Causes and treatment methods of fouling in the hot

2022-08-26
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Causes and treatment methods of scaling in heat exchangers

scaling in heat exchangers costs a lot every year, which will affect the progress of safety production in serious cases. Fouling of heat exchanger refers to the layer of solid substance that gradually accumulates on the solid surface when the heat exchanger contacts with the unclean fluid. The influence of fouling on heat exchange equipment mainly includes: because the fouling layer has a very low thermal conductivity, it increases the heat transfer resistance and reduces the heat transfer efficiency of heat exchange equipment; When there is a scaling layer on the surface of the heat exchange equipment, the flow area of the fluid channel in the heat exchange equipment will be reduced, resulting in an increase in the resistance when the fluid flows through the equipment, thus consuming more pump power and increasing the production cost

according to the mechanism of scaling layer deposition, dirt can be divided into particle dirt, crystal dirt, chemical reaction dirt, corrosion dirt, in addition to the classic bromine flame retardant dirt, biological dirt, etc

1. Particle fouling: the accumulation of solid particles suspended in the fluid on the heat exchange surface. This kind of fouling also includes the precipitation layer of larger solid particles on the horizontal heat exchange surface due to gravity, that is, the deposition of the so-called precipitated fouling and other colloidal particles

2. Crystalline fouling: deposits formed by the crystallization of inorganic salts dissolved in the fluid on the heat exchange surface, which usually occurs during supersaturation or cooling. Typical dirt such as calcium carbonate, calcium sulfate and silica scaling layer on the cooling water side

3. Chemical reaction dirt: dirt generated by chemical reaction on the heat transfer surface. The heat transfer surface material does not participate in the reaction, but can be used as a catalyst for chemical reaction

4. Corrosive dirt: dirt caused by corrosive fluid or corrosive impurities in the fluid corroding the heat exchange surface. Generally, the degree of corrosion depends on the composition of the fluid, the temperature and the pH value of the fluid being treated

5. Biological fouling: except for seawater cooling devices, general biological fouling refers to microbial fouling. It may produce slime, which in turn provides conditions for the reproduction of biological dirt. This kind of dirt is very sensitive to temperature. Under appropriate temperature conditions, biological dirt can generate a considerable thickness of dirt layer

6. Solidified dirt: dirt formed by the solidification of fluid on the supercooled heat exchange surface. For example, when water is below the freezing point, it solidifies into ice on the heat exchange surface. The uniformity of temperature distribution has a great influence on this kind of dirt

the following points should be considered for the technology to prevent scaling: 1. Prevent the formation of scaling; 2. Prevent the adhesion between substances after scaling and the deposition on the heat transfer surface; 3. Remove deposits from heat transfer surfaces

the measures taken to prevent scaling include the following aspects:

I. measures to be taken in the design stage

in the design stage of heat exchanger, when considering potential fouling, the following aspects should be considered: 1. The heat exchanger is easy to clean and maintain (such as plate heat exchanger); 2. After the installation of the heat exchange equipment, the dirt can be cleaned on the industrial site without dismantling the equipment; 3. The least dead zone and low velocity zone should be taken; 4. At present, the velocity distribution in the heat exchanger should be uniform to avoid large velocity gradient and ensure uniform temperature distribution (such as baffle area); 5. On the premise of ensuring the reasonable pressure drop and no corrosion by means of long-term contract, equity participation or cross shareholding, increasing the flow rate will help to reduce dirt; 6. The influence of heat exchange surface temperature on fouling formation should be considered

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