A cooling towers is a heat rejection device that rejects waste heat to the atmosphere through the cooling of a water stream to a lower temperature. Cooling system may either use the evaporation of water to remove process heat and cool the working fluid to near the wet-bulb air temperature or, in the case of closed circuit dry cooling towers, rely solely on air to cool the working fluid to near the dry-bulb air temperature.
Common applications include cooling the circulating water used in oil refineries, petrochemical and other chemical plants, thermal power stations and HVAC systems for cooling buildings. The classification is based on the type of air induction into the tower: the main types of cooling towers are
-natural draft and
-induced draft.
Cooling towers vary in size from small roof-top units to very large hyperboloid structures (as in the adjacent image) that can be up to 200 metres (660 ft) tall and 100 metres (330 ft) in diameter, or rectangular structures that can be over 40 metres (130 ft) tall and 80 metres (260 ft) long. The hyperboloid cooling towers are often associated with nuclear power plants, although they are also used in some coal-fired plants and to some extent in some large chemical and other industrial plants. Although these large towers are very prominent, the vast majority of cooling towers are much smaller, including many units installed on or near buildings to discharge heat from air conditioning.
Power stations utilise a substantial amount of water in the generation of electricity. At a thermal power plant, such as TIPO, fuel is used to heat demineralised water to turn it to high pressure steam. This steam is used to spin turbines and generate electricity before being cooled by the cooling water, which flows through two condensers on either side of each of the steam turbines, and then returning to the boiler. It is this process that the cooling towers support – and it plays a pivotal role in the efficiency of electricity generation at TIPO.
To optimise water utilisation, some power stations cycle it. To do this, they have cooling towers, of which at TIPO there are 12. These large towers recover the warmed water, which then continues to be circulated where chemistry is permitting.