Page 288 - Advanced Mine Ventilation

Premining Degasification of Coal Seams 265

Figure 15.12 Optimum width of longwall panels in pittsburgh seam.

15.7 Field Observations of Optimum Longwall Panel
Width

The Pittsburgh coal seam of Pennsylvania and Northern West Virginia is a moderately
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gassy coal seam with a gas content of 100e250 ft /ton. Premining degasification is
done with in-seam horizontal drilling and about 50% of the gas is draineddprior to
mining. The rate of mining varies from 70 to 100 ft/day. The total methane emissions
and ventilation air at the tailgate of longwalls 1000 to 1600 ft wide panels are plotted
against the panel width in Fig. 15.12.
An optimum width of 1300 50 ft is indicated.
Longwall panel width can also be controlled by high specific gob emissions. It will
be discussed in Chapter 16. For highly gassy mines with specific gas emissions of
30 MMCF/acre or more, the optimum width is reduced to 750 50 ft.

Problems

15.1. Using Eq. (15.6), calculate total methane emissions at the tailgate, Q, of a highly gassy
coal seam; given:
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3
Qo ¼ 200 CFM, A ¼ 200 ft /ton, B ¼ 60 ft /ton
Ave C(X) for a 1000 ft long face ¼ 200 CFM.
15.2. Calculate the volume of air/min needed to dilute the above Q to 0.8%, and verify if the gas
layering index exceeds 5.00.