1. John Edwards, P&I Design Ltd
Dynamics Seminar
Section 6 Continuous Distillation
John Edwards, P&I Design Ltd
August, 2014 1

2. CONTINUOUS DISTILLATION SET UP DYNAMIC MODE
SIMULATION SUITE
CHEMCAD SOFTWARE
CONTINUOUS DISTILLATION SET UP DYNAMIC MODE
Switch to dynamic mode under convergence
Set Run Time to 600 minutes with 0.5 minute step size
Record desired streams 6 N-Pentane and 7 I-butane
Select Run Time plot options
Run from Initial State
Plot results

3. DYNAMIC DISTILLATION SIMULATION DYNAMIC COLUMN CONFIGURATION
SIMULATION SUITE
CHEMCAD SOFTWARE
DYNAMIC DISTILLATION SIMULATION DYNAMIC COLUMN CONFIGURATION

4. CONTINUOUS DISTILLATION RESULTS
SIMULATION SUITE
CHEMCAD SOFTWARE
CONTINUOUS DISTILLATION RESULTS
D6.02 page 134
CHEMCAD Job: FEEDCHANGEDCOLMDYNAMIC

5. CONTINUOUS DISTILLATION DYNAMIC COLUMN FEED CHANGE
SIMULATION SUITE
CHEMCAD SOFTWARE
CONTINUOUS DISTILLATION DYNAMIC COLUMN FEED CHANGE
Step change of feeds should be avoided as the column will take a long time to recover due to lags in the system.
Feed forward control systems are used to adjust the column overheads and bottoms operation to compensate for feed changes and minimize upsets.
Don’t expect steady state and dynamic mass balances to match exactly. Longer runs will produce closer matches. The simulation has not considered variable liquid hold up introduced by considering the effect of column internals.

6. DYNAMIC DISTILLATION SIMULATION DYNAMIC COLUMN FEED CHANGE
SIMULATION SUITE
CHEMCAD SOFTWARE
DYNAMIC DISTILLATION SIMULATION DYNAMIC COLUMN FEED CHANGE
CHEMCAD can calculate the holdup on each stage as a function of time using tray sizing and layout information.
It cannot do this for packed columns, but the user can input holdup profiles for this situation.
Condenser and reboiler holdups are handled differently.
Calculated holdups can be used to make dynamic responses more realistic.
Mass transfer geometries can be used to incorporate mass transfer effects into the flowsheet, further improving realism.

7. CONTINUOUS DISTILLATION SET UP DYNAMIC SIEVE TRAY COLUMN
SIMULATION SUITE
CHEMCAD SOFTWARE
CONTINUOUS DISTILLATION SET UP DYNAMIC SIEVE TRAY COLUMN
D6.03 page 134
CHEMCAD Job: FEEDCHANGEDCOLMDYNAMICSIEVETRAY
Introducing column hold ups
Pressure drop is constant during dynamic simulations.
The Variable Pressure option would recalculate the top pressure at each time step.

8. CONTINUOUS DISTILLATION SET UP DYNAMIC TRAY COLUMN
SIMULATION SUITE
CHEMCAD SOFTWARE
CONTINUOUS DISTILLATION SET UP DYNAMIC TRAY COLUMN

9. CONTINUOUS DISTILLATION DYNAMIC TRAY COLUMN RESULTS
SIMULATION SUITE
CHEMCAD SOFTWARE
CONTINUOUS DISTILLATION DYNAMIC TRAY COLUMN RESULTS
D6.03 page 136
Tray 24 selected for lower section temperature control

10. CONTINUOUS DISTILLATION FEED CHANGE - COLUMN BOTTOMS CONTROL
SIMULATION SUITE
CHEMCAD SOFTWARE
CONTINUOUS DISTILLATION FEED CHANGE - COLUMN BOTTOMS CONTROL
D6.04 page 137

11. CONTINUOUS DISTILLATION SPECIFY CONTROL LOOP AND STRATEGY
SIMULATION SUITE
CHEMCAD SOFTWARE
CONTINUOUS DISTILLATION SPECIFY CONTROL LOOP AND STRATEGY

12. CONTINUOUS DISTILLATION SPECIFY REBOILER WITH DYNAMIC VESSEL
SIMULATION SUITE
CHEMCAD SOFTWARE
CONTINUOUS DISTILLATION SPECIFY REBOILER WITH DYNAMIC VESSEL

13. CONTINUOUS DISTILLATION REBOILER LEVEL CONTROL RESULTS
SIMULATION SUITE
CHEMCAD SOFTWARE
CONTINUOUS DISTILLATION REBOILER LEVEL CONTROL RESULTS
D6.04 page 139
Initial High Level to prevent reboiler running dry
Tune Level Control (Loop P = 25% I = 15 m)

14. CONTINUOUS DISTILLATION REBOILER FLOWS
SIMULATION SUITE
CHEMCAD SOFTWARE
CONTINUOUS DISTILLATION REBOILER FLOWS
D6.04 page 139

15. CONTINUOUS DISTILLATION FULL CONTROL MODEL
SIMULATION SUITE
CHEMCAD SOFTWARE
CONTINUOUS DISTILLATION FULL CONTROL MODEL
D6.05 page 140

16. CONTINUOUS DISTILLATION SPECIFY EQUIPMENT
SIMULATION SUITE
CHEMCAD SOFTWARE
CONTINUOUS DISTILLATION SPECIFY EQUIPMENT

17. CONTINUOUS DISTILLATION REFLUX CONTROL
SIMULATION SUITE
CHEMCAD SOFTWARE
CONTINUOUS DISTILLATION REFLUX CONTROL

18. CONTINUOUS DISTILLATION SCDS COLUMN SPECIFICATION
SIMULATION SUITE
CHEMCAD SOFTWARE
CONTINUOUS DISTILLATION SCDS COLUMN SPECIFICATION

19. CONTINUOUS DISTILLATION RESULTS – COLUMN PROFILES
SIMULATION SUITE
CHEMCAD SOFTWARE
CONTINUOUS DISTILLATION RESULTS – COLUMN PROFILES
D6.05 page 145

20. CONTINUOUS DISTILLATION RESULTS – TEMPERATURE PROFILE
SIMULATION SUITE
CHEMCAD SOFTWARE
CONTINUOUS DISTILLATION RESULTS – TEMPERATURE PROFILE

21. CONTINUOUS DISTILLATION RESULTS – STAGE 24 TEMPERATURE
SIMULATION SUITE
CHEMCAD SOFTWARE
CONTINUOUS DISTILLATION RESULTS – STAGE 24 TEMPERATURE

22. CONTINUOUS DISTILLATION COLUMN OVERHEAD CONTROL
SIMULATION SUITE
CHEMCAD SOFTWARE
CONTINUOUS DISTILLATION COLUMN OVERHEAD CONTROL
D6.06 page 147

23. CONTINUOUS DISTILLATION COLUMN OVERHEAD CONTROL
SIMULATION SUITE
CHEMCAD SOFTWARE
CONTINUOUS DISTILLATION COLUMN OVERHEAD CONTROL
D6.06 page 147

24. CONTINUOUS DISTILLATION FEEDFORWARD CONTROL
SIMULATION SUITE
CHEMCAD SOFTWARE
CONTINUOUS DISTILLATION FEEDFORWARD CONTROL
D6.07 page 148

25. CONTINUOUS DISTILLATION FEEDFORWARD CONTROL
SIMULATION SUITE
CHEMCAD SOFTWARE
CONTINUOUS DISTILLATION FEEDFORWARD CONTROL
D6.07 page 149

26. CONTINUOUS DISTILLATION FEEDFORWARD CONTROL
SIMULATION SUITE
CHEMCAD SOFTWARE
CONTINUOUS DISTILLATION FEEDFORWARD CONTROL
D6.07 page 149

27. CONTINUOUS DISTILLATION RELIEF CONDITION
SIMULATION SUITE
CHEMCAD SOFTWARE
CONTINUOUS DISTILLATION RELIEF CONDITION

28. CONTINUOUS DISTILLATION RELIEF CONDITION
SIMULATION SUITE
CHEMCAD SOFTWARE
CONTINUOUS DISTILLATION RELIEF CONDITION

29. CONTINUOUS DISTILLATION RELIEF CONDITION
SIMULATION SUITE
CHEMCAD SOFTWARE
CONTINUOUS DISTILLATION RELIEF CONDITION

30. CONTINUOUS DISTILLATION RELIEF CONDITION
SIMULATION SUITE
CHEMCAD SOFTWARE
CONTINUOUS DISTILLATION RELIEF CONDITION
INCREASING COLUMN PRESSURE REDUCES TEMPERATURE ∆T
DUTY REDUCES FROM 3.9E06 to 2.5e06 kcal/h at relief
Latent heat increases from 89.9 to 125 kcal/kg
This effect reduces Relief flow by Factor 0f 1.4
Duty 3.9 e06 kcal/h requires kg/h
Duty 2.5 e06 kcal/h requires kg/h
Dynamic simulation predicts ≈ 6000 kg/h
Dynamic simulation gives Better understanding of
Distillation column behavior at relief conditions