Fundamentals: frequently asked questions

Why is natural gas turned into a liquid?#

Because gas is mostly empty space. Cooling methane to minus 162 degrees Celsius shrinks it about 600 times, which is what makes it economic to carry across an ocean in a ship rather than pushing it down a pipeline.

Is LNG stored under pressure?#

No. Large-scale LNG is kept cold rather than compressed, at close to atmospheric pressure in insulated tanks. It stays liquid because it is cold, and it stays cold because a little of it is always allowed to boil off.

What is LNG actually made of?#

Mostly methane, typically 85 to 95 per cent, with some ethane, propane and butane. Water, carbon dioxide, sulphur and mercury are stripped out before liquefaction because they would freeze solid or corrode the equipment.

How long does the journey take?#

A cargo from the US Gulf Coast reaches north-west Europe in roughly ten days and north-east Asia in about a month via the Panama Canal. Qatar to Japan is around three weeks.

Does LNG evaporate on the way?#

Yes, a small fraction each day, called boil-off. On modern ships that vapour is burned as fuel or reliquefied and returned to the tanks, so it is not simply lost.

From How LNG works.

What temperature is LNG stored at?#

About minus 162 degrees Celsius, at atmospheric pressure. Pure methane boils at minus 161.5 degrees; a real cargo is a mixture, so it boils across a range near that figure rather than at a single point.

How heavy is LNG?#

Between roughly 430 and 470 kilograms per cubic metre depending on composition, so about 45 per cent the density of water. A cubic metre of LNG weighs a little under half a tonne, and LNG floats on water.

Is LNG stored under pressure?#

No. It is held at close to atmospheric pressure in insulated tanks, and stays liquid because it is cold rather than because it is compressed. This is the opposite of LPG, which is liquefied by pressure at ambient temperature.

Can LNG explode?#

Not as a liquid, and not in the open air in the way a confined vapour cloud can. Liquid LNG will not burn at all. Its vapour burns only when mixed with air at between about 5 and 15 per cent by volume, and outside that range the mixture is either too lean or too rich to ignite.

Is LNG toxic?#

No. It is not toxic, not corrosive and not carcinogenic. The hazards it presents are cryogenic burns from contact, asphyxiation if vapour displaces air in a confined space, and fire if vapour reaches an ignition source within its flammable range.

Is LNG vapour heavier or lighter than air?#

Both, depending on temperature. Methane is lighter than air at ambient temperature, but vapour boiling off a spill is so cold that it is initially denser than the air around it and hugs the ground. It becomes buoyant and rises once it warms to somewhere around minus 110 degrees Celsius.

From The physical properties that govern everything.

Why can't natural gas just be compressed instead of chilled?#

Above its critical temperature of about minus 82.6 degrees Celsius, methane cannot be condensed to a liquid by any pressure at all. Compressed natural gas exists and is used, but it stays a gas, so it achieves an expansion ratio of a few hundred to one at best rather than 600 to one, in heavy pressure vessels.

How much energy does liquefaction consume?#

Typically 8 to 12 per cent of the energy in the feed gas, most of it driving the refrigerant compressors. The exact figure depends on the process, the ambient temperature and whether the drivers are gas turbines or electric motors.

What is the total energy cost of the LNG chain?#

Liquefaction is the largest single loss at 8 to 12 per cent. Shipping consumes a further 2 to 4 per cent as boil-off and fuel on a long voyage, and regasification perhaps 1 to 2 per cent. End to end, delivering LNG typically costs somewhere between 10 and 20 per cent of the gas.

Would a colder or warmer temperature work?#

Colder wastes energy for nothing. Warmer means the liquid boils faster, so the cargo is lost more quickly. Minus 162 is not a choice; it is where methane boils at atmospheric pressure, and holding the liquid at atmospheric pressure is what keeps tanks out of the pressure-vessel category.

Why does ambient temperature affect plant output?#

Because the refrigeration cycle rejects its heat to the surroundings, usually through air coolers or seawater. On a hot day the cycle has to work harder for the same output, so a plant that makes its nameplate figure in winter can fall several per cent short in summer.

From Why minus 162 degrees, and what the cold costs.

How many bcm is 1 Mtpa of LNG?#

About 1.36 billion cubic metres of natural gas per year. So a 10 Mtpa export terminal produces roughly 13.6 bcm a year of gas equivalent.

How much gas is in a cubic metre of LNG?#

About 600 cubic metres of gas at standard conditions. That expansion ratio is the entire reason for liquefying it in the first place.

How many tonnes is a full LNG cargo?#

A 174,000 cubic metre cargo is roughly 78,000 tonnes, using a density near 450 kilograms per cubic metre. Density varies with composition, so treat it as an approximation.

Why do different sources give different conversions?#

Because LNG composition varies, and because some sources use higher heating value and others lower. Factors between about 1.34 and 1.38 bcm per Mtpa are all defensible.

What does bcf/d mean?#

Billion cubic feet per day, common in North America. One bcf/d is roughly 10.3 bcm a year, or about 7.6 Mtpa of LNG.

From Mtpa, bcm and cubic metres.

Why do two sources give different capacities for the same terminal?#

Usually because they are counting different things. One may quote nameplate design capacity and the other actual output; one may include trains under construction and the other only those operating; or the two may convert between mass and volume with different assumed gas compositions.

Can I add proposed capacity to operating capacity?#

No. A proposed project may never be built, and historically many are not. Adding the two produces a number that describes no possible world. Every capacity figure on this site is reported by status for exactly this reason.

What is nameplate capacity?#

The design output of a plant under reference conditions. Real output routinely exceeds it in cold weather and falls short in hot, so nameplate is a specification rather than a measurement or a forecast.

Why does a terminal's capacity change between tracker releases?#

Either the facility changed, through debottlenecking or a new train, or the compiler found a better source for a figure that was always approximate. The change log distinguishes what the data did from what the world did, but it cannot always tell you which happened.

Is storage capacity the same as terminal capacity?#

No, and confusing them is a common error. For an import terminal the number that matters is send-out, the rate gas can be pushed into the grid. Storage volume tells you how much buffer the terminal holds, which is a different question.

From Reading a capacity figure without being misled.

What are the stages of the LNG value chain?#

Production from a gas field, treatment to remove impurities, liquefaction, storage and loading at an export terminal, shipping by LNG carrier, unloading and storage at an import terminal, regasification, and send-out into a pipeline grid.

Which stage costs the most?#

Liquefaction, by a wide margin, in both capital and energy. An export terminal is the most expensive single asset in the chain and consumes 8 to 12 per cent of the gas it processes.

How long does a cargo take to deliver?#

The voyage itself is typically one to four weeks depending on the route. Qatar to north-west Europe is around two weeks; the US Gulf to Japan through Panama is around three, and considerably longer if the canal is unavailable and the ship routes via the Cape.

Who owns the different stages?#

It varies enormously. Some chains are integrated end to end by one company; others split every stage between different owners, with the plant tolling gas for a customer who owns the molecules and charters the ship separately.

What happens to the gas after regasification?#

It enters the receiving country's pipeline grid and is indistinguishable from domestically produced or piped gas. Odorant is added downstream, because it would freeze in the liquid.

From The LNG value chain end to end.

At what distance does LNG become cheaper than a pipeline?#

Onshore, somewhere between about two and four thousand kilometres, though the crossover moves with terrain, volume and the cost of capital. Offshore the crossover is much shorter, because subsea pipelines are far more expensive per kilometre than onshore ones.

Why is a pipeline cheaper over short distances?#

Because it has no liquefaction plant. Liquefaction is the largest single cost in the LNG chain in both capital and energy, and it is incurred regardless of how far the cargo travels. A pipeline's cost scales with distance; LNG's is mostly fixed at the ends.

Does LNG have advantages beyond cost?#

Yes, and they often decide the question. A cargo can be sent anywhere, so a buyer is not locked to one supplier and a seller is not locked to one market. A pipeline is a fixed asset between two fixed points and creates a dependency in both directions.

Can a pipeline and LNG serve the same market?#

Frequently, and the competition between them sets the price. Several European markets are supplied by both, and the LNG price effectively caps what piped supply can charge.

Which is lower in emissions?#

Piped gas, generally, because it avoids the 8 to 12 per cent energy cost of liquefaction and the fuel burned in shipping. The comparison narrows if the pipeline is very long or leaky, since upstream and transmission methane leakage can dominate either chain.

From LNG against pipeline gas.

When was the first LNG cargo shipped?#

In January 1959, when the Methane Pioneer, a converted wartime cargo ship, carried LNG from Lake Charles in Louisiana to Canvey Island on the Thames. It was a demonstration voyage rather than a commercial trade.

What was the Cleveland LNG disaster?#

On 20 October 1944, a storage tank at the East Ohio Gas Company in Cleveland failed and released LNG into the street and sewer system. The resulting fires killed 128 people. The tank had been built with a low-nickel steel because of wartime alloy shortages, and the failure set the industry back by more than a decade.

Which country exported LNG commercially first?#

Algeria, from the CAMEL plant at Arzew to Canvey Island in the United Kingdom, beginning in 1964. It was the first sustained commercial LNG trade rather than a demonstration.

When did the United States start exporting LNG from the lower 48 states?#

In February 2016, from Sabine Pass in Louisiana. Alaska had exported to Japan from Kenai since 1969, but the shale gas boom turned the country from a prospective importer into the largest exporter within about a decade.

Why did Qatar matter so much?#

Because it built at a scale nobody had attempted, using trains roughly twice the size then conventional and the largest carriers ever constructed. That drove the unit cost of LNG down sharply and made the commodity a genuinely global trade rather than a set of regional ones.

From A short history of LNG.