Page 139 - Advanced Mine Ventilation

120 Advanced Mine Ventilation

Table 8.6 The “n” and “k” Values for Various Ranks of Coal Particles (Below 37 mm)

Coal Type Density (gm/cc) n K (mm) Average (n)
Anthracite
Sample 1 1.6 0.88 20 (0.76)
Sample 2 1.6 0.89 18.5
Sample 3 1.5 0.52 11.5

Low-Volatile Bituminous
Sample 1 1.32 1.00 15.5 (1.05)
Sample 2 1.34 1.09 6.7

High-Volatile Bituminous A
Sample 1 1.28 1.20 16 (1.17)
Sample 2 1.31 1.21 16.5
Sample 3 1.35 1.12 15.5
Sample 4 1.32 1.20 13
Sample 5 1.34 1.16 11.8
Sample 6 1.38 1.15 14

High-Volatile Bituminous B
Sample 1 1.38 1.23 19 (1.23)

Lignite
Sample 1 1.40 1.15 14.5 (1.11)
Sample 2 1.43 1.06 13.3

As far as the growth of CWP is concerned, only a few elements, besides carbon,
play an important role; namely silicon and iron. Silica may play the most important
role. It occurs both as an oxide and in the crystalline form. Trydimite and cristobalite
forms of crystalline silica are more fibrogenic than alpha quartz. Most coal seams
contain less than 2% silica, but the coal mine respirable dust in US and British mines
contain 4%e5% silica [15,16]. Silica concentrations appear to increase as the coal dust
3
gets finer in size. The PEL for silica varies from 0.1 to 0.2 mg/m and generally ap-
pears adequate. Apart from the total concentration of silica, another important issue
is the bioavailability of silica. Balsaitis and Wallace [17] and Conner et al. [18]
have used electron microscopy coupled with energy-dispersive X-ray analysis to
explore the composition of silica particles and found that they were heavily occluded
with clay in lower rank coals, making lower rank coal dust less fibrogenic even if they
may have a higher total concentration of silica.