Safe re-mining method for residual coal in goaf of high gas / spontaneous combustion extra-thick coal seam

Abstract

The invention discloses a safe re-mining method for residual coal in a goaf of a high-gas / spontaneous combustion extra-thick coal seam. The safe re-mining method comprises the following steps: step 1, planning a re-mining system and designing a re-mining roadway; secondly, punching, grouting and filling are conducted on a goaf in front of excavation, and then a re-mining roadway is excavated; thirdly, an open-off cut is excavated through an advanced grouting and filling method; 4, extracting goaf gas and injecting nitrogen; and 5, residual coal re-mining is carried out according to a conventional mining method. Due to drilling, grouting and diagenesis in advance, the sealing performance of a re-mining roadway is guaranteed, and meanwhile, curtain grouting is conducted on a re-mining working face, so that gas extraction is facilitated, a large amount of air is prevented from entering residual coal, oxygen permeation is reduced, nature is prevented, the residual coal which cannot be mined is changed into the residual coal which can be mined, and the coal recovery rate is increased.

Description

Technical Field

[0001] The present invention relates to the field of coal mining, in particular to the safe re-mining of coal left in goafs, and further to the safe re-mining of coal left in goafs of high-gas / spontaneous-ignition and extra-thick coal seams. Background Art

[0002] To rationally develop and protect coal resources and improve their recovery rate, the National Development and Reform Commission promulgated the "Interim Regulations on the Management of Recovery Rates in Coal Mines" on December 9, 2012. These regulations set clear recovery rate requirements for mining areas and working faces. The recovery rate standards for underground coal mines are: for coal seams less than 1.3 meters thick, a recovery rate of 85% or greater; for coal seams between 1.3 and 3.5 meters thick, a recovery rate of 80% or greater; and for coal seams greater than 3.5 meters thick, a recovery rate of 75% or greater. However, before the issuance of the regulations, recovery rates failed to meet these requirements, leaving large amounts of remnant coal buried in underground goafs. If re-mining (referring to the safe recovery and mining of residual coal resources) is to be carried out, the National Development and Reform Commission stipulates that the following conditions must be met: 1. A legal production mine with complete and valid certificates and licenses; 2. A low-gas mine; 3. A mine with a simple and medium hydrogeological type; 4. A mine with no tendency to rock burst; 5. A mine with a coal seam spontaneous combustion tendency grade of Class II or Class III, and no coal seam spontaneous combustion has occurred within the mining area.

[0003] Before the issuance of the Regulations, the actual recovery rate of extra-thick coal seams (thickness greater than 8 meters) was only 40% to 50% during the mining process. Even with the top coal caving method, the recovery rate was less than 60%. The remaining coal in these goafs is more than 3.5 meters thick, and its coal seam structure is relatively intact, which is very suitable for secondary mining. However, for extra-thick coal seams containing high gas content and extra-thick coal seams with a spontaneous combustion tendency level of Class 1, re-mining is explicitly prohibited, which results in a huge waste of resources. Therefore, it is very necessary to invent a method for safe re-mining of remnant coal in goafs of high-gas extra-thick coal seams and spontaneous combustion extra-thick coal seams, so as to solve the problem of extending the service life and improving the resource recovery rate of such mines facing resource depletion.

[0004] It's important to note that spontaneous combustion in coal seams occurs when air, after prolonged contact with the coal, penetrates the coal's porous structure. The coal reacts with oxygen, gradually raising its temperature. When the temperature exceeds the coal's ignition point, spontaneous combustion occurs. Based on this cause of spontaneous combustion, resolving the issue of prolonged air contact with the coal can prevent it. This principle applies to coal seams of any degree of spontaneous combustion tendency. Summary of the Invention

[0005] To address the issue of safe recovery of residual coal in goafs of high-gas / spontaneous-ignition, extra-thick coal seams, the present invention provides a new method for remining, which converts unminable residual coal into mineable residual coal, thereby maximizing resource recovery.

[0006] A safe re-mining method for residual coal in goafs of high-gas / spontaneous-ignition and extra-thick coal seams adopts the following technical solutions:

[0007] The first step is to plan the mining system and design the mining tunnels.

[0008] Based on the information in the mining engineering plan during the initial top coal caving operation, the distribution of the residual coal in the caving zone of the goaf is determined. Based on this distribution, the re-mining working face is planned and the re-mining roadway development map is designed. The re-mining roadway includes a transport chute and a return air chute. The designed transport chute and return air chute are developed from the transport uphill and track uphill in the original coal pillar toward the residual coal. The cross-sectional dimensions of the transport chute and return air chute are designed based on the residual coal thickness, belt conveyor capacity, and ventilation capacity. The cross-sectional dimensions of the cutting eye are designed based on the mining process.

[0009] The second step is to excavate the secondary mining tunnel

[0010] According to the designed development map and the cross-sectional dimensions of the re-mining roadway, re-mining roadways are excavated from the transport uphill and track uphill sections of the original coal pillar. When the excavation reaches 3-5 meters away from the original production stop line (i.e., the boundary line of the coal pillar), the goaf in front of the excavation is perforated and grouting is carried out. After the slurry forms a solid or solidified rock, the excavation is continued. When the excavation reaches 3-5 meters away from the boundary of the grouting rock area, the area in front is perforated and grouting is carried out again. This process is repeated until the transport chute and the return air chute are excavated, ensuring that a stable roadway is excavated in the coal left in the goaf.

[0011] The third step is to dig and cut the eye

[0012] Then, the cutting eye is excavated from the transport chute toward the return air chute. During the excavation, the grouting filling method in the second step is followed until the transport chute and the return air chute are connected and the cutting eye is excavated. At this time, the surrounding rock of the secondary mining roadway designed in the caving zone and the residual coal has been consolidated, thus forming a stable mining system.

[0013] Step 4: Extract gas

[0014] After the mining system is formed, drilling is done on the side of the transport chute and the return air chute close to the goaf to extract the gas in the goaf coal, and nitrogen is injected through the borehole to maintain the gas pressure balance;

[0015] Step 5: Re-mining of the remaining coal

[0016] After a safe re-mining working face is formed, re-mining work shall be carried out according to conventional mining methods.

[0017] Furthermore, in the second step of excavating the secondary mining tunnel, the drilling and grouting depth should be greater than 10 meters, and the drilling direction of each grouting hole should be inclined toward the two sides and the top of the tunnel section, so that the secondary mining tunnel has a solidified surrounding rock thickness of at least 2 meters, so that the secondary mining tunnel is in a stable surrounding rock.

[0018] Furthermore, in the second step of excavating the secondary mining tunnel, the grouting material ratio for drilling and grouting is: cement: fly ash = 1:1~1:3, additive: 3% sodium silicate, water-cement ratio: 0.6:1~0.8:1, and the final grouting pressure is set to 4~6MPa.

[0019] Furthermore, while excavating the secondary mining tunnel in the second step, a fiber optic monitoring system can be deployed. Distributed fiber optic sensors (DTS / DAS) are embedded at a distance of 2m on one side of the secondary mining tunnel close to the goaf to monitor temperature and strain changes in real time, ensure the sealing of the tunnel excavation area, and prevent gas from the goaf from entering the secondary mining tunnel.

[0020] Furthermore, when extracting gas from the goaf and coal in the fourth step, miniature air pressure sensors are arranged every 5m to monitor the pressure and prevent deformation of the roadway; the pressure difference control standard is: ΔP<100Pa.

[0021] Furthermore, when extracting gas from the goaf and the residual coal in the fourth step, a fixed gas detector is installed to monitor the gas concentration in the goaf in real time during the gas extraction process.

[0022] Furthermore, in the fourth step, when extracting gas from the goaf and residual coal, the extraction system layout parameters are as follows:

[0023] (1) Gas extraction drilling layout parameters:

[0024] Drill hole spacing: 2.5±0.5m (adjusted according to coal permeability), drill hole diameter: Φ108mm, drill hole depth: 1.5~2.0m penetrating the coal pillar into the goaf, inclination: +3°~+5° (favorable for natural gas collection), extraction negative pressure: 13~15kPa; nitrogen injection control pressure: 0.3~0.5MPa, nitrogen purity: ≥97%, nitrogen injection flow rate: 1.0~1.5m 3 / min;

[0025] The criteria for determining the mining conditions for gas extraction are: CH4 concentration ≤ 1.0% for 24 consecutive hours, oxygen concentration ≤ 12%, and temperature gradient < 1°C / h.

[0026] Furthermore, during the fifth step of the residual coal mining operation, the gas outburst volume must be monitored at any time to ensure that the gas concentration meets the mining condition determination criteria.

[0027] The method provided by the present invention has the following advantages:

[0028] (1) When excavating the re-mining tunnel, drilling and grouting are used to form a stable area in the goaf section in advance, which is conducive to the excavation of a stable re-mining tunnel and ensures the sealing of the re-mining tunnel, so that a curtain is formed around the re-mining work area; after the curtain is formed, firstly, it prevents air from being sucked into the goaf coal from the tunnel when extracting gas, reduces the amount of oxygen permeation, and prevents the spontaneous combustion of the flammable coal seam; secondly, after the curtain is formed, it avoids large-scale gas flow, which is conducive to extraction; thirdly, after the curtain is formed, it prevents a large amount of air from entering the coal during a long period of re-mining, reduces the amount of oxygen permeation, and prevents the spontaneous combustion of the flammable coal seam.

[0029] (2) By drilling and extracting gas in the re-mining tunnel, the gas content is reduced, resulting in a low-gas coal seam, ensuring production safety during re-mining. During the gas extraction process, nitrogen is injected to balance the internal air pressure, preventing oxygen-containing air from entering the loose coal seam under negative pressure, reducing the amount of oxygen-containing air, and preventing spontaneous combustion of the flammable coal seam.

[0030] (3) This method of recovering the remaining coal, which can be called "curtain grouting and shielding in goaf", can safely recover the remaining coal in the goaf of high-gas / spontaneous combustion thick coal seams after top coal mining, turning unminable remaining coal into mineable remaining coal, improving the coal recovery rate and reducing resource waste; at the same time, it can increase the production service life of the mining area and solve the problem of most old mining areas facing the shortage of coal for production succession. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. The drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0032] Figure 1 It is the layout diagram of the double mining tunnel of the present invention;

[0033] Figure 2 This is a diagram of the initial state of the double mining tunnel excavation of the present invention;

[0034] Figure 3 This is a state diagram of the excavation process of the double mining tunnel of the present invention;

[0035] Figure 4 This is a state diagram of the excavation of a double mining tunnel according to the present invention;

[0036] Figure 5 This is a gas extraction drilling arrangement diagram of the present invention.

[0037] In the figure: 1--goaf; 2--coal pillar; 3--grouting hole; 4--transport uphill; 5--track uphill; 6--transport chute; 7--cutting eye; 8--return air chute; 9--gas extraction borehole; 10--solidified body. DETAILED DESCRIPTION

[0038] The embodiments of the present invention are described in detail below with reference to the accompanying drawings so that the advantages and features of the present invention can be more easily understood by those skilled in the art, thereby making a clearer and more precise definition of the protection scope of the present invention.

[0039] A certain mine is a high-gas coal mine, in which the third coal seam is a first-level self-igniting coal seam with an original thickness of 10m. It was mined for the first time using top coal caving, with a mining height of 3m and a coal caving height of 3.5m. The remaining 3.5m of height was left in the goaf and was not mined. In order to mine out these remaining coals, according to a method for re-mining remaining coal in the goaf of a high-gas / spontaneous-ignition extra-thick coal seam provided by the present invention, the following embodiments are proposed.

[0040] A safe re-mining method for residual coal in goaf of high-gas / spontaneous combustion extra-thick coal seams, specifically comprising the following steps:

[0041] The first step is to determine the distribution of the residual coal in the caving zone of the goaf 1 according to the information in the mining engineering plan during the first top coal mining. Based on the distribution, the re-mining working face is planned and the re-mining roadway development map is designed. The re-mining roadway includes a transport chute 6 and a return air chute 8. The transport chute 6 and the return air chute 8 are developed from the transport uphill 4 and the track uphill 5 in the original coal pillar respectively, and are developed in the direction of the residual coal. The planning and design are as follows: Figure 1 As shown; the design of the secondary mining tunnel is as follows:

[0042] 1. According to the thickness of the coal, the belt conveyor capacity and the ventilation capacity, the mining roadway includes the transport chute 6 and the return air chute 8, which are designed to be rectangular in cross section, 3 meters wide and 2.5 meters high. They are developed in the coal and are 1,800 meters long. They are arranged from the original track uphill 1 and the return air uphill 2 towards the coal area respectively. 2. According to the coal mining process, the cutting eye 7 is designed to be 200 meters long, 3 meters wide and 3 meters high. The above design layout is as follows Figure 1 shown.

[0043] Step 2: Excavation of secondary mining tunnels

[0044] like Figure 2As shown, according to the design layout, the re-mining tunnel (i.e., the transport drift 6 and the return air drift 8) is excavated; when the transport uphill 4 and the track uphill 5 in the original coal pillar are respectively excavated to a distance of 1 meter from the original production stop line (i.e., the boundary of the coal pillar 2), a grouting hole 3 is drilled in the forward area to carry out grouting filling, ensuring that the slurry forms a filling area in front of the tunnel development, and after the grouting solidifies into a solidified body 10, the excavation is continued forward. At this time, a stable tunnel is excavated in the coal left in the goaf, and the safety of the excavation construction and the sealing of the tunnel are guaranteed to prevent air from entering the goaf from the tunnel, reduce the probability of coal spontaneous combustion and avoid gas leakage; as shown in FIG. Figure 3 As shown, when the excavation is 3 to 4 meters away from the boundary of the solidified body 10, the front area is drilled and grouting is performed, and after solidification, excavation is continued, and this process is repeated until the transport chute 6 and the return air chute 8 are excavated.

[0045] The depth of the above-mentioned grouting holes 3 is greater than 10 meters, and the drilling direction of each grouting hole 3 should be inclined toward the two sides and the top of the tunnel section, so that the secondary mining tunnel has a solidified surrounding rock thickness of at least 2 meters, so that the secondary mining tunnel is in a stable surrounding rock.

[0046] The ratio of the above grouting materials is: cement: fly ash = 1:1 to 1:3, additive: 3% sodium silicate, water-cement ratio: 0.6:1 to 0.8:1, and the final grouting pressure is set to 4 to 6 MPa.

[0047] While the secondary mining tunnel is being excavated, a fiber optic monitoring system can also be deployed. Distributed fiber optic sensors (DTS / DAS) are pre-buried at a distance of 2m on one side of the secondary mining tunnel close to the goaf to monitor temperature and strain changes in real time, ensure the sealing of the tunnel excavation area, and prevent gas from goaf 1 from entering the secondary mining tunnel.

[0048] In the third step, a cutting eye 7 is excavated from the transport chute 6 toward the return air chute 8. The excavation is carried out according to the grouting filling method in the second step until the transport chute 6 and the return air chute 8 are opened, and the cutting eye 7 (i.e., the mining working face) is excavated to form a mining system. The above process is as follows: Figure 4 shown.

[0049] The fourth step is as follows Figure 5 As shown, after the mining system is formed, a gas extraction borehole 9 is drilled on the side of the transport chute 6 and the return air chute 8 close to the goaf to extract gas from the goaf and the residual coal; after the gas is extracted, nitrogen is injected through the borehole, and a pressure sensor is installed to monitor the pressure to prevent the deformation of the tunnel; at the same time, a fixed gas detector is installed to monitor the gas concentration in the goaf 1 in real time during the gas extraction process.

[0050] The layout parameters of the gas drainage system are as follows:

[0051] (1) Gas extraction drilling layout parameters:

[0052] Drill hole spacing: 2.5±0.5m (adjusted according to coal permeability), drill hole diameter: Φ108mm, drill hole depth: 1.5~2.0m penetrating the coal pillar into the goaf, inclination: +3°~+5° (favorable for natural gas collection), extraction negative pressure: 13~15kPa; nitrogen injection control pressure: 0.3~0.5MPa, nitrogen purity: ≥97%, nitrogen injection flow rate: 1.0~1.5m 3 / min;

[0053] When installing air pressure sensors for pressure monitoring, miniature air pressure sensors are arranged every 5m, and the pressure difference control standard is: ΔP<100Pa.

[0054] The criteria for determining the mining conditions for gas extraction are: CH4 concentration ≤ 1.0% for 24 consecutive hours, oxygen concentration ≤ 12%, and temperature gradient < 1°C / h.

[0055] The fifth step is that at this time, the gas in the goaf and the remaining coal has reached the mining conditions, forming a working face that can be safely re-mined. Coal mining machines are arranged on the working face, and re-mining work is carried out according to conventional ordinary mining methods. During the re-mining operation, the gas outburst volume must be checked at any time to ensure safety.

[0056] Of course, the above description is not a limitation of the patent of the present invention, and the patent of the present invention is not limited to the above examples. Changes, modifications, additions or substitutions made by technicians in this technical field within the essential scope of the patent of the present invention should also fall within the scope of protection of the patent of the present invention.

Claims

1. A safe re-mining method for coal left in goaf of high-gas / spontaneous combustion extra-thick coal seam, characterized by: The following technical solutions are adopted: The first step is to plan the mining system and design the mining tunnels. Based on the distribution of residual coal after the initial top coal caving, a re-mining system is planned. The transport chute and return air chute are developed from the transport uphill and track uphill sections of the original coal pillar towards the residual coal. The cross-sectional dimensions of the transport chute, return air chute, and cut are designed based on the residual coal thickness, transport capacity, ventilation capacity, and mining process. The second step is to excavate the secondary mining tunnel From the original track uphill and the return air uphill, re-mining tunnels are excavated in the direction of the remaining coal in the goaf. When excavating, the area in front of the excavation is first drilled and grouting is injected, and then excavation is continued after solidification is formed; The third step is to dig and cut the eye Then, cut holes are excavated from the transport drift toward the return air drift to form a mining system. The excavation is carried out according to the grouting filling method in the second step. Step 4: Extract gas After the mining system is formed, drilling holes are used to extract gas from the coal in the goaf, and nitrogen is injected through the holes to maintain internal pressure balance; The fifth step is to carry out re-mining of the remaining coal on the re-mining working face according to conventional mining methods.

2. The method for safely recovering coal in goaf of high-gas / spontaneous-ignition extra-thick coal seams according to claim 1, characterized in that: In the second step, the drilling and grouting filling should be carried out when the excavation is 3-5 meters away from the original production stop line or the boundary of the grouting and diagenesis area. The excavation should be carried out after the slurry forms a solid or solidified rock, and the excavation can be carried out again. The same process can be repeated until the transport chute and the return air chute are excavated.

3. A safe re-mining method for coal in goaf of high-gas / spontaneous-ignition extra-thick coal seam according to claim 1 or 2, characterized in that: In the second step, the grouting hole is drilled and filled with grouting, the depth of the grouting hole is greater than 10 meters, and the drilling direction of the grouting hole should be inclined toward the sides and top of the tunnel section, so that the thickness of the solidified surrounding rock of the secondary mining tunnel is at least 2 meters; The grouting material ratio is: cement: fly ash = 1:1~1:3, additive: 3% sodium silicate, water-cement ratio: 0.6:1~0.8:1, and the final grouting pressure is set to 4~6MPa.

4. The method for safely recovering coal in goaf of high-gas / spontaneous-ignition extra-thick coal seams according to claim 1, characterized in that: During gas extraction in the fourth step, the extraction system layout parameters are as follows: borehole spacing: 2.5±0.5m, borehole diameter: Φ108mm, borehole depth: at least 5-8m through the filling into the goaf, borehole inclination: +3°~+5°, extraction negative pressure: 13-15kPa; nitrogen injection pressure: 0.3-0.5MPa, nitrogen purity: ≥97%, nitrogen injection flow rate: 1.0-1.5m 3 / min.

5. The method for safely recovering coal in goaf of high-gas / spontaneous-ignition extra-thick coal seam according to claim 4, characterized in that: During gas extraction, fixed gas detectors are installed to monitor the gas concentration in the goaf in real time.

6. A safe re-mining method for coal left in goaf of high-gas / spontaneous combustion extra-thick coal seam according to any one of claims 1 to 4, characterized in that: In the second step, distributed fiber optic sensors are pre-buried at a distance of 2m on one side close to the goaf to monitor temperature and strain changes in real time, ensure the sealing of the tunnel excavation area, and prevent gas from the goaf from entering the re-mining tunnel.

7. A safe re-mining method for coal in goaf of high-gas / spontaneous combustion extra-thick coal seam according to any one of claims 1 to 4, characterized in that: During the fifth step of the re-mining operation, the gas outburst volume is monitored in real time to ensure that the CH4 concentration is ≤1.0%, the oxygen concentration is ≤12%, and the temperature gradient is <1℃ / h for 24 consecutive hours.

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