Large cooling towers

Construction and Design of Large Cooling Towers Zerna, Wolfgang Mungan, Ihsan... 

For the large cooling towers built in the last few decades, the thin reinforced Crete shell, reinforced in two axes on both surfaces, has proved eminently suitatable. For structural, thermodynamic and flow optimization reasons rota-tionally hyperbolic shapes are desirable, and occasionally also cylinders. These shapes are at same time aesthetically pleasing because they make the gigantic dimensions of the structures seem tolerable. 

The utihty iadustry utilizes fans typically from 6.7—10 m diameter ia banks of 8 to 12 fans ia wet cooling towers. These towers cool the water used to condense the steam from the turbiaes. Many towers may be needed ia large plants requiring as many as 50 to 60 fans 12 m in diameter. These fans typically utilize velocity recovery stacks to recoup some of the velocity pressure losses and convert it to useful static pressure work. 

After only 4 months of service, the main condenser at a large fossil utility began to perforate. Initial perforations were due to erosion-corrosion (see Case History 11.5). Small clumps of seed hairs entering the condenser after being blown into the cooling tower were caught on surfaces. The entrapped seed hairs acted as sieves, filtering out small silt and sand particles to form lumps of deposit (Fig. 6.24A and B). Immediately downstream from each deposit mound, an erosion-corrosion pit was found. 

To simulate the next summer s condition the plant was run at the desired production rate and two cooling tower fans were turned off. It turned out that the cold water temperature rose to slightly above that predicted for the next summer. A thorough inspection of critical temperatures and the plant s operation indicated that the plant would barely make it the next summer. Process side temperatures were at about the maximum desired, with an occasional high oil temperature alarm on the large machines. 

TEAO - Totally Enclosed Air Over where the motor has large cooling fins and depends on the cooling tower air stream for air movement. The motor shaft protrudes from the enclosure at one place only. 

Large towers often have the motor mounted horizontally connected to a right angle gear drive. The motor can be closely coupled- in the air stream- or connected with a drive shaft with the motor outside the air stream. Maintenance personnel typically prefer the external TEFC motor- when available- for its easier access. Cooling tower fans- like all fans- operate in accordance with the fan laws one of which states that the horsepower required to drive a fan increases to the cube of fan speed. 

Gear boxes are used on just about all large field erected cooling towers and many factory assembled towers- all of the propeller ty e fan, draw-through type. Almost all are right angle gear drives with the input shaft horizontal and the output... 

A large natural-draft cooling tower collapsed in a 70-mph (110-km/hr) v/ind, probably due to imperfections in the shape of the tower, which led to stresses greater than those it was designed to take and caused bending collapse [10]. 

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