Factors affecting scale formation in sea water environments - An experimental approach

Sea water is a complex aqueous environment with a large tendency for scale formation, which is usually ascribed to scaling from dissolved salts and suspended particles. Scale formation is causing many problems in thermal processes such as desalination and steam generation plants. In a typical desalination plant, ca. 40 % of the heat transfer area is provided to allow for scale formation problems, which is equivalent to a ca. 10 % increase of the whole capital cost of the plant. The main constituents forming scale in sea water environments, i.e., calcium carbonate, calcium sulfate and magnesium hydroxide, are extensively investigated in the present work. In order to obtain a better understanding of the scaling tendency of the seawater environment, an experimental unit was precisely designed and coupled with a data acquisition system for continuous monitoring of the investigated parameters. Significant factors affecting scale formation such as concentration of salts, flow velocity, water temperature and pH of the environments were studied at length using mild steel and stainless steel (smooth and rough). Hydrodynamic parameters such as Reynolds number and shear stress were used in the analysis of the collected data and revealed the role of shear stress in the effective removal of scale. The Kern-Seaton scale model was used to calculate the fouling resistance in each case and the values obtained were compared with the experimental results. A modification of this model was also undertaken to provide better agreement with experimental findings