Hyperbolic, natural draft cooling towers

In an atmospheric spray tower the air movement - is dependent on atmospheric conditions and the aspirating effect of the spray nozzles. Natural-draft cooling tower operation depends on a chimney or stack to induce air movement. Mechanical-draft cboling towers utilize fans to move ambient air through the tower. Deck-filled towers contain tiers of splash bars or decks to assist in the breakup of water drops to increase the total water surface and subsequently the evaporation rate. Spray-filled towers depend only on spray nozzles for water breakup. Coil shed towers are comprised of a combination structure of a cooling tower installed on top of a substructure that contains atmospheric section coils. Hyperbolic natural-draft cooling towers are typically large-capacity systems. 

Natural-draft cooling towers with a hyperbolic configuration are usually constructed of concrete, have a large dimension and, consequently, large capacities. They are generally used in power plants. Figure 4.3 also illustrates this design. 

Shell or stack. Hyperbolic structure of natural draft cooling tower, designed to induce air flow through the entire tower. 

Figure 9.18. Main types of cooling towers, (a) Atmospheric, dependent on wind velocity, (b) Hyperbolic stack natural draft, (c) Hyperbolic assisted with forced draft fans, (d) Counterflow-induced draft, (e) Crossflow-induced draft, (f) Forced draft, (g) Induced draft with surface precooler for very hot water also called wet/dry tower, [(fc)-(e) from Cheremisinoff and Cheremisinoff, 1981).

Cooling towers are classified according to the method by which air is introduced to the tower. The principal types are atmospheric spray, natural-draft, mechanical-draft, deck-filled, spray-filled, coil shed and hyperbolic towers. Most industrial cooling tower installations are field-erected units designed for specific thermal characteristics. 

In 1974 the Atlantic City Electric Co. placed Unit 3 of its B L England Station into commercial operation. Condenser cooling for the unit is provided by circulating sea water in a closed-cycle, natural-draft system. The cooling tower selected for the site was a hyperbolic, counterflow unit. The thermal test instrumentation procedures and test data as well as drift measurement results are given. The paper indicates that the tower operates within design specifications for thermal performance and that it meets the environmental criteria regarding the drift. 

Cooling towers may operate on natural draft, as in the case of wind-cooled towers for small home airpower generating stations (Fig. 8.12). In process plants, the towers are more often aided by fans, either forced or induced draft operations, to improve the cooling capacity (Fig. 8.13). 

Some cooling towers operate with natural draft. This is possible because the warmer, humid air inside the tower is less dense than the colder, drier outside air. Many such towers are hyperbolic and may require an overall height of 220 ft. The fill used in such a column must be quite open to avoid any significant pressure drop. Such fill can have a tee- or vee-shaped cross section molded from perforated plastic sheets. Corrugated sheets made of asbestos and cement are popular in large natural draft towers. A ceramic cellular block that is stacked into the tower also is used. These fills, however, provide a small interfacial area per cubic foot so mass transfer is rather low per foot of packed depth. 

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