Modeling & control of Reactive Distillation

1. Modeling & control of Reactive Distillation Jianjun Peng Supervisors: Dr. Edgar Dr. Eldridge

2. Outline • Background information • Research objectives • Modeling • Experimental plans • Conclusions TWMCC

3. A A+B A, B E Reactivesection C A,B,E C A,B,E Reactivesection reactor B A, B B C A Reactive distillation Conventional process Reactive Distillation: Example 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 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? TWMCC

6. Reflux Ratio Influence TWMCC

7. Pressure Influence TWMCC

8. Product Rate Influence 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 TWMCC

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

12. Rate-based Models(2) Vkyi,k Lk-1xi,k-1 fLi,k fVi,k Vapor Liquid Catalyst N, E N, E QVk Vk+1yi,k+1 Lkxi,k QLk TWMCC

13. Equilibrium or Rate-based? Equilibrium models Rate-based models - Not rigorous+ Rigorous + Simple - Complicated ? Tray efficiency or HETP? Mass transfer 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 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? TWMCC

16. Model Assumptions • Overall mass transfer • Pseudo-homogeneous reaction • Pseudo-steady state energy balances • negligible vapor holdup TWMCC

17. Model Solution • Aspen Custom Modeler (ACM)* custom models* built-in DAE solvers* built-in property models* integrated PID controllers* modeling language 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 TWMCC

19. Reactive Distillation Column 6 in. diameter 34 ft. T-T Catalytic Packing Structured Packing Backcracking Reactor Experimental Plans • 6 inch reactive distillation pilot plant • TAME system • Experiments - steady state - dynamic - controller implementation TWMCC

20. Future Work • Solving the model with ACM • Simulations and comparisons • Experiments: steady state and dynamic • MPC and NMPC implementation 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 TWMCC