A. Scale The formation of scale, whether it is surface water or groundwater, they contain minerals, of which calcium, magnesium carbonate, sulfate, silicate and iron oxide are the main ones. Most of the circulating cooling water used for Brazed plate heat exchangers in chemical production is processed, and most of the salts have been treated, but the solubility of some salts decreases with increasing temperature, and some salts with increasing temperature High and decompose to form compounds with lower solubility; circulating water will continue to evaporate and concentrate as it is used. The concentration of untreated examples gradually increases, and it will crystallize and deposit after exceeding its saturation concentration; in the process of water treatment, due to other reasons As a result, the previous analysis and detection, supplementation of medicines, and the system's sewage discharge are not timely, and the concentration of a certain substance is too high or increased to silence on the inner wall of the system and form scale.
Classification of scale formation in Brazed plate heat exchangers :
a. Carbonate scale The carbonate content is more than 50%.
b. Sulfate scale The content of sulfate is more than 50%.
c. Silicate scale The content of silicate is more than 20%.
d. Mixed scale which contains at least the above three components.
B. Rust scale The formation of rust scale is mainly rust scale, and its formation usually has the following reasons: Aware that the basic surface of the steel is corroded during the rolling process or natural conditions, and the formed oxide scale is mainly FeO, Fe2O3, Fe3O4 and their hydrates; the second is that the equipment substrate is chemically eroded by the medium, and it is divided into acidic and alkaline environments, such as FeS and FeCl2 produced in the oil refining system; the third is that the equipment substrate is subjected to the circulating water system Corrosion of microorganisms, such as sulfur suan salt reducing bacteria, iron bacteria, etc., and their corrosion products are FeSO4, FeS, etc.
Classification of rust in Brazed plate heat exchanger:
Iron oxides, hydrates, iron fungi, FeS, etc.
C. Grease, petroleum refining, petrochemical, coal chemical, organic fine chemical and other industries, the raw materials used will be more or less deposited into the entire system during the production process, and the properties will also change due to the production process, forming a variety of Oil dirt, such as heavy oil, residual oil, petroleum coke, coal tar, kerosene and other difficult-to-clean substances.
D. Biological slime The formation of biological slime is the number and types of microorganisms living in water. Their optimal incubation temperature is 30-38 ℃, so the cooling water in the petrochemical industry is very suitable for the growth and reproduction of microorganisms. Not only do they multiply to form gel-like clumps, but also aggregate inorganic substances such as sand, Fe2O3, Fe (OH) 3, Mn3O4, Al2O3, CaSO4, SiO2, CaCO3 and other solids, so that they form so-called slime . This kind of slime is usually easy to mix with limescale with inorganic as the main component.
Classification of biological slime:
Divided into algae, iron bacteria, sulfur bacteria, fungi, sulfur suan salt, reducing bacteria.
E. Special material scale During the reflection or flow process of the medium in the system, due to the friction of the wall and the physical and chemical properties of the medium, as time accumulates, they will deposit on the inner wall of the system to form the special material scale of the medium itself.
Classification of special material scale in Brazed plate heat exchanger:
Its type is not necessarily the same as the type of medium. During its contact with the wall, it changes due to its own physical and chemical properties. It will also form materials with similar composition and deposit.