Theory of Scale Formation and Prevention Scale Formation and Prevention
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چکیده
Most commercial water contains alkaline earth metal cations such as magnesium, calcium and barium, and anions such as carbonate, bicarbonate, sulfate, silicate, oxalate, phosphate, etc. Different combinations of these anions and cations will give rise to potentially scalant systems, such as calcium carbonate, calcium silicate, calcium sulfate, calcium oxalate, barium sulfate, magnesium sulfate, etc. Thus when combinations of these anions and cations are present in concentrations which exceed the solubility of their reaction products, precipitates form until their product solubility concentrations are no longer exceeded. For instance, when the concentrations of the calcium ions and carbonate ions exceed the solubility of calcium carbonate, reaction product will precipitate out. As various precipitates accumulate, they form scale; scale is a serious problem because it prevents effective heat transfer, interferes with fluid flow, enhances corrosion and invites bacteria. Scale is an expensive problem in many industrial systems, causing delays and shut-downs for cleaning and removal. This is most prominent in the pulp and paper industries, where scale causes major problems in digesters, evaporators, liquor heaters, deinking and bleach plants as well as headbox, felts, screens, etc. In order to understand the relationship between scale formation and/or scale prevention, we need to visit the following phenomena:
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