Gas control technology for coal roadway floor roadway in downward mining of close distance outburst coal seam group

Abstract

A gas control technology for coal roadway floor roadway in downlink mining of close distance outburst coal seam group relates to the technical field of coal mine gas control. In the close distance coal seam group, the coal roadway is excavated in the non-outburst or weak outburst coal seam, the coal roadway is used as the gas control floor roadway of the upper outburst coal seam, the gas of the upper outburst coal seam is comprehensively pre-drained, the pressure relief gas of the upper outburst coal seam during the mining is drained by using the coal roadway floor roadway, and the gas of the coal seam is controlled. After the gas control of the outburst coal seam, the downlink mining can be carried out, the mining conditions of the outburst coal seam are not damaged, the rock floor roadway or the roof roadway does not need to be constructed, the coal roadway is used as the floor roadway of the upper outburst coal seam, the effect of safe and efficient gas control of the floor roadway is achieved, no additional investment is increased, the gas can be pre-drained, and the pressure relief gas of the upper coal seam and the coal seam can be drained.

Description

Technical Field

[0001] This invention relates to a gas control technology for the floor roadway in a downhill mining roadway of a coal seam group with close proximity to outbursts, and relates to the field of coal mine gas control technology. Background Technology

[0002] Methane gas is the primary hazard in underground coal mining and a top priority for safety in most underground coal mines in my country. After decades of development, methane control technologies are now relatively mature, particularly bottom roadway cross-seam extraction and protective layer mining. Practice has proven that protective layer mining is the preferred technology for fundamentally controlling mine methane disasters. However, protective layer mining is subject to many limitations, such as the availability of coal seam groups, suitable spacing between coal seams, and the availability of low-methane protective layer mining conditions. For some closely spaced coal seam groups, if the lower non-outburst-prone coal seam is selected as the lower protective layer for priority mining, while the methane in the upper protected layer is easier to control, it also disrupts the mining conditions of the protected layer. The protected layer is located in the caving zone after the lower coal seam is mined, with fractured roof and floor, poor support conditions, and numerous difficulties during the recovery of the protected layer. For such coal mines, the lower protective layer technology is not suitable.

[0003] Roof roadways and floor roadways are good choices for controlling gas outbursts in coal seams. Because they are located in the rock strata above or below the outburst coal seam and are protected by rock pillars, they can effectively prevent the risk of gas outbursts during the control of outburst coal seams. However, roof roadways and floor roadways also have some problems. First, they are expensive, which makes many mines unwilling to construct them. If they are in close coal seam groups, the close spacing between the coal seams makes it easy to accidentally penetrate the coal seam when excavating roof roadways or floor roadways, which can easily cause outburst accidents. When constructing roof roadways, only downward pre-drainage boreholes can be constructed, which have poor drilling, slag removal, and drainage effects, and have limited pre-drainage effect on the outburst coal seam.

[0004] Therefore, for outburst coal seams in close proximity to each other, how to reduce the cost of coal seam gas control without damaging the mining conditions of the coal seams is the priority issue for this invention. Summary of the Invention

[0005] The purpose of this invention is to address the deficiencies or shortcomings of existing technologies by providing a gas control technology for the bottom roadway in a short-distance coal seam group mining operation. This technology eliminates the need for additional construction of rock roof or floor roadways and does not increase the number of roadways. It only requires adjusting the roadway excavation sequence to achieve the gas control effect of rock floor roadways. The principle is simple, the investment is small, and the gas control time is saved. It can achieve good results for mines with similar coal seam and gas occurrence conditions.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: it includes tunneling coal roadways, pre-draining gas, gas extraction, and gas control. In a group of closely spaced coal seams, a coal roadway is tunneled in a non-outburst or weakly outburst coal seam. The coal roadway is used as a bottom roadway for gas control of the upper outburst coal seam. Gas from the upper outburst coal seam is pre-drained in a comprehensive manner. At the same time, depressurized gas from the coal seam where the bottom roadway is located is extracted, and gas in this coal seam is controlled.

[0007] Furthermore, the steps for gas control are as follows: Step 1: In nearby coal seams, select coal seams that are not prone to outbursts or have weak outbursts as the gas control coal seams for the upper coal seams.

[0008] Step 2: In the lower coal seam, first excavate the machine roadway, ventilation roadway, and cut-off hole. If necessary, excavate the waist roadway as the bottom roadway for gas control of the upper outburst coal seam.

[0009] Step 3: Using the coal roadway of the lower coal seam, construct cross-layer boreholes to pre-drain the coal roadway strips within a certain range near the machine roadway, ventilation roadway, and cut-off point of the upper outburst coal seam, or use the coal roadway of the lower coal seam to perform regional grid-style pre-drainage of the upper outburst coal seam.

[0010] Step 4: Utilize the cross-seam boreholes already drilled in the lower coal seam to extract the goaf and depressurized gas during the mining of the upper outburst coal seam.

[0011] Step 5: Use the coal roadway in the lower coal seam to pre-drain the gas in the working face of the lower coal seam. At the same time, when the upper outburst coal seam is being mined, the boreholes in this coal seam can also intercept and drain the depressurized gas in this coal seam to prevent the gas in the lower coal seam from flowing into the mining face of the upper outburst coal seam. Attached Figure Description

[0012] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0013] Figure 1 This is a schematic diagram of the occurrence of coal seams in the downward mining of near-distance outburst coal seam groups in this invention.

[0014] Figure 2 This is a schematic diagram illustrating the principle of using a lower non-outburst coal seam roadway to control strip gas in an upper outburst coal seam in this invention.

[0015] Figure 3 This is a schematic diagram illustrating the principle of using a lower non-outburst coal seam roadway to control gas in an upper outburst coal seam area in this invention; Figure 4 This is a schematic diagram illustrating a specific embodiment of the present invention. Implementation

[0016] See Figure 1-4 As shown, the technical solution adopted in this specific implementation method is as follows: It includes coal roadway excavation, pre-gas extraction, gas drainage, and gas control. In a group of closely spaced coal seams, a coal roadway is excavated in a non-outburst or weakly outburst coal seam. This coal roadway serves as the bottom roadway for gas control in the upper outburst coal seam, eliminating the need to construct a rock bottom roadway or roof roadway. Utilizing the coal roadway as the bottom roadway in the upper outburst coal seam achieves both safe and efficient gas control in the bottom roadway configuration without additional investment. It comprehensively pre-extracts gas from the upper outburst coal seam and simultaneously extracts depressurized gas from the coal seam where the bottom roadway is located. This invention addresses the gas control of the coal seam in a downhill mining roadway within a cluster of closely spaced outburst-prone coal seams. A cluster of closely spaced outburst-prone coal seams refers to a group of at least two coal seams located close together. If the lower seam is mined first, the mining conditions of the upper seam are likely to be compromised, making effective and safe mining impossible. Therefore, the upper seam must be mined first, i.e., downhill mining. Furthermore, since the upper seam poses a greater risk of outburst than the lower seam, gas control of the upper seam is necessary for safe mining.

[0017] More specifically, the steps for gas control are as follows: Step 1: In nearby coal seams, select coal seams that are not prone to outbursts or have weak outbursts as the gas control coal seams for the upper coal seams.

[0018] Step 2: In the lower coal seam, first excavate the machine roadway, ventilation roadway, and cut-off hole. If necessary, excavate the waist roadway as the bottom roadway for gas control of the upper outburst coal seam.

[0019] Step 3: Using the coal roadway of the lower coal seam, construct cross-layer boreholes to pre-drain the coal roadway strips within a certain range near the machine roadway, ventilation roadway, and cut-off point of the upper outburst coal seam, or use the coal roadway of the lower coal seam to perform regional grid-style pre-drainage of the upper outburst coal seam.

[0020] Step 4: Utilize the cross-seam boreholes already drilled in the lower coal seam to extract the goaf and depressurized gas during the mining of the upper outburst coal seam.

[0021] Step 5: Use the coal roadway in the lower coal seam to pre-drain the gas in the working face of the lower coal seam. At the same time, when the upper outburst coal seam is being mined, the boreholes in this coal seam can also intercept and drain the depressurized gas in this coal seam to prevent the gas in the lower coal seam from flowing into the mining face of the upper outburst coal seam.

[0022] More specifically, the coal seam selection method for the aforementioned coal roadway is as follows: the selected coal seam is the coal seam immediately below the outburst coal seam, or a coal seam with no or weak outburst risk at a suitable distance below it, which is used as the bottom roadway for gas control. Using the gas control technology of this invention, the outburst coal seam can still be mined downwards after gas control, without damaging the mining conditions of the outburst coal seam.

[0023] To be more specific, the aforementioned pre-gas extraction is a sampling and testing process that uses gas detection equipment. After the pre-gas extraction of the upper outburst coal seam is deemed qualified, the upper outburst coal seam is mined first, and then the lower coal seam is mined in sequence.

[0024] More specifically, the pre-drainage of gas preferably utilizes the bottom roadway of the lower coal seam to pre-drain the gas in the strips of the upper outburst coal seam, or to pre-drain the gas in the entire working face area of ​​the upper coal seam; if necessary, a side roadway is excavated in the lower coal seam to perform grid-like pre-drainage of the upper outburst coal seam.

[0025] To be more specific, during the tunneling of the coal roadway, boreholes are drilled simultaneously along the coal seam to pre-extract gas from the working face of the lower coal seam.

[0026] See on-site construction case studies Figure 4 Since the C2 coal seam is a dangerous outburst-prone seam, the C3 coal seam, which is not dangerous, should be considered first as a protective layer. However, the interlayer spacing between the C2, C3, and C4 coal seams is relatively small. If the C3 coal seam is selected as the lower protective layer for mining first, the average distance between the C3 coal seam and the upper C2 coal seam is 13.49m. From the perspective of spacing, the distance is relatively close. According to the minimum permissible interlayer spacing formula, it is close to the critical value of the safety spacing for outburst prevention. When mining the C3 coal seam, the upper outburst-prone coal seam is locally in the caving zone and mostly in the fracture zone. There is a possibility that coal and gas will break through the intermediate rock layer and directly flow into the working face of the protective layer. At the same time, the caving zone is calculated based on the mining height of the C3 coal seam. The small spacing may destroy the mining conditions of the upper coal seam.

[0027] According to the relevant provisions of the "Coal Mine Safety Regulations" and the "Detailed Rules for the Prevention and Control of Coal and Gas Outbursts", "when mining the lower protective layer, the mining conditions of the protected layer shall not be damaged." Whether the use of a lower protective layer in a coal mine will damage the mining conditions of the upper coal seam needs to be demonstrated. The following uses the ratio discrimination method and the "three-zone" discrimination method to determine whether the C2 coal seam is protected when the C3 coal seam is mined first.

[0028] ① Ratio test Production practice and research have shown that when the ratio of the distance between the protective layer and the protected layer to the mining height of the protective layer, K, is greater than 7.5, it generally will not affect the mining of the upper coal seam. The mining activities of the upper coal seam should be carried out 4 to 6 months after the mining of the lower coal seam.

[0029] The ratio K is used to determine the value, i.e.: K=H / M In the formula: H is the vertical distance between the upper and lower coal seams, in meters; M represents the lower coal seam mining height, measured in meters (m).

[0030] The ratio K of C3 coal seam protection to C2 coal seam in a coal mine is shown in Table 1.

[0031] Vertical distance H 13.49 M 1.5 Ratio K 8.9 The relatively small K values ​​of coal seams C2 and C3 indicate that the coal seam groups are closely spaced, and the impact of mining the lower protective layer on the mining conditions of the upper protective layer should be considered.

[0032] ② "Three-band" discrimination method When using the longwall mining method with complete caving, after the working face is mined, the overlying strata of the coal seam undergo regular movement, deformation, and destruction, which are divided into three zones: the caving zone, the fracture zone, and the flexural subsidence zone. The "three-zone" discrimination method states that if the distance between the upper and lower coal seams is greater than the height of the caving zone and the fracture zone of the lower coal seam, the lower coal seam can be mined first.

[0033] The height of the caving zone and the height of the fracture zone are calculated using the following formulas: Height of the collapse zone: H m =(MW) / (K-1)cosα In the formula: H m The height of the collapse zone, in meters (m). M represents the thickness of the coal seam being mined, in meters (m). W represents the subsidence value of the roof slab during the collapse process (0~0.2), taken as 0.2m; K is the coefficient of rock fragmentation (1.1~1.25), taken as 1.2; α is the dip angle of the coal seam, which is taken as 12°.

[0034] The calculated height of the caving zone after mining the C3 coal seam is shown in Table 2.

[0035] Fall zone height 6.35 The overlying strata of the coal mine are mudstone and fine sandstone. The height of the fracture zone in each coal seam is calculated using the following formula: Formula 1 for fracture zone height: H i =100M / (3.5M+5)+4 Formula 2 for fracture zone height: H i =10M 1 / 2 +5 Formula 3 for fracture zone height: H i=100M / (3.3n+3.8)+5.1 In the formula: H i The height of the fracture zone is expressed in meters (m). M represents the coal thickness, in meters (m). N represents the layer thickness. When there is only one mining operation, n represents the extraction height.

[0036] Table 3 shows the calculated height of caving and fracture zones after the mining of the C3 coal seam.

[0037] Fall zone height 6.35 Formula 1 for fracture zone height 18.63 Formula 2 for fracture zone height 17.24 Formula 3 for fracture zone height 22.24 Height of caving zone and fracture zone 23.59 As shown in Table 1-3, if the first coal seam is C3, the height of its caving zone and fracture zone will be greater than the distance between the C2 and C3 coal seams by 13.49m. This will damage the mining conditions of the C2 coal seam and make it difficult to mine the C2 coal seam in the later stages.

[0038] Meanwhile, when C3 coal seam was selected as the lower protective layer, the upper C2 coal seam was an outburst-prone coal seam and was close to the lower C4 coal seam. The gas inflow from adjacent seams was also large, increasing the difficulty of gas control during the mining of C3 coal seam. From the perspective of protecting resources and facilitating initial gas control, a pre-drainage working face was arranged in C3 coal seam. Gas was pre-drained along the coal seam, and cross-layer boreholes were drilled upwards to pre-drain the gas strips of C2 coal seam and downwards to pre-drain the gas of C4 coal seam. The effectiveness of the anti-outburst measures in C2 coal seam was tested. Only after the pre-drainage effect was determined to be effective could the C2 coal seam be tunneled and the working face be pre-drained along the coal seam. After the C2 coal seam working face was mined, the C3 coal seam working face below it was mined. After the C3 coal seam working face was mined, the C4 coal seam working face was mined. That is, the non-outburst-prone C3 coal seam roadway was used to eliminate the outburst of the outburst-prone C2 coal seam, and then mining was carried out layer by layer from top to bottom.

[0039] After adopting the above technical solution, the beneficial effects of this invention are as follows: When the nearby coal seam group does not have the conditions for downward mining, and the first mining seam is an outburst coal seam, the coal roadway of the lower non-outburst coal seam can be excavated first. The coal roadway of the lower coal seam can be used as the bottom roadway of the upper coal seam. In the coal roadway of the lower coal seam, upward cross-layer drilling is carried out to control the gas of the upper outburst coal seam. After the gas of the upper outburst coal seam is controlled to a satisfactory level, the upper outburst coal seam can be mined back to realize downward mining, thereby avoiding the damage to the mining conditions of the upper coal seam caused by upward mining. At the same time, this invention does not require the construction of additional rock roof roadways or floor roadways, and does not increase the number of roadways. It only needs to adjust the roadway excavation sequence to achieve the gas control effect of rock floor roadways. The principle is simple, the investment is small, and the gas control time is saved. It can play a good role in mines with the same coal seam and gas occurrence conditions.

[0040] The above description is only used to illustrate the technical solution of the present invention and is not intended to limit it. Any other modifications or equivalent substitutions made by those skilled in the art to the technical solution of the present invention, as long as they do not depart from the spirit and scope of the technical solution of the present invention, should be covered within the scope of the claims of the present invention.

Claims

1. A method for controlling gas in the floor roadway of a coal roadway during downhill mining of a coal seam group with close proximity to the outburst, characterized in that: It includes coal roadway excavation, pre-gas extraction, gas drainage, and gas control. In a group of closely spaced coal seams, coal roadways are excavated in non-outburst or weakly outburst coal seams. After the coal roadway is excavated, it is selected as the bottom roadway for gas control of the upper outburst coal seam. The gas of the upper outburst coal seam is comprehensively pre-extracted, and the depressurized gas of the coal seam where the bottom roadway is located is extracted and the gas of this coal seam is controlled. The steps for gas control are as follows: Step 1: In nearby coal seams, select coal seams that are not prone to outbursts or have weak outbursts as the gas control coal seams for the upper coal seams; Step 2: In the lower coal seam, first excavate the machine roadway, ventilation roadway, and cut-out, then excavate the waist roadway as the bottom roadway for gas control in the upper outburst coal seam; Step 3: Using the coal roadway of the lower coal seam, construct cross-layer drilling to pre-drain the coal roadway strips within a certain range near the machine roadway, ventilation roadway, and cut-off point of the upper outburst coal seam, or use the coal roadway of the lower coal seam to perform regional grid-style pre-drainage of the upper outburst coal seam; Step 4: Utilize the cross-seam boreholes already drilled in the lower coal seam to extract the goaf and depressurized gas during the mining of the upper outburst coal seam. Step 5: Use the coal roadway in the lower coal seam to pre-drain the gas in the working face of the lower coal seam. At the same time, when the upper outburst coal seam is being mined, the boreholes in this coal seam can intercept and drain the depressurized gas in this coal seam to prevent the gas in the lower coal seam from flowing into the mining face of the upper outburst coal seam.

2. The method for controlling gas in the floor roadway of a short-distance outburst coal seam group during downward mining according to claim 1, characterized in that: The specific coal seam selection method for the aforementioned coal roadway is as follows: the selected coal seam is the coal seam immediately adjacent to the bottom of the outburst coal seam, or a coal seam with no or weak outburst risk at a suitable distance below it, which is used as the bottom roadway for gas control.

3. The method for controlling gas in the floor roadway of a short-distance outburst coal seam group during downward mining according to claim 1, characterized in that: The aforementioned pre-gas extraction is a sampling and testing process that uses gas detection equipment. After the pre-gas extraction of the upper outburst coal seam is deemed qualified, the upper outburst coal seam is mined first, and then the lower coal seam is mined in sequence.

4. The method for controlling gas in the floor roadway of a short-distance outburst coal seam group during downward mining according to claim 1, characterized in that: The aforementioned pre-drainage gas utilizes the bottom roadway of the lower coal roadway to pre-drain the gas in the strips of the upper outburst coal seam, or to pre-drain the gas in the entire working face area of ​​the upper coal seam; a waist roadway is excavated in the lower coal seam to perform grid-like pre-drainage of the upper outburst coal seam.

5. The method for controlling gas in the floor roadway of a short-distance outburst coal seam group during downward mining according to claim 1, characterized in that: During the tunneling of the coal roadway, boreholes are drilled simultaneously along the coal seam to pre-extract gas from the working face of the lower coal seam.

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