A concealed fire source prevention device and method

Abstract

This invention discloses a concealed fire source control device, comprising a seamless steel pipe, a liquid CO₂ storage tank, a foaming material storage tank, and a stabilizer storage tank. The seamless steel pipe has an application port at its end and a self-activating foam head inside. One end of the self-activating foam head has a curved pipe section. The curved pipe section is connected to the liquid CO₂ storage tank and the stabilizer storage tank via a liquid CO₂ delivery pipe and an injection pipe. A phase change control unit and a static mixing device are sequentially installed on the liquid CO₂ delivery pipe. The static mixing device is connected to the foaming material storage tank via an injection pipe. The concealed fire source control device also includes a foam structure monitoring module, a fire zone control effect monitoring module, and a ground monitoring center. The concealed fire source control method includes: drilling, CO₂ delivery and phase change, mixing and foaming, foaming and control, and monitoring and feedback. This invention can achieve efficient coverage and cooling of concealed fire sources, filling coal fissures, isolating air, and inhibiting coal oxidation and reignition.

Description

Technical Field

[0001] This invention belongs to the field of underground coal mine safety technology, specifically relating to a concealed fire source prevention device and method. Background Technology

[0002] Hidden ignition sources pose a significant threat to mine safety during coal mining. Their formation is primarily caused by spontaneous combustion of coal and oxidation of coal remaining in goaf areas. After mining, coal left in goaf areas undergoes slow oxidation under suitable temperature, humidity, and ventilation conditions. If the heat cannot be dissipated in time, it will spontaneously combust when the temperature reaches the coal's ignition point, forming a hidden ignition source.

[0003] Traditional methods for controlling concealed fire sources have many shortcomings. For example, water injection is limited by water's permeability; for deep fire sources or those obstructed by fissures, water cannot effectively reach the fire source. Grouting, while covering a certain area, may not completely fill the ignition path of highly concealed fire sources and can easily pollute the underground environment. Chemical extinguishing agents are costly and may have adverse effects on the underground environment and personnel health. Furthermore, these traditional methods have limited effectiveness in extinguishing fires in complex geological conditions and concealed fire sources whose locations are difficult to determine, thus failing to effectively ensure safe production in coal mines. Summary of the Invention

[0004] The purpose of this invention is to provide a concealed fire source prevention device and method, which can achieve efficient covering and cooling of concealed fire sources, filling of coal body fissures, blocking air, and inhibiting coal oxidation and reignition.

[0005] To achieve the above objectives, the present invention provides a concealed fire source prevention device, comprising a seamless steel pipe, a liquid CO2 storage tank, a foaming material storage tank, and a stabilizer storage tank. The liquid CO2 storage tank, the foaming material storage tank, and the stabilizer storage tank are arranged on the outer side of the front end of the seamless steel pipe. An application port is provided at the end of the seamless steel pipe. A self-activating foam head is provided inside the seamless steel pipe near the application port. A curved pipe section is provided at the end of the self-activating foam head away from the application port.

[0006] The curved section of the pipeline is connected to the liquid CO2 storage tank via a liquid CO2 delivery pipeline. The liquid CO2 delivery pipeline, located inside the seamless steel pipe, is equipped with a phase change control unit and a static mixing device in sequence facing the application port. The static mixing device is connected to the foaming material storage tank via an injection pipeline, and an injection pump is installed on the injection pipeline.

[0007] A stabilizer inlet is provided at the connection between the front end of the curved pipe section and the liquid CO2 delivery pipe, and it is connected to the stabilizer storage tank through an injection pipe. A micro injection pump is provided on the injection pipe.

[0008] Concealed fire source prevention devices also include:

[0009] A cell structure monitoring module is used to monitor the stability of the cell structure during the foaming process.

[0010] The fire prevention and control effect monitoring module is used to monitor downhole temperature and gas concentration information;

[0011] The ground monitoring center is used to receive feedback information from the bubble structure monitoring module and the fire zone prevention and control effect monitoring module for centralized control or alarm.

[0012] As a further aspect of the present invention: the phase change control unit includes a pressure regulating unit and a temperature regulating unit. The pressure regulating unit along the fluid transport direction includes a pressure pump, a regulating valve and a pressure sensor arranged in sequence. The temperature regulating unit is located after the pressure regulating unit along the fluid transport direction and includes a heating device, a cooling device and a phase change temperature sensor.

[0013] As a further aspect of the present invention: both the liquid CO2 storage tank and the foaming material storage tank are equipped with level gauges, the liquid CO2 storage tank is also equipped with a pressure gauge and a safety valve, the foaming material storage tank is equipped with a stirring device, and the top of the foaming material storage tank is equipped with a feeding port with a sealing cap.

[0014] As a further aspect of the present invention: the liquid CO2 conveying pipeline adopts a multi-layer composite structure, including an outer anti-corrosion and pressure-resistant protective layer, a middle insulation layer and an inner low-temperature and chemical corrosion resistant material layer. The pipelines are connected by a combination of flanges and gaskets, and fixed by supports and hangers. The connection part is provided with expansion and contraction allowance.

[0015] As a further aspect of the present invention: the static mixing device is equipped with twisted blades or spiral blades for achieving rapid and uniform mixing of multiple fluids.

[0016] As a further aspect of the present invention, the cell structure monitoring module acquires cell structure information using at least one of microstructure monitoring, physical property monitoring, and optical monitoring.

[0017] A method for preventing concealed fire sources, based on the aforementioned concealed fire source prevention device, includes:

[0018] A borehole layout system is used to plan and construct boreholes based on underground geological conditions and suspected concealed fire sources in coal mines, so that the boreholes can reach the target area.

[0019] CO2 delivery and phase change control system, including liquid CO2 storage tank, liquid CO2 delivery pipeline and phase change control unit; used to deliver liquid CO2 to the end of the borehole and control its phase change to generate an impact effect;

[0020] A foaming material injection system includes foaming material, a foaming material storage tank, an injection pump, an injection pipeline, a nucleating agent, a micro-injection pump, and an injection pipeline; it is used to inject foaming material into the end of a borehole, wherein the foaming material is mixed with supercritical CO2 formed by phase change of liquid CO2 in a static mixing device and then enters the environmental coal body through a self-excited foaming head;

[0021] The monitoring and feedback system includes a cell structure monitoring module and a fire zone prevention effect monitoring module. The cell structure monitoring module is used to monitor the stability of the cell structure during the foaming process. The fire zone prevention effect monitoring module is used to monitor downhole temperature and gas concentration information. Based on the monitoring data, the system controls the liquid CO2 delivery rate, phase change conditions, foaming material, nucleating agent, and stabilizer injection rate.

[0022] The specific steps are as follows:

[0023] Drilling operations: Drilling is carried out using downhole drilling equipment according to the designed drilling layout plan. The drilling direction, depth and geological conditions are monitored in real time to ensure that the drilling accurately reaches the vicinity of the target area.

[0024] CO2 transport and phase change: Liquid CO2 is delivered to the end of the borehole through a liquid CO2 transport pipeline. The phase change control unit adjusts the pressure and temperature parameters to cause the liquid CO2 to undergo a phase change, thus obtaining supercritical CO2.

[0025] Mixed foaming: Under the action of the injection pump, the foaming material and nucleating agent flow through the injection pipeline to the static mixing device at the end of the borehole, where they are mixed with supercritical CO2 after being regulated by the phase change control unit to form a homogeneous system of foaming material / supercritical CO2. This homogeneous system continues to flow along the pipeline to the application port and the high-temperature and low-pressure coal body.

[0026] Foaming and Prevention: Due to changes in the self-activated foaming head, application port, and the temperature and pressure environment of the coal body itself, the foaming material / supercritical CO2 homogeneous system will undergo a phase change again or maintain a supercritical state. That is, some supercritical CO2 phase change impact foaming promotes the formation of cell structure. The foamed material directly reduces the temperature of the fire zone. The other part of the foaming material / supercritical CO2 system that has not undergone phase change directly enters the environmental coal body. Supercritical CO2 rapidly penetrates into the cracks and pores of the coal body with its own molecular motion ability, and at the same time, it also carries the foaming material into these parts. Finally, the phase change impact increases the pores, and the foaming material fills the cracks and pores of the coal body, isolating air and preventing coal oxidation to achieve the purpose of preventing hidden fire sources.

[0027] Monitoring and Feedback: The phase change control unit uses phase change temperature and pressure sensors to monitor the temperature and pressure of liquid CO2 in real time for adjustment. The cell structure monitoring module monitors the cell structure formation during foaming in real time to precisely control the addition of stabilizer via a micro-injection pump. The fire prevention effect monitoring module uses borehole temperature and gas concentration sensors installed in the coal body around the borehole end to monitor changes in borehole ambient temperature and various gas concentration parameters in real time, reflecting the combustion and extinguishing status of concealed fire sources. Based on the monitoring data, the prevention effect is evaluated, and alarms or adjustments are made as needed to the liquid CO2 delivery rate, phase change conditions, foaming materials, nucleating agents, and stabilizer injection amounts.

[0028] As a further embodiment of the present invention: the foaming material is one of the following: a polyurethane foaming material containing ammonium polyphosphate flame retardant, a phenolic foaming material composed of melamine pyrophosphate and pentaerythritol, and an expandable graphite composite melamine foaming material.

[0029] As a further aspect of the present invention: the nucleating agent is premixed with the foaming material or added directly and stirred evenly by a stirring device.

[0030] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0031] (1) Fire extinguishing efficiency:

[0032] This invention utilizes the impact force generated by the phase change of liquid CO2 to rapidly foam the material and propel it deep into the concealed fire source. The resulting foamed system quickly lowers the temperature of the fire zone, forming a stable fire barrier while simultaneously filling the pores of the coal and isolating it from air. Compared to traditional methods, this approach more quickly stops the spread of fire and effectively inhibits reignition.

[0033] (2) Adaptability to complex environments:

[0034] With a precise borehole layout system, the position, angle and depth of the boreholes can be flexibly adjusted according to different geological conditions (such as faults, folds, roofs and floors of different rock types) and the characteristics of suspected concealed fire sources, so as to achieve coverage of various complex downhole environments.

[0035] The CO2 delivery and phase change control system can adapt to complex downhole environments and achieve stable phase change of liquid CO2. Moreover, the foaming material injection system can effectively foam and function in complex geological structures, such as easily fractured roofs and karst areas, according to different geological stress conditions and coal seam fracture characteristics.

[0036] (3) Environmental protection and safety aspects:

[0037] The liquid CO2 used in this invention is an environmentally friendly substance that is non-toxic and harmless, and will not pollute the underground environment. The selected foaming material has also been carefully designed to prevent the generation of harmful substances during use.

[0038] Throughout the entire fire prevention and control process, the monitoring and feedback system monitors underground environmental parameters in real time to ensure the safety of the operation and prevent new safety hazards such as explosions or poisoning from arising during the fire prevention process itself. Furthermore, the materials do not cause long-term pollution to underground air or water resources after extinguishing the fire. They effectively cover and cool concealed fire sources, fill coal fissures, isolate air, and inhibit coal oxidation and reignition, expanding new approaches to the precise control of fire sources in large, concealed underground areas. Attached Figure Description

[0039] Figure 1 This is a schematic diagram of the concealed fire source prevention device of the present invention;

[0040] Figure 2 A schematic diagram for concealing fire sources.

[0041] In the diagram: 1. Seamless steel pipe, 2. Injection pipe, 3. Micro-injection pump, 4. Stabilizer storage tank, 5. Foaming material storage tank, 6. Feed port, 7. Nucleating agent, 8. Stirring device, 9. Injection pipe, 10. Injection pump, 11. Pressure gauge, 12. Safety valve, 13. Level gauge, 14. Liquid CO2 storage tank, 15. Liquid CO2 delivery pipe, 16. Phase change control unit, 17. Pressure pump, 18. Regulating valve, 19. Pressure sensor, 20. Heating device, 21. Phase change temperature sensor, 22. Cooling device, 23. Static mixing device, 24. Stabilizer inlet, 25. Bend section, 26. Self-generating foam head, 27. Application port, 28. Physical property monitoring module, 29. Optical monitoring module. Detailed Implementation

[0042] The present invention will be further illustrated by the following examples.

[0043] like Figure 1 As shown, a concealed fire source prevention device includes a seamless steel pipe 1, a liquid CO2 storage tank 14, a foaming material storage tank 5, and a stabilizer storage tank 4. The liquid CO2 storage tank 14, the foaming material storage tank 5, and the stabilizer storage tank 4 are arranged on the outer side of the front end of the seamless steel pipe 1. An application port 27 is provided at the end of the seamless steel pipe 1. A self-activated foam head 26 is provided inside the seamless steel pipe 1 near the application port 27. A bent pipe section 25 is provided at the end of the self-activated foam head 26 away from the application port 27.

[0044] The curved pipe section 25 is connected to the liquid CO2 storage tank 14 through the liquid CO2 conveying pipe 15. The liquid CO2 conveying pipe 15 located inside the seamless steel pipe 1 is provided with a phase change control unit 16 and a static mixing device 23 in sequence facing the application port 27. The static mixing device 23 is connected to the foaming material storage tank 5 through the injection pipe 9. An injection pump 10 is provided on the injection pipe 9.

[0045] The injection pump 10 is a screw pump or a plunger pump, and the injection pipe 9 is made of high-pressure resistant and corrosion-resistant material with an inner diameter of 30-120 mm.

[0046] A stabilizer inlet 24 is located at the connection point between the bend in the pipe section 25 and the liquid CO2 delivery pipe 15. This inlet is connected to the stabilizer storage tank 4 via an injection pipe 2, which is equipped with a micro-injection pump 3. The micro-injection pump 3 and the injection pipe 2 uniformly add the stabilizer, in solution or dispersion form, to the foaming system through the stabilizer inlet 24. The location of the stabilizer inlet 24 ensures that the stabilizer can take effect immediately upon detection of a problem. Different response strategies are developed based on the degree of instability; for example, for mild instability, the amount of stabilizer added can be appropriately increased; for moderate instability... In addition to increasing the amount of stabilizer added, the injection rate of the foaming material can be slightly reduced. For severely unstable foaming materials, it may be necessary to pause the injection of foaming material, adjust the amount of stabilizer added and other relevant parameters, and continue the foaming process after the cell structure stabilizes. The micro-injection pump 3 has a precise flow control function, which can accurately inject the stabilizer solution or dispersion into the impact foaming system according to the preset addition amount and frequency. The micro-injection pump 3 is designed as an integral part of the foaming material injection pump 10. The injection pipe 2 is suspended above the injection pipe 9 and is detachable, with an inner diameter of 10-20 mm.

[0047] Concealed fire source prevention devices also include:

[0048] A cell structure monitoring module is used to monitor the stability of the cell structure during the foaming process.

[0049] The fire prevention and control effect monitoring module is used to monitor downhole temperature and gas concentration information;

[0050] The ground monitoring center is used to receive feedback information from the bubble structure monitoring module and the fire zone prevention and control effect monitoring module for centralized control or alarm.

[0051] Furthermore, the phase change control unit 16 includes a pressure regulating unit and a temperature regulating unit. The pressure regulating unit along the fluid transport direction includes a pressure pump 17, a regulating valve 18, and a pressure sensor 19 arranged in sequence. The temperature regulating unit is located after the pressure regulating unit along the fluid transport direction and includes a heating device 20, a cooling device 22, and a phase change temperature sensor 21.

[0052] The temperature control unit, based on the principle of heat exchange, regulates the CO2 temperature at the borehole tip via heating device 20 or cooling device 22. The pressure control unit controls the CO2 pressure via pressure sensor 19, regulating valve 18, and pressure pump 17, ensuring stable phase change of CO2 at the borehole tip. The pressure pump 17 is a piston-type or diaphragm-type booster pump with a booster ratio of 1.5-5 times. The booster equipment activates when the pressure falls below the required supercritical pressure of 7.38 MPa. The pressure sensor 19 is a high-precision piezoresistive type with an accuracy of ±0.01 MPa, enabling pressure monitoring.

[0053] The heating device 20 can employ electric heating wires, evenly covering the bottom and front walls of the heating tank surrounding the liquid CO2 delivery pipeline 15. Temperature is regulated by controlling power. Alternatively, a hot oil circulation heating system can be used, where hot oil flows through a heat exchanger in the pipeline wall for heat transfer. The cooling device 22 can utilize a liquid nitrogen or cold water circulation system. Liquid nitrogen vaporizes and absorbs heat, or cold water flows through cooling coils and removes heat, evenly covering the top and rear walls of the heating tank. When CO2 needs to transition to a supercritical state, the heating device 20 is activated to raise the temperature to over 31.1°C. The power of the heating device 20 is precisely adjusted between 1 and 10 kW according to the CO2 flow rate and phase change requirements. A phase change temperature sensor 21 is installed after the heating device 20 or cooling device 22, with an accuracy of ±0.1°C. It monitors the CO2 temperature in real time and feeds back the signal to the control system to automatically adjust the operation of the heating or cooling device 22.

[0054] To achieve stable delivery control, both the liquid CO2 storage tank 14 and the foaming material storage tank 5 are equipped with level gauges 13. The liquid CO2 storage tank 14 is also equipped with a pressure gauge 11 and a safety valve 12. The foaming material storage tank 5 is equipped with a stirring device 8, and its top has a filling port 6 with a sealed cap. The liquid CO2 storage tank 14 is made of high-strength, high-pressure resistant, and low-temperature resistant metal. Its shape can be cylindrical or spherical, and its design conforms to pressure vessel standards. Its volume depends on the extent and scale of the concealed ignition source being treated. The level gauges 13 on the liquid CO2 storage tank 14 employ high-precision ultrasonic and radar level gauges. The safety valve 12 opens at a pressure slightly higher than the normal operating pressure to prevent overpressure explosion of the storage tank. The foam material storage tank 5 is made of corrosion-resistant material, and its volume needs to be determined according to the range and scale of the concealed fire source being treated; the stirring device 8 adopts a double-layer inclined blade turbine stirring blade, and the speed can be adjusted between 10-100 rpm to prevent the foam material from settling or separating; the liquid level gauge 13 on the foam material storage tank 5 adopts a glass tube liquid level gauge or a magnetic float liquid level gauge.

[0055] Furthermore, the liquid CO2 conveying pipeline 15 is a seamless steel pipe 1 made of high-quality carbon steel or alloy steel that is resistant to low temperature and high pressure, with an inner diameter of 20-100 mm. It adopts a multi-layer composite structure, including an outer anti-corrosion and pressure-resistant protective layer coated with epoxy coal tar paint or polyethylene coating, an intermediate insulation layer made of polyurethane foam or rock wool, and an inner layer of low-temperature and chemical corrosion resistant material made of polytetrafluoroethylene or stainless steel lined. The pipelines are connected by flanges and gaskets and fixed by supports and hangers. The connection part has a flexibility, which is achieved by metal bellows or spring-type expansion joints, with a flexibility of 5-20 mm.

[0056] Furthermore, the static mixing device 23 is equipped with twisted blades or spiral blades for achieving rapid and uniform mixing of multiple fluids.

[0057] Furthermore, the cell structure monitoring module acquires cell structure information using at least one of physical property monitoring and optical monitoring methods.

[0058] The physical property monitoring module 28 inserts viscosity and density sensors into the foamed material to measure the viscosity and density values ​​of the foamed material in real time. When abnormal changes occur in the viscosity value or abnormal fluctuations occur in the density, it is determined that the cell structure may be unstable.

[0059] The optical monitoring module 29 is equipped with a light emitting and detection device around the foaming container or pipe. It emits light into the foaming material and obtains information about the cell structure by detecting parameters such as the intensity and angle of the scattered light. When abnormal changes in the light scattering parameters are detected, it indicates that the cell structure may be unstable.

[0060] A method for preventing concealed fire sources, based on the aforementioned concealed fire source prevention device, includes:

[0061] A borehole layout system is used to plan and construct boreholes based on underground geological conditions and suspected concealed fire sources in coal mines, so that the boreholes can reach the target area.

[0062] The CO2 delivery and phase change control system includes a liquid CO2 storage tank 14, a liquid CO2 delivery pipeline 15, and a phase change control unit 16; the phase change control unit 16 is used to deliver liquid CO2 to the end of the borehole and control its phase change to generate an impact effect.

[0063] The foaming material injection system includes foaming material, foaming material storage tank 5, injection pump 10, injection pipe 9, nucleating agent 7, micro-injection pump 3 and injection pipe 2; it is used to inject foaming material into the end of the borehole. The foaming material is mixed with supercritical CO2 formed by phase change of liquid CO2 in a static mixing device 23 and then enters the environmental coal body through a self-excited foaming head 26.

[0064] The monitoring and feedback system includes a cell structure monitoring module and a fire zone prevention effect monitoring module. The cell structure monitoring module is used to monitor the stability of the cell structure during the foaming process. The fire zone prevention effect monitoring module is used to monitor downhole temperature and gas concentration information. Based on the monitoring data, the system controls the liquid CO2 delivery rate, phase change conditions, foaming materials, nucleating agent 7, and stabilizer injection rate.

[0065] The specific steps are as follows:

[0066] Drilling Construction: Drilling is carried out using downhole drilling equipment according to the designed drilling layout plan. The drilling direction, depth, and geological conditions are monitored in real time to ensure accurate drilling to the vicinity of the target area. The drilling layout plan is a drilling network plan based on the obtained geological conditions. Geological conditions include the detection and identification of coal seam parameters (thickness, dip angle, hardness), roof and floor lithology, and geological structures (faults, folds, etc.). Combined with temperature monitoring and gas composition analysis, suspected concealed ignition sources are identified. The drilling network plan uses modeling technology to draw the drilling positions, angles, and depths, forming a three-dimensional coverage network. For example, around goaf areas, the drilling is arranged in a fan-shaped or checkerboard pattern. The drilling equipment should be designed to cover areas where hidden fire sources may exist; high-performance drilling equipment suitable for underground operations, such as tunnel drilling rigs for coal mines, should be selected; during construction, drilling parameters such as drilling pressure, rotation speed, and flushing fluid flow rate should be adjusted according to different rock strata properties; for rock strata with high hardness, drilling pressure should be increased appropriately, rotation speed should be reduced, and suitable drill bits, including diamond drill bits and carbide drill bits, should be selected; the borehole deviation should be monitored in real time, and data should be fed back through the inclination meter installed on the drill rod. If the deviation exceeds the range, the drilling direction should be adjusted in time; at the same time, mud wall protection or casing wall protection methods should be used to prevent borehole collapse. For deeper boreholes, segmented drilling and segmented wall protection measures should be adopted.

[0067] CO2 Transport and Phase Change: Liquid CO2 is delivered to the end of the borehole through the liquid CO2 transport pipeline 15. The phase change control unit 16 adjusts the pressure and temperature parameters to cause the liquid CO2 to undergo a phase change, resulting in supercritical CO2 with high diffusivity and solubility. It can quickly diffuse into foaming materials and penetrate into the cracks and pores of the coal body. Phase change conditions: When the temperature is higher than 31.1℃ and the pressure is higher than 7.38MPa, it becomes supercritical and CO2 undergoes a phase change.

[0068] Mixed foaming: Under the action of injection pump 10, foaming material and nucleating agent 7 flow through injection pipe 9 to static mixing device 23 at the end of borehole, and mix with supercritical CO2 after being regulated by phase change control unit 16. During the mixing process, CO2, with its high diffusivity and solubility in supercritical state, mixes quickly, uniformly and fully with foaming material to form a homogeneous system of foaming material / supercritical CO2. This homogeneous system continues to flow along the pipe to application port 27 and high temperature and low pressure coal body.

[0069] Foaming and Prevention: Due to changes in the self-activated foam head 26, application port 27, and the temperature and pressure environment of the coal body itself, the foaming material / supercritical CO2 homogeneous system will undergo another phase transition or maintain a supercritical state. This manifests as a partial disruption of thermodynamic stability, prompting phase separation in the system. CO2 is released, forming gas nuclei, and the nucleating agent 7 begins to function, providing core sites. CO2 gas in the system begins to diffuse into the gas nuclei, causing them to grow continuously. This is partly due to the supercritical CO2 phase transition impact foaming, promoting the formation of a pore structure. The foamed material directly lowers the temperature of the fire zone. The other part of the foaming material / supercritical CO2 system that has not undergone phase transition directly enters the environmental coal body. Supercritical CO2, with its own molecular motion, rapidly penetrates into the cracks and pores of the coal body, simultaneously carrying the foaming material into these areas. Ultimately, the phase transition impact increases the porosity, causing the foaming material to fill the cracks and pores of the coal body, isolating air and preventing coal oxidation, thus achieving the purpose of preventing hidden fire sources. The implementation effect is as follows: Figure 2 As shown;

[0070] Monitoring and Feedback: The phase change temperature sensor 21 and pressure sensor 19 in the phase change control unit 16 monitor the temperature and pressure of liquid CO2 in the phase change control unit 16 in real time for adjustment; the cell structure monitoring module monitors the state of the cell structure formed during the foaming process in real time, so as to precisely control the addition of stabilizer through the micro-injection pump 3 to prevent phenomena such as bubble merging, rupture or collapse, ensuring the smooth progress of the foaming process and improving the effect of foamed material on concealed fire source prevention; the fire zone prevention effect monitoring module sets a borehole temperature sensor and a gas concentration sensor in the coal body around the borehole end. The borehole temperature sensor is a thermocouple or thermistor type, with a measurement range of -20℃ to 150℃. At 0℃, with an accuracy of ±0.5℃; the gas concentration sensors include an infrared absorption CO2 concentration sensor, a laser oxygen concentration sensor, and a laser carbon monoxide concentration sensor, possessing corresponding high-precision measurement capabilities. The CO2 concentration accuracy reaches ±0.01%, the oxygen concentration accuracy reaches ±0.1%, and the carbon monoxide concentration accuracy reaches ±0.1ppm. This enables real-time monitoring and feedback of fire zone combustion and extinguishing, real-time monitoring of borehole ambient temperature and changes in various gas concentration parameters, reflecting the combustion and extinguishing status of concealed fire sources, evaluating the prevention and control effect based on monitoring data feedback, and, when necessary, alarming or adjusting the liquid CO2 delivery rate, phase change conditions, foaming material, nucleating agent 7, and stabilizer injection amount.

[0071] Furthermore, the foaming material is one of the following: polyurethane foaming material containing ammonium polyphosphate flame retardant, phenolic foaming material composed of melamine pyrophosphate and pentaerythritol, and expandable graphite composite melamine foaming material.

[0072] Polyurethane foam containing ammonium polyphosphate flame retardant, in which ammonium polyphosphate decomposes when heated to produce substances such as phosphoric acid and ammonia, which promotes the dehydration and carbonization of polyurethane material to form a porous carbonaceous foam layer, and ammonia dilutes the oxygen concentration.

[0073] Phenolic foaming material composed of melamine pyrophosphate and pentaerythritol. At high temperature, melamine pyrophosphate decomposes to produce phosphoric acid and melamine, etc. Phosphoric acid catalyzes the carbonization reaction of phenolic resin, and together with pentaerythritol promotes the formation of an expanded carbon layer.

[0074] Expandable graphite composite melamine foam material: at high temperatures, expandable graphite rapidly expands to form a worm-like carbonaceous structure, creating a multi-layered heat insulation and oxygen barrier inside the foam material. Melamine releases nitrogen gas, further reducing the oxygen concentration.

[0075] Furthermore, the nucleating agent 7 is premixed with the foaming material or added directly and stirred evenly by the stirring device 8.

[0076] This invention integrates drilling, conveying, injection, and monitoring into a concealed fire source prevention technology, consisting of four parts: a drilling layout system, a CO2 delivery and phase change control system, a foaming material injection system, and a monitoring and feedback system.

Claims

1. A concealed fire source prevention method, based on a concealed fire source prevention device, the concealed fire source prevention device including a seamless steel pipe (1), a liquid CO2 storage tank (14), a foaming material storage tank (5) and a stabilizer storage tank (4), the liquid CO2 storage tank (14), the foaming material storage tank (5) and the stabilizer storage tank (4) are arranged on the outer side of the front end of the seamless steel pipe (1), the end of the seamless steel pipe (1) is provided with an application port (27), a self-initiating foam head (26) is provided inside the seamless steel pipe (1) near the application port (27), and a bent pipe section (25) is provided at the end of the self-initiating foam head (26) away from the application port (27). The curved pipe section (25) is connected to the liquid CO2 storage tank (14) through the liquid CO2 conveying pipe (15). The liquid CO2 conveying pipe (15) located in the seamless steel pipe (1) is provided with a phase change control unit (16) and a static mixing device (23) in sequence facing the application port (27). The static mixing device (23) is connected to the foaming material storage tank (5) through the injection pipe (9). An injection pump (10) is provided on the injection pipe (9). A stabilizer inlet (24) is provided at the connection between the front end of the curved pipe section (25) and the liquid CO2 conveying pipe (15), and is connected to the stabilizer storage tank (4) through the injection pipe (2). A micro injection pump (3) is provided on the injection pipe (2). Concealed fire source prevention devices also include: A cell structure monitoring module is used to monitor the stability of the cell structure during the foaming process. The fire prevention and control effect monitoring module is used to monitor downhole temperature and gas concentration information; The ground monitoring center is used to receive feedback information from the bubble structure monitoring module and the fire zone prevention and control effect monitoring module for centralized control or alarm. Its characteristic is that the concealed fire source prevention method includes: A borehole layout system is used to plan and construct boreholes based on underground geological conditions and suspected concealed fire sources in coal mines, so that the boreholes can reach the target area. CO2 transport and phase change control system, including liquid CO2 storage tank (14), liquid CO2 transport pipeline (15) and phase change control unit (16); the phase change control unit (16) is used to transport liquid CO2 to the end of the borehole and control its phase change to generate an impact effect; The foaming material injection system includes foaming material, foaming material storage tank (5), injection pump (10), injection pipe (9), nucleating agent (7), micro-injection pump (3) and injection pipe (2); used to inject foaming material into the end of the borehole, which is mixed with supercritical CO2 formed by phase change of liquid CO2 in a static mixing device (23) and then enters the environmental coal body through a self-excited foaming head (26); The monitoring and feedback system includes a cell structure monitoring module and a fire zone prevention and control effect monitoring module; the cell structure monitoring module is used to monitor the stability of the cell structure during the foaming process; the fire zone prevention and control effect monitoring module is used to monitor downhole temperature and gas concentration information; based on the monitoring data feedback, the liquid CO2 delivery amount, phase change conditions, foaming material, nucleating agent (7) and stabilizer injection amount are controlled; The specific steps are as follows: Drilling operations: Drilling is carried out using downhole drilling equipment according to the designed drilling layout plan. The drilling direction, depth and geological conditions are monitored in real time to ensure that the drilling accurately reaches the vicinity of the target area. CO2 transport and phase change: Liquid CO2 is transported to the end of the borehole through the liquid CO2 transport pipeline (15). The phase change control unit (16) adjusts the pressure and temperature parameters to cause the liquid CO2 to undergo a phase change, thereby obtaining supercritical CO2. Mixed foaming: Under the action of injection pump (10), foaming material and nucleating agent (7) flow through injection pipe (9) to static mixing device (23) at the end of borehole, and mix with supercritical CO2 after being regulated by phase change control unit (16) to form a homogeneous system of foaming material / supercritical CO2. This homogeneous system continues to flow along the pipe to the application port (27) and high temperature and low pressure coal body; Foaming and Prevention: Due to the self-generated foam head (26), application port (27) and the changes in temperature and pressure environment of the coal body, the foaming material / supercritical CO2 homogeneous system will undergo phase change again or maintain the supercritical state. That is, some supercritical CO2 phase change impact foaming promotes the formation of foam structure. The foamed material directly reduces the temperature of the fire zone. The other part of the foaming material / supercritical CO2 system that has not undergone phase change directly enters the environmental coal body. Supercritical CO2 quickly penetrates into the cracks and pores of the coal body by virtue of its own molecular motion ability. At the same time, it also drives the foaming material into these parts. Finally, the phase change impact increases the pores, and the foaming material fills the cracks and pores of the coal body, isolates the air, and prevents coal oxidation to achieve the purpose of preventing and controlling hidden fire sources. Monitoring and feedback: The phase change temperature sensor (21) and pressure sensor (19) in the phase change control unit (16) monitor the temperature and pressure of liquid CO2 in the phase change control unit (16) in real time so as to make adjustments; the foam structure monitoring module is used to monitor the state of the foam structure formed during the foaming process in real time so as to accurately control the addition of stabilizer through the micro injection pump (3); the fire zone prevention and control effect monitoring module is to set the borehole temperature sensor and gas concentration sensor in the coal body around the end of the borehole to monitor the changes in borehole ambient temperature and various gas concentration parameters in real time, reflect the burning and extinguishing status of the hidden fire source, evaluate the prevention and control effect based on the monitoring data feedback, and alarm or adjust the liquid CO2 delivery amount, phase change conditions, foaming material, nucleating agent (7) and stabilizer injection amount when necessary.

2. The method for preventing concealed fire sources according to claim 1, characterized in that, The phase change control unit (16) includes a pressure regulating unit and a temperature regulating unit. The pressure regulating unit along the fluid transport direction includes a pressure pump (17), a regulating valve (18), and a pressure sensor (19) arranged in sequence. The temperature regulating unit is located after the pressure regulating unit along the fluid transport direction and includes a heating device (20), a cooling device (22), and a phase change temperature sensor (21).

3. The method for preventing concealed fire sources according to claim 1, characterized in that, A level gauge (13) is installed on both the liquid CO2 storage tank (14) and the foam material storage tank (5). A pressure gauge (11) and a safety valve (12) are also installed on the liquid CO2 storage tank (14). A stirring device (8) is installed inside the foam material storage tank (5). A feeding port (6) with a sealing cap is provided at the top of the foam material storage tank (5).

4. The method for preventing concealed fire sources according to claim 1, characterized in that, The liquid CO2 transport pipeline (15) adopts a multi-layer composite structure, including an outer anti-corrosion and pressure-resistant protective layer, an intermediate insulation layer and an inner low-temperature and chemical corrosion resistant material layer. The pipelines are connected by flanges and gaskets and fixed by supports and hangers. The connection part is provided with expansion and contraction allowance.

5. The method for preventing concealed fire sources according to claim 1, characterized in that, The static mixing device (23) is equipped with twisted blades or spiral blades for achieving rapid and uniform mixing of multiple fluids.

6. The method for preventing concealed fire sources according to claim 1, characterized in that, The cell structure monitoring module acquires cell structure information using at least one of physical property monitoring and optical monitoring methods.

7. The method for preventing concealed fire sources according to claim 1, characterized in that, The foaming material is one of the following: polyurethane foaming material containing ammonium polyphosphate flame retardant, phenolic foaming material composed of melamine pyrophosphate and pentaerythritol, and expandable graphite composite melamine foaming material.

8. The method for preventing concealed fire sources according to claim 1, characterized in that, The nucleating agent (7) is mixed evenly by premixing with the foaming material or by adding it directly and by stirring with a stirring device (8).

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