A Thermodynamic Approach for Conceptual Design of Chemical Processes

Abstract

Abstract The purpose of this paper is to develop a new thermodynamic approach for conceptual design of chemical processes. The approach is based on a concept of reducible superstructure and exergy load distribution analysis. It starts by building a specific reducible structure of the process flowsheet called the “competitive process” superstructure. A two-step exergy analysis is carried out on the superstructure to reduce it to a final optimal flowsheet topology. In the first step, only the design options with the highest impact on the utilizable exergy coefficient of the overall flowsheet is 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 approach was applied for the design of a gas separation section within a benzene synthesis chemical plant. It has been found that the overall exergy efficiency of the benzene synthesis is highest with the design option using a membrane for hydrogen recuperation and an absorber for benzene recuperation. The final step is the relocation of the absorber achieved through the application of the exergy load distribution analysis. Compared with the previous solutions obtained by the hierarchic and mathematical approaches, a new flowsheet for benzene synthesis has been proposed. It consumes the least amount of raw materials, such as hydrogen and toluene, and produces the least amount of discharged gas as waste.