OKAFOR UDODIRI ud4okafor@yahoo.comABSTRACT

LNG (Liquefied Natural Gas) is a form of natural gas that evolved due to the problem of transporting natural gas over a long distance such as from one country to another or one continent to another. It has specific properties which makes it a better form of natural gas and which also present problems in making handling of this gas difficult.Storage and transportation of LNG accounts for about 35 percent of the capex in the business of buying, processing and selling of natural gas.This paper examines the previous technology involved in the storage of liquefied natural gas; looks into some modifications made in the present storage methods, and also would examine problems faced in the storage of LNG.The transportation of these products would be examined, focusing mainly on different methods of transportation by sea and on the effective handling of these products on vessels and ships. The short transport of this gas from the storage vessels to the point where it would be loaded to the ship would be also analyzed as it involves transportation through pipelines.Some problems associated with the storage and transportation of LNG would also be evaluated and means of avoiding, reducing and converting it to useful process would be considered.The economics and commercial aspect of transporting LNG would be looked into making the Nigerian- International market a point of reference.

INTRODUCTIONBACKGROUND STUDY/ LITERATURE REVIEWA liquefied gas is the liquid form of a substance which, at ambient temperature and at atmospheric pressure, would be a gas. An alternative way of describing a liquefied gas is to give the temperature at which the saturated vapor pressure is equal to atmospheric pressure — in other words the liquid's atmospheric boiling point. OVERVIEW OF LIQUEFIED NATURAL GAS PRODUCTIONLNG (Liquefied Natural Gas) is processed from natural gas found in• Underground wells, which are mainly gas bearing (non-associated gas) • Condensate reservoirs (pentanes and heavier hydrocarbons) • Large oil fields (associated).The raw feed gas is first stripped of condensates. This is followed by the removal of acid gases (carbon dioxide and hydrogen sulphide). Carbon dioxide must be removed as it freezes at a temperature above the atmospheric boiling point of LNG and the toxic compound hydrogen sulphide is removed as it causes atmospheric pollution when being burnt in a fuel. Acid gas removal saturates the gas stream with water vapor and this is then removed by the dehydration unit. The gas then passes to a fractionating unit where the NGLs are removed and further split into propane and butane. Finally, the main gas flow, now mostly methane is liquefied into the end product, liquefied natural gas (LNG). To lower the temperature of the methane gas to about -162°C (its atmospheric boiling point) there are three basic liquefaction processes in current use. These are outlined below:— Pure refrigerant cascade process — three stages are involved in this process, each having its own refrigerant, compressor and heat exchangers. The first cooling stage utilizes propane, the second is a condensation stage utilizing ethylene and, finally, a sub-cooling stage utilizing methane is involved. The cascade process is used in plants commissioned before 1970. • Mixed refrigerant process — whereas with pure refrigerant process (as described above) a series of separate cycles are involved, with the mixed refrigerant process (usually methane, ethane, propane and nitrogen), the entire process is achieved in one cycle. The equipment is less complex than the pure refrigerant cascade

process but power consumption is substantially greater and for this reason its use is not widespread. • Pre-cooled mixed refrigerant process — this process is generally known as the MCR process (Multi-Component Refrigerant) and is a combination of the pure refrigerant cascade and mixed refrigerant cycles. It is by far the most common process in use today.

BRIEF DIAGRAM SHOWING THE LNG PROCESS

PROPERTIES OF LIQUIFIED NATURAL GAS

• Colorless, odorless and non-corrosive liquid• Atmospheric point -1600c to -163oc• Density 458 – 463 kg/m3• 1 m3 liquid equals some 600sm3 of gas• Critical temperature -82.5• Critical pressure 44.7 bar absolute• Cryogenic insulated storage• Quickly vaporized • Liquid not flammable but gas burns• Liquid is cold: burns

• Heating value 21-24 MJ/L

• Flash point- 160oc

• Flammability range 5-15

• Auto ignition 540 oc

IN SUMMARY THE LNG VALUE CHAIN INVOLVES1. Natural gas production, the process of finding and producing natural gas for delivery to a processing facility.2. Liquefaction, the conversion of natural gas into a liquid state so that it can be transported in ships.3. Transportation, the shipment of LNG in special purpose ships for delivery to markets.4. Re-gasification, conversion of the LNG back to the gaseous phase by passing the cryogenic liquid through vaporizers.5. Distribution and delivery of natural gas through the national natural gas pipeline system and distribution to end users.

STATEMENT OF PROBLEMThe effective handling of liquefied natural gas when stored or being transported is a very important issue in the value chain of production and sales.Inappropriate knowledge of the mechanisms governing the maintaining this gas at liquid state poses more risk to the personnels in charge and the environment .

PURPOSE OF STUDYThis study presents a detailed and explanatory work on 1. The principles, types and processes involved in the storage of liquefied natural gas.2. The principles, types and processes involved in the transportation of liquefied natural gas.3. The hazards that have occurred in the storage of this gas and analyze the reasons why such were experienced.4. Commercial procedure in the transport of LNG

THEORYThe subject matter of this work is how LNG is kept cold?Insulation, as efficient as it is, will not keep the temperature of LNG cold by itself.LNG is stored as a boiling cryogen -- a very cold liquid at its boiling point given the pressure at which it is being stored. Stored LNG is analogous to boiling water, only 472°F colder. The temperature of boiling water (212°F) does not change, even with increased heat, as it is cooled by evaporation (steam generation). In much the same way, LNG will stay at near constant temperature if kept at constant pressure. This phenomenon is called auto refrigeration. As long as the steam (LNG boil off vapor) is allowed to leave the tea kettle (tank), the temperature will remain constant.As previously discussed the basis governing the storage and transport of liquefied gases is1. Insulation2. Autorefrigeration AutorefrigerationAuto-refrigeration is a phenomenon common to liquefied natural gases. Liquefied compressed gases exist in both the liquid and gaseous phases at ambient temperatures with pressures ranging from 2 psig up to 2,500 psig. That is, there is a gaseous layer over the liquefied gas within vessel. The vapour produced above the surface of a boiling cargo due to evaporation is called Boil-off. It is caused by heat ingress or a drop in pressure. The ability to adequately discharge this vapour at a concise rate solves the bulk problem.InsulationInsulation is a very important factor in preventing heat exchange between a system and surrounding, materials and inert gases mostly act insulators. The ability to determine the best material composition, layout and structure is the basis for keeping liquefied gases close to its boiling pointDISCUSSIONSTORAGE OF LNGLNG can be stored as a fully refrigerated liquid at atmospheric pressure and at low temperature equal to the cargo's boiling point in:• Single containment-double-wall tanks • Double-containment tanks • In-ground tanksSINGLE CONTAINMENT-DOUBLE-WALL TANKSingle containment tanks are most usually provided with an outer shell surrounding the primary tank. They are constructed so that only the primary containment is required to meet the low-temperature of 1620C requirements for LNG storage. The outer shell is primarily for the retention and protection of loosely filled insulation and to contain nitrogen purge-gas pressure. The outer shell is not designed to contain refrigerated liquid in the event of leakage from the primary container.

The diagram below shows two complete tanks with an annular gap of about 0.5 meters in between. The annular space is filled with granular insulation ( perlite) and a nitrogen breather system is provided to accommodate volume changes in the inter-space, resulting from atmospheric pressure changes and inner tank expansion or contraction. A suspended roof, inside the outer tank dome, fits inside the inner tank.The outside tank/ outer shell is made up of carbon, The inner tank, in contact with the LNG liquid, is made of materials suitable for cryogenic service. It has a flat metallic bottom and a cylindrical metal wall both built of materials suitable for cryogenic temperatures (usually nine percent nickel steel). The inner tank bottom rests on a rigid insulation material, such as foam glass. The strength of the total tank must withstand the hydrostatic load of the LNG. This hydrostatic head determines the thickness of the inner tank side walls. The tanks also have an insulation layer with a flat suspended deck supported by an outside domed roof vapor barrier or outer tank (often made of carbon steel). The bund wall contains any liquid leakage. Also, its position minimizes boil-off rate from any leakage by preventing liquid from spreading over a large area of warm ground. FIGURE 1. SINGLE CONTAINMENT-DOUBLE-WALL TANK

DOULE WALL-DOUBLE CONTAINMENT TANKDouble containment storage tanks are a development of the single-wall tank. They provide increased safety margins against tank leakage by introducing an extra inner tank. The outer shell acts in the same way as a bund and contains any liquid leakage from the inner shell — but in this case it also avoids vapor release to atmosphere. The mini-bund, as shown below, is provided to contain minor leaks from pipelines, valves and flanges. FIGURE 2. DOULE WALL-DOUBLE CONTAINMENT TANK

IN GROUND STORAGE In-ground tanks are a popular option for storing LNG which provides:— • High-integrity storage with virtually no risk of spillage • High seismic protection against earthquakes, and • Minimal visual impact on the environment The main features of one such in-ground LNG storage tank are illustrated in the Figure below. Primary containment is by a stainless steel membrane, supported (as in ships' membrane type tanks) by rigid polyurethane foam insulation. This, in turn, is supported within a reinforced concrete caisson. The roof is a dome-shaped carbon steel structure supporting a suspended deck with glass wool insulation FIGURE 3. IN GROUND STORAGE TANK

Example of a typical feature of a storage tankTank Design Data Design Type Above ground, Membrane, Suspended Deck

Gross Liquid Capacity 200,000 m3Normal Working Capacity 1,020 m3Design Temperature of Product -170 0CDesign Pressure 29kpaOperating Pressure 50 ~ 350 mbarg.Operating Level 5 ~ 8.81 mBOG rate 0.53 vol%/dayLNG Pump 50 m3/h x 2, 15barInner Tank Features- Diameter 84.18 m- Shell Height 37.92 mOuter Tank Features- Diameter 86.71 m- Height 52.21 m- Wall Thickness 1.2 m

LIQUIFIED NATURAL GAS TRANSPORTHISTORY OF THE MARINE TRANSPORT OF LNG• 1912: First LNG plant built in West Virginia• 1914: Godfrey Cabot patents a barge to carry liquid gas, waterborne transportation technically feasible• 1959: METHANE PIONEER, converted cargo ship, carries 5000m3 of LNG between Lake Charles and UK demonstrating feasibility of waterborne transportation.• 1964: Methane Princes & Methane Progress, 27400m3, become first commercial LNG vessels, operating between Algeria and the UK• 1969: Gas Transport membrane system vessels Polar Alaska & Arctic Tokyo, 71000m3, begin service from Alaska to Tokyo• 1971: Kvaerner develops 88000m3 Moss spherical containment system• 1975: 100 km3 size exceeded with delivery of Frenchbuilt BEN FRANKLIN, 12000m3• 1979: Formation of Society of International Gas Tanker and Terminal Operators (SIGTTO) to promote safe and reliable operation of gas tankers and terminals• 1993: Polar Eagle and Arctic Sun, 83.5km3, with IHI prismatic containment system begin service from Alaska to Tokyo

CLASSIFICATION OF LNG CARRIERS LNG carriers are classified by their cargo containment designs they are:1. Kvaerner-moss spherical tank2. Membrane system• Gaz transport • Technigaz membrane systems e.g. Mark iii, no96, cs13. IHI prismatic

WORLD DISTRIBUTION OF LNG CARRIERS

TECHNIGAZ 11%GAZ TRANSPORT 37%KVAERNER MOSS SPHERICAL TANK 51%OTHERS 1%

FIGURE 4. LNG VESSELS DISTRIBUTION

LNG VESSEL TYPES AND DESIGN STRUCTURE

1. KVAERNER-MOSS

FIGURE 6 SCHEMATIC DIAGRAM OF KVAERNER- MOSSThe Kvaerner moss design is a type B independent tank of the spherical type. A Type 'B' tank requires only a partial secondary barrier in the form of a drip tray. The hold space in this design is normally filled with dry inert gas. However, when adopting modern practice, it may be filled with dry air provided that inerting of the space can be achieved if the vapor detection system shows cargo leakage. A protective steel dome covers the primary barrier above deck level and insulation is applied to the outside of the tank.

FIGURE 7. VESSEL OF THE KVAERNER MOSS TYPEGAZ TRANSPORT MEMBRANE SYSTEM Gaz Transport system comprises of a thin Invar primary barrier. Invar is a stainless steel alloy containing about 36 per cent nickel and 0.2 per cent carbon. This is attached to the inner (cold) surface of perlite-filled plywood boxes used as primary insulation. These boxes have thickness of between 200 and 300 millimeters. These, in turn, are attached to an identical inner layer of Invar (the secondary barrier) and, finally, a further set of similar perlite-filled boxes is used for secondary insulation. Invar is chosen for the membranes because of its very low coefficient of thermal expansion, thus making expansion joints, or corrugation, in the barriers unnecessary. Newer designs of the Gaz Transport system utilize Invar membranes of 0.7 millimeters thickness in strakes of 0.5 meters width and strengthened plywood boxes to hold the perlite insulation. The perlite is processed with silicon to make it impervious to water or moisture. The thickness of the insulation boxes can be adjusted to obtain the required amount of boil-off. FIGURE 8. GAZ TRANSPORT MEMBRANESTechnigaz membrane system The Technigaz system, features a primary barrier of stainless steel (1.2 millimeters in thickness) having raised corrugations, or waffles, to allow for expansion and contraction. In the original Mark I design, the insulation that supports the primary membrane consisted of laminated balsa wood panels held between two plywood layers; the face plywood formed the secondary barrier. The balsa wood panels were interconnected with specially designed joints comprising PVC foam wedges and plywood scabs and were supported on the inner hull of the ship by wooden grounds. In the latest design (Mark III) the balsa wood insulation is replaced by reinforced cellular foam. Within the foam there is a fiberglass cloth/aluminum laminate acting as secondary barrier. FIGURE 9. TECHNIGAZ MEMBRANE SYSTEMIHI PRISMATICIHI prismatic is a Type 'B' tank, of prismatic shape in LNG service. The prismatic Type 'B' tank has the benefit of maximizing ship-hull volumetric efficiency a

nd having the entire cargo tank placed beneath the main deck. Where the prismatic shape is used, the maximum design vapor space pressure is, as for Type 'A' tanks, limited to 0.7 barg.

FIGURE 10. IHI PRISMATIC LNG TANK

VESSEL DESIGN AND EQUIPMENT LAYOUTCARGO PIPELINEPipelines carry liquid and vapor to and from the ship this lines are fitted to the ship via the manifold the connection. The liquid loading line is led through the tank dome to the bottom of each cargo tank; the vapor connection is taken from the top of each cargo tank. Provision must be made in the design and fitting of cargo pipelines to allow for thermal expansion and contraction. This is best achieved by the fitting of expansion loops or, by using the natural geometry of the pipework.CARGO VALVES AND STRAINERSIsolating valves are provided, in LNG vessels having a MARVS( Maximum Allowable Relief Valve Setting)of 0.7 bar comprises of one manually operated globe valve and a remotely operated isolation valve fitted in series. Emergency shutdown valves are also provided at the vapour and liquid line.CARGO PUMPS Cargo pumps fitted on board refrigerated gas carriers are normally of centrifugal design and may be either of the deep well or submerged type. They may operate alone or in parallel with one another. Ice prevention at cargo pumps The formation of ice or hydrates may occur in ships carrying LNG . Furthermore, hydrates may be transferred from the terminal during loading operations. Hydrates from the shore can be removed by cargo filters in the terminal loading lines. Hydrate formations may enter cargo pumps, block lubricating passages, unbalance impellers and seize bearings. To prevent such damage it is common practice to inject a small quantity of freezing-point depressant into the cargo pump, especially submerged pumps. When deep well pumps are not in operation, it is recommended that manual rotation of the shafts be carried out during cool-down and loading to prevent freezing of the impellers. CARGO VAPORISERS A means of producing cargo vapor from liquid is often required on LNG gas carriers. For example, vapor may be needed to gas-up cargo tanks or to maintain cargo tank pressure during discharge. This latter need will be more obvious in the absence of a vapor return line from shore. Accordingly, a vaporiser is usually installed on board for these purposes. Cargo vaporizers may be either vertical or horizontal shell and tube heat exchangers. They are used with either steam or sea water as the heating source. BOIL-OFF CONTROL There must be a means to control cargo vapour pressure in cargo tanks during cargo loading and on passage. A reliquefaction plant is fitted for this purpose. This equipment is designed to perform the following essential functions: • To cool down the cargo tanks and associated pipelines before loading; • To reliquefy the cargo vapour generated by flash evaporation, liquid displacement and boil-off during loading; and • To maintain cargo temperature and pressure within prescribed limits while at sea by reliquefying the boil-off vapour. LNG boil-off and vapour-handling systems The older LNG ships use steam turbine-driven compressors to handle boil-off vapors. Newer designs incorporate electrically driven equipment. Boil-off vapors are produced during cool-down, loading and during the loaded and ballast voyages.A low-duty compressor handles the boil-off whilst on passage: a high-duty compressor handles cargo vapors produced during cool-down and loading, returning these vapors to shore.

When a ship is at sea, the low-duty compressor collects the boil-off gas from a header connected to each cargo tank. It then passes the boil-off through a steam heater and into the engine room . There are a number of automatic protective devices built into the system to ensure safe operation and these must be regularly inspected and maintained. Protective systems include continuous monitoring for leakage and automatic shut-down in the event of system malfunction or leak detection. The compressors are provided with surge controls and other protective devices. LNG is the only liquefied gas product allowed by the Gas Codes to be burnt in the ship's boilers. The other gases, having densities heavier than air, are considered to be hazardous for this purpose.

INERT GAS AND NITROGEN SYSTEMS LNG ships were once provided with storage facilities for liquid nitrogen but newer designs include a nitrogen generation plant. However, up to now, the quantity of nitrogen produced on board has not been of sufficient volume for tank-inerting operations. It is fitted mainly for interbarrier space inerting. Where cargo tank inerting is required on LNG ships, nitrogen from the shore, or combustion-generated inert gas is used. Nitrogen production on ships The most common system utilized for the production of nitrogen on ships is an air separation process. This system works by separating air into its component gases by passing compressed air over hollow fibre membranes. The membranes divide the air into two streams — one is essentially nitrogen and the other contains oxygen, carbon dioxide plus some trace gases. This system can produce nitrogen of about 95 to 97 per cent purity. The capacity of these systems depends on the number of membrane modules fitted and is dependent on inlet air pressure, temperature and the required nitrogen purity. FIGURE 11.NITROGEN PRODUCTION ON SHIP

SEQUENCE OF OPERATION FOR LNG TRANSPORTATION FIGURE 12. TYPICAL SEQUENCE OF OPERATION FOR A VESSEL FROM THE SHIP BUILDER TO THE POINT OF DISCHARGE OF CARGO (LNG)TANK INSPECTIONBefore any cargo operations are carried out it is essential that cargo tanks are thoroughly inspected for cleanliness; that all loose objects are removed; and that all fittings are properly secured. In addition, any free water must be removed. Once this inspection has been completed, the cargo tank should be securely closed and air drying operations may startDRYINGDrying the cargo handling system in any refrigerated ship is a necessary precursor to loading. Water vapour and free water must all be removed from the system. If this is not done, the residual moisture can cause problems with icing and hydrate formation within the cargo system. The reasons are clear when it is appreciated that the quantity of water condensed when cooling down a 1000m3 tank containing air at atmospheric pressure, 30°C and 100% humidity to 0°C would be 25 liters. Whatever method is adopted for drying, care must be taken to achieve the correct dew point temperature. Malfunction of valves and pumps due to ice or hydrate formation can often result from an inadequately dried system. While the addition of antifreeze may be possible to allow freezing point depression at deep-well pump suctions, such a procedure must not substitute for thorough drying. INERTINGInerting cargo tanks, cargo machinery and pipelines is undertaken primarily to ensure a non-flammable condition during subsequent gassing-up with cargo. For this purpose, oxygen concentration must be reduced from 21 per cent to a maximum of

five per cent by volume although lower values are often preferred .The two methods used are the• Displacement• Dilution

GASSING UPGassing up is done to remove inert gas from the cargo tank is. This is achieved by gassing-up, using vapour from the cargo to be loaded at ambient temperature and venting the incondensibles to atmosphere. Gassing up could also be done during a change of grade from one LNG to another, it may first be necessary to remove the vapour of the previous cargo with vapour of the cargo to be loaded.

COOL DOWNCooling down is necessary to avoid excessive tank pressures (due to flash evaporation) during bulk loading. Cool-down consists of spraying cargo liquid into a tank at a slow rate. The lower the cargo carriage temperature, the more important the cool down procedure becomes. Before loading an LNG cargo, ship's tanks must be cooled down slowly in order to minimize thermal stresses. The rate, at which a cargo tank can be cooled, without creating high thermal stress, depends on the design of the containment system and is typically 10°C per hour. The normal cool-down procedure takes the following form. Cargo liquid from shore (or from deck storage) is gradually introduced into the tanks either through spray lines, if fitted for this purpose, or via the cargo loading lines. The vapours produced by rapid evaporation may be taken ashore or handled in the ship's reliquefaction plant. Additional liquid is then introduced at a rate depending upon tank pressures and temperatures. If the vapour boil-off is being handled in the ship's reliquefaction plant, difficulties may be experienced with incondensibles, such as nitrogen, remaining from the inert gas.LOADINGWhen LNG is being loaded, it is necessary to consider the location, pressure, temperature and volume of the shore tanks as well as the terminal's pumping procedures. Fully refrigerated ships usually load from fully refrigerated storage where tanks typically operate at a pressure of approximately 60 millibars. This pressure will allow the cargo at the bottom of a full shore tank to sustain a temperature perhaps one degree Centrigrade warmer than its atmospheric boiling point. When this cargo is pumped to the jetty, the pumping energy required for transfer is dissipated in the liquid as heat, to which must be added the heat flow into the liquid through the pipelines. The cargo may, therefore, arrive on the ship at an even warmer temperature. When loading without a vapour return line being used, the vapour which is displaced by the incoming liquid must be reliquefied on board. The power required for this, and to compensate for the pumping energy and the heat flux through the insulation, may leave little capacity for cooling the cargo during loading. The early stages of loading can be critical, particularly where significant distances exist between the storage tank and jetty. The ship's tank pressures must be regularly checked . Loading rates should be reduced, and if necessary stopped, when difficulties are experienced in maintaining acceptable tank pressures. A rise in ship's tank pressure in the early stages of loading can also be controlled to some extent by loading limited quantities of liquid into the cargo tank via the top sprays, if fitted. This will help to condense some of the cargo vapours. BULK LOADINGA close watch and monitoring should be kept on the ship's cargo tank pressures, temperatures, liquid levels and interbarrier space pressures, throughout the loading operation. Towards the end of loading, transfer rates should be reduced as. On completion of loading, ship's pipelines should be drained back to the cargo tanks. Remaining

liquid residue can be cleared by blowing ashore with vapour, using the ship's compressor. Alternatively, this residue may be cleared by nitrogen injected into the loading arm to blow the liquid into the ship's tanks. Once liquid has been cleared and pipelines have been depressurized, manifold valves should be closed and the hose or loading arm disconnected from the manifold flange. In many ports it is a requirement, before disconnection takes place, for the hard arm, hose and pipelines at the manifold to be purged free from flammable vapour. The maximum volume to which any tank may be filled is governed by the following formula:—

where: LL = loading limit expressed in per cent which means the maximum liquid volume relative to the tank volume to which the tank may be loaded. FL = filling limit = 98 per cent unless certain exceptions apply. ρR =

�elative density of ca

�go at the

�efe

�ence tempe

�atu

�e.

ρL = �elative density of the ca

�go at the loading tempe

�atu

�e and p

�essu

�e.

LOADED VOYAGE• Ca

�go tempe

�atu

�e cont

�ol

It is necessa�y to maintain st

�ict cont

�ol of ca

�go tempe

�atu

�e and p

�essu

�e th�

oughout the loaded voyage. In LNG ships, the boil-off is bu�ned as fuel in the

ship's main boile�. Boil off is the main natu

�al cont

�ol of LNG tempe

�atu

�e

• LNG boil-off as fuel Although it is feasible to

�eliquefy LNG boil-off vapou

�s, the equipment

�equi

�e

d is complex and expensive and, to date, full-scale equipment has not been installed on boa

�d ships. As methane vapou

�s, at ambient tempe

�atu

�e, a

�e lighte

� tha

n ai� boil-off is used as fuel fo

� the ship's main p

�opulsion du

�ing sea passage

s. LNG is the only ca�go which is pe

�mitted to be used as fuel in this manne

�.

Daily boil-off �ates du

�ing the loaded voyage va

�y with changes in ba

�omet

�ic p

�essu

�e (unless absolute p

�essu

�e cont

�ol is adopted), ambient tempe

�atu

�e and se

a conditions. Fo� this

�eason, a close watch must be kept on tank p

�essu

�es and

inte�-ba

��ie

� space p

�essu

�es. On no account should ca

�go tank p

�essu

�es be allo

wed to fall below atmosphe�ic. Typical figu

�es fo

� LNG ca

��ie

� boil-off

�ates a

�e f

�om 0.10 to 0.15 pe

� cent of the ca

�go volume pe

� day du

�ing the loaded voyag

e and 0.10 pe� cent pe

� day fo

� the ballast voyage. It should be noted that LNG

often contains a small pe�centage of nit

�ogen, which will boil-off p

�efe

�entiall

y, thus �educing the calo

�ific value of the boil-off gas at the beginning of the

loaded voyage. DISCHARGINGDischa

�ging is done at the te

�minals o

� the

�egasification plant, this is done a

t specific discha�ge flow

�ate and vapou

� p

�essu

�e conside

�ation.

BALLAST VOYAGEBallast voyage is the voyage of the

�etu

�ning vessel f

�om dispo

�t back to loadin

g. It is a f�equent p

�actice in LNG t

�anspo

�t to

�etain a small quantity of ca

�g

o on boa�d afte

� discha

�ge and the amount

�etained is known as the heel. This p

�oduct is used to maintain the tanks at

�educed tempe

�atu

�e du

�ing the ballast vo

yage but this p�ocedu

�e only applies when the same g

�ade of ca

�go is to be loade

d at the next loading te�minal.

In gene�al, the quantity

�etained on boa

�d as a heel depends on:—

• Comme�cial ag

�eements

• The type of gas ca��ie

�

• The du�ation of the ballast voyage

• The next loading te�minal's

�equi

�ements, and

• The next ca�go g

�ade

In the case of a la�ge LNG ca

��ie

�, as much as 2,000 to 3,000 cubic mete

�s of li

quid may be �etained in the tanks on depa

�tu

�e f

�om the discha

�ge po

�t; the actu

al volume, depending on the size and type of ca�go containment, the length of th

e voyage and fuel policy. These ships a�e no

�mally fitted with sp

�ay cool-down p

umps in each ca�go tank to p

�ovide liquid to sp

�ay lines fitted in the uppe

� pa

�t of each tank. This system is used f

�om time to time on the ballast voyage to m

inimize tank the�mal g

�adients. The f

�equency of this ope

�ation will depend on s

hip size and type and the du�ation of the ballast voyage.

MEASURING THE AMOUNT OF CARGO LOADEDCa

�go measu

�ement is done majo

�ly by taking in to conside

�ation by the tank cali

b�ation. Ce

�tain co

��ections a

�e taken in to conside

�ation when taking the volum

e of the tank.• TRIM CORRECTION• LIST CORRECTION• FLOAT CORRECTION• TAPE CORRECTION• TANK SHELL EXPANSION AND CONTRACTION

HEALTH, SAFETY AND ENVIRONMENT IN LNG STORRAGE AND TRANSPORTHaza

�d facto

�s associated with LNG handling a

�e:

• Flammability • Explosion• Vapo

� clouds

• Low tempe�atu

�e (f

�ostbite)

• Roll ove�

• Rapid phase t�ansition

FLAMMABILITYThe flammability

�ange is the

�ange between the minimum and maximum concent

�atio

ns of vapo� (pe

�cent by volume) in which ai

� and LNG vapo

�s fo

�m a flammable mix

tu�e that can be ignited and bu

�n.

Figu�e 13 below indicates that the uppe

� flammability limit and lowe

� flammabili

ty limit of methane, the dominant component of LNG vapo�, a

�e 5 pe

�cent and 15 p

e�cent by volume,

�espectively. When fuel concent

�ation exceeds its uppe

� flamma

bility limit, it cannot bu�n because too little oxygen is p

�esent. This situatio

n exists, fo� example, in a closed, secu

�e sto

�age tank whe

�e the vapo

� concent

�ation is app

�oximately 100 pe

�cent methane. When fuel concent

�ation is below the

lowe� flammability limit, it cannot bu

�n because too little methane is p

�esent.

An example is leakage of small quantities of LNG in a well-ventilated a�ea.

FIGURE 13. LNG FLAMMABILITY LIMIT

A compa�ison of the p

�ope

�ties of LNG to those of othe

� liquid fuels, indicates

that the Lowe� Flammability Limit of LNG is gene

�ally highe

� than othe

� fuels. T

hat is, mo�e LNG vapo

�s would be needed (in a given a

�ea) to ignite as compa

�ed

to LPG o� gasoline.

EXPLOSION. An explosion happens when a substance

�apidly changes its chemical state – i.e.,

is ignited – o� is uncont

�ollably

�eleased f

�om a p

�essu

�ized state. Fo

� an uncont�

olled �elease to happen, the

�e must be a st

�uctu

�al failu

�e – i.e., something mus

t punctu�e the containe

� o

� the containe

� must b

�eak f

�om the inside. LNG tanks

sto�e the liquid at an ext

�emely low tempe

�atu

�e, about -256°F (-160°C), so no p

�ess

u�e is

�equi

�ed to maintain its liquid state. Sophisticated containment systems

p�event ignition sou

�ces f

�om coming in contact with the liquid. Since LNG is st

o�ed at atmosphe

�ic p

�essu

�e – i.e., not p

�essu

�ized – a c

�ack o

� punctu

�e of the co

ntaine� will not c

�eate an immediate explosion.

VAPOR CLOUDS. As LNG leaves a tempe

�atu

�e-cont

�olled containe

�, it begins to wa

�m up,

�etu

�nin

g the liquid to a gas. Initially, the gas is colde� and heavie

� than the su

��oun

ding ai�. It c

�eates a fog – a vapo

� cloud – above the

�eleased liquid.As the gas wa�

ms up, it mixes with the su��ounding ai

� and begins to dispe

�se. The vapo

� clou

d will only ignite if it encounte�s an ignition sou

�ce while concent

�ated within

its flammability �ange. Safety devices and ope

�ational p

�ocedu

�es a

�e intended

to minimize the p�obability of a

�elease and subsequent vapo

� cloud having an af

fect outside the facility bounda�y.

FREEZING LIQUID/FROST BITE If LNG is

�eleased, di

�ect human contact with the c

�yogenic liquid will f

�eeze t

he point of contact. Containment systems su��ounding an LNG sto

�age tank, thus,

a�e designed to contain up to 110 pe

�cent of the tank’s contents. Containment syst

ems also separate the tank from other equipment. Moreover, all facility personnel must wear gloves, face masks and other protective clothing as a protection from the freezing liquid when entering potentially hazardous areas. ROLLOVER. When LNG supplies of multiple densities are loaded into a tank one at a time, they do not mix at first. Instead, they layer themselves in unstable strata within the tank. After a period of time, these strata may spontaneously rollover to stabilize the liquid in the tank. As the lower LNG layer is heated by normal heat leak, it changes density until it finally becomes lighter than the upper layer. At that point, a liquid rollover would occur with a sudden vaporization of LNG that may be too large to be released through the normal tank pressure release valves. At some point, the excess pressure can result in cracks or other structural failures in the tank. To prevent stratification, operators unloading an LNG ship measure the density of the cargo and, if necessary, adjust their unloading procedures accordingly. LNG tanks have rollover protection systems, which include distributed temperature sensors and pump-around mixing systems.RAPID PHASE TRANSITION. When released on water, LNG floats – being less dense than water – and vaporizes. If large volumes of LNG are released on water, it may vaporize too quickly causing a rapid phase transition (RPT).7 Water temperature and the presence of substances other than methane also affect the likelihood of an RPT. An RPT can only occur if there is mixing between the LNG and water. RPTs range from small pops to blasts large enough to potentially damage to lightweightstructures. Other liquids with widely differing temperatures and boiling points can create similar incidents when they come in contact with each other.EARTHQUAKE AND TERRORISM

MAJOR LNG INCIDENTS1. Cleveland, Ohio, 1944In 1939, the first commercial LNG peakshaving facility(storage facility built during winter period when demand is high and supply low) was built in West Virginia.In 1941, the East Ohio Gas Company built a second facility in Cleveland. Thepeakshaving facility operated without incident until 1944, when the facility was expanded to include a larger tank. A shortage of stainless steel alloys during World War II led to compromises in the design of the new tank. The tank failed shortly after it was placed in service. The LNG that escaped formed a vapor cloud that filled the surrounding streets and storm sewer system. Natural gas vapor in the storm sewer system was ignited. The Cleveland event resulted in the deaths of 128 people in the adjoining residential area. 2. Staten Island, New York, February 19733. Cove Point, Maryland, October 1979In October 1979, an explosion occurred within an electrical substation at the CovePoint, MD receiving terminal. LNG leaked through an inadequately tightened LNG pump electrical penetration seal, vaporized, passed through 200 feet ofunderground electrical conduit, and entered the substation. Since natural gas was never expected in this building, there were no gas detectors installed. The normal arcing contacts of a circuit breaker ignited the natural gas-air mixture, resulting in an explosion. The explosion killed one operator in the building, seriously injured a second and caused about $3 million in damages.

LNG RegulationsThe following regulations provide guidelines for the design, construction and operation of LNG facilities.• 49CFR Part 193 Liquefied Natural Gas Facilities: Federal Safety Standards- This section covers siting requirements, design, construction, equipment, operations, maintenance, personnel qualifications and training, fire protection, and security.• 33CFR Part 127 Waterfront Facilities Handling Liquefied Natural Gas and LiquefiedHazardous Gas - This federal regulation governs import and export LNG facilities or other waterfront facilities handling LNG. Its jurisdiction runs from the unloading arms to the first valve outside the LNG tank.• NFPA 59A Standard for the Production, Storage, and Handling of Liquefied Natural Gas (LNG) – This is an industry standard issued by the National Fire Protection Association (NFPA).41 NFPA 59A covers general LNG facility considerations, process systems, stationary LNG storage containers, vaporization facilities, piping systems and components, instrumentation and electrical services, transfers of natural gas and refrigerants, fire protection, safety and security. It also mandates alternative requirements for vehicle fueling for industrial and commercial facilities using American Society of Mechanical Engineers (ASME) pressure vessel containers. This standard includes requirements for LNG facilities to withstand substantial earthquakes. The NFPA standard for level of design means that the LNG facilities are strongly fortified for other events such as wind, flood, earthquakes and blasts.The latest update of NFPA 59A was published in 2001.• NFPA 57 Standard for Liquefied Natural Gas (LNG) Vehicular Fuel Systems – This standard covers vehicle fuel systems, LNG fueling facilities, installation requirements for ASME tanks, fire protection, safety and security for systems onboard vehicles and infrastructure storing 70,000 gallons of LNG or less.

EUROPEAN STANDARDS INCLUDE THE FOLLOWING.• EN 1473 - The European Norm standard EN 1473 Installation and equipment for Liquefied Natural Gas - Design of onshore installations evolved out of the British Standard, BS 777742 in 1996. It is a standard for the design of onshore LNG terminals. This standard is not prescriptive but promotes a risk-based approachfor the design.• EN 1160 – Installation and equipment for Liquefied Natural Gas – General Characteristics of Liquefied Natural Gas contains guidance on properties of materials commonly found in LNG facility that may come into contact with LNG.• EEMUA 14743 - Recommendations for the design and construction of refrigerated liquefied gas storage tanks. This document contains basic recommendations for the design and construction of single, double and full containment tanks for the bulk storage of refrigerated liquefied gases (RLGs) down to -165°C, covering the use of both metal and concrete materials.

COMMERCIAL DOCUMENTATION AND THIRD PARTY ADMINISTRATIONBefore any cargo undergoes transport certain documents are to be cleared and signed. Some of them are:1. Bill of lading It contains the vessel name, name of captain, destination, spa reference, cargo quantity and dates. It is the most important document2. Certificate of quantityIt contains the quantity of cargo loaded in different units3. Certificate of qualityIt contains the quality of cargo loaded in terms of its chemical composition4. Certificate of originIt contains mainly the name of the vessels originating port5. Receipt of documentIt contains all the documents issued by the shore to the ship6. Certificate of loadingIt states mainly when cargo was loaded, the name of the buyer and the quantity loaded7. Cargo manifestIt gives a brief summary of the loaded cargo and the vessel

THIRD OFFICIALS IN DOCUMENTATION1. DPR (Department Petroleum Resources) is the regulator of the oil and gas industry. They are provide;• Approvals and clearance of load • Approve custody transfer methods adopted• Safeguards government interest; accurate report of export, compliance with regulations• Certifies each FOB loadings; issues COL2. INDEPENDENT INSPECTOR(SURVEYORS)• Independently verifies/ validate custody transfer process• Opinion binding on parties in case of dispute• Represents parties at disports3. Boarding officials• Includes NPA, customs, immigration, port health, NDLEA, Navy• Visits/inspects each vessels before giving clearance to load4. Agents• Ensure payment of port dues• Convey port officials to/from vessels

CONCLUSIONFrom the study of liquefied natural gas storage and transportation I have arrived at an agreed fact that• The main principle governing the ability of liquefied natural gas to remain at its boiling point of about 1620c in storage tanks and ship vessels is the ability to effectively control heat ingress into the system and effectively control the vapor from the liquid(boil off gas)• The various choice of storage tank for LNG containment depend on the location(geological and seismic activity), ambient conditions and materials• The transport of LNG through vessels is the cost effective as compared to pipeline.• The choice of cargo containment and ship facility layout is dependent on the disport and loading terminal loading configurations• Major LNG disasters are caused mainly by negligence and poor safety conditions a

nd not because of inadequate technology to check the problem.

NOMENCLATUREAutoignition temperatureThe lowest temperature at which a gas will ignite after an extended time of exposure(e.g., several minutes).British Thermal Unit (BTU)A BTU is the amount of heat required to change the temperature of one pound of water by one degree Fahrenheit.Cryogenics The study of the behaviour of matter at very low temperatures. Critical Pressure The pressure at which a substance exists in the liquid state at its critical temperature. (In other words it is the saturation pressure at the critical temperature). Density A description of oil by measurement of its volume to weight ratio.Explosion The sudden release or creation of pressure and generation of high temperature as a result of a rapid change in chemical state (usually burning), or a mechanical failure.Flammability limit Is the concentration of fuel (by volume) that must be present in air for an ignition to occur when an ignition source is present.Frost Heave The pressure exerted by the earth when expanding as a result of ice formations. It is a situation which can arise as a result of the low temperature effects from a storage tank being transmitted to the ground beneath. Heel The amount of liquid cargo retained in a cargo tank at the end of discharge. It is used to maintain the cargo tanks cooled down during ballast voyages by recirculating through the sprayers. MTPA (Million Tonnes per Annum). Tonnes or Metric Ton is approximately 2.47 cubic meter of LNG.Hydrates The compounds formed by the interaction of water and hydrocarbons at certain pressures and temperatures. They are crystalline substances Inert Gas A gas, such as nitrogen, or a mixture of non-flammable gases containing insufficient oxygen to support combustion ISGOTT International Safety Guide for Oil Tankers and Terminals Vapour Density The density of a gas or vapour under specified conditions of temperature and pressure Peakshaving LNG FacilityA facility for both storing and vaporizing LNG intended to operate on an intermittent basis to meet relatively short term peak gas demands.

ACKNOWLEDGEMENTMy sincere gratitude goes out to the staff of Nigeria LNG who impacted some knowledge in me and lit up the urge to write this paper.I thank my friends for their constructive criticism I also give a deep gratitude to my parents and siblings for their support

CONVERSION TABLES1 billion cubic meter NG 1 billion cubic feet NG 1 million tones

oil equivalent 1 million tones LNG 1 trillion British thermal unit 1 million barrels oil equivalent thermal units1 billion cubic meter NG 1 35.3 0.90 0.73 36 6.291 billion cubic feet NG 0.028 1 0.026 0.021 1.03 0.181 million tones oil equivalent 1.111 39.2 1 0.805 40.4 7.331 million tones LNG 1.38 48.7 1.23 1 52.0 8.681 trillion British thermal unit 0.028 0.98 0.025 0.02 1 0.171 million barrels oil equivalent thermal units 0.16 5.61 0.14 0.125.8 1

Energy Units1 metric tonne=2204.621kilo joule=0.948Btu1Btu=1.055kj1 kilowatt-hour(kwh)=3412Btu

REFERENCEAmerican Petroleum Institute (API) http://api-ec.api.orgBob Curt, Marine Transportation of LNG, Presentation at the Qatar LNG Intertanko Conference, Qatar, (29 March, 2004)International Maritime Organization (IMO) http://www.imo.org.McGUIRE and WHITE. 2000. Liquefied Gas Handling Principles on Ships and in Terminals, 3rd Edition, London Witerbry publishersPhil Bainbridge, VP BP Global LNG, LNG in North America and the Global Context, IELE/AIPN Meeting University of Houston, October 2002.

Stowe Dagogo, Storage Facility Overview of NLNG, Presentation at the NLNG internship seminar, Bonny Nigeria, (31 December, 2010)