Retrofit model for heat exchanger network design

Abstract

This research proposes a solution method based upon mathematical programming for a Heat Exchanger Network (HEN) retrofit. The retrofitting of HENs is a common project to reduce plant operating costs, including utility costs. A retrofit design consists of four features, such as the addition or removal of the heat exchanger area, adding a new heat exchanger, repiping, and splitting. Four features were used to design a HEN by GAMS and Visual C++. The retrofit in this research has two steps (retrofit, and relocation). The stage model, using the mixed integer linear programming (MIP) of Yee and Grossmann (1999), was used to develop the retrofit model. Not only was minimization of the utility cost, but also minimization of the addition or removal area were of concern in the optimal design of the heat exchanger network. HEN problems from literatures and a crude preheating train of with light and heavy crude oil feeds were used to demonstrate the effectiveness of the approach in terms of the solution quality and time. These examples are retrofitted with relocation, and the estimated result of the retrofit, was a 6% to 40% energy saving at hot and cold utilities.