Increasing cycles of concentration can allow processors to reuse waters and minimize water use. The typical practical contaminant maximums in recirculating cooling water are shown.
  • Alkalinity: total alkalinity (M alkalinity). A practical limit is often 500 mg/L as CaCO3, although up to 800 mg/L CaCO3 might be achievable, depending upon water chemistry.

  • Ammonia (NH3).Up to 20 to 40 mg/L can be tolerated if the copper content is low, water temperatures are not too high, good microbiological control is maintained, and waterside surfaces are kept clean.

  • Chemical Oxygen Demand (COD). Say, less than 100 mg/L

  • Calcium. A practical limit for total hardness is often 600 mg/L as CaCO3, although with top quality inhibitors and tight control, up to 1200 mg/L as CaCO3 might be achievable.

  • Chlorides. The lower the better, as chloride is a depassivating ion and reduces the corrosion resistance of many constructional metals. Perhaps 500-600 mg/L chloride in carbon steel systems, but only 200 mg/L maximum in systems containing 304 stainless steel. Also, the system metal surfaces must be kept scrupulously clean!

  • Iron. Iron salts (and to a lesser extent manganese salts) are often to be found in recovered waters and can be ignored unless the level rises to perhaps 0.3 mg/L or more.

  • Oil, Solvents and Hydrocarbons. Even small traces of oil can reduce chemical inhibitor performance and impede heat transfer and therefore must be eliminated.

  • pH. Typically, from pH 7.0 to 90.0

  • Phosphate. Phosphate in recovered waters can often be used as the basis of a chemical inhibitor program. Say 2-3 mg/L total PO4.

  • Silica. The limit of solubility in recirculating cooling water is typically around 150 to 175 mg/L and should not be exceeded.

  • Sulfate. Sulfates are causative agents (along with oxygen, hydrogen, etc.) of various types of concentration cell corrosion, Usually, say, 1800 mg/L is the maximum limit but this varies with several factors. Up to 2,300 mg/L has been tolerated in suitably conditioned systems.

  • Suspended solids (SS). Maximum tolerated levels of SS in recirculating water is perhaps 50 to 60 mg/L.


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