Select thermodynamic models for process simulation
A Practical Guide to a Three Steps Methodology
Select thermodynamic models for process simulation

Select thermodynamic models for process simulation
A Practical Guide to a Three Steps Methodology

Jean-Charles de Hemptinne, Jean-Marie Ledanois, Pascal Mougin and Alain Barreau

DOI: https://doi.org/10.2516/ifpen/2011001
ISBN: 978-2-90163-813-1
EAN: 9782901638131

The choice of a modelling approach is very often guided by the experience on other systems, or by the availability of parameter databases. This is acceptable in the sense that most industrial computations are based on previous cases that worked correctly. Yet, it may also be dangerous, and it is then recommended to submit the problem to a thermodynamic analysis.

Our purpose is to provide a vademecum that should help the practicing engineer in finding the right questions to answer when faced with a novel type of thermodynamic problem: when the questions are correctly stated, the answer is half on its way.

The construction of the book, that may seem awkward at first, is designed for this purpose. It is constructed on three pillars (chapters 2, 3 and 4) that each represent a different point of view converging to the same goal: the development of an adequate thermodynamic set of models for an industrial problem. We believe that in order to analyse completely a physical modelling problem, these three pillars must be correctly mastered (figure 0.1):

  1. understanding the fundamental principles,
  2. use of the available mathematical models, and
  3. knowledge of the system physical (phase) behaviour.

The domain of application that is aimed is petroleum and energy process design. Yet, readers working in other fields of chemical engineering may also find interesting topics.

image Figure 0.1: Triangular representation of the fundamental questions in thermodynamic problem-solving

The first chapter goes into the details of the philosophy of the approach. The main messages we want to carry here is:

The second chapter summarises some of the basic principles of thermodynamics (what O’Connell [4] calls ‘Always True’). It is written so that most concepts and equations that the chemical engineer may need are provided in a very concise form. It contains two main sections:

The third chapter is the heart of this book. Rather than providing an exhaustive list of thermodynamic models, it emphasises the use of these models, starting from the concept of the fluid composition. In fact, this composition must be regarded as a set of parameters to be used with the chosen mathematical model. The link between this parameter + equation combination and the true physical behaviour is performed through a comparison with experimental data. This should explain the construction of the third chapter that has three parts:

The fourth chapter puts the modelling issue in the perspective of the true physical behaviour of a physical system. The phase behaviour depends greatly on the type of mixture that is considered. This is why a number of important industrial mixtures are discussed. For each system, some model recommendations are suggested. The discussion is organised in two main parts:

The true originality of our approach is presented in the final, fifth chapter. It both concludes the theoretical part of this endeavour (which is the book), and introduces the practical part that will be proposed on the web. The intention is to publish electronically a number of case studies that illustrate industrial examples that have been treated at IFP Energies nouvelles. The solution pattern will follow as closely as possible the approach suggested in this fifth chapter. The same final chapter also lists some important industrial processes in order to guide the engineer in his problem-analysis.

This user guide is not designed as a thermodynamics textbook. Many very good thermodynamic handbooks exist for helping teachers in designing a course in a logical, linear fashion (Elliot & Lira [1], Prausnitz et al. [2], Smith & Van Ness [3], O’Connell [4], Vidal [5]…). Teachers can use this document as suggested below, but will be disappointed by the lack of demonstrations, and the non-linear conception of the logic.

This manual is not either a review of the existing thermodynamic models, that would help developers in understanding and code the most adapted model to their situation. Other authors have made a significant effort in summarizing the models in a logical fashion, stressing their strengths and weaknesses and providing indications on how they should be coded, if needed (Poling et al. [6]; Kontogeorgis & Folas [7]; Mollerup & Michelsen [8]; Riazi [9]…). Thermodynamic experts will be disappointed by the lack of completeness, of numerical parameters and of algorithmic analysis.