Page 194 - Advances In Productive, Safe, and Responsible Coal Mining

Out-of-seam dilution: Economic impacts and control strategies 173

9.4.2 Advanced engineering controls for reducing OSD

Two critical aspects of controlling OSD are alignment of the continuous miner in the
face area and guidance of the machine during cutting. Efforts to automate those func-
tions are discussed in this section. An essential component of any automated coal-
mining method is seam-following technology. This is usually achieved through
detecting the coal-rock interface. Multiple coal-rock interface detection (CID) tech-
nologies have been developed for this purpose [19]. A few common and viable
(for Illinois Basin coal) options are briefly described. The National Mining Associa-
tion and the Office of Industrial Technologies of the US Department of Energy have
identified horizon sensing as a critical technology that should be a priority for future
coal-mining-related research.

9.4.2.1 Natural gamma radiation (NGR)

NGR is the most advanced CID technology with more than 150units employed
around the world [20]. This method works on the principle that shale, clay, silt,
and mud have higher levels of naturally occurring radioactivity than coal due to their
containing small quantities of radioactive potassium (K-40), uranium, and thorium.
Measured NGR decreases exponentially as a function of coal thickness; thus, atten-
uation of the NGR sensor toward coal can be used to measure coal thickness between
the sensor and the rock interface. NGR technology has many features that make it a
viable option in automated mining operations. It can measure coal thicknesses from
1.0 to 20in. (2.5–50cm). The unit is compact and easily mounted on mining
machines. It has a display panel that is easyto readbyoperators usingremotecontrol
devices. The most prevalent applications to date have been on longwall units. There
are a few inherent weaknesses that arise from distribution of radioactive material in
the coal seam. For example, NGR levels vary from seam to seam requiring units to
be calibrated for each seam in which they will be used. A related issue is that NGR
levels can vary within a seam depending on levels of radioactive constituents present
at the time of geologic deposition. Also, rock partings (in-seam dilution) can show
false seam boundaries. The applicability of NGR systems in Illinois may be limited
since black shale is a typical immediate roof layer and it has radiation properties that
are similar to coal.

9.4.2.2 Vibration-based CID

When coal and rock are cut, different patterns of vibration are generated. By analyzing
these vibrations, the CID sensor can detect when the machine has started cutting
boundary rock instead of coal. Vibrations analyzed include machine vibrations,
in-seam seismic vibrations, and acoustic vibrations [21], with each having strengths
and weaknesses depending on the application. When analyzing machine vibration,
sensors can be mounted on the machine. This method has good potential when adap-
tive signal discrimination technologies are used to interpret vibration data. Feedback
is immediate when the machine starts to cut rock, so mining can be stopped with