Geology Reference
In-Depth Information
Figure 9.2.8. Gas collection technique using a stainless steel canister, South Canyon, Colorado. G.B. Stracher
extracting coal-fire gas from a borehole into a fire in an underground coal-mine tunnel at the South Cañon Number
1 Coal Mine fire, Colorado. Photo by Janet L. Stracher, 2004.
In Situ Chemical Analyses
A
number of portable gas analyzers are available from scientific-instrument-distributing companies for use in the
field, including instruments transportable by hand for quickly obtaining in situ analysis of a coal-fire gas
component. One limitation of these analyzers is that only a limited number of gases (typically from one to five)
may be analyzed for simultaneously. The accuracy of these instruments is a function of their design, and some are
only useful for determining the lower and upper compositional limits of a gas component.
One such instrument is manufactured by the Dräger Company (Figure 9.2.9). The Dräger system consists of a
hand-operated Dräger pump, Dräger tubes for the gases one wishes to analyze for, and a high-temperature gas
extraction line made of flexible Teflon
®
or some other material. There is a button and counter on top of the pump.
The counter records the number of times the pump has been pressed to extract a gas sample. Before a sample is
extracted, the button is pressed to reset the counter to zero. A Dräger glass tube for the gas one wishes to analyze
for is broken off at both ends with a small glass cutter on the bottom of the pump. Each tube has an arrow on it. The
end of the tube that the arrow points to is then inserted into the pump. The flexible gas extraction line is next
inserted over the other end of the Dräger tube. This gas extraction line is then inserted into a gas vent or fissure.
Then, the pump is pressed by hand and released. This sucks gas from the opening through the flexible extraction
line and into the tube. As the gas goes into the tube, it reacts with a chemical reagent in it. The reagent then changes
color from the top to the bottom (end in the pump) of the tube, i.e., if the gas analyzed for is present within
detection limits. Graduated scales on the side of the Dräger tube are used to read the gas concentration. If the pump
is pressed 1 time, the scale labeled
n
n
= 1 is read; if the pump is pressed 10 times, the scale labeled
= 10 is read;
and so on.
Several portable mercury analyzers on the market, including the RA-915+ mercury analyzer (Figure 9.2.10), are
useful for the measurement of Hg emissions at coal-fire gas vents. This instrument is currently in use for studying
