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Liquefied natural gas - Wikipedia, the free encyclopedia

h t t p : / / e n . w i k i p e d i a . o r g / w i k i / L N G # L N G _ s a f e t y _ a n d _ a c c i d e n t s

Liquefied natural gas

From Wikipedia, the free encyclopedia (Redirected from LNG)

Liquefied natural gas or LNG is natural gas that has been converted to liquid form for ease of storage or transport.

The liquefaction process involves removal of certain components (such as dust, helium, or impurities that could cause difficulty downstream, e.g. water, and heavy hydrocarbons) and then condensed into a liquid at close to atmospheric pressure (Maximum Transport Pressure set around 25 kPa (3.6psi)) by cooling it to approximately -163 degrees Celsius. LNG is transported in specially designed cryogenic sea vessels or cryogenic road tankers; and stored in specially designed tanks. LNG is about 1/614th the volume of natural gas at standard temperature and pressure (STP), making it much more cost-efficient to transport over long distances where pipelines do not exist. Where moving natural gas by pipelines is not possible or economical, it can be transported by LNG vessels. The most common tank types are membrane (TGZ Mark III and GT96) and Moss Rosenberg (spheres) or Self-Supporting Prismatic Type.

Contents

1 Basic facts on LNG

1.1 Trade in LNG 2 LNG environmental concerns 3 LNG safety and accidents 4 LNG storage 5 LNG Transportation 6 LNG refrigeration 7 LNG, LPG, and CNG

    • 7.1

      Liquefied natural gas (LNG)

    • 7.2

      Compressed natural gas (CNG)

    • 7.3

      Liquid petroleum gas (LPG)

8 References 9 See also 10 External links

Basic facts on LNG

LNG offers an energy density comparable to petrol and diesel fuels and produces less pollution, but its relatively high cost of production and the need to store it in expensive cryogenic tanks have prevented its widespread use in commercial applications. It can be used in natural gas vehicles, although these are more commonly designed to use compressed natural gas.

Conditions required to condense natural gas depend on its precise composition, the market that it will be sold to and the process being used, but typically involve temperatures between 120 and 170 degrees Celsius (pure methane liquefies at 161.6 °C) and pressures of between 101 and 6000 kPa (14.7 and 870 lbf/in² [approx 1-60 atm]). High pressure natural gas that is condensed is then reduced in pressure for storage and shipping.

The density of LNG is roughly 0.41 to 0.5 kg/L, depending on temperature, pressure and composition. In comparison water has a density of 1.0 kg/L.

LNG does not have a specific heat value as it is made from natural gas, which is a mixture of different gases. The heat value depends on the source of gas that is used and the process that is used to liquefy the gas. The higher heating value of LNG is estimated to be 24 MJ/L at 164 degrees Celsius. This corresponds to a lower heating value of 21 MJ/L.

The natural gas fed into the LNG plant will be treated to remove water, hydrogen sulfide, carbon dioxide and other components that will freeze (e.g., benzene) under the low temperatures needed for storage or be destructive to the liquefaction facility. Purified LNG typically contains more than 90% methane. It also contains small amounts of ethane, propane, butane and some heavier alkanes. The purification process can be designed to give almost 100% methane.

The most important infrastructure needed for LNG production and transportation is an LNG plant consisting of one or more LNG trains, each of which is an independent unit for gas liquefaction. The largest LNG train is the SEGAS Plant in Egypt with a capacity of 5 million ton per annum (mtpa). Exxon Mobil operating Qatargas stage 2, of which one train has a production

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12/16/2007 8:35 PM

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