Fouling Monitoring in Thermosiphon Reboiler

Abstract

A method to monitor the fouling resistance of a heat exchanger, especially the thermosiphon reboiler, is presented. The historical hourly data of reboiler and distillation column are used to analyze fouling factor. The initial value of overall heat transfer coefficient and the current overall heat transfer coefficient are needed to calculate fouling resistance. Since the initial heat transfer coefficient is not constant but is affected by operating conditions such as shell/tube flow rate and temperature, a relationship between initial heat transfer coefficient and these operating conditions has to be developed to calculate the fouling factor. However, sometimes important data such as tube-side flow, inlet/outlet temperature of hot/cold fluid, and liquid level in shell/tube, which are needed to bring out the fouling condition of equipment, are missing. With such insufficient information, the fouling behavior can be analyzed by building a new equation based on measurable data. Dimensional analysis determines the structure of the function; parameters of each term are obtainable using short-term plant data after cleaning, assuming that there is no fouling during this period. As it is not easy to measure actual fouling factor temporal change in the heat exchanger tube, the calculated fouling resistance is compared with the relative amount of solid material removed from the equipment during cleaning, and it is evaluated qualitatively. The comparison shows good agreement. In addition, the evolution of the fouling resistance of some thermosiphon reboilers over a period of a few months or even years can be matched using this model.