Technical Information

In mid 2005, SIEMAG TECBERG (Pty) Ltd. (a 100 %-owned subsidiary of the German company SIEMAG TECBERG GmbH in Haiger) in Johannesburg, South Africa, received an order for the construction and supply of 4 complete three-chamber pipe feeder systems (P.E.S.) for the central air cooling of the MOAB KHOTSONG gold mine. With an exchange capacity of 60 MW, it is the largest unit worldwide. The gold-ore mine is located around 240 km to the south of Johannesburg and is owned by AngloGold Ashanti, South Africa.

In South-African mines, gold ore is mined at depths of up to -4,000 metres and then hoisted to the surface for processing. In the so-called gold reefs, the rock temperatures may be as high as 55 °C and more. The use of machinery below ground to increase production capacity further increases these temperatures. In addition, the humidity of the air is extremely high due to the high volumes of water required for drilling work. Depending on the location of the mine, the temperature of the ventilating air above ground at the shaft entry may also reach 32 °C in the summer months.

Some of the air being drawn in is pre-cooled above ground. However, when all these factors are taken into account, it is safe to say that work at the gold reefs would be completely impossible without a cooling system. In order to cool the working areas below ground down to below 30 °C effectively, large quantities of cooling water have to be prepared by refrigerating machinery above ground and then piped below ground. The three-chamber pipe feeder systems (P.E.S.) are installed close to the main shaft at levels of -1,200 and -2,400 metres.

According to the flow plan (overall cooling concept), the cooling-water volume of 2 x 1,150 m³/h is pumped at 1.5 °C through two insulated shaft pipes DN400, PN150 in each case from above ground to the two parallel three-chamber pipe feeder systems DN300, PN150 at level -1,200 m. After pressure compensation from 125 bar to 3 bar, the cold water (2 °C) is fed into the so-called cold-water dam at -1,200 m through the cold-water outlet of the P.E.S. At the same time, the warm water (25 °C) is piped in the opposite direction from the warm-water dam (level -1,200 m) through the low-pressure warm-water inlet of the P.E.S. for pressure adjustment from 3 to 125 bar, and then into the two shaft pipes DN400 for re-cooling above ground.

Both processes are carried out at energy-saving low pumping powers according to the “communicating pipes” principle. This substantially eliminates all the lifting work of the high-pressure pumps which have drive powers of approx. 3 x 2,500 kW.
In the South-African gold-mining industry, the high-pressure pumps are part of a mine’s standard safety equipment. The three high-pressure pumps remain switched off during P.E.S. cooling operations.

At the next state, the same process as described above takes place between the levels of -1,200 and -2,400 metres. For this project, SIEMAG TECBERG switched two P.E.S. systems in series for the first time in order to achieve a cooling capacity of 60 MW down to depths of -2,400 m while saving a high degree of energy.

In order to reach the -3,200 metre zone, two further P.E.S. systems are currently being planned for MOAB KHOTSONG.