A system and method for improving coal seam gas extraction concentration by using high-heat flue gas

Abstract

The application discloses a system and method for improving coal seam gas extraction concentration by using high-heat flue gas, comprising a gas storage tank, a temporary gas storage tank, a coaxial sleeve heat exchange system, a gas injection well, an extraction well and a monitoring system; the high-heat flue gas is first introduced into the heat exchange system in the extraction well to form a radial temperature gradient in the wellbore, and the in-situ thermal diffusion separation and concentration of the gas and the flue gas are realized by using the principle of thermal gravity column; the low-heat flue gas after heat exchange and temperature reduction is injected into the gas injection well after backflow collection, and the coal seam gas is driven to move to the extraction well by multi-element gas competitive adsorption. The method adopts an intermittent process of 'heat injection displacement - well shut-in concentration storage - low-flow extraction - cyclic gas injection', and is matched with concentration monitoring to determine the economic extraction end point. The application can significantly improve the extraction gas concentration without adding a ground concentration device, prolong the economic extraction period, realize the step-by-step utilization of flue gas waste heat and carbon dioxide geological storage, and has gas resource benefits and carbon emission reduction benefits.

Description

Technical Field

[0001] This invention relates to the field of coalbed methane extraction and utilization technology, and in particular to a system and method for increasing the concentration of coalbed methane extraction using high-heat flue gas. Background Technology

[0002] Coal seam gas extraction is not only a core means of coal mine disaster management but also an important approach to unconventional natural gas resource development. Gas injection displacement technology, which drives gas migration into the extraction space by injecting gas into the coal seam, is currently the mainstream gas production enhancement technology. Among them, flue gas, as industrial waste gas, is rich in N2 and CO2, which can simultaneously increase the extraction flow rate and improve the final recovery rate, while also possessing the potential for CO2 geological sequestration, and has broad application prospects.

[0003] However, existing gas injection displacement projects have two major problems: First, after the gas injection breakthrough in the mid-to-late stages of extraction, the CH4 purity drops sharply. Low-concentration gas below 30% is difficult to utilize directly as a resource, and gas below 1% basically loses its resource attributes, resulting in a significant shortening of the project's economic lifespan. Second, current coal seam gas extraction is mostly aimed at disaster mitigation, typically only proceeding when the coal seam gas content drops to 8m³. 3 When the gas level reaches 0.06 t, extraction is stopped, and a large amount of residual gas is discharged into the atmosphere as exhaust gas, which not only wastes resources but also becomes a significant source of carbon emissions from coal mines. In addition, high-heat flue gas from industrial sources usually needs to be cooled before being injected into the coal seam, and the residual heat is not effectively utilized. The cooling process itself is also accompanied by indirect carbon emissions.

[0004] Therefore, how to maintain a high extraction concentration, extend the economic extraction cycle, and improve the overall recovery rate during the gas injection displacement process, while making full use of the waste heat and carbon sequestration value of flue gas, is a key technical problem that urgently needs to be solved in this field. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art and provide a system and method for increasing the concentration of coalbed methane extraction by utilizing high-heat flue gas. Through the synergistic effect of in-situ thermal diffusion enrichment in the wellbore and coalbed gas injection displacement, the problem of sudden drop in methane concentration after gas injection breakthrough is solved. At the same time, the waste heat of flue gas is utilized in stages and CO2 is geologically sealed, thereby improving the resource efficiency and carbon efficiency of methane extraction.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is: a system for increasing the concentration of coal seam gas extraction by utilizing high-heat flue gas, comprising a target coal seam, an injection well, an extraction well, a sealing section, a gas storage tank, a temporary gas storage tank, a heat exchange system, and a monitoring system; the sealing section seals the wellhead of the extraction well.

[0007] The heat exchange system is arranged inside the extraction well and vertically fixed to the lower part of the well sealing section, including an outer heat pipe, an inner heat pipe, a sealing section and a return section; the inner heat pipe is located inside the outer heat pipe, and the two are arranged coaxially to form a coaxial double-pipe structure; The system creates a downward annular flow channel between the inner and outer tubes, and an upward return flow channel inside the inner tube. The sealing section seals the bottom of the outer and inner tubes of the heat pipe, while the return flow section is located at the bottom of the inner tube to connect the outer and inner tubes, creating a downward flow channel inside the outer tube and an upward return flow channel inside the inner tube. This allows the high-temperature flue gas injected into the heat exchange system to descend along the outer annular space, bend back through the return flow section, and then ascend along the inner tube space, completing the heat exchange process.

[0008] The gas storage tank is used to store uncooled high-heat flue gas from sources such as thermal power plants and coking plants. The tank body is insulated to reduce heat loss. It is connected to the outer tube of the heat pipe through a heat injection pipeline, and the high-heat flue gas is injected into the downward flow channel, where it exchanges heat with the gas around the heat exchange system in the extraction well and is cooled before entering the upward return channel. One end of the return pipeline is connected to the upper outlet of the inner tube of the heat pipe, and the other end is connected to the temporary gas storage tank, which transports and stores the low-heat flue gas after heat exchange and cooling. The temporary gas storage tank is connected to the injection well through a gas injection pipeline to provide a gas source for gas injection displacement.

[0009] Packers are installed in both the upper and lower strata of the target coal seam in the gas injection well to limit the gas injection range to the target coal seam section and prevent gas from entering the upper and lower strata. A packer is installed in the strata below the target coal seam in the extraction well to block the gas passage in the lower strata. The extraction pipeline extends into the well through the sealing section, with the extraction port located at a predetermined distance below the sealing section, corresponding to the high-level gas-rich area in the wellbore. A flow-limiting valve is installed on the extraction pipeline to precisely control the extraction flow rate and avoid disturbing the stratification of concentrations within the wellbore. Monitoring systems are deployed inside both the gas injection and extraction wells to monitor the gas pressure and component concentration in each well in real time, providing real-time data support for process control.

[0010] Furthermore, the monitoring system includes a distributed optical fiber sensor and a gas component sensor, which are deployed along the well depth to continuously measure gas pressure, CH4 concentration, and flue gas component concentration along the well depth; the return section consists of multiple vent holes on the inner tube of the heat pipe to facilitate the flue gas after heat exchange in the downflow channel to enter the downflow return channel and exit the heat exchange system.

[0011] Furthermore, the extraction port of the extraction pipeline is located 2m below the well sealing section, close to the outer tube of the heat pipe, to accurately collect the high-concentration methane accumulated in the upper part.

[0012] Furthermore, multiple heat injection ports are arranged in a ring around the inner heat pipe at the upper end of the outer heat pipe, and all of these ports are connected to the gas storage tank through heat injection pipelines. This method enables the high-temperature flue gas to be evenly distributed inside the outer heat pipe during injection, thereby improving heat exchange efficiency.

[0013] Furthermore, multiple sets of injection well-extraction well combinations can be arranged in parallel in the same mining area, sharing gas storage and gas storage facilities, and consuming industrial high-heat flue gas production capacity on a large scale.

[0014] A method for increasing coalbed methane extraction concentration using high-heat flue gas, based on the above system, includes the following steps: Step 1: Continuous Displacement Extraction Stage: Start the heat injection pipeline to introduce high-temperature flue gas into the heat exchange system. The high-temperature flue gas in the storage tank is then introduced into the heat exchange system, allowing it to exchange heat with the surrounding environment within the extraction well and cool down. This creates a temperature gradient at different locations within the extraction well (i.e., the temperature is higher closer to the outer heat pipe and gradually decreases further away, creating a heat diffusion effect). Simultaneously, open the return pipeline and the injection pipeline. The low-temperature flue gas, after heat exchange, is buffered in a temporary storage tank and then injected into the injection well. At the same time, open the extraction pipeline and set the extraction negative pressure. Utilize the displacement effect of the flue gas to drive the coal seam gas towards the extraction well for conventional continuous extraction.

[0015] Step Two: Well Sealing and Low-Flow Extraction Start-up: The CH4 concentration extracted from the extraction well is monitored in real time by the monitoring system. When the concentration drops to the first preset concentration threshold φ1, the gas injection pipeline and the extraction pipeline are closed, and the well sealing stage begins. During the well sealing period, high-heat flue gas is continuously introduced to maintain the temperature gradient in the extraction well. The heat diffusion and gravity settling effect are used to enrich CH4 in the upper part of the well and flue gas in the lower part. The low-heat flue gas that flows back is stored in a temporary gas storage tank. When the CH4 concentration at the extraction port rises back to the second preset concentration threshold φ2, the flow limiting valve is opened to stably extract high-concentration gas in a low-flow mode.

[0016] Step 3: Gas injection displacement: During the low-flow extraction process, the concentration is continuously monitored. When the CH4 concentration drops to φ1 again, the extraction pipeline is closed and the gas injection pipeline is opened. The low-heat flue gas stored in the temporary gas storage tank is injected into the gas injection well. Through competitive adsorption, the adsorbed gas in the coal seam is desorbed and diffused into the extraction well.

[0017] Step 4: Re-shut down the well and extract: When the CH4 concentration in the extraction well rises back to φ2, close the gas injection pipeline and reopen the flow limiting valve to extract at a small flow rate, completing one gas injection-shut down the well-extraction cycle.

[0018] Step 5: Cycle and Shutdown Determination: Repeat Steps 3 and 4 to continue multiple rounds of cyclic extraction; based on monitoring data, calculate the length of the high-concentration gas section, gas reserves, and concentration recovery cycle, and evaluate the pure gas production efficiency per unit time. When the extraction revenue is lower than the operating cost, stop the extraction operation.

[0019] Furthermore, the first preset concentration threshold φ1 is set to 30%, which is the industry-recognized critical value for the resource utilization of low-concentration methane; the second preset concentration threshold φ2 is set to 60%~90%, which can be adjusted according to downstream utilization needs; the flow rate range of the low-flow extraction is 10~500L / h, preferably 100L / h, in order to maintain the stability of concentration stratification in the wellbore.

[0020] Furthermore, the economic benefit assessment is based on: the length *l* of the well section with a CH4 concentration > 30% and the corresponding total gas volume *Q*, calculated using the following formula:

[0021] In the formula, φ(x) represents the CH4 concentration distribution in the vertical direction of well 51; x=0 represents the location of the wellhead on the ground.

[0022] Based on the previous well concentration recovery time t, calculate the recoverable pure gas volume per unit time; when this value is lower than the economic break-even point, it is determined to be uneconomical and extraction is terminated.

[0023] Compared with the prior art, the present invention has the following advantages: 1. This invention is the first to apply the Clusius-Dickel thermogravity column principle to extraction wells. It utilizes the waste heat of flue gas to form a stable temperature gradient in the extraction well, and achieves in-situ enrichment of gas through heat diffusion and gravity convection. Combined with the well-sealing enrichment and low-flow extraction process, the extraction concentration is greatly improved, and more than 60% high-concentration gas can be produced sustainably. This solves the industry problem of a sharp drop in concentration after gas injection breakthrough from the source, without the need for additional surface enrichment devices.

[0024] 2. This invention reinjects the low-heat flue gas after heat exchange into the coal seam and promotes gas desorption through multi-element competitive adsorption. The multi-round cyclic gas injection-shutdown process can deeply mine residual gas in the coal seam, extend the economic life of the project, improve the overall recovery rate, reduce the direct emission of exhaust gas, and reduce carbon emissions in the coal mining process.

[0025] 3. The high-heat flue gas of the present invention is first used for thermal separation and enrichment in the extraction well, and the residual heat is fully utilized before being reinjected into the coal seam. This avoids the energy waste and indirect carbon emissions from direct cooling of flue gas, and achieves efficient utilization of energy in stages.

[0026] 4. During the gas injection process of this invention, the coal seam adsorbs CO2 from the flue gas, achieving geological sequestration, which can be converted into carbon asset revenue; the utilization of gas resources to replace fossil energy can also generate indirect emission reduction benefits, forming a multi-value synergistic gain of "gas development + waste heat utilization + carbon sequestration", effectively improving comprehensive benefits. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the overall structure of the system of the present invention.

[0028] Figure 2 This is a cross-sectional structural diagram of the heat exchange system described in an embodiment of the present invention.

[0029] Figure 3 This is a top view of the wellhead of the extraction well described in an embodiment of the present invention.

[0030] Figure 4 This is a schematic diagram of the process flow for hot flue gas displacement CH4 extraction according to an embodiment of the present invention.

[0031] In the diagram: 1-Gas storage tank, 2-Temporary gas storage tank, 31-Heat injection pipeline, 32-Return pipeline, 33-Gas injection pipeline, 34-Extraction pipeline, 4-Heat exchange system, 41-Outer heat pipe, 42-Inner heat pipe, 43-Sealing section, 44-Return section, 51-Extraction well, 52-Gas injection well, 6-Target coal seam, 7-Packer, 8-Sealing section, 9-Flow limiting valve, 10-Monitoring system. Detailed Implementation

[0032] The present invention will be further described below.

[0033] like Figure 1 As shown in the figure, the system for increasing the concentration of coalbed methane extraction using high-heat flue gas described in this embodiment mainly consists of five parts: a gas storage unit, a heat exchange and enrichment unit, a gas injection and displacement unit, an extraction unit, and a monitoring unit.

[0034] The gas storage unit includes a gas storage tank 1 and a temporary gas storage tank 2. The gas storage tank 1 is used to store uncooled high-temperature flue gas from the surrounding thermal power plant. The tank body adopts a rock wool + vacuum insulation layer structure to reduce heat loss during transportation and storage. The temporary gas storage tank 2 is used to buffer and store low-temperature flue gas after heat exchange, and to stabilize the gas injection pressure and flow rate.

[0035] The core of the heat exchange and enrichment unit is the heat exchange system 4 located within the extraction well 51, and its structure is as follows: Figure 2As shown, it is a concentric double-layer casing structure, with a length covering the main well section above the target coal seam 6; the outer heat pipe 41 and the inner heat pipe 42 are both high-temperature resistant and corrosion-resistant steel pipes, and the bottom is sealed by welding through the sealing part 43 to form the outer ring downward cavity and the inner pipe upward cavity; the return part 44 is located on the lower side wall of the inner pipe, and is made of multiple vent holes distributed in a ring, so that the high-heat flue gas of the outer ring can be turned back into the inner pipe upward; the high-heat flue gas dissipates heat to the gas in the wellbore through the pipe wall during the downward movement of the outer ring, forming a radial temperature gradient in the wellbore with "high temperature near the wall and low temperature in the center", which provides conditions for heat diffusion separation.

[0036] The gas injection displacement unit includes a gas injection pipeline 33 and a gas injection well 52. The gas injection well 52 vertically penetrates the target coal seam 6. A set of packers 7 is installed in the roof and floor strata of the target coal seam 6. The space between the two sets of packers is the gas injection section, which ensures that all the injected low-heat flue gas enters the target coal seam 6 and avoids gas leakage.

[0037] The extraction unit includes an extraction well 51, a sealing section 8, an extraction pipeline 34, and a flow-limiting valve 9; the extraction well 51 and the gas injection well 52 are arranged at a preset well spacing, and a packer 7 is installed below the target coal seam 6 inside the well to block the gas passage of the lower rock strata; a flange-type sealing section 8 is installed at the wellhead, the structure of which is as follows: Figure 3 As shown, 12 heat injection pipeline interfaces, 1 return pipeline interface, 1 extraction pipeline interface, and 1 monitoring system cable interface are reserved. The 12 heat injection pipeline interfaces are evenly distributed in a circle with the return pipeline interface as the center, and all interfaces are sealed. The extraction pipeline 34 is lowered along the well wall, and the extraction port is located 2m below the well sealing section 8, close to the outer pipe 41 of the heat pipe, corresponding to the gas enrichment zone above the extraction well. A high-precision flow limiting valve 9 is installed on the surface section of the extraction pipeline 34, which can stably control the extraction flow rate within the range of 10~500L / h.

[0038] The monitoring unit is a distributed monitoring system 10. Fiber optic pressure sensors and infrared gas component sensors are deployed along their respective well depths in both the extraction well 51 and the injection well 52, with a sampling interval of 0.5m. It can acquire real-time data on gas pressure, CH4 concentration, CO2 concentration and N2 concentration throughout the entire well section and transmit the data to the ground control room for process control.

[0039] In this embodiment, 5 to 10 sets of gas injection well-extraction well combinations can be arranged in the same mining area, sharing gas storage tank 1 and temporary gas storage tank 2, to achieve large-scale consumption of flue gas and enhanced extraction of continuous gas.

[0040] A method for increasing coal seam gas extraction concentration using high-heat flue gas, such as... Figure 4 As shown, based on the above system implementation, the specific implementation steps are as follows: Step 1, Initial Continuous Displacement and Extraction: Open the outlet valve of gas storage tank 1, and introduce high-temperature flue gas at 300℃ into heat exchange system 4 at a pressure of 0.5MPa through injection pipeline 31. The flue gas flows downward along the outer ring, turns back through return section 44, and then flows upward along the inner pipe. After heat exchange with the surrounding environment of the extraction well, the temperature drops to about 80℃, becoming low-temperature flue gas. The low-temperature flue gas enters temporary gas storage tank 2 through return pipeline 32, and then is injected into the target coal seam section 6 of injection well 52 at a pressure of 0.3MPa through injection pipeline 33. Simultaneously, extraction pipeline 34 is opened, and the extraction negative pressure is set to -20kPa for conventional continuous extraction. The flue gas injected into the coal seam drives CH4 to migrate towards extraction well 51 through competitive adsorption and displacement. At this stage, the extraction concentration is high, and gas is produced rapidly at a large flow rate.

[0041] Step 2, Well Sealing and Low-Flow Extraction: The CH4 concentration at the outlet of extraction pipeline 34 is monitored in real time by monitoring system 10. When the concentration continuously decreases to 30% (i.e., φ1), it indicates that the gas injection has broken through. At this time, the main valves of gas injection pipeline 33 and extraction pipeline 34 are closed, and the well sealing stage begins. During the well sealing period, high-heat flue gas is continuously introduced to maintain the temperature gradient in the extraction well. Under the Clusius-Dickel thermogravity column effect, CH4 with smaller molecular weight is driven by thermal diffusion to accumulate in the low-temperature center and upper part, while N2 and CO2 with larger molecular weight settle in the high-temperature wall and lower part, gradually forming a "high at the top and low at the bottom" concentration stratification in the wellbore. The returned low-heat flue gas is continuously stored in temporary gas storage tank 2.

[0042] When the CH4 concentration at the extraction port is monitored to rise to 80% (i.e., φ2), the flow limiting valve 9 is slowly opened to stabilize the extraction flow rate at 100L / h and carry out stable extraction at a small flow rate. The small flow rate can avoid the negative pressure of extraction disturbing the concentration stratification in the wellbore and achieve continuous production of high-concentration gas.

[0043] Step 3, Gas Injection Displacement: During the low-flow extraction process, the gas enriched in the upper part of the wellbore is gradually extracted, and the concentration slowly decreases. When the CH4 concentration drops to 30% again, the extraction pipeline 34 is closed and the gas injection pipeline 33 is opened. The low-heat flue gas stored in the temporary gas storage tank 2 is injected into the gas injection well 52 at 0.3MPa. After the flue gas enters the coal seam, it replaces the adsorbed CH4 through competitive adsorption, which promotes the desorption of more gas and its diffusion to the vicinity of the extraction well 51.

[0044] Step 4, Cyclic well extraction: When the CH4 concentration in extraction well 51 rises back to 80%, close the gas injection pipeline 33 and open the flow limiting valve 9 to start the next round of low-flow extraction, completing a complete cycle of "gas injection displacement - well closure for concentration - low-flow extraction".

[0045] Step 5: Economic Benefit Assessment and Production Shutdown: Repeat Steps 3 and 4 for multiple rounds of cyclic extraction. After each cycle, based on the profile data from monitoring system 10, calculate the length l of the well section with CH4 concentration > 30%, and calculate the total gas volume Q of that section in conjunction with coal seam parameters. Simultaneously, record the concentration recovery time t of this cycle and calculate the pure gas production per unit time. When the pure gas revenue per unit time for two consecutive cycles is lower than the comprehensive costs of flue gas transportation and equipment operation, the extraction is deemed no longer economically viable, and heating and extraction operations are stopped, and the well site is closed.

[0046] The core innovative principle of this invention comprises two parts: the wellbore thermogravity column enrichment mechanism and the coal seam multi-element gas competitive adsorption and displacement mechanism.

[0047] Clusius-Dickel thermogravity column enrichment mechanism: Under the combined action of the radial temperature gradient and gravity field in the wellbore, the binary gas mixture undergoes thermal diffusion (Soret effect) and convective diffusion coupling; the smaller molecular weight CH4 migrates to the low-temperature zone (wellbore center and upper part), while the larger molecular weight flue gas components migrate to the high-temperature zone (well wall and lower part), ultimately forming a stable axial concentration stratification. The flue gas and methane exhibit interdiffusion and thermal diffusion behavior, as shown in the following equation:

[0048] In the formula, dN1 and dN2 are the number of molecules of flue gas and methane passing through the ds area per unit time, respectively; n1 and n2 are the molecular densities of flue gas and methane, respectively; λ1 and λ2 are the mean free paths of flue gas and methane, respectively; v1 and v2 are the average velocities of flue gas and methane, respectively; k is the Boltzmann constant; p is the total gas pressure; σ 1,2 This represents the average molecular diameter of flue gas and methane; m1 and m2 are the molecular masses of flue gas and methane, respectively. Note: Flue gas (nitrogen and carbon dioxide) is not further subdivided here; all indicators are the results of processing parameters of the mixed gas.

[0049] During the low-flow gas extraction process, the interior of extraction well 51 gradually reaches a stable state, at which point...

[0050] The gas concentration distribution inside extraction well 51 is then obtained by solving the following formula:

[0051] As the well stagnation time increases, the gas in well 51 gradually concentrates in the upper part (i.e., CH4 is highly enriched near the wellhead), and the flue gas gradually concentrates in the lower part. At this time, by using low-flow extraction to extract only the top enriched layer, a high concentration of gas can be stably obtained, and in-situ enrichment of gas in the wellbore can be achieved.

[0052] Multi-component gas competitive adsorption and displacement mechanism: The adsorption of gases by coal seams conforms to the extended Langmuir model, and the adsorption capacity of binary gases satisfies:

[0053] In the formula, Q1 and Q2 are the adsorption amounts of flue gas and methane, respectively; P1 and P2 are the partial pressures of flue gas and methane, respectively; a1, a2, b1, and b2 are the adsorption constants of flue gas and methane, respectively; and P1 + P2 = p.

[0054] After the flue gas is injected, the partial pressure of CH4 decreases, and the adsorption amount decreases accordingly. A large amount of adsorbed CH4 is desorbed into free state and migrates to the extraction well; at the same time, the coal seam adsorbs CO2, achieving geological sequestration.

[0055] The two mechanisms work synergistically: the heat of the flue gas is used for enrichment in the extraction well, and the gas itself is used for coal seam displacement and carbon sequestration, achieving efficient utilization of energy and matter in a cascade manner.

[0056] 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 system for increasing the concentration of coal seam gas extraction using high-heat flue gas, characterized in that, It includes a target coal seam, a gas injection well, a extraction well, and a sealing section, wherein the sealing section seals the wellhead of the extraction well. Its features include a gas storage tank, a temporary gas storage tank, a heat exchange system, and a monitoring system. The heat exchange system is arranged inside the extraction well and fixed at the lower part of the well sealing section, including an outer heat pipe, an inner heat pipe, a sealing section, and a return section; the inner heat pipe is located inside the outer heat pipe, and the two are arranged coaxially; the sealing section seals and connects the bottom of the outer heat pipe and the inner heat pipe, and the return section is arranged at the lower part of the inner heat pipe to connect the outer heat pipe and the inner heat pipe, so that a downward flow channel is formed inside the outer heat pipe and an upward return flow channel is formed inside the inner heat pipe; The gas storage tank is used to store high-heat flue gas. It is connected to the outer pipe of the heat pipe through a heat injection pipeline. The high-heat flue gas is injected into the downward flow channel, where it exchanges heat with the gas around the heat exchange system in the extraction well to cool down before entering the upward return channel. One end of the return pipeline is connected to the upper outlet of the inner pipe of the heat pipe, and the other end is connected to the temporary gas storage tank, which is used to transport the cooled low-heat flue gas to the temporary gas storage tank. The temporary gas storage tank is connected to the gas injection well through a gas injection pipeline. Packers are installed inside the gas injection well at the upper and lower rock strata of the target coal seam to limit the gas injection zone. A packer is installed inside the extraction well at the location of the rock strata below the target coal seam; the extraction pipeline passes through the sealing section and extends into the extraction well, with the extraction port located at a predetermined distance below the sealing section; a flow limiting valve is installed on the extraction pipeline to control the extraction flow rate; monitoring systems are installed inside both the gas injection well and the extraction well to monitor the gas pressure and component concentration in each well in real time.

2. The system according to claim 1, characterized in that, The monitoring system includes a distributed optical fiber sensor and a gas component sensor, which are deployed along the well depth to continuously measure gas pressure, CH4 concentration and flue gas component concentration along the well depth; the reflux section consists of multiple vent holes deployed on the inner tube of the heat pipe.

3. The system according to claim 1, characterized in that, The extraction port of the extraction pipeline is located 2m below the well sealing section, and the extraction pipeline is arranged close to the outer tube of the heat pipe.

4. The system according to claim 1, characterized in that, Multiple heat injection ports are arranged in a ring around the inner heat pipe at the upper end of the outer heat pipe. All heat injection ports are connected to the gas storage tank through heat injection pipelines.

5. The system according to claim 1, characterized in that, Multiple sets of gas injection wells and extraction wells are arranged in the same mining area, sharing gas storage tanks and temporary gas storage tanks to collaboratively absorb the high-heat flue gas production capacity.

6. A method for increasing the concentration of coal seam gas extraction using high-heat flue gas, characterized in that, The system implementation based on any one of claims 1 to 5 includes the following steps: Step 1: Simultaneously start the heat injection pipeline, return pipeline, and gas injection pipeline to introduce the high-heat flue gas from the gas storage tank into the heat exchange system. This allows the high-heat flue gas to exchange heat with its surrounding environment within the extraction well, creating a temperature gradient at different locations within the extraction well. The low-heat flue gas, after heat exchange, enters the temporary gas storage tank through the return pipeline and is then injected into the gas injection well through the gas injection pipeline. At the same time, start the extraction pipeline and set the extraction negative pressure. The low-heat flue gas displaces the gas in the target coal seam and transports it to the extraction well for continuous extraction. Step 2: Monitor the CH4 concentration extracted from the extraction well in real time through the monitoring system; when the CH4 concentration drops to the first preset concentration threshold, close the gas injection pipeline and the extraction pipeline, and enter the well shut-in stage; during the well shut-in period, continuously introduce high-heat flue gas into the heat exchange system to maintain the temperature gradient in the extraction well, and store the returned low-heat flue gas in the temporary gas storage tank; when the CH4 concentration at the extraction port rises back to the second preset concentration threshold, open the flow limiting valve to extract gas in a low-flow mode. Step 3: Monitor the CH4 concentration in real time during the extraction process. When the concentration drops to the first preset concentration threshold again, close the extraction pipeline, open the gas injection pipeline, and inject the low-heat flue gas in the temporary gas storage tank into the gas injection well to displace and replace the gas in the target coal seam. Step 4: When the CH4 concentration in the extraction well rises back to the second preset concentration threshold, close the gas injection pipeline and reopen the flow limiting valve to extract gas in a low flow mode. Step 5: Repeat steps 3 and 4 to evaluate the economic benefits of extraction based on the monitoring data from the monitoring system. Stop the operation when the extracted gas has no economic value.

7. The method according to claim 6, characterized in that, The first preset concentration threshold is 30%, which corresponds to the critical concentration for the utilization of low-concentration gas resources; the second preset concentration threshold ranges from 60% to 90%; and the extraction flow rate in the low-flow mode is 10 to 500 L / h.

8. The method according to claim 6, characterized in that, In step five, the specific method for evaluating the economic benefits of extraction is as follows: Calculate the length l of the well section with CH4 concentration greater than 30% and the corresponding total gas amount Q in the extraction well, and at the same time, calculate the time t required for the concentration to recover to the second preset concentration threshold during the previous cycle's well-closing phase; when the amount of pure gas that can be extracted per unit time is lower than the economic threshold, it is determined that there is no economic benefit and extraction is stopped.

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