A visual test system and method for simulating hot flue gas storage and methane extraction

Abstract

The application discloses a kind of visual test system and method of simulated hot flue gas sealing and methane extraction, and hot flue gas injection system is realized with the accurate configuration and injection of hot flue gas with different temperature and different gas mixing ratio, in combination with the in-situ reservoir stress temperature simulation function of triaxial core holder system, the simulation test research of the whole process of "hot flue gas fracturing-hot flue gas sealing-CH4 displacement and extraction" under in-situ condition can be realized;Using ultrasonic and acoustic emission technology and combining in-situ CT scanning technology, the dynamic visual monitoring of the internal pore and fracture structure and development of sample during the test process is realized;And through optical fiber monitoring system and wearable flexible sensor system, the temperature field, stress field and deformation field distribution cloud of sample surface and its surrounding gas can be real-time inversion;So as to realize the evolution characteristics and interaction law of temperature field, stress field, flow field and strain field of sample surface and its surrounding gas during the whole process of dynamic distributed monitoring test.

Description

Technical Field

[0001] This invention relates to a visualization test system and method, specifically a visualization test system and method for simulating hot flue gas storage and methane extraction, belonging to the field of carbon sequestration and CH4 extraction technology. Background Technology

[0002] Given China's national energy structure characterized by "abundant coal, scarce oil, and limited gas," coal accounts for more than 50% of my country's energy consumption. Coal-fired power plants are the main mode of coal consumption, and CO2 accounts for approximately 30% to 50% of the annual emissions of hot flue gas from coal-fired power plants. To reduce CO2 emissions into the atmosphere, CO2 sequestration is widely considered the most effective potential solution for achieving carbon neutrality. my country's deep unminable coal seams have a huge volume of CH4 adsorption, indicating a promising prospect for CH4 resource utilization. In addition, these coal seams are buried deep underground, making direct mining difficult, which can provide good geological conditions for hot flue gas sequestration. Some scholars predict that the CO2 sequestration capacity of unminable coal seams at depths of 1500 to 2000 meters is approximately 55.8 billion tons. However, deep unminable coal seams generally have the characteristics of high ground stress, low porosity, and low permeability, which increases the difficulty of hot flue gas injection and CH4 extraction. It is necessary to use fracturing and permeability enhancement measures to promote the development of coal seam pore and fracture structures, providing efficient transport channels for hot flue gas sequestration and CH4 extraction.

[0003] The hot flue gas produced by coal combustion in coal-fired power plants mainly consists of CO2, N2, H2O(g), and trace amounts of SOx and NO. X The composition and temperature range are 50-300℃, which is much higher than the reservoir temperature of deep, unminable coal seams. Injecting hot flue gas into the fractured coal seam can promote the desorption of CH4 gas in the coal body due to its high temperature. In addition, the CO2 in the hot flue gas can replace a large amount of adsorbed CH4 gas in the target deep, unminable coal seam due to competitive adsorption advantage, thus promoting the production of a large amount of CH4 gas in the target deep, difficult-to-mine coal seam. This improves the efficiency of coal seam methane mining while achieving hot flue gas sequestration.

[0004] Domestic and international scholars have conducted extensive research on the displacement of CH4 from coal seams using single-component gases such as CO2 or N2. However, research on the impact of high-temperature hot flue gas containing multiple gas components on the drainage efficiency of CH4 from coal seams is insufficient. Furthermore, existing studies on the effectiveness of gas injection for methane drainage in coal seams often focus only on single processes such as adsorption, seepage, displacement, and storage. Current research on gas injection for CH4 displacement mainly concentrates on monitoring flow field parameters including gas pressure, flow rate, and gas composition. Research on the coupled dynamic monitoring of multiple parameters such as strain, temperature, and damage in the coal body throughout the entire process of "coal seam fracturing-hot flue gas storage-CH4 extraction" is lacking. The method has its shortcomings. Monitoring of coal-related parameters typically involves attaching strain gauges to the coal body. However, this method often suffers from poor sealing, and the sensors are easily damaged during loading due to their close contact with the coal. Furthermore, this method usually only allows for monitoring of localized areas of the coal body, making it difficult to achieve distributed monitoring throughout the coal. Additionally, current CT combined with displacement techniques mostly involve simply removing the samples before and after displacement from the holder and placing them on the CT control console for scanning. However, this approach typically cannot reflect the real-time development of the internal pore and fracture structure of the coal body under in-situ conditions during the "coal fracturing-hot flue gas sealing-CH4 extraction" process.

[0005] Therefore, to address the aforementioned technical deficiencies, there is an urgent need to provide a visual testing system and method capable of visualizing the internal pore and fracture structure of the coal body and dynamically monitoring damage development throughout the entire process of "coal body fracturing - hot flue gas storage - CH4 extraction" under in-situ conditions. This system should dynamically and distributedly track the evolution characteristics and interaction mechanisms of the "temperature field - stress field - deformation field - flow field" across the entire coal body. Based on the obtained evolution characteristics and interaction mechanisms, the parameters for subsequent actual hot flue gas storage and CH4 extraction should be optimized, thereby maximizing the amount of hot flue gas stored and the CH4 extraction efficiency in deep, unminable coal seams. Summary of the Invention

[0006] To address the problems existing in the prior art, this invention provides a visual experimental system and method for simulating hot flue gas storage and methane extraction. This system enables visualization of the internal pore and fracture structure of the coal body and dynamic monitoring of damage development throughout the entire process of "coal body fracturing - hot flue gas storage - CH4 extraction" under in-situ conditions. It dynamically and distributedly tracks the evolution characteristics and interaction mechanisms of the "temperature field - stress field - deformation field - flow field" across the entire coal body. Based on the obtained evolution characteristics and interaction mechanisms, it optimizes the parameters for subsequent actual hot flue gas storage and CH4 extraction, thereby maximizing the amount of hot flue gas stored and the efficiency of CH4 extraction in deep, unminable coal seams.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is: a visual experimental system for simulating hot flue gas storage and methane extraction, comprising: a hot flue gas injection system, a CH4 and He injection system, a triaxial core holder system, a damage monitoring system, a CT in-situ scanning system, a multi-field monitoring system, and a tail gas analysis and processing system.

[0008] The hot flue gas injection system includes a multi-component gas injection system, a water injection system, and a hot flue gas generation system. The multi-component gas injection system includes CO2 cylinders, N2 cylinders, and cylinders containing other components of the hot flue gas. All three types of cylinders are connected to the hot flue gas generation system to supply the various components of the hot flue gas to the system. The water injection system includes a water tank and a constant-speed, constant-pressure pump. The water tank is connected to the hot flue gas generation system via the pump to supply water to the system. The system includes a gas stirring device, a thermostatic tank, and an air compressor. The gas stirring device is installed inside the thermostatic tank and is used to stir and mix the gas inside the tank. The air compressor is connected to the thermostatic tank through a pipeline and is used to pressurize the gas inside the thermostatic tank. The thermostatic tank is connected to the triaxial core holder system through a pipeline and is used to mix, stir, heat, and pressurize the gas injected into the tank before delivering it to the triaxial core holder system. A vacuum pump is installed on the pipeline between the hot flue gas distribution system and the triaxial core holder system.

[0009] The CH4 and He injection system includes CH4 gas cylinders and He gas cylinders. Both CH4 gas cylinders and He gas cylinders are connected to the triaxial core holder system through pipelines and are used to deliver CH4 gas and He gas to the triaxial core holder system, respectively.

[0010] The triaxial core holder system includes a triaxial core holder body and a hydraulic constant speed and constant pressure pump. The triaxial core holder body has a sample placement space inside. The hydraulic constant speed and constant pressure pump is connected to the triaxial core holder body and is used to pump hydraulic oil into the triaxial core holder body to apply confining pressure to the sample inside it, control the upper and lower pressure heads to apply axial pressure, and control the temperature of the sample through the hydraulic oil.

[0011] The damage monitoring system includes an acoustic emission monitoring unit and an ultrasonic monitoring unit. The acoustic emission monitoring unit is installed inside the body of the triaxial core holder and is used to monitor the damage signals generated inside the sample in real time. The ultrasonic monitoring unit is installed inside the body of the triaxial core holder and is used to monitor the ultrasonic wave velocity, attenuation and reflection characteristics of ultrasonic waves propagating inside the sample in real time.

[0012] The CT in-situ scanning system includes an X-ray source, a detector, and a rotating console. The main body of the triaxial core holder is mounted on the rotating console and can rotate with the console. The X-ray source and the detector are located on both sides of the main body of the triaxial core holder, so that the X-rays emitted by the X-ray source pass through the sample and are received by the detector, which is used to scan the internal spatial structure of the sample in real time.

[0013] The multi-field monitoring system includes a fiber optic monitoring system and a wearable flexible sensor system. The fiber optic monitoring system is installed inside the triaxial core holder and is used to monitor the real-time temperature of the hydraulic fluid around the sample, the real-time radial deformation of the sample, and the pressure of the hydraulic fluid around the sample. The wearable flexible sensor system is installed on the sample surface and is used to monitor the real-time temperature of the sample surface, the real-time stress of the sample surface, the gas pressure and gas concentration on the sample surface, and the axial and circumferential strain of the sample surface.

[0014] The exhaust gas analysis and treatment system includes a gas analyzer and an exhaust gas collection device. One end of the gas analyzer is connected to the main body of the triaxial core holder through a pipeline, and the other end is connected to the exhaust gas collection device. It is used to analyze the components of the exhaust gas discharged after passing through the interior of the triaxial core holder in real time, and then discharge it to the exhaust gas collection device.

[0015] Furthermore, the pipelines between the hot flue gas distribution system and the triaxial core holder system, and the pipelines between the triaxial core holder system and the exhaust gas analysis and treatment system, are all equipped with high-precision gas flow meters.

[0016] Furthermore, the constant temperature tank is equipped with a gas temperature sensor and a gas pressure sensor, and the triaxial core holder body is equipped with a liquid temperature sensor.

[0017] Furthermore, the acoustic emission monitoring unit includes a transmission rod and an acoustic emission acquisition instrument. One end of the transmission rod extends into the body of the triaxial core holder and contacts the sample surface, while the other end is equipped with an acoustic emission probe. The acoustic emission probe is connected to the acoustic emission acquisition instrument through an acoustic signal amplifier. The ultrasonic monitoring unit includes an ultrasonic emission probe, an ultrasonic receiving probe, and an ultrasonic acquisition instrument. The ultrasonic emission probe and the ultrasonic receiving probe are respectively fixed to the upper pressure head and the lower pressure head. The ultrasonic acquisition instrument is connected to both the ultrasonic emission probe and the ultrasonic receiving probe, so that the ultrasonic waves excited by the ultrasonic emission probe pass through the sample and are received by the ultrasonic receiving probe and transmitted to the ultrasonic acquisition instrument.

[0018] Furthermore, the fiber optic monitoring system includes an axial fiber optic displacement sensor, multiple integrated radial fiber optic monitoring units, and a fiber optic data acquisition system. The axial fiber optic displacement sensor is mounted on the lower pressure head and connected to the fiber optic data acquisition system via a data cable to monitor the axial deformation of the sample. Multiple integrated radial fiber optic monitoring units are evenly distributed on the inner wall of the triaxial core holder and connected to the fiber optic data acquisition system via fiber optic sensor connectors. Each integrated radial fiber optic monitoring unit includes a fiber optic temperature sensor, a fiber optic pressure sensor, and a radial fiber optic displacement sensor. The fiber optic temperature sensor is used to monitor the temperature change of the hydraulic fluid around the sample in real time, the radial fiber optic displacement sensor is used to obtain the radial displacement of the inner wall of the holder relative to the sample in different areas, and the fiber optic pressure sensor is used to obtain the pressure change of the hydraulic fluid around each area of ​​the sample.

[0019] Furthermore, the wearable flexible sensor system includes a flexible layer and multiple integrated sensor units. The multiple integrated sensor units are evenly distributed on the flexible layer, which wraps around the outside of the sample. The integrated sensor units include a temperature sensor, a stress sensor, a gas sensor, and a strain sensor. The temperature sensor is used to monitor temperature changes in different areas of the sample surface in real time. The stress sensor is used to monitor stress changes in different areas of the sample surface in real time. The gas sensor is used to monitor gas pressure and gas concentration changes in different areas of the sample surface in real time. The strain sensor consists of a radial strain sensor and an axial strain sensor, used to monitor axial and circumferential strain changes in different areas of the sample surface in real time.

[0020] Furthermore, the gas analyzer is any one of the following: infrared absorption gas analyzer, laser absorption gas analyzer, and mass spectrometry gas analyzer.

[0021] Furthermore, the other components of the hot flue gas include sulfur oxides, nitrogen oxides, and oxygen.

[0022] Furthermore, a high-precision gas flow meter and a pressure gauge are installed between the gas analyzer and the main body of the triaxial core holder, respectively, to monitor the flow rate and pressure of the exhaust gas discharged from the main body of the triaxial core holder; a low-range volumetric flow meter, a medium-range volumetric flow meter, and a high-range volumetric flow meter are installed between the gas analyzer and the main body of the triaxial core holder, and the three volumetric flow meters are set in parallel.

[0023] The specific steps of the above-mentioned method for methane extraction and closed-loop carbon fixation from unminable coal seams using hot flue gas displacement are as follows:

[0024] A. Preparation of core samples and setup of the test system: Collect coal from the coal mine and cut it into several core samples of the same size. Clean the surface of the samples. Then, make through holes in the center of each sample for subsequent injection of hot flue gas. Select any sample, attach and wrap the wearable flexible sensor system on the surface of the sample, put it into the triaxial core holder system, and complete the assembly of each system.

[0025] B. Determining Initial Permeability: Based on the required simulated deep geostress and temperature environment, set the axial pressure, confining pressure, and temperature values; start the hydraulic constant-speed, constant-pressure pump of the triaxial core holder system to pump hydraulic oil, causing the triaxial core holder system to apply axial pressure and confining pressure to the sample and heat the sample until the set axial pressure, confining pressure, and temperature values ​​are reached, then stop heating and pressurizing, and maintain the current pressure and temperature; then start the CT in-situ scanning system to complete a CT scan of the sample in the current state; after completion, turn on the vacuum pump and open the valves of each pipeline to control the hot flue gas injection system, CH4, and He. The internal pipelines of the injection system, triaxial core holder system, and exhaust gas analysis and treatment system were evacuated. After evacuation, the outlet valve of the triaxial core holder body was closed, while the inlet valve remained open. Simultaneously, He gas was injected into the triaxial core holder body through the pipeline via a He gas cylinder. The injection volume was recorded using a high-precision gas flow meter, and the free space volume in the triaxial core holder body was calibrated using the ideal gas law. After calibration, the outlet valve was opened, and after the volumetric flow meter reading stabilized, the initial permeability of the sample was calculated. Finally, the He gas was discharged to the exhaust gas collection device.

[0026] C. CH4 Adsorption Pre-equilibrium: Simulating the initial CH4 occurrence in deep coal seams; setting the CH4 gas pressure value, keeping the inlet valve open and the outlet valve closed, CH4 gas is introduced into the triaxial core holder body, and a high-precision gas flow meter records the CH4 injection volume. When the set pressure value is reached, the inlet valve is closed, and the sample is allowed to adsorb CH4 for 24-48 hours. During the adsorption period, the changes in gas pressure, temperature, ultrasonic signal, acoustic emission signal, and fiber optic signal in the triaxial core holder body are collected at intervals by the damage monitoring system and multi-field monitoring system. The internal structure of the sample during the CH4 adsorption process is scanned in real time using a CT in-situ scanning system to achieve multi-parameter dynamic visualization monitoring of the sample during the methane adsorption process. After the adsorption is completed, the changes in gas pressure, temperature, strain, ultrasonic signal, and acoustic emission signal in the triaxial core holder body are recorded under the adsorption equilibrium state. The internal structure of the sample at this time is CT scanned to obtain the internal structure of the sample under the CH4 adsorption equilibrium state, thereby determining the original pore structure and internal damage of the sample before hot flue gas injection.

[0027] D. Hot Flue Gas Fracturing Process: First, the proportions, temperatures, and injection pressures of various gases in the hot flue gas are set. The hot flue gas injection system first injects CO2, N2, other components of the hot flue gas, and water into the hot flue gas generation system according to the set proportions. A gas stirring device ensures uniform mixing of all gases. The hot flue gas generation system heats the gas to the set temperature to generate the required hot flue gas. Then, the outlet valve is closed, the inlet valve is open, and the air compressor is activated to pressurize the hot flue gas until the injection pressure is reached. At this point, the hot flue gas is injected into the triaxial core holder body through pipelines to fracturing the sample. During the injection and fracturing process, a data acquisition system collects real-time data on the temperature, pressure, flow rate, ultrasonic signals, acoustic emission signals, and fiber optic signals of the sample surface and surrounding gases. In-situ CT scanning of the sample was performed to achieve dynamic and visual monitoring of multiple parameters of the core sample during fracturing, thereby obtaining the internal flow field transport, temperature field evolution, pore and fracture structure characteristics, and damage patterns of the core during the displacement of CH4 by hot flue gas. When the gas pressure at the inlet of the triaxial core holder suddenly depressurizes or the gas flow rate at the outlet suddenly increases, the hot flue gas fracturing is stopped. The changes in gas pressure, temperature, strain, ultrasonic signal, acoustic emission signal, and fiber optic signal of the sample surface and surrounding gas at this time are recorded, and the sample is scanned in real time to obtain the internal flow field transport, temperature field evolution, pore and fracture structure characteristics, and damage patterns of the sample after fracturing. After the outlet valve is opened and the volumetric flow meter reading stabilizes, the gas pressure at the inlet and outlet of the triaxial core holder is recorded to calculate the permeability of the sample after fracturing.

[0028] E. Hot flue gas displacement of CH4 sample: The inlet and outlet valves remain open. The injection pressure of the hot flue gas during displacement is set. Then, through the hot flue gas distribution system, hot flue gas is injected into the triaxial core holder at the set pressure to displace the CH4 adsorbed on the sample. During this process, the data acquisition system collects and records in real-time the temperature, pressure, flow rate, ultrasonic signals, acoustic emission signals, and fiber optic signals of the sample surface and surrounding gases. Real-time in-situ CT scanning of the sample is also performed to achieve multi-parameter dynamic visualization monitoring during the hot flue gas displacement of CH4 sample, thereby obtaining information on the flow field transport, temperature field evolution, and pore structure characteristics within the sample during the hot flue gas displacement of CH4 sample. The study investigated the characteristics and damage patterns of the sample. It recorded the flow rates at the inlet and outlet, and monitored and recorded the composition, concentration, and flow rate of the exhaust gas in real time using a gas analyzer. This allowed for real-time acquisition of the hot flue gas injection rate, CH4 gas extraction rate, and interaction between the hot flue gas and CH4 gas during the CH4 displacement process in the triaxial core holder. The displacement process was stopped when the CH4 concentration in the exhaust gas reached the critical CH4 concentration. The study also recorded changes in the gas pressure, temperature, strain, ultrasonic signals, acoustic emission signals, and fiber optic signals on and around the sample surface. Real-time CT scanning of the sample's internal spatial structure was performed to obtain the flow field transport, temperature field evolution, pore and fracture structure characteristics, and damage patterns within the sample after displacement.

[0029] F. Hot flue gas storage process: After the displacement test is completed, the inlet and outlet valves are closed, and the hot flue gas is stored in the body of the triaxial core holder. During this period, the gas pressure, temperature, strain, ultrasonic signal, and acoustic emission signal of the sample surface and surrounding gas are monitored in real time. CT scans of the sample are also used in real time to achieve dynamic and visual monitoring of sample parameters during the hot flue gas storage process, thereby obtaining the flow field transport, temperature field evolution, pore and fracture structure characteristics, and damage patterns during the storage process. After the storage test is completed, the inlet and outlet valves are opened. After the flow data stabilizes, the gas pressure at the inlet and outlet of the triaxial core holder body is recorded, and the permeability after hot flue gas storage is calculated, completing the entire test process.

[0030] Compared with existing technologies, the present invention combines a hot flue gas injection system, a CH4 and He injection system, a triaxial core holder system, a damage monitoring system, a CT in-situ scanning system, a multi-field monitoring system, and an exhaust gas analysis and processing system, which has the following advantages:

[0031] (1) This invention achieves precise configuration and injection of hot flue gas with different temperatures and different gas mixing ratios through a hot flue gas injection system. Combined with the in-situ reservoir stress and temperature simulation function of the triaxial core holder system, it can realize the simulation test study of the whole process of "hot flue gas fracturing - hot flue gas storage - CH4 displacement and extraction" under in-situ conditions. Using ultrasonic and acoustic emission technology, the damage signals generated inside the sample can be monitored in real time. Combined with in-situ CT scanning technology, it realizes dynamic visualization monitoring of the pore and fracture structure and development of the sample inside the whole process of "coal seam fracturing - hot flue gas storage - CH4 displacement and extraction" under in-situ conditions.

[0032] (2) This invention achieves non-destructive testing of the temperature field, stress field, and deformation field of each region of the sample under triaxial stress loading by installing an optical fiber monitoring system on the inner wall of the triaxial core holder. The optical fiber sensor network is built into the holder and does not directly contact the sample. Therefore, it does not need to be directly loaded during the test, which ensures the accuracy and safety of the sensor and the sealing of the holding system. Furthermore, the temperature field, stress field, and deformation field distribution cloud map of the gas around the coal body can be retrieved in real time based on the optical fiber sensor network. Thus, dynamic distributed monitoring of the temperature field, stress field, flow field, and strain field evolution characteristics of the gas around the sample during the entire process of "fracturing-hot flue gas sealing-CH4 extraction" is realized.

[0033] (3) The flexible layer of the wearable flexible sensor system of the present invention is composed of known polymer materials, which have good plasticity and adaptability. On the one hand, it can be customized in shape and size to completely cover and fit the core surface. In the clamping system, it has high adaptability to the deformation and loading strength of the sample and is not easily damaged. It also has the characteristics of high sensitivity. Through the integrated sensor unit, it can monitor the small stress and strain changes in each area of ​​the sample; thereby, it can invert the surface temperature, stress, strain and multi-component gas distribution cloud map of the sample in real time; thereby realizing dynamic distributed monitoring of the temperature field, stress field, flow field and strain field evolution characteristics of the sample surface during the entire process of "fracturing-hot flue gas sealing-CH4 extraction".

[0034] (4) This invention monitors simultaneously using a fiber optic monitoring system, a wearable flexible sensor system, a damage monitoring system, and a CT in-situ scanning system. It also changes the coal quality used in the sample, the composition ratio of the hot flue gas, the axial pressure, the confining pressure, the temperature, the CH4 gas pressure during adsorption, and the injection pressure during hot flue gas fracturing and displacement. After testing all these changes, data under various conditions can be obtained, providing data support for subsequent actual hot flue gas storage and CH4 extraction. Attached Figure Description

[0035] Figure 1 This is a schematic diagram of the overall structure of the present invention;

[0036] Figure 2 This is a schematic diagram of the overall structure of the CT in situ scanning system in this invention;

[0037] Figure 3 This is a circumferential cross-sectional view of the wearable flexible sensor system and integrated radial fiber optic sensor network deployed in this invention.

[0038] Figure 4 This is a schematic diagram of the integrated radial fiber optic sensor network of the fiber optic monitoring system in this invention;

[0039] Figure 5 This is a schematic diagram of the integrated radial fiber optic monitoring unit of the fiber optic monitoring system in this invention;

[0040] Figure 6 This is a schematic diagram of the integrated sensor unit layout of the wearable flexible sensor system in this invention;

[0041] Figure 7 This is a schematic diagram of the integrated sensor unit of the wearable flexible sensor system in this invention.

[0042] In the diagram: 1-CO2 cylinder; 2-N2 cylinder; 3-Other component gas cylinders for hot flue gas; 4-Pressure reducing valve; 5-High-precision gas flow meter; 6-Water tank; 7-Water injection constant speed and pressure pump; 8-Motor; 9-Rotating shaft; 10-Stirring blade; 11-Thermostatic tank; 12-Gas temperature sensor; 13-Air compressor; 14-Gas pressure sensor; 15-CH4 cylinder; 16-He cylinder; 17-Conduction rod; 18-Acoustic emission probe; 19-Acoustic signal amplifier; 20-Acoustic emission acquisition instrument; 21-Ultrasonic emission probe; 22-Ultrasonic receiving probe; 23-Ultrasonic acquisition instrument; 24-X-ray source; 25-Detector; 26-Rotating control console; 27-Integrated... 27-1-Radial fiber optic monitoring unit; 27-2-Fiber optic temperature sensor; 27-3-Fiber optic pressure sensor; 27-4-Radial fiber optic displacement sensor; 27-5-Axial fiber optic displacement sensor; 27-6-Fiber optic sensor connector; 37-7-Wearable flexible sensor system; 37-8-Sample; 37-9-Integrated sensor unit; 37-1-Temperature sensor; 37-2-Stress sensor; 37-3-Gas sensor; 32-4-Strain sensor; 37-5-Gas analyzer; 37-6-Tail gas collection device; 37-7-Inlet valve; 37-7-Outlet valve; 37-1-Low-range volumetric flow meter; 37-2-Medium-range volumetric flow meter; 37-37-3-High-range volumetric flow meter; 38-Vacuum pump. Detailed Implementation

[0043] The present invention will be further described below.

[0044] like Figure 1As shown, a visualization test system for simulating hot flue gas storage and methane extraction includes: a hot flue gas injection system, a CH4 and He injection system, a triaxial core holder system, a damage monitoring system, a CT in-situ scanning system, a multi-field monitoring system, and a tail gas analysis and processing system; the multi-field monitoring system is a distributed "temperature field-stress field-deformation field" monitoring system.

[0045] The hot flue gas injection system includes a multi-component gas injection system, a water injection system, and a hot flue gas generation system. The multi-component gas injection system includes a CO2 cylinder 1, an N2 cylinder 2, and other hot flue gas component cylinders 3, which include sulfur oxides, nitrogen oxides, and oxygen. All three cylinders are connected to the hot flue gas generation system to supply the various components of the hot flue gas. The water injection system includes a water tank 6 and a constant-speed, constant-pressure water injection pump 7. The water tank 6 is connected to the hot flue gas generation system via the pump 7 to supply water to the system. The hot flue gas generation system includes a gas stirring device, a constant-temperature tank 11, and an air compressor 13. The gas stirring device, housed within the constant-temperature tank 11, consists of a motor 8, a rotating shaft 9, and stirring blades 10, and is used to agitate the gas within the tank. The gas is mixed and stirred. Air compressor 13 is connected to constant temperature tank 11 through pipeline to pressurize the gas in constant temperature tank 11. Constant temperature tank 11 is connected to triaxial core holder system through pipeline to mix, stir, heat and pressurize the gas injected into the tank before delivering it to triaxial core holder system. Vacuum pump 38 is installed on the pipeline between the hot flue gas injection system and the triaxial core holder system. Constant temperature tank 11 is equipped with gas temperature sensor 12 and gas pressure sensor 14. Liquid temperature sensor is installed inside the main body of triaxial core holder.

[0046] The CH4 and He injection system includes CH4 cylinder 15 and He cylinder 16. Both CH4 cylinder 15 and He cylinder 16 are connected to the triaxial core holder system through pipelines and are used to deliver CH4 gas and He gas to the triaxial core holder system, respectively.

[0047] The triaxial core holder system includes a triaxial core holder body and a hydraulic constant speed and constant pressure pump. The triaxial core holder body has a sample placement space inside. The hydraulic constant speed and constant pressure pump is connected to the triaxial core holder body and is used to pump hydraulic oil into the triaxial core holder body to apply confining pressure to the sample inside it, control the upper and lower pressure heads to apply axial pressure, and control the temperature of the sample through the hydraulic oil.

[0048] The damage monitoring system includes an acoustic emission monitoring unit and an ultrasonic monitoring unit. The acoustic emission monitoring unit is installed inside the triaxial core holder body and is used to monitor damage signals generated inside the sample in real time. The ultrasonic monitoring unit is installed inside the triaxial core holder body and is used to monitor the ultrasonic wave velocity, attenuation, and reflection characteristics of ultrasonic waves propagating inside the sample in real time. The acoustic emission monitoring unit includes a transmission rod 17 and an acoustic emission acquisition instrument 20. One end of the transmission rod 17 extends into the triaxial core holder body and contacts the surface of the sample 31, and the other end is equipped with an acoustic emission probe 18. The acoustic emission probe 18 is connected to the acoustic emission acquisition instrument 20 through an acoustic signal amplifier 19. The ultrasonic monitoring unit includes an ultrasonic emission probe 21, an ultrasonic receiving probe 22, and an ultrasonic acquisition instrument 23. The ultrasonic emission probe 21 and the ultrasonic receiving probe 22 are fixed to the upper pressure head and the lower pressure head, respectively. The ultrasonic acquisition instrument 23 is connected to the ultrasonic emission probe 21 and the ultrasonic receiving probe 22, so that the ultrasonic waves excited by the ultrasonic emission probe 21 are received by the ultrasonic receiving probe 22 after passing through the sample and transmitted to the ultrasonic acquisition instrument 23.

[0049] like Figure 2 As shown, the CT in-situ scanning system includes an X-ray source 24, a detector 25, and a rotating console 26. The main body of the triaxial core holder is mounted on the rotating console 26 and can rotate with the console. The X-ray source 24 and the detector 25 are located on both sides of the main body of the triaxial core holder, so that the X-rays emitted by the X-ray source 24 pass through the sample and are received by the detector 25, which is used to scan the internal spatial structure of the held sample in real time.

[0050] The multi-field monitoring system includes a fiber optic monitoring system and a wearable flexible sensor system. The fiber optic monitoring system is installed inside the triaxial core holder and is used to monitor the real-time temperature of the hydraulic fluid around the sample, the real-time radial deformation of the sample, and the pressure of the hydraulic fluid around the sample. The wearable flexible sensor system is installed on the surface of the sample 31 and is used to monitor the real-time temperature of the sample surface, the real-time stress of the sample surface, the gas pressure and gas concentration on the sample surface, and the axial and circumferential strain of the sample surface.

[0051] like Figures 3 to 5As shown, the fiber optic monitoring system includes an axial fiber optic displacement sensor 28, 40 integrated radial fiber optic monitoring units 27, and a fiber optic data acquisition system. The axial fiber optic displacement sensor 28 is mounted on the lower pressure head and connected to the fiber optic data acquisition system via a data cable, used to monitor the axial deformation of the sample 31. The 40 integrated radial fiber optic monitoring units 27 are evenly distributed on the inner wall of the triaxial core holder body to form an integrated radial fiber optic sensor network, and are connected to the fiber optic data acquisition system via fiber optic sensor connectors 29. Each integrated radial fiber optic monitoring unit 27 includes a fiber optic temperature sensor 27-1, a fiber optic pressure sensor 27-2, and a radial fiber optic displacement sensor 27-3, wherein the fiber optic temperature sensor 27-1 is used to monitor the hydraulic pressure around the sample in real time. The temperature change of the fluid is monitored by a radial fiber optic displacement sensor 27-3, which acquires the radial displacement of the inner wall of the clamp relative to the sample 31 in different regions of the sample. This allows for dynamic monitoring of the radial deformation of the clamped sample throughout the entire process of "fracturing-hot flue gas sealing-CH4 extraction," and real-time plotting of the radial strain distribution cloud map on the coal surface. A fiber optic pressure sensor 27-2 acquires the pressure changes of the hydraulic fluid surrounding each region of the sample, thereby acquiring the stress field changes around the sample under triaxial stress loading and real-time plotting of the stress field distribution cloud map on the coal surface. Furthermore, the change in liquid volume inside the clamp can be obtained through the change in liquid pressure in the high-precision fiber optic pressure sensor within the clamp, thus dynamically monitoring the volume deformation of the sample throughout the entire process of "fracturing-hot flue gas sealing-CH4 extraction," satisfying the following equation:

[0052] ΔV=C f ×V0×ΔP

[0053] In the formula, C f The compressibility coefficient of the hydraulic oil is given by Pa. -1 V o ΔP represents the volume of hydraulic oil under initial confining pressure loading before hot flue gas injection, in ml; ΔP represents the change in the high-precision fiber optic pressure sensor in the clamp before and after hot flue gas injection, in Pa.

[0054] like Figure 3 , Figure 6 and Figure 7As shown, the wearable flexible sensor system includes a flexible layer and 40 integrated sensor units 32. The 40 integrated sensor units 32 are evenly distributed on the flexible layer, which wraps around the sample. The 40 integrated sensor units 32 are arranged in five rows equidistantly along the axial direction on the sample surface, with eight integrated sensor units arranged in each row. Each integrated sensor unit 32 includes a temperature sensor 32-1, a stress sensor 32-2, a gas sensor 32-3, and a strain sensor 32-4. The temperature sensor 32-1 can be a thermistor or an infrared sensor to monitor temperature changes in different areas of the sample surface in real time, and then retrieve the temperature field distribution cloud map of the coal body surface in real time based on the 40 integrated sensor units 32. The stress sensor 32-2 can be a piezoelectric sensor or an optical sensor to monitor stress changes in different areas of the sample surface in real time, and then retrieve the stress field distribution cloud map of the coal body surface in real time based on the 40 integrated sensor units 32. Forty integrated sensor units 32 are used to invert the stress field distribution cloud map of the coal body surface in real time; gas sensors 32-3 include gas pressure sensors and gas concentration sensors, used to monitor the changes in CH4 / CO2 / CH4 gas pressure and CH4 / CO2 / CH4 gas concentration in different regions of the sample in real time, and then invert the distribution cloud map of each gas pressure field and gas concentration field on the coal body surface in real time based on the 40 integrated sensor units 32; strain sensors 32-4 consist of radial strain sensors and axial strain sensors, used to monitor the changes in axial strain and circumferential strain in different regions of the sample surface in real time, and then invert the distribution cloud map of radial strain field and axial strain field on the coal body surface in real time based on the 40 integrated sensor units 32; thus realizing dynamic distributed monitoring of the temperature field, stress field, flow field and strain field evolution characteristics of the sample surface during the entire process of "fracturing-hot flue gas sealing-CH4 extraction";

[0055] The exhaust gas analysis and treatment system includes a gas analyzer 33 and an exhaust gas collection device 34. The gas analyzer 33 is any one of an infrared absorption gas analyzer, a laser absorption gas analyzer, and a mass spectrometry gas analyzer. One end of the gas analyzer 33 is connected to the main body of the triaxial core holder via a pipeline, and the other end is connected to the exhaust gas collection device 34. It is used to perform real-time analysis of the exhaust gas components discharged after passing through the interior of the triaxial core holder, and then discharge the gas to the exhaust gas collection device 34 after completion.

[0056] The pipelines between the hot flue gas injection system and the triaxial core holder system, and between the triaxial core holder system and the tail gas analysis and treatment system, are all equipped with high-precision gas flow meters 5. These high-precision gas flow meters 5 are mass flow meters. Volumetric flow meters suffer from unstable readings due to gas pressure and temperature variations, while mass flow meters directly measure the gas mass flow rate. Furthermore, the mass flow meter reading is unaffected by gas pressure and temperature, thus enabling accurate acquisition of the hot flue gas injection volume, hot flue gas storage volume, and CH4 extraction volume throughout the entire process of "coal seam fracturing - hot flue gas sealing - CH4 extraction," as well as quantitative multi-element gas injection. Multiple pressure-reducing valves are installed at various points in the pipeline as needed to reduce the pressure of the gas released from the gas cylinder, facilitating its transport within the pipeline.

[0057] As an improvement of the present invention, a high-precision gas flow meter 5 and a pressure gauge are installed between the gas analyzer and the main body of the triaxial core holder, respectively, to monitor the flow rate and pressure of the exhaust gas discharged from the main body of the triaxial core holder; a low-range volumetric flow meter 37-1 (0~50ml / min), a medium-range volumetric flow meter 37-2 (50~500ml / min), and a high-range volumetric flow meter 37-3 (500~2000ml / min) are installed between the gas analyzer and the main body of the triaxial core holder, and the three volumetric flow meters are set in parallel to match the permeability measurement of the clamped samples with different pore fracture structures and damage development degrees.

[0058] All the components or parts of the above-mentioned hot flue gas injection system, CH4 and He injection system, triaxial core holder system, damage monitoring system, CT in-situ scanning system, multi-field monitoring system and exhaust gas analysis and treatment system are existing equipment or parts that can be purchased from the market.

[0059] The specific steps of the above-mentioned method for methane extraction and closed-loop carbon fixation from unminable coal seams using hot flue gas displacement are as follows:

[0060] A. Preparation of core samples and setup of the test system: Collect coal from the coal mine and cut it into several core samples 31 of the same size. Clean the surface of the samples. Then, make a through hole in the center of each sample 31 for subsequent injection of hot flue gas. Select any sample 31, attach and wrap the wearable flexible sensor system on the surface of the sample, put it into the triaxial core holder system, and complete the assembly of each system.

[0061] B. Determining Initial Permeability: Based on the required simulated deep geostress and temperature environment, set the axial pressure, confining pressure, and temperature values; start the hydraulic constant-speed and constant-pressure pump of the triaxial core holder system to pump hydraulic oil, so that the triaxial core holder system applies axial pressure and confining pressure to the sample and heats the sample until the set axial pressure, confining pressure, and temperature values ​​are reached, then stop heating and pressurizing, and maintain the current pressure and temperature; then start the CT in-situ scanning system to complete a CT scan of the sample in the current state; after completion, turn on the vacuum pump 38 and open the valves of each pipeline to control the hot flue gas injection system, CH4 and He injection system, and the triaxial core holder system. The internal pipelines of the triaxial core holder system and the exhaust gas analysis and treatment system were evacuated for 24 hours. After the evacuation was completed, the outlet valve 36 of the triaxial core holder body was closed, while the inlet valve 35 remained open. At the same time, He gas was injected into the triaxial core holder body through the pipeline via the He gas cylinder 16. The injection volume was recorded by the high-precision gas flow meter 5 and the free space volume in the triaxial core holder body was calibrated by combining the ideal gas law. After the calibration was completed, the outlet valve 36 was opened. After the volume flow meter reading stabilized, the initial permeability of the sample was calculated. After completion, the He gas was discharged to the exhaust gas collection device 34.

[0062] C. CH4 Adsorption Pre-equilibrium: Simulating the initial CH4 occurrence in deep coal seams; setting the CH4 gas pressure value, keeping the inlet valve 35 open and the outlet valve 36 closed, CH4 gas is introduced into the triaxial core holder body, and the high-precision gas flow meter 5 records the CH4 injection volume. When the set pressure value is reached, the inlet valve 35 is closed, and the sample is allowed to adsorb CH4 for 24-48 hours. During the adsorption period, the changes in gas pressure, temperature, ultrasonic signal, acoustic emission signal, and fiber optic signal in the triaxial core holder body are collected every 10 seconds by the damage monitoring system and multi-field monitoring system. The internal structure of the sample during the CH4 adsorption process is scanned in real time using a CT in-situ scanning system to achieve multi-parameter dynamic visualization monitoring of the sample during the methane adsorption process. After the adsorption is completed, the changes in gas pressure, temperature, strain, ultrasonic signal, and acoustic emission signal in the triaxial core holder body are recorded under the adsorption equilibrium state. The internal structure of the sample at this time is CT scanned to obtain the internal structure of the sample under the CH4 adsorption equilibrium state, thereby determining the original pore structure and internal damage of the sample before hot flue gas injection.

[0063] D. Hot flue gas fracturing process: First, the proportions, temperatures, and injection pressures of various gases in the hot flue gas are set. The hot flue gas mixing system injects CO2, N2, other components of the hot flue gas, and water into the hot flue gas generation system according to the set proportions. The gas is stirred and mixed evenly by a gas stirring device. The hot flue gas generation system is heated to the set temperature to generate the required hot flue gas. Then, the outlet valve 36 is closed, the inlet valve 35 is open, and the air compressor 13 is turned on to pressurize the hot flue gas until the injection pressure is reached. At this point, the hot flue gas is injected into the triaxial core holder body through pipelines to fracturing the sample. During the injection fracturing process, the temperature, pressure, flow rate, ultrasonic signals, acoustic emission signals, and fiber optic signals of the sample surface and surrounding gas are collected in real time by the data acquisition system. Real-time in-situ CT scanning of the sample enables dynamic and visual monitoring of multiple parameters of the core sample during fracturing, thereby obtaining the flow field migration, temperature field evolution, pore and fracture structure characteristics, and damage patterns inside the core during the displacement of CH4 by hot flue gas. When the gas pressure at the inlet of the triaxial core holder suddenly depressurizes or the gas flow rate at the outlet suddenly increases, hot flue gas fracturing is stopped. The changes in gas pressure, temperature, strain, ultrasonic signal, acoustic emission signal, and fiber optic signal on and around the sample surface are recorded at this time, and real-time CT scanning of the sample is performed to obtain the flow field migration, temperature field evolution, pore and fracture structure characteristics, and damage patterns inside the sample after fracturing. After opening the outlet valve 36 and waiting for the volumetric flow meter reading to stabilize, the gas pressure at the inlet and outlet of the triaxial core holder is recorded to calculate the permeability of the sample after fracturing.

[0064] E. Hot flue gas displacement of CH4 sample: Inlet valve 35 and outlet valve 36 remain open. The injection pressure of the hot flue gas during displacement is set. Then, through the hot flue gas distribution system, hot flue gas is injected into the triaxial core holder at the set pressure to displace the CH4 adsorbed on the sample. During this process, the data acquisition system collects and records in real-time the temperature, pressure, flow rate, ultrasonic signals, acoustic emission signals, and fiber optic signals of the sample surface and surrounding gases. Real-time in-situ CT scanning of the sample is also performed to achieve multi-parameter dynamic visualization monitoring during the hot flue gas displacement of CH4 sample. This allows for the acquisition of the flow field transport, temperature field evolution, pore and fracture structure characteristics, and damage patterns within the sample during the hot flue gas displacement of CH4 sample. The process involves recording the flow rates at the inlet and outlet, and using a gas analyzer to monitor and record the composition, concentration, and flow rate of the exhaust gas in real time. This allows for the real-time acquisition of the hot flue gas injection rate, CH4 gas extraction rate, and interaction between the hot flue gas and CH4 gas during the hot flue gas displacement of CH4 in the triaxial core holder. The displacement process is stopped when the CH4 concentration in the exhaust gas reaches the critical CH4 concentration (i.e., within the range of 10% to 20%). The changes in gas pressure, temperature, strain, ultrasonic signal, acoustic emission signal, and fiber optic signal of the sample surface and surrounding gas are recorded at this time. Real-time CT scanning of the internal spatial structure of the sample is also performed to obtain the flow field transport, temperature field evolution, pore and fracture structure characteristics, and damage patterns inside the sample after the displacement is completed.

[0065] F. Hot flue gas storage process: After the displacement test is completed, the inlet valve 35 and the outlet valve 36 are closed to store the hot flue gas inside the triaxial core holder. During this period, the gas pressure, temperature, strain, ultrasonic signal, and acoustic emission signal of the sample surface and surrounding gas are monitored in real time. The sample is also scanned in real time using CT to achieve dynamic and visual monitoring of the sample parameters during the hot flue gas storage process, thereby obtaining the flow field transport, temperature field evolution, pore and fracture structure characteristics, and damage patterns during the storage process. After the storage test is completed, the inlet valve 35 and the outlet valve 36 are opened. After the flow data stabilizes, the gas pressure at the inlet and outlet of the triaxial core holder is recorded, and the permeability after hot flue gas storage is calculated to complete the entire test process.

[0066] Subsequently, by changing the coal quality used in the sample, changing the composition ratio of the hot flue gas, changing the axial pressure, confining pressure, temperature, CH4 gas pressure during adsorption, and changing the injection pressure during hot flue gas fracturing and displacement, various changes can be tested to obtain data under different conditions, providing data support for subsequent actual hot flue gas storage and CH4 extraction.

[0067] 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 visualized test system for simulating thermal sequestration of hot flue gas and methane extraction from a coal-fired power plant, characterized in that, The system comprises a hot flue gas injection system, a CH4 and He injection system, a triaxial core holder system, a damage monitoring system, a CT in-situ scanning system, a multi-field monitoring system and a tail gas analysis and processing system. The hot flue gas injection system comprises a multi-component gas injection system, a water injection system and a hot flue gas generation system. The multi-component gas injection system comprises CO2 gas cylinders, N2 gas cylinders and hot flue gas other component gas cylinders, all of which are connected with the hot flue gas generation system and used for conveying various component gases of the hot flue gas to the hot flue gas generation system; the water injection system comprises a water tank and a water injection constant-speed and constant-pressure pump, the water tank is connected with the hot flue gas generation system through the water injection constant-speed and constant-pressure pump and used for conveying water to the hot flue gas generation system; the hot flue gas generation system comprises a gas stirring device, a constant-temperature tank and an air compressor, the gas stirring device is arranged in the constant-temperature tank and used for stirring and mixing the gases in the tank, the air compressor is connected with the constant-temperature tank through a pipeline and used for pressurizing the gases in the constant-temperature tank, and the constant-temperature tank is connected with the triaxial core holder system through a pipeline and used for conveying the mixed, stirred, heated, preserved and pressurized gases in the tank to the triaxial core holder system; a vacuum pump is arranged on the pipeline between the hot flue gas injection system and the triaxial core holder system; The CH4 and He injection system comprises CH4 gas cylinders and He gas cylinders, both of which are connected with the triaxial core holder system through pipelines and used for conveying CH4 gas and He gas to the triaxial core holder system, respectively; The triaxial core holder system comprises a triaxial core holder main body and a hydraulic constant-speed and constant-pressure pump, the triaxial core holder main body is internally provided with a sample placing space, and the hydraulic constant-speed and constant-pressure pump is connected with the triaxial core holder main body and used for pumping hydraulic oil to the triaxial core holder main body to apply confining pressure to the sample in the triaxial core holder main body and control the upper and lower pressure heads to apply axial pressure, and the temperature of the sample is controlled through the hydraulic oil; The damage monitoring system comprises an acoustic emission monitoring unit and an ultrasonic monitoring unit, the acoustic emission monitoring unit is arranged in the triaxial core holder main body and used for monitoring the damage signals generated in the sample in real time, and the ultrasonic monitoring unit is arranged in the triaxial core holder main body and used for monitoring the ultrasonic wave velocity, attenuation and reflection characteristics of the ultrasonic wave propagating in the sample in real time; The CT in-situ scanning system comprises an X-ray source, a detector and a rotating console, the triaxial core holder main body is arranged on the rotating console and can rotate with the console; the X-ray source and the detector are respectively arranged on the two sides of the triaxial core holder main body, so that the X-rays emitted by the X-ray source can be received by the detector after passing through the sample, and the internal space structure of the clamped sample can be scanned in real time. ​ The multi-field monitoring system comprises a fiber-optic monitoring system and a wearable flexible sensor system, the fiber-optic monitoring system is arranged in the triaxial core holder body and is used for monitoring the temperature of the hydraulic fluid around the sample, the radial deformation of the sample, and the pressure of the hydraulic fluid around the sample; the wearable flexible sensor system is wrapped around the surface of the sample and is used for monitoring the real-time temperature of the sample surface, the real-time stress of the sample surface, the gas pressure and the gas concentration on the sample surface, and the axial and circumferential strain of the sample surface. The tail gas analysis and processing system comprises a gas analyzer and a tail gas collecting device, one end of the gas analyzer is connected with the triaxial core holder body through a pipeline, the other end is connected with the tail gas collecting device, and the tail gas analyzer is used for analyzing the composition of the tail gas discharged from the triaxial core holder body in real time, and the tail gas is discharged to the tail gas collecting device after the analysis is completed.

2. The visualized test system for simulating thermal sequestration of coal-fired power plant flue gas and methane extraction according to claim 1, characterized in that, The pipelines between the hot flue gas injection system and the triaxial core holder system and between the triaxial core holder system and the tail gas analysis and processing system are provided with high-precision gas flow meters.

3. The visualized test system for simulating thermal sequestration of coal-fired power plant flue gas and methane extraction according to claim 1, characterized in that, The constant-temperature tank is provided with a gas temperature sensor and a gas pressure sensor, and the triaxial core holder body is provided with a liquid temperature sensor.

4. The visualized test system for simulating thermal sequestration of coal-fired power plant flue gas and methane extraction according to claim 1, characterized in that, The acoustic emission monitoring unit comprises a conducting rod and an acoustic emission acquisition instrument, one end of the conducting rod extends into the triaxial core holder body and is in contact with the surface of the sample, the other end is provided with an acoustic emission probe, and the acoustic emission probe is connected with the acoustic emission acquisition instrument through an acoustic signal amplifier; the ultrasonic wave monitoring unit comprises an ultrasonic wave emission probe, an ultrasonic wave receiving probe and an ultrasonic wave acquisition instrument, the ultrasonic wave emission probe and the ultrasonic wave receiving probe are respectively fixed on the upper and lower pressure heads, and the ultrasonic wave acquisition instrument is connected with the ultrasonic wave emission probe and the ultrasonic wave receiving probe, so that the ultrasonic wave emitted by the ultrasonic wave emission probe is received by the ultrasonic wave receiving probe after passing through the sample and is transmitted to the ultrasonic wave acquisition instrument.

5. The visualized test system for simulating thermal sequestration of coal-fired power plant flue gas and methane extraction according to claim 1, characterized in that, The fiber-optic monitoring system comprises an axial fiber displacement sensor, a plurality of integrated radial fiber monitoring units and a fiber data acquisition system, the axial fiber displacement sensor is arranged on the lower pressure head and is connected with the fiber data acquisition system through a data line and is used for monitoring the axial deformation of the sample; the plurality of integrated radial fiber monitoring units are uniformly arranged on the inner wall of the triaxial core holder body and are connected with the fiber data acquisition system through fiber sensor connectors; each integrated radial fiber monitoring unit comprises a fiber temperature sensor, a fiber pressure sensor and a radial fiber displacement sensor, wherein the fiber temperature sensor is used for monitoring the temperature change of the hydraulic fluid around the sample in real time, the radial fiber displacement sensor is used for obtaining the radial displacement of the holder inner wall relative to the sample in different regions of the sample, and the fiber pressure sensor is used for obtaining the pressure change of the hydraulic fluid around the sample in different regions.

6. The visualized test system of coal-fired power plant hot flue gas sealing and methane extraction according to claim 1, characterized in that, The wearable flexible sensor system comprises a flexible layer and a plurality of integrated sensor units uniformly distributed on the flexible layer, the flexible layer being wrapped outside the sample, the integrated sensor units comprising a temperature sensor, a stress sensor, a gas sensor and a strain sensor, wherein the temperature sensor is used to monitor the temperature change of different areas of the sample surface in real time, the stress sensor is used to monitor the stress change of different areas of the sample surface in real time, the gas sensor is used to monitor the gas pressure change and the gas concentration change of different areas of the sample surface in real time, and the strain sensor is composed of a radial strain sensor and an axial strain sensor and is used to monitor the axial strain and the hoop strain change of different areas of the sample surface in real time.

7. The visualized test system of coal-fired power plant for CO2 capture and CH4 extraction according to claim 1, wherein, The gas analyzer is any one of an infrared absorption method gas analyzer, a laser absorption method gas analyzer and a mass spectrometry method gas analyzer.

8. The visualized test system of coal-fired power plant for thermal sequestration of flue gas and methane extraction according to claim 1, characterized in that, The other components of the hot flue gas include sulfur oxides, nitrogen oxides and oxygen.

9. The visualized test system of coal-fired power plant for CO2 capture and CH4 extraction according to claim 2, wherein, The gas analyzer and the triaxial core holder body are provided with a high-precision gas flow meter and a gas pressure gauge for monitoring the tail gas flow and the tail gas pressure discharged from the triaxial core holder body; the gas analyzer and the triaxial core holder body are provided with a low-range volumetric flow meter, a medium-range volumetric flow meter and a high-range volumetric flow meter, and the three volumetric flow meters are arranged in parallel.

10. A method of operating a visualized test system for simulating thermal flue gas sequestration and methane extraction in a coal-fired power plant according to any one of claims 1 to 9, characterized in that, The specific steps are as follows: A, prepare the core sample and lay out the test system: collect the coal body in the coal mine, cut it into a plurality of core samples of the same size, clean the surface of each sample, then drill a through hole in the center of each sample for subsequent hot flue gas injection, select any sample, attach the wearable flexible sensor system to the surface of the sample, place the sample in the triaxial core holder system, and complete the assembly of each system; B, determine the initial permeability: set the axial pressure value, the confining pressure value and the temperature value according to the required simulated deep geostress and temperature environment; start the hydraulic constant speed and constant pressure pump of the triaxial core holder system to pump hydraulic oil, so that the triaxial core holder system applies axial pressure and confining pressure to the sample and heats the sample, until the set axial pressure value, confining pressure value and temperature value are reached, stop heating and pressurizing, and keep the current pressure and temperature; then start the CT in-situ scanning system to complete a CT scan of the sample in the current state; after completion, start the vacuum pump and open the valves of each pipeline to vacuumize the internal pipelines of the hot flue gas injection system, the CH4 and He injection system, the triaxial core holder system and the tail gas analysis and treatment system; after vacuumization, close the outlet valve of the triaxial core holder body and keep the inlet valve open, at the same time, inject He gas into the triaxial core holder body through the pipeline from the He gas cylinder, record the injection amount through the high-precision gas flow meter and calibrate the free space volume in the triaxial core holder body by combining the ideal gas state equation; after calibration, open the outlet valve, and after the volumetric flow meter shows a stable reading, calculate the initial permeability of the sample, and then discharge the He gas to the tail gas collection device; C, CH4 adsorption pre-equilibrium: simulate the CH4 occurrence in deep coal seam under initial conditions; set the CH4 gas pressure value, continue to keep the inlet valve open and close the outlet valve, introduce CH4 gas into the triaxial core holder body, record the CH4 injection amount by the high-precision gas flow meter, close the inlet valve when the set pressure value is reached, and wait for 24-48 h to allow the sample to adsorb CH4, collect the gas pressure, temperature, ultrasonic signal, acoustic emission signal, and optical fiber signal changes in the triaxial core holder body at intervals during the adsorption period, and use the CT in-situ scanning system to scan the internal structure of the sample in real time during the CH4 adsorption process, to realize the multi-parameter dynamic visualization monitoring of the sample during the methane adsorption process; after the adsorption is completed, record the changes of gas pressure, temperature, strain, ultrasonic signal and acoustic emission signal in the triaxial core holder body under the adsorption equilibrium state, and perform CT scanning on the internal structure of the sample at this time to obtain the internal structure of the sample under the CH4 adsorption equilibrium state, and then determine the original pore structure and internal damage of the sample before hot flue gas injection; D, hot flue gas fracturing process: first set the ratio of various gases in the hot flue gas, the temperature value and the injection pressure, the hot flue gas injection system first injects CO2 gas, N2 gas, other component gases of hot flue gas and water into the hot flue gas generation system according to the set ratio, mixes and stirs the various gases uniformly through the gas stirring device, and heats the hot flue gas generation system to the set temperature value, thereby generating the required hot flue gas, then the outlet valve is closed and the inlet valve is opened, and the air compressor is started to pressurize the hot flue gas until the injection pressure is reached, then the hot flue gas is injected into the triaxial core holder body through the pipeline to fracture the sample, and the data acquisition system is used to collect the temperature, pressure, flow rate, ultrasonic signal, acoustic emission signal and optical fiber signal of the gas around the sample surface in real time during the hot flue gas fracturing process, and the CT in-situ scanning is performed on the sample in real time to realize the multi-parameter dynamic visualization monitoring of the core sample during the fracturing process, thereby obtaining the flow field migration, temperature field evolution, pore and fracture structure characteristics and damage law of the core during the hot flue gas displacement of the core CH4; when the gas pressure at the inlet of the triaxial core holder body suddenly drops or the gas flow rate at the outlet suddenly increases, stop the hot flue gas fracturing; record the changes of gas pressure, temperature, strain, ultrasonic signal, acoustic emission signal and optical fiber signal of the gas around the sample surface, and perform real-time CT scanning on the sample to obtain the flow field migration, temperature field evolution, pore and fracture structure characteristics and damage law of the sample after fracturing; Open the outlet valve, and record the gas pressure at the inlet and outlet of the triaxial core holder body after the volume flow meter reading stabilizes, thereby calculating the permeability of the sample after fracturing. E. Hot flue gas displacement process of CH4 in the sample: continue to keep the inlet valve and outlet valve open, set the injection pressure of hot flue gas during displacement, then inject hot flue gas into the triaxial core holder body at a set pressure value through the hot flue gas injection system to displace and remove the CH4 adsorbed by the sample, during which the temperature, pressure, flow rate, ultrasonic signal, acoustic emission signal and optical fiber signal of the gas on and around the sample surface are collected and recorded in real time by the data acquisition system, and the sample is scanned in situ by CT in real time to realize multi-parameter dynamic visualization monitoring during the hot flue gas displacement process of CH4 in the sample, so as to obtain the flow field migration, temperature field evolution, pore and fracture structure characteristics and damage law of the sample during the hot flue gas displacement process of CH4 in the sample; record the flow rates at the inlet and outlet, and monitor and record the tail gas composition, concentration and flow rate in real time by the gas analyzer during the displacement process, so as to obtain the hot flue gas injection amount and CH4 gas extraction amount during the hot flue gas displacement process of CH4 in the triaxial core holder body, as well as the interaction between hot flue gas and CH4 gas, stop the displacement process when the CH4 concentration in the tail gas reaches the critical CH4 concentration; record the changes of the gas pressure, temperature, strain, ultrasonic signal, acoustic emission signal and optical fiber signal of the gas on and around the sample surface at this time, and perform real-time CT scanning on the internal space structure of the sample at this time to obtain the flow field migration, temperature field evolution, pore and fracture structure characteristics and damage law of the sample after displacement; F. Hot flue gas storage process: after completing the displacement test, close the inlet valve and outlet valve, store the hot flue gas in the triaxial core holder body, monitor the gas pressure, temperature, strain, ultrasonic signal and acoustic emission signal of the gas on and around the sample surface in real time, and use CT to scan the sample in real time to realize dynamic visualization monitoring of the sample parameters during the hot flue gas storage process, so as to obtain the flow field migration, temperature field evolution, pore and fracture structure characteristics and damage law during the storage process; after the storage test is completed, open the inlet valve and outlet valve, record the gas pressures at the inlet and outlet of the triaxial core holder body after the flow rate data is stable, calculate the permeability after hot flue gas storage, and complete the entire test process.

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