{"id":18048,"date":"2018-06-06T18:30:43","date_gmt":"2018-06-06T18:30:43","guid":{"rendered":"http:\/\/sitepourvtc.com\/?page_id=18048"},"modified":"2022-11-21T13:36:40","modified_gmt":"2022-11-21T13:36:40","slug":"cooling-towers-dry-wet-natural-draught","status":"publish","type":"page","link":"https:\/\/sitepourvtc.com\/nuclear-power-plant\/turbine-generator-power-conversion-system\/cooling-system-circulating-water-system\/cooling-towers-dry-wet-natural-draught\/","title":{"rendered":"Cooling Towers &#8211; Dry, Wet &#8211; Natural draught"},"content":{"rendered":"<div   id="8n9s8rpp6h"    class=\"su-quote su-quote-style-default\"><div   id="8n9s8rpp6h"    class=\"su-quote-inner su-u-clearfix su-u-trim\">The<strong> cooling towers<\/strong> are buildings that reject waste <strong>heat to the atmosphere<\/strong> by cooling a water stream to a lower temperature. <strong>Cooling towers <\/strong>are usually built in places with a lack of water resources. By using cooling towers, the cooling water requirement is reduced, and only makeup water is to be supplied. The cooling towers significantly reduce the cooling water demand, but it is achieved at the expense of large capital costs.<\/div><\/div>\n<p><a href=\"http:\/\/sitepourvtc.com\/wp-content\/uploads\/2017\/06\/Cooling-System-Cooling-Tower-min.png\"><img loading=\"lazy\" class=\"alignright size-medium wp-image-18044\" src=\"http:\/\/sitepourvtc.com\/wp-content\/uploads\/2017\/06\/Cooling-System-Cooling-Tower-min-300x258.png\" alt=\"Cooling System - Cooling Tower\" width=\"300\" height=\"258\" srcset=\"https:\/\/sitepourvtc.com\/wp-content\/uploads\/2017\/06\/Cooling-System-Cooling-Tower-min-300x258.png 300w, https:\/\/sitepourvtc.com\/wp-content\/uploads\/2017\/06\/Cooling-System-Cooling-Tower-min.png 1019w\" sizes=\"(max-width: 300px) 100vw, 300px\" \/><\/a>With respect to the heat transfer mechanism employed, the main types are:<\/p>\n<p><strong>Dry cooling towers<\/strong> operate by heat transfer through a surface that separates the working fluid from ambient air, such as in a tube to air heat exchanger, utilizing convective heat transfer. They do not use evaporation; hence the consumption of makeup water is minimal.<\/p>\n<p><strong>Wet cooling towers <\/strong>(or open circuit cooling towers) operate on the principle of <strong>evaporative cooling<\/strong>. Evaporative cooling is the addition of water vapor into the air, which causes a lowering of the temperature of the air and the water. The energy needed to evaporate the water is taken from the remaining mass of water, thus<strong> reducing its temperature<\/strong>. The cooling water from the plant is pumped to a height of about <strong>10 m<\/strong> and distributed over the <strong>cooling tower fill<\/strong>, cascading down the fill to the well at the bottom. Inside the wet cooling tower, fills are added to increase contact surface as well as contact time between air and water to provide better heat transfer.<\/p>\n<p>Nearly all nuclear power plants, which use cooling towers, use <strong>wet cooling towers<\/strong> based on the principle of evaporative cooling. Some water, about <strong>1%,<\/strong> goes into the air in the form of water vapor by absorbing its latent heat of vaporization from the remaining water and thus causes the reduction in the water temperature as ambient air is drawn past a flow of water. The remaining water (cooled) is collected in a sump at the bottom of the tower and returned back to the condenser.<\/p>\n<p>The types of cooling towers based on the draught (method of air circulation) are:<\/p>\n<ul>\n<li><strong>Natural draught cooling towers<\/strong>. Natural draught cooling towers utilize buoyancy via a tall <strong>hyperboloid chimney<\/strong>. <strong>Hyperboloid cooling towers<\/strong> are typical for natural draught cooling towers because of their structural strength and because of the fact that the hyperboloid shape also aids in <strong>accelerating the upward convective airflow<\/strong>, improving cooling efficiency. In this cooling tower, the hot cooling water (e.g., 25\u00b0C) from the condenser is pumped to a height of about 10 m, enters the tower, and then sprayed over the trays. <strong>Water droplets<\/strong> fall down and meet the colder air entering from the bottom of the tower, which is open to the atmosphere. Hot water (e.g., 25\u00b0C) gives up its heat to the air and gets cooled (e.g., 22\u00b0C). Warm, moist air <strong>naturally rises<\/strong> due to the density differential compared to the dry, cooler outside air. Warm moist air is less dense than drier air at the same pressure. This moist air buoyancy produces an upwards current of air through the hyperboloid tower. The cooled water falls down in the form of rain and gets collected in the pond at the bottom of the tower.<\/li>\n<li><strong>Mechanical draught cooling towers.<\/strong> In general, in the mechanical draught cooling towers, the air is circulated using a mechanical device like a fan or a blower.\n<ul>\n<li><strong>Forced draught cooling towers<\/strong>. Forced draught cooling towers use the fan, which is installed at the bottom of the tower. This produces high entering and low exiting air velocities; therefore, these towers are more susceptible to recirculation.<\/li>\n<li><strong>Induced draught cooling towers.<\/strong> Induced draught cooling towers use the fan, which is installed at the top of the tower. This produces low entering and high exiting air velocities, reducing the possibility of recirculation in which discharged air flows back into the air intake.<\/li>\n<\/ul>\n<\/li>\n<\/ul>\n<p style=\"text-align: center;\">Special link: <a href=\"https:\/\/sketchfab.com\/models\/eeed3c79649640b3a370546e9fea53ff\">3D model of NPP &#8211; sketchfab.com<\/a><\/p>\n<p><a href=\"http:\/\/sitepourvtc.com\/wp-content\/uploads\/2017\/09\/nuclear-power-plant-min.png\"><img loading=\"lazy\" class=\"aligncenter size-full wp-image-18637\" src=\"http:\/\/sitepourvtc.com\/wp-content\/uploads\/2017\/09\/nuclear-power-plant-min.png\" alt=\"nuclear power plant-min\" width=\"300\" height=\"200\" \/><\/a><\/p>\n<div   id="8n9s8rpp6h"    class=\"collapsible-container\">\n<h2>Cooling System &#8211; Circulating Water System<\/h2>\n<p>The <strong>cooling system<\/strong> or the <strong>circulating water system<\/strong> provides a continuous supply of <strong>cooling water<\/strong> to the <a title=\"Main Condenser \u2013 Steam Condenser\" href=\"http:\/\/sitepourvtc.com\/nuclear-power-plant\/turbine-generator-power-conversion-system\/main-condenser-steam-condenser\/\"><strong>main condenser<\/strong><\/a> to remove the heat rejected by the turbine and auxiliary systems (e.g., the <a title=\"Turbine Bypass System \u2013 Turbine Steam Dump System\" href=\"http:\/\/sitepourvtc.com\/nuclear-power-plant\/turbine-generator-power-conversion-system\/turbine-bypass-system-turbine-steam-dump-system\/\">turbine bypass system<\/a>). \u00a0In this process, the cooling water becomes hot. This energy is rejected to the atmosphere via <strong>cooling towers<\/strong> or directly to the seawater or a river. Note that not all nuclear power plants have cooling towers, and conversely, the same kind of cooling towers are often used at large coal-fired power plants.<\/p>\n<p><strong>Cooling System in Wet Steam Turbines<\/strong><\/p>\n<p>In a typical <a title=\"Condensing Steam Turbine\" href=\"http:\/\/sitepourvtc.com\/nuclear-power-plant\/turbine-generator-power-conversion-system\/what-is-steam-turbine-description-and-characteristics\/condensing-steam-turbine\/\"><strong>condensing steam turbine<\/strong><\/a>, the exhausted steam condenses in the condenser, and it is at a pressure well below atmospheric (absolute pressure of <strong>0.008 MPa, <\/strong>which corresponds to 41.5\u00b0C). This steam is in a partially condensed state (point F), typically of a quality near 90%.<\/p>\n<figure id=\"attachment_17781\" aria-describedby=\"caption-attachment-17781\" style=\"width: 290px\" class=\"wp-caption alignright\"><a href=\"http:\/\/sitepourvtc.com\/wp-content\/uploads\/2017\/05\/Rankine-Cycle-Ts-diagram.png\"><img loading=\"lazy\" class=\"size-medium wp-image-17781\" src=\"http:\/\/sitepourvtc.com\/wp-content\/uploads\/2017\/05\/Rankine-Cycle-Ts-diagram-300x276.png\" alt=\"Rankine Cycle - Ts diagram\" width=\"300\" height=\"276\" srcset=\"https:\/\/sitepourvtc.com\/wp-content\/uploads\/2017\/05\/Rankine-Cycle-Ts-diagram-300x276.png 300w, https:\/\/sitepourvtc.com\/wp-content\/uploads\/2017\/05\/Rankine-Cycle-Ts-diagram.png 649w\" sizes=\"(max-width: 300px) 100vw, 300px\" \/><\/a><figcaption id=\"caption-attachment-17781\" class=\"wp-caption-text\">Rankine cycle &#8211; Ts diagram<\/figcaption><\/figure>\n<p>The pressure inside the <strong>condenser <\/strong>(thus the enthalpy of outlet steam) is given by the <strong>ambient air<\/strong> <strong>temperature<\/strong> (i.e., the water temperature<strong>\u00a0in the cooling system<\/strong>). and other parameters:<\/p>\n<ul>\n<li>air temperature, pressure, and humidity in case of cooling into the atmosphere<\/li>\n<li>water temperature and the flow rate in case of cooling into a river or sea<\/li>\n<\/ul>\n<p>An increase in the ambient temperature may cause a proportional increase in pressure of exhausted steam (<strong>\u0394T = 14\u00b0C<\/strong> is usually a constant); hence the<a title=\"Thermal Efficiency of Steam Turbine\" href=\"http:\/\/sitepourvtc.com\/nuclear-power-plant\/turbine-generator-power-conversion-system\/theory-of-steam-turbines-thermodynamics\/thermal-efficiency-of-steam-turbine\/\"> thermal efficiency<\/a> of the power conversion system may decrease. In other words, the <strong>electrical output<\/strong> of a power plant <strong>may vary<\/strong> with <strong>ambient conditions<\/strong>, while the thermal power remains constant.<\/p>\n<p>It must be noted there is also<strong> a lower limit<\/strong> for the steam outlet temperature, thus for the cooling system. Below 0.008 MPa and 41.5 \u00b0C, the specific volume of exhausted steam significantly increases, which requires <strong>huge blades in the last rows<\/strong> of a low-pressure stage of the <a title=\"What is Steam Turbine \u2013 Description and Characteristics\" href=\"http:\/\/sitepourvtc.com\/nuclear-power-plant\/turbine-generator-power-conversion-system\/what-is-steam-turbine-description-and-characteristics\/\">steam turbine<\/a>. Moreover, with a decrease in the turbine exhaust pressure, the<a title=\"Vapor Quality \u2013 Dryness Fraction\" href=\"http:\/\/sitepourvtc.com\/nuclear-engineering\/materials-nuclear-engineering\/properties-steam-what-is-steam\/vapor-quality-dryness-fraction\/\"> vapor quality<\/a> decreases (or dryness fraction). At some point, the expansion must be ended to avoid damages that could be caused to blades of steam turbine by <a href=\"http:\/\/sitepourvtc.com\/nuclear-engineering\/materials-nuclear-engineering\/properties-steam-what-is-steam\/vapor-quality-dryness-fraction\/\">low-quality steam<\/a>.<\/p>\n<figure id=\"attachment_17811\" aria-describedby=\"caption-attachment-17811\" style=\"width: 659px\" class=\"wp-caption aligncenter\"><a href=\"http:\/\/sitepourvtc.com\/wp-content\/uploads\/2017\/05\/Condenser-steam-parameters.png\"><img loading=\"lazy\" class=\"size-large wp-image-17811\" src=\"http:\/\/sitepourvtc.com\/wp-content\/uploads\/2017\/05\/Condenser-steam-parameters-1024x334.png\" alt=\"Typical parameters in a condenser of condensing turbines\" width=\"669\" height=\"218\" srcset=\"https:\/\/sitepourvtc.com\/wp-content\/uploads\/2017\/05\/Condenser-steam-parameters-1024x334.png 1024w, https:\/\/sitepourvtc.com\/wp-content\/uploads\/2017\/05\/Condenser-steam-parameters-300x98.png 300w, https:\/\/sitepourvtc.com\/wp-content\/uploads\/2017\/05\/Condenser-steam-parameters.png 1065w\" sizes=\"(max-width: 669px) 100vw, 669px\" \/><\/a><figcaption id=\"caption-attachment-17811\" class=\"wp-caption-text\">Typical parameters in a condenser of condensing turbines<\/figcaption><\/figure>\n<p>In modern <a href=\"http:\/\/sitepourvtc.com\/nuclear-power-plant\/\"><strong>nuclear power plants<\/strong><\/a>, the overall thermal efficiency is about <strong>one-third <\/strong>(33%), so <strong>3000 MWth<\/strong> of thermal power from the fission reaction is needed to generate <strong>1000 MWe<\/strong> of electrical power. Therefore, about <strong>2000MWth<\/strong> of <strong>unusable energy<\/strong> must be rejected to fulfill the <a title=\"Second Law of Thermodynamics\" href=\"http:\/\/sitepourvtc.com\/nuclear-engineering\/thermodynamics\/laws-of-thermodynamics\/second-law-of-thermodynamics\/\"><strong>second law of thermodynamics<\/strong><\/a>.<\/p>\n<p>To maintain the parameters inside the condenser (0.008 MPa and 41.5 \u00b0C), the <strong>cooling water<\/strong> must be sufficiently cold, and there cannot be a large temperature difference between the outlet and inlet water temperature; hence the <b>flow rate<\/b>\u00a0through the cooling system must be<strong> very high<\/strong>. The flow rate through the cooling system (with <strong>wet cooling towers<\/strong>) may be up to <strong>100 000 m<sup>3<\/sup>\/h<\/strong> (27.7 m<sup>3<\/sup>\/s). The condenser inlet water may have about<strong> 22\u00b0C<\/strong> (strongly depending on ambient conditions), while the condenser outlet may have about <strong>25\u00b0C<\/strong>.<\/p>\n<p>The seawater cooling systems operate at higher flow rates, for example, 130 000 m<sup>3<\/sup>\/h. In general, the energy can be rejected to the atmosphere via cooling towers or directly to the seawater or a river.<\/p>\n<p><a href=\"http:\/\/sitepourvtc.com\/wp-content\/uploads\/2017\/05\/Condenser-LP-Heaters-Deaerator-min.png\"><img loading=\"lazy\" class=\"aligncenter size-large wp-image-17843\" src=\"http:\/\/sitepourvtc.com\/wp-content\/uploads\/2017\/05\/Condenser-LP-Heaters-Deaerator-min-1024x497.png\" alt=\"Condenser - LP Heaters - Deaerator\" width=\"669\" height=\"325\" srcset=\"https:\/\/sitepourvtc.com\/wp-content\/uploads\/2017\/05\/Condenser-LP-Heaters-Deaerator-min-1024x497.png 1024w, https:\/\/sitepourvtc.com\/wp-content\/uploads\/2017\/05\/Condenser-LP-Heaters-Deaerator-min-300x146.png 300w, https:\/\/sitepourvtc.com\/wp-content\/uploads\/2017\/05\/Condenser-LP-Heaters-Deaerator-min.png 1109w\" sizes=\"(max-width: 669px) 100vw, 669px\" \/><\/a><\/p>\n<\/div>\n<div   id="8n9s8rpp6h"    class=\"su-divider su-divider-style-dotted\" style=\"margin:20px 0;border-width:2px;border-color:#999999\"><\/div>\n<div   id="8n9s8rpp6h"     class=\"lgc-column lgc-grid-parent lgc-grid-100 lgc-tablet-grid-100 lgc-mobile-grid-100 lgc-equal-heights \"><div   id="8n9s8rpp6h"     class=\"inside-grid-column\">\u00a0 <div   id="8n9s8rpp6h"    class=\"su-accordion su-u-trim\"><div   id="8n9s8rpp6h"    class=\"su-spoiler su-spoiler-style-default su-spoiler-icon-plus su-spoiler-closed\" data-scroll-offset=\"0\"><div   id="8n9s8rpp6h"    class=\"su-spoiler-title\" tabindex=\"0\" role=\"button\"><span class=\"su-spoiler-icon\"><\/span>References:<\/div><div   id="8n9s8rpp6h"    class=\"su-spoiler-content su-u-clearfix su-u-trim\"><strong>Nuclear and Reactor Physics:<\/strong>\n<ol>\n<li>J. R. Lamarsh, Introduction to Nuclear Reactor Theory, 2nd ed., Addison-Wesley, Reading,\u00a0MA (1983).<\/li>\n<li>J. R. Lamarsh, A. J. Baratta, Introduction to Nuclear Engineering, 3d ed., Prentice-Hall, 2001, ISBN: 0-201-82498-1.<\/li>\n<li>W. M. Stacey, Nuclear Reactor Physics, John Wiley &amp; Sons, 2001, ISBN: 0- 471-39127-1.<\/li>\n<li>Glasstone, Sesonske. Nuclear Reactor Engineering: Reactor Systems Engineering,\u00a0Springer; 4th edition, 1994, ISBN:\u00a0978-0412985317<\/li>\n<li>W.S.C. Williams. Nuclear and Particle Physics.\u00a0Clarendon Press; 1 edition, 1991, ISBN:\u00a0978-0198520467<\/li>\n<li>Kenneth S. Krane. Introductory Nuclear Physics, 3rd Edition, Wiley, 1987,\u00a0ISBN:\u00a0978-0471805533<\/li>\n<li>G.R.Keepin. Physics of Nuclear Kinetics.\u00a0Addison-Wesley Pub. Co; 1st edition, 1965<\/li>\n<li>Robert Reed Burn, Introduction to Nuclear Reactor Operation, 1988.<\/li>\n<li>U.S. Department of Energy, Nuclear Physics and Reactor Theory.\u00a0DOE Fundamentals Handbook,\u00a0Volume 1 and 2.\u00a0January\u00a01993.<\/li>\n<\/ol>\n<p><strong><\/strong><strong>Advanced Reactor Physics:<\/strong><\/p>\n<ol>\n<li>K. O. Ott, W. A. Bezella, Introductory Nuclear Reactor Statics, American Nuclear Society, Revised edition (1989), 1989, ISBN: 0-894-48033-2.<\/li>\n<li>K. O. Ott, R. J. Neuhold, Introductory Nuclear Reactor Dynamics, American Nuclear Society, 1985, ISBN: 0-894-48029-4.<\/li>\n<li><span style=\"font-weight: 400;\">D. L. Hetrick, Dynamics of Nuclear Reactors, American Nuclear Society, 1993, ISBN: 0-894-48453-2.\u00a0<\/span><\/li>\n<li>E. E. Lewis, W. F. Miller, Computational Methods of Neutron Transport, American Nuclear Society, 1993, ISBN: 0-894-48452-4.<\/li>\n<\/ol>\n<p>Other References:<\/p>\n<p><a title=\"Diesel Engine\" href=\"http:\/\/www.likvidace-vozidla-praha.cz\/vznetovy-motor-dieseluv-cyklus\/\">Diesel\u00a0Engine &#8211; Car Recycling<\/a><\/p><\/div><\/div><\/div><div   id="8n9s8rpp6h"    class=\"su-divider su-divider-style-dotted\" style=\"margin:15px 0;border-width:2px;border-color:#999999\"><\/div><\/div><\/div><div   id="8n9s8rpp6h"    class=\"su-divider su-divider-style-default\" style=\"margin:15px 0;border-width:2px;border-color:#999999\"><\/div><div   id="8n9s8rpp6h"     class=\"lgc-column lgc-grid-parent lgc-grid-33 lgc-tablet-grid-33 lgc-mobile-grid-100 lgc-equal-heights \"><div   id="8n9s8rpp6h"     class=\"inside-grid-column\"><\/div><\/div><div   id="8n9s8rpp6h"     class=\"lgc-column lgc-grid-parent lgc-grid-33 lgc-tablet-grid-33 lgc-mobile-grid-100 lgc-equal-heights \"><div   id="8n9s8rpp6h"     class=\"inside-grid-column\">\n<h2>See above:<\/h2>\n<p>Turbine Generator<a href=\"http:\/\/sitepourvtc.com\/nuclear-power-plant\/turbine-generator-power-conversion-system\/\" class=\"su-button su-button-style-flat\" style=\"color:#606060;background-color:#ffffff;border-color:#cccccc;border-radius:10px;-moz-border-radius:10px;-webkit-border-radius:10px\" target=\"_self\"><span style=\"color:#606060;padding:7px 20px;font-size:16px;line-height:24px;border-color:#ffffff;border-radius:10px;-moz-border-radius:10px;-webkit-border-radius:10px;text-shadow:0px 0px 0px #000000;-moz-text-shadow:0px 0px 0px #000000;-webkit-text-shadow:0px 0px 0px #000000\"><i class=\"sui sui-link\" style=\"font-size:16px;color:#5d5d5d\"><\/i> <\/span><\/a><\/p><\/div><\/div><div   id="8n9s8rpp6h"     class=\"lgc-column lgc-grid-parent lgc-grid-33 lgc-tablet-grid-33 lgc-mobile-grid-100 lgc-equal-heights \"><div   id="8n9s8rpp6h"     class=\"inside-grid-column\"><\/div><\/div>\n","protected":false},"excerpt":{"rendered":"<p>With respect to the heat transfer mechanism employed, the main types are: Dry cooling towers operate by heat transfer through a surface that separates the working fluid from ambient air, such as in a tube to air heat exchanger, utilizing convective heat transfer. They do not use evaporation; hence the consumption of makeup water is &#8230; <a title=\"Cooling Towers &#8211; Dry, Wet &#8211; Natural draught\" class=\"read-more\" href=\"https:\/\/sitepourvtc.com\/nuclear-power-plant\/turbine-generator-power-conversion-system\/cooling-system-circulating-water-system\/cooling-towers-dry-wet-natural-draught\/\" aria-label=\"More on Cooling Towers &#8211; Dry, Wet &#8211; Natural draught\">Read more<\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"parent":18042,"menu_order":0,"comment_status":"closed","ping_status":"closed","template":"","meta":{"generate_page_header":""},"_links":{"self":[{"href":"https:\/\/sitepourvtc.com\/wp-json\/wp\/v2\/pages\/18048"}],"collection":[{"href":"https:\/\/sitepourvtc.com\/wp-json\/wp\/v2\/pages"}],"about":[{"href":"https:\/\/sitepourvtc.com\/wp-json\/wp\/v2\/types\/page"}],"author":[{"embeddable":true,"href":"https:\/\/sitepourvtc.com\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/sitepourvtc.com\/wp-json\/wp\/v2\/comments?post=18048"}],"version-history":[{"count":4,"href":"https:\/\/sitepourvtc.com\/wp-json\/wp\/v2\/pages\/18048\/revisions"}],"predecessor-version":[{"id":35381,"href":"https:\/\/sitepourvtc.com\/wp-json\/wp\/v2\/pages\/18048\/revisions\/35381"}],"up":[{"embeddable":true,"href":"https:\/\/sitepourvtc.com\/wp-json\/wp\/v2\/pages\/18042"}],"wp:attachment":[{"href":"https:\/\/sitepourvtc.com\/wp-json\/wp\/v2\/media?parent=18048"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}