If you’ve ever wondered why we see large white storage tanks in ports, or why natural gas has become so prominent in recent years, the explanation usually lies in LNG plants. In this article, I will explain clearly and without unnecessary technical jargon what an LNG plant is, what it is used for, and how it works, from the arrival of the gas all the way through to its final use. The aim is to fully answer the questions of readers who are new to this topic: to understand the concept, the key processes, and the applications, without any promotional content.
What an LNG plant is exactly
An LNG (liquefied natural gas) plant is an industrial facility designed to liquefy, store, transport, and/or regasify natural gas. There are two main types:
- Liquefaction plant: takes natural gas in gaseous phase and cools it to approximately –162 °C to convert it into liquid. Liquefying it decreases its volume by about 600-fold, making it easier to transport by ship over long distances where there are no pipelines.
- Regasification terminal: receives LNG from dedicated tankers, stores it in cryogenic tanks, then heats it to return it to its gaseous state (regasify it) and inject it into the grid.
Both types are distinct parts of the same chain: produce–liquefy–transport–regasify–distribute.
Why natural gas is liquefied
Gas takes up a lot of space. Liquefying it multiplies transport capacity 600-fold, reduces logistics costs, and allows energy to be delivered to islands, remote regions, or countries without pipelines. That is why LNG is key to security of supply and flexibility in the gas market.
How an LNG liquefaction plant works
Although each project uses specific technologies, the typical flow includes:
1) Gas pre-treatment
Before cooling, the gas must be purified to prevent certain compounds from freezing and blocking equipment.
- Dehydration: removal of water.
- Removal of CO₂, H₂S, and mercury: to prevent corrosion and formation of solids.
- Separation of heavy hydrocarbons: to meet LNG specifications.
2) Compression
The gas is compressed to improve the efficiency of the cooling cycle and accommodate process pressures.
3) Cascade cooling (liquefaction)
One or several refrigeration cycles are used. The most common are:
- Mixed refrigerant (MR) cycle: mixture of light hydrocarbons (methane, ethane, propane, nitrogen) optimised to cool gradually.
- Cascade cycles: stages with different refrigerants (propane, ethane/ethane-propane, methane) that progressively reduce the temperature to –162 °C.
The result is LNG in liquid phase with very little nitrogen and other gas content.
4) Cryogenic storage
The LNG is kept in insulated double-walled tanks (known as full containment). They are designed to minimise boil‑off gas (BOG), i.e. the vapour that is inevitably generated by temperature differences.
5) Handling the boil-off gas
This BOG is recompressed and reliquefied or used as fuel in the plant itself, avoiding losses and emissions.
6) Loading to LNG carriers
The LNG is transferred to the ship via cryogenic arms, maintaining safety conditions and controlled temperature.
How a regasification terminal works
When the LNG reaches its destination, the process is reversed:
1) Unloading and storage
The ship docks and transfers the LNG to cryogenic tanks. Temperature, level, and pressure are continuously monitored.
2) High-pressure pumping
Cryogenic pumps drive the LNG towards the vaporisers. Pumping the liquid before heating it improves efficiency.
3) Vaporisation (regasification)
The LNG is heated and returned to its gaseous state using different technologies:
- Open rack vaporisers (ORV): heat exchangers that use seawater as a heat source.
- Submerged combustion vaporisers (SCV): burn gas to heat water, which in turn heats the LNG.
- Closed-loop vaporisers: use glycol or other thermal fluids heated by boilers or waste energy.
- Integrated solutions with industrial or geothermal waste heat: to improve energy efficiency.
4) Conditioning and delivery
The regasified gas is measured, analysed, and conditioned (odorising it as required) for injection into the grid, in compliance with pressure and quality specifications.
Key components you will see in an LNG plant
- Large diameter cryogenic tanks with containment and detection systems.
- Loading arms for safe transfer to/from ships.
- Compressors and cryogenic pumps.
- Heat exchangers with plates and fins, coils or tube bundle.
- Gas treatment units (sweetening, dehydration).
- Safety systems: gas and fire detection, interlocks, pressure relief, containment dykes.
- Control room with DCS/SCADA for continuous operation.
Safety and environment: key essentials
- Process safety: LNG is practically pure methane. It is not toxic but it is cryogenic and can form cold clouds that may displace oxygen when it evaporates. That is why classified zones, ventilation and detection systems, and strict procedures are in place.
- Emissions: the aim is to minimise fugitive methane and optimise BOG. Modern terminals use recovery and reliquefaction, and, when this is not feasible, controlled oxidation.
- Energy use: liquefaction is the most intensive stage. Plants use efficient turbomachinery, thermal integration, and, in some cases, renewable electrical energy to reduce their carbon footprint.
- Thermal impact: if seawater is used for vaporisation, temperature and chlorination are controlled in order to protect the marine environment.
Where LNG is used
- Supply to grid: after regasification, the gas feeds power stations, industries, and homes.
- Virtual gas (small-scale LNG): LNG can be transported by road in cryogenic tanker trucks to supply industries located far from the grid.
- Transport: LNG as fuel reduces SOx and particulate emissions in ships and heavy goods vehicles compared with conventional fuels.
Demand peaks: terminals and satellite plants serve as seasonal storage to meet peak demand.