Module 0

What an LNG plant actually does

Overview

Every LNG plant on earth does the same job: take natural gas, strip out everything that would freeze, then chill it to −162 °C so it becomes a liquid that takes up 1/600th of the space. The five plant types differ in scale, where they sit, and why they exist.

LNG — nameplate facts
What it isNatural gas (mostly methane, CH₄) cooled to a liquid at roughly −162 °C at near-atmospheric pressure
Volume reductionAbout 600:1 — a full LNG ship carries the energy of a pipeline running for weeks
DensityRoughly 420–470 kg/m³ (lighter than water — it floats and evaporates)
Typical composition85–99% methane, some ethane, propane, butane, trace nitrogen. No CO₂, water, mercury or H₂S — they're removed before liquefaction
Energy cost of making itRoughly 8–12% of the feed gas is burned as fuel to run the plant (baseload); worse at small scale
Units you'll hearmtpa (million tonnes per annum) for plant size · m³ for tanks and ships · tpd (tonnes per day) for small plants · MMBtu for price
Where the chain lives

Onshore plants and offshore systems are different worlds

Overview

The chemistry stays the same, but layout, access, utilities, safety barriers and product export change completely. Switch environments to walk through the major modules and see how the full facility fits together.

The LNG chain

An LNG plant sits in the middle of a chain. Upstream, gas comes out of the ground (offshore platforms, coal seam gas wells, or a pipeline network). Downstream, LNG gets shipped, stored, and turned back into gas (regasified) at the customer's end. The plant types on this site are all about the middle step — liquefaction — but each one connects to the chain differently.

The six process blocks every plant has

Whether it's an 8 mtpa export train or a 50 tpd container plant behind a mine site, the gas passes through the same logical stages. The equipment gets bigger or smaller, but the order doesn't change. This is a genuine sequence, so it's numbered.

  1. Inlet and pressure control. Gas arrives, gets metered, and any liquids (condensate, water) are knocked out in a slug catcher or inlet separator.
  2. Acid gas removal. CO₂ and H₂S are stripped out, usually with an amine solvent (MDEA). CO₂ freezes at −78 °C and would block the cold exchangers as dry ice. Small plants often use membranes or pressure-swing adsorption instead.
  3. Dehydration. Water is pulled down to under 1 ppm using molecular sieve beds. Any water left becomes ice in the cold box.
  4. Mercury removal. Mercury attacks aluminium, and the main cryogenic heat exchangers are aluminium. A bed of sulphur-impregnated carbon takes it out to parts-per-trillion levels.
  5. Heavies removal / NGL extraction. Pentanes and heavier (C5+) and aromatics like benzene are removed in a scrub column so they don't freeze. Bigger plants also fractionate out ethane, propane and butane — some is sold as LPG, some is used as refrigerant make-up.
  6. Liquefaction. The gas is chilled through a refrigeration cycle to about −160 °C, let down in pressure (end flash), and sent to storage. The refrigeration cycle is the thing that most defines the plant technology.

After that: storage tanks, boil-off gas (BOG) handling, and loading — into a ship, a road tanker, or straight back into a pipeline.

The refrigeration technologies

You can't understand the plant types without knowing the four families of liquefaction process. Each plant type tends to pair with one or two of these.

ProcessHow it worksWhere you'll find it
Propane pre-cooled mixed refrigerant (C3MR, AP-X)Propane loop pre-cools gas to about −35 °C, then a mixed refrigerant of nitrogen, methane, ethane and propane does the deep chill in a big spiral-wound exchanger. AP-X adds a nitrogen loop for extra capacity.Most of the world's baseload trains — Gorgon, North West Shelf, Qatar
Cascade (ConocoPhillips Optimized Cascade)Three separate pure-refrigerant loops in series: propane → ethylene → methane. Simple to operate, easy to turn down, uses brazed-aluminium plate-fin exchangers.Darwin LNG, Wheatstone, APLNG, QCLNG, GLNG, Sabine Pass
Single / dual mixed refrigerant (SMR, DMR, PRICO)One (SMR) or two (DMR) mixed-refrigerant loops. Fewer machines than cascade, more flexible than C3MR. DMR suits FLNG because no propane storage is needed on deck.Mid-scale, FLNG (Prelude uses DMR), peak-shavers
Nitrogen expanderNitrogen gas is compressed, cooled, and expanded through a turbo-expander to get cold. Less efficient, but the refrigerant is inert — no flammable inventory, no refrigerant make-up, quick start/stop.Small-scale, peak-shaving, some FLNG (PFLNG Satu, Coral Sul)

The five plant types at a glance
TypeTypical sizeJobUsual processAustralian example
Baseload3–8 mtpa per train, 10–30+ mtpa per siteExport gas by ship, 24/7 for 20–40 yearsC3MR, AP-X, CascadeGorgon, Wheatstone, NWS, Ichthys, Pluto
Mid-scale0.5–2 mtpa per train, built in modulesSame export job, smaller fields or phased buildSMR, DMR, PRICO, IPSMRFew in Australia; Elba Island and Calcasieu Pass (US) are the models
Small-scale5–500 tpd (under 0.2 mtpa)Fuel for trucks, mines, ships and off-grid powerNitrogen expander, SMREVOL LNG Kwinana (WA)
Peak-shavingSmall liquefier, big tank, big vaporiserStore gas cheap, send it out on the coldest daysNitrogen expander, SMRDandenong LNG (Vic)
Floating (FLNG)0.5–3.6 mtpa on one hullLiquefy offshore over a stranded fieldDMR, nitrogen expanderPrelude (Browse Basin, off Broome)

Module 1 — Baseload

The big export plants. Where most Australian LNG jobs are.

Module 2 — Mid-scale

Modular trains built in a yard and bolted together.

Module 3 — Small-scale

LNG as a diesel replacement — mines, trucks, ships.

Module 4 — Peak-shaving

Storage plants that beat winter price spikes.

Module 5 — Floating LNG

The whole plant on a ship, moored over the field.

Module 6 — Plant operator

Control room thinking, field rounds, alarm response, operating modes and shift handover.

Module 7 — Process instrumentation

Trace signal loops, read engineering documents, practise calibration, diagnose faults and understand final elements.

Module 8 — Hazardous areas

Explore gas zones, decode Ex markings, compare protection concepts and recognise installation defects.

Field handbook library

Open a separate printable companion for every plant type and technical module.
Safety across every plant type

LNG itself won't burn — the vapour does, once it warms up and mixes with air at 5–15% concentration. The hazards that don't change with plant size: cryogenic burns and brittle fracture of ordinary carbon steel from a spill; rapid phase transition (RPT) if LNG hits water; asphyxiation from methane or nitrogen in enclosed spaces; vapour clouds that hug the ground while cold then rise as they warm; and rollover in storage tanks when layers of different density mix suddenly and release a burst of boil-off gas.

Glossary
Train
One complete liquefaction unit. Plants have one or several trains running in parallel.
mtpa
Million tonnes per annum. One mtpa is roughly 1.4 billion cubic metres of gas a year, or enough to run about 1.3 GW of gas power flat out.
Boil-off gas (BOG)
LNG constantly evaporates a little from heat leak. That vapour has to be compressed and reliquefied, burnt as fuel, or sent to the pipeline.
Cold box
An insulated steel box packed with brazed-aluminium plate-fin heat exchangers. The compact alternative to a spiral-wound exchanger.
MCHE
Main cryogenic heat exchanger — the giant spiral-wound tube exchanger at the heart of a C3MR train, often 50 m tall.
End flash
Dropping the pressure of the just-liquefied LNG so it's at storage conditions. The flash gas is nitrogen-rich and becomes fuel.
Turndown
How far a plant can drop below full rate and still run stably. Cascade plants turn down well; C3MR less so.
Regasification
Turning LNG back into gas by warming it, using seawater, ambient air or burners.