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Aspen for Process Creation

This text explores the various reactor types, design geometries, and simulation techniques in process synthesis. Learn about reaction kinetics, multiphase reactors, and equilibrium reactors. Use Aspen software to specify reactant conversions and extents of reaction for multiple phases and reactions.

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Aspen for Process Creation

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  1. Aspen for Process Creation Chapter 4&5 Terry A. Ring

  2. Onion Model of Process Design

  3. Process Synthesis-1 • Reaction 3 • Direct Chlorination • Pyrolysis

  4. Reactor Types • Ideal • PFR • CSTR • Real • Unique design geometries and therefore RTD • Multiphase • Various regimes of momentum, mass and heat transfer

  5. Reactors in Process Simulators • Stoichiometric Model • Specify reactant conversion and extents of reaction for one or more reactions • Two Models for multiple phases in chemical equilibrium • Kinetic model for a CSTR • Kinetic model for a PFR • Custom-made models (UDF) Used in early stages of design

  6. Stoichiometric Reactor • C chemical Species • υi,j stoichiometric coefficient for ith species in jth reaction • Aj chemical formula of jth species • R chemical reactions

  7. Stoichiometric Reactor Example • Reactions • 1 Methane Synthesis • 2 Coking • Conversion, Xk, of key component, k • Xk=(nk-in – nk-out)/ nk-in • Extent of Reaction • ξi= (ni,j-in – ni,j-out)/ νi,j 1 Rxn

  8. Reactions with low conversions? • Due to slow kinetics • Due to non-favorable Equilibrium • Solution • Set up reactor • Followed by Separator • Recycle reactant to extinction

  9. Equilibrium Reactor-1 • Single Equilibrium • aA +bB  rR + sS • ai activity of component I • Gas Phase, ai = φiyiP, • φi== fugacity coefficient of i • Liquid Phase, ai= γi xi exp[Vi (P-Pis)/RT] • γi = activity coefficient of i • Vi =Partial Molar Volume of i Van’t Hoff eq.

  10. Equilibrium Reactor-2 • Total Gibbs Free Energy is minimized at T&P • Specify components that are entering system and T&P of System • Specify possible reaction products • Note, no reactions are defined! • Gives outlet composition at equilibrium

  11. Equilibrium Reactors • To determine the potential products given some reactants • Use Gibbs Reactor • To determine equilibrium for a given reaction(s) • Use Equilibrium Reactor • To determine what operating conditions for a given reactor • Use Equilibrium Reactor • Vary T and P to get highest conversion • To determine heat of reaction • Use Stoichiometric Reactor • Conversion at 100%

  12. Examples • Which reaction takes place? • C + ½ O2 CO • C + O2  CO2 • What temperature (or pressure) is required for a reaction? • Run equilibrium reactor at different T and P.

  13. Separations • What conditions are to be used for a flash after reaction? • Run flash with different T and P.

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