Optimal heat exchanger network synthesis with operability and safety consideration

Abstract

Heat exchanger network (HEN) in the industries is very complex as it considers many problems and situations. Quantitative part such as cost of the heat exchanger and external utilities as well as the qualitative part such as safety, operability and flexibility are part of the design objective. This study presents a method for optimal HEN design which considers the inherent safety and operability aspects in the design. Data will be extracted for pinch study and safety assessment. The construction of continuous hot and cold Stream Temperature vs Enthalpy Plot (STEP) prioritized the inherent safety index than the heat capacity flowrate (FCp). The high ISI of hot and cold streams are matched together and vice versa. Thus, the focus of safety can centralized on a particular heat exchanger. The pinch temperature and minimum utility can be determined from STEP. The disturbance propagation path through the HEN and the affected streams are analysed. The modification of network by downstream path concept is performed in order to reduce the disturbance propagation path and affected streams. The ?Tmin violation and energy penalty is determined due to the changes of network. The flexibility and the structural controllability of each of the alternative network are determined and compared. Highest percentage of changes in every streams of the network and index of structural controllability near to 1 indicates that network is the most flexible and controllable. The application of this method on Case Study 2 shows alternative network 3 is the most flexible and controllable with 22% and 0.917 respectively.