Construction of Lethabo started in 1980. Extensive environmental studies
were conducted in accordance with Eskom's Environmental policy. It was
established that the rehabilitation programmes implemented as part of Eskom's
normal operations would contribute considerably to the restoration and
revaluation of the whole area.
The station comprises of six 618MW Production Units. A Production Unit
consists of one boiler, a turbine and generator. Power is produced at 20kV and
at 13.5kA and send to a step-up transformer where the voltage is increased to
275kV for efficient transmission.
The first set of Lethabo Power Station's six generating units went into
commercial operation in December 1985. The last of the generating sets were
commissioned in December 1990. A unique aspect of Lethabo is the unusually low
grade and quality of coal that is burnt in the power generation process. The
coal burnt has an average calorific value of about 16 MJ/kg. Very few power
stations can burn this quality of coal, with most boilers requiring coal fuel of
values in excess of 20 MJ/kg. At full load, the power station consumes about
50,000 tons of fuel per day.
The ash content of the coal ranges between 35% and 42%, which means that
the power station produces approximately 20,000 tons of ash per day. After
mining operations, the open pit is filled with spoils and over burden, which was
removed during mining. Ash is deposited onto this area to a level of 50 meters
above ground level. The ash dumps (mountains) are covered with 350mm of fertile
soil and revegitated, covered with grass.
During site clearing 350 hectares of Bluegum plantation had to be removed.
190,000 Bluegum trees were cleared over a period of five months. Removal of the
trees saw a significant increase in the underground water table. Due to this, a
very sophisticated piling foundation system for all the major structures were
required. The piles were installed in competent soil layers at depths of more
than 25 meters, and the top 15 meters of each pile was isolated from the upper
layers of heaving clays. In total, 11,000 piles were sunk and foundations were
then constructed on these piles. A 750mm void was left under the foundations to
allow for expansion and contraction of the underlying soils. At the time of
construction, the piling contract at Lethabo was the largest contract of its
kind in South Africa.
Lethabo Power Station is also termed a ZLED-station
(Zero-Liquid-Effluent-Discharge). This means that the whole station is a closed
system and no water from our processes are allowed to leave the power station
premises. An extensive water recycling and cleaning desalination is in
Tel: (016) 457-5111