A Energy efficient distillation - SINTEF · Monz – main vendor for BASF Krupp-Uhde Sulzer Rashig Linde Others MW Kellogg (UK) UOP (USA) UK, Japan, Indonesia, South Africa The Kaibel-column

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Energy efficient distillation

Ivar J. Halvorsen, Maryam Ghadrdan, Deeptanshu Dwivedi, Mohammad Shamsuzzoha and

Sigurd Skogestad

1st Trondheim Gas TechnologyConference,

21 - 22 October 2009

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Distillation in the gas value chain

Distillation plays an important role in splitting rawproduction streams into more useful product streams withspecified compositions

Figure, ref http://www.sintef.no/Projectweb/Trondheim_GTS/

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Distillationconsumes energy

2-5% of the world industry heat consumption

There is a potential for more energy efficient solutions

Picture: Fractionation columnsat the Snøhvit LNG-plant in Hammerfest

Foto: I.Halvorsen

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BEEDIST (Basic Energy Efficient Distillation Technology)

Founded by the Norwegian Research Council through the GASSMAKS programSINTEF/NTNU 2008-2012Objectives

Study new integrated distillation arrangementsFor 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 operationDevelop laboratory2 PhD + post doc

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NTNU lab4-product Kaibel-

column with a dividing wall

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3-product Petlyuk arrangement

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An ideal reversible processrequires:

H

C

C

TTST

Q−

Δ−=

1min

Distillate product

Feed

Heating at TH

Cooling at Tc

Bottom product( )i

iiln xS RxΔ = −∑

Where entropy of mixing is

Q

Q

Teoretical minimum energy

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Increasing purity require energy-Mixing gives irreversible loss

Can we find a minimum enegy route

to pure A?

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A

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Remixing at end ofcolumn 1 Position along path

from feed to A outlet

A-composition

Feed C1 Feed C2 A-product

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Minimum energy path to the mountain top

Choose the minimum-energy route

Irreversible losses in potential energy

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Conventional alternatives for 3-product separation: Sequence of binary columns

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BC

A B

C

Direct Split: DS

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A

BC

Indirect split: IS

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ABC

BD

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B

C

B

Prefractionator arrangement

Alternatives for 3-product separation...

The prefractionatordoes the simple A/C

split

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Conventional Prefractionator arrangementwith a single main column

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B

C

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Apply full thermal coupling

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The Petlyuk column

removes mixing loss at the interconnections

Saves 20-30% energy

The Petlyuk path

avoids mixing loss

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The dividing wall column (DWC)

The Petlyuk arrangement in a single shellSeparates a single feed into three separate products in one columnJust a single reboiler and condenserSaves 20-30% in both energy and capital

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The Vmin-diagram –for simple energy asessment

D/F

V/F

ABC

D

F

V

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Industrial DWC/Petlyuk applications

German-speaking community dominatesBASF: 40 DWCs in operation. Increasing. G. Kaibel pionerMonz – main vendor for BASFKrupp-UhdeSulzerRashigLinde

OthersMW Kellogg (UK)UOP (USA)UK, Japan, Indonesia, South Africa

The Kaibel-column4-product DWC!

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Why consider a Petlyuk arrangementLarge potential energy savings compared to conventionalcolumns (20-30%)

Or – increase production for given energy supply

Capital cost savings due to more compact equipment => smaller footprint and removal of reboiler/condenser unitsUsage:

In theory: Anywhere (almost) where distillation is a suitableseparation technology and more than 2 products are produced. In practice: Some cases may be unsuitable due to requiredtemperature/pressure range, height, or if liquid/vapor load in different sections are very different. Practical variations can be made, e.g. side-strippers/rectifiersRevamping of existing conventional columns may have significantpotential

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Critical for obtaining the teoretical savingsin practice: How to control the splits

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vapor split(Rv)

liquid split(Rl)

Split-ratio

Energy

TeoreticalVmin

Tool: Self optimizing control

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Extend to 4-product DWC:The Kaibel column – (1987)

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4 products in a single

shell!

Saves 30-40 %

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The Kaibel column at NTNU A

B

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D

Feed(ABCD)A

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B

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H=8m

D=5/8cm

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First really big 4-product DWC

Kaibel column

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Control study (Strandberg 2009)

Need to adjust liquid splitonline in order to stabilizeprefractionator

Stabilizing Control by 4 temperature loops

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Step response test on pilot column

Prefractionatortemperaturebelow feedcontrolled by adjusting theliquid split

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More results:

Master thesis by Martin Kvernland 2009Matlab model exension includes heat loss and vaporbypass for stage inefficiencyImplemented a 4x4 MPC with a reduceded linear statespace model (reduced from original 200 to 15 states)The MPC controller in Matlab can be interfaced to Labview via OPC

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UniSim Simulation for Kaibel Column

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MATLABAdvanced Optimization

& Execution ControlHYSYS/UNISIMRigorous Simulation

Execution control

Variables values

20 21 22 23 24 25 26 27 28 290.75

0.8

0.85

0.9

0.95

1

S1 Rate (kmol/hr)

Com

posi

tions

(mol

e fra

c)

xDxS1xS2xB

20 21 22 23 24 25 26 27 28 290.82

0.84

0.86

0.88

0.9

0.92

0.94

0.96

0.98

1

S2 Rate (kmol/hr)

Com

posi

tions

(mol

e fra

c)

xDxS1xS2xB

0.2 0.25 0.3 0.35 0.4 0.45 0.5 0.55 0.6 0.650.5

0.55

0.6

0.65

0.7

0.75

0.8

0.85

0.9

0.95

1

Liquid split

Com

posi

tions

(mol

e fra

c)

xDxS1xS2xB

0.4 0.45 0.5 0.55 0.6 0.65 0.7 0.75 0.8 0.85 0.90.4

0.5

0.6

0.7

0.8

0.9

1

Vavpor split

Com

posi

tions

(mol

e fra

c)

xDxS1xS2xB

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Reflux Ratio

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posi

tions

(mol

e fra

c)

xDxS1xS2xB

Toolbox for rigorous simulationsby Maryam Ghadrdan

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Further work

Model development and refinement Both in Matlab and Unisim/HysysLab column experimentsControl structure design (including selfoptimising control)Optimizing control / minimum energy controlOptimal process design Extended Petlyuk arrangementsAlternative structures like HIDiC, Heat integrated and other energy efficient arrangements

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Extended 4-product Petlyuk DWC with multiple dividing walls

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What about complexity in

design and operation?

Teoreticalsavings up

to 50%

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What about refit?A Butane case (butane/C5+) and butane splitter (iC4/nC4):

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Add direct coupling and save 32 %

Simple refit of exisiting columns is equivalent to the full Petlyuk arrangement

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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 stagesConstant relative volatilityConstant molar flowConstant pressureNo internal heat exchange

Then, exact analytic solution is obtained

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zA:zB:zC:

αA:αB:

qf:

Conventional : Vmin=2.03Petlyuk Column: Vmin=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

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1

1.5

2

D/F

VT/F

P

R

Savings

0 0.2 0.4 0.6 0.8 10

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C3

C2

V(Rl,Rv)

Rl

RC4

P

C1

Characterisitcs of operation

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Feed condition for the Kaibel Distillation

Four components: Methanol+Ethanol+1-Propanol+1-ButanolFlow rate F=1.0 Kgmole/h, q=1 (saturated liquid)Composition z=[0.25, 0.25, 0.25, 0.25]EOS WilsonPressure AtmosphericRelative volatility α= [8.27: 4.84: 2.30: 1.0]

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Minimum Energy – competition No Configuration Ideal Vmin/F Ideal

SavingsUniSimSavings

1 Four product extended Petlyuk 1.16 51%

33%

16%

0%(reference)

-10%(loss)

2 Kaibel column 1.59 >26%

0%(reference)

3 Prefractionator+single main column

1.98

4 Conventional direct sequence (3 columns)

2.38

5 Prefractionator+2 separate columns

2.62

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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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How to apply DWC/Petlyuk columns

Make sure to do a reasonable design in terms ofplacement of the dividing wall/design split.Important: Make sure to indentify the optimality region for the expected actual feed variations, and thereby clarifythe 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 actualproduct value/energy cost, and dynamic controllabilityanalysis.