60
2 Environmental Conditions in the Mine
2.6.5 Explosives
Heat released from explosives can be approximated from the explosion heat at
constant volume. This ranges from 3 MJ kg
−1 for explosive emulsions and heavy
ANFO, and 3.9 MJ kg
−1 for the ANFO, to 4.9 MJ kg
−1 for the aluminized ANFO
17 .
Of this released energy, approximately 50–95% eventually becomes heat. However,
not all of this heat will go directly to the air masses, because a large part first passes
into the rock, delaying the process. A smaller part is used as energy in the rock
fragmentation.
2.6.6 Heat of the Rock Mass
Rocks can experience temperature variations due to: (a) exposure to a mining atmosphere whose temperature is falling; (b) transfer of the rocks from one area inside
the mine to another one at a lower temperature; (c) evacuation of stored heat after
blasting.
If the temperature variation, the mass of exposed or displaced material and the
rock’s specific heat are known, it is possible to estimate the heat emitted by means
of Eq. 2.23:
q = ˙
mC p
T i − T f
(2.23)
where
• q: Rate of heat flow (kW) or heat (J).
• ˙
m: Mass flow rate (kg s
−1 ) or mass (kg).
• C p : Specific heat (kJ kg
−1 °C
−1 ). Frequent values for different types of rocks can
be found in Eppelbaum, Kutasov and Pilchin (2014).
• T i : Initial temperature (°C).
• T f : Final temperature (°C).
Exercise 2.2 A blasting of 30 m
3 of rock with a specific explosive consumption of
5 kg m
−3 is being carried out in a development end. It is estimated that 75% of all
the heat generated by blasting remains in the rock an hour after the blasting takes
place. Determine:
(a) The heat released by blasting, and
(b) The temperature increase experienced by the rock.
Data: Explosive heat at a constant volume: 3.5 MJ kg
−1 ; specific heat of the rock:
0.22 kcal kg
−1 °C
−1 .
17 Data extracted from the commercial catalogue of Maxam Ltd.
2 Environmental Conditions in the Mine
2.6.5 Explosives
Heat released from explosives can be approximated from the explosion heat at
constant volume. This ranges from 3 MJ kg
−1 for explosive emulsions and heavy
ANFO, and 3.9 MJ kg
−1 for the ANFO, to 4.9 MJ kg
−1 for the aluminized ANFO
17 .
Of this released energy, approximately 50–95% eventually becomes heat. However,
not all of this heat will go directly to the air masses, because a large part first passes
into the rock, delaying the process. A smaller part is used as energy in the rock
fragmentation.
2.6.6 Heat of the Rock Mass
Rocks can experience temperature variations due to: (a) exposure to a mining atmosphere whose temperature is falling; (b) transfer of the rocks from one area inside
the mine to another one at a lower temperature; (c) evacuation of stored heat after
blasting.
If the temperature variation, the mass of exposed or displaced material and the
rock’s specific heat are known, it is possible to estimate the heat emitted by means
of Eq. 2.23:
q = ˙
mC p
T i − T f
(2.23)
where
• q: Rate of heat flow (kW) or heat (J).
• ˙
m: Mass flow rate (kg s
−1 ) or mass (kg).
• C p : Specific heat (kJ kg
−1 °C
−1 ). Frequent values for different types of rocks can
be found in Eppelbaum, Kutasov and Pilchin (2014).
• T i : Initial temperature (°C).
• T f : Final temperature (°C).
Exercise 2.2 A blasting of 30 m
3 of rock with a specific explosive consumption of
5 kg m
−3 is being carried out in a development end. It is estimated that 75% of all
the heat generated by blasting remains in the rock an hour after the blasting takes
place. Determine:
(a) The heat released by blasting, and
(b) The temperature increase experienced by the rock.
Data: Explosive heat at a constant volume: 3.5 MJ kg
−1 ; specific heat of the rock:
0.22 kcal kg
−1 °C
−1 .
17 Data extracted from the commercial catalogue of Maxam Ltd.