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PRES_Dejanovic_et al.pdf
1. 1
I. Dejanović, I.J. Halvorsen, S. Skogestad, H. Jansen, Ž. Olujić
University of Zagreb, Croatia; SINTEF, Norway; NTNU, Norway; Julius MONTZ GmbH, Germany;
Delft University of Technology, the Netherlands
Cost-effective design
of energy efficient four-product dividing wall
columns
16th Conference Process Integration,
Modelling and Optimisation for Energy
Saving and Pollution Reduction
2. 2
STATE OF THE ART
Established: 3-product DWCs
• More than 200 in operation worldwide.
• Packed and tray columns.
• Know-how pioneers: BASF SE and Julius
MONTZ GmbH.
Proven in practice: about 30 % savings in
energy, capital and plot area
Next step: 4-product DWCs
• Potential gains could increase to 50%
compared to conventional, three-column
sequences
• Complex internal configurations: design
and operation concerns increase.
• Subject of academic studies: providing
basic and technically sound know-how
3. 3
AVAILABLE CONCEPTUAL DESIGN TOOLS
SHORT-CUT DESIGN
• Vmin diagram method (I.J. Halvorsen).
• Identification of feasible internal configurations.
• Initial values for detailed simulations.
A B
B C
C D
A B C B C D
A B C D
A B C D
VT/F
D/F
1-q
0 1
PAB
PBC
PCD
PAC PBD
PAD
DETAILED STAGE NUMBER AND REFLUX CALCULATION
• Use of commercial process simulators.
• Thermodynamically equivalent conventional column sequences.
• Minimizig N(R+1)
HYDRAULIC DESIGN
• Packed DWC dimensioning considerations and methods
• Main design and operation concern: vapor splits
4. 4
Starting point: 4-P Kaibel DWC ("2-4" configuration)
CD
ABCD
A
B
C
D
AB
• Single partition wall (G. Kaibel, BASF, 1987)
• Theoretical savings: > 30% compared to conventional 3 column sequences
• Not a full Petlyuk arrangement, but practical
One column in operation in a BASF plant
A B C D
A B
C D
A
B
C
D
C 1
C 2
C 3
Feed
D
S 1
S 2
B
5. 5
Fully extended 4-P Petlyuk arrangement
CD
ABCD
ABC
A
B
BCD C
D
AB
BC A, B, C, D
A
A, B, C
B, C, D
B
C
D
A, B
B, C
C, D
C1
C2.1
C2.2
C3.1
C3.2
C3.3
V/B
S1
S2
R
N1.1
N1.2
N3.1
N2.2
N2.3
N2.4
N2.1 N3.2
N3.3
N3.4
N3.5
N3.6
RV1
RV2
RV3
RL1
RL2
RL3
A B C D
A
B
C
D
Easiest separation performed in each sub-column minimizes energy
requirement
6. 6
Vmin diagram for a 4-P ("2-3-4" configuration)
Vmin diagram
contains all internal
DWC rates at min
reflux
Highest peak – sets overall
Petlyuk/DWC Vmin
7. 7
DESIGN CASE: 15 component feed ⟶ 4 products
Based on actual plant data
Base case configuration
Product specs:
• C5-C6 fraction < 1.3 mass % benzene
• BRC > 67 mass % benzene
• Toluene purity > 97 mass %
C1
C2
C3
Feed
D (C5-C6)
S1 (BRC)
S2 (toluene)
B (heavies)
31.7 t/h
8.0 t/h
7.4 t/h
3.9 t/h
12.4 t/h
8. 8
Differences in peak heights give operational/design flexibility
Vmin diagram: Internal configuration layout tool
A, B, C, D
A
A, B, C
B, C, D
B
C
D
A, B
B, C
C, D
C1
C2.1
C2.2
C3.1
C3.2
C3.3
CD
ABCD
ABC
A
B
BCD C
D
AB
BC
9. 9
Aligning PAC and PDB eliminates vapor connection with C3.2 – simpler design and
construction (one vapor split eliminated!)
Vmin diagram: Internal configuration layout tool
A, B, C, D
A
A, B, C
B, C, D
B
C
D
A, B
B, C
C, D
C1
C2.1
C2.2
C3.1
C3.2
C3.3
CD
ABCD
ABC
A
B
BCD C
D
AB
BC
10. 10
Vmin diagram: Internal configuration layout tool
A, B, C, D
A
A, B, C
B, C, D
B
C
D
A, B
B, C
C, D
C1
C2.1
C2.2
C3.1
C3.2
C3.3
CD
ABCD
ABC
A
B
BCD C
D
AB
BC
11. 11
Moving prefractionator operating point to align PAD and PBD allows
elimination of section C2.2
A, B, C, D
A
A, B, C
B
C
D
A, B
B, C
C, D
C1
C2.1
C3.1
C3.2
C3.3
Vmin diagram: Internal configuration layout tool
CD
ABCD
ABC
A
B
C
D
AB
BC
12. 12
Vmin diagram: Internal configuration layout tool
A, B, C, D
A
A, B, C
B, C, D
B
C
D
A, B
B, C
C, D
C1
C2.1
C2.2
C3.1
C3.2
C3.3
CD
ABCD
ABC
A
B
BCD C
D
AB
BC
13. 13
Vmin diagram: Internal configuration layout tool
CD
ABCD
ABC B
BCD C
D
A
BC
Moving C2.1 operating point to align PAC and PAB allows
elimination of section C3.1
A, B, C, D
A
A, B, C
B, C, D
B
C
D
B, C
C, D
C1
C2.1
C2.2
C3.2
C3.3
14. 14
Alternative configurations of a 4-P DWC
A B C D
D
B
A
C
A
B
C
D
A B C D
A B C D
A
B
C
D
B
C
D
A
A B C D
2-4 2-3-4 2-2-4 2-3-3
Details on preliminary rigorous simulation, dimensioning and cost estimation of these configurations can be found in:
Dejanović, Matijašević, Halvorsen, Skogestad, Jansen, Kaibel, Olujić, Chem.Eng.Res.Des., 89 (2011) 1155-1167
Olujić, Dejanović, Kaibel, Jansen, Chem. Eng. Technol., 35 (2012) 1392-1404
Halvorsen, Dejanović, Skogestad, Olujić, Chem.Eng.Res.Des., 91 (2013), in print.
15. 15
Separation task:
F, q, xi, rLK,i, rHK,i
Vmin diagram (N³4Nmin):
DPF, BPF, LT, VT, LB, VB, RL,
RV,D, S, B
min(V/B)
Ni(0)
RL(0), RV(0)
min(N(R+1)
min(Qr)
Detailed model
Converged DWC profile
Dimensioning
Short-cut
Reflux and stage calculation procedure
18. 18
Stage and energy requirements of considered
configurations
Configuration Conventional 2-4 2-3-4 2-2-4 2-3-3
Column C1 C2 C3 - - - -
Top pressure bar 1.70 2.70 1.01 2.53 2.57 2.57 2.57
Stages, total - 40 38 38 169 202 174 202
Stages, main
column
- 129 130 130 116
Trays - 61 59 59
Reboiler heat duty MW 10.0 5.82 4.81 4.81 4.81
19. 19
Converged column
profiles
Determine critical stage –
maximum vapour load
Dshell(0)
Wall position below/
above feed stage
Δp<3 mbar/m
Pressure drop –
packed beds
H(bed)=N*HETP
Choice of packing type
Choice of internals
(collectors and
distributors)
Initial values of free area:
Distributors: φ(0)=0,40
Colectors: φ(0)=0,25
Equal pressure
drops
Final dimensions and
pressure drops
FG
Yes
Yes
No
No
No
No
Dimensioning procedure
20. 20
Design rules:
Up to 20 equilibrium stages in a single bed;
Δp < 3 mbar/m;
Liquid collectors:
CT for side stream draw-off
CT for liquid loads > 20 m3/m2h
CC for lower liquid loads
Predictive models:
•Delft Model for structured packings
•Rix & Olujić model for internals
Chimney tray collector (CT)
Chevron collector (CC)
Narrow trough distributor (NT)
Various packing types and sizes to maximize flexibility:
B1-250, B1-250MN, B1-350, and B1-350MN
B1-250M
Equipment choice/modeling considerations
23. 23
Configuration Conventional 2-4 2-3-4 2-2-4 2-3-3
Equipped with Sieve trays Struct. packings Struct. packings Struct. packings Struct.packings
Equipment costs ($)
Shell 1,886,347 1,076,376 976,932 976,932 949,585
Internals 1,011,708 2,100,466 1,982,504 1,622,853 1,847,310
Reboiler 743,701 384,685 327,778 237,754 230,719
Condenser 571,972 234,103 238,622 325,641 325,641
Total 4,213,728 3,795,629 3,525,877 3,163,181 3,353,255
Operating costs ($/year)
Cooling water 196,233 107,354 85,883 86,632 85,384
Fuel oil 1,482,288 731,389 601,674 596,894 596,894
Total 1,678,523 838,742 687,557 683,526 682,227
Savings - 50% 59% 59% 59%
Total annualized costs ($/year)
TAC ($/year) 2,075,552 1,218,305 1,040,145 999,844 1,017,603
Savings - 42% 50% 52% 52%
A B C D
A
B
D
C
A B C D
A
B
D
C
A B C D
A
B
D
C
b) kolona s vertikalnom i
horizontalnom stijenkom
a) Kaibelova kolona c) kolona s više vertikalnih
stijenki
C D
A B
C D
A B
A B C D
A
B
D
C
A B C D
A
B
D
C
A B C D
A
B
D
C
b) kolona s vertikalnom i
horizontalnom stijenkom
a) Kaibelova kolona c) kolona s više vertikalnih
stijenki
C D
A B
C D
A B
A,B,C,D
A
B
D
C
Cost comparison
24. 24
Four-product packed DWC can be designed and constructed using available
process and mechanical design tools, know-how and equipment
Single partition ”2-4” configuration is an attractive option in present case
Maximizing energy saving gains requires consideration of alternative
multipartition configurations
TAC is not a decisive factor for the choice of alternatives
Simplest, ”2-2-4” DWC appears to be the most adequate choice for first
attempt in this respect
Conclusions
1.1 2.2 3.3
2.1 3.2
3.4
3.5
1.2
”2-2-4”
