TPG 4140 Natural Gas 2011
LNG – Fundamental Principles
Jostein Pettersen
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2010-09-26
Outline
• Why LNG?
• What is LNG ?
• Applications of LNG
• LNG trade and LNG chain
• Gas pre-treatment
• Gas liquefaction
• LNG storage and loading
• LNG transport
• LNG receiving terminals
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2010-09-26
Why produce LNG?
LNG is mainly produced for transportation purposes
•In situations where the gas market is far from the source of the natural gas it
is more economical to transport the gas as LNG instead of in a natural gas
pipeline.
•LNG also offers greater flexibility than pipeline gas
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2010-09-26
What is LNG ?
LNG = Liquefied Natural Gas
LNG is a cryogenic liquid
A cryogenic liquid is the liquid form of any element or compound
that liquefies at a temperature below –73 °C (-100 °F) at atmospheric
pressure. Common cryogenic liquids are: Nitrogen, Oxygen, Helium,
Hydrogen and LNG
• LNG is natural gas that has been cooled and condensed
to a liquid
• At atmospheric pressure LNG has a temperature of about
–162 ºC or -260 ºF
• LNG contains about 85-95 % methane
• LNG is colorless, odorless, non-corrosive and non-toxic
• Evaporated LNG can displace oxygen and cause human
suffocation
• Flammability range, 5-15 vol % concentration in air
• Autoignition temperature, 540°C
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2010-09-26
LNG Density
1 m3 LNG corresponds
to 600 Sm3 natural gas
S = Standard state, 15°C, 1 atm
At temperatures above -110 ºC
LNG vapour is lighter than air
LNG is lighter than water
LNG Density: 450 kg/m3
Water density: 1000 kg/m3
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2010-09-26
Main components in LNG
Component
Formula
MW (kg/kmol)
NBP (°C) NFP (°C)
Nitrogen
N2
28.013
- 195.5
- 209.9
Methane
CH4
16.043
- 161.6
-182.5
Ethane
C2H6
30.07
-88.6
-183.3
Propane
C3H8
44.097
-42.0
-187.7
nButane
nC4H10
58.124
-0.5
-138.4
iButane
iC4H10
58.124
-11.8
-159.6
nPentane
C5H12
72.151
36.06
-129.8
MW=Molecular weight
NBP=Normal Boiling Point
NFP= Normal Freezing Point
One mol is defined as 6.022•1023 atoms/molecules of a substance
The volume of one mol is 23.644 liters at standard conditions (15°C, 1 atm.)
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2010-09-26
Types of LNG plants
• Base-load plants
Large plants which are directly based on a specific gas field development and are the main
plants for handling the gas. A base-load plant has typically a production capacity of above 3
Mtpa (million tons per annum) of LNG. The main world-wide LNG production capacity come
from this type of plants
• Peak-shaving plants
Smaller plants that are connected to a gas network. During the period of the year when gas
demand is low, natural gas is liquefied and LNG is stored. LNG is vaporized during short
periods when gas demand is high. These plants have a relatively small liquefaction capacity
(as 200 tons/day) and large storage and vaporization capacity (as 6000 tons/day). Especially
in the US many such plants exist
• Small-scale plants
Small-scale plants are plants that are connected to a gas network for continuous LNG
production in a smaller scale. The LNG is distributed by LNG trucks or small LNG carriers to
various customers with a small to moderate need of energy or fuel. This type of LNG plants
typically has a production capacity below 500 000 tpa. In Norway and China several plants
within this category is in operation.
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2010-09-26
LNG Chain
LNG Cold Utilization
Cold Energy
Power
Recover
y
Gas
Production
Remote
Cooling
Pipelin
e
15-20 %
Super Freeze/
Cryogenic
Storag
e
LNG
Plant
30-45 %
Air
Nitrogen,
Oxygen,
Liquefaction:
Argon
LNG
Shipping
2010-09-26
Electricit
Transmissio
y
n
En
Use
d
r
Gas
Distributio
n
Gas
Marketing
En
Use
d
r
LNG
Receiving
Terminal
10-30 % 15-25 %
Cost Distribution in the LNG value Chain – (numbers are indicative)
8-
Power
Generatio
n
Heating value and Wobbe Index
The final LNG product has requirements for heating value and wobbe index
UHV=Upper Heating Value, LHV=Lower heating value
Substance
Nitrogen
Methane
Ethane
Propane
Butane
Pentane
UHV
kJ/kg
0
55496
51875
50345
49500
49011
UHV
kWh/kg
0
15,42
14,41
13,98
13,75
13,61
GHV
WobbeIndex =
=
spgr
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2010-09-26
UHV
MJ/Sm3
0
37,66
65,97
93,90
121,69
149,56
GHV
MW
28.964
LHV
kJ/kg
0
50010
47484
46353
45714
45351
GHV:
spgr:
MW:
LHV
kWh/kg
0
13,89
13,19
12,88
12,70
12,60
LHV
MJ/Sm3
0
33,93
60,39
86,45
112,38
138,39
Gross Heating Value (MJ/Sm3)
(same as Upper Heating Value)
specific gravity (-)
Molecular weight (kg/kmol)
Gross Calorific Value range for various pipeline
networks
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Applications of LNG
• Pipeline gas for household and industry
• Gas fired power production
• Maritime fuel
• Fuel for cars and buses
• LNG cold utilization
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Natural gas liquefaction plants
Shtokman
Snøhvit
Kenai
Mariscal
Sucre
Deltana
Angola LNG
Brass
LNG
Source: CERA
RasGas 1-5
RasGas 6/7
Persian LNG
Abu Dhabi
LNG
Oman LNG
Sakhalin
Damietta
Gassi
Touil
Skikda
Atlantic
Idku
LNG Mauritania
Bolivia LNG
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Yamal
Marsa el Brega
Peru LNG
NLNG
1-6
NLNG 7/8/9
Pars LNG
QG IV (Iran)
QG III
QG II
QG I
Baltic LNG
Arzew
OK
LNG
NIOC LNG
Bintulu
Arun
Yemen
LNG
Brunei
Central Salawesi
Tangguh
Ichthys
Sunrise
Darwin LNG
Bontang
Pilbara
Gorgon
Pluto
Browse Basin
Australia
NWS 1-5
Akwa Ibom
Liquefaction Plant – Existing/
Under Construction
Equatorial
Guinea
Liquefaction Plant – Proposed
Gas processing and
liquefaction
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Simplified LNG plant block diagram
Fuel
gas
(CO2 and H2S)
CH4/N2
End
flash
HHC
Extraction
(C5+)
Power
&
heat
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(C4 and C3)
Jetty
Plant example: Atlantic LNG –
Trinidad (Air cooled)
Jetty
Compressors
Air cooled
condensers
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Cold boxes
(Heat exchangers)
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
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MDEA process for CO2 removal
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Water removal by adsorption
• Adsorption in to a solid material
− Used in “deep” gas processing like Kårstø, Snøhvit with cold process systems
− Removal of smaller amounts of water
− Extreme dryness, down to 0.1 ppm
• Porous structure that contains very large internal surface area
− 200 – 800 m2/g
• Strong affinity for water
− 5 – 15 % by weight
• Solids like
− Molecular sieve (3A or 4A type)
− Silica gel
• Regenerative process
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Water removal by adsorption
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Natural gas path through liquefaction
pressure-enthalpy diagram (C1:89.7% C2:5,5% C3:1.8% N2:2.8%)
100
-200oC
-100oC
-150oC
-50oC
0oC
Precooling
Liquefaction
Subcooling
50oC
Pressure [bara]
Expansion
10
JT Throttling
1
-900
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End
-800 flash -700
-600
-500LNG
-400
-300
Enthalpy [kJ/kg]
-200
-100
0
100
200
Liquefaction process
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Vapour pressure of pure fluids relevant for LNG
Refrigerant Vapour Pressure
processes
100
CO2
C1
Pressura(Bara)
N2
Ethylene
C2
C3
10
n-C4
LNG Range
1
-200
-150
-100
-50
Temp(C)
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0
50
Liquefaction process licensors –
Base load LNG plants (3+ Mtpa)
• Air Products and Chemicals Inc (APCI)
− World leader since since the 1970s – ca 80 operating trains
− C3MR process ( ca 70 trains)
− AP-XTM Hybrid (QatarGas II, III and IV, RasGas III: Six trains of 7.8 Mtpa each, Start up 2008)
• ConocoPhillips (Optimised) Cascade
−
−
−
−
−
• Shell
Trinidad: Atlantic LNG - 4 trains
Egypt: Idku
Alaska: Kenai (Operating since 1969!)
Australia: Darwin LNG
Equatorial Guinea
DMR – Double Mixed Refrigerant (Sakhalin, 2 x 4.8 Mtpa –start-up 2007)
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
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Simplified cascade process for natural gas
liquefaction
1.4 bar
45 bar
1.4 bar
19 bar
1.4 bar
LNG -155 °C
-96 °C
Methane
Ethylene
Propane
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-32 °C
7 bar
12 °C
NG
Cascade Process (ConocoPhillips)
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Temperature stages in cascade process
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Example of single-mix refrigerant cycle for
natural gas liquefaction (Prico cycle)
Composition:
NG
12 °C
30 bar
NG
6,5 °C
12 °C
99,8 °C
-155 °C
LNG
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5 bar
-155 °C
-155,5 °C
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
Temperature – enthalpy diagram of Prico example
150
Mixed refrigerant dew point line
Mixed refrigerant 30 bar
Mixed refrigerant bubble point line
100
NG
12 °C
30 bar
50
NG 60 bar
6,5 °C
Temperature, C
12 °C
99,8 °C
0
-155 °C
LNG
5 bar
-155 °C
NG dew point line
-155,5 °C
-50
Mixed refrigerant 5 bar
NG bubble point
line
-100
-150
-200
-1500
-1000
-500
0
Enthalpy, x 10^6 kJ/hr
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500
1000
1500
Hot/Cold Composite Curves for
Single Mixed Refrigerant Cycle
40
20
0
-20
Temperature, C
-40
-60
-80
-100
-120
-140
-160
-180
0
200
400
600
800
1000
Duty, x 10^6 kJ/hr
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1200
1400
1600
1800
2000
C3MR Process
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Heat exchangers
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Kettle type heat exchanger
Refrigerant vapour to
compressor suction
• Shell and tube exchanger with
separator function
Hot stream
inlet
Refrigerant liquid
supply (if needed)
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Refrigerant liquid feed
Hot stream
outlet
• Flooded
• Tube bundle submerged in boiling
liquid
Cryogenic Heat Exchangers
Spiral-Wound Heat Exchangers
Plate-Fin Heat Exchangers
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Spiral Wound Heat Exchanger (SWHE)
• Picture showing Snøhvit subcooler (25-HX102)
• Specialized ”proprietary” type of heat
exchanger
• Large capacity in one unit
• Reasonably robust, and well proven in gas
liquefaction
• Issues
− Complexity of thermal/hydraulic
analysis
− Flow distribution on shell side
− Exclusive knowledge
− Leakage – but tubes can be plugged
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Spiral Wound LNG Heat Exchanger
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Plate fin (PFHE)
• Stack of plain and folded plates
• Brazed in vacuum furnace
• Compact, multi stream capability
• Pressures up to ca 120 bar
• Issues
− Thermal stress
− Flow distribution and flow
instability
− For clean service only!
− Limited size (brazing process)
− Cannot be repaired or plugged
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Fin height 5-10 mm
1
2
3
4
5
6
7
8
9
10
11
12
13
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Block or Core
Header
Nozzle
Width
Stacking height
Length
Passage outlet
Cover sheet
Parting sheet
Heat transfer fin
Distribution fin
Side bar
End bar
Production of plate-fin
heat exchangers (Linde)
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LNG storage and
loading
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LNG tank containment principles
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Above-ground full-containment LNG tank design
• Pre-stressed concrete outer walls
constructed by slipforming, sheathed
internally with a gas-tight layer of
nickel-alloyed steel.
• Inner tank in nickel-alloyed steel,
separated from the outer walls by a
layer of perlite - a variety of volcanic
obsidian highly suitable for insulation
• Extra layer of steel and insulation at
the transition between outer wall and
tank bottom to protect it against
strong local stresses should the
inner tank begin to leak.
• Heating cables under the tanks will
ensure that the ground remains
above 0°C in order to prevent frost
heaving.
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Rollover - principles
evaporation
heat
T2> T1
ρ2< ρ1
T1
ρ1
Light components evaporates
Density increases
ρ2 becomes larger than ρ1 due to
heat
composition change
Rollover of the liquid phases
may then occur
This gives a sudden pressure
increase due to flash vaporization
T = Temperature (°C)
ρ = Density (kg/m3)
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Typical storage and loading system
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LNG ships
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LNG transportation – technical aspects
• LNG is transported at – 163 deg. C and at atmospheric pressure
• This extreme low temperature require that the LNG is transported and handled with special
consideration, i.e.
− Completely separated from the ship’s hull
− LNG temperature must be maintained during the voyage – requiring efficient insulation
of the cargo tanks
− All cargo handling equipment must be able to operate at the extreme low temperature
of -163 degr. C
• Two basically different cargo containment systems are used:
− Self supported independent tanks (Moss Rosenberg spherical tanks, IHI SPB,
cylindrical tanks)
− Membrane tanks (Gaz Transport and Technigaz (GTT))
• Market share between the two concepts has been about. 50/50 - but the membrane concept
has been increasingly selected for recent newbuilding orders.
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Spherical tank cargo containment systems
(Moss Rosenberg )
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Spherical LNG cargo tanks – pros & cons
• Advantages
− Independent from the ship’s hull – hull stresses not transferred into the cargo tanks
− Very robust design
− No sloshing problems
− Can operate with partly filled tanks
− Allow simultaneous building of hull and cargo tanks
− Easy to inspect
− Easy to detect and repair leakages
• Disadvantages
− Low volumetric utilisation of the hull
− Larger physical dimensions for same capacity compared with prismatic tanks
− Visibility from bridge reduced compared with ships with prismatic tanks
− Require return cargo (‘heel’) on ballast voyage to keep cargo tanks cooled
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LNGC – Membrane cargo containment system
(GT No. 96, MK I and MK III, and CS1)
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Mark III (Technigaz) Membrane system
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Inside membrane tank
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Membrane cargo containment system (GTT) – pros &
cons
• Advantages
− High volumetric utilisation of ship’s hull
− Less sensitive to temperature changes as inner membrane (invar steel) has very low
thermal contraction coefficient
− Limited need for heel on ballast voyage
• Disadvantages
− Cargo tanks are an integrated part of the ship’s hull - hull stresses transferred to cargo
tanks
− Does not allow simultaneous construction of hull and cargo tanks
− Difficult to detect and costly to repair leakages
− Restricted filling ratio
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LNG Carriers
Growth in the average capacity
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LNG Receiving
Terminals
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Gas quality parameters – N2 injection
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Sabine Pass LNG Terminal
Artist’s Rendition
Source: Cheniere Energy, Inc.
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LNG receiving terminal - principles
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Vaporizer options
• Need a heat source
Basically the following options are available (or a combination of them):
• Heat from seawater
− Open Rack Vaporizers – ORV
• Heat of combustion, by burning a portion of the natural gas
− Submerged Combustion Vaporizers – SCV
• Heat from waste heat recovery or by direct burning of natural gas
− Direct Fired Heaters – DFH
• Heat from ambient air
− Ambient Air Vaporizers - AAV
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New technology entering the market
• Offshore LNG terminals has been an issue since the early 1990s
• In general floating storage and re-gasification unit (FSRU) can be divided into two
groups
− Near-shore terminals. Gravity based structures (GBS) sited at 15 to 25
meters water depth. Normally constructed in concrete, due to its durability
and track record in offshore oil and gas operations in general. Concrete is
also the preferred choice for secondary containment in the LNG storage
system.
− Offshore terminals. For the far shore options several different designs have
been proposed based on vessel design, barge design or partly submerged
structures. As an alternative to traditional low temperature storage sub sea
caverns have also been proposed.
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Example of offshore solution: Høegh SRV
• Dedicated ships
• Required modifications:
− Connection for submerged
turret buoy and flexible export
riser
− Regasification plant onboard
− Send out capacity 400 t/h, i.e.
about 7 days discharge time
− Weather limit for continous
sendout: Hs = 11 m
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Thank you
64 - 2010-09-26