Geology Reference
In-Depth Information
Figure 2.2.1. Figure illustrating the general layout of a modern coal mine. Although incomplete in every detail, it
illustrates the mining methods and technology employed. Modified with permission from Consol Energy Inc. 1992
poster by Stanley Michalski, 2009.
As the title suggest, the advance longwall system mines the panel by advancing into the coal seam and
simultaneously developing the parallel entries moving farther away from the main entry. Retreat longwall
mining is the reverse of the advance longwall method and is used where unstable roof and floor conditions
exist throughout the mine. In retreat longwall mining, the parallel entries are first driven to the farthest limit
of the designated mining panel and a connection is made between the parallel entries before production
begins. Longwall mining then begins at the farthest or outer end of the panel and
back to the
main entry. The principal disadvantage of the retreat system is that lead time between driving the parallel
entries and coal production is much greater than in the advance longwall system in which coal production
can begin almost immediately. The tools, support system, and coal conveyance out of the mine are the same
for both methods. Mining is completed when the panel between the parallel entries has been completely
extracted.
“
retreats
”
Production costs per ton of coal are generally lower with the longwall method than with the room-and-pillar
method, due to fewer roof-control problems, lower roof-support costs, reduced maintenance costs, minimal
dust control cost, and a higher tonnage yield per man. Ventilation problems are also greatly reduced, as the
air must be coursed over only one working area. The room-and-pillar method of mining requires air to be
passed through several areas requiring a complex network of ventilation control devices. In addition, the
training of personnel for longwall mining can be accomplished more quickly than the training required for
the room-and-pillar method. About 50% of the underground coal mined in the United States today is by the
longwall-mining system (American Coal Council, 2008).
