LNG: An eco-friendly cryogenic fuel for sustainable development

Applied Energy 88 (2011) 4264–4273

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Applied Energy journal homepage: www.elsevier.com/locate/apenergy

LNG: An eco-friendly cryogenic fuel for sustainable development Satish Kumar a, Hyouk-Tae Kwon b, Kwang-Ho Choi b, Wonsub Lim a, Jae Hyun Cho a, Kyungjae Tak a, Il Moon a,⇑ a b

Department of Chemical and Biomolecular Engineering, Yonsei University 262-Seongsanno, Seodaemun-gu, Seoul 120-749, Republic of Korea GS Engineering & Construction, GS Yeokjeon Tower, 537 Namdaemun-ro 5-ga, Joong-gu, Seoul 100-722, Republic of Korea

a r t i c l e

i n f o

Article history: Received 9 July 2010 Received in revised form 7 June 2011 Accepted 21 June 2011 Available online 20 July 2011 Keywords: Compressed natural gas Liquefied natural gas Cryogenic fuel Green house gases Pollution prevention

a b s t r a c t As the demand of natural gas has sharply increased in the last two decades at the global level, the transportation of natural gas from different parts (gas producing to the consuming areas) of the world has become more significant. Liquefaction of natural gas provides a safer and economical alternative for transportation and also increases its storage capabilities. The liquefaction process requires the natural gas to be cooled using various methods of cryogenic processes and also be depressurized to atmospheric conditions for easier and safer storage. LNG transported in cryogenic vessels offers several advantages over pipeline transport of natural gas especially when the gas consuming areas are far away from the gas producing areas. Moreover, LNG as an automobile fuel has a definite edge over other fuels. This article presents an overview on the characteristics of LNG, present state of affairs of LNG, its import from overseas, CNG vs. LNG as an automobile fuel, eco-friendliness of natural gas fuel, etc. It also discusses the potential of natural gas production from different sources. Ó 2011 Elsevier Ltd. All rights reserved.

Contents 1. 2. 3.

4. 5. 6.

7. 8. 9.

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Important features of LNG . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.1. LNG vs. CNG and LPG . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Worldwide use of LNG . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.1. Transportation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.2. Electricity production . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Storage and transport of LNG . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Worldwide LNG technology. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Worldwide potential of natural gas vis-a-vis LNG . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.1. Fossil natural gas. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.2. Town gas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.3. Biogas. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.4. Hydrates. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Lifecycle greenhouse gas emissions of LNG vs. oil & coal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Conclusions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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Abbreviations: L-NGV, liquefied natural gas vehicle; LNG, liquefied natural gas; CNG, compressed natural gas; LPG, liquefied petroleum gas; LFG, landfill gas; MT, million tone; MMTA, million metric tone per annum; MJ/m3, megajoule per cubic meter; GGE, gasoline per gallonequivalent; DGE, diesel per gallonequivalent; NGV, natural gas vehicles; LDV, light duty vehicles; GVR, gas vehicle report; PPG, pound per gallon; PPB, parts per billion; bpd, barrels per day; CO2, carbon dioxide; CO, carbon monoxide; NOx, nitrogen oxides; SOx, sulfur oxides; GHG, green house gas. ⇑ Corresponding author. Tel.: +82 2 2123 2761; fax: +82 2 312 6401. E-mail addresses: [email protected] (S. Kumar), [email protected] (I. Moon). 0306-2619/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.apenergy.2011.06.035

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1. Introduction

2. Important features of LNG

The worldwide energy demand is increasing continuously and is projected to grow by an average of 1.2% per year [1]. Owing to the abundance and the availability of fossil fuels resources, it can be estimated that they will continue to play a significant role in the world’s energy economy. Fossil fuels currently provide about 85% of the world’s commercial energy needs. It has been anticipated that China [2], which today meets almost 90% of its power needs with coal, will see its energy demand for power generation more than double by the next century, surpassing US demand by more than one-third [2,3]. Currently, automobile is responsible for more than half of total oil demand and this demand is expected to grow substantially. Demand in developed countries is expected to be essentially flat in contrast to developing countries as economic growth and rising prosperity leads to a dramatic increase in personal vehicles. At the same time, global CO2 emissions are projected to rise by close to 30% between 2005 and 2030, even with improved energy efficiency and growth in nuclear and renewable energies [1]. Therefore, in order to fulfill the increasing energy demand and to reduce the environment CO2% a drive to find alternative fuels [4] to replace hydrocarbons such as diesel and petrol has resulted in a plethora of different fuels—few of which are commercially available in significant quantities. Natural gas is one of them which is widely available and renewable (through the production of biogas or bio-methane), offers greenhouse gas reductions and produces fewer emissions compared to other traditional and alternative fuels. Natural gas can be used either as compressed natural gas (CNG), liquefied natural gas (LNG) or even blended with hydrogen. The use of natural gas vehicles (NGVs) also facilitates energy security and energy diversity. Thus, natural gas has emerged as the most preferred fuel due to its inherently environmental benignity, greater efficiency and cost effectiveness. For long distance transportation of natural gas, natural gas liquefaction has many advantages over pipeline transportation. A comparison of world’s natural gas supplies via pipeline vs. LNG is represented in Fig. 1. Like all natural gases, LNG is cleaner than coal and oil, and offers an opportunity to diversify energy supplies. Hence, within the gas market the use of LNG has gained much recognition globally and it is the right moment to review the status of LNG development with regard to various resources of natural gas, storage, transportation, utilization of LNG in different sectors and to trace the desirability of LNG technology.

Natural gas is a mixture of paraffinic hydrocarbons such as methane, ethane, propane and butane, etc. Small amounts of higher hydrocarbons such as ethylene may be present apart from carbon dioxide, a trace amount of hydrogen sulfide and nitrogen. Since, LNG is the cleanest form of natural gas and contains more than 98% methane therefore, it becomes synonyms to methane. Natural gas is a low density (0.789 basis air) and low sulfur content fuel as compared to gasoline, and is practically free from carbon monoxide emission. Natural gas is converted to LNG by cooling it down to 162 °C [5], at which it becomes a liquid and this process reduces its volume [6] by a factor of more than 600. The ability to convert natural gas to LNG, which can be shipped on specially built ocean-going ships, provides consumers with access to vast natural gas resources worldwide. LNG is a clear, odorless, non-toxic, non-corrosive, cryogenic liquid at atmospheric pressure. The density of LNG is approximately 0.4–0.5 kg/L, depending on temperature, pressure and composition, compared to water at 1.0 kg/L. Thus LNG, if spilled on water, floats on top and vaporizes rapidly. In the absence of an ignition source, LNG evaporates quickly and disperses, leaving no residue. Hence, no environmental cleanup needed for LNG spills on water or land. LNG, when vaporized in gaseous form, will only burn in concentrations of between 5% and 15% mixed [7] in the air. The removal of acid gases (gas sweetening) such as CO2 and H2S, from natural gas before liquefaction is an important process for producing pure methane. The comparison of various important properties of LNG with other liquid fuels is given in Table 1 [8].

400

Production Pipeline trade LNG trade

Index ( 2001= 100 )

350

CNG and LPG are often confused with LNG while CNG and LPG have quite different properties than LNG at similar conditions of temperature and pressure. CNG is a mixture of hydrocarbons consisting of approximately 80–90% methane in gaseous form, and it is colorless, non-carcinogenic, non-toxic, inflammable and lighter than air. Because of its low energy density, it is compressed to pressure of 200–250 kg/ cm2 (to enhance the vehicle on-board storage in a cylinder). Superior to petroleum, it operates at one-third the cost of conventional fuel and is hence, increasingly becoming popular with automobile owners. As far as LPG is concerned, it is a clean, high octane, abundant and eco-friendly fuel. It is obtained from natural gas through fractionation and from crude oil through refining. It is a mixture of petroleum gases like propane and butane. LPG is a gas at atmospheric pressure and normal temperatures, but it can be liquefied when moderate pressure is applied or when the temperature is sufficiently reduced (42 °C). This property makes the fuel an ideal

Table 1 Comparison of physical and chemical properties of LNG with diesel, gasoline and LPG.

300

250

200

150

100

2.1. LNG vs. CNG and LPG

2005

2010

2015

2020

2025

2030

Fig. 1. Comparison of natural gas supply in the form of LNG vs. pipeline.

Properties

LNG

Diesel

Gasoline

LPG

Auto ignition point (°C) Flash point (°C) Boiling point (°C) Flammable range (%) Stored pressure Toxic Carcinogenic Health hazards

540

316

257

454–450

187 160

60 204

45 32

104 42

5–15

N/A

1.3–6

2.1–9.5

Atmospheric No No None

Atmospheric Yes Yes None

Atmospheric Yes Yes Eye irritant

Pressurized No No None

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energy source for a wide range of applications, as it can be easily condensed, packaged, stored and utilized. When the pressure is released, the liquid makes up about 250 times its volume as gas, so large amounts of energy can be stored and transported compactly. In liquefied form, the volume of LNG is 600 times less than the same amount of natural gas at room temperatures while the volume of CNG is 1% less of its original volume. LNG shipping is therefore an economic way of transporting large quantities of natural gas over long distances as compared to other natural gases such as CNG and LPG [9,10]. LNG is transported and stored at normal atmospheric pressure and LNG carriers are purpose-built tank vessels for transporting LNG at sea. The energy density of LNG is 435 Kg/m3 as compared to 175 kg/ 3 m for compressed natural gas (CNG) at 200 bar. This means that for a given capacity fuel tank, an LNG powered vehicle can travel up to 2.4 times the distance of the CNG counterpart, or in another way, for a given vehicle range, an LNG powered vehicle needs up to 2.4 times smaller fuel tank capacity than its CNG counterpart. Again, an LNG powered vehicle costs less than a CNG powered vehicle for manufacturing. The capital and maintenance costs of LNG refueling stations are a fraction of their CNG counterparts and they do not require any electricity. Hence, LNG offers special advantages over CNG and LPG in terms of easier transportation, storage and better density than gaseous methane. LNG also offers additional flexibility as liquefied to compressed natural gas (L-CNG). Additionally, LNG has a role of contributing to the development of biogas-to-biomethane as a vehicle fuel, both for gas purification and transport. 3. Worldwide use of LNG 3.1. Transportation The use of LNG in transport sector is increasing rapidly in many parts of the world [11]. It is the most commonly used as a clean burning alternative vehicle fuel in thousands of heavy duty trucks, buses and waste collection trucks as compared to passenger cars because on average passenger cars stand idle more often, which would give rise to high evaporative losses. The use of LNG requires storage facilities for the cold (-162 °C) liquid natural gas at the roadside refueling stations and special fuelling equipment which can handle cryogenic temperatures [12]. In addition, the trucks must be equipped with special dual fuel engines to use LNG. Moreover, the fuel tank on board of the truck needs to be adapted for LNG usage. These requirements make the use of LNG relatively expensive. LNG is superior to gasoline and oil in terms of calorific value, which is evident from Table 2 [13,14]. It makes available 41 KJ/kg for refrigeration as compared to 21.2 kJ/kg for liquid nitrogen. This characteristic of being able to obtain high refrigeration enables LNG to be used towards cooling in water jackets or improving the inter-cooling between compressor stages. In a high output turbo-charged piston engine, the refrigeration effect lowers the overall intake charge temperature. This improves power output and reduces the tendency towards knock and pre-ignition. It could be efficiently used as aircraft engine and ships engine fuel owing to its high octane number and easier maintenance. A re-

cent study has revealed that LNG would be the preferred feedstock for power, chemical, fertilizer [15] and petrochemical plants in future. Big power companies are moving away from coal towards LNG and, in future, it is likely to replace naphtha as the main fuel for the plants. Its consumption is expected to grow from, presently, 12.5 million tons to 50 million tons by 2016–2017 [16]. Moreover, LNG has good antiknock characteristics therefore it can be used with higher compression than gasoline inside the motor without premature ignition of the fuel/air mixture [17]. Natural gas (LNG) offers a higher thermal efficiency and lower specific energy consumption than gasoline and oil, hence, it is expected as a promising fuel for the future. In addition because of more stringent standards against environmental emissions and its regulations as well as economic reason, natural gas is considered as a clean-burning, alternative fuel for the transportation sector. A brief review on the use of LNG as a transport fuel is reported below. Natural gas has been used as fuel for transportation for decades and currently, about 11.4 million NGVs of different types are running either on CNG or LNG worldwide, which correspond to a share of 1% of the total vehicles population [11,17]. The leading users of NGVs are Pakistan (2.7 million), Iran (1.95 million), Argentina (1.9 million), Brazil (1.6 million), and India (1.0 million) [17] as represented in Fig. 2, with the Asia–Pacific region leading with a global market share with 5.7 million NGVs, followed by Latin America with almost 4 million vehicles. In Latin America and Asia, the increase of natural gas vehicles has been particularly strong in recent years when oil prices escalated [18]. These countries together have more than half of the worldwide existing stock of natural gas vehicles. In Iran and India, the stock of natural gas vehicles amounted to more than 800,000, followed by Italy (5, 80,000). However, LNG as a road fuel has already been introduced in the UK [16]. There are about 3000 LNG vehicles in US that run on LNG and most LNG vehicles are government owned; there are 40 governments – owned 40 LNG fuelling stations at the same time. Today, approximately 50 LNG vehicle fueling stations are available worldwide [19]. The 10 countries following the front runners – among them are China, Russia and the US–have obviously lower stock figures. However, they are well above the German stock figure (64,454 NGVs). With regard to the total car population of a given country, Bangladesh has more than 20%, Armenia 13%, Pakistan14%, Argentina and Brazil have 10% natural gas fueled cars. In contrast, the share of natural gas fueled cars in Europe is very low. Even in Italy, where CNG was already used as fuel for cars in the1930s; natural gas vehicles have a share of only 1.1% of the total car population. In Germany, the corresponding share is only 0.1%. In addition to cars, buses and trucks the two-and three-wheel vehicles are also driving with natural gas. However, cars dominate the natural gas vehicles fleet in those countries where natural gas is widely used as a vehicle fuel. One exemption is India, where natural gas cars have a share of 38% natural gas vehicles stock and two and three-wheeler natural gas vehicles play an important role. Another exception is the Ukraine with a share of natural gas cars amounting only to 6%. In Ukraine, buses as well as truck shave a share of 25%, while, other vehicles even reach a share of about

Table 2 Comparison of energy contents of LNG vs. CNG, diesel, gasoline and LPG. Fuel

CNG

LNG

Diesel

Gasoline

LPG

Energy content (gross heating value)

37–40 MJ/m3 46–49 MJ/kg

25 MJ/L

38.3 MJ/L

34.5 MJ/L

25.4 MJ/L

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Korea, South Sweden Japan Venezuela Malaysia Uzbekistan Bulgaria Germany Russia Armenia Peru United States Egypt Bolivia Bangladesh Ukraine Thailand Colombia China Italy India Brazil Argentina Iran Pakistan 0

500000

1000000

1500000

2000000

2500000

Natural Gas Vehicles Fig. 2. World’s leading NGVs users. Source: GVR Gas vehicle report 2009.

44%. To compare this with European countries, Germany’s natural gas cars have a share of 79% of the total natural gas vehicles population, while the share of trucks amounts to 18%, and the share of buses is very low (2%). LNG is included as a substitute of crude oil in automotive fuel chains in a number of studies [20–23]. Williams et al. [20] and Gover et al. [21] studied only a small number of natural gas based chains. The focus of Gover et al. [21] was specifically on future fuel chain options for the UK. The use of LNG as a transportation fuel in the heavy trucking industry has been reported by William et al. and Litzake et al. [24–26]. According to their report LNG can directly substitute the diesel fuel and for heavy-duty vehicle applications, such as haul trucks, LNG is the most viable option for long range use. The amount of fuel that can be stored in a liquefied state with cryogenic tanks greatly exceeds a CNG system. Further, the usefulness of LNG as a motor fuel and refrigerant has been reported by Kirillov [27]. As per their report, LNG is effective not merely as a cheap and ecologically clean fuel. It may, at the same time, be a source of refrigeration as well. In addition to the use of LNG as motor fuel, it is also projected to be a potential fuel for shipping industry [28,29]. Recently, China and Norway has developed LNG marine engine [30] and it is expected that this step will be promising in extending the LNG technology. According to this news, even though a LNG fueled engine is more expensive than a conventional engine but it will be viable investment as LNG is less expensive than diesel. Hence, LNG is providing an economic alternative to diesel in the heavy duty trucking industry, in port facility vehicles, and increasingly in marine and rail applications. Although the use of LNG as vehicle fuel is capturing wider attention worldwide, yet LNG faces some significant challenges to achieving its full potential share of the global NGV market. The challenges are listed as follows: I. There are very few global regulations for L-NGV applications and there are many remaining gaps in the existing international standards. The lack of harmonized standards and regulations impede opportunities to reduce the cost of manufacturing and purchasing different LNG equipment. II. A number of countries have their own national interest and policies regarding the utilization of energy for transportation which prohibits the development of various types of L-NGVs in the areas where there could be a strong LNG market.

III. Many manufacturers of heavy-duty engines and vehicles – even those producing NGVs – have not yet adapted their products for LNG. There are too few products, in particular, for the very heavy truck-haulage industry or for larger offroad vehicle applications where LNG could provide economic and environmental benefits. IV. Retrofit systems being installed on various heavy duty trucks operate at slightly different working pressures, requiring the LNG to be delivered at different pressures. This complicates the opportunity to develop a network of harmonized LNG fuelling stations. V. Consistency of fuel quality, particularly in the cryogenic processing of biogas and in LNG fuelling stations faces special challenges that need to be addressed. Hence, in order to accept LNG as a vehicle fuel it is recommended to add more global regulations for L-NGV and to develop infrastructures (LNG fuelling stations and LNG kits for heavy to light duty vehicles) along with more advanced technologies. 3.2. Electricity production The use of LNG is not only limited up to transport sector but it is also useful in the production of electricity. The utilization of the cryogenic exergy of LNG for the production of electricity has been reported by many research groups [31–35]. In [35] the authors propose the introduction of a combined Rankine–Brayton cycle with CO2 as a working fluid. An additional source of heat is necessary, which is obtained by means of combustion of some amount of CH4 in oxygen, producing combustion gases with a large content of CO2 (95%). The transmission of heat to the evaporating LNG would be very irreversible. Deng et al. [36] proposed a combined plant producing electricity and refrigeration. The process would utilize the cryogenic exergy of LNG, but also the chemical exergy of some amount of CH4 burnt in oxygen. This solution would not comply with the principle of combined cogeneration processes, because the cold cycle can be combined with the refrigeration cycle without any additional heat source. The working fluid would be CO2 having very inconvenient thermal properties. Hence, in the proposed installation large exergy losses would appear. Use of natural gas for power generation has been reported by Oliveira et al. [37] and Oshima et al. [38]. According to Okamura et al. [39] LNG is a major source of energy for transport and power

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generation sector, in Japan. They analyzed that the use of LNG contribute greatly to improving the atmospheric environment and reducing CO2 emissions. The possibilities of the utilization of cryogenic exergy of LNG for electricity production without any additional combustion of any its portion, have been analyzed by Szargut et al. [40] and Dispenza et al. [41]. According to their study LNG delivered by sea-ships contains considerable cryogenic exergy which can be utilized for electricity production before its evaporation and introduction into the system of pipelines. The liquefaction of natural gas consumes a considerable amount of exergy [42] and some part of that consumption may be recovered by means of a cold power plant utilizing the cryogenic exergy of LNG. The simplest method of that utilization might be based on the principle of a cold Rankine cycle absorbing the evaporation heat from the environment and rejecting the heat of condensation to preheat and evaporate LNG. Querol et al. [43] have reported the method of power generation from LNG. They carried out the thermoeconomics of different power generation methods and found that the use of LNG for power generation is effective. In addition to transportation and generation of power, LNG is also used in fertilizer industry [15] and it is also gaining foothold for cooking, heating homes instead of LPG. 4. Storage and transport of LNG Types of storage facilities for LNG depend on whether the liquid is to be used to meet winter shortages of gas (Peak shaving facilities to meet the seasonal fluctuating gas demand) or to supply base load gas by long distance shipment. In the later case, complete ships cargos should be loaded into and unloaded from LNG tankers. Apart from the necessary insulation for minimizing evaporation losses, it is essential to keep the LNG cargo away from contact with the ship structure as mild steel becomes brittle below 223 K, and could lead a disastrous situation. Evaporation losses may be as low as 0.1% per day for the tank contents, provided insulation is sufficient. For ocean going vessel reliquefaction facilities, facilities usually cater for about a 0.3% boil-off. LNG on shore can be contained in double walled metal tanks not dissimilar to those used in ships, i.e. aluminum or nickel steel inner vessels or membranes, surrounded by insulation and external weather-proofing. In addition, pre stressed concrete tanks can also be erected above ground, or can be cast below the surface. Finally,

existing underground spaces specially prepared for LNG storage can be used. The main advantage of in-ground tanks, both concrete and natural, is that they do not require containment dykes to collect products from leaking or burst containers. The attraction of above-ground tanks, on the other hand, is improved control of heat leakage and also the possibility of repairs.

5. Worldwide LNG technology The introduction of LNG dates back in 19th century when the first practical compressor and refrigeration machine was engineered in Munich, Germany, in 1873 [44] and after that LNG gains foothold in the energy market. Currently, there are 26 liquefaction and 60 re-gasification terminals in different countries. In addition to these existing terminals, there are many liquefaction and re-gasification terminal projects that have been either proposed or are under construction all around the world [45]. Today, Qatar has achieved a major production milestone of 77 million tonnes per annum of LNG, confirming the country’s position as the world’s leading producer and supplier of liquefied natural gas (LNG). Qatar’s natural gas liquefaction facilities and related industries are located in Ras Laffan industrial city, site of the world’s largest LNG exports of more than 31 million metric tons per year. Qatar’s heavy industrial base, located in Messaged, includes a refinery with 140,000 barrels per day (bpd) capacity, a fertilizer plant for urea and ammonia, a steel plant, and a petrochemical plant, and several new petrochemical plants are planned to build in the coming years. All these established and planned industries are natural gas based. Most are joint ventures between US, European, and Japanese firms and the state-owned Qatar Petroleum (QP). The US is the major equipment supplier for Qatar’s oil and gas industry, and US companies are playing a major role in the development of the oil and gas sector and petrochemicals [46]. PETRONAS is also playing a major role in proliferation of LNG production, distribution and utilization. The PETRONAS LNG complex in Bintulu, Malaysia, is the world’s second largest integrated LNG facility at a single location with a combined production capacity of about 23 MMT per annum and LNG is being supplied from this installation to South Korea [16]. By the end of 2008 Qatar (30 MMT), Malaysia (23 MMT) and Indonesia (20 MMT) were major LNG exporters and the three biggest LNG importers were Japan

Libya US Norway Eq.Guinea UAE Brunai Oman Egypt Trinidad Australia Nigeria Algeria Indonesia Malaysia Quatar 0

5

10

15

20

25

MMTY Fig. 3. World’s major LNG exporting countries. Source: Global LNG Info.

30

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Argentina Domenic Rep. Puerto Rico Greece UK Itlay Mexico Belgium Portugal China Turkey India Taiwan France USA Spain S.Korea Japan 0

10

20

30

40

50

60

70

MMTY Fig. 4. World’s major LNG importing countries. Source: Global LNG Info.

(70 MMT), South Korea (30 MMT) and Spain (24 MMT) as shown in Figs. 3 and 4 [47]. The world’s natural gas consumption is increasing and the history of natural gas indicates that the consumption of natural gas was 2.5% more in 2008 as compared to 2007 and the contribution of LNG to this consumption was 7%. Further, the contribution of LNG to natural gas consumption is projected to increase by 6.7% per year from 2005 to 2020 [48]. At the same time, the production of natural gas is also increasing continuously to meet this growing global energy demand and the production of LNG was found 3.8% more in year 2008 in comparison to 2007 [18]. Further, natural gas production is expected to grow more than 50% by 2030 [49] when it will overtake coal as the second-biggest global fuel source. Most of the natural gas demand is expected from the power generation [40], transportation [11], industrial and commercial sectors, attracted by the fact that gas is not only an efficient fuel source but also produces lower emissions than oil or coal. LNG is projected to be a significant component of the

overall natural supply portfolio. Global natural gas demand in terms of LNG is reported in Fig. 5. The above facts reflect that LNG technology is expanding and it will be helpful in diversifying the natural gas. 6. Worldwide potential of natural gas vis-a-vis LNG The natural gas industries have a great potential to supply natural gas because of the availability of worldwide natural gas resources and the successful conversion of natural gas into an easily transportable LNG. The major sources of natural gas are fossil natural gas, town gas, biogas and hydrates. 6.1. Fossil natural gas Natural gas is commercially produced from oil and natural gas fields. Gas produced from oil wells is called associated gas. The natural gas industry is producing gas from increasingly more challeng-

Fig. 5. Schematic representation of growing global LNG demand. Source: Cedigaz, BP, Shell.

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ing resource types: sour gas [50], tight gas, shale gas [51] and coal bed methane gas [52]. The world’s total natural gas reserves are 6254.364 Tcf located in different regions/countries as reported in Table 3[53]. Russia has the world’s largest natural reserves hence; it is the largest producer of natural gas, through the Gazprom Company. The world’s second largest gas field is Qatar’s offshore North Field, estimated to have 891 Tcf [46] of gas in place—enough to last more than 200 years at optimum production levels. The next largest natural gas field is the South Pars Gas Field in Iranian waters in the Persian Gulf connected to Qatar’s North Field [54]. Because natural gas is not a pure product, when non-associated gas is extracted from a field under supercritical (pressure/temperature) conditions, it may partially condense upon isothermal depressurizing—an effect called retrograde condensation. The liquids thus formed may get trapped by depositing in the pores of the gas reservoir. One method to deal with this problem is to re-inject dried gas free of condensate to maintain the underground pressure and to allow re-evaporation and extraction of condensates. 6.2. Town gas Town gas is a mixture of methane and other gases, [55] mainly the highly toxic CO2, which can be used in a similar way to natural gas and can be produced by treating coal chemically. This is a historic technology, still used as best solution in some local circumstances, although coal gasification is not usually economical at current gas prices. However, depending upon infrastructure considerations, it remains a future possibility. Most town gashouses located in the eastern United States in the late 19th and early 20th century, were simple by-product coke ovens which heated bituminous coal in air-tight chambers. The gas driven off from the coal was collected and distributed through town-wide networks of pipes to residences and other buildings where it was used for cooking and lighting purposes. The coal tar that collected in the bottoms of the gashouse ovens was often used for roofing and other water-proofing purposes, and also, when mixed with sand and gravel, was used for creating bitumen for the surfacing of local streets. 6.3. Biogas Biogas typically refers to a gas produced by the anaerobic digestion or fermentation of biodegradable materials (biomass). Biogas is manly composed of 60–70% methane, 30–40% CO2 and low amount of other gases. Sources of biogas include swamps, marshes, and landfills as well as sewage sludge and manure by way of anaerobic digester, in addition to enteric fermentation particularly in cattle. Methanogenic archea are responsible for all biological sources of methane, some in symbiotic relationships with other life forms, including termites, ruminants, and cultivated crops. The future sources of methane, the principal component of natural gas are landfill gas (LFG) [56–58], biogas [59], and methane

hydrate. Biogas and LFG are already used in some areas but their use could be greatly expanded. LFG is a type of biogas which is produced from the decomposition of waste in landfills. If the gas is not removed, the pressure may get so high that it works its way to the surface, causing damage to the landfill structure, unpleasant odor, vegetation die-off and an explosion hazard. Once water vapors are removed, about half of landfill gas is methane and rest of the gas is carbon dioxide. In addition to CO2 and methane the small amounts of nitrogen, oxygen, hydrogen and H2S also exists in LFG, but their concentration varies widely. Landfill gas cannot be distributed through natural gas pipelines unless it is cleaned up to the same quality. It is usually more economical to combust the gas on site or within a short distance of the landfill using a dedicated pipeline. Water vapor is often removed, even if the gas is combusted on site. Biogas [59] is usually produced using agricultural waste materials, such as unusable parts of plants and manure. Biogas can also be produced from domestic waste that otherwise goes to landfills. In general, the waste materials do not generate any income, even they require money to get rid of it. However, the utilization of the waste materials can contribute to the economy and sustainable energy balances. Anaerobic lagoons produce biogas from manure, while biogas reactors can be used for manure or plant parts. Once biogas is upgraded to the required level of purity, it can be used as an alternative vehicle fuel in the same form as conventionally derived natural gas (CNG & LNG). 6.4. Hydrates Huge quantities of natural gas (primarily methane) exist in the form of hydrates under sediment on offshore continental shelves and on land in arctic regions that experience permafrost such as those in Siberia (hydrates require a combination of high pressure and low temperature to form). However, as of 2010 no technology has been developed to produce natural gas economically from hydrates. All these natural gas resources can open up avenues for augmentation of natural gas/LNG production over the world. Therefore, it may be concluded that the existing non-exhaustive natural gas resources and the worldwide LNG technology (as well as forthcoming) can meet the future energy demands. Further, the worldwide shale gas developments, especially in US and Canada, are adding to the energy security. 7. Lifecycle greenhouse gas emissions of LNG vs. oil & coal Production, transport and exploitation of the energy, all have a great impact on the environment and ecosystems [60]. The majority of the world’s energy is still gained from ecologically unacceptable energy sources, especially fossil fuels which are still dominant energy sources [61]. Since fossil fuels have coal as their base, normal combustion of these fuels results in carbon dioxide (CO2) emission which is a greenhouse gas [62]. This carbon dioxide mostly ends up in the atmosphere, and with its greenhouse effect, causes

Table 3 World’s proven gas reserves by region. Country/region North America Central & South America Europe Middle East Africa Asia Pacific

Amount of natural gas [at end 2009] (Trillion cubic feet) 308.794 266.541 169.086 2591.653 494.078 430.412

Table 4 Comparison of fossil fuel emissions (in PPB Btu of Energy Input). Pollutant

LNG

Oil

Coal

Carbon dioxide Carbon monoxide Nitrogen oxides Sulfur dioxide Particulate Mercury

117,000 40 92 1 7 0.000

164,000 33 448 1112 84 0.007

208,000 208 457 2591 2774 0.016

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global warming. Carbon monoxide (CO) which is produced during incomplete combustion of fuel (combustion without the needed amount of oxygen) is more dangerous as compared to CO2. CO is an extremely poisonous gas without color, taste or scent, and its concentration of just 0.6% can cause death after only 15 min of the inhalation [63,64]. Apart from CO2 and CO the combusted coal and oil releases NOx and SOx particles while combustion of LNG provides an excellent means to reduce particle emissions (PM) to near 99%, sulfur oxides (SOx) emissions to near 100%, nitrogen oxides (NOx) to 80%, and 70% fewer GHG emissions [64,65] as reported in Table 4. Due to the clean-burning nature of natural gas, LNG powered heavy-duty vehicles can achieve low emission rates without excessive and expensive emission control equipment as is required for diesel engines. When burned for power generation, the results are even more dramatic [65], SO2emissions are virtually eliminated and CO2 emissions are reduced significantly. Therefore, the increased use of LNG in place of other fossil fuels, like coal and oil, can significantly reduce the emission of greenhouse gases in the atmosphere [66]. Moreover, LNG vessel operations are generally more environmentally friendly than other ships because they use natural gas rather than oil as their primary fuel source for propulsion. LNG is currently being used to fuel public transit vehicles in clean air programs and is accounted for 7% of the world natural gas demand [67]. The role of LNG in GHG reduction in comparison to coal and oil has been reported by many investigators [26–28,68–70]. Arteconi et al. have studied the comparison of diesel and LNG fuel for use in heavy-duty vehicles in term of GHG emissions throughout their life-cycle, in the setting of the European market and they found that LNG afforded a 10% reduction in GHG emission in comparison to diesel fuel [71]. Further, on the basis of life cycle analysis of GHG emission from different fuels Stefano et al. [72] have reported LNG as a green energy for future. Graham et al. [73] have compared the GHG emissions from a variety of heavy-duty vehicles and engines operating on a range of different fuels including diesel, biodiesel, compressed natural gas (CNG), hythane (20% hydrogen, 80% CNG), and liquefied natural gas (LNG), and with different advanced after treatment technologies were studied by chassis dynamometer testing, engine dynamometer testing or on-road testing. The results of this study represent that different choices in fuels may have different effects on GHG emissions. The use of natural gas (either as compressed, liquefied, or blended with hydrogen) can reduce GHG emissions at the tailpipe by 10–20% on a CO2-equivalent basis compared to diesel fuel. A study on life cycle assessment of GHG emissions from LNG and coal fired generation was conducted by CLNG (Center for Liquefied Natural Gas) [74]. According to this study coal produces 161% grater emissions on a life cycle basis than that of LNG. Moreover, this analysis indicates that the cleanest coal scenario releases 73% more emissions from a life cycle perspective than LNG. According to Andress et al. [75] CNG and LNG provide modest benefits in reducing GHG emissions when used directly as a motor vehicle fuel. GHG reductions benefits are much greater when natural gas is used to produce hydrogen. Nitrogen oxide (NOx) emissions reduction of over 75% compared to diesel fuel vehicle has been reported by Frailey [76]. Chen et al. [77] have studied the comparison of two types of air fuelled engines for zero emission road transportation. Their investigation represents that the shaft work output and the coolth of both the fuels increase with increasing working pressure or temperature. Given the working pressure and temperature, liquid air powered engines have a slightly lower specific work outputs than compressed air powered engines. The volumetric energy density of

liquid air, however, is much higher than that of compressed air, and liquid air has much higher coolth than compressed air. The available evidences show that LNG produces the lower GHG emissions as compared to traditional fossil fuels hence; it is an ecofriendly fuel. 8. Discussion The gas industry has entered an exciting phase of rapid growth from all supply chain and technology perspectives. LNG is clearly destined to play a key role in future global energy development by providing the sustainable energy supplies and services needed for social and economic development. For such developments to progress, the construction of large-scale inter-regional natural gas supply networks (pipeline and LNG) is required across the globe. Natural gas is composed essentially of methane, which can be obtained also through anaerobic fermentation of different organic products yielding biogas (60% methane). The role of methane as a fuel has shown increasing importance due to the growth in digester construction all over the world, and especially in developing countries. Further, burning of one molecule of methane (CH4) in presence of oxygen releases one molecule CO2 and two molecules of H2O and 890 kJ/mol [78] heat is liberated out as represented below:

CH4 ðgÞ þ 2O2 ðgÞ ! CO2 ðgÞ þ 2H2 OðlÞ þ 890 kJ=mol Therefore, methane’s relative abundance and clean burning process makes it a very attractive fuel. However, it is a gas and not liquid or solid, methane is difficult to transport from the areas that produce it to the areas that consume it. Converting methane to forms that are more easily transported, such as LNG and methanol, is an active area of research. Hence, demand for LNG as a clean fuel is increasing and LNG is often considered the best form of energy that will be the bridging fuel to a sustainable energy system, sometime after 2050 [79]. According to Marcogaz [80] the natural gas industry is in a good position regarding sustainability compared with other fossil fuels, as it has a good track record of health & safety, labor standards, waste minimization, GHG reductions and affordable prices. Moreover, [81] the combination of higher natural gas prices, rising demand for natural gas and lower LNG production costs (represented in Fig. 6) are setting the stage for a dramatic increase in LNG trade. While LNG already enjoys very favorable economics over petroleum and other transportation fuels—with fuel cost savings typically reported in the 30% range – the continued high price of petroleum and growing supply/low price of natural gas is expected to further decouple these traditionally linked energy markets and provide cost savings to fuel hungry end users. $ per tonne of annual capacity 700

Regasification Shipping Liquefaction

600 500 400 300 200 100 0 mid 1990s

2002

2010

2030

Fig. 6. Schematic representation of reducing unit cost of LNG project. Source: IEA.

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Where there exists an LNG production plant, peak shaving or gas processing facility, loading facility or receiving terminal, or even a natural gas pipeline, LNG vehicle fuel will offer the lowest cost fuel option for heavy-duty transportation in the immediate region. For example, where there is an LNG receiving terminal in an industrial port complex, LNG vehicle fuel can also be made available for use in local port delivery trucks, off-road yard tractors, locomotives, ferries and commercial harbor craft, and for coldironing large ocean going vessels [82]. Thus, LNG cost reduction and increasing supplies of LNG, accompanied by increased flexibility in LNG trade are adding to the security of gas supply [83]. The software program, developed by Miana et al. [84] for the analysis of the LNG ageing process during ship transportation can help the terminal operators to manage re-gasification plants in a safer and more efficient manner. The current level of global trade in LNG is anticipated to nearly double by 2020 and, potentially, triple by 2030 and beyond, so the market for liquefied natural gas vehicles (L-NGVs) should strengthen concurrently as more countries incorporate LNG into their energy strategies [85,86]. Moreover, LNG has a safe history of transportation by LNG trains. Even if it escapes it will evaporate and not pollute waterways and oceans like oil can [87]. Using LNG will produce less greenhouse gases than using coal for electricity generation. Therefore, a switch from oil based to natural gas (LNG) based fuel chains may be a good way to reduce both the carbon emissions of current fuel chain and to keep a high degree of flexibility regarding future developments. Further, growth of the LNG is required because of the energy shortage in certain areas, and the problem of environmental pollution. Improving technology leading to even greater safety and lower relative costs could enable this need to be satisfied. The use of LNG is however, quite a different area of technology, as briefly discussed above. Generally, it will use a combination of known, existing technology, and new technology. The greatest challenges for the use of LNG are to secure the ready acceptance by the public and the production of safe systems to generate, store, distribute and consume. So to use LNG as an alternate source of energy requires modification in existing technology [88], development of more infrastructure and public awareness about this fuel. Hence, emphasis should also be laid on infrastructure development and the use of LNG in heavy vehicles. The use of LNG should be subsidized taking into consideration the environmental advantages of LNG over oil and coal. The growing estimates on LNG suggest that accessible supplies of this least carbon-intensive fossil fuel may be far more abundant than previously assumed. This unexpected development creates opportunities for deploying LNG in a variety of sectors-including power generation, industry and transportation – to help displace oil and coal, thereby reducing greenhouse gas emissions and improving air quality. Beyond providing a cleaner, market ready alternative to oil and coal, LNG can facilitate the systematic changes that will underpin the development of a more energy-efficient and renewable energy based economy.

9. Conclusions Like all natural gases, LNG is cleaner than coal or oil and offers an opportunity to diversify energy supplies. LNG will be the most viable option for automobile for long range use in comparison to CNG as LNG offers special advantages over CNG, that it can be transported and stored easily and with better density than gaseous methane. LNG also offers additional flexibility as liquefied-to-compressed natural gas (L-CNG) Therefore, it has been considered as a safe and clean fuel for future. Main factors that contribute to the global growth of LNG include climate change, escalating oil price,

the decreasing LNG costs, increasing overall energy needs, fuel switching, the availability of natural gas from various offshore/onshore sites, the scope of utilization of low grade coal for LNG production, recovery of coal bed methane and the availability of natural gas from biogas resources. The existing cryogenic gas industries can suitably diversify in the LNG field because of their historical depth of knowledge and width of expertise in handling and storage of cryogenic liquids. Moreover the implementation of new safety measurements, increasing demand of LNG and expending LNG technology will drive LNG to become a globally promising fuel alternative.

Acknowledgements This research was supported by a grant from the GAS Plant R&D Center funded by the Ministry of Land, Transportation and Maritime Affairs (MLTM) of the Korean government and also respectfully supported by BK 21 Program funded by the Ministry of Education (MOE) of Korea.

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