BBE has conceptualised and designed a unique and innovative water thermal storage scheme for Impala Platinum in the North West province which promises to achieve significant power savings.  The challenge has been to introduce water thermal storage into the cooling systems on seven shafts using existing water storage dams for both hot and cold water storage at different times during the day.

Five of the shafts have dams where the hot and cold water is stored, relying on thermal stratification alone.  In these dams, the height to diameter ratio is such that the hot water remains above the cold with minimal mixing.  The shape of the other two shaft dams (shallow, large diameter) has required another means of keeping the hot and cold water separate.

Each dam has been fitted with five plasticised canvas bladders, with a combined capacity of 3 megalitres per dam, the largest measuring 30 m X 7 m (wide) X 6 m (high) when full.  The bladders are secured to the base of the dam and a piping system feeds and extracts the cold water in and out of the bladder while the hot water is fed and extracted from the surrounding space.

The capital costs for the simultaneous storage of hot and cold water in the same reservoir has been achieved at a fraction of the cost of a new dam.

Electrical operating costs are reduced by producing more cold water than is required during off-peak tariff periods, then switching the refrigeration machines off during the peak tariff periods of the day and using the stored cold water.  The saving is achieved through the tariff differential.