Dividingwall column review and Design comparisons

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Dividing-wall column reviewandDesign comparisons
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Outline

• Introduction of DWC
• background
• Remixing effect and Petlyuk column
• Whether to use DWC or not
• Industry review
• Academic groups
• Design methods
• Design comparisons

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Background
Introduction of DWC /

• DWC (Dividing-Wall column) is introduced by
  Wright in 1949.
• However, lack of reliable design method and
  concerns about the operation and control of DWC
  have prevented the widespread application.
• People started to pay much attention to DWC after
  the Energy Crisis (1980).
• In 1985, BASF built the first commercial DWC.
• There are now more than 100 columns installed
  worldwide.

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Remixing effect
Introduction of DWC / Remixing effect and Petlyuk
column/

• Remixing effect leads to a thermal inefficiency

Composition profile of the middle component In
the columns of the direct sequence.
Schultz, M. A., D. G. Stewart, et al. (2002).
"Reduce costs with dividing-wall columns."
Chemical Engineering Progress 98(5) 64-71.
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Petlyuk column
Introduction of DWC / Remixing effect and Petlyuk
column/

• Eliminate the remixing effect

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DWC
Introduction of DWC / Remixing effect and Petlyuk
column/
Adiabatic wall
Thermodynamically equivalent
Side-draw section
prefractionator
Dividing-Wall Column, DWC
Petlyuk column 1965
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Introduction of DWC / Remixing effect and Petlyuk
column / DWC
Component B mole fraction
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Whether to use DWC or not
Introduction of DWC /

• DWC might be suitable
• High product purity
• When high-purity middle product is desired, DWC
  should be considered.
• Middle product in excess
• DWC is most advantageous with the feed
  composition
• 60-70 B and A ?C
• Uniform relative volatility
• When B is a significant portion of the feed, DWC
  can be more
• advantageous as long as the split between A/B is
  as difficult as B/C.

A typical rule of thumb
Schultz, M. A., D. G. Stewart, et al. (2002).
"Reduce costs with dividing-wall columns."
Chemical Engineering Progress 98(5) 64-71.
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Introduction of DWC / Whether to use DWC or not

• DWC might not be suitable
• High pressure difference
• There is a high pressure difference between the
  columns in the
• conventional tow-column sequence
• Utilities at different T
• The conventional sequence requires utilities at
  different temperatures for
• Each column (refrigeration and cooling water)

As with any guidelines, there are exceptions, but
these can be useful during the screening process.
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Industry review
Introduction of DWC /

• Germany
• BASF
• In 1985, BASF constructed the first commercial
  DWC. BASF is also believed to be the leader in
  the total number of such columns in existence.
  (28 DWCs)
• Uhde GmbH
• Linde AD
• Linde AG have built the tallest DWC (100m 5.2m
  diameter) for Sasol.
• British
• Kellogg
• Kellogg has designed a DWCs for BP, which
  increases 50 purity of middle component.
• U.S.
• UOP LLC
• Japan

DWCs are being used to separate a range of
products, including various hydrocarbon streams,
esters, alcohols, aldehydes, ketones and amines.
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Academic groups
Introduction of DWC /

• R. Smith (UMIST,UK)
• Triantafyllou, C. and R. Smith (1992)
• Lestak F., Smith R and Dhole VR. (1994)
• Abdul Mutalib, M. I. and R. Smith (1998)
• Amminudin, K.A. and R. Smith (2001)
• They proposed a design model to confirm potential
  energy savings comparing with the conventional
  arrangement, and set up pilot-scale columns to
  study controllability and operability.

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Introduction of DWC / Academic groups

• S. Skogestad (Norwegian Univ Sci Technol,
  Norway)
• Wolff, E.A. and S. Skogestad (1995)
• Ivar J. Halvorsen and S. Skogestad
  (1999,2003,2004)
• They have done the extended researches about
  Petlyuk arrangement, and have done a series
  researches about steady state behavior, dynamic
  behavior, and control strategy.
• Prof. Y. H. Kim (Dong-A University, Korea)
• He has proposed some rigorous design of fully
  thermally coupled distillation column

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Design methods
Introduction of DWC /

• Proprietary software
• Aspen Plus HYSYS
• R. Smith
• Short-cut method (Fenske-Underwood-Gilliland)
  1992
• Use Fenske equation to find the minimum number of
  trays Nmin at the total reflux conditions.
• Use Underwoods equations to find the minimum
  reflux ratio Rmin.
• Use the values in the Gilliland correlation and
  estimate the required number of theoretical trays
  for an given operating reflux ratio Rmin.

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Introduction of DWC / Design methods / R. Smith

• Equilibrium stage composition
• concept 2001

Amminudin, K. A., R. Smith, et al. (2001).
"Design and optimization of fully thermally
coupled distillation columns part 1 Preliminary
design and optimization methodology." Chemical
Engineering Research Design 79(A7) 701-715.
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Introduction of DWC / Design methods /

• Prof. Y. H. Kim
• The design is based on the minimum tray structure
  to give high thermodynamic efficiency by making
  liquid composition profile similar to the residue
  curves of equilibrium distillation.
• Sotudeh
• Improved short-cut method 2007
• The method is based on Underwood equation only.
• Determine the minimum vapor flow Vmin and minimum
  reflux ratio Rmin.
• Choose an operating reflux ratio in the range of
  1.2-1.5 Rmin.
• Calculate the total number of trays in the tower
  and the side stream location.

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Design comparisons
SR side-rectifier SS side-stripper FC fully
thermally coupled DSLV direct split
(modified) ISLV indirect split (modified)
Agrawal, R. and Z. T. Fidkowski (1998). "Are
thermally coupled distillation columns always
thermodynamically more efficient for ternary
distillations?" Industrial Engineering
Chemistry Research 37(8) 3444-3454.
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Efficiency
Design comparisons /

• Efficiency
• aA relative volatility of A with respect to C
• aB relative volatility of B with respect to C
• aAB relative volatility of A with respect to B
• ESI (ease of separation index)

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Equimolar mixture
Design comparisons /
The most efficient configuration to distill an
equimolar mixture as a fuction of aA and aB
ZAZBZC
For aA and aB lt 11
DSLV
ISLV
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A-rich, B-rich and C-rich feed
Design comparisons /
C-rich feed 0.05 0.05 0.9
B-rich feed 0.05 0.9 0.05
A-rich feed 0.9 0.05 0.05
DSLV is almost the most efficient
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ESI 1
Design comparisons /
aAB is kept equal to aBC
1.21/ 1.10/ 1
4 / 2/ 1
25/ 5/ 1
Separation is relatively difficult
Separation is relatively easy
DS zone ? ISLV zone ? FC zone ?
DSLV is almost the most efficient
FC is most efficient close to equimolar feed
SS SR small ZB DSLV small ZC ISLV small ZA
FC prefers lower ZB !?
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ESI gt 1
Design comparisons /
ESI 1.36 1.65/ 1.10/ 1
ESI 1.5 6/ 2/ 1
ESI 1 4/ 2/ 1
As ESI ? DSLV zone ? SR zone ?
When ESI gt 1.5 ,SR is almost always the most
efficient in C-rich feed
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ESI lt 1
Design comparisons /
ESI 0.51 2.05/ 2.0/ 1
ESI 0.65 2.6/ 2.1/ 1
ESI 1 4/ 2/ 1
As ESI decreases, the SR zone become
disappeared ISLV and SS zone occupy the most
space For A-rich feed, DSLV and SS are most
efficient For C-rich feed, ISLV and SS are most
efficient For highly B-rich feed (ZB gt 0.9), DSLV
is most efficient
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The 2nd most efficient configuration
Design comparisons /
ESI 1 4/ 2/ 1
ESI 1 4/ 2/ 1
As expected, the 2nd most efficient
configurations are those obtained by
interchanging the most efficient configurations
across the boundary in the figure above.
When ESI ?1 and two most efficient configurations
are considered, the FC has larger composition
space (not valid when ESI is much different from
1)
The second most efficient configuration at each
composition
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Reference

• Schultz, M. A., D. G. Stewart, et al. (2002).
  "Reduce costs with dividing-wall columns."
  Chemical Engineering Progress 98(5) 64-71.
• Amminudin, K. A., R. Smith, et al. (2001).
  "Design and optimization of fully thermally
  coupled distillation columns part 1 Preliminary
  design and optimization methodology." Chemical
  Engineering Research Design 79(A7) 701-715.
• Sotudeh, N. and B. H. Shahraki (2007). "A method
  for the design of divided wall columns." Chemical
  Engineering Technology 30(9) 1284-1291.
• Agrawal, R. and Z. T. Fidkowski (1998). "Are
  thermally coupled distillation columns always
  thermodynamically more efficient for ternary
  distillations?" Industrial Engineering
  Chemistry Research 37(8) 3444-3454.