Efficient mine cooling

Bluhm Burton Engineering (BBE) is currently implementing energy management ventilation and refrigeration systems for mines to reduce overall and to manage energy consumption. BBE's Director, Raymond Funnell, has underscored that there is a boom in the mining industry and that the building of new power stations addressing needs could take 10-15 years. Thus, for the next 15 years, the South Africa's power crisis is likely to get worse. Moreover, mines are going deeper, and more power will be needed for ventilation and refrigeration, thus aggravating the situation. In July 2007, BBE launched ventilation energy management projects at Impala Platinum, Kloof gold mine and Driefontein gold mine in South Africa. The firm is retrofitting existing surface fan stations with automatic inlet guide vane control. This approach allows the fans to operate at reduced flow during peak electrical demand periods, while still maintaining high efficiency. BBE recently completed an ice thermal storage system for the surface refrigeration installation at AngloGold Ashanti's Mponeng mine, near Carltonville. This system will maximize cooling during critical summer periods and reduce electrical costs in winter and midseason by minimizing electrical power consumption during the evening peak power tariff period. After extensive modifications, an existing refrigeration machine is used to cool glycol to temperatures as low as -7°C; this glycol is then pumped in closed circuit through a submerged coil bank comprising over 100 km of steel piping. Ice is formed on the submerged coil bank during standard and off-peak power tariff periods. This ice is then melted to provide cooling in order to reduce the load on all refrigeration machines during the peak power tariff period. Roughly 800 tonnes of ice are made and melted in a daily cycle. A world first in mining applications, the system is also generating significant energy savings. Thanks to a deviation in ambient temperatures during different times of the day, refrigeration duty ranges from 10 MW, for the peak daily condition, to only 5 MW during off-peak periods. By using ice-thermal storage to even out daily deviations, it is possible to use a smaller refrigeration machine for the average duty of about 7.5 MW and to reduce power consumption. The system can also be used for load-shifting during peak electrical demand.