Last edited 24 Sep 2020

Cooling tower design and construction

[edit] Introduction

Cooling towers rejectheat through theevaporation ofwater in a movingair stream within thecooling tower. Thetemperature andhumidity of theair stream increases through contact with the warmwater, and thisair is then discharged. The cooledwater is collected at the bottom of thetower.

Cooling towers were invented during the industrialisation of the 19th century through thedevelopment of condeners for use with the steam engine. By the early 20th century, advances incooling towers were fueled by the rapidly growingelectric power industry. Where there wereareas of availableland, thesystems took theform ofcooling ponds, whereas incity areas they werecooling towers, either positioned onbuilding rooftops or as free-standingstructures.

[edit]Hyperboloid structure

Hyperboloid structures are often designed as talltowers, where thestrength of thehyperboloid’s geometry is used to support an object high off theground. They have superior stability andresistance to externalforces than ordinarystructures; however, the drawback is the shape resulting in lowspace efficiency. This means they are most suited to purpose-drivenstructures such ascooling towers.

Thehyperboloid shape is particularly suited tocooling tower construction as the wide base provides a largespace for thewater andcooling system. The narrowing effect of thetower helps with the laminar flow of the evaporatedwater as itrises. As thetower widens out at the top, it supports the turbulent mixing as the heatedair makes contact with the atmosphericair.

The firsthyperboloid structure was a 37-metre latticewater tower,built in 1896 for the All-Russian Exhibition located in Pilibino, Russia.

Dutchengineers Frederikvan Iterson and Gerard Kuypers patented thehyperboloid cooling tower in 1918, with the first beingbuilt near Heerlen that year. The UK saw the firsttower beingbuilt in 1924 in Liverpool, to coolwater used at a coal-firedelectrical power station.

[edit]Construction

Cooling towers can be small-scale roof-topinstallations, medium-sizedpackaged units, or very largestructures sometimes associated withindustrial processes orpower stations with their characteristic plume ofwater vapour in theexhaust air.

These largecooling towers can be up to 200metres (660 ft) tall and 100 m (320 ft) in diameter. They are oftenconstructed ashyperboloid, doubly-curvedconcrete shell structures supported on a series ofconcrete struts. Thefoundations typically consist of an inclinedpond wall forming a circular ‘tee’beam with a wideconcrete strip. Thebeam acts to resist thelateral load of thetower’s shell structure. As well as the ‘tee’beam,piled foundations are normally required to minimise differentialsettlement and reduce therisk ofcracking.

Thecooling system is housed in thetower’s base which is typically the bottom 10metres, the rest of thetower consisting of an emptyshell. Thewater falls and collects in apond at the base of thetower, formed by a baseslab and thepond wall.

In natural-draught cooling towers the openstructure at the base allows a natural movement ofair. Mechanical-draught cooling towers usefans to provide adraught, where it is necessary tomaintain or not exceed a fixedtemperature level. Thecosts associated with theoperation of mechanical-draught may be higher, but it is more efficient than naturaldraught.