Page 103 - Advances In Productive, Safe, and Responsible Coal Mining

Mine ventilation networks optimized for safety and productivity 87

3
US coal mining regulations require a minimum air quantity of 1.4m /s (3000cfm)
3
in each heading; 4.2m /s (9000cfm) in each heading while active mining is going on;
3
and 14m /s (30,000cfm) at each longwall face. In most practical mining applications,
these minimum quantities are exceeded by a factor of 2–4 in order to meet dilution
specifications for methane and dust.
Many continuous miner sections use auxiliary exhaust fans to provide additional
air quantity in the active face and to exhaust methane and dust directly to the return
airway. Each continuous miner and longwall section must be ventilated on a separate
split of fresh air, and return air from one section must not be used to ventilate another
mining section. This is in stark contrast to European mining systems that use single-
entry gate roads and may operate gate development ahead of the longwall face on the
same split of air. Even in this case, these combined operations must still meet statutory
requirements for methane, dust, and other contaminants.
Unlike for coal mines, US regulations do not provide for specific minimum ven-
tilation quantities for underground metal and nonmetal mines. Dust and contaminant
regulations are similar, though, and if mines release flammable gases, limitations sim-
ilar to coal mines apply.

6.4.1 Methane control

Most underground coal operations cannot dilute the methane released from the coal
seam by ventilation alone. These mines actively drain methane prior to, during, and
after mining. Coalbed methane (CBM) drainage is accomplished through the follow-
ing methods:
l Methane drainage boreholes drilled into the coal seam from the surface: Often, multiple ver-
tical holes are drilled from a single location and are deflected 90° into a horizontal “daisy”
pattern once they reach the coal seam. Within the coal seam, holes are often “fracked” to
improve gas flow. Some mines establish pipeline networks at the surface to capture the
extracted methane and sell it.
l In-seam gas drainage holes drilled from underground locations: Methane drainage from
underground boreholes is also common in the industry. In seam drilling is usually easier,
but underground gas drainage lines must be closely monitored for leakage.
l Roof and floor drainage holes: Often, coalbed methane that has penetrated roof and floor
strata seeps out into mine openings, particularly if these strata are porous or contain cracks
or fissures. Drainage can be accomplished by drilling from the underground workings or
from the surface and, if necessary, fracking the strata.
l Gob ventilation boreholes: Longwall gob areas often fill with methane and must be drained,
along with methane accumulations in the hanging wall strata. Often, rider coal seams above
the mined horizon are broken up in the subsidence process as the longwall gob forms releas-
ing additional methane into the gob area that requires drainage.

6.4.2 Continuous miner dust control

Respirable dust with particles sizes below 10μm can lead to lung diseases, including
coal miners’ pneumoconiosis (CWP), also known as black lung disease, silicosis, and
other debilitating respiratory illnesses. Recent reports [3] indicate a resurgence in