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.
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.
A large refrigeration system is used to liquefy natural gas by cooling it to about minus 260 degrees Fahrenheit.
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.
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.
The ship's safety systems are divided into ship handling and cargo system handling.
LNG is transported by special ships that moor at Dominion 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.
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 1.8 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.
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.
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.
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.
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.