Geology Reference
In-Depth Information
Stracher 1995). The exhalation
condensation process is analogous to the way minerals form in fumarolic
environments (Lindgren, 1933; Stoiber and Rose, 1974; Smithsonian Institution, 2003). Using a four-step
analytical technique called thermodynamic loop analysis, Stracher (1995) derived a P
-
T stability diagram for
the condensation of orthorhombic sulfur from anthracite gas associated with the Centralia mine fire, Pennsylvania.
The significance of any such stability diagram is that it serves as an environmental indicator of conditions that tend
to favor the condensation of gaseous exhalations as opposed to the absorption of those exhalations into the
atmosphere. In addition, such diagrams reveal information about gas composition.
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Fortunately, thermodynamic data is available for additional condensates associated with the Centralia fires, as well
as coal fires in Russia. Consequently, the authors are currently deriving
stability diagrams for these materials.
In addition, samples collected from coal fires in La Plata County, Colorado, and condensates from Indonesia and
northern China have the potential to serve as environmental P
P
-
T
T indicators.
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Catastrophic Coal Fires
S
ome of the oldest, largest, most prevalent, and environmentally catastrophic coal fires in the world are described
below. Environmental hazards associated with these fires and techniques used to control them are briefly discussed.
Northern China
China leads the world in coal production (Table 6.1.1); with one-third of the global output, coal accounts for about
three-fourths of China
s total energy consumption (Williams, 1999; WCI, 2000). Its reserves are concentrated in the
Xinjiang Uygur and Ningxia Hui autonomous regions of northwest and north-central China, respectively. Coal
fires burning throughout these regions and across northern China (Figure 6.1.1) started by lightning, spontaneous
combustion, and mining operations on all scales. The fires were estimated to consume up to 200 million tons of
coal per year (Rosema et al., 1993; Discover, 1999) and may account for as much as 2
'
3% of the annual world
emission of atmospheric CO
2
from burning fossil fuels (Cassells and van Genderen, 1995; Zhang and Kroonen-
berg, 1996). More recent studies by Voigt et al. (2004) however, claim that 20 million tons of coal are consumed
each year in China by uncontrolled fires, while about 200 to 300 million tons of coal in China are inaccessible each
year because fires are an obstacle to mining operations.
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Xinjiang contains some of the largest untapped coal reserves in the world. Underground coal fires in the Liu
Huangou coalfield have been burning for over 20 years and possibly as long as 40 years. Chinese officials suspect
the fires started by accidents inside small illegal mineshafts dug by local farmers. Particulates and noxious gases
released by combustion are blown by winds over the region
'
s capital city, Urumqi (Figure 6.1.1), one of the 10
worst polluted cities in the world. The estimated cost of extinguishing the fires over a 4-year period is at least $10
million (the United States) (Wingfield-Hayes, 2000).
In the Rujigou coalfield of Ningxia, underground coal fires are responsible for land subsidence and the release of
hydrogen sulfide into the atmosphere (Discover, 1999). The length, width, and depth of surficial cracks induced by
subsidence are as much as several kilometers long, tens of meters wide, and hundreds of meters deep. These cracks
promote subsurface burning by providing a conduit through which oxygen can circulate to support combustion.
Subsidence due to underground fires in northwest China has been identified with thermal, microwave, and optical
satellite data (Prakash et al., 2000). Research using synthetic aperture radar (SAR) to identify subsidence has
yielded promising results (Prakash, 2003).
Optical and thermal images acquired by the Beijing Remote Sensing Corporation (BRSC) and heat measurements
from surface and subsurface detectors have been used to determine coal fire size, depth of greatest intensity, and
burning direction (Vekerdy et al., 1999; ITC, 2003, and references therein). Temperatures exceeding 800°C for
surface fires have been recorded with ground-based thermal detectors (Prakash and Gupta, 1999). Combining the
information acquired for numerous fires with Global Positioning System (GPS) and geologic data, ITC scientists in
cooperation with the BRSC, the Netherlands Institute of Applied Geoscience, and the Environmental Analysis and
Remote Sensing firm in the Netherlands designed the computer-based geographic information system, COAL-
MAN (Vekerdy et al., 1999, 2000). COALMAN is used to assist Chinese firefighters in the field by generating a
time series of firefighting maps and subsurface images of the fire. The COALMAN project was funded by the
