Retrofit of Heat Exchanger Networks Including Process Modifications

Jose M. Ponce-Ortega, Department of Chemical Engineering, Universidad Michoacana de San Nicolas de Hidalgo, Ciudad Universitaria, Edificio M, Morelia, Michoacan, 58060, Mexico, Arturo Jimenez-Gutierrez, Departamento de Ingeniería Química, Instituto Tecnológico de Celaya, Ave. Tecnológico y García Cubas, Celaya, Gto., 38010, Mexico, and Ignacio E. Grossmann, Dept of Chemical Engineering, Carnegie Mellon University, 5000 Forbes Ave, Pittsburgh, PA 15213.

This paper presents a new formulation for the retrofit of heat exchanger networks that takes into account process modifications. The method accounts for the interactions between the process conditions and the heat integration options to provide an optimal structure for a redesigned heat exchanger network. The formulation is based on a superstructure that considers explicitly the plant layout and the piping arrangement, which yields a mixed-integer nonlinear programming model. The model presented here includes the treatment of isothermal process streams that exchange their latent heats, in addition to the streams commonly considered with sensible heat loads. The objective function consists of the maximization of the total annual profit for the retrofit process, which includes the income from products sales and the expenses due to raw materials, capital cost for new units, utility costs and the piping modification costs. Several cases of study are presented, and the results show that a significant improvement in the process profitability can be obtained with the simultaneous approach presented in this work for process retrofit with respect to the sole consideration of the heat exchanger networks.