Liquefied Natural Gas (LNG) is a natural gas (predominantly methane, CH4,) with some mixture of ethane C2H6) that has been converted to liquid form for ease and safety of non-pressurized storage or transport. It takes up about 1/600th the volume of natural has in the gaseous state (at standard conditions for temperature and pressure). It is odorless, colorless, non-toxic and non-corrosive. Hazards include flammability after vaporization into a gaseous state, freezing and asphyxia. The liquefaction process involves removal of certain components such as dust, acid gases, helium, water and heavy hydrocarbons, which could cause difficulty downstream. The natural gas is then condensed into a liquid at close to atmospheric pressure by cooling it to approximately - 162 °C (-260 °F); maximum transport pressure is set at around 25 kPa (4 psi).
LLNG quality is one of the most important issues in the LNG business. Any gas which does not conform to the agreed specifications in the sale and purchase agreement is regarded as
“off-specification” (off-spec) or “off-quality” gas or LNG. Quality regulations serve three purposes:
1 - to ensure that the gas distributed is non-corosive and non-toxic, below the upper limits for H2S, total Sulphur, CO2 and Hg content;
2 - to guard against the formation of liquids or hydrates in the networkds, through maximum water and hydrocarbon dewpoints;
3 - to allow interchangeability of the gases distributed via limits on the variation range for parameters affecting combustion; content of inert gases, calorific value, Wobbe index, Soot Index, Incomplete Factor, Yellow Tip Index, etc