Cooling Towers 101

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Eliecer Brathwaite

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Aug 3, 2024, 4:30:11 PM8/3/24

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When the water and air meet, a small amount of water is evaporated, creating a cooling action. The cooled water is then pumped back to the condenser or process equipment where it absorbs heat. It will then be pumped back to the cooling tower to be cooled once again. Cooling Tower Fundamentals provides a level of basic cooling tower knowledge and is a great resource for those wanting to learn more.

Because of this vertical airflow, it is not possible to use the open, gravity-flow basins typical in crossflow designs. Instead, counterflow towers use pressurized, pipe-type spray systems to spray water onto the top of the fill.

Field-erected cooling towers (FEP) Field-erected towers are primarily constructed at the site of ultimate use. All large cooling towers, and many of the smaller towers, are prefabricated, piece-marked, and shipped to the site for final assembly. The manufacturer usually provides labor and supervision for final assembly. Field-erected towers can be crossflow or counterflow, depending on the application. For power and heavy industrial applications, the field-erected Marley F400 counterflow tower can be customized to meet your exact specifications for performance, structure, drift and plume abatement.

SPX Cooling Tech, LLC is a leading global manufacturer of cooling towers, evaporative fluid coolers, evaporative condensers and air cooled heat exchangers. For a century, we have provided exceptional quality equipment and service to the HVAC, process cooling, industrial, and refrigeration markets.

A cooling tower is a device that rejects waste heat to the atmosphere through the cooling of a coolant stream, usually a water stream, to a lower temperature. Cooling towers may either use the evaporation of water to remove heat and cool the working fluid to near the wet-bulb air temperature or, in the case of dry cooling towers, rely solely on air to cool the working fluid to near the dry-bulb air temperature using radiators.

Common applications include cooling the circulating water used in oil refineries, petrochemical and other chemical plants, thermal power stations, nuclear 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.

Cooling towers vary in size from small roof-top units to very large hyperboloid structures 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. Hyperboloid cooling towers are often associated with nuclear power plants,[1] although they are also used in many coal-fired plants and to some extent in some large chemical and other industrial plants. The steam turbine is what necessitates the cooling tower. 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. Cooling towers are also often thought to emit smoke or harmful fumes by the general public, when in reality the emissions from those towers mostly do not contribute to carbon footprint, and consist solely of water vapor.[2][3]

Cooling towers originated in the 19th century through the development of condensers for use with the steam engine.[4] 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.[5] However the condensers require an ample supply of cooling water, without which they are impractical.[6][7] While water usage is not an issue with marine engines, it forms a significant limitation for many land-based systems.[citation needed]

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.[4][7] 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.[6][8]

A hyperboloid cooling tower was patented by the Dutch engineers Frederik van Iterson and Gerard Kuypers in the Netherlands on August 16, 1916.[9] The first hyperboloid reinforced concrete cooling towers were built by the Dutch State Mine (DSM) Emma in 1918 in Heerlen.[10] The first ones in the United Kingdom were built in 1924 at Lister Drive power station in Liverpool, England.[11] On both locations they were built to cool water used at a coal-fired electrical power station.

According to Gas Technology Institute (GTI) report, the indirect dew point evaporative cooling Maisotsenko Cycle (M-Cycle) is a theoretically sound method of reducing a fluid to dew point temperature which is lower than its wet bulb temperature. The M-cycle utilizes the psychrometric energy (or the potential energy) available from the latent heat of water evaporating into the air. While its current manifestation is as the M-Cycle HMX for air conditioning, through engineering design this cycle could be applied as a heat and moisture recovery device for combustion devices, cooling towers, condensers, and other processes involving humid gas streams.

In 2021, researchers presented a method for steam recapture. The steam is charged using an ion beam, and then captured in a wire mesh of opposite charge. The water's purity exceeded EPA potability standards.[13]

An HVAC (heating, ventilating, and air conditioning) cooling tower is used to dispose of ("reject") unwanted heat from a chiller. Liquid-cooled chillers are normally more energy efficient than air-cooled chillers due to heat rejection to tower water at or near wet-bulb temperatures. Air-cooled chillers must reject heat at the higher dry-bulb temperature, and thus have a lower average reverse-Carnot cycle effectiveness. In areas with a hot climate, large office buildings, hospitals, and schools typically use one or more cooling towers as part of their air conditioning systems. Generally, industrial cooling towers are much larger than HVAC towers.HVAC use of a cooling tower pairs the cooling tower with a liquid-cooled chiller or liquid-cooled condenser. A ton of air-conditioning is defined as the removal of 12,000 British thermal units per hour (3.5 kW). The equivalent ton on the cooling tower side actually rejects about 15,000 British thermal units per hour (4.4 kW) due to the additional waste heat-equivalent of the energy needed to drive the chiller's compressor. This equivalent ton is defined as the heat rejection in cooling 3 US gallons per minute (11 litres per minute) or 1,500 pounds per hour (680 kg/h) of water by 10 F (5.6 C), which amounts to 15,000 British thermal units per hour (4.4 kW), assuming a chiller coefficient of performance (COP) of 4.0.[14] 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 that share a common piping water loop. In this type of system, the water circulating inside the water loop removes heat from the condenser of the heat pumps whenever the heat pumps are working in the cooling mode, then the externally mounted cooling tower is used to remove heat from the water loop and reject it to the atmosphere. By contrast, when the heat pumps are working in heating mode, the condensers draw heat out of the loop water and reject it into the space to be heated. When the water loop is being used primarily to supply heat to the building, the cooling tower is normally shut down (and may be drained or winterized to prevent freeze damage), and heat is supplied by other means, usually from separate boilers.

Industrial cooling towers can be used to remove heat from various sources such as machinery or heated process material. The primary use of large, industrial cooling towers is to remove the heat absorbed in the circulating cooling water systems used in power plants, petroleum refineries, petrochemical plants, natural gas processing plants, food processing plants, semi-conductor plants, and for other industrial facilities such as in condensers of distillation columns, for cooling liquid in crystallization, etc.[15] The circulation rate of cooling water in a typical 700 MWth coal-fired power plant with a cooling tower amounts to about 71,600 cubic metres an hour (315,000 US gallons per minute)[16] and the circulating water requires a supply water make-up rate of perhaps 5 percent (i.e., 3,600 cubic metres an hour, equivalent to one cubic metre every second).

If that same plant had no cooling tower and used once-through cooling water, it would require about 100,000 cubic metres an hour[17] A large cooling water intake typically kills millions of fish and larvae annually, as the organisms are impinged on the intake screens.[18] A large amount of water would have to be continuously returned to the ocean, lake or river from which it was obtained and continuously re-supplied to the plant. Furthermore, discharging large amounts of hot water may raise the temperature of the receiving river or lake to an unacceptable level for the local ecosystem. Elevated water temperatures can kill fish and other aquatic organisms (see thermal pollution), or can also cause an increase in undesirable organisms such as invasive species of zebra mussels or algae.

A cooling tower serves to dissipate the heat into the atmosphere instead, so that wind and air diffusion spreads the heat over a much larger area than hot water can distribute heat in a body of water. Evaporative cooling water cannot be used for subsequent purposes (other than rain somewhere), whereas surface-only cooling water can be re-used.Some coal-fired and nuclear power plants located in coastal areas do make use of once-through ocean water. But even there, the offshore discharge water outlet requires very careful design to avoid environmental problems.