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Introduction to Thermophysical Property Models and ASPEN Plus Unit Operations

Introduction to Thermophysical Property Models and ASPEN Plus Unit Operations. CHE/CBE 450/550 September 8, 2008. Thermophysical Properties. Crucial for engineering design Phase behavior (single and multi-phase) Heat exchange Compression/expansion Reactions

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Introduction to Thermophysical Property Models and ASPEN Plus Unit Operations

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  1. Introduction to Thermophysical Property Models and ASPEN Plus Unit Operations CHE/CBE 450/550 September 8, 2008

  2. Thermophysical Properties • Crucial for engineering design • Phase behavior (single and multi-phase) • Heat exchange • Compression/expansion • Reactions • Required for mass and energy balances • Required for sizing equipment and determining length and time scales • Property methods • Data • Equations/Correlations • Equations of state (EOS) • Activity coefficient models • Transport coefficient correlations

  3. Pure Components • Data (ex. Steam tables) • Equations of state • Relate Pressure/Volume/Temperature (PVT) behavior of fluids • Mostly for gases, and some liquids • Examples (cubic EOS) • Ideal gas law PV = NRT • Good for low pressure/density gases • Peng-Robinson • Good for nonpolar species (hydrocarbons, permanent gases) • Moderate to high pressure • Soave-Redlich Kwong • Good for nonpolar and slightly polar species (hydrocarbons, permanent gases, better for water, methanol, etc.) • Moderate to high pressure

  4. Peng-Robinson EOS

  5. Soave-Redlich-Kwong EOS

  6. Thermophysical Properties • ASPEN Plus properties • Thermodynamic and transport • Pure or mixture • Multi-phase • Example – CO vapor properties

  7. Unit Operations in ASPEN • Heat Exchanger Input • Enter outlet temperature, pressure and/or heat duty • Example: CO heat exchanger • Compressor Input • Mode of operation (isentropic, efficiencies, etc.) • Outlet pressure • Stages • Example: air compressor

  8. Mixtures At low-to-moderate pressures • Phase Equilibrium • VLE • Fugacity Equality • EOS for mixtures • PR, SRK, etc, • Mixing rules and interaction parameters • Gamma/phi method • EOS for vapor phase • Activity coefficient model for liquid phase

  9. Mixtures At low-to-moderate pressures • Phase Equilibrium • LLE • Fugacity Equality • Gamma/phi method • Activity coefficient model for both liquid phases

  10. Activity Coefficient Models • UNIQUAC • UNIversal QUAsiChemical • Combinatorial (entropy) and residual (energy) terms • Good for solutions containing molecules of different sizes • Good for non-electrolyte systems, nonpolar and polar • Can handle partial miscibility • Energy terms fitted to data (2 adjustable parameters) • UNIFAC • UNIversal Functional Activity Coefficient • Same idea as UNIQUAC, but predictive (no adjustable, fitted parameters) • NRTL, Van Laar, Margules, Reg Soln Theory

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