Retrofit design selection

Various criteria were proposed for the optimal selection of the equipment configuration and the number and sizes of units. In grass-root design, the capital cost of equipment is mostly used as the optimization criterion. In retrofit design a more appropriate objective function seems to be the net profit, which has to be maximized. Papageorgaki and Reklaitis (1993) formulated the criterion as follows ... 

From Fig. 11.11 it is possible to verify the improvement in terms of carbon emission from the base case design to the retrofit design proposed (black bars lower than gray bars). Flowever, this retrofit design involved the recovery of water, so metrics related to water impact should be also assessed. The IChemE metrics have been selected to assess the water impact of the new retrofit design [63]. For the social assessment the health and safety issues were considered, through the appHcation of the Inherent Safety Index defined by Fleikldla [60]. The results obtained for the environmental and social assessments are summarized in Table 11.4. 

In a retrofit batch design, we optimize the batch plant profitability defined as the total production value minus the cost of any new equipment. The objective is to obtain a modified batch plant structure, an operating strategy, the equipment sizes, and the batch processing parameters. Discrete decisions correspond to the selection of new units to add to each stage of the plant and their type of operation. Continuous decisions are represented by the volume of each new unit and the batch processing variables which are allowed to vary within certain bounds. 

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