Optimal cleaning schedule for heat exchangers in a heat exchanger network

In process plants incorporating heat exchangers networks for heat recovery, fouling of heat-transfer surfaces hinders correct production activity and increases energy consumption thus giving rise to economic losses. The losses can be reduced if on-line cleaning of heat exchangers is applied. The scheduling of cleaning interventions on the individual exchangers in the HEN can be based on a priori knowledge of the time behaviour of the thermal resistance of fouling. In this paper, the mathematical model of the influence of fouling on heat exchanger and HEN operation is outlined and an example of its application is presented. Heat exchanger cleaning is postulated to maximise the avoided loss understood as the value of energy recovered if cleaning the HEN, minus the value of energy recovered without HEN cleaning, minus the cost of HEN cleaning. The mathematical formulation of the avoided loss is given and the computational approach to its maximisation is outlined. The example of optimal scheduling of cleaning interventions in a HEN comprising 10 heat exchangers is considered and numerical results are presented.