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3.4 WATER CONSERVATION
3.4.1 Dry Cooling at Power Stations
Conventional coal-fired power stations operate on the principal of
converting thermal energy to electricity. Large quantities of waste heat
are generated and are dissipated to the environment by partially
evaporating water in a wet cooling draft tower. Even though this technique
is efficient, large volumes of water are lost to evaporation. To overcome
this loss of water, a recent innovation, known as dry cooling, is an
approach which dissipates the waste heat to the atmosphere through an
air-cooled heat exchanger. This technique operates on the principle of a
closed water circuit in which the water on one end is in contact with the
heat source and, on the other end, is in contact with an air cooling
system. The heat picked up from the heat source is dissipated in the air
Extent of Use
The Matimba Power Station in South Africa, run by the Electricity Supply
Commission (ESKOM), operates on this technology. This technique also being
introduced at ESKOM's three new power stations.
Level of Involvement
This technology may be utilised by power utilities who have trained,
skilled human resources.
The costs are the full investment costs for a new power station.
Effectiveness of theTechnology
The technique is five times more water efficient than conventional
wet-cooled techniques, and, therefore, significantly impacts water
conservation potentials within the power generation industry. The quantity
of water consumed per unit of electricity delivered is as little as 0.68
litres compared to 6 litres in older conventional stations, and 4 litres
in newer, wet-cooled stations.
This is an appropriate technology for use in regions prone to water
shortages, and which utilise thermal power stations as a source of energy.
No negative environmental impacts have been recorded.
Use of this technology limits the impact of droughts on power
production, and reduced the need to situate power station in close
proximity to rivers or other water sources.
This technology has an higher capital cost and is less efficient than
wet-cooled systems. Use of this technology also requires raw water of an
appropriate quality. This requirement may mean that an higher quality
feedwater be produced, which may required some degree of pretreatment.
This technique poses no cultural problems.
Further Development of the Technology
There is need for further study of the effect of heat exchanger height
on recirculation, which has been observed to be something of a problem in
Water Research Commission, Post Office Box 824, Pretoria
0001, South Africa.
Department of Water Affairs 1986. Management of the Water Resources
of the Republic of South Africa, Government Printer, Pretoria.
Department of Water Affairs 1987. Water - Meeting The Needs Of The
Nation: 1912- 1987. Seventy - Five Years Of Service To The Nation.
ESKOM (Electricity Supply Commission) 1987. Electricity Is The
Driving Energy Of Our Modern Society And The Power Behind The Growth Of
Van Der Elst, W.J. and E.O.G. Wilhelm 1991. Studies Of Hot Air
Recirculation In Power Station Forced Draught Cooling Systems. WRC
Report No. 335/1/91, Water Research Commission, Pretoria.