Chemical Engineering Department Seminar
Carnegie Mellon University, Pittsburgh, 27 March 2012
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
NTNU
with important contributions from
Audun Aspelund, PhD, 20 March 2012
Chao Fu, PhD, September 2012
Danahe Marmolejo Correa, PhD, Spring 2013
30.03.2012
T. Gundersen
Slide no. 1
Comments from a “UK University” October 1988
NTNU
Promoting Optimization (Math Programming)
was quite challenging in those Days !
30.03.2012
T. Gundersen
Slide no. 2
Thermodynamics and Innovative Design
for Energy Efficiency and Carbon Capture
NTNU
is not about Architecture (the Stata Center at MIT)
30.03.2012
T. Gundersen
Slide no. 3
BIGCCS
International CCS Research Centre
Budget 80 MUSD over 8 years
> 20 PhDs and > 10 Post.docs
Objectives:
2009-2016
1. Reduce CCS Cost by 50%
2. CO2 Capture Rate of 90%
NTNU
3. Fuel-to-Power Penalty ≤ 6 % pts
Innovations are required
30.03.2012
T. Gundersen
BIGCCS Director: Mona J. Mølnvik
BIGCCS Board Chair: Nils A. Røkke
SINTEF Energy Research
NTNU Coordinator: Truls Gundersen
Slide no. 4
Climate Change and CO2 Emissions
NTNU
Ref.: IPCC, Climate change 2007: The physical science basis
3 Main Options:
Mark Twain:
”Climate is what to expect,
weather is what you get”
30.03.2012
T. Gundersen
1.
2.
3.
Energy Efficiency
CO2 Capture & Storage
Renewable Energies
Slide no. 5
Thermodynamics and Innovative Design
for Energy Efficiency and Carbon Capture
Greek-to-English:
Therme = Warm = Heat
(Thermie = Calorie)
Dynamis = Force = Power
Heat & Power
Physics
NTNU
Chem. Engng.
Mech. Engng.
Obvious link: Thermodynamics & Energy Efficiency
30.03.2012
T. Gundersen
Slide no. 6
Content of the Presentation
NTNU

2 “subambient” Processes

Scenario: 2 types of Power Stations

Design Methodologies


Examples will focus on Energy Efficiency and CCS
Innovations will be discussed

Round up with a Summary
♦ LNG and ASU (Air Separation Units)
♦ Supercritical pulverized Coal based Plant
♦ Combined Cycle Natural Gas based Plant
♦ Both of the Oxy-combustion type for CO2 Capture
♦ Thermodynamics based (Pinch & Exergy Analyses)
♦ Optimization based (Math Programming & Superstructures)
♦ Patent Application for new ASU cycles
♦ Liquefied Energy Chain with offshore LNG
30.03.2012
T. Gundersen
Slide no. 7
Audun Aspelund: A Liquefied Energy Chain (LEC)
Combined Transport of Natural Gas and CO2
Air
O2
Air Separation
ASU
NG
NTNU
LNG
NG
LIN
30.03.2012
LCO2
W
H2O
LNG
Natural Gas
Liquefaction
Oxyfuel
Power Plant
CO2
Liquefaction
T. Gundersen
CO2
Slide no. 8
Danahe Marmolejo Correa: Exergy Analysis & LNG
Why is the PRICO Process so inefficient?
2b
@ 306 K
& 9.8 bar
Natural Gas (6)
@ 300 K & 50 bar
K-102
3
@ 305 K
& 24.2 bar
2
@ 361 K
& 24.4 bar
INTERC-101
LNG (8)
@ 109 K & 1.2 bar
VLV-201
4
@ 111 K & 24 bar
HX-101
COND-101
K-101
NTNU
7
@ 113 K & 49.8 bar
5
@ 108 K & 4.2 bar
VLV-101
Mixed Refrigerant (1)
@ 294 K & 4 bar
2a
@ 346 K & 10 bar
30.03.2012
T. Gundersen
Slide no. 9
Chao Fu: ASU Cycles with up to 20% Energy Savings
Current State-of-the-Art:
NTNU
Linde’s Classical Coupled Column Design
30.03.2012
T. Gundersen
Slide no. 10
Chao Fu: ASU Cycles with up to 20% Energy Savings
NTNU
Recuperative Vapor Recompression Cycle - Patented
30.03.2012
T. Gundersen
Slide no. 11
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.

NTNU
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)

30.03.2012
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
T. Gundersen
Slide no. 12
The Exergy of Heat
Without 1st Law Losses:
Wcycle = QH – QC
Without 2nd Law Losses:
Thermal Efficiency:
(QC /QH) = (QC /QH)rev = TC /TH
NTNU
Carnot Efficiency:
ηmax as function of TH
0.800
0.700
0.600
0.500
Exergy of Heat:
0.400
TC = 0ºC
0.300
TC = 15ºC
0.200
TC = 25ºC
0.100
0.000
0
30.03.2012
T. Gundersen
200
400
600
800
Slide no. 13
Using Exergy in Subambient Processes?
&
NTNU
@ 298 K (25°C)
& 50~70 bar
Liquefaction
@ 109 K (-164°C)
& 1 bar
Work
30.03.2012
T. Gundersen
Slide no. 14
Classification &
Decomposition
of Exergy
3rd class:
Energy
Randomness
4th class:
Origin
Reactional
Chemical
Concentrational
Disordered
2nd
class:
Carrier
Thermo-mechanical
ETM
Carried by Matter
NTNU
Temperature part
ET
Pressure part
Ep
Kinetic
1st
Exergy
class:
Open/Closed
Systems
Exergy Parts or
Components
Mechanical
Potential
Ordered
Electrostatic
Electrical
Flow Exergy
Electrodynamic
Nuclear
Non-flow
Exergy
Disordered
Heat
EQ
Radiation
Carried by Energy
Ordered
Electrical
D. Marmolejo-Correa, T. Gundersen, ”A Comparison of Exergy Efficiency Definitions
with focus on Low Temperature Processes”, submitted to Energy, October 2011.
30.03.2012
T. Gundersen
Slide no. 15
Exergy
Physical
Mechanical
Kinetic
Potential
Chemical
Thermomechanical
Temperature Pressure
based
based
Mixing & Chemical
Separation Reaction
Kotas T.J., The exergy method of thermal plant analysis,
Krieger Publishing Company, Florida, USA, 1995.
NTNU
Classification of
Exergy Types
Bejan A., Tsatsaronis G. and Moran M., Thermal design
and optimization, Wiley, New York City, 1996.
30.03.2012
T. Gundersen
Slide no. 16
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
NTNU

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
30.03.2012
T. Gundersen
Slide no. 17
Special Behavior of Temperature based Exergy
Thermo-mechanical
Exergy of a Stream
Exergy of Heat
.
NTNU
2.0
.
Exergy, E
Exergy ratio of Heat, EQ / Q
.
1.5
1.0
0.5
0.0
T < T0
(T , p )
T0
(T0 , p )
0
0.5
30.03.2012
1
2
3
4
5
Dimensionless Temperature, T T0
T. Gundersen
0
p
p0
(T0 , p0 )
Slide no. 18
Consider Expansion above/below Ambient
Assume Isentropic Expansion of Ideal Gas,
with Cp = 1.0 kJ/kgK and k = Cp / Cv = 1.4
5 bar
523K
Exp
NTNU
1 bar
330.2K
Ambient T0=298 K
5 bar
223K
30.03.2012
Exp
1 bar
140.8K
T. Gundersen
Slide no. 19
Consider Heat and Exergy Transfer
above/below Ambient Temperature
Exergy Transfer
Temperature (°C)
Heat Transfer
NTNU
200
Source
150
100
4
Sink
50 2
0
-50
-100
1
E (kW)
3
0
20
40
1
4
60
80
100
120
Sink
Source
2
3
-150
Hot Stream (exergy)
30.03.2012
T. Gundersen
Cold Stream (exergy)
Slide no. 20
What is Exergy Efficiency?
(Internal)
NTNU
Exergy
Consumed
Process or
Unit Operation
Exergy
Produced
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.
3/30/2012
T. Gundersen
Slide no. 21
Exergy Efficiency Definitions
(Internal)
Exergy
Consumed
NTNU
Process or
Unit Operation
Exergy
Produced
Brodyansky
et al. (1994)
Bejan et al.
(1996)
Kotas
(1995)
Marmolejo-Correa
and Gundersen (2012)
”Exergy
Efficiency”
”Exergetic
Efficiency”
”Rational
Efficiency”
”Exergy Transfer
Effectiveness (ETE)”
D. Marmolejo-Correa, T. Gundersen, ”Exergy Transfer Effectiveness for Low
Temperature Processes”, to be submitted to Intl. Jl. of Thermodynamics, 2012.
3/30/2012
T. Gundersen
Slide no. 22
Applied to the simple PRICO Process
NTNU
Brodyansky
et al. (1994)
30.03.2012
Bejan et al.
(1996)
Kotas
(1995)
T. Gundersen
Marmolejo-Correa
and Gundersen (2012)
Slide no. 23
LNG as energy carrier:
International Trade
6.9% annual growth
in the last 20 years
NTNU
Source: BP Statistical Review of World Energy 1990-2010
30.03.2012
T. Gundersen
Slide no. 24
Liquefied Natural Gas Value Chain
NTNU
30.03.2012
T. Gundersen
Slide no. 25
Liquefaction of Natural Gas
NTNU
T. Shukri (Poster Wheeler, UK), ”LNG Technology Selection”, Hydrocarbon Engineering, February 2004
30.03.2012
T. Gundersen
Slide no. 26
Some LNG Processes
Pure
Refrigerant
Cycles
Optimized Cascade
by Conoco-Phillips
Mixed
Refrigerant
Cycles
PRICO
by Black &Veatch
Expansion
Cycles
Mixed Fluid
Cascade (MFC)
by Linde-Statoil
Reversed Brayton
Cycle
by TGE
NTNU
Pre-cooled Mixed
Refrigerant
(C3MR) by Shell
AP-X by APCI
30.03.2012
T. Gundersen
Slide no. 27
Cascade Liquefaction Process
Natural gas
Propane
-40°C
Ethene
NTNU
-93°C
Methane
Fuel gas
-163°C
FV2001, U 14
LNG
30.03.2012
T. Gundersen
Slide no. 28
Liquefaction using
Multicomponent Mixtures
NTNU
30.03.2012
T. Gundersen
Slide no. 29
Linde and Statoil: Mixed Fluid Cascade
3 Mixed Refrigerants
T (K)
300
250
NTNU
200
R1
R2
R3
150
100
30.03.2012
ΔH (kW)
T. Gundersen
Slide no. 30
A new Process Synthesis Methodology
utilizing Pressure based Exergy
in Subambient Processes
ExPAnD = Extended Pinch Analysis and Design

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
NTNU
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.
30.03.2012
T. Gundersen
Slide no. 31
Application: A Liquefied Energy Chain (LEC)
NTNU

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.
30.03.2012
T. Gundersen
Slide no. 32
NG 0.3%
CO2 75.7%
Pumping and
LNG production
heating of LCO2
CO2 75.7%
LNG
LNG
LCO2
CO2 75.7%
LN
G
89
.1%
Power 42.5%
CCS powerplant
.7%
CO2 Liquefaction
CO2 12.9%
NG 85.2
0.1 CO2 %
LNG vaporization
NG 0.4%
LCO2 ship
5
27
CO
LCO2
Power
C02 0.4%
NG 0.4%
CO2 0.3%
NG 0.4%
CO2 0.4%
LNG
LCO2
NG 0.3%
NG 89.1%
LNG ship
CO2 0.4%
NG 89.9%
NG 3.6%
LNG production
NG 0.4%
CO2 9.8%
NG 9.8%
NG 100%
CO2 84.7%
Combined process
for Liquefaction of
NG and heating of
LCO2
NG 100%
LNG
LNG
LNG
Combined ship
CO2 84.7%
NG 99.6%
CO2 84.7%
LN2
LCO2
Combined process
for heatin of LNG
and liqiefaction of
CO2
CO2 14.2%
C02 0.7%
CO2 0.4%
NG 0.4%
NG 100%
NG 5.4%
NTNU
NG 94.2 %
”Conventional” ship-based energychain: Loss NG during transport 14%, CO2 emissions 24.3%, Efficiency 42.5%
NG 99.6%
CCS power plant
Power 47.1%
CO2 84.7%
LCO2
Power
New combined energy-chain: Loss NG during transport 5.8%, CO2 emissions 15.3%, Efficiency 47.1%
30.03.2012
T. Gundersen
Slide no. 33
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
TH1,out
 Composite & Grand Composite Curves for Idea
Generation related to Process Improvements
 Exergy Efficiency to Quantify Improvements
NTNU
TC3,out
TC2,in
♦ Optimization has also been included
 New Superstructure allows Simultaneous
Optimization of Networks with Heat
Exchangers, Pumps, Compressors and
Expanders using Math Programming
C-2
E-3
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.
30.03.2012
T. Gundersen
E-2
TC3,in
TC2,out
TC1,in
TC1,out
TH2,out
TH2,in
TH3,out
TC4,in
TH1,in
C-1
E-1
TH3,in
TC4,out
TH4,in
C-3
Slide no. 34
Offshore Process without Pressure Manipulations
N2-4
N2-3
N2-2
N2-1
CO2-2
NG-3
NG-2
CO2-3
K-100
HX-101
NG-1
HX-102
CO2-1
P-101
LNG
LIQ-EXP-102
20
NTNU
Temperature [C]
HX-101
-30
-80
•
•
•
•
HX-102
-130
LIN: 1.75 kg/kgLNG
LCO2: 0.41 kg/kgLNG
Power Deficit
Exergy Efficiency: 55.7%
-180
0
5
10
15
20
25
30
Heat flow [MW]
Hot CC
30.03.2012
Cold CC
T. Gundersen
Slide no. 35
Offshore Process with Pressure Manipulations
N2-4
N2-7
N2-5
N2-3
CO2-4
CO2-3
N2-2
N2-1
CO2-2
NG-4
NG-3
NG-2
P-102
HX-101
NG-1
NTNU
EXP-101
N2-6
HX-102
K-100
P-101
LNG
CO2-1
LIQ-EXP-102
20
Temperature [C]
HX-101
P-100
-30
-80
HX-102
-130
-180
0
5
10
15
20
25
Heat flow [MW]
Hot CC
30.03.2012
30
•
•
•
•
•
LIN: 1.25 kg/kgLNG
LCO2: 1.50 kg/kgLNG
Power Surplus
Exergy Efficiency: 84.1%
No Power Export: 76.3%
Cold CC
T. Gundersen
Slide no. 36
Offshore Process in Balance with respect to
Thermal and Mechanical Energy
20
Temperature [C]
HX-101
NTNU
-30
-80
HX-102
-130
-180
0
5
10
15
20
25
30
Heat flow [MW]
Hot CC
30.03.2012
Cold CC
T. Gundersen
•
•
•
•
LIN: 1.0 kg/kgLNG
LCO2: 2.2 kg/kgLNG
Power Balance
Exergy Efficiency: 85.7%
Slide no. 37
The Offshore Process in the LEC
N2-7
EXP-101
N2-8
K-101
N2-9
N2-4
EXP-102
N2-5
N2-10
N2-12
N2-11
N2-6
N2-3
CO2-4
CO2-3
NTNU
P-102
NG-1
N2-1
CO2-2
NG-2
K-100
N2-2
NG-3
NG-5
NG-4
HX-101
HX-102
LIQ-EXP-101
P-101
NG-PURGE
NG-6
CO2-1
LIQ-EXP-102
V-101
P-100
LNG
No flammable Refrigerants and no Gas Turbines !!
30.03.2012
T. Gundersen
Slide no. 38
Detailed Features of the Offshore Process
Composite Curves - Offshore Process
100
Temperature [C]
50
0
-50
-100
Hot CC
Cold CC
-150
-200
0
2
NTNU
4
6
8
Duty [MW]
Single Components (here CO2 and N2) exhibit Multicomponent 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.
30.03.2012
T. Gundersen
Slide no. 39
Simulation-Optimization of the entire LEC
LNG
NG
LNG
S
t
The field
o
site
LIN
r
process
a
LCO2 g
e
N2
CO2
LNG
LNG
S LNG
NG
t
The market
o
site
r LIN
process CO2
a
g LCO2
e
LNG
P3
LIN
P2
P1
F2
LCO2
F1
Electricity
Power
process
with CO2
capture
Water
N2
LIN
LCO2
LCO2
The simple chain
The complete chain
NTNU
CO2-Recycle
T2
CO2-7
CO2-9
N2-7
EXP-101
T3
N2-8
T4
P6
N2-12
N2-9
LCO2
N2-13
EXP-102
V-101
T5
N2-11
CO2-3
P-102
HX-101
K-100
P4
30.03.2012
NG-5
NG-4
LIQ-EXP-101
P-101
N2-11
NG-PURGE
P2
VF1
CO2-1
LIQ-EXP-102
NG-1
HX-102
LNG
NG @ 25
N2-0
4 stage compression
K101-K104
HX-101
P3
NG-5
P-101
T. Gundersen
2 stage compression
K105-K106
NG-4
P-102
LNG
P1
F3
N2-1
N2-8
P3
F1
CO2-1
N2-16
N2-9
V-101
P-100
CO2-4
F1
CO2-12
CO2-13
NG-3
LIN
NG-6
CO2-0
CO2-10
CO2-11
NG-2
V-102
HX-102
K-107
N2-15
T7
N2-10
N2-1
T1
Offshore
N2-12
N2-2
CO2-2
NG-3
NG-2
T6
F2
N2-3
CO2-4
CO2-5
F4
N2-10
P2
CO2-6
CO2-8
EXP-102
N2-5
N2-6
NG-1
K-108
P1
P5
K-101
N2-4
N2-14
F2
EXP-101
Onshore
Slide no. 40
Optimization Variables
Field Site
Process
(offshore)
NTNU
Market Site
Process
(onshore)
30.03.2012
Stream
Type I
Type II
Name
Unit
kPa
Initial
value
600
Lower
bound
550
Upper
bound
1000
CO2-1
Global
Pressure
P1
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
NG-3
Local
N2-4
Local
N2-5
Global
N2-7
Local
N2-8
Gobal
N2-9
Pressure
P4
kPa
9000
8000
10000
Temperature
T1
°C
-61
-70
-50
Temperature
T2
°C
-40
-60
0
Pressure
P5
kPa
600
400
1000
Temperature
T3
°C
-40
-60
20
Pressure
P6
kPa
2800
1500
3500
Local
Temperature
T4
°C
-40
-60
20
Stream
Type I
Type II
Name
Unit
LCO2
Global
Pressure
P1
kPa
Initial
value
600
Lower
bound
550
Upper
bound
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
N2-11
Local
Global
N2-13
Local
N2-15
Local
Temperature
T7
°C
-96
-115
-80
Void fraction
Temperature
VF1
T5
°C
0.4
-101
0.1
-115
0.5
-80
Temperature
T6
°C
-115
-132
-92
T. Gundersen
Slide no. 41
Progress of the Optimization
1
36
35
34
33
32
31
NTNU
30
29
28
0
0
50
100
150
200
Best known objective
250
Current best
300
350
400
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.
30.03.2012
T. Gundersen
Slide no. 42
Supercritical Oxy-Combustion Pulverized Coal-based Power Plant
Power
Cycle*
ASU
NTNU
FGD
567 MW
* Reference: DOE/NETL,
Report NO.: 2007/1291
CPU
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.
30.03.2012
T. Gundersen
Slide no. 43
Some key Production Figures
Steam
Turbine
N2
Electricity
Generator
Condenser
Air
Air
Separation
Unit
Combustor
HRSG
Fan
LP
Compressor
Gypsum
Ash
Inerts
CO2
Purification
Tower
Fan
Coal
Mill
FGD
ESP
O2
NTNU
Limestone
Slurry
CO2
Drier
H2O
Fan
HP
Compressor
CO2
For Storage
• 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
30.03.2012
T. Gundersen
Slide no. 44
Efficiency Penalties for CO2 Capture
ASU
Steam
Turbine
N2
Condenser
Air
Air
Separation
Unit
Combustor
CPU
Electricity
Generator
HRSG
Limestone
Slurry
Inerts
CO2
Purification
Tower
ESP
Fan
O2
Ash
Coal
Fan
LP
Compressor
Gypsum
H2O
Fan
Mill
CO2
Drier
FGD
HP
Compressor
Specs on Oxygen:
~ 95 mol%, 1.25 bar
Efficiency Penalty (%)
12
NTNU
CPU
ASU
10
8
CO2
For Storage
3,6
3.7
6
4
2
6,6
2,0
1,4
0
Base case
Theoretical Case
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
30.03.2012
T. Gundersen
Slide no. 45
1393 MW
Coal
(HHV)
Air
Power
Plant
η without=
CCS
Power
560
= 40.2%
1393
560 MW
124 MW
567 + 124 + 69
=
η total = 40.5%
1879 MW
1879
Coal
(HHV)
NTNU Air
ASU
O2
Power
Plant
Net
Power
567 MW
Exhaust
H2O
η with=
CCS
3/30/2012
Our Research
Motivation
567
= 30.2%
1879
CPU
69 MW
CO2
T. Gundersen
124
= 6.6% pts
1879
69
=
= 3.7% pts
1879
1
∆ηASU
=
1
∆ηCPU
Improving the ASU by 20%
gives 4.4% more Power !!
or 1.32% points
Slide no. 46
Conventional ASU – here producing 95% O2
A4-2
A4-1
Extracted N2
A7-1
Condenser
A4-3
A3-1
A3-2
A3-3
A4-4
N2 waste A7-3
O2
A5-2
A1-5
MHE
A1-4
Impurities
A2-2 A2-3
HP
LP
A5-1
A2-1
A7-2
Reboiler
PPU
NTNU
A1-3
Energy Consumption
♦ Actual: 0.193 kWh/kgO2
♦ Ideal: 0.049 kWh/kgO2
A1-2
A1-1
Exergy Losses
♦ Air Compressor: 38%
♦ Distillation Cols.: 28%
MAC
Air
A0
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
Slide no. 47
30.03.2012
T. Gundersen
Distribution of Exergy Losses
45
Exergy losses [%]
40
38.4
35
Coolers: 17.6
30
AU2: The pre-purification unit
Valves: 2.7
Heat exchanger: 3.0
25
20
15
11.9
12.6
7.2
LP: 14.6
5
HP: 1.6
0
AU1
AU2

AU3: The main heat exchanger
Condenser/reboiler: 6.3
Compressor: 20.8
10
NTNU
AU1: The main air compressor
28.2
AU3
AU4
AU5: The tail N2 turbine
AU6: The waste N2
1.7
AU5
AU4:The air distillation system
AU6
Largest Sources of Exergy Losses
♦ Distillation System (28.2%)
 LP Column
♦ Main Air Compressor (38.4%)
 Interstage Coolers
 Compression Process itself
30.03.2012
T. Gundersen
Slide no. 48
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
NTNU
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.
30.03.2012
T. Gundersen
Slide no. 49
Recuperative Vapor Recompression Cycle
NTNU
Specific Shaftwork for Separation: 0.178 kWh/kgO2
Fu C. and Gundersen T. “Innovative air separation processes for Oxy-Combustion plants”,
2nd International Oxy-fuel Combustion Conference, Yeppoon, Australia, September 2011.
30.03.2012
T. Gundersen
Slide no. 50
McCabe-Thiele Diagram for Distributed Reboiling
1
0.9
Feed
line
0.8
17
Equilibrium
line
y (N2)
0.6
0.5
13
11
1
7
0.8
0.7
19
19
Equilibrium
line
0.6
Operating
line
0.5
0.4
0.4
0.3
0.3
21
Operating
line
21
0.2 23
0.2
0.1
0.1
NTNU
9 7
Feed
11
13
line 15
17
0.9
y (N2)
0.7
15
9
0
0
0
0.2
0.4
x (N2)
0.6
0.8
1
0
0.2
0.4
x (N2)
0.6
0.8
1
Column Grand Composite Curve for Distributed Reboiling
30.03.2012
T. Gundersen
Slide no. 51
Vapor Recompression with Dual-Reboiler
NTNU
Specific Shaftwork for Separation: 0.166 kWh/kgO2
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
30.03.2012
T. Gundersen
Slide no. 52
Intermediate & Recuperative
Vapor Compression Cycle
NTNU
Specific Shaftwork for Separation: 0.159 kWh/kgO2
30.03.2012
T. Gundersen
Slide no. 53
Performance Comparison
NTNU
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
30.03.2012
T. Gundersen
Slide no. 54
Is this the Optimum (Local or Global)?
NTNU
30.03.2012
T. Gundersen
Slide no. 55
Summary of the Presentation

Demonstrated the use of Thermodynamics in Design

Demonstrated Innovations

Demonstrated Energy Efficiency

Applications relate to Carbon Capture & Storage

Hopefully demonstrated the Power of using PSE
(Process Synthesis and Process Integration) in
designing Energy and Production Systems
NTNU
♦ Pinch Analysis and Exergy Analysis
♦ McCabe-Thiele and Column Grand Composite Curve
♦ The Liquefied Energy Chain (LEC)
♦ New Air Separation Cycles (ASUs)
♦ LEC with 47.1% efficiency vs. 42.5% for Conventional
♦ New ASU cycles saving almost 20% on Energy
30.03.2012
♦ Making environmentally friendly LNG even more friendly
♦ Elegant CCS solution for natural gas based Power Stations
♦ Making the Oxy-combustion route even more attractive
T. Gundersen
Slide no. 56