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Aspen for Process Creation

Aspen for Process Creation. Chapter 4&5 Terry A. Ring. Onion Model of Process Design. Process Synthesis-1. Reaction 3 Direct Chlorination Pyrolysis. Reactor Types. Ideal PFR CSTR Real Unique design geometries and therefore RTD Multiphase

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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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