Heat exchanger network retrofit optimization with heat exchanger design

Abstract

Heat exchanger networks (HENs) are structures that promote heat transfer between hot and cold process streams, with the goal of reducing utility consumption. One highly relevant industrial application of HENs is the retrofit of existing networks, in which an investment is made in an already operational network to intensify heat recovery. Compared to the design of a new HEN, the retrofit problem is significantly more complex, as it must incorporate the characteristics of an existing operating network. From a mathematical standpoint, this is a problem with a drastic combinatorial explosion and significant nonlinearities, leading to convergence issues, multiple local optima, and high computational effort. As a result, existing works in the literature are full of simplifications, especially in the calculations involving the network’s heat exchangers. A more detailed modeling of both the design of new exchangers and the retrofit of existing ones not only leads to more profitable solutions but also to more realistic ones, since modifications to the service of existing exchangers must take into account a series of practical operational issues. This thesis presents a robust network retrofit methodology that efficiently handles all the nonlinearities of the problem, incorporating detailed calculations for the exchangers in the network.