Goaf fire prevention and extinguishment and heat recovery system and method based on distributed temperature measurement optical fiber

Abstract

The application provides a goaf fire prevention and extinguishing and heat recovery system and method based on distributed temperature measurement optical fibers, a nitrogen injection main pipeline is laid along an axis of a goaf, a plurality of nitrogen injection branch pipelines are connected to the main pipeline in parallel along a radial direction, both of them contain protective pipe shells and internal nitrogen injection, water passing and optical fiber pipelines, the nitrogen injection branch pipelines are provided with a directional control system and nitrogen injection holes to form a fire prevention and extinguishing network; the temperature measurement optical fibers are arranged in the pipelines and connected to demodulators, independent optical fiber pipelines are arranged between adjacent branch pipelines to form a distributed monitoring network, accurate and real-time monitoring of hidden fire sources is realized, the water passing pipelines of the nitrogen injection branch pipelines are converged to independent axial water passing pipelines and extended to outside of the goaf, and a water pump of the nitrogen injection main pipeline forms a waste heat circulation recovery system. The application realizes deep integration of fire source monitoring, fire prevention and extinguishing and waste heat circulation recovery, improves a mine safety guarantee level and helps energy ladder utilization and green mine construction.

Description

Technical Field

[0001] This invention relates to the field of fire prevention and extinguishing in coal mine goaf areas, and particularly to a fire prevention, extinguishing and heat recovery system and method for goaf areas based on distributed temperature-measuring optical fibers. Background Technology

[0002] Coal is the "ballast" for a stable supply of energy security in my country. Safety is paramount in coal mining and a crucial factor in safeguarding national energy security and supply. As the depth of coal mining in my country continues to increase, complex geological structures and ventilation leaks in goafs greatly increase the risk of spontaneous combustion, making the management of such disasters increasingly difficult. With the continuous development and updating of coal mining methods and technologies in my country, the method of mining thick coal seams with top-coal caving and full-height extraction in a single operation is widely used. Due to the influence of these mining technologies, the amount of residual coal in goafs has increased, raising the potential risk of spontaneous combustion from the oxidation of loose coal and increasing the probability of coal seam ignition, leading to more mine fires.

[0003] Spontaneous combustion in goafs occurs during coal mining when oxygen introduced through air leaks in the working face reacts physically and chemically with loose coal left in the goaf. The coal oxidizes, generating a large amount of heat. If this heat is not dissipated in time, it accumulates and eventually causes spontaneous combustion. Besides causing coal mine fires, spontaneous combustion in goafs can also lead to secondary accidents such as gas explosions and coal dust explosions, which are no less dangerous than gas, roof collapse, and water inrush accidents.

[0004] Currently, traditional fire prevention and extinguishing measures such as nitrogen injection and grouting have significant limitations. In particular, the widely used nitrogen injection technology often employs a crude injection method with a fixed flow rate and large-area coverage. This method lacks precise judgment of the fire source location and its development trend, and the timing, volume, and location of nitrogen injection are often arbitrary, leading to low nitrogen utilization and high fire prevention and extinguishing costs. Furthermore, it fails to capture and effectively utilize the oxidation heat energy in the goaf in a timely manner, resulting in heat dissipation, energy waste, and safety risks. Summary of the Invention

[0005] In view of the problems existing in the prior art, the present invention aims to provide a goaf fire prevention and extinguishing and heat recovery system and method based on distributed temperature measurement optical fiber, so as to realize the integration of accurate real-time monitoring of hidden fire sources in the goaf, efficient fire prevention and extinguishing and low-grade waste heat recovery and utilization, fundamentally improving the mine safety guarantee level, while realizing the goal of energy cascade utilization and green mine construction.

[0006] To achieve the above objectives, this invention proposes a fire prevention, extinguishing, and heat recovery system for goaf areas based on distributed temperature-sensing optical fibers, including a nitrogen injection pipeline.

[0007] The nitrogen injection pipeline includes a main nitrogen injection pipeline and nitrogen injection branch pipelines. The main nitrogen injection pipeline is laid along the axial direction of the goaf and its front end extends into the goaf. There are multiple nitrogen injection branch pipelines, which are laid out in the goaf and laid side by side along the radial direction of the goaf. Each nitrogen injection branch pipeline is connected to the main nitrogen injection pipeline in sequence.

[0008] Both the main nitrogen injection pipeline and the branch nitrogen injection pipelines include a protective casing and nitrogen injection pipes, water pipes, and fiber optic pipes installed within the protective casing. The protective casings, nitrogen injection pipes, water pipes, and fiber optic pipes of both pipelines are connected correspondingly. The main nitrogen injection pipeline is a nitrogen injection main pipe, with its inlet end connected to a nitrogen source and its exhaust end sealed by a first gas path automatic switching valve. The branch nitrogen injection pipeline is a nitrogen injection branch pipe, with its inlet end equipped with a directional nitrogen injection control system and its outlet end sealed. Several nitrogen injection holes are provided on the outer circumference of both the branch pipe and its corresponding protective casing. This forms a nitrogen injection fire prevention and extinguishing system.

[0009] The fiber optic duct is equipped with a temperature-sensing fiber optic cable, and the outermost end of the temperature-sensing fiber optic cable is connected to a fiber optic demodulator. An independent fiber optic duct is also installed between two adjacent nitrogen injection branch ducts. Each independent fiber optic duct is laid parallel to the nitrogen injection branch duct and is connected to the fiber optic duct of the main nitrogen injection duct, thus forming a distributed fiber optic monitoring network.

[0010] The outlet of the water supply pipe of the nitrogen injection branch pipeline is connected to an independent water supply pipe. This independent water supply pipe is also laid along the axial direction of the goaf and extends outside the goaf. Its outer end is connected to a return outlet valve. The inlet of the water supply pipe of the nitrogen injection main pipeline is connected to a water pump, and the outlet is in a closed state; thus forming a waste heat circulation and recovery system.

[0011] The air inlet end of the nitrogen injection branch pipe is also equipped with an explosion-proof solenoid valve, and the water inlet end of the water pipe of the nitrogen injection branch pipe is also equipped with an explosion-proof solenoid valve. The directional nitrogen injection control system, the explosion-proof solenoid valve, and the fiber optic demodulator are all connected to the computer control system.

[0012] In the above scheme: the air inlet of each nitrogen injection branch pipe is connected to the nitrogen injection main pipe through a second automatic gas path switching valve. Both the first and second automatic gas path switching valves include a valve pipe, an opening valve plate and a locking valve plate fixed in the valve pipe, and a sliding valve plate disposed between the opening and locking valve plates. The sliding valve plate can slide along the axial direction of the valve pipe. Each opening valve plate has through holes at all four ends and at its center. The center of the locking valve plate also has a matching through hole corresponding to the center through hole of the opening valve plate. Similarly, each of the four ends of the sliding valve plate also has matching through holes corresponding to the four end through holes of the opening valve plate. In the first automatic gas switching valve, the opening valve plate, sliding valve plate, and locking valve plate are arranged sequentially from back to front; in the second automatic gas switching valve, the locking valve plate, sliding valve plate, and opening valve plate are arranged sequentially from back to front. When nitrogen is introduced into the nitrogen injection main pipe, the nitrogen rushes into the first automatic gas switching valve, squeezing the sliding valve plate inside it to slide towards the locking valve plate until it is in contact with the locking valve plate, thereby closing the first automatic gas switching valve. When nitrogen rushes into the second automatic gas switching valve, it squeezes the sliding valve plate inside it to slide towards the opening valve plate until it is in contact with the opening valve plate, thereby opening the second automatic gas switching valve.

[0013] This structure introduces a purely mechanical automatic gas path switching valve. This valve does not require external power or control signals and can automatically and reliably switch between nitrogen injection and gas extraction states solely based on the pressure changes in the pipeline itself. It achieves automated functions such as preventing leakage during nitrogen injection and assisting in reset during gas extraction. Due to its purely mechanical characteristics, it enhances the inherent safety and operational reliability of the system in complex downhole environments.

[0014] In the above scheme: the protective shell of the nitrogen injection branch pipeline is designed to be disconnected at the installation position of the directional nitrogen injection control system. The directional nitrogen injection control system is straddling the two protective shell sections and located at the front end of the explosion-proof solenoid valve. The directional nitrogen injection control system includes a spring reset chamber, a rotary positioning and interface unit, and a nitrogen driving chamber, which are sequentially movably sleeved outside the corresponding nitrogen injection branch pipeline from front to back.

[0015] The nitrogen-driven chamber is equipped with an annular piston, which is integrally formed with the nitrogen injection branch pipe and can slide axially. The nitrogen injection branch pipe has an air inlet that connects to the nitrogen-driven chamber, and a telescopic section is provided in the pipe section between the corresponding explosion-proof solenoid valve and the directional nitrogen injection control system, so that the nitrogen injection branch pipe has a telescopic range that can move axially relative to the protective pipe shell.

[0016] The inner wall of the rotary positioning and interface unit is provided with three mechanical limit stops, the circumferential azimuth angles of the three mechanical limit stops are 0°, 45° and 90° respectively, and they are staggered along the axial direction.

[0017] The protective casing of the nitrogen injection branch pipeline is provided with three rows of fixed nitrogen injection holes along its axial direction, with the three rows of fixed nitrogen injection holes located on both sides and the top end respectively;

[0018] The nitrogen injection branch pipe is provided with multiple circles of movable nitrogen injection holes along its axial direction. Each circle of movable nitrogen injection holes includes three circumferentially arranged movable nitrogen injection holes, which are respectively located on both sides and the upper end of the nitrogen injection branch pipe. A mechanical limit block that can abut against a mechanical limit stop point is also provided on the outer circumference of the nitrogen injection branch pipe;

[0019] The rotation positioning and interface unit is equipped with a rotation motor. The rotation motor can drive the rotation positioning and interface unit to rotate around the corresponding nitrogen injection branch pipe, so as to drive the rotation positioning and interface unit to rotate to a predetermined angle, making the mechanical limit block correspond to the path of a certain mechanical limit stop point;

[0020] A return spring is provided along the axial direction in the spring return chamber. When nitrogen is injected, the gas enters the nitrogen driving chamber and acts on the rear end face of the annular piston, pushing the annular piston and the nitrogen injection branch pipe fixedly connected thereto to move forward against the resistance of the return spring until the mechanical limit block abuts against the mechanical limit stop point;

[0021] When the mechanical limit block abuts against the mechanical limit stop point with a circumferential azimuth angle of 0°, the movable nitrogen injection holes on the nitrogen injection branch pipe are exactly aligned and connected with a row of fixed nitrogen injection holes on the left side of the protection pipe shell; when the mechanical limit block abuts against the mechanical limit stop point with a circumferential azimuth angle of 45°, the movable nitrogen injection holes on the nitrogen injection branch pipe are exactly aligned and connected with a row of fixed nitrogen injection holes on the upper end of the protection pipe shell; when the mechanical limit block abuts against the mechanical limit stop point with a circumferential azimuth angle of 90°, the movable nitrogen injection holes on the nitrogen injection branch pipe are exactly aligned and connected with a row of fixed nitrogen injection holes on the right side of the protection pipe shell.

[0022] The telescopic section can be a hose structure. Traditional nitrogen injection pipes usually can only spray unidirectionally. However, in this system, the rotation positioning and interface unit is driven by a rotation motor, and by using the staggered distribution of three mechanical limit stop points at 0°, 45°, and 90°, the axial movement amount of the nitrogen injection pipeline is determined by circumferential positioning; enabling the nitrogen injection branch pipe to inject nitrogen into specific areas such as the upper, left, and right directions according to the fire source direction, truly achieving "hitting where it is pointed", avoiding the waste caused by the diffusion of nitrogen in non-fire areas, realizing the upgrade from "injecting nitrogen according to the pipeline" to "precisely injecting nitrogen according to the spatial vector", and greatly improving the inerting efficiency and nitrogen utilization rate.

[0023] In the above solution: The nitrogen injection pipeline, water pipeline, and optical fiber pipeline in the protection pipe shell are arranged in a "pin" shape to avoid interference.

[0024] In the above solution: The temperature measurement optical fiber is an armored sensing optical fiber. The temperature measurement optical fiber is laid along the axial direction of the optical fiber pipeline and is arranged closely against the inner side of the pipe wall. The close arrangement avoids the vibration or position offset of the optical fiber caused by fluid flow, ensures the fixity of the temperature measurement point, and makes the temperature data have extremely high spatial resolution and accuracy.

[0025] In the above scheme: both the nitrogen injection pipe and the water supply pipe are metal pipes; the diameter of the nitrogen injection hole is 10mm; the inner diameter of the protective shell is 100~160mm; and the independently arranged optical fiber pipe and water supply pipe are uniformly covered with protective shells. The inner diameter range of the protective shell is sufficient to accommodate the nitrogen injection pipe, water supply pipe, and optical fiber pipe; the metal pipe combines high strength with excellent thermal conductivity.

[0026] This invention also proposes a method for fire prevention, extinguishing, and heat recovery in goaf areas based on distributed temperature-sensing optical fibers, including the aforementioned fire prevention, extinguishing, and heat recovery system for goaf areas based on distributed temperature-sensing optical fibers, and further comprising the following steps:

[0027] Step 1: Threshold setting and routine monitoring;

[0028] In the control unit of the fiber optic demodulator, a nitrogen injection trigger temperature threshold and a temperature change rate warning value are set. The system is in real-time monitoring mode. The fiber optic demodulator continuously emits laser pulses to the sensing fiber and receives backscattered light signals. By analyzing the Raman scattered light intensity ratio and optical time domain information, the temperature and its change trend at each point along the fiber optic pipeline in the goaf area are calculated and recorded in real time. The position of the measuring point is accurately located, and a digital twin model is established in the computer control system.

[0029] Step 2: Early Warning and Automatic Activation;

[0030] When the distributed optical fiber monitoring network detects that the temperature in a certain area is rising continuously and the daily temperature rise rate reaches the temperature change rate warning value, or the active temperature value exceeds the set nitrogen injection trigger temperature threshold, the computer control system will determine that there is a risk of spontaneous combustion in the area and display the location of the high temperature point in the digital twin model, and at the same time activate the nitrogen injection fire prevention and extinguishing system and the waste heat circulation and recovery system.

[0031] Step 3: The gas and water circuits will automatically open;

[0032] The computer control system sends an opening command to the explosion-proof solenoid valve in the area corresponding to the hazard. The explosion-proof solenoid valve opens, and the nitrogen injection branch pipe in that area connects to the nitrogen injection main pipe. The water pipe of the nitrogen injection branch pipe connects to the water pipe in the nitrogen injection main pipe. The nitrogen source switch valve and the water pump switch valve start simultaneously, nitrogen enters the nitrogen injection pipe, and cooling water enters the water pipe. The explosion-proof solenoid valve in areas not corresponding to the hazard remains closed. During nitrogen injection, the nitrogen injection pipe is under positive pressure. The second gas path automatic switching valve at the air inlet end of the nitrogen injection branch pipe automatically opens to supply nitrogen into the nitrogen injection branch pipe. The first gas path automatic switching valve at the air extraction end of the nitrogen injection main pipe automatically closes to prevent nitrogen from leaking from the air extraction end of the nitrogen injection main pipe.

[0033] Step 4: Execute directional nitrogen injection;

[0034] The computer control system drives the directional nitrogen injection control system at the corresponding location based on the location of the high-temperature point, and injects nitrogen gas through the nitrogen injection hole to the goaf.

[0035] Step 5: Inerting fire extinguishing and residual heat recovery;

[0036] After nitrogen is released, it naturally rises and diffuses throughout the high-temperature area, diluting the oxygen concentration and achieving inerting for fire prevention and extinguishing. At the same time, circulating water flows through water pipes arranged near the high-temperature area, absorbing excess heat from the surrounding rock and gas in the goaf. The water temperature rises, carrying away the heat energy, achieving cooling and waste heat recovery.

[0037] Step Six: Nitrogen injection completed and system reset;

[0038] When the distributed temperature measurement fiber optic network detects that the temperature in the risk area continues to drop and stabilizes below the safety threshold, the following shutdown procedures will be executed sequentially:

[0039] 1. Close the nitrogen source switch valve and the water pump switch valve;

[0040] 2. Close the explosion-proof solenoid valve to cut off the gas and water supply lines;

[0041] 3. Reset the directional nitrogen injection control system;

[0042] 4. All system components are restored to standby monitoring state, awaiting the next warning;

[0043] Step 7: Loop monitoring and closed-loop control;

[0044] After the system is reset, the distributed temperature measurement fiber optic network continues to monitor the temperature of the goaf around the clock, forming an intelligent closed-loop control of "monitoring-early warning-directional nitrogen injection and cooling-effect evaluation-system reset".

[0045] In the above scheme: In step four, the working steps of the directional nitrogen injection control system are as follows: The rotary motor drives the rotary positioning and interface unit of the corresponding nitrogen injection branch pipe to rotate to a predetermined angle, so that the mechanical limit block enters the corresponding limit path; Nitrogen gas rushes into the nitrogen gas drive chamber, pushing the annular piston and the nitrogen injection branch pipe fixed thereto to overcome the resistance of the reset spring and move forward until the mechanical limit block abuts against the corresponding mechanical limit stop, so that the movable nitrogen injection hole on the nitrogen injection branch pipe is aligned and connected with the fixed nitrogen injection hole in the corresponding direction on the protective tube shell;

[0046] In the above scheme, the warning value for the temperature change rate is a daily temperature increase of 5~10℃.

[0047] The above scheme also includes an extraction pump. The nitrogen injection main pipe has a branch at its outer end, and the extraction pump is connected to this branch. When it is necessary to sample the gas in the goaf, the nitrogen source switch valve is closed and the extraction pump switch valve is opened. Under the action of the extraction pump, the nitrogen injection pipeline is under negative pressure. The sliding valve plate in the first gas path automatic switching valve slides towards the opening valve plate until it is in contact with the opening valve plate, thereby realizing the automatic opening of the first gas path automatic switching valve and thus realizing the extraction of gas from the goaf. At the same time, the second gas path automatic switching valve at the air inlet end of the nitrogen injection branch pipe is automatically closed under negative pressure to prevent the nitrogen backflow in the nitrogen injection branch pipe from affecting the composition of the extracted gas from the goaf. Finally, by analyzing the gas composition and concentration distribution in the goaf, the leakage channels and collapse conditions in the goaf are inverted, and the ventilation system is optimized.

[0048] The beneficial effects of this invention are:

[0049] 1. It has achieved a fundamental shift in fire prevention and extinguishing work from "passive response" to "active early warning." By installing a distributed fiber optic monitoring network, it enables real-time perception across the entire area, continuously and in real-time acquiring temperature information for the entire goaf area. This overcomes the blind spots of traditional point-based temperature measurement and achieves early and accurate location of hidden fire sources and areas with abnormal temperature rises.

[0050] 2. Based on the precise temperature field data obtained from the temperature-sensing fiber optic cable, the system can not only intelligently determine the timing and amount of nitrogen injection, but also achieve precise control of the injection direction through the directional nitrogen injection control system. The directional nitrogen injection control system can inject nitrogen into specific areas such as the top, left, and right based on the location of the fire source, achieving an upgrade from "nitrogen injection according to pipeline" to "precise nitrogen injection according to spatial vector," greatly improving inerting efficiency and nitrogen utilization.

[0051] 3. This invention integrates a waste heat recovery system with a fire prevention and extinguishing nitrogen injection system. The waste heat recovery loop directly reduces the temperature of the coal while absorbing heat, and the inerting environment maintained by nitrogen injection ensures the safety of the heat extraction process.

[0052] 4. Successfully recovering the heat generated by the oxidation of residual coal in the goaf can heat the water flow in the pipeline, providing hot water for simple cleaning of coal mine workers, turning the oxidation heat energy in the goaf into a "treasure", increasing the well-being of miners and achieving energy-saving benefits.

[0053] 5. This invention can utilize existing engineering conditions such as roadways and boreholes to lay out sensor networks and pipelines without requiring large-scale additional development projects, thus having minimal impact on normal mine production operations and being easy to implement. Attached Figure Description

[0054] Figure 1 This is a schematic diagram of the structure of the present invention.

[0055] Figure 2This is a schematic diagram of the nitrogen injection pipeline.

[0056] Figure 3 A schematic diagram showing the layout and structure of the two-air-path automatic switching valve.

[0057] Figure 4 A schematic diagram of the directional nitrogen injection control system. Detailed Implementation

[0058] like Figure 1 As shown in Figure 4, a fire prevention, extinguishing and heat recovery system for goaf areas based on distributed temperature-measuring optical fibers mainly consists of nitrogen injection pipelines.

[0059] The nitrogen injection pipeline includes a main nitrogen injection pipeline 1 and nitrogen injection branch pipelines 2. The main nitrogen injection pipeline 1 is laid along the axial direction of the goaf and its front end extends into the goaf. There are multiple nitrogen injection branch pipelines 2, which are laid out in the goaf and laid side by side along the radial direction of the goaf. Each nitrogen injection branch pipeline 2 is connected to the main nitrogen injection pipeline 1 in sequence.

[0060] Both the nitrogen injection main pipeline 1 and the nitrogen injection branch pipeline 2 include a protective casing 3 and nitrogen injection pipes 4, water pipes 5, and fiber optic pipes 6 installed within the protective casing 3. The protective casing 3 (which can be connected via quick-release clips 26), nitrogen injection pipes 4, water pipes 5, and fiber optic pipes 6 are connected to each other. The nitrogen injection pipe 4 of the nitrogen injection main pipeline is the main nitrogen injection pipe, with its inlet end (i.e., the rear end of the main nitrogen injection pipe) connected to a nitrogen source and its exhaust end (i.e., the front end of the main nitrogen injection pipe) closed by the first gas path automatic switching valve 7. The nitrogen injection pipe 4 of the nitrogen injection branch pipeline 2 is the branch nitrogen injection pipe, with a directional nitrogen injection control system 8 installed at its inlet end and a sealed outlet end. Several nitrogen injection holes 9 are provided on the outer circumference of both the branch nitrogen injection pipe and its corresponding protective casing 3. This forms a nitrogen injection fire prevention and extinguishing system.

[0061] A temperature-sensing optical fiber is installed inside the optical fiber duct 6. The outermost end of the temperature-sensing optical fiber is connected to an optical fiber demodulator 10. An independent optical fiber duct 6 is also installed between two adjacent nitrogen injection branch ducts 2. Each independent optical fiber duct 6 is laid parallel to the nitrogen injection branch duct 2 and is connected to the optical fiber duct 6 of the main nitrogen injection duct 1, thus forming a distributed optical fiber monitoring network.

[0062] The outlet of the water pipe 5 of the nitrogen injection branch pipeline 2 is connected to an independent water pipe 5. This independent water pipe 5 is also laid along the axial direction of the goaf and extends outside the goaf. Its outer end is connected to a return outlet valve 11. The inlet of the water pipe 5 of the nitrogen injection main pipeline 1 is connected to a water pump 12, and the outlet is in a closed state; thus forming a waste heat circulation and recovery system.

[0063] The nitrogen injection branch pipe is also equipped with an explosion-proof solenoid valve 13 at the air inlet end, and the water inlet end of the water pipe 5 of the nitrogen injection branch pipe 2 is also equipped with an explosion-proof solenoid valve 13. The directional nitrogen injection control system 8, the explosion-proof solenoid valve 13, and the fiber optic demodulator 10 are all connected to the computer control system 14.

[0064] Ideally, the inlet ends of the nitrogen injection branch pipes are connected to the nitrogen injection main pipe via the second automatic gas path switching valve 15. Both the first and second automatic gas path switching valves 7 and 15 include valve pipes and an opening valve plate 16 and a locking valve plate 17 fixed within the valve pipes, as well as a sliding valve plate 18 positioned between the opening and locking valve plates 16 and 17. The sliding valve plate 18 can slide axially along the valve pipe. The opening valve plate 16 has through holes at all four ends and at its center. The locking valve plate 17 also has a matching through hole at its center corresponding to the central through hole of the opening valve plate 16. Similarly, the sliding valve plate 18 has matching through holes at all four ends corresponding to the four end through holes of the opening valve plate 16.

[0065] In the first automatic gas path switching valve 7, the opening valve plate 16, the sliding valve plate 18, and the locking valve plate 17 are arranged in sequence from back to front; in the second automatic gas path switching valve 15, the locking valve plate 17, the sliding valve plate 18, and the opening valve plate 16 are arranged in sequence from back to front.

[0066] When nitrogen is introduced into the nitrogen injection main pipe, the nitrogen rushes into the first gas path automatic switching valve 7, squeezing the sliding valve plate 18 inside to slide towards the locking valve plate 17 until it is in contact with the locking valve plate 17, thereby closing the first gas path automatic switching valve 7; when nitrogen rushes into the second gas path automatic switching valve 15, it squeezes the sliding valve plate 18 inside to slide towards the opening valve plate 16 until it is in contact with the opening valve plate 16, thereby opening the second gas path automatic switching valve 15.

[0067] This structure introduces a purely mechanical automatic gas path switching valve. This valve does not require external power or control signals and can automatically and reliably switch between nitrogen injection and gas extraction states solely based on the pressure changes in the pipeline itself. It achieves automated functions such as preventing leakage during nitrogen injection and assisting in reset during gas extraction. Due to its purely mechanical characteristics, it enhances the inherent safety and operational reliability of the system in complex downhole environments.

[0068] Ideally, the protective shell 3 of the nitrogen injection branch pipe 2 is designed to be disconnected at the installation position of the directional nitrogen injection control system 8. The directional nitrogen injection control system 8 is installed between the two protective shells 3 and is located at the front end of the explosion-proof solenoid valve 13. The directional nitrogen injection control system 8 includes a spring reset chamber 19, a rotary positioning and interface unit 20, and a nitrogen drive chamber 21, which are sequentially movably sleeved outside the corresponding nitrogen injection branch pipe from front to back.

[0069] The nitrogen-driven chamber 21 is equipped with an annular piston 27, which is integrally formed with the nitrogen injection branch pipe and can slide axially. The nitrogen injection branch pipe has an air inlet 28 that connects to the nitrogen-driven chamber 21, and a telescopic section 22 is provided in the pipe section between the explosion-proof solenoid valve 13 and the directional nitrogen injection control system 8, so that the nitrogen injection branch pipe has a telescopic range that can move axially relative to the protective pipe shell 3.

[0070] The inner wall of the rotary positioning and interface unit 20 is provided with three mechanical limit stops 23. The circumferential azimuth angles of the three mechanical limit stops 23 are 0°, 45° and 90° respectively, and they are staggered along the axial direction.

[0071] The protective casing 3 of the nitrogen injection branch pipeline 2 is provided with three rows of fixed nitrogen injection holes along its axial direction. The three rows of fixed nitrogen injection holes are located on its two sides and the top.

[0072] The nitrogen injection branch pipe has multiple rings of movable nitrogen injection holes along its axial direction. Each ring of movable nitrogen injection holes includes three movable nitrogen injection holes arranged circumferentially. The three movable nitrogen injection holes are located on both sides and the upper end of the nitrogen injection branch pipe, respectively. A mechanical limit block 24 that can abut against the mechanical limit stop 23 is also provided on the outer circle of the nitrogen injection branch pipe.

[0073] The rotary positioning and interface unit 20 is equipped with a rotary motor, which can drive the rotary positioning and interface unit 20 to rotate around the corresponding nitrogen injection branch pipe, thereby driving the rotary positioning and interface unit 20 to rotate to a predetermined angle, so that the mechanical limit block 24 corresponds to a certain mechanical limit stop 23.

[0074] A return spring 25 is provided in the spring return chamber 19 along its axial direction. When nitrogen is injected, the gas enters the nitrogen drive chamber 21 and acts on the rear end face of the annular piston 27, pushing the annular piston 27 and the nitrogen injection branch pipe fixed thereto to overcome the resistance of the return spring 25 and move forward until the mechanical limit block 24 abuts against the mechanical limit stop 23.

[0075] When the mechanical limit block 24 abuts against the mechanical limit stop 23 with a circumferential azimuth angle of 0°, the movable nitrogen injection hole on the nitrogen injection branch pipe is aligned and connected with a row of fixed nitrogen injection holes on the left side of the protective shell 3; when the mechanical limit block 24 abuts against the mechanical limit stop 23 with a circumferential azimuth angle of 45°, the movable nitrogen injection hole on the nitrogen injection branch pipe is aligned and connected with a row of fixed nitrogen injection holes at the upper end of the protective shell 3; when the mechanical limit block 24 abuts against the mechanical limit stop 23 with a circumferential azimuth angle of 90°, the movable nitrogen injection hole on the nitrogen injection branch pipe is aligned and connected with a row of fixed nitrogen injection holes on the right side of the protective shell 3.

[0076] The retractable section 22 can be a flexible hose structure. Traditional nitrogen injection pipes can usually only inject in one direction. However, this system uses a rotary motor to drive the rotary positioning and interface unit 20. By utilizing the staggered distribution of three mechanical limit points 23 at 0°, 45°, and 90°, the nitrogen injection pipe 4 can determine the axial movement by means of circumferential positioning. This allows the nitrogen injection branch pipe to inject nitrogen into specific areas such as the top, left, and right according to the location of the fire source, truly achieving "point-and-shoot". This avoids the waste caused by nitrogen diffusion in non-fire areas and realizes the upgrade from "nitrogen injection according to pipeline" to "precise nitrogen injection according to spatial vector", which greatly improves the inerting efficiency and nitrogen utilization rate.

[0077] Ideally, the nitrogen injection pipe 4, water supply pipe 5, and fiber optic pipe 6 inside the protective casing 3 should be arranged in a triangular pattern to avoid interference.

[0078] Ideally, the temperature-sensing fiber should be armored, laid along the six axes of the fiber optic conduit, and closely attached to the inner wall of the conduit. This close attachment prevents vibration or positional shift of the fiber due to the flow of nitrogen or water, ensuring the stability of the temperature measurement point and resulting in extremely high spatial resolution and accuracy of the temperature data.

[0079] Ideally, both the nitrogen injection pipe 4 and the water supply pipe 5 are metal pipes, with a nitrogen injection hole diameter of 10mm and a protective shell 3 inner diameter of 100~160mm. The independently installed fiber optic pipe 6 and the water supply pipe 5 are uniformly covered with protective shells 3. The inner diameter of the protective shell 3 is sufficient to accommodate the nitrogen injection pipe 4, the water supply pipe 5, and the fiber optic pipe 6, and the metal pipes combine high strength with excellent thermal conductivity.

[0080] A method for fire prevention, extinguishing, and heat recovery in goaf areas based on distributed temperature-sensing optical fibers, comprising the aforementioned fire prevention, extinguishing, and heat recovery system for goaf areas based on distributed temperature-sensing optical fibers, mainly consists of the following steps:

[0081] Step 1: Threshold setting and routine monitoring;

[0082] In the control unit of the fiber optic demodulator 10, a nitrogen injection trigger temperature threshold and a temperature change rate warning value are set. The system is in real-time monitoring mode. The fiber optic demodulator 10 continuously emits laser pulses to the sensing fiber and receives backscattered light signals. By analyzing the Raman scattering light intensity ratio and optical time domain information, the temperature and its change trend at each point along the fiber optic pipeline in the goaf are calculated and recorded in real time. The position of the measuring point is accurately located, and a digital twin model is established in the computer control system 14.

[0083] Step 2: Early Warning and Automatic Activation;

[0084] When the distributed optical fiber monitoring network detects that the temperature in a certain area is rising continuously and the daily temperature rise rate reaches the temperature change rate warning value, or the active temperature value exceeds the set nitrogen injection trigger temperature threshold, the computer control system 14 will determine that there is a risk of spontaneous combustion in the area and display the location of the high temperature point in the digital twin model, and at the same time activate the nitrogen injection fire prevention and extinguishing system and the waste heat circulation and recovery system.

[0085] Step 3: The gas and water circuits will automatically open;

[0086] The computer control system 14 sends an opening command to the explosion-proof solenoid valve 13 in the area corresponding to the hazard. The explosion-proof solenoid valve 13 opens, and the nitrogen injection branch pipe in that area connects to the nitrogen injection main pipe. The water pipe 5 of the nitrogen injection branch pipe 2 connects to the water pipe 5 in the nitrogen injection main pipe 1. The on / off valve of the nitrogen source and the on / off valve of the water pump 12 start simultaneously, and nitrogen enters the nitrogen injection pipe 4, while cooling water enters the water pipe 5. The explosion-proof solenoid valve 13 in areas not corresponding to the hazard remains closed. During nitrogen injection, the nitrogen injection pipeline is under positive pressure. The second gas path automatic switching valve 15 at the air inlet end of the nitrogen injection branch pipe automatically opens to supply nitrogen into the nitrogen injection branch pipe. The first gas path automatic switching valve 7 at the air extraction end of the nitrogen injection main pipe automatically closes to prevent nitrogen from leaking from the air extraction end of the nitrogen injection main pipe.

[0087] Step 4: Execute directional nitrogen injection;

[0088] The computer control system 14 drives the directional nitrogen injection control system 8 at the corresponding location based on the location of the high-temperature point to inject nitrogen, so that the nitrogen gas flows to the goaf through the nitrogen injection hole 9.

[0089] Step 5: Inerting fire extinguishing and residual heat recovery;

[0090] After nitrogen is released, it naturally rises and diffuses throughout the high-temperature area, diluting the oxygen concentration and achieving inerting for fire prevention and extinguishing. At the same time, circulating water flows through water pipes arranged near the high-temperature area, absorbing excess heat from the surrounding rock and gas in the goaf. The water temperature rises, carrying away the heat energy, thus achieving cooling and waste heat recovery.

[0091] Step Six: Nitrogen injection completed and system reset;

[0092] When the distributed temperature measurement fiber optic network detects that the temperature in the risk area continues to drop and stabilizes below the safety threshold, the following shutdown procedures will be executed sequentially:

[0093] 1. Close the nitrogen source switch valve and the water pump 12 switch valve;

[0094] 2. Close the explosion-proof solenoid valve 13 to cut off the gas and water circuits;

[0095] 3. Reset the directional nitrogen injection control system 8;

[0096] 4. All system components are restored to standby monitoring state, awaiting the next warning.

[0097] Step 7: Loop monitoring and closed-loop control;

[0098] After the system is reset, the distributed temperature measurement fiber optic network continues to monitor the temperature of the goaf around the clock, forming an intelligent closed-loop control of "monitoring-early warning-directional nitrogen injection and cooling-effect evaluation-system reset".

[0099] In the above scheme: In step four, the working steps of the directional nitrogen injection control system 8 are as follows: The rotary motor drives the rotation positioning and interface unit 20 of the corresponding nitrogen injection branch pipe 2 to rotate to a predetermined angle, so that the mechanical limit block 24 enters the corresponding limit path; Nitrogen gas rushes into the nitrogen gas drive chamber 21, pushing the annular piston 27 and the nitrogen injection branch pipe fixed thereto to overcome the resistance of the reset spring 25 and move forward until the mechanical limit block 24 abuts against the corresponding mechanical limit stop 23, so that the movable nitrogen injection hole on the nitrogen injection branch pipe is aligned and connected with the fixed nitrogen injection hole in the corresponding direction on the protective shell 3.

[0100] At the same time, when the nitrogen injection branch pipe establishes positive nitrogen injection pressure, the second air path automatic switching valve 15 at the air inlet end of the nitrogen injection branch pipe automatically switches, and the sliding valve plate 18 blocks the sealing lock plate 17 under the pressure of air to prevent nitrogen backflow.

[0101] Ideally, the warning value for the rate of temperature change should be a daily temperature increase of 5-10°C.

[0102] Ideally, it should also include an extraction pump, with a branch at the outer end of the nitrogen injection main pipe to which the extraction pump is connected. When it is necessary to sample the gas in the goaf, the nitrogen source switch valve is closed, and the extraction pump switch valve is opened. Under the action of the extraction pump, the nitrogen injection pipeline is under negative pressure. The sliding valve plate 18 in the first gas path automatic switching valve 7 slides towards the opening valve plate 16 until it is in contact with the opening valve plate 16, thereby automatically opening the first gas path automatic switching valve 7 and extracting the gas from the goaf. At the same time, the second gas path automatic switching valve 15 at the air inlet end of the nitrogen injection branch pipe is automatically closed under negative pressure to prevent the backflow of nitrogen in the nitrogen injection branch pipe from affecting the composition of the extracted gas from the goaf. Finally, by analyzing the gas composition and concentration distribution in the goaf, the leakage channels and collapse conditions in the goaf can be inverted to optimize the ventilation system.

Claims

1. A fire prevention, extinguishing, and heat recovery system for goaf areas based on distributed temperature-sensing optical fibers, comprising a nitrogen injection pipeline, characterized in that: The nitrogen injection pipeline includes a main nitrogen injection pipeline (1) and nitrogen injection branch pipelines (2). The main nitrogen injection pipeline (1) is laid along the axial direction of the goaf and its front end extends into the goaf. There are multiple nitrogen injection branch pipelines (2), which are laid out in the goaf and laid side by side along the radial direction of the goaf. Each nitrogen injection branch pipeline (2) is connected to the main nitrogen injection pipeline (1) in sequence. The nitrogen injection main pipeline (1) and nitrogen injection branch pipeline (2) both include a protective shell (3) and a nitrogen injection pipe (4), a water supply pipe (5) and an optical fiber pipe (6) arranged in the protective shell (3), and the protective shell (3), nitrogen injection pipe (4), water supply pipe (5) and optical fiber pipe (6) of the two are connected to each other; wherein, the nitrogen injection pipe (4) of the nitrogen injection main pipeline is a nitrogen injection main pipe, its air inlet end is connected to a nitrogen source, and its air extraction end is closed by the first air path automatic switching valve (7); the nitrogen injection pipe (4) of the nitrogen injection branch pipeline (2) is a nitrogen injection branch pipe, its air inlet end is provided with a directional nitrogen injection control system (8), its air outlet end is sealed, and the nitrogen injection branch pipe and its corresponding protective shell (3) are provided with several nitrogen injection holes (9); thereby forming a nitrogen injection fire prevention and extinguishing system; The optical fiber duct (6) is equipped with a temperature measuring optical fiber, and the outermost end of the temperature measuring optical fiber is connected to an optical fiber demodulator (10). An independent optical fiber duct (6) is also installed between two adjacent nitrogen injection branch ducts (2). Each independent optical fiber duct (6) is laid parallel to the nitrogen injection branch duct (2) and is connected to the optical fiber duct (6) of the main nitrogen injection duct (1); thus forming a distributed optical fiber monitoring network. The outlet of the water pipe (5) of the nitrogen injection branch pipeline (2) is connected to an independent water pipe (5). The independent water pipe (5) is also laid along the axial direction of the goaf and extends to the outside of the goaf. Its outer end is connected to a return outlet valve (11). The inlet of the water pipe (5) of the nitrogen injection main pipeline (1) is connected to a water pump (12), and the outlet is closed. Thus, a waste heat circulation and recovery system is formed. The nitrogen injection branch pipe is also equipped with an explosion-proof solenoid valve (13) at the air inlet end, and the nitrogen injection branch pipe (2) is also equipped with an explosion-proof solenoid valve (13) at the water inlet end of the water pipe (5). The directional nitrogen injection control system (8), the explosion-proof solenoid valve (13) and the fiber optic demodulator (10) are all connected to the computer control system (14).

2. The fire prevention, extinguishing, and heat recovery system for goaf areas based on distributed temperature-measuring optical fibers according to claim 1, characterized in that: The air inlet of each nitrogen injection branch pipe is connected to the nitrogen injection main pipe through a second gas path automatic switching valve (15). Both the first gas path automatic switching valve (7) and the second gas path automatic switching valve (15) include a valve pipe and an opening valve plate (16) and a locking valve plate (17) fixed in the valve pipe, as well as a sliding valve plate (18) disposed between the opening valve plate (16) and the locking valve plate (17). The sliding valve plate (18) can slide along the axial direction of the valve pipe. The four ends and center of the opening valve plate (16) are provided with through holes. The center of the locking valve plate (17) is also provided with a matching through hole corresponding to the center through hole of the opening valve plate (16). The four ends of the sliding valve plate (18) are also provided with matching through holes corresponding to the four end through holes of the opening valve plate (16). In the first automatic gas switching valve (7), the opening valve plate (16), the sliding valve plate (18), and the locking valve plate (17) are arranged in sequence from back to front; in the second automatic gas switching valve (15), the locking valve plate (17), the sliding valve plate (18), and the opening valve plate (16) are arranged in sequence from back to front. When nitrogen is introduced into the nitrogen injection main pipe, the nitrogen rushes into the first gas path automatic switching valve (7), squeezing the sliding valve plate (18) inside to slide towards the locking valve plate (17) until it is in contact with the locking valve plate (17), thereby closing the first gas path automatic switching valve (7); when nitrogen rushes into the second gas path automatic switching valve (15), it squeezes the sliding valve plate (18) inside to slide towards the opening valve plate (16) until it is in contact with the opening valve plate (16), thereby opening the second gas path automatic switching valve (15).

3. The fire prevention, extinguishing, and heat recovery system for goaf areas based on distributed temperature-measuring optical fibers according to claim 2, characterized in that: The protective shell (3) of the nitrogen injection branch pipeline (2) is designed to be disconnected at the installation position of the directional nitrogen injection control system (8). The directional nitrogen injection control system (8) is spanned between the two protective shells (3) and located at the front end of the explosion-proof solenoid valve (13). The directional nitrogen injection control system (8) includes a spring reset chamber (19), a rotary positioning and interface unit (20), and a nitrogen drive chamber (21) that are sequentially and movably sleeved outside the corresponding nitrogen injection branch pipeline from front to back. The nitrogen-driven chamber (21) is provided with an annular piston (27), which is integrally formed with the nitrogen injection branch pipe and can slide axially; the nitrogen injection branch pipe has an air inlet (28) that connects to the nitrogen-driven chamber (21), and a telescopic section (22) is provided in the pipe section between the corresponding explosion-proof solenoid valve (13) and the directional nitrogen injection control system (8), so that the nitrogen injection branch pipe has a telescopic range that can move axially relative to the protective pipe shell (3); The inner wall of the rotary positioning and interface unit (20) is provided with three mechanical limit stops (23), the circumferential azimuth angles of the three mechanical limit stops (23) are 0°, 45° and 90° respectively, and they are staggered along the axial direction; The protective casing (3) of the nitrogen injection branch pipeline (2) is provided with three rows of fixed nitrogen injection holes along its axial direction, and the three rows of fixed nitrogen injection holes are located on its two sides and the top end respectively; The nitrogen injection branch pipe is provided with multiple circles of movable nitrogen injection holes along its axial direction. Each circle of movable nitrogen injection holes includes three circumferentially arranged movable nitrogen injection holes, which are respectively located on both sides and the upper end of the nitrogen injection branch pipe. A mechanical limit block (24) capable of abutting against the mechanical limit stop point (23) is further provided on the outer circle of the nitrogen injection branch pipe; The rotation positioning and interface unit (20) is equipped with a rotation motor, which can drive the rotation positioning and interface unit (20) to rotate around the corresponding nitrogen injection branch pipe, so as to drive the rotation positioning and interface unit (20) to rotate to a predetermined angle, making the mechanical limit block (24) correspond to the path of a certain mechanical limit stop point (23); A return spring (25) is arranged along the axial direction in the spring return chamber (19). When injecting nitrogen, the gas enters the nitrogen driving chamber (21), acts on the rear end face of the annular piston (27), and pushes the annular piston (27) and the nitrogen injection branch pipe fixedly connected thereto to move forward against the resistance of the return spring (25) until the mechanical limit block (24) abuts against the mechanical limit stop point (23); When the mechanical limit block (24) abuts against the mechanical limit stop point (23) with a circumferential azimuth angle of 0°, the movable nitrogen injection holes on the nitrogen injection branch pipe are exactly aligned and communicated with a row of fixed nitrogen injection holes on the left side of the protection pipe shell (3); when the mechanical limit block (24) abuts against the mechanical limit stop point (23) with a circumferential azimuth angle of 45°, the movable nitrogen injection holes on the nitrogen injection branch pipe are exactly aligned and communicated with a row of fixed nitrogen injection holes on the upper end of the protection pipe shell (3); when the mechanical limit block (24) abuts against the mechanical limit stop point (23) with a circumferential azimuth angle of 90°, the movable nitrogen injection holes on the nitrogen injection branch pipe are exactly aligned and communicated with a row of fixed nitrogen injection holes on the right side of the protection pipe shell (3).

4. The fire prevention, extinguishing, and heat recovery system for goaf areas based on distributed temperature-measuring optical fibers according to claim 1, characterized in that: The nitrogen injection pipeline (4), the water passing pipeline (5) and the optical fiber pipeline (6) in the protection pipe shell (3) are arranged in a "pin" shape.

5. The fire prevention, extinguishing, and heat recovery system for goaf areas based on distributed temperature-measuring optical fibers according to claim 1, characterized in that: The temperature measurement optical fiber is an armored sensing optical fiber, and the temperature measurement optical fiber is laid along the axial direction of the optical fiber pipeline (6) and is arranged closely against the inner side of the pipe wall.

6. The fire prevention, extinguishing, and heat recovery system for goaf areas based on distributed temperature-measuring optical fibers according to claim 1, characterized in that: The nitrogen injection pipeline (4) and the water passing pipeline (5) are both metal pipes. The diameter of the nitrogen injection hole is 10 mm. The inner diameter of the protection pipe shell (3) is 100 - 160 mm. The optical fiber pipeline (6) and the water passing pipeline (5) independently arranged are both sleeved with the protection pipe shell (3) outside.

7. A method for fire prevention, extinguishing, and heat recovery in goaf areas based on distributed temperature-sensing optical fibers, characterized in that, Including the goaf fire prevention and heat recovery system based on distributed temperature measurement optical fiber according to any one of claims 1 - 6, the following steps are further included: Step 1. Threshold setting and normal monitoring; Set the nitrogen injection trigger temperature threshold and the temperature change rate warning value in the control unit of the optical fiber demodulator (10). The system is in the real-time monitoring mode. The optical fiber demodulator (10) continuously emits laser pulses to the sensing optical fiber and receives the backscattered light signal. By analyzing the Raman scattering light intensity ratio and the optical time domain information, the temperature of each point on the path where the optical fiber pipeline is laid in the goaf and its change trend are calculated and recorded in real time, and the position of the measurement point is accurately located, and a digital twin model is established in the computer control system (14); Step 2. Early warning and automatic start; When the distributed optical fiber monitoring network detects that the temperature in a certain area is rising continuously and the daily temperature rise rate reaches the temperature change rate warning value, or the active temperature value exceeds the set nitrogen injection trigger temperature threshold, the computer control system (14) will determine that there is a risk of spontaneous combustion in the area and display the location of the high temperature point in the digital twin model, and at the same time start the nitrogen injection fire prevention and extinguishing system and the waste heat circulation and recovery system. Step 3: The gas and water circuits will automatically open; The computer control system (14) sends an opening command to the explosion-proof solenoid valve (13) in the area corresponding to the hazard. The explosion-proof solenoid valve (13) opens, and the nitrogen injection branch pipe in the area is connected to the nitrogen injection main pipe. The water pipe (5) of the nitrogen injection branch pipe (2) is connected to the water pipe (5) in the nitrogen injection main pipe (1). The nitrogen source switch valve and the water pump (12) switch valve start at the same time. Nitrogen enters the nitrogen injection pipe (4), and cooling water enters the water pipe (5). The explosion-proof solenoid valve (13) in the non-hazard area remains closed. When injecting nitrogen, the nitrogen injection pipe is under positive pressure. The second air path automatic switching valve (15) at the air inlet end of the nitrogen injection branch pipe opens automatically to supply nitrogen into the nitrogen injection branch pipe. The first air path automatic switching valve (7) at the air extraction end of the nitrogen injection main pipe closes automatically to prevent nitrogen from leaking from the air extraction end of the nitrogen injection main pipe. Step 4: Execute directional nitrogen injection; The computer control system (14) drives the directional nitrogen injection control system (8) at the corresponding location according to the location of the high temperature point to inject nitrogen, so that the nitrogen gas flows to the goaf through the nitrogen injection hole (9); Step 5: Inerting fire extinguishing and residual heat recovery; After nitrogen is released, it naturally rises and diffuses throughout the high-temperature area, diluting the oxygen concentration and achieving inerting for fire prevention and extinguishing. At the same time, circulating water flows through water pipes arranged near the high-temperature area, absorbing excess heat from the surrounding rock and gas in the goaf. The water temperature rises, carrying away the heat energy, achieving cooling and waste heat recovery. Step Six: Nitrogen injection completed and system reset; When the distributed temperature measurement fiber optic network detects that the temperature in the risk area continues to drop and stabilizes below the safety threshold, the following shutdown procedures will be executed sequentially: 1) Close the nitrogen source switch valve and the water pump (12) switch valve; 2) Close the explosion-proof solenoid valve (13) to cut off the gas and water circuits; 3) Reset the directional nitrogen injection control system (8); 4) All system components are restored to standby monitoring state, awaiting the next warning; Step 7: Loop monitoring and closed-loop control; After the system is reset, the distributed temperature measurement fiber optic network continues to monitor the temperature of the goaf around the clock, forming an intelligent closed-loop control of "monitoring-early warning-directional nitrogen injection and cooling-effect evaluation-system reset".

8. The method for fire prevention, extinguishing, and heat recovery in goaf areas based on distributed temperature-sensing optical fibers according to claim 7, characterized in that: In step four, the working steps of the directional nitrogen injection control system (8) are as follows: the rotary motor drives the rotary positioning and interface unit (20) of the corresponding nitrogen injection branch pipe (2) to rotate to a predetermined angle, so that the mechanical limit block (24) enters the corresponding limit path; nitrogen gas rushes into the nitrogen gas drive chamber (21), pushing the annular piston (27) and the nitrogen injection branch pipe fixed thereto to overcome the resistance of the reset spring (25) and move forward until the mechanical limit block (24) abuts against the corresponding mechanical limit stop (23), so that the movable nitrogen injection hole on the nitrogen injection branch pipe is aligned and connected with the fixed nitrogen injection hole in the corresponding direction on the protective shell (3).

9. The method for fire prevention, extinguishing, and heat recovery in goaf areas based on distributed temperature-sensing optical fibers according to claim 7, characterized in that: The warning value for the rate of temperature change is a daily temperature increase of 5-10℃.

10. The method for fire prevention, extinguishing, and heat recovery in goaf areas based on distributed temperature-measuring optical fibers according to claim 7, characterized in that: It also includes an air pump. The nitrogen injection main pipe has a branch at its outer end, and the air pump is connected to the branch. When it is necessary to sample the gas in the goaf, the nitrogen source switch valve is closed and the air pump switch valve is opened. Under the action of the air pump, the nitrogen injection pipeline is under negative pressure. The sliding valve plate (18) in the first gas path automatic switching valve (7) slides to the side of the opening valve plate (16) until it is in contact with the opening valve plate (16), so that the first gas path automatic switching valve (7) is automatically opened, thereby realizing the extraction of gas in the goaf. At the same time, the second gas path automatic switching valve (15) at the air inlet end of the nitrogen injection branch pipe is automatically closed under negative pressure to prevent the nitrogen in the nitrogen injection branch pipe from flowing back and affecting the composition of the gas extracted from the goaf. Finally, by analyzing the gas composition and concentration distribution in the goaf, the air leakage channel and collapse situation in the goaf are inverted, and the ventilation system is optimized.

Images