Synthesis of Heat Exchanger Networks and Utility Systems: sequential initialization procedure and simultaneous MINLP algorithm

This work presents an extended version of the method recently proposed by (Martelli et al. 2015) for the simultaneous synthesis of Heat Exchanger Networks (HEN) and Utility Systems. The algorithm simultaneously determines the optimal selection of utility systems, their design, as well as the heat exchanger network between process-process, process-utility and utility-utility streams that minimize the total annual cost. The algorithm exploits an ad hoc sequential approach to find a good starting solution for the challenging synthesis problem. The Mixed Integer NonLinear Programming (MINLP) problem related to the simultaneous synthesis problem is then tackled with a specifically developed two-stage algorithm in which the Variable Neighborhood Search optimizes the integer variables and the Sequential Quadratic Programming algorithm optimizes the real variables. The algorithm is tested on the optimization of the HEN and Heat Recovery Steam Cycle of an Integrated Gasification Combined Cycle featuring 27 streams (1664 binary variables).