1. Rigorous Simulation of Divided-wall Columns
M. Shamsuzzoha, Maryam Ghadrdan, Ivar J. Halvorsen, Sigurd Skogestad
The 15th NPCW'09, Telemark University College, Porsgrunn, Norway January

2. Trondheim, Norway

3. NTNU/SINTEF
Trondheim

4. Minimum Energy for the Four-Product Kaibel Distillation Column
Introduction
What is Petlyuk columns
Experimental setup
Assessment by the Vmin diagram
Rigorous simulation
Summary
ABCD A B D C

5. BEEDIST (Basic Energy Efficient Distillation Technology)
NTNU lab
Founded by the Norwegian Research Council through the GASSMAKS program
SINTEF/NTNU
Objectives
Study new integrated distillation arrangements
For reduction of capital cost and energy consumption (+ CO2-emission related to the energy).
20-40% savings in reach.
Evaluate application in natural gas processing and conversion.
Design and operation
Develop laboratory
2 PhD + post doc
4-product Kaibel-column with a dividing wall
ABC A B C AB BC
3-product Petlyuk arrangement
ABCD CD A B D C AB

6. What is a Petlyuk arrengement ?
Integrated distillation column arrangement
Separates a single feed into three separate products
Just a single reboiler and condenser
Why?
Saves energy and capital
Distillation consumes 3-5% of the industry energy consumption world-wide =>Need more energy efficient solutions
ABC A B C

7. Industrial DWC/Petlyuk applications
German-speaking community dominates
BASF: 40 DWCs in operation. Increasing. G. Kaibel pioner
Monz – main vendor for BASF
Krupp-Uhde
Sulzer
Rashig
Linde
Others
MW Kellogg (UK)
UOP (USA)
UK, Japan, Indonesia, South Africa
The Kaibel-column 4-product DWC!

8. Equivalent Petlyuk arrangements
Classical Petlyuk arrangement
Dividing Wall Column (DWC)
ABC A B C AB BC
Liquid split
Vapor split
Fully thermally coupled sections

9. Conventional alternatives for 3-product separation: Sequence of binary columns
Direct Split: DS
Indirect split: IS
ABC BC A B C
ABC AB A B C

10. Prefractionator arrangement
Alternatives for 3-product separation...
Prefractionator arrangement A AB
ABC B
The prefractionator does the simple A/C split while B distributes to both ends B BD C

11. Conventional Prefractionator arrangement with a single main columnAB
ABC B BC C

12. Apply full thermal coupling
Petlyuk column AB
ABC B BC C

13. Why consider a Petlyuk arrangement
Large potential energy savings compared to conventional columns (20-30%)
Or – increase production for given energy supply
Capital cost savings due to more compact equipment => smaller footprint and removal of reboiler/condenser units
Usage:
In theory: Anywhere (almost) where distillation is a suitable separation technology and more than 2 products are produced.
In practice: Some cases may be unsuitable due to required temperature/pressure range, height, or if liquid/vapor load in different sections are very different.
Practical variations can be made, e.g. side-strippers/rectifiers
Revamping of existing conventional columns may have significant potential

14. Critical: How to set the splits
The potential savings are easily lost unless the splits are adjusted properly
Do it right and obtain all the benefits!
liquid split (side draw) A
liquid split (Rl) D1 A
ABC
ABC B B V1
vapor split (Rv)
vapor split (side draw) C C

15. Extend to 4-product DWC: The Kaibel column – (1987)
ABCD CD A B D C AB
Separates 4 products in a single shell!
Total reflux section
Can save %

16. Minimum energy- Definitions and assumptions
Vapour flow rate (V) generated from all reboilers is used as the energy measure
Ideal Assumptions
Infinite number of stages
Constant relative volatility
Constant molar flow
Constant pressure
No internal heat exchange
Then, exact analytic solution is obtained

17. Minimum energy (Vapor flow rate V)
Sharp splits: Flat optimum at a line segment (optimality region)
Optimality region depends on feed properties
Rapid increased vapor flow outside optimality region

18. The Vmin-diagram Operation point f(D/F,V/F) V/F
Distillate (D)
Binary column – multicomponent feed
D/F
V/F 1
Feed (F)
ABC
Vapor rate (V)
Feed comp. distribution ? Minimum energy ?
Two degrees of freedom – choose D/F,V/F

19. The Vmin-diagram – 3 component example
V/F D F
ABC
Vmin boundary V
Preferred A/C split
D/F

22. Characterisitcs of operation

24. Schematic diagram of the experimental setup of 4-product Kaibel-arrangement
ABCD A B D C

25. The Kaibel column at NTNU, Trondheim, Norway
ABCD CD A B D C AB
Lab installation:
Height: 8 meters
Atmospheric pressure
Vacuum glass sections
4 products
Contact: Sigurd Skogestad, or Ivar J. Halvorsen B
Feed (ABCD) C D

26. Feed condition for the Kaibel Distillation
Four components: Methanol+Ethanol+1-Propanol+1-Butanol
Flow rate F=1.0 Kgmole/h, q=1 (saturated liquid)
Composition z=[0.25, 0.25, 0.25, 0.25]
EOS Wilson
Pressure Atmospheric
Relative volatility α= [8.27: 4.84: 2.30: 1.0]

27. UniSim Simulation for Kaibel Column

28. Steady-State Simulation for Kaibel Column
KAIBEL DISTILLATION COLUMN

29. Minimum Energy – competitionNo
Configuration
Ideal Vmin/F
Ideal
Savings
UniSim Savings 1
Four product extended Petlyuk
1.16
51% 2
Kaibel column
1.59
33%
>26% 3
Prefractionator+ single main column
1.98
16% 4
Conventional direct sequence (3 columns)
2.38 0%
(reference) 5
Prefractionator+
2 separate columns
2.62
-10%
(loss)

30. Vmin-diagram for the Kaibel column

31. Vmin-diagram for the Kaibel column using UniSim
Rigorous calculation confirms ideal shortcut method
V/F
D/F

32. Further work Status: Startup of new PhDs Directions:
Further studies with Unisim (extended from ideal mixtures)
Further development of Matlab models
Alternative structures like HIDiC, Heat integrated and other energy efficient arrangements
Dynamic studies
Optimizing control
Lab column experiments
ABCD CD A B D C AB

34. How to apply DWC/Petlyuk columns
Make sure to do a reasonable design in terms of placement of the dividing wall/design split.
Important: Make sure to indentify the optimality region for the expected actual feed variations, and thereby clarify the requirements for on-line adjustment of:
None of the split ratios (E.g. in case of quadrangle shaped reg.)
Just the liquid split (In case of a line segment reg.)
Both split ratios (in case of a very short line segment)
Determine the final control strategy based the actual product value/energy cost, and dynamic controllability analysis.

35. Key issues for full thermal coupling
Liquid and vapour flows in equilibrium avoids irreversible loss due to mixing (Petlyuk 1965) =>
Explains why Petlyuk columns beat the other arrangements
Require operation of every internal column at its “preferred split”
Underwood roots “carry over” the coupling (Halvorsen 2001) =>
Valid for any operating point
Simple sequential calculation sequence
Extremely simple assessment for n-product Petlyuk arrangement based only on feed properties.