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Liquefaction Process


The LNG chain begins with the liquefaction of natural gas. In the liquefaction process, natural gas is cooled to -161ºC, reducing its volume by a factor of 600. This reduction in volume makes it economically feasible to transport the natural gas using LNG tankers. The main stages in a liquefaction plant are pre-treatment, liquefaction, storage and loading tankers.

Natural gas goes into a liquid state after being frozen to temperatures of 
-161ºC in plants such as Atlantic LNG in Trinidad and Tobago. 

Planta de licuación de gas, Atlantic LNG - Trinidad & Tobago


The goal of pre-treatment is to eliminate the pollutants (CO2, H2S, H2O, Hg, etc.) of the natural gas extracted from the well. This protects the liquefaction processing equipment and complies with the specifications of the LNG market. This section of the plant includes the sweetening unit (elimination of CO2 and H2S acid gases), the dehydration unit and the mercury removal unit.


During the liquefaction stage, the natural gas is cooled to -161ºC through a refrigeration  process similar to that used by everyday freezers or the air conditioning in our cars; it covers the phases of compressioncondensation and expansion  of one or a number of refrigerants and their heat exchange with the natural gas. 

There are a number of technologies on the market that enable natural gas liquefaction  depending on the size of the plant where it will be carried out. Thus, the typical categories taken into account when classifying liquefaction plants are:

- Mini, small and medium-scale plants: Capacity below 3 MTPA (million tonnes per annum)
- Large-scale plants: Capacity between 3 and 6 MTPA
- Mega-scale plants: Capacity of over 6 MTPA.

Technological activity in LNG consists of process selection and conceptual design, as well as analytical support for both plants in operation and ongoing projects.

The liquefaction activities carried out by the LNG department covers the full range of capacities. In the area of small and medium-scale liquefaction, activities include those relating to the identification of technology selection criteria; with regard to large-scale plants, it is worth mentioning the studies carried out to identify criteria for selecting compressor drivers and the development of tools for evaluating the viability of liquefaction projects

Of particular interest at the mega-scale plants are the so-called mega-trains (trains with individual capacities of more than 6 MTPA). Case studies are being conducted as part of the technological activities in the LNG area that may enable comparisons  to be made between liquefaction plants composed of mega-trains and plants composed of lower-capacity modules.


Back to Liquefied Natural Gas

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28045, Madrid (Spain)
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