Liquefied Natural Gas FAQ
What is LNG?
Liquefied natural gas, or LNG, is natural gas in its liquid form. When natural gas is cooled to -260 degrees Fahrenheit (-162 degrees Celsius), it becomes a clear, colorless, odorless liquid. LNG is neither corrosive nor toxic. Natural gas is primarily methane, with low concentrations of other hydrocarbons, water, carbon dioxide, nitrogen, oxygen and some sulfur compounds. During the process known as liquefaction, natural gas is cooled below its boiling point, removing most of these compounds. The remaining natural gas is primarily methane with only small amounts of other hydrocarbons. LNG will float if spilled on water, because LNG weighs less than half (about 3.5 lbs.) of what water weighs.
Why use LNG?
Natural gas is the cleanest burning fossil fuel. It produces less emissions and pollutants than either coal or oil. The North American supply basins are maturing and as demand for natural gas increases throughout the United States, alternative sources of natural gas are being investigated. Natural gas is available outside of North America, but this gas is not accessible by pipelines. Natural gas can be imported to the United States from distant sources in the form of LNG. Since LNG occupies only a fraction (1/600) of the volume of natural gas, and takes up less space, it is more economical to transport across large distances and can be stored in larger quantities. LNG is a price-competitive source of energy that could help meet future economic needs in the United States.
Why do you liquefy natural gas?
Liquefying natural gas makes it easier to transport, and far more energy dense than natural gas. When natural gas is cooled and liquefied, the density increases 600 times. In other terms, the same volume of natural gas vapor, when cooled and liquefied, occupies 1/600th the volume or space. As a liquid, natural gas becomes more comparable in energy content to other liquid fuels; for example, the energy in 1.68 gallons of LNG is equal to about 1 gallon of diesel. As a fuel, LNG is very versatile, can be used in just about any way diesel is used: for drilling rigs, mine haul trucks, boilers, dryers, power generation, marine fuel, locomotives, and over-the-road trucks.
What is the difference between LNG and LPG?
LPG, or liquid petroleum gas, is either propane or butane. It is a product of the refining process of crude oil. It can be stored by maintaining the liquid under pressure, about 100 psig.
Natural gas is a fossil fuel that is gathered mainly by drilling, similar to drilling for oil. Once natural gas is collected it can be processed and cooled to approximately -260 F, at which time it changes to a liquid and becomes LNG.
Is LNG dangerous or flammable?
As a liquid, LNG is not explosive. LNG vapor will only explode if in an enclosed space, and disperses quickly in open air. When LNG vapor mixes with air it is flammable, but only within the range of five to 15 percent of natural gas in air.
If it is less than five percent natural gas in air, there is not enough natural gas in the air to burn. If the vapor is more than 15 percent natural gas in air, there is too much gas in the air and not enough oxygen for it to burn.
Does LNG provide less power than other fuels?
The best way to compare the power LNG to other fuels is compare the Btu value of a set unit of measure. In US gallons, the conversions are as follows:
One gallon diesel = 139,000 Btu
One gallon gasoline = 125,000 Btu
One gallon LPG = 91,000 Btu
One gallon LNG = 82,650 Btu
LNG provides about 61 percent of the energy that the same volume of diesel fuel provides.
How safe is LNG?
LNG is very safe, and will not ignite as a liquid. As is warms and changes back to a vapor it is still a very safe fuel, because of its high ignition temperature of 1000 F, and the narrow flammable range of 5 – 15 percent in air.
What happens if you have a leak or spill LNG?
When cold LNG comes in contact with warmer air, it becomes a visible vapor cloud. As it continues to get warmer, the vapor cloud becomes lighter than air and rises. Once all the LNG vaporizes, there is no contamination or residual waste to clean up.
Can LNG be stored?
Yes, LNG can be stored. There are several factors that affect the length of time it can be stored as a liquid. One is the insulation of the vessel it is stored in. Another is the quantity being stored and the size of the vessel.
As LNG ages, it continues to warm and change from a liquid to a vapor. Good insulation decreases the warm up rate. Small tanks for vehicle fueling have a higher boil-off rate and can hold for about five days, while new tanks of 9,500 gallons for LNG delivery have a lower boil-off rate and can hold for more than 50 days.
What safety precautions should I take when working around LNG?
Cryogenic burns are the primary risk. Any exposed skin that comes in contact with LNG will get a cryogenic burn. LNG is a liquid at -260 F; however, even as the liquid warms and becomes a vapor it is still very cold, -100 F to -200 F. All equipment, instruments and piping that comes in contact with LNG will be extremely cold. Moist skin coming in contact with cold metal parts will freeze instantly and could adhere to other materials. Personal protective equipment should always be worn, consisting of cryogenic gloves, fire resistant long-sleeve shirt, long pants, and a face shield to protect the head from splashing liquid.