Cooling towers or cooling towers are structures designed to lower the temperature of water and other media. The primary use of large industrial cooling towers is to lower the temperature of cooling water used in power plants, oil refineries, petrochemical plants, natural gas processing plants, and other industrial facilities.
In relation to the mechanism used for heat transfer, the main types are:.
In a wet cooling tower, hot water can be cooled to a temperature lower than ambient if the air is relatively dry (see: dew point).
With respect to the air draft in the tower, there are three types of cooling towers:
Under certain environmental conditions, clouds of water vapor (fog) can be seen emerging from a wet cooling tower (see image).
Cooling towers use water evaporation to reject heat from a process such as electrical power generation. Cooling towers vary in size from small to very large structures that can exceed 220 meters in height and 100 meters in length. Smaller towers are usually built in factories, while larger ones are built directly on site.
History
Cooling towers originated in the 19th century, through the development of condensers for use of engine steam.[1] Condensers use relatively cold water to condense the steam that the cylinders or turbines create. This reduces the pressure which consequently reduces the consumption of steam and, therefore, fuel, at the same time increasing the power and recycling the water in the boiler.[2].
In any case, condensers require an ample supply of cooling water, without which they become completely impractical.[3][4].
Cooling water consumption is estimated to reduce the energy available for most thermal plants.
By the end of the century, a few evaporation methods, in order to recycle cooling water, were used in areas lacking a constant water source; reliable in times of demand; or otherwise suitable to meet cooling needs.[1][4] In areas with available land, systems took the form of cooling ponds; In areas with limited land, such as cities, they took the form of cooling towers.[3][5].
These primary cooling towers were positioned on the roofs of buildings, as well as on free-standing structures, and were cooled by air from fans or some other natural source.[3][5] A 1911 American engineering book describes a design as .[5].
Cooling tower structure
Introduction
Cooling towers or cooling towers are structures designed to lower the temperature of water and other media. The primary use of large industrial cooling towers is to lower the temperature of cooling water used in power plants, oil refineries, petrochemical plants, natural gas processing plants, and other industrial facilities.
In relation to the mechanism used for heat transfer, the main types are:.
In a wet cooling tower, hot water can be cooled to a temperature lower than ambient if the air is relatively dry (see: dew point).
With respect to the air draft in the tower, there are three types of cooling towers:
Under certain environmental conditions, clouds of water vapor (fog) can be seen emerging from a wet cooling tower (see image).
Cooling towers use water evaporation to reject heat from a process such as electrical power generation. Cooling towers vary in size from small to very large structures that can exceed 220 meters in height and 100 meters in length. Smaller towers are usually built in factories, while larger ones are built directly on site.
History
Cooling towers originated in the 19th century, through the development of condensers for use of engine steam.[1] Condensers use relatively cold water to condense the steam that the cylinders or turbines create. This reduces the pressure which consequently reduces the consumption of steam and, therefore, fuel, at the same time increasing the power and recycling the water in the boiler.[2].
In any case, condensers require an ample supply of cooling water, without which they become completely impractical.[3][4].
Cooling water consumption is estimated to reduce the energy available for most thermal plants.
By the end of the century, a few evaporation methods, in order to recycle cooling water, were used in areas lacking a constant water source; reliable in times of demand; or otherwise suitable to meet cooling needs.[1][4] In areas with available land, systems took the form of cooling ponds; In areas with limited land, such as cities, they took the form of cooling towers.[3][5].
A lightweight metal plate, in effect a chimney stack, much shorter vertically and much more elongated laterally. At the top there is a set of distribution channels, into which the water from the condenser must be pumped; From these it drains onto "mats" made of wooden slats or woven wire screens, which fill the space inside the tower
A hyperboloid cooling tower was patented by Dutch engineers Frederik van Iterson and Gerard Kuypers in 1918.[6] The first hyperboloid cooling towers were built in 1918 near Heerlen. The first towers in the United Kingdom were built in 1924 at the Lister Drive power station in Liverpool, England, to cool water used in a coal-fired power station.[7].
According to the Gas Technology Institute (GTI) Report, Maisotsenko Cycle (Cycle M) indirect dew point evaporative cooling is a theoretically sound method for reducing a fluid to a dew point temperature that is lower than its wet bulb temperature. The M cycle uses the psychrometric energy (or potential energy) available from the latent heat of water evaporating into the air. While its current manifestation is the HMX M Cycle 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 wet gas streams.
Cooling water consumption by power and indoor processing plants is estimated to reduce energy availability for most thermal power plants by 2040–2069.[8].
In 2021, researchers presented a method for vapor recovery. The vapor is charged by an ion beam and then captured on an oppositely charged wire mesh. The purity of the water exceeded EPA potability standards.[9].
The cooling tower used as a chimney
In some modern power plants equipped with gas purification ducts such as the Staudinger Power Plant Grosskrotzenburg and the Rostock Power Plant the cooling tower is also used as a chimney. In plants that do not have gas purification ducts this causes problems with corrosion.
Material balance of a wet cooling tower
Quantitatively, the material balance around a wet cooling tower system is controlled by the structural operating variables: flow rate, evaporation and wind losses, racking rate, and concentration cycles:
In the sketch above, the water pumped from the tower reservoir is cooling water routed through process chillers and condensers in an industrial facility. The cold water absorbs heat from the hot process streams that need to be cooled or condensed, and the absorbed heat heats the circulating water (C). The heated water returns to the top of the cooling tower and falls in fine jets—presenting a large surface area for air cooling—onto the fill material inside the tower. As it drips, it comes into contact with the air that rises through the tower, by natural draft or forced by large fans. This contact causes a small amount of water to be lost through wind drag (W) and another part of the water (E) through evaporation. The heat necessary to evaporate the water is derived from the water itself, which cools the water upon its return to the original tank and where it is available for circulation again. The evaporated water leaves the salts it contains dissolved among the bulk of the water that has not undergone evaporation, which causes the concentration of salts to increase in the circulating cooling water. To prevent the concentration of salts in the water from becoming too high, part of the water is removed (D) for discharge. A new quota of fresh water (M) is supplied to the tower reservoir to compensate for losses due to evaporated water, wind, and withdrawn water.
The balance of water in the entire system is:.
Since the evaporated water (E) has no salts, the chloride balance of the system is:.
and, consequently:
From a simplified tower heat balance:
Wind losses (W), in the absence of manufacturer data, can be estimated to be:.
The concentration cycles in the cooling towers in an oil refinery are normally between 3 to 7. In some large power plants. Cooling tower concentration cycles can be much higher.
Heat transfer methods
With respect to the heat transfer mechanism used, the main types are:.
In a wet cooling tower (or open circuit cooling tower), hot water can be cooled to a temperature "lower" than the dry bulb temperature of the ambient air, if the air is relatively dry (see dew point and psychrometry). As ambient air passes through a flow of water, a small portion of the water evaporates and the energy required to evaporate that portion of the water is taken from the remaining mass of water, thereby reducing its temperature. Approximately 2300 kilojoules per kilogram of thermal energy is absorbed by the evaporated water. Evaporation results in saturated air conditions, which reduces the temperature of the water processed by the tower to a value close to the wet bulb temperature, which is lower than the ambient dry bulb temperature, the difference determined by the initial humidity of the ambient air.
To achieve better performance (more cooling), a medium called "filling" is used to increase the surface area and contact time between air and water flows. "Splash fill" consists of material placed to disrupt the flow of water and cause splashing. "Film fill" is made up of thin sheets of material (usually PVC) over which water flows. Both methods create a greater surface area and contact time between the fluid (water) and the gas (air), to improve heat transfer.
References
[1] ↑ a b International Correspondence Schools (1902). A Textbook on Steam Engineering. Scranton, Pa.: International Textbook Co. 33–34 of Section 29:"Condensers".: https://archive.org/details/textbookonsteame04inteiala
[3] ↑ a b c Heck, Robert Culbertson Hays (1911). The Steam Engine and Turbine: A Text-Book for Engineering Colleges. New York: D. Van Nostrand. pp. 569-570.: https://archive.org/details/steamengineturbi00heck
[4] ↑ a b Watson, Egbert P. (1906). «Power plant and allied industries». The Engineer (With Which is Incorporated Steam Engineering) (Chicago: Taylor Publishing Co.) 43 (1): 69-72.: https://books.google.com/books?id=cKUiAQAAMAAJ
[5] ↑ a b c Snow, Walter B. (1908). The Steam Engine: A Practical Guide to the Construction, Operation, and care of Steam Engines, Steam Turbines, and Their Accessories. Chicago: American School of Correspondence. pp. 43-46.: https://archive.org/details/steamenginepract00amerrich
[8] ↑ van Vliet, Michelle T. H.; Wiberg, David; Leduc, Sylvain; Riahi, Keywan (2016). «Power-generation system vulnerability and adaptation to changes in climate and water resources». Nature Climate Change 6 (4): 375-380. Bibcode:2016NatCC...6..375V. ISSN 1758-678X. doi:10.1038/nclimate2903.: http://adsabs.harvard.edu/abs/2016NatCC...6..375V
These primary cooling towers were positioned on the roofs of buildings, as well as on free-standing structures, and were cooled by air from fans or some other natural source.[3][5] A 1911 American engineering book describes a design as A lightweight metal plate, in effect a chimney stack, much shorter vertically and much more elongated laterally. At the top there is a set of distribution channels, into which the water from the condenser must be pumped; From these it drains onto "mats" made of wooden slats or woven wire screens, which fill the space inside the tower.[5].
A hyperboloid cooling tower was patented by Dutch engineers Frederik van Iterson and Gerard Kuypers in 1918.[6] The first hyperboloid cooling towers were built in 1918 near Heerlen. The first towers in the United Kingdom were built in 1924 at the Lister Drive power station in Liverpool, England, to cool water used in a coal-fired power station.[7].
According to the Gas Technology Institute (GTI) Report, Maisotsenko Cycle (Cycle M) indirect dew point evaporative cooling is a theoretically sound method for reducing a fluid to a dew point temperature that is lower than its wet bulb temperature. The M cycle uses the psychrometric energy (or potential energy) available from the latent heat of water evaporating into the air. While its current manifestation is the HMX M Cycle 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 wet gas streams.
Cooling water consumption by power and indoor processing plants is estimated to reduce energy availability for most thermal power plants by 2040–2069.[8].
In 2021, researchers presented a method for vapor recovery. The vapor is charged by an ion beam and then captured on an oppositely charged wire mesh. The purity of the water exceeded EPA potability standards.[9].
The cooling tower used as a chimney
In some modern power plants equipped with gas purification ducts such as the Staudinger Power Plant Grosskrotzenburg and the Rostock Power Plant the cooling tower is also used as a chimney. In plants that do not have gas purification ducts this causes problems with corrosion.
Material balance of a wet cooling tower
Quantitatively, the material balance around a wet cooling tower system is controlled by the structural operating variables: flow rate, evaporation and wind losses, racking rate, and concentration cycles:
In the sketch above, the water pumped from the tower reservoir is cooling water routed through process chillers and condensers in an industrial facility. The cold water absorbs heat from the hot process streams that need to be cooled or condensed, and the absorbed heat heats the circulating water (C). The heated water returns to the top of the cooling tower and falls in fine jets—presenting a large surface area for air cooling—onto the fill material inside the tower. As it drips, it comes into contact with the air that rises through the tower, by natural draft or forced by large fans. This contact causes a small amount of water to be lost through wind drag (W) and another part of the water (E) through evaporation. The heat necessary to evaporate the water is derived from the water itself, which cools the water upon its return to the original tank and where it is available for circulation again. The evaporated water leaves the salts it contains dissolved among the bulk of the water that has not undergone evaporation, which causes the concentration of salts to increase in the circulating cooling water. To prevent the concentration of salts in the water from becoming too high, part of the water is removed (D) for discharge. A new quota of fresh water (M) is supplied to the tower reservoir to compensate for losses due to evaporated water, wind, and withdrawn water.
The balance of water in the entire system is:.
Since the evaporated water (E) has no salts, the chloride balance of the system is:.
and, consequently:
From a simplified tower heat balance:
Wind losses (W), in the absence of manufacturer data, can be estimated to be:.
The concentration cycles in the cooling towers in an oil refinery are normally between 3 to 7. In some large power plants. Cooling tower concentration cycles can be much higher.
Heat transfer methods
With respect to the heat transfer mechanism used, the main types are:.
In a wet cooling tower (or open circuit cooling tower), hot water can be cooled to a temperature "lower" than the dry bulb temperature of the ambient air, if the air is relatively dry (see dew point and psychrometry). As ambient air passes through a flow of water, a small portion of the water evaporates and the energy required to evaporate that portion of the water is taken from the remaining mass of water, thereby reducing its temperature. Approximately 2300 kilojoules per kilogram of thermal energy is absorbed by the evaporated water. Evaporation results in saturated air conditions, which reduces the temperature of the water processed by the tower to a value close to the wet bulb temperature, which is lower than the ambient dry bulb temperature, the difference determined by the initial humidity of the ambient air.
To achieve better performance (more cooling), a medium called "filling" is used to increase the surface area and contact time between air and water flows. "Splash fill" consists of material placed to disrupt the flow of water and cause splashing. "Film fill" is made up of thin sheets of material (usually PVC) over which water flows. Both methods create a greater surface area and contact time between the fluid (water) and the gas (air), to improve heat transfer.
References
[1] ↑ a b International Correspondence Schools (1902). A Textbook on Steam Engineering. Scranton, Pa.: International Textbook Co. 33–34 of Section 29:"Condensers".: https://archive.org/details/textbookonsteame04inteiala
[3] ↑ a b c Heck, Robert Culbertson Hays (1911). The Steam Engine and Turbine: A Text-Book for Engineering Colleges. New York: D. Van Nostrand. pp. 569-570.: https://archive.org/details/steamengineturbi00heck
[4] ↑ a b Watson, Egbert P. (1906). «Power plant and allied industries». The Engineer (With Which is Incorporated Steam Engineering) (Chicago: Taylor Publishing Co.) 43 (1): 69-72.: https://books.google.com/books?id=cKUiAQAAMAAJ
[5] ↑ a b c Snow, Walter B. (1908). The Steam Engine: A Practical Guide to the Construction, Operation, and care of Steam Engines, Steam Turbines, and Their Accessories. Chicago: American School of Correspondence. pp. 43-46.: https://archive.org/details/steamenginepract00amerrich
[8] ↑ van Vliet, Michelle T. H.; Wiberg, David; Leduc, Sylvain; Riahi, Keywan (2016). «Power-generation system vulnerability and adaptation to changes in climate and water resources». Nature Climate Change 6 (4): 375-380. Bibcode:2016NatCC...6..375V. ISSN 1758-678X. doi:10.1038/nclimate2903.: http://adsabs.harvard.edu/abs/2016NatCC...6..375V