What is LNG?
LNG stands for liquefied natural gas. LNG is natural gas cooled and condensed
into a liquid. It is mostly methane with small amounts of ethane, propane and
other liquefied petroleum gases and is generally handled at slightly above atmospheric
pressure, which requires a very low temperature.
Why liquefy natural gas?
Converting natural gas to a liquid reduces its volume by about 600 to 1, which
means one LNG tanker can transport enough LNG to equal 600 tanker ships carrying
natural gas. Liquefying natural gas makes it feasible to transport natural gas
by tanker and to store it in preparation for re-gasification and delivery to
markets.
How is natural gas liquefied?
A large refrigeration system is used to liquefy natural gas by cooling it to
about minus 260 degrees Fahrenheit.
Where does LNG come from?
LNG supplies come primarily from locations where large gas discoveries have
been made, such as Algeria, Trinidad, Venezuela, Nigeria, Norway, Qatar, Oman
and Australia. Some LNG is produced in Alaska as well. Typically these locations
are in remote areas that do not have high demand for natural gas, making LNG
a very economically viable alternative.
How is LNG
transported?
LNG is transported in large, specially designed ships. These ships are
double-hulled and have a capacity of 138,000 cubic meters or more.
The vessels are fitted with a special cargo containment
system inside the inner hull to maintain the LNG at atmospheric pressure
and minus 260 degrees Fahrenheit.
There are about 130 ships currently in the LNG fleet
and more than 50 additional ones are on order.
What safety features are designed into LNG ships?
The ship's safety systems are divided into ship handling and cargo system
handling.
LNG is transported by special ships that
moor at Cove Point's offshore dock. The LNG cargo is transferred through
a series of pipes to insulated storage tanks. A portion of the pipes are
underwater.
The ship-handling safety features include sophisticated radar
and positioning systems that alert the crew to other traffic and hazards around
the ship. Also, distress systems and beacons automatically send out signals
if the ship is in difficulty. The cargo-system safety features include an extensive
instrumentation package that safely shuts down the system if it starts to operate
out of predetermined parameters. Ships are also equipped with gas- and fire-detection
systems.
What facilities make up an LNG import terminal?
An LNG import terminal consists of docks for ships to bring LNG onshore,
LNG storage tanks, vaporizers, and other equipment to turn LNG from a
liquid back into natural gas. View
a facility drawing.
What safety features are designed into LNG import
terminals?
At onshore facilities, safety features include methane detectors, Ultraviolet
or Infrared (UV/IR) fire detectors, and closed-circuit TV.
A vaporization system transforms the liquid into gas, and the send-out capacity
is 1 billion cubic feet per day.
Other safety features include offsite monitoring, training
requirements for personnel, and restricted access to terminal property. In addition,
the stringent design parameters for LNG import terminals require that proper
measures are in place in the unlikely event of a spill or equipment failure.
How safe is LNG compared to other substances handled in
ports and land-based facilities?
LNG is not explosive, toxic, or carcinogenic. Vaporized LNG is lighter than
air. If a spill occurs, the vapor will rise and dissipate, leaving no trace
in the environment. Although portions of an LNG vapor cloud may be flammable,
the flame speed of an unconfined cloud is slow and it will not explode. In contrast,
gasoline and fuel oil are extremely flammable and, in their liquid state, are
toxic. If these hydrocarbons are spilled, the environmental impact is severe.
Will LNG burn?
LNG itself does not burn because it does not contain oxygen. Natural gas burns
only within the narrow range of a 5 to 15 percent gas-to-air mixture. If the
fuel concentration is lower than 5 percent, it cannot burn because of insufficient
fuel. If the fuel concentration is higher than 15 percent, it cannot burn because
there is insufficient oxygen. For LNG to burn, it must be released, vaporize,
mix with air in the ignitable ratio, and find an ignition source.
Will LNG explode?
LNG will not explode because it contains no oxygen to react with the fuel. Even
LNG vapors in an open environment cannot explode because there is not enough
oxygen to react with the fuel. LNG spill studies have shown that high winds
rapidly dissipate the LNG vapor and low winds (or no wind) keep the flammable
vapor cloud very close to the source.
Is an LNG spill detectable?
Within an LNG facility or onboard a ship, there are various types of hazard
detectors used to alert personnel to a leak or spill. These could include detectors
for the presence of gas, flame, smoke, high temperatures or low temperatures.
While LNG vapors have no odor or color, if an LNG release occurred, LNG's low
temperature will cause water vapor to condense in the air and form a visible
white cloud that would be readily apparent.
