What is Cooling tower?

A cooling tower is a device that discharges waste heat to the atmosphere by cooling a coolant stream, usually a stream of water, to a lower temperature.Cooling towers can use the evaporation of water to remove process heat and cool the working fluid to near wet-bulb air temperature, or in the case of dry cooling towers, rely on air alone to cool the working fluid to near dry-bulb temperature. Bulbs using radiators air temperature.Common applications include cooling circulating water used in refineries, petrochemical and other chemical plants, thermal power plants, nuclear power plants, and HVAC systems used to cool buildings.Classified according to the way of entering the tower: the main types of cooling towers are natural ventilation and induced draft cooling towers.Cooling towers vary in size from small rooftop units to very large double-curved structures (as shown in the adjacent images), up to 200 meters (660 feet) in height and 100 meters (330 feet) in diameter, or rectangular Structures that can exceed 40 meters (130 feet) in height and 80 meters (260 feet) in length.Hyperboloid cooling towers are commonly associated with nuclear power plants,although they are also used in some coal-fired power plants and to some extent in some large chemical plants and other industrial plants.While these large towers are very conspicuous, the vast majority of cooling towers are much smaller and include many that are installed on or near buildings to remove heat from air conditioning.Cooling towers are also often perceived by the public as emitting smog or noxious gases, when in reality the emissions from these towers have no carbon footprint and consist only of water vapour.

Classification by use 

Heating, ventilation and air conditioning (HVAC):

HVAC (heating, ventilation, and air conditioning) cooling towers are used to dispose of ("reject") unwanted heat from the chiller.Liquid-cooled chillers are generally more energy efficient than air-cooled chillers because the tower water rejects heat at or near wet bulb temperature. Air-cooled chillers must reject heat at a higher dry bulb temperature and therefore have a lower average reverse Carnot cycle efficiency.In regions with hot climates, large office buildings, hospitals and schools often use one or more cooling towers as part of their air conditioning systems.Typically, industrial cooling towers are much larger than HVAC towers. HVAC uses cooling towers Pair a cooling tower with a liquid-cooled chiller or a liquid-cooled condenser.A ton of air conditioner is defined as the removal of 12,000 Btu (3.5 kW) per hour.The equivalent tonne on the cooling tower side actually rejects about 15,000 British thermal units (4.4 kW) per hour due to the additional waste heat equivalent of energy required to drive the chiller compressor.This equivalent ton is defined as the heat rejection of 3 US gallons per minute (11 L/min) or 1,500 lbs/hr (680 kg/hr) of water cooled to 10 °F (5.6 °C), which is equivalent to 15,000 imperial heat per hour unit (4.4 kW), assuming a chiller coefficient of performance (COP) of 4.0.This COP is equivalent to an Energy Efficiency Ratio (EER) of 14.

Cooling towers are also used in HVAC systems that have multiple water source heat pumps sharing a common piped water loop. In this system, whenever the heat pump works in cooling mode, the water circulating inside the water cycle takes heat from the condenser of the heat pump, and then uses an external cooling tower to take heat from the water cycle and discharge it to the atmosphere.In contrast, when the heat pump is operating in heating mode, the condenser draws heat from the circulating water and discharges it into the space to be heated.When the water circuit is used primarily to heat the building, the cooling tower is usually shut down (and may be drained or winterized to prevent freeze damage) and heat is supplied by other means, usually from a separate boiler.

Industrial cooling towers 

Industrial cooling towers are used to remove heat from various sources, such as machinery or heated process materials.The main purpose of large industrial cooling towers is to remove heat absorbed by power plants, oil refineries, petrochemical plants, natural gas processing plants, food processing plants, semiconductor plants and other industrial circulating cooling water systems.The cooling water circulation rate of a typical 700 MWth coal-fired power plant is about 71,600 cubic meters per hour (315,000 US gallons per minute).Equivalent to one cubic meter per second).If the same plant had no cooling towers and used once-through cooling water, it would require around 100,000 cubic meters per hour Large cooling water intake typically kills millions of fish and larvae per year as organisms affect intake measurement screen.Vast amounts of water have to be constantly returned to the ocean, lake or river and constantly resupplied to the factories.In addition, the discharge of large quantities of hot water may raise the temperature of the receiving river or lake to levels unacceptable to the local ecosystem.Elevated water temperatures can kill fish and other aquatic organisms (see heat pollution), or they can lead to increases in harmful organisms such as zebra mussels or invasive species of algae.The role of cooling towers is to dissipate heat into the atmosphere, where wind and air diffusion spread heat over a much larger area than hot water can in a body of water.Evaporative cooling water cannot be used for subsequent use (except when it rains somewhere), while only surface cooling water can be reused.Some coal-fired and nuclear plants located in coastal areas do take advantage of a single pass of seawater.But even there, offshore discharge water outlets need to be very carefully designed to avoid environmental problems.

Oil refineries also have very large cooling tower systems.A typical large refinery processes 40,000 metric tons of crude oil per day (300,000 barrels (48,000 cubic meters) per day) and circulates approximately 80,000 cubic meters of water per hour through its cooling tower system.The tallest cooling towers in the world are the two 202-meter (663-foot) cooling towers at the Kalisindh Thermal Power Station in Jalawal, Rajasthan, India.