1、外文原文：Methane control for mechanised longwall top-coal caving faces in high gas content mines（Guoming Cheng, Kan Huang, Fuzhang Yan, Weilin Li and Sijing Wang）In China, mechanised longwall top-coal caving technology (LTCT) has been widely used under suitable thick coal seam conditions due to its low
2、cost, high production and productivity since it was introduced in 1982. It has even been applied in some high gas-content mines (e.g. No. 5 Mine, Yangquan coalfield), where methane is the most serious hazard affecting production in the mine. With the introduction of LTCT in 1992, the frequency of pr
3、oduction delays greatly increased due to excess methane. In order to solve these problems, China University of Mining and Technology (CUMT) has been carrying out methane research jointly with Yangquan Coal Group Co. (YCGC) since 1993. The major focus of the research was concerned with the gas source
4、 and emission characteristics of the longwall top-coal caving face (LTCF) and the methane drainage methods from the adjacent strata during initial and normal mining. The research has helped the mine to control methane-related production delays to tolerable levels. The methane problems during normal
5、mining were solved by the adoption of the high-level strike drainage roadway (HSDR). The methane concentration during initial mining was kept below the statutory limits by the adoption of the mid-level drainage roadway (MDR). In this way, the methane-related production delay problems were successful
6、ly solved by introduction of the HSDR in conjunction with the MDR. This paper analyses the gas source and emission characteristics of LTCF, and describes the experiences and methodologies adopted in methane control at the LTCF during normal and initial mining.BACKGROUNDChina is a large coal-producin
7、g country where underground mining of thick seams (i.e. more than 45 m thick) accounts for about 4050% of the national total coal output. The main mining methods of thick seams can be divided into two types longwall top-coal caving and longwall multislice mining. The latter was the major mining meth
8、od in the past. LTCT was introduced in China in 1982, and is now widely used under suitable geomining conditions due to its low cost, high production and productivity.10,13 Through constant research,25,8,11,12,14,15 significant improvements have been made in LTCT, and the maximum production of a LTC
9、F has reached up to 042 Mt per month in Dongtan mine, Yanzhou coalfield.At present, LTCT has been applied in thick seams ranging from 45 m to 12 m, even in difficult geomining conditions, such as three soft (soft roof, seam and floor), two hard (hard roof and seam), bigger slope angle of coal seam (
10、less than 35) and high gas-content mines。While high production and productivity have been achieved using the technique, there are still some problems restricting its application,15 gas being one of the main hazards, especially in some high gas content mines (e.g. No. 5 mine, YCGC, etc).The No. 5 min
11、e at YCGC is classified as gassy, and LTCT was applied to mine the No. 15 seam in 1992. The methane problems at LTCF during normal mining were solved by the adoption of the HSDR. However, at the early stages of mining, the overlying strata was not relieved, and the fractured zone in the roof was not
12、 extended to the HSDR; therefore, it is very difficult for HSDR to draw methane out of the adjacent strata. As a result, before the LTCF advanced about 38 m from the face start line, large amounts of methane were emitted from the waste into the return. The methane content in the return cannot be kep
13、t below the statutory limits (1%) just by increasing air quantity. For example, the air quantity at No. 8109 face, which was the maximum air quantity at the previously mined faces, was 2200m3 min1, the methane emission rate was 29 m3 min1, and the content in the return was 12%. Hence, the production
14、 was often delayed due to excessive methane.Total down-time at the previously mined faces is shown in Fig. 1.MINING METHODSThe No. 15 seam has been extracted by the longwall retreating method using the LTCT since 1992. No.8204 face at the No. 5 mine is 160 m long and equipped with 105 powered suppor
15、ts (FDC440- 175/26 made in China). It has a panel length of 708m. The bottom section cut by the shearer is only 25m, the remaining 43 m flows onto the rear armoured face conveyor (AFC) under the influence of gravity, without cutting or blasting. The roof behind the face adopts fully caving method. L
16、ayout of the face is shown in Fig. 3. The face production per day was about 2120t.The sequence of operations included: (i) cutting the bottom coal; (ii) advancing the face supports; (iii) pushing forward the front AFC; (iv) advancing the rear AFC; and (v) while cutting the second web (each web 600 mm) of the bottom coal, the top coal is allowed to fall.Gas source of the LTCFThe gas source of the LTCF generally originates from the seam being worked and the
