Boiler Scaling, Fouling, and Deposition

We typically use scaling, fouling, deposition, and several other terms in the same context and fairly indiscriminately because there is no universal definition. In general, these physicochemical processes may take 

Mineral scales typically result from the effects of localized concentration of salts within the watersides of a boiler and the inverse solubility of many such salts at elevated temperatures. Scales often are hard, dense, and difficult to remove. They can be either crystalline or amorphous (lacking any characteristic crystalline shape). 

Silica and many of the metals commonly found in scales and deposits can form various permutations of oxides and salts, depending on the specific boiler area location and operating circumstances. Each mineral possesses distinct characteristics and may exert different effects. 

although the analysis of scales and deposits typically is carried out by a combination of wet chemistry techniques and atomic absorption spectroscopy, an identification of the specific nature of the crys- 

Although the risk of scale deposition and fouling in the boiler section is related to several factors such as the FW volume demands, boiler pressure, and heat flux density at various boiler surfaces, it is equally a function of the level of FW contaminants such as residual hardness, sulfates, silica, and iron. Thus, as a generality, the higher the quality of FW (reduced levels of contaminants), the lower the risk of deposition on boiler surfaces. 

---