A mixed integer nonlinear
programming (MINLP) model was developed based on the
three stage superstructure, which is shown in Fig. 10. In this
figure, red lines represent the process hot streams, and the
blue ones indicate the cold streams. The nodes in Fig. 10
indicate possible heat exchanges between hot and cold
streams at different stages. All the streams were split into
three branch streams before entering heat exchangers at each
stage. After heat exchange, the three substreams were mixed
isothermally and enter the next stage