towers, forced (mechanical) draft cooling towers, cooling ponds, or spray 

 canals (Figure 44). 



Figure 44. A mechanical draft cooling tower for power plant closed-cycle 

 condenser cooling (Source: Reference 137). 



2 4 



OUTLET AIR 



© (D 



INLET AIR \' 



® a 



INLET AIR 



COLD WATER 



Aquatic animals too large to pass through intake screens (3/8" mesh 

 on power plants) are "impinged on the screening and if the flow rate is 

 high they are unable to escape and will be killed. This problem is 

 associated mostly with the large volumes (over 100,000 gallons per minute) 

 and rates of flow (over 0.25 ft/sec) that are typical of electric power 

 plants [138]. Larger fishes appear to be capable of avoiding entrainment 

 and screen kills are mostly the smaller fishes, less than 5 inches. The 

 number of fishes impaled on power plant screens has exceeded five million 

 in a few weeks' time at one estuarine-sited power plant with open-cycle 

 cooling [138]. Where impingement problems are anticipated, they can best 

 be offset by locating intakes away from gathering areas of small fishes 

 and by eliminating canals, intake bays, forewells, or other containing 

 structures ahead of the intake that would attract fish [138]. 



If the demand for cooling water is modest, it may be practicable 

 to obtain it from wells or from municipal water systems. New refineries 

 near estuaries should use brackish water but be designed to avoid its 



170 



