As seen in Fig. 10, the
three stage superstructure is composed of twenty-seven heat
exchangers, with nine possible matches at each stage. Since
the perfect matches of process streams are not possible for
each process stream, a heat or cold utility was installed at the
outlet of the superstructure depending on whether a stream
requires heat or releases heat if desiring to reach the target
temperature. The objective function was defined as minimizing
the annualized capital cost, which consists of the
utility cost, the fixed charge for the heat exchangers