Simultaneous optimization of heat-integrated water networks involving process-to-process streams for heat integration

• An extension is presented of the superstructure and optimization model.
• Two strategies are proposed for the heat integration of process-to-process streams.
• New constraints are proposed for further simplifying the HEN model.
• Improved and novel designs are given for heat-integrated water networks.

This paper presents an extension of our recent work, in which we addressed the simultaneous synthesis of heat-integrated water networks. The novelty and goal of this work is the development of an extended superstructure and simultaneous optimization model of heat-integrated water networks now involving process-to-process streams, and other streams within the overall network, for heat integration. Those heat-integration opportunities have not yet been fully taken into account in most existing models of heat-integrated water networks. In this study, we presented two strategies for heat integration of process-to-process streams. The first one includes the placement of heat exchangers on each hot and cold process-to-process stream. The second allows for the cooling and splitting of hot streams, and heating and splitting of cold streams. This extended model was formulated as a non-convex mixed-integer non-linear programming (MINLP) problem. The objective was to minimize the total annual network cost. Two examples with single and multiple contaminants are used in order to demonstrate that involving process-to-process streams for heat integration, novel and improved solutions can be obtained compared to those reported in the literature.

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