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TPG 4140 Natural Gas 2011LNG – Fundamental PrinciplesJostein Pettersen

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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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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 itis more economical to transport the gas as LNG instead of in a natural gaspipeline.•LNG also offers greater flexibility than pipeline gas

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What is LNG ? LNG = Liquefied Natural Gas

LNG is a cryogenic liquidA cryogenic liquid is the liquid form of any element or compoundthat liquefies at a temperature below –73 °C (-100 °F) at atmosphericpressure. 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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LNG Density1 m3 LNG correspondsto 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 waterLNG Density: 450 kg/m3

Water density: 1000 kg/m3

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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 weightNBP=Normal Boiling PointNFP= Normal Freezing Point

One mol is defined as 6.022•1023 atoms/molecules of a substanceThe volume of one mol is 23.644 liters at standard conditions (15°C, 1 atm.)

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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 plantsSmaller 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 plantsSmall-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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LNG Chain

Gas Production

Pipeline

LNG Plant

LNG Shipping

LNG Receiving Terminal

PowerGeneratio

n

GasDistributio

n

ElectricityTransmissio

n

GasMarketing

EndUser

EndUser

Air Liquefaction:Nitrogen, Oxygen,

ArgonRemote Cooling

Super Freeze/ Cryogenic Storag

e

Cold Energy Power Recover

y

15-20 % 30-45 % 10-30 % 15-25 %

Cost Distribution in the LNG value Chain – (numbers are indicative)

LNG Cold Utilization

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Heating value and Wobbe Index

UHV=Upper Heating Value, LHV=Lower heating value

28.964MW

GHVspgr

GHVWobbeIndex ==GHV: Gross Heating Value (MJ/Sm3)

(same as Upper Heating Value)spgr: specific gravity (-)MW: Molecular weight (kg/kmol)

The final LNG product has requirements for heating value and wobbe index

Substance UHV UHV UHV LHV LHV LHVkJ/kg kWh/kg MJ/Sm3 kJ/kg kWh/kg MJ/Sm3

Nitrogen 0 0 0 0 0 0Methane 55496 15,42 37,66 50010 13,89 33,93Ethane 51875 14,41 65,97 47484 13,19 60,39Propane 50345 13,98 93,90 46353 12,88 86,45Butane 49500 13,75 121,69 45714 12,70 112,38Pentane 49011 13,61 149,56 45351 12,60 138,39

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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

Source: CERA

Kenai

ShtokmanSnøhvit

Yamal

Marsa el Brega Sakhalin

Deltana

Peru LNG

Bolivia LNG

Arzew

Mariscal Sucre

AtlanticLNG Mauritania

Angola LNG

Yemen LNG

Gassi Touil Skikda

Idku Arun

Bintulu BruneiCentral SalawesiTangguh

IchthysSunrise

Darwin LNG

Browse BasinAustralia NWS 1-5

PlutoGorgon

PilbaraBontang

Baltic LNG

Bontang

Damietta

Equatorial Guinea

Akwa Ibom

Liquefaction Plant – Existing/ Under ConstructionLiquefaction Plant – Proposed

NIOC LNG

Persian LNG

Abu Dhabi LNG

Oman LNG

Pars LNG (Iran)QG IV

QG IIIQG IIQG I

RasGas 1-5RasGas 6/7

OK LNG

NLNG 1-6

OK LNG

Brass LNG

NLNG 7/8/9

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Gas processing and liquefaction

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Simplified LNG plant block diagram

Endflash

HHCExtraction

CH4/N2

Fuelgas

Power&

heat

(C5+) (C4 and C3)

(CO2 and H2S)

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Air cooled condensers

Plant example: Atlantic LNG –Trinidad (Air cooled)

Compressors

Jetty

Jetty

Cold boxes(Heat exchangers)

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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%)

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

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Liquefaction process

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Vapour pressure of pure fluids relevant for LNG processes Refrigerant Vapour Pressure

1

10

100

-200 -150 -100 -50 0 50

Temp(C)

Pre

ssur

a(B

ara)

LNG Range

N2

C1 Ethylene

CO2

C2

C3

n-C4

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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− 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 –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

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

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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)

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

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Temperature – enthalpy diagram of Prico example

-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

LNG

NG

5 bar

30 bar

12 °C

-155 °C

12 °C

-155 °C -155,5 °C

6,5 °C

99,8 °C

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Hot/Cold Composite Curves for Single Mixed Refrigerant Cycle

-180

-160

-140

-120

-100

-80

-60

-40

-20

0

20

40

0 200 400 600 800 1000 1200 1400 1600 1800 2000

Duty, x 10^6 kJ/hr

Tem

pera

ture

, C

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C3MR Process

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Heat exchangers

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Kettle type heat exchanger

• Shell and tube exchanger with separator function

• Flooded

• Tube bundle submerged in boiling liquid

Refrigerant vapour to compressor suction

Refrigerant liquid feedRefrigerant liquidsupply (if needed)

Hot stream inlet

Hot stream outlet

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Cryogenic Heat Exchangers

Plate-Fin Heat Exchangers

Spiral-Wound Heat Exchangers

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Spiral Wound Heat Exchanger (SWHE)

• Picture showing Snøhvit subcooler (25-HX-102)

• 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

Fin height 5-10 mm

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123456789

10111213

Block or CoreHeaderNozzleWidthStacking heightLengthPassage outletCover sheetParting sheetHeat transfer finDistribution finSide barEnd bar

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Production of plate-finheat exchangers (Linde)

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LNG storage and loading

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LNG tank containment principles

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• 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.

Above-ground full-containment LNG tank design

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Rollover - principles

T1ρ1

T2> T1ρ2< ρ1

evaporation

heatheat

Light components evaporatesDensity increases

ρ2 becomes larger than ρ1 due tocomposition changeRollover of the liquid phases may then occurThis gives a sudden pressureincrease 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 CarriersGrowth 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 TerminalArtist’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