1 EFCE Working Party on Fluid Separations, Bergen, 23-24 May 2012 New results for divided-wall...

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EFCE Working Party on Fluid Separations, Bergen, 23-24 May 2012

New results for divided-wall columns

Deeptanshu Dwivedi (PhD Candidate, NTNU)Ivar Halvorsen (Senior Scientist, SINTEF)Sigurd Skogestad * (Professor, Department of Chemical

Engineering, NTNU, Trondheim)

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Trondheim

Oslo

UK

NORWAY

DENMARK

GERMANY

North Sea

SWEDEN

Arctic circle

3


• Introduction: Divided wall columns for 3- and 4-product separations• Structures

• “Vmin diagrams”

• Experiments: 4- Product Kaibel Column– Experimental Setup

– Control Structure

– Experimental Runs- Steady state profiles

– Experimental data- model fitting

– Experimental Runs- Vapor Split Experiment

• Conclusions

Outline

5


3-product separation: Conventional “direct split”

ABCA/B

A

BCB/C

B

C

6


Improvement: Prefractionator (Easy split first)

ABCA/C

AB

BC

C

B/C

B

A/B

A

B

ABCA/C

AB

BC

C

A/B

B/C

A

B

Simplification:

JOIN

7


Simplification: Direct coupling (“Petlyuk”)

A/B

B/C

ABC

AB

C

A

A/C

BC

B

C

ABC

A

BA/C

AB

BC

+ single shell (divided wall column)

Petlyuk column

8


Vmin diagram for three components

•Vmin | Petlyuk = max (VAB, VBC) = VBC

•VPrefractionator = VAC

9


4-product separation: Extended Petlyuk

A/B

B/C

C/D

ABCD

ABC

BCD

B

D

S1

S2

A/C

B/D

A/D

AB

CD

BC ABCD

D

B

S1

S2

ABC

BCD

AB

CD

BC

4-product extended Petlyuk column up to ~50 % energy savings

10


4-product separation: Simplified (“Kaibel column”)

D

ABCD

CD

A

B

C

AB

ABCD

AB

CD

D

A

B

C

B/C

A/B

B/CB/C

C/D

4-product extended Kaibel column up to ~30 % energy savings

11


Vmin diagram for four components

12


Experimental Set up

• 4 products• Packed Column • Magnetic funnel-liquid

split & Product valves• Number of theoretical

stages (experimentally determined): – Prefractionator: 13– Main column : 21

Feed

ABCD

A

(Methanol)

B

(Ethanol)

C

(Propanol)

D

(Butanol)

8m

13


Experimental Set up (Labview Interface)…

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Control Structure (As used in experiments)

• Boilup V=constant• 4 control degrees of freedom:

• Liquid split ratio RL1, • Reflux ratio RL2 (top) • Reflux ratio RL3 (middle)• Reflux ratio RL4 (bottom)

• Decentralized Control with 4 PI Temperature Controllers:

•T2s is adjusted to get large temperature change in the prefractionator•T3s, T5s, T7s is adjusted to get the temperature of product stages close to the boiling points of their main components

14

5

6

7

3

F

D

S1

S2

B

T5

T3

T7

TC

Rl2

Rl1

Rl3

Rl4

TC T3S

TC T5S

TC T7S

T2

2

T2S

V

15


Start-up

40 60 80 100 120 14080

85

90

T [

0 C]

T2 (measured)

T2 (setpoint)

40 60 80 100 120 1400.25

0.3

0.35

0.4

0.45

Out

put

Loop 1 controller output

40 60 80 100 120 14068

68.5

69

69.5

T [

0 C]

T3 (measured)

T3 (setpoint)

40 60 80 100 120 1400.8

1

1.2

1.4

1.6

Out

put


40 60 80 100 120 14080

85

90

T [0

C]

T5 (measured)

T5 (setpoint)

40 60 80 100 120 1400.7

0.8

0.9

1

Out

put


40 60 80 100 120 140100

105

110

115

time, min

T [0

C]

T7 (measured)

T7 (setpoint)

40 60 80 100 120 1400

0.5

1

Out

put

time, min


•T2s is adjusted to get large temperature change in the prefractionator

•T3s, T5s, T7s is adjusted to get the temperature of product stages close to the boiling points of their main components

Temperatures Reflux ratios

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Steady Profiles with 4 temperature loops

0 50 10080

81T

, C

0 50 100

0.4

0.45

0 50 10068

69

70

T,

C

0 50 1000.85

0.90.95

0 50 10086

87

88

T,

C

0 50 1000.8

0.9

1

0 50 100

110

111

time, min

T,

C

0 50 100

0.70.8

time, min

R/l Loop

D/l Loop

S1 Loop

S2 Loop

Output

TEMPERATURES Reflux ratios

14

5

6

7

3

F

D

S1

S2

B

T5

T3

T7

TC

Rl2

Rl1

Rl3

Rl4

TC T3S

TC T5S

TC T7S

T2

2

T2S

V

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Liquid Split Loop -2 C

Steady Profiles with 4 temperature loops..

0 10 20 30 4080

85T

,C

0 10 20 30 40

0.350.4

0.45

0 10 20 30 4068.5

69

69.5

T,C

0 10 20 30 400.9

0.95

1

0 10 20 30 4086

87

88

T,C

0 10 20 30 40

0.70.80.9

0 10 20 30 40111

112

113

time, min

T,C

0 10 20 30 400

0.5

1

time, min

R/l Loop

D/l Loop

S1 Loop

S2 Loop

Output


14

5

6

7

3

F

D

S1

S2

B

T5

T3

T7

TC

Rl2

Rl1

Rl3

Rl4

TC T3S

TC T5S

TC T7S

T2

2

T2S

V

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Distillate Loop ±1 C


0 10 20 30 4081

82

83T

,C

0 10 20 30 40

0.350.4

0.45

0 10 20 30 4068

70

72

T,C

0 10 20 30 40

0.70.80.9

0 10 20 30 4086

87

88

T,C

0 10 20 30 40

0.70.80.9

0 10 20 30 40111

112

113

time, min

T,C

0 10 20 30 400

0.5

1

time, min

R/l Loop

D/l Loop

S1 Loop

S2 Loop

Output


14

5

6

7

3

F

D

S1

S2

B

T5

T3

T7

TC

Rl2

Rl1

Rl3

Rl4

TC T3S

TC T5S

TC T7S

T2

2

T2S

V

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0 10 20 3081.5

82

82.5T

,C

0 10 20 300.36

0.38

0.4

0 10 20 3068.5

69

69.5

T ,

C

0 10 20 300.9

0.95

1

0 10 20 3086

88

90

T ,

C

0 10 20 30

0.70.80.9

0 10 20 30111.5

112

112.5

time, min

T,C

0 10 20 300.5

0.6

0.7

time, min

R/l Loop

D/l Loop

S1 Loop

S2 Loop

Output

S1 Loop ± 1 C



14

5

6

7

3

F

D

S1

S2

B

T5

T3

T7

TC

Rl2

Rl1

Rl3

Rl4

TC T3S

TC T5S

TC T7S

T2

2

T2S

V

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S2 Loop ± 1 C

0 10 20 3081.5

82

82.5T

,C

0 10 20 300.38

0.4

0.42

0 10 20 3068.5

69

69.5

T ,

C

0 10 20 300.9

0.95

1

0 10 20 3086.5

87

87.5

T ,

C

0 10 20 300.8

0.9

1

0 10 20 30111

112

113

time, min

T ,

C

0 10 20 300

0.5

1

time, min

R/l Loop

D/l Loop

S1 Loop

S2 Loop

Output


14

5

6

7

3

F

D

S1

S2

B

T5

T3

T7

TC

Rl2

Rl1

Rl3

Rl4

TC T3S

TC T5S

TC T7S

T2

2

T2S

V

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0 10 20 30 4080

82

84T

,C

0 10 20 30 40

0.350.4

0.45

0 10 20 30 4068

70

72

T ,

C

0 10 20 30 400.60.8

1

0 10 20 30 4086

88

90

T ,

C

0 10 20 30 40

0.70.80.9

0 10 20 30 40110

112

114

time, min

T ,

C

0 10 20 30 400

0.5

1

time, min

R/l Loop

D/l Loop

S1 Loop

S2 Loop

Output

All Loops ± 1 C


14

5

6

7

3

F

D

S1

S2

B

T5

T3

T7

TC

Rl2

Rl1

Rl3

Rl4

TC T3S

TC T5S

TC T7S

T2

2

T2S

V

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Model (lines) and experiments (points) fit well

D S1 S2 B

Simulation Experiment Simulation Experiment Simulation Experiment Simulation Experiment

Methanol 92.6% 92.6% 15.4% 17.2% 0.21% 0 0 0

Ethanol 7.3% 7.3% 51.5% 51.5% 4.52% 5.38% 0 0

Propanol 0 0 32.9% 31.2% 89.6% 89.6% 3.14% 6.68%

Butanol 0 0 0 0 5.67% 5.02% 96.86% 93.32%

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Vapor Split

• So far: Vapor split (Rv) kept constant

• But: Energy usage depends on Rv.

• Implement adjustable Rv• But: Difficult to set Rv at

desired value– Solution: Use Rv for temperature

control (feedback)

– The more precise liquid split (Rl) can be preset

V/F vs RV for Kaibel column

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Vapor Split Experiment..

From top left: Valve in fully open positionTop right: Rack and pinion arrangement

Schematic of the vapor split valve

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Vapor Split Experimental run (Kaibel Column)

0 5 10 15 20 25

88

90

92

T [

0 C]

T2 (measured) T

2 (setpoint)

0 5 10 15 20 250

0.5

1

Out

put

Loop 1 (RV

)

0 5 10 15 20 25

68

70

72T

[0 C

]

T3 (measured) T

3 (setpoint)

0 5 10 15 20 250

0.5

1

Out

put

Loop 2 (D)

0 5 10 15 20 25

86

88

90

T [

0 C]

T5 (measured) T

5 (setpoint)

0 5 10 15 20 250

0.5

1

Out

put

Loop 3 (S1)

0 5 10 15 20 25

112

114

116

time, min

T [

0 C]

T7 (measured) T

7 (setpoint)

0 5 10 15 20 250

0.5

1

Out

put

time, min

Loop 4 (S2)

1

4

5

6

7

3

RL1

2 T2S

V1 V2

T2

TC

RV

F

B

T3S

T3

TC

DRL2

S1RL3

T5S

T5

S2

T7

TC T7S

TC

RL4

Q

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Conclusions

• Four-Product Kaibel column– Experimentally demonstrated 4-point temperature control for

stabilizing and startup operation

– Experimentally demonstrated active vapor split control

– Experimental data fits well with the model

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• Introduction

• 4- Product Kaibel Column– Four-product Kaibel column

– Control Structure

– Experimental Setup

– Experimental Runs- Steady state profiles

– Experimental Runs- Vapor Split Experiment

• 3- Product Petlyuk Column– Three-product Petlyuk column

– The “Vmin diagrams”

– Control Structures

– Close Loop Results

• Conclusions

Outline

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Three-product Petlyuk column

A/B

B/C

ABC

AB

C

A

A/C

BC

B ABC

A

C

BA/C

AB

BC

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Control Structure 1

Feed

ABC

B

D

C22

C1

C21

CC

CC

CC

xC

xA

xB

xC

xB

S

CC

CC

• Five degrees of freedom including vapor split

• Control key impurities using “close-by” parings

• Side product has two side impurities

•In CS1, S is paired with heavy key (xC)

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Closed-loop result from CS1

0 500 1000 1500 20000.4

0.5

0.6

0.7

0.8

0.9

1

time, min

mol

e fr

actio

n

xD

xS

xr

0 500 1000 1500 20000.9

1

1.1

1.2

1.3

1.4

time, min

mol

/min

VB

0 500 1000 1500 20000.25

0.3

0.35

0.4

0.45

0.5

time, min

mol

/min

DSB

0 500 1000 1500 20000

0.2

0.4

0.6

0.8

time, min

mol

/mol

RL

RV

Fails for feed composition disturbance zf=[53 13 33]

from nominal equimolar feed

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Why CS1 failed ??

•For nominal equimolar feed, B/C is the most difficult split

•For the new feed A/B is more difficult feed and CS1 can not provide sufficient vapor in top section of main column

34


Control Structure 2

Feed

ABC

B

D

C22

C1

C21

CC

CC

CC

xC

xA

xB

xC

xB

S

CC

CC

>

xA

• Same as CS1, but boilup now has a maximum select controller with:

• light key, xA at S or,

• light key, xB at reboiler

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Closed loop results from CS2

0 500 1000 1500 20000.95

0.96

0.97

0.98

0.99

1

time, min

mol

e fr

actio

n

xD

xS

xr

0 500 1000 1500 20001.3

1.4

1.5

1.6

1.7

1.8

time, min

mol

/min

VB

0 500 1000 1500 20000.1

0.2

0.3

0.4

0.5

0.6

time, min

mol

/min

DSB

0 500 1000 1500 2000

0.4

0.5

0.6

0.7

0.8

time, min

mol

/mol

RL

RV

•Works for all feed composition disturbance from nominal equimolar feed

•The purity of bottom product may be over purified for some disturbances

1 EFCE Working Party on Fluid Separations, Bergen, 23-24 May 2012 New results for divided-wall...

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Transcript of 1 EFCE Working Party on Fluid Separations, Bergen, 23-24 May 2012 New results for divided-wall...