SPX Cooling Technologies Cooling Tower Marley MD - Manual (Page 19)

19
Water Treatment and Blowdown
Maintaining Water Quality:
The steel used in MD towers has been galvanized with a heavy zinc coat-
ing averaging 2.0 mils in thickness. The MD stainless steel option is even
more corrosion resistant than galvanized steel in certain environments.
Other materials used (PVC fill, drift eliminators, and louvers, aluminum
fans, etc.) are selected to offer maximum service life in a “normal” cooling
tower environment, defined as follows:
Circulating water with a pH between 6.5 and 8; a chloride content (as NaCl)
below 500 mg/L; a sulfate content (SO4) below 250 mg/L; total alkalinity
(as CaCO
3
) below 500 mg/L; calcium hardness (as CaCO
3
) above 50
mg/L; a maximum inlet water temperature not to exceed 125°F (51.7°C);
no significant contamination with unusual chemicals or foreign substances;
and adequate water treatment to minimize scaling.
• Startup Conditions: The water conditions during the initial tower opera-
tion are crucial in preventing premature corrosion of galvanized steel
(white rust). For at least the first eight weeks of operation, pH should
be controlled between 6.5 and 8.0 with hardness and alkalinity levels
between 100 and 300 mg/L (expressed as CaCO
3
).
• Chlorine (if used) shall be added intermittently, with a free residual not
to exceed 1 mg/L—maintained for short periods. Excessive chlorine
levels may deteriorate sealants and other materials of construction.
• An atmosphere surrounding the tower no worse than “moderate indus-
trial”, where rainfall and fog are no more than slightly acid, and they do
not contain significant chlorides or hydrogen sulfide (H
2 S).
• Many proprietary chemicals exist for control of scale, corrosion, and
biological growth and should be used prudently. Also, combinations
of chemicals may cause reactions which reduce treatment effective-
ness, and certain chemicals such as surfactants, biodispersants and
antifoams may increase drift rate.
Unless you purchased a stainless steel MD, the structure of your MD
tower consists primarily of galvanized steel, therefore your water
treatment program must be compatible with zinc. In working with
your water treatment supplier, it is important that you recognize
the potential effects on zinc of the specific treatment program you
choose.
Operation
Note