May 29, 2017

Ice cooling the most viable option for ultra-deep mines in Africa

Ice has become probably the most viable cooling option, if not the best option, as African mining goes ultra deep in search of ore, thanks, in great part to modern ice cooling technology.

Brisset Pierre, a French mine ventilation specialist, is not surprised at the growing niche of modern ice cooling technologies, as what are regarded as conventional systems  have limitations in the deep mining environment below 1000 metres.

“Heat and humidity are a constant issue and a limiting factor in underground mines. Moving deeper into a mine, the virgin rock temperature might exceed 60 degrees Celsius.  With the added heat of excavation, the working conditions become critical for mining personnel, with detrimental effects to their health, safety and performance.”

“The thermal limit for unimpaired cognitive performance stands below 28 degrees wet bulb. Beyond this threshold, productivity drops, while injury and heat stroke risks quickly rise. Hence, cooling plays a major role in strategy of underground mines,” Brisset notes.

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 becomes 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 temperature rise (heat gains related to pressure increase as air goes down, according to the Joule-Thomson effect.

Fortunately, modern ice cooling technology enables mines to achieve acceptable work conditions underground, enhance safety with productivity gains and provide impressive energy savings.

Says Brisset: “As it is colder than water and/or conditioned air and has a far larger mass cooling potential (latent heat of fusion 333kj/kg). It falls down a PVC pipe at a 2km in 90 second and still reaches the different mine levels at 0 degrees Celsius, with minimal heat loss.

“These unique properties make ice an attractive and energy-efficient cooling medium in the global deep-level cooling strategy, especially when implemented from the start.”

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