Method and device for determining particle size of residual gas of coal sample in well under normal pressure and not desorbable

Abstract

A kind of method and device for determining the particle size of residual gas of coal sample in well under normal pressure, a n-stage sealed crushing cavity is arranged in the coal sample tank, crushing blades are arranged in each crushing cavity, the outlet of underground compressed air source is communicated with the inlet of two-piece, the outlet of two-piece is communicated with the inlet of pneumatic motor through pipeline, the output shaft of pneumatic motor is connected with transmission shaft, screen mesh is installed at the bottom of the first-stage crushing cavity to the (n-1) -stage crushing cavity, the mesh diameter of screen mesh gradually decreases from the first-stage crushing cavity to the (n-1) -stage crushing cavity, opening and closing mechanism capable of opening and closing screen mesh holes to allow coal sample to fall is arranged at the bottom of screen mesh of the first-stage crushing cavity to the (n-1) -stage crushing cavity;Needle valve is installed at the side of the first-stage crushing cavity to the n-stage crushing cavity, flow meter is connected with the first-stage crushing cavity to the n-stage crushing cavity through needle valve respectively.The present application can quickly and accurately determine the particle size of residual gas of coal seam under normal pressure, and improve the efficiency of coal seam gas content determination.

Description

Technical Field

[0001] This invention relates to a method for determining the non-desorbable particle size of coal seam gas under normal pressure, specifically a method and apparatus for determining the non-desorbable particle size of residual gas in underground coal samples under normal pressure, belonging to the field of coal mine safety technology. Background Technology

[0002] In the field of coal mine safety technology, coal seam gas content has always been one of the important indicators for evaluating the risk of coal and gas outbursts. It is also an important parameter used for mine mining deployment, development and extension design, gas emission prediction, gas extraction effect evaluation, coalbed methane resource evaluation and regional verification.

[0003] Currently, most coal mines both domestically and internationally use the direct method to measure coal seam gas content. The direct method for measuring coal seam gas content is based on the national standard GB / T 23250-2009, "Direct Method for Determining Coal Seam Gas Content Underground." However, the sealed coal (rock) core sampler and the gas-gathering coal (rock) core sampler used in this method are relatively complex to use and maintain. Furthermore, the gas loss during sampling is difficult to estimate, and there are certain difficulties in sampling thin coal seams using these instruments, which are sometimes not accurate enough. In addition, the direct method also has some disadvantages in ensuring airtightness, which can easily lead to measurement errors.

[0004] The direct determination method for coal seam gas content consists of five parts: gas loss from the coal sample (X0), gas desorbed underground (X1), gas desorbed before coal sample crushing (X2), gas desorbed after coal sample crushing (X3), and non-desorbable gas under atmospheric pressure (X4). The non-desorbable gas (X4) is the amount of gas remaining in the coal body after the coal sample is crushed under atmospheric pressure. It cannot be desorbed under normal pressure, has no contribution to outburst prevention, and cannot be extracted and utilized. Therefore, it is necessary to quickly identify the non-desorbable particle size of residual coal seam gas under normal pressure on-site to reduce the gas content determination time, save manpower and resources, and improve efficiency. Summary of the Invention

[0005] The purpose of this invention is to provide a method and apparatus for determining the non-desorbable particle size of residual gas in underground coal samples under normal pressure. This method can quickly and accurately determine the non-desorbable particle size of residual gas in coal seams under normal pressure, improve the efficiency of coal seam gas content determination, and provide a basis for mine mining deployment, development and extension design, and gas emission prediction.

[0006] To achieve the above objectives, the present invention provides a method for determining the non-desorbable particle size of residual gas in underground coal samples under normal pressure, comprising the following steps:

[0007] ① Collect a certain mass of coal sample with a particle size greater than 10 mesh in the underground coal mine, and put the collected coal sample into the first-stage crushing chamber of a transparent sealed coal sample container;

[0008] ② Connect the underground compressed air source. After gas-liquid separation by the dual-unit, the compressed air enters the air inlet of the pneumatic motor. The pneumatic motor and the drive shaft are connected by a coupling. The pneumatic motor drives the drive shaft to rotate, and the drive shaft drives the crushing blades to rotate, crushing the coal sample in the first-stage crushing chamber. During the crushing process, the opening and closing mechanism under the screen of the first-stage crushing chamber is opened by operating the knob. During the crushing process, the coal sample will fall into the second-stage crushing chamber through the screen at the bottom of the first-stage crushing chamber. When no coal sample remains in the first-stage crushing chamber is observed by the naked eye, the crushing is stopped. During this process, the needle valve corresponding to the first-stage crushing chamber is opened, and the needle valves corresponding to other crushing chambers are kept closed. The flow meter measures the gas desorption rate S1 of the coal sample in the first-stage crushing chamber in real time. When the gas desorption rate S1 of the coal sample is <0.05ml / min, it is considered that the desorption is over. Record the cumulative gas desorption amount V1 of the coal sample in the first-stage crushing chamber, and close the needle valve corresponding to the first-stage crushing chamber.

[0009] ③ After the first stage of crushing is completed, the coal sample has completely fallen into the second stage crushing chamber. Start the second stage of crushing, close the opening and closing mechanism under the screen of the first stage crushing chamber by operating the knob, and at the same time open the opening and closing mechanism under the screen of the second stage crushing chamber by operating the knob. Then the crushing blade crushes the coal sample in the second stage crushing chamber. During the crushing process, the coal sample will fall into the third stage crushing chamber. Stop crushing when it is observed by the naked eye that there is no residual coal sample in the second stage crushing chamber. During this process, open the needle valve corresponding to the second stage crushing chamber and keep the needle valves corresponding to other crushing chambers closed. The flow meter measures the gas desorption rate S2 of the coal sample in the second stage crushing chamber in real time. When the gas desorption rate S2 of the coal sample is < 0.05 ml / min, it is considered that the desorption is over. Record the cumulative gas desorption amount V2 of the coal sample in the second stage crushing chamber and close the needle valve corresponding to the second stage crushing chamber.

[0010] ④ After the i-th stage (1≤i<n) of crushing and desorption is completed, the i+1-th stage crushing chamber is started. When the coal sample particle size is crushed to below 30×(i+1) mesh, crushing is stopped. At the same time, the flow meter measures the coal sample gas desorption rate Si. When Si<0.05ml / min, desorption ends. Record the cumulative amount of coal sample gas desorbed in the i-th stage crushing chamber Vi.

[0011] ⑤ Repeat step ③ until the nth stage of crushing is performed. Stop crushing after five minutes and record the cumulative amount of gas desorbed from the coal sample in the crushing chamber after the nth stage of crushing, Vn.

[0012] ⑥ When j is the smallest positive integer that satisfies the following inequality, the critical particle size of the residual gas in the coal sample that cannot be desorbed at normal pressure is 30 × j mesh.

[0013]

[0014] In the formula: j is an intermediate variable.

[0015] The coal sample collected from the underground mine has a mass of 500g or more.

[0016] A device for determining the particle size of non-desorbable residual gas in underground coal samples under normal pressure includes an underground compressed air source, a dual-unit assembly, a pneumatic motor, a drive shaft, a coal sample container, and a flow meter. The coal sample container is a transparent container mounted on a support. The coal sample container contains n-stage sealed crushing chambers, each equipped with crushing blades. The outlet of the underground compressed air source is connected to the inlet of the dual-unit assembly, and the outlet of the dual-unit assembly is connected to the inlet of the pneumatic motor via a pipeline. The output shaft of the pneumatic motor is connected via a coupling. The device is connected to the drive shaft. Screens are installed at the bottom of the first-stage crushing chamber to the (n-1)th-stage crushing chamber. The diameter of the screen holes gradually decreases from the first-stage crushing chamber to the (n-1)th-stage crushing chamber. An opening and closing mechanism is provided at the bottom of the screens in the first-stage crushing chamber to the (n-1)th-stage crushing chamber to allow the coal sample to fall. Needle valves are installed on the sides of the first-stage crushing chamber to the nth-stage crushing chamber. The flow meter is connected to the first-stage crushing chamber to the nth-stage crushing chamber through the needle valves.

[0017] Preferably, the coal sample container has at least four crushing stages.

[0018] Preferably, each crushing chamber has a protrusion on its inner wall, which allows the coal sample to be fully crushed in each crushing chamber.

[0019] To ensure the airtightness of the coal sample container's crushing chamber during crushing, the screen at the bottom of the crushing chamber remains closed during the crushing process and is opened after crushing is completed.

[0020] The opening and closing mechanism consists of nested partitions. A knob is installed at the front end of the partition, and a rubber protrusion is installed at the rear end of the partition. The rubber protrusion of each partition and the groove of the next partition can be fixed together by embedding, taking advantage of the large elastic deformation of rubber. The opening and closing mechanism can also ensure the airtightness of each crushing chamber during the crushing process.

[0021] Compared with existing technologies, this invention uses a dual-unit connection between the underground compressed air source and the pneumatic motor. The pressure-reducing valve in the dual-unit stabilizes the air source pressure, keeping it constant and reducing damage to valves or actuators caused by sudden changes in air pressure. The filter cleans the air source, filtering out moisture from the compressed air and preventing it from entering the device. This invention features multi-stage crushing chambers, each equipped with a boss and crushing blades, ensuring thorough crushing of the coal sample at each stage and guaranteeing the accuracy of the experimental results. A screen is installed at the bottom of the crushing chambers. After crushing, opening the screen's bottom mechanism allows coal samples with a particle size smaller than the screen's aperture diameter to automatically fall into the next crushing chamber, simplifying operation. Furthermore, the experimental setup is optimized, improving measurement efficiency and saving manpower and resources. This invention enables rapid and accurate determination of the non-desorbable particle size of residual coal seam gas at atmospheric pressure, improving the efficiency of coal seam gas content measurement and providing a basis for mine deployment, development and extension design, and gas emission prediction. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the structure of the present invention;

[0023] Figure 2 This is a top view of the screen opening and closing mechanism of the present invention when it is closed;

[0024] Figure 3 This is a schematic diagram of the opening and closing mechanism under screen I and the closing mechanism under screen II after the first stage of crushing in an embodiment of the present invention (other parts are not shown).

[0025] In the diagram: 1. Downhole compressed air source; 2. Dual unit; 3. Pneumatic motor inlet; 4. Pneumatic motor outlet; 5. Pneumatic motor; 6. Coupling; 7. Support; 8. Coal sample container; 9. Crushing blade I; 10. Crushing blade II; 11. Crushing blade III; 12. Crushing blade IV; 13. First-stage crushing chamber; 14. Second-stage crushing chamber; 15. Third-stage crushing chamber; 16. Fourth-stage crushing chamber; 17. Flow meter; 18. Needle valve I; 19. Needle valve II; 20. Needle valve III; 21. Needle valve IV; 22. Boss I; 23. Boss II; 24. Boss III; 25. Boss IV; 26. Screen I; 27. Screen II; 28. Screen III; 29. ​​Drive shaft; 30. Partition; 31. Knob; 32. Protrusion; 33. Groove. Detailed Implementation

[0026] The invention will now be further described with reference to the accompanying drawings.

[0027] like Figures 1-3 As shown, a method for determining the non-desorbable particle size of residual gas in underground coal samples under normal pressure includes the following steps:

[0028] ① Collect a certain mass of coal sample with a particle size greater than 10 mesh in the underground coal mine, and put the collected coal sample into the first-stage crushing chamber 13 of the transparent sealed coal sample container 8;

[0029] ② Connect the underground compressed air source 1. After gas-liquid separation via the dual-unit 2, the compressed air from the underground compressed air source 1 enters the pneumatic motor inlet 3. The pneumatic motor 5 is connected to the drive shaft 29 via a coupling 6. The pneumatic motor 5 drives the drive shaft 29 to rotate, which in turn drives the crushing blades to rotate, crushing the coal sample in the first-stage crushing chamber 13. Simultaneously, the opening and closing mechanism below the corresponding screen I 26 in the first-stage crushing chamber 13 is opened by operating the knob 31. During the crushing process, the coal sample falls through the screen I 26 at the bottom of the first-stage crushing chamber 13 into the second-stage crushing chamber. In the secondary crushing chamber 14, crushing is stopped when no residual coal sample is observed inside the first-stage crushing chamber 13. During this process, the needle valve corresponding to the first-stage crushing chamber 13 is opened, while the needle valves corresponding to other crushing chambers are kept closed. The flow meter 17 measures the gas desorption rate S1 of the coal sample in the first-stage crushing chamber 13 in real time. When the gas desorption rate S1 < 0.05 ml / min, desorption is considered to be over. The cumulative gas desorption amount V1 of the coal sample in the first-stage crushing chamber 13 is recorded, and the needle valve corresponding to the first-stage crushing chamber 13 is closed.

[0030] ③ After the first stage of crushing is completed, the coal sample has fallen into the second stage crushing chamber 14. Start the second stage of crushing. Close the opening and closing mechanism under the screen I 26 corresponding to the first stage crushing chamber 13 by operating knob 31. At the same time, open the opening and closing mechanism under the screen II 27 corresponding to the second stage crushing chamber 14 by operating knob 31. Then the crushing blade crushes the coal sample in the second stage crushing chamber 14. During the crushing process, the coal sample will fall into the third stage crushing chamber 15. Stop crushing when it is observed by the naked eye that there is no residual coal sample in the second stage crushing chamber 14. During this process, open the needle valve II 19 corresponding to the second stage crushing chamber 14 and keep the needle valves corresponding to other crushing chambers closed. The flow meter 17 measures the gas desorption rate S2 of the coal sample in the second stage crushing chamber 14 in real time. When the gas desorption rate S2 of the coal sample is < 0.05 ml / min, it is considered that the desorption is over. Record the cumulative gas desorption amount V2 of the coal sample in the second stage crushing chamber 14 and close the needle valve II 19 corresponding to the second stage crushing chamber 14.

[0031] ④ After the i-th stage (1≤i<n) of crushing and desorption is completed, the i+1-th stage crushing chamber is started. When the coal sample particle size is crushed to below 30×(i+1) mesh, crushing is stopped. At the same time, the flow meter measures the coal sample gas desorption rate Si. When Si<0.05ml / min, desorption ends. Record the cumulative amount of coal sample gas desorbed in the i-th stage crushing chamber Vi.

[0032] ⑤ Repeat step ③ until the nth stage of crushing is performed. Stop crushing after five minutes and record the cumulative amount of gas desorbed from the coal sample in the crushing chamber after the nth stage of crushing, Vn.

[0033] ⑥ When j is the smallest positive integer that satisfies the following inequality, the critical particle size of the residual gas in the coal sample that cannot be desorbed at normal pressure is 30 × j mesh.

[0034]

[0035] In the formula: j is an intermediate variable.

[0036] The coal sample collected from the underground mine has a mass of 500g or more.

[0037] A device for determining the non-desorbable particle size of residual gas in underground coal samples under normal pressure includes an underground compressed air source 1, a dual-unit assembly 2, a pneumatic motor 5, a drive shaft 29, a coal sample container 8, and a flow meter 17. The coal sample container 8 is a transparent container mounted on a support 7. The coal sample container 8 has n-stage sealed crushing chambers, each equipped with crushing blades. The outlet of the underground compressed air source 1 is connected to the inlet of the dual-unit assembly 2, supplying gas to the assembly. The outlet of the dual-unit assembly 2 is connected to the inlet 3 of the pneumatic motor via a pipeline. After gas-liquid separation by the dual-unit assembly 2, the gas is delivered to the inlet 3 of the pneumatic motor. The output shaft of the pneumatic motor 5 is connected to the drive shaft 29 via a coupling 6.

[0038] Screens are installed at the bottom of the first-stage crushing chamber to the (n-1)th-stage crushing chamber, with the screen aperture diameter gradually decreasing from the first-stage crushing chamber to the (n-1)th-stage crushing chamber. An opening and closing mechanism is provided at the bottom of the screens in the first-stage crushing chamber to the (n-1)th-stage crushing chamber to allow coal samples to fall. Needle valves are installed on the sides of the first-stage crushing chamber to the nth-stage crushing chamber, and flow meters are connected to the first-stage crushing chamber to the nth-stage crushing chamber through the needle valves.

[0039] Example

[0040] In one embodiment of the present invention, a coal sample container 8 is provided with four-stage grinding chambers, namely a first-stage grinding chamber 13, a second-stage grinding chamber 14, a third-stage grinding chamber 15, and a fourth-stage grinding chamber 16. The bottom screens corresponding to the bottom of the first-stage grinding chamber 13, the second-stage grinding chamber 14, and the third-stage grinding chamber 15 are screen I 26, screen II 27, and screen III 28, respectively, with sieve aperture diameters of 30 mesh, 60 mesh, and 90 mesh, respectively. The needle valves installed on the sides of the first-stage grinding chamber 13, the second-stage grinding chamber 14, the third-stage grinding chamber 15, and the fourth-stage grinding chamber 16 are needle valve I 1, respectively. 8. Needle valves II19, III20, and IV21; the corresponding bosses on the inner walls of the first-stage crushing chamber 13, the second-stage crushing chamber 14, the third-stage crushing chamber 15, and the fourth-stage crushing chamber 16 are boss I22, boss II23, boss III24, and boss IV25, respectively; the drive shaft 29 is composed of four sleeves with different diameters and heights. The top ends of each sleeve are correspondingly set in the first-stage crushing chamber 13, the second-stage crushing chamber 14, the third-stage crushing chamber 15, and the fourth-stage crushing chamber 16 from top to bottom. Crushing blades I9, II10, III11, and IV12 are sequentially installed on the top ends of the sleeves.

[0041] At the bottom of screens I 26, II 27, and III 28, an opening and closing mechanism is provided to open and close the corresponding screen mesh openings to allow coal samples to fall. The opening and closing mechanism consists of several nested partitions 30. The front end of each partition 30 is equipped with a knob, and the rear end of each partition 30 has a rubber protrusion. The rubber protrusion of each partition and the groove of the next partition can be fixed together by embedding, taking advantage of the large elastic deformation of rubber. When the coal sample container crushing chamber is crushing, the rubber protrusion of the previous partition can be embedded into the groove of the next partition by operating the knob 31. By operating in sequence, the screens can be kept in a closed state.

[0042] When the previous crushing chamber stops crushing, the control knob is used to bring the partition to a vertical position, allowing the coal sample to fall naturally into the next crushing chamber. The opening and closing mechanism of this invention operates by rotating the knob, similar to turning a valve switch. Closing is achieved by utilizing the good elasticity of rubber, which can be understood as inserting a rubber "protrusion" into a "groove." There is friction between the two, and the force exerted on the groove by the rubber deformation and compression results in closure. One partition is connected to another; once the first partition is fixed, the subsequent partitions can be fixed as well, ultimately closing the chamber.

[0043] The specific steps are as follows:

[0044] ① Collect 500g of coal sample with a particle size greater than 10 mesh in the underground coal mine, and then put the coal sample into the first-stage crushing chamber 13 of the sealed coal sample container 8;

[0045] ② First-stage crushing: Connect to the underground compressed air source 1. After gas-liquid separation through the dual-unit 2, the air source enters the pneumatic motor inlet 3. The pneumatic motor 5 is connected to the drive shaft 29 through the coupling 6. The pneumatic motor 5 drives the drive shaft 29 to rotate. The drive shaft 29 is equipped with crushing blades I9, which crush the coal sample in the first-stage crushing chamber 13. During the crushing process, the coal sample will pass through the screen I26 at the bottom of the first-stage crushing chamber 13 and enter the second-stage crushing chamber 14. Crushing is stopped when no coal sample remains in the first-stage crushing chamber 13 is observed by the naked eye. During this process, needle valve I18 is opened and needle valves II19, III20, and IV21 are closed. The flow meter 17 measures the gas desorption rate S1 of the coal sample in the first-stage crushing chamber 13 in real time. When S1 < 0.05 ml / min, desorption can be considered to be over. The cumulative gas desorption amount V1 of the coal sample in the first-stage crushing chamber 13 is recorded as 3816 ml, and needle valve I18 is closed.

[0046] ③ Second-stage crushing: After the first-stage crushing is completed, the coal sample has completely fallen into the second-stage crushing chamber 14. The second-stage crushing is started. The opening and closing mechanism under the screen I 26 corresponding to the first-stage crushing chamber 13 is closed by operating knob 31. At the same time, the opening and closing mechanism under the screen II 27 corresponding to the second-stage crushing chamber 14 is opened by operating knob 31. Then, the crushing blade II 10 crushes the coal sample in the second-stage crushing chamber 14. During the crushing process, the coal sample will fall into the third-stage crushing chamber 15. The crushing is stopped when no coal sample remains in the second-stage crushing chamber 14 is observed by the naked eye. During this process, needle valve II 19 is opened and needle valve I 18, needle valve III 20, and needle valve IV 21 are closed. The flow meter 17 measures the gas desorption rate S2 of the coal sample in the second-stage crushing chamber 14 in real time. When S2 < 0.05 ml / min, it can be regarded as the end of desorption. The cumulative gas desorption amount V2 of the coal sample in the second-stage crushing chamber 14 is recorded as 1088 ml, and needle valve II 19 is closed.

[0047] ④ Third-stage crushing: After the second-stage crushing is completed, the coal sample has completely fallen into the third-stage crushing chamber 15. Start the third-stage crushing. Close the opening and closing mechanism below the screen II 27 corresponding to the second-stage crushing chamber 14 by operating knob 31. Open the opening and closing mechanism below the screen III 28 corresponding to the third-stage crushing chamber 15 by operating knob 31. Then, the crushing blade III 11 crushes the coal sample in the third-stage crushing chamber 15. During the crushing process, the coal sample will fall into the fourth-stage crushing chamber 16. Stop crushing when no coal sample remains in the third-stage crushing chamber 15 is observed by the naked eye. During this process, open needle valve III 20 and close needle valve I 18, needle valve II 19, and needle valve IV 21. Flow meter 17 measures the gas desorption rate S3 of the coal sample in the third-stage crushing chamber 15 in real time. When S3 < 0.05 ml / min, it can be regarded as the end of desorption. Record the cumulative gas desorption amount V3 of the coal sample in the third-stage crushing chamber 15 as 124 ml and close needle valve III 20.

[0048] ⑤ Fourth stage crushing: After the third stage crushing is completed, the coal sample has fallen into the fourth stage crushing chamber 16. The crushing blade Ⅳ12 crushes the coal sample in the fourth stage crushing chamber 16. The flow meter 17 measures and records the coal sample gas desorption rate S4 and the cumulative coal sample gas desorption amount V4 in real time, which is 18ml.

[0049] ⑥ Therefore, when j=3, the critical particle size of the residual gas in the coal sample that cannot be desorbed under normal pressure is 90 mesh.

Claims

1. A device for determining the particle size of non-desorbable residual gas in underground coal samples under normal pressure, characterized in that, The system includes an underground compressed air source, a dual-unit assembly, a pneumatic motor, a drive shaft, a coal sample container, and a flow meter. The coal sample container is a transparent container mounted on a support. It contains n sealed pulverizing chambers, each equipped with pulverizing blades. The outlet of the underground compressed air source is connected to the inlet of the dual-unit assembly, and the outlet of the dual-unit assembly is connected to the inlet of the pneumatic motor via a pipeline. The output shaft of the pneumatic motor is connected to the drive shaft via a coupling. Screens are installed at the bottom of each pulverizing chamber from the first to the (n-1)th stage, with the screen aperture diameter gradually decreasing from the first to the (n-1)th stage. An opening / closing mechanism is provided at the bottom of the screens in each of these stages to allow the coal sample to fall. Needle valves are installed on the sides of each of the pulverizing chambers from the first to the nth stage, and the flow meter is connected to each of these chambers via the needle valves.

2. The device for determining the non-desorbable particle size of residual gas in underground coal samples under normal pressure according to claim 1, characterized in that, The coal sample container should have at least four grinding stages.

3. The device for determining the non-desorbable particle size of residual gas in underground coal samples under normal pressure according to claim 2, characterized in that, Each grinding chamber has a boss on its inner wall.

4. The device for determining the non-desorbable particle size of residual gas in underground coal samples under normal pressure according to claim 1, characterized in that, The opening and closing mechanism consists of nested partitions connected in front and behind. A knob is installed at the front end of the partition, and a rubber protrusion is installed at the rear end of the partition. The rubber protrusion of each partition is fixed together with the groove of the next partition by embedding. The screen mesh at the bottom of the crushing chamber remains closed during the crushing process and opens after the crushing is completed.

5. A method for determining the non-desorbable particle size of residual gas in underground coal samples under normal pressure, comprising the apparatus for determining the non-desorbable particle size of residual gas in underground coal samples under normal pressure as described in any one of claims 1-4, characterized in that, Includes the following steps: ① Collect a certain mass of coal sample with a particle size greater than 10 mesh in the underground coal mine, and put the collected coal sample into the first-stage crushing chamber of a transparent sealed coal sample container; ② Connect the underground compressed air source. After gas-liquid separation by the dual-unit, the compressed air enters the air inlet of the pneumatic motor. The pneumatic motor and the drive shaft are connected by a coupling. The pneumatic motor drives the drive shaft to rotate, and the drive shaft drives the crushing blades to rotate, crushing the coal sample in the first-stage crushing chamber. At the same time, the opening and closing mechanism under the screen of the first-stage crushing chamber is opened by operating the knob. During the crushing process, the coal sample will fall into the second-stage crushing chamber through the screen at the bottom of the first-stage crushing chamber. Crushing is stopped when no coal sample remains in the first-stage crushing chamber is observed by the naked eye. During this process, the needle valve corresponding to the first-stage crushing chamber is opened, and the needle valves corresponding to other crushing chambers are kept closed. The flow meter measures the gas desorption rate S1 of the coal sample in the first-stage crushing chamber in real time. When the gas desorption rate S1 of the coal sample is <0.05 ml / min, it is considered that the desorption is over. Record the cumulative gas desorption amount V1 of the coal sample in the first-stage crushing chamber, and close the needle valve corresponding to the first-stage crushing chamber. ③ After the first stage of crushing is completed, the coal sample has completely fallen into the second stage crushing chamber. Start the second stage of crushing, close the opening and closing mechanism under the screen of the first stage crushing chamber by operating the knob, and at the same time open the opening and closing mechanism under the screen of the second stage crushing chamber by operating the knob. Then the crushing blade crushes the coal sample in the second stage crushing chamber. During the crushing process, the coal sample will fall into the third stage crushing chamber. Stop crushing when it is observed by the naked eye that there is no residual coal sample in the second stage crushing chamber. During this process, open the needle valve corresponding to the second stage crushing chamber and keep the needle valves corresponding to other crushing chambers closed. The flow meter measures the gas desorption rate S2 of the coal sample in the second stage crushing chamber in real time. When the gas desorption rate S2 of the coal sample is < 0.05 ml / min, it is considered that the desorption is over. Record the cumulative amount of gas desorbed from the coal sample in the second stage crushing chamber V2, and close the needle valve corresponding to the second stage crushing chamber. ④ After the i-th stage of crushing and desorption is completed (1≤i<n), the i+1-th stage crushing chamber is started. When the coal sample particle size is crushed to below 30×(i+1) mesh, crushing is stopped. At the same time, the flow meter measures the coal sample gas desorption rate Si. When Si<0.05 ml / min, desorption ends. Record the cumulative amount of coal sample gas desorbed in the i-th stage crushing chamber Vi. ⑤ Repeat step ③ until the nth stage of crushing is performed. Stop crushing after five minutes and record the cumulative amount of gas desorbed from the coal sample in the crushing chamber after the nth stage of crushing, Vn. ⑥ When j is the smallest positive integer that satisfies the following inequality, the critical particle size of the residual gas in the coal sample that cannot be desorbed at normal pressure is 30 × j mesh. ≥0.99 In the formula: j is an intermediate variable.

6. The method for determining the non-desorbable particle size of residual gas in underground coal samples under normal pressure according to claim 5, characterized in that, The coal sample collected from the underground mine has a mass of 500g or more.

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