March 2016
|
World Coal
|
49
CHILLING
Pierre Brisset, KTI Piersch Kältertechnik, Germany,
describes the most recent
ice installations in mines and the positive results achieved.
T
he world’s deepest mines can
be found in South Africa.
Faced with the challenge of
increasing demand for more
ore at a cheaper cost, several mines have
resorted to ice technologies to manage
heat at lowmining levels. Modern ice
cooling systems enable mines to achieve
acceptable work conditions
underground, enhance safety with
productivity gains and provide
impressive energy savings.
Underground heat issues
and mine cooling
Heat and humidity are a constant issue
and a limiting factor in underground
mines. Moving deeper into a mine, the
virgin rock temperature may exceed
60˚C. With the added heat of
excavation, the working conditions
become critical for mine personnel,
with detrimental effects to their health,
safety and performance.
The thermal limit for unimpaired
cognitive performance underground
stands below 28˚C wet bulb. Beyond
this threshold, productivity drops,
while injury and heat stroke risks
quickly rise. Hence, cooling plays a
major role in the strategy of deep
underground mines.
Planning for ice in the
global mine-cooling
strategy
Mines can differ significantly and
therefore no one single cooling strategy
is applicable to all deep hot mines. The
best strategy often combines several air
and water cooling methods, sometimes
both at surface level and underground.
Below 1000 m, however, the air and
water-based cooling methods quickly
reach their limit. This is where ice
technology becomes a valid alternative
or complement.
As heat-loads increase with depth,
the heat-rejection capacities
underground become more limited. The
mass flow of water required to cool deep
mines – and the associated electricity
costs to pump it back – are huge.
Likewise, cold air circulation assumes
expensive airways. Furthermore, the
efficiency of surface chillers is impaired
by the thermal transfer between the
warm surrounding environment to the
lower levels (chilled water) and/or by
the auto-compression temperature rise
(heat gains related to pressure increase
as air goes down, according to the
Joule-Thomson effect).
Ice is colder than water and/or
conditioned air and has a far greater
mass cooling potential (latent heat of
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