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Basic Properties Of LNG Information Paper No. 1 Basic Properties of LNG GIIGNL’s Technical Study Group has overseen the development of this Information Se- ries of seven papers to provide factual information about Liquefied Natural Gas (LNG). In French, Spanish, Portuguese, or Italian speaking countries, the abbreviation GNL is used in place of LNG. This paper begins with a review of basic LNG properties, which is a pre- requisite for accurately assessing potential LNG safety hazards and risks. For more in- formation on these topics, additional references and weblinks are provided at the end of this paper. Introduction A number of LNG companies have made commitments to educate the general public about their product. For A basic knowledge of LNG must begin with an example, companies in Japan and South Korea have examination of its chemical and physical properties. gone to great lengths to share information about their Chemical and physical properties are fundamental to facilities with the local communities and to educate them understanding LNG correctly. The very properties which about LNG. For example, Osaka Gas Company and make LNG a good source of energy can also make it Tokyo Gas Company have installed Gas Science hazardous if not adequately contained. These properties Museums at each of their terminals; the first one opened determine how LNG behaves, affect our predictions in 1982. More than 50,000 children, among other about its behaviours, and influence how we assess and visitors, tour the museums every year and are able to manage safety risks. Furthermore, to accurately observe table-top demonstrations of LNG properties and understand and predict LNG behaviour, one must clearly behaviours. distinguish its properties as a liquid from its properties as a gas or vapour. LNG is natural gas which has been converted to liquid The reader will note that discussions of the properties of form for ease of storage or transport. LNG takes up LNG often contain ominous caveats like “depending about 1/600th of the volume of natural gas. Depending upon its exact composition” because such specifics upon its exact composition, natural gas becomes a liquid matter. It is inexact and inappropriate to make universal at approximately -162°C (-259°F) at atmospheric generalisations about LNG. It is especially important to pressure. be clear in thinking through how LNG would behave if accidentally or intentionally released (e.g., from a LNG’s extremely low temperature makes it a cryogenic terrorist attack), because the outcome would be liquid. Generally, substances which are -100°C (-48°F) profoundly influenced by the actual situation and site- or less are considered cryogenic and involve special specific conditions. technologies for handling. In comparison, the coldest recorded natural temperatures on earth are -89.4°C Misunderstanding LNG is not uncommon and is often (-129°F) at the height of winter in Antarctica and the caused by confusion, incomplete, or inaccurate coldest reported temperature in a town was recorded in information about LNG properties. Since properties Oymayakon (Sakha Republic) during Siberian winter determine behaviour and influence how we manage (-71.2°C; -96.16°F). To remain a liquid, LNG must be potential safety hazards and risks, having an accurate kept in containers which function like thermos bottles – understanding is key. 1 Information Paper No. 1 — Basic Properties of LNG they keep the cold in and the heat out. The cryogenic Table 1. Typical chemical composition of LNG temperature of LNG means it will freeze any tissue (plant (Source: Center for Energy Economics, or animal) upon contact and can cause other materials to www.beg.utexas.edu/energyecon/lng) become brittle and lose their strength or functionality. This is why the selection of materials used to contain LNG is so important. Chemical Chemical Low High LNG is odourless, colourless, non-corrosive, non- Formula flammable, and non-toxic. Natural gas in your home may Methane CH 87% 99% have been liquefied at some point but was converted into 4 its vapour form for your use. The reason the natural gas Ethane C H <1% 10% you use in your home has a smell is because an 2 6 odorising substance is added to natural gas before it is Propane C H >1% 5% sent into the distribution grid. This odour enables gas 2 8 leaks to be detected more easily. Butane C4H10 >1% >1% Key liquid and gas properties for LNG are: Nitrogen N2 0.1% 1% • Chemical Composition, Other Hydro- Various Trace Trace • Boiling Point, carbons • Density and Specific Gravity, • Flammability, and • Ignition and Flame Temperatures. 1.5 MPa or 200 psi). In the US, Canada, and Japan, LPG consists primarily of propane (Table 2). However, in many European countries, the propane content in LPG can be as low as 50% or less. Moreover, in some These properties are listed on Material Safety Data countries, LPG may contain a substantial portion of Sheets (MSDSs). [Click here to View MSDS.] propylene. Chemical Composition LPG’s differing composition and physical properties (from LNG) make its behaviour different as well. The propane and butane in LPG have different chemical Natural gas is a fossil fuel, meaning it has been created compositions from methane, the primary hydrocarbon in by organic material deposited and buried in the earth natural gas and LNG. Propane and butane can be stored millions of years ago. Crude oil and natural gas and transported as a mixture, or separately. Both are constitute types of fossil fuel known as “hydrocarbons” gases at normal room temperature and atmospheric because these fuels contain chemical combinations of pressure, like methane, readily vaporising. Propane hydrogen and carbon atoms. The chemical composition liquefies much more easily than LNG (at -43°C [-46°F] of natural gas is a function of the gas source and type of vs. -162°C [-259°F] for LNG) so it is substantially easier processing. It is a mixture of methane, ethane, propane to compress and carry in a portable tank. In fact, LPG is and butane with small amounts of heavier hydrocarbons stored as a liquid under pressure, whereas LNG is and some impurities, notably nitrogen and complex stored as a liquid only at very low temperatures and sulphur compounds, water, carbon dioxide and hydrogen ambient pressure. sulphide which may exist in the feed gas but are removed before liquefaction. Methane is by far the major component, usually, though not always, over 85% by Boiling Point volume. Table 1 displays the chemical compositions of the hydrocarbon compounds which make up natural gas, Boiling point is one of the most significant properties and the volume ranges in which they may be present in because it defines when gas becomes a liquid. LNG. Pipeline natural gas may contain small amounts of Webster-Merriman on line (www.webster-merriman.com) water vapour. defines “boiling point” as “the temperature at which a liquid boils” or converts rapidly from a liquid to a vapour LNG is often confused with liquefied petroleum gas or gas at atmospheric pressure. The boiling point of pure (LPG), which in turn is often incorrectly identified as water at atmospheric pressure is 100°C (212°F). propane. In fact, LPG is a mixture of mainly propane and butane gases that exist in a liquid state at ambient The boiling point of LNG varies with its basic temperatures when under moderate pressure (less than composition, but typically is -162°C (-259°F). 2 Information Paper No. 1 — Basic Properties of LNG Table 2. Typical composition of LPG in % by volume (Source: http://www.environment.gov.au/ settlements/transport/comparison/ pub/2ch10.pdf) Country Propane Butane Belgium 50 50 France 35 65 Ireland 100* 100* Italy 25 75 Germany 90 10 UK 100* 100* Denmark 50 50 Figure 1. LNG “boiling” at atmospheric pressure and Greece 20 80 temperature (Source: Osaka Gas Co. Ltd.) Netherlands 50 50 Spain 30 70 Table 3. Boiling points of water and some common Sweden 95 5 gases (Source: Adapted from the Engineer- ing Toolbox online, * NOTE: In Ireland and the U.K., LPG may be 100% of www.engineeringtoolbox.com/boiling-points- either basic gas. fluids-gases-d_155html) When cold LNG comes in contact with warmer air, water, or the environment, it begins to “boil” at that interface because the surrounding temperatures are warmer than the LNG’s boiling point, as shown in Figure 1. Table 3 shows the boiling points of water and common gases. The liquefaction process cools natural gas to change it to a liquid which reduces the volume occupied by the gas by approximately 600 times. LNG is converted back into natural gas for distribution to industrial and residential consumers. The LNG regasification process warms the LNG and converts it back into its gaseous form. Density and Specific Gravity Density is a measurement of mass per unit of volume and is an absolute quantity. Because LNG is not a pure substance, the density of LNG varies slightly with its actual composition. The density of LNG falls between NOTE: Absolute zero is the coldest temperature theoreti- 430 kg/m3 and 470 kg/m3 (3.5 to 4 lb/US gal). LNG is cally possible, and cannot be reached by artificial or less than half the density of water; therefore, as a liquid, natural means. By international agreement, absolute LNG will float if spilled on water. zero is defined as precisely 0 K on the Kelvin scale and is equivalent to -273.15°C/-459.67°F. Specific gravity is a relative quantity. The specific gravity 3 Information Paper No. 1 — Basic Properties of LNG of a liquid is the ratio of density of that liquid to density of begin to rapidly warm and reach temperatures of water (at 15.6°C/60°F).
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