Geology Reference
In-Depth Information
1988). Where it is plentiful and inexpensive, water is a desirable heat exchange medium because of its high heat
capacity and its latent heat of vaporization.
The Bureau used water injection with the suction-induced removal of heated gases in two projects. In theory,
when the water is injected into heated subterranean areas, it is converted to steam. Under the influence of an
exhaust fan, the steam is moved through the mine, absorbing more heat from the heated coal and roof strata. The
heated steam can be exhausted to the atmosphere or to a heat exchanger where its thermal energy can be used.
Calamity Hollow
During the cooldown phase of the Calamity Hollow Mine Fire Project (Chaiken et al., 1984), water was injected by
gravity flow through an array of 1-in hose and 2-in pipes. Prior to quenching, the average temperature of the exhaust
gas was 600°C. The system was operated at an injection rate of 7.6
3 gallons) per minute per borehole for 8
hours per day for 21 days. For an additional 10 days, the water was injected continuously. Over the 31 days, 10.6mL
(2.8 million gallons) of water was injected. The temperature of the exhaust was lowered to 162°C (Figure 16.5.4.),
and 75 648 million thermochemical calories (300 million BTU) of heat energy was released from the mine. The
estimated heat-removal efficiency was not high, 7 cal/g compared to the heat of vaporization of 540 cal/g. During the
operation of the system, much of the water was flowing out of the mine and was not reaching the burning material.
When the water injection rate was increased, the seepage rate also increased. However, the system achieved its
objective of cooling the combustion zone prior to excavation in a relatively short period of time.
-
11.4 L (2
-
Renton Mine Fire
Based on the Calamity Hollow project, an attempt was made to extinguish a fire in an abandoned mine at Renton,
Pennsylvania (Dalverny and Chaiken, 1988, 1991). Water was supplied by gravity to spray nozzles located at the
casing bottom in each borehole. In this configuration, the fan was operated for about 6 hours per day, 5 days per
week, at a water injection rate of ~3.8 L (1 gallon) per minute per borehole. After 4 months, the injection tubes were
reinstalled on the outside of the borehole casings, 0.3
2 ft) below the surface. In this arrangement, water
flowed down the casing and through the strata above the mine void. However, this modification did not improve
the cooling efficiency.
-
0.6m (1
-
700
12
Temperature
H
2
O Injection
600
10
500
8
400
6
300
4
200
2
100
0
0
0
5
10
15
Time (days)
20
25
30
35
Figure 16.5.4. Average exhaust temperature (°C) and cumulative water injection (10
6
L) versus time during a
quenching experiment at Calamity Hollow. From Chaiken et al. 1984, (Table 2).
