DRY-COOLED AND HOT-HEADED

The steam exiting from a turbine condenses by contact with metal tubes holding cold water, which itself is kept cool by circulating through the cooling towers¾the high concrete structures with a hyperbolic profile that cartoonists, in their erudition, use as the frightening symbol of a nuclear plant. They probably think that an ambidextrous philanthropist is a man who has two legs (he does!), for cooling towers are not peculiar to nuclear plants; they are used wherever large quantities of reject heat must be dissipated, not only in fossil-fired power plants, but also in steel works and other plants that do not generate any electricity at all.

The heat rejected to the atmosphere from the cooling towers represents much of the energy loss in electric power generation¾two thirds of the input energy contained in the fuel. But in a country like South Africa, the method wastes something far more precious than energy: water. Long before the current African drought, water was a precious commodity, and "wet" cooling towers use 2.5 liters (0.66 gallons) of water for each produced kilowatt-hour of electricity.

For the giant 4,000 MW coal-fired plant now under construction in Kendal, it was therefore decided to use dry cooling, making Kendal the world's largest dry-cooled power plant. Dry cooling works much like the cooling system with a radiator in a water-cooled car engine: the cooling water is split up into many small streams and gives up its heat via a large metal surface (tubes with fins), without evaporating in direct contact with the air. This involves a far larger cooling surface, i.e. more cooling towers with more costly equipment¾no less than five times the cost of wet cooling. However, with the sharp increase of water costs in South Africa, the investment pays off, for it saves 130 megaliters a day¾about double the consumption of a nearby industrial town of 113,000 people.