Plate heat exchanger is a kind of cooling equipment widely used in the atmospheric and pressure reduction workshop of oil refinery. According to the mechanism of scaling layer deposition, dirt can be divided into granular dirt, crystalline dirt, chemical reaction dirt, corrosion dirt, biological dirt, etc.

1) granular fouling: accumulation of solid particles suspended in the fluid on the heat exchange surface. The fouling also includes a layer of deposits formed by gravity on the horizontal heat exchange surface by larger solid particles, called deposited dirt and other colloidal particles.

2) crystallized dirt: sediment formed by the crystallization of inorganic salts dissolved in a fluid on the heat transfer surface, usually occurring during susulate or cooling. Typical fouling such as the cooling water side of the calcium carbonate, calcium sulfate and silica scale layer.

3) chemical reaction dirt: dirt produced 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) corrosion fouling: fouling caused by corrosion of heat exchange surface caused by corrosive fluid or corrosive impurities in the fluid. 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 seawater cooling device, general biological fouling refers to microbial fouling. It may produce slime, which in turn provides conditions for biological slime to multiply. Under the right temperature conditions, biological slime can generate a considerable thickness of dirt layer.

6) solidified dirt: dirt formed by solidification of fluid on the supercooled heat exchange surface. For example, when the water is below zero, it solidifies into ice on the heat exchange surface. The uniform distribution of temperature has a great influence on the fouling.