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Process Integration using Exergy Analysis in LNG Process
Danahe Marmolejo Correa, Truls GundersenDepartment of Energy and Process Engineering, Norwegian University of
Sciences of Technology
Extended Pinch Analysis and Design (ExPAnD) Exergy Classification and Decomposition
Composite Curves, Exergy Composite Curves and a novel Exergy Diagram for Heat Recovery Systems
Vertical Heat and Exergy Cascades LNG process design
Norwegian University ofScience and Technology
Exergy Sources and Sinks in Heat Exchange Thermo-mechanical Exergy and
Exergy of Heat
International Process Integration Jubilee ConferenceGothenburg Sweden, 18-20 March, 2012
Marmolejo−Correa, D. and Gundersen, T. (2012). A comparison of exergy efficiency definitions with focus on low temperature processes. Energy, 44, 477−89.
TE
0
0SExe
rgy,
E
S
p
0p
0T
0T T
,T p
0,T p
0 0,T p
TME
.
, Enthalpy H
pE
0.0
0.5
1.0
1.5
2.0
0 1 2 3 4 5
0Dimensionless Temperature, T T
Exe
rgy
rati
o of
Hea
t, E
Q/ Q
.
.
0.5
0 0, , ,TM T pE T p E T p E T p
-150.0
-100.0
-50.0
0.0
50.0
100.0
150.0
200.0
0 50 100 150 200
Tem
per
atu
re (°
C)
H (kW)
Hot Stream (energy) Cold Stream (energy)
1
2
3
4
1
2
3
4
Source
Sink
Source
Sink
-150.0
-100.0
-50.0
0.0
50.0
100.0
150.0
200.0
0 50 100 150
Tem
per
atu
re (°
C)
E (kW)
Hot Stream (exergy) Cold Stream (exergy)
1
23
4
2
1
4
3
Source
Source
Sink
Sink
Heat Transfer Exergy Transfer The Rule:• For process streams subject to a change in
exergy, from supply (Ts, ps) to target (Tt, pt) conditions:• Negative changes in exergy are categorized as
exergy Sources.• Positive changes in exergy are categorized as
exergy Sinks.
• For Work and Exergy accompanying Heatflows :• Supplied = Source• Produced = Sink• Both Supplied and Produced, then keep these
separate as Source and Sink.
Exergy Transfer Effectiveness
(ETE)
Exergy SinkETE
Exergy Source
“Given a set of process streams with a supply state (temperature, pressure, and resulting phase) and a target state, as well as utilities for power, heating, and cooling; design a system of heat exchangers, expanders, compressors, pumps and valves in such a way that the irreversibilities (or some cost objective) are minimized”
Using Exergy in Subambient Processes?
LowTemperature
Processes
Heat Pinch
Heat Recovery
0, 0C T
, Surplus minQ
, Deficit minQ
, Enthalpy H
, Destruction minE
Car
not F
acto
r, η C
00 0
ln 1
T
Tp
E
T
TE
T
TcT
Tm
Aspelund, A., Berstad D.O. and Gundersen, T. (2007). An extended pinch analysis and design procedure utilizing pressure based exergy for subambient cooling. Applied Thermal Engineering, 27(16): 2633-2649.
“Drawbacks”:• The Carnot factor is in a non-
linear relation with respect to enthalpy.
• Multiple data points must be calculated between supply and target conditions.
• The exergy targets are not explicitly shown in any of the diagrams.
Exe
rget
ic T
empe
ratu
re, T
ET
(T >
T0)
Exergy Pinch
Exergy Recovery
0TE
minT
, Deficit minE
, Surplus minE
, Rejection minE , TT based Exergy E
, Requirement minE
, Destruction minE
00
TETT
Composite Curves (CCs)
New Exergy Diagram Some Characteristics:
Heat Pinch
min 0T
, Enthalpy H
Heat Recovery
, Surplus minQ
, Deficit minQ
Tem
pera
ture
, T(T
> T
0)
0T
Reverse Brayton Process
6 (Natural gas)
7
3 AC-1002
COM-100-5
1 (Nitrogen)
4TUR-100
5
HX-100
LIQ-EXP-100
8
c
b
a
d
e
b
c
• Linear relation between
and .
• Only supply and target conditions are required.
• is always positive.
• The heat and exergy pinch points are placed in corresponding enthalpy and exergy intervals.
Exergy Composite Curves (ECCs)
cp constant
0
0
0
;
0 ;
;
CarnotQ
Carnot
Q T T
E T T
Q T T
CCs Initial New ECCs Initial
CCs Final New ECCs Final
Marmolejo−Correa, D. and Gundersen, T. A new graphical representation of exergy applied to low temperature process design. Submitted for a Special Issue (September 2012) of Industrial & Engineering Chemistry Research.
-200
-150
-100
-50
0
50
0 5 10 15 20 25 30 35 40
Cold Hot Enthalpy MW
1
, 1 , 2
37.3 25 CH C
H MWT T
2
, 2
, 1
13.8 92.5168 C
H
C
H MWT CT
2
1
1
2
3
Tem
pera
ture
(°C
)
3
, 3
0 168 CH
H MWT
0
25
50
75
100
125
150
0 5 10 15 20 25
Source Sink
, 2
, 2
6.8
31.9 T
HE
H
E MW
T K
, 1
, 1
14.3
117.7 T
TCE
C
E MW
T K
, 3
, 3
22.4
117.7 T
THE
H
E MW
T K
3
2
1
2
1
Exe
rget
ic T
empe
ratu
re (
K)
T based Exergy MW
-175
-125
-75
-25
25
75
125
0 20 40 60 80
Cold Hot
3
, 3
, 1
0 165168
H
C
H MWT CT C
1
, 1
70.0 85.7H
H MWT C
2
, 2
, 2
23.1 2522
H
C
H MWT CT C
2
1
1
2
3
Enthalpy MW
Tem
pera
ture
(°C
)
0
25
50
75
100
125
150
0 5 10 15 20
Source (above T0) Source (below T0) Sink
, 1
, 1
, 3
18.8
117.7
112.3
T
T
TCE
CE
H
E MW
T K
T K
, 2
, 2
9.4
0.0 T
THE
H
E MW
T K
, 1 6.1 TE
HT K
, 2
, 2
4.4
0.0 T
TCE
C
E MW
T K
2
1
3
21
Exe
rget
ic T
empe
ratu
re (
K)
T based Exergy MW
, ,
N
Des min Des ii
E E
Exergy Destruction
, , ,
Above PinchReq min Def min Des minE E E
Exergy Requirement
, , ,
Below PinchRej min Sur min Des minE E E
Exergy Rejected
, , , ,Des Total Des min Des ST Des CWE E E E