A method for efficiently recovering residual coal pillars by freezing accumulated water in room-and-pillar mining areas

Abstract

The present invention discloses a method for efficiently recovering residual coal pillars by freezing accumulated water in a room-and-pillar residual mining area. The method comprises the following steps: the feasibility of re-mining the residual coal pillars in the pillar-type goaf is determined based on mine production data and exploration data; artificial refrigeration is used to freeze the accumulated water in the room-and-pillar residual mining area, so that the liquid water becomes solid ice after freezing to replace the paste filling material; the collapsed roof and gangue in the entire goaf are wrapped in the frozen ice body to form a whole; the frozen ice fills the entire residual mining area in a full-filling manner; tunnels are excavated and coal mining working faces are arranged in the frozen ice blocks; then a coal cutter cuts the coal pillars and the frozen water together; as the mining working face advances, the residual coal pillars are gradually recovered, and at the same time, the accumulated water melted after cutting is extracted, thereby achieving the effect of efficiently recovering the residual coal pillars.

Description

Technical Field

[0001] The invention relates to a method for efficiently recovering residual coal pillars by freezing accumulated water in a room-and-pillar residual mining area, and belongs to the technical field of coal mining. Background Art

[0002] In recent years, international energy prices have risen sharply, and coal supply and demand have remained tight, further emphasizing the role of coal as a "ballast stone" in ensuring energy security. Shallow, high-quality coal resources are dwindling, and the re-mining of abandoned coal, due to outdated mining techniques, has become a crucial measure, following deep-seated resource extraction, to ensure coal supply. Furthermore, as proven coal reserves gradually decrease, the contradiction between the unlimited growth of coal demand and the finite nature of non-renewable resources is becoming increasingly acute. Improving resource recovery rates and developing energy-efficient mining areas have become another crucial task for coal mining companies in ensuring supply.

[0003] Due to historical limitations and mining technology, the average recovery rate of many early coal mines did not exceed 30%, and some small mines achieved recovery rates of only 10% to 20%. Consequently, many coal seams left behind by small coal mines remain in existing mining areas and shafts. The early room-and-pillar mining method, which combined mining and excavation, deployed a series of 5- to 7-meter-high coal rooms within the seam, with 20- to 30-meter-high rooms between them. While mining the coal resources within the rooms, narrow working faces were formed, typically advancing in groups. The coal pillars between the rooms served as roof support during room-and-pillar mining. After the rooms were mined, the pillars were largely abandoned, resulting in a significant waste of resources. Subsequently, much of the room-and-pillar goaf gradually filled with water, and the mechanical properties of the remaining coal pillars gradually deteriorated. Current common solid waste backfilling and re-mining methods (CN200910258318.9: A Solid Backfill Method for Recovering Room-Pillar Coal Pillars in Comprehensive Mining; CN201910756396.5: A Backfilling Mining Method for Recovering Residual Coal Pillars in Old Room-Pillar Goafs) require pumping out accumulated water from the goaf, determining the distribution of the remaining coal pillars, and then pumping paste material for backfilling and re-mining the coal pillars. Backfilling large goafs is costly and difficult. Therefore, there is an urgent need to find a method that can both effectively address water accumulation in room-and-pillar goafs and safely, efficiently, and economically recover the remaining coal pillars in room-and-pillar mining areas. Summary of the Invention

[0004] To solve the above problems, the present invention proposes a method for efficiently recovering the remaining coal pillars by freezing the accumulated water in the room-and-pillar goaf. The method is mainly aimed at efficiently recovering the remaining coal pillars in the room-and-pillar goaf that is mostly filled with accumulated water. It is mainly suitable for efficiently recovering the remaining coal pillars from the early and outdated room-and-pillar mining method.

[0005] Based on the investigation of the distribution of coal pillars and goaf groups in room-and-pillar goafs, the amount of water accumulated in the goafs, and the range of water accumulation, the present invention utilizes artificial refrigeration technology to freeze the water accumulated in the goafs, turning the liquid water into ice with a bearing capacity close to that of the coal sample. The frozen ice then becomes a filler to fill the room-and-pillar goafs, filling the entire goaf with a giant ice block formed from the frozen water. Simultaneously, this giant ice block forms a collaborative bearing body with the roof and floor of the residual mining area, the coal pillars, and the surrounding rock at the boundary of the goaf, jointly bearing the load transferred from the overlying rock strata. A mining tunnel and coal mining working face are set up in the ice blocks and remaining coal pillars formed after freezing, and then a coal cutter simultaneously cuts the coal pillars and the ice formed by the frozen water. As the mining working face advances, the accumulated water melted during the cutting process and the melted water from the ice debris during transportation after cutting are pumped out, and the coal resources of the remaining coal pillars are recovered. The purpose of efficiently recovering the remaining coal pillars is achieved without having to deal with a large amount of accumulated water at one time, and the problems of fire prevention and gas control in the mining of the remaining coal can be solved simultaneously.

[0006] The present invention provides a method for efficiently recovering residual coal pillars by freezing accumulated water in a room-and-pillar mining area, comprising the following steps:

[0007] (1) Carry out core drilling and peek, combine the original geological and technical data of the mine, the distribution of coal pillar groups and goaf groups, draw the distribution morphology map of the overlying rock layer of the goaf, the coal pillars left in the room-and-pillar goaf, and the goaf to guide safe production. At the same time, find out the height, amount and quality of water accumulation in the room-and-pillar goaf to serve the subsequent water freezing design of the goaf;

[0008] (2) Comprehensively consider the strength and Mohs hardness of coal samples measured by core drilling of the coal pillars left in the room-pillar goaf, and the strength and Mohs hardness of frozen ice measured by sampling the water in the room-pillar goaf. The room-pillar residual mining area is regarded as a complete unmined coal seam. The mechanical parameters of the coal body and ice body are combined to design the mining working face for recovering the coal pillars left in the room-pillar residual mining area, select equipment, design the working face roadway, and arrange the cutting holes.

[0009] (3) The existing roadway in the same layer parallel to the room-and-pillar goaf is used as a freezing auxiliary roadway, and a freezing workstation is arranged. A series of horizontal boreholes are drilled in the wall of the freezing auxiliary roadway toward the water accumulation area of ​​the goaf, and freezing pipes are arranged through the boreholes into the water accumulation area of ​​the goaf; when there is no suitable roadway to choose from in the coal seam where the room-and-pillar goaf is located, a roadway can be selected in the overlying stratum of the pillar goaf, and a series of vertical boreholes can be drilled from top to bottom. The freezing pipes are lowered and arranged through the roadway boreholes in the overlying stratum into the water accumulation area of ​​the goaf;

[0010] (4) A freezing workstation is arranged in the freezing auxiliary tunnel set up in step (3). The heat of the accumulated water is replaced by the circulating brine through the freezing pipe arranged in the accumulated water in the room-pillar goaf, so that the accumulated water in the room-pillar goaf enters the active freezing period, and the liquid phase water becomes ice with a certain bearing capacity. The temperature range of the frozen ice body in this stage is -20℃~-12℃. The characteristics of water changing with the shape of the container and the expansion of water volume when it freezes are utilized to make it fully connect with the top at the same time as it freezes. The ice after the accumulated water in the room-pillar goaf is frozen as a filling body. At the same time, the remaining coal pillars, collapsed rocks, etc. in the goaf are frozen into a frozen body with the accumulated water. The entire goaf is filled with huge ice blocks formed by the frozen accumulated water. The ice body after the accumulated water in the room-pillar goaf is frozen and forms a cooperative bearing body with the top and bottom plates of the room-pillar residual mining area, the coal pillars left in the room-pillar goaf to be recovered, and the coal pillars at the boundary of the room-pillar goaf, and jointly bears the load transferred by the overlying rock strata.

[0011] (5) When the accumulated water in step (4) is insufficient to completely reach the top after freezing, water is added through the borehole in step (3) during the freezing process of the accumulated water in step (4) to ensure that the ice body can fully reach the top after the accumulated water in the room-and-pillar goaf is frozen; when the accumulated water in the room-and-pillar goaf completely fills the goaf, the accumulated water in step (4) freezes and expands, and the amount of water in the room-and-pillar goaf is too much, water is pumped out through the borehole in step (3) to ensure that the ice body just reaches the top after the accumulated water in the room-and-pillar goaf is frozen;

[0012] (6) After the accumulated water in the room-and-pillar residual mining area is completely frozen, each freezing workstation in step (4) reduces the refrigeration capacity, and the freezing work enters the passive freezing period to ensure that the ice will not thaw and maintain the frozen ice body temperature constant at -10℃~-5℃;

[0013] (7) Then, excavate and arrange transportation and ventilation tunnels in the ice body maintained by passive freezing, use explosion-proof electric heating rods to gradually melt the ice body along the designed central axis of the tunnel, and at the same time extract the water formed by the melting of the ice body. After the tunnel of the designed size is melted in the ice body, freeze pipes are laid on the inner wall surface of the tunnel to maintain the freezing of the tunnel surface, avoid the heat radiation generated by the air introduced by the mine ventilation and the transportation of equipment, etc., which causes the tunnel surface to melt, and ensure that the tunnel maintains the designed shape and size; then, through the tunnel transportation and arrangement of relevant mining equipment, arrange the room-and-pillar goaf coal pillar recovery working face at the designated location, open the cutting hole, and arrange the coal pillar recovery working face;

[0014] (8) Under the maintenance of passive freezing, the frozen accumulated water and the remaining coal pillars are regarded as a whole. The coal cutter gradually cuts the ice body and coal pillars from the opening of the cutting hole, and the entire layer is mined to recover the remaining coal; part of the ice body melts during the cutting, and part of the ice body is cut into ice chips and the cut coal blocks are transported together through a scraper conveyor. Pumps and drainage ditches are arranged in the working face and transport tunnel to extract the water formed by the melting of ice chips during the cutting and transportation of the ice body.

[0015] In the above scheme, when each freezing pipeline is arranged in the water accumulation in the room-and-pillar residual mining area, a series of temperature sensors are lowered along with the pipeline and evenly arranged in the water accumulation in the room-and-pillar residual mining area. A real-time dynamic detection network is established to conduct real-time detection of the temperature of the water accumulation (frozen ice body) in the goaf.

[0016] In the above scheme, step (1) investigates the original geological and technical data of the mine to find out the width and height of the void group and the coal pillar group in the pillar-type residual mining area, uses a three-dimensional laser scanner to accurately detect the distribution direction, size and volume of the void group in the room-pillar residual mining area, and at the same time finds out the depth, distribution range and volume of the water accumulation in the room-pillar residual mining area.

[0017] In the above scheme, in step (2), the room-and-pillar residual mining area is regarded as a complete unmined coal seam for mining design, in which the relevant mechanical parameters are comprehensively considered based on the parameters of frozen ice (uniaxial compressive strength 3-6 MPa, Mohs hardness of about 2.8-4) and the mechanical parameters of coal samples determined by on-site drilling.

[0018] In the above scheme, in step (3), the existing tunnels on the same layer as the parallel room-and-pillar residual mining area coal pillar recovery working face tunnels are set as freezing auxiliary tunnels, freezing workstations are arranged in the freezing auxiliary tunnels, and freezing pipes are arranged through the tunnel wall holes of the freezing auxiliary tunnels to the accumulated water in the goaf. The number of tunnel wall holes is determined by the required cooling capacity, the accumulated water volume and the radius of the freezing pipes. The freezing pipes form a group of closed loops in the accumulated water in the goaf to circulate brine, replace the heat in the accumulated water, and freeze the accumulated water into ice.

[0019] In the above scheme, the model, power and number of freezing equipment in step (4) are determined based on the cooling capacity required by the volume of the empty area in the room-and-pillar residual mining area and the volume of water in the empty area as determined in step (2); the brine circulation system uses CaCl2 solution as the refrigerant, and the cooling water circulation system is naturally cooled by excavating a water pool; after the various freezing parameters are determined, the equipment is tested at a designated location in the underground freezing auxiliary tunnel, and formal construction is carried out after the entire system is operating correctly.

[0020] In the above scheme, the volume of the water in step (5) expands after freezing, and the volume of the ice after freezing is 1.1 times that of the original water. When the water in the goaf that was not connected to the top is accumulated and the distance between the water surface and the top plate accounts for less than 10% of the total height of the goaf, the ice body can fully connect to the top after freezing; when the accumulated water is small and cannot connect to the top after freezing, the amount of ice is increased by artificial water injection to connect to the top, and then fill the entire room-and-pillar type residual mining area, thereby supporting the rock layer on the top plate of the residual mining area.

[0021] In the above scheme, after the accumulated water in the room-and-pillar residual mining area in step (6) freezes, the uniaxial compressive strength of the ice body is 3MPa~6MPa under passive freezing maintenance, and the tensile strength is about 1 / 2 of the compressive strength. Under the lateral constraint of the surrounding rock of the underground goaf, the compressive strength of the ice body is 5~10MPa, which is close to the strength of the gangue concrete paste filling material.

[0022] In the above scheme, when the working face width is greater than 50m, if it is difficult to completely freeze all the water in the goaf by laying pipes through the holes drilled in the wall of the freezing auxiliary tunnel in step (3) to the water in the goaf, an ice body 10-20m inward from the boundary rock of the residual mining area can be frozen. Then, a tunnel is excavated and the working face is arranged within the frozen ice body inside the boundary rock of the residual mining area; the excavated transport tunnel is widened, and an auxiliary chamber is excavated in it for the subsequent arrangement of the freezing workstation. The transport tunnel also functions as a freezing tunnel.

[0023] In the above scheme, the passive freezing period in step (6) refers to the freezing effect of the accumulated water in the room-and-pillar residual mining area during the previous active freezing period (the temperature range of the frozen ice body during the active freezing period is -20°C~-12°C). The liquid water gradually freezes and the freezing is basically completed. At this time, the frozen ice body only needs to maintain the frozen state to ensure that it will not thaw. The temperature of the circulating brine increases, and the temperature range of the frozen ice body increases to -10°C~-5°C, so as to achieve energy saving and economy as much as possible; at the same time, the Mohs hardness of the frozen ice body is reduced, which is conducive to cutting by the coal cutter.

[0024] In the above scheme, the coal cutter described in step (8) gradually cuts the ice body and coal pillars from the opening of the cutting eye, and the entire layer is mined to recover the remaining coal pillars. This means that under the maintenance of passive freezing, the frozen accumulated water and the remaining coal pillars are regarded as a whole layer of unmined coal seam. The coal cutter cuts under the support and protection of the hydraulic support, and the roof collapses as it is mined.

[0025] Beneficial effects of the present invention:

[0026] (1) This invention determines the feasibility of re-mining the coal pillars left in the room-and-pillar goaf based on the mine production data and exploration data. It uses artificial refrigeration to freeze the accumulated water in the room-and-pillar goaf, so that the liquid water freezes into solid ice to replace the paste filling material, and the collapsed roof and gangue in the entire goaf are wrapped in the frozen ice body to form a cooperative carrier. The frozen ice fills the entire goaf in a completely filled manner, and tunnels are excavated and coal mining working faces are arranged in the frozen ice. Then, the coal cutting machine cuts the coal pillars and the frozen ice together. As the mining working face advances, the remaining coal pillars are gradually recovered, and the accumulated water melted after cutting is simultaneously extracted, achieving the effect of efficiently recovering the remaining coal pillars.

[0027] (2) Compared with the traditional method of recovering coal pillars after mining by filling with solid waste paste materials, there is no need to deal with a large amount of accumulated water in the residual mining area at one time before recovering the coal pillars. Instead, the ice chips melted after cutting are gradually extracted during the mining process, creating conditions for the orderly and efficient utilization of the accumulated water in the goaf.

[0028] (3) The room-and-pillar goaf is filled with frozen ice, and the remaining coal pillars are mined under the support of the frozen ice. The frozen ice filling the goaf can solve the problem of gas prevention and control in the mining of the remaining coal, and the low temperature environment provided can avoid the frequent fire accidents during the mining of the remaining coal. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 This is a cross-section of the rock strata in the room-and-pillar goaf;

[0030] Figure 2 This is a schematic diagram of the distribution of coal pillars and goafs left in room-and-pillar goafs;

[0031] Figure 3 Schematic diagram of the freezing pipeline layout and frozen ice distribution in room-and-pillar goaf.

[0032] In the figure: 1—overlying rock strata in the goaf, 2—remaining coal pillars in the room-and-pillar goaf, 3—water accumulation in the room-and-pillar goaf, 4—coal pillars at the boundary of the room-and-pillar goaf; 5—mining tunnel, 6—frozen auxiliary tunnel, 7—freezing workstation, 8—freezing pipeline, 9—ice body after the water in the room-and-pillar goaf is frozen. DETAILED DESCRIPTION

[0033] The present invention is further illustrated below by way of examples, but is not limited to the following examples.

[0034] In order to have a clearer understanding of the technical objectives, features and effects of the present invention, the method of freezing accumulated water in room-and-pillar goaf and recovering residual coal pillars is now further described in detail with reference to the accompanying drawings.

[0035] A certain mine is now facing the problem of exhausted resources and low resource recovery rate. It is urgent to seek new methods and ideas to increase the recovery rate and extend the service life of the mine. Recovering the remaining coal pillars of the No. 2 coal seam mined in the early room-and-pillar method has become a good solution to the current predicament of the mine. The No. 2 coal seam of the mine is 4.2 meters thick. Due to the constraints of the early backward mining technology, it was mined using the room-and-pillar mining method. During coal mining, coal pillars of different shapes were left between the coal rooms to support the roof. The recovery rate of the entire layer of coal resources was less than 40%. After mining, most areas of the goaf were gradually filled with mine water. It is a typical room-and-pillar residual mining area with a large amount of high-quality mineable coal. Drawing on the traditional paste filling mining method, it is necessary to extract and treat a large amount of accumulated water in the goaf at one time, and then set up a filling pipeline for filling. The cost is high, and there is an urgent need to find a scientific, efficient and economical coal pillar recovery method. In view of the above situation, the implementation process of the present invention is further described in detail below with reference to the accompanying drawings. The specific implementation steps are as follows:

[0036] (1) Based on the original geological and technical data of the mine, the distribution of coal pillar groups and goaf groups was analyzed, and the overlying rock layer 1 of the goaf, the coal pillars left in the room-and-pillar goaf 2 and the distribution morphology of the goaf were drawn to guide safe production. At the same time, it was found that the height of the water accumulation 3 in the room-and-pillar goaf was 4m, and the amount of water accumulation accounted for 80% of the volume of the goaf in the pillar goaf.

[0037] (2) Before mining design, the uniaxial compressive strength of the coal pillar 2 remaining in the room-and-pillar goaf was measured by core drilling to be 10.6 MPa, and the Mohs hardness was between 1.8 and 2. At the same time, the uniaxial compressive strength of the frozen ice (under a freezing environment of -10°C to -5°C) was measured to be between 3 MPa and 6 MPa, and the Mohs hardness was between 2.8 and 4. Taking into account the mechanical parameters such as the compressive strength and Mohs hardness of the coal pillar and the frozen ice, the room-and-pillar goaf was considered as a complete unmined coal seam, and the mining design and equipment selection for the mining face of the coal pillar remaining in the room-and-pillar goaf were carried out, as well as the design of the working face roadway and the layout of the cut holes.

[0038] (3) The working face of the room-and-pillar goaf is 180 m long. It is difficult to freeze all the water 3 in the room-and-pillar goaf by drilling through the existing tunnel parallel to the boundary of the room-and-pillar goaf and setting up the freezing pipeline 8. Therefore, it is chosen to drill holes from the surrounding rock at the boundary of the residual mining area to the goaf. Part of the water in the goaf is frozen inward from the surrounding rock at the boundary of the residual mining area to form an ice body 20 m wide. After the water in the frozen range is frozen, the temperature of the circulating brine increases in a small range, and the temperature range of the frozen ice body increases from -12℃~-20℃ in the active freezing period to -5℃~-10℃.

[0039] (4) Then, the mining tunnel 5 is excavated and arranged in the ice body maintained by the passive freezing in step (3). The ice body is gradually melted along the designed central axis of the tunnel using explosion-proof electric heating rods. At the same time, the water formed by the melting of the ice body is extracted to melt the mining tunnel 5 of the designed size in the ice body. The freezing pipeline is laid on the inner wall surface of the mining tunnel 5 to maintain the freezing of the surface of the mining tunnel 5, avoid the melting of the tunnel surface due to the heat radiation of the air introduced by the mine ventilation and the transportation of equipment, and ensure that the mining tunnel 5 maintains the designed shape and size.

[0040] (5) The transport tunnel excavated in step (4) is widened, and an auxiliary chamber is excavated on one side thereof for the subsequent arrangement of the freezing workstation 7. One side of the mining tunnel 5 serves as the freezing auxiliary tunnel 6.

[0041] The following reference solutions are provided for the selection and arrangement of freezing equipment:

[0042] The freezer uses SKD136.1.H screw unit, which has a designed cooling capacity of 116960Kcal / h and a single motor power of 114KW.

[0043] Each refrigeration unit is equipped with a brine circulation pump, IS150-125-315 type, with a single flow rate of 200m 3 / h, motor power 37KW;

[0044] The cooling water circulation pump of the freezing station is IS150-125~315B type, with a single flow rate of 173m 3 / h, motor power 18.5KW;

[0045] Each freezing station must be equipped with a brine circulation pump and a cooling water circulation pump as backup;

[0046] The main parameters and indicators involved in freezing construction are as follows:

[0047] Refrigerant: Freon R-22,

[0048] Refrigeration oil: Hanbell HBR-B03 refrigeration oil,

[0049] Freezing brine temperature: active period: -25℃~-20℃, passive period: -20℃~-15℃,

[0050] The average temperature of the frozen water is -12℃~-8℃.

[0051] Freezing brine delivery pipe: flexible metal pipe that is resistant to low temperatures.

[0052] The specific freezing parameters and details are as follows:

[0053] The brine circulation system uses CaCl2 solution as the refrigerant; the cooling water circulation system is cooled naturally by digging a water pool; after determining the freezing parameters, the equipment is tested and formal construction begins after the entire system is operating correctly.

[0054] (6) In the freezing auxiliary tunnel 6 set up in step (5), several groups of freezing workstations 7 are arranged along the direction of the mining working face according to the freezing construction plan. Through the freezing pipe 8 arranged in the water 3 in the room-pillar goaf, the heat of the water is replaced by the circulating brine, so that the water 3 in the room-pillar goaf enters the active freezing period, and the liquid water becomes ice with a certain bearing capacity, and the temperature range of the frozen ice body is maintained at -12℃~-20℃; by utilizing the characteristics of water changing with the shape of the container and the volume expansion of water when it freezes, it is fully connected to the top while freezing. The ice body 9 after the water in the room-pillar goaf is frozen serves as a filling body, and at the same time, the coal pillars 2 left in the room-pillar goaf, collapsed rocks, etc. are all frozen into the ice blocks. The entire goaf is filled with huge ice blocks formed by the frozen water. The ice body 9 after the water in the room-pillar goaf is frozen and together with the top and bottom plates of the room-pillar residual mining area, the coal pillars 2 left in the room-pillar goaf to be recovered, and the coal pillars 4 at the boundary of the room-pillar goaf form a whole with a certain bearing capacity.

[0055] (7) The amount of water accumulated in the room-and-pillar goaf accounts for 80% of the volume of the pillar goaf. The volume of the accumulated water in step (5) expands by 1.1 times during the freezing process. The amount of water accumulated in the room-and-pillar goaf is insufficient. Water is supplemented by drilling holes in step (3) to ensure that the ice body 9 just touches the top after the water accumulated in the room-and-pillar goaf freezes.

[0056] (8) After the accumulated water in the room-and-pillar goaf is completely frozen and solidified, the freezing workstation 7 arranged along the direction of the coal mining face in step (5) reduces the refrigeration capacity, and the freezing work enters a passive freezing period to ensure that the ice will not thaw and maintain the temperature of the frozen ice body constant at -10°C to -5°C;

[0057] (9) Then, under the maintenance of passive freezing, check and improve the excavation and arrangement of transportation and ventilation tunnels in step (4), transport and arrange relevant mining equipment through the tunnels, and arrange the coal pillar recovery working face of the room-and-pillar goaf at the designated location to open the cutting hole and arrange the coal pillar recovery working face.

[0058] (10) Under the maintenance of passive freezing, the ice body 9 after the water in the room-pillar goaf is frozen and the coal pillar 2 left in the room-pillar goaf is regarded as a whole. The coal cutter gradually cuts the ice body and the coal pillar from the opening of the cutting hole, and the whole layer is mined to recover the remaining coal. As the mining working face advances, the roof rock layer collapses as it is mined.

[0059] (11) Part of the ice melts during cutting, and part of the ice is cut into ice chips, which are transported together with the coal blocks formed by cutting through a scraper conveyor. Part of the cut ice chips gradually melt during the transportation process. Pumps and drainage ditches are arranged in the working face and transportation lanes to extract the water formed by the melting of ice chips during the cutting and transportation of the ice.

Claims

1. A method for efficiently recovering residual coal pillars by freezing accumulated water in a room-and-pillar mining area, characterized in that The following steps are involved: (1) Carry out core drilling and peek, combine the original geological and technical data of the mine, the distribution of coal pillar groups and goaf groups, draw the overlying rock strata of the room-pillar residual mining area, the coal pillars left in the room-pillar residual mining area and the distribution morphology of the room-pillar residual mining area to guide safe production. At the same time, find out the height, amount and quality of water accumulation in the room-pillar residual mining area to serve the subsequent water freezing design of the room-pillar residual mining area; (2) Comprehensively consider the strength and Mohs hardness of coal samples measured by core drilling of the residual coal pillars in the room-pillar mining area, and the strength and Mohs hardness of frozen ice measured by sampling the accumulated water in the room-pillar mining area. The room-pillar mining area is regarded as a complete unmined coal seam. The mechanical parameters of the coal body and ice body are combined to design the mining working face for the recovery of the residual coal pillars in the room-pillar mining area, select equipment, design the working face tunnels, and arrange the cutting holes. (3) The existing roadway in the same layer parallel to the room-pillar residual mining area is used as a freezing auxiliary roadway, and a freezing workstation is arranged. A series of horizontal boreholes are drilled from the wall of the freezing auxiliary roadway toward the water accumulation area of ​​the room-pillar residual mining area, and freezing pipes are arranged through the boreholes into the water accumulation area of ​​the room-pillar residual mining area; when there is no suitable roadway to be selected in the coal seam where the room-pillar residual mining area is located, a roadway is selected in the overlying rock layer of the room-pillar residual mining area, and a series of vertical boreholes are drilled from top to bottom. The freezing pipes are lowered and arranged through the roadway boreholes in the overlying rock layer into the water accumulation area of ​​the room-pillar residual mining area; (4) A freezing workstation is arranged in the freezing auxiliary tunnel set up in step (3). The heat of the accumulated water is replaced by the circulating brine through the freezing pipe arranged in the accumulated water in the room-pillar residual mining area, so that the accumulated water in the room-pillar residual mining area enters the active freezing period, and the liquid phase water becomes ice with bearing capacity. The temperature range of the frozen ice body in this stage is -20℃~-12℃; the characteristics of water changing with the shape of the container and the volume expansion of water when it freezes are utilized to make it fully connect with the top at the same time of freezing. The ice after the accumulated water in the room-pillar residual mining area is frozen as a filling body, and at the same time, the remaining coal pillars, collapsed rocks and accumulated water in the room-pillar residual mining area are frozen into a frozen body. The entire room-pillar residual mining area is filled with huge ice blocks formed by the frozen accumulated water; the ice body after the accumulated water in the room-pillar residual mining area is frozen and forms a cooperative bearing body with the top and bottom plates of the room-pillar residual mining area, the coal pillars in the room-pillar residual mining area to be recovered and the coal pillars at the boundary of the room-pillar residual mining area, and jointly bears the load transferred by the overlying rock formation; (5) When the accumulated water in step (4) is insufficient to completely connect the top after freezing, water is added through the borehole in step (3) during the freezing process of the accumulated water in step (4) to ensure that the ice body in the room-pillar residual mining area can fully connect the top after the accumulated water in the room-pillar residual mining area is frozen; when the accumulated water in the room-pillar residual mining area completely fills the room-pillar residual mining area, the accumulated water in step (4) freezes and expands, and the amount of water in the room-pillar residual mining area is too much, water is pumped out through the borehole in step (3) to ensure that the ice body in the room-pillar residual mining area just connects the top after the accumulated water in the room-pillar residual mining area is frozen; (6) After the accumulated water in the room-and-pillar residual mining area is completely frozen, each freezing workstation in step (4) reduces the refrigeration capacity, and the freezing work enters the passive freezing period to ensure that the ice will not thaw and maintain the frozen ice body temperature constant at -10℃~-5℃; (7) Then, excavate and arrange transportation and ventilation tunnels in the ice body maintained by passive freezing, gradually melt the ice body along the designed central axis of the tunnel using explosion-proof electric heating rods, and at the same time extract the water formed by the melting of the ice body. After the tunnel of the designed size is melted in the ice body, freeze pipes are laid on the inner wall surface of the tunnel to maintain the freezing of the tunnel surface, avoid the heat radiation generated by the air introduced by the mine ventilation and the transportation of equipment causing the tunnel surface to melt, and ensure that the tunnel maintains the designed shape and size; then, through the tunnel transportation and arrangement of relevant mining equipment, arrange the room-and-pillar residual mining area coal pillar recovery working face at the designated location, open the cutting hole, and arrange the coal pillar recovery working face; (8) Under the maintenance of passive freezing, the frozen accumulated water and the remaining coal pillars are regarded as a whole. The coal cutter gradually cuts the ice body and coal pillars from the opening of the cutting hole, and the entire layer is mined to recover the remaining coal; part of the ice body melts during the cutting, and part of the ice body is cut into ice chips and the cut coal blocks are transported together through a scraper conveyor. Pumps and drainage ditches are arranged in the working face and transport tunnel to extract the water formed by the melting of ice chips during the cutting and transportation of the ice body.

2. The method for efficiently recovering residual coal pillars by freezing accumulated water in a room-and-pillar mining area according to claim 1 is characterized in that: When each freezing pipeline is arranged in the accumulated water in the room-and-pillar residual mining area, a series of temperature sensors are lowered along with the pipeline and evenly arranged in the accumulated water in the room-and-pillar residual mining area. A real-time dynamic detection network is established to conduct real-time detection of the temperature of the accumulated water or frozen ice in the room-and-pillar residual mining area.

3. The method for efficiently recovering residual coal pillars by freezing accumulated water in a room-and-pillar mining area according to claim 1, characterized in that: Step (1) by investigating the original geological and technical data of the mine, the width and height of the void group and the coal pillar group in the room-and-pillar residual mining area are determined, and a three-dimensional laser scanner is used to accurately detect the distribution direction, size and volume of the void group in the room-and-pillar residual mining area, and at the same time, the depth, distribution range and volume of the water accumulation in the room-and-pillar residual mining area are determined; In step (2), the room-and-pillar residual mining area is regarded as a complete unmined coal seam for mining design, wherein the relevant mechanical parameters are comprehensively considered based on the parameters of the frozen ice and the mechanical parameters of the coal sample determined by on-site drilling; the parameters of the frozen ice are: uniaxial compressive strength of 3-6 MPa, and Mohs hardness of 2.8-4.

4. The method for efficiently recovering residual coal pillars by freezing accumulated water in a room-and-pillar mining area according to claim 1, characterized in that: In step (3), the existing tunnels in the same layer as the tunnels for coal pillar recovery working face in the room-pillar residual mining area are set as freezing auxiliary tunnels, freezing workstations are arranged in the freezing auxiliary tunnels, and freezing pipes are arranged through the tunnel wall holes of the freezing auxiliary tunnels to the accumulated water in the room-pillar residual mining area, wherein the number of tunnel wall holes is determined by the required cooling capacity, the accumulated water volume and the radius of the freezing pipes. The freezing pipes form a group of closed loops in the accumulated water in the room-pillar residual mining area to circulate brine, displace the heat in the accumulated water, and freeze the accumulated water into ice.

5. The method for efficiently recovering residual coal pillars by freezing accumulated water in a room-and-pillar mining area according to claim 4, characterized in that: When the width of the working face is greater than 50m, if it is difficult to completely freeze all the accumulated water in the room-and-pillar residual mining area by laying pipes through the tunnel wall drilling holes of the freezing auxiliary tunnel in step (3), an ice body of 10 to 20m is frozen inward from the boundary surrounding rock of the room-and-pillar residual mining area; then, tunnels are excavated and working faces are arranged in the frozen ice body inside the boundary surrounding rock of the room-and-pillar residual mining area; and the excavated transport tunnel is widened, and an auxiliary chamber is excavated in it for the subsequent arrangement of freezing workstations. The transport tunnel also has the function of a freezing tunnel.

6. The method for efficiently recovering residual coal pillars by freezing accumulated water in a room-and-pillar mining area according to claim 1, characterized in that: The model, power and number of freezing equipment in step (4) are determined based on the cooling capacity required by the volume of the empty area in the room-and-pillar residual mining area and the volume of water in the empty area as determined in step (2); CaCl2 solution is selected as the refrigerant in the brine circulation system, and the cooling water circulation system is naturally cooled by excavating a water pool; after the various freezing parameters are determined, the equipment is tested at a designated location in the underground freezing auxiliary tunnel, and formal construction is carried out after the entire system is operating correctly.

7. The method for efficiently recovering residual coal pillars by freezing accumulated water in a room-and-pillar mining area according to claim 1, characterized in that: In step (5), the volume of water expands after freezing, and the volume of ice after freezing is 1.1 times that of the original water. When water accumulates in the room-and-pillar residual mining area that was not connected to the roof, and the distance between the water surface and the roof accounts for less than 10% of the total height of the room-and-pillar residual mining area, the ice body can fully connect to the roof after freezing; when the accumulated water is small and cannot connect to the roof after freezing, artificial water injection is used to increase the amount of ice to connect to the roof, thereby filling the entire empty area of ​​the room-and-pillar residual mining area and supporting the rock layer of the roof of the room-and-pillar residual mining area.

8. The method for efficiently recovering residual coal pillars by freezing accumulated water in a room-and-pillar mining area according to claim 1, characterized in that: After the accumulated water in the room-and-pillar residual mining area in step (6) freezes, the uniaxial compressive strength of the ice body is 3MPa~6MPa under passive freezing maintenance, and the tensile strength is 1 / 2 of the compressive strength. The compressive strength of the ice body is 5~10MPa under the lateral constraint of the surrounding rock of the room-and-pillar residual mining area underground.

9. The method for efficiently recovering residual coal pillars by freezing accumulated water in a room-and-pillar mining area according to claim 8, characterized in that: The passive freezing period in step (6) refers to the freezing effect of the accumulated water in the room-and-pillar residual mining area during the previous active freezing period. The liquid water gradually freezes and the freezing is basically completed. At this time, the frozen ice body only needs to maintain the frozen state to ensure that it will not thaw. The temperature of the circulating brine increases, and the temperature range of the frozen ice body increases to -10°C~-5°C. At the same time, the Mohs hardness of the frozen ice body is reduced, which is conducive to cutting by the coal cutter.

10. The method for efficiently recovering residual coal pillars by freezing accumulated water in a room-and-pillar mining area according to claim 1, characterized in that: The coal cutter described in step (8) gradually cuts the ice body and coal pillars from the opening of the cutting eye, and the entire layer is mined to recover the remaining coal pillars. This means that under the maintenance of passive freezing, the frozen accumulated water and the remaining coal pillars are regarded as a whole layer of unmined coal seam. The coal cutter cuts under the support and protection of the hydraulic support, and the roof collapses as it is mined.

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