Factors affecting scaling during heat exchanger cleaning

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There are many factors that affect scaling; aspects such as fluid velocity, flow pattern, composition and concentration of the fluid components, as well as the structure of the heat exchanger, all have an impact on the formation of fouling. From a practical standpoint, it is only by identifying the key factors that we can effectively address the problem of scaling. For a given fluid, the main factors affecting fouling in heat exchangers include the following: (1) Fluid flow velocity: In heat exchangers, the effect of flow velocity on fouling must take into account both its impact on fouling deposition and its impact on fouling erosion. For various types of fouling, the increase in erosion rate caused by higher flow velocities is more significant than the rate of fouling deposition; therefore, the rate of fouling growth decreases as flow velocity increases. However, in the actual operation of heat exchangers, an increase in flow rate leads to higher energy consumption; therefore, a higher flow rate is not necessarily better. It is necessary to consider both energy consumption and fouling. (2) Temperature of the heat transfer wall surface: Temperature plays an important role in chemical reaction-induced scaling and scaling due to salt crystallization. An increase in fluid temperature generally leads to an increase in the rates of chemical reactions and crystallization, which in turn affects the amount of fouling that accumulates, resulting in a higher rate of fouling growth. (3) Heat transfer surface material and surface quality: For commonly used materials such as carbon steel and stainless steel, the deposition of corrosion products can lead to scaling; whereas the use of non-metallic materials with good corrosion resistance, such as graphite or ceramics, makes scaling less likely to occur. The surface quality of the heat exchange surface material affects the formation and deposition of fouling; the greater the surface roughness, the more favorable it is for fouling to form and accumulate. Generally, the areas that need to be cleaned in heat exchangers are divided into the water (steam) side and the fluid side during cleaning, as most heat exchangers operate as heat transfer systems using water or steam as the heat carrier. The most common type of heat exchanger is the tubular heat exchanger, and it is primarily the tube side or shell side of this type of exchanger that needs to be cleaned.