Page 294 - Advanced Mine Ventilation

Postmining Degasification of Coal Mines 271

16.2 European Gob Degasification Methods

European coal seams are generally steeply inclined, tectonically disturbed, and seated
deeper than US coal seams. Several coal seams are deposited in each basin and, typi-
cally, worked simultaneously. East European coal seams are not only gassy but also
prone to instantaneous outbursts. Longwall mining system is the most common
method of mining coal. Both advancing and retreating longwalls are employed in vary-
ing proportions. Most of the methane emission takes place in the gob areas following
mining operations and strata movement leading to tremendous improvements in
permeability.
European methane control techniques can be broadly classified in the following
three groups:

1. The packed cavity method and its variants.
2. The cross-measure borehole method.
3. The superjacent method.
Each of these techniques is discussed below.

16.2.1 Packed Cavity Method and Its Variants
Early methods of methane control consisted of simply isolating the worked out area in
the mine using pack walls, partial or complete stowing, plastic sheets, or massive stop-
pings. A network of pipeline which passed through these isolation barriers was laid in
the gob, and methane was drained using vacuum pumps. Fig. 16.3 shows typical lay-
outs for a caving longwall face. Fig. 16.4 shows a similar layout for a partially stowed
longwall face.
Lidin [3] has reviewed several variants of this technique. Methane capture ratios
quoted by him are shown in Table 16.2.

Figure 16.3 Packed cavity method for a caved longwall face.