Comparison Between Characteristics of Mechanical- and Natural-Draft Cooling Towers

Location Must be located in an area at some distance from the plant proper. This is necessary for air supply considerations and because of problems associated with fogging and drift from discharging air. Noise considerations also tend to dictate site selection. Can be built adjacent to plant buildings, on centers 1.5 (d) where d = base diameter, so that piping costs are reduced. Their position must be chosen so as not to interfere with power plant exhaust plumes. 

Materials of Construction May be constructed of wood, metal or concrete. The structure must be designed to withstand wind or earthquake stress, dead loads such as weight of tower and circulating water and vibrations from mechanical equipment. Constructed of thin concrete shells that have good wind resistance. 

Initial Investment Can be built with less expensive materials like wood, asbestos-cement board and plastic imaterials. Fan cost is higher. Built with relatively expensive materials such as prestressed, precast and reinforced concrete and asbestos-cement for fill. 

Operation Maintenance Costs Pumping head is less, so power cost for the circulating water pumps is less. Power cost for fans is considerable. Cost of maintaining fans and associated drives and transmissions is also significant. Total operating cost will favor natural-draft towers. 

Recirculation, Fogging These are major problems. Design accommodation, restrictions on tower dimensions, orientation with prevailing winds, and added capacity for recirculation can boost tower cost. Because of its elevated discharge, the natural-draft tower rarely has the trouble with recirculation and fogging. 

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Table 4.1 Comparison Between Characteristics of Mechanical- and Natural-Draft Cooling Towers...

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