Cooling towers selection

In the first design, a small L G ratio must be used. Since G cannot be increased beyond certain limitations (because of economics), L should be small. Experiments on cooling towers have indicated that their characteristics break sharply when L approaches a critical point varying with design. The 

What constitutes the ideal tower To some, it is one that heats the air to the inlet-water temperature, whereas to others, it is a tower that cools the water to the wet-bulb temperature. The term effectiveness coefficient or efficiency of the tower gives an indication of how close we are to the ideal case. In cooling tower practice, such a coefficient can be meaningless as the general attitude throughout industry is that the most efficient tower is the one that is simply the most economical, 

In this plot, the size corresponding to the selected condition for a typical tower design is called the 100% design. The curve shows percentage variation of the tower size if any two of the conditions are kept constant and the others varied. 

In general, it is desirable to choose operating conditions requiring minimum energy potential of the air utilized. However, in practice it is not possible to 

Large volumes of excess air necessitate that large fan capability be utilized. 

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Cheremisinoff, N. P. and P. N. Cheremisinoff, Cooling Towers, Selection, Design and Practice, Ann Arbor Science Publishers, Inc. (1981). 

Pfeiffer, E. L., Preliminary Cooling Tower Selection, Foster Wheeler Corp., Bui. CT-49-6, reprinted from Chem. Eng (date not given). 

INDUSTRIAL Water Society Guide to Mechanical Draught Evaporative Cooling Towers Selection. Operation and Maintenance (London, 1987). 

Knuesch, T. Environmental Aspects of Cooling Tower Selection, Process Eng. (November 1978). 

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—Selection, Design Practice—Nicholas P. 

The problem of cooling tower selection is not merely to determine the required size and cost of a tower to meet a given set of conditions, but also to select the optimum des conditions on the basis of overall plant economy. The following examples show how the charts (Figures 3-2 through 3-5) are used and deal with the various problems involved in selecting the optimum tower. 

A decade ago it was not uncommon to specify 85° F cold water and to select exchangers for 88 to 90° F cold water. To some engineers it seemed logical to include a small 3°F safety factor in the calculations. However, this 3°F safety factor quite often turned out to be a 50% safety factor as far as the price and size of the cooling tower were concerned. Table 3-5 indicates that a tower sized to cool 28,500 gpm from 118 to 88° F with an 80° F wet bulb would cost 361,920, or 12.70 per gpm. A cooling tower selected to cool 28,500 gpm with the 3°F safety factor or from 115 to 85° F with an 80°F wet bulb would cost 532,480, or 18.68 per gpm. This is approximately 50% more in cost, length of concrete basin and fan horsepower. 

Design wet bulb temperature is determined by geographical location. Usually the wet bulb temperature selected is not exceeded more than 5% of the time in any area. Wet bulb temperature is a factor in cooling tower selection. The higher the wet bulb temperature the smaller the tower required to give a specified approach to the wet bulb at a constant range and gpm. 

A cooling tower selected to cool 28,500 gpm of water from 118 to 88° F at 70° F wet bulb would be smaller than a cooling tower selected to cool 28,500 gpm from 118 to 88°F at an 80°F wet bulb. In spite of the fact that the wet bulb temperature has increased, the reduction of approach from 18 to 8°F dictates that the tower must be larger. Table 3-9 indicates the effect of wet bulb temperature in sizing a tower when the gpm and range remain constant. 

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