Common Water Impurities
The following factors indicate the problems that poor-quality water may cause to the engineering plant and to human health:
• Metal corrosion
• Scale formation on the heat transfer surface
• Dezincification
• Plumbosolvency
• Biological health hazards
Water supplies should never be assumed to be chemically pure. Groundwater from wells and springs contains dissolved impurities. Its properties depend
TABLE 4.13 Common Water Impurities
|
continues) |
Constituent |
Formula |
Problems caused |
Methods of treatment |
Manganese |
Mn(Il) |
See iron |
See iron |
Nitrate |
NO, |
Increased solid content assists in the reduction of metal embrittlement Health problems with infants if used in foods |
Distillation Demineralization |
Oil |
Scale Sludge Foaming Fouling of pipe work and heat exchangers |
Baffle separators Strainers Coagulation Diatomaceous earth |
|
Oxygen |
0, |
Severe metallic corrosion |
Addition of corrosion inhibitors, sodium sulfite Automatic air vents, deaeration |
PH |
PH = log-^ H+ |
Graded into acidic or alkaline water Scale 0-14: 0 = highly acidic 7 = neutral 14 = highly alkaline |
Increased by alkaline addition Decreased by The addition of acid |
Silica |
Si 0, |
Scale buildup on Surrounding surfaces, reducing flow and heat transfer |
Removed by applying hot magnesium salts Demmeralization Processes |
Sulphate |
So4 |
Increased solid content Combines with Ca to form calcium sulfate salt |
Distillation Demineralization |
Suspended Solids |
Clogs pipelines Fouls heat exchanger Surfaces |
Settling Filtration |
|
Total solids |
Sum of dissolved and suspended solids |
See dissolved and suspended solids |
On the nature of the ground over which it flows or passes through. Surface water from lakes and rivers contains silt, dissolved impurities, and organic matter; its quality varies widely depending on flow rate.
Table 4.13 lists and briefly describes some of the impurities found in typical water supplies. As can be seen, a wide range of problems have been considered, and no one method of treatment is suitable for all cases. The
Pharmaceutical industry and silicon chip manufacturers require the greatest purity in the water used.
Posted in INDUSTRIAL VENTILATION DESIGN GUIDEBOOK