Cooling water system precipitate formation

When the number of concentrations of the circulating water is in the order of 3-7, some of the salts dissolved can exceed their solubility limits and precipitate, causing scale formation in pipes and coolers. The purpose of the treatment of the cooling water is to avoid scale formation. This is achieved by the injection of sulfuric acid to convert Ca and Mg carbonates (carbonate hardness) into more soluble sulfates. The amount of acid used must be limited to maintain some residual alkalinity in the system. If the system pH is reduced to far below 7.0, it would result in an accelerated corrosion within the system. As stated earlier, scale formation and/or corrosion tendency is defined by the Saturation Index (Langelier Index) and Stability Index (Ryznar equation). 

Scale formation results from the precipitation of CaCOs andMg(OH)2. Precipitation of CaCOs is a particular problem in heated water systems such as steam power generation systems, industrial cooling systems, and home hot water systems because the equilibrium between HCOJ and CO3 increasingly favors as the temperamre in-... 

The saturation levels for common cooling-water scales were calculated, including calcium carbonate, calcium sulfate, amorphous silica, and magnesium hydroxide. Brudte saturation levels were included because of the potential for magnesium silicate formation as a result of the adsorption of silica upon precipitating magnesium hydroxide. Three categories of systems were encountered [24] ... 

The EBDS process is shown schematically in Fig. 12.3, An electrostatic precipitator is used to remove flya,sh from the flue gases before they pass to the treatment system to prevent contamination of the fertilizer byproduct. The flue gas is then cooled from about 200°C to 60-80°C in a water spray cooler, and ammonia is added. The conditioned flue gas enters the irradiation chamber (reactor), where high-energy electrons generate hydroxyl (OH) and hydroperoxyl (HOi) radical-s by collision with the water molecules. These radicals play the major role in the formation of sulfuric and nitric acid,s that react with ammonia to form the sulfate and nitrate. 

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