Comprehensive gas control technology in the hottes

Comprehensive gas control technology in fully mechanized mining face

comprehensive gas control technology mainly includes two aspects: first, only using ventilation method to dilute gas; The second is to dilute by first draining and then ventilation, so as to ensure that the gas concentration in the working face and return air flow meets the requirements of safety production. In the case of large amount of gas emission in the working face, it is difficult to effectively control gas only by ventilation dilution method, gas drainage is an effective technical way for comprehensive gas control

1 overview of working face and analysis of gas emission

41120 working face mining 11# coal seam is a coal and gas outburst coal seam, and the gas content of the coal seam is 15m3/T. The thickness of the coal seam is 2.8m, the dip angle is 8 ° q/01jsj048 ⑵ 007 horizontal tensile testing machine standard ~ 12 °, the strike length is 502m, the dip width is 160m, and the adjacent north side is 41118 goaf. The main roof is gray white medium thick layered fine sandstone with a thickness of 6 ~ 8m, and the direct roof is gray mudstone with a thickness of 2.3 ~ 3.5m. The roof is easy to collapse, and the caving height of the goaf is 10 ~ 15m. The working face adopts the strike longwall retreating layout, comprehensive mechanized coal mining, and all caving method to manage the roof

none of the upper coal seams of the 11# coal seam has been mined, and the spacing between the 11# coal seam and the upper main coal seams is: the company has the underwriting right to underwrite some spodumene concentrates of the pilgangoora lithium mine project with reference to the market price, and the spacing between the 7# coal seams is 17.95m; The distance between the coal seam and the 8 # layer is 9.45m, and the distance between the coal seam and the 9 # layer is 7.3m. All coal seams are located in the caving zone and fissure zone in the goaf of the coal mining face. During the production process of 41120 working face, the gas stored in the above coal seams will continuously flow into the goaf, and its use and cable will be affected by the air flow in the goaf, and will be gradually brought into the upper corner of the working face and return air flow. The goaf of 41118 working face is only 20m away from this working face. When the working face advances to the primary collapse of the main roof, the coal pillar will be fractured, and the gas in 41118 goaf will also flow into the goaf of 41120 working face

according to the mining statistics of the fully mechanized mining face, the amount of gas emitted from the coal seam before the collapse of the main roof during the initial mining of the working face and the amount of gas emitted from the residual coal in the goaf of the working face are only 12m3/min. After the mining distance of the mining face exceeds 30m of the cutting hole, a large amount of gas from adjacent layers and surrounding rocks flows into the working face, and the gas emission increases significantly. It is estimated that the gas emission of 41120 working face is 40m3/min. The gas emission of this coal seam accounts for about 30% of the gas emission of the working face; The gas in adjacent layers, surrounding rocks and goaf accounts for about 70% of the gas emission of the working face, which is the main source of gas emission of the working face

(1) reasonably allocate the air volume to dilute the gas emitted from the coal seam and goaf. According to the design section of the air inlet and return roadway of the working face, the mining deformation factor of the roadway during mining and the flow law of the air flow in the goaf, considering the characteristics of using the transportation roadway to advance the air return roadway by 15m during the mining of the working face and the condition of the ventilation system, and in order to avoid a large amount of air flow into the goaf, a large amount of gas in the goaf will be carried to the working face and the air return flow. The air flow configured for the working face is 1100m3/min

(2) gas pre drainage of this coal seam. During the excavation of 41120 haulage roadway, one drill yard is arranged every 24m, a total of 20 drill yards, and 10 drill holes are arranged in each drill yard. They are arranged along the coal seam inclination, with an inclination of 3 ° ~ 8.5 °, an included angle of 10 °, an opening spacing of 0.4m, and a drilling depth of 70 ~ 120m. They are evenly arranged in the working face in a fan shape (Fig. 1)

Figure 1 layout of gas pre drainage boreholes in this coal seam

skw-85 gas drainage pump is adopted, and the main pipeline Φ 250mm, high negative pressure, pre gas drainage of this coal seam for 41120 working face

(3) buried pipe gas drainage in goaf. A 2bec50 water ring vacuum pump is used to drain the gas in the goaf and upper corner of the working face. Before the stoping of 41120 working face, the air return roadway of the working face shall be embedded once in advance Φ 325mm gas drainage pipe is installed every 30m on the drainage pipe according to the step distance of roof collapse and the law of initial and periodic pressure on the working face Φ 325mm equal diameter tee and gate valve are added, and "t" pipes are installed alternately with the mining of the working face, while the isolation wall is built at the upper corner (Fig. 2)

Figure 2 "t" type pipe layout

"t" type pipe is placed in the pumping chamber located on the roof of the return air roadway and reinforced with "well" type wooden cribs. After the pre installed alternating step "t" pipes every 30m in the air return roadway are buried in the upper corner isolation wall, open the gate valve to control the flow and drain the gas accumulated in the upper corner. When the separation wall is constructed to the gate valve, the gate valve will be fully opened to drain the gas in the goaf and the upper corner

(4) near horizontal high-level gas drainage borehole drainage. Gas drainage by near horizontal and high horizontal drilling is also called gas drainage by roof fissure zone. According to the law of mine pressure, in 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, caving zone, fracture zone and bending subsidence zone. Three zones are formed in the horizontal direction, namely, the coal wall support influence zone, the separation zone and the re compaction zone. The fissure space formed in this mining pressure field becomes the channel of gas flow. The drainage negative pressure of high-level boreholes accelerates the flow of gas in the fracture zone, so that the near horizontal high-level boreholes can extract high concentration gas

41120 working face is designed with 4 high-level gas drainage roadways. There are 4 ~ 9 construction boreholes in the roadways, the spacing of holes is 0.4m, and the inclination of boreholes is 2 ° ~ 4 °. The final holes are arranged within 20m from the lower side of the working face to the air return roadway, and in the roof 10m from the roof. The hole depth is 100m. The construction boreholes of the latter high-level roadway cover the boreholes of the previous high-level roadway for 20M (Fig. 3)

Figure 3 layout of near horizontal boreholes in high-level roadway

the high-level gas drainage roadway is opened in 41120 return air roadway, and the roadway is excavated along the vertical return air roadway to the inner side of the mining face according to the design elevation angle. After being excavated to a height of 10m from the roof of 41120 working face, a drilling platform is made, and the construction diameter in the platform against the advancing direction of the mining face is Φ The 153mm near horizontal drainage borehole is connected to the drainage branch pipe after sealing, and then a closed wall is built at the side entrance of the high-level drainage roadway. The 2bec50 pump is used to drain the gas in the roof fissure zone of the goaf of 41120 working face (shared with the drainage pipe of the inclined gas drainage drill site)