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EXAMPLE: 7000 gpm circulating rate, 15° cooling range. To maintain 4
concentrations, the required blowdown is .38% or .0038 times 7000 gpm
which is 26.6 gpm.
If tower is operated at 4 concentrations, circulating water will contain four
times as much dissolved solid as the make-up water, providing none of the
solids form scale or are otherwise removed from the system.
CHEMICAL TREATMENT–In some cases chemical treatment of the cir-
culating water is not required if adequate blowdown is maintained. In most
cases, however, chemical treatment is required to prevent scale formation and
corrosion. Sulfuric acid or one of the polyphosphates is most generally used
to control calcium carbonate scale. Various proprietary materials containing
chromates, phosphates or other compounds are available for corrosion control.
When water treatment chemicals are required, the services of reliable water
treating companies should be obtained.
Biofilm, a gelatinous organic growth, and algae, a green moss, may grow
in the cooling tower or heat exchangers. Their presence can interfere with
cooling efficiencies. Proprietary compounds are available from water treating
companies for the control of slime and/or algae; however, compounds which
contain copper are not recommended. Chlorine and chlorine containing
compounds are effective algaecides and slimicides. If used, chlorine should
be added as intermittent (or shock) treatment only as frequently as needed
to control the slime and algae. Chlorine and chlorine containing compounds
should be added carefully since very high levels of chlorine may occur at or
near the point of entry into the circulating water system.
FOAMING–Heavy foaming sometimes occurs when a new tower is put into
operation. This type of foaming generally subsides after a relatively short pe-
riod of operation. Persistent foaming can be caused by the concentrations of
certain combinations of dissolved solids or by contamination of the circulating
water with foam-causing compounds. This type of foaming can sometimes be
minimized by increasing the blowdown, but in some cases foam depressant
chemicals must be added to the system. Foam depressants are available from
a number of chemical companies.
maintenance
