rigorous simulation of divided-wall columns
DESCRIPTION
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 29-30 2009. Trondheim, Norway. NTNU/SINTEF Trondheim. A. B. ABCD. C. D. - PowerPoint PPT PresentationTRANSCRIPT
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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 29-30 2009
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Trondheim, Norway
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NTNU/SINTEFTrondheim
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Minimum Energy for the Four-Product Kaibel Distillation Column
IntroductionWhat is Petlyuk columnsExperimental setup Assessment by the Vmin diagram
Rigorous simulation Summary
ABCD
A
B
D
C
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BEEDIST (Basic Energy Efficient Distillation Technology)
Founded by the Norwegian Research Council through the GASSMAKS program
SINTEF/NTNU 2008-2012 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
ABCD
CD
A
B
D
C
AB
NTNU lab4-product Kaibel-
column with a dividing wall
ABC
A
B
C
AB
BC
3-product Petlyuk arrangement
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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
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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!
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Equivalent Petlyuk arrangements
Classical Petlyuk arrangement
Dividing Wall Column (DWC)
ABC
A
B
C
AB
BC
ABC
BC
A
B
C
AB Liquid split
Vapor split
Fully thermally coupled sections
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Conventional alternatives for 3-product separation: Sequence of binary columns
ABC
BC
A B
C
Direct Split: DS
ABC
AB
A
BC
Indirect split: IS
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ABC
BD
A
AB
B
C
B
Prefractionator arrangement
Alternatives for 3-product separation...
The prefractionator does the simple A/C
split while B distributes to both
ends
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Conventional Prefractionator arrangementwith a single main column
ABC
BC
A
AB
B
C
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Apply full thermal coupling
ABC B
C
A
AB
B
C
Petlyuk column
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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
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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!
ABC
A
B
C
ABC
A
B
C
vapor split (Rv)
vapor split (side draw)
liquid split (side draw) liquid split
(Rl)D1
V1
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Extend to 4-product DWC:The Kaibel column – (1987)
ABCD
CD
A
B
D
C
AB
Total reflux section
Separates 4 products in a single shell!
Can save 30-40 %
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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
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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
( , , )minV f Splits Feed Specs
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The Vmin-diagram
ABC
Distillate (D)
Feed (F)
Vapor rate (V)
D/F
V/F
1
Operation point f(D/F,V/F)
Two degrees of freedom – choose D/F,V/F
Binary column –multicomponent feed
Feed comp. distribution ? Minimum energy ?
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The Vmin-diagram – 3 component example
D/F
V/F
Vmin
boundary
ABC
D
F
V
Preferred A/C split
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zA:
zB:
zC:
A:
B:
qf:
Conventional : Vmin
=2.03Petlyuk Column: V
min=1.37
Reboiler SAVINGS: 32.80%Condenser SAVINGS: 32.80%
C 0.2 0.4 0.6 0.8 A
0.2
0.4
0.6
0.8
B
0 0.2 0.4 0.6 0.8 10
0.5
1
1.5
2
D/F
VT/F
P
R
Savings
0 0.2 0.4 0.6 0.8 10
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
C3
C2
V(Rl,R
v)
Rl
RC4
P
C1
Rv
Characterisitcs of operation
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Schematic diagram of the experimental setup of 4-product Kaibel-arrangement
T50
6
2
1
3
T34
T66
VB
Rv
L/D
Rl
S1
S2
F, Z_F, q
x, B
D, x, d
x, S1
x, S2
TS-7
TS-1
TS-2
TS-3
TS-4
TS-5
5
7
4
TS-6
TEE101
TEE100
T34
ABCD
A
B
D
C
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The Kaibel column at NTNU, Trondheim, Norway
Lab installation: Height: 8 meters Atmospheric pressure Vacuum glass sections 4 products Contact: Sigurd Skogestad, or
Ivar J. Halvorsen
A
B
C
D
Feed (ABCD)
ABCD
CD
A
B
D
C
AB
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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]
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UniSim Simulation for Kaibel Column
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Steady-State Simulation for Kaibel Column
KAIBEL DISTILLATION COLUMN
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Minimum Energy – competition
No Configuration Ideal Vmin/F IdealSavings
UniSimSavings
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)
0%(reference
)
5 Prefractionator+2 separate columns
2.62 -10%(loss)
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Vmin-diagram for the Kaibel column
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 10
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
D/F
V/F
Vmin
-diagram
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Vmin-diagram for the Kaibel column using UniSim
Rigorous calculation confirms ideal shortcut method
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 10
0.2
0.4
0.6
0.8
1
1.2
1.4
V/F
D/F
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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
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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:1. None of the split ratios (E.g. in case of quadrangle shaped reg.)
2. Just the liquid split (In case of a line segment reg.)
3. 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.
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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.