Boil-Off in Large and Small Scale LNG Chains

Faculty of Engineering Science and Technology

Department of Petroleum Engineering and Applied Geophysics

BOIL-OFF IN LARGE- AND SMALL-SCALE

LNG CHAINS

Diploma Thesis Rafa Sedlaczek

Trondheim

May 2008

http://www.pdfcomplete.com/cms/hppl/tabid/108/Default.aspx?r=q8b3uige22

BOIL-OFF IN LARGE- AND SMALL-SCALE LNG CHAINS

ii

Abstract

One of the challenges in transporting and storing LNG is the generation of methane

through the boil-off. Boil-off is caused by the heat added into the LNG during the storage

and loading/unloading operations. In this thesis work, as a background, the world-trade in

LNG is reviewed in overall numbers. The analysis of LNG shipping technologies is

presented. The current technologies used to store LNG are reviewed. The different types of

tanks are described, and their advantages and disadvantages discussed. New, types of LNG

storage tanks (C/C LNG tank and ACLNG) are also described, with their potential

advantages and disadvantages. The sources of boil-off gas for large-scale LNG receiving

terminal are described, discussed and illustrate for a specific set of assumptions. Because

of the larger relative value of methane evaporating during the storage, the boil-off

consideration can be even more important in small-scale than in large-scale LNG chain. As

a typical small-scale LNG facility the L-CNG refuelling station is considered. Heat leak

into the LNG storage tank is calculated. The effect of a number of buses, fuelled each day

on the possible total fuel loss rate is analyzed. It is found that by increasing the number of

buses, fuelled each day, the total fuel loss rate can be reduced significantly. To prevent

boil-off of natural gas emissions, usually it is re-circulated. Some typical approaches for

the use of boil-off gas are presented, for both large- and small-scale LNG chains.



iii

Acknowledgements

There are many people who contributed to my thesis and many events that influenced my

work during the last few months. I would like at least to mention them here.

First of all, I would like to express my sincere appreciation to the person without whom

this thesis would never come to life, my supervisor Professor Jon Steinar Gudmundsson. I

am deeply grateful for the advice, support, useful and helpful assistance, patience and

enthusiasm.

I wish to thank Dr Hab. In. Stanisaw Nagy, my supervisor from AGH University of

Science and Technology in Cracow, thanks to whom my Erasmus Link Scholarship was

possible. I am also grateful for his support, and patience during our cooperation.

Special thanks to Mr Otto Skovholt from StatoilHydro for his generous suggestions and

commitment.

Special thanks to Professor Jan Falkus form AGH University of Science and Technology

in Cracow, Poland for making my Erasmus Link Scholarship possible.

I am grateful to all my teachers who, giving me a small part of their wide knowledge, got

me to the stage when I am writing this thesis.



iv

List of Contents

Abstract........................................................................................................................... ii

Acknowledgements ........................................................................................................ iii

List of Contents ...............................................................................................................iv

List of Tables...................................................................................................................vi

List of Figures ............................................................................................................... vii

Abbreviations................................................................................................................. ix

1 Introduction............................................................................................................. 1

2 What is Liquefied Natural Gas? ............................................................................. 3

3 LNG market ............................................................................................................ 5

3.1 Abundant world natural gas reserves and LNG potential.................................... 5 3.2 LNG market structure ........................................................................................ 7 3.3 LNG exporters................................................................................................... 9 3.4 LNG importers .................................................................................................12 3.5 Growing world LNG trade................................................................................14 3.6 Small-scale LNG trend .....................................................................................16

4 LNG storage tanks .................................................................................................18

4.1 Background ......................................................................................................18 4.2 Single containment tanks (SCT) .......................................................................19 4.3 Double containment tanks (DCT) .....................................................................21 4.4 Full containment tanks (FCT) ...........................................................................23 4.5 Membrane tanks ...............................................................................................25 4.6 New LNG storage technologies ........................................................................27

5 LNG vessel types ....................................................................................................32

5.1 Evolution of LNG fleet.....................................................................................32 5.2 Kvaerner - Moss spherical tanks .......................................................................34 5.3 Membrane tanks ...............................................................................................36 5.4 Prismatic tanks .................................................................................................38

6 Large-scale LNG chain ..........................................................................................40

6.1 LNG value chain ..............................................................................................40 6.2 Thermal analysis of boil-off of LNG for the unloading mode............................42 6.3 Thermal analysis of boil-off of LNG for the holding mode ...............................47 6.4 Thermal analysis of the LNG storage tank ........................................................50 6.5 BOR in large-scale LNG chain .........................................................................59

7 Small-scale LNG chain...........................................................................................64

7.1 Background ......................................................................................................64 7.2 Thermal analysis of boil-off of LNG in cryogenic tanks ...................................66 7.3 Dynamic process during storage and fueling.....................................................72


BOIL-OFF IN LARGE- AND SMALL-SCALE LNG CHAINS v

8 Use of boil-off gas ...................................................................................................78

8.1 Use of BOG at ships .........................................................................................78 8.2 Use of BOG at receiving terminals ...................................................................80 8.3 Use of BOG in small-scale LNG chain .............................................................82

9 Discussion ...............................................................................................................84

10 Conclusions.............................................................................................................87

References ......................................................................................................................88

Appendix A. Composition of Natural Gas and LNG....................................................91

Appendix B. Major trade movements Natural Gas and LNG (2006) .......................93

Appendix C. Major trade movements LNG (2006) ...................................................94

Appendix D. Maps of LNG facilities worldwide ...........................................................95

Caribbean, South & Central America ...........................................................................95 Asia Pacific Countries - Map A....................................................................................96 Asia Pacific Countries - Map B....................................................................................97 Africa ..........................................................................................................................98 Western Europe Map A.............................................................................................99 Western Europe Map B ...........................................................................................100 Mexico.......................................................................................................................101 Middle East Countries................................................................................................102 Northeastern Europe ..................................................................................................103 Southwest Pacific Rim Countries ...............................................................................104 United States of America West Coast Map A ..........................................................105 United States of America Gulf Coast Map B ...........................................................106 United States of America East Coast Map C............................................................107 Canada.......................................................................................................................108

Appendix E. Conversion tables ...................................................................................109

Appendix F. Methane density at liquid and gaseous states ........................................110



vi

List of Tables

Table 5.1 Features of LNG membrane cargo containment systems...................................37

Table 6.1 Dimensions of the LNG tank ............................................................................55

Table 6.2 Concrete properties at normal temperature........................................................55

Table 6.3 Insulation layers of wall ...................................................................................56

Table 6.4 Bottom slab configuration. ...............................................................................57

Table 6.5 BOG and BOR for numerical example..............................................................58

Table 6.6 Boil-off gas sources, an example study.............................................................59

Table 6.7 Average emissions intensity of various life-cycle stages of LNG imported by

Japan ...............................................................................................................................62

Table A.1 Examples of Gas compositions ........................................................................91

Table A.2 Examples of LNG compositions ......................................................................92

Table A.3 Frequently used conversions ..........................................................................109

Table A.4 Typical liquid-vapour conversions .................................................................109

Table A.5 Methane pressure and density at liquid and gaseous states .............................110



vii

List of Figures

Figure 3.1 Proved world natural gas reserves, January 1, 2007. ......................................... 5

Figure 3.2 World LNG exporters, January 1, 2007 ...........................................................11

Figure 3.3 World LNG importers, January1, 2007............................................................11

Figure 4.1 Various types of LNG tanks [15].....................................................................18

Figure 4.2 Features of a typical single containment LNG tank..........................................19

Figure 4.3 Features of a typical double containment LNG tank. .......................................21

Figure 4.4 Features of a typical full containment LNG tank..............................................23

Figure 4.5 Membrane LNG storage tank multiples structure.............................................25

Figure 4.6 ACLNG tank details........................................................................................28

Figure 4.7 A CryoTank design .........................................................................................31

Figure 5.1 Changes of LNG cargo tanks types..................................................................32

Figure 5.2 Age of LNG fleet ...........................................................................................33

Figure 5.3 LNG carrier equipped with Moss tanks. ..........................................................34

Figure 5.4 Inside view of SPB tank. .................................................................................38

Figure 6.1 The LNG chain-from production to user..........................................................40

Figure 6.2 Boil-off gas generated by insulated pipeline heat gain. ....................................44

Figure 6.3 An LNG storage tank with the liquid stratified ................................................48

Figure 6.4 Heat flow rates through the roof ......................................................................50

Figure 6.5 Configuration of the LNG tank wall ................................................................52

Figure 6.6 Configuration of the LNG tank wall using equivalent concrete. .......................53

Figure 7.1 Conceptual sketch of small-scale LNG chain...................................................64

Figure 7.2 Boil-off rate as a function of thickness of superinsulation................................68

Figure 7.3 Thermal conductance as a function of thickness of insulation. .........................69

Figure 7.4 The vapour pressure curve for methane ...........................................................70

Figure 7.5 Percentage of LNG to be boiled to reduce saturated vapour pressure. ..............71

Figure 7.6 Predicted saturated pressure for 50 m3 tank with an initial fill of 25 m3 LNG. .74

Figure 7.7 Average fuel consumption...............................................................................75

Figure 7.8 Total fuel loss with number of buses. ..............................................................76

Figure 7.9 Boil-off rate as a percentage of daily consumption of the LNG for the LNG

tank..................................................................................................................................77

Figure 8.1 Process flow-scheme of boil-off re-liquefaction unit. ......................................79



viii

Figure 8.2 LNG storage tank with module of electric generator or liquefier......................83



ix

Abbreviations

LNG Liquefied Natural Gas

LPG Liquefied Petroleum Gas

CNG Compressed Natural Gas

NG Natural Gas

BOG Boil-Off Gas

BOR Boil-Off Rate

OECD Organisation for Economic Co-Operation and Development

IEA International Energy Agency

SCT Single Containment Tank

DCT Double Containment Tank

FCT Full Containment Tank

ACLNG All-Concrete LNG Tank

C/C Concrete/Concrete Tank (Cryo Tank)

EEMUA Engineering Equipments and Materials Users Association

CO2 Carbon Dioxide

CO2e Carbon Dioxide Equivalent

SOx Sulphur Oxides

NOx Nitrogen Oxides

CH4 Methane

L-CNG Liquid to Compressed Natural Gas

NGV Natural Gas Vehicles

GHG Greenhouse Gases

IMO International Maritime Organisation

MSCM Thousand Standard Cubic Metres

BCM Billion Cubic Metres (1,000,000,000 = 109)

BCF Billion Cubic Feet (1,000,000,000 = 109)

TCM Trillion Cubic Metres (1,000,000,000,000 = 1012)

BTU British Thermal Unit


BOIL-OFF IN LARGE- AND SMALL-SCALE LNG CHAINS 1

1 Introduction

Liquefied natural gas (LNG) is natural gas that has been cooled to the point that it

condenses to a liquid, which occurs at a temperature of approximately -162C and at

atmospheric pressure. Liquefaction reduces the volume by approximately 600 times,

making it more economical to transport between continents. LNG is transported by special

made ships to terminals, and then stored at atmospheric pressure in super-insulated tanks.

However the ship cargo tanks, storage tanks and almost all equipment used to process

LNG are well insulated, there is always some heat leak into the LNG. Heat entering the

LNG, referred as heat inleak causes the LNG to warm up. To keep the pressure and the

temperature constant heat adsorbed by the LNG has to be released by boiling off some of

the liquid to gas. This is known as auto-refrigeration.

Methane, the primary constituent of boil-off gas is a potent greenhouse gas when released

to the atmosphere. It is worthy to note that while the quantity of CH4 emissions does not

appear significant compared to CO2, considering the global warming potential of CH4

(methane is about 21 times more greenhouse gas than carbon dioxide), these emissions are

responsible for about 13% of total CO2e emissions. Flaring alone contributes to more than

1 percent to global emissions of CO2 (IEA, 2008).

Boil-off gas is essentially gasified LNG at atmospheric pressure and it has substantial fuel

value. Excepting all negative impact that natural gas emissions exert on the environment it

is not economically profitable to dispose boil-off gas by venting or flaring. That is why at

both production and receiving sites the boil-off gas handling system is designed and

installed. Of course handling of boil-off gas requires compression equipment that is costly

to install and operate, so every possible effort is made to reduce the quantity of boil-off gas

produced.

However, currently LNG industry contributes only small part of global emissions of CH4

from the oil and gas sector, it can become a potent source of greenhouse gas emissions in

the near future. According to the International Energy Agency (IEA), LNG will account

even for 70% of the increase in gas trade by 2030. If this were to happen, LNG would

make up 50% of internationally traded gas by 2030. It is clear that these large amounts of



LNG would generate large quantities of boil-off gas, which would become a significant

source of CH4 emissions. Due to increasing demand world wide, by the United Nations and

other global organisations, to combat greenhouse gas emissions, it is evident how

important boil-off gas generation will be.

In this thesis work the sources of boil-off gas in large-scale receiving terminals will be

discussed. As a result the boil-off from the storage volumes will be estimated for the

specific set of assumptions.

As a typical small-scale facility the L-CNG refuelling station will be considered. Natural

gas is being promoted as a transportation fuel for heavy vehicles such as trucks and city

buses, to lessen the dependency on oil and to reduce greenhouse gas emissions. However

this solution has many advantages the disadvantage is that the boil-off of LNG can cause

excessive pressure build-up in LNG tanks, and therefore methods have to be found to

reduce the pressure of the boil-off gas and to prevent venting of the boil-off natural gas in

storage vessels and transportation tanks. In this thesis work the thermodynamic and heat

transfer methods to analyse the pressure and temperatures changes in LNG tanks will be

used. The effect of number of buses, fuelled each day on the total fuel loss due to boil-off

will be also presented.



2 What is Liquefied Natural Gas?

To answer the question what the liquefied natural gas is we have to define natural gas.

Natural gas comes from reservoirs beneath the earths surface. Sometimes it occurs

naturally and is produced by itself (non-associated gas), sometimes it comes to the surface

with crude oil (associated gas), and sometimes it is produced constantly such as in landfill

gas. Natural gas is a fossil fuel, meaning that it is derived from organic material deposited

and buried in the earth millions of years ago. Other fossil fuels are coal and crude oil.

Together crude oil and gas constitute a type of fossil fuel known as hydrocarbons

because the molecules in these fuels are combinations of hydrogen and carbon atoms. The

main component of natural gas is methane. Methane is composed of one carbon and four

hydrogen atoms (CH4). When natural gas is produced from the earth, it includes many

other molecules, like ethane (used for manufacturing), propane (which we commonly use

for barbeques), butane (used in lighters) and heavier hydrocarbons. Small quantities of

nitrogen, oxygen, carbon dioxide, sulphur compounds, and water may also be found in

natural gas. [1]

According to the Department of Energy (DOE 2008), liquefied natural gas (LNG) is

natural gas that has been cooled to the point that it condenses to a liquid, which occurs at a

temperature of approximately -161C and at atmospheric pressure. Natural gas is turned

into a liquid using a refrigeration process in a liquefaction plant. The unit where LNG is

produced is called a train. Feed gas to the liquefaction plant comes from the production

field. This gas must be clean and dry before liquefaction can take place. The gas is

scrubbed of entrained hydrocarbon liquids and dirt and treated to remove trace amounts of

two common natural gas contaminants: hydrogen sulphide and carbon dioxide. Next, the

gas is cooled to allow water to condense and then further dehydrated to remove even small

amounts of water vapour. The clean and dry gas may then be filtered before liquefaction

begins. Liquefaction takes place through cooling of the gas using heat exchangers. In these

vessels, gas circulating through aluminium tube coils is exposed to a compressed

hydrocarbon-nitrogen refrigerant. Heat transfer is accomplished as the refrigerant

vaporizes, cooling the gas in the tubes before it returns to the compressor. The liquefaction

process can have variations. For example, the Phillips Cascade, which employs three heat

exchangers with successively colder refrigerants (propane, ethane, methane) and



independent compressors for each exchanger refrigerant combination. Together the series

of exchangers comprise a single LNG train. [2]

As a result of liquefaction process we get liquefied natural gas (LNG). Liquefying natural

gas reduces its volume by a factor of 600, which means that LNG at -162C uses 1/600th

of the space required for a comparable amount of gas at room temperature and atmospheric

pressure and reaches the density of 420 to 490 kilograms per cubic metre. Because the

liquefaction process requires the removal of some of the non-methane components such

as water and carbon dioxide from the production gas, LNG is typically made up mostly of

methane plus a few percent of ethane, even less propane and butane, and trace amounts of

nitrogen. And, like methane, the main component of LNG, is odourless, colourless, non-

corrosive, and non-toxic. [1]

Liquefied natural gas is very save. As a liquid, LNG cannot explode or burn. The lighter

than air property of methane actually makes it less hazardous than some other fuels, such

as propane or butane whose gases are heavier than air and tend to settle closer to the

ground. In gaseous form, LNG vapour can burn if it is within 5-15% natural gas in the air.

If it is less than 5% natural gas in the air, the gas is too diluted to burn. If it is more than

15% natural gas in the air, there is not enough oxygen for it to burn. When spilled on water

or land, LNG will not mix with the water or soil or leave a residue, but evaporates and

dissipates into the air. [3]



3 LNG market

3.1 Abundant world natural gas reserves and LNG potential

Historically, world natural gas reserves have, for the most part, trended upward. As of

January 1, 2007, proved world natural gas reserves (proved reserves are those that could be

economically produced with the current technology), as reported by BP Statistical Review

of Energy were estimated at 181.46 trillion cubic metres (TCM) 1.39 TCM (about 1

percent) higher than the estimate for 2006. Much of this gas is considered stranded

because it is located in regions distant from consuming markets. [4]

The largest revisions to natural gas reserve estimates were reported for Kazakhstan,

Turkmenistan, and China. Kazakhstan added an estimated 0.99 TCM (a 54-percent

increase over 2006 proved reserves), Turkmenistan 0.82 TCM (41 percent), and China 0.77

TCM (50 percent). Declines in natural gas reserves were reported for the Netherlands (a

decrease of 0.34 TCM), Trinidad and Tobago (0.2 TCM), Argentina (0.085 TCM), Nigeria

(0.085 TCM), and Italy, Norway, the United Kingdom, and Saudi Arabia (about

0.057 TCM each). [4]

Figure 3.1 Proved world natural gas reserves, January 1, 2007.

Almost three-quarters of the worlds natural gas reserves are located in the Middle East

and Eurasia (Figure 3.1). Russia, Iran, and Qatar combined accounted for about 58 percent



of the worlds natural gas reserves as of January 1, 2007. Reserves in the rest of the world

are fairly evenly distributed on a regional basis. [4]

Natural gas, in the form of liquefied natural gas or LNG, has the potential to be exported

from countries with large, proven natural gas reserves and relatively high reserves-to-

production ratios. Some countries meeting this criterion include the Republic of Peru,

Republic of Venezuela, Azerbaijan Republic, Republic of Kazakhstan, Islamic Republic of

Iran, Republic of Iraq, State of Kuwait, State of Qatar, United Arab Emirates (also known

as Al Imarat al-Arabiyah al-Muttahidah), Republic of Yemen, Federal Republic of Nigeria,

and Independent State of Papua New Guinea. However, not all of these countries are

exporters of natural gas as LNG due to domestic need, inaccessibility to international

natural gas trade and infrastructure, geopolitics, and lack of capital or technological

investment. [5]

The 15 countries (Algeria, Australia, Brunei (Darussalam), Equatorial Guinea, Egypt,

Indonesia, Libya (also known as the Socialist People's Libyan Arab Jamahiriya), Malaysia

(also known as Persekutuan Tanah Malaysia), Nigeria, Norway, Oman, (also known as

Saltanat Uman), Qatar, (also known as Dawlat Qatar), Trinidad and Tobago, United Arab

Emirates (also known as Al Imarat al-Arabiyah Al-Muttahidah), United States of America)

that currently export LNG have approximately 34 percent of world natural gas reserves. [6]

In addition to expansions by current LNG exporters, Russia with 26.3 percent of the

worlds reserves is poised to become LNG exporting country, as it is currently building its

first liquefaction facilities. At least six additional countries (Angola, Bolivia, Iran, Peru,

Venezuela, and Yemen) with 19 percent of the worlds reserves are potential LNG

exporters. [6]

According to an industry LNG consultant Andy Flower the economic crossover - the point

at which transporting LNG via tanker is cheaper than transporting natural gas via pipelines

- occurs at a distance of around 2,000 kilometres (1,250 miles) for offshore pipelines and

around 3,800 kilometres (2,375 miles) for onshore pipelines. [6]



3.2 LNG market structure

LNG is traded globally in two major markets - the Atlantic Basin and the Pacific Basin.

The Atlantic Basin is usually defined as made up of all land masses (including islands) that

lie adjacent to or within the Atlantic Ocean, so it will include all activity in Europe, Africa

(including North and West Africa), and the Western Hemisphere (not including the

Alaskan terminal on the Pacific Ocean). The term Pacific Basin will be used to describe

LNG activity along the Pacific Rim (including Alaska) and in South Asia (including India).

[7]

The Atlantic Basin LNG market consist of current LNG producing countries Abu Dhabi,

Algeria, Egypt, Equatorial Guinea, Libya, Nigeria, Norway Oman, Qatar, and Trinidad &

Tobago, and LNG consuming countries Belgium, Dominican Republic, France, Greece,

Italy, Mexico, Portugal, Spain, Turkey, the UK, and the US (including Puerto Rico), as

well as future LNG producers Angola, Russia, Venezuela, and Yemen, and possible future

LNG consumers Brazil, Canadian East Coast, Germany and the Netherlands. [7]

The Pacific Basin LNG market consists of present LNG producers Abu Dhabi, Australia,

Brunei, Indonesia, Malaysia, Oman, Qatar, and the US (Alaska), producing projects under

construction in Peru, Russia (Sakhalin), and Yemen, and current LNG consumers China

(including Taiwan), India, Japan, and South Korea, together with future Pacific Basin LNG

producers Iran and Papua New Guinea, and future LNG importers Canadian West Coast,

Mexicos West Coast, Indonesia, Pakistan, Singapore, Thailand, and the US West Coast.

[7]

Although the Atlantic and Pacific LNG markets are beginning to blend, significant

differences between them continue to exist. LNG trade evolved differently in the Atlantic

and Pacific basins, and this continues to affect import volume, pricing systems, and

contract terms. Importing countries in the Pacific Basin are almost totally dependent on

LNG while countries in the Atlantic Basin use domestic supplies and pipeline imports as

well as LNG to meet natural gas demand. Because current LNG importers in the Pacific

Basin did not have access to domestic or piped imported gas, LNG imports into the region



increased rapidly in the 1980s and early 1990s as these countries sought alternatives to oil.

Security of supply was a more important consideration in the Pacific Basin than price. [7]

When comparing the two basins you can see that, the Pacific basin is larger, but the

Atlantic basin is growing now a bit faster. The Pacific basin is the largest LNG-producing

region in the world, supplying nearly 60 % of all global exports in 2006. Indonesia alone

supplied 14 percent. Countries in the Middle East, led by Qatar, exported 15 percent, while

countries in the Atlantic Basin, led by Algeria, exported about 38 percent that year.

Expansions in Nigeria, Trinidad and Tobago and Egypt, as well as new facilities in

Norway and Equatorial Guinea, would increase annual Atlantic Basin liquefaction capacity

significantly in the near future. [4]

The LNG import in the Pacific basin is also larger. Three countries in the Pacific Basin

(Japan, South Korea, and Taiwan) accounted for 60 percent of global LNG imports in

2006. Eight European countries (Belgium, France, Greece, Italy, Portugal, Spain, Turkey

and the UK) received 27 percent of global LNG import, and the US accounted for almost 8

percent of global LNG import in the same year. Regasification capacity continues to grow

as most Atlantic Basin importers are planning expansions. [4]



3.3 LNG exporters

Worldwide, there are 26 existing export, or liquefaction, marine terminals, located on or

off shore, in 15 countries. Countries that currently export LNG (start up date of earliest

liquefaction terminal is in parentheses) are: [5]

Algeria, Republic of (1971)

Australia, Commonwealth of (1989)

Brunei (Darussalam), State of (1972)

Equatorial Guinea, Republic of (2007)

Egypt, Arab Republic of (2004)

Indonesia, Republic of (1977)

Libya (also known as the Socialist People's Libyan Arab Jamahiriya) (1970)

Malaysia (also known as Persekutuan Tanah Malaysia) (1983)

Nigeria, Federal Republic of (1999)

Norway, Kingdom of (2007)

Oman, Sultanate of (also known as Saltanat Uman) (2000)

Qatar, State of (also known as Dawlat Qatar) (1997)

Trinidad and Tobago, Republic of (1999)

United Arab Emirates (also known as Al Imarat al-Arabiyah Al-Muttahidah) (1977)

United States of America (1969)

Asia/Pacific Basin LNG producers accounted for nearly 60 percent of total world LNG

exports in 2006. During 2006, industry reports suggest that Qatar surpassed Indonesia to

become the worlds largest LNG exporter, shipping about 15 percent of worlds total LNG

export. The majority of Qatars LNG is imported by Japan, South Korea and India with

smaller volumes going to Spain and Belgium. Indonesia was the second worlds largest

LNG producer and exporter in 2006, shipping about 14 percent of the worlds total LNG

exports. Most of Indonesias LNG is imported by Japan with smaller volumes going to

Taiwan and South Korea. Malaysia, the worlds third-largest LNG exporter, ships

primarily to Japan with smaller volumes to Taiwan, South Korea and India. Australia

exports LNG from the Northwest Shelf, primarily to supply Japanese, South Korea and

India utilities. About 90 percent of Brunei Darussalam output goes to Japanese customers.



10

The only liquefaction facility in the United States was constructed in Kenai, Alaska, in

1969, and it has exported LNG to Japan for more than 30 years. [8]

Atlantic Basin LNG producers accounted for about 38 percent of total world LNG exports

in 2006. Algeria, the worlds fourth-largest LNG exporter, serves mainly Europe (France,

Belgium, Spain, and Turkey) and the United States via Sonatrachs four liquefaction

complexes. Nigeria also exports mainly to Europe (Spain, France, Portugal, Turkey and

Belgium) but also has delivered cargos under short-term contracts to the United States.

Trinidad and Tobago exports LNG to the United States (the largest supplier of LNG to the

U.S.), Spain, the UK, Puerto Rico and the Dominican Republic. Egypt was the eighth

largest LNG exporter in 2006, shipping about 7 percent of the worlds total LNG export

mainly to Europe (Spain, France, the UK, Belgium, Greece and Italy) but also to the US

and Asian countries. Omans LNG was shipped mainly to South Korea, Japan, India and

Taiwan. Brunei, the first Asian exporter of LNG, exports mainly to Japan, with small

quantities going to South Korea. The UAE exports mainly to Japan and a small part to

India. [8]

In October 2007 Norways Snhvit plant loaded its first cargo. Snhvit is the first

Norwegian and European production and export facility for liquefied natural gas (LNG).

Most of the output from the Snhvit facility has already been contracted to El Paso for

delivery to the United States, with smaller amounts going to Iberdrola in Spain. Statoil

planed to have an initial capacity of 4.1 million ton per year and a potential expansion to

8.2 million ton per year, but series of problems at Norways Snhvit plant resulted in

slippage in the start-up of the already delayed project and restricted production to only two

cargoes in 2007. [8]

Liquefaction capacity in both regions has been increasing steadily so far, but it is expected

that planned expansion could dramatically increase liquefaction capacity in the near future.

Russia is becoming the newest Asia/Pacific Basin exporter. Its first LNG plant is under

construction on Sakhalin Island off the countrys east coast. This large facility is scheduled

to begin operation in 2008. Planned expansions of existing plants in the Atlantic Basin

could also dramatically increase its liquefaction capacity. [8]



11

Figure 3.2 World LNG exporters, January 1, 2007

Figure 3.3 World LNG importers, January1, 2007



12

3.4 LNG importers

Worldwide, there are 60 existing import, or regasification, marine terminals, on or off

shore, spread across 18 different countries. In addition to these existing terminals, there are

approximately 182 regasification terminal projects that have been either proposed or are

under construction all around the world. It is not expected that all of the proposed terminals

will be constructed. Countries that currently import LNG (start up date of earliest

regasification terminal is in parentheses) are: [5]

Belgium, Kingdom of (1987)

China, People's Republic of (2006)

Dominican Republic (2003)

France (also known as the French Republic) (1972)

Greece (also known as the Hellenic Republic) (2000)

India, Republic of (2004)

Italy (also known as the Italian Republic) (1971)

Japan (also known as Nihon, Nippon, Nihon Koku) (1969)

Mexico (also known as the United Mexican States) (2006)

Portugal (also known as the Portuguese Republic) (2003)

Puerto Rico, Commonwealth of (U.S. Outlying Territory) (2000)

South Korea, Republic of (1986)

Spain, Kingdom of (1969)

Taiwan (Republic of China) (1990)

Turkey, Republic of (1992)

United Kingdom (2005)

United States of America (1971) Four countries in the Asia/Pacific BasinJapan, South Korea, India and Taiwan

accounted for almost 64 percent of global LNG imports, while Atlantic Basin LNG

importers took delivery of the remaining 36 percent. Japan remains the worlds largest

LNG consumer, although its share of global LNG trade has fallen slightly over the past

decade as the global market has grown. Japans largest LNG suppliers are Indonesia

Malaysia, Australia, Brunei, Qatar and UAE, with substantial volumes also imported



13

Africa, Trinidad and Tobago and USA. South Korea, the second-highest LNG importer in

the world behind Japan, currently gets most of its LNG from Qatar, Malaysia, Oman and

Indonesia with smaller volumes coming from Australia, Brunei, and Egypt. CPC operates

Taiwan's only LNG receiving terminal at Yungan township of Kaohsiung, where LNG is

imported from Indonesia and Malaysia, with smaller volumes from Australia, Nigeria,

Egypt and Oman. India has started receiving LNG shipments in January 2004 with the

start-up of the Dahej terminal in Gujarat state. Currently India is becoming one of the most

important LNG players in the world, shipping mainly from Qatar, with small quantities

from Oman, Egypt, the UEA, Algeria, Nigeria and Australia. Spain has one of the worlds

most rapidly growing natural gas markets, being the biggest LNG importer in Europe. In

2006 Spain received about 11.5 percent of the worlds total LNG import, mainly from

Africans countries such as Nigeria, Egypt, Algeria and Libya, but also from Qatar,

Trinidad and Tobago and Oman. Most French LNG imports come from Algeria, with

smaller quantities from Nigeria and Egypt. Italy and Turkey receive LNG mainly from

Algeria with smaller quantities from Nigeria and Egypt. Belgium has one regasification

terminal and receives most of its LNG from Algeria. [8]

Imports by Atlantic Basin countries are expected to grow as many expand storage and

regasification terminal capacity. France is constructing a new, offshore LNG receiving

terminal at Fos Cavaou, and Exxon Mobil has also proposed building an LNG import

terminal near Fos Cavaou by 2009. However the greatest growth in LNG import capacity

is expected in the U.S. and in the United Kingdom. The US currently gets most of its LNG

from Trinidad and Tobago, with smaller quantities from Egypt, Nigeria, Algeria and

Norway. The US is planning to build four new LNG regasification terminals on the

Atlantic and Gulf Coasts from 2007 through 2010 to meet the 58-percent increase in LNG

imports that is projected for that timeframe. Currently, the UK has a single LNG import

terminal, the NGTs Grain LNG on the Isle of Grain and imports mainly from Algeria with

smaller quantities from Egypt and Trinidad and Tobago. Exxon Mobil and Qatar

Petroleum have received regulatory approval for the South Hook LNG receiving terminal

in Milton Haven, Wales. The terminal will receive its LNG from the Qatargas II

liquefaction project in Ras Laffin. Finally, BG has collaborated with Netherlands-based

Petroplus and Malaysia-based Petronas to also build an LNG receiving terminal in Milton

Haven, on the site of an existing natural gas storage facility owned by Petroplus. [8]



14

3.5 Growing world LNG trade

The number of countries involved in the LNG trade has expanded significantly in recent

years. In 1995, there were 8 LNG exporting countries and 9 LNG importing countries. By

2008, this had increased to 15 exporting countries and 18 importing countries, with even

more countries in the process of developing infrastructure to either export or import LNG

in the near future. The market also saw significant expansion in delivered quantities of

LNG during this time period, growing by 7.3% per year, or almost doubling to 211 billion

cubic metres in 2006. [9]

The international trade in LNG will continue to grow in coming years. The price of natural

gas has been growing in recent years when the costs of liquefying, transporting, and

regasifying LNG have fallen significantly. Rising gas import demand, especially in North

America, desire to making gas market more diverse and also the desire of gas producers

to monetize their gas reserves is setting the stage for increased LNG trade in the

years ahead. [9]

Continued expansion of demand has motivated an interest in expanding the role of LNG

imports. The traditional consuming natural gas markets in Asia (Japan, Taiwan and South

Korea) have virtually no indigenous production and, as a result, those countries rely

principally on LNG for gas supply. The production in the US, Canada and Mexico has

remained almost flat. This is especially telling given the continuous increases in drilling

activity in recent years, and higher gas prices providing incentive to develop more costly

unconventional natural gas resources in significant quantities. In Western Europe, the

North Sea gas fields and the onshore fields in France, Germany and Italy are in decline, or

has begun slowed considerably in recent years. Therefore, all three traditional OECD

natural gas markets are faced with the need to secure gas supplies from other sources in

order to satisfy growth in demand. [9]

Large distances between potential producers and consumers favour using the LNG

infrastructure. The majority of worlds natural gas resources are in the Middle East,

Central Asia and Russia with the traditional gas markets in OECD countries accounting for

less than 10% of the global reserve base. Some significant resources are also in Africa,



15

Latin America and Southeast Asia. However, each of these regions is distant from the

major consuming markets in North America, Europe and Asia. Because of the distance gas

cannot practically or economically be transported in its gaseous state via pipeline. Thus,

LNG provides a means of linking remote gas to markets. Moreover consumers in OECD

Europe have an additional incentive to diversify sources of supply to LNG imports, driven

by fears of over-reliance on gas supply from Russia. Concerns arise from potential supply

disruptions caused by Russian disputes with transit countries as well as longer term

concerns over whether Russia will be able to invest sufficiently to maintain export

capacity, particularly if its domestic consumption continues strong growth. [9]

Emerging natural gas markets, such as China and India, are set to grow rapidly, albeit

from a low base, and will also require increases in imports. Both have LNG and pipeline

options, but geopolitical pressures make it probable that LNG will represent a significant

share of supply to each of these emerging gas markets. Longer supply chains from a

relatively concentrated number of suppliers may lead to an increase in vulnerability to

supply disruption because of technical, logistical or geopolitical incidents. [9]

All the consideration showed above leads to consensus that LNG trade will grow faster

than natural gas demand. The World Energy Outlook by the IEA (2006) expects LNG

trade to grow by 6.6% per year between 2004 and 2030, from 90 BCM (8.7 BCF/day) to

470 BCM (45.5 BCF/day). By comparison world natural gas demand is projected to

increase by 2% per year, meaning the contribution of LNG to meeting demand is expected

to grow substantially. In fact, the IEA projects that LNG will account for 70% of the

increase in gas trade by 2030. If this were to happen, LNG would make up 50% of

internationally traded gas by 2030, compared to around 22% in 2004. [9]



16

3.6 Small-scale LNG trend

The LNG market is dominated by a large-scale LNG value chain. Typically an LNG

production and distribution system is a huge investment. Since all these investments have

to be in place before the gas can move to market, LNG developments usually require long-

term contracts with specific customers to secure financing. These contracts normally

specify delivery of gas to a particular location for a duration of 20-25 years. Historically,

LNG has almost exclusively been consumed by big power plants and, to some extent,

supplied to gas grids for domestic consumption in densely populated areas. [9]

We are now seeing some new possibilities for trading of LNG. Many places there are also

reserves of "stranded" natural gas-resources that are abandoned because currently there is

no economical way to get it to the markets. With natural gas becoming such an important

and marketable commodity, producers would like to recover and get some value out of

these resources which to a certain degree already are partly processed. As a way to meet

these demands there is a growing interest in small scale LNG process and plant solutions to

help solve the challenges mentioned above from a number of countries on almost all

continents. [10]

Small-scale distribution of LNG is a new approach. The source for LNG could be a small-

scale LNG production facility, either a base-load LNG plant or an LNG receiving terminal.

According to data provided by Gasnor (2007) production capacities of small scale LNG

plants vary in the range from 2000 up to 500 000 tons of LNG per year. By comparison, a

typical large scale plant has a production capacity of between 2.5 and 7.5 million tons of

LNG per year. Compared to the large-scale LNG market, small-scale LNG distribution

system would use smaller ships, in the range from 1 500 m3 to around 10 000 m3 LNG

(Gasnor 2007). The receiving facilities and local storage tanks are based on a modular

design in order to support standardized solutions with good scalability. Small-scale LNG is

mainly delivered to industrial end users, but can be also delivered to smaller domestic

users and as fuel for vehicles (mainly buses and heavy duty trucks). [11]

Small-scale distribution of LNG gives many profits to new categories of consumers.

Small-scale LNG could become cost-competitive with alternatives such as fuel oils. This



17

could make natural gas available in regions with lower levels of demand than are

commercially viable with pipelines or larger ships. Small-scale LNG is flexible, can cover

widely dispersed demand at modest investment cost, is suitable to relatively small volumes

of gas, and allows for competition. There are important environmental benefits to be

gained from replacing oil fuel with gas: emissions of CO2, NOx, SOx and particulate

matters are significantly reduced. This alternative may be an important contribution to

reaching ambitious targets for reducing emissions to the atmosphere from human activities.

That is also why this development is capturing the attention and interest of high-ranking

politicians around the world. [12]

Nowadays in Norway you can see a great interest of the small-scale distribution of LNG.

Norway is rich in energy resources, particularly oil and gas, but a country with a somewhat

difficult geography. Oil and gas have been produced since 1971, but only offshore. Thus

all major pipelines are offshore, only on-shore for few kilometres to receiving terminals.

However these few kilometres of large pipelines do not form an integrated onshore grid,

they provide the opportunity for taking out some gas and distributing it locally.

Transporting liquid natural gas in bulk (LNG) is emphasized as the most appropriate

solution for a country with the topography and population pattern of Norway. LNG is also

the most suitable fuel for vessel and ship operators who are concerned about costs and

environment.

The small-scale distribution system for LNG in Norway is dominated by Gasnor. Gasnor

established two production facilities for LNG at Karmy and at Kollsnes and now is

building a third production plant for LNG at Kollsnes. At these LNG plants, a high

pressure gas is received from an export pipeline (Statpipe and Troll). Gasnor operates one

small LNG vessel and one another should be delivered in autumn 2008. The LNG is stored

in local terminals, and distributed to the end user through a pipeline. Some of the local

terminals are designed for one single industrial user, but mainly the terminals are designed

as a regional terminal for several customers and/or further distribution by tank lorries.

Gasnor also deliver LNG to other gas distribution companies in Norway, and some LNG as

fuel for heavy duty trucks and buses in England and Sweden. Nowadays in Norway there

are about 30 LNG small-scale LNG terminals in operation. [13]



18

4 LNG storage tanks

4.1 Background

There are variety of types of LNG tanks throughout the world according to energy needs

and site environment. All of these tanks have to fulfil three basic functions:

the liquefied gas must be stored without leakage,

the heat absorption of the gas must be kept as small as possible,

the tank must be leak tight in both directions (should prevent LNG from leakage

and also should prevent any impurities from entering the tank)

In general, storage tanks are broken down to three categories: underground storage tanks,

in-ground storage tanks and above ground storage tanks as shown in Figure 4.1.

Figure 4.1 Various types of LNG tanks [15]

In Europe the above ground storage tanks have been adopted by most recent LNG projects.

The above ground storage tanks can be subdivided, according to structural details in: single

containment tanks (SCT), double containment tanks (DCT), full containment tanks (FCT)

and full containment membrane tanks.

Due to the high costs and schedule implications of constructing traditional storage tanks

some new LNG storage techniques are still developed. Two projects of modern LNG

storage tanks are presented in this work. They are the All-concrete LNG (ACLNG) tank,

developed by Arup Energy, and concrete/concrete LNG tank (C/C tank), presented by

StatoilHydro.



19

4.2 Single containment tanks (SCT)

A conventional single containment LNG storage tank consists of a suitable cryogenic metal

inner container (economic current favour 9% nickel steel) designed to hold the LNG, with

a carbon steel outer tank designed to contain the natural gas vapours at pressures up to 2.5

psig (0.17 bar), and a steel roof. This design pressure can be increased with additional

engineering of the top roof to the wall joint, but at additional cost. The required distance

between the bund and the tank adds significantly to the total land area. Insulations

surround the inner tank to control heat leak into the tank. The outer tank is not designed to

contain the LNG in the event of an inner tank leak. A secondary means of LNG

containment (in case of a rupture of the inner tank) is generally provided, such as

engineered earthen dike design to contain 110% of the full volume of LNG from the inner

tank. Single containment tanks were the first type developed and are now used mainly in

remote locations. [14]

Figure 4.2 Features of a typical single containment LNG tank.



20

Advantages: [14]

Generally the lowest installed cost per cubic meter of LNG storage (the cost of SCT

is about 65% that of a corresponding FCT).

Faster schedule, engineering and construction schedule can usually be reduced by

several months from the typical 36 months for FCT.

Regulatory approval of SCT designs has been consistent over the years and not a

cause for approval delays.

Side and bottom LNG outlets can be used as long as certain other requirements are

met.

Disadvantages: [14]

In the event of an inner tank failure or spill, the outer tank steel shell will not

contain the LNG and the vapours will be free to go to atmosphere.

Requires an external dike for secondary LNG containment; typically the large,

engineered earthen dike to contain 110% of the full contents of the LNG tank.

Thermal radiation and vapour dispersion zones are very large and this tank requires

a very large tract of land, highest for the conventional designs.

These tanks have lower design pressures than full containment tanks. The lower

pressure design results in increased size and the cost of the vapour handling system.

Added maintenance costs to periodically repair and recoat the outer tank paint

system to prevent corrosion.

A system needs to be designed to remove accumulated storm water runoff from

inside the secondary containment dike.

Poor resistance to external forces such as flying debris; breach of outer shell is

more likely than other tank designs considered.



21

4.3 Double containment tanks (DCT)

A conventional double containment LNG storage tank is essentially a single containment

tank surrounded by a close-in, reinforced open top concrete outer container design to

contain all spill or leak from the inner tank, but not to hold any vapour realized during a

spill. Like a SCT DCT consists of a suitable cryogenic metal inner container (economics

currently favour 9% nickel steel) designed to hold the LNG, with a carbon steel outer tank

designed to contain the natural gas vapours at pressures up to 2.5 psig (0.17 bar), and a

steel roof. This design pressure can be increased with additional engineering of the top roof

to the wall joint, but at additional cost. Insulations surround the inner tank to control heat

leak into the tank. The outer tank is not designed to contain the LNG in the event of an

inner tank leak. In addition to this outer carbon steel wall, the DCT design also includes a

concrete outer container which functions as a secondary means of LNG containment. This

outer container is an engineered reinforced concrete cylinder surrounding the outer carbon

steel tank shell and is designed to contain the full tank volume plus some safety margin.

[14]

Figure 4.3 Features of a typical double containment LNG tank.



22

Advantages: [14]

Lower installed cost per cubic meter of LNG storage than FCT.

Engineering and construction schedule can likely be reduced by several months

from the typical 36 months for FCT.

Regulatory approval of DCT design has set a precedent for future approvals.

Smaller thermal exclusion zones and reduced conventional onshore land

requirement (due to protection provided by outermost concrete container), similar

to FCT, but at a lower cost than FCT.

Resistance to external forces is improved with the high reinforced concrete dike.

Disadvantages: [14]

Higher installed cost per cubic meter of LNG storage than SCT.

In the event of the inner tank failure or spill, the outer tank steel shell will not

contain the LNG and the vapours will be free to go to atmosphere due to the open

top of the high concrete secondary containment wall.

Lower pressure design in the same as SCT, this increases the size and cost of the

vapour handling system when compared to FCT.

Increased soil bearing requirements (over SCT) and higher foundation, loads due

to the weight of the outer concrete containment dike.

Added maintenance cost to periodically repair and recoat the outer tank paint

system to prevent corrosion.

System need to be designed to remove accumulated storm water runoff from

inside the secondary containment dike.

Personnel entry into the annular space between the outer tank shell and the

concrete dike for maintenances is generally considered as a confined space and

requires special procedures.



23

4.4 Full containment tanks (FCT)

A conventional full containment LNG storage tank consists of a suitable cryogenic metal

liner container (economics currently favour 9% nickel steel) designed to hold the LNG,

with a reinforced concrete outer tank designed to contain the natural gas vapours at

pressures up to 4.3 psig (0.3 bar), and a reinforced concrete roof. The outer concrete tank is

also designed to contain cryogenic LNG in the event of an inner tank leak or rupture.

Insulation surrounds the inner tank to control heat leak into the tank. Different types of

insulation are used in different parts of the tank. Typically, the annular space between the

inner and outer tanks is filled with loose perlite. In addition, a resilient blanket, such as

fibreglass material, is installed on the outside of the inner tank. This blanket provides

resiliency of the perlite. The reinforced concrete roof is lined with carbon steel, with the

liner also functioning as framework for the concrete. Heat leak from the roof of the tank is

limited by installing insulation on the suspended deck (which is suspended from the roof).

There is no insulation immediately beneath the roof, and the vapour space between the

suspended deck and the tank roof will be close to ambient temperature. For the bottom

insulation most of the LNG tanks use cellular glass (foam glass). [14]

Figure 4.4 Features of a typical full containment LNG tank.



24

Advantages: [14]

Highest integrity design: in the event of the inner tank failure, the outer tank is

design to contain both an LNG spill and the vapour generated.

No side or bottom penetration; all pipelines pass through the roof, so in the event of

external pipeline failure the tank contents do not spill out of the tank.

Smallest thermal exclusion zone; resulting in the smallest footprint, tank spacing

and the most efficient use of land. Also land required to be under control of the

owner to avoid problems related to adjacent properties is minimized.

Inherent higher pressure capabilities than either SCT or DCT; allows the use of

smaller capacity vapour handling system, reducing the capital and operating costs

for the vapour recovery system.

Best resistance to external forces with complete reinforced concrete outer shell.

Concrete finish minimizes coating maintenance of the outer tank.

Concrete shell can be designed to withstand realistic impacts from missiles or

flying objects.

The effect of cold-shock, if any, will most likely be restricted to a small area, and

generally should not affect the vapour-tight integrity of the tank.

Disadvantages: [14]

Highest cost per cubic meter of LNG for the conventional flat-bottomed tank

designs.

Marginally the longest engineering and construction schedule (nominally 36

months from tank contractor approval to proceed).

Increased soil bearing requirements and foundation loads compared to SCT due to

the higher weight for the outer concrete wall.

Tank profile is roughly the same as the SCT and DCT designs.



25

4.5 Membrane tanks

A conventional full containment membrane tank consists of a cylindrical thin metal

membrane primary container, designed to hold LNG. This inner membrane tank is

structurally supported by an outer pre-stressed concrete cylindrical tank. The outer

concrete tank also serves as the secondary leak containment. Insulation surrounds the inner

tank to control heat leak into the tank. The reinforced concrete roof is lined with carbon

steel, with the liner also functioning as framework for the concrete, just like in ordinary

full containment system. Applications of membrane tanks have been far less than the other

types of tanks except in Japan and Korea. [15]

The side wall and bottom slab of membrane storage tank has a multiplex structure with

three layers: reinforced concrete, insulation and a membrane, as shown in Figure 4.5.

Figure 4.5 Membrane LNG storage tank multiples structure. [15]

(1) A two millimetre membrane layer maintains LNG and gas tightness. The

membrane is corrugated to absorb contraction due to the difference in ambient

temperature and LNG temperature which is minus 162 degrees Celsius. [15]

(2) Rigid polyurethane foam (PUF) insulation restricts the permeation of heat from

outside and transfers the internal gas and LNG pressure exerted on the tank side

wall and bottom slab. [15]



26

(3) Reinforced concrete layer, which support all structure and it is also designed to

contain cryogenic LNG in the event of an inner tank leak or rupture. [15]

Advantages: [15]

A membrane-type tank is characterized by higher flexibility in storage capacity

comparing to the 9% Ni type.

A membrane-type tank system can be built inside the gravity-based structures to

provide a relatively large storage volume.

Lower material costs due to less steel consumption comparing to the 9% Ni type.

Disadvantages: [15]

Because the wall insulation system on a membrane tank is also a structural

component its efficiency is only about one-half of the wall insulation on a full

containment tank. Lower thermal efficiency creates boil-off gas that must be

removed by compressors.

Construction of membrane tanks are more labour intensive and require higher

skilled workers.

The membrane on an LNG tank is only 1.5 mm thick which makes it more likely to

be damaged during construction. The thickness of inner tank plates for a full

containment tank average about 25 mm.

However, a membrane-type tank requires a sequential construction schedule

wherein the outer concrete structure has to be completely built before the insulation

and the membrane can be installed within a cavity within the outer structure. This

normally requires a long construction period which adds substantially to the costs.

Membrane-type tanks are designed by principles known as "experimental design".

Where new shapes and sizes are required or when different environmental and/or

seismic loading conditions are to be encountered, the satisfactory performance of

membrane-type tanks at various LNG levels is difficult to insure.



27

4.6 New LNG storage technologies

Metal-lined concrete tanks have been used for the primary containment of LNG for many

years. However, these types of tanks are very expensive. LNG storage tanks account for a

large portion, often up to a third or more, of the cost of a LNG terminal. Moreover the

speed of delivery of an LNG terminal usually depends on the time to construct the tanks.

This is most evident at import terminals. Traditional tank solutions must be built in a

sequential manner with the secondary container being advanced to a considerable degree

before the primary container can start in earnest. Due to the cost and schedule implications

of constructing traditional storage tanks, every possible effort is made to reduce material

and time-related costs. Two of the modern solutions, which can reduce construction time

and costs significantly, are presented below.

ACLNG tanks

The All-concrete LNG (ACLNG) tank was originally developed in-house by Arup

Energy. A proposed ACLNG storage tank consist of primary containment walls and slab

constructed in post-tensioned reinforced concrete without a liner and a secondary container

in post-tensioned reinforced concrete with a moisture vapour barrier applied. The joint

between primary container walls and the slab is monolithic. Base insulation is formed of

weather-proofed blocks and a secondary bottom is ideally constructed from a non-metallic

material such as a Mylar sandwich. The secondary container and foundation

arrangements are essentially identical to those of conventional 9% Ni tanks. Variations

from a conventional tank are needed to suit the primary container geometry and the chosen

construction method. [16]

Construction of concrete primary containers without a metallic liner was made possible by

examining concretes permeability in cryogenic conditions. Concrete exhibits excellent

performance at cryogenic temperatures, many properties improving as the temperature

falls. A key design parameter is the permeability of concrete, as this affects the total

quantity of LNG lost from the primary container. This must be added to the boil-off gas to

assess the operational performance of the tank. The most definitive tests performed

demonstrated that an intrinsic permeability, K', of 10-18 m could be obtained for typical

concrete mix designs and that a permeability as low as 10-19 was possible. Concrete mix



28

design does not require special consideration, although aggregates having similar

coefficients of thermal contraction to cement paste are preferable. Water-cement ratios

should not exceed 0.45. Admixtures such as silica fume that reduce permeability can be

considered if readily available in country. [16]

Figure 4.6 ACLNG tank details [16]

Potential advantages: [16]

The ability to construct the primary and secondary containers in parallel and the

elimination of metallic liners considerably shortens the construction schedule

compared to conventional 9% Ni tanks.

Cost differentials increase where construction takes place in less developed

countries.



29

The overall delivery schedule of the All-concrete tank is 25 months from contract

award to ready-for-cool-down.

The use of weather-proof insulation materials permits the insulation works to

proceed before the tank walls and roof have been constructed

The adoption of a non-metallic secondary bottom minimizes the need for specialist

steel fabricators associated with 9% Ni tanks

Substantial cost savings could be realized when the concept becomes established in

the market place

Potential disadvantages: [16]

The perception of concrete is that it will crack and leak and this will cause extra

quantity of LNG lost from the primary container.

Use of slipform construction demands a very high level of planning and preparation

not normally associated with static forms, since once started the slide will continue

to the top of the wall in one continuous operation, what sometimes is hard to put

into practice.

Material supply to the slipform is critical to the continuous operation. Concrete

batch plants must have redundant capacity. Reinforcement must be bent and clearly

tagged and stored for delivery to the form with at least 3 days supply available,

what can give some extra challenges.

Construction of ACLNG tank is the challenge of civil engineering and requires

higher skilled workers.

It is a new technology, which has been never confirmed in practice before, so it can

cause some maintenance problems.

C/C tanks

The concrete/concrete (C/C) tank was originally developed by StatoilHydro. CryoTank is a

registered trademark in Norway, and the inner tank (liquid containment) is a unique

solution patented world wide. It is a land based Full Containment tank which complies

with standard EN 14620, and also to the near finished recommendations from the EEMUA.

The patented design principle concerns the inner tank or the liquid containment. The

sandwich wall is the key solution, with an outer reinforced concrete layer, which for big

tanks is supplied with pre-stressing. A 1-millimeter high ductile metallic sheet liner is



30

completely welded to each other and to the bottom steel wall base on which the concrete

wall rests. The last inner layer is also concrete which secures stable form and protection of

the liner against impact and fatigue forces. The bottom steel plate is conventional and

welded to the wall steel base. The containment is then liquid sealed. There are no particular

requirements to the concrete quality and the amount of pre-stressing, apart from having

sufficient strength. All reinforcement in the inner tank is Cryobar. [17]

The outer tank can be conventional, or the thick carbon steel liner of the outer tank can be

substituted by ductile metallic steel sheet liner of the same material as the inner tank liner

substituted the thick carbon steel liner of the outer tank. This outer liner is welded to a new

type of vertical liner strips that again are anchored in the concrete. The dome is

conventional. The bottom of the outer tank can be also improved. Carbon steel is

substituted by 5-millimeter ductile steel plates, which also cover the tank wall five metres

up from the bottom. Foam glass insulation is put behind the ductile bottom plate and

placed inside the wall and underneath the bottom. Insulation protects the concrete corner in

case of LNG pooling. Hence the commonly used extra bottom for corner protection is not

required. The wall insulation is about twice the thickness of conventional tanks. This is

governed by necessary space to operate when erecting the liners. Other insulation is

conventional. [17]

Potential advantages: [17]

CryoTank tanks can be more than twice as large as conventional tanks, i.e. larger

than 400,000 m3. This increased size can be achieved by minor increased diameter

and increased height. This implies smaller footprint as well as less costly and time-

consuming construction.

The construction time will be reduced by 6 -12 months. For import terminals this

implies early sale and increased present value.

A CryoTank of the same size as a conventional tank will be 10 to 20% cheaper.

Increasing the size, fewer tanks are necessary. Substituting three smaller tanks with

two larger tanks reduces cost by 30 to 40 %.

CryoTank can be made more resistant to earthquake. Sloshing breakers can also be

installed.

Reliability against leakage with the welded steel liner.



31

CryoTank has double insulation in the walls compared to conventional tanks. More

insulation combined with increased height gives smaller surface and the boil-off is

reduced to the half of what standards require.

Potential disadvantages: [17]

Use of slipform construction demands a very high level of planning and preparation

not normally associated with static forms.

Construction method for thin plate liners is especially developed for the CryoTank

so it requires higher skilled workers.

It is a new technology, which has been never confirmed in practice before, so it can

cause some maintenance problems.

Figure 4.7 A CryoTank design [17]



32

5 LNG vessel types

5.1 Evolution of LNG fleet

The LNG carrier (Liquefied Natural Gas) is product of the late twentieth century. LNG

carrier is a ship designed for transporting liquefied natural gas (LNG). LNG carriers have

two principal parts, the basic ship comprising the hull and propulsion plant, and the

cryogenic section consisting of containment tanks and cargo handling arrangements. They

are double-hulled, and specially designed and insulated to prevent leakage or rupture in an

accident. The LNG is stored in a special containment system within the inner hull where it

is kept at pressure in the range of 1,060 to 1,080 millibar (absolute) and -160C. [25]

Gas carrier tanks, according to International Maritime Organization (IMO) rules, must be

one of three types. Those are ones built according to standard oil tank design (Type A),

others that are of pressure vessel design (Type C), and, finally, tanks that are neither of the

first two types (Type B). All LNG tanks are Type B from the Coast Guard perspective,

because Type B tanks must be designed without any general assumptions that go into

designing the other tank types. There are three general Type B tank designs for LNG. The

first type of design, the membrane tank, is supported by the hold it occupies. The other two

designs, spherical and prismatic, are self-supporting. [18]

Figure 5.1 Changes of LNG cargo tanks types. [19]



33

Existing LNG carriers cargo containments systems reflect one of two main designs:

spherical design produced by Kvaerner-Moss, and membrane design by two firms:

Technigaz and Gaz Transport. Figure 5.1 shows that spherical design was used by most of

LNG ships till 2003. Nowadays there are ordered 21 of 145 new vessels with Moss tanks

only and the rest are being built with membrane design. Technigaz technology will be

installed in 44% of new buildings and 41% new LNG carriers will be equipped with Gaz

Transport membrane. [19]

LNG fleet is in the midst of an unprecedented expansion. At December 2000 there were

119 vessels of summary tanks capacity 12,003 MSCM. The prediction was that in 2005

would be 148 LNG carriers and 172 ships in 2010. Nobody predicted that LNG market

would start develop so quickly. At the beginning of XXI century some new players entered

LNG market. They ordered a lot of ships to serve their new LNG projects. These ships

started to be delivered in 2003 17 new vessels, in 2004 20 and in 2005 - 29. At the end

of 2005 LNG fleet comprised 195 ships (47 more then was predicted in 2000) of summary

tanks capacity 23,143 MSCM. 224 LNG carriers were sailed across the oceans on 1st

March 2007 and they were able to carry 27,279.5 MSCM liquefied natural gas. New orders

will boost the global LNG fleet to over 300 vessels in 2008, and to 369 at the end of 2010.

[19]

Figure 5.2 Age of LNG fleet [19]



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5.2 Kvaerner - Moss spherical tanks

This is the most well known tank that many people equate with the appearance of an LNG

carrier. The large spherical tanks, almost half of which appear to protrude above a ship's

deck, is often what people visualize when someone says "LNG carrier." The early sphere

designs were shells of 9-percent nickel steel. Subsequently, aluminium was used. The

sphere is installed in its own hold of a double-hulled ship, so that it is supported around its

equator by a steel cylinder (called a skirt). The covered insulation surrounding the sphere

can channel any leakage to a drip tray located under the sphere's "south pole." [18]

Figure 5.3 LNG carrier equipped with Moss tanks. [20]

(1) Moss spherical tanks - developed by Norwegian firm Moss Rosenberg Verft AS (now

Moss Maritime). [20]

(2) Tank material, aluminium alloy. [20]

(3) Tank dome, located at the top of the tank, it contains the entrance for servicing, as well

as for the various pipes that go inside the tank. [20]

(4) Tank thickness, between 25 and 60 mm (150 mm at the equatorial rings). [20]



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(5) Thermal insulation features, Moss tanks are covered with thermal insulation panels

(200 to 300 mm thick). Each multilayer panel is comprised of phenolic resin foam on

the low-temperature side (tank side), polyurethane foam on the ambient temperature

side, and aluminium-plastic sheet on the exterior. [20]

(6) Pipe tower, made with the same materials as the tanks, this shaft, about 3 m in

diameter, is placed vertically in the middle of the tank to accommodate

loading/unloading pipes, cargo pumps (located at the bottom of the shaft) to discharge

LNG to onshore facilities, stairs and instrumentation. [20]

(7) Contraction, when loaded with LNG of approx. 162C, the tank contracts about 150

mm in diameter. However, this deformation is absorbed by contractions of the

cylinder-shaped support at the equator of the tank.[20]

(8) Cylinder-shaped support, in order to reduce the entrance of heat into the tank, part of

the structure is made of stainless steel (thermal brake).[20]

(9) Propulsion plant (can use the boil-off gas). [20]

Some of the known advantages, from an operators viewpoint, for spherical tanks are: they

cause no operational problems, they show a great tolerance in the event of faulty operation

and an inherent ability to limit the consequences of damage, and they can be pressurized

for emergency discharge of LNG or as an alternate to pumping.

Some of the known disadvantages are: they protrude through the deck and cause a

visibility problem from the bridge, have a higher centre of gravity, have a higher boil-off

rate. In addition the older 9-percent nickel steel tanks have shown significant amounts of

swallow cracking after years of service. The cracks develop next to the welds due to the

effect of the heat of the welding on the original material (known as the "heat-affected

zone''). The cracks can be repaired by gouging them out and welding in new material.

Aluminium tanks can have a different cracking problem. Attaching the aluminium tank to a

steel cylinder is a difficult process, due to the metals involved, and cracks are liable to

develop where those materials are joined.



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5.3 Membrane tanks

In general membrane cargo tanks are composed of a layer of metal (primary barrier), a

layer of insulation, another liquid-proof layer, and another layer of insulation. Those

several layers are then attached to the walls of the externally framed hold. There are three

types of "Membrane" type, which are "TGZ Mark III system" (this design is originally by

Technigaz), "GT NO96 system" (this is Gaz Transport's tank design) and "CS 1 system".

"CS 1 system" is a new system which adopts merits of both "TGZ Mark III system" and

"GT NO96 system".

GTT Mark III

First sealing barrier is made of a stainless steel with waffles to absorb the thermal

contraction when the tank is cooled down. Second sealing barrier, made of Triplex, has a

function of preventing the cargo from leaking out during a predetermined period of time

when the primary barrier is broken down. The insulation layers are made of polyurethane

foam. Plywood is installed between the first and second sealing barriers and the first and

second insulation barriers, allows constant load to be applied to the sealing barriers due

Boil-Off in Large and Small Scale LNG Chains

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