**4. Illustrative Example**

The methodology described in Section 3 is illustrated using a four-stream example. The example was adapted from Lal et al. [34] with some modifications for demonstration purposes and was used as an initial network in a retrofitting process. In Figure 3, the initial network, the average stream data, and six different retrofit proposals are presented. These retrofit proposals are partly inspired by design proposals obtained by applying the Bridge analysis methodology presented in [34]. The main objective of the different retrofit proposals was to reduce the utility consumption in the heaters of the HEN. Table 1 shows the hot utility demand of the initial network as well as the hot utility demand and the hot utility savings of the six retrofit proposals.

**Figure 3.** Initial network with average stream data and six different retrofit proposals.


**Table 1.** Hot utility demand for the initial heat exchanger network (HEN) and the different retrofit proposals as well as the potential savings for average operating conditions.

The initial network consists of two process-to-process HEX and four utility HEXs. In Table 2, the design characteristics of the existing process-to-process HEX are listed. For simplicity, it was assumed that the utility HEXs are not limited by size, i.e., any possible duty can be satisfied. For process-to-process HEX, a constant overall heat transfer coefficient (i.e., U-value) of 0.523 kW/(m2 ◦C) was assumed.

**Table 2.** Design characteristics of the initial network.

