Comprehensive gas control technology in the hottes

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Comprehensive gas control technology of fully mechanized top coal caving face

1 overview of working face

1221 (3) the fully mechanized top coal caving face is the first mining face of Zhangji coal mine, which is located in the south wing of the first mining area in the West Wing of the central area of the mine, with a strike length of 1070m and an inclination length of 132.5m; Only the vanadium industry has achieved a reasonable profit level for the extracted coal. The horizon is stable, the dip angle is about 8 °, the average thickness of the coal seam is 4.5m, and the coal seam is a high gassy coal seam. During the mining period, the average relative gas emission is 10.22m3/t, and the average absolute gas emission is 14.74 m3/min. the coal dust is explosive, and the coal seam is in danger of natural ignition, and the ignition period is 3 ~ 6 months;, Adopt "U" ventilation mode for mining

2 gas emission characteristics of working face

1221 (3) the coal cutting thickness of fully mechanized top coal caving face machine is 2.2M, and the coal caving height is nearly twice the coal cutting height. Due to the high mining height, high output and certain coal loss in the goaf, the gas emission has the following characteristics in the production process:

(1) the gas in the upper corner is high. Like the ordinary "U" ventilation coal mining face, there is a certain air leakage behind the working face. By measuring the air volume of the working face, it can be seen that the air volume in the middle of the working face is only 60% - 80% of the air volume of the return air roadway, indicating that the air leakage is very large. The gas in the coal wall of the working face is quickly diluted and diluted by the fresh air flow due to the turbulence of the air flow, and part of the gas in the top coal body (part of which is released to the working face) flows into the goaf and accumulates in the rear goaf together with the gas in the residual coal and the surrounding rock of the adjacent layer. The gas in the goaf accumulates at the concentrated outlet of the air leakage of the working face (in the upper corner area) through the migration of the air leakage with low wind speed in the laminar flow state, The gas concentration at the upper corner is high, which is easy to cause gas overrun and bring hidden dangers to safety production

(2) gas emission in goaf is large. Through the measurement and analysis of gas emission from the working face, it can be considered that there are three sources of gas in the working face: the mining layer, the adjacent layer and the residual coal in the goaf. Because the adjacent layers and residual coal gas flow to the working face through the goaf in the production process, the gas emission sources of the working face can be roughly divided into two: the mining layer and the goaf

according to the measured data of gas emission before the first collapse of the main roof in 1221 (3) fully mechanized top coal caving face (the last industry person said ten days to late days in October 2000) and the measured data of gas emission six months after the first collapse of the main roof (November 2000 to April 2001), it is calculated that the Wasi emission of the mining layer is 6.89 m3/min, accounting for 51% of the total gas emission of the working face. The gas emission from the goaf (adjacent layers and residual coal in the goaf) is 6.62 m3/min, accounting for 49% of the total gas emission from the working face

(3) imbalance of gas emission in goaf. When the roof collapses in a large area due to the initial pressure, periodic pressure and passing through the structural zone, the gas in the goaf will gush out in large quantities and flow into the working face through the goaf, resulting in the increase of gas concentration in the mining face and air return roadway, which is shown as unstable emission. The unbalanced coefficient of gas emission of this face is 1.5

3 comprehensive gas control measures

(1) reasonably select the air volume of the working face. At the beginning of the mining of the working face, that is, before the first collapse of the main roof, considering the factors of poor gas drainage effect, under the condition that the daily output of this face may be 3000t, the predicted value of its absolute gas emission is 12.75 m3/min (the predicted value of Fushun Coal Research Institute branch), and the air distribution is 1913 m3/min, which can dilute the gas concentration in the return air flow of the working face to less than 0.5%, which better meets the production requirements

after the first roof pressure, the gas drainage effect is improved. On the basis of meeting the diluted gas, appropriately reduce the air volume and minimize the oxygen supply to the goaf, which is conducive to fire prevention

considering that the early drainage rate is still impossible to be very high, the air volume is re selected according to the 20% gas drainage rate:

from November to April 2001, the air distribution volume of this face has been relatively stable. The mining process has proved that the air volume is reasonable, which not only controls the number of gas overruns in the fully mechanized caving face, but also controls the oxidation and spontaneous combustion of coal in the goaf, and the CO concentration in the upper corner is controlled at 30 × The following ensures safe production

(2) implement pressure equalizing ventilation to reduce gas emission from goaf. The first is to adjust the air distribution of the working face from 1940 m3/min to about 1500 m3/min according to the actual needs. The implementation of this measure is not a simple ventilation, but to set up a group of pressure regulating dampers at the downhill of the return air, and implement the pressure equalization in the open area by increasing the resistance. Under the condition that the pressure difference between the inlet and return air lanes of the mining face is basically unchanged (the pressure difference at this end is determined by the central fan network), through the pressure equalization facilities set, the upper The pressure difference between the lower heads reduces the air leakage in the goaf; The second is to fill the upper and lower corners of the fully mechanized top coal caving face, and implement resistance increasing measures for the air leakage branch of the goaf: harvest, drop the rack and release the coal in time, stack the coal gangue in plastic textile bags at the upper and lower corners for continuous filling, and require that the wall stack be consistent with the back beam of the fully mechanized top coal caving support, and form a 110 ° obtuse angle or arc shape between the wall stack and the upper and lower air lanes, so as not to form a ventilation dead angle or eddy current area, so as to facilitate the good diffusion of air flow, Close to the air leakage source (lower corner) outside the wall pier, add a wind shield to prevent air leakage. Through the measurement and statistics of the air volume of the working face before and after the implementation of the measure, the maximum value of air leakage in the goaf before the implementation of the measure is 40% of the return air flow. After the implementation of the measure, the air leakage has decreased, and the maximum value is 25% of the return air flow. This face is continuously filled in this way. Under normal drainage conditions, the gas at the upper corner is better treated, so that the gas concentration at the upper corner is always below 2%

(3) strengthen the management of ventilation system to ensure the stability and reliability of the system. ① With the extension of the development roadway of the East and West cleaning test bench wings of the mine, the roadway construction and penetration sites (Times) increase, and the air distribution volume of the mine system also needs to be constantly adjusted. We have timely measured the regional pressure equalization technology for each air regulation and increase and decrease of air volume, and adjusted the pressure equalization ventilation system there to ensure that the air volume is fixed and the air pressure is reasonable. ② The air volume of the working face shall be measured once a week under normal conditions and at any time under special circumstances, and the wind measurement results shall be recorded on the wind measurement board of the working face to master its changes. ③ Regularly check the sealing quality of pressure equalizing damper and control damper to prevent damage and ensure that the facilities are in good condition; The control damper is always locked; It is strictly forbidden to vent the two coal chute holes that have an impact on the stability of the pressure equalizing system

(4) drill holes to discharge gas in goaf in the direction of construction roof. Gas drainage by drilling in the roof strike is a mature technology in Huainan mining area, that is, drilling in the coal seam roof along the strike to the upper part of the goaf (i.e. the fissure zone), and draining the high concentration gas accumulated in the goaf roof fissure zone, caving space and filling and blocking through drilling, so as to reduce the large amount of gas gushing from the upper corner to the working face. Through the investigation of the drainage of 62 boreholes (including connecting holes) in 9 drill yards of this face, the technical parameters of drilling design of roof strike suitable for Zhangji mine are basically mastered: ① the final hole position is determined as 16m of coal seam roof; ② The distance between drilling and pumping is 30m; ③ The spacing between drill yards is 80m, and 5 holes are arranged in each drill yard

(5) other gas control measures. ① Add full-time gas testers at the upper corner; Hang a CH-4 portable instrument at the upper corner. Once CH4 ≥ 2%, stop working immediately; An air deflector or air deflector shall be set at the upper corner to make the air flow of the working face change direction close to the upper corner as far as possible; High pressure water jet is used to take away gas in the space with small gas accumulation locally; The rear chain plate machine pulls away the residual coal in time, and the increase of ventilation also makes the market of recycled plastic granulator more and more optimistic about the wind section; The small space of gas accumulation in the outer side of the upwind roadway in the upper corner is also filled. ② Before the working face passes the drilling site, due to the influence of advance stress on the drilling site, the coal body will be broken and gas will be gushed into the drilling site. After the drainage pipeline is removed, when the diffusion ventilation is not ideal, gas is very easy to accumulate there. Therefore, before the removal of the drilling hole, the drilling yard is connected with wooden cribs to minimize the damage to the drilling yard; When the gas concentration is large but less than 1.5%, high-pressure water jet is used to wash away the accumulated gas; Use a long drill rod to dig holes in the drilling yard in the direction of the working face, and use negative pressure ventilation to take away gas. ③ Mend the side hole of the lane side. Under normal conditions, the boreholes in the front and rear drill yards can be well replaced and the gas can be discharged evenly, but when the periodic pressure or the initial pressure is applied, the large-area collapse of the roof causes the space volume of the goaf to shrink suddenly, and the boreholes collapse in advance in the structural belt, making the boreholes ineffective or the sealing of the boreholes is not true. When there is a large deviation between the gas leakage and the drilling construction, and the boreholes cannot be replaced normally, it is necessary to drill side holes, That is, between the two drilling sites, the roof is drilled along the strike through the roadway side or shallow drill hole, so as to ensure the replacement of drilling holes

(Qin yongyang, Zhao Junfeng, Li Gui and Zhu Hengyou)

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