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