Steady-State Plug Flow Reactor Analysis by means of Minimum Entropy

Abstract

Abstract This paper describes how a methodology based on minimum entropy can be used to assessing and improving the performance of Plug Flow Reactors (PFRs) and illustrates this with a generic application to reactive systems. Such reactors have been designed and assessed by means of mass and energy balances based on the First Law of Thermodynamics, jointly with kinetic concepts. Despite systematic use of the first principles to represent the system, they alone may not satisfy the constraints of Nature to which the processes are normally submitted. Therefore, the Second Law of Thermodynamics, particularly the concept of entropy, is needed to deal properly with the restrictions, because without considering it in its structure, the system can have a poor performance, due to the inherent irreversibilities present on them. The developed approach puts the classical mass and energy balances together with the entropy balance with a view to obtaining the entropy production rate. Typical reactions that use PFRs have been used to depict the behavior of entropy production rates and their minimum values, as well of conversion and temperature associated with such processes. The results indicate that the profiles of the entropy production rate and their minimum values do not present significant differences. Furthermore, a positive correlation has been noted with the outside temperature related to conversion, unlike that observed in relation to the entropy production rate along the length of the reactor, both results favorable to the optimization procedure. The conclusion that can be drawn is that such system works under the minimum entropy production, operating with the highest expected performance, and that the analysis was able to present substantial details for assessing and improving of the process, reaching the desired objectives.