1. Chemstations, Inc – Houston, TX – 800.243.6223 – http://www.chemstations.net Short Cut - Fenske-Underwood-Gilliland - Limited design, Rating Tower - Rigorous - Inside-Out Algorithm - Usual specifications - Simple columns Tower Plus - Rigorous - Inside-Out Algorithm - Extended specifications - Complex columns SCDS - Rigorous - Simultaneous corrections method - Usual specifications Distillation columns in CHEMCAD

2. Chemstations, Inc – Houston, TX – 800.243.6223 – http://www.chemstations.net Short Cut Method (SHOR) Fenske-Underwood-Gilliland method One feed and two products Design mode – Calculates reboiler and condenser duties, determines number of theoretical stages, finds optimum feed tray location (Fenske, Kirkbride) Rating mode – Calculates reboiler and condenser duties, computes fractional recovery of key components Generally not useful beyond initial column estimates: constant molar underflow requirement is too unrealistic SHOR column

3. Chemstations, Inc – Houston, TX – 800.243.6223 – http://www.chemstations.net Simultaneous Correction Method: Large number of stages Stable with non-linear (non-ideal) thermodynamics Run time = B * (NCOMP) 2 * NSTAGES Mass transfer and tray efficiencies Dynamics SCDS Column

4. Chemstations, Inc – Houston, TX – 800.243.6223 – http://www.chemstations.net TOWR column Inside-Out Method: Fast with EOS thermodynamics Large number of components, small number of stages Run time = A * NCOMP * (NSTAGES) 2 No mass transfer or stage efficiencies Complex columns Dynamics

5. Chemstations, Inc – Houston, TX – 800.243.6223 – http://www.chemstations.net EOS thermodynamicsTower Non-ideal thermodynamicsSCDS Three phase distillationSCDS Reactive distillationSCDS Mass transferSCDS Complex columnTower Plus Trays > 100SCDS Components > 20Tower General Recommended Selection

6. Chemstations, Inc – Houston, TX – 800.243.6223 – http://www.chemstations.net Degrees of Freedom.. Simple absorber0 Reboiler1 Condenser1 Side exchanger1 Pumparound2 Side stripper1 Distillations Models…

7. Chemstations, Inc – Houston, TX – 800.243.6223 – http://www.chemstations.net Typical Specifications Relatively “Safe”: One material balance specification (D, B) One heat balance specification (R/D, V/B) May require estimates: Compositions Temperatures Recoveries Heat loads Poor Choices: Two material balance specifications Pure stream temperature Distillations Models…

8. Chemstations, Inc – Houston, TX – 800.243.6223 – http://www.chemstations.net Column Estimate Guidelines No estimate better than poor estimate Avoid pure component temperature Avoid azeotrope temperature Tray 2, N-1 temperatures for unusual problems Use thermodynamic (phase) plots for guidance Use profile options for difficult problems Use preliminary material balances Distillations Models…

9. Chemstations, Inc – Houston, TX – 800.243.6223 – http://www.chemstations.net Column Convergence – Problem Recognition SCDS: Profile oscillations Increasing errors Many NR steps, decreasing size Inside-Out: Increasing errors Many Jacobian Inversions Distillations Models…

10. Chemstations, Inc – Houston, TX – 800.243.6223 – http://www.chemstations.net Column Convergence – Problem Management Review thermo Poor specifications Specification conflicts? Poor estimates? High pressure? Close boiling? Dry trays? (adjust T profiles) Create restart profiles Use damping factors Converged with poor mass balance? (tighten tolerances) All else fails? (reduce tray efficiencies) Distillations Models…

11. Chemstations, Inc – Houston, TX – 800.243.6223 – http://www.chemstations.net Dehydration of ethanol using normal pentane as the entrainer

12. Chemstations, Inc – Houston, TX – 800.243.6223 – http://www.chemstations.net Note: To find multicomponent azeotropes you can use CC-Batch

13. Chemstations, Inc – Houston, TX – 800.243.6223 – http://www.chemstations.net binodal plot (fixed temperature) liquid boiling envelope (fixed P)

14. Chemstations, Inc – Houston, TX – 800.243.6223 – http://www.chemstations.net 1. Fix bottoms composition at 99.99% EtOH. 2. Pick tie line that crosses relevant boundaries. Fixes composition of decanter liquid phases. 3. Determine distillate flowrate by pegging water flowrate. 4. Pick y(n) on tie line so that it is in equilibrium with homogeneous liquid. 5. Determine organic phase flowrate using lever rule. material balance line excluding condenser tie line

15. Chemstations, Inc – Houston, TX – 800.243.6223 – http://www.chemstations.net

16. Composition of combined feed Composition of top tray liquid Liquid compositions on trays y(n) Simulation results

17. Chemstations, Inc – Houston, TX – 800.243.6223 – http://www.chemstations.net Design considerations in Azeotropic Distillation Entrainer requirements Column sequence Reflux ratio Number of stages Effect of trace impurities

18. Chemstations, Inc – Houston, TX – 800.243.6223 – http://www.chemstations.net

19. distillation boundary Distillation boundaries can be crossed but it is almost always very difficult to take advantage of it.

20. Chemstations, Inc – Houston, TX – 800.243.6223 – http://www.chemstations.net H(TCE,25C) = 650 atm. T = 85 F P = 14.7 psia H2O = 696,000 lb/hr TCE = 69 lb/hr TCE = 1 ppb Air VOC Stripping… Distillations Models… H(TCE in H2O) = 650 atm.

21. Chemstations, Inc – Houston, TX – 800.243.6223 – http://www.chemstations.net Debutanizer – Split Iso and N butanes Feed: C3 83.06 lbmoles/hr iC44329.755 nC4 725.09 iC5 62.12 nC71286.98 Distillations Models…