Experimental method for simulating gas desorption under pressure in coal mine underground reverse circulation sampling process

Abstract

The invention discloses an experimental method for simulating gas desorption under pressure in a coal mine underground reverse circulation sampling process, and relates to the technical field of coal mine gas safety. The required experimental device comprises a gas supply unit, a constant-temperature water bath unit, a vacuum degassing unit, an isovolumetric pressure swing adsorption and desorption unit and a data acquisition unit, the constant-volume pressure swing adsorption and desorption unit comprises a buffer reference tank, a coal sample tank and a positive pressure reference tank which are sequentially connected in series from front to back, the constant-temperature water bath unit comprises a constant-temperature water bath box, the buffer reference tank, the coal sample tank and the positive pressure reference tank are all located in the constant-temperature water bath box, and a back pressure valve is arranged on a pipeline connected with an outlet of the positive pressure reference tank. According to the invention, pressure, temperature and flow data can be synchronously obtained, dynamic analysis of diffusion coefficients is supported, and experimental support is provided for accurate calculation of gas loss and gas content after underground coal mine reverse circulation sampling.

Description

Technical Field

[0001] The present invention relates to the technical field of coal mine gas safety, and particularly relates to an experimental method for simulating the pressure - assisted desorption of gas during the reverse - circulation sampling process in a coal mine underground. Background Art

[0002] Coal mine gas is one of the main disasters threatening the safe production of coal mines. The accurate determination of its content is crucial for gas drainage design, disaster warning, and coalbed methane resource assessment. At present, the reverse - circulation sampling technology is widely used in the direct determination of underground gas content. By combining double - wall drill pipes and compressed air, it can quickly and accurately extract coal samples from the bottom of the hole without withdrawing the drill, avoiding the problems of coal sample mixing and gas loss caused by excessive exposure time in the hole, thus improving the accuracy of gas content determination. The coal sample is sent to the sampling tank through the air flow, during which it experiences a process from positive pressure to atmospheric pressure. The traditional gas loss calculation formula cannot accurately estimate this process, directly affecting the reliability of subsequent gas content determination.

[0003] Currently, the existing experimental devices and methods in the prior art have obvious deficiencies in simulating the real desorption environment underground, mainly having the following technical problems: (1) Conventional gas adsorption - desorption experiments are usually carried out under atmospheric pressure conditions and cannot reproduce the pressurized and pressure - mutation scenarios during the reverse - circulation sampling process. For example, when the coal sample is transferred from the high - pressure environment of the borehole to the ground, the pressure drops instantaneously from several megapascals to atmospheric pressure. This dynamic process will cause a drastic change in the desorption rate, and the experimental devices in the prior art are difficult to accurately simulate the desorption in a positive - pressure environment and transient pressure changes. In addition, most of the experimental devices in the prior art adopt an open system, and the desorption pressure cannot be independently controlled, resulting in systematic deviations between the experimental data and the actual underground working conditions. (2) In terms of experimental parameter control, the experimental devices in the prior art have weak co - regulation capabilities for temperature, adsorption equilibrium pressure, and desorption pressure. The precise matching of the adsorption equilibrium pressure and the desorption pressure is the key to simulating the pressure - assisted desorption underground. However, due to problems such as insufficient airtightness, pressure feedback delay, and low automation level in the experimental devices of the prior art, it is difficult to stably maintain the adsorption equilibrium or accurately adjust it to the required pressure, and the pressure - assisted and variable - pressure desorption cannot be achieved or there are problems with unstable pressure control. (3) The prior art cannot reproduce the law of pressure - assisted desorption of coal samples in the laboratory. During the pressure - assisted desorption process, the gas diffusion coefficient changes dynamically with the pressure gradient, but the experimental devices in the prior art are difficult to capture the change law of the transient desorption rate. In addition, the simulation of variable - pressure desorption (such as rapidly decreasing from high pressure to atmospheric pressure) requires rapid response and pressure buffering functions, while most of the prior art adopts a rigid pressure - reduction design and cannot restore the pressure relaxation process of reverse - circulation sampling underground, further exacerbating the error in loss amount calculation.

[0004] In summary, the existing gas adsorption and desorption experimental devices have significant defects in aspects such as pressure dynamic simulation, multi-parameter collaborative control, and data acquisition accuracy, which restrict the accuracy of coal mine gas content determination.

[0005] Therefore, the existing technology needs to be further improved. Summary of the Invention

[0006] The purpose of the present invention is to provide an experimental method for simulating the pressure-assisted desorption of gas during the reverse circulation sampling process in a coal mine underground. By simulating the underground reverse circulation sampling environment, it can truly simulate the sudden change in pressure during reverse circulation sampling and support multi-stage variable pressure desorption under isochoric conditions, achieve precise control of the pressure-assisted desorption process, solve the problem of inaccurate calculation of gas loss, and provide reliable data support for the prevention and control of coal mine gas disasters.

[0007] To achieve the above purpose, the present invention adopts the following technical solutions:

[0008] An experimental method for simulating the pressure-assisted desorption of gas during the reverse circulation sampling process in a coal mine underground, comprising the following steps:

[0009] a. Prepare the required experimental device: The experimental device includes a gas supply unit, a constant temperature water bath unit, a vacuum degassing unit, an isochoric variable pressure adsorption and desorption unit, and a data acquisition unit;

[0010] The isochoric variable pressure adsorption and desorption unit includes a buffer reference tank, a coal sample tank, and a positive pressure reference tank connected in series in sequence from front to back. The constant temperature water bath unit includes a constant temperature water bath box. The buffer reference tank, the coal sample tank, and the positive pressure reference tank are all located in the constant temperature water bath box. A back pressure valve is provided on the pipeline connected to the outlet of the positive pressure reference tank; the pipeline connected to the outlet of the coal sample tank is divided into a first branch and a second branch. The positive pressure reference tank and the back pressure valve are located on the first branch; the second branch is designed in parallel with the first branch;

[0011] b. Check the airtightness of the experimental device, dry the required coal samples and place them in the coal sample tank; inflate the experimental device for calibration and then degas it through the vacuum degassing unit;

[0012] c. Perform gas adsorption: Set the temperature of the constant temperature water bath box, and fill the buffer reference tank with methane gas at a certain pressure through the gas supply unit. When the adsorption equilibrium pressure in the coal sample tank reaches the preset value, that is, after the coal sample tank reaches adsorption equilibrium, stop introducing methane gas into the coal sample tank;

[0013] d. Pressure - assisted desorption: Close the second branch and open the first branch. Introduce methane gas into the positive - pressure reference tank, and make the pressure in the coal - sample tank greater than that in the positive - pressure reference tank. During the desorption process, the adsorption amount of the coal sample gradually decreases, causing the pressure of the gas in the positive - pressure reference tank to drop. At this time, adjust through the back - pressure valve to keep the pressure in the positive - pressure reference tank at a stable pressure all the time; the desorbed gas is discharged after passing through the gas flowmeter, and the data acquisition unit records and uploads the collected data.

[0014] e. Atmospheric - pressure desorption: After pressure - assisted desorption for a period of time, close the first branch and open the second branch. The gas pressure quickly drops to atmospheric pressure, and the pressure - assisted desorption is converted to atmospheric - pressure desorption through the second branch.

[0015] In the above experimental method for simulating the pressure - assisted desorption of gas during the reverse - circulation sampling process in underground coal mines, in step a, the gas supply unit includes a high - pressure gas cylinder and a metering loop. Methane gas is filled in the high - pressure gas cylinder, and the injection amount of methane gas is accurately controlled through the metering loop.

[0016] In the above experimental method for simulating the pressure - assisted desorption of gas during the reverse - circulation sampling process in underground coal mines, in step a, the vacuum degassing unit includes a vacuum pump and a vacuum gauge. The vacuum degassing unit is connected to the pipeline connecting the high - pressure gas cylinder and the buffer reference tank. A free - volume calibration tank is also connected to the pipeline connecting the high - pressure gas cylinder and the buffer reference tank. Known - volume and - pressure gas is injected into the experimental device through the free - volume calibration tank, and the free - space volume of the experimental device is indirectly calculated using the pressure change.

[0017] In the above experimental method for simulating the pressure - assisted desorption of gas during the reverse - circulation sampling process in underground coal mines, in step c, the specific steps of gas adsorption are as follows: Through the gas supply unit, methane gas at a certain pressure is flushed into the buffer reference tank until a stable pressure is reached, and then the methane gas is introduced into the coal - sample tank. As the methane gas is filled, the pressure in the coal - sample tank gradually increases, and gas molecules begin to contact the surface of the coal sample and are adsorbed.

[0018] In the above experimental method for simulating the pressure - assisted desorption of gas during the reverse - circulation sampling process in underground coal mines, in step c, the temperature of the constant - temperature water bath is set at 25 °C.

[0019] In the above experimental method for simulating the pressure - assisted desorption of gas during the reverse - circulation sampling process in underground coal mines, corresponding electromagnetic valves are respectively set on the buffer reference tank, the coal - sample tank, and the positive - pressure reference tank, and whether to introduce methane gas is controlled through their respective electromagnetic valves.

[0020] The above experimental method for simulating the pressure - desorption of gas during the reverse - circulation sampling in coal mines places the coal sample in a vacuum drying oven for drying treatment, and the drying temperature is 100°C.

[0021] The above experimental method for simulating the pressure - desorption of gas during the reverse - circulation sampling in coal mines installs a gas flowmeter behind the back - pressure valve, records the gas flow rate and cumulative volume through the gas flowmeter; dynamically compensates for pressure fluctuations through the back - pressure valve to achieve precise control of adsorption and desorption pressures.

[0022] The above experimental method for simulating the pressure - desorption of gas during the reverse - circulation sampling in coal mines is provided with corresponding solenoid valves on both the first branch and the second branch, and the opening or closing of the first branch and the second branch is achieved through the solenoid valves.

[0023] Compared with the prior art, the present invention brings the following beneficial technical effects:

[0024] The present invention proposes an experimental method for simulating the pressure - desorption of gas during the reverse - circulation sampling in coal mines. It adopts a series structure of a buffer reference tank, a coal - sample tank, and a positive - pressure reference tank, and forms a closed - loop pressure - regulation system in cooperation with the back - pressure valve. Through the active pressure control of the back - pressure valve, it realizes the full - process dynamic simulation of the pressure in the coal - sample tank from high - pressure adsorption equilibrium to pressure - desorption (the positive - pressure reference tank maintains a constant pressure), and then to rapid pressure reduction to atmospheric pressure.

[0025] The present invention, through the coordinated control of the back - pressure valve and the positive - pressure reference tank, actively maintains the pressure of the positive - pressure reference tank constant (pressure adjustable) during the desorption stage, breaking through the limitation that the traditional open system cannot stably control the desorption pressure. The introduction of the back - pressure valve makes the desorption process always under a controllable pressure gradient, realizing the laboratory simulation of the real pressure - desorption environment.

[0026] The present invention realizes stable pressure - desorption and variable - pressure desorption. The present invention can simultaneously obtain pressure, temperature, and flow data, support the dynamic analysis of the diffusion coefficient, and provide experimental support for the accurate calculation of gas loss and gas content after reverse - circulation sampling in coal mines. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] The following further describes the present invention with reference to the drawings:

[0028] Figure 1 is a schematic structural diagram of the experimental device of the present invention;

[0029] Figure 2 is a curve graph showing the change in the cumulative gas desorption volume under different desorption pressures when the gas pressure is 1.6 MPa;

[0030] In the figure:

[0031] 1. High-pressure gas cylinder, 2. Quantitative loop, 3. First pressure sensor, 4. First solenoid valve, 5. Free volume calibration tank, 6. Pressure regulating valve, 7. Second pressure sensor, 8. Vacuum pump, 9. Vacuum gauge, 10. Second solenoid valve, 11. Constant temperature water bath, 12. Buffer reference tank, 13. Third pressure sensor, 14. Third solenoid valve, 15. Coal sample tank, 16. Positive pressure reference tank, 17. Fourth solenoid valve, 18. Fourth pressure sensor, 19. Fifth solenoid valve, 20. Fifth pressure sensor, 21. Back pressure valve, 22. Gas flowmeter, 23. Data acquisition unit, 24. Sixth solenoid valve, 25. Seventh solenoid valve, 26. Eighth solenoid valve. Detailed implementation mode

[0032] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present application.

[0033] The main technical concept of the present invention is: adopting a series structure of a buffer reference tank, a coal sample tank, and a positive pressure reference tank, and cooperating with a back pressure valve to form a closed pressure regulation system. Through the active pressure control of the back pressure valve, the full-process pressure dynamic simulation of the coal sample tank from high-pressure adsorption equilibrium to pressure desorption (the positive pressure reference tank maintains a constant pressure), and then to rapid pressure reduction to atmospheric pressure is realized. The experimental method of the present invention can realize a three-stage experimental process of "pressure desorption (constant pressure) - rapid pressure reduction - atmospheric pressure desorption". By quickly switching each solenoid valve, the complete pressure path of the coal sample from the high-pressure environment of the borehole through air flow transportation (positive pressure) to the ground (atmospheric pressure) is simulated, and the laboratory reduction of the underground pressure relaxation process can be realized. During the adsorption stage, the adsorption equilibrium pressure is precisely controlled through the buffer reference tank. During the desorption stage, the desorption back pressure is preset through the positive pressure reference tank, and the desorption is driven by the pressure difference, and the pressure fluctuation is dynamically compensated through the back pressure valve to realize the independent and precise control of the adsorption / desorption pressure.

[0034] As Figure 1 shown, an experimental device for simulating the pressure desorption of gas during the reverse circulation sampling process in coal mines includes a gas supply unit, a constant temperature water bath unit, a vacuum degassing unit, an isochoric variable pressure adsorption and desorption unit, a data acquisition unit, and a number of solenoid valves and pressure sensors.

[0035] The number of solenoid valves specifically includes the first solenoid valve 4, the second solenoid valve 10, the third solenoid valve 14, the fourth solenoid valve 17, the fifth solenoid valve 19, the sixth solenoid valve 24, the seventh solenoid valve 25, and the eighth solenoid valve 26. The pressure sensors include the first pressure sensor 3, the second pressure sensor 7, the third pressure sensor 13, the fourth pressure sensor 18, and the fifth pressure sensor 20.

[0036] The gas supply unit includes a high-pressure gas cylinder 1, a metering loop 2, and a first pressure sensor 3. Through the metering loop 2, the input amount of methane gas from the high-pressure gas cylinder 1 to other tanks can be accurately controlled, enabling precise automatic control of the gas injection volume (5 mL to 50 mL) and multi-gas quantitative proportion injection. The first pressure sensor 3 can monitor the pressure of the methane gas. The first solenoid valve 4 is located on the pipeline connecting the high-pressure gas cylinder 1 and the free volume calibration tank 5. A pressure regulating valve 6 is also provided behind the first solenoid valve 4 to regulate the pressure of the methane gas.

[0037] The function of the free volume calibration tank 5 is as follows: The free volume calibration tank serves as a reference container with a known volume and helps determine the free space volume of the experimental device through the pressure change method. Its core function is to indirectly calculate the total volume (including pipelines, chambers, etc.) in the experimental device that is not occupied by the sample by combining the pressure measurement values with the gas state equation (such as the ideal gas law).

[0038] The isochoric pressure swing adsorption and desorption unit includes a buffer reference tank 12, a coal sample tank 15, and a positive pressure reference tank 16 connected in series from front to back. Each tank is equipped with a corresponding solenoid valve and pressure sensor. A back pressure valve 21 is provided at the outlet of the positive pressure reference tank 16 to ensure that the gas pressure in the positive pressure reference tank 16 remains constant. After the methane gas is output, it is discharged into the air through a gas flowmeter 22, which can record the gas velocity and cumulative amount of the gas. The pipeline connected to the outlet of the coal sample tank is divided into a first branch and a second branch. The positive pressure reference tank and the back pressure valve are located on the first branch, and a fifth solenoid valve and a fifth pressure sensor are also provided on this first branch, and the fifth solenoid valve and the fifth pressure sensor are located in front of the back pressure valve 21; the second branch is designed in parallel with the first branch. The starting end of the second branch is connected to the outlet of the coal sample tank, and the end is connected to the pipeline behind the back pressure valve 21. The first branch and the second branch designed in parallel can achieve a three-stage experimental process of "pressure desorption (constant pressure) - rapid pressure reduction - atmospheric pressure desorption".

[0039] The experimental method of the present invention will be further described below in combination with the above experimental device.

[0040] An experimental method for simulating the pressure desorption of gas during the reverse circulation sampling process in a coal mine underground according to the present invention includes the following steps:

[0041] Step 1: Check the airtightness of the experimental device. Correctly connect the free volume calibration tank 5, the buffer reference tank 12, the sample tank 15 without experimental coal samples, and the positive pressure reference tank 16 to the high-pressure gas cylinder 1, and ensure that the connections are tight. Close the seventh solenoid valve 25 connected to the atmosphere of the experimental device, open the high-pressure gas cylinder 1, and start inflating each tank with a pressure of 5 MPa. After the second pressure sensor 7, the third pressure sensor 13, the fourth pressure sensor 18, and the fifth pressure sensor 20 show that the pressure is gradually stable, close the high-pressure gas cylinder 1; maintain the pressure for 24 hours, observe the pressure and collect data. If the pressure remains stable within 24 hours, it indicates that the experiment can be carried out; if the pressure shows a significant decrease, it means that the airtightness of the experimental device is poor, there is a leakage point, and it does not meet the experimental requirements. It is necessary to gradually check the airtightness of the experimental device. After checking and repairing, repeat the above steps before the experiment can be carried out.

[0042] Calibrate the free space volume. Use helium to calibrate the free space volume of the coal sample tank 15 at the experimental temperature, and keep the ambient temperature constant at 25°C during the calibration process.

[0043] Vacuum degassing: Close the first solenoid valve and the seventh solenoid valve, open the other solenoid valves, start the vacuum pump 8, and degas the entire device pipeline in a vacuum environment. When the vacuum gauge 9 shows that the vacuum degree is less than 4 Pa, close the vacuum pump 8, and if the pressure remains unchanged within 4 hours, it is considered that the degassing is completed.

[0044] Step 2: Methane adsorption experiment. Set the temperature of the constant temperature water bath to 25°C and keep the temperature stable. Open the first solenoid valve and the second solenoid valve, close the other solenoid valves, and fill the buffer reference tank 12 with methane gas at a certain pressure through the high-pressure gas cylinder 1. Then close the first solenoid valve and the second solenoid valve, open the third solenoid valve, and the methane gas inside the buffer reference tank 12 enters the coal sample tank 15 containing the experimental coal samples. As the methane gas is filled, the pressure in the coal sample tank gradually increases, and gas molecules begin to contact and be adsorbed on the surface of the coal sample. After a period of time, the adsorption rate and desorption rate of the gas by the coal sample reach equality. At this time, the coal sample tank reaches the high-pressure adsorption equilibrium state, that is, the amount of gas adsorbed per unit time is the same as the amount of gas desorbed, and the pressure in the tank and the adsorption amount of the coal sample no longer change significantly. At this time, the adsorption equilibrium pressure (the pressure in the tank does not change within 2 hours) is reached in the coal sample tank 15, and the gas supply is stopped; if the pressure in the coal sample tank 15 is less than the preset adsorption equilibrium pressure, repeat the above steps and continue to fill the coal sample tank 15 with methane gas until the pressure in the coal sample tank 15 reaches the preset adsorption equilibrium pressure (0.7 MPa, 1.5 MPa, 2.0 MPa).

[0045] Step 3: Pressure-assisted desorption experiment: Charge methane at a certain pressure (0.4 MPa, 0.6 MPa, 0.8 MPa, 1.0 MPa) into the positive-pressure reference tank 16. Open the fifth solenoid valve, and keep the rest of the solenoid valves closed. Open the valve of the coal sample tank 15, preset a certain pressure (0.4 MPa, 0.6 MPa, 0.8 MPa, 1.0 MPa) for the back pressure valve 21, open the seventh solenoid valve to start the pressure-assisted desorption experiment. Set the pressure of the coal sample tank 15 to be greater than that of the positive-pressure reference tank 16. The coal sample tank 15 starts to desorb, and methane flows from the coal sample tank 15 to the positive-pressure reference tank 16. During the desorption process, as the gas continues to desorb, the adsorption amount of the coal sample gradually decreases, and the gas pressure in the tank also decreases accordingly until the pressure of the coal sample tank 15 is equal to or less than the pressure of the positive-pressure reference tank 16, that is, the preset pressure of the back pressure valve, then the desorption process ends. Due to the action of the preset pressure of the back pressure valve 21, the positive-pressure reference tank 16 always maintains a stable pressure. Methane passes through the back pressure valve 21, through the solenoid valve 25, and finally flows out from the gas flowmeter 22. The desorbed gas will be collected, recorded in real time, and automatically uploaded to the data acquisition unit.

[0046] Step 4: Variable-pressure desorption: Simulate the process of coal chips being transported to the coal sample tank by wind pressure and desorbing to normal pressure during the reverse circulation positive-pressure sampling process. After 5 minutes of the above pressure-assisted desorption process, quickly close the fifth solenoid valve, open the fourth solenoid valve and the seventh solenoid valve, and keep the rest of the solenoid valves closed to achieve the process of quickly changing from pressure-assisted desorption to normal-pressure desorption.

[0047] Step 5: After testing all experimental groups, organize the experimental data and convert the adsorption amount and desorption amount into volumes under standard conditions. Figure 2 For a 200 g coal sample at an ambient temperature of 25 °C, after reaching adsorption-desorption equilibrium under a gas pressure of 1.6 MPa, when the desorption pressures are 0.4 MPa, 0.6 MPa, 0.8 MPa, and 1.0 MPa respectively, the curve of the cumulative gas desorption amount versus time. From Figure 2 it can be seen that under the condition of pressure-assisted desorption, the desorption amount of the coal sample decreases with the increase of the desorption pressure, and the smaller the desorption pressure, the faster the gas desorption rate.

[0048] The parts not described in the present invention can be realized by referring to the prior art.

[0049] Those of ordinary skill in the art of this technology should recognize that the above embodiments are only used to illustrate the present application, rather than to limit the present application. As long as within the scope of the substantial spirit of the present application, appropriate changes and variations made to the above embodiments fall within the scope of protection required by the present application.

Claims

1. An experimental method for simulating the pressure - assisted desorption of gas during the reverse - circulation sampling process in underground coal mines, characterized in that, It includes the following steps: a. Prepare the required experimental device: The experimental device includes a gas supply unit, a constant temperature water bath unit, a vacuum degassing unit, an isochoric pressure swing adsorption and desorption unit, and a data acquisition unit; The isochoric pressure swing adsorption and desorption unit includes a buffer reference tank, a coal sample tank, and a positive pressure reference tank connected in series from front to back. The constant temperature water bath unit includes a constant temperature water bath box. The buffer reference tank, the coal sample tank, and the positive pressure reference tank are all located in the constant temperature water bath box. A back pressure valve is provided on the pipeline connected to the outlet of the positive pressure reference tank; The pipeline connected to the outlet of the coal sample tank is divided into a first branch and a second branch. The positive pressure reference tank and the back pressure valve are located on the first branch; The second branch is designed in parallel with the first branch; b. Check the airtightness of the experimental device, dry the required coal sample and place it in the coal sample tank; After calibrating the experimental device by inflating it, degas it through the vacuum degassing unit; c. Perform gas adsorption: Set the temperature of the constant temperature water bath box, and fill the buffer reference tank with methane gas at a certain pressure through the gas supply unit. When the adsorption equilibrium pressure preset in the coal sample tank is reached, that is, after the coal sample tank reaches adsorption equilibrium, stop introducing methane gas into the coal sample tank; d. Pressure desorption: Close the second branch and open the first branch, introduce methane gas into the positive pressure reference tank, and make the pressure in the coal sample tank greater than the pressure in the positive pressure reference tank. During the desorption process, the adsorption amount of the coal sample gradually decreases, causing the pressure of the gas in the positive pressure reference tank to drop. At this time, adjust through the back pressure valve to keep the pressure in the positive pressure reference tank at a stable pressure all the time; The desorbed gas is discharged after passing through a gas flowmeter, and the data collected is recorded and uploaded by the data acquisition unit; e. Atmospheric pressure desorption: After pressure desorption for a period of time, close the first branch and open the second branch, and the gas pressure quickly drops to atmospheric pressure, realizing the conversion from pressure desorption to atmospheric pressure desorption through the second branch.

2. The experimental method for simulating the pressure - assisted desorption of gas during the reverse - circulation sampling process in a coal mine underground, as described in claim 1, is characterized in that: In step a, the gas supply unit includes a high-pressure gas cylinder and a metering loop. Methane gas is filled in the high-pressure gas cylinder, and the injection amount of methane gas is accurately controlled through the metering loop.

3. An experimental method for simulating the pressure - assisted desorption of gas during the reverse - circulation sampling process in a coal mine underground, as claimed in claim 2, wherein: In step a, the vacuum degassing unit includes a vacuum pump and a vacuum gauge. The vacuum degassing unit is connected to the pipeline connecting the high-pressure gas cylinder and the buffer reference tank. A free volume calibration tank is also connected to the pipeline connecting the high-pressure gas cylinder and the buffer reference tank. Known volume and pressure gas is injected into the experimental device through the free volume calibration tank, and the free space volume of the experimental device is indirectly calculated using the pressure change.

4. An experimental method for simulating the pressure - assisted desorption of gas during the reverse - circulation sampling process in a coal mine underground, as claimed in claim 1, wherein: In step c, the specific steps of gas adsorption are as follows: After filling the buffer reference tank with methane gas at a certain pressure through the gas supply unit and reaching a stable pressure, introduce the methane gas into the coal sample tank. As the methane gas is filled, the pressure in the coal sample tank gradually increases, and gas molecules begin to contact the surface of the coal sample and are adsorbed.

5. An experimental method for simulating the pressure - relief desorption of gas during the reverse - circulation sampling process in a coal mine underground, as claimed in claim 1, wherein: In step c, the temperature of the constant temperature water bath box is set to 25 °C.

6. An experimental method for simulating the pressure - assisted desorption of gas during the reverse - circulation sampling process in underground coal mines, as described in claim 1, is characterized in that: The buffer reference tank, the coal sample tank, and the positive pressure reference tank are respectively provided with corresponding electromagnetic valves, and whether to introduce methane gas is controlled through their respective electromagnetic valves.

7. An experimental method for simulating the pressure - assisted desorption of gas during the reverse - circulation sampling process in underground coal mines according to claim 1, characterized in that: Place the coal sample in a vacuum drying oven for drying, and the drying temperature is 100°C.

8. An experimental method for simulating the pressure - assisted desorption of gas during the reverse - circulation sampling process in underground coal mines according to claim 1, characterized in that: The gas flowmeter is installed behind the back pressure valve. The gas flow rate and cumulative volume are recorded by the gas flowmeter; the back pressure valve dynamically compensates for pressure fluctuations to achieve precise control of the adsorption and desorption pressures.

9. An experimental method for simulating the pressure - assisted desorption of gas during the reverse - circulation sampling process in underground coal mines according to claim 1, characterized in that: Corresponding solenoid valves are provided on both the first branch and the second branch, and the solenoid valves are used to open or close the first branch and the second branch.

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