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Fouling
Fouling is a progressive process and can be defined as deposition of undesirable materials on the heat exchanger surface .
In the chemical process industries , some of the major issues faced in heat exchangers are fouling , vibration , leakages , and increased energy consumption . All these issues have a direct impact on the performance of the heat exchanger and effect the performance of downstream equipment .
By Mrinal Das - Senior Vice President Projects & Engineering Purchase , Dorf Ketal Chemical
Many of these issues are interlinked . For example , a lot of exchanger leakages occur from flow distribution issues . If the flow through the exchanger is not uniform , then high flow velocities can cause an additional problem , vibration . This vibration can increase the effect of erosion in exchangers which then leads to frequent leakage creating problematic maintenance and associated costs . Hence it becomes essential to use analytical tools to address flow distribution issues inside heat exchangers . Out of all the above issues , the most troublesome and common issue is fouling .
Fouling in heat exchangers Fouling is a progressive process and can be defined as deposition of undesirable materials on the heat exchanger surface . Undesirable materials could be inorganic salts , polymers , sludge , sediments , crystals , coking products , biological deposits etc . Fouling in a heat exchanger directly impacts the heat transfer and flow . Fouling results from the synergistic consequence of transient mass momentum and heat transfer phenomenon between fluids and surfaces . The fouling process significantly depends on operating conditions like temperature , pressure , viscosity , density , thermal conductivity . Fouling in a process plant causes significant reduction in thermal performance , increase in pressure drop , promoting corrosion and eventually failures in heat exchangers .
Common fouling types Generally , about six types of liquid-side fouling mechanisms are observed in process plants viz . corrosion fouling , biological fouling , particulate fouling , chemical reaction fouling , precipitation or crystallisation fouling , freezing / solidification fouling . Common types of fouling are chemical , biological , deposition , and corrosion . Chemical fouling occurs from chemical reactions in the fluid stream resulting in the deposition of material on the heat exchanger surface . This type of fouling is common for chemically sensitive materials when the fluid is heated to temperatures near its decomposition ( degradation ) temperature . Coking of hydrocarbon materials on the heat transfer surface is also a common chemical fouling issue . Biological fouling occurs when biological organisms grow on heat transfer surface . It is common fouling mechanism where untreated or improperly treated water is used as coolant . Corrosion fouling results from a chemical reaction which involves heat exchanger surface materials . Many metals such as copper and aluminum form adherent oxide coatings which serve to passivate the surface and prevent further corrosion . Many metal oxides which are corrosion products exhibit quite a low thermal conductivity and even relatively thin coatings of oxides may significantly affect heat exchanger performance . Deposition fouling occurs when fluid particles settle onto the inorganic surfaces area . This is generally seen when www . heat-exchanger-world . com Heat Exchanger World February 2023
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