A low-temperature quick-freezing coal gas desorption inhibition site coring system and method

Abstract

The application discloses a low-temperature quick-freezing coal-gas-desorption-inhibiting fixed-point coring system and method, drilling is first conducted to a required sampling depth position by a drilling mechanism; liquid nitrogen is injected into the bottom of the hole by a liquid nitrogen and water injection device, and the liquid nitrogen is phase changed and gasified to absorb heat and rapidly reduce the temperature of the surrounding coal body; then, the cooled coal body is drilled, broken and collected, and since the temperature of the coal body is low during the breaking, the coal-gas-desorption loss during the breaking and sampling process is greatly reduced; after the sampling is completed, water is first injected into the sampling cavity and then liquid nitrogen is injected into the sampling cavity by the liquid nitrogen and water injection device, the water in the sampling cavity is rapidly frozen into ice by the low-temperature characteristics of the liquid nitrogen, the coal sample is wrapped to form a frozen coal sample, the coal sample is sealed in the ice by the ice wrapping, the temperature of the coal sample is low, and the coal-gas-desorption loss during the un-drilling and taking-out process is effectively reduced due to the sealing property of the ice wrapping; and thus the required coal sample is provided for subsequent high-precision coal seam gas content testing.

Description

Technical Field

[0001] This invention belongs to the field of coal borehole sampling technology, specifically a fixed-point coring system and method for inhibiting coal gas desorption by low-temperature quick-freezing. Background Technology

[0002] Methane gas is a byproduct of coal mining and a major cause of disasters in coal mines. To effectively manage methane gas, understanding the occurrence patterns of methane gas in coal seams is the first step, especially the testing of the key indicator of methane content in coal seams. The accuracy of this test affects the scale of subsequent methane control measures and directly impacts the effectiveness of methane control.

[0003] Coal seam gas content testing involves sampling gas-bearing coal from the coal seam using sampling equipment, conducting gas desorption tests, and adding the estimated gas loss during sampling to determine the total gas content of the coal seam. Therefore, coal seam sampling is a crucial step in coal seam gas content testing, as gas within the coal is continuously desorbed and lost during the sampling process. Studies have found that the greater the gas loss, the larger the error in the estimated value, thus reducing the accuracy of the gas content test. Currently, coal seam sampling mainly uses two methods: fixed-point and non-fixed-point sampling. In application, it has been found that non-fixed-point sampling methods, such as the orifice-to-powder method, suffer from problems such as sample mixing, small coal particle size, and excessive abrasion, leading to lower measured gas content values. Fixed-point sampling does not have these problems, but during the sampling process, from the initial exposure of the coal block to the loading and testing, gas loss occurs due to desorption. The degree of desorption is most significantly affected by temperature; the higher the temperature, the faster the gas desorption rate. During borehole sampling, the rotating drill bit repeatedly rubs against the coal sample, generating heat and causing the coal to heat up rapidly. This promotes the desorption of gas from within the coal block, resulting in significant gas loss during sample extraction, which hinders the improvement of gas content testing accuracy. Furthermore, in fixed-point sampling using coring tubes at greater depths, the long drill rod retraction time (often tens of minutes) after the coal sample is inserted into the coring tube, coupled with prolonged exposure to air and continuous desorption, further increases gas loss. These issues constitute significant challenges to high-precision testing of coal seam gas content.

[0004] Therefore, the research direction of this invention is to provide a new sampling system and method that can rapidly reduce the temperature of coal blocks and suppress the gas desorption rate of coal blocks during fixed-point sampling, and can continuously suppress it during the sampling process, so as to provide the coal samples required for subsequent high-precision testing of coal seam gas content. Summary of the Invention

[0005] To address the problems existing in the prior art, this invention provides a fixed-point coring system and method for inhibiting coal gas desorption by low-temperature rapid freezing. The system rapidly reduces the temperature of the coal seam at the bottom of the borehole by liquid nitrogen phase change heat absorption, and simultaneously uses water injection to freeze and encapsulate the coal sample, thereby effectively inhibiting the gas desorption rate during coal sample collection and providing the required coal sample for subsequent high-precision testing of coal seam gas content.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is: a fixed-point coring system for inhibiting coal gas desorption by low-temperature quick-freezing, including a coring tube, a liquid nitrogen and water injection device, and a drilling mechanism;

[0007] The drilling mechanism includes a hollow drill rod and a hydraulic drilling rig. The hydraulic drilling rig is mounted on a base. One end of the hollow drill rod is coaxially connected to the output end of the hydraulic drilling rig through a limiting mechanism, so that the hydraulic drilling rig can drive the hollow drill rod to rotate synchronously for drilling.

[0008] The coring tube includes an inner tube, an outer tube, and a coring drill bit. The inner tube is installed inside the outer tube and is fixedly connected to the inner wall of the outer tube by a bracket, forming an annular air passage between them. One end of the outer tube is coaxially connected to the other end of the hollow drill rod, and a vent is provided at the connection between the hollow drill rod and the outer tube to allow the hollow drill rod to communicate with the annular air passage inside the outer tube. A sampling chamber is provided inside the inner tube for storing coal samples after sampling. The coring drill bit is installed at the other end of the outer tube and has a coring port that communicates with the sampling chamber. A through hole is opened on the side wall of the inner tube near the coring drill bit to allow the annular air passage to communicate with the sampling chamber.

[0009] The liquid nitrogen and water injection device includes a compressed air tank, a liquid nitrogen tank, a water storage tank, and a T-junction. An inlet is located on the side of the hollow drill rod near the limiting mechanism. One port of the T-junction is connected to the inlet via a pipeline. The upper part of the liquid nitrogen tank has an air inlet and a liquid nitrogen discharge pipe, one end of which extends to the bottom of the liquid nitrogen tank. The upper part of the water storage tank has an air inlet and a water injection pipe, one end of which extends to the bottom of the water storage tank. The outlet of the compressed air tank is connected to the air inlets of the liquid nitrogen tank and the water storage tank via pipelines, respectively. The other end of the liquid nitrogen discharge pipe is connected to the other end of the water injection pipe. The ends are connected to the other two ports of the tee connector respectively; when it is necessary to cool the collected coal sample, compressed air is introduced into the liquid nitrogen tank through the air inlet, driving the liquid nitrogen to pass through the liquid nitrogen discharge pipe, tee connector, hollow drill rod, annular air channel, sampling chamber and core sampling port to discharge to the bottom of the hole to cool the coal sample; when it is necessary to inject water into the coal sample in the sampling chamber, compressed air is introduced into the water storage tank through the air inlet, driving the water to pass through the water injection pipe, tee connector, hollow drill rod, annular air channel and through hole to inject into the sampling chamber, and the water is frozen into ice in the subsequent sampling chamber due to the low temperature, thus encasing the coal sample.

[0010] Furthermore, there are multiple hollow drill rods, which are coaxially arranged and connected by drill rod connecting grooves.

[0011] Furthermore, a first control ball valve is installed on the liquid nitrogen discharge pipe, a second control ball valve is installed on the pipe between the compressed air tank and the liquid nitrogen tank, a third control ball valve is installed on the pipe between the compressed air tank and the water storage tank, a fourth control ball valve is installed on the water injection pipe, and a gas proportioning valve is installed at the outlet of the compressed air tank. These valves facilitate the control of the on / off states of different pipes.

[0012] Furthermore, the liquid nitrogen tank is equipped with a thermocouple-type level gauge to monitor the liquid nitrogen level inside the tank; the water storage tank is equipped with a buoyancy-type level gauge to monitor the water level inside the tank; and the pipelines between the compressed air tank and the liquid nitrogen tank, and between the compressed air tank and the water storage tank, are all equipped with pressure gauges to monitor the compressed air pressure passing through their respective pipelines.

[0013] Furthermore, the liquid nitrogen discharge pipe is a cryogenic pipe, and the water injection pipe is a pressure-resistant flexible hose.

[0014] The working method of the above-mentioned low-temperature quick-freezing method for inhibiting coal gas desorption in fixed-point coring is as follows:

[0015] Step 1: Coal Seam Drilling Construction: First, preset the coal seam depth for which gas content needs to be measured and the upward drilling position. Then, assemble and connect the sampling system. Initially, all valves are closed. At this time, the coring tube is not installed at the end of the hollow drill rod. Install the ordinary drill bit at the end of the hollow drill rod. Start the hydraulic drilling machine, driving the hollow drill rod and ordinary drill bit to rotate synchronously and drill towards the preset upward drilling position until the preset depth is reached. Then, shut down the hydraulic drilling machine and remove the hollow drill rod from the borehole.

[0016] Step 2: Coal Sample Cooling and Collection with Liquid Nitrogen: First, disassemble the ordinary drill bit and install the coring tube at the end of the hollow drill rod. Start the hydraulic drilling machine, driving the hollow drill rod and coring tube to extend upwards into the borehole until the coring drill bit of the coring tube reaches the preset drilling position, then stop the hydraulic drilling machine. Open the gas proportioning valve, the first control ball valve, and the second control ball valve to allow compressed air to enter the liquid nitrogen tank through the air inlet, driving liquid nitrogen to pass sequentially through the liquid nitrogen discharge pipe, the tee joint, the hollow drill rod, the annular air passage, the sampling chamber, and the coring port to be discharged to the bottom of the hole. At this time, due to the high temperature at the bottom of the hole, the liquid nitrogen vaporizes into nitrogen gas, which absorbs heat, causing the bottom of the hole and the surrounding coal body to cool down rapidly. After injecting for a period of time, close the gas proportioning valve, the first control ball valve, and the second control ball valve. Then, restart the hydraulic drilling machine, driving the coring drill bit to break up the low-temperature coal body at the current depth. Due to the low temperature of the coal body, the breaking up at this time can greatly reduce the coal gas desorption rate, thus allowing the broken coal pieces to enter the sampling chamber through the sampling port, completing the coal sample cooling and collection with liquid nitrogen.

[0017] Step 3: Coal Sample Freezing and Sealing: Open the gas proportioning valve, the third control ball valve, and the fourth control ball valve to allow compressed air to enter the water storage tank through the air inlet, driving water to flow sequentially through the water injection pipe, the tee joint, the hollow drill rod, the annular air passage, and the through hole into the sampling chamber. After a period of time, close the gas proportioning valve, the third control ball valve, and the fourth control ball valve, and drain the water from the hollow drill rod and the annular air passage. Then, reopen the gas proportioning valve, the first control ball valve, and the second control ball valve to inject liquid nitrogen into the sampling chamber. As the sampling chamber is filled with water, it freezes into ice due to the low temperature, encasing the coal sample and sealing it. This method of sealing the coal sample in ice not only keeps the temperature low but also effectively reduces the amount of gas desorption loss during the drilling process. After a period of time, close the gas proportioning valve, the first control ball valve, and the second control ball valve. Finally, restart the hydraulic drilling rig to retract the hollow drill rod and the core tube until it is removed from the upward-grown hole, completing the coal sample collection.

[0018] Compared with existing technologies, this invention combines a coring tube, a liquid nitrogen and water injection device, and a drilling mechanism. First, the drilling mechanism, equipped with a conventional drill bit, drills into the coal seam to the desired sampling depth. Then, the drill is withdrawn, the conventional drill bit is replaced with a coring tube, and the tube is inserted to the required sampling depth. Liquid nitrogen is injected into the bottom of the borehole at the current depth using the liquid nitrogen and water injection device. The liquid nitrogen undergoes phase change and vaporization, absorbing heat and rapidly reducing the temperature of the surrounding coal, effectively decreasing the rate of gas desorption from the surrounding coal. Next, the drilling mechanism drives the coring drill bit in the coring tube to drill and break up the cooled coal, allowing the broken coal pieces to enter the sampling chamber. Internal storage significantly reduces gas desorption losses during coal sampling due to the low temperature of the coal body during crushing. After sampling, the sampling chamber is filled with water using a liquid nitrogen and water injection device, followed by the injection of liquid nitrogen. The low temperature of the liquid nitrogen causes the water in the sampling chamber to quickly freeze, encasing the coal sample and sealing it as a frozen sample. This ice-encasing method not only keeps the coal sample at a low temperature but also effectively reduces gas desorption losses during the drilling and extraction process. Finally, the coring tube is removed from the drill and the frozen coal sample is transferred to the test chamber. This invention is based on the characteristic that the lower the temperature of the coal body, the slower the gas desorption. By using liquid nitrogen at a low temperature of -195.8℃, the coal body to be sampled is first cooled with liquid nitrogen before sampling. Then, the low-temperature coal body is broken up to collect coal samples, thereby effectively suppressing the loss of coal sample gas desorption during collection. Then, the liquid nitrogen is combined with water to quickly condense into ice, which is used to wrap the collected coal sample and freeze it into a whole. During the long process of drilling and transportation, the coal sample is wrapped and frozen by ice, which greatly reduces the loss of gas desorption and provides the coal sample required for subsequent high-precision testing of coal seam gas content. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the overall layout of the present invention.

[0020] In the diagram: 1-Coring drill bit, 2-Through hole, 3-Frozen coal sample, 4-Coring tube, 5-Ventilation port, 6-Hollow drill rod, 7-Drill rod connecting groove, 8-Base, 9-Limiting mechanism, 10-Hydraulic drilling rig, 11-Liquid nitrogen discharge pipe, 12-First control ball valve, 13-Liquid nitrogen tank, 14-Thermocouple level gauge, 15-Second control ball valve, 16-Pressure gauge, 17-Compressed air tank, 18-Gas proportional regulating valve, 19-Third control ball valve, 20-Buoyancy level gauge, 21-Water storage tank, 22-Fourth control ball valve, 23-T-connector. Detailed Implementation

[0021] The present invention will be further described below.

[0022] like Figure 1 As shown, a low-temperature quick-freezing system for inhibiting coal gas desorption includes a core tube, a liquid nitrogen and water injection device, and a drilling mechanism.

[0023] The drilling mechanism includes a hollow drill rod 6 and a hydraulic drill rig 10. The hydraulic drill rig 10 is mounted on a base 8. One end of the hollow drill rod 6 is coaxially connected to the output end of the hydraulic drill rig 10 through a limiting mechanism 9, so that the hydraulic drill rig 10 can drive the hollow drill rod 6 to rotate synchronously for drilling. The limiting mechanism 9 is used to limit the maximum extension distance of the hollow drill rod 6. There are multiple hollow drill rods 6, which are coaxially arranged and connected through drill rod connecting grooves 7.

[0024] The coring tube includes an inner tube, an outer tube, and a coring drill bit 1. The inner tube is installed inside the outer tube and is fixedly connected to the inner wall of the outer tube by a bracket, forming an annular air passage between them. One end of the outer tube is coaxially connected to the other end of the hollow drill rod 6, and a vent 5 is provided at the connection between the hollow drill rod 6 and the outer tube to allow the hollow drill rod 6 to communicate with the annular air passage inside the outer tube. A sampling chamber is provided inside the inner tube for storing coal samples after sampling. The coring drill bit 1 is installed at the other end of the outer tube and has a coring port that communicates with the sampling chamber. A through hole 2 is opened on the side wall of the inner tube near the coring drill bit 1 to allow the annular air passage to communicate with the sampling chamber.

[0025] The liquid nitrogen and water injection device includes a compressed air tank 17, a liquid nitrogen tank 13, a water storage tank 21, and a three-way connector 23. An inlet is located on the side of the hollow drill rod 6 near the limiting mechanism 9. One port of the three-way connector 23 is connected to the inlet via a pipeline. The liquid nitrogen tank 13 has an air inlet and a liquid nitrogen discharge pipe 11 at its upper part, with one end of the discharge pipe 11 extending to the bottom of the liquid nitrogen tank 13. The water storage tank 21 has an air inlet and a water injection pipe at its upper part, with one end of the water injection pipe extending to the bottom of the water storage tank 21. The outlet of the compressed air tank 17 is connected to the air inlet of the liquid nitrogen tank 13 and the air inlet of the water storage tank 21 via pipelines. The liquid nitrogen discharge pipe 11... The other end and the other end of the water injection pipe are respectively connected to the other two ports of the tee connector 23; when it is necessary to cool the collected coal sample, compressed air is introduced into the liquid nitrogen tank 13 through the air inlet to drive the liquid nitrogen through the liquid nitrogen discharge pipe 11, the tee connector 23, the hollow drill rod 6, the annular air channel, the sampling chamber and the core sampling port to discharge to the bottom of the hole to cool the coal sample; when it is necessary to inject water into the coal sample in the sampling chamber, compressed air is introduced into the water storage tank 21 through the air inlet to drive the water through the water injection pipe, the tee connector 23, the hollow drill rod 6, the annular air channel and the through hole 2 to inject into the sampling chamber, and the water is frozen into ice in the subsequent sampling chamber due to the low temperature to wrap the coal sample.

[0026] The liquid nitrogen discharge pipe 11 is equipped with a first control ball valve 12, which is a cryogenic ball valve. A second control ball valve 15 is installed on the pipeline between the compressed air tank 17 and the liquid nitrogen tank 13. A third control ball valve 19 is installed on the pipeline between the compressed air tank 17 and the water storage tank 21. A fourth control ball valve 22 is installed on the water injection pipe. A gas proportioning valve 18 is installed at the outlet of the compressed air tank 17. These valves facilitate the control of the opening and closing of different pipelines. The liquid nitrogen tank 13 is equipped with a thermocouple-type level gauge 14 to monitor the liquid nitrogen level in the liquid nitrogen tank 13. The water storage tank 21 is equipped with a buoyancy-type level gauge 20 to monitor the water level in the water storage tank 21. Pressure gauges 16 are installed on the pipeline between the compressed air tank 17 and the liquid nitrogen tank 13, and on the pipeline between the compressed air tank 17 and the water storage tank 21, to monitor the air pressure of the compressed air passing through their respective pipelines.

[0027] As an improvement of the present invention, the liquid nitrogen discharge pipe 11 is a cryogenic pipe and the water injection pipe is a pressure-resistant hose.

[0028] The aforementioned water storage tank 21, compressed air tank 17, liquid nitrogen tank 13, limiting mechanism 9, and hydraulic drilling rig 10 are all existing equipment. This invention only utilizes their functions and does not improve their structure.

[0029] The working method of the above-mentioned low-temperature quick-freezing method for inhibiting coal gas desorption in fixed-point coring is as follows:

[0030] Step 1: Coal Seam Drilling Construction: First, preset the coal seam depth for which the gas content needs to be measured and the upward drilling position. Then, after assembling and connecting this sampling system, all valves are initially closed. At this time, the coring tube is not installed at the end of the hollow drill rod 6. Install the ordinary drill bit at the end of the hollow drill rod 6. Start the hydraulic drilling machine 10, which drives the hollow drill rod 6 and the ordinary drill bit to rotate synchronously and drill towards the preset upward drilling position until the preset depth is reached. Then, shut down the hydraulic drilling machine 10 and remove the hollow drill rod 6 from the borehole.

[0031] Step 2: Coal Sample Cooling and Collection with Liquid Nitrogen: First, disassemble the ordinary drill bit and install the coring tube at the end of the hollow drill rod 6. Start the hydraulic drilling machine 10 to drive the hollow drill rod 6 and the coring tube into the upward drilling hole until the coring drill bit 1 of the coring tube reaches the preset drilling position and then stop the hydraulic drilling machine 10. Open the gas proportioning valve 18, the first control ball valve 12 and the second control ball valve 15 to allow compressed air to enter the liquid nitrogen tank 13 through the air inlet, driving the liquid nitrogen to pass through the liquid nitrogen discharge pipe 11, the three-way connector 23, the hollow drill rod 6, the annular air passage, the sampling chamber and the coring port to be discharged to the bottom of the hole. At this time, due to the high temperature at the bottom of the hole, the liquid nitrogen vaporizes into nitrogen gas, which absorbs heat, causing the bottom of the hole and the surrounding coal to cool down rapidly. The temperature is measured by pressure gauge 1. 6. Monitor the compressed air pressure through the pipeline and control the flow rate and pressure of compressed air entering the liquid nitrogen tank 13 through the gas proportional regulating valve 18, thereby realizing the flow control of liquid nitrogen injected into the borehole. Thermocouple level gauge 14 is used to monitor the liquid nitrogen level in the liquid nitrogen tank 13 and know the liquid nitrogen usage in real time. After continuous injection for a period of time, close the gas proportional regulating valve 18, the first control ball valve 12 and the second control ball valve 15. Then restart the hydraulic drilling machine 10 and drive the core drill bit 1 to break the low-temperature coal body at the current depth. Since the coal body temperature is low, the breaking can greatly reduce the coal body gas desorption rate, so that the broken coal blocks enter the sampling chamber through the sampling port to complete the coal sample liquid nitrogen cooling and collection.

[0032] Step 3, Coal Sample Freezing and Sealing: Open the gas proportional control valve 18, the third control ball valve 19, and the fourth control ball valve 22 to allow compressed air to enter the water storage tank 21 through the air inlet, driving water to sequentially flow through the water injection pipe, tee joint 23, hollow drill rod 6, annular air passage, and through hole 2 into the sampling chamber. The pressure gauge 16 monitors the compressed air pressure through the pipeline, and the gas proportional control valve 18 controls the flow rate and pressure of compressed air entering the water storage tank 21, thereby controlling the flow rate of water injected into the sampling chamber. The buoyancy level gauge 20 is used to monitor the water level in the water storage tank 21, providing real-time information on water usage. After a period of time, close the gas proportional control valve 18, the third control ball valve 19, and the fourth control ball valve 22, and... After the water in the hollow drill rod 6 and the annular air passage is drained, the gas proportioning valve 18, the first control ball valve 12, and the second control ball valve 15 are opened again to inject liquid nitrogen into the sampling chamber. As the sampling chamber is filled with water, it freezes into ice due to the low temperature, thus encasing the coal sample and sealing it. By encasing the coal sample in ice, the temperature is kept low, and the airtightness of the ice effectively reduces the amount of gas desorption loss during the retraction process. After a period of time, the gas proportioning valve 18, the first control ball valve 12, and the second control ball valve 15 are closed. Finally, the hydraulic drilling rig 10 is restarted, driving the hollow drill rod 6 and the core tube to retract until they are removed from the upward-grown hole, completing the coal sample collection.

[0033] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A fixed-point coring system for inhibiting coal gas desorption by low-temperature rapid freezing, characterized in that, This includes the coring tube, liquid nitrogen and water injection device, and drilling mechanism; The drilling mechanism includes a hollow drill rod and a hydraulic drilling rig. The hydraulic drilling rig is mounted on a base. One end of the hollow drill rod is coaxially connected to the output end of the hydraulic drilling rig through a limiting mechanism, so that the hydraulic drilling rig can drive the hollow drill rod to rotate synchronously for drilling. The coring tube includes an inner tube, an outer tube, and a coring drill bit. The inner tube is installed inside the outer tube and is fixedly connected to the inner wall of the outer tube by a bracket, forming an annular air passage between them. One end of the outer tube is coaxially connected to the other end of a hollow drill rod, and a vent is provided at the connection between the hollow drill rod and the outer tube to allow communication between the hollow drill rod and the annular air passage inside the outer tube. A sampling chamber is provided inside the inner tube for storing coal samples after sampling. The coring drill bit is installed at the other end of the outer tube and has a coring port that communicates with the sampling chamber. A through hole is opened on the side wall of the inner tube near the coring drill bit to allow communication between the annular air passage and the sampling chamber. The liquid nitrogen and water injection device includes a compressed air tank, a liquid nitrogen tank, a water storage tank, and a T-junction. An inlet is located on the side of the hollow drill rod near the limiting mechanism. One port of the T-junction is connected to the inlet via a pipeline. The upper part of the liquid nitrogen tank has an air inlet and a liquid nitrogen discharge pipe, one end of which extends to the bottom of the liquid nitrogen tank. The upper part of the water storage tank has an air inlet and a water injection pipe, one end of which extends to the bottom of the water storage tank. The outlet of the compressed air tank is connected to the air inlets of the liquid nitrogen tank and the water storage tank via pipelines, respectively. The other end of the liquid nitrogen discharge pipe is connected to the other end of the water injection pipe. The ends are connected to the other two ports of the tee connector respectively; when it is necessary to cool the collected coal sample, compressed air is introduced into the liquid nitrogen tank through the air inlet, driving the liquid nitrogen to pass through the liquid nitrogen discharge pipe, tee connector, hollow drill rod, annular air channel, sampling chamber and core sampling port to discharge to the bottom of the hole to cool the coal sample; when it is necessary to inject water into the coal sample in the sampling chamber, compressed air is introduced into the water storage tank through the air inlet, driving the water to pass through the water injection pipe, tee connector, hollow drill rod, annular air channel and through hole to inject into the sampling chamber, and the water is frozen into ice in the subsequent sampling chamber due to the low temperature, thus encasing the coal sample.

2. The fixed-point coring system for inhibiting coal gas desorption by low-temperature quick-freezing according to claim 1, characterized in that, The hollow drill rods are multiple in number, and the multiple hollow drill rods are coaxially arranged and connected by drill rod connecting grooves.

3. The low-temperature quick-freezing method for inhibiting coal gas desorption using a fixed-point coring system according to claim 1, characterized in that, The liquid nitrogen discharge pipe is equipped with a first control ball valve, the pipeline between the compressed air tank and the liquid nitrogen tank is equipped with a second control ball valve, the pipeline between the compressed air tank and the water storage tank is equipped with a third control ball valve, the water injection pipe is equipped with a fourth control ball valve, and the outlet of the compressed air tank is equipped with a gas proportioning valve.

4. The low-temperature quick-freezing method for inhibiting coal gas desorption using a fixed-point coring system according to claim 1, characterized in that, The liquid nitrogen tank is equipped with a thermocouple-type level gauge to monitor the liquid nitrogen level inside the tank; the water storage tank is equipped with a buoyancy-type level gauge to monitor the water level inside the tank; the pipelines between the compressed air tank and the liquid nitrogen tank, and between the compressed air tank and the water storage tank, are all equipped with pressure gauges to monitor the compressed air pressure passing through their respective pipelines.

5. The low-temperature quick-freezing method for inhibiting coal gas desorption using a fixed-point coring system according to claim 1, characterized in that, The liquid nitrogen discharge pipe is a cryogenic pipe, and the water injection pipe is a pressure-resistant flexible hose.

6. A method for operating a fixed-point coring system for inhibiting coal gas desorption by low-temperature quick-freezing according to any one of claims 1 to 5, characterized in that, The specific steps are as follows: Step 1: Coal Seam Drilling Construction: First, preset the coal seam depth for which gas content needs to be measured and the upward drilling position. Then, assemble and connect the sampling system. Initially, all valves are closed. At this time, the coring tube is not installed at the end of the hollow drill rod. Install the ordinary drill bit at the end of the hollow drill rod. Start the hydraulic drilling machine, driving the hollow drill rod and ordinary drill bit to rotate synchronously and drill towards the preset upward drilling position until the preset depth is reached. Then, shut down the hydraulic drilling machine and remove the hollow drill rod from the borehole. Step 2: Coal Sample Cooling and Collection with Liquid Nitrogen: First, disassemble the ordinary drill bit and install the coring tube at the end of the hollow drill rod. Start the hydraulic drilling machine, driving the hollow drill rod and coring tube to extend upwards into the drilling hole until the coring drill bit of the coring tube reaches the preset drilling position, then stop the hydraulic drilling machine. Open the gas proportioning valve, the first control ball valve, and the second control ball valve to allow compressed air to enter the liquid nitrogen tank through the air inlet, driving liquid nitrogen to pass sequentially through the liquid nitrogen discharge pipe, the tee joint, the hollow drill rod, the annular air passage, the sampling chamber, and the coring port to be discharged to the bottom of the hole. At this time, due to the high temperature at the bottom of the hole, the liquid nitrogen vaporizes into nitrogen gas, absorbing heat and rapidly cooling the bottom of the hole and the surrounding coal. After injecting for a period of time, close the gas proportioning valve, the first control ball valve, and the second control ball valve. Then, restart the hydraulic drilling machine, driving the coring drill bit to break up the low-temperature coal at the current depth, allowing the broken coal pieces to enter the sampling chamber through the sampling port, completing the coal sample cooling and collection with liquid nitrogen. Step 3: Coal Sample Freezing and Sealing: Open the gas proportioning valve, the third control ball valve, and the fourth control ball valve to allow compressed air to enter the water storage tank through the air inlet. This drives water to flow sequentially through the water injection pipe, the tee joint, the hollow drill rod, the annular air passage, and the through hole into the sampling chamber. After a period of time, close the gas proportioning valve, the third control ball valve, and the fourth control ball valve, and drain the water from the hollow drill rod and the annular air passage. Then, reopen the gas proportioning valve, the first control ball valve, and the second control ball valve to inject liquid nitrogen into the sampling chamber. As the sampling chamber is filled with water, it freezes into ice due to the low temperature, encasing the coal sample and sealing it. After a period of time, close the gas proportioning valve, the first control ball valve, and the second control ball valve. Finally, restart the hydraulic drilling rig to retract the hollow drill rod and the core tube until it is removed from the upward-grown hole, completing the coal sample collection process.

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