Page 189 - Advances In Productive, Safe, and Responsible Coal Mining

168 Advances in Productive, Safe, and Responsible Coal Mining

on the competitiveness of any individual coal-mining operation that implemented
OSD control measures. Similarly, widespread adoption of OSD control measures
improves the competitiveness of the entire coal industry.
It can be seen that productivity losses resulting from OSD mining have the greatest
impact on cost followed by quality deterioration due to OSD quality impacts. Addi-
tional costs incurred due to OSD in order of importance are processing and waste dis-
posal costs. There is general industry recognition of OSD impacts on productivity,
processing, and waste disposal; however, the cost of quality deterioration due to
the impact of OSD is a matter that has received little attention from the industry. It
is hoped that increasing understanding of the quality impact will provide the needed
incentive for coal mine operators to pay more attention to and increase efforts aimed at
minimizing OSD.

9.4 Controlling OSD

The first step in controlling OSD is to understand what causes it. Each mining oper-
ation has its own issues; however, OSD in ROM coal is principally a factor of either
weak roof and floor strata or coal seam height. In many cases, both of these factors are
involved. Chugh et al. [16] identified the most common causes of OSD as follows:
1. Poor roof and floor conditions due to weak or disturbed geology in the region of mining. This
cause is generally beyond the control of mine workers and results in unintentional extraction
of OSD.
2. Low coal seam heights that may occur universally throughout a mine or unexpectedly in
isolated areas. While seam height cannot be controlled, OSD produced from this cause is
typically discretionary in that it results from mining equipment operators cutting into the
roof or floor to gain height for operator comfort or equipment clearance (which overlaps with
the next cause) when marginal seam heights of 4–5ft (1.2–1.5m) are encountered. This is
termed operational OSD.
3. Larger and heavier equipment, which create one or both of the following effects:
a. Roof strata must be extracted to provide for increased clearance requirements.
b. Damaged weak floor strata are mixed with loose coal during cleanup operations.
OSD produced from this cause is termed engineered OSD in that it results from mine
plans and equipment designs that are engineered to maximize production capacity.
4. As just explained, not only high-capacity production systems generate engineered OSD, but
also they cause operational and unintentional OSD as described in the following examples:
a. Deep cuts tend to inhibit the mining machine operator’s ability to see the cutterhead and
discern if it is within the coal seam.
b. Advanced haulage systems give the mining machine operator less time for positioning the
machine and checking horizon control.
c. Modern coal processing systems have led to the perception that mining a clean product is
no longer important because any dilution will be removed during processing. This has
already been shown to be a gross misperception.
Considering that unintentionally produced OSD is beyond control given current tech-
nology (i.e., extractive equipment and mining methods), efforts to control OSD have
and should focus on operational and engineered OSD. Operationally, produced OSD is