Cooling towers natural draft tower

Figure 9-101. Component parts of modem natural draft tower. Used by permission of Hamon Cooling Towers, Inc.

Evaporation losses are about 1% of the circulation for every 10°F of cooling range. Windage or drift losses are 0.3-1.0% for natural draft towers and 0.1-0.3% for mechanical draft. Usually the salt content of the circulating water is limited to 3-7 times that of the makeup. Blowdown of 2.5-3% of the circulation accordingly is needed to maintain the limiting salt concentration. 

Natural Draft Towers, Cooling Ponds, Spray Ponds. 12-22... 

Natural Draft Towers, Cooling Ponds, Spray Ponds Natural draft towers are primarily suited to very large cooling water quantities, and the reinforced concrete structures used are as large as 80 m in diameter and 105 m high. 

Natural draft towers, cooling ponds, and spray ponds are infrequently used in new construction today in the chemical processing industry. Additional information may be found in previous Perry s editions. 

The giant natural-draft towers are used in Europe and in nuclear power plants in the United States. I ve only worked with these towers in one refinery in Lithuania, and their performance was poor. Air flow is generated by the air inside the tower being heated by the warm cooling water. Also, the molecular weight of the evaporated water is less than the molecular weight of air. A few tenths of an inch of water draft may be developed. 

Fig. 9. Natural-draft cooling tower (a) general tower drawing for countercurrent air—water dow arrangement (b) sectional drawing showing arrangement...

Natural-draft cooling towers are extremely sensitive to air-inlet conditions owing to the effects on draft. It can rapidly be estabUshed from these approximate equations that as the air-inlet temperature approaches the water-inlet temperature, the allowable heat load decreases rapidly. For this reason, natural-draft towers are unsuitable in many regions of the United States. Figure 10 shows the effect of air-inlet temperature on the allowable heat load of a natural-draft tower for some arbitrary numerical values and inlet rh of 50%. The trend is typical. 

Cooling-Tower Plumes. An important consideration in the acceptabiHty of either a mechanical-draft or a natural-draft tower cooling system is the effect on the environment. The plume emitted by a cooling tower is seen by the surrounding community and can lead to trouble if it is a source of severe ground fog under some atmospheric conditions. The natural-draft tower is much less likely to produce fogging than is the mechanical-draft tower. Nonetheless, it is desirable to devise techniques for predicting plume trajectory and attenuation. 

J. R. Singham, The Thermal Peformance of Natural Draft Cooling Towers, Imperial CoUege of Science and Technology, Department of Mechanical Engineering, London, 1967. 

FIG. 12-22 Universal performance chart for natural-draft cooling towers. (Risk and Steel, ASCE Symposium on Thermal Power Plants, October 1958. )... 

Cooling towers are broadly classified on the basis of the type of draft natural draft (natural convection), mechanical draft (forced convection) and mechanical and natural. Further distinction is made based on (1) the type of flow i.e. - crossflow, counterflow, cocurrent flow (2) the type of heat dissipation-wet (evaporative cooling), dry, wet-dry and (3) the type of application-industrial or power plant. Each of the major types of cooling towers has a distinct configuration. The major designs are summarized in Figures 1 through 8 and a brief description of each follows. 

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