Sampling system and method for inhibiting coal gas desorption by rapidly cooling hole bottom

Abstract

The invention discloses a sampling system and method for inhibiting coal gas desorption by rapidly cooling a hole bottom, a drilling mechanism constructs a drill hole to reach a required sampling depth, then a liquid nitrogen injection device injects liquid nitrogen into the hole bottom of the drill hole, the liquid nitrogen vaporizes and absorbs heat to rapidly reduce the temperature of a coal body at the hole bottom, and the desorption loss of the coal body before gas content testing is reduced. Meanwhile, nitrogen generated by vaporization of the liquid nitrogen enables the air pressure in the drill hole to be continuously increased; then the drilling mechanism drills and crushes the cooled coal body, high-pressure gas is injected into an annular gas channel through a compressed air pipeline, and due to the fact that the air pressure in a drill hole is high, the high-pressure gas enters an inner-layer hollow drill rod with the lower air pressure; a siphon effect is generated at the drill bit through continuous flowing of gas to form negative pressure, and broken coal briquettes are sucked in and conveyed to a coal sample recovery device for collection; according to the method, the temperature of the hole bottom coal seam can be rapidly reduced, rapid collection of coal briquettes is not affected, and it is guaranteed that required samples are provided for follow-up high-precision testing of the coal seam gas content.

Description

Technical Field

[0001] The invention belongs to the technical field of coal body drilling sampling, in particular to a sampling system and method for rapidly cooling the bottom of a hole to inhibit coal gas desorption. Background Art

[0002] Gas accidents have always been the primary problem restricting safe and efficient production in coal mines. The lack of understanding of the distribution rules of coal seam gas and inadequate gas control measures are the main reasons why coal mines are difficult to accurately control gas and prevent gas disasters. Coal seam gas content is an important parameter for reference of gas prevention and control measures. The accuracy of its test directly affects the setting of subsequent gas prevention and control measures and the effectiveness of the control.

[0003] At present, the gas content test is mainly carried out by drilling deep into the coal seam to break the coal body, so as to collect coal blocks at the depth of a certain hole, conduct gas desorption test, and then add the estimated gas loss to calculate the gas content of the coal seam. Studies have found that the greater the gas loss, the greater the error value of the estimated gas loss. Therefore, how to reduce the gas loss of coal blocks from exposure to canning test has become a difficult problem that plagues the field of gas content testing. The gas loss is mainly caused by the natural desorption of gas from the inside of the coal block to the outside, and its desorption degree is most significantly affected by temperature. The higher the temperature, the faster the gas desorption rate. During the drilling sampling process, when the drill bit rotates and drills, it will repeatedly rub against the contacted coal sample to generate heat, causing the coal body to heat up rapidly, which will promote the desorption of gas from the inside of the coal block to the outside, resulting in a large amount of gas loss during the coal sample extraction process. To avoid this phenomenon, the industry currently uses air cooling and water cooling to reduce the problem of coal sample overheating caused by friction. During the application process, it was found that air cooling is to inject low-temperature air into the bottom of the hole, but this method has a poor cooling effect on the coal sample. Water cooling is to inject low-temperature water into the bottom of the hole after drilling, but this method will increase the stickiness of the coal block and is not conducive to coal sample collection.

[0004] Therefore, how to quickly reduce the temperature of the coal seam at the bottom of the hole without affecting the rapid collection of coal blocks has become a difficult problem restricting the high-precision testing of coal seam gas content. Summary of the invention

[0005] In view of the problems existing in the above-mentioned prior art, the present invention provides a sampling system and method for rapidly cooling the bottom of a hole to suppress coal gas desorption, which rapidly reduces the temperature of the coal seam at the bottom of the hole through the heat absorption of liquid nitrogen phase change, and simultaneously utilizes the heat absorption phase change to form nitrogen combined with compressed air to form a negative pressure to achieve rapid collection of coal samples.

[0006] In order to achieve the above-mentioned purpose, the technical solution adopted by the present invention is: a sampling system for rapidly cooling the bottom of a hole to inhibit coal gas desorption, comprising a coal sample recovery device, a liquid nitrogen injection device, a compressed air pipeline and a drilling mechanism;

[0007] The drilling mechanism includes a drill bit, an inner hollow drill rod, an outer hollow drill rod and a hydraulic drill rig, the hydraulic drill rig is installed on a base, the inner hollow drill rod is installed in the outer hollow drill rod, and an annular air duct is left between the two; the drill bit is fixedly connected to one end of the inner hollow drill rod and one end of the outer hollow drill rod, and the drill bit is provided with a liquid nitrogen spray hole and a coal sample inlet, both of which are connected to the inside of the inner hollow drill rod; the other end of the inner hollow drill rod and the other end of the outer hollow drill rod are coaxially connected to the output end of the hydraulic drill rig through a limiting mechanism, so that the hydraulic drill rig can drive the inner hollow drill rod, the outer hollow drill rod and the drill bit to rotate synchronously for drilling; the limiting mechanism is used to fix the relative position between the inner hollow drill rod and the outer hollow drill rod; a vent is provided on the side wall of the inner hollow drill rod close to the drill bit, which is used to connect the annular air duct with the inside of the inner hollow drill rod.

[0008] The annular airway is connected to the compressed air network through a compressed air pipeline, and is used to inject high-pressure gas into the annular airway to clean coal dust during the drilling process, and to form a negative pressure siphon effect at the drill bit when collecting coal samples in combination with phase-change nitrogen, so that the coal samples are sucked into the inner hollow drill rod.

[0009] The coal sample recovery device includes a coal sample collection box and a coal dust collection box. The interior of the coal sample collection box is connected with the interior of the coal dust collection box. The coal dust collection box is connected with the interior of the inner hollow drill rod through a pipeline and a three-way joint. It is used to allow the coal sample to first enter the coal dust collection box to reduce the coal dust, and then enter the coal sample collection box for collection.

[0010] The liquid nitrogen injection device comprises a compressed air tank and a liquid nitrogen tank. The liquid nitrogen tank is provided with an air inlet and a drain pipe. Liquid nitrogen is contained in the liquid nitrogen tank. One end of the drain pipe extends to the bottom of the liquid nitrogen tank and the other end is connected to a three-way joint. The air inlet is connected to the compressed air tank through a pipeline, so that compressed air enters the liquid nitrogen tank through the air inlet to drive the liquid nitrogen to pass through the drain pipe, the three-way joint, the inner hollow drill rod and the liquid nitrogen spray hole in sequence and be discharged to the bottom of the hole to cool the coal sample.

[0011] Furthermore, the inner layer hollow drill rod and the outer layer hollow drill rod have the same length and are multiple, the multiple inner layer hollow drill rods are coaxially arranged and connected through the drill rod connecting groove; the multiple outer layer hollow drill rods are coaxially arranged and connected through the drill rod connecting groove.

[0012] Furthermore, the compressed air pipeline is equipped with a compressed air control ball valve; the pipeline between the three-way joint and the coal dust collection box is equipped with a sampling control ball valve; the discharge pipe is equipped with a liquid nitrogen control ball valve; and the pipeline between the compressed air tank and the liquid nitrogen tank is equipped with a gas ratio regulating valve. These valves are arranged to facilitate the control of the on-off of different pipelines.

[0013] Furthermore, the liquid nitrogen tank is equipped with a liquid level meter for monitoring the liquid level of liquid nitrogen in the liquid nitrogen tank; the pipeline between the compressed air tank and the liquid nitrogen tank is equipped with a pressure gauge for monitoring the air pressure of the compressed air passing through the pipeline.

[0014] Furthermore, the drainage pipe is a low-temperature resistant pipe, the pipeline between the three-way joint and the coal dust collection box is a wear-resistant braided pipe; the compressed air pipeline is a rubber hose; the coal sample collection box and the lower part of the coal dust collection box are both equipped with removable plugs to facilitate the removal of coal dust and coal samples.

[0015] The working method of the sampling system for rapidly cooling the bottom of the hole to inhibit coal gas desorption is as follows:

[0016] Step 1, coal seam drilling construction: first preset the coal seam depth and drilling position for measuring the gas content, then assemble and connect the sampling system, and all valves are closed in the initial state; start the hydraulic drill to drive the inner hollow drill rod, the outer hollow drill rod and the drill bit to rotate synchronously to drill towards the preset drilling position, and at the same time open the compressed air control ball valve to make the high-pressure gas in the compressed air network pass through the annular airway, the air vent and the inner hollow drill rod in turn, and spray into the borehole from the liquid nitrogen spray hole of the drill bit and the coal sample inlet, so that the coal dust generated by the drilling is discharged from the gap between the outer hollow drill rod and the borehole by the high-pressure gas, and the drilling is kept stable until the preset depth is reached, and the hydraulic drill and the compressed air control ball valve are closed.

[0017] Step 2: Cooling the coal sample with liquid nitrogen: Open the liquid nitrogen control ball valve, and control the gas ratio regulating valve to allow compressed air to enter the liquid nitrogen tank through the air inlet to drive the liquid nitrogen to be discharged to the bottom of the borehole at the current depth through the discharge pipe, three-way joint, inner hollow drill rod and liquid nitrogen spray hole in sequence. At this time, due to the high temperature at the bottom of the hole, the liquid nitrogen gasifies and turns into nitrogen to absorb heat, causing the bottom of the hole and the surrounding coal body to cool down rapidly and the air pressure in the borehole to continue to increase. After continuous injection for a period of time, the coal sample is cooled by liquid nitrogen, and the liquid nitrogen control ball valve and the gas ratio regulating valve are closed.

[0018] Step 3, coal sample collection: open the compressed air control ball valve and the sampling control ball valve, and the high-pressure gas in the compressed air network enters the inner hollow drill rod through the annular airway and the vent in turn. Due to the large amount of gasified nitrogen in the borehole, the air pressure is relatively high, that is, at this time, the high-pressure gas cannot be discharged into the borehole through the drill bit, so that the high-pressure gas enters the inner hollow drill rod with lower air pressure and then enters the coal dust collection box along the inner hollow drill rod and the three-way joint. At this time, due to the continuous flow of gas, a siphon effect is generated at the drill bit (near the coal sample inlet) to form Negative pressure, and at the same time, restart the hydraulic drill to make the drill bit continue to drill forward to break the coal seam at this depth. Due to the phase change gasification in the borehole to form nitrogen, the air pressure is high while the air pressure in the drill bit is low. The broken coal blocks are sucked into the coal sample inlet under the action of negative pressure, and enter the coal dust collection box with the air flow through the inner hollow drill rod and the three-way joint. The broken coal blocks enter the coal sample collection box after the coal dust is removed from the coal dust collection box, thereby obtaining the required coal sample. After completing the collection work, close the compressed air control ball valve and the sampling control ball valve, and stop the hydraulic drill.

[0019] Compared with the prior art, the present invention adopts a method of combining a coal sample recovery device, a liquid nitrogen injection device, a compressed air pipeline and a drilling mechanism. First, the drilling mechanism is used to drill a hole into the coal seam to reach the required sampling depth. Then, the liquid nitrogen injection device is used to inject liquid nitrogen into the bottom of the hole at the current depth. The liquid nitrogen phase changes and gasifies to absorb heat and quickly lowers the temperature of the surrounding coal body, effectively reducing the rate of gas desorption in the surrounding coal body. At the same time, the nitrogen generated by the gasification of liquid nitrogen causes the gas pressure in the borehole to continue to increase. Then, the drilling mechanism is used to heat the cooled coal body. After drilling and breaking, high-pressure gas is injected into the annular airway through the compressed air pipeline. Due to the large amount of gasified nitrogen in the borehole, the air pressure is relatively high, that is, at this time, the high-pressure gas cannot be discharged into the borehole through the drill bit, so that the high-pressure gas enters the inner hollow drill rod with lower air pressure and enters the coal dust collection box along the inner hollow drill rod and the three-way joint. At this time, due to the continuous flow of gas, a siphon effect is generated at the drill bit to form a negative pressure to suck the broken coal block and transport it to the coal sample recovery device; the coal sample recovery device removes the coal dust from the coal block and completes the coal sample collection work. The present invention makes use of the low temperature of liquid nitrogen (-195.8℃) to quickly cool the coal body at the bottom of the hole, inhibit the gas desorption amount of the coal block from exposure to the canning test process, thereby reducing the gas loss estimation error value and improving the accuracy of the gas content test; and the whole process is water-free cooling, so as not to affect the rapid collection of coal blocks, ensuring that the required samples are provided for the subsequent high-precision test of coal seam gas content. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is a schematic diagram of the overall layout of the present invention.

[0021] In the figure: 1-drill hole, 2-liquid nitrogen spray hole, 3-drill bit, 4-inner hollow drill rod, 5-outer hollow drill rod, 6-drill rod connecting groove, 7-compressed air pipe network, 8-rubber hose, 9-compressed air control ball valve, 10-limiting mechanism, 11-base, 12-hydraulic drilling rig, 13-tee joint, 14-sampling control ball valve, 15-wear-resistant braided tube, 16-coal sample collection box, 17-detachable plug, 18-coal dust collection box, 19-liquid nitrogen tank, 20-low temperature resistant pipe, 21-liquid nitrogen control ball valve, 22-liquid level meter, 23-compressed air tank, 24-gas ratio regulating valve, 25-pressure gauge, 26-coal sample inlet. DETAILED DESCRIPTION

[0022] The present invention will be further described below.

[0023] like Figure 1 As shown, the present invention includes a coal sample recovery device, a liquid nitrogen injection device, a compressed air pipeline and a drilling mechanism;

[0024] The drilling mechanism includes a drill bit 3, an inner hollow drill rod 4, an outer hollow drill rod 5 and a hydraulic drill rig 12, wherein the hydraulic drill rig 12 is mounted on a base 11, and the inner hollow drill rod 4 is mounted in the outer hollow drill rod 5, with an annular air passage left between the two; the drill bit 3 is fixedly connected to one end of the inner hollow drill rod 4 and one end of the outer hollow drill rod 5, and a liquid nitrogen spray hole 2 and a coal sample inlet 26 are provided on the drill bit 3, and the liquid nitrogen spray hole 2 and the coal sample inlet 26 are both connected to the inside of the inner hollow drill rod 4; the other end of the inner hollow drill rod 4 and the other end of the outer hollow drill rod 5 are coaxial with the output end of the hydraulic drill rig 12 through a limiting mechanism 10 The connection enables the hydraulic drill rig 12 to drive the inner hollow drill rod 4, the outer hollow drill rod 5 and the drill bit 3 to rotate synchronously for drilling; the limiting mechanism 10 is used to fix the relative position between the inner hollow drill rod 4 and the outer hollow drill rod 5; a vent is provided on the side wall of the inner hollow drill rod 4 close to the drill bit 3, so as to connect the annular airway with the inside of the inner hollow drill rod 4; the inner hollow drill rod 4 and the outer hollow drill rod 5 have the same length and are multiple, and the multiple inner hollow drill rods 4 are coaxially arranged and connected by the drill rod connecting groove 6; the multiple outer hollow drill rods 5 are coaxially arranged and connected by the drill rod connecting groove 6.

[0025] The annular airway is connected to the compressed air network 7 through a compressed air pipeline, which is used to inject high-pressure gas into the annular airway to clean coal dust during the drilling process, and to form a negative pressure siphon effect at the drill bit 3 in combination with phase-change nitrogen when collecting coal samples, so that the coal samples are sucked into the inner hollow drill rod 4.

[0026] The coal sample recovery device includes a coal sample collection box 16 and a coal dust collection box 18. The interior of the coal sample collection box 16 is connected to the interior of the coal dust collection box 18. The coal dust collection box 18 is connected to the interior of the inner hollow drill rod 4 through a pipeline and a three-way joint 13. It is used to allow the coal sample to first enter the coal dust collection box 18 to reduce the coal dust, and then enter the coal sample collection box 16 for collection.

[0027] The liquid nitrogen injection device comprises a compressed air tank 23 and a liquid nitrogen tank 19. The liquid nitrogen tank 19 is provided with an air inlet and a drain pipe. Liquid nitrogen is contained in the liquid nitrogen tank 19. One end of the drain pipe extends to the bottom of the liquid nitrogen tank 19, and the other end is connected to the three-way joint 13. The air inlet is connected to the compressed air tank 23 through a pipeline, so that compressed air enters the liquid nitrogen tank 19 through the air inlet to drive the liquid nitrogen to pass through the drain pipe, the three-way joint 13, the inner hollow drill rod 4 and the liquid nitrogen spray hole 2 in sequence and be discharged to the bottom of the hole to cool the coal sample.

[0028] The compressed air pipeline is equipped with a compressed air control ball valve 9; the pipeline between the three-way joint 13 and the coal dust collection box 18 is equipped with a sampling control ball valve 14; the drain pipe is equipped with a liquid nitrogen control ball valve 21; the pipeline between the compressed air tank 23 and the liquid nitrogen tank 19 is equipped with a gas ratio regulating valve 24. The provision of these valves facilitates the control of the on-off of different pipelines. The liquid nitrogen tank 19 is equipped with a liquid level gauge 22 for monitoring the liquid nitrogen level in the liquid nitrogen tank 19; the pipeline between the compressed air tank 23 and the liquid nitrogen tank 19 is equipped with a pressure gauge 25 for monitoring the air pressure of the compressed air passing through the pipeline.

[0029] As an improvement of the present invention, the drainage pipe is a low-temperature resistant pipe 20, the pipeline between the three-way joint 13 and the coal dust collection box 18 is a wear-resistant braided tube 15; the compressed air pipeline is a rubber hose 8; the lower part of the coal sample collection box 16 and the coal dust collection box 18 are both equipped with a detachable plug 17 to facilitate the removal of coal dust and coal samples.

[0030] The above-mentioned coal sample collection box 16, coal dust collection box 18, compressed air tank 23, liquid nitrogen tank 19, limit mechanism 10 and hydraulic drilling rig 12 are all existing equipment. The present invention only utilizes their functions and does not improve their structures. The process in which the coal dust collection box 18 removes coal dust after the coal blocks enter the coal sample collection box 16 for collection is also a function of the existing equipment.

[0031] The working method of the sampling system for rapidly cooling the bottom of the hole to inhibit coal gas desorption is as follows:

[0032] Step 1, coal seam drilling construction: first preset the coal seam depth and drilling position for measuring the gas content, then assemble and connect the sampling system, and all valves are in the closed state in the initial state; start the hydraulic drill 12, drive the inner hollow drill rod 4, the outer hollow drill rod 5 and the drill bit 3 to rotate synchronously to drill towards the preset borehole 1 position, and at the same time open the compressed air control ball valve 9, so that the high-pressure gas in the compressed air pipe network 7 passes through the annular airway, the air vent and the inner hollow drill rod 4 in turn, and is sprayed into the borehole from the liquid nitrogen spray hole 2 of the drill bit 3 and the coal sample inlet 26, so that the coal dust generated by the borehole 1 is discharged from the gap between the outer hollow drill rod 5 and the borehole 1 by the high-pressure gas, and the drilling 1 is kept stable until the preset depth is reached, and the hydraulic drill 12 and the compressed air control ball valve 9 are closed.

[0033] Step 2, liquid nitrogen cooling of the coal sample: open the liquid nitrogen control ball valve 21, and control the gas ratio regulating valve 24 to allow compressed air to enter the liquid nitrogen tank 19 through the air inlet, drive the liquid nitrogen to pass through the drain pipe, the three-way joint 13, the inner hollow drill rod 5 and the liquid nitrogen spray hole 2 in turn to be discharged to the bottom of the borehole at the current depth. At this time, due to the high temperature at the bottom of the hole, the liquid nitrogen gasifies and turns into nitrogen to absorb heat, so that the bottom of the hole and the surrounding coal body are quickly cooled down and the air pressure in the borehole 1 continues to increase. The air pressure of the compressed air passing through the pipeline is monitored by the pressure gauge 25, and the flow rate and pressure of the compressed air entering the liquid nitrogen tank 19 are controlled by the gas ratio regulating valve 24, so as to realize the flow control of the liquid nitrogen injected into the borehole 1. The liquid level meter 22 is used to monitor the liquid nitrogen level in the liquid nitrogen tank 19, and the amount of liquid nitrogen used is known in real time. After a period of continuous injection, the coal sample liquid nitrogen cooling is completed, and the liquid nitrogen control ball valve 21 and the gas ratio regulating valve 24 are closed.

[0034] Step 3, coal sample collection: open the compressed air control ball valve 9 and the sampling control ball valve 14, and the high-pressure gas in the compressed air pipe network 7 enters the inner hollow drill rod 4 through the annular airway and the vent in turn. Since a large amount of gasified nitrogen in the borehole 1 makes the air pressure high, that is, at this time, the high-pressure gas cannot be discharged into the borehole 1 through the drill bit 3, so that the high-pressure gas enters the inner hollow drill rod 4 with a lower air pressure, and then enters the coal dust collection box 18 along the inner hollow drill rod 4 and the three-way joint 13. At this time, due to the continuous flow of gas, a siphon effect is generated at the drill bit 3 to form a negative pressure, and at the same time, the gas is restarted. The hydraulic drill 12 makes the drill bit 3 continue to drill forward to break the coal seam at this depth. Since the air pressure caused by the phase change gasification in the borehole 1 to form nitrogen is high and the air pressure in the drill bit 3 is low, the broken coal blocks are sucked into the coal sample inlet 26 under the action of negative pressure, and enter the coal dust collection box 18 through the inner hollow drill rod 4 and the three-way joint 13 with the air flow. The broken coal blocks enter the coal sample collection box 16 after the coal dust is removed in the coal dust collection box 18, thereby obtaining the required coal sample. After completing the collection work, close the air pressure control ball valve 9 and the sampling control ball valve 14, and stop the hydraulic drill 12.

[0035] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A sampling system for rapidly cooling the bottom of a hole to inhibit coal gas desorption, characterized in that: It includes coal sample recovery device, liquid nitrogen injection device, compressed air pipeline and drilling mechanism; The drilling mechanism comprises a drill bit, an inner hollow drill rod, an outer hollow drill rod and a hydraulic drill rig, the hydraulic drill rig is installed on a base, the inner hollow drill rod is installed in the outer hollow drill rod, and an annular air passage is left between the two; the drill bit is fixedly connected to one end of the inner hollow drill rod and one end of the outer hollow drill rod, and the drill bit is provided with a liquid nitrogen spray hole and a coal sample inlet, both of which are connected to the inside of the inner hollow drill rod; the other end of the inner hollow drill rod and the other end of the outer hollow drill rod are coaxially connected to the output end of the hydraulic drill rig through a limiting mechanism, so that the hydraulic drill rig can drive the inner hollow drill rod, the outer hollow drill rod and the drill bit to rotate synchronously for drilling; the limiting mechanism is used to fix the relative position between the inner hollow drill rod and the outer hollow drill rod; a vent is provided on the side wall of the inner hollow drill rod close to the drill bit, which is used to connect the annular air passage with the inside of the inner hollow drill rod; The annular airway is connected to the compressed air network through a compressed air pipeline, and is used to inject high-pressure gas into the annular airway to clean coal dust during the drilling process, and to form a negative pressure siphon effect at the drill bit in combination with phase-change nitrogen when collecting coal samples, so that the coal samples are sucked into the inner hollow drill rod; The coal sample recovery device comprises a coal sample collection box and a coal dust collection box. The interior of the coal sample collection box is connected to the interior of the coal dust collection box. The coal dust collection box is connected to the interior of the inner hollow drill rod through a pipeline and a three-way joint, so that the coal sample first enters the coal dust collection box to reduce the coal dust, and then enters the coal sample collection box for collection; The liquid nitrogen injection device comprises a compressed air tank and a liquid nitrogen tank. The liquid nitrogen tank is provided with an air inlet and a drain pipe. Liquid nitrogen is contained in the liquid nitrogen tank. One end of the drain pipe extends to the bottom of the liquid nitrogen tank and the other end is connected to a three-way joint. The air inlet is connected to the compressed air tank through a pipeline, so that compressed air enters the liquid nitrogen tank through the air inlet to drive the liquid nitrogen to pass through the drain pipe, the three-way joint, the inner hollow drill rod and the liquid nitrogen spray hole in sequence and be discharged to the bottom of the hole to cool the coal sample.

2. According to claim 1, the sampling system for rapidly cooling the bottom of the hole to inhibit coal gas desorption is characterized in that: The inner layer hollow drill rod and the outer layer hollow drill rod have the same length and are multiple, the multiple inner layer hollow drill rods are coaxially arranged and connected through the drill rod connecting groove; the multiple outer layer hollow drill rods are coaxially arranged and connected through the drill rod connecting groove.

3. The sampling system for rapidly cooling the bottom of a hole to inhibit coal gas desorption according to claim 1 is characterized in that: The compressed air pipeline is equipped with a compressed air control ball valve; the pipeline between the three-way joint and the coal dust collection box is equipped with a sampling control ball valve; the drain pipe is equipped with a liquid nitrogen control ball valve; and the pipeline between the compressed air tank and the liquid nitrogen tank is equipped with a gas ratio regulating valve.

4. The sampling system for rapidly cooling the bottom of a hole to suppress coal gas desorption according to claim 1 is characterized in that: The liquid nitrogen tank is equipped with a liquid level meter for monitoring the liquid level of the liquid nitrogen in the liquid nitrogen tank; the pipeline between the compressed air tank and the liquid nitrogen tank is equipped with a pressure gauge for monitoring the air pressure of the compressed air passing through the pipeline.

5. The sampling system for suppressing coal gas desorption by rapid temperature reduction at the bottom of a hole according to claim 1 is characterized in that: The drain pipe is a low-temperature resistant pipe, the pipeline between the three-way joint and the coal dust collection box is a wear-resistant braided pipe; the compressed air pipeline is a rubber hose; the coal sample collection box and the lower part of the coal dust collection box are both equipped with removable plugs to facilitate the discharge of coal dust and coal samples.

6. A working method of a sampling system for rapidly cooling the bottom of a hole to inhibit coal gas desorption according to any one of claims 1 to 5, characterized in that: The specific steps are: Step 1, coal seam drilling construction: first preset the coal seam depth and drilling position for measuring gas content, then assemble and connect the sampling system, and all valves are closed in the initial state; start the hydraulic drilling rig to drive the inner hollow drill rod, the outer hollow drill rod and the drill bit to rotate synchronously to drill towards the preset drilling position, and at the same time open the compressed air control ball valve to make the high-pressure gas in the compressed air network pass through the annular airway, the vent and the inner hollow drill rod in turn, and spray into the borehole from the liquid nitrogen spray hole of the drill bit and the coal sample inlet, so that the coal dust generated by the drilling is discharged from the gap between the outer hollow drill rod and the borehole by the high-pressure gas, and the drilling is kept stable until the preset depth is reached, and the hydraulic drilling rig and the compressed air control ball valve are closed; Step 2, coal sample liquid nitrogen cooling: open the liquid nitrogen control ball valve, and control the gas ratio regulating valve to allow compressed air to enter the liquid nitrogen tank through the air inlet to drive the liquid nitrogen to be discharged to the bottom of the borehole at the current depth through the discharge pipe, the three-way joint, the inner hollow drill rod and the liquid nitrogen spray hole in sequence. At this time, due to the high temperature at the bottom of the hole, the liquid nitrogen gasification phase changes into nitrogen absorption, which quickly cools the bottom of the hole and the surrounding coal body and continuously increases the air pressure in the borehole. After continuous injection for a period of time, the coal sample liquid nitrogen cooling is completed, and the liquid nitrogen control ball valve and the gas ratio regulating valve are closed; Step 3, coal sample collection: open the compressed air control ball valve and the sampling control ball valve, and the high-pressure gas in the compressed air network enters the inner hollow drill rod through the annular airway and the air vent in turn. Due to the large amount of gasified nitrogen in the borehole, the air pressure is relatively high, so that the high-pressure gas enters the inner hollow drill rod and then enters the coal dust aggregate box along the inner hollow drill rod and the three-way joint. At this time, a siphon effect is generated at the drill bit to form a negative pressure. At the same time, the hydraulic drill rig is restarted to make the drill bit continue to drill forward to break the coal seam at this depth. The broken coal blocks are sucked into the coal sample inlet under the action of negative pressure, and enter the coal dust aggregate box through the inner hollow drill rod and the three-way joint with the air flow. The broken coal blocks enter the coal sample aggregate box after the coal dust is removed from the coal dust aggregate box, thereby obtaining the required coal sample. After completing the collection work, close the compressed air control ball valve and the sampling control ball valve, and stop the hydraulic drill rig.

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