Refrigeration

Harsh underground environmental conditions are mitigated by means of six York and two Sulzer 7 MW refrigeration systems on surface. Five of these units run continuously. In peak summer conditions this is increased to six or seven machines, with the balance available as standby capacity. The plant runs each day at 98% availability. The refrigerant used in units 1, 2, 7 and 8 is R134A and in units 3, 4, 5 and 6 is R22.

To meet underground ventilation requirements, a refrigeration plant with the capacity of 42 MW provides downcast air, chilled to 10°C, at 875 m³ per second. At the working face the average air velocity measures 0.8 m per second.

The chilled water circuit cools water to 5°C at the refrigeration plant, which then transfers partially to the surface bulk air coolers at the shaft, reducing air temperatures from nominal 25° to nominal 8° before transfer into the shaft and down into the workings. The remaining chilled water is fed underground in lagged pipes that feed to stope and development hydropower reticulation systems. In certain areas spot coolers are used.