All thermal power plants (including geothermal, solar thermal, biomass, coal-fired and even nuclear) produce waste heat as a by-product. The role of the cooling tower is to dissipate the waste heat, in order to allow the plants to operate efficiently.
There are two types of cooling towers: wet or dry. Wet cooling towers evaporate water into the air flowing through the tower. Dry cooling towers transfer heat from the power plant directly into the air.
Wet cooling towers are one of the largest consumers of water in power generation, due to evaporation loss, blow down water loss and drift water loss. A wet cooling tower for a 350 MWe coal-fired power plant, for example, consumes 5.5 billion litres of water per year.
In contrast, dry cooling towers save significant amounts of water by keeping the working fluid separated from the cooling air. However, these towers require more heat exchangers, and are also less efficient when ambient temperatures are higher.
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