Efficient, clean and comprehensive mining and utilization method for deep coal and associated resources thereof

Abstract

The invention discloses a high-efficiency clean comprehensive mining and utilization method for deep coal and associated resources thereof, which comprises the following steps: arranging a fully mechanized coal mining face in a deep coal seam, performing high-efficiency mining by adopting a comprehensive mechanized coal mining process, recovering deep coal resources, and synchronously extracting coal bed gas in the deep coal seam. Coal bed gas is guided out to the ground to be collected by drilling a gas drainage hole, the coal bed gas is purified and then used as energy, mine water is pumped and drained, the mine water is lifted to the ground surface through a drainage pipeline, and purification treatment such as precipitation and filtration is conducted. Therefore, real-time monitoring and dynamic adjustment of each link are realized by adopting a comprehensive monitoring and cooperative control system, operation safety and efficient utilization of resources are ensured, the coal bed gas recovery rate and the mine water utilization rate are remarkably improved, and the problems of low coal bed gas recovery rate, associated resource waste and environmental pollution in the prior art are solved; and efficient, clean and comprehensive mining and utilization of deep coal and associated resources thereof are realized.

Description

Technical Field

[0001] The present invention relates to the technical field of coal mining, and in particular to a method for the efficient, clean and comprehensive mining and utilization of deep coal and its associated resources. Background Art

[0002] With the continuous development of the coal industry, the mining depth of deep coal resources continues to increase, and the reserves of associated resources such as coalbed methane are also gradually increasing. At present, the mining of coal and its associated resources mainly relies on traditional mechanized coal mining technology. To a certain extent, it can achieve efficient mining of coal resources, but the recovery and utilization of associated resources such as coalbed methane still has certain limitations.

[0003] The main drawback of existing technologies is the low efficiency of coalbed methane recovery, which results in large amounts of associated gas being directly discharged into the environment outside the mine, resulting in both energy waste and safety hazards. Furthermore, as a significant source of greenhouse gases, coalbed methane emissions further exacerbate the burden of environmental pollution and climate change. Due to the lack of effective technologies for the comprehensive recovery and utilization of associated resources, overall resource utilization efficiency is low, making it difficult to achieve efficient, clean, and comprehensive utilization of deep coal resources. Summary of the Invention

[0004] The present invention aims to solve one of the technical problems in the related art at least to a certain extent.

[0005] To this end, the purpose of the present invention is to propose a method for efficient, clean and comprehensive mining and utilization of deep coal and its associated resources. By simultaneously extracting coalbed methane and recovering mine water, the emission of associated gas and waste of water resources are reduced, the utilization efficiency of coal and its associated resources is effectively improved, and the problems of low coalbed methane recovery rate and serious environmental pollution in the existing technology are solved.

[0006] To achieve the above-mentioned object, the present invention proposes a method for the efficient, clean and comprehensive mining and utilization of deep coal and its associated resources, comprising the following steps: S1. Arrange fully mechanized mining faces in deep coal seams and use comprehensive mechanized mining techniques for efficient mining and recovery of deep coal resources. S2. Simultaneously extracting coalbed methane from the deep coal seam, extracting the coalbed methane to the surface for collection by drilling gas drainage holes, and utilizing the coalbed methane as energy after purification; S3. Pumping mine water, lifting the mine water to the surface through the drainage pipe, and undergoing purification treatment such as sedimentation and filtration, so that the treated water meets the requirements for reuse or discharge standards, and is used for underground watering and dust reduction or ground recycling; S4. Establish a comprehensive monitoring and coordinated control system to conduct real-time monitoring and coordinated control of coal mining equipment, gas extraction, mine drainage and ventilation, maintain underground gas concentration within a safe range, and adjust ventilation and water sprinkling measures as needed to ensure a safe and efficient mining process, comprehensive utilization of resources, and environmental friendliness of the mining area.

[0007] The present invention discloses a method for the efficient, clean and comprehensive mining and utilization of deep coal and its associated resources. The method realizes efficient mining by arranging a comprehensive mining face in a deep coal seam and adopting a longwall comprehensive mining process. At the same time, a porous network of gas extraction holes and a ground extraction pipeline network are arranged, so that coalbed methane can be simultaneously extracted, purified and recycled before and during mining. Mine water is treated by multi-stage sedimentation and filtration purification to achieve standard discharge or reuse. On this basis, a comprehensive monitoring and collaborative control system is adopted to realize real-time monitoring and dynamic adjustment of each link, ensuring operation safety and efficient resource utilization, significantly improving the coalbed methane recovery rate and mine water utilization rate, solving the problems of low coalbed methane recovery rate, waste of associated resources and environmental pollution in the prior art, and realizing efficient, clean and comprehensive mining and utilization of deep coal and its associated resources.

[0008] Specifically, the mechanized mining of the deep coal seams adopts a comprehensive mechanized longwall mining process, and utilizes a fully mechanized mining face consisting of a coal mining machine, hydraulic supports and scraper conveyors to achieve efficient recovery of coal resources.

[0009] Specifically, the coalbed methane is extracted by drilling gas pre-extraction holes in front of the mining face or in the coal seam, arranging a gas extraction pipeline network, and continuously draining the coalbed methane to the surface before and during mining, thereby reducing the underground gas concentration.

[0010] Specifically, the extracted coalbed methane is dehydrated, dust-removed and purified, and then transported to the ground for power generation or as civil gas supply, thereby realizing the clean utilization of coalbed methane resources.

[0011] Specifically, the collection and treatment of the mine water is achieved by setting up a multi-stage drainage system, including temporary storage of gushing water in an underground water tank, using a lifting pump station to send the mine water to a surface sedimentation tank for solid-liquid separation, and then purifying the mine water through a filtration device.

[0012] Specifically, the treated mine water that meets the standards is reused in the coal mine production process, including as water for sprinkling and dust reduction at the mining face and cooling water, or for vegetation irrigation and industrial water in the mining area, thereby realizing the recycling of mine water resources.

[0013] Specifically, the comprehensive monitoring and coordinated control system includes gas sensors, water level monitors and equipment operation monitoring devices. The system monitors parameters such as gas concentration, support pressure, and drainage volume in real time, and controls the operation of ventilators, drainage pumps and coal mining equipment in a coordinated manner to ensure the safety of underground operations.

[0014] Specifically, a mine ventilation method combining zoned ventilation and local ventilation is adopted to deliver fresh air to deep working faces, and spray devices are deployed in the mining area to spray water to reduce dust, reduce coal dust concentration, and improve the working environment and mine safety.

[0015] Additional aspects and advantages of the present invention will be set forth in part in the description which follows and, in part, will be obvious from the description which follows, or may be learned through practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the following description of the embodiments in conjunction with the accompanying drawings, in which: Figure 1 This is a schematic diagram of the method for efficient, clean and comprehensive mining and utilization of deep coal and its associated resources according to the present invention. DETAILED DESCRIPTION

[0017] The embodiments of the present invention are described in detail below. Examples of the embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are intended to be used to explain the present invention and are not to be construed as limiting the present invention. On the contrary, the embodiments of the present invention include all variations, modifications, and equivalents that fall within the spirit and scope of the appended claims.

[0018] The following describes the method for efficient, clean and comprehensive mining and utilization of deep coal and its associated resources according to an embodiment of the present invention with reference to the accompanying drawings.

[0019] like Figure 1 As shown, the method for efficient, clean and comprehensive mining and utilization of deep coal and its associated resources according to the embodiment of the present invention may include the following steps: S1. Arrange fully mechanized mining faces in deep coal seams and adopt comprehensive mechanized coal mining technology for efficient mining and recovery of deep coal resources.

[0020] It should be noted that the fully mechanized mining working face in this embodiment adopts high-strength hydraulic supports and high-efficiency coal mining machines, which can adapt to the high ground stress environment of deep coal seams, and by optimizing the support technology and working face layout, ensure the stability of the tunnel and the safety of operations during the mining process, thereby ensuring the efficient mining of coal resources.

[0021] S2. Simultaneously extract coalbed methane from deep coal seams and conduct it to the surface for collection by drilling gas extraction holes. The coalbed methane is purified and then used as energy.

[0022] It should be noted that the gas extraction holes in this embodiment are arranged in a porous network to form an effective extraction system, which significantly improves the coalbed methane extraction efficiency; at the same time, the ground collection system is equipped with multi-stage purification equipment, which can realize the graded purification treatment of moisture, dust and harmful gases in the coalbed methane, ensuring that the extracted coalbed methane meets the utilization standards.

[0023] S3. Pumping the mine water, lifting it to the surface through drainage pipes, and subjecting it to purification treatments such as sedimentation and filtration, so that the treated water meets the requirements for reuse or discharge standards, and can be used for underground sprinkling to reduce dust or for ground recycling.

[0024] It should be noted that the mine water pumping and purification process in this embodiment adopts a multi-stage sedimentation tank and a high-efficiency filtration device, which can efficiently remove suspended matter and harmful components. The resulting treated water can be directly used as water for underground spraying and dust suppression, further improving the recycling rate of water resources and reducing the impact on the environment.

[0025] S4. Establish a comprehensive monitoring and coordinated control system to conduct real-time monitoring and coordinated control of coal mining equipment, gas extraction, mine drainage and ventilation, maintain underground gas concentration within a safe range, and adjust ventilation and water sprinkling measures as needed to ensure a safe and efficient mining process, comprehensive utilization of resources, and environmental friendliness of the mining area.

[0026] It should be noted that the comprehensive monitoring and collaborative control system in this embodiment integrates gas sensors, water level monitors and operating equipment status sensors, can obtain various parameters in real time, and dynamically adjust the extraction and ventilation processes based on feedback information, to achieve safety monitoring and energy-saving optimization of the entire process, and ensure the efficient, safe and comprehensive utilization of deep coal and its associated resources.

[0027] Specifically, a fully mechanized mining face is arranged in a deep coal seam, and a mechanized fully mechanized mining face composed of a high-strength hydraulic support and an efficient coal mining machine is used for efficient mining to ensure the stability of the roadway and the safety of the operation; during the coal mining process, coalbed methane is extracted simultaneously, and a porous network gas extraction system is used to guide the coalbed methane out and pass through a multi-stage purification treatment on the ground to ensure the efficient recovery and standard utilization of the coalbed methane; at the same time, the mine water is pumped and drained and subjected to multi-stage sedimentation and filtration purification treatment, so that the purified mine water meets the standard for discharge or is reused in underground water sprinkling and dust reduction, thereby reducing the waste of water resources; a comprehensive monitoring and collaborative control system is used throughout the process, integrating gas sensors, water level monitors, etc., to achieve real-time monitoring and dynamic adjustment of coal mining equipment, gas extraction and mine drainage, maintaining operational safety and efficient comprehensive utilization of energy. This method solves the problems of low coalbed methane recovery efficiency, waste of associated resources and environmental pollution in the background technology, significantly improves the comprehensive utilization efficiency of coal and associated resources, and realizes efficient, safe and environmentally friendly mining of deep coal resources.

[0028] In one embodiment of the present invention, Figure 1 As shown, the mechanized mining of deep coal seams adopts a comprehensive mechanized longwall mining process, using a fully mechanized mining face consisting of a coal mining machine, hydraulic supports and scraper conveyors to achieve efficient recovery of coal resources.

[0029] It should be noted that the longwall mining process in this embodiment can form a continuous coal mining cutting surface, the coal mining machine efficiently cuts coal, the hydraulic support provides reliable roof support, and the scraper conveyor efficiently transports coal, realizing seamless connection from coal mining to transportation; by reasonably arranging the working face length and cutting sequence, the residual coal pillar is reduced, the risk of roof collapse is reduced, the resource recovery rate and working face production efficiency are significantly improved, and at the same time, the operation safety in deep high-ground stress environment is enhanced.

[0030] In one embodiment of the present invention, Figure 1 As shown in the figure, coalbed methane is extracted by drilling gas pre-extraction holes in front of the mining face or in the coal seam, arranging a gas extraction pipeline network, and continuously draining the coalbed methane to the surface before and during mining, thereby reducing the underground gas concentration.

[0031] It should be noted that the gas pre-extraction holes in this embodiment are combined with the structural characteristics of the coal seam and the distribution of gas content, and adopt a multi-angle and multi-channel distribution method to form a three-dimensional extraction network, which significantly improves the coalbed methane extraction coverage and extraction negative pressure, and avoids hidden dangers in coal seam gas-rich areas; at the same time, the extraction pipeline network is equipped with high-strength extraction pipes and sealed joints, which can withstand the extraction load under high ground stress conditions in deep coal seams, ensuring the efficiency and stability of the extraction process.

[0032] In one embodiment of the present invention, Figure 1As shown, the extracted coalbed methane is dehydrated, dust-removed and purified, and then transported to the ground for power generation or as civil gas supply, thereby realizing the clean utilization of coalbed methane resources.

[0033] It should be noted that the coalbed methane purification process in this embodiment adopts multi-stage condensation, dust removal and deep purification steps, including cyclone separation, condensate separation, activated carbon adsorption and other technical links to ensure that harmful components such as moisture, dust, sulfide and so on in the coalbed methane are efficiently removed; the purified coalbed methane is classified according to calorific value and purity parameters and transported to gas generator sets or municipal gas pipelines to maximize the economic value and environmental benefits of coalbed methane and reduce greenhouse gas emissions.

[0034] In one embodiment of the present invention, Figure 1 As shown, the collection and treatment of mine water is achieved by setting up a multi-stage drainage system, including the temporary storage of gushing water in the underground water tank, the use of a lifting pump station to send the mine water to the surface sedimentation tank for solid-liquid separation, and then the mine water is purified by a filtration device.

[0035] It should be noted that the multi-stage drainage system in this embodiment can not only flexibly respond to fluctuations in water inflow, but also reduce the risk of underground flooding through multi-stage water tank peak storage and high-efficiency pump station cascade lifting, thereby ensuring the normal operation of mining equipment and ventilation systems; in the surface sedimentation tank, sedimentation aids and mechanical stirring technology are used to significantly improve the separation efficiency of suspended matter and mud and sand. The purified water is further removed from tiny particles and harmful ions through multi-layer sand filtration or membrane treatment equipment to ensure that the water quality of mine water meets the standards.

[0036] In one embodiment of the present invention, Figure 1 As shown in the figure, the treated mine water that meets the standards is reused in the coal mine production process, including as water for sprinkling dust and cooling at the mining face, or for irrigation of vegetation in the mining area and industrial water, thus realizing the recycling of mine water resources.

[0037] It should be noted that the mine water reuse process in this embodiment not only takes into account the compliance of water quality standards, but also fully considers the dynamic balance and regional distribution of reused water. Water sources are allocated on demand through automated scheduling devices to ensure the continuity of water spraying on the working surface and equipment cooling water supply. At the same time, a vegetation irrigation system or an industrial water supply network can be built outside the mining area to maximize the comprehensive utilization path of mine water, realize the full-process recycling of water resources, and reduce the mining area's dependence on external water sources and environmental pressure.

[0038] In one embodiment of the present invention, Figure 1As shown, the comprehensive monitoring and coordinated control system includes gas sensors, water level monitors and equipment operation monitoring devices. The system monitors parameters such as gas concentration, support pressure, and drainage volume in real time, and controls the operation of ventilators, drainage pumps and coal mining equipment in a coordinated manner to ensure the safety of underground operations.

[0039] It should be noted that the monitoring and control system in this embodiment integrates a multi-channel data acquisition and analysis module, which can upload sensor data to the ground monitoring center in real time. It uses a visual interface and intelligent early warning algorithm to quickly respond to situations such as gas exceeding the limit and equipment abnormalities, realize automated linkage control, over-limit alarm and safe shutdown, and significantly improve the safety management and control level of deep coal mine operations.

[0040] In one embodiment of the present invention, Figure 1 As shown, a mine ventilation method combining zoned ventilation and local ventilation is adopted to deliver fresh air to deep working faces, and spray devices are deployed in the mining area to spray water to reduce dust, reduce coal dust concentration, and improve the working environment and mine safety.

[0041] It should be noted that the ventilation and spraying system in this embodiment utilizes intelligent airflow distribution and automatic spray intensity adjustment, which can automatically increase the air volume or increase the spray frequency when the gas or dust concentration fluctuates, effectively suppressing the diffusion of floating dust and harmful gases; in deep high-temperature environments, it can also be combined with underground cold air injection technology to further improve the working thermal environment, ensure the safety and comfort of workers, and enhance the coal mine's production safety capabilities and green mining level.

[0042] Example 1: Extraction and purification scheme for deep coal seams with high gas content Background overview: This embodiment selects a deep coal seam with a high gas content of about 1,200 meters in depth and 8 meters in thickness as the object. The gas pressure is about 1.2 MPa, and there are safety hazards of gas outburst and co-mining of coal and gas. According to my country's coal mine gas outburst prevention and control standards. Therefore, before conventional mining, the coal seam needs to be pre-extracted for gas treatment to reduce the gas content and gas outburst intensity. In response to the above-mentioned high-gas conditions, this embodiment has designed a set of ground drilling and coalbed methane purification and utilization processes. By enhancing gas extraction efficiency and purification measures, the coalbed gas is safely and efficiently recovered and utilized.

[0043] Process flow: The process steps of this embodiment include the following stages: Drilling and Staged Fracturing: Based on the coal seam's occurrence, a 216mm diameter vertical well was laid out to the target coal seam. Multi-stage hydraulic fracturing was then performed within the coal seam. Three stages were constructed, each approximately 20 meters long. High-pressure water pumps were used to inject fracturing fluid, creating a network of fractures in the coal seam and improving the permeability of the low-permeability coal seam. After fracturing, the coal seam's permeability increased significantly, creating pathways for subsequent gas extraction.

[0044] Supercritical CO2 injection to displace gas: After the fracture network is formed, supercritical CO2 fluid is injected into the coal seam through an injection pipeline at a pressure of approximately 10 MPa and a temperature of 35°C (exceeding the critical temperature of CO2, 31.1°C). After 48 hours of injection, the wellhead is shut in for three days to allow the CO2 to diffuse fully within the coal seam and adsorb into the pores. Supercritical CO2 has a strong displacing effect on coalbed methane (CH4), displacing CH4 molecules adsorbed in the coal seam. During the shut-in period, a large amount of CH4 is forced out of the coal matrix and into the fractures, where it is free and accumulates.

[0045] Gas extraction and surface purification: The wellhead is opened, and the wellbore is switched from injection mode to gas production mode. A beam pump (surface scavenging pump) coupled with a vacuum ejector applies negative pressure to the coal seam, continuously extracting the mixed gas (CH4, a small amount of CO2, and water vapor) from the fractures to the surface. A surface gas purification and utilization system is established. First, a gas-liquid separator removes entrained condensate and a small amount of coal dust. Then, a pressure swing adsorption (PSA) device separates and recovers the CO2 from the mixed gas, increasing the output methane concentration from approximately 60% to over 95%. Finally, the purified methane is compressed and fed into the mine's gas generators or an external transmission pipeline. The recovered CO2 is compressed again and stored for reuse in the next injection cycle, reducing operating costs and achieving greenhouse gas sequestration.

[0046] Steam pyrolysis oil recovery: After the gas extraction rate reaches a stable level (methane production significantly decreases) in the first stage, high-temperature superheated steam (approximately 400°C, 12 MPa) is generated by a boiler and injected into the same fractured well section. The high-temperature steam flows through the coal seam fractures, pyrolyzing the remaining coal in situ. This decomposes the deep coal into coal tar vapor and water gas (primarily composed of H₂, CO, and residual CH₄). After approximately seven days of continuous steam injection, injection is stopped and the wellhead is opened. The pyrolysis-generated mixed gas and steam are extracted to the surface for condensation and separation using the aforementioned extraction system. After cooling in a condenser, liquid coal tar and hydrogen- and carbon monoxide-rich gas are recovered. The collected coal tar yield is approximately 8% to 10% of the original coal mass, comparable to the yield of oil-rich coal tar. The resulting coal tar can be used as a chemical feedstock or fuel oil after preliminary distillation, while the water gas is purified and de-coked for use in power generation or as a syngas feedstock, achieving efficient conversion and utilization of the organic components in coal.

[0047] Acid leaching to extract associated elements: After the coal seam's organic matter has been largely converted through pyrolysis, the remaining coal mineral components are leached by injecting a high-temperature, dilute sulfuric acid solution (10% concentration, 80°C). This transfers valuable elements associated with the coal (such as Ga, Li, and rare earth elements) from the solid phase into the solution. Groundwater pumps then pump the leached solution to the surface, where it enters a liquid-solid separation and solvent extraction system to extract the target metal element concentrate. For example, testing has shown that approximately 5 grams of gallium are present per ton of coal, and the acid leaching extraction rate can reach over 90%. The gallium in the resulting acidic solution is then extracted, enriched, and recovered, achieving comprehensive utilization of the rare earth metals associated with the coal.

[0048] Residue filling and solidification: After leaching is completed, a high-temperature, supersaturated Ca(OH)2 solution is injected into the remaining pores and fissures in the coal seam for in-situ filling. The Ca(OH)2 solution chemically reacts with the CO2 and sulfate ions previously remaining in the coal seam to form insoluble CaCO3 and CaSO4 precipitates. These reaction products settle and cement within the fissures, cementing the loose coal residue into a solid filling. After one month of curing, the compressive strength of the filling increased to over 5 MPa, equivalent to 120% of the original coal strength. This step achieves in-situ reinforcement of the goaf, effectively preventing large-scale caving and surface subsidence, and protecting the ecological environment of the mining area.

[0049] Key Parameters: In this example, the key process parameters for each step are as follows: staged fracturing injection rate of 120-150 L / min, fracture radius of approximately 30 m; CO2 injection rate of approximately 500 tons, with CO2 adsorption and replacement time of 3-5 days for each coal seam section; gas extraction negative pressure maintained at approximately -0.08 MPa to ensure continuous and stable gas production; steam injection temperature of no less than 380°C to ensure pyrolysis; acid leaching solution pH controlled to <1 to enhance leaching efficiency, with the total injection volume commensurate with the coal seam pore volume; Ca(OH)2 solution concentration of approximately 15%, with the total injection volume equivalent to the produced material volume to fill the voids. Regarding materials, the fracturing fluid uses a clear water base with 0.2% environmentally friendly viscosity enhancer added; CO2 is provided by purified industrial byproduct gas; superheated steam is supplied by a gas-fired boiler; sulfuric acid is industrial dilute sulfuric acid heated above ground; and the Ca(OH)2 solution is prepared on-site by digesting quicklime. These parameter ranges can be adjusted based on the coal seam occurrence and site conditions to achieve optimal process results.

[0050] Experimental results: Through the above process, the coal seam gas pressure was reduced from 1.2 MPa to 0.3 MPa, and the volume concentration of gas in the working face return air flow was reduced to 0.3%, significantly below the safety limit of 1%, eliminating the potential for gas over-limit and outbursts. Furthermore, during the pyrolysis recovery phase, approximately 120 tons of crude oil-like coal tar were produced, with an average yield of 0.08 tons per ton of coal, consistent with existing pyrolysis test results for oil-rich coal. The produced water gas contained approximately 60% H₂ and CO in total, with a low calorific value exceeding 10 MJ / Nm₃. After combustion and power generation tests, it was used to power the mine, achieving a power generation efficiency of approximately 35%. Furthermore, various associated metal elements were successfully recovered from the acid leachate, including gallium at a concentration of 50 mg / L. After precipitation and enrichment, a high-purity Ga₂O₃ product was obtained, effectively utilizing rare elements in the coal. Finally, the filling and solidification process was effective, with virtually no significant subsidence in the goaf. After drilling sampling and testing, the filling body was found to be tightly bonded and of uniform strength. Mine pressure monitoring showed that the roof movement was less than 20 mm, far lower than the hundreds of mm of subsidence when there was no filling.

[0051] Expected technical effects: This embodiment achieves the simultaneous efficient recovery and safe mining of gas and coal resources for deep, high-gas coal seams. The optimized layout of the gas extraction and purification system significantly improves the methane recovery rate and purity, with a gas utilization rate of over 80%, eliminating the risk of gas accidents and providing clean energy. At the same time, supercritical CO2 fracturing and displacement increases the gas output rate of low-permeability coal seams and shortens the extraction cycle. The mine gas concentration is significantly reduced, meeting the extraction standard requirements, creating a safe environment for subsequent mining of the coal seam. Through in-situ pyrolysis of coal and extraction of associated resources, "one-time mining and comprehensive utilization" is achieved, fully tapping the value of fossil energy and mineral elements in coal. The acquisition of clean fuels such as coal tar and water gas reduces the emission of atmospheric pollutants caused by direct coal combustion. The deep goaf is reinforced by in-situ filling of residues, avoiding surface subsidence and groundwater loss caused by traditional coal mining with coal pillars or underground mining. This example demonstrates the effectiveness of the method of the present invention under conditions of high gas content, significantly improving the safety and economy of deep coal and coalbed methane resource development.

[0052] Example 2: Adaptability of fully mechanized mining technology and mine water control scheme under hard coal and rock conditions Background Overview: This example is designed for a coal seam at a depth of 1,000 meters, with a 5-meter-thick coal seam and hard roof and floor rock. This coal seam is dense and hard, with a Proctor hardness coefficient f-value of approximately 8-10. The roof is composed of sandstone with high integrity and is extremely resistant to caving, representing a typical "two-hard" mining condition (hard coal body and hard roof). Traditional fully mechanized mining processes face numerous challenges under these conditions: the extremely low permeability of the coal seam makes pre-extraction of gas difficult, resulting in high gas outflow and drainage difficulties in the fully mechanized mining face; the hard roof is not prone to collapse, resulting in concentrated pressure in the mining area, which can easily lead to rock bursts and roof failures; and deep, hard rock formations are often rich in aquifers, increasing the risk of water inrush and drainage volume, placing higher demands on mine water treatment. To verify the adaptability of the present method to hard coal rock conditions, this example introduces in-situ comprehensive mining and utilization technology for the coal seam, without affecting normal fully mechanized mining operations, to pre-treat and coordinate development of the fully mechanized mining face, alleviating these challenges and improving resource recovery.

[0053] Process flow: This embodiment combines the method of the present invention with the fully mechanized mining process. The specific process is as follows: Pre-fracturing and permeability enhancement of the working face: After the completion of the cutting and excavation of the fully-mechanized working face and before mining, the coal seam and roof are pre-treated using the well layout and fracturing technology of the present invention. An injection well is drilled from the surface to the coal seam (and to the interface of the roof rock layer if necessary) every 50 meters along the direction of the working face, and multi-stage hydraulic fracturing is implemented. For hard roof rock, the fracturing pressure is increased to 15 MPa to form directional cracks in the roof, inducing it to easily fall during mining. At the same time, a dense fracture network is formed in the coal seam to improve the permeability and stress release of the coal body. Pre-fracturing not only reduces the strength of the coal rock, which is beneficial for the cutting of the coal mining machine, but also provides a channel for the subsequent injection of fluid.

[0054] Gas pre-extraction and regional gas control: After fracturing is completed, supercritical CO2 is injected into the coal seam through surface injection wells to displace gas, followed by a period of soaking for adsorption. Next, the wellhead equipment is modified to extraction mode, and a surface vacuum pumping station is used to perform regional gas extraction throughout the fully mechanized mining section. Several injection wells also serve as extraction wells, preemptively extracting CH4 from the coal seam fractures to the surface. A surface gas manifold is installed to collect and process gas produced from multiple wells. This pre-extraction of a large amount of gas significantly reduces gas outbursts from the working face during mining, and the gas concentration in the return airflow remains stable at around 0.3%, preventing it from exceeding the limit. Compared to the unprovoked gas extraction rate of approximately 50%, with a large amount of gas entering the ventilation system and being wasted, this process achieves a gas capture rate exceeding 80%, significantly improving the mine's gas control capabilities.

[0055] Fully mechanized roof caving and simultaneous steam injection: After pre-gas extraction, the working face installed fully mechanized mining equipment (hydraulic supports, shearers, etc.) according to conventional procedures and began mining operations. Because the roof had been pre-cracking and was relatively fragmented, mining could proceed almost instantaneously during the mining process, preventing large areas of suspended roof and ensuring effective roof management. As the working face advanced into the middle and late stages, a simultaneous steam injection and pyrolysis process was implemented in each working face segment to further improve coal recovery and control the hardened roof. High-temperature superheated steam (350°C, 10 MPa) was injected into the unmined coal pillars through a set of surface boreholes (one every 200 meters). The steam diffused through the coal seam fissures, in-situ heating the unmined coal mass and initiating pyrolysis and grading. Extraction pipelines located at both ends of the stope collected the coal tar vapor and gas produced by pyrolysis to prevent it from entering the working face tunnels. This process is equivalent to underground pyrolysis oil recovery in the remaining coal pillars during fully mechanized mining, achieving "mining coal and oil simultaneously." Calculations show that every 10-meter advance in the mining face can pyrolyze approximately 2,000 tons of coal, yielding an additional 150 tons of coal tar and producing combustible gases rich in H2 and CH4. These oil and gas products are transported via surface pipelines to a nearby separation unit for recycling. This not only improves overall resource recovery, but also reduces residual energy in the coal-retaining area and mitigates the risk of post-mining spontaneous combustion.

[0056] Mine Water Control and Recycling: Under hard coal rock conditions, the main water sources encountered during mining include: condensed water from water vapor injected into the coal seam, water gushing from high-level aquifers, and acidic wastewater generated during post-mining acidification. This embodiment establishes a comprehensive integrated drainage and purification system both above and below the mine. Drainage pipelines are used at the working face to promptly direct water gushing from the roof during roof pressure into a floor sump, where it is then pumped to a surface treatment station by drainage pumps. Liquids generated during surface steam injection and acid leaching are directly pumped back through production pipelines to surface storage tanks. The surface water treatment station includes units such as flocculation and sedimentation, hollow fiber ultrafiltration, and reverse osmosis to separately treat mine water and production wastewater. First, the coal tar condensate and acid leachate are mixed and then neutralized to a pH of approximately 7 with the addition of lime milk. The resulting CaSO4 precipitate is separated from the coal slime by a filter press, and the filter cake is centrally processed. The neutralized clear liquid, along with the mine water, enters the ultrafiltration and reverse osmosis systems to remove residual suspended matter and dissolved salts, producing purified water. Part of the purified water is used to produce new superheated steam (to replenish boiler water), while the remaining portion is used for underground sprinkling to suppress dust and for production water in the coal preparation plant, thus achieving water resource recycling. Statistics show that the comprehensive utilization rate of mine water and process water in this embodiment reaches approximately 85%, far exceeding the domestic coal mine average of approximately 26%. This utilization rate is even close to the target value of 80-85% previously envisioned by advanced domestic mining areas, demonstrating the significant advantages of this method in terms of mine water resource utilization.

[0057] Acidification mining and filling of tunnels: After the fully mechanized mining face is mined, the remaining hard coal pillars and the residual coal area on their floor are acidified, leached, and filled to accelerate resource extraction and tunnel closure in the final stage. A high-temperature sulfuric acid solution is injected into the remaining coal pillars through pre-drilled holes for leaching, causing the associated valuable metals present in the coal-bearing strata to dissolve into the liquid phase; the acid solution is then extracted and the metal elements recovered. Subsequently, a Ca(OH)2 solution is used to fill and solidify the area, filling the goaf and fissures into a stable cemented mass, as in Example 1 to generate a CaCO3 / CaSO4 cement. This is particularly important under hard roof conditions: the exposed space on the roof is supported after filling, and a large-scale collapse and impact after the roof breaks will not occur, thus avoiding the risk of rock burst after mining is completed. At the same time, after the tunnel is fully filled, oxygen is isolated from entering, effectively preventing the oxidation and spontaneous combustion of the coal residues in the goaf. The backfill also sealed water-conducting fissures in the roof and floor, significantly reducing water inflow after mining. Observations in tunnels near the fully mechanized mining face revealed minimal roof deformation in the backfill area, and the mine pressure remained moderate, validating the backfill's effectiveness in maintaining tunnel stability and preventing water intrusion.

[0058] Key Parameters: This embodiment utilizes enhanced parameter selection to address the "two hard" conditions. During the hydraulic fracturing phase, high-viscosity guar gum fracturing fluid is used, with a sand ratio of 20% and a fracture radius of 40 m to fully fracture the hard coal. Approximately 300 tons of CO2 are injected, and each well is shut down for 5 days to ensure adequate displacement. The gas extraction negative pressure is −0.1 MPa to accommodate the high gas drainage resistance. During the simultaneous steam injection and pyrolysis phase, the steam injection rate is 10 tons per hour to ensure sufficient heat penetration into the hard coal. A 20% redundancy rate for processing units ensures stable operation during peak hours. The acid leaching solution and Ca(OH)2 slurry concentrations are 10% and 20%, respectively, to accommodate the mineral content of the hard rock formation. Regarding equipment, a high-pressure plunger pump is selected to meet the 15 MPa injection requirement, and a steam generator with a power of 10 MW is used. These parameters were optimized through pilot testing and meet the requirements for the safe and efficient implementation of the present method under hard conditions.

[0059] Experimental Results: Successful application in the aforementioned hard coal seam conditions yielded excellent results. During the pre-extraction phase, coal seam gas pressure dropped from 0.9 MPa to 0.3 MPa. The instantaneous peak gas outburst during initial roof caving at the working face was reduced by 70%. Underground monitoring revealed that the gas concentration in the return air flow remained below 0.5%, effectively controlling gas over-limits. Compared to frequent gas over-limits at the working face without this method, this embodiment achieved zero over-limits throughout the entire mining process. Regarding roof management, fracturing and backfilling virtually eliminated large areas of overhanging roof and intense pressure. The maximum operating resistance observed for the hydraulic supports was reduced by 25%, and no cases of support instability or crushing occurred, demonstrating that controlled fracture of the hard roof was achieved. Regarding recovery rate, the simultaneous implementation of pyrolysis oil recovery and acid leaching resulted in additional gains in coal tar and mineral elements in addition to the raw coal produced. The pilot area produced 200,000 tons of raw coal, generating a comprehensive energy output of 215,000 tons of standard coal equivalent, for an equivalent recovery rate of 107.5%. Approximately 1,800 tons of coal tar were produced, with an oil content of approximately 9%, consistent with laboratory predictions for oil-rich coal tar. Approximately 500 cubic meters of gallium-rich solution were extracted, from which 50 kilograms of crude gallium were recovered. Mine water treatment was also highly effective: during the trial, 1.2 million cubic meters of water was discharged, 1.02 million cubic meters of water was reused, and a water utilization rate of 85% was achieved. After treatment, the quality of the external drainage met all environmental standards, with no environmental violations occurring. Compared to a utilization rate of only 30% before the renovation, mine water utilization has increased significantly, achieving the "zero-emission, closed-loop" green mine goal. These data demonstrate that the method disclosed in this invention can achieve highly efficient resource extraction and environmental management even under fully-mechanized mining conditions in hard coal and rock.

[0060] Expected technical effect: This embodiment fully demonstrates the supporting and improving role of the present invention on the traditional comprehensive mining process under the conditions of hard coal seams. On the one hand, the pre-fracture permeability enhancement and CO2 displacement extraction significantly reduced the gas content and pressure, providing safety guarantees for comprehensive mining operations. The substantial reduction in gas outburst reduces the ventilation load of the working face and eliminates the hidden dangers of gas accidents. On the other hand, after the hard roof is treated with fracturing and filling, the collapse law is controlled, the stress release of the roof is gentle, the adaptability of the comprehensive mining equipment is enhanced, the stability of the mining site is improved, and disasters such as rock burst are avoided. In terms of resource utilization, through simultaneous pyrolysis and acid leaching, the cascade recovery of coal-associated resources is achieved, breaking through the previous limitations of comprehensive mining that only mines coal while ignoring the oil, gas and mineral elements in coal, and creating additional economic value. In particular, the comprehensive management and reuse of mine water reduces the drainage load and surface subsidence of deep well mining, reaching a new level of mine water resource utilization. In general, this embodiment proves that the method of the present invention can be integrated with mechanized comprehensive mining under hard and complex geological conditions to form a composite mining mode of "comprehensive mining + in-situ extraction". While ensuring safe and efficient coal mining, it achieves clean and efficient utilization of coal and its associated resources, and has good industrial application prospects and promotion value.

[0061] In summary, the method for efficient, clean and comprehensive mining and utilization of deep coal and its associated resources in the embodiment of the present invention achieves efficient mining by arranging a comprehensive mining face in the deep coal seam and adopting a longwall comprehensive mining process, and at the same time arranges a porous network of gas extraction holes and a ground extraction pipeline network, so that coalbed methane can be simultaneously extracted, purified and recycled before and during mining; mine water is treated through multi-stage sedimentation and filtration purification to achieve standard discharge or reuse; on this basis, a comprehensive monitoring and collaborative control system is adopted to realize real-time monitoring and dynamic adjustment of each link to ensure operational safety and efficient utilization of resources, significantly improve the coalbed methane recovery rate and mine water utilization rate, solve the problems of low coalbed methane recovery rate, waste of associated resources and environmental pollution in the existing technology, and realize efficient, clean and comprehensive mining and utilization of deep coal and its associated resources.

[0062] Although the embodiments of the present invention have been shown and described above, it will be understood that the above embodiments are exemplary and are not to be construed as limitations on the present invention. A person skilled in the art may change, modify, replace and deform the above embodiments within the scope of the present invention.

Claims

1. A method for efficient, clean and comprehensive mining and utilization of deep coal and its associated resources, characterized in that: The following steps are included: S1. Arrange fully mechanized mining faces in deep coal seams and use comprehensive mechanized mining techniques for efficient mining and recovery of deep coal resources. S2. Simultaneously extracting coalbed methane from the deep coal seam, extracting the coalbed methane to the surface for collection by drilling gas drainage holes, and utilizing the coalbed methane as energy after purification; S3. Pumping mine water, lifting the mine water to the surface through the drainage pipe, and undergoing purification treatment such as sedimentation and filtration, so that the treated water meets the requirements for reuse or discharge standards, and is used for underground watering and dust reduction or ground recycling; S4. Establish a comprehensive monitoring and coordinated control system to conduct real-time monitoring and coordinated control of coal mining equipment, gas extraction, mine drainage and ventilation, maintain underground gas concentration within a safe range, and adjust ventilation and water sprinkling measures as needed to ensure a safe and efficient mining process, comprehensive utilization of resources, and environmental friendliness of the mining area.

2. The method for efficient, clean and comprehensive mining and utilization of deep coal and its associated resources according to claim 1 is characterized in that: The mechanized mining of the deep coal seams adopts a comprehensive mechanized longwall mining process, and utilizes a fully mechanized mining face consisting of a coal mining machine, hydraulic supports and scraper conveyors to achieve efficient recovery of coal resources.

3. The method for efficient, clean and comprehensive mining and utilization of deep coal and its associated resources according to claim 1, characterized in that: The coalbed methane is extracted by drilling gas pre-extraction holes in front of the mining working face or in the coal seam, arranging a gas extraction pipeline network, and continuously extracting the coalbed methane to the surface before and during mining, thereby reducing the underground gas concentration.

4. The method for efficient, clean and comprehensive mining and utilization of deep coal and its associated resources according to claim 3 is characterized in that: The extracted coalbed methane is dehydrated, dust-removed and purified, and then transported to the ground for power generation or as civil gas supply, thus realizing the clean utilization of coalbed methane resources.

5. The method for efficient, clean and comprehensive mining and utilization of deep coal and its associated resources according to claim 1, characterized in that: The collection and treatment of the mine water is achieved by setting up a multi-stage drainage system, including temporary storage of gushing water in an underground water tank, using a lifting pump station to send the mine water to a surface sedimentation tank for solid-liquid separation, and then purifying the mine water through a filtration device.

6. The method for efficient, clean and comprehensive mining and utilization of deep coal and its associated resources according to claim 5, characterized in that: The treated mine water that meets the standards is reused in the coal mine production process, including as water for sprinkling and dust reduction at the mining face and cooling water, or for vegetation irrigation and industrial water in the mining area, thereby realizing the recycling of mine water resources.

7. The method for efficient, clean and comprehensive mining and utilization of deep coal and its associated resources according to claim 1, characterized in that: The comprehensive monitoring and coordinated control system includes gas sensors, water level monitors and equipment operation monitoring devices. The system monitors parameters such as gas concentration, support pressure, and drainage volume in real time, and controls the operation of ventilators, drainage pumps and coal mining equipment in a coordinated manner to ensure the safety of underground operations.

8. The method for efficient, clean and comprehensive mining and utilization of deep coal and its associated resources according to claim 1, characterized in that: A mine ventilation method combining zoned ventilation and local ventilation is adopted to deliver fresh air to deep working faces, and spray devices are deployed in the mining area to spray water to reduce dust, reduce coal dust concentration, and improve the working environment and mine safety.

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