A multiperiod minlp model for improving the flexibility of heat exchanger networks

Abstract

A mixed integer nonlinear programming (MINLP) model is developed for the retrofit of heat exchanger networks in order to improve their ability to operate feasibly over a specified set of operating conditions (stream flowrates, stream inlet temperatures, overall heat transfer coefficients) at minimum cost. The model is based on a multiperiod match-network hyperstructure representation, which contains all possible retrofit alternatives embedded within, for all periods. Periods correspond to “critical” operating conditions identified through the solution of a flexibility analysis subproblem for the existing network. The resulting MINLP model also involves an explicit heat flow model and an objective function accounting for all structural modifications and operating cost. The solution of this MINLP problem provides a retrofitted network structure that is energy efficient and flexible to operate at the specified critical conditions.