<P> 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 . </P> <P> 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 . </P> <P> Cooling towers originated in the 19th century through the development of condensers for use with the steam engine . Condensers use relatively cool water, via various means, to condense the steam coming out of the cylinders or turbines . This reduces the back pressure, which in turn reduces the steam consumption, and thus the fuel consumption, while at the same time increasing power and recycling boiler - water . However the condensers require an ample supply of cooling water, without which they are impractical . The consumption of cooling water by inland processing and power plants is estimated to reduce power availability for the majority of thermal power plants by 2040--2069 . While water usage is not an issue with marine engines, it forms a significant limitation for many land - based systems . </P> <P> By the turn of the 20th century, several evaporative methods of recycling cooling water were in use in areas lacking an established water supply, as well as in urban locations where municipal water mains may not be of sufficient supply; reliable in times of demand; or otherwise adequate to meet cooling needs . In areas with available land, the systems took the form of cooling ponds; in areas with limited land, such as in cities, they took the form of cooling towers . </P>

Why cooling tower is used in steam power plant
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