Supertargeting-based hierarchic evaluation for setting paths in relaxation of retrofitted Heat Exchanger Networks

Abstract

The application of pinch analysis to the retrofit of existing heat exchanger networks is a complex task, which can be hardly standardised due to the large number of unquantifiable design considerations. Top-down and bottom-up approaches have been usually pursued, respectively oriented to relax a Maximum Energy Recovery (MER) configuration and to improve the existing network by removing network pinches. In this paper the bottom-up approach is critically examined, considering a well known case study represented by an aromatics plant; a MER design is also obtained and evaluated, to represent a target for process improvement. The final objective of researches in this sector is the identification of preferential routes for the improvement of the existing network. In this paper several retrofit routes are investigated, identifying six solutions that lead to a small number of topology changes. For each solution, a detailed thermal analysis provided the size, the number of shells and the temperature profiles associated with the operation of any heat exchanger; the solutions were relaxed to reduce the number of new units and the relaxed configurations were also evaluated. An analysis of the payback time associated with any retrofit option let us recognize that preferential routes could be identified by a preliminary evaluation of marginal costs.