9.0WATER QUALITY RECOMMENDATIONS
Water quality is often overlooked when the cooling system of a water cooled air compressor is examined. Water quality determines how effective the heat transfer rate, as well as the flow rate will remain during the operation life of the unit. It should be noted that the quality of water used in any cooling system does not remain constant during the operation of the system. The water makeup is affected by evaporation, corrosion, chemical and temperature changes, aeration, scale, and biological formations. Most problems in a cooling system show up first in a reduction in the heat transfer rate, then in a reduced flow rate, and finally with damage to the system.
There are many constituents in the water system that must be balanced to have a good stable system. The following is a list of the major components that should be monitored:
SCALE
Scale formation inhibits effective heat transfer, yet it does help prevent corrosion. Therefore, a thin uniform coating of calcium carbonate is desired on the inner surfaces.
Perhaps the largest contributor to scale formation is the precipitation of calcium carbonate out of the water. This is dependent on temperature and pH. The higher the pH value the greater the chance of scale formation. Scale can be controlled with water treatment.
CORROSION
In contrast to scale formation is the problem of corrosion. Chlorides cause problems because of their size and conductivity. Low pH levels promote corrosion, as well as high levels of dissolved oxygen.
FOULING
Biological and organic substances (slime) can also cause problems, but in elevated temperature environments such as cooling processes, they are not major concerns. If they create problems with clogging, commercial shock treatments are available.
To ensure good operation life and performance of the compressor cooling system, the recommended acceptable ranges for different water constituents are included below:
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| PARAMETER |
| CONCENTRATION |
| FREQUENCY OF ANALYSIS |
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| Corrosivity (hardness, |
| Langelier Index |
| Monthly |
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| pH, total dissolved solids, |
| 0 to 1 |
| (if stable for 3 to 4 months, |
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| temperature at inlet, |
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| analyze quarterly) |
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| alkalinity) |
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| Iron |
| < 2 ppm |
| Monthly |
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| Sulfate |
| < 50 ppm |
| Monthly |
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| Chloride |
| < 50 ppm |
| Monthly |
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| Nitrate |
| < 2 ppm |
| Monthly |
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| Silica |
| < 100 ppm |
| Monthly |
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| Dissolved oxygen |
| 0 ppm |
| Daily |
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| (as low as possible) |
| (if stable, analyze weekly) |
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| Oil and grease |
| < 5 ppm |
| Monthly |
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| Ammonia |
| < 1 ppm |
| Monthly |
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