Marley Aquatower 490A, Руководство пользователя

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17
Blowdown
A cooling tower cools water by continuously causing a portion of it to evapo-
rate. Although the water lost by evaporation is replenished by the makeup
system, it exits the tower as pure water—leaving behind its burden of dissolved
solids to concentrate in the remaining water. Given no means of control, this
increasing concentration of contaminants can reach a very high level.
In order to achieve water quality which is acceptable to the cooling tower (as
well as the remainder of your circulating water system), the selected water
treatment company must work from a relatively constant level of concentra-
tions. This stabilization of contaminant concentrations is usually accom-
plished by blowdown, which is the constant discharge of a portion of the
circulating water to waste. As a rule, acceptable levels on which to base a
treatment schedule are in the range of 2–4 concentrations. The following table
gives approximate blowdown rates (percent of total water flow rate constantly
wasted) to achieve those concentrations at various cooling ranges*:
Maintenance
Note
Blowdown Rate
Cooling Two Four
Range (°F) Concentrations Concentrations
10 0.7% 0.17%
15 1.1% 0.30%
20 1.5% 0.43%
* Range is the difference between hot water temperature entering the tower and
cold water temperature leaving the tower.
When water treatment chemicals are added, they should not be in-
troduced into the circulating water system via the cold water basin
of the cooling tower. Water velocities are lowest at that point, which
results in inadequate mixing and may damage the cooling tower.
Intermittent Wintertime Operation:
If periods of shutdown (nights, weekends, etc.) occur during freezing
weather, measures must be taken to prevent the water in the cold water
basin—and all exposed pipework—from freezing. Several methods are
used to combat this, including Marley automatic basin heater system.
Unless some means of freeze prevention is incorporated into your
system, the tower basin and exposed pipework should be drained at
the beginning of each wintertime shutdown period.
If tower basin is drained, verify that all basin heaters have been shut
off either by automatic cutoff or disconnect switch.
Caution
Warning