Methane Emission in Workings and Some Characteristic Gas Conditions in a Brown Coal Mine

摘要

The results of the investigation permit the following assertions to be made: in all the development workings there are aerodynamic conditions favourable for the formation of methane layers; that is, the mean velocity of the ventilation flow is usually within the limits 0.15 to 0.30 m/s, and the velocity profiles are characterised by maximum velocities at the floors - sources of methane, forming layers, are usually at a distance of 15-20 to 30-35 m from the face or at the intersections of minor geological disturbance - faults, etc. The intensity of these sources is of the order of 0.2 to 0.5 m exp 3 /min - methane layers are extremely stable and depending on the behavior of the source endure for several weeks, months and in some cases for the whole period of the development of the workings. At the junction of faces with the ventilation roadway, there are regions of complex gassy conditions, manifested by the formation of local pockets of methane and where, in the majority of cases, these is a dangerous explosive concentration of methane. Methane generated from the goaf enters the ventilation flow in the last 5 to 10 m of the face and usually directly into the ventilation roadway. During gas generation in excess of 0.5 to 0.6 m exp 3 /min from the goaf, accumulations higher than 2% are established, and when the gas generation is higher than 1.0 m exp 3 /min, explosively dangerous concentrations higher than 5% can occur. Pockets with methane content higher than 2% have a length of order 7 to 10 m, and with a content higher than 5% have a length of order 3.5 m depending on the aerodynamics at the junction. The thickness of the gas pocket is extremely variable and usually varies within the limits 15-20 to 30-40 cm. (ERA citation 10:029711)