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Scale treatment system of circulating water system


Scale treatment system of circulating water system

In the cold and hot water system, the scaling phenomenon of the heat exchanger, transmission pipeline, pump valve, and other equipment is very common. Scaling will shorten the service life of the equipment, accelerate metal corrosion, increase maintenance costs, and threaten the safe operation of the equipment. The resulting economic losses are huge. The annual economic losses caused by scaling in the United Kingdom and the United States reach 1.5 billion and 50 billion US dollars respectively.

Therefore, it is of great significance to solve the problem of system fouling. In this paper, the commonly used scale control technology and its research progress are reviewed, and the development direction of scale control technology is pointed out, which provides a certain theoretical reference for the follow-up research.

1 scale formation

The scale is an insoluble or slightly soluble salt with abnormal solubility, which is easy to precipitate and deposit on the vessel wall, especially on the metal surface. The formation process is as follows: the microcrystals are in the sub stable state of dissolution crystallization in a supersaturated solution, the crystals gather and adhere on the wall of the reactor, grow up orderly, and form scale. The formation of scale mainly depends on whether the salts are supersaturated and the growth process of crystal, which is closely related to the scale-forming ions, water quality, and the wall morphology.
The more saturated the scaling ion is and the higher the hardness of water is, the more serious the scaling tendency is; rough metal surface and impurities also have a catalytic effect on the crystallization process, which will promote the precipitation of scale.

Most of the scale is white or grayish-white in appearance, hard and dense, mainly composed of calcium and magnesium salts of carbonate, sulfate, calcium phosphate, and silicate, the most typical of which is the calcium carbonate scale. In addition, iron scale and copper scale may also be produced in industrial boilers.

  1. Scale control method

The former is to inhibit or eliminate scale formation, and the latter is to remove the scale formed in the system.

Anti scaling methods include a chemical method, physical method, biological method, and chemical/physical method. The author mainly introduces a chemical method and a physical method.

2.1 chemical methods

Chemical control methods mainly include lime softening method, adding alkali precipitation method, carbonization treatment, adding acid treatment, ion exchange softening method and adding scale inhibitor method, etc. the first four methods are relatively traditional, with the direct effect but large drug consumption. The waste liquid produced needs to be treated, and the application cost is high, so they have been gradually eliminated. At present, the more advanced treatment methods at home and abroad are the ion exchange softening method and adding scale inhibitor method.

2.1.1 ion exchange softening method

In the ion-exchange softening process, sodium type cation exchange resin was used to treat hard water. Ca2 + and Mg2 + in water were exchanged with Na + and combined with resin

This method can remove Ca2 + and Mg2 + scaling ions in water and achieve the purpose of scale inhibition. The ion exchange method can soften the water deeply, but the equipment needs to be regenerated repeatedly.

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