What causes scaling from water?
The formation of scale deposits occurs through a process of precipitation and crystallization involving mineral or inorganic impurities present in the water. When these contaminants come into contact with a heat transfer surface, their solubility limits are surpassed in the high-temperature zones, leading to the precipitation of solid particles. This phenomenon arises due to the inverse solubility behavior exhibited by certain scale-forming salts, wherein their solubility decreases as the temperature rises.
The formation of scale is not exclusively tied to temperature variations. Calcium carbonate and calcium sulfate can precipitate and form scale deposits on surfaces that are not subjected to heating. This occurs when the concentration or pH levels of the bulk water surpass the solubility limits of these compounds, causing them to precipitate and accumulate on the unheated surfaces.
Metallic surfaces provide favorable conditions for the initiation of crystal formation due to their rough texture and the relatively low fluid velocity near the surface. Corrosion processes on the metal surface create localized regions with elevated pH levels, which can trigger the precipitation of various salts present in the cooling water. Once these scale deposits form, they act as additional nucleation sites, leading to an accelerated rate of crystal growth and further scale accumulation.
Mitigation of scale formation can be accomplished through a combination of mechanical and chemical strategies. Operational approaches, such as modifying fluid flow patterns or adjusting heat transfer rates, can help alleviate scaling tendencies. Additionally, various chemical parameters can be manipulated to control scale formation. These include adjusting the pH and reducing the concentration of scale-forming elements in the influent water, as well as introducing specialized additives that inhibit crystal growth and prevent their adhesion to surfaces.
