Exergy based approach for process synthesis

The purpose of this study is to develop a new procedure for process synthesis based on a reducible superstructure and exergy load distribution analysis. The latter makes it possible to evaluate the impact of each competitive process included in the superstructure according to the specific performance criterion of the overall flowsheet. This criterion, utilizable exergy coefficient, is a function of three important aspects of the process design: efficient use of raw materials, energy efficiency and waste reduction. The procedure starts by building a specific reducible structure of the process flowsheet called the “competitive process” superstructure. The exergy load distribution analysis is carried out on the “competitive process” superstructure to reduce it to a final optimal flowsheet topology. It includes two steps. In the first step, only the alternatives with the highest impact on the utilizable exergy coefficient of the overall flowsheet are kept for subsequent analysis. In the next step, the distribution of exergy loads from the less efficient units to the more efficient ones makes it possible to relocate the units inside the flowsheet. The new procedure is tested for the design of a benzene synthesis chemical plant and is compared with previously published solutions found by the hierarchic and mathematical methods. The resulting flowsheet for benzene synthesis is different from the flowsheets found by the hierarchic and mathematical methods and consumes the least amount of raw materials.