An introduction to exergy and its evaluation using Aspen Plus

Abstract

The second law of thermodynamics describes how energy and entropy are configured in a system as well as how they are transferred through multiple systems. Exergy is a concept which is derived from the second law of thermodynamics. Exergy has been defined as “the ability to do work” or “the amount of work that can be extracted from a substance”. Due to the irreversibilities in real processes, exergy can be lost. Exergy can also be gained by receiving energy from other sources. The calculation of exergy and its losses is used in the analysis of industrial processes. Exergy analyses come in various methodologies and are used to optimize the economics and resource usage of a process or piece of equipment and to reduce its environmental impact. The use of exergy as an analysis tool has grown to a point where popular process modeling software includes it as a report option in process design models. The exergy analysis function of the modeling software Aspen Plus is demonstrated and discussed for an ethyl lactate process. Ethyl lactate is a monobasic ester that is being considered as a nontoxic replacement for petroleum-based solvents.