Getting to the bottom of ammonia usage in mining 

By Caixia Mao, Dec 09, 2014, 16:47 3 minute reading

Ammonia refrigeration technology is installed across the world in underground mines, which are considered to be an “extreme environment”. The climate friendly refrigeration technology has been applied in mines from South Africa to Poland, in safe and customised cooling solutions to overcome the increase in temperature associated with increasing depth, thereby ensuring miner safety.

As mines become deeper, the problems of heat in the workplace become more acute. For the mining industry the energy used to keep underground temperatures at tolerable levels is a key consideration. In practice ammonia is often used in the surface refrigeration plants due to its high COP and heat transfer, which offers significant reductions in operational costs. For example AngloGold Ashanti, one of the biggest mining corporations has installed ammonia refrigeration technology at its Mponeng gold mine in Gauteng in South Africa. In Poland, the JSW Group’s Borynia-Zofiówka-Jastrzębie coal mine also uses ammonia cooling.
Cooling systems in mining applications
In mining one of the biggest challenges is to provide a safe and cool enough environment for miners to work in. With gold and platinum mines that descend as far as 4km below surface, this is even more of a challenge. In this extreme environment, virgin rock temperature often exceeds 60°C, requiring sophisticated cooling methods and equipment to reduce temperatures. 
The systems employed usually incorporate different types of technologies to ensure a safe mine temperature, such as evaporative condensers, mechanical refrigeration plants, pre-cooling towers and bulk air coolers. The cooling systems typically work by sending ice or chilled water down into the mine to reduce the ambient mine temperature. 
Ammonia refrigeration hard ice solution for Mponeng gold mine 
At the Mpong mine in South Africa, one of the richest and deepest gold mines in the world, which reaches an average depth of 2.8km to 3.4km below surface, an innovative hard ice plant using plate ice makers and ammonia refrigeration screw compressor sets provides essential cooling. The refrigeration plant consists of six cell ammonia evaporative condensers from Tektower. 
As Stuart Loftus from Tektower explains, “In very deep or hot mines where the temperature can exceed 50°C, ice or chilled water cooling from the surface would not reduce the ambient temperature to a safe level, which means that a further cooling system would need to be installed underground to re-chill the water or ice coming from the surface.” 
For this reason ice is made by the ammonia refrigeration plant and sent down the mine into a dam. The cold melt water is then circulated the through air coolers. This is a much more energy efficient solution than a conventional chilled water refrigeration system because the latent heat capacity of a kilogram of ice means it can take up far more heat than a kilogram of cold water. 
The system offers significant savings in operational costs. Compared to a conventional water chiller plant, the hard ice systems offer savings of 6 788 kW per year in pumping power consumption. Compared to vacuum ice plants, the hard ice system offers savings of 581 kW per year in pumping power consumption.
Ammonia refrigeration for Polish coal mine
At the Borynia-Zofiówka-Jastrzębie coal mine in Poland, one the leading producers of high quality coking coal in Europe, two ammonia chillers from Geoclima form part of the surface cooling station. The system is designed to chill 300 mc/h of water from 29 °C down to 1,5 °C. 


By Caixia Mao

Dec 09, 2014, 16:47

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