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Practical Approach toPractical Approach toPractical Approach toPractical Approach to

DWC Design & OptimizationDWC Design & OptimizationDWC Design & OptimizationDWC Design & OptimizationPlant Basic Engineering TeamPlant Basic Engineering TeamPlant Basic Engineering TeamPlant Basic Engineering Team

Sang-il Park

Oct 06. 2015

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CONTENTSCONTENTSCONTENTSCONTENTS

1. Introduction to DWC

- Benefits

- Application

2. DWC simulation

- Comparison of Design Variables (conventional vs. DWC)

- Vapor & liquid split

3. B-Split

- Definition

- An optimal B-Split (case study)

- An optimal B-Split (Theoretical)

4. Design procedure

- 3 steps

- Case Study Result

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1. Introduction To DWC

▶ Dividing Wall Column (DWC)Fractionation Column that executes two different separations in one column

Graphics from Montz Catalogue <Montz Dividing Wall Column>

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1. Introduction To DWC

▶ Benefits of DWC1. Low Capital Investment (20~30%)

2. Low Operation Cost (20~30%)

- Remove Re-mixing

Graphics from CEP Journal “Reduce Costs with Dividing Wall Column”,

by Michael A. Schultz (UOP)

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1. Introduction To DWC

▶ Application of DWC3 product Separation

1. High purity is required for middle boiling point component

2. Middle product is in excess and lights and heavies are in fairly equal

3. Separation of A/B is as difficult as B/CTREATEDNAPHTHATREATEDNAPHTHA Stabilizer(DeC4)Stabilizer(DeC4) NaphthaSplitterNaphthaSplitter IsomerizationIsomerization15 bar15 bar1.5 bar1.5 bar

C4-C4-CCR ReformerCCR Reformer CCR ReformerCCR ReformerFEED C4-C4-IsomerizationIsomerizationBenzeneBenzene

Other Applications

1. Extractive Distillation (BASF BD process, Ude Morphylane)

2. Absorption + Distillation (GTC LPG Max)

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2. DWC simulation

▶ Design Variables in Conventional Column

1520253035

17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40

1.No. of stages

2.Feed Location

3.Draw Location

2. Feed location 3. Side Draw location

1. No of Stages Duty

No. Stages

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2. DWC simulation

▶ Design Variables in DWC- DWC structure

6. Main Lin

8. Main Lout(Liquid split ratio)

7. Main Vout(Vapor split ratio)

5. Main Vin

3. Feed location

4. Side Draw location

2. Prefractionator Tray No.

1. Main columnTray No.

1.No. of stages in main column

2.No. of stages in prefractionator

3.Feed location of prefractionator

4.Side draw location

5.Feed location of main column vapor in

6.Feed location of main column liquid in

7.Main column vapor out rate

8.Main column liquid out rate

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2. DWC simulation

▶ Vapor & Liquid Split in DWC

Liquid out Vapor out

Duty

Liquid out Vapor out

Duty

Optimal operating regions at a certain vapor & Liquid Split

The range and stable optimal regions depend on the feed composition and DWC structure

Graphics from Chem. Eng. “Study of structural characteristics of a dividing wall column using the sloppy distillation arrangement by

Moonyong LEE (Yongnam Univ.)

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2. DWC simulation

▶ Design Variables in DWC – Interaction No. of trays No. of trays No. of trays No. of trays at each at each at each at each sectionsectionsectionsection Liquid splitLiquid splitLiquid splitLiquid splitVapor SplitVapor SplitVapor SplitVapor SplitReboilerReboilerReboilerReboiler DutyDutyDutyDuty

Condenser Condenser Condenser Condenser DutyDutyDutyDuty

An easy and powerful design procedure of DWC is required

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3. B-Split

▶ B – Split (β) ; DefinitionThe fraction of component B that goes to the top of pre-fractionator out of total B flow

feed

After pre-fractionator

Final Product

Btop

Bbtm

Trying to find an optimal B-Split

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3. B-Split

▶ An optimal B-Split (case study)

Simulation Result of C4/C5/C6 Separation at a fixed DWC Structure

2468

-1.5 -1 -0.5 0 0.5 1 1.5Reboiler duty(A:B:C=1:2:1)

2712

-1.5 -1 -0.5 0 0.5 1 1.5Reboiler duty (A:B:C=1:1:2)

1.56.511.5-1.5 -1 -0.5 0 0.5 1 1.5Reboiler duty (A:B:C=2:1:1)

There is an optimum B-Split for DWC Design

B-split B-split B-split

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3. B-Split

▶ An optimal B-Split (Theoretical)

Halverson1) verified optimal B-Split is between “Preferred Split” and “Balanced Split”

a b c d

b: Preferred Split

c: Balanced Split

a

b

c

d

1) Ivar J. Halverson “Minimum Energy Requirement in complex Distillation Arrangements”, thesis for Dr.Ing., Norwegian University of Science and Technology

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3. B-Split

▶ An optimal B-Split (Theoretical)

The graph of Preferred / Balanced Split vs. ESI (ease of separability index, αAB/αBC)

00.10.20.30.40.50.60.70.80.910.5 0.7 0.9 1.1 1.3 1.500.10.20.30.40.50.60.70.80.91

0.5 0.7 0.9 1.1 1.3 1.5 00.10.20.30.40.50.60.70.80.910.5 0.7 0.9 1.1 1.3 1.5

Preferred splitBalanced splitInitial splitA:B:C=1:3:1 A:B:C=3:1:1 A:B:C=1:1:3

ESI

B-split

B/C cut hard

ESI increase

More B/C to bottom Large duty for Main-frac

Preferred Split dec. Blanced Split inc.

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4. Design Procedure

▶ 3- Steps

3 column simulation3 column simulation 2 column simulation2 column simulation DWC simulationDWC simulation

Design Each column with;

1) A/C nearly perfect cut

2) Use Initial B-Split

3) Optimization of each column

Design Each column with;

1) No touch on pre-fractionator

2) Stage elimination

3) Determine Draw location

Design DWC with;

1) No touch on the tray No.

2) Determine feed location

3) Total No. of tray optimization

Objective

Determine tray No. for

I/II/III/IV

Objective

Determine tray No. for

I/II/III/IV for DWC

Objective

Determine final DWC design with total No. of trays & V/L split

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4. Design Procedure

▶ Case Study (BTX separation)

Main DWC Design Parameters

B split (top / total) mole 0.51 L split (main / total) mole 0.64 V split (main / total) mole 0.40

Comparison between Conventional and DWC

Column name Benzene Toluene DWC Saving %No. of Actual Stage 55 65 100 17%Colum ID mm 4,000 4,400 4,800 Column Height m 43 49 70Column Weight kg 69,165 86,698 135,114 13%Condenser Gcal/hr -16.83 -23.54 -24.71 39%Reboiler Gcal/hr 19.61 23.38 26.95 37%

DWC DesignDWC DesignConventional DesignConventional Design

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