Longwall mining is the safest and the most efficient method of mining coal. Currently a little more than fifty percent of all underground mined coal is mined by this method. Driven by the demands of higher productivity, the prevalent trend is for longer and wider panels, higher horsepower equipment and faster rates of extraction. In mildly gassy mines (gas contents less than 3 m3/t) and even in moderately gassy mines (gas contents between 3 and 7 m3/t), limits on the width of panel and rates of extraction have not been reached. But in highly gassy mines (gas contents between 7 and 20 m3/t), there are indications that limits on both the width of the panel and rates of extraction are being reached. The width of the longwall panel is primarily limited by the volume of air reaching the tail-end of the face. The ventilation air quantities reaching the tail-end of the face should be not only enough to keep the methane concentrations below statutory limits (generally one percent) but also enough to prevent any gas layering. A third criterion for the adequacy of ventilation air is the ability of ventilation air leaking into the gob to push away the explosive methane-air mixture away from the gob area immediately behind the longwall face where active roof fall is still taking place (typically 30-45 m). Ventilation air reaching the tail-end of the longwall face depends on the air quantity reaching the head gate-end of the longwall face and air leak-off on the face. In general, the wider the longwall face, the higher is the leak-off on the face. The second group of variables that also controls the width of the longwall panel consists of (a) the rate of advance, (b) bleeder air quantities (c) specific methane emission for the gob areas and (d) efficiency and cost of gob gas capture. This paper will discuss only the first group of variables that controls the longwall panel width. The influence of the second group of variables will be discussed in a separate paper as a sequel to this paper
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