Cooling tower

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A cooling tower is a heat rejection device that rejects exhaust heat into the atmosphere by cooling the water flow to a lower temperature. The cooling tower can use water evaporation to remove process heat and cool the working fluid to near wet bulb ball temperature or, in the case of a closed cooling tower circuit , rely only on air to cool the working fluid to near dry bulb temperature.

Common applications include circulating water cooling used in oil refineries, petrochemicals and other chemical plants, thermal power plants and HVAC systems to cool buildings. This classification is based on the type of air induction to the tower: the main type of cooling tower is the natural design and the design of the cooling tower.

Cooling towers vary in size from small roof units to very large hyperboloid structures (as in adjacent images) that can reach up to 200 meters (660Ã, ft) in height and 100 meters (330Ã, ft) in diameter, or rectangular structures that can be more than 40 meters (130 feet) high and 80 meters (260 feet) long. Hyperboloid cooling towers are often associated with nuclear power plants, although they are also used in some coal-fired power plants and to some extent in some other large chemical and industrial plants. Although this large tower is very prominent, most of the cooling towers are much smaller, including many units installed in or near buildings to release heat from the air conditioner.

Video Cooling tower

Histori

The cooling towers originated in the 19th century through the development of condensers for use with steam engines. The condenser uses relatively cold water, in various ways, to condense the vapor out of the cylinder or turbine. This reduces the back pressure, which in turn reduces steam consumption, and thus fuel consumption, while at the same time improving the power and recycling of boiler water. But condensers need enough cooling water supply, without which they are not practical. The consumption of cooling water by land and power plants is estimated to reduce power availability for most thermal power plants by 2040-2069. Although water use is not a problem with marine engines, this has become a significant limitation for many ground-based systems.

At the turn of the 20th century, several evaporative methods for recycling cooling water were used in areas that lacked raw water supplies, as well as in urban locations where municipal sewers may not have sufficient supplies; reliable when needed; or sufficient to meet cooling requirements. In areas with available land, the system takes the form of a cooling pond; in areas with limited land, such as in cities, they take the form of cooling towers.

The initial tower is positioned either on the roof of the building or as a free standing structure, supplied with air by fans or relying on natural airflow. An American engineering book from 1911 describes a design as "a circular or rectangular plate shell - in essence, the stack of many chimneys is shortened vertically (20 to 40 feet high) and very much enlarged laterally.On top is a set distributing troughs , which water from the condenser must be pumped, from this trickle down "mat" made of wooden slats or wire mesh screen, which fills the space inside the tower. "

A hyperboloid cooling tower was patented by Dutch engineers Frederik van Iterson and Gerard Kuypers in 1918. The first hyperboloid cooling tower was built in 1918 near Heerlen. The first in Britain was built in 1924 at the Lister Drive power plant in Liverpool, England, to cool water used in coal-fired power plants.

Maps Cooling tower

Classification using

Heating, ventilation and air conditioning (HVAC)

An HVAC cooling tower (heating, ventilation, and air conditioning) is used to dispose ("resist") unwanted heat from the chiller. Air-cooled chillers are usually more energy-efficient than air-cooled coolers due to heat rejection to the water tower at or near the wet-bulb temperature. Air-cooled chillers must reject heat at higher dry-bulb temperatures, and thus have a lower average Carnot-reverse cycle. In hot climates, large office buildings, hospitals, and schools typically use one or more cooling towers as part of their air conditioning system. Generally, industrial cooling towers are much larger than HVAC towers.

Use of HVAC from cooling towers to install cooling towers with water cooling or water cooling. A ton AC is defined as the removal of 12,000 BTU/h (3500 W). The ton equivalent on the cooling tower side completely rejects about 15,000 BTU/hour (4400 W) because the additional waste is equivalent to the heat of the energy required to drive the cooling compressor. This ton equivalent is defined as heat rejection in cooling 3 US gallons/min (1,500 pounds/h) of water 10Ã, Â ° F (6Ã, Â ° C), which amounts to 15,000 BTU/h, assuming coefficient of chiller performance (COP) 4.0. This COP is equivalent to the energy efficiency ratio (EER) 14.

Cooling towers are also used in HVAC systems that have several water source heat pumps that share a common pipe circle of water . In this type of system, the water circulating in the water circle removes heat from the heat pump condenser whenever the heat pump is working in cooling mode, then an externally installed cooling tower is used to remove heat from the water loop and refuse to the atmosphere. Conversely, when the heat pump works in warm-up mode, the condenser draws heat from the water loop and rejects it into the space to be heated. When the water loop is used primarily to supply heat to the building, the cooling tower is usually closed (and can be dried or frozen to prevent frozen damage), and heat is supplied in other ways, usually from a separate boiler.

Industrial cooling tower

Industrial cooling towers can be used to remove heat from various sources such as engine or heated process material. The main use of large industrial cooling towers is to remove heat absorbed in 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 industries. facilities such as in a distillation column condenser, for coolant in crystallization, etc. The cooling water circulation rate at a typical 700 MW coal-fired power plant with a cooling tower reaches about 71,600 cubic meters per hour (315,000 US gallons per minute) and circulating water requires a 5 percent water supply make-up rate (ie 3,600 cubic meters per hour).

If the same factory does not have cooling towers and uses water disposable cooling , it will need about 100,000 cubic meters per hour. A large cooling water intake usually kills millions of fish and larvae every year, as the organisms hit the intake screen. Large amounts of water should be returned to the sea, lake, or river, from where it was obtained and continuously supplied to the plant. Furthermore, the use of large amounts of hot water may increase the temperature of the receiving stream or lake to an unacceptable level for local ecosystems. Increased water temperatures can kill fish and other aquatic organisms (see heat pollution ), or it may also lead to the increase of undesirable organisms such as invasive species from zebra mussels or algae. A cooling tower serves to dump heat into the atmosphere otherwise and wind and diffusion of air spreads heat in a much larger area than hot water can distribute heat in the body of water. Evaporative cooling water can not be used for the next purpose (other than rain somewhere), whereas only surface water cooling can be reused. Several coal and nuclear-fueled power plants located in coastal areas make use of seawater once-through. But even there, offshore drainage requires a very careful design to avoid environmental problems.

Oil refineries also have a very large cooling tower system. A large refinery that usually uses 40,000 metric tons of crude oil per day (300,000 barrels per day) circulating about 80,000 cubic meters of water per hour through its cooling tower system.

The world's highest cooling tower is a 202 meter (663 feet) Kalisindh cooling tower in Jhalawar, Rajasthan, India.

src: azchemistry.com

Classification by building

Package type

This type of cooling tower is a factory that has been assembled before, and can be easily transported by truck, because they are a compact engine. The capacity of the 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 mills, some chemical processing plants, or buildings such as hospitals, hotels, malls, automotive factories etc.

Because it is often used in or near residential areas, sound level control is a relatively more important issue for packet cooling towers.

Type of erection area

Facilities such as power plants, steel processing plants, petroleum refineries, or petrochemical plants typically install cooling towers of type built in the field due to their greater capacity for heat rejection. Towers set up in the field are usually much larger in size than the package type cooling towers.

A cooling tower built in the field has a pioneered fiber-reinforced plastic (FRP) structure, FRP cladding, a mechanical unit for air draft, drift eliminator, and fill.

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Method of heat transfer

In relation to the heat transfer mechanism used, the main types are:

• the dry cooling tower operates with heat transfers through a surface separating the working fluid from ambient air, as in an air heat exchanger, utilizing convective heat transfer. They do not use evaporation.
• wet towers (or open circuit cooling towers ) operate on the principle of evaporative cooling. The working fluid and the evaporating liquid (usually water) are one and the same.
• a fluid cooler (or closed circuit cooling tower ) is a hybrid that passes the working fluid through a tube bundle, where clean water is sprayed and a draft induced by an applied fan. The resulting heat transfer performance is much closer to the wet cooling tower, with the advantage provided by a dry coolant to protect the working fluid from environmental exposure and contamination.

In wet cooling towers (or open circuit cooling towers), warm water can be cooled to lower temperature than the air-dry ball temperature, if air is relatively dry (see dew and psychrometric dots). When ambient air is drawn through the water stream, a small portion of the water evaporates, and the energy required to evaporate the water is taken from the remaining water remaining, reducing its temperature. Approximately 970 BTU of heat energy is absorbed for every pound of evaporated water (2 MJ/kg). Evaporation produces a saturated air condition, lowering the temperature of water processed by the tower to a value near the wet ball temperature, which is lower than the temperature of the dry bulb, a difference determined by the initial humidity of the ambient air.

To achieve better performance (more cooling), a medium called content is used to increase surface area and contact time between air and water flow. Splash Content consists of materials placed to disrupt the flow of water causing splashes. The contents of the film consist of thin sheets of material (usually PVC) that become the flow of water. Both methods create increased surface area and contact time between liquid (water) and gas (air), to increase heat transfer.

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Airflow generator method

In connection with drawing air through the tower, there are three types of cooling towers:

• Natural design - Utilize buoyancy through the high chimney. Warm and humid air naturally increases due to differences in density compared to dry and colder outer air. The warm, damp air is less dense than the drier air at the same pressure. The buoyancy of this humid air produces upward airflow through the tower.
• Mechanical design - Use a power-driven fan motor to force or draw air through the tower.
  • Induced draft - Mechanical draft tower with exhaust fan (at the top) that pulls air through the tower. Fans induce humid hot air out of discharge. This produces low in and out of high air velocities, reducing the possibility of recirculation where the discharged air flows back to the air intake. The fan/fin settings are also known as draw-through .
  • Force Concept - Mechanical draft tower with blower-type fan on the intake. Fan forced air into the tower, creating a high speed of entry and low exit air velocity. Low exit velocity is much more susceptible to recirculation. With the fan on air intake, the fan is more susceptible to complications due to freezing conditions. Another disadvantage is that forced draft design usually requires more horsepower motors than an equivalent design of induction. The benefit of design forced design is its ability to work with high static pressure. Such arrangements can be installed in more limited space and even in some indoor situations. This fan/fin geometry is also known as blow-through .
• Fan assisted draft nature - A hybrid type that appears like a natural draft setup, although airflow is aided by fans.

The hyperboloid cooling tower (sometimes mistakenly known as hyperbolic) has become the design standard for all natural design cooling towers due to structural strength and minimum use of materials. Hyperboloid form also helps in accelerating upward convective airflow, improving cooling efficiency. This design is popularly associated with nuclear power plants. However, this association is misleading, because the same type of cooling tower is often used in large coal fired power plants as well. In contrast, not all nuclear power plants have cooling towers, and some even cool their heat exchangers with lakes, rivers or seawater.

Thermal efficiency up to 92% has been observed in hybrid cooling towers.

src: enerconusantara.com

Categorization by air to water

Crossflow

Usually the initial and long-term costs are lower, mostly due to the pump requirements.

Crossflow is a design in which the air flow is directed perpendicular to the water flow (see diagram on the left). The air stream enters one or more vertical faces from the cooling tower to fill the filler. Water flows (perpendicular to the air) through the gravitational field. The air continues through the charging and thus passes the flow of water into the open trial volume. Finally, the fan forces air out into the atmosphere.

A distribution or a hot water basin consisting of a deep pot with a hole or a nozzle at the bottom is located near the top of the crossflow tower. Gravity distributes water through the nozzle evenly throughout the filler.

Advantages of crossflow design:

• Gravitational water distribution allows the pump and maintenance to be smaller when in use.
• The no-pressure spray simplifies the flow of variables.

Lack of crossflow design:

• More susceptible to freezing than a backflow design.
• Flow variables are useless in some conditions.
• More susceptible to dirt buildup in fill than counterflow design, especially in dusty or sandy areas.

Flowback

In a counterflow design, the airflow is directly opposite to the water flow (see diagram on the left). The first air stream enters the open area beneath the filler medium, and then arranged vertically. Water is sprayed through a pressurized nozzle near the top of the tower, and then flows downward through charging, in contrast to the airflow.

Advantages of counterflow design:

• Spray water distribution makes the tower more resistant to freezing.
• Water spray breakers make heat transfer more efficient.

Disadvantages of counterflow design:

• Usually the initial and long-term costs are higher, mainly because of the pump requirements.
• It is difficult to use variable water flows, since the spray characteristics can be negatively affected.
• Usually noisy, because the water level drops larger than the bottom of the contents into a cold water basin

General aspects

A common aspect of both designs:

• The interaction of air and water flow allows partial equalization of temperature, and evaporation of water.
• The air, now filled with water vapor, is removed from the top of the cooling tower.
• "Collection collection" or "cold water basin" is used to collect and hold cooled water after interaction with airflow.

Both crossflow and counterflow designs can be used in natural design and in mechanical cooling towers.

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Circuit balance of wet cooling material

Quantitatively, the material balance around the cooling and evaporative cooling tower systems is governed by operational variables of volumetric flow rate of make-up, evaporation and loss of windage, draw-off rate, and concentration cycle.

In the adjacent diagram, the water pumped from the tower basin is the cooling water supplied through the cooling and condenser processes at an industrial facility. Cold water absorbs heat from heat process streams that need to be cooled or condensed, and the heat absorbed warms the circulating water (C). Warm water returns to the top of the cooling tower and drips down on top of the filler inside the tower. When it drips down, it's ambient air contact rises through the tower either by natural drafts or by the forced concept of using large fans in the tower. The contact causes a small amount of water to be lost as windage/drift (W) and some water (E) to evaporate. The heat required to evaporate water comes from the water itself, which cools the water back to the original water basin temperature and then the water is ready for recirculation. The evaporated water leaves the salt dissolved behind in most of the unvaporated water, thereby increasing the concentration of salt in the cooling water circulation. To prevent the concentration of water salt becoming too high, some of the water is pulled/blown (D) to dispose. Fresh water make-up (M) is supplied to the tower basin to compensate for the loss of evaporated water, the loss of water of the wind and the water being withdrawn.

Using flow rates and units of this concentration dimension:

Water balance across the system then:

M = E D W

Karena air yang menguap (E) tidak memiliki garam, keseimbangan klorida di sekitar sistem adalah:

${\ displaystyle MX_ {M} = DX_ {C} WX_ {C} = X_ {C} (D W)}  ÂÂ$

dan maka dari itu:

${\ displaystyle {X_ {C} \ over X_ {M}} = {\ text {Cycles of concentration}} = {M \ over (D W)} = { M \ over (ME)} = 1 {E \ over (D W)}}  ÂÂ$

Dari keseimbangan panas yang disederhanakan di sekitar menara pendingin:

${\ displaystyle E = {C \ Delta Tc_ {p} \ over H_ {V}}}  ÂÂ$

Windage (or drift) losses (W) is the total amount of water flow towers trapped in airflow into the atmosphere. From large industrial cooling towers, without manufacturer data, it can be assumed as:

W = 0.3 to 1.0 percent C for natural draft tower without drift windage eliminator

W = 0.1 to 0.3 percent C for draft induction cooling towers without eliminator drift windage

W = about 0.005 percent C (or less) if the cooling tower has windage inhibitor eliminator W = about 0.0005 percent C (or less) if the cooling tower has a windage drift eliminator and uses sea water as make-up water.

Concentration cycle

The concentration cycle represents the accumulation of dissolved minerals in the recirculating coolant water. A draw-off (or blowdown) disposal is used primarily to control the buildup of these minerals.

Chemical make-up water, including the amount of dissolved minerals, can vary greatly. The low mineral make-up of dissolved minerals such as those from surface water supplies (lakes, rivers etc.) tend to be aggressive against metals (corrosive). Make-up water from groundwater supplies (such as wells) is usually higher in minerals, and tends to scale (mineral deposits). Increasing the amount of minerals in the water by cycling can make water less aggressive against piping; However, excessive mineral content can cause scaling problems.

As the concentration cycle increases, water may not be able to hold minerals in solution. When the solubility of these minerals has been exceeded they can precipitate as mineral solids and cause heat exchange and fouling problems in cooling towers or heat exchangers. The recirculating water temperature, piping, and heat exchanger surfaces determine whether and where the minerals will precipitate from the recirculating water. Often professional water treatment consultants will evaluate the make-up water and cooling tower operating conditions and recommend an appropriate range for concentration cycles. The use of water treatment chemicals, pretreatment such as water softening, pH adjustment, and other techniques can affect acceptable concentration cycle ranges.

The concentration cycle in most of the cooling towers typically ranges from 3 to 7. In the United States, many water supplies use well water that has significant dissolved solids levels. On the other hand, one of the largest water supplies, for New York City, has a fairly low surface rainwater source of minerals; cooling towers in the city are often allowed to concentrate on 7 or more concentration cycles.

Because higher concentration cycles represent less make-up water, water conservation efforts can focus on improving the concentration cycle. Highly processed recycled water can be an effective means of reducing the consumption of drinking water cooling towers, in areas where drinking water is scarce.

src: www.nsctpl.com

Maintenance

Surfaces with visible biofilms (ie, mucus) should be cleaned.

Disinfectants and other chemical levels in cooling towers and hot tubs should be maintained continuously and monitored regularly.

Regular water quality checks (especially aerobic bacteria levels) using dipslides should be taken because the presence of other organisms can support legionella by producing the organic nutrients needed to thrive.

Water treatment

In addition to treating cooling water circulation in large industrial cooling systems to minimize scaling and fouling, water must be filtered to remove particulates, and also biocides and algaecides to prevent growth that can interfere with continuous water flow. Under certain conditions, biofilms of micro-organisms such as bacteria, fungi and algae can grow very quickly in cooling water, and can reduce the heat transfer efficiency of cooling towers. Biofilms can be reduced or prevented by using chlorine or other chemicals. Normal industrial practice is to use two biocides, such as oxidizing and non-oxidizing types to complement each other's strengths and weaknesses, and to ensure a wider spectrum of attacks. In most cases, low-level biocide oxidation is continuously used, then alternating to periodic shock doses of non-oxidizing biocides.

Legal

Legionnaires'

Another very important reason for using biocides in cooling towers is to prevent the growth of Legionella, including species that cause legionellosis or Legionnaire disease, especially L. pneumophila, or Mycobacterium avium . Various species of Legionella are the cause of Legionnaires disease in humans and transmission through aerosol exposure - inhaling droplets containing bacterial mist. Legionella's common sources include cooling towers used in open-air recirculating evaporative cooling systems, domestic hot water systems, fountains, and similar spreaders utilizing public water supplies. Natural sources include freshwater ponds and creeks.

French researchers found that Legionella bacteria traveled up to 6 kilometers (3.7 miles) by air from a large contaminated cooling tower at a petrochemical plant in Pas-de-Calais, France. The epidemic killed 21 out of 86 people who had laboratory-confirmed infections.

Drift (or windage) is a term for water droplets from process streams that are allowed to pass in the exhaust of the cooling tower. Drift Eliminator is used to withstand the usual deviation rate to 0.001-0.005% of the circulating flow rate. A typical drift eliminator provides some changes in the direction of airflow to prevent water drops. Well designed and well-equipped drift removers can greatly reduce water loss and the potential for Legionella or exposure to water treatment chemistry.

The CDC does not recommend that health care facilities regularly test the Legionella pneumophila bacteria . Scheduled microbiological monitoring for Legionella is controversial because its presence is not necessarily a potential proof of disease. The CDC recommends aggressive disinfection measures to clean and maintain devices that are known to deliver Legionella , but do not recommend regularly scheduled microbiological tests for bacteria. However, scheduled monitoring of drinking water within the hospital may be considered in certain settings where people are particularly vulnerable to illness and death from Legionella infection (eg hematopoietic stem cell transplant unit, or solid organ transplant unit). Also, following the outbreak of legionellosis, health officials agree that monitoring is necessary to identify sources and evaluate the effectiveness of biocides or other preventive measures.

Studies have found Legionella in 40% to 60% of cooling towers.

• Windage or Drift - Water droplets made from cooling towers with exhaust air. The drift droplets have the same dirt concentration as the water entering the tower. The rate of irregularities is usually reduced by using devices such as baffles, called drift eliminators, where air must travel after leaving the charging zone and spray the tower. Drift can also be reduced by using a warmer towing temperature tower.

• Blow-out - Water droplets blown out of the cooling tower by the wind, generally at the air intake openings. Water may also be lost, in the absence of wind, through splashing or drizzling. Devices such as wind screen, louvers, splash deflectors and water switchers are used to limit this loss.

• Plume - The saturated exhaust airflow leaves the cooling tower. The clot is visible when water vapor contains condensation in contact with the cooler ambient air, like the air saturated in the fog of a person's breath on a cold day. Under certain conditions, the cooling tower blob may cause a haze of icing or icing to its surroundings. Note that the water that evaporates in the cooling process is "pure" water, in contrast to the very small percentage of drift droplets or water coming out of the airways.

• Draw-off or Blow-down - Part of the circulated water flow removed (usually discharged to the drain) to maintain the Total Dissolved Solids ( TDS) and other impurities at acceptable low levels. Higher TDS concentrations in solution can result from greater cooling tower efficiency. But the higher the concentration of TDS, the greater the risk of scale, biological growth and corrosion. The amount of blow-down is mainly determined by the measurement by the electrical conductivity of the circulating water. Biological growth, scaling and corrosion can be prevented by chemicals (respectively, biocides, sulfuric acid, corrosion inhibitors). On the other hand, the only practical way to reduce electrical conductivity is by increasing the amount of blowdown discharge and then increasing the amount of clean make-up water.

• Pounding for cooling towers , also called zero blow-down for cooling towers , is a process to reduce the need for water bleeding with residual solids significantly from system by activating water to hold more solids in the solution.

• Make-up - Water to be added to the water circulation system to compensate for water loss such as evaporation, current loss, blow-outs, blow-downs, etc.

• Noise - The sound energy emitted by the cooling tower and heard (recorded) at a certain distance and direction. Sound is generated by the impact of falling water, by the movement of air by fans, the fan blades move in structure, vibration, structure and motor, gearbox or belt drive.

• Approach - The approach is the temperature difference between the cooled water temperature and the wetbob temperature entering the inlet (twb). Since the cooling towers are based on the principles of evaporative cooling, the efficiency of the maximum cooling tower depends on the temperature of the wet ball in the air. The wet-bulb temperature is a type of temperature measurement that reflects the physical properties of a system with a mixture of gases and vapors, usually air and water vapor

• Range - This range is the temperature difference between the warm water inlet and the discharge of the cooled water.

• Contents - Inside the tower, charging is added to increase the contact surface as well as the contact time between air and water, to provide better heat transfer. Tower efficiency depends on selection and amount of filling. There are two types of charging that can be used:
  • Type fill movie (causes water to spread into thin film)
  • Splash type fill (break the falling water stream and interrupt vertical progress)

• Full-Flow Filtration - Full flow filtration constantly compresses particles from the entire system flow. For example, in a 100-ton system, the flow rate will be about 300 gal/min. The filter will be selected to accommodate the entire flow rate of 300 gal/min. In this case, the filter is usually installed after the cooling tower on the discharge side of the pump. Although this is the ideal filtration method, for higher flow systems it may be costly.

• Side Filtration - Stream-side filtering, though popular and effective, does not provide complete protection. By side-flow filtering, a portion of the water is filtered continuously. This method works based on the principle that continuous removal of particles will keep the system clean. Manufacturers usually bundle a flow-side filter on slip, complete with pump and control. For high flow systems, this method is cost-effective. Making sizing properly a side-stream filtration system is essential to get a satisfactory filter performance, but there is some debate about how to size the right side-stream system. Many engineers measure the system to continuously filter the cooling towers basin water to a level equivalent to 10% of the total circulating flow rate. For example, if the total system flow is 1,200 gal/min (400-ton system), a 120 gal/mnt side flow system is specified.

• Concentration cycle - The maximum multiplier allowed for the amount of other substances in the circulating water compared to the amount of these substances in the make-up water.

• Processed wood - Structural material for cooling towers that were largely abandoned about 10 years ago. This is still used occasionally because of low initial cost, regardless of short life expectancy. The life of processed timber varies greatly, depending on the operating conditions of the tower, such as the frequency of discontinuation, circulating water treatment, etc. Under appropriate working conditions, the estimated age of the structural members of the treated wood is about 10 years.

• Laundering - Loss of wood preservative chemicals by water-washing activities flowing through the wood-cooling tower.

• FRP Pultruded - A common structural material for smaller cooling towers, fiber-reinforced plastics (FRP) is known for its high corrosion resistance capability. FRP is produced with pultrusion technology, and has become the most common structural material for small cooling towers. It offers lower costs and requires less maintenance than reinforced concrete, which is still used for large structures.

src: www.baltimoreaircoil.com

Production of fog

Under certain ambient conditions, moisture clumps (fog) can be seen rising from the discharge of the cooling tower, and can be misinterpreted as smoke from fire. If the outside air is at or near saturation, and the tower adds more water to the air, the air is saturated with drops of liquid water can be removed, which is seen as fog. This phenomenon usually occurs on cold and humid days, but is rare in many climates. Fogs and clouds associated with cooling towers can be described as homogenitus , as do other human-derived clouds, such as contrails and ship trajectories.

This phenomenon can be prevented by reducing the relative humidity of saturated exhaust air. For that purpose, in a hybrid tower, saturated air is mixed with a relatively low heated moisture air. Some air enters the tower above the drift eliminator level, passing through the heat exchanger. The relative humidity of dry air is even more directly reduced when heated when entering the tower. The dumped mixture has relatively low relative humidity and no visible fog.

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Salt-emission pollution

When a wet cooling tower with sea water make-up is installed in various industries located within or near the coast, the fine droplet emitted from the cooling tower contains nearly 6% of the sodium chloride stored on nearby land. Deposition of this sodium salt on adjacent agricultural/vegetative soils may convert it into alkaline sodic or alkaline sodic soils depending on soil properties and increase soil uniformity and surface water. The salt deposition problem of the cooling tower worsened where national pollution control standards were not imposed or applied to minimize drift emissions from wet cooling towers using make-up seawater.

Inhaled suspended particulate materials, measuring less than 10 micrometers (Âμm), may be present in the stream from the cooling tower. Larger particles above 10 Âμm in size are generally filtered in the nose and throat via cilia and mucus but particles smaller than 10 Âμm, referred to as PM ₁₀ , may settle in the bronchus and lungs and cause health problems. Similarly, particles smaller than 2.5 Ã,Âμm, (PM _2.5 ), tend to penetrate into the lung gas exchange areas, and very small particles (less than 100 nanometers) can pass through lungs to affect other organs. Although total particulate emissions from wet cooling towers with freshwater make-up are much less, they contain more PM ₁₀ and PM _2.5 of total emissions from wet cooling towers with makeup sea ​​water. This is due to the lower salt content in fresh water flow (below 2,000 ppm) compared to the salinity content of sea water hovering (60,000 ppm).

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Use as a waste gas stack

In some modern power stations equipped with smoke gas purification, such as GroÃÆ'Ÿkrotzenburg Power Station and Rostock Power Plant, cooling towers are also used as exhaust chimneys (industrial chimneys), thereby saving the cost of separate chimney structures. In plants without refining smoke gas, problems with corrosion can occur, because the reaction of raw gas smoke with water to form acid.

Sometimes, natural design cooling towers are constructed with structural steel in concrete places (RCC) when the natural draft tower construction time exceeds the time of construction of crop residues or local soil has poor strength to bear heavy loads. the weight of RCC cooling towers or higher cement prices in locations to choose cheaper natural design cooling towers made of structural steel.

src: www.quantrol.com

Operation in freezing weather

Some cooling towers (such as smaller building air conditioning systems) are switched off seasonally, dried, and frozen to prevent frozen damage.

During winter, other sites continue to operate cooling towers with 4Ã, ° C (39Ã,  ° F) of water leaving the tower. Bottom heater, tower drainage, and other freezing protection methods are often used in cold climates. Operational cooling towers with malfunctions can freeze during very cold weather. Typically, freezing begins in the corners of the cooling tower with reduced or absent heat load. Severe clotting conditions can create an ever-increasing volume of ice, resulting in an increase in structural loads that can cause structural or collapse damage.

To prevent freezing, the following procedure is used:

• Use of a modulated water bypass system is not recommended during freezing weather. In such situations, the flexibility of variable speed motor control, two-speed motors, and/or multi-cell multi-cell motors should be considered a requirement.
• Do not operate the tower unattended. Remote sensors and alarms can be installed to monitor tower conditions.
• Do not operate towers without heat load. The basin heater can be used to keep the water in the tower pan at a temperature above freezing. Heat trace ("heating tape") is a resistive heating element mounted along a water pipe to prevent freezing in cold climates.
• Keep the design water flow rate above the contents of the tower.
• Manipulate or reduce airflow to keep the water temperature above freezing.

src: spxcooling.com

Fire hazard

Cooling towers built in whole or in part from flammable materials may support internal fire propagation. The fires can be very intense, due to the high surface-to-surface ratio of the tower, and fires can be further intensified by natural convection or a fan-assisted draft. The resulting damage can be severe enough to require replacement of all cells or tower structures. For this reason, some codes and standards recommend that flammable cooling towers be equipped with an automatic fire spray system. Fires can spread internally inside tower structures when cells are not operating (as for maintenance or construction), and even when towers are in operation, especially those induced-type designs, due to the presence of relatively dry areas within the tower.

src: metalub.com

Structural Stability

Being a very large structure, cooling towers are prone to wind damage, and some spectacular failures have occurred in the past. At the Ferrybridge power station on November 1, 1965, the station was the location of a major structural failure, when three cooling towers collapsed due to vibrations at 85 mph (137 km/h) of wind. Although the structure has been built to withstand higher wind speeds, the cooling tower form causes the west wind to be channeled into the tower itself, creating a vortex. Three of the original eight cooling towers were destroyed, and five others were heavily damaged. The tower was then rebuilt and the eight cooling towers were reinforced to tolerate adverse weather conditions. The building codes were changed to include improved structural support, and wind tunnel tests were introduced to examine tower structures and configurations.

src: deskarati.com

See also

References

External links

• What is a cooling tower? - Institute of Cooling Technology
• "Cooling Towers" - including diagrams - Virtual Nuclear Tourist
• Guide of wet cooling towers for particulate matter, Canada Environment.
• Striking images of the European cooling tower left by Reginald Van de Velde, Lonely Planet, February 15, 2017 (see also excerpt from radio interview, World Update , BBC, November 21, 2016)

Source of the article : Wikipedia