Exergy based approach for process synthesis

The purpose of this study is to develop a new procedure for process synthes is based on a reducible superstructure and exergy load distribution analysi s. The latter makes it possible to evaluate the impact of each competitive process included in the superstructure according to the specific performanc e criterion of the overall flowsheet. This criterion, utilizable exergy coe fficient, is a function of three important aspects of the process design: e fficient use of raw materials, energy efficiency and waste reduction. The p rocedure starts by building a specific reducible structure of the process f lowsheet called the "competitive process" superstructure. The exergy load d istribution analysis is carried out on the "competitive process" superstruc ture to reduce it to a final optimal flowsheet topology. It includes two st eps. In the first step, only the alternatives with the highest impact on th e utilizable exergy coefficient of the overall flowsheet are kept for subse quent analysis. In the next step, the distribution of exergy loads from the less efficient units to the more efficient ones makes it possible to reloc ate the units inside the flowsheet. The new procedure is tested for the des ign of a benzene synthesis chemical plant and is compared with previously p ublished solutions found by the hierarchic and mathematical methods. The re sulting flowsheet for benzene synthesis is different from the flowsheets fo und by the hierarchic and mathematical methods and consumes the least amoun t of raw materials. (C) 2000 Elsevier Science Ltd. All rights reserved.