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  • Writer's pictureSarah Whiteford

What is Liquefied Natural Gas?

Updated: Apr 6, 2021

Liquefied Natural Gas is natural gas that starts in a gaseous state and is cooled to -260° Fahrenheit, forming a liquid. Why so cold? Natural gas is naturally in a gaseous state, but cooling it down shrinks its size, making it 600 times smaller! The main benefit is making it much more compact makes it easier to transport. But let’s start with natural gas.

What is natural gas?

Natural Gas is a fossil fuel energy source that is found deep underground, where we also find crude oil. It’s mostly methane, known as CH4, which means it’s made of one carbon atom and 4 hydrogen atoms. In its natural state there are also some hydrocarbon gas liquids, carbon dioxide, and water mixed in.

Credit: U.S. Energy Information Administration

How is natural gas formed?

Natural gas also forms similarly to crude oil. Over millions and millions of years, animal and plant remains build up on the ocean floor. Over time they are covered with silt and sand, immense pressure and heat eventually turn this layer into oil, coal, and natural gas. Once formed, it can actually migrate with the rocks and sediments below the surface moving between natural fissures and fractures. Some can even find its way to the surface, although the natural gas that might power your stove or home is found deep underground.

Are there different types of natural gas?

There are four types of natural gas:

  1. Conventional Natural Gas is natural gas that has moved into large cracks and spaces within rocks.

  2. Unconventional Natural Gas occurs in the tight spaces in sedimentary rock like shale or sandstone.

  3. Associated Natural Gas is found with crude oil deposits.

  4. Coalbed Methane is found in coal deposits.

Even though there are different types of natural gas, once purified they can all be used the same way.

Credit: U.S. Energy Information Administration

How is natural gas found?

You might be wondering how these deposits are found if they are deep below the surface of the Earth. Geologists help to find natural gas through seismic surveys. These seismic waves travel through the Earth and are measured to determine where gas is located. A thumper truck with a vibrating pad can send these waves, or sometimes a small amount of explosives is used to send a wave through the Earth.

Credit: U.S. Energy Information Administration

How do we retrieve natural gas?

Drilling for conventional natural gas is straightforward, once the pipe is in the right spot, the gas starts to flow up. Other types of natural gas that are in shale or rock formations need some help. They get this help through fracking or hydraulic fracturing. This breaks up the rock allowing the gas to escape. Once natural gas is removed from the ground, then it can be processed. This is where Liquefied Natural Gas comes in.

Credit: U.S. Energy Information Administration

How is natural gas processed?

Now the natural gas is processed and distilled down to CH4, cleaning out other molecules. These other molecules can sometimes even be used to chill the gas down at the next stage or processing. If it’s being transported by pipeline or a short distance, this is where the gas would be sent to the home or business that might use it for power, with no liquefaction necessary. If it’s being transported over a long distance, it needs to be cooled. Huge refrigerators cool the natural gas to -260° Fahrenheit, shrinking the volume to 1/600th of its previous size. Now a light blue liquid, it is pumped into super cooled cryogenic tanks. It can then be shipped in ocean going vessels to different locations around the world.

Shipping is great for long distance transport, but a lot of gas is moved via pipeline. Natural gas travels through vast networks of pipelines, most of them underground. There are over 2 million miles of pipelines around the world, including more than 70,000 natural gas pipelines in the United States alone. Check out how oil and natural gas pipelines work and how pipelines are cleaned and inspected through pipeline pigging.

Credit: Metropolitan Utilities District

Does natural gas smell like rotten eggs?

Well, yes and no. Natural gas is also the cleanest burning fossil fuel. It produces water vapor, carbon dioxide, and small amounts of nitrogen oxides when burned. In its natural state, it’s colorless and odorless, meaning it’s not visible to the naked eye, nor can you smell it. But why does the stove smell right before the burner is lit? Why are people extra careful if they smell it – what are they smelling? They are actually smelling mercaptan, a harmless chemical added to natural gas to make it stink like rotten eggs or hydrogen sulfide. The smell is there to warn you in case of a leak so you can get to safety. The stinky odor makes it safer to use, as without this strong scent, there would be no way to detect a gas leak.

Credit: U.S. Energy Information Administration

How long has natural gas been in use?

Natural gas has been in use for more than 200 years, since it lit the streetlights of Baltimore, Maryland in 1816. Today it heats about half of American homes and can be used to power vehicles such as forklifts or cook food in an oven or on a grill. The process of natural gas liquefaction was actually developed in the 19th century, so although the process has been refined, it’s the same basic process that was used in the 1800’s!

If that wasn't enough, check out this short video on the natural gas liquefaction process from Shell:

Happy Friday & Stay Safe!


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