Liquefied natural gas

Liquefied natural gas, or LNG, is a highly efficient way to transport energy across the globe. It consists primarily of methane, a simple hydrocarbon with the chemical formula CH4. It also contains smaller amounts of ethane, propane, butane, and nitrogen. By cooling this natural gas into a liquid state, it becomes much easier to manage. In its liquid form, the gas occupies only about 1/600th of the volume it would take as a gas at standard temperature and pressure.

This massive reduction in volume allows huge amounts of energy to be moved by ship or truck. While LNG is colorless, odorless, and non-toxic, it presents hazards like flammability once it vaporizes. It can also cause freezing or asphyxiation if handled improperly.

The liquefaction process is a precise sequence of chemical and thermal steps. First, the feedstock gas undergoes pre-treatment to remove impurities. Components like water, carbon dioxide, hydrogen sulfide, mercury, and heavy hydrocarbons must be removed. If these remained, they could freeze and cause damage to the machinery downstream.

Once purified, the gas enters a liquefaction unit. Here, the gas is cooled to temperatures between −145 °C and −163 °C. This is often achieved by circulating the gas through aluminum tube coils. A compressed refrigerant is used to absorb the heat from the gas. As the refrigerant vaporizes, the heat transfer causes the gas in the coils to cool until it condenses into a liquid.

There are several different methods used to achieve this cooling. One historical method is the Linde process, which uses the Joule–Thomson effect. This involves cooling the gas by passing it through an orifice, causing it to expand and drop in temperature. A more modern version is the Optimized Cascade Process developed by Phillips Petroleum Company. This method uses three successive refrigeration cycles to increase efficiency. It uses propane for precooling, ethylene or ethane for intermediate cooling, and methane for the final liquefaction.

This stepwise approach provides better operational stability and thermodynamic efficiency.

The history of LNG is rooted in the scientific study of gases. In the 17th century, Robert Boyle discovered the relationship between gas pressure and volume. Later, in 1886, Karol Olszewski successfully liquefied methane. The first large-scale use of liquefaction in the United States occurred in 1918. During this time, the U.S. government liquefied natural gas to extract helium. This helium was needed for British dirigibles during World War I.

In 1937, Lee Twomey patented a process for large-scale liquefaction. He intended to use the liquid to support energy loads during cold weather snaps.

Early attempts at commercial storage faced significant challenges. In 1940, the East Ohio Gas Company built the first full-scale commercial LNG plant in Cleveland, Ohio. The plant used large spheres to store the liquid. However, a cylindrical tank ruptured in 1944, leading to a fire that caused 130 fatalities. This tragedy delayed the industry for years. It took new research into low-temperature alloys and better insulation to revive the field. By 1959, the Methane Pioneer ship delivered LNG from the U.S. to Great Britain. This helped restart the global industry and led to the first purpose-built LNG carrier, the Methane Princess, in 1964.

Today, the energy density of LNG makes it a vital global commodity. Its energy density is approximately 2.4 times that of compressed natural gas (CNG). While its energy density is comparable to propane, it is only 60 percent that of diesel.

The global market is highly concentrated. As of 2023, the United States, Australia, and Qatar held the most export capacity. Meanwhile, China, Japan, and South Korea were the largest importers. The United States has seen a massive boom in production due to hydraulic fracturing. By 2023, the U.S. had become the world's largest exporter, moving significant volumes of gas annually.

Once the LNG reaches its destination, it must be returned to a gaseous state through regasification. The liquid is pumped into a vaporizer and heated until it turns back into gas.

This gas is then sent through pipeline networks to reach homes and industries. This entire cycle connects distant energy sources to local consumers. The industry remains complex, with production concentrated in a few areas. This can create choke points in the global supply chain, as seen when political conflicts affect major exporters like Qatar.