An open recirculating cooling system uses the same water
repeatedly to cool process equipment. Heat absorbed from the
process must be dissipated to allow reuse of the water. Cooling
towers, spray ponds, and evaporative condensers are used for
this purpose. recirculating cooling systems save a tremendous
amount of fresh water compared to the alternative method, once-
through cooling. The quantity of water discharged to waste is
greatly reduced in the open recirculating method, and chemical
treatment is more economical. However, open recirculating
cooling systems are inherently subject to more treatment-related
problems than once-through systems: cooling by evaporation
increases the dissolved solids concentration in the water,
raising corrosion and deposition tendencies the relatively
higher temperatures significantly increase corrosion potential
the longer retention time and warmer water in an open
recirculating system increase the tendency for biological growth
airborne gases such as sulfur dioxide, ammonia or