Fouling, the undesired deposition of material on heat-transfer surfaces, represents a severe threat to the operability and economics of many industrial processes in the petrochemical, chemical, specialties, pharmaceutical and food industries. It appears in all types of heat exchange without and with phase change. Mitigation approaches include measures to modify the chemical or biochemical component system, to adjust process parameters (such as pressures, temperatures or concentrations), to optimize operational aspects or to design the best-suited equipment and plant. The latter is of special importance, as it represents the process hardware, which is responsible for the largest contribution to the investment and may not be changed easily once installed.
At today’s Heat Exchanger lecture, “Heat Exchanger Design Under Fouling Conditions” (12:00, Conclusio 2), Stephan Scholl of the Institute for Chemical and Thermal Process Engineering (ICTV) presents a strategy for heat-exchanger design under fouling conditions. The full design process can be divided into three individual steps: equipment-type selection, configuration and sizing. Each of these steps offers separate degrees of freedom to maximize fouling mitigation through optimum equipment design. Based on the following selection of different examples, this will be demonstrated.
– reboiler selection: forced circulation flash evaporator versus thermosiphon
– direct versus indirect evaporation and condensation
– reduction of thermal stress through optimized equipment configuration
– surface coatings for fouling mitigation
– operational aspects (steam quenching, pump-around in cooling water)
Based on a thorough understanding of the governing fouling mechanisms in a specific case, combined with the knowledge on the degrees of freedom in equipment design, economical and efficient equipment design under fouling conditions can be achieved.