Description
Liquefied natural gas or LNG is natural gas (predominantly methane,
CH4) that has been converted temporarily to liquid form for ease of
storage or transport.
Liquefied natural gas takes up about 1/**0th the volume of natural
gas in the gaseous state. It is odorless, colorless, non-toxic and
non-corrosive. Hazards include flammability, freezing and
asphyxia.
A typical LNG process. The gas is first extracted and transported
to a processing plant where it is purified by removing any
condensates such as water, oil, mud, as well as other gases such as
CO2 and H2S. An LNG
process train will also typically be designed to remove trace
amounts of mercury from the gas stream to prevent mercury
amalgamizing with aluminium in the cryogenic heat exchangers. The
gas is then cooled down in stages until it is liquefied.
LNG is finally stored in storage tanks and can be loaded and
shipped.
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 (maximum
transport pressure set at around *5 kPa/3.6 psi) by cooling it to
approximately ***2 °C (***0 °F).
LNG achieves a higher reduction in volume than compressed natural
gas (CNG) so that the energy density of LNG is 2.4 times that of
CNG or *0% of that of diesel fuel [1] This makes LNG cost efficient
to transport over
long distances where pipelines do not exist. Specially designed
cryogenic sea vessels (LNG carriers) or cryogenic road tankers are
used for its transport.
