Use of Exergy in Energy-Efficient Process Design Methodology for Sub-Ambient Processes

This paper presents a targeting and design methodology that can be implemented for any kind of processes where pressure-based exergy also known as mechanical exergy has an important contribution in the total exergy conversion and transfer. Though, it was thought for processes that operate at sub-ambient conditions or for processes in which at some stage the ambient conditions are crossed. Exergy Analysis is commonly used as a post design tool, however, benefits in terms of energy-efficient processes can be obtained since the early stages of conceptual designs. Exergy efficiencies, Exergetic composite curves and cascades as well as Extended Grid Diagrams are valuable tools that had to be implemented and some invented in order to fully describe the methodology potential for energy-efficient process design.

The correct placement of compressors and expanders is also analyzed from a different optic, the minimization of number of units.

An educational example is used to demonstrate the methodology. In this example, several assumptions were made to facilitate the understanding and explanation of the design method however interesting results were obtained.