Modeling%20

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Modeling control of Reactive Distillation

• Jianjun Peng
• Supervisors Dr. Edgar Dr.
  Eldridge

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Outline

• Background information
• Research objectives
• Modeling
• Experimental plans
• Conclusions

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Reactive Distillation Example
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The Good vs. the Bad

• The good higher conversion reduced
  capital cost, energy
• The bad - more difficult to design
  control - poor understanding of the process

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AspenPlus Simulations

• AspenPlus Radfrac
• Equilibrium model
• Tert-Amyl Methyl Ether (TAME) system
• Steady state
• Objective How different is reactive distillation
  comparing to ordinary distillation?

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Reflux Ratio Influence
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Pressure Influence
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Product Rate Influence
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Research Objectives

• Dynamic model - for the purpose of control
• Model predictive control - PID may not be
  adequate
• Controller implementation - pilot plant with
  Delta V control system
• Experimental validation

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Equilibrium Models

• Vapor-liquid equilibrium at each stage(section
  for packed column)
• Tray efficiency or HETP
• One mass balance for each stage

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Rate-based Models

• Mass transfer equations
• Vapor-liquid equilibrium only at interface
• Transport properties - mass transfer
  coefficients - heat transfer coefficients
• NO tray efficiency or HETP

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Rate-based Models(2)
Vkyi,k
Lk-1xi,k-1
fLi,k
fVi,k
Vapor
Liquid
Catalyst
N, E
N, E
QVk
Vk1yi,k1
Lkxi,k
QLk
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Equilibrium or Rate-based?
Equilibrium models Rate-based models
- Not rigorous Rigorous
Simple - Complicated
? Tray efficiency or HETP ? Mass
transfer
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Model Comparison

• Jin-Ho Lee etc. (1998) - individual
  efficiency hard to predict - rate-based
  model is preferred
• R. Baur (2000) - smaller window for
  multiplicity in rate-based model -
  rate-based model is preferred
• No experimental validation
• No details about mass transfer
• No details about the behavior of reactive
  distillation

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Modeling

• Mass transfer - Maxwell-Stefan equations -
  Overall mass transfer? - Empirical mass
  transfer coefficients
• Reaction - heterogeneous or pseudo-homogeneous?
• Dynamics - vapor holdup? - energy holdup?

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Model Assumptions

• Overall mass transfer
• Pseudo-homogeneous reaction
• Pseudo-steady state energy balances
• negligible vapor holdup

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Model Solution

• Aspen Custom Modeler (ACM) custom models
  built-in DAE solvers built-in property
  models integrated PID controllers modeling
  language

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Simulation Plans

• Comparison with equilibrium model
• Comparison with more rigorous rate-based model
  (Sebastien Lextrait)
• Parameter influence - reflux ratio, boil-up
  ratio, pressure, feed composition
• Dynamic response - feed, reflux ratio, boil-up
  ratio

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Experimental Plans

• 6 inch reactive distillation pilot plant
• TAME system
• Experiments - steady state - dynamic
  - controller implementation

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Future Work

• Solving the model with ACM
• Simulations and comparisons
• Experiments steady state and dynamic
• MPC and NMPC implementation

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Concluding Remarks

• Reactive distillation is advantageous, but
  poorly understood.
• A dynamic rate-based model has been developed.
• Future contributions
• Solving the rate-based dynamic model
• Controller development using simulations
• MPC implementation on Delta V
• Experimental validation