LNG liquefaction facilities

The liquefaction process

At the production site, the gas is separated from other hydrocarbons and water typically produced from the reservoir. In the liquefaction process, the produced gas is treated to further remove water and remaining condensates, acid gases (such as CO² and H₂S), mercaptans and mercury. These compounds will freeze and cause corrosion or other difficulties under the low temperatures needed for storage and transport of LNG.

After pre-treatment, the gas is cooled down by a refrigerant mixture in different stages until it is liquefied. Once liquefied, the LNG is stored in storage tanks at approximately ambient pressure.

The LNG is transferred from the storage tanks and into the LNG carriers that will transport it to the re-gasification facilities.

Liquefaction process technologies

There are several optimized processes for liquefaction of natural gas with different licensed technologies. The basic process operations are the same in all of them but they use different refrigerant mixtures for cooling and liquefaction of the gas as well as different types of cryogenic heat exchangers. 

Modifying the heating value to fit demands

Usually natural gas markets can be divided in three markets depending on the heating value of the gas required: Asia (Japan, Korea, Taiwan) where gas distributed is rich, UK and US markets, where the distributed gas is lean and Continental Europe, where the acceptable heating value range is wider.

There are some methods to adjust the heating value of the produced LNG to the desired level. A lower heating value is obtained by removing more of the heavier hydrocarbons from the gas and achieving a leaner gas. Blending with LNG of different specification can also be used to adjust the heating value of the final product.