SPX Cooling Technologies MARLEY CLASS 800 - Manual (Page 19)

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these values it is possible to calculate the index and predict the corrosive tendencies
of the tower water toward concrete. An explanation and method of calculating
the Langelier index can be found in all books on water treatment. Maintaining a
positive Langelier index provides excellent protection of concrete.
Slime, a gelatinous organic growth, and algae, a green or brown plant growth,
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, if used, should be introduced at a point in the circulating
water system that will promote rapid dispersal, and residual chlorine
should not exceed one part per million parts water (1 ppm).
Scaling
Scale can be caused by the uncontrolled presence of sulfates, silicates,
carbonates, or oxides, and their effect can be accentuated by the presence
of suspended muds. Some suggestions and limitations follow:
• Calcium sulfate may be introduced in the make-up water stream
and/or produced by the use of sulfuric acid for pH adjustment. The
concentration of calcium sulfate should be kept below 1000 ppm, expressed
as CaCO
3
.
• Calcium carbonate generally will not form scale in the cooling tower if
carbonate scaling does not occur in the condenser. However, if make-up
water contains surplus free carbon dioxide, scaling may be inhibited in the
condenser but may occur in the fill because of CO
2
stripping.
• Silica scale is virtually impossible to remove. However, silica scale is unlikely
if concentrations of SiO
2
are held below 150 ppm.
• Oxides, such as iron oxide, can coat all parts of the system if soluble iron
is present in concentrations above 0.5 ppm. Iron oxides do not usually
develop into thick scales but, like mud, can accentuate the development
of other scales.
Foaming
Heavy foaming sometimes occurs when a new tower is put into operation.
This type of foaming generally subsides after a relatively short period 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.
Water Treatment
Caution