Introduction to LNG - Bruno Bronzan

8/21/2019 Introduction to LNG - Bruno Bronzan

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PREFACE

The main purpose of this book is to introduce readers to the world of LNG. The book

generally describes whole chain of LNG: production, transport and delivery to

consumers. The book is assigned, in the first place, to the officers and crew sailing on

these most challenging merchants ships and then to all others whose wonder to know

what these three letters really means.

A ship at sea depends upon the knowledge, skills and selfreliance of the crew to carry

out necessary operation and maintenance. !ne of the most important skills is a prompt

respond to any problem. To achieve that you first must to be well informed.

"ntention of this book is not to be operation manual than to be reading matter about

LNG and LNG ships written by someone who sail on this ships.

#or the onboard specific problems you must read ship operation manuals. This

$nglish edition of the book builds upon earlier %roatian edition. &ome chapter has

been e'panded to include many news and updated information. The author would beglad to hear about all ob(ections.

The author e'press his deeply grateful to all persons helped him in preparation and

review of this book.

BIOGRAPHY

)runo )ron*an was born on April +, -/0.in 1ubrovnik, 2epublic of %roatia. The

primary school education he completed in &ara(evo, 2epublic of )osnia and

3er*egovina. The secondary marine school 4marine engineering5 he completed in

1ubrovnik. 3e sailed as an Assistant 6arine $ngineer on the ships of 7Atlantska

plovidba 1ubrovnik8, and thereupon passed an e'amination for a 6arine $ngineer.

"n -0 he enrolled the &ara(evo 9niversity &chool !f 6achinery. 3e graduated from

this &chool of 6achinery, ma(or in 6otors and 6otor ehicles. 3e graduated from

this &chool in -+ by defending his graduate thesis titled: 7#unctional ;arameters

Analy*e of 6otor alve Gear 1istributor &ystem.7

&ince uid Natural

Gas of the Algerian company &ociete Nationale du Transport 6aritime des

3ydrocarbures et des ;roduits %himi>ues. "n


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INTRODUCTION

According world biggest energy companies and world energy strategy burning natural

gas is something we shall do more and more in +- st century. The natural gas as a clean

energy is way to keep running present level of industrial production, increaseindustrial production in less developed countries and in same time decrease level of

air pollution. Air pollution is one of essential alarms that switch on gas burning

instead oil and coal burning. %!+ emission control is recogni*ed as the essential issue

related to the greenhouse effect. 9se of natural gas must be e'panded because it

produces less %!+ emission than any other fossil fuel. The countries and the

companies that recogni*ed this fact and invested in LNG business en(oy today

advantage of that good decision.

Transporting natural gas over long distance by pipeline is very costly. LNG transport

by ships provide cheaper and more fle'ible link between resources and markets.

1emand for LNG is e'pected to increase more than double over the ne't decade. "n

this book you can find general introduction to LNG world.The book is divided in four main parts:

• general introduction about natural gas and LNG production, consumption and trade

• production of LNG including preparation of row gas for li>uefaction, li>uefaction

process and storage

• transportation by ships,

• LNG receiving terminals including regasification and distribution to consumers.

"n first part readers are generally informed about natural gas, composition and

formation, reasons for li>uefactions, chains of LNG and LNG trade. There are more

and more production plants and receiving terminals in the world. LNG carrierscoming out from shipyards without long term contracts. LNG production and

transportation reduction cost has become ma(or topic.

"n second part are described: properties of methane , natural gas and li>uefied natural

gasB how to prepare natural gas for li>uefactionB theoretical and real process of

li>uefaction. The different types of LNG storage tanks are presented.

"n third part reader can find everything about LNG transport by ships includingB cargo

containment systems, cargo and machinery e>uipment, cargo operation, gas burning,

propulsion plant. !ne of the most important parameter in LNG carriers e'ploitation is

coefficient of evaporation or so called boil off. "t is interesting to see how this

parameter change with change of cargo tanks insulation thickness and what is optimal

insulation thickness. Analyses of optimal system parameters and calculation of cargotanks optimal insulation thickness is presented in this part.

"n forth part are described: receiving terminals with base process characteristics,

future floating receiving terminals, peak shaving plants, LNG satellite stations and

actual and future consumers of natural gas. !ne of the most important potential

consumers are natural gas vehicles NG what can have great impact on LNG trade.

The industrialised world suffer from heavy air pollution, especially in big cities and

mainly from e'haust gases from vehicles. Nowadays practically every car company

has one or more types of NG developed although not yet available on the market.

+


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CONTENTS

;reface

)iography"ntroduction

I

-.-. %omposition and natural gas formationCCCCCC.

-.+. Natural gas sourcesCCCCCCCCCCCCCC

-.. Natural gas useCCCCCCCCCCCCCCC..

-.=. 2easons for li>uefaction CCCCC..CCC..CC.--

-./. ;roduction plants CCCCCCCCCCCCCC--

-.?. LNG carriersCCCCCCCCCCCCCCCC-+-.0. 2eceiving terminals and consumersCCCCCCC..-+

-.. LNG tradeCCCCCCCCCCCCCCCCC.-+

II

-. METHANE, NATURAL GAS AND LNG PROPERTIES…….14

-.-. The methane propertiesCCCCCCCCCCCCCCCC..-=

-.+. The natural gas propertiesCCCCCCCCCCCCCCC...-/

-.. ;hysical properties, composition and characteristics of LNGCC.-?

+. TRANSPORT OF NATURAL GAS FROM GAS WELLS……..18

TO LIQUEFACTION PLANT

. LIQUEFACTION PLANTS………………………………………19

=. HISTORY DEVELOPMENT OF GAS LIQUEFACTION……..2

=.-. #irst li>uefaction plant, storage and vaporising of natural gasCC.+-

=.+ 3istory production of LNG in Algeria CCCCCCCCCC...+-

=.. 3istory of LNG transportationCCCCCCCCCCCCCC.++

!. PREPARATION OF NATURAL GAS FOR LIQUEFACTION…22/.-. 2emoval of li>uids, solids and mercuryCCCCCCCCCCC.++

/.+. Acid gases removalCCCCCCCCCCCCCCCCCCC.+

/.+.-.%hemical absorptionCCCCCCCCCCCCCCCCCC.+

/.+.+.;hysicall absorptionCCCCCCCCCCCCCCCCCC..+=

/.+.. ;hysicalchemical absorptionCCCCCCCCCCCCCC..+=

/.+.=.AdsorptionCCCCCCCCCCCCCCCCCCCCCC.+=

/..1ryingCCCCCCCCCCCCCCCCCCCCCCCC..+=

".LIQUEFACTION OF NATURAL GAS…………………………….2!

?.-. Theoretical work for li>uefactionCCCCCCCCCCCCCC+/

?.+. Li>uefaction by


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?.=.%ascade cycles of li>uefaction natural gasCCCCCCCCCCC+

?.=.-. %lassical cascade cycleCCCCCCCCCCCCCCCCC...+

?.=.+. "ntegrated cascade cycleCCCCCCCCCCCCCCCC.C-

?.=..A;%" processCCCCCCCCCCCCCCCCCCCCC...+

?./. &eparation Df heavy products contained in natural gas to be li>uefied..

?.?. 1enitrogenation of li>uefied natural gasCCCCCCCCCCCC=

#. LNG STORAGE TAN$S………………………………………………%4

0.-.3istory of LNG storageCCCCCCCCCCCCCCCCCCC=

0.+.General re>uirements for LNG storage tanksCCCCCCCCCC.../

0..1ifferent types of LNG storage tanksCCCCCCCCCCCCC...?

0..-. LNG storage in fro*en groundCCCCCCCCCCCCCCC..?

0..+. &elfsupporting tanksCCCCCCCCCCCCCCCCCCC0

0... 6embrane tanksCCCCCCCCCCCCCCCCCCCCC

0.=. ;ipelines and e>uipment of LNG tanksCCCCCCCCCCCCC

0./. )ehaviour of LNG inside the tankCCCCCCCCCCCCCCC=D

. LNG L!A1"NG AN1 9NL!A1"NG A26&CCCCCCCCCCC=-

III

-.CARGO CONTAINMENT SYSTEMS ON LNG SHIPS………………44

-.-. %onstruction rulesCCCCCCCCCCCCCCCCCCCCC..==

-.+. Types of cargo containment systemsCCCCCCCCCCCCCC.=?

-.. &ystem with selfsupporting spherical tanksCCCCCCCCCCC.=0

-.=. %argo containment system with membrane tanksCCCCCCCCC.=

-.=.-. 6embrane system Ga*Transport, No?+CCCCCCCCCCC..=-.=.+. 6embrane system Techniga* 6ark "CCCCCCCCCCCCC../-

-./.=. 6embrane system Techniga* 6ark """CCCCCCCCCCCCC/+

-./. %haracteristics of membrane systemsCCCCCCCCCCCCCC./

-.?. 6embrane systems leak testCCCCCCCCCCCCCCCCC../

-.?.-. 6ethod for checking the effectiveness of the barriersCCCCCCC./

-.?.+. "n service global tightness testCCCCCCCCCCCCCCCC../=

-.0. %omparison of different cargo containment systemsCCCCCCCCC/?

2. MATERIALS IN LNG INDUSTRY…………………………………….!"

+.-. 6aterials for systems constructionCCCCCCCCCCCCCCCC/?

+.+. 1ouble hull material selectionCCCCCCCCCCCCCCCCCC/

+.. "nsulation materials for containment systemsCCCCCCCCCCCC/

+..-.Types of insulating materials CCCCCCCC.CCCCCCCCC/

%. INSTALLATION COMMON TO ALL SYSTEMS……………………"

.-. %argo piping systemCCCCCCCCCCCCCCCCCCCCC.?D

.+. 2elief systemCCCCCCCCCCCCCCCCCCCCCCCC?+

.+.-. %argo tanks relief valvesCCCCCCCCCCCCCCCCCCC?+

.+.+. ;rimary and secondary insulation spaces relief valvesCCCCCCC .?

.+.. Lines relief valvesCCCCCCCCCCCCCCCCCCCCC..?.. %argo alvesCCCCCCCCCCCCCCCCCCCCCCCC?

=


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.=. %argo pumpsCCCCCCCCCCCCCCCCCCCCCCCC..?=

.=.-. &tripping or spray pumpsCCCCCCCCCCCCCCCCCCC?/

.=.+. $mergency cargo pumpCCCCCCCCCCCCCCCCCCC.?/

./. %argo %ompressor roomCCCCCCCCCCCCCCCCCCCC??

.?. Gas heatersCCCCCCCCCCCCCCCCCCCCCCCCC..??

.0. LNG vapori*erCCCCCCCCCCCCCCCCCCCCCCCC.??.0.-. #orcing LNG vapori*erCCCCCCCCCCCCCCCCCCCC?0

.. %offerdam heating systemCCCCCCCCCCCCCCCCCCC?0

4. CARGO OPERATIONS………………………………………………….."9

=.-.%argo control roomCCCCCCCCCCCCCCCCCCCCCC..?

=.+. 1rying and aerationCCCCCCCCCCCCCCCCCCCCCC.0D

=.. "nerting CCCCCCCCCCCCCCCCCCCCCCCCCCC0D

=..-. "nert gas and dry air generatorCCCCCCCCCCCCCCCCC...0-

=.=. Gas fillingCCCCCCCCCCCCCCCCCCCCCCCCCC..0=

=./. %ooling downCCCCCCCCCCCCCCCCCCCCCCCCC0/

=.?. LoadingCCCCCCCCCCCCCCCCCCCCCCCCCCC..0?=.0. Loaded passage , )oil off gas burningCCCCCCCCCCCCCCC...00

=.. 9nloadingCCCCCCCCCCCCCCCCCCCCCCCCCCC0

=.. )allast voyageCCCCCCCCCCCCCCCCCCCCCCCCC0

=.-D. Earming upCCCCCCCCCCCCCCCCCCCCCCCCC..D

=.--. !ne tank operationCCCCCCCCCCCCCCCCCCCCCCC-

=.-+. Nitrogen distributionCCCCCCCCCCCCCCCCCCCCCC.+

=.-. $mergency operationCCCCCCCCCCCCCCCCCCCCCC=

=.-.-. $mergency cargo pump installationCCCCCCCCCCCCCCC...=

=.-.+. Eater leakageCCCCCCCCCCCCCCCCCCCCCCCC.=

=.-.. Gas leakageCCCCCCCCCCCCCCCCCCCCCCCCC./

=.-.=. Li>uid leakageCCCCCCCCCCCCCCCCCCCCCCCC/

/. %9&T!1F T2AN$2 &F&T$6 AN1 6$A&92"NG $9";6$NTCCC?

/.-. Level measurementCCCCCCCCCCCCCCCCCCCCCCC..0

/.-.-. 2adar type gaugeCCCCCCCCCCCCCCCCCCCCCCC..0

/.-.+. %apacitance level gaugeCCCCCCCCCCCCCCCCCCCCC0

/.-.. #loat level gaugeCCCCCCCCCCCCCCCCCCCCCCCC

/.+. Temperature measurementCCCCCCCCCCCCCCCCCCCCC

/.. ;ressure measurementCCCCCCCCCCCCCCCCCCCCCC

/.=. olume calculationCCCCCCCCCCCCCCCCCCCCCCC.././. 1ensityCCCCCCCCCCCCCCCCCCCCCCCCCCCC..

/.?. Gross calorific valueCCCCCCCCCCCCCCCCCCCCCCC..D

/.0. &ampling of LNGCCCCCCCCCCCCCCCCCCCCCCCCD

/.. Gas detectionCCCCCCCCCCCCCCCCCCCCCCCCCCD

/..-. "nfrared gas analyserCCCCCCCCCCCCCCCCCCCCCC.D

/..+. %atalytic gas analyserCCCCCCCCCCCCCCCCCCCCCC-

?. #"2$ #"G3T"NG $9";6$NT CCCCCCCCCCCCCCCCCCC-

?.-. #ire detection e>uipment CCCCCCCCCCCCCCCCCCCCC.-

?.+. #ire e'tinguishing e>uipmentCCCCCCCCCCCCCCCCCCC...-?.+.-.6ain fire sea water systemCCCCCCCCCCCCCCCCCCCC.-

/


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?.+.+. Eater spray systemCCCCCCCCCCCCCCCCCCCCCCC+

?.+.. 1ry powder systemCCCCCCCCCCCCCCCCCCCCCCC+

?.+.=. %!+ systemCCCCCCCCCCCCCCCCCCCCCCCCCC+

0. PROPULSION PLANTS ON LNG CARRIERS…………………………….940.-. &teamturbine propulsion plantsCCCCCCCCCCCCCCCCCCC=

0.-.-. )oiler fuel oil systemCCCCCCCCCCCCCCCCCCCCC..0

0.-.+. )oiler fuel gas systemCCCCCCCCCCCCCCCCCCCCCC0

0.-.. 1amp system CCCCCCCCCCCCCCCCCCCCCCCCC.

0.+. 2eview of alternative propulsion plantsCCCCCCCCCCCCCCC..-D-

0.+.-. 1iesel engine propulsion plants CCCCCCCCCCCCCCCCC-D-

0.+.+. 1ual fuel low speed diesel engineCCCCCCCCCCCCCCCC..-D-

0.+.. ;ropulsion plants with gas turbineCCCCCCCCCCCCCCCC..-D-

0.+.=. 1ieselelectric propulsion plantCCCCCCCCCCCCCCCCC...-D+

0.. &hip reli>uefaction unitsCCCCCCCCCCCCCCCCCCCCC-D

0..-. 9nit for complete boil off reli>uefactionCCCCCCCCCCCCCC-D=0..+. 9nit for partial boil off reli>uefactionCCCCCCCCCCCCCCC-D/

8. ANALYSE OF OPTIMAL SYTEM PARAMETERS………………………..1!

.-. )oil offCCCCCCCCCCCCCCCCCCCCCCCCCCCC-D/

.+. 9se of boil offCCCCCCCCCCCCCCCCCCCCCCCCC.-D/

.. Analysis of energetic needs for steam propulsion plantsCCCCCCCCC-D?

..-. Analysis of energetic needs for full ahead steamingCCCCCCCCCC-D?

..+. Analysis of energetic needs on anchorageCCCCCCCCCCCCC-D0

... Analysis of energetic needs for unloadingCCCCCCCCCCCCC.-D

.=. Analysis of fuel and gas consumption for different loads propulsion plantC.-D

9. CALCULATION OF OPTIMAL CARGO CONTAINMENT

SYSTEM INSULATION THIC$NESS……………………………………….19

.-. 3eat e'change theoretical thesisCCCCCCCCCCCCCCCCCC.-D

.-.-. 3eat e'change by conductionCCCCCCCCCCCCCCCCCC..--D

.-.+. $'changing heat by convectionCCCCCCCCCCCCCCCCCC--=

.-.. $'changing heat by radiationCCCCCCCCCCCCCCCCC..C--/

.+. %alculation of vapori*ation gas coefficientCCCCCCCCCCCCCC--?

.+.-. %alculation of isolation conductivityCCCCCCCCCCCCCCC..--?

.+.+. 1efining characteristic tank surfaceCCCCCCCCCCCCCCCC-+D

.+.. 1ouble hull characteristic surface temperature calculationCCCCCCC.-+-.+.=. &pherical tanks characteristic areas temperature calculationCCCCCC-+?

.+./. 6embrane tanks characteristic areas temperature calculationCCCCCC-+0

.. "nsulation system total heat flow calculation .CCCCCCCCCCCC.-+

..-. &pherical tanks insulation heat flow calculationCCCCCCCCCCC-+

..+. 6embrane tanks insulation heat flow calculationCCCCCCCCCC. -+

.=. )oil off coefficient calculationCCCCCCCCCCCCCCCCCC..-+

./. $vaporated gas >uantity calculationCCCCCCCCCCCCCCCCC-+

.?. Available steam >uantity calculation CCCCCCCCCCCCCCCC-D

.?.-. Available steam calculation, by burning of minimal >uantity of fuel oilC.-D

.?.+. Available steam calculation, by burning of evaporated gasCCCCCC..-D

.0. 2e>uired steam >uantity calculationCCCCCCCCCCCCCCCC..-D.0.-. 2e>uired steam >uantity calculation at full speedCCCCCCCCCC..-D

?


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.0.+. 2e>uired steam >uantity calculation at anchorCCCCCCCCCCCC--

.. 2e>uired and available steam >uantity difference calculationCCCCCCC--

.. 2e>uired fuel oil >uantity calculationCCCCCCCCCCCCCCCC.--

.-D. 1amp steam >uantity calculationCCCCCCCCCCCCCCCC-+

.-+. #orcing vapori*ation gas >uantity calculationCCCCCCCCCCCC.-+

.-. "nsulation cost calculationCCCCCCCCCCCCCCCCCCCC.-+.-=. %alculation resultsCCCCCCCCCCCCCCCCCCCCCC..-

IV

1. RECEIVING TERMINALS…………………………………………………..1%8

+. )A&"% ;2!%$&& %3A2A%T$2"&T"%& !# T$26"NALCCCCCCCC-

+.-. uantity of vapori*ed gasCCCCCCCCCCCCCCCCCCCCC-

+.+. &torage capacityCCCCCCCCCCCCCCCCCCCCCCCC..-=D

+.. ;rocess of gas vapori*ationCCCCCCCCCCCCCCCCCCCC.-=D+.=. LNG heat e'changersCCCCCCCCCCCCCCCCCCCCCC..-=+

+.=.-. &ea water heat e'changersCCCCCCCCCCCCCCCCCCCC-=+

+.=.+. LNG evaporation by gas firingCCCCCCCCCCCCCCCCCC.-=

+./. %alorific value ad(ustmentCCCCCCCCCCCCCCCCCCCC-==

. #L!AT"NG T$26"NALCCCCCCCCCCCCCCCCCCCC..-=/

=. ;$AH &3A"NG ;LANTCCCCCCCCCCCCCCCCCCCC.-=/

/. LNG &AT$LL"T$ &TAT"!N&CCCCCCCCCCCCCCCCCC..-=/

?. %!N&96$2& !# NAT92AL GA& AN1 LNGCCCCCCCCCCCC-=?

?.-. $lectric power plants with gas

turbinesCCCCCCCCCCCCCCC.-=?

?.+. Natural gas for air condition and heatingCCCCCCCCCCCCCCC-=0?.. ehicles on natural gas and LNGCCCCCCCCCCCCCCCCCC-=0

?..-. #uel cell cars CCCCCCCCCCCCCCCCCCCCCCCCC-=

?.=. ;ro(ects of alternative natural gas transportCCCCCCCCCCCCCC-=

Literature

List of illustrations

List of tables

List of symbols

Greek symbols

Non dimensional symbols of similarity

&hortcuts

0


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I1.1. COMPOSITION AND NATURAL GAS FORMATION

Natural gas is mi'ture of gases which are on atmospheric pressure and temperature

in gaseous state. %omposition of natural gas is different and depending of finding

place. The most part in that mi'ture of hydrocarbons has methane with smaller parts

of ethane , propane and butane. The natural gas contains small parts of gases which

are not hydrocarbons and those are %!+ , hydrogen, helium, mercury vapour etc.

About formation of natural gas e'ist two theories. According organic theory natural

gas originate from remains of plants, bacterium, seaweeds, *ooplankton and

phytoplankton. The biomass was deposited by millions of years on the bottom of the

rivers, lakes and seas and then covered by layers of mud. )y movement of earth crust biomass moved deeper inside of earth where it was decomposed under high pressure

and temperature. The pure methane was created by depth to -DDD m. !n the bigger

depths the biomass first decomposed to organic substances. Then hydrocarbon

decomposition led to creation of petroleum and gas.

The inorganic theory of the natural gas formation suppose insertion of huge >uantity

of methane from of that time atmosphere to the earth crust during earth crust

formation. According this theory the considerable larger >uantities of natural gas lies

deeper inside of earth.

1.2. NATURAL GAS SOURCES

The biggest natural gas reserves are in 9&A, 2ussia, %anada, 6iddle $ast, "ndonesia,

Nigeria and Algeria. $stimated natural gas world accumulations are -D'-D-+ mn.

These large >uantities put natural gas in leading position of energy supply for this

century.

According 9&A geological institutes huge >uantities of natural gas lies on the sea

bottom in form of gas hydrate. The methane hydrates is natural gas fro*en on the

ocean floor by high pressure and free*ing temperature. 6ethane hydrates come from

natural gas formed mainly by decaying plant material. The gas seeps up through

sediments to the ocean floor, where it escapes in small amounts. !ver time the gas,

mi'ed with sea water, is fro*en and forms outcroppings.Eorldwide natural gas hydrate in marine is growing interests in potential energy

resources in the future. The gas corporations investigates the formation and

decomposition of the natural gas hydrate for the technological development of gas

storage and transportation.

Natural gas hydrate, which is a nonconventional type of natural gas, distributes

worldwide, especially enormous amounts in marine and permafrost. "t would become

a target of natural gas resources in near future. Therefore most recently many

countries such as


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most important energy resources.

1.%. NATURAL GAS USE

&ince the -=D natural gas has been recogni*ed as one of the most useful products of

natureIs chemistry. Thanks to advance in technology, the natural gas becomeimportant as versatile fuel and e'cellent source of raw material.

Natural gas and petroleum on the earth surface was noticed by humans long time ago.

)efore more than +DDD years ago %hinese transported natural gas by bamboo wood to

the temples for lighting. #irst commercial use of natural gas in $urope was in Genova

in -D+, when city streets were lightened by natural gas. #rom that time consumption

of natural gas is in constant increase. "n the beginning of petroleum e'ploitation

natural and petroleum gas were vented to the atmosphere, only small part of that gas

was used as fuel. )y the time gas networks were built what improved use of natural

gas as high efficient fuel .

"n 9&A natural gas was used first time in ;ittsburgh where it was transported by

pipeline. Till -/D 9&A was only important natural gas producer. After second half of last century production of natural gas begins to increase in the others countries.

4$urope, 2ussia and %anada.5According world energy planning forecasts natural gas

will take the most important place in this century. #igure -. shows share of natural gas

in world energy consumption.

0

5

10

15

20

25

30

1940 1960 1980 2000 2020

Natural gas %

Figure 1.

S&'() *+ '-('/ 0' 3*(/ ))(05 6*7-*

2easons for sudden natural gas consumption increase are:

perfect fuel with high calorific value,

public opposition to nuclear energy,

air friendly fuel,

energy strategic and political reasons.

Natural gas has advantage in regard to others primary forms of energy because it

can be used directly. !ther primary forms of energy must be transformed to the

others energy forms what means higher investments and losses. )ecause of very smallemission of no'ious combustion e'haust gases and better efficiency burning of


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natural gas increase in domestic and industry use. Natural gas, beside as fuel, is basic

raw material in the petrochemical industry. #igure +. shows increase of natural gas

production.

0

500

1000

1500

2000

2500

3000

3500

1960 1980 2000 2020

Natural gas x

bil. m3

Figure 2.

I6()') *+ '-('/ 0' (*6-*

#igure . shows increase of natural gas trade.

0

100

200

300

400

500

600

700

1960 1980 2000 2020

Natural gas x bil.M3

Figure 3.

I6()') *+ '-('/ 0' -(')

)y consumption increase of natural gas transport to the consumers become a

problem. The natural gas is transported by land and sea pipeline 1J -/DDmm under

pressure up to -DD bars in gaseous state. )ecause of friction between gas and pipeline

walls pressure in the line drops. #or transport by this way to long distance pressure inthe pipeline need to be increased. This is accomplished by the compressors in

-D


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compressor stations. To the overseas countries gas is transported by the ships in li>uid

state.

1.4. REASONS FOR NATURAL GAS LIQUEFACTION

2easons for li>uefaction and transport by ships in li>uid state are: high cost of construction, maintenance and e'ploitation of land and under sea

pipelines. There is limit distance above that transport by ships is cheaper,

by li>uefaction natural gas volume decrease si' hundred times what open

possibility to transport large >uantity of energy,

world trade and increase of natural gas consumption create more consumers

all around the globe so transport by sea is only possible way,

political and strategic reasons.

!n figure =. is shown augmentation of LNG trade .

0

10

20

3040

50

60

70

80

90

100

1965 1980 1995 2010 2025

Natural gas x

bil m3

Figure 4.

I-)('-*'/ LNG -(') 6()')

Natural li>uefied gas business include:

preparation for li>uefaction, li>uefaction and storage in production plants,

loading and transport by ships,

receiving, storage, evaporation and delivery to the consumers by receiving terminals.

1.!. PRODUCTION PLANTS

There are more and more production plants in the world. $ach production plants

consists of three main units. 9nit for preparation of raw gas for li>uefaction ,

li>uefaction unit and storage. The biggest world LNG e'porter is "ndonesia with D K

--


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of world LNG trade. !ther LNG producers are Alger, 6alaysia, )runei, Australia,

Abu 1habi, atar, Nigeria, Trinidad, !man and $gypt.

1.". LNG CARRIERS

Eorld LNG fleet has about -=D ships. "n +DD/ seven ships will be older than / years.

)etween +DD/ and +D-D forecasts are =D new ships more. "n same time -0 ships will

be older than / years, what is considered as ma'imum ships e'ploitation life.

Li>uefied natural gas with temperature of -?- °% and pressure --DD mbar is

transported in ships tanks that can have different shape. The most known design are

6oss 2osenberg spherical tanks and Ga*TransportMTechniga* membrane tanks.

3eat transfer to the li>uid cargo from the insulation spaces cause the li>uid to boil and

vapor to be formed. The cargo tank boiloff and it must be removed in order to

maintain e>uilibrium within the tanks at the designed operating pressure. The volume

of boiloff is also increased on passage due to the energy dissipated by the agitation of

the cargo caused by the motion of the ship. The boil off coefficient is between D.-/K

and D.+/K of total gas >uantity on board and per day.

All ships have steam turbine propulsion plants because of easiest way to burn boil off

in the ship steam boilers.

1.#. RECEIVING TERMINALS AND CONSUMERS

6ore than half receiving terminals are in uid is performed in range

above critical pressure what considerably reduce costs of regasification.

1.8. LNG TRADE

"n -, over 0K of LNG production was sold to customers under longterm

contract. )ut it seems that the part of business is going to change to short term

trading. 1emand is e'pected to double from D mtpa in - to -0D mtpa by +D-D

with new buyers and sellers entering the market. )uyers are looking for more fle'iblecontracts. %hange in production plant costs can be reduced and competition between

shipyards has resulted in a reduction of LNG tanker costs.

The main limitation to the growth of short term trading is lack of shipping capacity.

The lack of shipping capacity became evident at a time when the cost of new ships

reached a historically low level as shipyards competed for new orders. Low costs and

shortage of capacity have resulted in several companies ordering new build

vessels not committed to a particular pro(ect or trade.

LNG pricing formula usually links pricing of LNG to the price of crude oil. The

e'act formula are usually considered commercial secrets, typical formula have the

following structure:

; J )ase ;rice ' 4&O %5 P HQEhere:

-+


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& is the market price of specified cocktail of crude oils imported on a specific day .

% is the market price of the specified cocktail of crude oils imported on day one of

the contract,

H is an ad(ustment factor often with specified limits.

;rice is determined by finding acceptable or competitive price when considering

possible use of an alternative fuel. The sum of natural gas price should be e>ual tosum of a substitute fuel price. This result in different prices depending on various

categories of customers according to their various uses of natural gas.

Natural gas has a curious position in the international energy market since it

can fulfill a wide range of energy needs. There is no world price of natural gas.

LNG business characteristics are: large and diverse reserves, ability to develop

markets, great financial strength, willingness to invest.

LNG compete with alternative fuels on a total cost basis in addition to

being more environmentally friendly. #or e'ample coal and fuel oil is a competing

fuel for power generation. Also LNG competes with pipeline gas in several markets

technological innovations enabled LNG plants to run safely, efficiently and cost

effectively.$stimated LNG chain cost are as follows

field development -D+DK,

li>uefaction +//K,

shipping -/+/ K,

receiving terminal /-/K,

gas distribution or power generation +// K.

All three LNG chain parts, production, transport and regasification plant are trying to

reduce operating costs.

3alf the cost of whole LNG chain refer to production plants. "mprove of li>uefaction

process is best way to reduce overall costs.

LNG transport companies are looking at diesel electric propulsion as one of potential

possibilities to reduce operating costs. "ncreased vessel capacity generates an overall

reduction of the transporting costs. LNG receiving terminals and regasification plants

include electricity production plant.

$lectricity production plants, powered by burning natural gas in gas turbines, grows

all around globe. These plants with improved efficiency 4gas turbine cooling down

system is used to heat LNG5 provide low priced and clean energy.

;otential cost reductions remains in all elements of LNG chain

-


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II1. METHANE, NATURAL GAS AND LNG PROPERTIES

The main task before handling natural gas and natural li>uefied gas is to determine

which thermo physical characteristics need to be known,

which mathematical method are available for determination of these

characteristics,

which measurement method enable direct determination of these

characteristics.

Natural gas and natural li>uefied gas handling include: li>uefaction, storage, loading,

transport, unloading, regasification and delivery to consumers. All these operations

are taken out on different temperatures and pressures and generally include formation

of two state, li>uid and gaseous. The most important property of li>uefied gas is its

saturated vapor pressure and temperature relationship . To design pipeline, separators,

heat e'changers etc. one should know:

phase diagrams,

enthalpy,

density,

viscosity,

thermal conductivity.

;hase diagrams are different for different gas wells because of different gas mi'tures.Above characteristics are determine by using mathematical models for different

components of gas mi'ture. Thermo dynamical functions e'pressed by state e>uation

with p, and T parameters are basic method for understanding of properties and

behavior of li>uefied natural gas.

The most used method is analogy with referent fluid. The methane as main

component of natural gas and li>uefied natural gas is used as referent fluid.

1.1. THE METHANE PROPERTIES

The methane is first in the group of saturated hydrocarbons and consists of one atom

of carbon and four atoms of hydrogen. !n atmospheric pressure and temperaturemethane is in gaseous state and it is very difficult to be li>uefied.

)oiling point at - bar absoluteCCCCCCCCCCCCC. -?-./ °%

Li>uid density at boiling pointCCCCCCCCCCCCC. =+?.D kgOm

apor relative densityCCCCCCCCCC. CCCCCC D.//= ?-

Gas volumeOli>uid volume ratio at -?-./ °% at - bar absolute C ?-

#lammable limits in air by volume CCCCCCCCCCC.. /. to -=K

Autoignition temperatureCCCCCCCCCCCCCCC // o%

3igher specific energy4Gross 3eating value at -/ °%5CCCC..///D k


15/154

The autoignition temperature of methane is the lowest temperature to which the gas

needs to be heated to cause selfsustained combustion without ignition by a spark or

flame. The flammable limits is a range between minimum and ma'imum

concentration of gas vapor in air which form a flammable mi'ture. 6inimum ignition

energy for flammable gas vapor mi'tures is less than one mili(oule. This is an energylevel which is substantially e'ceeded by any sparks or electrostatic discharges.

The vapor of methane have not to'ic properties but when present in sufficient

concentration, e'cludes o'ygen and leads to asphy'ia. The asphy'ia is condition

when the blood is deprived of an ade>uate supply of o'ygen so loss of consciousness

may follow. 6ethane is a greenhouse gas and as such a pollutant.

1.2. PROPERTIES OF NATURAL GAS

&ince natural gas include not only methane, before mentioned characteristics differ

from pure methane. Table -. shows natural gas from different sources.

Table -. Natural gas from different wells

Natural gas Alger Libya )runei North sea "ran Alaska

6ethane ?, ?, ,D /, ?, ,/

$thane 0, -,= /,- ,- -,+ D,-

;ropane ,+ ,- =, +,0 D,= D

)utane D,? ,/ -, D, D,+ D

;entane D,- -,+ D,+ D, D,- D3e'ane D D D,- D,/ -, D,=

Natural gas contains methane, ethane , propane, butane and pentane. )eside these

saturated hydrocarbons natural gas contains nitrogen, carbon dio'ide, sulphur

hydrogen, helium, water vapor and mercury vapor. #or determining way of

production it is important to know state of phase of that particular natural gas mi'ture.

Natural gas mostly appear as one phase system determined by pressure and

temperature of that wells or as two phase system including gas and li>uid.#igure /. shows two phase diagram for gas and li>uid

-/


16/154

;

pc %

-DD

0/

li>uid K /D

/

+D

Tc T

Figure 5.

P&') '0('7 *+ &5(*6'(:* 7;-()

"n diagram two phase range is separated form one phase range by boundary curves of

evaporation and condensation. )oundary curve of evaporation and condensation

represent group of points of e>uilibrium states 4p, T5 at which gas li>uid phase

changes happen. The evaporation and condensation curve (oin together in point %

which is called critical point and which is defined by critical pressure pc and critical

temperature Tc. The critical temperature of a gas is the temperature above which a gas

can not be li>uefied however great is pressure. The critical pressure of gas is pressure

at which gas e'ists in a li>uid state at its critical temperature.

1.%. PHYSICAL PROPERTIES, COMPOSITION

AND CHARACTERISTICS OF LNG

Natural gas is a mi'ture of hydrocarbons which, when li>uefied, form a clear

colorless and odorless li>uid. LNG is transported and stored at a temperature very

close to its boiling point at atmospheric pressure 4appro'imately -?DR%5.

The actual LNG composition of each loading terminal will vary depending on its

source and on the li>uefaction process, but the main constituent will always be

methaneB other constituents will be small percentages of heavier hydrocarbons, .

ethane, propane, butane, pentane, and a small percentage of nitrogen.#or most engineering calculations it can be assumed that the physical properties of

pure methane represent those of LNG. 3owever, for custody transfer purposes when

accurate calculation of the heating value and density is re>uired, the specific

properties based on actual component analysis must be used.

1uring a normal sea voyage, heat is transferred to the LNG cargo through the cargo

tank insulation, causing vapori*ation of part of the cargo 4 boiloff.5

The composition of the LNG is changed by this boiloff because the lighter

components, having lower boiling points at atmospheric pressure, vapori*e first.

Therefore the discharged LNG has a lower percentage content of nitrogen and

methane than the LNG as loaded, and a slightly higher percentage of ethane, propane

and butane, due to methane and nitrogen boiling off in preference to the heavier gases.The boiloff vapor from LNG is lighter than air , therefore when vapor is vented to

-?


17/154

atmosphere, the vapor will tend to rise above the vent outlet and will be rapidly

dispersed. Ehen cold vapor is mi'ed with ambient air the vaporair mi'ture will

appear as a readily visible white cloud due to the condensation of the moisture in the

air. "t is normally safe to assume that the flammable range of vaporair mi'ture does

not e'tend significantly beyond the perimeter of the white cloud.

Ehen spilled on water: )oiling of LNG is rapid, due to the large temperature difference between the

product and water,

LNG continuously spreads over an indefinitely large area, it results in a

magnification of its rate of evaporation until vapori*ation is complete,

No coherent ice layer forms on the water,

The flammable cloud of LNG and air may e'tend for large distances downward

4only methane when warmer than -DDR% is lighter than air5 because of the absence of

topographic features which normally promote turbulent mi'ing.

"f there is no immediate ignition of an LNG spill, a vapor cloud may form. The

vapor cloud is long, thin, cigar shaped and, under certain meteorological conditions,may travel a considerable distance before its concentration falls below the lower

flammable limit. This concentration is important, for the cloud could ignite, with the

flame traveling back towards the originating pool. The cold vapor is denser than air

and thus, at least initially, hugs the surface. Eeather conditions largely determine the

cloud dilution rate, with a thermal inversion greatly lengthening the distance traveled

before the cloud becomes nonflammable.

The ma(or danger from an LNG vapor cloud occurs when it is ignited. The heat from

such a fire is a ma(or problem. A deflagrating 4simple burning5 is probably fatal to

those within the cloud and outside buildings but is not a ma(or threat to those beyond

the cloud.

Low e'plosion limits 4L$L5 is gas concentration in air under which heat >uantity

generated by combustion is not enough for self sustain of combustion reaction.

9pper e'plosion limit49$L5 represent too high concentration of gas in air above that

is no more enough of air for combustion.

Table +. shows e'plosion limits for other components of natural gas mi'ture. "t may

conclude that with higher concentration of heavier components Low $'plosion Limit

tend to decrease.

Table +. L$L for heavier components of natural gas

Natural gas Gas composition L$L K6ethane D /.+=

$thane -/ .++

;ropane = +.0

)utane - -.?

%ontact with LNG or with materials chilled to its temperature of about -?DR% will

damage living tissue. The symptoms of cold burns are painful in the affected area

6ost metals lose their ductility at these temperaturesB LNG may cause the brittle

fracture of many materials. "n case of LNG spillage on the shipSs deck, the high

thermal stresses generated from the restricted possibilities of contraction of the platingwill result in the fracture of the steel.

-0


18/154

Ehen loaded in the cargo tanks, the pressure of the vapor phase is maintained

substantially constant, slightly above atmospheric pressure. The e'ternal heat passing

through the tank insulation generates convection currents within the bulk cargo,

causing heated LNG to rise to the surface and is then boiledoff.

The heat necessary for vapori*ation comes from the LNG, and as long as the vapor iscontinuously removed by maintaining the pressure as substantially constant, the LNG

remains at its boiling temperature. "f the vapor pressure is reduced by removing more

vapor than generated, the LNG temperature will decrease. "n order to make up the

e>uilibrium pressure corresponding to its temperature, the vapori*ation of LNG is

accelerated, resulting in an increased heat transfer from LNG to vapor. )y varying the

pressure above the li>uid it is possible to boil li>uid at different temperatures.

1ecreasing the pressure above the li>uid lowers the boiling point temperature and

increase boil off >uantity. "ncreasing pressure above li>uid raises the boiling point

temperature and decrease boil off >uantity.

The properties of the LNG, i.e. the boiling point, density and heating value, have a

tendency to increase during the voyage.

2. TRANSPORT OF NATURAL GAS

FROM WELLS TO LIQUEFACTION PLANTS

Transport of natural gas from gas wells to the terminals, usually situated at the

seaside, need some preparation. The heavier component and water can condensate in

pipeline during transport because of temperature drop. Therefore these components

need to be removed from natural gas. 2emoval is perform in primary separation units.

After primary separation gas pass through unit which contains separations units,

dehydration unit and compressors stations. This unit components depend of

composition, pressure and temperature of natural gas and for what specific purpose

gas is designated. "f natural gas is designated to li>uefaction plants then dew points of

gas need to be lowered (ust to avoid problems of condensation and corrosion in

pipeline. There are several ways to natural gas dew point lowering:

cooling down by e'ternal refrigeration plant is used for gas coming from wells

with low pressure,

by uids,

adsorption by hydroscopic solids.

These process are perform in dehydration units of li>uefaction plants too.

"f dynamic pressure of gas wells is too low and not enough to transport then gas need

to pass through compressors stations. %ompressor stations contains centrifugal

compressors and numbers depend of desired gas pressure and >uantity.

-


19/154

%. LIQUEFACTION PLANTS

Natural gas li>uefaction process perform in very comple' plants. These plants are

usually situated at seaside. These huge plants spread on few s>uare kilometers

contains:units for preparation and li>uefaction,

storage tanks,

units for loading LNG to the ships,

units for common purposes.

%ommon purpose units include:

sea water pumping stations,

electric power generating units,

steam generating units,

control air compressor station,

nitrogen production units, workshops,

firefighting and safety department.

LNG production plants can be organi*ed by two way:

centrali*ed arrangement of units,

modular arrangement of units distribution.

LNG production plant with centrali*ed arrangement has only one unit for

gas preparation, steam power plant, sea water station, one control unit, one workshop

etc. !nly li>uefaction unit are separated on modular way.

6odularly arranged plants can be operating independently. "n #igure ?. schematically

is described chain of operations for production of LNG.

-


20/154

Acid gases

Eater

LNG storage

NGL storage

;entane storage

Figure 6.

LNG /


21/154

characteristic by methodical drawing diagrams for carbon dio'ide in p coordinates.

!n basis of this diagrams it is possible to define condition of li>uefaction.

"n -00 %ailletet in ;aris and ;ictet in Geneve had published process of air

li>uefaction using Andrews results.

- !l*ewski continued based on works of %ailletet and ;ictet. 3e use evaporation

of ethylene, under low pressure, to achieve temperature of -/D °%. This was usedfor li>uefaction of methane, nitrogen and carbon mono'ide

!n the end of - century %. Linde use contra flow heater e'changer and uefaction of air.

G. %laude in the beginning of +Dth century improve the Linde process by adding one

more heat e'change and e'pander.

Li>uefaction of different gases and development of low temperature technology

resulted by development of different branches of industries. &eparation of gas

mi'tures on their main components is the most important application of this

technology.

!ne of the first application was treatment of gas obtained from coke. )y li>uefaction

of this gas mi'ture is possible to have almost pure hydrogen. 3ydrogen was then used

to get mi'ture N+ P 3+ what was used for sensiti*ing of ammoniac. This type of plant

spread all around world in period between two world wars.

&econd e'ample of application was production of helium from natural gas . 9&A

natural gas contain D./ - K of helium. 1uring the first world war in --0 in Te'as

first such plant was built. This helium was used for the military air balloon .

4.1. FIRST PLANT FOR LIQUEFACTION, STORAGE

AND EVAPORATION OF NATURAL GAS

"n - $ast !hio Gas %o. was supplying natural gas to city of %leveland by two pipeline long +/D km and diameter of DDmm. As this was not enough during winter

they decided to build plant for li>uefaction, storage and evaporation in the city.

2eason for such decision was: it is cheaper to li>uefy and storage a natural gas, during

summer when consumption is low, than to build new pipeline.

;lant production rate was +DD mOh by cycle ammoniacethylenemethane.

%ompressor station contains ? reciprocating compressors using about +=DD kE.

&torage capacity was ' +/DD m in three spherical tanks. $vaporation unit rate was

--/ m Oh .

4.2. HYSTORY OF LNG PRODUCTION IN ALGERIA

"n -/? huge wells of natural gas was found in 3assi2Imel /DD km south from Alger.

Gas >uantity over passed needs of Algeria so it was decided to e'port natural gas to

$urope. At that time was impossible to make pipeline under sea. !nly way to e'port

that gas was li>uefaction and transport by ships. "n -?+ &hell and %ontinental !il %o

started to build first li>uefaction plant. ;lant was named %A6$L 4%ompagnie

Algeriene du 6ethane Li>uide5. ;lant was opened -?= and first LNG delivery was

to 9H -?/.

Today plant name is GL=@ with production rate about -.= G m of gas. The length of

pipeline is about /DD km.

&econd plant was built in &kikda and is connected with same well in 3assi2Imel by

pipeline length ?DDkm. #irst three unit were built in -0+ and -+ three unit more.total production rate is about ./ G m.

+-


22/154

Third and fourth production plants in Algeria were built in -+ near )ethiua with

production rate of -D G m.

=.. HYSTORY OF LNG TRANSPORTATION

The first LNG carrier was a converted dry cargo ship, the Normarti renamed the

6ethane ;ioneer. "n this conversion, the cargo was carried in five self supportingaluminum tanks, fitted into two holds internally insulated with a balsa. #irst shipment

was from Lake %harles to %anvey "sland 9H. The success of the 6ethane ;ioneer

e'periment pointed the way to commerciali*ation of the sea transportation of LNG.

"n !ctober -?=, the first commercial LNG scheme came into operation when the

6ethane ;rincess carried first cargo of LNG from Ar*ew to %anvey "sland.

The 6ethane ;rinces and her sister ship 6ethane ;rogress each had nine prismatic

self supporting aluminum tanks, fitted into three holds. $ach of these holds was

internally insulated with a balsa plywood panel system, based on that used earlier in

the 6ethane ;ioneer.

These ships were (oined in -?/ by the uires treatment to remove heavier hydrocarbons and non

hydrocarbon constituent to ensure the gas is in a technically acceptable for

li>uefaction. The part of li>uefaction plant where raw natural gas has to be prepared

is very important for whole process. Natural gas from wells contains methane, small

>uantities of heavy hydrocarbons pentane and he'ane , light hydrocarbons ethane ,

propane and butane and changeable >uantities of humidity, carbon dio'ide, hydrogen

sulphur , nitrogen, mercury and small >uantities of different impurities. "mpurities

and some raw natural gas components which have unfavorable influence to

li>uefaction process can be divided on:

components which became li>uids during li>uefaction4 %!+, 3+! and heavy

hydrocarbons5,

to'ically components,

corrosive and erosive components4 mercury and hard particles5,

inert components4 nitrogen and helium5.

2aw natural gas treatment can be divided in three main parts

separation of mercury and hard particles,

removal of acid gases, drying.

After treatment natural gas must contain

less than - ppm of water,

less than /D ppm of %!+,

less than = ppm of 3+&.

Natural gas that satisfy above re>uirements is considered ready for li>uefaction.

!.1. REMOVAL OF LIQUIDS, SOLIDS AND MERCURY

Li>uid removal is insured by separators large enough to handle the most of li>uid

++


23/154

carry over. &olids and dust removal is insured by :

oil bath scrubbers 4-D -/ microns si*e5, disadvantage is li>uid carry over,

centrifugal separators,

gas filters.

Li>uid and solid removal is usually combined in separators achieving both and solidremoval. The separators are installed ahead of the li>uefaction plant in the metering

unit where pressure control is performed.

"n order to protect the aluminum and aluminum alloys from corrosion caused by

mercury it is necessary to bring down the mercury content to a very low level.

The mercury removal units include of a fi'ed bed of adsorbent. Adsorbing mass is a

sulpfur impregnated coal based activated carbon.

!.2. ACID GASES REMOVAL

Acid gases removal include:

chemical absorption, physical absorption,

physicalchemical absorption,

adsorption.

!.2.1. C&)76'/ ':*(-*

"n feed gas pretreatment units acid gas are removed by monoethanolamine process.

This process use -/K a>ueous solution which reacts with the acid gas components.

)y temperature increase and pressure reduce the acid gas are released. #igure 0.

shows the principle of unit. 2aw gas enters at bottom of absorber and leaves the top

after acid gas removal. Lean amine at ambient temperature is fed on top tray while

rich amine after acid gas pickup leaves the bottom and is flashed in a drum. After

heat e'change with lean amine the warmed up rich amine feeds the regenerator. Acid

gas is vented at reflu' drum. Lean amine is cooled against rich amine and cooling

water and pumped from amine surge tank to the absorber.

Treated gas

#uel gas Acid gases

2egenerator 2eflu' drum

Absorber

2aw gas

$'pansion tank steam

;ump

Amine tank

+


24/154

Figure 7.

C&)76'/ ':*(-*

!.2.2 P&56'/ ':*(-*

These process use organic solvents to perform acid gas removal. !ne of the process is

&ele'ol used for raw gas with high content of %!+ and 3+&.

!.2.%.P&56'/6&)76'/ ':*(-*

&ulfinol process uses a mi'ture solvents which allows it to behave as both a chemical

and physical process. The mi'ture is composed of sulfolane acting as the physical

solvent and 1";A 4dii*opropanolamine5.

!.2.4. A*(-*

;rocess of adsorption use molecular sieves to remove water and acid gases from raw

gas.

!.%. DRYING

1uring acid gas removal feed gas is saturated with water. !ne part of water is

removed by cooling the gas stream. #or complete dehydration there are two process:

absorption by glycol solution

adsorption on solid dessicant

#irst process use hygroscopic property of glycol solution. The glycol unit consists of

an absorber, regenerator, separator, filter, compressor and cooler.

&econd process consists of molecules attraction on the surface of solid adsorbant. #or

gas dehydration usually are used ne't products: silica gel,

activated alumina,

molecular sieves.

&ilicagel is obtained by neutrali*ing soda silicate solutions by mineral acids. This

product is washed, dryed and activated by thermal treatment. 9sed in form of hard

granules, it is very hygroscopic and thus very effective as an absorbent of fluids. "t

can be regenerated by heating to drive off the absorbed matter.

Alumina trihydrate is the purified product obtained from bau'ite. Activated alumina is

desiccant medium which operates by the absorption of water molecules. 6olecular

sieves are crystalline, alkalimetal aluminosilicates. #irst molecular sieves were

*eolithes which are natural crystals.

+=


25/154

6*7()*(

6**/)( )'('-*(

N'-('/ 0'

W'-)(

(5)(

F/-)( (5 0'

()0))('-*(

Figure 8.

N'-('/ 0' (50

". LIQUEFACTION OF NATURAL GAS

The natural gas to be li>uefied is usually available at pressure D0D bars and at

ambient temperature. "n order to li>uefy natural gas it has to be cooled to a

temperature of -?- °%, so it can be stored at pressure little above atmospheric

pressure. The e'act temperature depend on the composition of li>uefied natural gas.

3eavier hydrocarbons like butane, propane and ethane are e'tracted during the

process of li>uefaction. Nitrogen content can be reduced in order to increase the

heating value of the li>uefied gas and prevent transmission of useless mass of

nitrogen. There are three real ways of natural gas li>uefaction:


26/154

and temperature t J+/ °% presented by point 6o in hs diagram. To li>uefier natural

gas under atmospheric pressure gas have to be cool down to boiling temperature t s presented by point 6 in h-s and T-s diagrams.

"n T-s diagram is presented reversible li>uefaction process. The gas defined with

initial state of surroundings 6o by isothermal process going to state defined by point

N. )y adiabatic e'pansion gas take li>uid state defined by point 6.

h

6o

t- p-

tkts

-8

6

-I

ef

&

Figure 9.

T&)*()-6'/ 3*(= +*( 0' /uefaction is e>ual or higher than theoretical work of li>uid state

1≥ e+ h – ho – T(s-so) 4?.-5

+?


27/154

)y applying inde' from hs diagram have ne't e'pression

1≥ e+ h>1 @ h1 @ T( >1-s1 ) T(s – s1 @h-h>1 4?.+5

Theoretical work ef can be red from hs diagram and by help of the tangent line at point 6o on isobar p- . "t can be calculated assuming natural gas as ideal gas.

$'pression 4h- hI-5 can be written as

h1 @ h’ 1 r 1 T –Ts)c 4?.5

r - heat of evaporation at p-4k1 c / T/T r 1T 4?.=5

#or methane at atmospheric pressure evaporation heat is r - J /=,=0 k


28/154

The simplest li>uefaction cycle based on the production of cold by free e'pansion

is shown in #igure -+. "n order to achieve a ma'imum thermal effect it is preferable to

use high pressures and low temperature.

compressor

/

heat e'changer uefied gas -.- bar -?D °%

Figure 12.

Luefaction unit under pressure of ?D bar and temperature of +/ °%.

Gas from initial state 4 +5 pass through heat e'changer and cool down to the state of

point . $'pansion through e'pansion valve is shown by curve from to state 4= 5

defined by -.- bar and -?D °%. ;art of gas is li>uefied and saturated part of gas pass

through heat e'changer up to state /. &ee Ts diagram, #igure -. ;osition of point /depend of heat e'changer efficiency.

Li>uefaction by this simple process use to much energy, about -DDD kuefied gas. The specific energy is too high because of:

the temperature differential at the cold end is too high,

e'pansion through valve is irreversible process.

T

2 = 1 2 1

% !

4> 4 4?

+


29/154

Figure 13.

Luefaction of natural gas, specially in large si*e units, the cascade cycles are

used. These cycles use hydrocarbons obtained from natural gas as cooling media.

There are two cascade cycles:

classical cascade cycle,

integrated cascade cycle.

".4.1.C/'6'/ 6'6') 656/)

+


30/154

The classical cascade cycle consists of three identical units in cascadeB

propane stage operating between atmospheric pressure and ./ bars,

ethylene stage operating between atmospheric pressure and -/./ bars,

methane stage operating between atmospheric pressure and +? bars.

)y heat e'change with natural gas, which is going to be li>uefied, cooling media4refrigerant5 evaporates. The refrigerant vapor is the compressed and reli>uefied by

heat e'change first against cooling water and subse>uently against mi'ed refrigerant.

After last series of heat e'changers with methane natural gas e'pand to D.? bars. )y

that way temperature of natural gas is decreased to -?D °%. The number of cascades

and the choice of fluids are such that condensation pressures remain the critical

pressures in order to make it possible to operate in a *one of high latent condensation

heat. ;art of gas which evaporates in process of li>uefaction is used as fuel for plant.

&pecific energy needed for li>uefaction by this cycle is -=DD k


31/154

Figure 15.

C/'6'/ 6'6') 656/)

".4.2.I-)0('-) 6'6') 656/)

This cycle is made up of succession of pressuri*ed condensations followed by low

pressure vapori*ations. "n this case the cascade is not formed with one fluid having

fi'ed condensation temperature when pressure is given. %ooling fluid is a mi'ture of

several fluids whose temperature varies continuously as a function of >uantity

condensed. A mi'ed refrigerant cycle works between +./ and == bars abs. with only

one stage. The fluid composition of the cycle is as follows:

nitrogen K,

methane -K,

ethylene -K,

ethane +K, propane -?K,

n. butane =K.

&pecific energy needed for li>uefaction by this cycle is -= kuefaction by cascade cycles need less specific energy than in other processes..

&hown schemas are simplified because of easier understanding of process. 2eal

plants consists of considerable more heat e'changers, so for e'ample classical

cascade cycle has /D heat e'changers connected by very comple' line system.

-


32/154

Natural gas

Compressor of

propane

epansion

!a"!es

#eat e$%anger separator

Compressor of refrigerant

$ompressor

Liquid -161°C& 1,1 bar

#eat e$%anger

Figure 16.

I-)0('-) C'6') 656/)

".4.%. APCI PROCESS

The process is an A;%" patent 4Air ;roducts and chemical "nc.5 and uses a mi'ed

refrigeration system 6%2 which contains

K nitrogen,

=D K methane,

/= K ethane,

K propane.

Natural gas 4=+ bar, D°%5 is cooled against propane down to -°% and then against6%2 down to -=°%. At that point, it is flashed from += bars down to -. bars in a

+


33/154

drum and in nitrogen stripper to remove helium and nitrogen. The LNG is flashed

again from -. bars to -.D bars before sending to storage tanks.

6%2 is compressed from to == bars by two compressors and the cooled down and

partly condensed in a sea water cooler and propane condenser. Li>uid and vapor

phases are separated and cooled down in main heat e'changer. These two multi

components fluids are then e'panded through uefaction plant and

sent to a distilling column. !btained hydrocarbons are ethane, butane, propane and

gasoline. $thane is always rein(ected in LNG

Gasoline is sent to storage while butane and propane can be:

sent to storage, or

used as make up for 6%2 cooling fluid or can be in(ected back to LNG.

&eparation of

heavier components


34/154

".". DENITROGENATION OF LIQUFIED NATURAL GAS

Natural gas to be li>uefied can contain large >uantities of nitrogen. "n order to lower

LNG transport costs and avoid waste of energy needed to li>uefy nitrogen it is useful

to eliminate N+ before li>uefaction process.

There are two ways to eliminate N+: by simple flashing on dispatch to storage,

by processing in a distilling column.

)y the first way it is suffice to ad(ust the temperature before e'pansion. The most of

nitrogen occurs in the flash mi'ed with fi'ed >uantity of methane.

)y second way the nitrogen is e'tracted at the top of column along with the >uantity

of methane used as a fuel of the plant.

$limination is not complete but usually ade>uate.

#. LNG STORAGE

#.1. HYSTORY OF LNG STORAGE

"n -=D in %leveland !3"! 9&A LNG storage was implemented for first time. At

that time LNG storage was intended to regulate gas consumption during the winter.

1esign and re>uirements for construction at that time were:

gas tight of containment system at -?- °%,

insulation good enough to limit evaporation,

e'ternal protection of insulation to avoid damaging effects of moisture.

Three storage tanks were built of ./K of Ni steel with double wall. %apacity of each

tank was +/DD m. "nsulation material was cork and implemented between two tanks

wall. After three year of satisfactory operation of these three storage tanks it was

decided to build fourth tank4 =/DD m5 with a different shape. 6aterial of the walls

was same .// Ni and insulation was made from mineral wool. After years of

e'ploitation there were some cracks on the wall of the fourth tank. This was repaired

by welding and tank put in service.

!n !ct. +D, -== a leakage of this tank led to first disaster in the history of LNG. The

inflammation of the gases caused =/DD m tank to collapse. $'plosion in city caused

very considerable damage.

This accident caused slow down of LNG industry and considerably increasere>uirements for building new storage tanks in particular: free *ones around tanks,

li>uid recovery, cooling down re>uirements, materials etc.

"n -= the 6oscow region was provided with -DD of 0/m storage cylinders. !nly

cylinders were used. This storage concept was accepted later for %hicago peak

shaving plant.

"n -/ 6ethane ;ioneer unloaded its first cargo from Lake %harles to two +/DD m

storage tanks of %onvey "sland in Great )ritain.

Apart from accident in %leveland there were some others reported:

cracks in tanks operated in fro*en ground 9&A -0D,

e'ternal gas leakage from double wall tank in 1A& "sland in -0,

the 63" membrane was found cracked in &odegaura, tank e'plosion in &taten "sland in -0, due to poor degassing.

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All accidents can be distinguished as:

construction accidents,

operation accidents,

repair accidents.

0.+. GENERAL RULES FOR LNG STORAGE TAN$S

LNG storage facilities development can be considered by:

capacity,

safety standards,

technology of building and applied materials,

control of construction.

Eith increase of LNG trade storage capacity increase too. #rom +DDD m in the

beginning it increase to -+/DDD m.A LNG storage tanks should fulfill the following re>uirements:

full sealing,

to withstand loads resulting from fluid stored,

to retain li>uid in case of e'ceptional condition,

to maintain insulation integrity,

to resist e'ternal aggressions,

to ensure in service check of tanks integrity.

There are various e'isting international standards for design of LNG installations,

design and construction of low pressure, low temperature tanks, storage and handling

of LNG etc. Ehile some of these ade>uately cover about the design aspects of the

storage tanks, some of them cover the safety aspects of the LNG handling. As a

specific instance, the hydrostatic test of the storage tanks and the duration of such test

specified differently in various codes. The site for LNG Terminal must provide ease

of access to the personnel, e>uipment, materials etc. from offsite locations to reach the

site for fire fighting or controlling spill associated ha*ards or for the evacuation of the

personnel.

As per the norms laid in the standard, storage or any process e>uipment handling

LNG, with a capacity more than /Dm shall not be located in buildings.

)asic design considerations for storage tanks are discussed in ne't sentences.

A single containment tank shall be surrounded by a bund wall or dyke to contain anyleakage. Gas detection system is used to monitor the natural gas concentration in the

insulation space.

1yke is provided for the following tanks : single containment tank, double

containment with metallic outer tank, full containment with metallic outer tank and

membrane tank. The containment volume of the dyke is e>uivalent to --D K capacity

of the largest tank within the dyke.

Ade>uate number of cold detectors for monitoring leakage of LNG at the tank roof

should be provided. Tanks with an open annular space and not filled with perlite

insulation should have a pump to remove the li>uid.;ressure relief valve should be entirely separate from the vacuum relief valve. "n

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order to take care of malfunction of any of the relief valves due to blockage in the

sensor line, one e'tra relief valve is installed. Necessary provision is provided to

protect the tank from overpressure as well as to take care of the safe discharge.

Nitrogen or dry chemical powder in(ection provided at the mouth of safety relief

valve discharge.

2ollover ;rotection. "nlet piping must be designed to avoid stratification of LNG 4by providing top and bottom fill lines5. ;rovision for density measurement on tank must

be provided for the entire height of the tank. #or taking care of over pressuri*ation

due to roll over, one of the following options are provided:

flare system,

rupture disc to be provided on the tank with isolation valve 4lock open

condition5 releasing to atmosphere.

1ensity meters and temperature sensors along the height of the storage tanks is

provided.

!verfill ;revention. Two independent type level measuring instruments are provided

for the tank. The level instrument is e>uipped to provide remote reading and high

level alarm signals in the control room. "n addition, independent switches for high

level alarm and highhighlevel alarm with cut off are provided. The highhighLevel

instrument should be hard wired directly to close the li>uid inlet valves to the tank.

The design level of the storage tank must be the ma'imum li>uid level specified by

the designer or manufacturer or D./ m below the top of the shell, whichever is lower.

&afety re>uirements. Tanks should be tight enough to prevent any evaporation losses

and also to avoid ingress of air and moisture.

#or the storage tanks, water sprays must be provided on the tank shell including the

roof and the appurtenances on the tank. #or single containment tanks as well asdouble or full containment tanks having metallic outer tank, and membrane tank

which are having a dyke, high e'pansion foam systems must be provided.

The possibility of an ad(acent tank fire must be taken into consideration when

designing insulation for LNG storage tanks.

"f electrical heating system is provided to the tank, it shall consist of a number of

independent parallel circuits so designed that electrical failure of anyone circuit does

not affect power supply to the remaining circuits.

#.%. DIFFERENT TYPES OF LNG STORAGE TAN$S

There are three ma(or types of LNG storage tanks: storage tanks in fro*en ground,storage tanks with self supporting internal tanks and membrane storage tanks.

0..-. LNG &T!2AG$ "N #2!@$N G2!9N1

"n regions where the earth>uake is often or where the environment does not permit

very elevated construction, tanks are often buried.

"n the fro*en ground storage, the ground has to be fro*en to make it impervious and to

make it strong structurally. !n being cooled to below -DD °% it becomes as strong as

concrete and is maintained indefinitely in this condition by the cold in the stored

li>uid. The vapori*ing rate for these tanks are very high at the beginning and remain

close to to =K a day what is much more

than the rate of the other tanks. !ther problems e'perienced with this system are

?


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related to ground displacement and to the frost progression what can be ha*ardous for

peripheral installations.

filling line 2elief valve

#ro*en ground =D m #ro*en ground

"nsulation of mineral wool pump

Figure 18.

LNG S-*('0) +(*) 0(*

0..+. &$L# &9;;!2T"NG TANH&

&elf supporting LNG storage tanks have double wall. "nternal tank in contact with

li>uid is independent of the e'ternal container and has the mechanical characteristics

re>uired to retain li>uid on its own. 6aterial of internal tank is K Ni or aluminum

alloy. The e'ternal tank is carbon steel. "nsulation material is perlite and glass wool.

"nsulation for the bottom is foamglass with mechanical characteristic that provide

satisfactory load distribution. The insulation space is under nitrogen pressure.

LNG output is from tank bottom.

"mproved version of double metallic tank wall include:

internal and e'ternal cryogenic steel wall,

intermediate aluminum foil,

reinforced concrete wall around tank as high as the tank wall.

;ressure in the tank is -.- bar. )oil off coefficient for the tank capacity of -+DDDm is

D.- K per day. $vaporated gas >uantity depend of insulation thickness and tankcapacity. The consideration of terrorist attack or aircraft impact led to a closed pre

stressed concrete tank.

2einforced or double integrity self supporting tank are different from previous ones

due to presence of an e'ternal prestressed concrete container which can be used to

retain LNG in case of internal container leakage.

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Tank

9' ni$(e" !r aluminum

"nsulation

Carbon stee"

!uter tank

;erlitensulation

foundation

bund

Figure 19.

D*:/) 3'// LNG -*('0) -'=

Tank

9' ni$(e" !r aluminum

"nsulation

K Nickel outer tank

;erlitensulation

foundation

%oncrete bund

Figure 20.

R)+*(6) *:/) -)0(-5 )/+ *(-0 -'=

0.. 6$6)2AN$ TF;$ TANH&

The main characteristic is that the sealing efficiency and mechanical strength function

are separated. &ealing efficiency is provided by a membrane that is not submitted to

stresses. Li>uid weight is transferred by insulation to the concrete envelope.

6embrane material is D= or D= L stainless steel or invar. "nsulation material are:

polyurethane 4;95 foam panels, perlite bo'es or balsa wood. The main advantage of

this tanks is that membrane in contact with LNG is only sub(ected to low in service

stresses and that the separation of the insulation spaces from gaseous phase enablescontinuous in service check of the membrane integrity. There are two types of


39/154

membrane LNG storage tanks:

Techniga* membrane tanks,

Ga*Transport membrane tanks.

The Techniga* membrane is a -.+ mm thick stainless steel corrugated sheet welded to

the T"G process with no filler material. %orrugations of the membrane are press formed. This structure provides the membrane deformation capabilities of / m

deflection along +D m in length. The insulation is associated to the e'ternal concrete

wall constitutes the second cryogenic barrier. "nsulation panels are glued to the

concrete. The cold face of the panel incorporates playwood ensuring satisfactory

seating of the membrane. The membrane is punctually secured to the installation by

metallic anchor points inserted in the insulation.

The Ga*Transport techni>ue include invar membrane 4?K Ni5 having a very low

e'pansion coefficient and thickness a D.0 mm. "nsulation is made of playwood bo'es

filled with perlite and glued into e'ternal structure.

)ecause of often earth>uake


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The retention basin is provided with a primary pit which receives the overflowing

LNG. )oth primary pit and channels are covered in colloidal concrete intended to

limit evaporations in case of LNG overflow.

#ire fighting means are:

a water system constantly under pressure designed to water sprinkle the whole

tank, powder stations,

foam generators capable to fill the basin over + meters in height in -/ minutes.

&urveillance of the tanks is ensured by cameras and sensors which detect cold, smoke

and flames.

;rior to starting up a se>uence of operations must be conducted in order to:

cancel the risk of e'plosion,

lower the moisture content in order to limit the risks of icing.

These operations include: nitrogen inerting of the tank, gassing up and cooling down

of the tank.

0./. )$3A"!2 !# LNG "N &T!2AG$ TANH&

"n LNG storage tanks sometimes forms different density li>uid layers. This mainly

happens when in tank with certain >uantity of li>uid was added LNG with different

density. &tratification is stable if heavier li>uid is under lighter li>uid.

2ollover is phenomenon where the stability of two stratified layers of li>uid is

disturbed by a change in their relative density resulting in a spontaneous rapid mi'ing

of the layers. This is accompanied by sudden increased of vapori*ation that can

increase pressure in the tanks rapidly causing relief valves to open.

To avoid the stratification of LNG layers in storage tanks there are ne't facilities

filling line on top and bottom of tank,

filling through no**les on different levels of tank,

filling of tank through perforated pipes.

#re>uent filling and discharging of the tank contribute to better li>uid mi'ing so

avoiding rollover.

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8. LNG LOADING J UNLOADING ARMS

Ehen handling with LNG safety is on first place. LNG loading and unloading

e>uipment is considered as most potentially dangerous e>uipment. LNG transfer from

ship to the terminal and vice versa is accomplished using hard loading arms.

A typical marine hard arm used for LNG is shown in #igure +-.The shore fi'ed connection part of e>uipment on (etty and movable arms are

connected by swivel (oints. The swivel (oint provide the re>uired range of movement

between ship and shore connection. A counter balance weight is provided to reduce

deadweight of the arm on the ship side and to reduce the power to manoeuvre the

arms. The range of movement is determined by:

tidal variation,

shipIs draft and trim,

allowance to range fore and aft and drift away from berth.

The hard arms design has manual or automatic emergency disconnect arrangements in

the event that the operating limits are approached or some others emergency occurs.

The hard arms and ship lines can be connected by:

bolted flanges,

>uick connect and disconnect coupling.

uick connectOdisconnect coupling can be under manual control or remotely

hydraulically operated. 1uring cargo transfer the (oint is maintained by a positive

lock, independent of the hydraulic power supply.

6ain parts of e>uipment are:

base plate with connection to dockside piping,

inboard and outboard leg, counterweights,

swivel (oints,

hydraulic control system,

;owered emergency release system including two ball valves,

hydraulic couplings to the ship piping,

nitrogen purging system,

portable remote control system.

The ;owered emergency release coupling system is located at lower end of the arm. "t

consists of a hydraulically released coupling flanked above and below by a

hydraulically operated ball valve. "n emergency the two ball valves first close, thencoupling release. The lower ball valve remains attached to the shipIs manifold. The

upper ball valve with arm is free to luff clear of the ship.

The swivel (oints are most important parts of this e>uipment. This characteristic way

of sealing was developed by 9&A space program ATLA& for nitrogen supply.

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Figure 21.

L*'0/*'0 '(7

- base, + swivel (oint, inboard pipe, =swivel (oint, /outboard line, ?coupling

0counterweights, counterweights, sheave, -D cable.

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Figure 22.

P*3)() )7)(0)65 ()/)') 6*/0

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III1. CARGO CONTAINMENT SYSTEMS ON LNG SHIPS

1.1. CONSTRUCTION RULES

The main intention of all international norms and rules for the ships carrying LNG is

to provide safe carriage of li>uefied natural gas. These rules prescribe design and

constructional solutions of ships and installed e>uipments to minimi*e risks to ships,

crew and the environment.

&ince the introduction of li>uefied gas carriers into the merchant shipping, it was

recogni*ed that there was a need for an "nternational code for the carriage of li>uefied

gases in bulk.

At the beginning of the -0DSs The 6arine &afety %ommittee 46&%5 of the

"nternational 6aritime !rgani*ation 4"6!5, known then as the "nternational

%onsultative 6aritime !rgani*ation 4"6%!5, started work on a Gas %arrier %ode

with the participation of the ma(or country delegations representing Gas %arrier

owners, the "nternational Association of %lassification &ocieties, the 9nited &tates

%oast Guard and several other "nternational associations.

"t was resulted by the S%ode for the %onstruction and $>uipment of &hips %arrying

Li>uefied Gases in )ulkS introduced under Assembly 2esolution A+ 4"5 in

November -0/.

This was the first code developed by "6! having direct applicability to Gas %arriers.

The basic philosophy behind the codeIs re>uirements is safety. All rules andre>uirements can be classified by three main groups:

to avoid contact between LNG and noncryogenic materials,

to avoid formation of e'plosive mi'ture,

to move away all ignition sources from spaces where gas and air can be in

contact.

#irst group of re>uirements concern construction of the containment systems and use

of the cryogenic materials. The cryogenic materials 4alloys5 have e'cellent

mechanical properties at low temperatures. All containment system must be provided

with a partial or complete secondary barrier to ensure overall system integrity in the

event of primary barrier leakage. The LNG carriers with spherical tanks have reducedsecondary barrier which consists of drip tray at bottom of the tank.

The membrane LNG ships must always be provided with complete secondary barrier.

&econd group of rules re>uire use of tight piping, use of double wall pipes, inert gas

use and gas detection system use in spaces near cargo.

Third group of rules define danger areas in which can be installed only intrinsic safety

electrical e>uipment. "ntrinsic safe e>uipment is incapable of releasing sufficient

electrical or thermal energy to cause ignition of ha*ardous atmosphere with easily

ignited concentration.

As all conventional LNG carriers are also sub(ected to risk of collision and grounding.

To avoid effects of these situations it is formulated certain number of re>uirements.

These rules define dimension and position of cargo tank in regard to shipIs hull. The

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cargo tanks are moved away from hull creating by that way additional space for

ballast tanks.

LNG carriers can be sub(ected:

to different dynamical stresses due to cargo load,

to thermal stress due to low cargo temperature.

Therefore these ships have the double hull which:

limits effects of hypothetic damage,

improve the ship rigidity what is favourable specially in regard the membrane

containment system, because of fle'ure stresses, and in case of containment system

with spherical tanks, because of torsion stresses,

creates ballast space what is very important on this kind of ships because of

unloaded voyage.

1uring normal e'ploitation heat e'change through insulation can produce double hull

temperature drop of /°% to -D °% in regard to ambient temperature. #or referent

ambient temperature of - °% double hull temperature can drop to + °%. "t

re>uires use of alloyed steel for double hull and cofferdamIs walls heating.

1ue to real danger of contact between LNG and double hull it was logical to built

secondary barrier around the cargo tanks. The membrane containment system is based

on thin primary barrier so these systems must be always provided by complete

secondary barriers. The secondary barrier must be capable to keep LNG in event of

primary barrier leakage. The secondary barrier significantly complicates and increase

cost of construction these ships. Therefore for membrane containment system rules

re>uire two membranes while for containment system with spherical tanks rules

re>uires only partial secondary barrier.As for all tankers for li>uid cargo so for LNG tankers it was necessary to study cargo

motions in the tanks. &hip motions cause cargo motion that can become synchroni*ed

4sloshing5 and damage specially the membrane and e>uipment in the tanks. #or the

sloshing problem was necessary to:

reduce free surface of top of the membrane tanks,

limit loading levels of cargo, so in e'ploitation loading level is ma'imum level

of the tank while on return ballast voyage in tanks remain minimum of cargo

to maintain the tanks temperature at re>uired values.

The top part of membrane tanks is chamfered at =/ deg. to minimi*e free surface

effects. The bottom part is also chamfered to enable the tank to follow the shape of theship.

The containment systems with spherical tanks have no sloshing problem because of

their design shape.

The successful operation of the LNG tankers depend of shipIs hull structure, cargo

containment system, e>uipment and crew skill. 1ifferent types of cargo containment

systems and unusually dimensions re>uire highest technical e'pertise and research to

solve all technical problems .

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1.2.TYPES OF CARGO CONTAINMENT SYSTEMS

arious cargo containment systems have been proposed and designed. 1ue to their

economy and reliability only two cargo containment systems are adopted:

self supporting system

systems with membrane tanks.

&elf supporting tanks do not form part of shipIs hull and do not contribute to the hull

strength. &elf supporting tank type ) is applied for LNG carriers. This type of

containment system is sub(ected to a much accurate type of stress analyses that

include fatigue and crack propagation analyses.

%argo containment system with membrane tanks are not self sup

Introduction to LNG - Bruno Bronzan

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