Natural Gas Turned into a Liquid

Liquefied natural gas (LNG) is natural gas that has been cooled until it becomes a liquid. Natural gas is mostly methane, the simplest hydrocarbon. At normal air pressure, methane turns into a liquid at about −162 °C. LNG plants cool the gas to about this temperature and then store it as a cold liquid at a pressure only a little above atmospheric pressure.

LNG is not a different fuel. When it is warmed again, it becomes ordinary natural gas. It is burned in the same power stations, factories and homes as gas that arrives by pipeline. The liquid form is only a way of storing and moving the gas.

About 600 times smaller

The main reason for making LNG is volume. When natural gas becomes a liquid, it takes up about 1/600 of the space it filled as a gas at normal temperature and pressure. In other words, one cubic metre of LNG becomes about 600 cubic metres of gas when it warms up.

This change is what makes it practical to carry gas across oceans. A modern LNG carrier holds about 170,000 cubic metres of liquid. As gas, the same cargo would fill roughly 100 million cubic metres — far too much to carry in any ship.

What LNG looks like and how it behaves

• It is a clear, colourless liquid, a little like water to look at.
• It has no smell. Odorant is added only later, if the national gas network requires it.
• It is not toxic and not corrosive, but it is extremely cold and its vapour is flammable.
• It is lighter than water, so if it is spilled on water it floats and boils away.
• It is kept as a boiling liquid. Heat that leaks into a tank makes a small part of it evaporate. This vapour is called boil-off gas.