A method for recycling strip coal pillars based on the freezing of old goaf water

Abstract

This invention discloses a method for backfilling and recovering strip coal pillars based on the freezing of water in old workings. The method involves initially freezing the water in the workings by laying freezing pipes on the floor of the water-filled roadways on both sides of the strip coal pillar, constructing retaining walls, and replenishing with mine water. After freezing, freezing pipes are laid again along the frozen ice surface, while the retaining walls are raised and mine water is replenished for refreezing, until the entire water-filled roadway space is frozen. The strip coal pillar between the two frozen roadways is then mined. After mining, high-fluidity cement slurry is used to fill the mined space. Simultaneously with mining and filling, the next adjacent water-filled roadway is filled with water and frozen. Once the cement filling reaches reliable strength, the frozen roadway on one side is thawed, and the mine water and freezing pipes are transferred to the next water-filled roadway. This process is repeated until all coal pillars are mined and backfilled. This technology is safe, reliable, adaptable, and environmentally friendly, providing a new technical method for recovering strip coal pillars in water-rich old workings.

Description

Technical Field

[0001] This invention relates to a method for backfilling and recovering strip coal pillars in water-rich old goafs, and more particularly to a method applicable to backfilling and recovering strip coal pillars in water-rich old goafs with an inclination angle of 5° to 15°. Background Technology

[0002] For strip mining areas at the boundary of the mining field, due to the presence of a large number of coal rooms and empty roadways, the old working water, production water, and rock fissure water from the mine and adjacent mines will continuously flow into them due to the influence of coal seam dip angle, structure, and water-conducting fissures formed by mining. This results in a large amount of water accumulating in the coal rooms within the strip mining area, or even filling them completely, making it impossible to recover the strip coal pillars normally.

[0003] The most common solution currently is to pump out the accumulated water. However, due to the monocline structure and the overlying sandstone aquifer, the water in the coal seam is continuously replenished by old working water, fissure water, and production water from the mine and adjacent mines. Under these circumstances, although pumping can reduce the amount of water, it cannot completely remove it, making pumping an ineffective solution. Therefore, developing a strip coal pillar filling and recovery method that eliminates the need for pumping and utilizes frozen water to support the roof has become a major technical challenge for the coal industry. Summary of the Invention

[0004] The purpose of this invention is to provide a method for backfilling and recovering strip coal pillars based on the freezing of old working water, so as to solve the problems mentioned in the background art.

[0005] To achieve the above objectives, the present invention provides the following technical solution:

[0006] A method for backfilling and recovering strip coal pillars based on the freezing of old goaf water is characterized by comprising the following steps:

[0007] Step 1: Number the strip coal pillars in the target area sequentially from one side boundary to the other as No. 1 coal pillar, No. 2 coal pillar, ... N coal pillar. In the same order, number the water accumulation lanes sequentially as No. 1 water accumulation lane, No. 2 water accumulation lane, ... N+1 water accumulation lane. First, carry out water replenishment and freezing work on No. 1 water accumulation lane and No. 2 water accumulation lane on both sides of No. 1 coal pillar.

[0008] Step 2: Using a mobile mixing and pumping vehicle equipped with a 4-inch rubber corrugated pipe, the silt on the bottom of the No. 1 and No. 2 water accumulation tunnels is pumped to the underground sorting chamber for sorting. The sorted coal slurry water is then subjected to sedimentation and dewatering treatment to obtain concentrated coal slurry water with a water content of 15%, which will be used as roadway filling material. The mobile mixing and pumping vehicle is placed at the edge of the water accumulation area, and the 4-inch rubber corrugated pipe opening is placed at the bottom of the deepest silt in the water accumulation area using an automated pipe-grabbing robotic arm. By adjusting the position of the pipe opening, all the silt on the bottom of the water accumulation tunnel is cleared out.

[0009] Step 3: Lay frozen pipelines on the floor of No. 1 and No. 2 waterlogging tunnels. Before laying, use a ZYWL-4500D kilometer directional drilling rig to drill holes in the coal wall at the lower end of the waterlogging tunnel in the waterless area above the waterlogging tunnel to form a pipe trench for fixing the frozen pipelines. The pipe trench is 0.8m deep, 160mm in diameter, and has the same slope as the tunnel slope. The lowest point of the pipe trench opening is flush with the tunnel floor.

[0010] Step 4: After the pipe trench is formed, an automated pipe-grabbing robotic arm is used to push the frozen pipe route from the waterless area above the waterlogged tunnel along the floor to the bottom and into the pipe trench. The pipe route is parallel to the coal pillar strip, with the pipe route 0.5m to 0.7m away from the coal pillar strip and the pipe route spacing 1.3m to 1.5m. In the waterless area, the pipe route is fixed to the floor with bolts. The frozen pipe route is welded from a seamless steel pipe with a wall thickness of 7mm and an outer diameter of 150mm. A polyethylene pipe with a diameter of 55mm is built in the middle as the liquid supply pipe. An ammonia-salt water circulation system is used for freezing.

[0011] Step 5: Install temperature and displacement sensors on the top slab of the water accumulation tunnel to monitor the temperature of the frozen ice and the deformation of the top slab. Build a retaining wall at the exit of the water accumulation tunnel. The retaining wall should be 1m thick and 50cm high. Seal the gap between the retaining wall and the freezing pipeline with cement. Lay the main freezing pipeline in the transport tunnel outside the retaining wall. The main pipeline is buried in the bottom rock layer and connected to the freezing pipeline inside the wall.

[0012] Step Six: Draw a drainage branch pipe from the mine drainage system to discharge some of the mine water into the retaining wall, or use a diaphragm pump to pump old working water from other waterlogged roadways into the retaining wall, so that the water level inside the retaining wall is flush with the bottom edge of the freezing pipe opening on the retaining wall. By calculating the existing water volume in the roadway, add 6% of the water volume mass of medical degreased cotton fiber into the water using a high-pressure air pipe, and stir it evenly through the high-pressure air pipe to improve the mechanical strength of the frozen ice.

[0013] Step 7: Open the freezing valve, keep the freezing temperature below -35℃, freeze for no less than 24 hours, and ensure that the compressive strength of the ice is no less than 5MPa;

[0014] Step 8: Based on Step 7, after freezing for 24 hours, lay the frozen pipeline along the sloping ice surface formed by freezing, and at the same time raise the retaining wall and fix the frozen pipeline through the retaining wall. The height of the retaining wall is 50cm higher than the newly laid pipeline.

[0015] Step 9: Drain the mine water or old working water into the retaining wall again through the drainage branch pipe or diaphragm pump of the mine drainage system, so that the water level inside the retaining wall is level with the bottom edge of the frozen pipe opening on the retaining wall. Calculate the existing water volume in the roadway, and add 6% of the water volume of medical degreased cotton fiber to the water by blowing it with a high-pressure air pipe, and blow it evenly with a high-pressure air pipe.

[0016] Step 10: Repeat steps 7, 8 and 9 in sequence until the entire waterlogged alley is completely filled with water and frozen.

[0017] Step 11: After the No. 1 and No. 2 water accumulation tunnels are completely filled with water and frozen, and the roof temperature sensor reading is below -10℃ and the displacement sensor reading is less than 50mm, the No. 1 coal pillar is mined by tunneling machine, loading machine, and transporting coal by trackless rubber-tired vehicle. During the mining process, the water diversion channel is blocked by grouting anchor cable support for the roof, hanging plastic geogrids on both sides and applying concrete grout, and digging water diversion trenches on the bottom of the transport tunnel to ensure that there is no seepage or water spray in the working space.

[0018] Step 12: While mining the No. 1 coal pillar, follow the same method as Steps 2 to 10 to fill and freeze the No. 3 water accumulation tunnel.

[0019] Step Fourteen: After the No. 1 coal pillar is mined out, CD-BP type thin spray material is used to spray the top and bottom plates and two sides of the mined space to form a waterproof and closed space. A filling retaining wall with a thickness of n is built at the exit position of the mined space. CD-BP type thin spray material is also sprayed on the inside of the retaining wall. A filling pipeline is installed at the top position of the retaining wall. The grouting material prepared by cement, fly ash, 15% concentrated coal slurry water and mine water in a mass ratio of 1:3.5:3:5 is pumped into the retaining wall to fill the mined space.

[0020] Step 15: After the space of No. 3 waterlogged tunnel is completely filled with water and frozen, the No. 2 coal pillar is mined by tunneling machine, loading machine, and transporting coal by trackless rubber-tired vehicle. During the mining process, the water channel is blocked by grouting anchor cable support, surrounding rock spraying, and digging water diversion trenches on the bottom of the transport tunnel to ensure that there is no seepage or water spray in the working space.

[0021] Step 16: After the compressive strength and deformation strength of the filling material reach the predetermined values, the No. 1 water storage tunnel is thawed. The heat required for thawing is input from the outside and transported to the No. 1 water storage tunnel through pipelines. A mobile boiler structure can be used to supply hot water to the water storage tunnel, and the mobile boiler structure can be connected to the pipelines in the water storage tunnel where the freezing work is being carried out, that is, connected to the heat pipes that extract and discharge heat, so as to utilize the heat recovered from freezing, reduce energy consumption during thaw, and transport some of the thawed old empty water to other water storage tunnels to be frozen. At the same time, the frozen pipeline is recovered and transferred to the No. 4 water storage tunnel for freezing work. The thaw work can be carried out simultaneously with the freezing work, thereby realizing energy recovery and utilization.

[0022] Step 17: Repeat steps 14 to 16 to complete the mining and backfilling of all strip coal pillars in the target mining area;

[0023] Step 18: After the mining and backfilling work is completed, drill holes at the top of the retaining walls of all waterlogged tunnels. Place the pumping pipes connected to the mine drainage system along the drill holes into the thawed waterlogged tunnels, pump the water in the tunnels to the surface sewage treatment plant for purification and use as domestic water, thus achieving recycling.

[0024] Preferably, the thickness of the retaining wall in the water accumulation tunnel is determined based on the coal seam burial depth, surrounding rock conditions, height and dip angle of the water accumulation tunnel, and the expansion coefficient of the old working water after freezing.

[0025] Preferably, the thickness n of the filling retaining wall established in the mining space of the strip coal pillar is determined according to the coal seam burial depth, roof and floor conditions, coal seam thickness and dip angle.

[0026] Preferably, for the triangular blind zone formed at the top of the water accumulation lane after the water filling and freezing cycle operation, the ice body can be completely connected to the top by drilling holes and injecting water into the top of the already sealed retaining wall.

[0027] Preferably, the pumping flow rate for water accumulation in the roadway after thawing is determined based on the total replenishment of old working water, production water, and rock fissure water in this mine and adjacent mines, and ensures that the water accumulation surface is located in the roadway floor area below the retaining wall when the replenishment and pumping flow are dynamically balanced.

[0028] Preferably, the defrosting heat in step sixteen mainly comes from two sources: one part is self-heating, which consumes some energy to achieve heating, and the other part is the heat recovered during the freezing process. This part of the heat is mainly used for heat preservation and preheating of the heat transmission pipeline, thereby reducing some energy consumption. That is, the defrosting and the next freezing operation mentioned in step fifteen are carried out simultaneously.

[0029] Compared with the prior art, the beneficial effects of the present invention are:

[0030] 1. This method of recycling strip coal pillars based on the freezing of old workings water makes full use of the water in the roadway and replaces coal resources with cement slurry, effectively reducing overburden movement and surface subsidence. It provides a safe, green and efficient new model for recycling strip coal pillars in inclined coal seams rich in old workings water, which has great scientific and engineering significance and broad application prospects. Attached Figure Description

[0031] Figure 1 This is a schematic diagram and AA-direction cross-section of the mining area of ​​the rich old cave-water strip of the present invention;

[0032] Figure 2This is a schematic diagram and a cross-sectional view along the AA direction after laying frozen pipes, building retaining walls and replenishing water along the bottom slab of the waterlogged alleyway according to the present invention.

[0033] Figure 3 This is a schematic diagram and a cross-sectional view along the AA direction of the present invention, showing the laying of freezing pipelines and the construction of retaining walls along the frozen ice surface.

[0034] Figure 4 This is a schematic diagram and a cross-sectional view along line AA after the second layer of freezing is completed in this invention;

[0035] Figure 5 This is a schematic diagram and a cross-sectional view along direction AA of the No. 1 and No. 2 water accumulation tunnels of the present invention after they are completely frozen.

[0036] Figure 6 This is a schematic diagram of the mining of the No. 1 coal pillar of this invention;

[0037] Figure 7 This is a schematic diagram of the filling of the mining space of the No. 1 coal pillar according to the present invention;

[0038] Figure 8 This is a schematic diagram of the mining of the No. 2 coal pillar of the present invention;

[0039] Figure 9 This is a schematic diagram showing the completion of all coal pillar mining and backfilling in this invention.

[0040] In the diagram: 1. No. 1 coal pillar; 2. No. 1 water accumulation tunnel; 3. No. 2 water accumulation tunnel; 4. Frozen pipeline; 5. Water accumulation tunnel retaining wall; 6. Transport tunnel; 7. Frozen main pipeline; 8. Tunneling machine; 9. Loader; 10. Trackless rubber-tired vehicle; 11. Filling retaining wall; 12. Grouting pipeline; 13. Cement grout. Detailed Implementation

[0041] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0042] This invention provides a technical solution for a method of backfilling and recovering strip coal pillars based on the freezing of old workings, comprising the following steps:

[0043] Example 1:

[0044] Step 1: Number the strip coal pillars in the target mining area sequentially from one side boundary to the other as No. 1 coal pillar 1, No. 2 coal pillar ... N coal pillar. In the same order, number the water accumulation tunnels sequentially as No. 1 water accumulation tunnel 2, No. 2 water accumulation tunnel 3 ... N+1 water accumulation tunnel. First, carry out water replenishment and freezing work on No. 1 water accumulation tunnel 2 and No. 2 water accumulation tunnel 3 on both sides of No. 1 coal pillar 1.

[0045] Step 2: Using a mobile mixing and pumping vehicle equipped with a 4-inch rubber corrugated pipe, the silt on the bottom plate of No. 1 waterlogging tunnel 2 and No. 2 waterlogging tunnel 3 is pumped to the underground sorting chamber for sorting. The sorted coal slurry water is then subjected to sedimentation and dewatering treatment to obtain concentrated coal slurry water with a water content of 15%, which will be used as roadway filling material. The mobile mixing and pumping vehicle is placed at the edge of the waterlogging area, and the 4-inch rubber corrugated pipe opening is placed at the bottom of the deepest silt in the waterlogging area using an automated pipe-grabbing robotic arm. By adjusting the position of the pipe opening, all the silt on the bottom plate of the waterlogging tunnel is cleared out.

[0046] Step 3: Lay frozen pipelines on the floor of No. 1 Water Accumulation Lane 2 and No. 2 Water Accumulation Lane 3. Before laying, use a ZYWL-4500D kilometer directional drilling rig to drill holes in the coal wall at the lower end of the water accumulation lane in the waterless area above the water accumulation lane to form a pipe trench for fixing the frozen pipeline. The pipe trench is 0.8m deep, 160mm in diameter, and has the same slope as the roadway slope. The lowest point of the pipe trench opening is flush with the roadway floor.

[0047] Step 4: After the pipe trench is formed, an automated pipe-grabbing robotic arm is used to push the frozen pipe 4 from the waterless area above the waterlogged tunnel along the bottom of the floor to the bottom of the pipe trench, so that the pipe 4 is parallel to the strip coal pillar 1. The distance between the pipe 4 and the strip coal pillar is 10.5m to 0.7m, and the spacing between the pipes 4 is 1.3m to 1.5m. In the waterless area, the pipe 4 is fixed to the floor with a sleeve. The frozen pipe 4 is welded from a seamless steel pipe with a wall thickness of 7mm and an outer diameter of 150mm. A polyethylene pipe with a diameter of 55mm is built in the middle as a liquid supply pipe. An ammonia-salt water circulation system is used for freezing.

[0048] Step 5: Install temperature and displacement sensors on the top slab of the water accumulation tunnel to monitor the temperature of the frozen ice and the deformation of the top slab. Construct a retaining wall 5 at the outlet of the water accumulation tunnel. The retaining wall 5 is 1.0m thick and 50cm high. Seal the gap between the retaining wall 5 and the freezing pipe 4 with cement. Lay the main freezing pipe 7 in the transport tunnel 6 outside the retaining wall 5. The main freezing pipe 7 is buried in the bottom rock layer and connected to the freezing pipe 4 in the wall.

[0049] Step 6: Draw a pipe from the mine drainage system to discharge some of the mine water into the retaining wall 5, or use a diaphragm pump to pump old working water from other waterlogged roadways into the retaining wall 5, so that the water level inside the retaining wall 5 is flush with the bottom edge of the freezing pipe opening on the retaining wall 5. Calculate the existing water volume in the roadway, and use a high-pressure air pipe to blow 6% of the water volume of medical degreased cotton fibers into the water, and blow it evenly through the high-pressure air pipe to improve the mechanical strength of the frozen ice.

[0050] Step 7: Open the freezing valve, keep the freezing temperature below -35℃, freeze for no less than 24 hours, and ensure that the compressive strength of the ice is no less than 5MPa;

[0051] Step 8: After freezing for 24 hours, lay the freezing pipe 4 along the sloping ice surface formed by freezing, and at the same time raise the retaining wall 5, and fix the freezing pipe 4 through the retaining wall 5. The height of the retaining wall 5 is 50cm higher than the newly laid pipe.

[0052] Step 9: Drain the mine water or old working water into the retaining wall 5 through the branch pipe or diaphragm pump of the mine drainage system, so that the water level in the retaining wall 5 is flush with the bottom edge of the freezing pipe on the retaining wall 5. Calculate the existing water volume in the roadway, and add 6% of the water volume of medical degreased cotton fiber to the water by blowing it with a high-pressure air pipe, and stir it evenly by blowing it with a high-pressure air pipe.

[0053] Step 10: Repeat steps 6 through 9 in sequence until the entire waterlogged alley is completely filled with water and frozen.

[0054] Step 11: After No. 1 waterlogging tunnel 2 and No. 2 waterlogging tunnel 3 are completely filled with water and frozen, and the reading of the roof temperature sensor is below -10℃ and the reading of the displacement sensor is less than 50mm, the No. 1 coal pillar 1 is mined by tunneling machine 8 excavating coal, loader 9 loading coal, and trackless rubber-tired vehicle 10 transporting coal. During the mining process, the water diversion channel is blocked by grouting anchor cable support for the roof, hanging plastic geogrids and concrete grout on both sides, and digging water diversion trenches on the bottom plate of transport tunnel 6 to ensure that there is no seepage or water spray in the working space.

[0055] Step 12: While mining the No. 1 coal pillar 1, follow the same method as steps 2 to 10 to fill and freeze the No. 3 water accumulation tunnel.

[0056] Step 13: After the No. 1 coal pillar 1 is mined out, CD-BP type thin spray material is used to spray the top and bottom plates and two sides of the mined space to form a waterproof closed space. A filling retaining wall 11 with a thickness of n is built at the exit position of the mined space. CD-BP type thin spray material is also sprayed on the inside of the retaining wall 11. A filling pipeline 12 is installed at the top of the retaining wall 11. The grouting material prepared by cement, fly ash, 15% concentrated coal slurry water and mine water in a mass ratio of 1:3.5:3:5 is pumped into the retaining wall 11 to achieve filling of the mined space.

[0057] Step 14: After the compressive strength and deformation strength of the filling body 13 reach the predetermined values, the No. 1 water accumulation lane 2 is thawed, and some of the thawed old water is transported to other water accumulation lanes to be frozen. At the same time, the frozen pipeline 4 is retrieved and transferred to the No. 4 water accumulation lane to prepare for freezing work.

[0058] Step 15: After the space of No. 3 waterlogged tunnel is completely filled with water and frozen, the No. 2 coal pillar is mined by tunneling machine 8 excavating coal, loader 9 loading coal, and trackless rubber-tired vehicle 10 transporting coal. During the mining process, the water diversion channel is blocked by grouting anchor cable support for the roof, surrounding rock spraying, and digging water diversion trenches on the bottom of the transport tunnel to ensure that there is no seepage or water spray in the working space.

[0059] Step 16: Repeat steps 12 to 15 to complete the mining and backfilling of all strip coal pillars within the target mining area;

[0060] Step 17: After the mining and backfilling work is completed, drill holes at the top of the retaining wall 11 in all waterlogged tunnels. Place the pumping pipes connected to the mine drainage system along the drill holes into the thawed waterlogged tunnels, pump the water in the tunnels to the surface sewage treatment plant for purification and use as domestic water, and achieve recycling.

[0061] Example 2:

[0062] After the No. 3 waterlogged tunnel is completely filled with water and frozen, the No. 2 coal pillar is mined by tunneling machine, loading machine, and transporting coal by trackless rubber-wheeled vehicle. During the mining process, the water channel is blocked by grouting anchor cable support, surrounding rock spraying, and digging water diversion trenches on the bottom of the transport tunnel to ensure that there is no seepage or water spray in the working space.

[0063] Once the compressive strength and deformation strength of the filling material reach predetermined values, the No. 1 water storage tunnel is thawed. The heat required for thawing is input from the outside and transported to the No. 1 water storage tunnel through pipelines. A mobile boiler structure can be used to supply hot water to the water storage tunnel, and the mobile boiler structure can be connected to the pipelines in the water storage tunnel where freezing is being carried out, that is, connected to the heat pipes that extract and discharge heat, thereby utilizing the heat recovered from freezing, reducing energy consumption during thaw, and transporting some of the thawed old empty water to other water storage tunnels waiting to be frozen. At the same time, the frozen pipeline is recovered and transferred to the No. 4 water storage tunnel for freezing work. The thaw work can be carried out simultaneously with the freezing work, thereby realizing energy recovery and utilization.

[0064] In this embodiment, freezing and thawing are carried out simultaneously when the next mining operation is completed. The heat generated during freezing is fully utilized and recycled, greatly reducing energy consumption during thawing.

[0065] In the description of this invention, it should also be noted that, unless otherwise explicitly specified and limited, the terms "set," "install," "connect," and "link" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0066] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for backfilling and recovering strip coal pillars based on the freezing of old goaf water, characterized in that, Includes the following steps: Step 1: Number the strip coal pillars and water accumulation tunnels in the target area. After numbering them in sequence, first replenish water and freeze the water accumulation tunnels on both sides of the No. 1 coal pillar. Step 2: Use a mobile mixing and pumping truck and rubber corrugated pipe to remove the silt from the bottom of the waterlogged tunnel, and obtain concentrated coal slurry water through sorting and sedimentation treatment, which will be used as the subsequent backfill material. Step 3: Lay freezing pipes on the bottom slab of the waterlogged alley after the silt has been removed, and use a directional drilling rig to drill pipe trenches. Then, use an ammonia brine circulation system for freezing. Step 4: Install temperature and displacement sensors on the roof of the waterlogged tunnel to monitor the temperature of the ice and the deformation of the roof after freezing. Set up a retaining wall to control the water level. Then, introduce old working water into the retaining wall through the mine drainage system or diaphragm pump, and add medical degreased cotton fibers to improve the strength of the frozen ice. Step 5: Open the freezing valve, keep the freezing temperature below -35℃, and freeze for no less than 24 hours to ensure that the compressive strength of the ice is no less than 5MPa. After freezing for 24 hours, further reinforce the ice surface formed by freezing and lay the freezing pipeline. At the same time, increase the height of the retaining wall to stabilize the freezing system. Step Six: Drain the mine water or old working water into the retaining wall through the drainage branch pipe or diaphragm pump of the mine drainage system, so that the water level inside the retaining wall is level with the bottom edge of the freezing pipe on the retaining wall. Calculate the existing water volume in the tunnel. Use a high-pressure air pipe to blow 6% of the water volume of medical degreased cotton fiber into the water and blow it evenly through the high-pressure air pipe. Finally, repeat Step Five and Step Six in sequence until the entire waterlogged tunnel space is completely filled with water and frozen. Step 7: After the freezing is complete, coal pillar mining will be carried out. During the mining process, grouting support will be used to ensure the stability of the roof, prevent water seepage or water accumulation from affecting the working space, and ensure the smooth progress of coal pillar mining. Step 8: After the coal pillar mining is completed, the frozen heat is recovered and thawing is carried out through a heat transfer system to reduce energy consumption during the thawing process. Simultaneously, freezing and thawing are carried out to achieve efficient energy recovery and ultimately complete the coal pillar mining and backfilling recovery in the target area.

2. The method for backfilling and recovering strip coal pillars based on the freezing of old workings water, as described in claim 1, is characterized in that: In step one, when numbering the strip coal pillars and water accumulation tunnels within the target area, the strip coal pillars within the target area are first numbered sequentially from one boundary to the other as No. 1 coal pillar, No. 2 coal pillar, ..., No. N coal pillar. In the same order, the water accumulation tunnels are sequentially numbered as No. 1 water accumulation tunnel, No. 2 water accumulation tunnel, ..., No. N+1 water accumulation tunnel. First, water replenishment and freezing work are carried out on No. 1 water accumulation tunnel and No. 2 water accumulation tunnel on both sides of No. 1 coal pillar.

3. The method for backfilling and recovering strip coal pillars based on the freezing of old workings water according to claim 1, characterized in that: In step two, when obtaining concentrated coal slurry water, firstly, a mobile mixing and pumping vehicle is used with a 4-inch rubber corrugated pipe to pump the sludge from the bottom of the No. 1 and No. 2 water accumulation tunnels to the underground sorting chamber for sorting. The sorted coal slurry water is then subjected to sedimentation and dewatering treatment to obtain concentrated coal slurry water with a water content of 15%, which will be used as roadway filling material. The mobile mixing and pumping vehicle is placed at the edge of the water accumulation area, and an automated pipe-grabbing robotic arm is used to place the 4-inch rubber corrugated pipe opening at the bottom of the deepest sludge in the water accumulation area. By adjusting the position of the pipe opening, all the sludge on the bottom of the water accumulation tunnel is cleared out.

4. The method for backfilling and recovering strip coal pillars based on the freezing of old workings water according to claim 1, characterized in that: In step three, when laying frozen pipelines on the floor of the cleared silt-filled waterlogged roadway and drilling trenches using a directional drilling rig, the frozen pipelines are first laid on the floor of waterlogged roadways No. 1 and No.

2. Before laying, a directional drilling rig is used to drill holes in the coal wall at the lower end of the waterlogged roadway in the waterless area above, forming trenches to fix the frozen pipelines. The slope is the same as the roadway slope, and the lowest point of the trench opening is flush with the roadway floor. After the trench is formed, an automated pipe-grabbing robotic arm is used to push the frozen pipelines from the waterless area above the waterlogged roadway along the floor to the lower end and into the trench, so that the pipelines are flush with the coal strip. The columns are parallel, and the pipeline is 0.5m to 0.7m away from the coal pillar. The pipeline spacing is 1.3m to 1.5m. In waterless areas, the pipeline is connected to the coal pillar using bolts. The base plate is firmly fixed. The freezing pipe is welded from a seamless steel pipe with a wall thickness of 7mm and an outer diameter of 150mm. The inner polyethylene pipe with a diameter of 55mm is used as the liquid supply pipe. Then, an ammonia-salt water circulation system is used for freezing.

5. The method for backfilling and recovering strip coal pillars based on the freezing of old goaf water according to claim 1, characterized in that: Step four involves monitoring the temperature of the frozen ice and the deformation of the roof after freezing, and setting up a retaining wall for water level control. First, temperature and displacement sensors are installed on the roof of the waterlogged tunnel to monitor the temperature of the frozen ice and the deformation of the roof. A retaining wall with a thickness of 1m and a height of 50cm is built at the outlet of the waterlogged tunnel. The gap between the retaining wall and the freezing pipeline is sealed with cement. The main freezing pipeline is laid in the transport tunnel outside the retaining wall. The main pipeline is buried in the bottom rock layer and connected to the freezing pipeline inside the wall. Then, a drainage branch pipe is drawn from the mine drainage system to discharge some mine water into the retaining wall, or a diaphragm pump is used to pump old working water from other waterlogged tunnels into the retaining wall so that the water level inside the retaining wall is flush with the bottom edge of the freezing pipe opening on the retaining wall. By calculating the existing water volume in the tunnel, 6% of the water volume mass of medical degreased cotton fiber is added to the water by blowing it through a high-pressure air pipe and stirred evenly through the high-pressure air pipe to improve the mechanical strength of the frozen ice.

6. The method for backfilling and recovering strip coal pillars based on the freezing of old workings water according to claim 1, characterized in that: After the coal pillar is frozen in step seven, the following steps shall be taken when mining the coal pillar: Step S1: After the No. 1 and No. 2 water accumulation tunnels are completely filled with water and frozen, and the reading of the roof temperature sensor is below -10℃ and the reading of the displacement sensor is less than 50mm, the No. 1 coal pillar is mined by tunneling machine, loading machine, and transporting coal by trackless rubber-tired vehicle. During the mining process, the water channel is blocked by grouting anchor cable support, plastic geogrid and concrete slurry on both sides, and water diversion trenches are dug in the bottom of the transport tunnel to ensure that there is no seepage or water spray in the working space. At the same time, the No. 3 water accumulation tunnel is filled with water and frozen in the same way. Step S2: After the No. 1 coal pillar is mined out, CD-BP type thin spray material is used to spray the top and bottom plates and two sides of the mined space to form a waterproof and closed space. A filling retaining wall with a thickness of n is built at the exit of the mined space. CD-BP type thin spray material is also sprayed on the inside of the retaining wall. A filling pipeline is installed at the top of the retaining wall. A grouting material prepared by cement, fly ash, 15% concentrated coal slurry water and mine water in a mass ratio of 1:3.5:3:5 is pumped into the retaining wall to fill the mined space. After the compressive strength and deformation strength of the filling body reach the predetermined values, the No. 1 water accumulation roadway is thawed and some of the thawed old working water is transported to other water accumulation roadways to be frozen. At the same time, the freezing pipeline is retrieved and transferred to the No. 4 water accumulation roadway for freezing work. Step S3: After the space of No. 3 waterlogged tunnel is completely filled with water and frozen, the No. 2 coal pillar is mined by tunneling machine, loading machine, and transporting coal by trackless rubber-tired vehicle. During the mining process, the water channel is blocked by grouting anchor cable support, surrounding rock spraying, and digging water diversion trenches on the bottom of the transport tunnel to ensure that there is no seepage or water spray in the working space. Step S4: Repeat steps S1 to S3 to complete the mining and backfilling of all strip coal pillars in the target mining area.

7. The method for backfilling and recovering strip coal pillars based on the freezing of old workings water according to claim 1, characterized in that: The thickness n of the filling retaining wall built in the strip coal pillar mining space is determined according to the coal seam burial depth, roof and floor conditions, coal seam thickness and dip angle. The thickness of the water accumulation roadway retaining wall is determined according to the coal seam burial depth, surrounding rock conditions, water accumulation roadway height, dip angle and the expansion coefficient of old working water after freezing.

8. The method for backfilling and recovering strip coal pillars based on the freezing of old workings water according to claim 1, characterized in that: For the triangular blind spot formed at the top of the water accumulation lane after water filling and freezing cycle operations, the ice can be completely connected to the top by drilling holes and injecting water into the top of the already sealed retaining wall.

9. The method for backfilling and recovering strip coal pillars based on the freezing of old goaf water according to claim 1, characterized in that: The pumping flow rate for water accumulation in the tunnel after thawing is based on the old working water, production water, and rock fissure water in this mine and adjacent mines. The total replenishment volume is determined, and the water level is ensured to be located in the tunnel floor area below the retaining wall when the replenishment volume and the pumping volume are dynamically balanced.

10. The method for backfilling and recovering strip coal pillars based on the freezing of old workings water according to claim 1, characterized in that: The defrosting heat in step eight comes from two sources: one is self-heating, which consumes some energy to achieve heating, and the other is the heat recovered during the freezing process. This part of the heat is used for insulation and preheating of the heat transfer pipeline, thereby reducing some energy consumption. In other words, defrosting and the next freezing operation are carried out simultaneously.

Images