Page 73 - Advanced Mine Ventilation

56 Advanced Mine Ventilation

1.2

0.9
Spacing
Width
0.6
0.5

0.3

400 600 700 800 1000 1200
Width of Longwall Face, ft.
Figure 4.10 Optimal spacing of gob wells on a longwall face.

4.8 Air Quantity Requirements for Development
Headings

It is generally not possible to achieve a good rate of advance (such as 100 ft/day) in a
three-heading development without advance degasification. Horizontal boreholes
drilled in advance (to be discussed in Section 4.3) generally capture 50% of total
methane emissions. For moderately gassy mines, the development section still gener-
ates 250e400 cfm of methane. To dilute it properly, 50,000 cfm is generally needed at
the last open cut.
For highly gassy mines, the air quantities are not much higher than 50,000 cfm/
section because 70 to 80% of gas in coal is predrained by vertical, hydraulically frac-
tured wells supplemented by in-mine horizontal drilling.
The air quantities estimated here are higher than those mines where a conveyor is
not used for coal transport. US mining laws require part of the air to be used for belt
entry ventilation as a separate split.

4.9 Estimation of Total Required Ventilation Air

Once the quantity of air required for each longwall face and development sections has
been determined, the total required volume of air to be handled by the mine fan(s)
needs to be estimated. This is done by adding to the air quantity needed at the working
faces all leakages and air quantities needed in nonworking locations, such as diesel