Page 212 - Advances In Productive, Safe, and Responsible Coal Mining

Coal mine methane: Control, utilization, and abatement 191

pre- and postdrainage systems to achieve enhanced safety, environmental mitigation,
and energy recovery.
Selection of horizontal boreholes, cross-measure boreholes, vertical boreholes, or
gob gas vent holes is somewhat dependent on the gassiness of the coal seam and the
fractured rock strata. The number of boreholes, their locations, and their
degasification durations can be changed based on site-specific factors [16].
Degasification techniques are mainly dependent on reservoir properties of coal
seams being mined. Good methane control planning depends on accurate information
on these reservoir properties and the total gas emission space created by mining oper-
ations [4]. Reservoir properties are highly dependent on the depth and rank of the coal
seam, which are good indicators of the gassiness, but direct measurement of gas con-
tent (amount of gas contained in a tonne of coal) is highly recommended. In general,
reservoir properties governing CMM emissions can be divided into two groups [4]:
(i) properties that determine the capacity of the seam for total gas production;
e.g., adsorbed gas and porosity, and (ii) properties that determine the rate of gas
flow; e.g., permeability, reservoir pressure, and diffusivity of coal.
Thakur et al. [2] summarized the advantages for coal seam degasification as
follows:
reduced CMM concentrations in the mine air leading to improved safety;
l
reduced air requirements and corresponding savings in ventilation costs;
l
l faster advance of development headings and economy in the number of airways;
l improved coal productivity;
l additional revenue from the sale of CMM;
l additional uses of degasification boreholes; e.g., water infusion to control respirable dust;
l exploration of coal seams to locate geological anomalies in advance of mining; and
l liberation of CMM into the atmosphere is avoided.

10.3.3 Auxiliary control measures

Ventilation has long been the primary means of controlling CMM emissions at the
mining face. However, as mining has progressed into gassier areas, supplemental
means have become of interest for continued safe and productive mining operations.
Ventilation models use predictions of CMM inflows in face areas and gate roadways
to help design systems that will prevent unwanted disasters. To develop these predic-
tive data, CMM is monitored by means of intermittent sampling with portable meth-
ane detectors and continuous monitoring with machine-mounted methane monitors.
Aside from improving the ventilation to reduce CMM accumulations in eddy
zones, the chance of a methane ignition can be reduced by directly addressing the igni-
tion source. When a shearer cutter bit strikes rock, abrasion from the rock grinds down
the rubbing surface of the bit, producing a glowing hot metal streak on the rock surface
behind the bit. The metal streak is often hot enough to ignite methane, causing a
so-called frictional ignition. There are many well-known methane ignition sources
in coal mines, ranging from frictional ignitions caused by cutting bits to electrical
sparks, roof falls, aluminum impacting on iron, smoking materials, explosives and
detonators, spontaneous combustion, and naked flames. In addition, Kissell [4]