1
Classification: Internal Status: Draft
Natural Gas Liquefaction
TEP 10 – Gas Processing and LNG – Fall 2008
Jostein Pettersen
2
Simplified LNG plant block diagram
Endflash
HHCExtraction
CH4/N2
Fuelgas
Power&
heat
2
3
Hammerfest LNG plant - block flow diagram
Slugcatcher
Inlet facilities/Metering
CO2removal
De-hydration
Mercuryremoval
Natural gasliquefaction
LPG Storage
CondensateStorage
MEGRecovery
Condensatetreatment
CO2 dryingand
recompressionNitrogenremoval
Fractionation(RefrigerantMake-up)
Fuel gassystem
C1 / C2 / C3 Refrig. Make-up
CO2 reinjection(to pipeline)
Feed frompipeline
Lean MEG(to pipeline)
LNGStorage
LNGStorage
N2 to atm.
UtilitySystems
FlareFacilities
Controlroom
4
Gas conditioning (pre-treatment)• Acid Gas (CO2 and H2S) removal
– Acid gas causes corrosion, reduces heating value, and may freeze and create solids in cryogenic process
– Typical requirements for LNG: Max 50 ppmv CO2, Max 4 ppmv H2S(ppmv - parts per million by volume)
• Dehydration (water removal)
– Water will freeze in cryogenic process
– Typical requirement: Max 1 ppmw (weight) H2O
• Mercury removal
– Mercury can cause corrosion problems, especially in aluminium heat exchangers
– Requirement: Max 0.01 μg/Nm3
3
5
Gas quality constraints for gas liquefaction
Source: Advantica
6
Natural gas and LNG compositionDesign data for Hammerfest LNG plant
Component Slug catcher Liquefaction plant LNGNitrogen 2,51 2,67 1,10Methane 80,02 86,34 91,92Ethane 4,97 6,54 5,59Propane 2,50 2,68 1,11Butane 1,22 1,23 0,23Pentane 0,58 0,35 0,04C6+ 1,62 0,15 0Aromatics 0,23 0,02 0CO2 5,20 0,005 0,005H2S 0,0005 0 0Water 0,81 0 0MEG 0,35 0 0Total 100 100 100
Composition mol %
4
7
Example of ageing/weathering during LNG transport
40.25
40.3
40.35
40.4
40.45
40.5
40.55
0 2 4 6 8 10 12 14 16
Day
GC
V (M
J/Sm
³)
Calculated ageing effect during the voyage from Melkøya to USA, Cove Point
Calculated according to ISO 6976 – based on real gas
8
Nitrogen RemovalNitrogen need to be removed from LNG in order to meet
•Storage and transport specification (Roll Over)
•Fuel gas requirements
•LNG Heating Value requirements
Systems to handle N2 will vary in complexity, from simple end flash drums, to complex distillation columns systems for separating N2 from the LNG
5
9
Example of end flash with LNG turbineFlash gas (containing nitrogen) used as fuel gas
°
LNG EXPANDER
ENDFLASH
M
HP FUEL GAS
LNG RUNDOWN
Gen Set
Gen Set°
LNG EXPANDER
ENDFLASH
M
HP FUEL GAS
LNG RUNDOWN
Gen Set
Gen Set
High-pressure LNGfrom cryogenic HE
LNG at near-atmospheric pressurepumped to storage tank
10
Sulphurrecovcery
Utilities
Slugcatcher
Condensatestabilization
Utility powerand steam
Qatargas LNG plant layout
6
11
Qatargas
CO2absorber
Gas turbinesand
compressors
MCR Heat Exchanger CCR
12
Air cooledcondenser
s
Atlantic LNG – Trinidad(Air cooled)
Compressors
Jetty
Jetty
Cold boxes(Heat exchangers)
7
Classification: Internal Status: Draft
LAYOUT - HAMMERFEST LNG PLANT
Slug catcher
HP flare
LP flare Camp area
Condensate storagetank
LNG storagetanks
Product jettyLPG storage tank
Storage & loadingsubstationN2 cold box
NG Cold boxProcesssubstation
Electrical power generation
Compression area, barge
Process area, barge
Construction jetty
Subsea roadtunnel
Administration building / controlroom
Sea water outlet /sea water inletHolding basin / waste water
treatmentUtilitysubstationMDEA storage / fuel gas
Compressed air and inert gas facilitiesLandfall
Offshore utility substationMEG process
areaMEG substationMEG storage tank
areaHot oil and chemical storage
tanksPig receiver
Grid substation
Area 2 Area 3Area 1
14
Gas liquefaction process - idealExample: Natural gas at 60 bar, 10oC ambient temperature
-270
-230
-190
-150
-110
-70
-30
10
50
-6 -4 -2 0Entropy, kJ/(kgK)
Tem
pera
ture
, °C
-273
W
Q
p=1.3 bar
20 bar
60100• Heat is removed as the gas is
cooled at gliding temperature
• Ambient temperature 10oC
• Heat removed during liquefaction
(Q), and ideal work (W), are shown
as areas
• Gas pressure has a large influence
on work
• Ideal work of liquefaction: Natural gas
at 60 bar: 0.11 kWh/kg
(0.8 % of Lower Heating Value)
8
15
Energy (fuel gas) use for liquefaction
• Liquefaction process 2nd law(exergy) efficiency typicallyaround 50%
• Typical fuel use 5-10% of feed
• Ambient temperature and feedgas pressure has large effect
0
5
10
15
20
0 20 40 60 80 100
Exergy efficiency of liquefaction cycle, %
Ener
gy in
put a
s %
of L
HV
30 %50 %100 %
Efficiency of power generation:
Hammerfest
16
Natural gas cooling• Cooling of natural gas stream occurs
over large temperature span
• Heat must be removed from natural gas stream at varying temperature
• Temperature of evaporating refrigerantmust be as high as possible to reducepower need for heat pumping
• Close match between NG temperaturecurve and refrigerant temperature canbe achieved by
Heat transferred
T, oC
10oC
-160oC
NG
Ambient temperature (air / sea water)
Pumping of heat
- using many stages ofevaporation temperature(cascade process), or
- using a refrigerant thatevaporates at glidingtemperature (mixed refrigerantprocess)
9
17
0,01
0,1
1
10
-250 -150 -50 50 150
Temperature, deg C∆W
/∆Q
- C
hang
e in
wor
k (M
W) p
er M
W
heat
tran
sfer
red,
for 1
K d
elta
T
Temperature difference in heat exchangers is increasinglyimportant at lower temperatures
• Sub-ambient temperature
• ∆W = extra power input needed to compensate for heat transfer acrossa temperature difference of ∆T = 1 K
• ∆W grows more than exponentiallyas temperature level T is reduced
Ambient temp 10oC
Reduced workoutput
Increased workinput
To
T
S
∆T = 1 K
∆Q
∆SC
∆SH
∆W = T0 ∆S = To(∆SC - ∆SH)• Consequence: ∆T need to be
reduced as much as possible at low temperatures
18
Natural gas path through liquefactionpressure-enthalpy diagram (C1:89.7% C2:5,5% C3:1.8% N2:2.8%)
1
10
100
-900 -800 -700 -600 -500 -400 -300 -200 -100 0 100 200
Enthalpy [kJ/kg]
Pres
sure
[bar
a]
-200oC -150oC -100oC -50oC 0oC 50oC
PrecoolingLiquefactionSubcooling
Expansion
JT Throttling
End flash LNG
10
19
Simple vapour compression refrigeration system –Flow circuit
Fluid to be cooled
Heat sink(Air/water) Condenser
Evaporator
Evaporatingrefrigerant
Condensing refrigerant
High pressure
Low pressure
Compressor
Expansion valve
20
T [oC]: -60 -20 0 20 40 60 80 100-40
0,1
1,0
10,0
100,0
-700 -600 -500 -400 -300 -200 -100 0 100 200 300Enthalpy [kJ/kg]
Pres
sure
[bar
a]
Refrigeration cycle in ph-coordinates (propane)
1
2
3
4
4
2
1
3
Evaporation at -30oC Condensation at 30oC 40oC at Compressor
discharge
Evaporatingtemperature –30oC
Condensingtemperature 30oC
11
21
-80
-60
-40
-20
0
20
40
60
80
100
120
-700 -600 -500 -400 -300 -200 -100 0 100 200 300Enthalpy [kJ/kg]
Tem
pera
ture
[°C
]
Refrigeration cycle in Th-coordinates (propane)
p = 1 bar
2 bar
10
15 20
25
22
Vapour pressure of pure fluids relevant for LNG processes
Refrigerant Vapour Pressure
1
10
100
-200 -150 -100 -50 0 50
Temp(C)
Pres
sura
(Bar
a)
LNG Range
N2
C1 Ethylene
CO2
C2
C3
n-C4
12
23
Data for some relevant fluids
NBP dhNBP
[°C] [kg/kJ] [°C] [bara] [°C] [bara]Nitrogen N2 -195,75 202,678 -210,0 0,125 -146,95 33,944Methane CH4 -161,45 522,080 -182,5 0,117 -82,55 46,002Ethylene C2H4 -103,71 487,132 -169,2 0,0012 9,20 50,359
Carbon dioxide CO2 -78,45 392,780 -56,6 5,170 31,05 73,765Ethane C2H6 -88,65 496,999 -182,8 0,000013 32,25 48,839Propane C3H8 -42,07 431,517 -187,6 1,960E-09 96,67 42,496n-Butane C4H10 -0,45 389,746 -138,3 6,740E-06 152,05 37,997
Critical pointTriple point
Normal boiling point, at 1.013 bara
Enthalpy of evaporation at NBP
Normal sublimation temperature (NBP lower than triple point temp)
[kJ/kg]
24
Phase envelope(for a given composition)
Critical
Cricondenbar
Cricondentherm
Bubblepoint Curve
Dew Point Curve
QualityLines
Temperature
Pres
sure 75%
50%
25%
Bubble Point Curve Boundary between liquid phase and 2-phase region
Dew Point Curve Boundary between gas phase and 2-phase region.
Critical Point Location where bubble point and dew-point curves meet.
Cricondentherm Highest T in phase envelope.
Cricondenbar Highest P in phase envelope.
Quality Lines Lines of constant volumetric or molar percentage of a phase.
13
25
Tx-diagram example:Cooling C2/C3 at a constant pressure of 5 bara
-60
-55
-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
5
0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100Weight-% Ethane
Tem
pera
ture
[°C
]
Bubble Dew
Temp/concentrationof first liquidcondensed
Temp/concentrationof last vapour to condense
Equilibrium betweenliquid and vapour
ΔT
Two-phase
Superheatedvapour
Subcooledliquid
(Saturated)
26
Mixed-fluid process in Th-coordinates(50/50 w-% C2/C3)
-80
-60
-40
-20
0
20
40
60
80
100
120
-800 -700 -600 -500 -400 -300 -200 -100 0 100 200 300Enthalpy [kJ/kg]
Tem
pera
ture
[°C
]
p = 1 bar
2 bar
10
15 20
25
14
27
Process licensors – Base load LNG plants• Air Products and Chemicals Inc (APCI)
– World leader since since the 1970s– More than 130 Mtpa installed, 50 Mtpa under construction, more than 60 operating trains
– C3MR process ( < 60 trains)
– AP-XTM Hybrid (Qatar Gas II, 2 x 7.8 Mtpa, Start up 2008 and 2009)
• ConocoPhillips (Optimised) Cascade– Trinidad: Atlantic LNG - 4 trains
– Egypt: Idku
– Alaska: Kenai (Operating since 1969!)
– Australia: Darwin LNG
– Equatorial Guinea
• Shell DMR – Double Mixed Refrigerant (Sakhalin, 2 x 4.8 Mtpa)PMR (same as C3MR – but parallel MR circuits) – no references
• Linde/Statoil MFC® Mixed Fluid Cascade Process (Snøhvit, 4.3 Mtpa – start up 2007)
• Axens Liquefin™ (No references)
Mtpa = Million tonnes per year
28
Cascade process for natural gas liquefaction
MethaneEthylenePropane
NG12 °C-32 °C
1.4 bar 7 bar
-96 °C
1.4 bar 19 bar
LNG -155 °C
1.4 bar 45 bar
15
29
Mixed-fluid process in Th-coordinates(50/50 w-% C2/C3)
-80
-60
-40
-20
0
20
40
60
80
100
120
-800 -700 -600 -500 -400 -300 -200 -100 0 100 200 300Enthalpy [kJ/kg]
Tem
pera
ture
[°C
]
p = 1 bar
2 bar
10
15 20
25
30
Principles of mixed refrigerant cycle(Prico single-mix cycle)
LNG
NG
5 bar
30 bar
12 °C
-155 °C
12 °C
-155 °C -155,5 °C
6,5 °C
99,8 °C
Composition:
NG Refrig
C1 0.897 0.360
C2 0.055 0.280
C3 0.018 0.110
nC4 0.001 0.150
N2 0.028 0.100
16
31
Temperature - Enthalpy
-200
-150
-100
-50
0
50
100
150
-1500 -1000 -500 0 500 1000 1500
Enthalpy, x 10^6 kJ/hr
Tem
pera
ture
, C
Mixed refrigerant dew point line
Mixed refrigerant bubble point line
NG bubble point line
NG dew point line
Mixed refrigerant 30 bar
Mixed refrigerant 5 bar
NG 60 bar
32
Mixed Fluid Cascade (MFC®) process (Linde-Statoil)
• Three mixed refrigerant circuits
– Precooling (Mainly: C2, C3)
– Liquefaction (Mainly: C1, C2, C3)
– Subcooling (Mainly: N2, C1, C2)
• Cascade connection of the circuits
• Precooling in two (sometimes three) stages
• No fractionation of the mixed refrigerant flows
• Expander on subcooling cycle
X1
NG
LNG
CW1
C2
CW2
E1A
E1B
E2
E3
PrePre--coolingcoolingSectionSection
LiquefactionLiquefactionSectionSection
SubSub--coolingcoolingSectionSection
CW3A/B
C1
C3G
17
33
Heavy hydrocarbon extractionScrubber column (Snøhvit)
• Natural gas liquids (NGL/LPG) are formed during precooling, and can/must be separated from the gas stream
• Propane and butane are valuable products
• Extraction process is needed to reach lean gas specifications, LNG specs demand that C3 and C4 is removed
• A relatively simple solution is to use a scrubber columnthat separates out liquid components which are formedduring cooling of the natural gas
• Some LPG is fractionated to give pure C1, C2 and C3 for refrigerant make-up
LPG FractionationRefrigerant make-up
Precooling
-25oC -50oC
Scrubber column
Natural gasfrom pre-processing
34Feedgas from
pre-processing
N2/CH4 tonitrogenremoval
CH4 fromnitrogenremoval
LNG
LPG FractionationRefrigerant make-up
Precooling Subcooling
Nat
ural
Gas
Liq
uefa
ctio
nC
ircui
ting
Lique-faction
18
35
Natural gas circuiting
36
Composite temperature curves - HammerfestOverall Heat / Temperature Diagram for Cold Equipment in System 25
Snøhvit A Plant Feed Stock
110 130 150 170 190 210 230 250 270 2900
40
80
120
160
200
240
280
320
360
Temperature [K]
Hea
t [M
W]
Hot (sum) Cold (sum)
Precooling Refrigerant
Lique-faction Refri-gerant
Subcooling Refrigerant
Reboi ler
19
37
Precooling cicruit
38
25-HA-101
25-HG-101 A-D
25-V
D-1
07
25-PA-102 A/B
25-HA-105
25-PA-103 A/B
25-V
E-10
1
25-HG-105
25-HG-102 A-F
25-HA-112
G
G
LCM
PCM
SC
I
SC
IIM
25-HA-111
25-V
D-1
02
25-V
D-1
01
25-HX-101
25-HX-102
25-KA-101
25-KA-102
25-HA-114
25-HA-104
25-V
D-1
06
25-V
D-1
05
25-V
E-10
2
25-KA-103
25-HX-103
25-PA-101A/B
25-EG-102
25-EG-101
25-CT-102
25-CT-101
25-HA-113
21
26
42
27
42
27
25-V
D-1
07A
25-V
D-1
09
26C
42
26
25-V
D-1
10
25-V
D-1
1125
-VD
-112
SW SW
SW
SW
SW
HO
SW
26D
26C
27A
27A
46A
46A
27A
26B
26A
27A
26B
OVERVIEW
25-144
25-1
54
25-155
25-1
56
21-102 25-138
25-139
25-153
25-1
52
25-2
12
25-15125-150
26-205
25-215 25-149
25-149.1
25-1
4825-2
25
25-141
25-1
42
25-219
25-144.1
25-157
25-156.1 25-156.2
25-162
25-161
25-158
25-163
25-1
65
27-130
25-1
66
25-167
27-131
25-1
59
25-160
25-196.4
25-2
05
25-1
02
25-1
96
25-1
96.2
25-168
25-1
96.1
25-1
96.3
25-2
0025
-201
25-263.1
25-263
25-1
95
25-2
02
25-103
25-263.2
25-198
25-193
25-122.1
25-1
21.2
25-1
21.1
25-209
25-1
20
25-1
21
25-2
07 25-2
10
25-122.2
25-123
25-124
25-181
25-2
81.1
25-253
25-2
5425
-255
25-2
5625
-257
25-125
25-1
26
25-2
06
25-133
25-133.125-133.2
25-134
25-1
3525
-136
25-177
25-140
25-140.1 25-140.2
25-137
25-258
25-2
5925
-260
25-2
61
25-1
27
25-2
62
25-1
28
25-179
25-211
25-1
29
25-1
30
25-1
31
25-1
32
25-1
32.1
25-132.2
25-1
71
25-172
25-1
73
25-104
25-251
25-247
25-24825-252
25-2
49
25-264
25-26525-269
25-2
70
25-272
25-2
71
25-2
73
25-274
25-277
25-278 25-279
25-266
26-1
84
26-1
12
25-112
25-1
08
25-109
25-801
25-805
25-8
04
25-802
25-8
03
25-110
26D
26-1
7526
-180
25-2
80
25-115
26A26-139
26-174
25-183
25-116
25-810
25-808
25-806
25-809
25-117
25-2
23
25-105
25-106
25-815
25-114
25-81225-813
25-2
68
25-111
25-1
13
25-820
25-816
25-819
25-114
25-818
25-118
25-117
26-1
02
25-189
26-1
40
42-104 25-169
25-143
MIN. FLOW LINE
ANTISURGE
START UP RECYCLE
25-807
25-817
25-8
11
25-1
90
MIN
. FLO
W
25-203 25-202ANTISURGE
MIN
. FLO
W
25-133
25-122
MIN
. FLO
W
ANTI
SU
RG
E
ANTISURGE
START-UP LINE
25-V
D-1
16
25-V
D-1
15
25-VD-104
25-VD-114
25-VD-103
25-HG-104
25-HG-103 A/B
25-FV-1725A
25-FV-1203
25-F
V-14
51
25-FV-1531
25-PV-1316
25-H
V-13
02
25-F
V-16
5425
-FV-
1657
27-FV-1025
25-T
V-1
268
25-164
25-PV-1255B
25-141
25-UV-1548
25-FV-1550
25-F
V-15
49
25-LV-1007
25-U
V-1
011
25-U
V-1
012
25-PV-146425-PV-1626
25-LV-1463
25-LV-1321A25-LV-1321B
25-F
V-1
219A
25-F
V-1
219B
25-LV-1327A25-LV-1327B
25-F
V-12
21A
25-F
V-12
21B
25-LV-1448
25-LV-1430A25-LV-1430B
25-F
V-1
224A
25-F
V-1
224B
25-LV-1435A25-LV-1435B
25-FV-1227A25-FV-1227B
25-U
V-10
10
25-F
V-1
546
25-U
V-1
877
25-PV-1559
25-P
V-1
560B
25-P
V-1
560C
25-F
V-1
236A
25-F
V-1
236B
25-U
V-18
78
25-U
V-1
308
25-FV-1543
25-UV-1879
25-U
V-10
09
25-PV-1560A
25-PV-1561A
25-PV-1282B
25-PV-1282A25-HV-1138
25-P
V-15
61B
25-P
V-15
61C
25-F
V-15
62A
25-F
V-15
62B
20
Classification: Internal Status: Draft
39PROSESS STRØM
25-HA-101
25-HG-103
25-HX-101
25-HX-102
25-HX-103
25-PA-101
25-PA-102
25-PA-103
25-VD-107
25-VE-102
26-VE-101
27-VE-102
27-VE-101
27-KA-101
25-CT-10225-HA-105 25-VE-101
25-HG-101
Classification: Internal Status: Draft
40PROSESS STRØMVÆSKEDANNINGSKRETS
25-CT-102
25-HA-101
25-HA-105
25-HX-101
25-HX-102
25-HX-103
25-PA-101
25-PA-102
25-PA-103
25-VD-107
25-VE-101
25-VE-102
26-VE-101
27-VE-102
27-VE-101
27-KA-101
25-HA-114
25-KA-102
25-VD-105
25-HG-101
25-HG-102
25-HG-103
21
Classification: Internal Status: Draft
41PROSESS STRØMVÆSKEDANNINGSKRETSFORKJØLINGSKRETS
25-CT-102
25-HA-101
25-HA-105
25-HG-101
25-HX-101
25-HX-102
25-HX-103
25-PA-101
25-PA-102
25-PA-103
25-VD-107
25-VE-101
25-VE-102
26-VE-101
27-VE-102
27-VE-101
27-KA-101
25-HA-114
25-HG-102
25-KA-102
25-VD-105
25-VD-10225-VD-103
25-HA-112
25-HA-111
25-HG-105
25-HG-104
25-VD-101
25-VD-115
25-VD-109
25-VD-112
25-VD-110
25-VD-116 25-KA-101
25-HG-103
Classification: Internal Status: Draft
42PROSESS STRØMVÆSKEDANNINGSKRETSFORKJØLINGSKRETSUNDERKJØLINGSKRETS
25-CT-102
25-HA-101
25-HA-105
25-HG-101
25-HX-101
25-HX-102
25-HX-103
25-PA-101
25-PA-102
25-PA-103
25-VD-107
25-VE-101
25-VE-102
26-VE-101
27-VE-102
27-VE-101
27-KA-101
25-HA-114
25-HG-102
25-KA-102
25-VD-105
25-VD-10225-VD-103
25-HA-112
25-HA-111
25-HG-105
25-HG-104
25-VD-101
25-VD-115
25-VD-109
25-VD-112
25-VD-110
25-VD-116 25-KA-101
25-CT-101
25-HA-104
27-HA-113
25-KA-103
25-VD-106
25-HG-103
22
Classification: Internal Status: Draft
43VÆSKEDANNINGSKRETS
25-HX-101
25-HX-102
25-HA-114
25-KA-102
25-VD-105
25-HG-10225-VD-104
Classification: Internal Status: Draft
44FORKJØLINGSKRETS
25-HG-101
25-HG-102
25-VD-10225-VD-103
25-HA-112
25-HA-111
25-HG-105
25-HG-104
25-VD-101
25-VD-115
25-VD-109
25-VD-112
25-VD-110
25-VD-116 25-KA-101
27-HG-101
23
Classification: Internal Status: Draft
45UNDERKJØLINGSKRETS
25-HX-101
25-HX-102
25-HG-102
25-CT-101
25-HA-104
27-HA-113
25-KA-103
25-VD-106
25-VD-114
46
Liquefaction technology – present and prediction(Source: Shell)
24
47
Compressor driver alternatives• Steam turbine
– Refrigerant compressor(s) driven by steam turbine
– Common in older LNG plants
– Steam plant needed, including boiler, feedwater treatment etc.
• Gas turbine
– Direct mechanical compressor drive using gas turbine
– Small plot area, low CAPEX
– Most common solution today
– Capacity of plant determined by available gas turbine sizes
• Electric
– Only Snøhvit so far, but considered in several current developments
– Increased availability, potential use of high-efficiency combined-cycle technology
48
Compressor driver trends
25
49
Mixed Fluid Cascade (MFC) process and energy system at Hammerfest
GG
Pre-coolingCycle
Lique-factionCycle
Sub-coolingCycle
SCCExp./Gener.
LNG Expander/Generator
Plate FinHeatExchangers
Spiral WoundHeatExchangersGenerator
NG
LNG
M
M
M
SCC Compressor
PCC Compressor
LCC Compressor
ElectricPowerGener.
5 x GE LM 6000 GTwith waste heat recovery
G
G
G
G
G
Process heatconsumers
Fuel gasAir
Hotoilcycle
Electric Powerfrom the Grid
Seawater cooling
Cold box
Unit 25
Cycle compression and seawater cooling
Unit 25
Electric power generationwaste heat recovery,hot oil cycleUnit 81 and 50
50
Parallel drivers/compressors (increasing availability) ”Two in one” concept
26
51
Process availability (on-stream time)
GT0.98 *
= 0.96
On-line Availability
= 0.97
= 0.94
GT0.98 *
GT0.98 *
GT0.98 *
GT0.98
GT0.98
GT
GT0.99
Fraction of time
2 circuits
2 circuits1 paralleldriver/compr
3 circuits
52
Heat rejectionAir cooling Water cooling
Tube-in-shellheat exchanger
27
53
Heat rejectionAir cooling
• Large plot area needed
• Lower process efficiency (less LNG for given power input)
• Lower CAPEX than water cooling
• Larger seasonal variation in capacity and efficiency
Water cooling
• More compact plant
• Costly corrosion-resistant materials needed(e.g. titanium)
• High process efficiency
• May need chlorination to prevent fouling
54
Air cooled condensers
28
55
Cooling of LNG plants