c28420-lecture8-2009 - SEPARATION PROCESSES PRINCIPLES...

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SEPARATION PROCESSES PRINCIPLES (28240) LECTURE 8 Rate-based Models for distillation olumns; Short ath evaporation columns; Short-path evaporation model & reactive distillation model
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Rate-based models for distillation The methods presented in Chapters 10 and 11 assumed that equilibrium is achieved at each stage, with respect to heat and mass transfer. However, in most industrial applications (or real processes), the equilibrium is never reached. The Rate-Based Model is an alternative to equilibrium based models, where th ema s sand energy balances are developed separately for each phase around a stage. A stage can be a ay llection f ays r gment f acked ction tray, a collection of trays, or a segment of a packed section.
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Rate-based models for distillation odel bjective Model Development Model Objective Develop a general model for a vapor-liquid eparator taged olumn) perating t teady separator (staged column) operating at steady state. odel ssumptions Model assumptions 1. There is equilibrium between vapor-liquid only at the interface 2. No chemical reactions occur 3. Entrainment of liquid drop si nv a por and q p p occlusion of vapor in liquid are negligible. 4. Vertical column with countercurrent flow 5. Continuous operation
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Rate-based model for a stage Model derivation Define system boundary yy Derive model equations Balance equations (mass, energy, . .) Constraint equations onstitutive equations Constitutive equations Analyze model equations Select solution strategy gy Solve model equations Provide data for known variables Initial estimate for unknown ariables Figure 12.1 Non-equilibrium stage for rate-based method. variables
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Rate-based model for a stage Figure 12.1 Non-equilibrium stage for rate-based method. Figure 10.1 General equilibrium stage (system boundary).
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Model derivation: Balance equations
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Model derivation: Constraint equations
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Model derivation: Constraint equations
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Model analysis MERSHQ ND = N V –N E = 2NC + 9N+1 II L V L yxyNT T T L V ,,,, , , ,, , , ij j j i j j xyxyNT IL F V F L V , LV L V , , , , Thermodynamiccorrelation (need constitutive equations) , , , Transport correlation (need constitutive equations) j j j j j j KH H H H NNe e
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Constitutive equations IL F V F L V , , , , , Thermodynamiccorrelation (need constitutive equations) ij j j j j KH H H H Models for the physical equilibrium constant; models for enthalpies LV L V ,, , , , Transport correlation (need constitutive equations) j j NNe e Mass transfer rates mass flux overall mass transfer coefficients individual mass transfer coefficients eat transfer rates heat flux overall heat transfer coefficients Heat transfer rates heat flux overall heat transfer coefficients individual heat transfer coefficients Additional consitutive equations odels for viscosity, surface tension, thermal conductivity, Models for viscosity, surface tension, thermal conductivity, density
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Constitutive equations: Transport model
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Constitutive equations: Transport model
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Constitutive equations: Transport model
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This note was uploaded on 11/20/2009 for the course CHME DTU-abroad taught by Professor Rafiqulgani during the Fall '09 term at Rensselaer Polytechnic Institute.

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c28420-lecture8-2009 - SEPARATION PROCESSES PRINCIPLES...

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