Guide to Understanding Natural Gas and Natural Gas Liquids

February 19, 2014

Natural gas is a crucial part of the United States energy sector, providing energy for fuel, heating, cooking, and much more. Our natural gas resources are also bountiful and with advances in drilling technology and methods, more accessible than ever. Despite its pervasiveness, many citizens are still unsure what exactly natural gas is, and how it relates to substances such as natural gas liquids, gas-to-liquids, and liquefied natural gas.

Overview of Natural Gas, Natural Gas Liquids, Liquefied Natural Gas, and Gas-To-Liquids

Natural Gas – Natural gas is a hydrocarbon gas. It consists primarily of methane but may also include other alkanes, carbon dioxide, nitrogen, and hydrogen sulfide. Natural gas is flammable and can be used for energy. It may be found in reserves by itself, or associated with crude oil.

Natural Gas Liquids – Natural gas liquids are condensable hydrocarbons that are often associated with natural gas or crude oil.
They include: ethane, propane, butane, isobutane, and pentane. Since they are condensable (may be referred to as condensates) they often form in natural gas wells when the pressure begins to lessen. Alternatively, they may form at the surface, or be formed through refrigeration and distillation.

Gas-To-Liquids – The term gas-to-liquids refers to the refining process of converting natural gas into a liquid. One of the most common processing techniques to do this is methanol to gasoline (MTG), which uses syngas as an intermediate to convert methanol into gasoline. Others types include the Fischer–Tropsch process and Syngas to Gasoline Plus process (STG+).

Liquefied Natural Gas – Liquefied natural gas (LNG) refers to natural gas that has undergone extreme cooling to the point of becoming liquefied. In it’s liquid state, a given amount of LNG takes up about 1/600th the space as natural gas. This makes it much easier to transport but it does require regasification terminals.

A Closer Look at Natural Gas

What Is Natural Gas? – Natural gas is a fossil fuel that forms when animal or plant remains are exposed for thousands of years to extremely high levels of pressure and heat. The pressure and heat breaks down the energy that was originally found in the plant or animal and stores it in the chemical bonds of the natural gas. Methane, which is the simplest alkane (consisting of one carbon atom and four hydrogen atoms) is the predominant compound in natural gas. Natural gas may also contain more complex alkanes such as ethane, propane, butane, isobutane, or pentane. It also commonly includes small percentages of carbon dioxide, hydrogen sulfide, and nitrogen. Natural gas is considered a nonrenewable resource; however, advances in drilling and discovery technologies have led many to believe that it is much more abundant than previously thought.

Where Is Natural Gas Found? – Natural gas may be found either associated with crude oil or in formations by itself. It may also be found in coalbeds. Advances in technology have allowed natural gas to be recovered from challenging environments such as shale formations. Natural gas is found all over the world including in the United States, Canada, Russia, Qatar, Turkmenistan, and Iran to name just a few major natural gas producing countries.

What is Natural Gas Used For? – Natural gas is an important source of energy for residential heating and cooking. On the industrial level, it is commonly used for electricity generation and as chemical feedstock for the manufacture of certain products such as plastics and other commercially used organic chemicals. Natural gas is rising in prominence as a fuel alternative to sources derived from crude oil. Natural gas that is associated with crude oil and recovered as a byproduct, may be burned off, or pumped back into wells if it is not economic to transport to market.

How is Natural Gas Processed? – Prior to its use residential or industrial applications natural gas must be processed to remove impurities such as carbon dioxide, nitrogen, helium, water and water vapor, etc. Natural gas is compressed at compressor stations to facilitate its travel through the pipelines. Scrubbers are also typically present at these compressor stations to begin removing water and other impurities. More extensive processing is commonly done in the downstream sector at processing plants. Natural gas may also be processed to create natural gas liquids (NGLs), gas-to-liquids (GTLs), and liquefied natural gas (LNG).

A Closer Look at Natural Gas Liquids

What are Natural Gas Liquids? – Natural Gas Liquids (NGLs) are hydrocarbons that have condensed from the natural gas’ gaseous state into a liquid state. This may occur naturally in the wellsite when pressure is reduced, or at the surface. It may also be intentionally induced by distillation and refrigeration in gas plants and refineries. Methane is not an NGL because it is lighter and its boiling point is lower. Common NGLs include ethane, propane, butane, isobutane, and pentane.

What are NGLs used for? – NGLs are used for a wide range of commercial and industrial purposes. They may be used as petrochemical feedstock, heating, cooking, or for gasoline blending. Common uses for different types of NGLs:

Ethane – Ethane can be used for petrochemical feedstock to yield ethylene which is used in the manufacturing of plastics. It is also used in the production of anti-freeze, detergent, and other commercial products. Though it usually has more value as petrochemical feedstock it may also be used directly for fuel depending on market conditions and its geographic location.

Propane – Propane may also be used for either petrochemical feedstock to create ethylene and propylene or it may be used for fuel and energy, again depending largely on the economy of transportation and market conditions. When it is used for energy it commonly powers stoves, gas grills, clothes dryers, generators, and water heaters, etc. As a fuel source it may be used to power lawnmowers, outboard motors, and forklifts. It is frequently sold in compressed cylinders and often mixed with butane or other hydrocarbons.

Butane & Isobutane – Butane has two isomers. The “normal” isomer consists of four carbon atoms joined together in a continuous, unbranching chain. The other isomer, isobutane, three of the carbon atoms are joined to the fourth, resulting in a clustered branch. The two different isomers have different chemical and physical properties with make them useful in different ways.

  • Butane – The standard isomer of butane is commonly used as petrochemical feedstock to produce synthetic rubber. It can also be used to make liquefied petroleum gas (LPG), lighter fuel, or as a blending component in gasoline.
  • Isobutane – Isobutane is used in refinery alkylation to make gasoline and for use in other chemical processes. It is also used in refrigerants and aerosols.
  • Pentane – Pentane is commonly used as a blowing agent in the production of polystyrene foam and as a chemical solvent. It is also a common component of gasoline.
  • Pentane Plus – NGLs heavier than pentane are commonly referred to as pentane plus, natural gasoline, or “debutanized” natural gasoline. As the name implies they are used in gasoline as well as ethanol blends, and in oil sands production.

Natural gas and natural gas liquids have a wide range of important commercial, industrial, and residential applications. In response to the need for efficient, cost effective transport the gas-to-liquids and liquefied natural gas processing methods were developed. In the next part of this two-part series we will take a closer look at these important processing techniques and the advantages they offer.