A Cost-Based Model for Clean Cycle Optimization

6 A COST-BASED MODEL FOR CLEAN CYCLE OPTIMIZATION  

The cost-based strategy with considerations of critical services is more appropriate for the process industry. Although several cost-based methods are available, the one developed by Smeenk and Kers (2001) is selected for discussion here as the method provides insights for cost-beneht trade-off in determining the clean cycle. 

the overall performance for a heat exchanger network can be measured by the network terminal temperature (7 ). 7 declines over time due to exchanger fouling resulting in increased furnace duty. 

To dehne a nominal base case to focus on fouling alone, typical feed rate, standard physical properties, and temperatures for all streams entering the network are used to model the heat exchanger network. The terminal temperature calculated for the nominal case is called nominal terminal temperature. To calculate the nominal terminal temperature at any point of time, the heat transfer coefficients for heat exchangers are calculated using spot online readings of temperature and flow rates based on equation (6.1) (f/jA,- = gj/ATini,i)- The UA values calculated are then used 

FIGURE 7.3. Heat exchanger network with a single train. 

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