Page 65 - Advanced Mine Ventilation

48 Advanced Mine Ventilation

Figure 4.5 Degasification plan for a longwall panel in moderately gassy coal seams.

provided by the combination of a main fan and a bleeder fan. Very high pressure
bleeder fans are not desirable for coal mines because all coal seams are liable to spon-
taneous combustion. High pressure differential promotes spontaneous combustion (to
be discussed in Section 4.4).

4.3 Mildly Gassy Coal Seams

A typical layout for a longwall face operating in a mildly gassy coal seam is shown in
Fig. 4.3.

4.3.1 Premining Degasification
3
In coal seams with gas contents less than 100 ft /t, there is generally no need for pre-
mining degasification. However, it may be desirable to drill the longwall panel hori-
zontally at 1000-foot intervals for exploration and respirable dust control.

4.3.2 Postmining Degasification
At least one gob well within 1000 ft from the setup entry is recommended because
longwall gobs always produce some gas. Normally, there exists a very good longitu-
dinal communication over the longwall panels, and a single gob well can have a
drainage radius of 3000 to 5000 ft. A second gob well may be needed to cover a
15,000- to 20,000-foot long panel. The gob well diameter can range from 4 to 8 in.,
and gas production can be enhanced with blowers.

4.3.3 Ventilation Layout and Quantities

A preferred ventilation layout for a very large longwall panel is shown in Fig. 4.3. The
main fan shaft provides all the intake air. The bleeder fan assists the main return fan.
The internal return may not always be necessary unless the ventilation air on the face
declines below the quantities shown in Table 4.1.