Page 162 - Advanced Mine Ventilation

142 Advanced Mine Ventilation

Efficiency of collection by sedimentation is given by Eq. (10.6) for one row of filter.

gs
E S ¼ (10.6)
h
U 0 1 þ
R
where U 0 is the velocity of air entering the filter.
Finally, the efficiency of collection by diffusion is given by Eq. (10.7).

2

DR 3
E D ¼ 2:88 (10.7)
Uh
The efficiency of a model filter for various dust particle sizes is given in
Table 10.2 [4].
Experimental observations confirm that the net efficiency of all filters is usually
greater than the efficiency for any one mechanism but is less than their arithmetic
sum. It is also clear that the filter efficiency must tend to 1 (100% collection) for
very large and very small particles. The curve of efficiency, E, against particle radius,
r, therefore must have a minimum for some value of r ¼ r min , where r min decreases as
the flow velocity increases. A r min of 0.15 mm appears to be the most common exper-
imental value [5,6].

10.3 Dust Control in Continuous Miner Section

A continuous miner is the machine used to drive tunnels/roadways in a mine to create
mains, gate roads, and longwall panels. All four techniques to control respirable dust
(discussed earlier) have been used, but premining infusion of the coal seam is not
commonly done because of high cost. Most common dust control techniques comprise
use of water sprays to suppress dust, use of water scrubbers in most cases, and
adequate ventilation to dilute the respirable dust concentrations below statutory limits.

Table 10.2 Efficiency of a Model Filter (%)

U 0 [ 1 cm/s U 0 [ 20 cm/s
Particle Radius (mm) E i E h E S E D E i E h E S E D
0.01 0 0 0 1 0 0 0 1
0.1 0.03 0.02 0.01 0.95 0.43 0.02 0 0.33
0.3 0.17 0.16 0.06 0.67 0.97 0.16 0 0.14
1.0 0.8 0.86 0.41 0.35 1 0.86 0.03 0.06
3.0 1 1 1 0.17 1 1 0.2 0.03

Assumptions: Fiber radius ¼ 10 mm; Filter thickness ¼ 0.2 cm; h/R ¼ 0.7.