At present, there are two methods to prevent or control scale, chemical and physical, and the physical methods used in China are magnetization treatment and electrostatic treatment, which are mostly used in a single equipment or small system, and its technology has yet to be mastered.
For large and medium-sized circulating cooling water systems, it is more mature, economical and effective to use chemical methods to treat. The most common limescale is calcium carbonate, so various methods focus on solving calcium carbonate deposition problems, such as:
1.Remove part of the scaling ions, the scaling ions of calcium carbonate scale are calcium and carbonate (converted from bicarbonate) ions, when the calcium ions and alkalinity in the supplementary water are high, part of the hardness and alkalinity can be removed in the pretreatment process, that is, softened supplementary water is used. The demineralized water has low scale ions, which is conducive to improving the concentration factor of circulating water, and the commonly used softening methods are ion exchange method and lime softening method.
2.Add acid or carbon dioxide to reduce the pH value of the circulating water and stabilize the bicarbonate.
3.Anti-scale and corrosion inhibitors are added to the recirculated water to destroy the crystalline growth of scale salts such as calcium carbonate and prevent scale deposition.
The above scale inhibition measures can only delay the cycle of system fouling, no matter how the system will inevitably have fouling, so descaling is a necessary supplement in operation. Generally, descaling is divided into two types: one is physical cleaning, including but not limited to manual cleaning, mechanical cleaning, ultrasonic cleaning, etc.;The second is chemical cleaning, according to the type of scale to choose the appropriate cleaning agent, can be a single cleaning or the whole system cleaning, generally after cleaning need to be pre-filmed, so that the fresh metal surface in the activated state, or the metal surface of the protective film is damaged in advance to generate a complete and corrosion-resistant protective film.
In addition, it should be noted that a large amount of foam will occur during the cleaning process with surfactant, so prepare the defoamer in advance, and add 3-5mg l of defoamer to the pool when a large amount of foam is generated, and the foam will be eliminated soon.
What chemicals can be used for scale inhibition and descaling of circulating cooling water?