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Out-of-seam dilution: Economic impacts and control strategies 165

Table 9.3 Summary of percent increases in ash, sulfur, and trace
element concentrations in clean coal due to OSD mining

Mine and Yield Ash S As Hg Pb Se
unit
Mine 1 #1 0.23 0.11 0.33 0.68 0.55 1.39 0.05
Mine 1 #2 1.09 7.60 0.95 7.45 5.99 1.49 30.3
Mine 1 #4 0.56 1.59 0.54 3.31 0.77 1.01 13.5
Mine 1 #5 0.00 0.00 0.00 0.00 0.00 0.00 0.00
Mine 2 #1 5.33 22.5 17.6 24.78 3.76 6.62 4.70
Mine 2 #3 10.09 44.3 0.29 15.51 2.71 23.77 143
Mine 2 #4 7.03 4.73 0.96 23.40 0.67 6.12 118
Mine 3 #W 0.18 0.06 0.03 0.61 0.01 0.13 2.06
Mine 3 #2 0.46 0.13 0.05 0.30 0.09 0.07 0.23
Mine 4 2.86 3.90 1.29 10.46 3.04 1.08 19.6
#EHG
Mine 5 #2 1.08 0.62 1.05 2.04 0.08 1.12 1.97
Mine 5 #W 5.38 17.8 3.05 63.71 32.59 24.44 258
Mine 5 #MS 1.18 0.12 0.91 1.37 0.59 2.53 0.06
Average 2.7 8.0 1.9 11.8 3.8 5.4 45.5

Cleaning simulated at 1.9 SG cut point.

and most trace element concentrations including Hg, As, and Se, which have been the
subject of potential environmental legislation.
The impact of OSD on clean coal quality is highly variable across different mines
and units. This is particularly true for mercury. The increase in mercury content from
OSD varied from as low as a fraction of 1% to as high as 33%. Overall, it appears that
even when OSD is eliminated and drastic reductions in some very undesirable trace
elements, such as mercury, do not occur, their concentration is nevertheless definitely
reduced. Due to extremely high mitigation and credit costs projected for these
elements, even small reductions have the potential to translate into large quality cost
savings. Associated reductions in heating value can also amount to significant penal-
ties. When these are avoided in combination with cost savings from eliminating OSD
mining that will be described in the next section, there is certainly sufficient incentive
to implement some form of OSD control.

9.3.2 Cost impacts of OSD

Once OSD impacts on product quality were understood, the effect of OSD on mine
economics was modeled for a “typical” Illinois coal mine using average OSD mining
characteristics, average OSD qualities, and average product quality changes due to
OSD as presented in Tables 9.2 and 9.3. Quality impacts were estimated separately
for OSD removed from roof and floor strata and include effects of reduced heating