Post on 29-Dec-2015
Modeling & control of Reactive Distillation
Jianjun Peng
Supervisors: Dr. Edgar Dr. Eldridge
02/19/2001 TWMCC 2
Outline
• Background information
• Research objectives
• Modeling
• Experimental plans
• Conclusions
02/19/2001 TWMCC 3
Reactive Distillation: Example
) :s(azeotrope CB, BABAC
A+B
Conventional process
C
C
A, B
BA
reactor
E
A,B,E A,B,E
A, B
A
C
B
Reactive distillation
Reactivesection
Reactivesection
02/19/2001 TWMCC 4
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
02/19/2001 TWMCC 5
AspenPlus Simulations
• AspenPlus Radfrac
• Equilibrium model
• Tert-Amyl Methyl Ether (TAME) system
• Steady state
• Objective: How different is reactive distillation comparing to ordinary distillation?
02/19/2001 TWMCC 6
Reflux Ratio Influence
0.978
0.979
0.98
0.981
0.982
0.983
0.984
0.985
0.986
0.987
0 1 2 3 4 5 6 7 8 9
Reflux Ratio
TAM
E c
om
po
siti
on
02/19/2001 TWMCC 7
Pressure Influence
0.6
0.65
0.7
0.75
0.8
0.85
0.9
0.95
0 1 2 3 4 5 6 7 8 9
pressure, atm
TAM
E c
ompo
sitio
n
02/19/2001 TWMCC 8
Product Rate Influence
0
0.2
0.4
0.6
0.8
1
0 0.05 0.1 0.15 0.2
product / feed
conversion
TAME composition
02/19/2001 TWMCC 9
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
02/19/2001 TWMCC 10
Equilibrium Models
• Vapor-liquid equilibrium at each stage(section for packed column)
• Tray efficiency or HETP
• One mass balance for each stage
02/19/2001 TWMCC 11
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
02/19/2001 TWMCC 12
Rate-based Models(2)
N, E N, E
Vapor Liquid Catalyst
Vk+1
yi,k+1
Vk
yi,k
Lk-1
xi,k-1
Lk
xi,k
QVk
fVi,k
QLk
fLi,k
02/19/2001 TWMCC 13
Equilibrium or Rate-based?
Equilibrium models Rate-based models
- Not rigorous + Rigorous
? Tray efficiency or HETP ? Mass transfer
+ Simple - Complicated
02/19/2001 TWMCC 14
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
02/19/2001 TWMCC 15
Modeling
• Mass transfer - Maxwell-Stefan equations - Overall mass transfer? - Empirical mass transfer coefficients
• Reaction - heterogeneous or pseudo-homogeneous?
• Dynamics - vapor holdup? - energy holdup?
02/19/2001 TWMCC 16
Model Assumptions
• Overall mass transfer
• Pseudo-homogeneous reaction
• Pseudo-steady state energy balances
• negligible vapor holdup
02/19/2001 TWMCC 17
Model Solution
• Aspen Custom Modeler (ACM)* custom models* built-in DAE solvers* built-in property models* integrated PID controllers* modeling language
02/19/2001 TWMCC 18
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
02/19/2001 TWMCC 19
Experimental Plans
• 6 inch reactive distillation pilot plant
• TAME system• Experiments
- steady state - dynamic - controller implementation
Catalytic Packing
StructuredPacking
Reactive DistillationColumn
6 in. diameter34 ft. T-T
Backcracking Reactor
02/19/2001 TWMCC 20
Future Work
• Solving the model with ACM
• Simulations and comparisons
• Experiments: steady state and dynamic
• MPC and NMPC implementation
02/19/2001 TWMCC 21
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