and the depths of the two layers are 1.6 m and 2.4 m respectively; the pore air pressure sensors 7 and volumetric water content sensors 8 perpendicular to the transverse survey line (i.e., M3, M4, M5, and M6) are buried in a single layer with a depth of 1.6 m. A total of 9 pore air pressure sensors and 12 water content sensors are buried. After all the sensors are buried, the surface of the garbage dump body 11 is sealed to ensure that the model has good airtightness during subsequent tests. Specifically, it includes first laying a 1.5 mm thick HDPE (High Density Polyethylene) geomembrane and welding it with the geomembranes on the four surrounding walls of the model. Then, a layer of sandy soil with a compacted thickness of 0.3 cm is covered on it. In addition, in order to prevent the overlying layer from being lifted during the subsequent high-pressure gas injection process, a surcharge layer of at least 20 kPa is added above it.

[0056] A screw air compressor 1 is used in this large-scale model test system, with a specification of power 45 kW, pressure 0.8 MPa, and flow rate 7.1 m 3 / min, which is used as the power equipment for supplying air in cooperation with the distribution box and pressure regulating valve 2. A vertically movable water tank serves as the water source for recharging, and can also assist in regulating the liquid level height after recharging. Two liquid flow meters installed at the openings on the east and west sides are used to record the liquid flow rates during the water injection and free drainage stages. A digital display pressure gauge installed at the wellhead of the IW well is used to monitor the gas pressure at the wellhead during high-pressure gas injection. In addition, a computer is used to collect the data information output by each sensor in real time.

[0057] For the air foam displacement test, first, water is recharged into the model tank through the opening at the bottom on the west side of the water tank to a position 0.2 m below the surface of the garbage dump body, and then the water inlet on that side is closed. Then, it is left standing for 8 h to open the pore channels in the garbage dump body so that the originally clustered stagnant water can be connected in series into sheets. Then, the openings on the east and west sides are opened simultaneously, and the water in the model tank is freely drained under the action of gravity until no water flows out. At this point, the pre-treatment stage of this test has been completed, which provides a condition for the air foam displacement test to be carried out under the condition of the initial state being the field water holding rate.

[0058] On this basis, high-pressure foam injection is carried out into the landfill body through the shaft in the center of the model tank to further displace the moisture therein. First, an SDS surfactant solution with a mass concentration of 0.1% is prepared in the storage tank. Then, the air compressor 1 is started, and the injection pressure is adjusted to 10 kPa through 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 valve opening and closing. The foam generated by the foam generator 5 is injected into the landfill body 11 through the opening section of the shaft 15. During the air foam displacement process, the wellhead air pressure is measured by the pressure gauge at the wellhead of the shaft 15, the air pressure and water content changes during the air foam displacement process are monitored in real time by the pore air pressure sensor 7 and the volumetric water content sensor 8 in the landfill body 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 effluent leachate and toxic gases are treated separately by the gas-liquid separation device 10 at the drainage port. When the water content of the landfill body 11 is reduced to the preset target or no water flows out under the current injection pressure, the air compressor 1 and the storage tank valve are closed to end the dehydration.

[0059] Please refer to Figure 8, in which Figure 8 Figure (a) is the distribution map of the volumetric water content after air foam displacement treatment with an injection pressure of 10 kPa and an SDS surfactant solution with a mass concentration of 0.1%, Figure 8 Figure (b) is the distribution map of the volumetric water content after displacement treatment with only air. It can be seen by comparison that the air foam displacement scheme of the present invention further reduces the volumetric water content of the landfill body 11 and makes the dehydration more uniform everywhere, effectively improving the dehydration effect of the heterogeneous landfill body 11.

[0060] From the description of the specific embodiments above, it can be seen that by adopting the above technical solutions, the following technical effects are achieved.

[0061] On the one hand, the surfactant in the air foam can reduce the surface tension of the leachate, promote the stripping and migration of the residual leachate. On the other hand, due to the large plugging pressure difference formed by foam displacement, it can displace the water in some small pores, thus reaching a lower residual saturation and enabling the water content to be further reduced on the basis of the field water holding capacity.

[0062] The air foam forms a viscoelastic fluid in the high-permeability area, selectively plugs the large pores or fractures, and forces the subsequent injected fluid to turn to the low-permeability area, which can effectively improve the dehydration effect of the heterogeneous landfill body.

[0063] 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.

[0064] 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.

[0065] 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 stockpiled waste based on air foam displacement, which is used for dehydrating the waste heap in a landfill site, is characterized in that, The method includes: Driving vertical shafts into the waste landfill body, and a plurality of percolation holes are provided on the peripheral wall of the vertical shafts; Injecting air foam into the vertical shafts, and the air foam moves along the vertical shafts and displaces the leachate in the waste landfill body through the percolation holes; Detecting whether the moisture content of the waste landfill body within a preset depth is less than a preset moisture content threshold; if so, stopping injecting air foam into the vertical shafts and injecting air into the vertical shafts; and Detecting whether the gas concentration reaches a preset standard threshold; if so, stopping injecting air into the vertical shafts.

2. The in-situ dewatering method for stockpiled waste based on air foam displacement according to claim 1, characterized in that, Injecting air foam into the vertical shafts specifically includes: Configuring a foam generator connected to the vertical shafts; and Configuring an air compressor and a foaming agent storage tank to respectively inject air and foaming agent into the foam generator, so that the air and the foaming agent are mixed in the foam generator to generate the air foam.

3. The in-situ dewatering method for stockpiled waste based on air foam displacement according to claim 2, characterized in that The foaming agent is an SDS surfactant.

4. The in-situ dewatering method for stockpiled garbage based on air foam displacement according to claim 3, characterized in that, The concentration of the SDS surfactant ranges from 0.05% to 0.2%.

5. The in-situ dewatering method for stockpiled waste 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 in-situ dewatering method for stockpiled waste based on air foam displacement according to claim 5, characterized in that The foam generator is provided with a transparent observation window for observing the air foam therein.

7. The in-situ dehydration method for stockpiled garbage based on air foam displacement according to claim 1, characterized in that, The method further includes performing a sealing and covering treatment on the surface of the waste landfill body.

8. The in-situ dewatering method for stockpiled waste based on air foam displacement according to claim 7, characterized in that The sealing and covering treatment includes covering a geomembrane on the surface of the waste landfill body and covering a soil layer on the geomembrane.

9. The in-situ dewatering method for stockpiled waste based on air foam displacement according to claim 1, characterized in that The moisture content threshold is taken from 25% to 35%, and the standard thresholds include: CH4 volume fraction < 5%, O2 volume fraction > 15%, H2S mass concentration < 0.1 mg / m 3 .

10. The in-situ dehydration method for stockpiled waste based on air foam displacement according to claim 1, characterized in that The method further includes arranging a gas-liquid separation device on the drainage pipeline for discharging the gas-liquid mixture from the waste landfill body to separate the leachate and the gas.

11. An in-situ dewatering system for stockpiled waste based on air foam displacement, characterized in that, The system dehydrates the waste landfill body of the landfill site by using the method described in any one of claims 1 to 10.

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