OAPEC-IFP Joint Seminar 17 – 19 June 2008 1
SELECTING AN LNG PROCESS
Not an easy task
Pierre Boutelant
OAPEC-IFP Joint Seminar 17 – 19 June 2008 2
Looking for Efficiency
• A better efficiency (kW per ton of LNG)
Less Capex for a given production
Savings on natural gas resources
Less CO2 to atmosphere
OAPEC-IFP Joint Seminar 17 – 19 June 2008 3
SEVERAL PROCESSES ARE AVAILABLE
• Today a fierce competition between the « Old » and the « New » processes.
• Before comparing efficiencies, the bases must be clearly defined so as to compare « apples with apples ».
OAPEC-IFP Joint Seminar 17 – 19 June 2008 4
C3/MR
LNG
Feed Gas
CW
CW
Propane cycle MR cycle
CW
OAPEC-IFP Joint Seminar 17 – 19 June 2008 5
APX
LNG
Feed Gas
CW
CW
CW
N2 CyclePropane cycle MR cycle
CW
OAPEC-IFP Joint Seminar 17 – 19 June 2008 6
Cascade
C3
C2=
C1
Natural Gas
PFHE PFHE PFHE
LNG
OAPEC-IFP Joint Seminar 17 – 19 June 2008 7
DMR
Naturalgas
LNG
First mixedrefrigerantcycle
OAPEC-IFP Joint Seminar 17 – 19 June 2008 8
MFCP
Naturalgas
LNG
Pre-coolingMR cycle
LiquefactionMR cycle
Plate-finExchangers
Sub-coolingMR cycle
Spiral-woundheat-exchanger
Spiral-woundheat-exchanger
OAPEC-IFP Joint Seminar 17 – 19 June 2008 9
Liquefin
Plate finsHeat Exchanger
C2+
-30 °C
-60 °C
LNG
Natural Gas
-150 °C
-160 °C
OAPEC-IFP Joint Seminar 17 – 19 June 2008 10
Enthalpy curvesfor Liquefin process
Pre-cooling
-80
-60
-40
-20
0
20
40
60
0 50 100 150 200 250
MW
Cryogenic Section
-160-140-120-100
-80-60-40-20
0
0 50 100 150
Temperature, °C
MW
Temperature, °C
OAPEC-IFP Joint Seminar 17 – 19 June 2008 11
Enthalpy Curves – Pre Cooling
-80
-60
-40
-20
0
20
40
60
0 50 100 150 200 250
Enthalpy (MW)
Te
mp
éra
ture
(°C
)
OAPEC-IFP Joint Seminar 17 – 19 June 2008 12
The « Key » Parameters
• Their selected value have a direct effect on the theoretical plant production
• Condensing temperature of pre-cooling medium
• Amount of Flash Gas • LPG’s recovery rate• Compressors’ efficiency
OAPEC-IFP Joint Seminar 17 – 19 June 2008 13
Condensing temperatureof pre-cooling refrigerant
C2+
-30 °C
-60 °C
LNG-150 °C
OAPEC-IFP Joint Seminar 17 – 19 June 2008 14
LNG Production vs MR1 condensing temperature
100
101
102
103
39 40 41 42 43 44 45
Condenser outlet temperature, °C
% LNGproduction
OAPEC-IFP Joint Seminar 17 – 19 June 2008 15
Less surface required for refrigerant fluids condensers
Condensers’ LMTD
20
25
30
35
40
45
50
55
60
0 50 100 150 200 250 300 350
Duty
Temperature,°C
Same final condensation temperature
Propane
MR Condensation
Air or Water
Same condensation duty
LMTD higher (+35%) ⇒ Condenser 35% smaller
OAPEC-IFP Joint Seminar 17 – 19 June 2008 16
Flash Gas quantity
C2+
-30 °C
-60 °C
LNG-150 °C
Flash gas
-160 °C
OAPEC-IFP Joint Seminar 17 – 19 June 2008 17
LNG Production vs Flash Gas quantity
100
101
102
103
104
105
106
100 110 120 130 140
Relative quantity of Flash Gas %
LNG relative production %
OAPEC-IFP Joint Seminar 17 – 19 June 2008 18
LPG recovery rate
C2+
-30 °C
-60 °C
LNG-150 °C
OAPEC-IFP Joint Seminar 17 – 19 June 2008 19
LNG Production vs LPG recovery rate
91
92
93
94
95
96
97
98
99
100
30 40 50 60 70 80 90
91
92
93
94
95
96
97
98
99
100
30 40 50 60 70 80 90
C3 recovery rate (% of total C3 in the Feed Gas)
LNG Production %
OAPEC-IFP Joint Seminar 17 – 19 June 2008 20
Compressors efficiency
C2+
-30 °C
-60 °C
LNG-150 °C
OAPEC-IFP Joint Seminar 17 – 19 June 2008 21
LNG Production vs compressorsefficiency
LNG Production vs Compressors Polytropic efficiency
79 80 81 82 83 84 85
96
98
100
102
104
LNGRelative
Production %
Compressors Polytropic Efficiency %
OAPEC-IFP Joint Seminar 17 – 19 June 2008 22
CONCLUSION (1)
• In addition to “classical” conditions such as• Feed gas pressure & composition• Ambient temperature, etc.
• The selected data for the following “external” parameters must be known :• T approach on MR condensers • Compressors’ polytropic efficiency• Amount of Flash Gas • LPG recovery rate
• Altogether they can artificially affect the process efficiency up to 20 %
OAPEC-IFP Joint Seminar 17 – 19 June 2008 23
Conclusion (2)
• The various LNG processes available today have different efficiencies
• The “absolute” efficiency is meaningless
• Before comparing the « vendors’ » efficiency, make sure that processes have been optimized for YOUR project, hence on identical bases.
OAPEC-IFP Joint Seminar 17 – 19 June 2008 24
Thank you for your attention