Салқындату мұнаралары: Жылуды атмосфераға тарату құрылғысы

Device which rejects waste heat to the atmosphere through the cooling of a water stream

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 tall and in diameter, or rectangular structures that can be over tall and long. 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. 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.

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. While water usage is not an issue with marine engines, it forms a significant limitation for many land based systems. 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. An American engineering textbook from 1911 described one design as "a circular or rectangular shell of light plate—in effect, a chimney stack much shortened vertically (20 to 40 ft. high) and very much enlarged laterally. At the top is a set of distributing troughs, to which the water from the condenser must be pumped; from these it trickles down over "mats" made of wooden slats or woven wire screens, which fill the space within the tower". The first hyperboloid reinforced concrete cooling towers were built by the Dutch State Mine (DSM) Emma in 1918 in Heerlen. The first ones in the United Kingdom were built in 1924 at Lister Drive power station in Liverpool, England. 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. 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. 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.

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 The equivalent ton on the cooling tower side actually rejects about 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 or of water by , which amounts to , 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 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. 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) 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 A large cooling water intake typically kills millions of fish and larvae annually, as the organisms are impinged on the intake screens. 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. Petroleum refineries may also have very large cooling tower systems. A typical large refinery processing 40,000 metric tonnes of crude oil per day ( per day) circulates about 80,000 cubic metres of water per hour through its cooling tower system. The world's tallest cooling tower is the tall cooling tower of the Pingshan II Power Station in Huaibei, Anhui Province, China.

These types of cooling towers are factory preassembled, and can be simply transported on trucks, as they are compact machines. The capacity of package type towers is limited and, for that reason, they are usually preferred by facilities with low heat rejection requirements such as food processing plants, textile plants, some chemical processing plants, or buildings like hospitals, hotels, malls, automotive factories, etc. Due to their frequent use in or near residential areas, sound level control is a relatively more important issue for package type cooling towers.

Facilities such as power plants, steel processing plants, petroleum refineries, or petrochemical plants usually install field erected type cooling towers due to their greater capacity for heat rejection. Field erected towers are usually much larger in size compared to the package type cooling towers. A typical field erected cooling tower has a pultruded fiber reinforced plastic (FRP) structure, FRP cladding, a mechanical unit for air draft, and a drift eliminator.

On 16 August 1916, Frederik van Iterson took out the UK patent (108,863) for Improved Construction of Cooling Towers of Reinforced Concrete. The patent was filed on 9 August 1917, and published on 11 April 1918. In 1918, DSM built the first hyperboloid natural draft cooling tower at the Staatsmijn Emma, to his design. Hyperboloid (sometimes incorrectly known as hyperbolic) cooling towers have become the design standard for all natural draft cooling towers because of their structural strength and minimum usage of material. The hyperboloid shape also aids in accelerating the upward convective air flow, improving cooling efficiency. These designs are popularly associated with nuclear power plants. However, this association is misleading, as the same kind of cooling towers are often used at large coal fired power plants and some geothermal plants as well. The steam turbine is what necessitates the cooling tower. Conversely, not all nuclear power plants have cooling towers, and some instead cool their working fluid with lake, river or ocean water.

Clean visible dirt & debris from the cold water basin and surfaces with any visible biofilm (i. e., slime). Disinfectant and other chemical levels in cooling towers and hot tubs should be continuously maintained and regularly monitored. Regular checks of water quality (specifically the aerobic bacteria levels) using dipslides should be taken as the presence of other organisms can support legionella by producing the organic nutrients that it needs to thrive.

Besides treating the circulating cooling water in large industrial cooling tower systems to minimize scaling and fouling, the water should be filtered to remove particulates, and also be dosed with biocides and algaecides to prevent growths that could interfere with the continuous flow of the water.

Among the issues that cause the most damage and strain to a water tower's systems is scaling. When an unwanted material or contaminant in the water builds up in a certain area, it can create deposits that grow over time. This can cause issues ranging from the narrowing of pipes to total blockages and equipment failures. or Mycobacterium avium. The various Legionella species are the cause of Legionnaires' disease in humans and transmission is via exposure to aerosols—the inhalation of mist droplets containing the bacteria. Common sources of Legionella include cooling towers used in open recirculating evaporative cooling water systems, domestic hot water systems, fountains, and similar disseminators that tap into a public water supply. Natural sources include freshwater ponds and creeks. French researchers found that Legionella bacteria travelled up to through the air from a large contaminated cooling tower at a petrochemical plant in Pas de Calais, France. That outbreak killed 21 of the 86 people who had a laboratory confirmed infection. Drift (or windage) is the term for water droplets of the process flow allowed to escape in the cooling tower discharge. Drift eliminators are used in order to hold drift rates typically to 0.001–0.005% of the circulating flow rate. A typical drift eliminator provides multiple directional changes of airflow to prevent the escape of water droplets. A well designed and well fitted drift eliminator can greatly reduce water loss and potential for Legionella or water treatment chemical exposure. Also, about every six months, inspect the conditions of the drift eliminators making sure there are no gaps to allow the free flow of dirt. The US Centers for Disease Control and Prevention (CDC) does not recommend that health care facilities regularly test for the Legionella pneumophila bacteria. Scheduled microbiologic monitoring for Legionella remains controversial because its presence is not necessarily evidence of a potential for causing disease. The CDC recommends aggressive disinfection measures for cleaning and maintaining devices known to transmit Legionella, but does not recommend regularly scheduled microbiologic assays for the bacteria. However, scheduled monitoring of potable water within a hospital might be considered in certain settings where persons are highly susceptible to illness and mortality from Legionella infection (e. g. hematopoietic stem cell transplantation units, or solid organ transplant units). Also, after an outbreak of legionellosis, health officials agree that monitoring is necessary to identify the source and to evaluate the efficacy of biocides or other prevention measures. Studies have found Legionella in 40% to 60% of cooling towers.

Under certain ambient conditions, plumes of water vapor can be seen rising out of the discharge from a cooling tower, and can be mistaken as smoke from a fire. If the outdoor air is at or near saturation, and the tower adds more water to the air, saturated air with liquid water droplets can be discharged, which is seen as fog. This phenomenon typically occurs on cool, humid days, but is rare in many climates. Fog and clouds associated with cooling towers can be described as homogenitus, as with other clouds of man made origin, such as contrails and ship tracks. This phenomenon can be prevented by decreasing the relative humidity of the saturated discharge air. For that purpose, in hybrid towers, saturated discharge air is mixed with heated low relative humidity air. Some air enters the tower above drift eliminator level, passing through heat exchangers. The relative humidity of the dry air is even more decreased instantly as being heated while entering the tower. The discharged mixture has a relatively lower relative humidity and the fog is invisible.

Issues related to applied meteorology of cooling towers, including the assessment of the impact of cooling towers on the cloud enhancement were considered in series of models and experiments. One of the results by Haman's group indicated significant dynamic influences of the condensation trails on the surrounding atmosphere, manifested in temperature and humidity disturbances. The mechanism of these influences seemed to be associated either with the airflow over the trail as an obstacle or with vertical waves generated by the trail, often at a considerable altitude above it.

When wet cooling towers with seawater make up are installed in various industries located in or near coastal areas, the drift of fine droplets emitted from the cooling towers contain nearly 6% sodium chloride which deposits on the nearby land areas. This deposition of sodium salts on the nearby agriculture/vegetative lands can convert them into sodic saline or sodic alkaline soils depending on the nature of the soil and enhance the sodicity of ground and surface water. The salt deposition problem from such cooling towers aggravates where national pollution control standards are not imposed or not implemented to minimize the drift emissions from wet cooling towers using seawater make up. Respirable suspended particulate matter, of less than 10 micrometers (μm) in size, can be present in the drift from cooling towers. Larger particles above 10 μm in size are generally filtered out in the nose and throat via cilia and mucus but particulate matter smaller than 10 μm, referred to as PM10, can settle in the bronchi and lungs and cause health problems. Similarly, particles smaller than 2.5 μm, (PM2.5), tend to penetrate into the gas exchange regions of the lung, and very small particles (less than 100 nanometers) may pass through the lungs to affect other organs. Though the total particulate emissions from wet cooling towers with fresh water make up is much less, they contain more PM10 and PM2.5 than the total emissions from wet cooling towers with sea water make up. This is due to lesser salt content in fresh water drift (below 2,000 ppm) compared to the salt content of sea water drift (60,000 ppm). recommend that combustible cooling towers be provided with an automatic fire sprinkler system. Fires can propagate internally within the tower structure when the cell is not in operation (such as for maintenance or construction), and even while the tower is in operation, especially those of the induced draft type, because of the existence of relatively dry areas within the towers.

Being very large structures, cooling towers are susceptible to wind damage, and several spectacular failures have occurred in the past. At Ferrybridge power station on 1 November 1965, the station was the site of a major structural failure, when three of the cooling towers collapsed owing to vibrations in winds. Although the structures had been built to withstand higher wind speeds, the shape of the cooling towers caused westerly winds to be funneled into the towers themselves, creating a vortex. Three out of the original eight cooling towers were destroyed, and the remaining five were severely damaged. The towers were later rebuilt and all eight cooling towers were strengthened to tolerate adverse weather conditions. Building codes were changed to include improved structural support, and wind tunnel tests were introduced to check tower structures and configuration.