Fouling Mechanisms

Somerscales and Knudsen (1981) have identified six categories off fouling:

1. Particulate fouling. The accumulation ofsolid particles is suspended in the process stream on the heat transfer surfaces. Typical examples include dust deposition, particles carried in condenser cooling water, and unburned fuel, or fly ash. If the solid deposition is due to gravity, the process is referred to as sedimentation fouling.
2. Precipitation fouling. Dissolved substances carried in the process stream are precipitated on the heat transfer surfaces. Examples include carbonates, sulfates, and carbonates. Scaling occurs when precipitation occurs on heated rather than cooled surfaces.
3. Chemical reaction fouling. In certain cases, deposits on the heat transfer surfaces which are not, in themselves, reactants are formed by chemical reactions. In this type off ouling, cracking and coking ofhydrocarbons and polymerization are typical examples.
4. Corrosion fouling. In this type of fouling, the heat transfer surface reacts, at certain pH levels, to produce products that adhere to the heat transfer surfaces, and in turn, this may promote the attachment of additional fouling materials. Sulfur in fuel oil and sulfur products in the flue gas, such as sulfur dioxide, can lead to sulfuric acid. This has caused, for example, significant damage to heat exchange surfaces in air heaters in the power industry.
5. Biological fouling. Materials such as algae, bacteria, molds, seaweed, and barnacles carried in the process stream cause biological fouling of the heat transfer surfaces. A prime example of biological fouling is in marine power plant condensers.
6. Freezing fouling. In this type off ouling, a liquid, or some ofits higher-eltingpoint components will deposit on a subcooled heat transfer surface.