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128 Advanced Mine Ventilation

Figure 9.2 Schematic diagram of a Bleuler rotary mill.

a Ro-Tap shaker for 10 minutes to obtain samples for experimentation. The minus 400
mesh (37 mm) material was carefully weighed to 0.1 gm. Three grindings were done
for each sample, and an average yield of 37 mm particles was determined. Later,
the three samples were mixed and used for experimentation.

9.3 Yield of Respirable Dust

The observations made and the calculated data obtained for all 18 coal samples are
shown in Table 9.3. For each sample of coal, the yield of 37 mm particles is shown
in the first three columns. The average yield of 37 particles is shown in the fourth
column.
The maximum respirable size is taken as 10 mm equivalent diameter in conformity
with standards of the Atomic Energy Commission, United States. The corresponding
1/2
Stoke’s diameter for a given coal type is given by 10/(r) , where r is the density of
coal.
This maximum respirable size was calculated for each coal type. This is shown in
Table 9.3. Corresponding to this maximum respirable size, the percentage weight of
undersize material is obtained from the respective graphs of mass distribution
discussed in Chapter 8. A typical calculation of total yield of respirable dust is given
as follows:
From sample number 1:
Average yield of 37 mm particles ¼ 67.3%.
Maximum respirable size for sample number 1 ¼ 10/(r) 1/2 ¼ 10/(1.569) 1/2 ¼ 8.00 mm.