Pre-disposal hierarchical prevention and control method for coal spontaneous combustion in water-draining process of overlying water-filled goaf

Abstract

This invention discloses a pre-set, phased prevention and control method for spontaneous combustion of coal in the goaf during the drainage process of overlying water-filled goaf areas. It includes a comprehensive drainage process for preventing spontaneous combustion of coal in the goaf and a multi-path inert medium co-transport technology system. Relying on three inert medium transport modes—directional transport through borehole channels, guided diffusion through fracture insertion holes, and continuous replenishment through water-filled holes—the entire process of prevention and control is completed sequentially. Before operation, inert gas boreholes are deployed at the end of the drainage boreholes to replace oxygen in the area. The nitrogen injection volume per hole is calculated by coupling the number of boreholes, elevation difference, spatial distance, and a circular control unit to estimate the water accumulation. Outward-expanding support-type directional gas injection components are deployed in the fractures. During operation, the components continuously supply nitrogen, and the negative pressure generated by the drainage draws in surrounding nitrogen into the prevention and control area. After operation, the drainage boreholes are converted into inert medium replenishment channels. Through the coordinated action of a dual-tank injection system for film formation and a pneumatic multi-stage atomization device, the support borehole walls are first stabilized, and then the inert medium is continuously replenished.

Description

Technical Field

[0001] This invention relates to the field of coal spontaneous combustion prevention technology in goaf areas, and in particular to a pre-set, phased prevention and control method for coal spontaneous combustion during the drainage process in overlying water-filled goaf areas. This method is used for phased and effective coordinated prevention and control of the risk of spontaneous combustion of residual coal in overlying goaf areas under mine drainage operation conditions. Background Technology

[0002] Currently, many mines both domestically and internationally need to drain accumulated water in the goaf area after the upper coal seam is mined through boreholes before or during the mining process to ensure safe operation. During the drainage and flow of water, due to changes in water level, spatial pressure difference, and fluid coupling, a negative pressure induced airflow, similar to a "siphon effect," is easily formed in the fracture network of the goaf area at the end of the drainage borehole. This drives outside air to continuously flow into the goaf, forming a gas inflow phenomenon centered on a low-pressure zone. This type of negative pressure induced airflow has obvious staged and unstable characteristics. In the initial stage of drainage, it manifests as local gas disturbance, but after continuous drainage and channel opening, it gradually evolves into a stable air intake channel, allowing oxygen to be transported along the fracture path to the deep coal remnant area of ​​the goaf, significantly enhancing the oxidation reaction conditions of the coal. At the same time, after the waterlogged coal undergoes a drying process, its pore structure and active groups change, further increasing its spontaneous combustion sensitivity. Under negative pressure induced oxygen supply conditions, it is more prone to low-temperature oxidation heat accumulation, thereby inducing spontaneous combustion disasters.

[0003] To mitigate the risk of spontaneous combustion of residual coal in goaf areas caused by negative pressure-induced oxygen supply during water drainage, existing methods primarily rely on a single transport path for inerting medium injection, lacking the coordinated utilization of borehole channels, fracture spaces, and multi-source gas flow channels within the goaf. Furthermore, current nitrogen injection processes often determine injection volume based on experience or simple parameters, lacking comprehensive analysis of key factors such as the number of boreholes, spatial elevation differences, and transport path distances. This makes it difficult to accurately match inerting gas transport capacity, resulting in insufficient inerting or low gas utilization efficiency in localized areas. Additionally, given the fracture development characteristics of goaf areas, existing technologies typically lack effective directional gas injection and stable support mechanisms, hindering the continuous guided diffusion of inerting gas along fracture spaces and making it difficult to form a stable inerting environment in deep fracture areas. In terms of time, existing control measures primarily focus on passive treatment after water drainage, lacking a comprehensive, coordinated control mechanism, especially the means to pre-construct an inerting gas environment before water drainage. This makes it difficult to effectively regulate the composition of the negative pressure-induced gas flow, resulting in the gas entering the goaf still being predominantly air, and causing a disconnect between control measures at different stages. After water drainage boreholes are completed, they are often not effectively reused and fail to be transformed into continuous inert medium transport channels. The lack of coordinated and continuous replenishment of inhibitors and inert gases makes it difficult to maintain the inert environment in the goaf later, and the oxidation process of residual coal is difficult to continuously suppress. Therefore, there is an urgent need to propose a comprehensive prevention and control method for spontaneous combustion of coal in goafs throughout the entire water drainage process. This method involves constructing a multi-path coordinated transport system for inert media, encompassing directional transport through borehole channels, fracture-guided diffusion, and continuous replenishment through water hole conversion. This system aims to achieve precise transport and continuous supply of inert media at different stages, thereby effectively suppressing the oxidation and spontaneous combustion process of residual coal in the goaf. Summary of the Invention

[0004] In view of this, the present invention discloses a pre-set, phased prevention and control method for coal spontaneous combustion inerting during the drainage process in overlying waterlogged goaf areas. This method effectively addresses the issues of oxygen enhancement and staged disconnection in prevention and control measures caused by negative pressure-induced airflow during drainage, and achieves multi-path coordinated transport and continuous control of inert media throughout the entire process within the goaf area. The technical solution adopted by the present invention is as follows:

[0005] A pre-set, phased prevention and control method for spontaneous combustion of coal in the goaf during the drainage process of overly waterlogged goaf areas is characterized by including a whole-process drainage process for preventing spontaneous combustion of coal in the goaf and a multi-path inerting medium collaborative transportation technology system in the goaf area. The method utilizes three inerting medium transportation methods: borehole channel directional transportation, fracture insertion hole guided diffusion, and water hole conversion continuous replenishment. These methods achieve pre-embedded inerting environment before drainage operations, negative pressure induced gas replacement during drainage operations, and continuous inerting / inhibition inhibition after drainage operations. The nitrogen injection volume per borehole in the borehole channel directional transportation method is determined by coupling the number of boreholes, elevation difference, and spatial distance with the estimated water accumulation volume within the circular control unit. The fracture insertion hole guided diffusion method is implemented using an externally expanding support-type directional gas injection component. The water hole conversion continuous replenishment method is achieved through the synergistic effect of an inhibition film-forming dual-tank liquid injection system and a pneumatic multi-stage atomization device.

[0006] In one specific implementation, the pre-set staged prevention and control method for coal spontaneous combustion inerting during the drainage process of the overlying water-accumulated goaf is based on the dynamic changes in the gas environment and oxygen supply conditions of the goaf during the drainage process. It constructs a whole-process prevention and control process consisting of pre-embedded inerting environment before drainage operation, negative pressure induced gas replacement during drainage operation, and continuous inerting / resistance inhibition after drainage operation. It is implemented in conjunction with the multi-path inerting medium collaborative transportation technology system in the goaf. Specifically, before the drainage operation, inert gas boreholes are arranged around the end of the drainage borehole, and guided diffusion is achieved through fracture insertion holes. Nitrogen is injected directionally into the affected area and fracture space of the drainage borehole to form a local inerting control zone, reducing the regional oxygen content from the source. During the drainage operation, inert gas is continuously replenished through the fracture space. The drainage process creates a low-pressure core area, guiding the inert gas to migrate to the low-pressure area and replacing the gas entering the goaf, making it predominantly inert gas. After the drainage operation is completed, the original drainage borehole is converted into an inert medium transport channel. First, nitrogen and a film-forming agent are introduced to stabilize the borehole wall, and then nitrogen and an inhibitor are continuously injected to further inertify and inhibit the overlying goaf coal, thereby maintaining a low-oxygen environment and inhibiting the oxidation of the coal. The goaf multi-path inert medium synergistic transport technology system includes three methods: directional transport through borehole channels, guided diffusion through fracture insertion holes, and continuous replenishment through water hole conversion. This system corresponds to the directional transport, spatial diffusion and subsequent continuous replenishment of inert gases, and can achieve coordinated control of different stages and different spatial paths.

[0007] In one specific implementation scheme, the borehole channel directional transport inerting medium technology is applied to the pre-construction and embedding stage of the inerting environment before drainage operations. Before drainage operations, multiple inerting gas boreholes are arranged around the end of the drainage borehole, based on the mine's spatial structure characteristics, goaf distribution, and on-site construction conditions. Nitrogen gas is continuously introduced into these boreholes to replace the oxygen in the vicinity of the drainage borehole, thereby creating a low-oxygen environment dominated by inerting gas at the end of the borehole and within its influence range. This constructs an inerting gas surrounding the end area of ​​the drainage borehole, achieving pre-control of the gas environment in the target area. Specifically, the inerting gas boreholes are preferably constructed directionally from a high-level roadway or a horizontal adjacent roadway towards the end area of ​​the drainage borehole, enabling the inerting gas to be transported along the borehole axis and enter the goaf fracture network, thereby improving the accessibility and range of action of the inerting gas within the target area. Where construction conditions permit, two or three inert gas boreholes can be arranged, dispersed among each other, with an included angle of not less than 90° to enhance the diffusion and coverage of the inert gas in the space and avoid overlapping gas transport paths or local enrichment. When site conditions limit the required angle arrangement, the number of inert gas boreholes can be reduced according to the actual situation to ensure the rationality of the borehole layout and construction feasibility. Through the above-mentioned borehole layout and nitrogen injection method, the inert gas preferentially occupies the end of the borehole and the surrounding space before the start of the drainage operation, reducing the oxygen entry capacity and providing a stable inerting basis for gas migration and replacement under the negative pressure induced airflow during the subsequent drainage process.

[0008] In one specific implementation scheme, during the nitrogen injection operation, the amount of nitrogen injected into each inert gas borehole needs to be rationally allocated based on the borehole layout and terrain conditions. Specifically, the number of boreholes, the elevation difference Δh between the beginning and end of the water drainage borehole, and the spatial distance D between the end of the inert gas borehole and the end of the water drainage borehole all affect the gas transport efficiency and coverage effect. To ensure the directionality and uniformity of the nitrogen injection operation, a circular control unit is constructed around the end of the water drainage borehole, preferably with an area of ​​500 m². 2The estimated water accumulation in this area is denoted as W. Based on the combination of the number of boreholes, the elevation difference Δh, and the spatial distance D, a spatial coordination coefficient n, an elevation difference correction coefficient p, and a path attenuation coefficient q can be introduced to calculate the nitrogen injection volume V of a single inert gas borehole, so that it satisfies the relationship: V=n×W×p×q. When the number of nitrogen injection boreholes is 1, 2, or 3, the spatial coordination coefficient n of the nitrogen injection points is taken as 2.0-2.4, 0.8-1.0, and 0.5-0.6, respectively. When the elevation difference Δh between the drainage boreholes is less than 10 m, between 10 and 30 m, or greater than 30 m, the elevation difference correction coefficient p is taken as 1, 1.1-1.2, and 1.2-1.4, respectively. When the spatial distance D between the end of the nitrogen injection borehole and the end of the drainage borehole is less than 10 m, between 10 and 40 m, or greater than 40 m, the transport path attenuation correction coefficient q is taken as 1, 1.1-1.3, and 1.3-1.5, respectively. This method quantifies nitrogen injection operations and achieves spatial directional control, ensuring that inert gas effectively covers the area surrounding the drainage boreholes, providing stable conditions for subsequent inerting and inhibition operations.

[0009] In one specific implementation, the fracture-hole guided diffusion inerting medium transport technology is applied to the pre-construction embedding of the inerting environment before water drainage operations and the negative pressure induced gas replacement stage during water drainage operations. During implementation, an outward-expanding support-type directional gas injection component is deployed in the fractures around the water drainage borehole end to guide inert gas along the channel into the fracture network. Utilizing the guiding design of the component, the gas can extend and branch along the fractures, gradually filling the fracture space, achieving directional diffusion and uniform coverage. Firstly, through fracture-hole guided diffusion, the original air inside the fractures is replaced with inert gas, achieving the pre-construction embedding of the inerting environment before water drainage operations. During water drainage, the negative pressure induced airflow formed by the water flow preferentially draws in the replaced nitrogen gas inside the fractures, while the outward-expanding support-type directional gas injection component continuously injects nitrogen gas, achieving continuous replenishment, thereby maintaining a high-concentration inerting environment in the fractures throughout the entire operation phase.

[0010] In one specific implementation, the externally supported directional gas injection component includes an outer protective column with a hollow nitrogen injection pipe inside for nitrogen delivery and injection. A parabolic flow guide net is installed within the hollow nitrogen injection pipe to evenly disperse the nitrogen. One end of the hollow nitrogen injection pipe has a quick-connect pneumatic connector for connection to an external nitrogen supply system; the other end is fitted with a coaxial double-cone tapered nozzle. This nozzle consists of a pneumatically driven spinning inner cone and a porous gas distribution outer cone, which are coaxially fixed together by an anti-vibration ceramic bearing. This allows the nozzle to generate a spinning flow during injection, thereby enhancing spray uniformity. The porous gas distribution outer cone has three layers of nozzle holes, with the innermost layer having a quadrilateral layout and the outer two layers having a hexagonal layout, evenly discharging inert nitrogen. A buffer and anti-impact head is provided at the nozzle's front end to buffer impact forces during component placement or operation, ensuring stable nozzle positioning. A porous anti-clogging flow guide cover is fitted around the nozzle to prevent nozzle blockage.

[0011] The outer protective column is equipped with a fixed push-pull connecting rod on its inner side. This fixed push-pull connecting rod is connected to the connecting rod push-torsion and outward expansion struts on the outer side of the outer protective column. The connecting rod push-torsion can move the fixed push-pull connecting rod axially, thereby driving the outward expansion struts to open radially. The outward expansion struts extend out of the protective column and are fixed by a limiting base. Their outer surface has external serrations to enhance the mechanical engagement force with the coal seam fractures. When the connecting rod push-torsion is activated, the outward expansion struts expand radially and abut against the fracture wall, achieving physical support and stable positioning of the coal seam fractures. This ensures that the component can be reliably fixed within the fracture and creates stable spatial conditions for gas injection. An expansion trigger channel is also provided inside the outer protective column. This channel is connected to the hollow nitrogen injection pipe and the uniform-hole gas filling ring, and its opening and closing are controlled by a leak-sealing and venting valve. When inert gas needs to be injected, the leak-sealing and venting valve is opened, and nitrogen gas enters the expansion trigger channel along the hollow nitrogen injection pipe. It is then evenly distributed to multiple venting ports through a uniformly perforated inflation ring, preferably four ports evenly distributed on the ring. The nitrogen gas ultimately enters the expanding double-concave sealed airbag. Under gas pressure, the expanding double-concave sealed airbag expands in a predetermined direction, providing support for the fracture wall and forming a sealed inerting space to prevent nitrogen from overflowing into the roadway and threatening personnel safety. By adjusting the opening and closing of the leak-sealing and venting valve, the expansion degree of the expanding double-concave sealed airbag and the nitrogen delivery rate can be controlled, thereby flexibly adjusting the support force and inerting effect of the component under different fracture environments.

[0012] In one specific implementation, the original drainage borehole is retained after the drainage operation is completed and used as an injection channel for inert media. During nitrogen injection, a dual-tank injection system for inhibiting film formation and a pneumatic multi-stage atomization device are used to deliver the film-forming agent into the borehole via a nitrogen carrier. Nitrogen and the film-forming agent are thoroughly mixed in the atomization device to form a micron-level gas-liquid mixture, ensuring the uniformity and stability of the injected gas flow. This mixture is transported axially into the borehole along the drainage borehole axis and adheres to the borehole wall, forming a continuous and uniform film layer on the borehole wall surface. The function of this film layer is to stabilize the borehole wall, maintain the borehole structure, and prevent gas from escaping along the borehole channel, thereby providing a stable and controllable channel environment for the subsequent injection of inhibitors and nitrogen. After the film-forming agent has solidified and stably adhered, the injection during the film-forming stage stops. Based on this, using the same dual-tank injection system for inhibiting film formation and a pneumatic multi-stage atomization device, nitrogen and the inhibitor are mixed and atomized in the same manner and then injected into the drainage borehole. The inhibitor, carried by nitrogen, enters the overlying goaf through a stable borehole channel, achieving subsequent inerting and maintaining a low-oxygen environment around the end of the drainage borehole. This effectively inhibits coal-oxygen contact and low-temperature oxidation reactions. The entire control process achieves an integrated continuous operation mode of first constructing a stable protective layer on the borehole wall and then implementing inhibitor and inerting control. This effectively ensures the integrity and long-term stability of the surrounding rock structure and significantly improves the transport and diffusion efficiency of the inhibitor and nitrogen in the overlying goaf, strengthening the overall control effectiveness of coal spontaneous combustion in the goaf.

[0013] In one specific implementation, the film-forming dual-tank injection system includes a dual-tank reservoir, a gas control unit, a liquid output unit, a delivery pipeline unit, and a flow control unit. The dual-tank reservoir stores the film-forming agent and the inhibitor respectively, and has an internal anti-corrosion coating and a pressure-sensitive gas-liquid isolation layer. This layer is used to automatically open and close the film-forming pneumatic-liquid valve and the inhibitor pneumatic-liquid valve under nitrogen pressure, ensuring the safety and stability of the liquid during long-term storage. The gas control unit consists of a main gas valve, a film-forming gas valve, and an inhibitor gas valve, used to control the nitrogen flow direction and injection sequence, and is connected to the reservoir. The liquid output unit includes a film-forming pneumatic-liquid valve and an inhibitor pneumatic-liquid valve, connected to the dual-tank reservoir, used to control the precise delivery of the liquid. The delivery pipeline unit includes a nitrogen pipeline, a film-forming agent pipeline, and an inhibitor pipeline. The nitrogen pipeline is connected to a pneumatic multi-stage atomizing device and, through a bypass pipeline, to the dual-tank reservoir to ensure stable mixing and delivery of the gas and liquid. The flow control unit includes a nitrogen flow meter, a metering pump, and a flow self-matching unit. It controls the pump's operation via flow signals to achieve a preset ratio match between liquid delivery and nitrogen flow, ensuring uniform gas-liquid mixing and stable flow. During operation, when the main gas valve and film-forming gas valve are open while the inhibitor gas valve is closed, nitrogen enters the film-forming agent reservoir through a bypass pipeline. This pressurizes the pressure-sensitive gas-liquid isolation layer and drives the film-forming pneumatic-liquid valve to open. The film-forming agent is then delivered to a pneumatic multi-stage atomizer and transported along the borehole, adhering to the borehole wall surface to form a continuous, solidified film. This stabilizes the borehole wall and prevents gas escape, providing a reliable channel for subsequent inhibitor injection. After the film-forming agent has been delivered and solidified, the film-forming gas valve is closed and the inhibitor gas valve is opened. Nitrogen enters the inhibitor reservoir, driving the inhibitor pneumatic-liquid valve to open, allowing the inhibitor to be delivered along the borehole to the target area via the pneumatic multi-stage atomizer, smoothly entering the overlying goaf. Throughout the injection process, the flow self-matching unit adjusts the operating parameters of the metering pump according to the nitrogen flow meter signal to ensure a constant ratio of nitrogen to liquid, thereby achieving stable gas injection, uniform distribution of inhibitor, and preventing local blockage and gas escape.

[0014] In one specific implementation, the pneumatic multi-stage atomizing device comprises an internal liquid tube, an outer ring gas tube, a stepped contraction channel, a speed-increasing throat, a staggered herringbone-shaped porous baffle, a gradually expanding trumpet-shaped guide tube, a baffle-type swirl-mixing atomizer, an air-driven transverse rotary cutter, and a fixed column. The internal liquid tube and the outer ring gas tube are arranged coaxially. The internal liquid tube is used to transport the film-forming agent or inhibitor, while the outer ring gas tube is used to transport nitrogen. Through this coaxial structure, the liquid can form a preliminary jet mist under the entrainment of the gas, achieving preliminary gas-liquid mixing.

[0015] The gas-liquid mixture first passes through a stepped contraction channel. The progressively contracting design of the channel accelerates the flow velocity and pre-shapes the flow field, providing stable inlet conditions for subsequent atomization. The gas-liquid mixture then sequentially enters an acceleration throat and a gradually expanding trumpet-shaped guide tube. The acceleration throat further enhances the kinetic energy of the gas-liquid mixture, forming a high-energy stream. The gradually expanding trumpet-shaped guide tube acts as a gradual diffuser and guide, with long guide cones attached to its inner wall to help guide the gas-liquid flow to a uniform distribution while mitigating the impact of local turbulence, ensuring the gas-liquid mixture is evenly distributed within subsequent pipe sections. The acceleration throat contains three layers of staggered herringbone-shaped porous baffles, each layer consisting of two baffles arranged in opposite positions. Each baffle has an alternating length, creating overlapping areas locally, and adjacent layers of baffles are offset at a 120° angle. This unique arrangement allows for multiple collisions, cutting, and rotations of the gas-liquid mixture, achieving initial fine atomization and uniform mixing. A baffled vortex atomizer is installed inside the expanding trumpet-shaped guide tube. This atomizer rotates under the action of the gas-liquid mixture. Irregular openings are located above it to further shear, baffle, and vortex the gas-liquid flow, ensuring thorough mixing and dispersion. Two air-push transverse vortex cutters are installed at the rear end of the expanding trumpet-shaped guide tube. These cutters are supported by fixed columns and consist of two V-shaped folded blades. When the gas-liquid mixture passes through the air-push transverse vortex cutters, it is subjected to transverse shearing force, further cutting, rotating, and diffusing the gas and liquid, enhancing the atomization effect and resulting in more uniform droplet size and wider coverage. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1 A schematic diagram of a pre-set, tiered prevention and control method for spontaneous combustion of coal during the drainage process in overlying water-accumulated goaf areas;

[0018] Figure 2 A schematic diagram illustrating the enhanced mechanism of coal spontaneous combustion in goaf induced by siphoning of drainage water;

[0019] Figure 3 This is a schematic diagram of nitrogen-injected inert coal bodies within the overlying goaf.

[0020] Figure 4 A schematic diagram illustrating the factors affecting nitrogen injection volume in a single inert gas borehole;

[0021] Figure 5This is a schematic diagram of an externally supported directional gas injection component;

[0022] Figure 6 A schematic diagram showing the functional deployment of an externally supported directional gas injection component;

[0023] Figure 7 Schematic diagram of a dual-tank injection system for film-forming inhibition;

[0024] Figure 8 This is a schematic diagram of a pneumatic multi-stage atomizing device. Detailed Implementation

[0025] The embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0026] Optionally, in one specific implementation, see [link to relevant documentation]. Figure 1 This invention addresses the risk of spontaneous combustion caused by coal fissure exposure and negative pressure-induced oxygen reabsorption during water drainage operations in overlying goaf areas. It proposes a pre-set, phased prevention and control method for coal spontaneous combustion during water drainage in overlying goaf areas. The method consists of two main modules: a whole-process water drainage process for preventing and controlling coal spontaneous combustion in goaf areas and a multi-path inertization medium collaborative transportation technology system in goaf areas. This method achieves embedded, phased inertia control and closed-loop management of the risk of coal spontaneous combustion in overlying goaf areas.

[0027] The entire process of preventing spontaneous combustion of coal in the goaf during water drainage includes pre-construction and embedding of an inerting environment before water drainage operations, negative pressure induced gas replacement during water drainage operations, and continuous inerting / inhibition inhibition after water drainage operations. Before water drainage operations, a comprehensive analysis of the disturbance influence domain at the end of the water drainage borehole is conducted. Based on the characteristics of the fracture network, possible gas flow channels and negative pressure risk areas are identified. Combining two inerting medium transport methods—directional transport through borehole channels and guided diffusion through fracture insertion—nitrogen is filled into the environment surrounding the end of the water drainage borehole and within the fractures to form a surrounding interface inerting control zone, achieving pre-construction and embedding of the inerting environment. Directional transport through borehole channels is achieved by constructing high-level / horizontal inerting gas boreholes to precisely inject a fixed amount of nitrogen into the negative pressure influence domain. The nitrogen injection volume of a single inerting gas borehole is determined based on the unit water volume, the number of boreholes, the elevation difference, and the spatial distance. To achieve the inert medium transport method of fracture-guided diffusion, the development areas of mining-induced fractures in the goaf are first accurately identified and located to determine the target path and coverage area for gas transport. Then, by deploying outward-expanding support-type directional gas injection components, nitrogen is guided and diffused along the fractures, allowing the inert gas to gradually fill and cover the fracture network, effectively replacing the original oxygen inside the fractures and forming a continuous and stable inert environment. This provides a reliable gas barrier for subsequent water drainage operations and goaf safety management.

[0028] During the drainage operation, due to the continuous discharge of water, a negative pressure migration field is formed at the end of the drainage borehole and in the surrounding fractures. The air that originally migrated along the fractures is replaced by inert nitrogen, making the gas drawn into the negative pressure zone mainly nitrogen. At the same time, the outward-expanding support-type directional gas injection component continuously replenishes nitrogen into the fractures, ensuring that the inert gas maintains continuous coverage and a high concentration in the fracture network, thereby effectively replacing the original oxygen and achieving the suppression of oxygen in the goaf and the stable maintenance of the inertized environment. After the drainage operation is completed, the oxidation risk increases significantly due to the continuous exposure of the remaining coal. By converting the original drainage borehole into an inert / inhibitory medium transport channel, inert gas and inhibitors are transported to the exposed coal in the overlying goaf, achieving continuous inertization coverage and flame retardant treatment of the coal, thereby effectively reducing oxygen infiltration, suppressing low-temperature oxidation and spontaneous combustion risks, and ensuring the safety of operations in the goaf. The continuous supply method of the water hole conversion is achieved through the coordinated use of an inhibitory film-forming dual-tank injection system and a pneumatic multi-stage atomization device. During implementation, inert gas and film-forming agent, atomized by a pneumatic multi-stage atomization device, are first injected into the borehole to stabilize the borehole wall; then, inert gas and inhibitor, atomized by a pneumatic multi-stage atomization device, are introduced and reach the overlying goaf area through the stabilized drainage borehole.

[0029] Optionally, in one specific implementation, see [link to relevant documentation]. Figure 2The overlying goaf may be connected to groundwater, leading to increased water accumulation. Grouting during mining may also create significant water accumulation. To ensure safe mining, it is typically necessary to drain the water in the goaf after the overlying coal seam is mined through boreholes. This eliminates potential water hazard risks and provides stable conditions for subsequent operations. During water drainage, as the boreholes continuously drain water, the water flows along pores and fractures, creating a significant "siphon effect" and forming a localized low-pressure cavity around the end of the drainage borehole. Multiple fractures exist between the overlying goaf and the surface environment, while other fractures connect to the coal seam being mined. The mined coal seam roadway maintains a fresh airflow, creating a high-pressure, high-oxygen environment. Under this significant pressure difference, air from the surface and roadway flows along the pressure gradient from the high-pressure area to the low-pressure cavity area, passing through the fracture network into the overlying goaf. This carries oxygen into the pores of the water-soaked coal, causing the oxygen to tightly encapsulate the water-soaked coal body. During this process, the negative pressure formed at the borehole tip not only continuously induces air intrusion but also further promotes the penetration, diffusion, and accumulation of oxygen in pores and fractures, significantly increasing the local oxygen concentration. This significantly enhances the conditions for low-temperature oxidation of the coal and markedly increases the risk of spontaneous combustion. Under the hydrodynamic scouring effect caused by the drainage operation, the coal dust and gravel filling the coal seams in the goaf are directionally washed away and stripped by the water flow, migrating with the water flow. At the same time, fine coal dust blocking the pores and microfractures inside the coal seam is also washed away by the water flow. This process significantly improves the pore structure of the coal seam, increases its porosity and specific surface area, directly expands the effective contact area between the coal seam and oxygen, and enhances the exposure of active sites on the coal surface. Ultimately, this leads to a significant increase in the low-temperature oxidation sensitivity of the coal seam, raising the risk level of spontaneous combustion of residual coal in the goaf. The drainage operation triggers a negative pressure siphon effect, driving oxygen from the surface and roadway airflow to continuously migrate and accumulate in the goaf, resulting in a significant increase in the overall oxygen concentration in the overlying goaf. Simultaneously, the water flow creates a seepage and scouring effect within the pore and fracture network, progressively removing coal dust particles filling the spaces between coal blocks and within the pores, clearing seepage channels, widening fracture openings, and effectively increasing the specific surface area of ​​the coal and the effective contact interface between coal and oxygen. The coupled and superimposed mechanisms of siphon-induced dynamic air intake and water drainage for coal washing and gap widening enhance the basic conditions for low-temperature oxidation of the coal body from both the oxygen source supply and reaction interface dimensions, ultimately leading to a significant increase in the risk of spontaneous combustion of residual coal in the overlying goaf.

[0030] Optionally, in one specific implementation, see [link to relevant documentation]. Figure 3Without pre-embedded inerting environment control, continuous drainage operations in the overlying goaf will create a low-pressure cavity at the end of the drainage borehole. Driven by the pressure gradient, outside air continuously seeps into this low-pressure space, gradually forming a stable negative pressure air domain around the borehole and inside the goaf. As the residual coal in the goaf is gradually exposed, a large amount of oxygen in the incoming air can directly contact, adsorb, and undergo a low-temperature oxidation reaction with the surface of the fresh coal, causing the oxidation process of the residual coal to continue to intensify, ultimately resulting in a significant increase in the risk of spontaneous combustion of the coal in the goaf. If, before the drainage operation is implemented, pre-embedded inerting environment is deployed in advance, relying on the combined transport path of directional transport through the borehole channel and the guided diffusion through fracture holes, a closed inerting control zone with full nitrogen coverage can be formed around the end of the drainage borehole. This inerting layer can effectively block the surrounding air domain, construct a physical isolation barrier, and block the seepage and intrusion channels of outside oxygen into the low-pressure cavity. Subsequent drainage operations are carried out based on this pre-constructed inert environment. The low-pressure cavity formed at the end of the borehole changes its negative pressure suction medium from naturally drawing in outside air to preferentially drawing in inert nitrogen gas enriched in the surrounding area, thus avoiding the core hidden danger of oxygen migrating in with negative pressure at the source. At the same time, the nitrogen gas drawn and diffused by negative pressure can fully fill the voids and fissures between coal blocks and further penetrate into the microporous structure inside the coal body, comprehensively occupying the oxidation active sites on the coal surface, inhibiting the process of oxygen molecule adsorption and low-temperature oxidation reaction. From multiple dimensions such as spatial isolation, medium replacement, and occupation of active sites, the risk of spontaneous combustion of residual coal in the goaf is fundamentally controlled.

[0031] Optionally, in one specific implementation, see [link to relevant documentation]. Figure 4 When implementing nitrogen inerting operations, a quantitative nitrogen injection mode should be adopted. The nitrogen injection flow rate of the inerting gas boreholes needs to be precisely allocated based on the layout of the inerting gas boreholes and the actual terrain undulations. First, a 500 m² area should be constructed centered on the end of the drainage borehole. 2A circular control unit is used to statistically determine the estimated water accumulation W within its range. Following the principle of water-based gas supply and nitrogen replenishment through drainage, the inerting nitrogen supply and transport parameters are optimized based on three key influencing factors: the number of boreholes, the vertical height difference Δh between the beginning and end of the water drainage boreholes, and the spatial distance D between the end of the inerting gas borehole and the end of the water drainage borehole. This achieves precise dynamic matching between nitrogen injection and drainage. The location and number of inerting gas boreholes affect the inerting zone. When on-site construction conditions allow for sufficient space, two or three inerting gas injection boreholes can be deployed in high-level / horizontal roadways. These boreholes are arranged in a dispersed layout, with the angle between adjacent boreholes preferably not less than 90°. This layout enhances the diffusion coverage of inerting gas within the goaf, effectively avoiding problems such as overlapping gas transport paths and excessive local inerting gas accumulation, thus improving the uniformity of inerting across the entire area. If the above-mentioned angled layout requirements cannot be met due to limitations such as on-site tunnel layout and geological conditions, the number of inert gas boreholes can be appropriately reduced based on the actual project situation. This ensures the rationality of the overall borehole layout and the inerting control effect while considering construction feasibility. The vertical height difference Δh between the head and tail of the drainage borehole directly determines the intensity of the negative pressure siphon effect; the greater the vertical height difference, the more significant the siphon suction effect, and the stronger the ability of external oxygen to infiltrate and migrate into the goaf. Therefore, as the vertical height difference increases, the nitrogen injection rate of single-hole inert gas should be increased accordingly to match the enhanced negative pressure suction intensity and ensure the inerting barrier effect. The spatial distance D between the tail of the inert gas borehole and the tail of the drainage borehole directly determines the containment and full-area coverage effect of nitrogen on the low-pressure area at the tail of the drainage borehole. The greater the spatial distance, the longer the transport path of the inert gas along the fracture network, the more significant the loss along the way, and the weaker the containment and isolation ability of the drainage borehole tail area, resulting in a gradual decrease in the overall inerting protection effect. Therefore, as the spatial distance increases, it is necessary to simultaneously increase the nitrogen injection flow rate and total supply of a single inert gas borehole to compensate for the gas loss caused by long-distance transportation and ensure that a continuous and sealed nitrogen inert barrier can be formed around the end of the drainage borehole.

[0032] Optionally, in one specific implementation, see [link to relevant documentation]. Figure 5 , 6The main body of the externally expanded support type directional gas injection component consists of an outer protective column and a hollow nitrogen injection pipe installed inside it. One end of the hollow nitrogen injection pipe is equipped with a quick-connect pneumatic connector, and the other end is equipped with a coaxial double-cone tapered nozzle. A parabolic flow guide net is installed inside the hollow nitrogen injection pipe to stabilize the airflow and ensure that nitrogen is transported smoothly inside the pipe. The coaxial double-cone tapered nozzle includes a pneumatically spun inner cone and a porous gas distribution outer cone, which are coaxially connected by an anti-vibration ceramic bearing. The outer surface of the pneumatically spun inner cone is provided with a spiral guide groove and a built-in pneumatic fan. Driven by nitrogen gas flow, it can rotate at high speed around the anti-vibration ceramic bearing, causing the gas to form a swirling flow field, which enhances the radial diffusion and axial penetration ability of nitrogen in the crack. The front end of the coaxial double-cone tapered nozzle is provided with a buffer stabilizing anti-impact head, and the outer side is fitted with a porous anti-clogging guide shroud, which can realize the direct flow of nitrogen and swirling diffusion, while filtering coal dust impurities and preventing nozzle blockage. The porous gas distribution outer cone adopts two nozzle layout forms, quadrilateral and hexagonal, and is set in three layers. The innermost layer is a quadrilateral nozzle layout, and the outer two layers are hexagonal nozzle layouts. The pneumatically spun inner cone further optimizes the airflow organization effect by relying on its own guide groove and pneumatic fan structure. The outer protective column is equipped with a fixed push-pull connecting rod on its inner side. The fixed push-pull connecting rod is connected to a connecting rod push-torque and an outward expansion support rod. The connecting rod push-torque is located on the outer side of the outer protective column and drives the fixed push-pull connecting rod to move axially. The outward expansion support rod passes through the outer protective column and is fixed by a limiting base. Its outer surface has external serrations. The connecting rod push-torque drives the outward expansion support rod to open radially and abut against the crack wall, realizing the stable fixation of the component in the irregular crack. The outer protective column is also equipped with an expansion trigger channel. The expansion trigger channel is connected to the hollow nitrogen injection pipe and the uniformly perforated gas filling ring, and its opening and closing are controlled by a leak-stopping and venting valve. The uniformly perforated gas filling ring has four gas outlets evenly arranged at 90° angles, which can reasonably plan the opening position and the distribution of the gas outlets. The injected nitrogen enters the expansion double concave sealed airbag through the expansion trigger channel and the uniformly perforated gas filling ring. After the airbag is inflated, it can tightly fit against the crack wall to form an annular sealing strip and seal the gas leakage channel. The entire component relies on outward-expanding struts for mechanical support and positioning, expandable double-concave sealed airbags for flexible sealing, and coaxial double-cone tapering nozzles for uniform swirling air injection. All structural components work together to achieve the overall functions of stable placement of the component, sealing of cracks and air isolation, and directional and balanced diffusion of inert gas, meeting the construction needs before on-site water drainage.

[0033] Optionally, in one specific implementation, see [link to relevant documentation]. Figure 6When the outward-expanding support type directional gas injection component is in its initial, non-operational state, its outward-expanding struts remain in a retracted posture and do not form an interlocking support with the fracture wall. The expanding double-concave sealed airbag is also in an uninflated state. At this time, there are multiple through gaps and leakage channels between the component and the surrounding irregular fracture wall. Under this initial working condition, the component itself lacks reliable positioning constraints and is extremely susceptible to slippage or even detachment due to factors such as roadway airflow and gas injection disturbance. At the same time, during subsequent nitrogen injection operations, inert gas will continuously leak and dissipate along the gap between the component and the fracture wall towards the roadway. This not only significantly reduces the effective inerting gas volume and decreases the nitrogen enrichment concentration and overall inerting coverage effect in the overlying goaf, but the nitrogen leaked into the roadway will also change the local air composition and dilute the oxygen content, thereby affecting the normal working environment and personal safety of underground workers. When the nitrogen inerting operation is officially carried out, the operator applies an upward thrust to the connecting rod and completes the set push stroke displacement Δm. Through the internal transmission structure, the fixed push-pull connecting rod is driven to generate axial displacement synchronously, which in turn drives the outward expansion strut to expand radially outward, so that the end of the outward expansion strut tightly fits the irregular crack wall with uneven surface. With the help of the external serrations on the surface of the outward expansion strut forming a mechanical interlocking structure with the rock wall, the component is firmly fixed to the wall inside the crack, fundamentally eliminating the problem of component shaking, displacement or even slippage under high pressure gas injection conditions. Simultaneously, the leak-sealing and venting valve is opened, and inert gas is smoothly delivered from the hollow nitrogen injection pipe through the expansion trigger channel to the uniformly sized gas filling ring, and then slowly delivered through the evenly distributed gas outlets on the ring to the expanding double-concave sealed airbag. Under the action of gas pressure, the airbag gradually inflates and expands, adaptively conforming to the fracture contour. Relying on its own double-concave structure, it forms a multi-layer closed-loop annular sealing barrier, completely sealing all kinds of connecting gaps around the component, and completely cutting off all seepage paths for nitrogen to diffuse and leak to the roadway side. While completing the mechanical support positioning and flexible sealing, the continuously introduced nitrogen gas is ejected through the coaxial double-cone tapered nozzle at the front end of the outward expansion support directional gas injection component. Relying on the swirling disturbance effect generated by the internal wind-driven spinning structure of the nozzle, the inert gas is driven to achieve long-distance directional transport and all-round diffusion along the fracture network of the goaf, steadily improving the nitrogen concentration and coverage uniformity of the target inerting area, and efficiently completing the construction requirements for inerting and suppressing oxygen in the goaf coal residue.

[0034] Optionally, in one specific implementation, see [link to relevant documentation]. Figure 7The dual-tank injection system for film-forming inhibition consists of a dual-tank reservoir, a gas control unit, a liquid output unit, a delivery pipeline unit, and a flow control unit. The dual-tank reservoir is an independent dual-tank structure, storing the film-forming agent and the inhibitor respectively. The inner wall of the tank is coated with an anti-corrosion film, and an internal pressure-sensitive gas-liquid isolation layer is installed to achieve physical isolation and pressure-linked control between the gas and liquid phases. The gas control unit includes a main gas valve, a film-forming gas valve, and an inhibitor gas valve, connected to a nitrogen pipeline via a bypass pipeline to achieve directional delivery of nitrogen to the dual-tank reservoir. The liquid output unit consists of a film-forming pneumatic-liquid valve and an inhibitor pneumatic-liquid valve, respectively connected to the outlet of the dual-tank reservoir, and can be used for pressure... The gas-liquid isolation layer automatically opens under pressure, enabling output control of the liquid medium. The delivery pipeline unit includes a nitrogen pipeline, a film-forming agent pipeline, and an inhibitor pipeline. The nitrogen pipeline is connected to the inert medium injection pipeline via a pneumatic multi-stage atomizing device. The film-forming agent pipeline and the inhibitor pipeline are connected to a metering pump and finally converge into the pneumatic multi-stage atomizing device. The flow control unit consists of a nitrogen flow meter, a metering pump, and a flow self-matching unit. The flow self-matching unit dynamically adjusts the operating parameters of the metering pump based on the real-time detection signal from the nitrogen flow meter, ensuring that the delivery volume of the film-forming agent and inhibitor is precisely matched with the nitrogen flow rate according to a preset ratio, thus guaranteeing the atomization mixing effect.

[0035] The water-hole conversion and continuous replenishment of inertizing medium transportation adopts a two-stage operation mode: Stage I is the film-forming and wall-solidifying stage, where nitrogen and film-forming agent are mixed and atomized by a pneumatic multi-stage atomizer and injected into the drainage water borehole. The droplets adhere to and solidify on the borehole fracture wall to form a continuous solidified film, sealing the fractures inside the drainage water borehole; Stage II is the inertization and inhibition stage. After the film layer solidifies, the valve-controlled mode is switched, and nitrogen and inhibitor are mixed and atomized and injected into the borehole. In the closed space formed by the solidified film, the inert gas and inhibitor are uniformly transported, ultimately achieving dual protection of fracture wall sealing and residual coal inertization and inhibition. The entire system achieves orderly transportation of the two media through valve-controlled mode switching, realizes gas-liquid linkage opening and closing based on the pressure-sensitive gas-liquid isolation layer, and ensures stable gas-liquid ratio by combining the flow self-matching unit, which can efficiently complete the continuous operation of fracture film formation sealing and inertization and inhibition.

[0036] Optionally, in one specific implementation, see [link to relevant documentation]. Figure 8The pneumatic multi-stage atomizing device adopts an inner and outer sleeve coaxial layout, including an inner liquid tube and an outer gas tube, which are used to transport the film-forming agent or inhibitor liquid medium and nitrogen inert gas, respectively. Along the fluid transport direction, a stepped contraction channel, a speed-increasing throat, a gradually expanding trumpet-shaped guide tube, and a pneumatically propelled transverse vortex cutter are arranged sequentially. A staggered herringbone-shaped porous baffle is located inside the speed-increasing throat, and a baffled vortex atomizer is located inside the gradually expanding trumpet-shaped guide tube. All units are connected sequentially to jointly complete the multi-stage atomization and vortex mixing of the gas and liquid phases. Nitrogen gas is input through the outer ring gas pipe at the left end of the device, and film-forming agent or inhibitor liquid is input through the built-in liquid pipe. The gas and liquid phases first enter the stepped contraction channel, where they are accelerated and initially mixed by the flow channel constriction at the speed-increasing throat. The speed-increasing throat is equipped with three layers of staggered herringbone-shaped porous baffles along the axial direction. Each layer of baffles consists of two baffles with a long and short structure, which are symmetrically arranged in opposite positions in the flow channel, forming a local area of ​​superimposed airflow disturbance. The three layers of baffles are arranged in a forward-tilted staggered manner, with a circumferential misalignment angle of 120° between adjacent layers of baffles. As the gas-liquid mixture flows through this region, it undergoes multiple porous impacts and flow disturbances on the porous baffles. The liquid film is repeatedly torn, sheared, and broken into a group of relatively uniform droplets, thus completing the first-stage atomization process of the device. The gas-liquid mixture after the first-stage atomization enters the gradually expanding trumpet-shaped guide tube. Multiple long guide cones are attached to the inner wall of the tube to guide the airflow to form a stable boundary layer along the wall, ensuring that the gas-liquid mixture is evenly distributed in subsequent tube sections. The internal baffle swirling atomizer further shears, breaks up, and swirls the droplets, reducing the droplet size. The process begins with a first step of refinement, completing the second stage of atomization. Subsequently, the gas-liquid mixture enters a pneumatically driven transverse rotary cutter supported by a fixed column. Inside, two V-shaped folded fan blades rotate under the impetus of high-speed airflow, applying transverse cutting and vortex disturbance to the mixture, achieving a third stage of enhanced atomization. Ultimately, this forms a finely sized, uniformly distributed inert medium mixture, which is output from the right end of the device. The entire process, through the synergistic effect of the three-stage progressive atomization units, significantly improves the mixing uniformity and atomization effect of the gas and liquid phases, ensuring the efficient diffusion and uniform coverage of the inhibitor and nitrogen in the goaf.

Claims

1. A pre-set, tiered prevention and control method for spontaneous combustion of coal during the drainage process in overlying waterlogged goaf areas, characterized in that, The invention includes a process for preventing spontaneous combustion of coal in goaf during the entire process of water drainage and a multi-path inerting medium collaborative transportation technology system for goaf. The method utilizes three inerting medium transportation methods: borehole channel directional transportation, fracture insertion hole guided diffusion, and water hole conversion continuous supply. These methods achieve pre-construction embedding of the inerting environment before water drainage, negative pressure induced gas replacement during water drainage, and continuous inerting / inhibition inhibition after water drainage. The nitrogen injection volume of a single borehole in the borehole channel directional transportation method is determined by coupling the number of boreholes, elevation difference, and spatial distance with the estimated water accumulation in the circular control unit. The fracture insertion hole guided diffusion method is implemented using an externally expanding support type directional gas injection component. The water hole conversion continuous supply method is achieved through the synergistic effect of an inhibition film-forming dual-tank liquid injection system and a pneumatic multi-stage atomization device.

2. The process for preventing spontaneous combustion of coal in goaf during the entire process of water drainage as described in claim 1, characterized in that, It includes the following steps: S1, Inertization environment pre-construction embedded before water drainage operation: Centered on the end of the water drainage borehole, multiple inert gas boreholes are arranged around the end of the water drainage borehole according to the actual situation of the mine. Nitrogen gas is introduced into the inert gas boreholes to replace the oxygen in the area near the water drainage borehole and form an inertization control zone. At the same time, an outwardly expanding support type directional gas injection component is set in the fracture near the end of the water drainage borehole, and nitrogen gas is continuously introduced into the fracture using a fracture insertion hole guided diffusion method. S2, Negative pressure induced gas replacement during water drainage operation: During the water drainage operation, the externally expanded support type directional gas injection component is kept continuously injecting nitrogen into the fracture; the negative pressure gas flow formed during the water drainage process is used to make the gas entering the space near the water drainage borehole mainly nitrogen. S3, Continuous inert / inhibition inhibition after drainage operation: After the drainage operation is completed, the original drainage borehole is converted into an inert / inhibition medium injection channel, and inhibitors and nitrogen are continuously injected.

3. The borehole tunnel directional transport according to claim 1, characterized in that, Before the drainage operation, multiple inert gas boreholes are arranged around the end of the drainage borehole to form an inerting control zone around the end of the drainage borehole. Inert gas boreholes are drilled from the high-level or horizontal adjacent roadway to the end of the drainage borehole. When the site conditions allow for the construction of two or three boreholes, the included angle between each inert gas borehole shall not be less than 90°. When the included angle condition is not met, the number of inert gas boreholes shall be reduced accordingly.

4. The directional transport via borehole tunnel according to claim 1, characterized in that: During nitrogen injection, the nitrogen injection volume of a single inert gas borehole is determined by the coupling of the number of inert gas boreholes, the elevation difference Δh between the beginning and end of the drainage borehole, and the spatial distance D between the end of the inert gas borehole and the end of the drainage borehole; a 500 m² area is constructed with the end of the drainage borehole as the center. 2 The circular control unit is denoted as W, and the estimated water accumulation in the control unit is recorded as W. The number of inert gas boreholes, the elevation difference Δh, and the spatial distance D correspond to the spatial coordination coefficient n, the elevation difference correction coefficient p, and the path attenuation coefficient q, respectively. The nitrogen injection amount V of a single inert gas borehole satisfies the relationship: V=n×W×p×q.

5. The outwardly expanding support type directional gas injection component according to claim 1, characterized in that: It includes an outer protective column and a hollow nitrogen injection pipe installed inside it. One end of the hollow nitrogen injection pipe is equipped with a quick-connect pneumatic connector, and the other end is equipped with a coaxial double-cone tapered nozzle. The coaxial double-cone tapered nozzle includes a wind-driven self-rotating inner cone and a porous gas distribution outer cone, which are coaxially connected by a shock-resistant ceramic bearing. Its front end is equipped with a buffer stabilizing anti-impact head, and its outer side is equipped with a porous anti-clogging guide cover. The outer protective column is provided with a fixed push-pull connecting rod inside. The fixed push-pull connecting rod is connected to the connecting rod push-torque and the outward expansion support rod respectively. The connecting rod push-torque is located on the outside of the outer protective column and drives the fixed push-pull connecting rod to move axially. The outward expansion support rod passes through the outer protective column and is fixed by the limiting base. Its outer surface is externally attached serrated. The connecting rod push-torque drives the outward expansion support rod to open radially and abut against the crack wall. The outer protective column is also provided with an expansion trigger channel, which is connected to the hollow nitrogen injection pipe and the uniformly perforated inflation ring respectively, and is controlled to open and close by a leak-stopping and venting valve. The uniformly perforated inflation ring is provided with multiple gas outlets, so that the injected nitrogen enters the expansion double concave sealed airbag through the expansion trigger channel and the uniformly perforated inflation ring.

6. The water-hole conversion continuous replenishment according to claim 1, characterized in that: After the drainage operation is completed, the original drainage borehole is retained as an inert medium injection channel. A dual-tank injection system for inhibiting film formation and a pneumatic multi-stage atomization device are used to co-transport and atomize nitrogen and film-forming agent to form a gas-liquid mixture, which is then delivered into the drainage borehole to allow the film-forming agent to adhere to the borehole wall and form a solidified film. After the solidified film is formed, the delivery of the film-forming agent is stopped. Subsequently, nitrogen and inhibitor are mixed and atomized in the same manner through the dual-tank injection system for inhibiting film formation and a pneumatic multi-stage atomization device and delivered to the overlying goaf through the drainage borehole.

7. The inhibition film-forming dual-tank injection system according to claim 6, characterized in that, include: A dual-tank liquid storage tank is used to store film-forming agents and inhibitors. The dual-tank liquid storage tank is equipped with an anti-corrosion coating and a pressure-sensitive gas-liquid isolation layer. The gas control unit includes a main gas valve, a film-forming gas valve, and an inhibitor gas valve, which are connected to a dual-tank reservoir. The liquid output unit includes a film-forming pneumatic-liquid valve and an inhibitor pneumatic-liquid valve, which are respectively connected to the dual-tank reservoir. The delivery pipeline unit includes a nitrogen pipeline, a film-forming agent pipeline, and an inhibitor pipeline. The flow control unit includes a nitrogen flow meter, a metering pump, and a flow self-matching unit installed on the nitrogen pipeline, which are respectively connected to the nitrogen flow meter and the metering pump. The nitrogen pipeline is connected to a pneumatic multi-stage atomizing device and also to the dual-tank reservoir via a bypass pipeline.

8. The water-hole conversion continuous replenishment according to claim 1, characterized in that, The process includes the following steps: When the main gas valve and film-forming gas valve are opened and the inhibitor gas valve is closed, nitrogen enters the dual-tank reservoir containing the film-forming agent through the bypass pipeline. The corresponding pressure-sensitive gas-liquid isolation layer is pressurized, driving the film-forming pneumatic-liquid valve to open. After the film-forming agent has been delivered, the film-forming gas valve is closed and the inhibitor gas valve is opened. Nitrogen enters the dual-tank reservoir containing the inhibitor, and the corresponding pressure-sensitive gas-liquid isolation layer is pressurized, driving the inhibitor pneumatic-liquid valve to open. In each of the above steps, based on the detection signal of the nitrogen flow meter, the operating parameters of the metering pump are adjusted by the flow self-matching unit to match the delivery volume of the corresponding liquid with the nitrogen flow rate according to a preset ratio.

9. The pneumatic multi-stage atomizing device according to claim 6, characterized in that, The system includes a built-in liquid pipe, an outer ring gas pipe, a stepped contraction channel, a speed-increasing throat, staggered herringbone-shaped porous baffles, a gradually expanding trumpet-shaped guide pipe, a baffle-type vortex atomizer, an air-driven transverse rotary cutter, and a fixed column. The outer ring gas pipe and the built-in liquid pipe are coaxially arranged, respectively delivering nitrogen and a film-forming agent or inhibitor. The speed-increasing throat, the gradually expanding trumpet-shaped guide pipe, and the air-driven transverse rotary cutter are connected sequentially along the fluid transport direction. The staggered herringbone-shaped porous baffles are arranged in three layers, tilted forward and staggered along the axial direction, with a staggered angle of 120° between adjacent baffles, to atomize the gas-liquid mixture. The inner wall of the gradually expanding trumpet-shaped guide pipe is attached with a guide cone strip, and a baffle-type vortex atomizer is installed inside to further atomize the gas-liquid mixture. The air-driven transverse rotary cutter is located behind the gradually expanding trumpet-shaped guide pipe and is supported and fixed by the fixed column. It consists of two V-shaped folded fan blades to enhance the atomization of the gas-liquid mixture.

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