CFD STUDY ON HOT SPOT LOCATION IN LONGWALL GOB
Samuel Lolon, Univ. of Utah, Salt Lake City, UT
Felipe Calizaya, Univ. of Utah, Salt Lake City, UT
Introduction
Spontaneous combustion in underground coal mines
has become a serious problem particularly in the caved
area (gob). Recent statistic has shown that approximately
17% of total 87 underground coal mine fires in the United
States are attributed to spontaneous combustion (De Rosa,
2004). Spontaneous combustion results from a self-
heating process in exothermic conditions. The accumulated
heat, if not removed, is conducive to the rapid increase of
temperature and may result in mine fires or explosions.
It is well accepted that the interaction between oxygen
and coal substances is the main cause for spontaneous
combustion, while other factors such as pyrite, moisture,
and bacteria play a secondary role to the self-heating of
coal. Therefore, only coal oxidation is considered in this
study.
Coal oxidation occurs as coal comes into contact with
air. This process involves complex phenomena in terms of
heat transfer, chemical surface absorption, and energy
balance related to inherent properties of coal (Wang et al.,
2003). For simulation purpose, overall reactions can be
simplified as suggested by Mitchell (1990):
C + O2 CO2 + heat
[65
°
- 94
°
C]
(1)
CO2 + C 2CO + heat [100
°
- 150
°
C]
(2)
Stoichiometric reactions (1) and (2) show that 2.66 grams
of oxygen are required to oxidize 1.0 gram of carbon. Once
the temperature exceeds 100˚C, the reaction has little
chance to stop.
The crucial step in reducing spontaneous combustion
risk is locating the ignition point of spontaneous
combustion (hot spot). This information is useful in the
effort of developing a preventive method effectively. In
this study, this was conducted based on the best gathered
information: ventilation surveys conducted in an existing
longwall mine located in the western US; the laboratory
experiments performed on a physical gob model; a