Transportul GNL

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FUTURE OF LNGTRANSPORTATION:VARIOUSPROPULSION ALTERNATIVES

The AuthorsBarun Gupta

4

th

yearMarine Engineering and Research Institute,

P-19, Taratolla Road, Kolkata-88

E-mail: [email protected]

Kumar Surendra Prasad

4

th

yearMarine Engineering and Research Institute,

P-19, Taratolla Road, Kolkata-88

E-mail: [email protected]


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CONTENTS

CHAPTER: 1 LIQUIFIED NATURAL GAS 8

1.1 INTRODUCTION 81.1.1 WHAT IS NATURAL GAS? 81.2 THE FORMATION OF NATURAL GAS 101.3 NATURAL GAS UNDER THE EARTH 111.4 HOW MUCH NATURAL GAS IS THERE? 161.4.1 NATURAL GAS RESOURCE ESTIMATES 171.4.2 WHERE ARE THESE RESERVES? 191.5 WORLD NATURAL GAS RESERVES 191.6 USES OF NATURAL GAS 201.7 WHAT IS LNG? 211.8 PROPERTIES 221.9 SOME INTERESTING FACTS ABOUT LNG 221.10 NEED FOR TRANSPORTATION: 23

CHAPTER: 2 MODES OF TRANSPORTATION 26

2.1 PIPE LINES:- 262.1.1 INTERSTATE NATURAL GAS PIPELINES :- 272.1.2 PIPELINE COMPONENTS:- 282.1.2.1 Pipes:- 282.1.2.2 Compressor Stations:- 292.1.2.3 Metering Stations:- 302.1.2.4 Valves:- 302.1.2.5 Control Stations and SCADA Systems:- 302.1.3 PIPELINE CONSTRUCTION:- 312.1.4 PIPELINE INSPECTION AND SAFETY:- 332.2 CNG: A COMPETITIVE TECHNOLOGY TO LNGFOR THE TRANSPORT OF NATURAL GAS:-

35

2.2.1 COMPRESSED NATURAL GAS:- 352.2.2 SAGA/ MOSS ROSENBERG CNG DESIGN 1976:- 362.2.3 MODERN CNG CARRIER CONCEPTS :- 362.2.4 THE CNG TRANSPORT TECHNOLOGY:- 372.2.5 CNGVS. LNG 382.2.6 ADVANTAGES OF CNGOVER LNG:- 402.2.7 DISADVANTAGES:- 402.3 TRANSPORTATION BY LNG CARRIERS:- 412.3.1 CONVENTIONAL LNG CARRIER 422.3.2 THE BASIC SHIP STRUCTURE:- 422.3.2.2 The Market Where Time Stood Still :- 43

2.3.2.3 Taller Spheres:- 43

2The future of LNG transportation: Various Propulsion Alternatives by B. Gupta & K. Prasad

Available online at Martin's Marine Engineering Page - www.dieselduck.net


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2.3.2.4 The Shape Of Things To Come:- 442.3.2.5 To Boil Off ... Or Not? 44

CHAPTER 3 TRADITIONAL STEAM PROPULSION 46

3.1 BASIC CHARACTERISTICS:- 463.2. MARKET REQUIRMENTS:- 473.2.1 OPERATING ECONOMY 473.2.2 ENVIRONMENTAL-FRIENDLINESS:- 483.2.3 SAFETY:- 483.2.4 RELIABILITY:- 483.2.5 REDUNDANCY:- 483.2.6 MAINTANABILITY:- 483.2.7 CREWABILITY:- 48

3.2.8 OTHERS:- 493.3 WINDS OF CHANGE:- 493.4 ALTERNATIVE PROPULSION CONCEPT:- 49

CHAPTER 4 SLOW SPEED DIESEL ENGINES 51

4.1 SLOW SPEED DIESEL WITH BOGRELIQUEFACTION:- 514.2 GAS-DIESEL ENGINE ALTERNATIVES:- 524.2.1 ME-GI -- THE DUAL FUEL ENGINE:- 564.2.2 ECONOMICAL EVALUATION:- 62

4.2.3 INVESTMENT COST:- 634.2.4 EXHAUST EMISSIONS:- 634.2.5 WHATS SPECIAL IN IT-A COMPARATIVE ANALYSIS :- 644.2.6 REDUCED FUEL CONSUMPTION 684.2.7 OPERATIONAL SAFETY & FLEXIBILITY 684.2.8 FLEXIBILTYREGARDINGEXHAUSTGASEMISSION 694.2.9 ADVANTAGES :- 69

CHAPTER 5 DUAL FUEL DIESEL-ELECTRIC PROP. 71

5.1 AZIPOD PROPULSION - ELECTRIC MARINE PROPULSION:- 72

5.2 CRP AZIPOD PROPULSION - HIGH-EFFICIENCY CONTRA-ROTATING PROPULSIONSYSTEM 725.3 COMPACT AZIPOD PROPULSION - MARINE ELECTRIC THRUSTER SYSTEM:- 745.4 FIRST LARGE SIZE DUAL FUEL ELECTRIC CARRIER:- 745.5 ADVANTAGES:- 765.6 FOUR GENERATING SETS:- 775.7 HIGH TOTAL EFFICIENCY:- 775.8 OUTLINE OF THE DF-ELECTRIC LNGCARRIER:- 775.8.1 OPERATING ECONOMY:- 785.8.2 ENVIRONMENTAL-FRIENDLINESS:- 795.8.3 SAFETY:- 795.8.4 RELIABILITY:- 80




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5.8.5 REDUNDANCY:- 805.8.6 MAINTAINABILITY:- 805.8.7 CREWABILITY:- 805.8.8 OTHERS:- 805.9 FUTURE OPERATING PROFILES:- 805.10 MARKET INTRODUCTION:- 81

CHAPTER 6 GAS TURBINE ALTERNATIVES 82

6.1 AERO-DERIVATIVE MARINE GAS TURBINES:- 826.2 ADVANTAGES OF MARINE AERO-DERIVATIVE GAS TURBINES:- 836.2.1 OPERATION: 836.2.2 MAINTENANCE: 836.2.3 RELIABILITY AND AVAILABILITY: 84

6.2.4 ENVIRONMENT: 846.2.5 NOISE AND VIBRATION: 846.2.6 VESSEL DESIGN: 846.2.7 PROPULSION PLANT DESIGN: 846.2.8 INSTALLATION: 856.3 DISADVANTAGES OF MARINEAERO-DERIVATIVEGASTURBINES:- 856.3.1 THERMAL EFFICIENCY: 856.3.2 LIQUID FUEL QUALITY RESTRICTIONS:] 856.3.3 INITIAL INVESTMENTS: 866.4 GASTURBINEMYTHS AND MISUNDERSTANDINGS 866.5 MARINE GAS TURBINE APPLICATIONS 87

CHAPTER 7 GAS TURBINE ELECTRIC DRIVE 89

7.1 GAS TURBINE ELECTRIC DRIVE COMBINE CYCLE PROPULSION 907.2 THE ADVANTAGES ARE: 917.3 THE DISADVANTAGE ARE: 917.4 NORMAL CRUISING SPEED: 917.4.1 LOADED: 917.4.2 MANEUVERING: 927.4.3 HARBOUR LOAD: 927.4.4 CARGO DISCHARGE: 92

7.4.5 EMERGENCY SITUATIONS: 927.5 GAS TURBINE ELECTRIC PODDED DRIVE LNG CARRIER 937.6 GAS TURBINE ELECTRIC DRIVE COMBINE CYCLE PROPULSION 947.6.1 THE ADVANTAGES ARE: 957.6.2 THE DISADVANTAGE ARE: 957.7 NORMAL CRUISING SPEED: 967.7.1 LOADED: 967.7.2 IN BALLAST: 967.7.3 MANEUVERING: 967.7.4 HARBOUR LOAD: 977.7.5 CARGO DISCHARGE: 977.7.6 EMERGENCY SITUATIONS: 97




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7.8 INCREASING LNG CARRIER CARGO CAPACITY 97

CHAPTER 8 RELIQUIFICATION TECHNOLOGY 99

8.1 BOIL-OFF CYCLE:- 1008.2 NITROGEN CYCLE:- 1008.3 CONTROL SYSTEM:- 1018.4 REDUNDENCY:- 1028.5 LIQUIFICATION PLANT:- 103

CHAPTER 9 VOYAGE ANALYSIS 105

9.1 SELECTION OF ALTERNATIVES 1059.2 ONE-TIME INVESTMENT COSTS 1059.3 RECURRING VARIABLE COSTS 1069.4 WHAT AFFECTS THE VARIABLE COSTS? 1079.4.1 OPERATING ROUTE 1079.4.2 FUEL FLEXIBILITY 1089.4.3 VALUE OF LNG 1099.4.4 PRICE OF HFO 1119.4.5 MEMBRANE OR MOSS? 1129.4.6 SINGLE OR TWIN PROPULSOR? 1139.5 SHIPYARD PREMIUM 1139.6 CONCLUSION 114

CHAPTER 10 COMPARATIVE STUDY 115

10.1 COMPARISION BETWEEN STEAM,DIESEL &DIESEL-ELECTRIC- 11810.2 ECONOMICAL COMPARISON OF THE DIFFERENT PROPULSION SYSTEMS12110.3 RESULTS 12210.4 CONCLUSIONS 12510.5 COMPARISON 126




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CHAPTER: 1

LIQUIFIED NATURAL GAS

1.1 Introduction

Natural Gas is a vital component of the world's supply of energy. It is one of thecleanest, safest, and most useful of all energy sources. Despite its importance,however, there are many misconceptions about natural gas. For instance, theword 'gas' itself has a variety of different uses, and meanings. When we fuel ourcar, we put 'gas' in it. However, the gasoline that goes into your vehicle, while afossil fuel itself, is very different from natural gas. The 'gas' in the commonbarbecue is actually propane, which, while closely associated and commonlyfound in natural gas, is not really natural gas itself. While commonly grouped inwith other fossil fuels and sources of energy, there are many characteristics ofnatural gas that make it unique. Below is a bit of background information aboutnatural gas, what exactly it is, how it is formed, and how it is found in nature.

1.1.1 What is Natural Gas?

Natural gas, in itself, might be considered a very uninteresting gas - it iscolorless, shapeless, and odorless in its pure form. Quite uninteresting - exceptthat natural gas is combustible, and when burned it gives off a great deal ofenergy. Unlike other fossil fuels, however, natural gas is clean burning and emitslower levels of potentially harmful byproducts into the air. We require energyconstantly, to heat our homes, cook our food, and generate our electricity. It isthis need for energy that has elevated natural gas to such a level of importancein our society, and in our lives.




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Found in reservoirs underneath the earth, natural gas is commonly associatedwith oil deposits. Production companies search for evidence of these reservoirs

by using sophisticated technology that helps to find the location of the naturalgas, and drill wells in the earth where it is likely to be found. Once brought fromunderground, the natural gas is refined to remove impurities like water, othergases, sand, and other compounds. Some hydrocarbons are removed and soldseparately, including propane and butane. Other impurities are also removed,like hydrogen sulfide (the refining of which can produce sulfur, which is then alsosold separately). After refining, the clean natural gas is transmitted through anetwork of pipelines, thousands of miles of which exist in the United Statesalone. From these pipelines, natural gas is delivered to its point of use.

Natural gas can be measured in a number of different ways. As a gas, it can be

measured by the volume it takes up at normal temperatures and pressures,commonly expressed in cubic feet. Production and distribution companiescommonly measure natural gas in thousands of cubic feet (Mcf), millions of cubicfeet (MMcf), or trillions of cubic feet (Tcf). While measuring by volume is useful,natural gas can also be measured as a source of energy. Like other forms ofenergy, natural gas is commonly measured and expressed in British thermalunits (Btu). One Btu is the amount of natural gas that will produce enough energyto heat one pound of water by one degree at normal pressure. To give an idea,one cubic foot of natural gas contains about 1,027 Btus. When natural gas isdelivered to a residence, it is measured by the gas utility in 'therms' for billingpurposes. A therm is equivalent to 100,000 Btu's, or just over 97 cubic feet, of

natural gas.

1.2 The Formation of Natural Gas

Natural gas is a fossil fuel. Like oil and coal, this means that it is, essentially, theremains of plants and animals and microorganisms that lived millions andmillions of years ago. But how do these once living organisms become aninanimate mixture of gases?

There are many different theories as to the origins of fossil fuels. The most widelyaccepted theory says that fossil fuels are formed when organic matter (such asthe remains of a plant or animal) is compressed under the earth, at very highpressure for a very long time. This is referred to as thermogenic methane. Similarto the formation of oil, thermogenic methane is formed from organic particles thatare covered in mud and other sediment. Over time, more and more sediment andmud and other debris are piled on top of the organic matter. This sediment anddebris puts a great deal of pressure on the organic matter, which compresses it.This compression, combined with high temperatures found deep underneath theearth, break down the carbon bonds in the organic matter. As one gets deeperand deeper under the earths crust, the temperature gets higher and higher. Atlow temperatures (shallower deposits), more oil is produced relative to natural




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gas. At higher temperatures, however, more natural gas is created, as opposedto oil. That is why natural gas is usually associated with oil in deposits that are 1to 2 miles below the earth's crust. Deeper deposits, very far underground, usually

contain primarily natural gas, and in many cases, pure methane.

Natural gas can also be formed through the transformation of organic matter bytiny microorganisms. This type of methane is referred to as biogenic methane.Methanogens, tiny methane producing microorganisms, chemically break downorganic matter to produce methane. These microorganisms are commonly foundin areas near the surface of the earth that are void of oxygen. Thesemicroorganisms also live in the intestines of most animals, including humans.Formation of methane in this manner usually takes place close to the surface ofthe earth, and the methane produced is usually lost into the atmosphere. Incertain circumstances, however, this methane can be trapped underground,

recoverable as natural gas. An example of biogenic methane is landfill gas.Waste-containing landfills produce a relatively large amount of natural gas, fromthe decomposition of the waste materials that they contain. New technologies areallowing this gas to be harvested and used to add to the supply of natural gas.

A third way in which methane (and natural gas) may be formed is through abiogenic process. Extremely deep under the earth's crust, there exist hydrogen-rich gases and carbon molecules. As these gases gradually rise towards thesurface of the earth, they may interact with minerals that also exist underground,in the absence of oxygen. This interaction may result in a reaction, formingelements and compounds that are found in the atmosphere (including nitrogen,

oxygen, carbon dioxide, argon, and water). If these gases are under very highpressure as they move towards the surface of the earth, they are likely to formmethane deposits, similar to thermogenic methane.

1.3 Natural Gas Under the Earth

Although there are several ways that methane, and thus natural gas, may beformed, it is usually found underneath the surface of the earth. As natural gashas a low density, once formed it will rise towards the surface of the earththrough loose, shale type rock and other material. Most of this methane willsimply rise to the surface and dissipate into the air. However, a great deal of thismethane will rise up into geological formations that 'trap' the gas under theground. These formations are made up of layers of porous, sedimentary rock(kind of like a sponge, that soaks up and contains the gas), with a denser,impermeable layer of rock on top. This impermeable rock traps the natural gasunder the ground. If these formations are large enough, they can trap a greatdeal of natural gas underground, in what is known as a reservoir. There are anumber of different types of these formations, but the most common is createdwhen the impermeable sedimentary rock forms a 'dome' shape, like an umbrellathat catches all of the natural gas that is floating to the surface.




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There are a number of ways that this sort of 'dome' may be formed. For instance,faults are a common location for oil and natural gas deposits to exist. A faultoccurs when the normal sedimentary layers sort of 'split' vertically, so thatimpermeable rock shifts down to trap natural gas in the more permeablelimestone or sandstone layers. Essentially, the geological formation which layersimpermeable rock over more porous, oil and gas rich sediment has the potential

to form a reservoir. The picture below shows how natural gas and oil can betrapped under impermeable sedimentary rock, in what is known as an anticlinalformation. To successfully bring these fossil fuels to the surface, a hole must bedrilled through the impermeable rock to release the fossil fuels under pressure.Note that in reservoirs that contain oil and gas, the gas, being the least dense, isfound closest to the surface, with the oil beneath it, typically followed by a certainamount of water.

With natural gas trapped under the earth in this fashion, it can be recovered bydrilling a hole through the impermeable rock. Gas in these reservoirs is typicallyunder pressure, allowing it to escape from the reservoir on its own.

Natural gas is nothing new. In fact, most of the natural gas that is brought outfrom under the ground is millions and millions of years old. However, it was notuntil recently that methods for obtaining this gas, bringing it to the surface, andputting it to use were developed.

Before there was an understanding of what natural gas was, it posed somewhatof a mystery to man. Sometimes, such things as lightning strikes would ignitenatural gas that was escaping from under the earth's crust. This would create afire coming from the earth, burning the natural gas as it seeped out fromunderground. These fires puzzled most early civilizations, and were the root of




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much myth and superstition. One of the most famous of these types of flameswas found in ancient Greece, on Mount Parnassus approximately 1,000 B.C. Agoat herdsman came across what looked like a 'burning spring', a flame rising

from a fissure in the rock. The Greeks, believing it to be of divine origin, built atemple on the flame. This temple housed a priestess who was known as theOracle of Delphi, giving out prophecies she claimed were inspired by the flame.

These types of springs became prominent in the religions of India, Greece, andPersia. Unable to explain where these fires came from, they were often regarded

as divine, or supernatural. It wasn't until about 500 B.C. that the Chinesediscovered the potential to use these fires to their advantage. Finding placeswhere gas was seeping to the surface, the Chinese formed crude pipelines out ofbamboo shoots to transport the gas, where it was used to boil sea water,separating the salt and making it drinkable.

Britain was the first country to commercialize the use of natural gas. Around1785, natural gas produced from coal was used to light houses, as well asstreetlights.

Manufactured natural gas of this type (as opposed to naturally occurringgas) was first brought to the United States in 1816, when it was used to light the

streets of Baltimore, Maryland. However, this manufactured gas was much lessefficient, and less environmentally friendly, than modern natural gas that comesfrom underground.

Naturally occurring natural gas was discovered and identified in America as earlyas 1626, when French explorers discovered natives igniting gases that wereseeping into and around Lake Erie. The American natural gas industry got itsbeginnings in this area. In 1859, Colonel Edwin Drake (a former railroad




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conductor who adopted the title 'Colonel' to impress the townspeople) dug thefirst well. Drake hit oil and natural gas at 69 feet below the surface of the earth.

Most in the industry characterize this well as the beginning of the natural gasindustry in America. A two-inch diameter pipeline was built, running 5 and




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miles from the well to the village of Titusville, Pennsylvania. The construction ofthis pipeline proved that natural gas could be brought safely and relatively easilyfrom its underground source to be used for practical purposes.

In 1821, the first well specifically intended to obtain natural gas was dug inFredonia, New York, by William Hart. After noticing gas bubbles rising to thesurface of a creek, Hart dug a 27 foot well to try and obtain a larger flow of gas tothe surface. Hart is regarded by many as the 'father of natural gas' in America.Expanding on Hart's work, the Fredonia Gas Light Company was eventuallyformed, becoming being the first American natural gas company.

During most of the 19th century, natural gas was used almost exclusively as asource of light. Without a pipeline infrastructure, it was difficult to transport thegas very far, or into homes to be used for heating or cooking. Most of the natural

gas produced in this era was manufactured from coal, as opposed to transportfrom a well. Near the end of the 19th century, with the rise of electricity, naturalgas lights were converted to electric lights. This led producers of natural gas tolook for new uses for their product.

In 1885, Robert Bunsen invented what is now known as the Bunsen burner. Hemanaged to create a device that mixed natural gas with air in the rightproportions, creating a flame that could be safely used for cooking and heating.

The invention of the Bunsen burner opened up new opportunities for the use ofnatural gas in America, and throughout the world. The invention of temperature-




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regulating thermostatic devices allowed for better use of the heating potential ofnatural gas, allowing the temperature of the flame to be adjusted and monitored.Without any way to transport it effectively, natural gas discovered pre-WWII was

usually just allowed to vent into the atmosphere, or burnt, when found alongsidecoal and oil, or simply left in the ground when found alone.

One of the first lengthy pipelines was constructed in 1891. This pipeline was 120miles long, and carried natural gas from wells in central Indiana to the city ofChicago. However, this early pipeline was very rudimentary, and was not veryefficient at transporting natural gas. It wasn't until the 1920's that any significanteffort was put into building a pipeline infrastructure. However, it wasn't until afterthe World War II that welding techniques, pipe rolling, and metallurgicaladvances allowed for the construction of reliable pipelines. This post-war pipelineconstruction boom lasted well into the 60's, and allowed for the construction of

thousands of miles of pipeline.

Once the transportation of natural gas was possible, new uses for natural gaswere discovered. These included using natural gas to heat homes and operateappliances such as water heaters and oven ranges. Industry began to usenatural gas in manufacturing and processing plants. Also, natural gas was usedto heat boilers used to generate electricity. The transportation infrastructure hadmade natural gas easy to obtain, and it was becoming an increasingly popularform of energy.

1.4 How Much Natural Gas is there?

There is an abundance of natural gas in North America, but it is a non-renewableresource, the formation of which takes thousands and possibly millions of years.Therefore, understanding the availability of our supply of natural gas is importantas we increase our use of this fossil fuel.

This section will provide a framework for understanding just how much naturalgas there is in the ground available for our use, as well as links to the mostrecent statistics concerning the available supply of natural gas.

As natural gas is essentially irreplaceable (at least with current technology), it isimportant to have an idea of how much natural gas is left in the ground for us touse. However, this becomes complicated by the fact that no one really knowsexactly how much natural gas exists until it is extracted. Measuring natural gas inthe ground is no easy job, and it involves a great deal of inference andestimation. With new technologies, these estimates are becoming more andmore reliable; however, they are still subject to revision. A commonmisconception about natural gas is that we are running out, and quickly.However, this couldn't be further from the truth. Many people believe that pricespikes, such as were seen in the 1970's, and more recently in the winter of 2000,indicate that we are running out of natural gas. The two aforementioned periods




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of high prices were not caused by waning natural gas resources - rather, therewere other forces at work in the marketplace. In fact, there is a vast amount ofnatural gas estimated to still be in the ground. In order to understand exactly

what these estimates mean, and their importance, it is useful first to learn a bit ofindustry terminology for the different types of estimates.

1.4.1 Natural Gas Resource Estimates

Below are three estimates of natural gas reserves. The first, compiled by theEnergy Information Administration (referred to as the EIA), estimates that thereare 1,190.62 Tcf of technically recoverable natural gas in the United States.




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This includes undiscovered, unproved, and unconventional natural gas. As canbe seen from the table, proved reserves make up a very small proportion of thetotal recoverable natural gas resources. The following table includes an estimate

of natural gas resources compiled by the National Petroleum Council in 1999 inits report Natural Gas - Meeting the Challenges of the Nation's Growing NaturalGas Demand. Information on this report may be found here.




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This estimate places U.S. natural gas resources higher than the EIA, at 1,779 Tcfremaining. It is important to note that different methodologies and systems ofclassification are used in various estimates that are completed. There is no single

way that every industry player quantifies estimates of natural gas. Therefore, it isimportant to delve into the assumptions and methodology behind each study togain a complete understanding of the estimate itself.There are a myriad of different industry participants that formulate their ownestimates regarding natural gas supplies, such as production companies,independent geologists, the government, and environmental groups, to name afew. While this leads to a wealth of information, it also leads to a number ofdifficulties. Each estimate is based on a different set of assumptions, completedwith different tools, and even referred to with different language. It is thus difficultto get a definitive answer to the question of how much natural gas exists. Inaddition, since these are all essentially educated guesses as to the amount of

natural gas in the earth, there are constant revisions being made. Newtechnology, combined with increased knowledge of particular areas andreservoirs mean that these estimates are in a constant state of flux. Furthercomplicating the scenario is the fact that there are no universally accepteddefinitions for the terms that are used differently by geologists, engineers,accountants, and others.

1.4.2 Where Are These Reserves?

Most of the natural gas that is found in North America is concentrated in relativelydistinct geographical areas, or basins. Given this distribution of natural gas

deposits, those states which are located on top of a major basin have the highestlevel of natural gas reserves. As can be seen from the map below, U.S. naturalgas reserves are very concentrated around Texas and the Gulf of Mexico.

1.5 World Natural Gas Reserves




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The EIA, in conjunction with the Oil and Gas Journal and World Oil publications,estimates world proved natural gas reserves to be around 5,210.8 Tcf. As can beseen from the graph, most of these reserves are located in the Middle East with

1,836.2 Tcf, or 34 percent of the world total, and Europe and the FormerU.S.S.R. with 2158.7, or 42 percent of total world reserves.

1.6 Uses Of Natural Gas

For hundreds of years, natural gas has been known as a very useful substance.The Chinese discovered a very long time ago that the energy in natural gas couldbe harnessed, and used to heat water. In the early days of the natural gasindustry, the gas was mainly used to light streetlamps, and the occasional house.However, with much improved distribution channels and technologicaladvancements, natural gas is being used in ways never thought possible.

There are so many different applications for this fossil fuel that it is hard toprovide an exhaustive list of everything it is used for. And no doubt, new uses arebeing discovered all the time. Natural gas has many applications, commercially,in your home, in industry, and even in the transportation sector! While the usesdescribed here are not exhaustive, they may help to show just how many thingsnatural gas can do.

According to the Energy Information Administration, energy from natural gasaccounts for 24 percent of total energy consumed in the United States, making ita vital component of the nation's energy supply.




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Natural gas is used across all sectors, in varying amounts. The graph abovegives an idea of the proportion of natural gas use per sector. The industrial sectoraccounts for the greatest proportion of natural gas use in the World, with the

residential sector consuming the second greatest quantity of natural gas.

1.7 What is LNG?

Liquefied natural gas (LNG) is natural gas that has been cooled to the point thatit condenses to a liquid, which occurs at a temperature of approximately -256 degF (-161 deg C) and at atmospheric pressure. Liquefaction reduces the volume byapproximately 600 times thus making it more economical to transport betweencontinents in specially designed ocean vessels, whereas traditional pipelinetransportation systems would be less economically attractive and could betechnically or politically infeasible. Thus, LNG technology makes natural gas

available throughout the world.

Natural gas liquefaction dates back to the 19th century when Britishchemist and physicist Michael Faraday experimented with liquefyingdifferent types of gases, including natural gas.

German engineer Karl Von Linde built the first practical compressorrefrigeration machine in Munich in 1873.

The first LNG plant was built in West Virginia in 1912. It began operationin 1917.

The first commercial liquefaction plant was built in Cleveland, Ohio, in1941. The LNG was stored in tanks at atmospheric pressure. Theliquefaction of natural gas raised the possibility of gas transportation todistant destinations.

To make LNG available for use, energy companies must invest in anumber of different operations that are highly linked and dependent uponone another. The major stages of the LNG value chain, excluding

pipeline operations between the stages, consist of the following: Exploration to find natural gas in the earths crust and production of the

gas for delivery to gas users. Most of the time natural gas is discoveredduring the search for oil.

Liquefaction to convert natural gas into a liquid state so that it can betransported in ships.

Shippingthe LNG in special purpose vessels.




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Storage and Regasification, to convert the LNG stored in specially madestorage tanks, from the liquefied phase to the gaseous phase, ready to bemoved to the final destination through the natural gas pipeline system.

1.8 Properties

Extremely low temperature: minus 260F (minus 162C). LNG will float on water - Specific gravity of LNG is about 0.45. - Slightly

less than half that of water. Odorless and colorless - LNG looks like boiling water. When exposed to

atmospheric temperatures and pressure, it vaporizes to about 600 timesits liquid volume.

Nontoxic, non-corrosive. Vapor Dissipation - As the vapor warms to minus 160F (minus 107C); it

becomes lighter than air and will dissipate. The natural gas vaporized fromLNG can cause asphyxiation in an unventilated confinement.

Explosion limit of LNG: 5 to 15%. Minimum ignition energy: 0.28mJ. Latent heat of vapourization: 510kJ/kg.

1.9 Some interesting facts about lng

According to World Oil, for the year 2001, worldwide proven reservesof natural gas showed an increase of 8.4 percent over year 2000.

According to LNGOne World 57, new LNG vessels were on order asof Dec 2002.

The LNG tanker fleet size is estimated to continue to grow to 193tankers by 2006.

India to have 10 new LNG vessels by 2010. Orders received last year in marine shipbuilding industries, South

Korea decreased relatively for almost all kinds of ships, except thosefor LNG carriers, which showed a 290% increase.

The above data shows that worlds is growingawareness in the field of natural gases. Now the question arises why

there is so much increase in its demand. The solution can beobtained by comparative study of various resources of energy ofwhich natural gas is also one.

The prevailing energy resources are fast loosing itspopularity in the modern world.

Oil has been harshly criticized as pollutant Coal, having high sulphur content, is considered as bad as worst. Nuclear power has lately been considered as being long-term

solution to the worlds energy problems, but even nuclear power has




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come under attack, and in many states, building programs for newpower station have been held up because of safety reasons.

Moreover, CO2 emission control from major fuels is recognized as

the essential issue related to the greenhouse effect, especially sincedemand for energy increasing.

Concern over worlds diminishing energy resources coupled with a growingawareness of the need to protect the environment, led to an upsurgeinterest in natural gas and construction of special natural gas carriers.

These conflicting demands for more energy and cleaner environmentpresent a considerable problem and natural gas promises to solve both ofthem, thus it was known as a glamour fuel of 1970s.

Until well into the 20th century, it was considered a nuisance and a by-product of crude oil production. Only when in remote areas of Wyoming,huge reserves of gas were discovered, nobody thought it was one of theenergies with a more than promising future. The proven reserves of naturalgas at the end of 2001 amounted to 170 trillion cubic meter, which areequivalent to 153-milliard toe. The petroleum reserves at the same date,amounted to 142.6 milliard toe, so, we see that the usable reserves of gasare higher than those ones of petroleum.

1.10 Need For Transportation:

By geographic areas, it is found in particular that, The former USSR, found particularly, the Russian Federation and

Turkmenistan have nearly one third of the world reserves. Iran, Qatar, Australia, Papua New Guinea, the United States, and in

Africa; Algeria, Nigeria, Libya and Egypt gather more than 90% of theproven reserves of this continent.

The OPEC countries have 45% of the world natural gas resources, muchlower that those they have in crude oil reserves, which amount to 78%.

Moreover, there are large reserves of natural gas in areas for which thereis no significant market. Such hydrocarbon reserves are stranded in NorthAfrica, West Africa, South America, Caribbean, the Middle East,Indonesia, Malaysia, Northwestern Australia and Alaska. In addition,markets for these natural gases include Japan, Taiwan, Korea, Europeand the U.S.

Therefore, there is a need for transportation of natural gases to areas where itis scarce from areas where it is in abundance.

23

The future of LNG Transportation: Propulsion alternatives by B. Gupta & K. Prasad

Available online, at Martin's Marine Engineering Page - www.dieselduck.ca


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Illustration 1:-According to the U.S. Energy Information Administration

(U.S. EIA), natural gas production in the U.S. is predicted to grow from 19.1

trillion cubic feet (Tcf) in 2000 to 28.5 Tcf in 2020.The total U.S. Demand fornatural gas is expected to rise from 2.8 Tcf in 2000 to about 33.8 Tcf by 2020adjusted for forecasted gains in energy efficiency and conservation). Theseprojections suggest that the U.S. could face a gap of 5Tcf by 2020.

Hence, she needs to import natural gas to meet her requirements.

Where natural gas supply and the intended consumer are reasonably close,pipelines can be used for transporting the gas. However, as most of the worldsupply is remote from the consumer areas, shipboard carriage is the onlyalternative. Another aspect of the carriage by pipeline is that the government and

private companies are reluctant to become involved with networks, which crossthe territory of the countries other than their own.

Illustration 2:- From the Russian Federation to Portugal, it is necessary to pass

through at least four different countries.

Therefore it can be said that shipping transport of LNG is not only growing,but taking more and more importance, as the sea transport, offers the nations thestrategic advantages such as

Non-dependence on pipelines, built over many different lands of differentnations.

The LNG trade gives more freedom and less dependence on third partiesfor importers.

LNG offers greater trade flexibility than pipeline transport, allowing cargoesof natural gas to be delivered where the need is greatest and thecommercial terms are most competitive. The figure below shows that as thedistance over which natural gas must be transported increases, usage ofLNG has economic advantages over usage of pipelines. Liquefying natural

gas and shipping it becomes cheaper than transporting natural gas inoffshore pipelines for distances of more than 700 miles or in onshorepipelines for distances greater than 2,200 miles.

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CHAPTER: 2

MODES OF TRANSPORTATION

2.1 Pipe lines:-

The efficient and effective movement of natural gas from producing regions toconsumption regions requires an extensive and elaborate transportation system.In many instances, natural gas produced from a particular well will have to travela great distance to reach its point of use. The transportation system for naturalgas consists of a complex network of pipelines, designed to quickly andefficiently transport natural gas from its origin, to areas of high natural gasdemand. Transportation of natural gas is closely linked to its storage, as well;

should the natural gas being transported not be required at that time, it can beput into storage facilities for when it is needed.

There are essentially three major types of pipelines along the transportationroute: the gathering system, the interstate pipeline, and the distribution system.

The gathering system consists of low pressure, low diameter pipelines thattransport raw natural gas from the wellhead to the processing plant. Shouldnatural gas from a particular well have high sulfur and carbon dioxide contents(sour gas), a specialized sour gas gathering pipe must be installed. Sour gas isextremely corrosive and dangerous, thus its transportation from the wellhead tothe sweetening plant must be done carefully.Pipelines can be characterized as interstate or intrastate. Interstate pipelinescarry natural gas across state boundaries, in some cases clear across thecountry. Intrastate pipelines, on the other hand, transport natural gas within aparticular state. This section will cover the fundamentals of interstate natural gas

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pipelines, but the technical and operational details discussed are essentially thesame for intrastate pipelines.

Natural gas pipelines are subject to regulatory oversight, which in many waysdetermines the manner in which pipeline companies must operate.

2.1.1 Interstate Natural Gas Pipelines :-

The interstate natural gas pipeline network transports processed natural gas fromprocessing plants in producing regions to those areas with high natural gasrequirements, particularly large, populated urban areas. As can be seen, thepipeline network extends across the entire country.

Interstate pipelines are the 'highways' of natural gas transmission. Natural gasthat is transported through interstate pipelines travels at high pressure in thepipeline, at pressures anywhere from 200 to 1500 pounds per square inch (psi).This reduces the volume of the natural gas being transported (by up to 600times), as well as providing propellant force to move the natural gas through thepipeline. This section will cover the components of the interstate pipeline system,the construction of pipelines, and pipeline inspection and safety.

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2.1.2 Pipeline Components:-

Interstate pipelines consist of a number of components which ensure theefficiency and reliability that is needed from a system that delivers such animportant energy source year round, twenty four hours a day, and consist of anumber of different components.

2.1.2.1 Pipes:-

Pipelines can measure anywhere from 6 to 48 inches in diameter, althoughcertain component pipe sections can consist of small diameter pipe, as small as0.5 inches in diameter. However, this small diameter pipe is usually used only ingathering and distribution systems. Mainline pipes, the principle pipeline in agiven system, are usually between 16 and 48 inches in diameter. Lateralpipelines, which deliver natural gas to or from the mainline, are typically between6 and 16 inches in diameter. Most major interstate pipelines are between 24 and36 inches in diameter. The actual pipeline itself, commonly called 'line pipe',consists of a strong carbon steel material, engineered to meet standards set bythe American Petroleum Institute (API).

Pipelines are produced in steel mills, which are sometimes specialized toproduce only pipeline. There are two different production techniques, one for

small diameter pipes and one for large diameter pipes. For large diameter pipes,from 20 to 42 inches in diameter, the pipes are produced from sheets of metalwhich are folded into a tube shape, with the ends welded together to form a pipesection. Small diameter pipe, on the other hand, can be produced seamlessly.This involves heating a metal bar to very high temperatures, then punching ahole through the middle of the bar to produce a hollow tube. In either case, thepipe is tested before being shipped from the steel mill, to ensure that it can meetthe pressure and strength standards for transporting natural gas.

Line pipe is also covered with a specialized coating to ensure that it does notcorrode once placed in the ground. The purpose of the coating is to protect the

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pipe from moisture, which causes corrosion and rusting. There are a number ofdifferent coating techniques. In the past, pipelines were coated with a specializedcoal tar enamel. Today, pipes are often protected with what is known as a fusion

bond epoxy, which gives the pipe a noticeable light blue color. In addition,cathodic protection is often used; which is a technique of running an electriccurrent through the pipe to ward off corrosion and rusting.

2.1.2.2 Compressor Stations:-

As mentioned, natural gas is highly pressurized as it travels through an interstatepipeline. To ensure that the natural gas flowing through any one pipeline remainspressurized, compression of this natural gas is required periodically along thepipe. This is accomplished by compressor stations, usually placed at 40 to 100mile intervals along the pipeline. The natural gas enters the compressor station,

where it is compressed by a turbine, motor, or engine.

Turbine compressors gain their energy by using up a small proportion of thenatural gas that they compress. The turbine itself serves to operate a centrifugalcompressor, which contains a type of fan that compresses and pumps the naturalgas through the pipeline. Some compressor stations are operated by using anelectric motor to turn the same type of centrifugal compressor. This type ofcompression does not require the use of any of the natural gas from the pipe,however it does require a reliable source of electricity nearby. Reciprocating

natural gas engines are also used to power some compressor stations. Theseengines resemble a very large automobile engine, and are powered by naturalgas from the pipeline. The combustion of the gas powers pistons on the outsideof the engine, which serves to compress the natural gas.

In addition to compressing natural gas, compressor stations also usually containsome type of liquid separator, much like the ones used to dehydrate natural gasduring its processing. Usually, these separators consist of scrubbers and filtersthat capture any liquids or other undesirable particles from the natural gas in thepipeline. Although natural gas in pipelines is considered 'dry' gas, it is notuncommon for a certain amount of water and hydrocarbons to condense out of

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the gas stream while in transit. The liquid separators at compressor stationsensure that the natural gas in the pipeline is as pure as possible, and usuallyfilters the gas prior to compression.

2.1.2.3 Metering Stations:-

In addition to compressing natural gas to reduce its volume and push it throughthe pipe, metering stations are placed periodically along interstate natural gaspipelines. These stations allow pipeline companies to monitor and manage thenatural gas in their pipes. Essentially, these metering stations measure the flowof gas along the pipeline, and allow pipeline companies to 'track' natural gas as itflows along the pipeline. These metering stations employ specialized meters tomeasure the natural gas as it flows through the pipeline, without impeding itsmovement.

2.1.2.4 Valves:-

Interstate pipelines include a great number of valves along their entire length.These valves work like gateways; they are usually open and allow natural gas toflow freely, or they can be used to stop gas flow along a certain section of pipe.There are many reasons why a pipeline may need to restrict gas flow in certainareas. For example, if a section of pipe requires replacement or maintenance,valves on either end of that section of pipe can be closed to allow engineers andwork crews safe access. These large valves can be placed every 5 to 20 miles

along the pipeline, and are subject to regulation by safety codes.

2.1.2.5 Control Stations and SCADA Systems:-

Natural gas pipeline companies have customers on both ends of the pipeline -the producers and processors that input gas into the pipeline, and the consumersand local distribution companies that take gas out of the pipeline. In order tomanage the natural gas that enters the pipeline, and to ensure that all customersreceive timely delivery of their portion of this gas, sophisticated control systemsare required to monitor the gas as it travels through all sections of what could bea very lengthy pipeline network. To accomplish this task of monitoring and

controlling the natural gas that is traveling through the pipeline, centralized gascontrol stations that collect, assimilate, and manage data received frommonitoring and compressor stations all along the pipe.

Most of the data that is received by a control station is provided by SupervisoryControl and Data Acquisition (SCADA) systems. These systems are essentiallysophisticated communications systems that take measurements and collect dataalong the pipeline (usually in a metering or compressor stations and valves) andtransmit them to the centralized control station. Flow rate through the pipeline,operational status, pressure, and temperature readings may all be used toassess the status of the pipeline at any one time. These systems also work in

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real-time, meaning that there is little lag time between the measurements takenalong the pipeline and their transmission to the control station.

This information, relayed to a centralized control station, allows pipelineengineers to know exactly what is happening along the pipeline at all times. Thisallows quick reactions to equipment malfunctions, leaks, or any other unusualactivity along the pipeline. Some SCADA systems also incorporate the ability toremotely operate certain equipment along the pipeline, including compressorstations, allowing engineers in a centralized control center to immediately andeasily adjust flow rates in the pipeline.

2.1.3 Pipeline Construction:-

As natural gas use increases, so does the need to have transportation

infrastructure in place to supply the increased demand. This means that pipelinecompanies are constantly assessing the flow of natural gas across the U.S., andbuilding pipelines to allow transportation of natural gas to those areas that areunderserved.

Constructing natural gas pipelines requires a great deal of planning andpreparation. In addition to actually building the pipeline, several permitting andregulatory processes must be completed. In many cases, prior to beginning thepermitting and land access processes, natural gas pipeline companies prepare afeasibility analysis to ensure that an acceptable route for the pipeline exists thatprovides the least impact to the environment and public infrastructure already inplace.

Assuming a pipeline company obtains all the required permits and satisfies all ofthe regulatory requirements, construction of the pipe may begin. Extensive

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surveying of the intended route is completed, both aerial and land based, toensure that no surprises pop up during actual assembly of the pipeline.

Installing a pipeline is much like an assembly line process, with sections of thepipeline being completed in stages. First, the path of the pipeline is cleared of allremovable impediments, including trees, boulders, brush, and anything else thatmay prohibit the construction. Once the pipeline's path has been clearedsufficiently to allow construction equipment to gain access, sections of pipes arelaid out along the intended path, a process called 'stringing' the pipe. These pipesections are commonly from 40 to 80 feet long, and are specific to theirdestination. That is, certain areas have different requirements for coating materialand pipe thickness.

Once the pipe is in place, trenches are dug alongside the laid out pipe. Thesetrenches are typically 5 to 6 feet deep, as the regulations require the pipe to be atleast 30 inches below the surface. In certain areas, however, including roadcrossings and bodies of water, the pipe is buried even deeper. Once the trenches

are dug, the pipe is assembled and contoured. This includes welding the sectionsof pipe together into one continuous pipeline, and bending it slightly, if needed, tofit the contour of the pipelines path. Coating is applied to the ends of the pipes(the coating applied at a coating mill typically leaves the ends of the pipe clean,so as not to interfere with welding), and the entire coating of the pipe is inspectedto ensure that it is free from defects.

Once the pipe is welded, bent, and coated, it can be lowered into the previouslydug trenches. This is done with specialized tracked construction equipmentacting in tandem to lift the pipe relatively uniformly and lower it into the trench.Once lowered into the ground, the trench is filled in carefully, to ensure that the

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pipe and its coating do not incur damage. The last step in pipeline construction isthe hydrostatic test. This consists of running water, at pressures higher than willbe needed for natural gas transportation, through the entire length of the pipe.

This serves as a test to ensure that the pipeline is strong enough, and absent ofany leaks of fissures, before natural gas is pumped through the pipeline.

Laying pipe across streams or rivers can be accomplished in one of two ways.Open cut crossing involves the digging of trenches on the floor of the river tohouse the pipe. When this is done, the pipe itself is usually fitted with a concretecasing, which both ensures that the pipe stays on the bottom of the river, andadd an extra protective coating to prevent any natural gas leaks into the water.Alternately, a form of directional drilling may be employed, in which a sort of'tunnel' is drilled under the river through which the pipe may be passed. Thesame techniques are used for road crossings - either an open trench is dug up

across the road and replaced once the pipe is installed, or a tunnel may be drilledunderneath the road.

Once the pipeline has been installed, and covered up, extensive efforts are takento restore the pipeline's pathway to its original state, or to mitigate for anyenvironmental or other impacts that may have occurred during the constructionprocess. This often includes replacing topsoil, fences, irrigation canals, andanything else that may have been removed or upset during the constructionprocess.

2.1.4 Pipeline Inspection and Safety:-

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In order to ensure the efficient and safe operation of the extensive network ofnatural gas pipelines, pipeline companies routinely inspect their pipelines forcorrosion and defects. This is done through the use of sophisticated pieces of

equipment known as pigs. Pigs are intelligent robotic devices that are propelleddown pipelines to evaluate the interior of the pipe. Pigs can test pipe thickness,and roundness, check for signs of corrosion, detect minute leaks, and any otherdefect along the interior of the pipeline that may either impede the flow of gas, orpose a potential safety risk for the operation of the pipeline. Sending a pig downa pipeline is fittingly known as 'pigging' the pipeline.

In addition to inspection with pigs, there are a number of safety precautions andprocedures in place to minimize the risk of accidents. In fact, the transportation ofnatural gas is one of the safest ways of transporting energy, mostly due to thefact that the infrastructure is fixed, and buried underground. According to the

Department of Transportation (DOT), pipelines are the safest method oftransporting petroleum and natural gas. While there are in excess of 100 deathsper year associated with electric transmission lines, according to the DOT'sOffice of Pipeline Safety in 2001, there were 2 deaths associated withtransmission pipelines, and 5 deaths associated with distribution systems. Tolearn more about pipeline safety, visit the DOT's Office of Pipeline Safety here.

A few of the safety precautions associated with natural gas pipelines include:Aerial Patrols - Planes are used to ensure no construction activities are takingplace too close to the route of the pipeline, particularly in residential areas.Unauthorized construction and digging is the primary threat to pipeline safety,

according to INGAA

Leak Detection - Natural gas detecting equipment is periodically used bypipeline personnel on the surface to check for leaks. This is especially importantin areas where the natural gas is not odorized.

Pipeline Markers- Signs on the surface above natural gas pipelines indicate thepresence of underground pipelines to the public, to reduce the chance of anyinterference with the pipeline.

Gas Sampling - Routine sampling of the natural gas in pipelines ensures itsquality, and may also indicate corrosion of the interior of the pipeline, or the influxof contaminants.

Preventative Maintenance- This involves the testing of valves and the removalof surface impediments to pipeline inspection.

Emergency Response - Pipeline companies have extensive emergencyresponse teams that train for the possibility of a wide range of potential accidentsand emergencies.

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The One Call Program- All of the states have instituted what is known as a 'onecall' program, which provides excavators, construction crews, and anyoneinterested in digging into the ground around a pipeline with a single phone

number that may be called when any excavation activity is planned. This callalerts the pipeline company, which may flag the area, or even sendrepresentatives to monitor the digging.

These are but a few of the efforts undertaken by the pipeline industry to ensurethe safety of the public and the environment, and to protect the integrity of theirpipelines

2.2 CNG: A Competitive Technology to LNG for the Transport ofNatural Gas:-

Existing means of transporting natural gas consist primarily of pipelines andLNG. Pipelines account for 75%, with LNG making for the rest. Pipelines are theobvious means for the onshore transport of natural gas. But for offshoretransport, as the water depth and distance between sources and users increase,pipelines become economically unattractive. LNG provides then an appropriateway of delivering natural gas from offshore. However, because of the largeupfront investment, LNG requires large reserves of natural gas near the facilitiesto support a LNG project and get acceptable returns capital investmentCompressed natural gas (CNG) technology provides an effective way for shorter-distance transport of the gas. The technology is aimed at monetizing offshore

reserves, which cannot be produced because of unavailability of pipeline orbecause the LNG option is very costly. Technically the technology is easy todeploy with less requirements for facilities and infrastructure.

2.2.1 Compressed Natural Gas:-

Compressed Natural Gas (CNG) as a mode of transport of natural gas is nowpursued with renewed interests. Earlier attempts in the 1960s to commercializethe technology were made with technical difficulties and along with therequirement of heavy investments made the commercial application of thetechnology unfeasible.

Ocean Transport Pressure System 1968

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CNG at 80 bar and -600C Approved by USCG Prototype built and tested in New Jersey, but not found to be commercial

2.2.2 Saga / Moss Rosenberg CNG Design 1976:-

CNG carrier capable of carrying a mixture of gas and oil at 100 bar Ideaconceived by Saga Petroleum in 1976 Concept drawings developed by Saga and Moss Rosenberg yard of NorwayLoading directly from sub-sea wells using well pressure for loading and water for

discharging the cargo.18,000 m3in 280 bottles

2.2.3 Modern CNG Carrier Concepts :-

With present developments in materials and their applications and CNGspromising outlook in handling and marketing associated gas and the exploitationof stranded reserves, have renewed the interest in commercializing thetechnology. One of the proponents of the CNG technology in the early 1990s wasCran & Stennings Technology Inc. that proposed a wellknown concept,Coselletm. The idea seeks to reduce the manufacturing cost of the gas

containment system. Spooling small diameter (6 inch) coiled tubing into largecarrousels achieves the purpose. The gas is pressured up to 3000 psi at ambienttemperatures. Similar methodology is used by others namely Trans Ocean Gas,a Canadian enterprise, and Knutsen O.A.S Shipping of Norway with varyingcharacteristics of the containment system7. Another approach to CNG isespoused Enersea Transport LLC, They developed the VOTRANStm conceptin which the natural gas is compressed and cooled to lower temperatures6. Thisreduces the volume of the compressed gas compared to just compressing it atambient temperatures. At the lower temperatures of 0 to 40oF the processworks at lower pressures than at ambient temperatures.

Many concepts are proposed for transportation of CNG but most of them arebased on transportation in pipeline/pressure vessels

EnerSea(steel, vertical pipes, 130 bar, -29C) Coselle(Williams) (steel, coiled, 275 bar, ambient) Knutsen (steel, vertical pipes, 250 bar, ambient) CETech: (Statoil, Teekay, Hegh) steel, horizontal pipes, 200-250 bar,

ambient) TransCanada(wrapped steel liner) Trans Ocean Gas (composite)

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2.2.4 The CNG Transport Technology:-

The technology is relatively simple. Natural gas, originally at certain temperatureand pressure is compressed to higher pressures and chilled to lowertemperatures. Specially designed ships, which have a containment system madeof stacked horizontal or vertical pipes, transport the cold compressed gas. The

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technology can be divided into three parts namely, compression, refrigerationand transportation. Transportation includes the loading, the voyage using theCNG carriers and unloading

CNG Cargo Containment System

2.2.5 CNG vs. LNGIn comparing CNG with LNG the same transporting ship real-volumetric capacityis used. However, in making the comparison it is worth remembering the disparityin the actual standard volume of the gas transported. For the same ship volume,LNG transports 2.1 Bcf of natural gas compared to a maximum volume of 1.2 Bcftransported as CNG.Keeping aside the difference in standard volumes, a proper comparison betweenthe two technologies warrants a review of the requirements and the respectivecosts involved for both. For any LNG project to be economically viable athroughput of 0.5 to 1 Bcf/d of natural gas is required. Typically a LNG plant of 3

MMtpa needs a gas at rate of 400-450 MMscf/d5. This translates into gasreserves of 5 to 8 Tcf for a project life of 20 years, depending on the amount ofcondensates in the gas5. CNG projects, on the other hand, do not require suchamount of reserves for the same throughput12. Fields with modest reserves andga s rates can support CNG projects10 For LNG projects, the liquefaction plantis the most capital intensive. They make for almost 50% of the total investmentfor a LNG project13. Taking an industry estimate of production cost of $200/tonof LNG per annum, a project handling 500 MMscf/d (3.8 million tonnes of LNGper annum) requires an investment of 750 million. A CNG plant with loadingfacilities including compressors, pipelines and buoys costs $30 to 40 million8 Thelower investment along with simplicity of the operations helps, in effect, in faster

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planning and commissioning of a CNG project. For CNG the shipping of thecompressed gas is the most capital intensive. The ships cost approximately $230million8 while for LNG the ships cost approximately $160 million15. Offloading of

the LNG requires special facilities namely a regasification terminal.Regasification facilities cost $500-550 million depending upon terminalcapacity13. CNG offloading facilities consisting of separators , scrubbers andheaters cost from $16 to 20 million8. Overall for CNG the total investment canrange from $1-2 billion mainly depending upon the number of ships required. ForLNG the investment can range from $1.5 to 2.5 billion depending on the marketneeds and number of ships required.

From Figures 2 and 3, one of the main attractions of CNG is that the bulk of theinvestment is in movable assets, while for LNG a very large of the investment isin fixed assets. The investment breakdown lowers the CNG investment risks, byproviding a way to recover most of the investment and allow its deployment inother projects or applications. The next step is to estimate and compare the unit

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price of gas delivered as CNG or LNG. For LNG the typical chain value perMMBTU of gas is15: Exploration and Production: $0.5- 1.0/MMBTU,Liquefaction: $0.8-1.2/MMBTU, Regasification and Storage: $0.3-0.5/MMBTU.

Shipping of LNG is a function of distance of transport and the discount factors.Assuming the ships for transporting LNG are newly built the unit cost of shippingrange from $0.4-1.5/MMBTU for distances from 500 to 5000 miles16. Thus, thetotal cost of producing and transporting LNG can range from $2 to $4.2per MMBTU for the distances considered. For CNG, keeping the same unit costfor exploration and production, the chain value per MMBTU is: Exploration andProduction: $0.5- 1.0/MMBTU, Processing and Transportation: $0.88-3.82/MMBTU for distances from 500 miles to 5000 miles. This translates into aunit cost of $1.38 to $4.82 per MMBTU. Taking a gas price of $0.75/MMBTU forboth CNG and LNG and liquefaction cost of $1.0/MMBTU with regasification costof $0.4/MMBTU, the unit price of LNG delivered is shown in Table 5.

DistanceTransportcost17 Unit cost

miles $/MMBTU $/MMBTU500 0.4 2.551000 0.5 2.651500 0.6 2.752000 0.7 2.852500 0.8 2.953500 1.1 3.25

5000 1.5 3.65Table 5- Estimated unit cost of transporting the

2.2.6 Advantages of CNG over LNG:-

Requirement of lower throughput of gas for a project Involvement of lower capital Ease of deployment faster implementation of a project Ability to access stranded reserves and monetize them Majority of the investment is in the shipping, making the assets movable

and reducing the risk involved

2.2.7 Disadvantages:-

Inability to transport large volumes of gas such LNGDisparity in the volume transport hinders commercial possibility of CNG

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2.3 Transportation By LNG Carriers:-

LNG carriers have been used to transport liquified natural gas overseas on acommercial basis since the late 1960s. Nowadays, a fleet of about 130 vesselstransports 5% of the world annual gas consumption from producer to consumer.Over the years, there have been many improvements in the designs, but themain propulsion system is still the same. In all other sectors of commercialshipping, the steam turbine has been replaced by much more efficient diesels,but LNG carriers stick with steam turbines. The main reason is for this is thesteam turbine propulsion system's unique capability to running on two cheapfuels simultaneously: Heavy Fuel Oil and Boil-off Gas. This feature, combinedwith a very high reliability, ensured the survival of the steam turbine in spite of its

very low thermal efficiency until now.

In 2002, Chantiers de l'Atlantique in France recieved the first order from Gaz deFrance for a 74,000 cubic meter diesel-electric driven LNG carrier. Dieselmanufacturer Wrtsil in Finland will deliver the dual-fuel diesel gensets. Thechoise to select diesels instead of the conventional steam turbine indicated thatthere are owners and/or charterers in the LNG shipping community who arewilling to try new technology, which increases thermal efficiency of the propulsionplant. A few LNG carrier operators have indicated they are interested in a morefuel efficient vessel, but charterers so far have been unwilling to considerengaging anything other than steam turbine driven LNG carriers.

Due to the small size of the LNC carrier ordered at Chantiers de l'Atlantique, itspower requirements are too low to lend itself for gas turbine drive. However,larger vessels, such as "K Freezia", with propulsion power requirements between24 and 30 MW, are ideally suited for the use of aero-derivative gas turbines. It isthese vessel that will be used in this review of alternative propulsion plants forLNG carriers.

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2.3.1 Conventional LNG Carrier

Name / Owner SK Summit / SK Shipping Co., Korea

Builder / Delivery Daewoo HI, Korea / 1999Dimensions 277 x 43.4 x 11.3 m (L x B x D)Cargo capacity (100%) 138,000 cubic meterSpeed 20.3 knFuel consumption 2,400 kg/h HFO + 3,950 kg/h BOGPropulsion machinery 1 Kawasaki UA-400 steam turbine, 29,830 kW

SK Summit represents the current standard in LNG carriers, 138,000 cubic metercargo capacity and a cruising speed of around 19 knots. As of November 2002,there are approximately 60 vessels rather similar to SK Summit on order, withabout 25 options. SK Summit is therefore a great example to be used as abenchmark when determining the relative merits of alternative LNG carrierspropulsion systems. Prices for these vessels hover between USD. 165M and

170M. Total project cost per vessel can reach USD. 200M as a result offinancing, delivery, project management, insurances, bank guarantees, etc.

2.3.2 The Basic Ship Structure:-

All LNG ships are double hulled and rely on insulation to keep LNG liquid at -260F (-162.2C). The cargo is carried at atmospheric pressure in speciallyinsulated tanks, referred to as the cargo containment system, inside the innerhull.

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The tanks can be either of the Moss spherical type, or the prismatic, membranetype which conforms to the shape of the ship's hull. Or again, in a development,they could be of a new pyramid type (see illustration) from Conoco Phillips, which

has just received Approval in Principle from ABS.

The Moss type is the design emblematic of the LNG ship in that the tops of thespheres protrude above the hull making the ships instantly recognizable.Pioneered by Norway's Moss Rosenberg in the 1970's, the design is now ownedby Moss Maritime a.s., Lysaker, Norway, a unit of Italy's ENI SAIPEM.

There are three types of membrane containment systems, the Gaz Transport andTechnigaz systems and a self-supporting prismatic membrane design from IHI,Japan. Gaz Transport and Technigaz are now one company, whose latestcontainment system, CS1, incorporates features from the existing Gaztransport

No 96 and Technigaz Mk III systems. CS1 uses reinforced polyurethane foaminsulation and two membranes, the first one 0.7 mm thick made of Invar (lowthermal contraction coefficient metal and high nickel content), the second madeof a composite aluminum-glass fiber called triplex. The system has beenrationalized to make assembly easier and is prefabricated allowing quickassembly on board.

2.3.2.2 The Market Where Time Stood Still :-

To marine industry veterans, today's LNG boom is deja vu all over again. There

was supposed to be this sort of LNG boom some 30 years ago. But in 1979,things soured when pricing disputes between U.S. buyers and Sonatrach ofAlgeria eventually led to the termination of contracts, the laying up of six LNGships (three of which were later scrapped) and the mothballing of two out of fourLNG terminals.

There was still growing LNG demand in other areas, but international LNG shipconstruction slowed until it got a further impetus in the 1990's. What's differentthis time around is that the newbuilding market is dominated by South Korea,with China already entering the market. And the technology is advancing. For thefirst time, some ships are being specified with diesel, rather than steam turbine,

propulsion, there are improvements in insulation of cargo containment systems,established containment systems are being twitched and new containmentsystems are being offered.

2.3.2.3 Taller Spheres:-

When is a sphere not a sphere? When it's a vertically stretched sphere.Kawasaki Kisen Kaisha, Ltd. ("K" Line), in partnership with Osaka GasInternational Transport Inc. ) and Nippon Yusen Kaisha (NYK), has concluded acontract for a new 153,000 m3 LNG carrier with Kawasaki ShipbuildingCorporation.




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The ship will be mainly used to carry LNG for Osaka Gas from the Qalhat LNGProject in Oman from 2009. It will have four spherical LNG tanks three of whichare being given a 2 m vertical stretch. This advantage enables tank capacity to

be increased by about 5.5 percent but within almost the same ship dimensionsand with the same fuel oil consumption.

2.3.2.4 The Shape Of Things To Come:-

A new entrant in the containment system market is Ocean LNG, Inc., Houston. Ithas developed a "more construction friendly LNG carrier" that can be built in"non-traditional LNG shipyards."

ABS has issued Approval In Principle (AIP) to Ocean LNG's tank containmentsystem and carrier design.

The tank design is cylindrical with spherical dished ends. The 180,000 m3version of Ocean LNG's ship design features five of these large 36 m diameterand 40 m high cylinder tanks each holding a volume of 36,000 m3 of LNG.

Compared to the spherical containment system, the Ocean system is expected toincrease cargo capacity within the same main hull dimensions by an estimated25 percent, while still providing full access for inspections of both the insulationand tank structure.

A key aspect of transporting LNG is the ability of the containment system towithstand dynamic sloshing loads of the LNG cargo when a tank is partially filled.

Membrane systems are particularly sensitive to sloshing loads.

The Ocean LNG tank design is fashioned according to IMO Type B independenttank design and based on the "leak before failure" principle.

The tanks are designed to minimize filling restrictions due to sloshing effects. Adetailed sloshing analysis of the tank and pump tower designs was recentlycompleted by ABS.

2.3.2.5 To Boil Off ... Or Not?

Since LNG tankers rely on insulation rather than refrigeration to keep their cargorefrigerated, a small percentage will "boil off." Traditionally, LNG tankers haveutilized this boil off as fuel in steam turbine based propulsion plant.

That's changing. One way or another, the diesel is coming on board. Oneapproach is to reliquefy the boil off gas, so that it remains as valuable cargo.Shipboard reliquefaction technology has matured considerably in recent years,making use of experience from land-based and LPG carrier installations. Among




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others Hamworthy KSE's patented Moss RS closed nitrogen cycle system forreliquefying boil-off gas offers a solution for pumping LNG back to the cargotanks and hence the opportunity to deliver more cargo to the buyers.

MAN B&W Diesel has produced a paper that thoroughly examines operatingcosts and additional income from the transport and sale of LNG. The paper,"LNG Carrier Propulsion by ME Engines and Reliquefaction," analyzes fuel oil,lube oil and maintenance costs for both propulsion and electrical powergeneration under various operating conditions on a comparison basis for adiesel-based solution against a steam plant. The evaluation shows thatsubstantial economic benefits can be gained from diesel propulsion inconjunction with gas reliquefaction over the steam turbine-powered option,simply because of the big difference in thermal efficiencies while the first cost ofthe various propulsion systems is virtually the same.

Overseas Shipholding Group (OSG) has ordered four 216,000 m3 LNG shipsfrom Hyundai and Samsung. Each vessel utilizes two MAN B&W ME engines formain propulsion. Each yard will deliver two vessels for the Rasgas II project forshipping Qatari gas to the U.K.

Main propulsion will be by two 6S70ME-C engines in each vessel. The enginesfor the Hyundai vessels will be built by Hyundai Heavy Industries, and for theSamsung vessels by HSD. The engines will be heavy fuel burning, and the boiloff gas will be returned to the tanks via onboard reliquefaction plants.

Apart from the reliquefaction solution, another means of utilizing the diesel is byusing the boil off gas as fuel. MAN B&W's ME-GI engine is a gas injection, dualfuel low speed diesel engine, which can burn any ratio of fuel and gas desired.

Wrtsil, meanwhile, has had considerable success with its DF dual-fuelengines. The first dual fuel electric LNG carrier, the 75,000 m3 Gaz de FranceEnergy, was recently completed by Chantiers de l'Atlantique of France and is inservice with Gaz de France.

Furthermore, Wrtsil has now made a breakthrough into the Korean market withan order from Hyundai Heavy Industries Co. Ltd. to supply four sets of Wartsila50DF dual-fuel engines to power a series of 155,000 m3 dual-fuel-electric LNGcarriers, with an option on four more sets.

The ships were ordered by BP Shipping of the U.K. and each ship will beequipped with two 12-cylinder and two nine-cylinder Wrtsil 50DF dual-fuelengines with an aggregate power of 39.9 MW, as prime movers in a dual-fuel/electric machinery arrangement. ML




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CHAPTER 3

TRADITIONAL STEAM PROPULSION:-

After having been predominantly flared off or re-injected for decades, natural gasis playing an increasingly important role in global energy consumption today.Clean combustion properties and abundant reserves are the main benefactorsfor this evolution from unsolicited by-product of oil production to preferred energysource. With natural gas reserves often located far away from energyconsumers and pipelines expensive or impractical to build, seabornetransportation of natural gas is on the rise as well. The most economic andcommon way to transport natural gas by sea is in liquefied form. LiquefiedNatural Gas (LNG) is today transported by a fleet of some two-hundreddedicated LNG carriers. With seaborne transportation of LNG expected to doublewithin this decade, a vast expansion of the LNG carrier fleet is imminent. At thesame time, increasing cargo volumes offer the possibility to apply economies ofscale, and ships are about to significantly grow in size. These circumstancescreate the need to verify the technical solutions that have been applied in LNGcarriers so far.

The LNG trade has traditionally been based on long-term shipping contractsand dedicated fleets of ships sailing on fixed routes and schedules between theworlds rather limited number of LNG terminals. The LNG supply chain does nothave much buffer capacity and it is very important that the cargo is delivered on

time. For the past forty years, steam turbine installations have dominatedonboard LNG carriers. The ease with which steam turbine installations can burnboil-off gas and their apparent reliability have kept them in the controlling positionthat has been taken over by diesel engine installations a long time ago in allother segments of the shipping industry. Steam turbine installations are howevernot very efficient. This has a negative impact on the operating economy andexhaust gas emissions of the ship. Exactly these issues play an increasinglyimportant role in LNG shipping these days. Encouraged by the latestdevelopments in its gas engine technology, Engine builders started looking for amore economic and environmentally friendly way to power LNG carriers.Machinery alternatives with two- and four-stroke diesel, high pressure gas-diesel

and low-pressure dual-fuel engines, in mechanical and electric propulsionarrangements, with and without boil-off reliquefaction, were studied. Dual-fuel-electric installations were found to be the most attractive alternative to steamturbine installations.

3.1 Basic Characteristics:-

Steam turbine propulsion dominates todays global LNG carrier fleet. The originalreasons for this have been the availability of high power output and the possibilityof using low-grade fuels as well as cargo boil-off gas. Maintenance of theturbines is relatively low-cost and infrequent and the systems are considered




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proven and reliable. Boil-off gas is a key issue. It must be disposed of in someway and for many years of LNG carrier construction the steam boiler was thesimplest solution. This feature has long been an obstacle to other propulsion

systems entering the LNG carrier market and made steam turbine the standardchoice for LNG carriers. The available quantity of boil-off gas depends on theship design and its operating conditions. Today, a natural boil-off rate of 0.15 %per day is typically considered as a design point. However, this is a nominalvalue and actual values as low as 0.10 % have been reported. During ballastvoyages the amount of available boil-off gas can be 10-50 % of the amountprevailing during laden voyages depending on how many tanks will contain asmall quantity of LNG for tank cooling. Whatever propulsion plant is chosen,there has to be some way of handling this boil-off gas either by utilising it as fuel,or reliquefying it. The composition of the boil-off and thus its energy value alsovaries during the voyage and is an important consideration for alternative power

plants. As nitrogen has a lower boiling point than methane, the nitrogen contentof the boil-off gas is high at the beginning of the laden voyage and decreasesduring the voyage. In ballast, boil-off gas is mainly generated from the tankcooling spray; the heavier hydrocarbons evaporate, thereby giving the boil-off ahigher energy content. The same result applies to forced boil-off gas. Safety is ofutmost importance in gas shipping, and LNG carriers have an excellent safetyrecord. The reliability of steam turbine propulsion has helped to achieve thistogether with strict terminal regulations and procedures, and robust ship designs.For example, propulsion power has to be available at all times whilst in port

3.2. Market Requirments:-

An attractive alternative should be outperforming the steam turbine installationwith respect to its apparent disadvantages, while at the same time at leastmatching it with respect to its advantages. It is therefore important to study theseadvantages and disadvantages. The main reason to remain faithful to the steamturbine installation in LNG carriers is the ease with which they can burn boil-offgas. Boil-off gas is an unavoidable by-product of the seaborne LNGtransportation concept. A small amount of cargo, approximately 0.13% per day inladen condition, is left to evaporate in order to control temperature and pressurein the ships cargo tanks. Both quantity and quality of the boil-off gas are subject

to variation.

3.2.1 Operating Economy

Although steam turbine installations can utilize boil-off gas very easily, they donot use it very efficiently. Losses in the boilers, steam turbine, high-speedreduction gear and shafting bring the efficiency of the propulsionmachinery to a level below 29% at full load. The efficiency of the electricpower generation machinery is below 25% at full load. Part-load efficiencies ofboth the propulsion and electric power generation machinery are even lower.Such low machinery efficiencies lead to a substantial amount of HFO being




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required for complementing the available boil-off gas. In laden conditions, some50% of the ships energy requirement is covered with HFO. In ballast condition,this share grows to 80%. Also for LNG carriers, like for any other kind of ship,

fuel costs are one of the most important components of the ships operatingcosts.

3.2.2 Environmental-Friendliness:-

The low

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