Geology Reference
In-Depth Information
Induced mine gas flow
KEY
+
+
+
Suction hole
Communicating hole
Combustion gas present
Case: A
+
-
No combustion
gas present
+
+
-
Possible fire
location
Case: B
+
-
-
Case: C
Figure 16.4.1. Schematic of US Bureau of Mines communication testing for MFD. From Kim and Chaiken
1993, p. 43.
use of MFD at Carbondale was considered a test under nonideal conditions because (1) the emission rate of C
2
to
C
5
hydrocarbon gases from anthracite is low and does not exhibit strong temperature dependence, (2) many of the
boreholes were cased through the coal seams, (3) the borehole diameters and depths were such that half of the rated
pressure drop of the suction fan would be used to overcome pipe resistance, and (4) a large rock fracture that
bisected the region could limit the effectiveness of the communication tests. To overcome these conditions, the
change in the absolute concentration of CH
4
in baseline and communication samples was used as the index of
combustion. Two suction fans were connected in series to offset casing resistance and improve communication
between boreholes. Pressure and gas composition data indicated that the casing length and the fault did not affect
the diagnostic results.
The tests conducted at Carbondale located two large and five small heated zones (Figure 16.4.4.). The noncontig-
uous combustion zones included one region lying adjacent to an apartment building that had not been detected
using temperature and CO concentration measurements. The presence of hydrocarbon gas indicated that coal was
heated above the normal underground temperature; time-dependent temperature monitoring indicated that the areas
of combustion were moving uphill away from the apartment complex.
A
B
Figure 16.4.2. Photos of the US Bureau of Mines MFD system. A
—
Carbondale Pennsylvania: suction fan with
connection to suction borehole, B
Renton, Pennsylvania: instrumented borehole for temperature, pressure, and
gas measurements, with suction fan in the background. From US Bureau of Mines project photos, 1986.
—
