Coal, heat and gas co-mining method based on gangue throwing and grouting combined filling

Abstract

The invention discloses a coal, heat and gas co-mining method based on gangue throwing and grouting combined filling, which comprises the following steps of: firstly, carrying out roadway-by-roadway filling mining on a lower group of coal, paving glass fiber felt cloth on a roadway top plate and installing a grouting pipeline before filling; coal seam mining and heat collection system installation are achieved in the modes of segmented gangue throwing, heat collection pipeline installation and connection, gangue throwing roof contact and grouting. The heat collection system takes mine water as a heat storage medium, after being heated, the mine water is conveyed to an upper group coal gas extraction drill site through a flow conveying pipeline and enters a drilling machine, and the drilling machine drills through hot water so as to improve the gas pre-extraction efficiency; coal slag and sewage generated by drilling are subjected to slag-water separation and purification treatment and then flow back to the next group of coal heating system to be heated for cyclic utilization. After all the drill holes in the drill site are formed, a plurality of holes are selected as heat injection holes, heated mine water is changed into hot steam through a steam generator to be conveyed to the heat injection holes to heat a coal body, and after the coal body is heated, gas drainage is carried out through a gas extraction hole.

Description

Technical Field

[0001] The present invention relates to the field of coal mining, and particularly to a method for co - mining coal, heat and gas based on combined filling of waste rock throwing and grouting. Background Art

[0002] Deep - mine geothermal resources are characterized by rich reserves, wide distribution, durability and stability, and environmental friendliness. Moreover, geothermal resources are closely related to mine - mining activities. During mine construction and production, it is sometimes inevitable to face mine geothermal energy. If it can be utilized, it will contribute to the safe and green mining of mines, while reducing energy consumption and production costs. At present, mine geothermal energy is mainly used for shaft anti - freezing, power generation, ground heating, and hot - water supply, etc. However, there is little research on promoting the desorption of coal - seam gas through geothermal energy and then improving the gas - drainage efficiency. For the problem of gas drainage in low - permeability and high - adsorption coal seams underground, although there are currently various borehole heat - injection methods, their heat energy sources are not directly from mine geothermal energy, no heat - circulation system is established, and heat - energy collection by using goaf filling underground is not carried out. Moreover, the current borehole heat - injection methods for promoting gas drainage are all aimed at the gas - drainage stage after borehole formation, and there is no relevant report on gas displacement during the drilling construction stage.

[0003] In addition, in terms of heat - energy extraction using goaf filling, most of the current filling materials are cement - based, high - water and other recycled materials. Although such materials have good fluidity and can better embed the heat - collection pipelines in them, as recycled materials, compared with underground waste rock, they have a large porosity, resulting in a low thermal - conductivity coefficient and low heat - collection efficiency. Moreover, the heat - resistance of cement - based and high - water materials is relatively poor, resulting in easy structural instability and strength attenuation in high - temperature environments, causing deformation and damage of the filling body.

[0004] Therefore, for mines with rich geothermal resources and high - gas coal seams, to solve the above problems, developing a combined mining method that can achieve co - mining of coal and heat and directly utilize the extracted heat energy to improve gas - drainage efficiency has become a major technical problem in the development of China's coal industry. Summary of the Invention

[0005] Aiming at the above - mentioned existing technical deficiencies, the purpose of the present invention is to provide a method for co - mining coal, heat and gas based on combined filling of waste rock throwing and grouting, which can solve the problems in the prior art that geothermal resources are not effectively used for gas drainage, the heat - energy collection and utilization system is imperfect, the gas - drainage efficiency is limited, and the resource collaborative development is insufficient.

[0006] To solve the above - mentioned technical problems, the present invention adopts the following technical solutions:

[0007] The present invention provides a method for co - mining coal, heat and gas based on combined backfilling of waste rock and grouting, which specifically includes the following steps:

[0008] S1. Divide the lower - group coal into several mining areas for combined backfilling of waste rock and grouting. Each mining area is divided into several strips and grouped and numbered, and the strip width is d;

[0009] S2. Drive the roadway of the first strip in the grouping order. Use a continuous miner to cut coal, a shuttle car to transport coal, a crusher to break coal, and convey the coal to the ground coal bunker by a belt conveyor. Support the roof and two sides of the roadway. When supporting, fix a fiberglass felt on the roof and arrange pressure sensors;

[0010] S3. Construct a filling retaining wall at one end of the excavated roadway and spray acrylic waterproof material. Lay grouting pipelines along the roof, set slurry outlets at the positions corresponding to the pressure sensors, and install electric remote - control valves; start from the filling retaining wall and carry out backward - type segmented throwing filling to form a waste - rock filling layer, and the filling length is b; select a PVC grouting pipeline with an inner diameter of 50 mm for the grouting pipeline, and fix the grouting pipeline to the exposed end of the roof bolt through a ring cable kit;

[0011] S4. When the distance between the upper interface of the waste - rock filling layer and the roof is the set distance a, stop filling, level and compact it, then install U - shaped heat - collecting pipelines on each section of the waste - rock filling layer, and at the same time drive and support the roadway of the second strip;

[0012] S5. After installing the U - shaped heat - collecting pipelines, continue to carry out waste - rock filling for the space above the waste - rock filling layer and the U - shaped heat - collecting pipelines. During the filling process, level and compact the waste rock and make the waste rock contact the roof, and the filling length is b;

[0013] S6. Use the methods in steps S2 - S5 to complete the driving, support, filling operations of other roadways and the installation of U - shaped heat - collecting pipelines;

[0014] S7. Build a filling retaining wall at the other end of the roadway and spray waterproof material. After the filling retaining wall is formed, inject slurry into the filling body through the grouting pipeline, monitor the roof pressure in real time and supplement the grouting until the filling body completely contacts the roof;

[0015] S8. Construct a gas drainage drill site in the upper - group coal roadway, drill and seal the bedding gas drainage holes, and connect the drill holes to a four - way blowout - prevention device, a slag - water separator and a water purification device;

[0016] S9. Lay a supply pipeline and a return pipeline between the lower - group coal filling area and the upper - group coal drill site, and connect the U - shaped heat - collecting pipeline to the inlet of the drill rig to form a heat - circulation system with mine water as the heat - transfer medium. Drive the drill rig to drill by heating the mine water, and realize the medium circulation by slag - water separation and purification;

[0017] S10. Select some of the boreholes as heat injection holes, seal them after removing their four-way blowout preventers, inject high-temperature steam into the heat injection holes through an explosion-proof steam generator, and at the same time use the geothermal energy extracted by the U-shaped heat extraction pipeline to heat the water inlet of the explosion-proof steam generator, so as to realize heat injection and gas co-extraction during the extraction stage.

[0018] Preferably, in step S1, the strips are divided into 3 groups, the number of strips in each group is n, the strip width d is 5 - 10 m, and the strips are numbered 1-1, 2-1, 3-1, 1-2, 2-2, 3-2... 1-n, 2-n, 3-n in sequence from one side of the cutting eye.

[0019] While backfilling the roadway of strip 1-1 and installing the heat extraction pipeline, start driving and supporting the roadway of strip 1-2. When backfilling the roadway of strip 1-2 and installing the heat extraction pipeline, start driving and supporting the roadway of strip 1-3, that is, complete the roadway driving support and backfilling installation work in the order of 1-1, 1-2, 1-3... 1-n, 2-1, 2-2... 2-n, 3-1... 3-n, and ensure that the roadway driving support and backfilling installation are carried out in parallel and simultaneously.

[0020] Preferably, in step S2, the roof and two sides of the roadway are supported by fiberglass bolts. A fiberglass felt cloth with a thickness of 15 cm is selected and fixed on the roof of the roadway through the bolt body and tray, and a pressure sensor is arranged every 10 m along the roof of the roadway.

[0021] Preferably, the filling material is gangue with a particle size of 5 - 20 cm separated by the underground TDS separation chamber. The first section of gangue is filled to a distance a of 1.5 m from the roof, and a U-shaped heat extraction pipeline is laid. When the second section of gangue is filled to the top, the single-section filling length is 7 m, which matches the single-section length of the U-shaped heat extraction pipeline.

[0022] Preferably, in step S3, the U-shaped heat extraction pipeline is fixed to the two sides of the roadway through a soft cable kit. The U-shaped heat extraction pipeline uses a pipe body with excellent heat conduction performance, and the surface of the pipe body is sprayed with thermal conductive silicone grease to improve the heat conduction coefficient.

[0023] Preferably, in step S7, during grouting, when the pumping pressure reaches 7 MPa or slurry backflow occurs, close the valve. Then, observe the monitoring values of each pressure sensor on the roof of the roadway every 24 h. If the monitoring value is lower than the set value of 0.1 MPa, remotely open the pipeline valve at its location for supplementary grouting until the filling body in the roadway is completely in contact with the roof.

[0024] Preferably, in step S8, a gas drainage drill site is constructed in the roadway of the upper coal seam group, and a longwall gas drainage hole is drilled using a ZYWL-6000D kilometer directional drill. First, the hole opening and hole sealing work are carried out: a 96mm drill bit is used for hole opening, 180mm and 225mm drill bits are used for hole enlargement, and a 4-inch hole sealing pipe is used in combination with a two-block-one-injection bladder for hole sealing. The hole sealing length is 15m. A four-way blowout prevention device, a slag-water solid-liquid separator, and a water purification device are sequentially installed outside the hole sealing pipe. Among them, 2-inch extraction branch pipes are installed on the four-way blowout prevention device and the slag-water solid-liquid separator respectively, and the extraction branch pipes are connected to the main mine gas drainage pipeline for pre-extraction.

[0025] Preferably, in steps S9-S10, a supply pipeline and a return pipeline are laid between the upper coal seam group gas drainage drill site and the lower coal seam group filling area. The supply pipeline and the return pipeline are wrapped with fiberglass felt cloth and connected to the main mine drainage system. Among them, a supply pump is installed on the supply pipeline, and a return pump and a heat storage medium replenishment valve are installed on the return pipeline. The supply pipeline is connected to the water inlet of the ZYWL-6000D kilometer directional drill, and the return pipeline is connected to the water outlet of the water purification device. Thus, a heat circulation system during the drilling period is formed.

[0026] Filtered and purified mine water is injected into the return pipeline through the heat storage medium replenishment valve. After filling, the supply pump, the return pump, the slag-water solid-liquid separator, and the water purification device are started to make the mine water in the pipeline circulate. After the water temperature reaches the predetermined value and remains stable, the drill is started to drill. After drilling, the drill is withdrawn, the machine is moved, and the valve of the gas extraction branch pipe is closed.

[0027] According to the above relevant method, other longwall gas drainage holes are sequentially drilled in the drill site, and one hole is selected as the heat injection hole every two holes. The spacing between the holes in the horizontal direction after entering the parallel section is t. The heat injection hole is below the extraction hole, and the vertical spacing between the heat injection hole and the extraction hole is k. The spacing between the heat injection hole and the extraction hole is determined according to the coal seam gas content, permeability coefficient, thermal conductivity, and extraction construction period.

[0028] The four-way blowout prevention device at the orifice of the heat injection hole is removed, and the hole is sealed with cement. An explosion-proof steam generator is installed in the gas drainage drill site. An explosion-proof steam generator with an automatic water replenishment function and an intelligent start-stop function is selected. Its steam delivery branch pipe extends into the heat injection hole 10m from the hole bottom. The hole sealing of the heat injection hole uses a cement layer with a thickness of not less than 20cm.

[0029] The steam delivery branch pipes of the explosion-proof steam generator are respectively sent into each heat injection hole. At the same time, a pressure relief pipe is installed at the orifice to connect the inside and outside of the hole, and a safety valve and a pressure gauge are installed on the pressure relief pipe outside the hole.

[0030] Connect the flow delivery pipeline laid between the upper coal group and the lower coal group to the water inlet of the explosion-proof steam generator. Install a mine water filtration and purification device on the return pipeline laid between the upper coal group and the lower coal group and connect it to the main mine drainage system.

[0031] Open the valves of the explosion-proof steam generator, flow delivery pump, return pump, and the main mine drainage system, and input high-temperature steam into the heat injection hole. After the steam pressure reaches the set pressure, open the gas drainage branch valve of the gas extraction hole to conduct gas drainage.

[0032] The beneficial effects of the present invention are as follows:

[0033] 1. Multi-resource collaborative development and efficient utilization: The present invention first conducts collaborative mining of deep coal resources, geothermal resources, and gas resources, realizing the organic integration of coal mining, backfilling, and extraction. When arranging the U-shaped heat extraction pipeline for backfill mining, directly separated gangue underground is selected as the backfill material, which not only realizes the utilization of solid waste, but also compared with recycled materials such as cement used in paste filling and high-water filling, gangue has a higher thermal conductivity, can achieve higher heat extraction efficiency, and at the same time, gangue has better heat resistance and can maintain structural stability in high-temperature environments, combining resource utilization and environmental benefits.

[0034] 2. Lay a fiberglass felt cloth above the U-shaped heat extraction pipeline. On the one hand, it can block the upward conduction and diffusion of geothermal resources, and on the other hand, it can form a heat energy concentration area below the fiberglass felt cloth to achieve efficient heat extraction of the heat extraction pipeline.

[0035] 3. Dual-stage heat energy-driven gas extraction: Establish a heat cycle system with mine water as the heat transfer medium, covering the drilling and extraction stages: Drilling stage: Drive the gas in the borehole by circulating mine water to reduce the risk of gas accumulation; Extraction stage: Inject high-temperature steam into the heat injection hole to promote the desorption of coal seam gas and shorten the extraction cycle. The heat injection hole and the gas extraction hole are arranged in upper and lower layers to achieve simultaneous heat injection and extraction and improve efficiency.

[0036] 4. In terms of using geothermal resources to promote gas extraction, for the first time, the gas during drilling is directly displaced by the heat storage medium and a heat cycle system is established, expanding the application scope of geothermal resources to promote gas extraction and realizing the dual-stage heat energy utilization during drilling and extraction.

[0037] 5. The heat injection hole and the gas extraction hole are arranged in an upper and lower layer layout, realizing simultaneous heat injection and extraction, and further shortening the extraction cycle. Moreover, the established heat cycle system uses mine water as the heat transfer medium and recycles the mine water, meeting the needs of low-carbon development in coal mines. Description of the Drawings

[0038] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the accompanying drawings required in the description of the embodiments or the prior art. Obviously, the accompanying drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other accompanying drawings can be obtained based on these drawings.

[0039] Figure 1 is a plan-sectional view after the filling of the first-stage filling cushion layer provided by the embodiment of the present invention;

[0040] Figure 2 is a plan-sectional view after the U-shaped heat extraction pipeline is installed on the first-stage filling cushion layer provided by the embodiment of the present invention;

[0041] Figure 3 is a plan-sectional view after the gob filling with waste rock in the first-stage filling area is completed provided by the embodiment of the present invention;

[0042] Figure 4 is a plan-sectional view after the gob filling with waste rock and the installation of the heat extraction pipeline in the 1-1 strip roadway are completed provided by the embodiment of the present invention;

[0043] Figure 5 is a plan-sectional view after the grouting in the 1-1 strip roadway is completed provided by the embodiment of the present invention;

[0044] Figure 6 is a schematic diagram of the heat extraction and utilization system during the drilling of the gas drainage holes provided by the embodiment of the present invention;

[0045] Figure 7 is a schematic diagram of the heat extraction and utilization system during the gas drainage provided by the embodiment of the present invention;

[0046] Figure 8 is a plan-sectional view of the layout of the gas drainage holes and the heat injection holes provided by the embodiment of the present invention.

[0047] In the figure: 1 - coal seam, 2 - intake airway of the filling mining area, 3 - return airway of the filling mining area, 4 - roof, 5 - floor, 6 - grouting pipeline, 7 - filling retaining wall, 8 - gob filling body with waste rock, 9 - U-shaped heat extraction pipeline, 10 - gob filling body with cemented waste rock and slurry, 11 - strip roadway, 12 - supply pipeline, 13 - return pipeline, 14 - supply pump, 15 - return pump, 16 - kilometer directional drill, 17 - slag-water solid-liquid separator, 18 - water purification device, 19 - storage heat medium replenishment valve, 20 - explosion-proof steam generator, 21 - drainage hole, 22 - heat injection hole, 23 - steam supply branch pipe of the steam generator. Detailed implementation manners

[0048] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0049] As Figures 1 to 8 shown, this embodiment provides a method for co - mining coal, heat, and gas based on combined backfilling of waste rock and grouting, specifically as follows:

[0050] (1) Divide the 15# coal seam 1 in the mine into several mining areas for combined backfilling of waste rock and grouting. Each mining area is divided into several strips, and the strips are divided into 3 groups, with 8 strips in each group. The strip width is 6 m. The strips are numbered 1 - 1, 2 - 1, 3 - 1, 1 - 2, 2 - 2, 3 - 2... 1 - 8, 2 - 8, 3 - 8 in sequence from one side of the cutting eye.

[0051] (2) First, drive the 1 - 1 strip. Use a continuous miner to cut coal, a shuttle car to transport coal, and a crusher to break coal. The coal is transported to the ground coal bunker by a belt conveyor. The roof 4 and the two sides of the roadway are supported by fiberglass bolts. During the support process, a 15 - cm - thick fiberglass felt is fixed on the roof of the roadway through the bolt body and the tray of the bolt, and a pressure sensor is arranged every 10 m along the roof of the roadway.

[0052] (3) Construct a filling retaining wall 7 with waste - rock blocks at one end of the driven strip roadway, and spray acrylic waterproof material on the surface of the filling retaining wall. Lay a PVC grouting pipeline with an inner diameter of 50 mm along the roof of the roadway. Set slurry outlets at the positions corresponding to the pressure sensors on the pipeline, and install electric remote - control valves. The grouting pipeline 6 is fixed to the exposed end of the roof bolt through a ring cable kit.

[0053] (4) Use a belt conveyor and a waste - rock filling machine to carry out backward - segmented throwing and filling on the floor 5 starting from the filling retaining wall to form a waste - rock filling body 8. The filling material is waste rock with a particle size of 5 - 20 cm separated by the underground TDS separation chamber. During the filling process, the waste rock is leveled and compacted by the waste - rock pushing mechanism, so that the distance between the upper interface of the filling layer and the roof is 1.5 m, and the filling length is 7 m.

[0054] (5) Place a U - shaped heat - extraction pipeline 9 with a single - section length of 7 m on the waste - rock filling layer and fix it to the two sides of the roadway, and temporarily seal the pipeline. The U - shaped heat - extraction pipeline uses a pipe body with excellent thermal conductivity. At the same time, to increase the thermal conductivity, thermal grease is sprayed around the pipe body.

[0055] (6) Use a belt conveyor and a waste rock filling machine to carry out waste rock filling in the space above the filling layer and the pipeline. The filling material is waste rock with a particle size of 5 - 20 cm separated by the underground TDS separation chamber. During the filling process, the waste rock is leveled and compacted by a waste rock pushing mechanism, and the waste rock is made to contact the roof. The filling length is 7 m;

[0056] (7) According to the methods in steps (4) - (6), segmentally carry out filling cushion layer for the roadway, install and connect the heat extraction pipelines, and fill and contact the roof. Finally, complete the waste rock filling and pipeline installation work in the whole roadway. After the heat extraction pipelines in the roadway are installed, connect the two ends of the pipelines to the supply pipeline of the filling mining area intake airway 2 and the return pipeline of the filling mining area return airway 3 respectively;

[0057] (8) Build a filling retaining wall at the other end of the roadway, and spray acrylic waterproof material on the surface of the filling retaining wall. After the retaining wall is formed, remotely control to simultaneously open the outlet valves of each grouting pipeline in the roadway. When the pumping pressure reaches 7 MPa or slurry backflow occurs, close the valves. Then, observe the monitoring values of each pressure sensor on the roadway roof every 24 hours. If the monitoring value is lower than the set value, remotely control to open the pipeline valve at its location for supplementary grouting until the filling body in the roadway is completely in contact with the roof. Finally, form the waste rock and slurry cemented filling body 10.

[0058] (9) While carrying out filling and installing heat extraction pipelines for the 1 - 1 panel roadway, start tunneling and supporting another panel roadway 11 in the grouping order. In this embodiment, it is the 1 - 2 panel roadway. When carrying out filling and installing heat extraction pipelines for the 1 - 2 panel roadway, start tunneling and supporting the 1 - 3 panel roadway, that is, complete the tunneling support and filling installation work in the order of 1 - 1, 1 - 2, 1 - 3... 1 - 8, 2 - 1, 2 - 2... 2 - 8, 3 - 1... 3 - 8, and ensure that the tunneling support and filling installation are parallel operations and carried out simultaneously.

[0059] (10) Construct a gas drainage drill field in the roadway of the upper coal seam, and use the ZYWL - 6000D kilometer directional drill 16 to drill the in - seam gas drainage holes 21. First, carry out the hole - opening and hole - sealing work: Use a 96 mm drill bit for hole - opening, use 180 mm and 225 mm drill bits for reaming, and use a 4 - inch hole - sealing pipe in cooperation with a two - plug - one - injection bladder for hole - sealing. The hole - sealing length is 15 m. A four - way blowout prevention device, a slag - water solid - liquid separator 17, and a water purification device 18 are sequentially installed outside the hole - sealing pipe. Among them, 2 - inch extraction branch pipes are installed on the four - way blowout prevention device and the slag - water solid - liquid separator respectively, and the extraction branch pipes are connected to the mine gas extraction main pipeline for pre - extraction.

[0060] (11) A flow supply pipeline 12 and a return pipeline 13 are laid between the gas drainage drill site in the upper coal seam group and the filling area in the lower coal seam group. A flow supply pump 14 is installed on the flow supply pipeline, and a return pump 15 and a heat storage medium replenishment valve 19 are installed on the return pipeline. The flow supply pipeline is connected to the water inlet of the ZYWL-6000D kilometer directional drill, and the return pipeline is connected to the water outlet of the water purification device. Thus, a heat circulation system during the drilling period is formed.

[0061] (12) Filtered and purified mine water is injected into the return pipeline through the heat storage medium replenishment valve. After it is filled, start the flow supply pump, return pump, slag water solid-liquid separator and water purification device to make the mine water in the pipeline circulate. After the water temperature reaches the predetermined value and remains stable, start the drill to start drilling. After the drilling is completed, retract the drill, move the machine and close the gas drainage branch valve.

[0062] (13) According to the relevant methods in steps (10) to (12), other bedding gas drainage holes are successively drilled in the drill site, and one hole is selected as the heat injection hole 22 every two holes. The horizontal spacing of each hole after entering the parallel section is 10 m. The heat injection hole is below the drainage hole, and the vertical spacing from the drainage hole is 3 m.

[0063] (14) Remove the four-way blowout prevention device at the orifice of the heat injection hole and seal the hole with cement. Install an explosion-proof steam generator 20 in the gas drainage drill site. Send the steam delivery branch pipes 23 of the steam generator into each heat injection hole respectively. At the same time, install a pressure relief pipe at the orifice to connect the inside and outside of the hole, and install a safety valve and a pressure gauge on the pressure relief pipe outside the hole.

[0064] (15) Connect the flow supply pipeline laid between the upper coal seam group and the lower coal seam group to the water inlet of the steam generator. Install a mine water filtration and purification device on the return pipeline laid between the upper coal seam group and the lower coal seam group and connect it to the main mine drainage system.

[0065] (16) Open the valves of the steam generator, flow supply pump, return pump and the main mine drainage system, input high-temperature steam into the heat injection holes. After the steam pressure reaches the set pressure, open the gas drainage branch valve of the drainage hole to carry out gas drainage.

[0066] This method is a green, efficient and significantly innovative method for co-mining coal, heat and gas, with great scientific and engineering significance and broad application prospects.

[0067] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalent technologies, the present invention also intends to include these changes and modifications.

Claims

1. A method for co - mining coal, heat and gas based on combined backfilling of waste rock and grouting, characterized in that, It includes the following steps: S1. Divide the lower group of coal into several gob-side grouting combined filling mining areas. Each mining area is divided into several strips and grouped and numbered. The strip width is d; S2. Drive the first strip roadway in the order of grouping, and then support the roof and two sides of the roadway. When supporting, fix fiberglass felt on the roof and arrange pressure sensors; S3. Construct a filling retaining wall at one end of the driven roadway and spray waterproof material. Lay grouting pipelines along the roof, set slurry outlets at the positions corresponding to the pressure sensors, and install electric remote control valves; start from the filling retaining wall and carry out backstepping sectional throwing filling to form a gangue filling layer, and the filling length is b; S4. When the distance between the upper interface of the gangue filling layer and the roof is the set distance a, stop filling, level and compact it, then install U-shaped heat extraction pipelines on each section of the gangue filling layer, and at the same time drive and support the second strip roadway; S5. After installing the U-shaped heat extraction pipelines, continue to carry out gangue filling in the space above the gangue filling layer and the U-shaped heat extraction pipelines. During the filling process, level and compact the gangue and make the gangue contact the roof. The filling length is b; S6. Use the methods in steps S2 - S5 to complete the driving, support, filling operations of other roadways and the installation of U-shaped heat extraction pipelines; S7. Build a filling retaining wall at the other end of the roadway and spray waterproof material. After the filling retaining wall is formed, inject slurry into the filling body through the grouting pipeline, monitor the roof pressure in real time and supplement the grouting until the filling body completely contacts the roof; S8. Construct a gas drainage drill field in the upper group of coal roadway, drill and seal the bedding gas drainage holes. Connect the drill holes to a four-way blowout prevention device, a slag-water separator and a water purification device; S9. Lay a supply pipeline and a return pipeline between the lower group of coal filling area and the upper group of coal drill field, and connect the U-shaped heat extraction pipeline with the drill inlet to form a heat circulation system with mine water as the heat transfer medium. Drive the drill by heating the mine water and realize medium circulation by means of slag-water separation and purification; S10. Select some drill holes as heat injection holes, seal them after removing their four-way blowout prevention devices, inject high-temperature steam into the heat injection holes through an explosion-proof steam generator, and at the same time heat the inlet water of the explosion-proof steam generator by the geothermal heat extracted by the U-shaped heat extraction pipeline to realize heat injection and gas co-extraction during the extraction stage.

2. The method for co-mining coal, heat and gas based on combined filling of waste rock throwing and grouting as claimed in claim 1, wherein In step S1, the strips are divided into 3 groups, the number of strips in each group is n, the strip width d is 5 - 10 m, and the strips are numbered 1-1, 2-1, 3-1, 1-2, 2-2, 3-2... 1-n, 2-n, 3-n in sequence from the cut-off side.

3. A method for co - mining coal, heat and gas based on combined backfilling of waste rock and grouting as claimed in claim 1, characterized in that, In step S2, use fiberglass-reinforced plastic bolts to support the roof and two sides of the roadway. Select fiberglass felt with a thickness of 15 cm and fix it on the roof of the roadway through the bolt body and tray. Arrange a pressure sensor along the roof of the roadway every 10 m.

4. For a method of co - mining coal, heat, and gas based on combined filling of waste rock and grouting as described in claim 1, in step S3, the filling material is waste rock with a particle size of 5 - 20 cm separated by the underground TDS separation chamber. The first - stage waste - rock filling reaches a distance a of 1.5 m from the roof, with a filling length of 7 m. When the second - stage waste - rock filling reaches the roof - contact, the filling length is 7 m, which matches the single - section length of the U - shaped heat - extraction pipeline.

5. A method for co - mining coal, heat and gas based on combined filling of waste rock throwing and grouting as claimed in claim 1, characterized in that, In step S3, the U - shaped heat - extraction pipeline is fixed to the two sides of the roadway through a soft cable kit, and the surface of the pipeline body of the U - shaped heat - extraction pipeline is sprayed with thermal conductive silicone grease to increase the thermal conductivity coefficient.

6. A coal, heat, and gas co - mining method based on combined filling of waste rock throwing and grouting as claimed in claim 1, characterized in that, In step S7, during grouting, when the pumping pressure reaches 7 MPa or slurry back - flow occurs, the valve is closed. Then, the monitoring values of each pressure sensor on the roadway roof are observed every 24 h. If the monitoring value is lower than the set value of 0.1 MPa, the pipeline valve at its location is remotely opened for supplementary grouting until the filling body in the roadway is completely in contact with the roof.

7. A coal, heat, and gas co-mining method based on combined filling of waste rock and grouting as claimed in claim 1, characterized in that In step S8, the hole - sealing adopts a two - plug - one - injection bladder hole - sealing process with a hole - sealing length of 15 m, and the extraction branch pipe is connected to the main mine gas extraction pipeline for pre - extraction.

8. A method for co - mining coal, heat and gas based on combined filling of waste rock throwing and grouting as claimed in claim 1, characterized in that, In step S9, the flow - sending pipeline and the return pipeline are wrapped with fiberglass felt and connected to the main mine drainage system.

9. A method for co - mining coal, heat and gas based on combined filling of waste rock and grouting as claimed in claim 1, wherein, In step S10, an explosion - proof steam generator with an automatic water - replenishing function and an intelligent start - stop function is selected. The steam delivery branch pipes of the explosion - proof steam generator are respectively sent to a position 10 m from the bottom of each heat - injection hole, and the hole - sealing of the heat - injection hole adopts a cement layer with a thickness of not less than 20 cm.

10. A method for co - mining coal, heat and gas based on combined backfilling of waste rock and grouting as claimed in claim 1, characterized in that, In step S10, one drilling hole is selected as a heat - injection hole every two drilling holes. The horizontal spacing of the extraction holes is t after entering the parallel section. The heat - injection holes are below the extraction holes, and the vertical spacing between the heat - injection holes and the extraction holes is k. The spacing between the heat - injection holes and the extraction holes is determined according to the coal - seam gas content, permeability coefficient, thermal conductivity coefficient, and extraction construction period.

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