Metal surface, fouling process

A variety of animals and plants, as well as colonies of microorganisms, may deposit from natural sea water onto the metal surface. The life processes and decomposition products may contribute directly to attack on the metal. Fouling may obstruct flow in heat exchangers and pipes, leading to such corrosive effects as are caused by overheating or impingement at local high-water velocities. 

Numerous reactor design variations have been employed in commercial processes. Polished stainless steel reactors have been used in place of glass-line tanks for some systems. The smooth surfaces (glass or polished metal) are desirable to minimize surface fouling. The use of stainless steel increases heat transfer rates and reduces maintenance costs. The stainless surface may, however, be more prone to fouling. 

The work by Bott and Gudmundsson [1977] with wax dissolved in kerosene demonstrates that the attainment of the equilibrium condition is likely to be a rapid process. It would appear from Fig. 8.19 that the asymptotic fouling resistance is reached after only 2 hours. Rapid deposition occurs in the first few minutes of exposure of the metal surface to the flowing waxy hydrocarbon. 

Underdeposit corrosion is likely to occur in cooling systems where scales or foulants exist. The presence of general fouling and scales can cause the formation of a differential cell, which begins the process of corrosion because of the difference in oxygen concentration at the metal surface beneath the deposit and the oxygen concentration in water, a differential cell forms, resulting in the corrosion reaction. 

Precipitation fouling may be defined as the phenomenon of a solid layer deposition on a heet transfer surface, primarily as a result of the presence of dissolved inorganic salts in the flowing solution which exhibit supersaturation under the process conditions. Deposits formed under various conditions have different mechanical characteristics. The term "scaling" is generally used to describe a dense crystalline deposit, well bonded to the metal surface. It is often associated with the crystallization of salts of inverse solubilities under heat transfer conditions. When the deposited layer is porous and loosely adherent, it is described by terms such as "soft scale," "powdery deposit," or "sludge."... 

The majority of easily detected compounds at solid anodes under constant applied potentials are self-stabUized via tt-resonance. Therefore, a desirable characteristic of electrodes in dc amperometry is inert. The electrode serves as a sink to provide and remove electrons with no direct involvement in the reaction mechanism. Since TT-resonance does not exist in polar ahphatic compounds (e.g., carbohydrates), stabilization of reaction intermediates is actively achieved via adsorption at clean noble metal electrodes. Faradaic processes that benefit from electrode surface interactions are described as electrocatalytic. Unfortunately, an undesirable consequence of this apiproach is the accumulation of adsorbed carbonaceous materials, which eventually foul the electrode surface. 

The problem of fouling of metal surfaces in the food processing industry has been particularly acute in the dairy industry. " The heat... 

Metal oxides found in RO feed streams typically originate from corroded pipes found in the RO process. These metal oxides can deposit on the membrane surface and decrease the membrane flux. This type of fouling can be prevented by using the proper materials of constmction in the piping system to prevent corrosion. 

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