Fixed-point coring system and method for inhibiting coal gas desorption through low-temperature quick freezing

Abstract

The invention discloses a fixed-point coring system and method for inhibiting coal gas desorption through low-temperature quick freezing. The fixed-point coring method comprises the steps that firstly, drilling is conducted through a drilling mechanism, and a depth position needing to be sampled is reached; liquid nitrogen is injected into the hole bottom through a liquid nitrogen and water injection device, and the temperature of the surrounding coal body is rapidly reduced through phase change gasification and heat absorption of the liquid nitrogen; drilling, crushing and collecting the cooled coal body, wherein the coal body temperature is low during crushing, so that the coal briquette gas desorption loss amount in the crushing and sampling process can be greatly reduced; after sampling is finished, water is injected into the sampling cavity through the liquid nitrogen and water injection device, the water in the sampling cavity is quickly condensed into ice through the low-temperature characteristic of the liquid nitrogen, the coal sample is wrapped to form frozen coal sample sealing, the coal sample can be sealed in the ice in an ice wrapping mode, the temperature is low, and the coal sample can be stored in the ice through the sealing performance of ice wrapping. The coal sample gas desorption loss amount in the drill withdrawing and taking-out process is effectively reduced; therefore, the required coal sample is provided for the subsequent high-precision test of the gas content of the coal seam.

Description

Technical Field

[0001] The invention belongs to the technical field of coal body drilling sampling, in particular to a fixed-point coring system and method for low-temperature quick freezing to inhibit coal gas desorption. Background Art

[0002] Gas is a byproduct of coal and also the main disaster factor in coal mines. In 2024 alone, coal mine gas accidents have caused dozens of deaths, seriously threatening life and property safety. To control gas well, it is the first step to understand the occurrence law of coal seam gas, especially the test of coal seam gas content, a key indicator. Its test accuracy affects the scale of subsequent gas prevention and control measures and is directly related to the effectiveness of gas control.

[0003] The gas content test of coal seams is to take out the gas-containing coal in the coal seams through sampling equipment for gas desorption test, and add the estimated gas loss during the sampling process to obtain the total gas content of the coal seams. Therefore, coal seam sampling is the key link in the coal seam gas content test, and the gas in the coal will continue to desorb and lose during the sampling process. Studies have found that the more gas loss, the greater the error of the estimated value, which reduces the accuracy of the gas content test. At present, there are two main sampling methods for coal seams: fixed-point and non-fixed-point sampling. When applied, it was found that non-fixed-point sampling methods such as orifice powder collection method have problems such as mixed samples, small coal sample particle size, and excessive wear, resulting in low measured gas content values. The fixed-point sampling method does not have the above problems, but during the sampling process, there will be gas loss caused by gas desorption from the exposure of coal blocks to the canning test. The degree of desorption is most significantly affected by temperature. The higher the temperature, the faster the gas desorption rate. During the drilling sampling process, the drill bit rotates and drills repeatedly to generate heat from friction with the contacted coal sample, causing the coal body to heat up rapidly, which in turn promotes the desorption of gas inside the coal block, resulting in a large amount of gas loss during the coal sample extraction process, which has become a problem that restricts the improvement of gas content testing accuracy. In addition, when fixed-point sampling is performed using a core tube from a greater depth, after the coal sample is loaded into the core tube, due to the greater depth of the borehole, the drill rod withdrawal time is long (often tens of minutes), and the coal sample is exposed to the air for a long time, and the exposure process is continuously desorbed, which will further lead to increased gas loss. The above problems have become a problem that restricts the high-precision testing of coal seam gas content.

[0004] Therefore, how to provide a new sampling system and method that can quickly reduce the temperature of coal blocks and inhibit the gas desorption rate of coal blocks during fixed-point sampling, and can continue to inhibit during the sampling process, thereby providing the required coal samples for subsequent high-precision testing of coal seam gas content, is the research direction required by the present invention. Summary of the invention

[0005] In view of the problems existing in the above-mentioned prior art, the present invention provides a fixed-point coring system and method for low-temperature quick freezing to inhibit coal gas desorption, which quickly reduces the temperature of the coal seam at the bottom of the hole through liquid nitrogen phase change heat absorption, and simultaneously uses water injection to freeze the coal sample, thereby effectively inhibiting the gas desorption rate during the coal sample collection process and providing the required coal samples for subsequent high-precision testing of the coal seam gas content.

[0006] In order to achieve the above-mentioned purpose, the technical solution adopted by the present invention is: a fixed-point coring system for low-temperature quick freezing to inhibit coal gas desorption, comprising 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 drill rig. The hydraulic drill rig is installed on a base. One end of the hollow drill rod is coaxially connected to the output end of the hydraulic drill rig through a limiting mechanism, so that the hydraulic drill rig can drive the hollow drill rod to rotate synchronously for drilling.

[0008] The core tube comprises an inner tube, an outer tube and a core drill bit. The inner tube is installed inside the outer tube, and the inner tube is fixedly connected to the inner wall of the outer tube through a bracket, so that an annular airway is formed between the two. 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, which is used to connect the hollow drill rod with the annular airway in the outer tube. A sampling cavity is provided in the inner tube, which is used to store coal samples after sampling. The core drill bit is installed at the other end of the outer tube, and a core port is provided on the core drill bit, which is connected to the sampling cavity. A through hole is provided on the side wall of the inner tube close to the core drill bit, which is used to connect the annular airway with the sampling cavity.

[0009] The liquid nitrogen and water injection device comprises a compressed air tank, a liquid nitrogen tank, a water storage tank and a three-way joint. An inlet is provided on the side of the hollow drill rod near the limiting mechanism, and one of the ports of the three-way joint is connected to the inlet through a pipeline; an air inlet and a liquid nitrogen discharge pipe are provided on the upper part of the liquid nitrogen tank, and one end of the liquid nitrogen discharge pipe extends to the bottom of the liquid nitrogen tank; an air inlet and a water injection pipe are provided on the upper part of the water storage tank, and one end of the water injection pipe extends to the bottom of the water storage tank; the outlet of the compressed air tank is respectively connected to the air inlet of the liquid nitrogen tank and the air inlet of the water storage tank through pipelines, and the other end of the liquid nitrogen discharge pipe is connected to the other end of the water injection pipe The ends are respectively connected with the other two ports of the three-way joint; when the collected coal sample needs to be cooled, the compressed air enters the liquid nitrogen tank through the air inlet to drive the liquid nitrogen to pass through the liquid nitrogen discharge pipe, the three-way joint, the hollow drill rod, the annular airway, the sampling cavity and the core sampling port in sequence and be discharged to the bottom of the hole to cool the coal sample; when the coal sample in the sampling cavity needs to be injected with water, the compressed air enters the water storage tank through the air inlet to drive the water to pass through the water injection pipe, the three-way joint, the hollow drill rod, the annular airway and the through hole in sequence and be injected into the sampling cavity, and the water in the subsequent sampling cavity is condensed into ice under the action of low temperature to wrap the coal sample.

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

[0011] Furthermore, 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 ratio regulating valve. These valves are provided to facilitate the control of the on-off of different pipelines.

[0012] Furthermore, the liquid nitrogen tank is equipped with a thermocouple level gauge for monitoring the liquid level of liquid nitrogen in the liquid nitrogen tank; the water storage tank is equipped with a buoyancy level gauge for monitoring the liquid level of water in the water storage tank; the pipeline between the compressed air tank and the liquid nitrogen tank, and the pipeline between the compressed air tank and the water storage tank are both equipped with pressure gauges for monitoring the air pressure of the compressed air passing through their respective pipelines.

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

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

[0015] Step 1, coal seam drilling construction: first preset the coal seam depth for measuring gas content and its upward drilling position, then assemble and connect the sampling system. Initially, all valves are in the closed state, and the core tube is not installed to the end of the hollow drill rod. Install the ordinary drill bit on the end of the hollow drill rod; start the hydraulic drill rig to drive the hollow drill rod and the ordinary drill bit to rotate synchronously and drill towards the preset upward drilling position until the preset depth is reached, then turn off the hydraulic drill rig and take the hollow drill rod out of the borehole.

[0016] Step 2, coal sample liquid nitrogen cooling collection: first disassemble the ordinary drill bit, and install the coring tube on the end of the hollow drill rod, start the hydraulic drill, drive the hollow drill rod and the coring tube to extend into the upward drilling, until the coring drill bit of the coring tube reaches the preset drilling position and stops the hydraulic drill; open the gas ratio regulating valve, the first control ball valve and the second control ball valve, so that the compressed air enters the liquid nitrogen tank through the air inlet and drives the liquid nitrogen to pass through the liquid nitrogen discharge pipe, the three-way joint, the hollow drill rod, the annular airway, the sampling cavity and the coring port in turn 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 gasification phase changes into nitrogen absorption, so that the bottom of the hole and the surrounding coal body cool down rapidly. After continuous injection for a period of time, close the gas ratio regulating valve, the first control ball valve and the second control ball valve; then restart the hydraulic drill to drive the coring drill bit to crush the low-temperature coal body at the current depth. Due to the low temperature of the coal body, the crushing can greatly reduce the gas desorption rate of the coal body at this time, so that the crushed coal blocks enter the sampling cavity through the sampling port to complete the coal sample liquid nitrogen cooling collection.

[0017] Step 3, freezing and sealing the coal sample: open the gas ratio regulating valve, the third control ball valve and the fourth control ball valve, so that the compressed air enters the water storage tank through the air inlet to drive the water to be injected into the sampling cavity through the water injection pipe, the three-way joint, the hollow drill rod, the annular airway and the through hole in turn, and close the gas ratio regulating valve, the third control ball valve and the fourth control ball valve after a period of time, and drain the water in the hollow drill rod and the annular airway; open the gas ratio regulating valve, the first control ball valve and the second control ball valve again, so that liquid nitrogen is injected into the sampling cavity. Since the sampling cavity is full of water, it condenses into ice under the action of low temperature, and the coal sample is wrapped to form a frozen coal sample for sealing. The coal sample can be sealed in ice by wrapping it in ice, which not only has a lower temperature, but also has a sealing property of the ice wrapping, which effectively reduces the gas desorption loss of the coal sample during the process of withdrawing the drill; after a period of time, close the gas ratio regulating valve, the first control ball valve and the second control ball valve; finally, restart the hydraulic drill to drive the hollow drill rod and the core tube to withdraw the drill until it is taken out from the upward borehole, and the coal sample collection work is completed.

[0018] Compared with the prior art, the present invention adopts a method of combining a coring tube, a liquid nitrogen and water injection device and a drilling mechanism. First, a common drill bit is installed through the drilling mechanism to drill a hole into the coal seam and reach the required sampling depth. Then, the drill is withdrawn and the common drill bit is replaced with a coring tube and sent to the required sampling depth. Liquid nitrogen is injected into the bottom of the borehole at the current depth through the liquid nitrogen and water injection device. Liquid nitrogen phase changes and gasifies to absorb heat and quickly reduce the temperature of the surrounding coal body, effectively reducing the rate of gas desorption in the surrounding coal body. Then, the drilling mechanism drives the coring drill bit of the coring tube to drill and crush the cooled coal body, so that the crushed coal blocks enter the sampling cavity. Internal storage, since the temperature of the coal body is low during crushing, the loss of coal gas desorption during the crushing sampling process can be greatly reduced; after the sampling is completed, the sampling chamber is filled with water through the liquid nitrogen and water injection device, and then liquid nitrogen is injected into the sampling chamber again. The low temperature characteristics of liquid nitrogen are used to make the water in the sampling chamber quickly condense into ice, and the coal sample is wrapped to form a frozen coal sample for sealing. The coal sample can be sealed in ice by wrapping in ice, which not only has a lower temperature, but also has a sealing property through ice wrapping, which effectively reduces the loss of coal gas desorption during the process of withdrawing the drill; finally, the core tube is withdrawn and the frozen coal sample is transferred to the test box. Based on the characteristic that the lower the coal temperature, the slower the gas desorption, the present invention utilizes low-temperature liquid nitrogen at -195.8°C to first cool the required sampling coal body with liquid nitrogen before sampling, and then crushes the low-temperature coal body to collect coal samples, thereby effectively suppressing the loss of gas desorption of the coal samples during collection; then, liquid nitrogen is combined with water to quickly condense into ice, which is used to wrap the collected coal samples and freeze them into a whole. During the long process of drilling withdrawal and transportation, the coal samples are wrapped and frozen in ice and sealed, thereby greatly reducing the gas desorption loss, thereby providing the required coal samples for subsequent high-precision testing of coal seam gas content. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0020] In the figure: 1-coring drill bit, 2-through hole, 3-frozen coal sample, 4-coring tube, 5-vent, 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 liquid level gauge, 15-second control ball valve, 16-pressure gauge, 17-compressed air tank, 18-gas ratio regulating valve, 19-third control ball valve, 20-buoyancy liquid level gauge, 21-water storage tank, 22-fourth control ball valve, 23-three-way connector. DETAILED DESCRIPTION

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

[0022] like Figure 1 As shown, a fixed-point coring system for low-temperature quick freezing to inhibit coal gas desorption includes a coring 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 installed 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; the hollow drill rod 6 is multiple, and the multiple hollow drill rods 6 are coaxially arranged and connected through a drill rod connecting groove 7.

[0024] The coring tube comprises an inner tube, an outer tube and a coring drill bit 1; the inner tube is installed inside the outer tube, and the inner tube is fixedly connected to the inner wall of the outer tube through a bracket, so that an annular airway is formed between the two; 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, which is used to connect the hollow drill rod 6 with the annular airway in the outer tube; a sampling cavity is provided in the inner tube, which is used to store coal samples after sampling; the coring drill bit 1 is installed at the other end of the outer tube, and a coring port is provided on the coring drill bit 1, which is connected to the sampling cavity; a through hole 2 is provided on the side wall of the inner tube close to the coring drill bit 1, which is used to connect the annular airway with the sampling cavity.

[0025] The liquid nitrogen and water injection device comprises a compressed air tank 17, a liquid nitrogen tank 13, a water storage tank 21 and a three-way joint 23. The hollow drill rod 6 is provided with an inlet near the side of the limiting mechanism 9, and one of the ports of the three-way joint 23 is connected to the inlet through a pipeline; an air inlet and a liquid nitrogen discharge pipe 11 are provided on the upper part of the liquid nitrogen tank 13, and one end of the liquid nitrogen discharge pipe 11 extends to the bottom of the liquid nitrogen tank 13; an air inlet and a water injection pipe are provided on the upper part of the water storage tank 21, and one end of the water injection pipe extends 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 through pipelines, respectively, and 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 three-way joint 23; when the collected coal sample needs to be cooled, the compressed air enters the liquid nitrogen tank 13 through the air inlet to drive the liquid nitrogen to pass through the liquid nitrogen discharge pipe 11, the three-way joint 23, the hollow drill rod 6, the annular airway, the sampling cavity and the core sampling port in sequence and discharge to the bottom of the hole to cool the coal sample; when the coal sample in the sampling cavity needs to be injected with water, the compressed air enters the water storage tank 21 through the air inlet to drive the water to pass through the water injection pipe, the three-way joint 23, the hollow drill rod 6, the annular airway and the through hole 2 in sequence and inject into the sampling cavity, and the water is subsequently condensed into ice by the low temperature in the sampling cavity to wrap the coal sample.

[0026] The liquid nitrogen discharge pipe 11 is equipped with a first control ball valve 12 which is a low temperature resistant ball valve, the pipeline between the compressed air tank 17 and the liquid nitrogen tank 13 is equipped with a second control ball valve 15, the pipeline between the compressed air tank 17 and the water storage tank 21 is equipped with a third control ball valve 19, the water injection pipe is equipped with a fourth control ball valve 22, and the outlet of the compressed air tank 17 is equipped with a gas ratio regulating valve 18. The provision of these valves facilitates the control of the on-off of different pipelines. The liquid nitrogen tank 13 is equipped with a thermocouple level gauge 14 for monitoring the liquid level of liquid nitrogen in the liquid nitrogen tank 13; the water storage tank 21 is equipped with a buoyancy level gauge 20 for monitoring the liquid level of water in the water storage tank 21; the pipelines between the compressed air tank 17 and the liquid nitrogen tank 13 and the pipelines between the compressed air tank 17 and the water storage tank 21 are both equipped with pressure gauges 16 for monitoring the air pressure of compressed air passing through their respective pipelines.

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

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

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

[0030] Step 1, coal seam drilling construction: first preset the coal seam depth for measuring the gas content and its upward drilling position, then assemble and connect the sampling system, initially all valves are in a closed state, at this time the core tube is not installed to the end of the hollow drill rod 6, and an ordinary drill bit is installed at the end of the hollow drill rod 6; start the hydraulic drill rig 10, drive the hollow drill rod 6 and the ordinary drill bit to rotate synchronously towards the preset upward drilling position, until the preset depth is reached, turn off the hydraulic drill rig 10 and take the hollow drill rod 6 out of the borehole.

[0031] Step 2: Collect coal samples by cooling 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 drill 10, drive the hollow drill rod 6 and the coring tube to extend into the upward drilling, until the coring drill bit 1 of the coring tube reaches the preset drilling position and stop the hydraulic drill 10; open the gas ratio regulating valve 18, the first control ball valve 12 and the second control ball valve 15, so that the compressed air enters the liquid nitrogen tank 13 through the air inlet and drives the liquid nitrogen to pass through the liquid nitrogen discharge pipe 11, the three-way joint 23, the hollow drill rod 6, the annular airway, the sampling cavity and the coring port in turn 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 gasification phase changes into nitrogen absorption, which quickly cools down the bottom of the hole and the surrounding coal body, and the pressure gauge 1 6 monitors the air pressure of the compressed air passing through the pipeline, and controls the flow rate and pressure of the compressed air entering the liquid nitrogen tank 13 through the gas ratio regulating valve 18, so as to realize the flow control of the liquid nitrogen injected into the borehole. The thermocouple liquid level gauge 14 is used to monitor the liquid level of the liquid nitrogen in the liquid nitrogen tank 13, and the amount of liquid nitrogen used is known in real time; after continuous injection for a period of time, the gas ratio regulating valve 18, the first control ball valve 12 and the second control ball valve 15 are closed; then the hydraulic drilling rig 10 is restarted to drive the coring drill bit 1 to crush the low-temperature coal body at the current depth. Since the coal body temperature is relatively low, the crushing can greatly reduce the coal body gas desorption rate at this time, so that the crushed coal blocks enter the sampling cavity through the sampling port, and the liquid nitrogen cooling collection of the coal sample is completed.

[0032] Step 3: Freeze and seal the coal sample: open the gas ratio regulating valve 18, the third control ball valve 19 and the fourth control ball valve 22, so that the compressed air enters the water storage tank 21 through the air inlet and drives the water to be injected into the sampling cavity through the water injection pipe, the three-way joint 23, the hollow drill rod 6, the annular airway and the through hole 2 in sequence, and the air pressure of the compressed air passing through the pipeline is monitored by the pressure gauge 16, and the flow rate and pressure of the compressed air entering the water storage tank 21 are controlled by the gas ratio regulating valve 18, so as to realize the flow control of the water injected into the sampling cavity, and the buoyancy level gauge 20 is used to monitor the liquid level of the water in the water storage tank 21, and know the water consumption in real time; after a period of time, close the gas ratio regulating valve 18, the third control ball valve 19 and the fourth control ball valve 22, and make After the water in the hollow drill rod 6 and the annular airway is drained; open the gas ratio regulating valve 18, the first control ball valve 12 and the second control ball valve 15 again to inject liquid nitrogen into the sampling chamber. Since the sampling chamber is filled with water, it condenses into ice under the action of low temperature, and wraps the coal sample to form a frozen coal sample for sealing. The coal sample can be sealed in ice by wrapping it in ice. Not only is the temperature low, but the sealing of the ice wrapping can effectively reduce the loss of coal sample gas desorption during the process of withdrawing the drill. After a period of time, close the gas ratio regulating valve 18, the first control ball valve 12 and the second control ball valve 15; finally, restart the hydraulic drilling rig 10 to drive the hollow drill rod 6 and the core tube to withdraw the drill until it is taken out from the upward borehole, completing the coal sample collection work.

[0033] 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 fixed-point coring system for low-temperature quick freezing to inhibit coal gas desorption, characterized in that: It includes a core tube, liquid nitrogen and water injection devices and a drilling mechanism; The drilling mechanism includes a hollow drill rod and a hydraulic drill rig, wherein the hydraulic drill rig is mounted on a base, and one end of the hollow drill rod is coaxially connected to the output end of the hydraulic drill rig through a limiting mechanism, so that the hydraulic drill rig can drive the hollow drill rod to rotate synchronously for drilling; The coring tube comprises an inner tube, an outer tube and a coring drill bit. The inner tube is installed inside the outer tube, and the inner tube is fixedly connected to the inner wall of the outer tube through a bracket, so that an annular airway is formed between the two. 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, which is used to connect the hollow drill rod with the annular airway in the outer tube. A sampling cavity is provided in the inner tube, which is used to store coal samples after sampling. The coring drill bit is installed at the other end of the outer tube, and the coring drill bit is provided with a coring port, which is connected to the sampling cavity. A through hole is provided on the side wall of the inner tube close to the coring drill bit, which is used to connect the annular airway with the sampling cavity. The liquid nitrogen and water injection device comprises a compressed air tank, a liquid nitrogen tank, a water storage tank and a three-way joint. An inlet is provided on the side of the hollow drill rod near the limiting mechanism, and one of the ports of the three-way joint is connected to the inlet through a pipeline; an air inlet and a liquid nitrogen discharge pipe are provided on the upper part of the liquid nitrogen tank, and one end of the liquid nitrogen discharge pipe extends to the bottom of the liquid nitrogen tank; an air inlet and a water injection pipe are provided on the upper part of the water storage tank, and one end of the water injection pipe extends to the bottom of the water storage tank; the outlet of the compressed air tank is respectively connected to the air inlet of the liquid nitrogen tank and the air inlet of the water storage tank through pipelines, and the other end of the liquid nitrogen discharge pipe is connected to the other end of the water injection pipe The ends are respectively connected with the other two ports of the three-way joint; when the collected coal sample needs to be cooled, the compressed air enters the liquid nitrogen tank through the air inlet to drive the liquid nitrogen to pass through the liquid nitrogen discharge pipe, the three-way joint, the hollow drill rod, the annular airway, the sampling cavity and the core sampling port in sequence and be discharged to the bottom of the hole to cool the coal sample; when the coal sample in the sampling cavity needs to be injected with water, the compressed air enters the water storage tank through the air inlet to drive the water to pass through the water injection pipe, the three-way joint, the hollow drill rod, the annular airway and the through hole in sequence and be injected into the sampling cavity, and the water in the subsequent sampling cavity is condensed into ice under the action of low temperature to wrap the coal sample.

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

3. According to claim 1, the fixed-point coring system for inhibiting coal gas desorption by low-temperature quick freezing is characterized in that: A first control ball valve is installed on the liquid nitrogen discharge pipe, a second control ball valve is installed on the pipeline between the compressed air tank and the liquid nitrogen tank, a third control ball valve is installed on the pipeline 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 ratio regulating valve is installed at the outlet of the compressed air tank.

4. According to claim 1, the fixed-point coring system for inhibiting coal gas desorption by low-temperature quick freezing is characterized in that: The liquid nitrogen tank is equipped with a thermocouple level gauge for monitoring the liquid level of liquid nitrogen in the liquid nitrogen tank; the water storage tank is equipped with a buoyancy level gauge for monitoring the liquid level of water in the water storage tank; the pipeline between the compressed air tank and the liquid nitrogen tank, and the pipeline between the compressed air tank and the water storage tank are both equipped with pressure gauges for monitoring the air pressure of the compressed air passing through their respective pipelines.

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

6. A working method of 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: Step 1, Coal Seam Drilling Construction: First, preset the coal seam depth and upward drilling position for measuring gas content, then assemble and connect the sampling system, initially all valves are in the closed state, at this time the core tube is not installed to the end of the hollow drill rod, and the ordinary drill bit is installed at the end of the hollow drill rod; start the hydraulic drill rig, drive the hollow drill rod and the ordinary drill bit to rotate synchronously and drill towards the preset upward drilling position, until the preset depth is reached, shut down the hydraulic drill rig and remove the hollow drill rod from the borehole; Step 2, coal sample liquid nitrogen cooling collection: first disassemble the ordinary drill bit, and install the coring tube on the end of the hollow drill rod, start the hydraulic drill, drive the hollow drill rod and the coring tube to extend into the upward drilling, until the coring drill bit of the coring tube reaches the preset drilling position and stops the hydraulic drill; open the gas ratio regulating valve, the first control ball valve and the second control ball valve, so that the compressed air enters the liquid nitrogen tank through the air inlet and drives the liquid nitrogen to pass through the liquid nitrogen discharge pipe, the three-way joint, the hollow drill rod, the annular airway, the sampling cavity and the coring port in turn 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 gasification phase changes into nitrogen absorption, so that the bottom of the hole and the surrounding coal body cool down rapidly. After continuous injection for a period of time, close the gas ratio regulating valve, the first control ball valve and the second control ball valve; then restart the hydraulic drill to drive the coring drill bit to crush the low-temperature coal body at the current depth, so that the crushed coal blocks enter the sampling cavity through the sampling port, and the coal sample liquid nitrogen cooling collection is completed; Step three, freezing and sealing the coal sample: open the gas ratio regulating valve, the third control ball valve and the fourth control ball valve, so that compressed air enters the water storage tank through the air inlet to drive water to be injected into the sampling cavity through the water injection pipe, the three-way joint, the hollow drill rod, the annular airway and the through hole in turn. After a period of time, close the gas ratio regulating valve, the third control ball valve and the fourth control ball valve, and drain the water in the hollow drill rod and the annular airway; open the gas ratio regulating valve, the first control ball valve and the second control ball valve again, so that liquid nitrogen is injected into the sampling cavity. Since the sampling cavity is full of water, it condenses into ice under the action of low temperature, and wraps the coal sample to form a frozen coal sample for sealing. After a period of time, close the gas ratio regulating valve, the first control ball valve and the second control ball valve; finally, restart the hydraulic drill to drive the hollow drill rod and the core tube to withdraw the drill until they are taken out from the upward borehole to complete the coal sample collection work.

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