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3.4 WATER CONSERVATION

3.4.1 Dry Cooling at Power Stations

Technical Description

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 contact section.

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.

Costs

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.

Suitability

This is an appropriate technology for use in regions prone to water shortages, and which utilise thermal power stations as a source of energy.

Environmental Benefits

No negative environmental impacts have been recorded.

Advantages

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.

Disadvantages

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.

Cultural Acceptability

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 these plants.

Information Sources

Contacts

Water Research Commission, Post Office Box 824, Pretoria 0001, South Africa.

Bibliography

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. Pretoria.

ESKOM (Electricity Supply Commission) 1987. Electricity Is The Driving Energy Of Our Modern Society And The Power Behind The Growth Of Tomorrow. Pretoria.

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.

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