Process modelling: selection of thermodynamic methods

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PROCESS MODELLING SELECTION OF THERMODYNAMIC METHODS by John E. Edwards jee@pidesign.co.uk

MNL031B 10/08 PAGE 1 OF 38

Process Modelling Selection of ThermodynamicMethods

Contents 1.0 2.0 2.1 2.2 2.3 2.4 3.0 3.1 3.2 3.3 4.0 4.1 4.2 5.0 Introduction Thermodynamic Fundamentals Thermodynamic Energies Gibbs Phase Rule Enthalpy Thermodynamics of Real Processes System Phases Single Phase Gas Liquid Phase Vapour liquid equilibrium Chemical Reactions Reaction Chemistry Reaction Chemistry Applied Summary Appendices I II III IV V VI VII VIII Enthalpy Calculations inCHEMCAD Thermodynamic Model Synopsis – Vapor Liquid Equilibrium Thermodynamic Model Selection – Application Tables K Model – Henry’s Law Review Inert Gases and Infinitely Dilute Solutions Post Combustion Carbon Capture Thermodynamics Thermodynamic Guidance Note Prediction of Physical Properties

Figures 1 2 3 4 5 6 7 8 9 10 Ideal Solution Txy Diagram Enthalpy Isobar Thermodynamic Phases van derWaals Equation of State Relative Volatility in VLE Diagram Azeotrope γ Value in VLE Diagram VLE Diagram and Convergence Effects CHEMCAD K and H Values Wizard Thermodynamic Model Decision Tree K Value and Enthalpy Models Selection Basis

PAGE 2 OF 38

MNL 031B Issued November 2008, Prepared by J.E.Edwards of P & I Design Ltd, Teesside, UK

www.pidesign.co.uk

Process Modelling Selection ofThermodynamic Methods

References 1. 2. 3. 4. 5. 6. C.C. Coffin, J.Chem.Education 23, 584-588 (1946), “A Presentation of the Thermodynamic Functions”. R.M. Felder and R.W. Rousseau, “Elementary Principles of Chemical Processes”, 2nd Edition, John Wiley and Sons. R.C. Reid, J.M. Prausnitz, B.E. Poling, “The Properties of Gases and Liquids”, 4th Edition, McGraw Hill. I. Smallwood, “SolventRecovery Handbook”, Edward Arnold, 1993. R.H.Perry, “Chemical Engineers’ Handbook”, McGraw Hill. R.Sander, “Compilation of Henry’s Law Constants for Inorganic and Organic Species of Potential Importance in Environmental Chemistry”, Max-Planck Institute, Version 3, April 1999. J.R.W.Warn, “Concise Chemical Thermodynamics”, van Rostrand Reinhold, 1969. Kent, R. L. and Eisenberg, Hydrocarbon Processing,Feb. 1976, p. 87-92. F.G. Shinskey, “Process Control Systems”, McGraw-Hill, 1967. O.Levenspiel, “Chemical Reaction Engineering”, Wiley, 2nd Edition, 1972. J.Wilday and J.Etchells, “Workbook for Chemical Reactor Relief Sizing”, HSE Contract Research Report 136/1998. H.S.Fogler, “Elements of Chemical Reaction Engineering”, 3rd Edition, Prentice Hall, p122. K.J.Laidler, “Theories of Chemical ReactionRates”, New York, R.E.Krieger, 1979, p38.

7. 8. 9. 10. 11. 12. 13.

Acknowledgements This paper has been developed from experience gained whilst working in the simulation field. This work has been supported throughout by Chemstations, Houston, Texas, TX77042 www.chemstations.com and the author is particularly indebted to Aaron Herrick and David Hill for their continued and unstinting help.PAGE 3 OF 38

MNL 031B Issued November 2008, Prepared by J.E.Edwards of P & I Design Ltd, Teesside, UK

www.pidesign.co.uk

Process Modelling Selection of Thermodynamic Methods

1.0

INTRODUCTION The selection of a suitable thermodynamic model for the prediction of the enthalpy-H and the phase equilibrium-K is fundamental to process modelling. An inappropriate model selection will resultin convergence problems and erroneous results. Simulations are only valid when the appropriate thermodynamic model is being used. The selection process is based on a detailed knowledge of thermodynamics and practical experience. Most simulators are provided with Wizards to aid selection which should be used with caution. The selection process is guided by considering the following:Process...
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