Multi-scale experimental device and method for permeating and injecting micron biochar turbid liquid into soil body

Abstract

The invention discloses a multi-scale experimental device and method for permeating and injecting micron biochar turbid liquid into a soil body, and belongs to the technical field of environmental engineering geology. The device comprises a soil column simulation sampling system, a site injection well simulation sampling system, an injection pressure control system, a data acquisition system and a waste liquid collection system which are arranged in parallel; the injection pressure control system provides constant pressure for turbid liquid injection, the data acquisition system acquires seepage parameters such as pore water pressure and flow in real time, and the waste liquid collection system is used for collecting experimental waste liquid. According to the invention, a soil column scale and site injection well scale micron biochar suspension permeation injection simulation experiment can be synchronously carried out, uniform constant-pressure injection of the suspension and lossless sampling of an undisturbed soil sample are realized, and a reliable experiment support is provided for research on a migration-retention-equilibrium dynamic evolution rule of the micron biochar suspension in a soil body; the technical bottlenecks that the prior art lacks a special multi-scale simulation device and experimental working conditions are disjointed from engineering practice are solved.

Description

Technical Field

[0001] This invention belongs to the field of environmental engineering geology technology, and in particular relates to a multi-scale simulation experimental device and method for the infiltration and injection of micron-sized biochar suspension into soil. Background Technology

[0002] Biochar possesses core characteristics such as high carbon stability, well-developed pore structure, excellent adsorption performance, alkalinity, and rich oxygen-containing functional groups, making it highly promising for applications in contaminated soil remediation, soil reinforcement, and soil carbon sequestration and emission reduction. Adding biochar to soil can promote the generation of alkaline substances by adjusting the soil pH, adsorbing and fixing organic pollutants and inhibiting their degradation and transformation, promoting soil particle aggregation to improve soil mechanical strength, and, due to its high carbon stability, enabling long-term carbon sequestration after burial.

[0003] In engineering practice and related research on biochar treatment of soil, the conventional method currently used is mixing. However, this method can only treat shallow soil layers, with limited treatment depth, making it difficult to meet the treatment needs of sites with deep soil layers. Overcoming the technical bottlenecks of difficulty and uneven injection of biochar suspension into soil is a necessary prerequisite for the large-scale application of biochar in soil treatment.

[0004] Employing micron-sized biochar with superior transport capacity and injecting it into deep soil pores via suspension infiltration represents a potential technological direction for solving deep soil treatment challenges. However, currently, the industry lacks dedicated equipment for studying the dynamic evolution of the transport-retention-equilibrium process of micron-sized biochar suspensions injected into soil. Conventional soil column infiltration devices can only conduct single-scale experiments, failing to replicate the actual working conditions of injection wells in the field. Furthermore, they struggle to achieve uniform injection of the suspension, constant pressure simulation, and non-destructive sampling of undisturbed soil samples, leading to significant discrepancies between laboratory research results and engineering practice, thus hindering effective guidance for field construction. Therefore, there is an urgent need to develop a dedicated multi-scale experimental device and method for injecting micron-sized biochar suspensions into soil. Summary of the Invention

[0005] To address the problems existing in the prior art, this invention provides a multi-scale experimental device and method for infiltrating and injecting micron-sized biochar suspension into soil. It can simultaneously conduct simulation experiments at the soil column scale and the site injection well scale, achieving uniform constant pressure injection of micron-sized biochar suspension, real-time monitoring of seepage parameters, and non-destructive sampling of undisturbed soil samples. This provides reliable experimental conditions for studying the dynamic evolution law and mechanism of the migration, retention, and equilibrium of micron-sized biochar suspension infiltrating and injecting into soil, and solves the technical bottlenecks in the prior art, such as the lack of dedicated experimental devices, the inability to achieve multi-scale synchronous simulation, and the disconnect between experimental conditions and engineering reality.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is: a multi-scale experimental device for infiltrating and injecting micron-sized biochar suspension into soil, including an injection pressure control system, a data acquisition system, a waste liquid collection system, a soil column simulation sampling system, and a site injection well simulation sampling system.

[0007] The injection pressure control system is connected to the soil column simulation sampling system and the site injection well simulation sampling system through liquid pipelines, and is used to provide constant gas pressure and stable injection pressure for the injection of micron-sized biochar suspension.

[0008] The data acquisition system is electrically connected to the soil column simulation sampling system and the site injection well simulation sampling system via data transmission lines, and is used to collect and record seepage parameters during the experiment.

[0009] The waste liquid collection system is connected to the soil column simulation sampling system and the site injection well simulation sampling system through liquid pipelines to collect the waste liquid flowing out during the experiment.

[0010] The soil column simulation sampling system and the site injection well simulation sampling system are set up in parallel to conduct simulation experiments of micron-sized biochar suspension infiltration and injection into soil at both the soil column scale and the site injection well scale.

[0011] Furthermore, the soil column simulation sampling system includes a sealing cap, an effluent collector, a first effluent valve, a pore water pressure sensor, a soil sample bucket, an injection liquid disperser, a first injection valve, and a first flow sensor. The soil sample bucket is a vertical cylindrical sealed cavity. The injection liquid disperser is located at the lower end of the soil sample bucket, and the effluent collector is located at the upper end of the soil sample bucket. The sealing cap is detachably and sealed on the top of the soil sample bucket. At least three sets of pore water pressure sensors are provided, evenly spaced along the axial direction of the soil sample bucket, to detect the pore water pressure at different depths of the soil sample. The inlet end of the injection liquid disperser is connected to the injection pressure control system via a liquid pipeline through the first injection valve and the first flow sensor. The outlet end of the effluent collector is connected to the waste liquid collection system via a liquid pipeline through the first effluent valve.

[0012] Furthermore, the injecting liquid disperser has a flat cavity structure with an injection hole in the middle of its side as the liquid inlet, and a number of dispersion holes are evenly distributed on its upper surface to divert the liquid entering through the injection hole into the soil sample bucket; the dispersion holes enable the uniform injection of the suspension at the bottom cross section of the soil sample, avoiding the generation of dominant seepage.

[0013] Furthermore, the effluent collector has a flat cavity structure with an effluent hole in the middle of its side as the effluent outlet. Several collection holes are evenly distributed on its lower plane. The liquid inside the soil sample bucket flows out through each collection hole and is collected and discharged through the effluent hole. The collection holes achieve uniform collection of the seepage liquid and avoid distortion of the seepage field at the top section of the soil sample.

[0014] Furthermore, the site injection well simulation sampling system includes an outer sleeve, an inner sleeve, a second injection hole valve, a second outflow hole valve, and a second flow sensor. The outer sleeve is a sealed cavity, and the inner sleeve is coaxially and detachably installed inside the outer sleeve to hold experimental soil samples. The inner sleeve includes a coaxially nested inner tube and an outer tube. The inner tube has several injection dispersion holes evenly distributed on its wall, and the outer tube has several outflow collection holes evenly distributed on its wall. The liquid inlet end of the inner tube is connected to the injection pressure control system through a liquid pipeline via the second injection hole valve and the second flow sensor. The liquid outlet end of the annulus between the outer tube and the outer sleeve is connected to the waste liquid collection system through a liquid pipeline via the second outflow hole valve, thus recreating the radial seepage conditions of the site injection well.

[0015] Furthermore, the injection pressure control system includes a gas cylinder, a pressure reducing valve, a gas valve, a pressure controller, a gas pipeline, a first suspension container, and a second suspension container. The outlet of the gas cylinder is connected to the gas pipeline via the pressure reducing valve, the gas valve, and the pressure controller. The gas pipeline is sealed to the top of the first suspension container and the second suspension container, respectively. The outlet of the first suspension container is connected to the soil column simulation sampling system, and the outlet of the second suspension container is connected to the site injection well simulation sampling system. The injection pressure is precisely controlled by the pressure controller to achieve stable simulation of constant pressure injection conditions.

[0016] Furthermore, the data acquisition system includes a data acquisition unit, a data transmission line, and a computer; the data acquisition unit is electrically connected to the pore water pressure sensor and the first flow sensor of the soil column simulation sampling system, and the second flow sensor of the site injection well simulation sampling system, respectively, via the data transmission line; the data acquisition unit is also connected to the computer via the data transmission line to transmit the collected seepage parameters to the computer in real time for storage and analysis.

[0017] Furthermore, the waste liquid collection system includes liquid pipelines and waste liquid tanks. The waste liquid tanks are connected to the outlet ends of the soil column simulation sampling system and the site injection well simulation sampling system through the liquid pipelines, so as to realize the centralized collection and treatment of experimental waste liquids.

[0018] The present invention also provides a multi-scale simulation experiment method for the infiltration and injection of micron-sized biochar suspension into soil, which is based on the above-mentioned multi-scale simulation experiment device and includes a soil column scale simulation experiment step and / or a site injection well scale simulation experiment step, which can realize the separate or simultaneous parallel conduct of the two scale experiments.

[0019] Furthermore, the specific steps of the soil column scale simulation experiment include: S11. Experimental preparation: The soil sample to be tested is layered into the soil sample bucket according to the preset dry density, compacted, and then sealed. A micron-sized biochar suspension of the preset concentration is prepared in the first suspension container. The airtightness of the pipeline and valve is checked, and the soil sample is saturated and pretreated.

[0020] S12. Experiment Start-up: Open the gas cylinder, gas valve, first outflow valve and first injection valve, set the preset injection pressure through the pressure controller, and start the constant pressure injection experiment; during the experiment, the detection data of the pore water pressure sensor and the first flow sensor are collected and recorded in real time through the data acquisition device. The acquisition frequency can be preset according to the experimental requirements.

[0021] S13. Experiment Termination: When the cumulative flow detected by the first flow sensor reaches the preset value, or the permeation injection time reaches the preset time, stop the injection and close the first outflow valve and the first injection valve in sequence.

[0022] S14. Undisturbed sampling: Open the sealing cap and slowly open the valve of the first injection hole. Use the stable liquid pressure at the injection end to push the soil sample in the soil sample bucket upwards completely to obtain an undisturbed undisturbed experimental soil sample for subsequent testing and analysis.

[0023] S15. Experimental Conclusion: Close the gas valve and gas cylinder, drain the residual liquid in the pipeline, disassemble and clean all parts of the experimental apparatus for use in subsequent experiments.

[0024] Furthermore, the specific steps of the site injection well-scale simulation experiment include: S21. Experimental preparation: The soil sample to be tested is layered and filled into the annulus between the inner tube and the outer tube of the inner sleeve according to the preset dry density. After compaction, the inner sleeve is sealed and installed in the outer sleeve. A micron-sized biochar suspension of the preset concentration is prepared in the second suspension container. The airtightness of the pipeline and valve is checked, and the soil sample is saturated and pretreated.

[0025] S22. Experiment Start-up: Open the gas cylinder, gas valve, second injection port valve, and second outflow port valve. Set the preset injection pressure through the pressure controller to start the constant pressure injection experiment. During the experiment, the detection data of the second flow sensor is collected and recorded in real time through the data acquisition device. The acquisition frequency can be preset according to the experimental requirements.

[0026] S23. Experiment termination: When the cumulative flow detected by the second flow sensor reaches the preset value, or the permeation injection time reaches the preset time, stop the injection and close the second injection hole valve, the second outflow hole valve, the gas valve and the gas cylinder in sequence.

[0027] S24. Uncirculated Sampling: Open the outer sleeve, remove the inner sleeve, and use a soil sampling ring to take soil samples from the inner sleeve at different radial distances to obtain undisturbed experimental soil samples at different radial positions for subsequent testing and analysis.

[0028] S25. Experimental Conclusion: Drain the residual liquid in the pipeline, disassemble and clean all parts of the experimental apparatus for use in subsequent experiments.

[0029] Compared with the prior art, the present invention has the following advantages: 1. This invention, by setting up a soil column simulation sampling system and a site injection well simulation sampling system in parallel, can conduct single-scale experiments independently, or conduct parallel comparative experiments at the soil column scale and the site injection well scale simultaneously, realizing synchronous simulation of multi-scale working conditions, greatly improving experimental efficiency. At the same time, it restores the transport law of micron-sized biochar suspension under two different engineering scales: one-dimensional seepage in the laboratory and radial seepage in the field, making the experimental results more consistent with engineering reality and providing more reliable experimental basis for the design of on-site construction parameters.

[0030] 2. This invention achieves uniform distribution and stable injection of micron-sized biochar suspension at the soil injection contact surface through the injection liquid disperser in the soil column simulation sampling system and the injection dispersion hole on the inner tube of the site injection well simulation sampling system. This effectively avoids dominant seepage of the suspension in the soil, ensures the uniformity of the seepage field inside the soil, and greatly improves the accuracy and repeatability of experimental results.

[0031] 3. The injection pressure control system of the present invention, through the cooperation of gas cylinder and gas pressure controller, can accurately and stably control the injection gas pressure, realize constant pressure injection of micron biochar suspension, perfectly reproduce the constant pressure injection conditions in the field engineering, and at the same time, the injection pressure can be flexibly adjusted to adapt to the experimental needs of different soils and different working conditions, thereby improving the applicability and experimental controllability of the device.

[0032] 4. This invention can monitor key seepage parameters such as pore water pressure and flow rate in real time and continuously through the data acquisition system, realizing dynamic data acquisition and storage throughout the entire experimental process. This provides complete and continuous data support for the analysis of the dynamic evolution law of the migration-retention-equilibrium of micron-sized biochar suspension in soil, avoiding errors and data interruption problems caused by manual sampling.

[0033] 5. This invention designs dedicated sampling methods for simulation systems of two scales. The soil column simulation sampling system can obtain a complete undisturbed soil column through hydraulic ejection, while the site injection well simulation sampling system can obtain undisturbed soil samples at different locations through radial sampling with a ring cutter. Both sampling methods can effectively avoid disturbance to the soil structure and biochar distribution during the sampling process, ensuring the accuracy of subsequent detection and analysis results. Attached Figure Description

[0034] Figure 1 This is a schematic diagram of the device in an embodiment of the present invention.

[0035] Figure 2 This is a schematic diagram of the structure of the injection liquid disperser in an embodiment of the present invention.

[0036] Figure 3 This is a schematic diagram of the effluent collector in an embodiment of the present invention.

[0037] Figure 4 This is a schematic diagram of the inner sleeve in an embodiment of the present invention.

[0038] In the diagram: I - Soil column simulation sampling system, II - Injection pressure control system, III - Site injection well simulation sampling system, IV - Data acquisition system, V - Waste liquid collection system; 1 - Sealing cap, 2 - Effluent collector, 2-1 - Effluent hole, 2-2 - Collection hole, 3 - First effluent hole valve, 4 - Pore water pressure sensor, 5 - Soil sample container, 6 - Injection liquid disperser, 6-1 - Injection hole, 6-2 - Dispersion hole, 7 - First injection hole valve, 8 - First flow sensor, 9 - First suspension container. 10-Gas cylinder, 11-Pressure reducing valve, 12-Gas valve, 13-Gas pressure controller, 14-Gas pipeline, 15-Second suspension container, 16-Outer sleeve, 17-Inner sleeve, 17-1-Inner tube, 17-2-Outer tube, 17-3-Injection dispersion hole, 17-4-Outflow collection hole, 18-Second injection hole valve, 19-Second outflow hole valve, 20-Second flow sensor, 21-Liquid pipeline, 22-Waste liquid tank, 23-Data acquisition unit, 24-Data transmission line, 25-Computer. Detailed Implementation

[0039] The present invention will be further described below.

[0040] like Figure 1 As shown in the figure, this embodiment discloses a multi-scale simulation experimental device for the infiltration and injection of micron-sized biochar suspension into soil. The core consists of five parts: soil column simulation sampling system I, injection pressure control system II, site injection well simulation sampling system III, data acquisition system IV, and waste liquid collection system V.

[0041] The injection pressure control system II is connected to the soil column simulation sampling system I and the site injection well simulation sampling system III via liquid pipeline 21, providing constant gas pressure and stable injection pressure for the injection of micron-sized biochar suspension. The data acquisition system IV is electrically connected to the soil column simulation sampling system I and the site injection well simulation sampling system III via data transmission line 24, and is used to collect and record seepage parameters during the experiment. The waste liquid collection system V is connected to the soil column simulation sampling system I and the site injection well simulation sampling system III via liquid pipeline 21, and is used to collect waste liquid flowing out during the experiment. The soil column simulation sampling system I and the site injection well simulation sampling system III are set up in parallel, which can simultaneously carry out simulation experiments of micron-sized biochar suspension infiltration injection into soil at the soil column scale and the site injection well scale.

[0042] Specifically, the soil column simulation sampling system I includes a sealing cap 1, an effluent collector 2, a first effluent valve 3, a pore water pressure sensor 4, a soil sample container 5, an injection liquid disperser 6, a first injection valve 7, and a first flow sensor 8. The soil sample container 5 is a vertically shaped, sealed cavity made of plexiglass, with an inner diameter of 100mm and a height of 300mm, suitable for the size requirements of conventional soil column experiments. The injection liquid disperser 6 is located at the lower end of the soil sample container 5, and the effluent collector 2 is located at the upper end of the soil sample container 5. The sealing cap 1 is detachably and securely installed on the top of the soil sample container 5 via threads, ensuring the cavity's airtightness during the experiment. Three sets of pore water pressure sensors 4 are evenly spaced along the axial direction of the soil sample container 5, corresponding to the upper, middle, and lower positions of the soil sample, respectively, to detect changes in pore water pressure at different depths of the soil sample. The inlet end of the injection liquid disperser 6 is connected to the first suspension container 9 of the injection pressure control system II via the liquid pipeline 21, the first injection hole valve 7, and the first flow sensor 8. The outlet end of the outflow liquid collector 2 is connected to the waste liquid tank 22 of the waste liquid collection system V via the liquid pipeline 21 and the outflow hole valve 3.

[0043] like Figure 2 As shown, the injection liquid disperser 6 is a flat circular cavity structure with a diameter matching the inner diameter of the soil sample container 5. An injection hole 6-1 is provided in the middle of its side, and several dispersion holes 6-2 with a diameter of 2 mm are evenly distributed on its upper surface with a hole spacing of 10 mm. The injection hole 6-1 is connected to the liquid pipeline 21. During the experiment, the micron-sized biochar suspension enters the disperser cavity through the injection hole 6-1, and then enters the bottom section of the soil sample evenly through each dispersion hole 6-2, realizing uniform injection across the entire cross section and avoiding excessively fast local flow rates that could lead to dominant seepage.

[0044] like Figure 3As shown, the effluent collector 2 is a flat circular cavity structure with a diameter matching the inner diameter of the soil sample container 5. An effluent hole 2-1 is provided in the middle of its side, and several collection holes 2-2 with a diameter of 2 mm are evenly distributed on its lower plane with a hole spacing of 10 mm. The effluent hole 2-1 is connected to the liquid pipeline 21. The seepage liquid flows evenly into the collector cavity through each collection hole 2-2 and then flows out through the effluent hole 2-1, ensuring the uniformity of the seepage field at the top of the soil sample and avoiding the influence of seepage boundary distortion on the experimental results.

[0045] Specifically, the site injection well simulation sampling system III includes an outer sleeve 16, an inner sleeve 17, a second injection port valve 18, a second outflow port valve 19, and a second flow sensor 20. The outer sleeve 16 is a cylindrical sealed cavity made of stainless steel, with an inner diameter of 300mm and a height of 400mm; the inner sleeve 17 is coaxially and detachably installed inside the outer sleeve 16 and is used to hold experimental soil samples. Figure 4 As shown, the inner sleeve 17 includes a coaxially nested inner tube 17-1 and an outer tube 17-2. The outer diameter of the inner tube 17-1 is 50 mm, and the inner diameter of the outer tube 17-2 is 250 mm. The annulus between the inner tube 17-1 and the outer tube 17-2 is used to fill soil samples to recreate the radial seepage structure between the injection well and the formation. Several injection dispersion holes 17-3 with a diameter of 3 mm are evenly distributed on the wall of the inner tube 17-1, with a hole spacing of 15 mm. Several outflow collection holes 17-4 with a diameter of 3 mm are evenly distributed on the wall of the outer tube 17-2, with a hole spacing of 15 mm. The liquid inlet end of the inner tube 17-1 is connected to the second suspension container 15 of the injection pressure control system II through the liquid pipeline 21 via the second injection hole valve 18 and the second flow sensor 20. The liquid outlet end of the annulus between the outer tube 17-2 and the outer sleeve 16 is connected to the waste liquid tank 22 of the waste liquid collection system V through the liquid pipeline 21 via the second outflow hole valve 19.

[0046] Specifically, the injection pressure control system II includes a gas cylinder 10, a pressure reducing valve 11, a gas valve 12, a gas pressure controller 13, a gas pipeline 14, a first suspension container 9, and a second suspension container 15. The gas cylinder 10 is a high-pressure nitrogen cylinder, and its outlet is connected to the gas pipeline 14 via the pressure reducing valve 11, the gas valve 12, and the gas pressure controller 13. The gas pipeline 14 is sealed to the top of both the first suspension container 9 and the second suspension container 15. Both the first suspension container 9 and the second suspension container 15 are pressure-resistant sealed containers with a rated pressure resistance of not less than 1 MPa. The outlet of the first suspension container 9 is connected to the soil column simulation sampling system I, and the outlet of the second suspension container 15 is connected to the site injection well simulation sampling system III. During the experiment, the pressure was reduced in the first stage by the pressure reducing valve 11, and then the output pressure was precisely controlled by the pressure controller 13. The pressure control accuracy can reach ±0.005MPa, providing a constant top pressure for the two suspension containers, thereby realizing the constant pressure injection of micron-sized biochar suspension.

[0047] Specifically, the data acquisition system IV includes a data acquisition unit 23, a data transmission line 24, and a computer 25. The data acquisition unit 23 is a multi-channel dynamic data acquisition instrument with an adjustable sampling frequency ranging from 0.1Hz to 100Hz. The data acquisition unit 23 is electrically connected via the data transmission line 24 to the pore water pressure sensor 4 and the first flow sensor 8 of the soil column simulation sampling system I, and the second flow sensor 20 of the site injection well simulation sampling system III. The data acquisition unit 23 is also connected to the computer 25 via the data transmission line 24 to transmit the collected seepage parameters, such as pore water pressure, real-time flow rate, and cumulative flow rate, to the computer 25 in real time for storage, display, and subsequent analysis.

[0048] Specifically, the waste liquid collection system V includes a liquid pipeline 21 and a waste liquid tank 22. The waste liquid tank 22 is a graduated PE material container. It is connected to the outlet of the soil column simulation sampling system I and the site injection well simulation sampling system III through the liquid pipeline 21 to realize the centralized collection of experimental waste liquid, which facilitates subsequent waste liquid treatment and seepage volume verification.

[0049] This embodiment also provides a multi-scale simulation experiment method for the infiltration and injection of micron-sized biochar suspension into soil. Based on the above-mentioned experimental device, it can carry out soil column-scale simulation experiments, site injection well-scale simulation experiments, or parallel comparison experiments of the two scales simultaneously, depending on the experimental requirements.

[0050] The specific steps for conducting a soil column-scale simulation experiment separately are as follows: S11. Experimental preparation: The soil sample to be tested is air-dried, crushed, and sieved through a 2mm sieve. It is then layered into the soil sample container 5 according to the preset dry density. After each layer is filled, it is compacted evenly. After filling, the effluent collector 2 and the sealing cap 1 are installed to complete the sealing. A micron-sized biochar suspension of the preset concentration is prepared in the first suspension container 9. After stirring evenly, the container is sealed. All pipelines are connected, and the valves are opened to introduce clean water. The airtightness of the pipelines and cavities is checked. After confirming that there is no leakage, the soil sample is vacuum saturated and pretreated. After saturation, it is left to stand for 12 hours for later use.

[0051] S12. Experiment Start-up: Open gas cylinder 10, adjust pressure reducing valve 11 to the preset first-level pressure, open gas valve 12, first outflow valve 3 and first injection valve 7, set the preset injection pressure through pressure controller 13, and start constant pressure injection experiment; during the experiment, the data acquisition device 23 collects and records the detection data of pore water pressure sensor 4 and first flow sensor 8 in real time at a sampling frequency of 1Hz, and displays the data change curve on computer 25 simultaneously.

[0052] S13. Experiment termination: When the cumulative flow detected by the first flow sensor 8 reaches the preset value, or the permeation injection time reaches the preset time, stop the injection and close the first outflow valve 3 and the first injection valve 7 in sequence.

[0053] S14. Undisturbed sampling: Slowly unscrew and remove the sealing cap 1, slowly open the first injection hole valve 7, and use the stable liquid pressure at the injection end to push the soil sample in the soil sample bucket 5 upwards completely. During the pushing process, control the pressure to be stable and avoid disturbing the soil sample to obtain an undisturbed undisturbed experimental soil column. Cut the soil into slices at preset intervals to detect parameters such as the content distribution of micron biochar and changes in pore structure in the soil sample.

[0054] S15. Experimental Conclusion: Close gas valve 12 and gas cylinder 10, open all valves, drain the residual liquid in the pipeline and cavity, disassemble soil sample container 5, injection liquid disperser 6, effluent liquid collector 2 and other components, rinse them with clean water, dry them and store them for use in subsequent experiments.

[0055] The specific steps for conducting a site-specific injection well-scale simulation experiment are as follows: S21. Experimental preparation: The soil sample to be tested is air-dried, crushed, and sieved through a 2mm sieve. It is then layered according to the preset dry density and filled into the annulus between the inner tube 17-1 and the outer tube 17-2 of the inner sleeve 17. After each layer is filled, it is compacted evenly. After filling, the inner sleeve 17 is placed into the outer sleeve 16 to complete the seal. A micron-sized biochar suspension of the preset concentration is prepared in the second suspension container 15. After stirring evenly, the container is sealed. All pipelines are connected, and the valves are opened to introduce clean water. The airtightness of the pipelines and cavities is checked. After confirming that there is no leakage, the soil sample is vacuum saturated and pretreated. After saturation, it is left to stand for 12 hours for later use.

[0056] S22. Experiment Start-up: Open gas cylinder 10, adjust pressure reducing valve 11 to the preset first-level pressure, open gas valve 12, second injection port valve 18 and second outflow port valve 19, set the preset injection pressure through pressure controller 13, and start constant pressure injection experiment; during the experiment, the data acquisition device 23 collects and records the detection data of second flow sensor 20 in real time at a sampling frequency of 1Hz, and displays the data change curve on computer 25 simultaneously.

[0057] S23. Experiment termination: When the cumulative flow detected by the second flow sensor 20 reaches the preset value, or the permeation injection time reaches the preset time, stop the injection and close the second injection hole valve 18, the second outflow hole valve 19, the gas valve 12 and the gas cylinder 10 in sequence.

[0058] S24. Uncirculated sampling: Open the end cap of the outer sleeve 16, take out the inner sleeve 17, and use a standard soil sampling ring cutter to take soil from different axial heights and radial distances of the inner sleeve 17 to obtain undisturbed experimental soil samples. These samples are used to detect parameters such as the content distribution and migration distance of micron-sized biochar at different radial positions, and to reconstruct the distribution pattern of biochar around the injection well in the field.

[0059] S25. Experimental Conclusion: Open all valves to drain the residual liquid in the pipeline and cavity. Disassemble the inner sleeve 17, outer sleeve 16 and other components, rinse them with clean water, dry them and store them for use in subsequent experiments.

[0060] When conducting parallel comparative experiments at two scales simultaneously, it is only necessary to simultaneously execute the experimental steps at the soil column scale and the site injection well scale, and keep the experimental parameters such as injection pressure, suspension concentration, and soil sample properties of the two systems consistent. This will enable synchronous simulation at two scales, obtain parallel comparative experimental data, and significantly improve experimental efficiency.

[0061] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A multi-scale experimental device for infiltrating and injecting micron-sized biochar suspension into soil, comprising an injection pressure control system, a data acquisition system, and a waste liquid collection system, characterized in that, It also includes a soil column simulation sampling system and a site injection well simulation sampling system; The injection pressure control system is connected to the soil column simulation sampling system and the site injection well simulation sampling system through liquid pipelines, and is used to provide constant gas pressure and stable injection pressure for the injection of micron biochar suspension. The data acquisition system is electrically connected to the soil column simulation sampling system and the site injection well simulation sampling system via data transmission lines, and is used to collect and record seepage parameters during the experiment. The waste liquid collection system is connected to the soil column simulation sampling system and the site injection well simulation sampling system through liquid pipelines, and is used to collect the waste liquid flowing out during the experiment. The soil column simulation sampling system and the site injection well simulation sampling system are set up in parallel to conduct simulation experiments of micron-sized biochar suspension infiltration and injection into soil at both the soil column scale and the site injection well scale.

2. The multi-scale experimental apparatus according to claim 1, characterized in that, The soil column simulation sampling system includes a sealing cap, an effluent collector, a pore water pressure sensor, a soil sample bucket, an injection liquid disperser, and a first flow sensor. The soil sample bucket is a vertical cylindrical sealed cavity. The injection liquid disperser is located at the lower end of the soil sample bucket, and the effluent collector is located at the upper end of the soil sample bucket. The sealing cap is detachably and sealed on the top of the soil sample bucket. At least three sets of pore water pressure sensors are provided, evenly spaced along the axial direction of the soil sample bucket, to detect the pore water pressure at different depths of the soil sample. The inlet end of the injection liquid disperser is connected to the injection pressure control system via a liquid pipeline through a first injection hole valve and a first flow sensor. The outlet end of the effluent collector is connected to the waste liquid collection system via a liquid pipeline through a first outflow hole valve.

3. The multi-scale experimental apparatus according to claim 2, characterized in that, The injecting liquid disperser has a flat cavity structure with an injection hole in the middle of its side as the liquid inlet. Several dispersion holes are evenly distributed on its upper surface to divert the liquid entering through the injection hole into the soil sample bucket.

4. The multi-scale experimental apparatus according to claim 2, characterized in that, The effluent collector has a flat cavity structure with an effluent hole in the middle of its side as the effluent outlet. Several collection holes are evenly distributed on its lower plane. The liquid inside the soil sample bucket flows out through each collection hole and is collected and discharged through the effluent hole.

5. The multi-scale experimental apparatus according to claim 1, characterized in that, The site injection well simulation sampling system includes an outer sleeve, an inner sleeve, a second injection port valve, a second outflow port valve, and a second flow sensor. The outer sleeve is a sealed cavity, and the inner sleeve is coaxially and detachably installed inside the outer sleeve to hold experimental soil samples. The inner sleeve includes a coaxially nested inner tube and an outer tube. The inner tube has several injection dispersion holes evenly distributed on its wall, and the outer tube has several outflow collection holes evenly distributed on its wall. The liquid inlet end of the inner tube is connected to the injection pressure control system through a liquid pipeline via the second injection port valve and the second flow sensor. The liquid outlet end of the annulus between the outer tube and the outer sleeve is connected to the waste liquid collection system through a liquid pipeline via the second outflow port valve.

6. The multi-scale experimental apparatus according to claim 1, characterized in that, The injection pressure control system includes a gas cylinder, a pressure reducing valve, a gas valve, a gas pressure controller, a gas pipeline, a first suspension container, and a second suspension container. The gas cylinder's outlet is connected to the gas pipeline via the pressure reducing valve, the gas valve, and the gas pressure controller. The gas pipeline is sealed to the top of both the first and second suspension containers. The outlet of the first suspension container is connected to the soil column simulation sampling system, and the outlet of the second suspension container is connected to the site injection well simulation sampling system.

7. The multi-scale experimental apparatus according to claim 1, characterized in that, The data acquisition system includes a data acquisition unit, a data transmission line, and a computer. The data acquisition unit is electrically connected to the pore water pressure sensor and the first flow sensor of the soil column simulation sampling system, as well as the second flow sensor of the site injection well simulation sampling system, via the data transmission line. The data acquisition unit is also connected to the computer via the data transmission line to transmit the collected seepage parameters to the computer in real time for storage and analysis.

8. The multi-scale experimental apparatus according to claim 1, characterized in that, The waste liquid collection system includes liquid pipelines and waste liquid tanks. The waste liquid tanks are connected to the outlets of the soil column simulation sampling system and the site injection well simulation sampling system through the liquid pipelines.

9. An experimental method for a multi-scale experimental apparatus according to any one of claims 1 to 8, characterized in that, This includes simulation test procedures at the soil column scale and / or site injection well scale.

10. The experimental method according to claim 9, characterized in that, The specific steps of the soil column scale simulation experiment include: S11. Experimental preparation: Fill the soil sample to be tested into the soil sample bucket and install the sealing cap. Prepare a micron-sized biochar suspension of the preset concentration in the first suspension container and complete the airtightness check of the pipeline and valve. S12. Experiment Start-up: Open the gas cylinder, gas valve, first outflow valve, and first injection valve. Set the preset injection pressure through the pressure controller to start the constant pressure injection experiment. During the experiment, the detection data of the pore water pressure sensor and the first flow sensor are collected and recorded in real time through the data acquisition device. S13. Experiment termination: When the cumulative flow detected by the first flow sensor reaches the preset value, or the permeation injection time reaches the preset time, stop the injection and close the first outflow valve and the first injection valve in sequence. S14. Uncirculated sampling: Open the sealing cap, open the valve of the first injection hole, and use the liquid pressure at the injection end to completely push out the soil sample in the soil sample bucket to obtain the uncirculated experimental soil sample. S15. Experimental conclusion: Close the gas valve and gas cylinder, drain the residual liquid in the pipeline, and clean the experimental apparatus. The site injection well-scale simulation experiment specifically includes: S21. Experimental preparation: Fill the soil sample to be tested into the annulus between the inner tube and the outer tube of the inner sleeve, seal the inner sleeve inside the outer sleeve, prepare a micron-sized biochar suspension of a preset concentration in the second suspension container, and complete the airtightness check of the pipeline and valve. S22. Experiment Start-up: Open the gas cylinder, gas valve, second injection port valve, and second outflow port valve. Set the preset injection pressure through the pressure controller to start the constant pressure injection experiment. During the experiment, the detection data of the second flow sensor is collected and recorded in real time through the data acquisition device. S23. Experiment termination: When the cumulative flow detected by the second flow sensor reaches the preset value, or the permeation injection time reaches the preset time, stop the injection and close the second injection hole valve, the second outflow hole valve, the gas valve and the gas cylinder in sequence. S24. Uncirculated sampling: Open the outer sleeve, take out the inner sleeve, and use a soil sampling ring to take soil radially from the inner sleeve to obtain undisturbed experimental soil samples at different radial distances. S25. Experimental conclusion: Drain the residual liquid in the pipeline and clean the experimental apparatus.

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