Thermodynamics and Innovative Design for Energy Efficiency...

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30.03.2012 T. Gundersen Slide no. 1

Thermodynamics and Innovative Design for Energy Efficiency and Carbon Capture

by

Truls Gundersen Department of Energy and Process Engineering

Norwegian University of Science and Technology (NTNU) Trondheim, Norway

with important contributions from

Audun Aspelund, PhD, 20 March 2012 Chao Fu, PhD, September 2012

Danahe Marmolejo Correa, PhD, Spring 2013

Chemical Engineering Department Seminar Carnegie Mellon University, Pittsburgh, 27 March 2012

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Comments from a “UK University” October 1988

Promoting Optimization (Math Programming) was quite challenging in those Days !

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is not about Architecture (the Stata Center at MIT)

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BIGCCS BIGCCS Director: Mona J. Mølnvik BIGCCS Board Chair: Nils A. Røkke

SINTEF Energy Research NTNU Coordinator: Truls Gundersen

International CCS Research Centre

Budget 80 MUSD over 8 years

> 20 PhDs and > 10 Post.docs

2009-2016 Objectives:

1. Reduce CCS Cost by 50% 2. CO2 Capture Rate of 90% 3. Fuel-to-Power Penalty ≤ 6 % pts

Innovations are required

http://www.geus.dk/index.htm

http://www.google.com/imgres?imgurl=http://www2.imec.be/content/user/Image/GDF_20SUEZ_20logo.jpg&imgrefurl=http://www2.imec.be/be_en/press/imec-news/archive-2009/total-gdf-suez-and-photovoltech-join-imec-08217-s-silicon-solar-cell-research.html&h=916&w=2922&sz=276&tbnid=Ph22kItMzsTMBM:&tbnh=47&tbnw=150&prev=/images?q=gdf+suez+logo&usg=__IyWh_4M-rKi-fkvvo2d_hqTDC9g=&sa=X&ei=7iVpTP6IAcKMOKLf2LgF&ved=0CBsQ9QEwAQ

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Ref.: IPCC, Climate change 2007: The physical science basis

Climate Change and CO2 Emissions

Mark Twain:

”Climate is what to expect, weather is what you get”

3 Main Options:

1. Energy Efficiency 2. CO2 Capture & Storage 3. Renewable Energies

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Obvious link: Thermodynamics & Energy Efficiency

Greek-to-English: Therme = Warm = Heat (Thermie = Calorie) Dynamis = Force = Power

Heat & Power

Physics

Chem. Engng.

Mech. Engng.

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Content of the Presentation 2 “subambient” Processes

♦ LNG and ASU (Air Separation Units) Scenario: 2 types of Power Stations

♦ Supercritical pulverized Coal based Plant ♦ Combined Cycle Natural Gas based Plant ♦ Both of the Oxy-combustion type for CO2 Capture

Design Methodologies ♦ Thermodynamics based (Pinch & Exergy Analyses) ♦ Optimization based (Math Programming & Superstructures)

Examples will focus on Energy Efficiency and CCS Innovations will be discussed

♦ Patent Application for new ASU cycles ♦ Liquefied Energy Chain with offshore LNG

Round up with a Summary

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Combined Transport of Natural Gas and CO2

Oxyfuel Power Plant

CO2 Liquefaction

Natural Gas Liquefaction

Air Separation ASU

NG

Air

LIN LNG

W

CO2

NG

LCO2

O2

LNG

H2O

Audun Aspelund: A Liquefied Energy Chain (LEC)

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Why is the PRICO Process so inefficient? Danahe Marmolejo Correa: Exergy Analysis & LNG

K-101

K-102

VLV-101

VLV-201

Mixed Refrigerant (1)@ 294 K & 4 bar

2a@ 346 K & 10 bar

2b@ 306 K & 9.8 bar

2@ 361 K

& 24.4 bar

3@ 305 K

& 24.2 bar

5@ 108 K & 4.2 bar

Natural Gas (6) @ 300 K & 50 bar

7 @ 113 K & 49.8 bar

LNG (8)@ 109 K & 1.2 bar

4@ 111 K & 24 bar

COND-101INTERC-101

HX-101

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Current State-of-the-Art:

Chao Fu: ASU Cycles with up to 20% Energy Savings

Linde’s Classical Coupled Column Design

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Recuperative Vapor Recompression Cycle - Patented

Chao Fu: ASU Cycles with up to 20% Energy Savings

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A short Tutorial on Exergy What is Exergy?

♦ ”The Maximum Amount of Work that can be produced if a “System” is brought to Equilibrium with its natural Environment through Reversible Processes”

♦ Equilibrium here refers to Composition, Pressure, Temperature, Velocity, Gravitational Level, etc.

Is Exergy related to Entropy? ♦ They are “inverse” properties ♦ Entropy is a measure of disorder (chaos) ♦ Entropy Production in processes due to Irreversibilities is

Equivalent to Exergy Losses (and Lost Work) Why use Exergy?

♦ Energy Forms have different Qualities, i.e. Exergy ♦ Subambient Refrigeration Compr. Work Exergy ♦ But: Exergy and Cost are often (not always) in Conflict

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The Exergy of Heat

ηmax as function of TH

0.000

0.100

0.200

0.300

0.400

0.500

0.600

0.700

0.800

0 200 400 600 800

TC = 0ºC

TC = 15ºC

TC = 25ºC

Without 1st Law Losses:

Wcycle = QH – QC

Without 2nd Law Losses:

(QC /QH) = (QC /QH)rev = TC /TH Thermal Efficiency:

Carnot Efficiency:

Exergy of Heat:

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Using Exergy in Subambient Processes?

@ 298 K (25°C) & 50~70 bar

@ 109 K (-164°C)

& 1 bar

Work

&

Liquefaction

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Exer

gy

Flow Exergy

Carried by Matter

Disordered

Chemical

Reactional

Concentrational

Thermo-mechanical ETM

Temperature part ET

Pressure part Ep

Ordered

Mechanical

Kinetic

Potential

Electrical

Electrostatic

Electrodynamic

Nuclear

Carried by Energy

Disordered

Heat EQ

Radiation

Ordered Electrical

Non-flow Exergy

1st class: Open/Closed Systems

2nd class: Carrier

3rd class: Energy Randomness

4th class: Origin

Exergy Parts or Components Classification &

Decomposition of Exergy

D. Marmolejo-Correa, T. Gundersen, ”A Comparison of Exergy Efficiency Definitions with focus on Low Temperature Processes”, submitted to Energy, October 2011.

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Classification of Exergy Types

Exergy

Physical Chemical

MechanicalThermo-mechanical

Kinetic Potential Temperaturebased

Pressurebased

Mixing &Separation

ChemicalReaction

Kotas T.J., The exergy method of thermal plant analysis, Krieger Publishing Company, Florida, USA, 1995.

Bejan A., Tsatsaronis G. and Moran M., Thermal design and optimization, Wiley, New York City, 1996.

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Our Modest Contributions to Exergy Discussed the Various Classifications

♦ OK, it is only a matter of words, but?

Looked for Ways to Standardize Terms and Definitions Illustrated the importance of Decomposition

♦ Explains behavior of Compressors/Expanders above/below T0 ♦ Results in Exergy Efficiencies that measure Design Quality

Discussed various Exergy Efficiencies ♦ Compared existing ones applied to LNG Processes ♦ Proposed a new Exergy Efficiency based on Sources & Sinks

New “Exergetic” Temperatures (beyond Scope here) New Graphical Diagrams and Representations New Targeting Procedure for Exergy

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0.0

0.5

1.0

1.5

2.0

0 1 2 3 4 50Dimensionless Temperature, T T

Exer

gy ra

tio o

f Hea

t, EQ

/ Q

.

.

0.5

Special Behavior of Temperature based Exergy Exergy of Heat

0

p

0p

( ),T p

( )0 ,T p

( )0 0,T p

0T

0T T<

Exer

gy, E

.

Thermo-mechanical Exergy of a Stream

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Consider Expansion above/below Ambient

5 bar 223K

Assume Isentropic Expansion of Ideal Gas, with Cp = 1.0 kJ/kgK and k = Cp / Cv = 1.4

Ambient T0=298 K

Exp

Exp

5 bar 523K

1 bar 330.2K

1 bar 140.8K

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Consider Heat and Exergy Transfer above/below Ambient Temperature

-150

-100

-50

0

50

100

150

200

0 20 40 60 80 100 120

Tem

pera

ture

(°C

)

E (kW)

Hot Stream (exergy) Cold Stream (exergy)

1

2 3

4

2

1

4

3

Source

Sink

Source

Sink

Heat Transfer Exergy Transfer

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3/30/2012 T. Gundersen Slide no. 21

Process orUnit Operation

ExergyConsumed

ExergyProduced

(Internal)

What is Exergy Efficiency?

D. Marmolejo-Correa, T. Gundersen, ”Challenges in Low Temperature Process Design and Optimization – Using Exergy as the Objective?”, AIChE Mtg., Salt Lake City, November, 2010.

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Process orUnit Operation

ExergyConsumed

ExergyProduced

(Internal)

Exergy Efficiency Definitions

D. Marmolejo-Correa, T. Gundersen, ”Exergy Transfer Effectiveness for Low Temperature Processes”, to be submitted to Intl. Jl. of Thermodynamics, 2012.

Brodyansky et al. (1994)

”Exergy Efficiency”

Bejan et al. (1996)

”Exergetic Efficiency”

Kotas (1995)

”Rational Efficiency”

Marmolejo-Correa and Gundersen (2012)

”Exergy Transfer Effectiveness (ETE)”

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Applied to the simple PRICO Process

Brodyansky et al. (1994)

Bejan et al. (1996)

Kotas (1995)

Marmolejo-Correa and Gundersen (2012)

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Source: BP Statistical Review of World Energy 1990-2010

6.9% annual growth in the last 20 years

LNG as energy carrier: International Trade

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Liquefied Natural Gas Value Chain

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T. Shukri (Poster Wheeler, UK), ”LNG Technology Selection”, Hydrocarbon Engineering, February 2004

Liquefaction of Natural Gas

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Pure Refrigerant

Cycles

Optimized Cascade by Conoco-Phillips

Mixed Refrigerant

Cycles

PRICO by Black &Veatch

Mixed Fluid Cascade (MFC) by Linde-Statoil

Expansion Cycles

Reversed Brayton Cycle

by TGE

Some LNG Processes

Pre-cooled Mixed Refrigerant

(C3MR) by Shell

AP-X by APCI

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FV2001, U 14

Natural gas

LNG

Fuel gas

Propane

Ethene

Methane

-40°C

-93°C

-163°C

Cascade Liquefaction Process

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Liquefaction using Multicomponent Mixtures

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100

150

200

250

300T (K)

ΔH (kW)

R2

R1

R3

Linde and Statoil: Mixed Fluid Cascade

3 Mixed Refrigerants

http://www.statoil.com/en/OurOperations/pipelines/Documents/veien_til_lng_engelsk_enkel.swf

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A new Process Synthesis Methodology utilizing Pressure based Exergy

in Subambient Processes

The Classical Heat Recovery Problem was redefined ”Given a Set of Process Streams with a Supply and Target State

(Temperature, Pressure and the resulting Phase), as well as Utilities for Heating and Cooling Design a System of Heat Exchangers, Expanders, Pumps and Compressors in such a way that the Irreversibilities (or Costs) are minimized”

10 Heuristic Rules were developed Automated by new Superstructure and Math Programming

Aspelund A., Berstad D.O. and Gundersen T. ”An Extended Pinch Analysis and Design Procedure utilizing Pressure based Exergy for Subambient Cooling”, Applied

Thermal Engineering, vol. 27, No. 16, pp. 2633-2649, November 2007.

ExPAnD = Extended Pinch Analysis and Design

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Application: A Liquefied Energy Chain (LEC)

Key Features of the “LEC” Concept ♦ Utilization of Stranded Natural Gas for Power Production ♦ High Exergy Efficiency of 46.4% (vs. 42.0% for traditional) ♦ Innovative and Cost Effective solution to the CCS Problem ♦ CO2 replaces Natural Gas injection for EOR ♦ Combined Transport Chain for Energy (LNG) and CO2

Aspelund A. and Gundersen T. ”A Liquefied Energy Chain for Transport and Utilization of Natural Gas for Power Production with CO2 Capture and Storage − Part 1”, Journal of Applied Energy, vol. 86, pp. 781-792, 2009.

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NG

0.4

%

CO

2 0.

4%

Combined process for Liquefaction of NG and heating of

LCO2

Combined ship

Combined process for heatin of LNG and liqiefaction of

CO2CCS power plant

NG 100% NG 99.6%NG 100%Power 47.1%

NG

5.4

%

C02

0.7

%

Power

New combined energy-chain: Loss NG during transport 5.8%, CO2 emissions 15.3%, Efficiency 47.1%

CO2 84.7%CO2 84.7%CO2 84.7%

NG 99.6%

CO2 84.7%

NG

94.

2 %

CO

2 14

.2%

LNGLNG LNG

LCO2 LCO2LN2

LNG production LNG ship LNG vaporization

CCS powerplant

LNG production LCO2 ship CO2 Liquefaction Pumping and heating of LCO2

NG 89.9% NG 89.1%

CO2 75.7% CO2 75.7%CO2 75.7%

NG 100%

NG

9.8

%

NG

0.4

%

Power 42.5%

LNG 89.1%

NG

3.6

%

NG

0.4

%

NG

0.3

%

CO

2 9.

8%

0.1

CO

2 %

CO

2 0.

4%

C02

0.4

%

CO

2 0.

3%

CO

2 12

.9%

Power

NG

0.4

%

CO

2 0.

4%

NG 0.4%NG 0.3%

”Conventional” ship-based energychain: Loss NG during transport 14%, CO2 emissions 24.3%, Efficiency 42.5%

CO2 75.7%

NG

85.

2

LNGLNG LNG

LCO2 LCO2LCO2

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Developing the Liquefied Energy Chain − Manual and Automated Design Procedures

The ExPAnD Methodology was used ♦ Original version uses 10 Heuristic Rules ♦ Combines Pinch Analysis & Exergy Analysis

Composite & Grand Composite Curves for Idea Generation related to Process Improvements

Exergy Efficiency to Quantify Improvements

♦ Optimization has also been included New Superstructure allows Simultaneous Optimization of Networks with Heat Exchangers, Pumps, Compressors and Expanders using Math Programming

E-2

C-1

E-1

C-3

E-3

C-2

TC1,in TC1,out

TC2,in TC2,out

TH1,inTC3,out

TC3,in

TH1,out

TH2,inTH2,out

TH3,inTH3,out

TC4,in TC4,out

TH4,in

TH4,out

E-2E-2

C-1C-1

E-1E-1

C-3C-3

E-3E-3

C-2C-2

TC1,in TC1,out

TC2,in TC2,out

TH1,inTC3,out

TC3,in

TH1,out

TH2,inTH2,out

TH3,inTH3,out

TC4,in TC4,out

TH4,in

TH4,out

A. Wechsung, A. Aspelund, T. Gundersen and P.I. Barton, ”Synthesis of Heat Exchanger Networks at Sub-Ambient Conditions with Compression and Expansion of Process Streams”, AIChE Jl., vol. 57, no. 8, pp. 2090-2108, 2011.

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NG-1

NG-2

LIQ-EXP-102

NG-3

LNG

P-101

N2-2N2-3

N2-1

CO2-1

CO2-2

N2-4

CO2-3

HX-101 HX-102K-100

Offshore Process without Pressure Manipulations

-180

-130

-80

-30

20

0 5 10 15 20 25 30Heat flow [MW]

Tem

pera

ture

[C]

Hot CC Cold CC

HX-101

HX-102

• LIN: 1.75 kg/kgLNG • LCO2: 0.41 kg/kgLNG • Power Deficit • Exergy Efficiency: 55.7%

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Offshore Process with Pressure Manipulations

• LIN: 1.25 kg/kgLNG • LCO2: 1.50 kg/kgLNG • Power Surplus • Exergy Efficiency: 84.1% • No Power Export: 76.3%

K-100

P-102NG-2

NG-1

NG-3

LIQ-EXP-102

NG-4

LNG

P-101

N2-2

N2-5N2-6

N2-3

EXP-101

N2-1

P-100

CO2-2

CO2-1

CO2-3

N2-4

CO2-4

HX-101 HX-102

N2-7

-180

-130

-80

-30

20

0 5 10 15 20 25 30Heat flow [MW]

Tem

pera

ture

[C]

Hot CC Cold CC

HX-101

HX-102

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Offshore Process in Balance with respect to Thermal and Mechanical Energy

• LIN: 1.0 kg/kgLNG • LCO2: 2.2 kg/kgLNG • Power Balance • Exergy Efficiency: 85.7%

-180

-130

-80

-30

20

0 5 10 15 20 25 30Heat flow [MW]

Tem

pera

ture

[C]

Hot CC Cold CC

HX-101

HX-102

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The Offshore Process in the LEC

K-100

P-102

V-101

NG-2

LIQ-EXP-101NG-1

NG-3 NG-4

LIQ-EXP-102

NG-5

NG-6

NG-PURGE

LNG

P-101

N2-2

N2-5

N2-10

N2-11

N2-6

N2-3

EXP-101

EXP-102

N2-1

P-100

CO2-2

CO2-1

N2-9K-101N2-8

CO2-3

N2-12

N2-4

N2-7

CO2-4

HX-101 HX-102

No flammable Refrigerants and no Gas Turbines !!

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Detailed Features of the Offshore Process

-200

-150

-100

-50

0

50

100

0 2 4 6 8Duty [MW]

Tem

pera

ture

[C]

Hot CCCold CC

Composite Curves - Offshore Process

Single Components (here CO2 and N2) exhibit Multi-component Behavior by Expansion and Compression

Aspelund A. and Gundersen T. ”A Liquefied Energy Chain for Transport and Utilization of Natural Gas for Power Production with CO2 Capture and Storage – Part 2, The Offshore and the Onshore Processes”, Journal of Applied Energy, vol. 86, pp. 793-804, 2009.

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Simulation-Optimization of the entire LEC

LIN LCO2 LCO2

LNGLNG

The field site

process

Storage

The market site

process

NG LNG LNG NG

P1 F1

LCO2CO2 P2

P3LINN2

N2

Powerprocess

with CO2 capture Water

Electricity

LNG

CO2

The simple chainThe complete chain

Storage

LNG

LCO2

LIN

LCO2F2

LIN

K-100

P-102

V-101

T1

LIQ-EXP-101NG-1

NG-4

LIQ-EXP-102

NG-5

NG-6

NG-PURGE

P3

P-101

N2-2

N2-10

N2-11

N2-6

N2-3

EXP-101

EXP-102

P2F2

P-100

CO2-2

F1

K-101

CO2-3

N2-12

T2

T4P6

CO2-4

HX-101 HX-102

P1

P5

P4

NG-2

T3

N2-1

CO2-1

LNG

N2-5

N2-8

NG-3

N2-4

N2-7

N2-9

NG-1HX-102

P3 P-101

NG-3

P-102

HX-101

N2-8N2-9

EXP-101

NG-4

NG-5

NG @ 25

V-101 CO2-4K-107

CO2-5CO2-6K-108

CO2-7

F4

CO2-8

CO2-11

CO2-9

CO2-13

CO2-Recycle

4 stage compressionK101-K104

N2-1

VF1

V-102

P2

N2-12

T5

P1

EXP-102

N2-14

T6

N2-16

F2

F32 stage compression

K105-K106

CO2-1

F1

CO2-0

N2-0

LCO2

LIN

LNG

CO2-12

CO2-10

N2-10

N2-13

T7N2-15

NG-2

N2-11

Offshore Onshore

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Optimization Variables Stream Type I Type II Name Unit Initial

value Lower bound

Upper bound

CO2-1 Global Pressure P1 kPa 600 550 1000

CO2-1 Global Flow rate F1 kg/h 80000 60000 150000

N2-1 Global Pressure P2 kPa 400 400 1000

N2-1 Global Flow rate F2 kg/h 65000 55000 65000

LNG Global Pressure P3 kPa 110 100 300

NG-2 Global Pressure P4 kPa 9000 8000 10000

NG-3 Local Temperature T1 °C -61 -70 -50

N2-4 Local Temperature T2 °C -40 -60 0

N2-5 Global Pressure P5 kPa 600 400 1000


N2-8 Gobal Pressure P6 kPa 2800 1500 3500


Field Site Process

(offshore)

Stream Type I Type II Name Unit Initial value

Lower bound

Upper bound

LCO2 Global Pressure P1 kPa 600 550 1000

CO2-0 Global Flow rate F1 kg/h 80000 60000 150000

LIN Global Pressure P2 kPa 400 400 1000

N2-0 Global Flow rate F2 kg/h 65000 55000 65000

LNG Global Pressure P3 kPa 110 100 300

CO2-12 Local Flow rate F3 kg/h 10500 9000 25000

CO2-6 Local Flow rate F4 kg/h 35000 30000 55000

N2-9 Local Temperature T7 °C -96 -115 -80

N2-11 Global Void fraction VF1 - 0.4 0.1 0.5



Market Site Process

(onshore)

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Progress of the Optimization

28

29

30

31

32

33

34

35

36

0 50 100 150 200 250 300 350 4000

1

Best known objective Current best Local search

Myklebust J., Aspelund A., Tomasgard, A., Nowak M. and Gundersen T., “An Optimization-Simulation Model of a Combined Liquefied Natural Gas and CO2 Value Chain”, INFORMS Annual Meeting, Seattle, November 2007.

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Supercritical Oxy-Combustion Pulverized Coal-based Power Plant

C. Fu and T. Gundersen, “Exergy Analysis of an Oxy-Combustion Process for Coal-fired Power Plants with CO2 Capture”, ECI, CO2 Summit: Technology and Opportunity, Vail, Colorado, USA, 6-10 June, 2010.

ASU

CPU

FGD

Power Cycle*

* Reference: DOE/NETL, Report NO.: 2007/1291

567 MW

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• Net power output: 567 MW

• Coal feed: 69 kg/s = 5 962 tons/day

• O2 feed: 161 kg/s (excess O2: 10%) = 13 910 tons/day

• Efficiency penalty related to CO2 capture: 10.3% points (ASU: 6.6% points)

• Power to produce O2 (95 mol%): 124 MW

Some key Production Figures

Air

Coal

Mill

HRSG

Steam Turbine

ElectricityGenerator

Condenser

Ash

ESP

Limestone Slurry

Gypsum

Fan Fan

Fan

CO2 For Storage

FGD CO2 Drier

CO2 Purification

TowerLP

Compressor

HP Compressor

Inerts

Air Separation

UnitCombustor

N2

O2

H2O

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Efficiency Penalties for CO2 Capture

Air

Coal

Mill

HRSG

Steam Turbine

ElectricityGenerator

Condenser

Ash

ESP

Limestone Slurry

Gypsum

Fan Fan

Fan

CO2 For Storage

FGD CO2 Drier

CO2 Purification

TowerLP

Compressor

HP Compressor

Inerts

Air Separation

UnitCombustor

N2

O2

H2O

ASU CPU

6,6

1,4

3,6

2,0

0

2

4

6

8

10

12

Base case Theoretical Case

Effic

ienc

y Pe

nalty

(%) CPU

ASU

Specs on Oxygen:

~ 95 mol%, 1.25 bar

3.7

Fu C. and Gundersen T., “Exergy Analysis of an Oxy-combustion Process for Coal-fired Power Plants with CO2 Capture”, submitted to Fuel, June 2011

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Our Research Motivation

Power Plant

Air Power

Coal 1393 MW (HHV)

560 MW

ASU Power Plant

CPU

Air O2

H2O

Exhaust

CO2

Coal 1879 MW (HHV)

Net Power

567 MW

69 MW

124 MW

without CCS560 40.2%

1393η = =

with CCS567 30.2%

1879η = =

total567 124 69 40.5%

1879η + +

= =

1ASU

1CPU

124 6.6% pts1879

69 3.7% pts1879

η

η

∆ = =

∆ = =

Improving the ASU by 20% gives 4.4% more Power !!

or 1.32% points

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Conventional ASU – here producing 95% O2

HP LP

Condenser

Reboiler

Air

A1-2

Impurities

A1-4

A1-5

A2-2 A2-3

A3-1 A3-2 A3-3

A5-1

A5-2

A7-1

A4-1A4-2

A4-3

A4-4

O2

N2 waste

Extracted N2

A0

A1-1A1-3

A2-1

A7-2

A7-3

PPU

MHE

MAC

Energy Consumption ♦ Actual: 0.193 kWh/kgO2 ♦ Ideal: 0.049 kWh/kgO2

Exergy Losses ♦ Air Compressor: 38% ♦ Distillation Cols.: 28%

Our Goal: ♦ Save 10-20%

Fu C. and Gundersen T., “Using Exergy Analysis to reduce Power Consumption in Air Separation Units for Oxy-combustion Processes, Energy, available on-line,

http://dx.doi.org/10.1016/j.energy.2012.01.065, February, 2012

http://dx.doi.org/10.1016/j.energy.2012.01.065

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Compressor: 20.812.6

Coolers: 17.6

7.2

28.2

1.7

11.9

HP: 1.6

LP: 14.6

Condenser/reboiler: 6.3

Heat exchanger: 3.0Valves: 2.7

0

5

10

15

20

25

30

35

40

45

AU1 AU2 AU3 AU4 AU5 AU6

Exe

rgy

loss

es [%

]

38.4

AU1: The main air compressor

AU2: The pre-purification unit

AU3: The main heat exchanger

AU4:The air distillation system

AU5: The tail N2 turbine

AU6: The waste N2

Distribution of Exergy Losses

Largest Sources of Exergy Losses ♦ Distillation System (28.2%)

LP Column ♦ Main Air Compressor (38.4%)

Interstage Coolers Compression Process itself

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How to reduce Compressor Work?

Simplified Equation for Ideal Gas indicates: ♦ Increase Compressor Efficiency

Responsibility of the Manufacturers ♦ Reduce Inlet Temperature

Beyond CW requires Refrigeration, thus more Work ♦ Reduce Pressure Ratio

Limited by Condenser/Reboiler Match, but there are ways around it …. !!

♦ Reduce Mass Flowrate through the Compressor Do we really need to compress the Oxygen?

Our Inventions are based on the last two: ♦ Reducing Compressor Flowrate and Pressure Ratio

Fu C. and Gundersen T. “Power Reduction in Air Separation Units for Oxy-Combustion Processes based on Exergy Analysis”, in E.N. Pistikopoulos et al. (eds.), 21st European Symposium on Computer

Aided Process Engineering (ESCAPE 21), Elsevier B.V., vol. 29, Part B, pp. 1794-1798, June 2011.

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Specific Shaftwork for Separation: 0.178 kWh/kgO2

Recuperative Vapor Recompression Cycle

Fu C. and Gundersen T. “Innovative air separation processes for Oxy-Combustion plants”, 2nd International Oxy-fuel Combustion Conference, Yeppoon, Australia, September 2011.

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Column Grand Composite Curve for Distributed Reboiling

McCabe-Thiele Diagram for Distributed Reboiling

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Vapor Recompression with Dual-Reboiler


Fu C. and Gundersen T., “Using PSE to develop Innovative Cryogenic Air Separation Processes”, accepted for the 11th Intl. Symp. on Process

Systems Engineering (PSE 2012), Singapore, 15-19 July, 2012

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Intermediate & Recuperative Vapor Compression Cycle


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Performance Comparison O2 purity,

% Specification Shaftwork

for Separation, kWh/kgO2 Power savings

Cycle 1 (reference) Conventional double column cycle

95.0 0.193 Ref. Case

Cycle 2 Vapor recompression cycle

95.4 0.178 -7.8 %

Cycle 3 Vapor recompression cycle with dual reboiler

95.5 0.166 -14.0 %

Cycle 4 Intermediate vapor recompression cycle

95.1 0.159 -17.6 %

OPEX is down; what about CAPEX ?? Fu C., Gundersen T. and Eimer D., “Air Separation”, GB Patent, Application number GB1112988.9, July 2011

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Is this the Optimum (Local or Global)?

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Summary of the Presentation Demonstrated the use of Thermodynamics in Design

♦ Pinch Analysis and Exergy Analysis ♦ McCabe-Thiele and Column Grand Composite Curve

Demonstrated Innovations ♦ The Liquefied Energy Chain (LEC) ♦ New Air Separation Cycles (ASUs)

Demonstrated Energy Efficiency ♦ LEC with 47.1% efficiency vs. 42.5% for Conventional ♦ New ASU cycles saving almost 20% on Energy

Applications relate to Carbon Capture & Storage ♦ Making environmentally friendly LNG even more friendly ♦ Elegant CCS solution for natural gas based Power Stations ♦ Making the Oxy-combustion route even more attractive

Hopefully demonstrated the Power of using PSE (Process Synthesis and Process Integration) in designing Energy and Production Systems

Thermodynamics and Innovative Design for Energy Efficiency...

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