Chlorine dioxide feed systems using liquid

Chlorine dioxide is produced on-site, as needed, for the application. At least two chemicals are combined to form chlorine dioxide. While a few proprietary chlorine dioxide feed systems exist, most systems used in water treatment plants combine chlorine gas (some use liquid sodium hypochlorite) with sodium chlorite (either solid or liquid). A chlorine dioxide solution is then fed at the point of application. Although chlorine dioxide feed systems are often a hybrid of gas and liquid (or solid), this discussion is included in the gas feed section of this book because the chlorine gas is commonly the controlling factor in this system. 

Diffusers are used to spread the chemical and to provide mixing energy. There are many different types of diffusers. Ozone and carbon dioxide feed systems commonly use fine bubble diffusers. Chlorine diffusers (Figures 2-5, 2-6, and 2-7) are often perforated pipe or even a simple open pipe. Many liquid chemicals are delivered into the process flow with diffusers. It is important to spread the chemical evenly in the water and to provide adequate mixing. 

The feed rate of chlorine and sodium chlorite is linked to the feed of chlorine dioxide because these are the primary chemicals used in most generation systems. The most common sources of chlorine are compressed gas and liquid sodium hypochlorite (12 percent trade is a common solution strength). Sodium chlorite is commonly used as a solid (about 65 percent sodium chlorite) and as a 25 percent strength solution. 

Feed systems can be hybrids, combining dry or gas feed with liquid feed components. Dry and liquid systems usually include a dry-to-liquid conversion (using a dissolving tank) that subsequently combines this liquid with another liquid. Gas-liquid hybrid systems can mix the gas with water first or with another liquid chemical in a reaction chamber. Chlorine dioxide generators using chlorine gas are an example of this type of system. The chlorine dioxide formed in the reaction is ultimately mixed with ejector water, and this solution is then mixed with process water at the point of delivery. 

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