underground dam at 2000 m below the
surface.
The following evaluates the potential
saving in pumping energy by
substituting ice for water.
Required water flow
First, the temperature rise of the water in
the vertical pipe should be accounted
for. In practice, the 5˚C water introduced
from the surface reaches the cold sink at
a temperature of approximately 13˚C.
If water is supplied at 13˚C to the
underground dam and if it is returned at
25˚C, then the mass flow of water (Mw)
required to fight a heat load (Q) of
15 MW is 299 l/sec.
1
For the same duty,
the required mass flow of ice (Mi) is only
36 kg /sec.
2
In other words, if ice is introduced
from surface, only 3100 short tpd must
be pumped-back instead of
25 800 short tpd of water.
Pumping energy saving
The required pumping power (P) is
according to the mass flow (M), the
elevation (H) and the pump efficiency
(ŋ), following the formula:
P = M x H/(367 x ŋ).
n
n
P is in kWe.
n
n
M in m
3
/h.
n
n
H is the water column in m.
n
n
ŋ is the water column in m x ŋ.
n
n
367 = 3600 sec. in one hour/g : 9.81.
Hence the power requirement, if it is
ice introduced from the surface, will be
940 kWe,
3
instead of 7820 kWe using
water.
4
The power saving is 6880 kWe
and the yearly energy saving is
59 443 000 kWh. At US$0.07/kWh, the
yearly saving represents over
US$4 million.
Surface ice cooling
system
In the following example, a 1200 short t
ice systemwas installed next to the shaft
head in the free state, and commissioned
in less than a month.
The property employs 3800 people
and mines to a depth of some 2400 m,
where the virgin rock temperature can
reach up to 50˚C. The mine operates
three shifts with a permanent presence
of hundreds of miners underground at
all times, who depend on refrigeration.
Without proper air-conditioning, it
would not be possible to stay
underground for long.
Ice is produced at the surface and
introduced into the centre of the mine at
a depth of 1800 m, to keep a large
reserve of cold water at 10˚C. This
2000 m
3
underground dam enables the
working environment, tools and
equipment to cool well under a 27˚C wet
bulb temperature.
By substituting water with ice, the
mine could decrease the mass flow
sevenfold . The estimated saving
exceeds 10 MW in pumping-power,
which equates to US$7 000 000/yr.
1300 short t modular ice plant.
A typical ice cooling system.
NB: the drawing shows two possible options that were not actually implemented in this
project: a heat recovery system to heat the top portion of the mine (for cold countries)
and an ice blender for pumping liquid ice along the haulages to the stope.
March 2016
|
World Coal
|
51
