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Track 2 of 7

Producing and liquefying

How raw feed gas is cleaned of everything that would freeze, then chilled through a refrigeration cycle until it condenses, and why a handful of firms build the equipment at the cold end.

An export terminal is mostly not a refrigerator. Before gas can be liquefied it has to be stripped of carbon dioxide, water, mercury, sulphur compounds and the heavier hydrocarbons, because every one of them freezes solid or attacks the metal at cryogenic temperature. The treatment section is frequently larger than the liquefaction section, and its size depends entirely on what came out of the ground.

The cold end is where the engineering concentrates. Several companies will license a refrigeration process, and the thermodynamics are in textbooks, but the ability to fabricate the object at the centre of a large train — a tower holding many kilometres of wound tubing, built to tolerances that survive decades of thermal cycling — sits with very few manufacturers.

This track follows gas from the wellhead to the loading jetty, and explains why plant capacity is quoted as a nameplate figure that real output routinely misses in both directions.

9 modules

All written.

  1. 01
    Feed gas: where it comes from and what is in it

    Feed gas is the raw natural gas delivered to a liquefaction plant before treatment, and its composition determines the size and content of the treatment section as well as what co-products the plant can sell.

  2. 02
    Gas treatment: acid gas, mercury, water and heavies

    Gas treatment is the sequence of processes removing carbon dioxide, water, mercury, sulphur compounds and heavy hydrocarbons from feed gas before liquefaction, because each of them would freeze, foul or damage the cold section.

  3. 03
    Liquefaction trains explained

    A liquefaction train is one complete, self-contained refrigeration line that chills treated natural gas until it condenses, and a large modern train produces roughly 5 to 8 million tonnes of LNG a year.

  4. 04
    The refrigeration cycles: C3MR, DMR, AP-X and SMR

    A liquefaction refrigeration cycle is the closed loop of compression, cooling and expansion that removes heat from feed gas, and the commercial processes differ mainly in how many loops they use and what refrigerant is in each.

  5. 05
    Coil-wound and plate-fin heat exchangers

    The main cryogenic heat exchanger is where feed gas finally condenses, built either as a coil-wound exchanger of tubing spiralled around a core or as a block of brazed aluminium plates and fins.

  6. 06
    Drivers: gas turbines, electric motors and the grid

    A driver is the machine turning a liquefaction plant's refrigerant compressors, either a gas turbine burning part of the feed gas or a large electric motor drawing power from a grid or on-site generation.

  7. 07
    Storage tanks, 9% nickel and high-manganese steel

    An LNG storage tank holds liquid at close to atmospheric pressure in an inner shell of cryogenic alloy, surrounded by insulation and, in the full containment design, an outer concrete wall capable of containing the entire contents.

  8. 08
    Loading jetties and the export terminal layout

    An LNG export terminal is laid out as a sequence from feed gas reception through treatment and liquefaction trains to storage and a marine loading jetty, with separation distances between blocks set by hazard analysis.

  9. 09
    FLNG explained

    Floating liquefaction, or FLNG, is a complete LNG plant built on a ship-shaped hull and moored over or near a gas field, so gas is liquefied at sea and loaded straight onto carriers without any onshore terminal.

Vocabulary for this track

29 terms, defined in full in the glossary.