Strip coal pillar filling and recycling method based on goaf water freezing

Abstract

The invention discloses a strip coal pillar filling and recycling method based on goaf water freezing, which comprises the following steps of: primarily freezing accumulated water in a roadway in a manner of laying a freezing pipeline, building a retaining wall and supplementing mine water on bottom plates of accumulated water roadways on two sides of a strip coal pillar, and laying the freezing pipeline again along a frozen ice surface after the freezing is finished; and meanwhile, the retaining wall is heightened, mine water is supplemented, and freezing is conducted again till the ponding lane space is completely frozen. Then mining the strip coal pillar between the two frozen roadways, filling the mining space with high-flow-state cement paste after mining, filling the next adjacent waterlogging roadway with water and freezing while mining and filling, and unfreezing the frozen roadway on one side of the cement filling body after the cement filling body reaches reliable strength, so as to obtain the waterlogging roadway with the high-flow-state cement paste. And transferring the mine water and the freezing pipeline to the next accumulated water lane, and repeating the steps until all the coal pillars are stoped and filled. The technology is safe, reliable, high in adaptability and environmentally friendly, and a new technical method is provided for recycling the strip coal pillars of the rich goaf ponding.

Description

Technical Field

[0001] The invention relates to a filling and recovery method for a strip coal pillar with rich old empty space and water accumulation, in particular to a filling and recovery method for a strip coal pillar with rich old empty space and water accumulation which is suitable for an inclination angle of 5° to 15°. Background Art

[0002] For the strip mining area at the boundary of the mining area, since there are a large number of coal rooms and empty tunnels inside, affected by the inclination of the coal seam, structure and water-conducting fissures formed by mining, old empty water, production water and rock fissure water from this mine and adjacent mines will continuously flow into it, causing a large amount of water accumulation in the coal rooms in the strip mining area, or even filling them up, making it impossible to recover the strip coal pillars normally.

[0003] At present, the most commonly used solution is to use a water pump to pump out the accumulated water. However, due to the influence of the monocline structure and the overlying sandstone aquifer, the accumulated water in the coal room will be continuously replenished by the old empty water, fissure water and production water of the mine and adjacent mines. In this case, although the amount of water can be reduced by pumping, it cannot be completely pumped out, so it is difficult to effectively solve the problem by pumping. Therefore, the development of a strip coal pillar filling and recovery method that does not require pumping and uses frozen accumulated water to support the roof has become a major technical problem in the development of the coal industry. Summary of the invention

[0004] The object of the present invention is to provide a strip coal pillar filling and recovery method based on freezing of old empty water to solve the problems raised in the above-mentioned background technology.

[0005] To achieve the above object, the present invention provides the following technical solutions:

[0006] A strip coal pillar filling and recovery method based on freezing of old empty water, characterized in that it comprises the following steps:

[0007] Step 1: The strip coal pillars in the target area are numbered from one side boundary to the other side as No. 1 coal pillar, No. 2 coal pillar...N coal pillar. In the same order, the waterlogging lanes are numbered as No. 1 waterlogging lane, No. 2 waterlogging lane...N+No. 1 waterlogging lane. First, the No. 1 waterlogging lane and No. 2 waterlogging lane on both sides of the No. 1 coal pillar are replenished with water and frozen;

[0008] Step 2: Use a walking mixing and pumping vehicle with a 4-inch rubber bellows to pump the sludge from the bottom plates of the No. 1 and No. 2 waterlogging lanes to the underground sorting chamber for sorting. The sorted coal sludge water is then precipitated and dehydrated to obtain concentrated coal sludge water with a water content of 15%, which will be used as tunnel filling material. The walking mixing and pumping vehicle is placed at the edge of the waterlogging area, and the 4-inch rubber bellows pipe mouth is placed at the bottom of the deepest sludge in the waterlogging area by using an automated pipe grabbing robot arm. All the sludge on the bottom plate of the waterlogging lane is cleared out by adjusting the pipe mouth position.

[0009] Step 3: Lay the freezing pipeline on the floor of No. 1 and No. 2 waterlogging lanes. Before laying, use the ZYWL-4500D kilometer directional drilling rig to drill holes in the coal wall at the lower end of the waterlogging lane in the waterless area above the waterlogging lane to form a pipe groove for fixing the freezing pipeline. The pipe groove has a depth of 0.8m and a diameter of 160mm. The slope is equal to the slope of the lane. The lowest point of the pipe groove opening is flush with the bottom plate of the lane.

[0010] Step 4: After the pipe groove is formed, an automated pipe grabbing robot arm is used to push the freezing pipeline from the waterless area at the top of the waterlogged lane along the floor to the bottom end and into the pipe groove, so that the pipeline is parallel to the strip coal pillar, the pipeline is 0.5m to 0.7m away from the strip coal pillar, and the pipeline spacing is 1.3 to 1.5m. In the waterless area, a sleeve bolt is used to fix the pipeline and the floor firmly. The freezing pipeline is welded with a seamless steel pipe with a wall thickness of 7mm and an outer diameter of 150mm, and a polyethylene pipe with a diameter of 55mm is built in as a liquid supply pipe, and an ammonia-brine circulation system is used for freezing;

[0011] Step 5: Install temperature sensors and displacement sensors on the top plate of the water lane to monitor the temperature of the ice body and the deformation of the top plate after freezing. Build a retaining wall at the exit of the water lane. The retaining wall is 1m thick and 50cm high. The gap between the retaining wall and the freezing pipeline is sealed tightly with cement. Lay a freezing main pipeline in the transport lane outside the retaining wall. The main pipeline is buried in the bottom rock layer and connected to the freezing pipeline in the wall.

[0012] Step 6: Draw out a drainage branch pipe from the mine drainage system to discharge part of the mine water into the retaining wall, or use a diaphragm pump to pump out the old empty water in other flooded lanes into the retaining wall, so that the water surface in 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 lane, use a high-pressure air pipe to blow 6% of the water volume into the water with medical absorbent cotton fiber, and stir it evenly through the high-pressure air pipe to improve the mechanical strength of the frozen ice body.

[0013] Step 7: Open the freezing valve, keep the freezing temperature below -35℃, the freezing time not less than 24h, and ensure that the compressive strength of the ice body is not less than 5MPa;

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

[0015] Step 9. Drain the mine water or old empty water into the retaining wall again through the drainage branch pipe or diaphragm pump of the mine drainage system, so that the water surface in the retaining wall is flush with the bottom edge of the freezing pipe opening on the retaining wall, calculate the existing water volume in the tunnel, and add 6% of the water volume by weight of medical absorbent cotton fiber into the water by blowing with a high-pressure air pipe, and stir it evenly through the high-pressure air pipe;

[0016] Step 10, repeating steps 7, 8 and 9 in sequence until the entire water-logged lane space is completely filled with water and frozen;

[0017] Step 11: After the No. 1 and No. 2 water-logging tunnels are completely filled with water and frozen, and the reading of the roof temperature sensor is lower than -10°C and the reading of the displacement sensor is less than 50mm, the No. 1 coal pillar is mined by using a roadheader to dig coal, a loader to load coal, and a trackless rubber-wheeled vehicle to transport coal. During the mining process, the water diversion channel is blocked by using grouting anchor cables to support the roof, hanging plastic geogrids and concrete slurry on both sides, and digging water diversion grooves on the bottom plate of the transport tunnel to ensure that there is no water seepage or water dripping in the working space;

[0018] Step 12: While mining the No. 1 coal pillar, fill and freeze the No. 3 flooded laneway in the same manner as steps 2 to 10;

[0019] Step 14: After the mining of the No. 1 coal pillar is completed, the top and bottom plates and both sides of the mining space are fully sprayed with CD-BP type thin spraying materials to form a waterproof closed space, and a filling retaining wall with a thickness of n is built at the exit position of the mining space. The CD-BP type thin spraying material is also sprayed on the inside of the retaining wall. A filling pipeline is installed at the top of the retaining wall. The grouting material prepared by cement, fly ash, 15% concentrated coal mud water, and mine water in a mass ratio of 1:3.5:3:5 is pumped into the retaining wall to fill the mining space;

[0020] Step 15: After the space of the No. 3 flooded tunnel is completely filled with water and frozen, the No. 2 coal pillar is mined by using a tunneling machine to dig coal, a loader to load coal, and a trackless rubber-wheeled vehicle to transport coal. During the mining process, the water channel is blocked by using grouting anchor cables to support the roof, surrounding rock spraying, and digging water diversion grooves on the bottom plate of the transport tunnel to ensure that there is no water seepage or water dripping in the working space;

[0021] Step 16: After the compressive strength and deformation resistance of the filling body reach the predetermined values, the No. 1 water-accumulating lane is thawed. The heat required for thawing is input from the outside, and the heat is transported to the No. 1 water-accumulating lane through pipelines. A mobile boiler structure can be used to introduce hot water into the water-accumulating lane, and the mobile boiler structure can be docked with the pipeline in the water-accumulating lane where the freezing work is being carried out, that is, docked with the heat pipeline that extracts and discharges heat, so as to utilize the heat recovered from the freezing, reduce the energy consumption during thawing, and transport part of the thawed old empty water to other water-accumulating lanes to be frozen. At the same time, the freezing pipeline is recovered and transferred to the No. 4 water-accumulating lane to prepare for freezing work. The thawing work can be carried out simultaneously with the freezing work, thereby realizing energy recovery and utilization;

[0022] Step 17, repeating steps 14 to 16 to realize the mining and filling of all strip coal pillars in the target mining area;

[0023] Step 18. After the mining and filling work is completed, drill holes at the top of the retaining walls of all flooded tunnels, and place the pumping pipes connected to the mine drainage system along the drill holes in the thawed flooded tunnels. Pump the accumulated water in the tunnels to the ground sewage treatment plant for purification and use as domestic water to achieve recycling.

[0024] Preferably, the thickness of the retaining wall of the water-logging tunnel is determined according to the buried depth of the coal seam, the surrounding rock conditions, the height and inclination of the water-logging tunnel, and the expansion coefficient of the old empty water after freezing.

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

[0026] Preferably, for the triangular blind area formed at the top of the waterlogged 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 on the top of the closed retaining wall.

[0027] Preferably, the drainage flow rate of accumulated water in the tunnel after thawing is determined based on the total recharge of old empty water, production water and rock fissure water in the mine and adjacent mines, and ensures that the water surface is located in the tunnel floor area below the retaining wall when the supply and drainage volumes are in dynamic balance.

[0028] Preferably, the thawing heat in step sixteen mainly comes from two parts. One part is self-heating, that is, part of the energy is consumed to achieve heating, and the other part is the heat recovered during the freezing process. This part of the heat is mainly used for insulation and preheating of the heat transfer pipeline, thereby reducing part of the energy consumption, that is, the thawing mentioned in step fifteen is carried out simultaneously with the next freezing work.

[0029] Compared with the prior art, the present invention has the following beneficial effects:

[0030] 1. This strip coal pillar filling and recovery method based on freezing of old goaf water makes full use of the accumulated water in the tunnel and replaces the coal resources with cement slurry, effectively reducing the movement of overburden and surface subsidence. It provides a safe, green and efficient new model for the recovery of strip coal pillars in old goaf water-rich inclined coal seams. It has great scientific and engineering significance and broad application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 It is a schematic diagram of the mining area of ​​the rich old empty water belt of the present invention and a cross-sectional diagram in the AA direction;

[0032] Figure 2It is a schematic diagram and AA section diagram of the present invention after laying a freezing pipeline along the bottom plate of a waterlogged laneway, building a retaining wall and replenishing water;

[0033] Figure 3 It is a schematic diagram and AA section diagram of laying a freezing pipeline along a frozen ice surface and building a retaining wall according to the present invention;

[0034] Figure 4 It is a schematic diagram and AA cross-sectional view of the second layer after the freezing of the present invention is completed;

[0035] Figure 5 It is a schematic diagram and AA section diagram of the first and second water accumulation lanes after being completely frozen according to the present invention;

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

[0037] Figure 7 It is a schematic diagram of filling the mining space of the No. 1 coal pillar of 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] Fig. 9 It is a schematic diagram after all coal pillars are mined and filled in the present invention.

[0040] In the figure: 1. No. 1 coal pillar; 2. No. 1 waterlogging lane; 3. No. 2 waterlogging lane; 4. Frozen pipeline; 5. Retaining wall of waterlogging lane; 6. Transport lane; 7. Frozen main road; 8. Tunneling machine; 9. Loader; 10. Rubber-tyred trackless vehicle; 11. Filling retaining wall; 12. Grouting pipeline; 13. Cement slurry. DETAILED DESCRIPTION

[0041] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0042] The present invention provides a technical solution for a strip coal pillar filling and recovery method based on freezing of old empty water, comprising the following steps:

[0043] Embodiment 1:

[0044] Step 1: The strip coal pillars in the target mining area are numbered from one side boundary to the other side as No. 1 coal pillar 1, No. 2 coal pillar...N coal pillar. In the same order, the waterlogging lanes are numbered as No. 1 waterlogging lane 2, No. 2 waterlogging lane 3...N+No. 1 waterlogging lane. First, the No. 1 waterlogging lane 2 and No. 2 waterlogging lane 3 on both sides of No. 1 coal pillar 1 are replenished with water and frozen;

[0045] Step 2: Use a walking mixing and pumping vehicle with a 4-inch rubber bellows to pump the sludge from the bottom plates of No. 1 waterlogged lane 2 and No. 2 waterlogged lane 3 to the underground sorting chamber for sorting. The sorted coal sludge water is then precipitated and dehydrated to obtain concentrated coal sludge water with a water content of 15%, which will be used as tunnel filling material. The walking mixing and pumping vehicle is placed at the edge of the waterlogged area, and the 4-inch rubber bellows pipe mouth is placed at the bottom of the deepest sludge in the waterlogged area by using an automated pipe grabbing robot arm. All the sludge on the bottom plate of the waterlogged lane is cleared out by adjusting the pipe mouth position.

[0046] Step 3: Lay the freezing pipeline on the floor of No. 1 waterlogging lane 2 and No. 2 waterlogging lane 3. Before laying, use the ZYWL-4500D kilometer directional drilling rig to drill holes in the coal wall at the lower end of the waterlogging lane in the waterless area above the waterlogging lane to form a pipe groove for fixing the freezing pipeline. The pipe groove has a depth of 0.8m and a diameter of 160mm. The slope is equal to the slope of the lane. The lowest point of the pipe groove opening is flush with the bottom plate of the lane.

[0047] Step 4: After the pipe groove is formed, an automated pipe grabbing robot arm is used to push the freezing pipe 4 from the waterless area at the top of the waterlogged lane along the floor to the bottom end and into the pipe groove, so that the pipe 4 is parallel to the strip coal pillar 1, the pipe 4 is 10.5m to 0.7m away from the strip coal pillar, and the distance between the pipes 4 is 1.3 to 1.5m. In the waterless area, a sleeve bolt is used to fix the pipe 4 to the floor securely. The freezing pipe 4 is welded from a seamless steel pipe with a wall thickness of 7mm and an outer diameter of 150mm, and a polyethylene pipe with a diameter of 55mm is built in as a liquid supply pipe, and an ammonia-brine circulation system is used for freezing;

[0048] Step 5: Install temperature sensors and displacement sensors on the top plate of the water lane to monitor the temperature of the ice body and the deformation of the top plate after freezing. Build a retaining wall 5 at the exit of the water lane. The retaining wall 5 is 1.0m thick and 50cm high. The gap between the retaining wall 5 and the freezing pipeline 4 is sealed tightly with cement. A freezing main pipeline 7 is laid in the transport lane 6 outside the retaining wall 5. The main pipeline 7 is buried in the bottom rock layer and connected to the freezing pipeline 4 in the wall.

[0049] Step 6: Draw a branch pipe from the mine drainage system to discharge part of the mine water into the retaining wall 5, or use a diaphragm pump to pump the old empty water in other flooded lanes into the retaining wall 5, so that the water surface in the retaining wall 5 is flush with the bottom edge of the freezing pipe opening on the retaining wall 5. By calculating the existing water volume in the lane, use a high-pressure air pipe to blow 6% of the water volume into the water with medical absorbent cotton fiber, and stir it evenly through the high-pressure air pipe to improve the mechanical strength of the frozen ice body.

[0050] Step 7: Open the freezing valve, keep the freezing temperature below -35℃, the freezing time not less than 24h, and ensure that the compressive strength of the ice body is not less than 5MPa;

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

[0052] Step 9: Drain the mine water or old empty water into the retaining wall 5 through the branch pipe of the mine drainage system or the diaphragm pump, so that the water surface in 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 lane, add 6% of the water volume by weight of medical absorbent cotton fiber into the water by blowing with a high-pressure air pipe, and stir evenly by blowing with the high-pressure air pipe;

[0053] Step 10, repeat steps 6 to 9 in sequence until the entire water-logged lane space is completely filled with water and frozen;

[0054] Step 11: After the No. 1 water-logging tunnel 2 and the No. 2 water-logging tunnel 3 are completely filled with water and frozen, and the reading of the roof temperature sensor is lower than -10°C and the reading of the displacement sensor is less than 50mm, the No. 1 coal pillar 1 is mined by using a tunneling machine 8 to dig coal, a loader 9 to load coal, and a trackless rubber-wheeled vehicle 10 to transport coal. During the mining process, the water diversion channel is blocked by using grouting anchor cables to support the roof, hanging plastic geogrids and concrete slurry on both sides, and digging water diversion grooves on the bottom plate of the transport tunnel 6 to ensure that there is no water seepage or water dripping in the working space;

[0055] Step 12: While mining the No. 1 coal pillar 1, fill and freeze the No. 3 flooded laneway in the same manner according to steps 2 to 10;

[0056] Step 13: After the mining of the No. 1 coal pillar 1 is completed, the top and bottom plates and both sides of the mining space are fully sprayed with CD-BP type thin spraying material to form a waterproof closed space, and a filling retaining wall 11 with a thickness of n is built at the exit position of the mining space. The CD-BP type thin spraying material is also sprayed on the inner side of the retaining wall 11, and a filling pipeline 12 is installed at the top position of the retaining wall 11. The grouting material prepared by cement, fly ash, 15% concentrated coal mud water, and mine water in a mass ratio of 1:3.5:3:5 is pumped into the retaining wall 11 to fill the mining space;

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

[0058] Step 15: After the space of the No. 3 water-logged tunnel is completely filled with water and frozen, the No. 2 coal pillar is mined by using a tunneling machine 8 to dig coal, a loader 9 to load coal, and a trackless rubber-wheeled vehicle 10 to transport coal. During the mining process, the water diversion channel is blocked by using grouting anchor cable support for the roof, surrounding rock spraying, and digging a water diversion groove on the bottom plate of the transport tunnel to ensure that there is no water seepage or water dripping in the working space;

[0059] Step 16, repeating steps 12 to 15 to realize the mining and filling of all strip coal pillars in the target mining area;

[0060] Step 17. After the mining and filling work is completed, drill holes at the top of the retaining walls 11 of all the flooded tunnels, and place the pumping pipes connected to the mine drainage system along the drill holes in the thawed flooded tunnels. Pump the accumulated water in the tunnels to the ground sewage treatment plant for purification and use as domestic water for recycling.

[0061] Embodiment 2:

[0062] Among them, after the space of the No. 3 flooded tunnel is completely filled with water and frozen, the No. 2 coal pillar is mined by using tunneling machines to dig coal, loaders to load coal, and trackless rubber-wheeled vehicles to transport coal. During the mining process, the water diversion channel is blocked by using grouting anchor cables to support the roof, surrounding rock spraying, and digging water diversion grooves on the bottom plate of the transport tunnel to ensure that there is no water seepage or water dripping in the working space;

[0063] Among them, after the compressive strength and deformation resistance of the filling body reach the predetermined values, the No. 1 water accumulation lane is thawed. The heat required for thawing here is input from the outside, and the heat is transported to the No. 1 water accumulation lane through pipelines. A mobile boiler structure can be used to introduce hot water into the water accumulation lane, and the mobile boiler structure can be connected with the pipeline in the water accumulation lane where the freezing work is being carried out, that is, it can be connected with the heat pipeline that sucks and discharges heat, so as to utilize the heat recovered from the freezing, reduce the energy consumption during thawing, and transport part of the thawed old empty water to other water accumulation lanes to be frozen. At the same time, the freezing pipeline is recovered and transferred to the No. 4 water accumulation lane to prepare for freezing work. The thawing work can be carried out simultaneously with the freezing work, thereby realizing energy recovery and utilization.

[0064] In this embodiment, when the next mining operation is completed, the freezing and thawing operations are performed simultaneously, making full use of the heat generated during freezing, recycling this part of the heat, and greatly reducing the energy consumption during thawing.

[0065] In the description of the present invention, it is also necessary to explain that, unless otherwise clearly specified and limited, the terms "set", "install", "connect", and "connect" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two elements. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

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

Claims

1. A strip coal pillar filling and recovery method based on freezing of old empty water, characterized in that: The following steps are involved: Step 1: Number the strip coal pillars and waterlogged lanes in the target area. After numbering them in sequence, firstly perform water replenishment and freezing treatment on the waterlogged lanes on both sides of the No. 1 coal pillar; Step 2: Use a walking mixing and pumping vehicle and a rubber bellows to remove the sludge at the bottom of the waterlogged lane, and treat the coal sludge water by sorting and sedimentation to obtain concentrated coal sludge water as subsequent filling material; Step 3: lay the freezing pipeline on the bottom plate of the flooded laneway where the sludge has been removed, and use a directional drill to drill the pipe groove, and then use the ammonia-salt water circulation system for freezing; Step 4: Install temperature and displacement sensors on the roof of the water-logged tunnel to monitor the temperature of the ice body and the deformation of the roof after freezing, and set up retaining walls to control the water level. Then, introduce old empty water into the retaining wall through the mine drainage system or diaphragm pump, and add medical absorbent cotton fibers to improve the strength of the frozen ice body. Step 5: Open the freezing valve, keep the freezing temperature below -35℃, and keep the freezing time for no less than 24 hours, ensuring that the compressive strength of the ice body is no less than 5MPa. After freezing for 24 hours, further reinforce the ice surface formed by freezing and lay the freezing pipeline, and at the same time increase the height of the retaining wall to stabilize the freezing system; Step 6: Drain the mine water or old empty water into the retaining wall through the drainage branch pipe of the mine drainage system or the diaphragm pump, so that the water surface in the retaining wall is flush with the bottom edge of the freezing pipe on the retaining wall, calculate the existing water volume in the tunnel, add 6% of the water volume by weight of medical absorbent cotton fiber into the water by means of high-pressure air pipe blowing, and stir evenly through the high-pressure air pipe, and finally, repeat steps 5 and 6 in sequence until the entire water-logged tunnel space is completely filled with water and frozen; Step 7: After the freezing is completed, the coal pillar is mined. During the mining process, grouting support is used to ensure the stability of the roof, prevent water seepage or accumulation from affecting the working space, and ensure the smooth mining of the coal pillar; Step 8. After the coal pillar mining is completed, the freezing heat is recovered and thawing operations are carried out through the heat transfer system to reduce the energy consumption of the thawing process. At the same time, freezing and thawing work are carried out simultaneously to achieve efficient energy recovery and finally complete the coal pillar mining and filling recovery in the target area.

2. The strip coal pillar filling and recovery method based on freezing of old empty water according to claim 1 is characterized by: When numbering the strip coal pillars and waterlogging lanes in the target area in step one, first number the strip coal pillars in the target area from one side boundary to the other side as coal pillar No. 1, coal pillar No. 2...No. N coal pillars. In the same order, number the waterlogging lanes as waterlogging lane No. 1, waterlogging lane No. 2...N+waterlogging lane No.

1. First, replenish water and freeze the No. 1 and No. 2 waterlogging lanes on both sides of the No. 1 coal pillar.

3. The strip coal pillar filling and recovery method based on freezing of old empty water according to claim 1 is characterized by: When obtaining concentrated coal sludge water in step 2, first, a walking-type mixing and pumping vehicle is used with a 4-inch rubber bellows to pump the sludge from the bottom plates of the No. 1 and No. 2 flooded tunnels to the underground sorting chamber for sorting. The sorted coal sludge water is then subjected to sedimentation and dehydration treatment to obtain concentrated coal sludge water with a water content of 15%, which will be used as tunnel filling material. The walking-type mixing and pumping vehicle is placed at the edge of the flooded area, and the automated pipe grabbing robot arm is used to place the pipe mouth of the 4-inch rubber bellows at the bottom of the deepest sludge in the flooded area, and all the sludge on the bottom plate of the flooded tunnel is cleared out by adjusting the position of the pipe mouth.

4. The strip coal pillar filling and recovery method based on freezing of old empty water according to claim 1 is characterized by: In step 3, when laying the freezing pipeline on the bottom plate of the waterlogged tunnel where the silt has been cleared and using a directional drill to dig the pipe groove, first, lay the freezing pipeline on the bottom plate ground of the No. 1 and No. 2 waterlogged tunnels. Before laying, use a directional drill to drill holes in the coal wall at the lower end of the waterlogged tunnel in the waterless area above the waterlogged tunnel to form a pipe groove for fixing the freezing pipeline. The slope is equal to the slope of the tunnel, and the lowest point of the pipe groove opening is flush with the tunnel bottom plate. After the pipe groove is formed, an automated pipe grabbing robot arm is used to grab the freezing pipe. The pipeline is pushed from the waterless area at the top of the waterlogged tunnel along the floor to the bottom end and enters the pipe trench, so that the pipeline is parallel to the strip coal pillar, the pipeline is 0.5m to 0.7m away from the strip coal pillar, and the pipeline spacing is 1.3 to 1.5m. In the waterless area, the pipeline is firmly fixed to the floor with bolts. The freezing pipeline is welded with seamless steel pipes with a wall thickness of 7mm and an outer diameter of 150mm, and a polyethylene pipe with a diameter of 55mm is built in as a liquid supply pipe. Then, an ammonia-brine circulation system is used for freezing.

5. The strip coal pillar filling and recovery method based on freezing of old empty water according to claim 1 is characterized by: Step 4: Monitor the temperature of the ice body and the deformation of the top plate after freezing, and set up a retaining wall for water level control. First, install a temperature sensor and a displacement sensor on the top plate of the water-accumulating tunnel to monitor the temperature of the ice body and the deformation of the top plate after freezing. Build a retaining wall at the exit of the water-accumulating tunnel with a thickness of 1m and a height of 50cm. The gap between the retaining wall and the freezing pipeline is sealed tightly with cement. A freezing main pipeline is laid in the transportation tunnel outside the retaining wall. The main pipeline is buried in the bottom rock layer and connected to the freezing pipeline in the wall. Subsequently, a drainage branch pipe is led out from the mine drainage system to discharge part of the mine water into the retaining wall, or a diaphragm pump is used to pump the old empty water in other water-accumulating tunnels into the retaining wall, so that the water surface in the retaining wall is flush with the bottom edge of the freezing pipe on the retaining wall. By calculating the existing water storage in the tunnel, a medical absorbent cotton fiber with a mass of 6% of the water storage is added to the water by a high-pressure air pipe, and is blown and stirred evenly by a high-pressure air pipe to improve the mechanical strength of the frozen ice body.

6. The strip coal pillar filling and recovery method based on freezing of old empty water according to claim 1 is characterized by: After freezing is completed in step 7, when mining the coal pillar, the following steps are taken: Step S1: After the No. 1 and No. 2 waterlogging lanes are completely filled with water and frozen, and the reading of the roof temperature sensor is lower than -10°C, and the reading of the displacement sensor is less than 50mm, the No. 1 coal pillar is mined by using a roadheader to dig coal, a loader to load coal, and a trackless rubber-wheeled vehicle to transport coal. During the mining process, the water diversion channel is blocked by using grouting anchor cables to support the roof, hanging plastic geogrids and concrete slurry on both sides, and digging water diversion grooves on the bottom plate of the transport lane to ensure that there is no water seepage or water dripping in the working space. At the same time, the No. 3 waterlogging lane is filled with water and frozen in the same way; Step S2: After the mining of No. 1 coal pillar is completed, the top and bottom plates and both sides of the mining space are fully sprayed with CD-BP type thin spraying material to form a waterproof closed space, and a filling retaining wall with a thickness of n is built at the exit position of the mining space. The CD-BP type thin spraying material is also sprayed on the inner side of the retaining wall. A filling pipeline is installed at the top connection position of the retaining wall, and a grouting material prepared by cement, fly ash, 15% concentrated coal mud water, and mine water in a mass ratio of 1:3.5:3:5 is pumped into the retaining wall to achieve the filling of the mining space; after the compressive strength and deformation resistance of the filling body reach the predetermined value, the No. 1 waterlogging lane is thawed, and the partially thawed old empty water is transported to other waterlogging lanes to be frozen, and at the same time, the freezing pipeline is recovered and transferred to the No. 4 waterlogging lane to prepare for freezing; Step S3: After the space of No. 3 flooded tunnel is completely filled with water and frozen, the No. 2 coal pillar is mined by using a tunneling machine to dig coal, a loader to load coal, and a trackless rubber-wheeled vehicle to transport coal. During the mining process, the water diversion channel is blocked by using grouting anchor cables to support the roof, surrounding rock spraying, and digging water diversion grooves on the bottom plate of the transport tunnel to ensure that there is no water seepage or water dripping in the working space; Step S4: Repeat steps S1 to S3 to realize the mining and filling of all strip coal pillars in the target mining area.

7. The strip coal pillar filling and recovery method based on freezing of old empty water according to claim 1 is characterized by: The thickness n of the filling retaining wall established in the strip coal pillar mining space is determined according to the coal seam burial depth, roof and floor conditions, coal seam thickness and inclination; the thickness of the water accumulation lane retaining wall is determined according to the coal seam burial depth, surrounding rock conditions, water accumulation lane height, inclination and the expansion coefficient of old empty water after freezing.

8. The strip coal pillar filling and recovery method based on freezing of old empty water according to claim 1 is characterized by: For the triangular blind area formed at the top of the waterlogged tunnel after the water filling and freezing cycle operations, the ice body can be completely connected to the top by drilling holes and injecting water on the top of the closed retaining wall.

9. The strip coal pillar filling and recovery method based on freezing of old empty water according to claim 1 is characterized by: After thawing, the drainage flow rate of accumulated water in the tunnel is determined based on the total recharge of old empty water, production water and rock fissure water in this mine and adjacent mines, and ensures that the water surface is located in the tunnel floor area below the retaining wall when the supply and drainage volumes are in dynamic balance.

10. The strip coal pillar filling and recovery method based on freezing of old empty water according to claim 1 is characterized by: The thawing heat in step eight mainly comes from two sources. One part is self-heating, that is, consuming part of the energy to achieve heating, and the other part is the heat recovered during the freezing process. This part of heat is mainly used for insulation and preheating of the heat transfer pipeline, thereby reducing part of the energy consumption, that is, thawing and the next freezing work are carried out simultaneously.

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