Geology Reference
In-Depth Information
Water used
/kg coal (l/kg)
Particle size (mm)
Figure 18.1.6. Experimentally observed relationship between water required for suppression per burning coal
mass vs. particle size using a spray.
extinguished coal, T
w
is the initial temperature of the water, and C
p,w
and
λ
are the specific and latent heats of
water, respectively.
m
c
C
p
;
c
Δ
T
c
m
w
¼
ð
18
:
1
:
1
Þ
C
p
;
w
ð
100
T
w
Þþλ
The amount of water required is found to be approximately 0.5 l·kg
1
. This is the same order of magnitude as the
experimental results. The difference can be attributed to the effect of heterogeneous heat transfer, fluid flow and
adsorption of water by the coal.
Conclusions
T
he small-scale combustion and suppression behavior of smoldering coal has been studied in the laboratory. The
smolder reaction was characterized by maximum temperatures of 700-1000°C, which were seen to be independent
of particle size for particle larger than 15 mm. Time to ignition showed a minimum for particles around 30 mm in
diameter, with larger particles requiring longer times due to limited heat transfer from the igniter to the fuel.
Smaller particles were limited by oxygen transport through the coal.
Water was identified as an effective extinguishing agent and was used in small-scale tests. The extinguishing of
subsurface fires is dictated by the ability of the delivery method to reach the source of the fire. It was shown that in
small-scale tests, significant differences in extinguishing efficiency can arise due to the nature of the extinguishing-
agent application. Water was used because, as shown, the overall quantity of extinguishing agent required is large
and therefore cost must be kept low. The amount of water required was measured to be on the order of 1 to 2 liters
of water per kg of burning coal.
Additional work is required to determine the effects of scale on the reaction. Especially important is determining a
relationship which will allow the extrapolation of data from small-scale experiments to applications involving
subsurface coal fires in the field.
Acknowledgments
T
he assistance of José Garcia, Freddy Jervis, and Wolfram Jahn in undertaking the experiments is appreciated.
Conversations with José Torero were enlightening and added to the depth of this chapter. The Engineering and
Physical Sciences Research Council, International Fire Investigators and Consultants, and the Small Grants scheme
