Home' Ships and Shipping : October 2009 Contents What is LNG?
LNG is liquefied natural gas, which is the very cold liquid form
of natural gas -- the fuel that's burned in gas stoves, home heaters,
and electric power plants. When it warms back up, LNG becomes
natural gas again. You can't liquefy natural gas without cooling it.
Many countries export and many others import LNG by ship.
What is LNG chemically?
LNG, as mentioned, is very cold natural gas that is in a liquid
form rather than gas. Chemically, it's mostly methane, with small
amounts of ethane, propane, and butane. LPG (liquefied petroleum
gas), sometimes referred to as bottled gas, is a heavier gas that can
be liquefied under pressure or by refrigeration. It is mostly propane
and butane. Gasoline is heavier still and is a liquid at room
temperature. Heating oil is even heavier and doesn't boil unless
heated. And asphalt is so heavy that it's a solid. But in a way they
are all pretty similar, because they all burn.
Where does LNG come from?
LNG comes from natural gas that's been cooled to below -256
degrees Fahrenheit (-160o Celsius), with some impurities removed.
Natural gas comes from underground gas fields by itself or in oil fields,
along with crude oil. There's very little difference between natural gas
and vaporised LNG; mostly LNG is a little purer; before liquefying, the
natural gas engineers remove pollutants such as sulphur.
Where do we get LNG?
We get liquefied natural gas from countries including Algeria,
Australia, Brunei, Malaysia, Nigeria, Trinidad and Tobago, Oman
and Qatar. In the future, we can expect to get LNG from even more
countries. Right now, there are 20 terminals worldwide where LNG
is liquefied and pumped aboard LNG ships, and approximately 40
terminals where LNG is pumped off LNG ships and stored in large
tanks on land and vaporised as needed by consumers.
Why do we have to transport LNG on tankers?
Normally, you ship natural gas by pipeline, but you can't build a
pipeline from the Middle East or Africa to the United States or
Australia, so engineers created ships capable of carrying the liquid
form of natural gas. Natural gas needs to be liquefied (cooled, as
above) because you'd need the volume capacity of 600 ships of
natural gas at ambient temperature pressure to equal one shipload of
LNG. Since you can't afford to build and operate that many ships to
carry that amount of natural gas, shipping LNG is the only practical
way to import the necessary quantities that client countries need.
Is LNG safe?
No fuel or petroleum product is completely safe: not coal, oil, or
liquefied natural gas, all of which are carried on ships. LNG is a fuel,
and, when it becomes a gas and mixes with air, it will burn. You can
never consider anything that burns completely safe, even fairly
innocuous materials like wood and cooking oil. But some are worse
than others, and liquefied natural gas is far from the worst. When
LNG vapour reaches an open flame, it easily catches fire and will
burn everything within the vapour-air mixture; the same as when
natural gas burns. Due to the extra care in designing, maintaining,
and operating LNG ships, they all have excellent safety records.
There have been some fires at shore facilities, but those are rare
events. However, if a ship catches fire, it could be very serious. That's
why the LNG industry and the shipping industry are very careful
about the movement of liquefied natural gas.
Is an LNG ship a floating bomb?
No. LNG contains a great deal of energy, but so does a pile of
coal. LNG is a liquid that won't burn until it becomes a vapour,
and the vapour won't burn until it mixes with air and becomes
diluted to between five percent and 15 percent LNG vapour in air.
Above 15 percent, there's not enough air for it to burn, and below
five percent, there's not enough LNG vapour to burn. LNG vapour
clouds burn when they are in the five-15 percent dilution range,
but they don't explode.
How do the hazards of LNG compare?
Some cargoes are more hazardous, and some are less. Some
cargoes are so bad that the Coast Guard doesn't allow them on
tankers -- liquefied chlorine is an example of one of these that
maritime professionals won't allow on tankers, because it is too
dangerous. On the other hand, they allow gasoline in tanks that
are built to much less stringent design requirements than liquefied
natural gas tanks. LNG's hazards are in between gasoline's hazards
and liquefied chlorine's hazards.
What do LNG tankers look like?
LNG tankers look different from regular tankers carrying oil and
chemicals. Each LNG tanker has two hulls so that, if a collision or
grounding punctures the outer hull, the ship will still float and the
LNG will not spill out. LNG tanks are either spherical with the
upper half of the sphere sticking out above the deck (so-called
"Moss"-type tankers as the design belongs to Norway's Moss
Maritime), or box-shaped. The ships tend to ride high in the water,
even when loaded. A typical LNG ship is 289 metres long and 46
metres wide, and many new ships being built even larger.
How are LNG ships designed?
LNG tank ships are designed with safety and security in mind.
They must meet tough international standards. These are
high-tech ships, using special materials and designs to safely
handle the very cold LNG. All ships have two hulls, in effect a
double ship that protects the cargo in the event of a collision,
grounding, or a terrorist act. Even before the ship construction has
begun, safety experts review the plans. The ships are inspected
during construction and are periodically inspected after
completion. International rules cover just about every safety
feature of these ships, as well as crew training standards.
What is LNG's safety record on ships?
Everyone involved in liquefied natural gas transportation takes
safety very seriously. There are many lives and a great deal of money
at stake. Governments and industries work together to make sure
these ships are designed, maintained, and manned with safety in
mind; industry maintains them with oversight by periodic
government inspection, and government sets the standards for crew
training. This has resulted in an outstanding safety record. Over the
last 35 years, there have been about 35,000 LNG voyages worldwide,
and on none of these has there been a significant LNG spill. LNG
ships are so well designed that, even when a submarine surfaced
directly under an LNG ship, there was no damage to the LNG tanks,
even though there was damage to the ship's bottom.
'Mesaimeer', a 2009-delivered, HHI-built, 216,000m3 "Q-Flex" tanker. Its
class is soon to be superseded by the even larger "Q-Max" series
October 2009 SHIPS AND SHIPPING
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