论文部分内容阅读
Decrease of the gas content in the worked seam by degassing before the start of winning has
proven its worth in some areas of German hard coal mines，on the one hand in order to remove the risk of gas/coal outbursts and on the other hand in order to reduce the gas inflow into the
longwall.The underground experiences of the last 30 years have led to a“hit list”of coal
seams with respect to their suitability of predegassing.Trials in the DMT-laboratory and also
results gained in the deposit show that the suitability of a seam for predegassing depends on
its rank.In seams with volatile matter of 20％～30％，high efficiency ratings are achieved as
a rule，with lower ratings both in seams with lower and with higher content of volatile matter.If the rock pressure is unusually high，the efficiency rating of the predegassing is lower，even in seams which would normally be suitable for this process.Under unfavourable conditions，for example below or above residual pillars，in-seam boreholes cannot be drilled successfully and
the method is not practicable.But if the worked seam was already stress relieved，the
predegassing has an optimal efficiency.Latast investigations show，that the distance of the in-seam boreholes from one another can be extended.But in that case the time，which is necessary
to reach the same reduction of the gas content，increases considerably.