The optimal integration between heat and work may significantly reduce the energy demand and consequently the process cost. This paper introduces a new mathematical model for the simultaneous synthesis of heat exchanger networks (HENs) in which the pressure levels of the process streams can be adjusted to enhance the heat integration. A superstructure is proposed for the HEN design with pressure recovery, developed via generalized disjunctive programming (GDP) and mixed-integer nonlinear programming (MINLP) formulation. The process conditions (stream temperature and pressure) must be optimized. Furthermore, the approach allows for coupling of the turbines and compressors and selection of the turbines and valves to minimize the total annualized cost, which consists of the operational and capital expenses. The model is tested for its applicability in three case studies, including a cryogenic application. The results indicate that the energy integration reduces the quantity of utilities required, thus decreasing the overall cost.

The optimal integration of work and its interaction with heat can represent large energy savings in industrial plants. This paper introduces a new optimization model for the simultaneous synthesis of work exchange networks (WENs), with heat integration for the optimal pressure recovery of process gaseous streams. The proposed approach for the WEN synthesis is analogous to the well-known problem of synthesis of heat exchanger networks In all case studies, the heat integration between WEN stages is essential to improve the pressure recovery, and to reduce the total costs involved in the process.

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Several methods for heat exchanger networks (HEN) design are based on the use of superstructures. The models they give rise to can lead to different design options to be explored in HEN synthesis. In this work, a stage-wise superstructure with new features for the optimal placement of heaters and coolers, including the possibility of the use of multiple utilities, is presented. In the model, those units can be placed in different stream split branches in all stages, differing from the usual allocation at stream ends. Such possibilities yield a more complex mathematical model. To solve it, an improved version of a previously presented hybrid meta-heuristic method was used. Three examples from the literature were studied. The use of the superstructure with the additional utility-related options, as well as the enhanced meta-heuristic solution method, led to configurations with lower associated total annual costs than those reported in previous works.