Bulk air cooling for mining has traditionally been accomplished using evaporative
cooling in an open system, where fresh air picks up cold water vapor. Lowering the
temperature of moderately humid intake airflow with this method saturates the
fresh air with cold service water. Monetarily speaking, centralized bulk air cooling
systems are better. Logistically speaking however, distributed cooling systems are
more effective.
When we take into account the piping and extra pumping required, plus the
associated cost of construction in the underground environment, a network of
distributed coolers and heat exchangers becomes prohibitive for large footprint
operations. Requiring a surface cooling plant to supply cold service water to the
underground is taxing on the system and adds levels of complexity not usually
necessary. In reality, an open-loop trade-off exists wherein a combination of
centralized and distributed cooling coexist. Self-contained cooling systems, with
remote heat exchangers, are more attractive since the piping and pumps are not
required to connect these to a centralized cooling system.
Let's say that we take the water vapor added by evaporative systems out of the
equation. This infers that airflow can be cooled below the dew point, which is a
condition that evaporative systems cannot, by nature, transfer for extended
vertical distances. Closed-loop refrigerant systems can chill airflow, while
dehumidifying fresh air, which will allow cooled air to travel much further –
vertically speaking. A cost-effective closed loop refrigerant system would allow
mine operators to extend surface cooling potential to a much greater depth.
My dissertation’s research has investigated two renewable cooling systems for
underground mines. The first system I’ve designed uses tanks of propylene glycol
chilled during the cold of wintertime. The second system design uses ice formed
from snow blown in underground storage tunnels.
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