Regasification: frequently asked questions

What are the stages inside an LNG import terminal?#

Unloading from the ship, storage in insulated tanks, pumping to intermediate then pipeline pressure, recondensing the boil-off, vaporising, metering and odorising, and injection into the grid.

Why is LNG pumped to high pressure before it is vaporised?#

Because compressing a gas costs far more energy than pumping a liquid. Raising the liquid to pipeline pressure first, then warming it, is dramatically cheaper than vaporising at low pressure and compressing afterwards.

What is a recondenser?#

A vessel where boil-off gas is brought into contact with cold incoming LNG so it condenses back into liquid. It avoids having to compress that vapour all the way to grid pressure.

How long does it take to unload an LNG cargo?#

Around twelve hours of pumping for a conventional cargo, with the full port call closer to a day once mooring, cooling the arms, checks and measurement are included.

Is regasification energy-intensive?#

Far less than liquefaction. Typically one to two per cent of throughput, and close to zero where seawater does the warming, against eight to twelve per cent to liquefy in the first place.

From What an import terminal actually does.

What does FSRU stand for?#

Floating storage and regasification unit. It is a vessel, either purpose-built or converted from an LNG carrier, that receives LNG from other ships, stores it, and vaporises it into a pipeline while moored.

Is an FSRU faster to deploy than an onshore terminal?#

Usually yes. An existing FSRU can be chartered and connected in a year or two where a jetty and pipeline already exist, while a new onshore terminal typically takes four years or more.

Is an FSRU cheaper?#

Cheaper to start and often dearer to keep. Capital cost is lower and largely rented rather than owned, but charter rates run for the life of the contract, so over fifteen or twenty years an onshore terminal can cost less per unit delivered.

Can an FSRU sail away?#

In principle yes, and that optionality is part of the appeal. Most keep their propulsion and can be redeployed or returned to trading as a carrier when a charter ends.

Why did Europe build so many FSRUs?#

Because they can be procured in months rather than years. After the loss of Russian pipeline supply, speed of delivery mattered more than lifetime cost.

From FSRU versus onshore regasification.

What is an open rack vaporiser?#

A vaporiser that warms LNG with seawater flowing down finned panels. It burns no fuel and is cheap to run, but needs seawater above roughly five degrees Celsius and a large intake and discharge.

What is a submerged combustion vaporiser?#

A vaporiser that burns gas in a water bath through which the LNG tubes pass. It works in any weather and starts quickly, at the cost of consuming roughly one and a half per cent of throughput as fuel.

Why do terminals fit more than one type?#

Because the cheapest option is rarely the most responsive. Seawater vaporisers carry the steady baseload and combustion vaporisers cover peaks, cold-water months and quick starts.

What is an ambient air vaporiser?#

A vaporiser drawing heat from the air over large finned towers. It uses almost no energy and needs a warm climate, a lot of land and time for the fins to defrost between cycles.

What happens to the cold?#

Usually nothing — it is discharged to sea or air. A small number of terminals recover it for air separation, chilled warehousing or power generation, because the cold itself is a usable resource.

From Vaporiser types: ORV, SCV and ambient air.

What is send-out capacity?#

The maximum rate at which a terminal can deliver gas into the grid, quoted in million cubic metres a day, million standard cubic feet a day, or as an annual equivalent. It is set by pumps and vaporisers rather than by tank volume.

Is send-out the same as terminal capacity?#

In practice yes, for an import terminal. Storage volume is a separate figure describing the buffer, and confusing the two is a common error when comparing terminals.

What is peak shaving?#

Holding gas in storage specifically to meet short demand peaks that production and pipelines cannot cover. Some terminals and small liquefaction plants exist almost entirely for this.

Why is send-out capacity often far above average use?#

Because it is sized for the coldest days of the year, not the average day. A terminal that runs at a third of capacity most of the year may still be undersized for a severe cold snap.

What limits send-out in practice?#

Usually the vaporisers and high-pressure pumps, sometimes the grid's ability to absorb gas at that point, and occasionally the boil-off handling if the recondenser cannot keep up at low flow.

From Send-out, peak shaving and the grid connection.

What is LNG rollover?#

The sudden mixing of two stratified layers of different density in a storage tank, which releases a large volume of vapour in a short time — potentially more than the relief system is sized for.

How does stratification happen?#

Usually by loading a cargo of one composition on top of a heel of another. The two settle into stable layers that warm and change independently until their densities converge and they invert.

How is rollover prevented?#

By monitoring density and temperature at several depths, choosing top or bottom filling to promote mixing according to the incoming cargo's density, and recirculating the tank when readings suggest layers are forming.

What is ageing in a storage tank?#

The gradual change in composition as lighter methane boils off preferentially, leaving the remaining liquid heavier and higher in heating value. It is measurable over weeks.

Does a terminal ever run out of cold?#

Not in the sense of the liquid warming up. Boil-off keeps the contents at temperature indefinitely; what a terminal runs out of is liquid, and it needs a minimum heel to keep the tank cold between cargoes.

From Storage operations: ageing, stratification and rollover.

How is LNG transported by road?#

In vacuum-insulated tanker trailers, typically holding a few tens of cubic metres, loaded at bays at an import terminal. They are unpressurised cryogenic vessels rather than pressure tankers.

What is an ISO tank?#

A vacuum-insulated cryogenic tank built inside a standard intermodal container frame, so a parcel of LNG can move by ship, rail and road without the liquid being transferred between vessels.

What is a satellite plant?#

A small storage and vaporisation facility, fed by road tanker rather than by pipeline or ship, that supplies a town, an industrial site or a fuelling network beyond the gas grid.

Why use LNG rather than extending a pipeline?#

Because a pipeline is only worth building at sufficient sustained volume. For a single factory, a remote town or a seasonal load, trucking liquid is cheaper than laying pipe that may never be fully used.

Does LNG boil off in a truck?#

Yes, slowly. Trailers are well insulated and hold pressure for days, so a delivery within the normal window loses very little. Long idle periods eventually require venting or use.

From Truck loading, ISO tanks and small-scale distribution.

What does break bulk mean in LNG?#

Splitting a full cargo into smaller parcels for onward delivery, usually at a hub terminal with reloading capability, so markets that cannot take a whole cargo can still be supplied.

Why can't a small market just receive a conventional cargo?#

Because a conventional cargo is roughly 78,000 tonnes and a small market may use that in a year. The berth, the dredging and the storage needed to receive one are also far beyond what such a market can justify.

What is reloading?#

Loading LNG from an import terminal's storage back onto a ship. A terminal that can reload can act as a redistribution hub and as a trading asset, not only as a supply point.

Which regions rely on break bulk?#

Archipelagic and island markets above all — the Caribbean, parts of Southeast Asia, the Baltic and Mediterranean islands — plus coastal markets whose ports cannot take a large vessel.

Is break bulk more expensive per unit?#

Considerably. Extra handling, smaller and less efficient vessels, more boil-off per tonne delivered, and infrastructure serving low volumes all add cost, which is why it exists where the alternative is no gas at all.

From Break bulk and island supply chains.