The chemical plant cooler has fouling blockage and corrosion problems in the heat exchange process, which affects the safe production of the chemical plant. For the cause and damage of the scale and corrosion of the cooler, the cooler plays an important role in the chemical production, and the cooler The scale of the unit is corroded, resulting in insufficient heat transfer and forced to stop cleaning or replacement of the cooler. In severe cases, it will affect the safety production.
It will increase the cost of running the enterprise. The four major causes of cooler fouling and corrosion are summarized.
Causes of scaling:
The accumulation of solid particles suspended in a fluid on a heat exchange surface is generally composed of fine particles of mud, dust, insoluble salts, gums, oil stains, and the like. When water containing these substances flows through the surface of the cooler, it is easy to form dirt deposits, forming scale corrosion, providing a hotbed for the survival and reproduction of certain bacteria. When the anti-corrosion measures are not correct, the heat exchange surface will eventually corrode and leak.
In addition to seawater cooling devices, general biofouling refers to microbial fouling. The most common microorganisms in circulating water systems are mainly iron bacteria, fungi and algae. Iron bacteria can convert Fe2+ dissolved in water into hydrates of water-insoluble Fe2O3, produce a large amount of iron oxide precipitates in water and establish oxygen concentration corrosion batteries to corrode metals. And the algae in the circulating water system often form a metal surface in the water to corrode the battery and cause corrosion under the deposit. Blocks also block the pipes in the cooler, reducing the flow of water and reducing heat transfer efficiency.
3. Crystallized dirt
In the cooling water circulation system, as the water evaporates, the concentration of dissolved salts (such as bicarbonate) in the water increases, some salts precipitate due to supersaturation, and some salts pass through the cooler heat transfer surface. It is thermally decomposed to produce a precipitate. These scales are composed of inorganic salts and are crystallized and dense, and are called crystal scales.
4. Corrosion of dirt
A corrosive fluid or a fluid containing corrosive impurities that corrode the heat exchange surface. The degree of corrosion depends on factors such as the composition of the fluid, the temperature, and the pH of the fluid being treated. Generally, the fouling cooling pipes in the cooling pipe are generally copper pipes and brass pipes, and the metal corrosion is mainly oxygen corrosion at a relatively high temperature (40 to 50 ° C), and the corrosion products of copper or copper alloys and calcium and magnesium precipitates. Mainly, causing a lot of corrosion and dirt.
5. Solidified dirt
The dirt formed by the solidification of the fluid on the supercooled heat exchange surface. For example, when the water is below the freezing point, it solidifies into ice on the heat exchange surface. The uniformity of the temperature distribution has a great influence on this type of fouling.
Causes of corrosion:
Most of the coolers are made of metal, and in nature most metals are often in the form of ores, or metal compounds, and corrosion is the process by which a metal returns to its natural state. The corrosion of the cooler mainly refers to the corrosion of the sheet. It is closely related to factors such as impure water quality, atmospheric pollution to water, inner wall condition and water flow rate.
The process in which the metal and the contacted substance directly undergo a redox reaction and are oxidized and lost.
2. Electrochemical corrosion
Electrochemical corrosion of metal surfaces and electrolyte solutions due to electrochemical interactions is the most common and common type of corrosion. Electrochemical corrosion usually occurs in the form of localized corrosion such as stress corrosion cracking, pitting corrosion (small pore corrosion), crevice corrosion.
3. Stress corrosion
Stress corrosion must have a specific corrosive environment and a sufficiently large tensile stress. CL- is another major cause of stress corrosion. CL- has a small radius and strong penetrating power. It easily penetrates the tiny pores in the protective film, destroys the local passivation film and enters the crack tip to generate HCL, which generates self-accelerating catalyzed accelerated corrosion process, while H+ precipitates at the tip and infiltrates. The leading edge of the crack can make the metal embrittlement. Temperature is an important factor causing stress corrosion cracking. The lower the temperature, the lower the Cl- concentration causing corrosion, and the more susceptible to stress corrosion cracking.
4. Biological corrosion
It is mainly caused by biological corrosion on the surface of the metal that is in contact with the medium such as circulating water of the cooling water system. The reason for bio-corrosion is that the organism will use organic corrosion inhibitor as food, bio-metabolism produces acid, destroys metal corrosion-resistant protective layer, biological metabolism consumes oxygen, causing uneven O2 concentration on metal surface and causing oxygen concentration corrosion.