Test apparatus and test method for coal gas adsorption-desorption followed by water injection

Abstract

This invention discloses a coal gas adsorption-desorption post-water injection test device, comprising a vacuum unit, a gas supply unit, an adsorption-desorption post-water injection unit, and a data acquisition and storage unit. The vacuum unit includes a vacuum pump, a first shut-off valve, and a vent valve. The gas supply unit includes a high-pressure methane cylinder, a high-pressure helium cylinder, a gas buffer tank, a second shut-off valve, and a third shut-off valve. The adsorption-desorption post-water injection unit includes a pressurized liquid storage tank, a desorption measuring cylinder, and a fourth shut-off valve. The data acquisition and storage unit includes a first gas pressure sensor, a second gas pressure sensor, a data acquisition unit, an industrial control computer, and a computer. This invention also provides a testing method for the coal gas adsorption-desorption post-water injection test device. The test device of this invention has a simple overall structure, a convenient testing method, and the simulated process is scientifically reliable and accurate, possessing good practical application value.

Description

Technical Field

[0001] This invention relates to the field of coal seam gas emission law testing, specifically a coal gas adsorption-desorption post-water injection test device and its testing method, which is mainly applicable to simulating and studying the gas adsorption and desorption law of in-situ coal reservoirs after the injection of external water. Background Technology

[0002] Methane gas is a significant hazard in coal mining. Once desorbed from broken coal and released into the working face, it can easily trigger severe gas disasters. Effectively suppressing methane gas emissions during coal mining is a critical issue that urgently needs to be addressed. Practice has proven that coal seam water injection can effectively block the diffusion and migration of methane gas within the coal seam, making it an effective technology for preventing and controlling coal mine gas disasters.

[0003] Currently, many scholars have conducted experimental research on the impact of water injection on gas adsorption and desorption in coal. How to effectively replicate the inhibitory effect of water on gas desorption during coal mining has become a key research area. For example, patents CN102053141A and CN106908347A both propose testing devices and methods for the influence of water injection on the gas desorption characteristics of pulverized coal. However, the stirring design of these testing devices damages the coal structure during operation, and they require pressurized water injection, making it difficult to control the moisture content and resulting in a complex testing process. Patent CN105738248A proposes a gas adsorption and desorption experimental device and method with controllable coal sample moisture content. However, the design of this experimental device is overly cumbersome and lacks a device for fully wetting the coal sample with injected water, which can easily lead to experimental errors due to water injection affecting the gas adsorption and desorption performance of lump coal or pulverized coal. Therefore, developing a simple and reliable post-water injection testing device and method for gas adsorption and desorption testing is of significant practical importance. Furthermore, previous experimental setups mostly involved first wetting coal samples before conducting gas adsorption and desorption tests on the wetted coal samples. This experimental method ignores the fact that the in-situ coal reservoir has already fully adsorbed gas before water injection, leading to significant differences between the experimental research and actual engineering conditions. Consequently, it is difficult to explain or even solve engineering problems encountered in practice. Therefore, there is an urgent need to develop a post-injection water test device that better suits engineering realities. Summary of the Invention

[0004] To address the aforementioned technical problems, the present invention aims to provide a coal gas adsorption-desorption followed by water injection test device and its testing method.

[0005] The above-mentioned objective of the present invention is achieved through the following technical solution:

[0006] A coal gas adsorption-desorption post-water injection test device includes a vacuum unit, a gas supply unit, an adsorption-desorption post-water injection unit, and a data acquisition and storage unit.

[0007] The vacuum pumping unit includes a vacuum pump, a first shut-off valve, and a vent valve;

[0008] The gas supply unit includes a high-pressure methane cylinder, a high-pressure helium cylinder, a gas buffer tank, a second shut-off valve, and a third shut-off valve.

[0009] The adsorption-desorption post-water injection unit includes a pressurized liquid storage tank, a desorption measuring cylinder, and a fourth shut-off valve.

[0010] The data acquisition and storage unit includes a first gas pressure sensor, a second gas pressure sensor, a data acquisition unit, an industrial control computer, and a computer.

[0011] The high-pressure methane cylinder and the high-pressure helium cylinder are respectively connected to the inlet end of the gas buffer tank through inlet pipes; the outlet end of the gas buffer tank is connected to the pressure-bearing liquid storage tank through a first pipe, and the pressure-bearing liquid storage tank is also connected to the desorption measuring cylinder through a third pipe. A fourth shut-off valve is provided on the third pipe. The vacuum pump is connected to the first pipe through a second pipe, and an exhaust pipe is provided at the connection between the first pipe and the second pipe. A first shut-off valve is provided on the second pipe, and a vent valve is provided on the exhaust pipe.

[0012] The first gas pressure sensor is installed on the gas buffer tank, and the second gas pressure sensor is installed on the pressurized liquid storage tank. The first and second gas pressure sensors are electrically connected to the data acquisition unit, which is connected to the industrial control computer, which is connected to the computer.

[0013] Furthermore, a vacuum gauge is provided on the vacuum pump.

[0014] Furthermore, a first pressure reducing valve and a second pressure reducing valve are respectively installed on the inlet pipes of the high-pressure methane cylinder and the high-pressure helium cylinder.

[0015] Furthermore, a second shut-off valve and a third shut-off valve are sequentially installed on the first pipeline, with the second shut-off valve located between the gas buffer tank and the vacuum pump, and the third shut-off valve located between the vacuum pump and the pressurized liquid storage tank.

[0016] Furthermore, the pressure-bearing liquid storage tank includes a tank body, and a partition plate is provided inside the tank body. The partition plate divides the tank body into a coal storage chamber and a liquid storage chamber. The partition plate has a central hole. A water injection hole and a high-pressure shut-off valve are provided at the bottom of the liquid storage chamber. A nut is installed on the outside of the water injection hole. The water injection hole can be opened or closed by rotating the nut.

[0017] The high-pressure shut-off valve is rotatably connected to the liquid storage chamber. The valve stem of the high-pressure shut-off valve is placed inside the liquid storage chamber, and an O-ring is provided at the top of the valve stem. By rotating the valve stem, the O-ring is tightly fitted or separated from the center hole of the partition plate, thereby controlling the isolation or connection between the coal storage chamber and the liquid storage chamber.

[0018] Furthermore, several volumetric spheres are placed in the liquid storage chamber.

[0019] Furthermore, T-shaped supports are provided on both sides of the exterior of the integrated pressure-bearing liquid storage tank. The bottom of the T-shaped supports is fixed. The exterior of the integrated pressure-bearing liquid storage tank is fixed with clamps. The left and right sides of the clamps are fixed to one end of the connecting rod, and the other end of the connecting rod is rotatably connected to the top of the two T-shaped supports.

[0020] The test method for the coal gas adsorption-desorption followed by water injection test device, implemented using the aforementioned coal gas adsorption-desorption followed by water injection test device, includes the following steps:

[0021] a. Place a certain mass of granular coal sample in the coal storage chamber inside the pressure-bearing liquid storage tank. Place a predetermined number of constant-volume balls into the liquid storage chamber inside the pressure-bearing liquid storage tank. Close the vent valve, the first shut-off valve, the first pressure reducing valve, the fourth shut-off valve, and the high-pressure shut-off valve. Open the second shut-off valve and the third shut-off valve. Then, open the high-pressure helium cylinder and the second pressure reducing valve to fill the test device with helium. Measure the gas pressure data of the first pipeline, the gas buffer tank, and the pressure-bearing liquid storage tank using the first gas pressure sensor and the second gas pressure sensor. Continuously observe the gas pressure changes using a computer to verify the airtightness of the test device.

[0022] b. After the airtightness test is completed, close the high-pressure helium cylinder and the second pressure reducing valve, open the vent valve to release the helium in the test device, close the vent valve after venting, open the first shut-off valve to start the vacuum pump for vacuuming, observe the vacuum gauge, and obtain the expected vacuum degree.

[0023] c. After the vacuuming is completed, turn off the vacuum pump and the first shut-off valve, rotate the valve stem of the high-pressure shut-off valve to make the O-ring seal fit tightly with the partition plate, so that the coal storage chamber and the liquid storage chamber in the pressure-bearing liquid storage tank are separated, open the high-pressure methane cylinder and the first pressure reducing valve, close the second shut-off valve and the third shut-off valve, fill the gas buffer tank with methane gas at a predetermined pressure, and then close the high-pressure methane cylinder and the first pressure reducing valve.

[0024] d. Open the second and third shut-off valves to introduce methane gas from the gas buffer tank into the pressurized liquid storage tank to the predetermined gas pressure. Then close the second and third shut-off valves to allow the coal sample in the pressurized liquid storage tank to reach the methane adsorption equilibrium time of no less than 12 hours. At the same time, measure the gas pressure data through the second gas pressure sensor and monitor and record the change of the methane adsorption equilibrium pressure value of the coal sample in the coal storage chamber of the pressurized liquid storage tank through a computer until the predetermined pressure value is reached.

[0025] e. Rotate the nut to open the water injection hole, and use a syringe to inject water into the lower liquid storage chamber of the pressurized liquid storage tank. After filling, tighten the nut to close the water injection hole. Rotate the valve stem of the high-pressure shut-off valve to separate the O-ring from the partition plate, connecting the coal storage chamber and the liquid storage chamber of the pressurized liquid storage tank. Rotate the pressurized liquid storage tank 360° back and forth to fully mix the water in the liquid storage chamber with the pre-adsorbed equilibrium coal sample in the coal storage chamber, thus achieving post-injection of water.

[0026] f. After the coal sample has been fully soaked in water after pre-adsorption equilibrium, the gas pressure data is measured by the second gas pressure sensor, and the gas pressure change of the pressure-bearing liquid storage tank is monitored and recorded by computer. Once the gas pressure value has no change, it is determined that the coal sample after water injection has reached methane adsorption equilibrium.

[0027] g. Then, after opening the fourth shut-off valve to release a certain amount of methane gas, immediately close it. Use a desorption measuring cylinder to measure the amount of methane gas released, while ensuring that the coal sample in the pressure-bearing liquid storage tank re-adsorbs to equilibrium and the adsorption time is not less than 12 hours. Measure the gas pressure data through the second gas pressure sensor, and monitor and record the gas pressure value after the pressure-bearing liquid storage tank reaches adsorption equilibrium through a computer. Release the methane gas from the pressure-bearing liquid storage tank step by step, calculate the amount of methane gas desorbed under different methane adsorption equilibrium pressures, and draw the coal sample adsorption gas isotherm at a predetermined moisture content.

[0028] h. After completing step g, repeat steps a to g in sequence, and adjust the initial free volume in the storage chamber of the pressure-bearing liquid storage tank by changing the number of constant volume balls to achieve different water injection volume control. This allows for the acquisition of coal sample adsorption gas isotherms under different moisture content conditions and analysis of the influence of water on the characteristics of coal adsorption gas.

[0029] i. After completing the coal gas adsorption test, proceed with steps b to f in sequence. Then, quickly open the venting valve and the third shut-off valve to release the free methane gas in the pressurized liquid storage tank and then quickly close them. At the same time, open the fourth shut-off valve and use the desorption measuring cylinder to measure the amount of methane gas desorbed in the pressurized liquid storage tank in real time. The desorption gas isotherm of the coal sample at the predetermined moisture content can be obtained.

[0030] j. Repeat steps b to f in sequence, and control the initial free volume in the storage chamber of the pressurized liquid storage tank by changing the number of constant volume balls to achieve different water injection volume control. Repeat step i to obtain the desorption gas isotherms of coal samples under different moisture contents and analyze the influence of water on the desorption and diffusion characteristics of gas in coal.

[0031] Furthermore, the pressure of the helium gas introduced in step a is 4–6 MPa.

[0032] Furthermore, the vacuuming process in step b shall last for no less than 4 hours.

[0033] Compared with the prior art, the present invention has the following beneficial effects:

[0034] The purpose of this invention is to simulate the changes in gas content in in-situ gas-bearing coal after water injection in actual mining environments using a post-injection water injection device. It scientifically studies the influence of different injection volumes on the gas adsorption and desorption characteristics of coal, demonstrating practical application value. The post-injection water injection device integrates the gas adsorption space and the liquid storage space of the coal sample, maintaining them as independent spaces. This ensures that the gas adsorption process and the liquid injection process do not interfere with each other, guaranteeing that the test conditions of both processes are consistent with the actual coal reservoir environment. Simultaneously, it utilizes the liquid's own weight to guide the liquid to flow naturally into the gas-bearing coal body, avoiding the impact interference of conventional high-pressure injection simulation devices. This highly accurate simulation demonstrates the gas adsorption and desorption process of coal after non-pressurized solution natural spraying during coal face mining, providing important theoretical support for post-injection water injection to prevent gas outburst disasters during coal face mining. The device has a simple overall structure, convenient testing methods, and a scientifically sound and reliable simulation process, demonstrating significant practical application value. Attached Figure Description

[0035] Figure 1 This is a schematic diagram of the coal gas adsorption-desorption followed by water injection test device of the present invention.

[0036] Figure 2 This is a schematic cross-sectional view of the integrated pressure-bearing liquid storage tank structure of the present invention;

[0037] 1 – Vacuum pump; 2 – High-pressure methane cylinder; 3 – High-pressure helium cylinder; 4 – Gas buffer tank; 51 – First pressure sensor; 52 – Second pressure sensor; 6 – Pressure-bearing liquid storage tank; 7 – Desorption measuring cylinder; 8 – Vacuum gauge; 9 – Data acquisition unit; 10 – Computer; 11 – Water injection hole; 12 – T-shaped support frame; 13 – Coal storage chamber; 14 – Liquid storage chamber; 15 – Partition plate; 16 – Valve stem; 17 – O-ring seal; 18 – Volumetric ball; 19 – Industrial control computer; 20 – Clamp; 21 – Connecting rod; 22 – Nut;

[0038] 101 - Vent valve; 102 - First shut-off valve; 103 - Second shut-off valve; 104 - Third shut-off valve; 105 - First pressure reducing valve; 106 - Second pressure reducing valve; 107 - Fourth shut-off valve; 108 - High-pressure shut-off valve.

[0039] 100 - First pipe; 200 - Second pipe; 300 - Third pipe; 400 - Exhaust pipe; 500 - Intake pipe. Detailed Implementation

[0040] The following description, in conjunction with the accompanying drawings and specific embodiments, further illustrates the detailed content and specific implementation of the present invention.

[0041] Example 1

[0042] Reference Figures 1-2 The coal gas adsorption-desorption post-water injection test device includes a vacuum unit, a gas supply unit, an adsorption-desorption post-water injection unit, and a data acquisition and storage unit.

[0043] The vacuum pumping unit includes a vacuum pump 1, a first shut-off valve 102, and a vent valve 101;

[0044] The gas supply unit includes a high-pressure methane cylinder 2, a high-pressure helium cylinder 3, a gas buffer tank 4, a second shut-off valve 103, and a third shut-off valve 104.

[0045] The adsorption-desorption post-water injection unit includes a pressurized liquid storage tank 6, a desorption measuring cylinder 7, and a fourth shut-off valve 107.

[0046] The data acquisition and storage unit includes a first gas pressure sensor 51, a second gas pressure sensor 52, a data acquisition unit 9, an industrial control computer 19, and a computer 10;

[0047] The high-pressure methane cylinder 2 and the high-pressure helium cylinder 3 are respectively connected to the inlet end of the gas buffer tank 4 through the inlet pipe 500; the outlet end of the gas buffer tank 4 is connected to the pressure-bearing liquid storage tank 6 through the first pipe 100, and the pressure-bearing liquid storage tank 6 is also connected to the desorption measuring cylinder 7 through the third pipe 300. A fourth shut-off valve 107 is provided on the third pipe 300. The vacuum pump 1 is connected to the first pipe 100 through the second pipe 200, and an exhaust pipe 400 is provided at the connection between the first pipe 100 and the second pipe 200. A first shut-off valve 102 is provided on the second pipe 200, and a vent valve 101 is provided on the exhaust pipe 400.

[0048] The first gas pressure sensor 51 is installed on the gas buffer tank 4, and the second gas pressure sensor 52 is installed on the pressure-bearing liquid storage tank 6. The first gas pressure sensor 51 and the second gas pressure sensor 52 are electrically connected to the data acquisition unit 9, the data acquisition unit 9 is connected to the industrial control computer 19, and the industrial control computer 19 is connected to the computer 10.

[0049] A vacuum gauge 8 is provided on the vacuum pump 1.

[0050] A first pressure reducing valve 105 and a second pressure reducing valve 106 are respectively installed on the inlet pipes 500 of the high-pressure methane cylinder 2 and the high-pressure helium cylinder 3.

[0051] A second shut-off valve 103 and a third shut-off valve 104 are sequentially provided on the first pipeline 100. The second shut-off valve 103 is located between the gas buffer tank 4 and the vacuum pump 1, and the third shut-off valve 104 is located between the vacuum pump 1 and the pressure-bearing liquid storage tank 6.

[0052] The pressure-bearing liquid storage tank 6 includes a tank body made of metal with a sealed interior. The tank body is equipped with a partition plate 15, which divides the internal part of the tank body into a coal storage chamber 13 and a liquid storage chamber 14. The partition plate 15 has a central hole. A water injection hole 11 and a high-pressure shut-off valve 108 are provided at the bottom of the liquid storage chamber 14. A nut 22 is installed on the outside of the water injection hole 11, and the water injection hole 11 can be opened or closed by rotating the nut 22.

[0053] The high-pressure shut-off valve 108 is rotatably connected to the liquid storage chamber 14. The valve stem 16 of the high-pressure shut-off valve 108 is placed inside the liquid storage chamber 14. The valve stem 16 is a rounded bolt with a handle at the bottom. The handle is placed outside the tank body for easy rotation. The top of the valve stem 16 is equipped with an O-ring seal 17. By rotating the valve stem 16 of the high-pressure shut-off valve 108, the O-ring seal 17 is tightly fitted or separated from the center hole of the partition plate 15, thereby controlling the isolation or connection between the coal storage chamber 13 and the liquid storage chamber 14.

[0054] Several volumetric balls 18 are placed inside the liquid storage chamber 14.

[0055] A volume-regulating ball 18 is placed inside the liquid storage chamber 14. By controlling the number of volume-regulating balls 18, the initial free volume inside the liquid storage chamber 14 is changed, thereby controlling different water injection volumes. After the liquid storage chamber 14 of the pressurized liquid storage tank 6 is filled with water, there is no more free space inside. Only the coal storage chamber 13 has free space inside the pressurized liquid storage tank 6. After rotating the high-pressure shut-off valve 108 to connect the coal storage chamber 13 and the liquid storage chamber 14 of the pressurized liquid storage tank 6, rotating the pressurized liquid storage tank 6 completes the natural injection of water from the liquid storage chamber 14 into the coal storage chamber 13, completing the post-watering process after the coal sample has reached gas adsorption equilibrium. After water injection, the free volume inside the pressurized liquid storage tank 6 is still the initial free volume of the coal storage chamber 13 before water injection, remaining unchanged. This realizes the entire process of coal gas adsorption and desorption under isovolumetric test conditions after water injection, eliminating the test accuracy problem caused by changes in free space.

[0056] T-shaped supports 12 are respectively provided on both sides of the exterior of the integrated pressure-bearing liquid storage tank 6. The bottom ends of the T-shaped supports 12 are fixed. Clamps 20 are fixed to the exterior of the integrated pressure-bearing liquid storage tank 6. The left and right sides of the clamps 20 are respectively fixed to one end of the connecting rod 21, and the other end of the connecting rod 21 is rotatably connected to the top of the two T-shaped supports 12. The rotation of the connecting rods 21 on both sides of the clamps 20 drives the integrated pressure-bearing liquid storage tank 6 to rotate 360° reciprocally in the vertical direction.

[0057] Vent valve 101, first shut-off valve 102, second shut-off valve 103, third shut-off valve 104, first pressure reducing valve 105, second pressure reducing valve 106, fourth shut-off valve 107, and high-pressure shut-off valve 108 are all connected to industrial control computer 19, and the operation of each valve is controlled by industrial control computer 19.

[0058] Example 2

[0059] The test method for the coal gas adsorption-desorption followed by water injection test device is implemented using the coal gas adsorption-desorption followed by water injection test device in Example 1, and includes the following steps:

[0060] a. Place a 50g granular coal sample into the coal storage chamber 13 inside the pressurized liquid storage tank 6. Place a predetermined number of constant volume balls 18 into the liquid storage chamber 14 inside the pressurized liquid storage tank 6. Close the vent valve 101, the first shut-off valve 102, the first pressure reducing valve 105, the fourth shut-off valve 107, and the high pressure shut-off valve 108. Open the second shut-off valve 103 and the third shut-off valve 104. Then open the high pressure helium cylinder 3 and the second pressure reducing valve 106 to fill the test device with helium at a pressure of 6MPa. Measure the gas pressure data of the first pipeline 100, the gas buffer tank 4, and the pressurized liquid storage tank 6 through the first gas pressure sensor 51 and the second gas pressure sensor 52. Continuously observe the gas pressure changes through the computer 10 to verify the airtightness of the test device.

[0061] b. After the airtightness test is completed, close the high-pressure helium cylinder 3 and the second pressure reducing valve 106, open the venting valve 101 to release the helium in the test device, close the venting valve 101 after venting, open the first shut-off valve 102 to start the vacuum pump 1 to perform vacuuming for 4 hours, observe the vacuum gauge 8, and obtain the expected vacuum degree.

[0062] c. After the vacuuming is completed, turn off the vacuum pump 1 and the first shut-off valve 102, rotate the valve stem 16 of the high-pressure shut-off valve 108 to make the O-ring 17 fit tightly with the partition plate 15, so that the coal storage chamber 13 and the liquid storage chamber 14 in the pressure-bearing liquid storage integrated tank 6 are separated, open the high-pressure methane cylinder 2 and the first pressure reducing valve 105, close the second shut-off valve 103 and the third shut-off valve 104, and fill the gas buffer tank 4 with methane gas at a predetermined pressure (5MPa), and then close the high-pressure methane cylinder 2 and the first pressure reducing valve 105;

[0063] d. Open the second shut-off valve 103 and the third shut-off valve 104, and put the methane gas in the gas buffer tank 4 into the pressurized liquid storage tank 6 to the predetermined gas pressure. Then close the second shut-off valve 103 and the third shut-off valve 104, so that the coal sample in the pressurized liquid storage tank 6 has an adsorption equilibrium time of not less than 12 hours. At the same time, the gas pressure data is measured by the second gas pressure sensor 52, and the changes in the methane adsorption equilibrium pressure of the coal sample in the coal storage chamber 13 of the pressurized liquid storage tank 6 are monitored and recorded by the computer 10 until the predetermined pressure value is reached.

[0064] e. Rotate the nut 22 to open the water injection hole 11, and use a syringe to inject water into the lower liquid storage chamber 14 of the pressurized liquid storage tank 6. Stop the injection when the liquid storage chamber 14 is full of liquid, tighten the nut 22 to close the water injection hole 11, rotate the valve stem 16 of the high pressure shut-off valve 108 to separate the O-ring 17 from the partition plate 15, connect the coal storage chamber 13 and the liquid storage chamber 14 of the pressurized liquid storage tank 6, and rotate the pressurized liquid storage tank 6 360° back and forth to fully mix the water in the liquid storage chamber 14 with the pre-adsorbed equilibrium coal sample in the coal storage chamber 13 to achieve post-injection water;

[0065] f. After the coal sample has been fully soaked in water after pre-adsorption equilibrium, the gas pressure data is measured by the second gas pressure sensor 52, and the gas pressure change of the pressure-bearing liquid storage tank 6 is monitored and recorded by the computer 10. Once the gas pressure value has no change, it is determined that the coal sample after water injection has reached methane adsorption equilibrium.

[0066] g. Then, the fourth shut-off valve 107 is opened to release a certain amount of methane gas and then immediately closed. The amount of methane gas released is measured using the desorption measuring cylinder 7. At the same time, the coal sample in the pressure-bearing liquid storage tank 6 is re-adsorbed to equilibrium and the adsorption time is not less than 12 hours. The gas pressure data is measured by the second gas pressure sensor 52 and the gas pressure value after the adsorption equilibrium of the pressure-bearing liquid storage tank 6 is monitored and recorded by the computer 10. The methane gas in the pressure-bearing liquid storage tank 6 is released step by step. The amount of methane gas desorbed under different methane adsorption equilibrium pressures is calculated. The adsorption gas isotherm of the coal sample at the predetermined moisture content can be plotted.

[0067] h. After completing step g, repeat steps a to g in sequence, and adjust the initial free volume in the storage chamber 14 of the pressure-bearing liquid storage tank 6 by changing the number of constant volume balls 18 to achieve different water injection volume control. This allows for obtaining coal sample adsorption gas isotherms under different moisture content conditions and analyzing the effect of water on coal adsorption gas characteristics.

[0068] i. After completing the coal gas adsorption test, proceed with steps b to f in sequence. Then, quickly open the venting valve 101 and the third shut-off valve 104 to release the free methane gas in the pressurized liquid storage tank 6 and then quickly close them. At the same time, open the fourth shut-off valve 107 and use the desorption measuring cylinder 7 to measure the amount of methane gas desorbed in the pressurized liquid storage tank 6 in real time. The coal sample desorption gas isotherm at the predetermined moisture content can be obtained.

[0069] j. Repeat steps b to f in sequence, and adjust the initial free volume in the storage chamber 14 of the pressure-bearing liquid storage tank 6 by changing the number of constant volume balls 18 to achieve different water injection volume control. Repeat step i to obtain the coal sample desorption gas isotherms under different moisture contents and analyze the influence of water on the desorption and diffusion characteristics of gas in coal.

[0070] Example 3

[0071] The difference from Example 2 is that in step a, the high-pressure helium cylinder 3 and the second pressure reducing valve 106 are opened to fill the test device with helium at a pressure of 4MPa.

[0072] This invention constructs a water injection system and an adsorption-desorption system. First, the adsorption and desorption equilibrium of the coal sample is achieved. Then, by rotating the pressure-bearing liquid storage tank 6 and opening the high-pressure shut-off valve 108, the liquid storage chamber 14 and the coal storage chamber 13 inside the pressure-bearing liquid storage tank are connected. The water in the liquid storage chamber 14 flows naturally into the coal storage chamber 13, realizing the post-injection water effect of the gas adsorption-desorption test. This process is more consistent with the fact that the coal sample has already adsorbed a large amount of gas in the actual engineering process, and provides a more reliable experimental tool for solving the problem of coal gas outburst during the coal mining process in the future.

[0073] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A coal gas adsorption-desorption followed by water injection test device, characterized in that, It includes a vacuum unit, a gas supply unit, an adsorption-desorption post-water injection unit, and a data acquisition and storage unit; The vacuum pumping unit includes a vacuum pump, a first shut-off valve, and a vent valve; The gas supply unit includes a high-pressure methane cylinder, a high-pressure helium cylinder, a gas buffer tank, a second shut-off valve, and a third shut-off valve. The adsorption-desorption post-water injection unit includes a pressurized liquid storage tank, a desorption measuring cylinder, and a fourth shut-off valve. The data acquisition and storage unit includes a first gas pressure sensor, a second gas pressure sensor, a data acquisition unit, an industrial control computer, and a computer. The high-pressure methane cylinder and the high-pressure helium cylinder are respectively connected to the inlet end of the gas buffer tank through inlet pipes; the outlet end of the gas buffer tank is connected to the pressure-bearing liquid storage tank through a first pipe, and the pressure-bearing liquid storage tank is also connected to the desorption measuring cylinder through a third pipe. A fourth shut-off valve is provided on the third pipe. The vacuum pump is connected to the first pipe through a second pipe, and an exhaust pipe is provided at the connection between the first pipe and the second pipe. A first shut-off valve is provided on the second pipe, and a vent valve is provided on the exhaust pipe. The first gas pressure sensor is installed on the gas buffer tank, and the second gas pressure sensor is installed on the pressurized liquid storage tank. The first gas pressure sensor and the second gas pressure sensor are electrically connected to the data acquisition unit, the data acquisition unit is connected to the industrial control computer, and the industrial control computer is connected to the computer. The pressure-bearing liquid storage tank includes a tank body with an internal partition plate that divides the tank body into a coal storage chamber and a liquid storage chamber. The partition plate has a central hole. A water injection hole and a high-pressure shut-off valve are provided at the bottom of the liquid storage chamber. A nut is installed on the outside of the water injection hole, and the water injection hole can be opened or closed by rotating the nut. The high-pressure shut-off valve is rotatably connected to the liquid storage chamber. The valve stem of the high-pressure shut-off valve is placed inside the liquid storage chamber, and an O-ring is provided at the top of the valve stem. By rotating the valve stem, the O-ring is tightly fitted or separated from the center hole of the partition plate, thereby controlling the isolation or connection between the coal storage chamber and the liquid storage chamber.

2. The coal gas adsorption-desorption followed by water injection test device as described in claim 1, characterized in that, A vacuum gauge is installed on the vacuum pump.

3. The coal gas adsorption-desorption followed by water injection test device as described in claim 1, characterized in that, A first pressure reducing valve and a second pressure reducing valve are respectively installed on the inlet pipes of the high-pressure methane cylinder and the high-pressure helium cylinder.

4. The coal gas adsorption-desorption followed by water injection test device as described in claim 1, characterized in that, A second shut-off valve and a third shut-off valve are sequentially installed on the first pipeline. The second shut-off valve is located between the gas buffer tank and the vacuum pump, and the third shut-off valve is located between the vacuum pump and the pressure-bearing liquid storage tank.

5. The coal gas adsorption-desorption followed by water injection test device as described in claim 1, characterized in that, Several constant-volume balls are placed in the liquid storage chamber.

6. The coal gas adsorption-desorption followed by water injection test device as described in claim 1, characterized in that, T-shaped supports are provided on both sides of the outside of the pressure-bearing liquid storage tank. The bottom of the T-shaped supports is fixed. The outside of the pressure-bearing liquid storage tank is fixed with clamps. The left and right sides of the clamps are fixed to one end of the connecting rod, and the other end of the connecting rod is rotatably connected to the top of the two T-shaped supports.

7. A test method for a coal gas adsorption-desorption followed by water injection test device, implemented using the coal gas adsorption-desorption followed by water injection test device as described in any one of claims 1-6, characterized in that, Includes the following steps: a. Place a certain mass of granular coal sample in the coal storage chamber inside the pressure-bearing liquid storage tank. Place a predetermined number of constant-volume balls into the liquid storage chamber inside the pressure-bearing liquid storage tank. Close the vent valve, the first shut-off valve, the first pressure reducing valve, the fourth shut-off valve, and the high-pressure shut-off valve. Open the second shut-off valve and the third shut-off valve. Then, open the high-pressure helium cylinder and the second pressure reducing valve to fill the test device with helium. Measure the gas pressure data of the first pipeline, the gas buffer tank, and the pressure-bearing liquid storage tank using the first gas pressure sensor and the second gas pressure sensor. Continuously observe the gas pressure changes using a computer to verify the airtightness of the test device. b. After the airtightness test is completed, close the high-pressure helium cylinder and the second pressure reducing valve, open the vent valve to release the helium in the test device, close the vent valve after venting, open the first shut-off valve to start the vacuum pump for vacuuming, observe the vacuum gauge, and obtain the expected vacuum degree. c. After the vacuuming is completed, turn off the vacuum pump and the first shut-off valve, rotate the valve stem of the high-pressure shut-off valve to make the O-ring seal fit tightly with the partition plate, so that the coal storage chamber and the liquid storage chamber in the pressure-bearing liquid storage tank are separated, open the high-pressure methane cylinder and the first pressure reducing valve, close the second shut-off valve and the third shut-off valve, fill the gas buffer tank with methane gas at a predetermined pressure, and then close the high-pressure methane cylinder and the first pressure reducing valve. d. Open the second and third shut-off valves to introduce methane gas from the gas buffer tank into the pressurized liquid storage tank to the predetermined gas pressure. Then close the second and third shut-off valves to allow the coal sample in the pressurized liquid storage tank to reach the methane adsorption equilibrium time of no less than 12 hours. At the same time, measure the gas pressure data through the second gas pressure sensor and monitor and record the change of the methane adsorption equilibrium pressure value of the coal sample in the coal storage chamber of the pressurized liquid storage tank through a computer until the predetermined pressure value is reached. e. Rotate the nut to open the water injection hole, and use a syringe to inject water into the lower liquid storage chamber of the pressurized liquid storage tank. After filling, tighten the nut to close the water injection hole. Rotate the valve stem of the high-pressure shut-off valve to separate the O-ring from the partition plate, connecting the coal storage chamber and the liquid storage chamber of the pressurized liquid storage tank. Rotate the pressurized liquid storage tank 360° back and forth to fully mix the water in the liquid storage chamber with the pre-adsorbed equilibrium coal sample in the coal storage chamber, thus achieving post-injection of water. f. After the coal sample has been fully soaked in water after pre-adsorption equilibrium, the gas pressure data is measured by the second gas pressure sensor, and the gas pressure change of the pressure-bearing liquid storage tank is monitored and recorded by computer. Once the gas pressure value has no change, it is determined that the coal sample after water injection has reached methane adsorption equilibrium. g. Then, after opening the fourth shut-off valve to release a certain amount of methane gas, immediately close it. Use a desorption measuring cylinder to measure the amount of methane gas released, while ensuring that the coal sample in the pressure-bearing liquid storage tank re-adsorbs to equilibrium and the adsorption time is not less than 12 hours. Measure the gas pressure data through the second gas pressure sensor, and monitor and record the gas pressure value after the pressure-bearing liquid storage tank reaches adsorption equilibrium through a computer. Release the methane gas from the pressure-bearing liquid storage tank step by step, calculate the amount of methane gas desorbed under different methane adsorption equilibrium pressures, and plot the methane adsorption isotherm of the coal sample at the predetermined moisture content. h. After completing step g, repeat steps a to g in sequence, and adjust the initial free volume in the storage chamber of the pressure-bearing liquid storage tank by changing the number of constant volume balls to achieve different water injection volume control, obtain the coal sample adsorption gas isotherm under different moisture content conditions, and analyze the effect of water on the coal adsorption gas characteristics. i. After completing the coal gas adsorption test, proceed with steps b to f in sequence. Then, quickly open the venting valve and the third shut-off valve to release the free methane gas in the pressurized liquid storage tank and then quickly close them. At the same time, open the fourth shut-off valve and use the desorption measuring cylinder to measure the amount of methane gas desorbed in the pressurized liquid storage tank in real time to obtain the coal sample desorption gas isotherm at the predetermined moisture content. j. Repeat steps b to f in sequence, and adjust the initial free volume in the storage chamber of the pressure-bearing liquid storage tank by changing the number of constant volume balls to achieve different water injection volume control. Repeat step i to obtain the desorption gas isotherms of coal samples under different moisture contents and analyze the influence of water on the desorption and diffusion characteristics of gas in coal.

8. The test method of the coal gas adsorption-desorption followed by water injection test device as described in claim 7, characterized in that, The pressure of helium gas introduced in step a is 4-6 MPa.

9. The test method of the coal gas adsorption-desorption followed by water injection test device as described in claim 7, characterized in that, The vacuuming process in step b shall last for no less than 4 hours.

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