Liquefied natural gas (LNG) is a form of natural gas that has been cooled down to liquid form for ease and safety of non-pressurized storage or transport. LNG takes up about 1/600th the volume of natural gas in the gaseous state and is odorless, colorless, non-toxic and non-corrosive. In this article, we will discuss the process of liquefying natural gas, the composition of natural gas, and the benefits and hazards of LNG.

The Liquefaction Process

  • The process of liquefying natural gas involves the removal of certain components such as dust, acid gases, helium, water, and heavy hydrocarbons. This is done to ensure that the downstream process is not affected by these impurities.
  • The natural gas is then condensed into a liquid at close to atmospheric pressure by cooling it to approximately -162’C (-260’F); the maximum transport pressure is set at around 25 kPa (4 psi) (gauge pressure), which is about one-fourth times atmospheric pressure at sea level.

Composition of Natural Gas

  • The gas extracted from underground hydrocarbon deposits contains a varying mix of hydrocarbon components. The main component is methane (CH4), along with ethane (C2H6), propane (C3H8) and butane (C4H10). Other gases also occur in natural gas, notably CO2.
  • These gases have wide-ranging boiling points and also different heating values, allowing different routes to commercialization and also different uses.

Removal of Impurities

  • The “acidic” elements such as hydrogen sulphide (H2S) and carbon dioxide (CO2), together with oil, mud, water, and mercury, are removed from the gas to deliver a clean sweetened stream of gas.
  • Failure to remove much or all of such acidic molecules, mercury, and other impurities could result in damage to the equipment. Corrosion of steel pipes and amalgamation of mercury to aluminum within cryogenic heat exchangers could cause expensive damage.

Separation of Liquefied Petroleum Fractions

  • The gas stream is typically separated into the liquefied petroleum fractions (butane and propane), which can be stored in liquid form at relatively low pressure, and the lighter ethane and methane fractions. These lighter fractions of methane and ethane are then liquefied to make up the bulk of LNG that is shipped.

Benefits and Hazards of LNG

  • Natural gas was considered during the 20th century to be economically unimportant wherever gas-producing oil or gas fields were distant from gas pipelines or located in offshore locations where pipelines were not viable.
  • In the past, this usually meant that natural gas produced was typically flared, especially since unlike oil, no viable method for natural gas storage or transport existed other than compressed gas pipelines to end users of the same gas. This meant that natural gas markets were historically entirely local, and any production had to be consumed within the local or regional network.
  • Developments of production processes, cryogenic storage, and transportation effectively created the tools required to commercialize natural gas into a global market which now competes with other fuels. Furthermore, the development of LNG storage also introduced a reliability in networks which was previously thought impossible.
  • Given that storage of other fuels is relatively easily secured using simple tanks, a supply for several months could be kept in storage. With the advent of large-scale cryogenic storage, it became possible to create long-term gas storage reserves. These reserves of liquefied gas could be deployed at a moment’s notice through regasification processes, and today are the main means for networks to handle local peak shaving requirements.
  • However, LNG also poses certain hazards. The main hazard is its flammability after vaporization into a gaseous state. LNG is also a cryogenic liquid, which means that it can freeze and cause damage to equipment and injury to personnel if not handled properly.
  • Additionally, if LNG is not vaporized properly, it can lead to asphyxia. It is important for LNG facilities to have proper safety measures in place to mitigate these hazards.

Liquefied natural gas (LNG) is a form of natural gas that has been cooled down to liquid form for ease and safety of non-pressurized storage or transport. The process of liquefying natural gas involves the removal of impurities and the separation of different hydrocarbon components. LNG has many benefits including its ability to create long-term gas storage reserves, its reliability in networks, and its ability to compete with other fuels in the global market. However, LNG also poses certain hazards, and proper safety measures must be in place to mitigate them. With the increasing demand for natural gas, LNG is becoming an increasingly important part of the energy industry.

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