One of the main issues of the optimization of energy use in chemical plants is represented by the problem of synthesizing heat exchanger networks (HENs). Pinch analysis and superstructure-based targeting approaches, such as those presented in the literature, should also take into account the impact of designing the corresponding heat exchanger network. This is of primary importance for the identification of the trade-offs between energy savings, added investment costs, as well as operability issues during multi-period, multi-modal operation. For these reasons, we have also proposed multi-period frameworks for synthesizing utility systems and HENs.
Methods and Results
Mian et al. 2016  proposed a sequential framework for the synthesis of utility systems and HENs and extended the formulation to account for thermal storage options. The derivative-free hybrid algorithm PGS-COM  has been coupled with the sequential approach for multi-period HENS.
Although it was necessary to limit the number of optimization variables at the upper level, results
indicated that optimizing penalty levels, utility sizes and design variables of storage yields a considerable improvement (39.5 %) in the total annual cost with respect to the original example.
The main limitation of the proposed approach is the number of variables that need to be optimized at the master level which risks significantly increasing the computational time required by PGS-COM. Nevertheless, the proposed approach can exploit the parallel computing capability of PGS-COM.
Mian et al.  proposed a framework for designing utility systems and heat exchanger networks. Multi objective optimization using a genetic algorithm was used at the upper level to optimize process/utility design variables, storage design variables and HEN structure. Modelling of utilities and sequential synthesis of the HEN was considered at the lower level. The algorithm was tested on the optimal design of a hybrid solar-driven gasification plant, adding thermal storage and renewable energy conversion options. It was shown that the optimization of the utility design, the operations scheduling as well as the heat recovery network, improves the waste-to-product efficiency up to 16% with respect to a non-optimized starting solution.
 A. Mian, E. Martelli, and F. Maréchal, “Framework for the Multiperiod Sequential Synthesis of Heat Exchanger Networks with Selection, Design, and Scheduling of Multiple Utilities,” Ind. Eng. Chem. Res., vol. 55, no. 1, pp. 168–186, Jan. 2016.
 E. Martelli and E. Amaldi, “PGS-COM: A hybrid method for constrained non-smooth black-box optimization problems: Brief review, novel algorithm and comparative evaluation,” Comput. Chem. Eng., vol. 63, pp. 108–139, Apr. 2014.
 A. Mian, E. Martelli, and F. Maréchal, “Multi-objective optimization of utility systems and heat exchanger networks: method and application to the solar assisted hydrothermal gasification case,” presented at the 27th European Symposium on Computer Aided Process Engineering, Barcelona, 2017.