Comprehensive gas control technology for fully mechanized mining face

1 Overview of the working face and analysis of gas emission

41120 Face # 11 coal seam mining, coal and gas outburst coal seam, coal seam gas content 15m3 / t. The thickness of the coal seam is 2.8m, the inclination angle is 8°~12°, the strike length is 502m, the inclination is 160m, and the adjacent north side is 41118 goaf. The old top is gray-white medium-thick layered fine sandstone with a thickness of 6~8m. The direct top is gray mudstone with a thickness of 2.3-3.5m. The roof is easy to fall, and the height of the goaf is 10~15m. The working face adopts a long-wall retreat arrangement, comprehensive mechanized coal mining, and all the fallen methods manage the roof.

The coal seams in the upper part of the 11# coal seam are not mined. The spacing between the main coal seams of the 11# coal seam and the upper part is: 17.95m from the 7# layer; 9.45m from the 8# layer, and 7.3m from the 9# layer. The coal seams are located in the caving zone and the fracture zone of the goaf in the coal mining face. In the production process of the 41120 working face, the gas existing in the above coal seam will continuously flow into the goaf, and at the same time, it will be gradually brought into the corner of the working face and the return flow by the wind flow of the goaf. The 41118 working face goaf is only 20m away from the working face. The working face is advanced to the old top and the coal pillar will be fractured. The 41118 goaf gas will also flow into the 41120 working face goaf.

According to the mining statistics of fully mechanized mining face, the amount of gas from the coal seam before the old roof collapsed during the initial mining period and the amount of gas from the remaining coal in the goaf of the working face is only 12m3/min. After the mining distance of the mining face exceeds the cutting eye by 30m, the gas in the adjacent layer and surrounding rock floods into the working face, and the gas emission is greatly increased. It is estimated that the gas emission of 41120 working face is 40m3/min. The gas emission from the coal seam accounts for about 30% of the gas emission from the working face; the gas in the adjacent layer, surrounding rock and goaf accounts for about 70% of the gas emission from the working face, which is the main source of gas emission from the working face.

2 Countermeasures for comprehensive gas management in working face

According to the analysis, the gas in the coal seam gas, the gas in the adjacent layer and the gas in the goaf of the 41118 working face constitute the main source of gas in the 41120 working face. The principle of divide and conquer was adopted in the formulation of the gas comprehensive management plan for the 41120 working face.

(1) Reasonably configure the air volume to dilute the gas from the coal seam and the goaf. According to the working face, the design section of the return airway, the mining deformation factor of the roadway during the mining and the flow law of the wind flow in the goaf, consider the characteristics of the 15m of the leading return airway of the transport lane and the condition of the ventilation system when the working face is recovered. In order to avoid a large amount of wind flow into the goaf, the gas in the goaf is carried to the working face and return air in a large amount, and the air volume of the working face is 1100m3/min.

(2) Pre-extraction of gas in this coal seam. During the tunneling of 41120 transportation lanes, 1 drilling rig is arranged every 24m, a total of 20 drilling rigs, 10 drilling holes are arranged for each drilling rig, and the inclination is arranged along the coal seam. The inclination angle is 3°～8.5°, and the angle of the drilling is 10 °, the opening pitch is >0.4m, the drilling depth is 70~120m, and the fan shape is evenly arranged in the working surface (Fig. 1).

The SKW-85 gas drainage pump is used, and the main road is Φ250mm, and the high negative pressure is applied to the 41120 working face for pre-extraction of the coal seam.

(3) Gas drainage in the goaf. A 2BEC50 water ring vacuum pump is used to pump the gas in the goaf and upper corner of the working face. 41120 working face before mining, in advance in the working face

Pre-buried 1趟Φ325mm gas drainage pipe, according to the rule of the top plate falling step and the initial pressure and cycle of the working face, install Φ325mm equal-diameter tee and add gate valve every 30m on the pumping pipe, with the working face The alternate mining and installation of the "T" type network pipe, while constructing the wall in the upper corner (Figure 2).

The “T” type network tube is placed in the pumping chamber inside the roof of the return air duct and is reinforced with “well” type raft. After the alternate stepping "T" type network pipe pre-installed every 30m in the return air lane is buried in the upper corner wall, the gate valve is opened to control the flow and the gas accumulated in the upper corner is pumped. When the wall is applied to the gate valve, the gate valve is fully opened to pump the gas in the goaf and the upper corner.

(4) Going to the near-horizontal high-level gas drainage and drilling. Toward the horizontal high level horizontal drilling and drainage, also known as the roof cracking zone to extract gas. According to the law of mine pressure, during the mining process, a mining stress field will be formed around the working face, and the mining stress field and its influence range will form three zones in the vertical direction, namely the falling zone, the fracture zone and the curved sinking zone. . Three zones are formed in the horizontal direction, namely the coal wall support affected zone, the separated zone and the re-compacted zone. The fissure space formed in this mining pressure field becomes a passage for gas flow. The pumping negative pressure through the high-level drilling accelerates the flow of gas in the fracture zone, so that the high-concentration gas can be extracted from the near-high-level drilling.

41120 working face design 4 high-level gas drainage roadway, 4~9 drilling holes in the roadway, the opening spacing is >0.4m, the drilling inclination angle is 2°~4°, and the final hole is arranged on the working surface from the lower side of the return airway Within 20m, the hole depth is 100m in the top plate 10m away from the top plate, and the drilling hole in the next high-level roadway covers 20m of the previous high-level roadway (Fig. 3).

The high gas drainage roadway is opened in the 41120 return airway, and the roadway is drilled along the vertical return airway to the inner side of the mining face according to the design elevation angle. After drilling to the height of 10m from the 41120 working face, a drilling platform is made and the platform is reversed. The surface is driven by a near-horizontal drainage hole with a diameter of Φ153mm. After sealing, it is connected to the drainage branch pipe, and then the closed wall is constructed at the high-level drainage roadway. The 2BEC50 pump is used to cover the crack zone of the goaf in the 41120 working face. The gas is pumped (shared with the sloping gas drainage drill pipe).