Source: The Role of Natural Gas Liquids (NGLs) in the American Petrochemical Boom
Natural gas coming directly from a well contains many natural gas liquids that are commonly removed. In most instances, natural gas liquids (NGLs) have a higher value as separate products, and it is thus economical to remove them from the gas stream. The removal of natural gas liquids usually takes place in a relatively centralized processing plant and uses techniques similar to those used to dehydrate natural gas.
There are two basic steps to the treatment of natural gas liquids in the natural gas stream. First, the liquids must be extracted from natural gas. Second, these natural gas liquids must be separated themselves, down to their base components.
Natural gas is a mixture of hydrocarbon gases and the ratio of these different components (gases) varies. The vast majority of natural gas, 70-90 percent, is methane. The remaining 10-30 percent is various NGLs, including ethane, propane, butane, and pentane. While NGLs are gaseous at underground pressure, the molecules condense at atmospheric pressure and turn into liquids. The composition of natural gas can vary by geographic region, the geological age of the deposit, the depth of the gas, and many other factors. Natural gas that contains a lot of NGLs and condensates is referred to as wet gas, while gas that is primarily methane, with little to no liquids in it when extracted, is referred to as dry gas.
When natural gas is extracted during production, it must be processed to separate the pure natural gas (methane) from the various other hydrocarbons and fluids to produce what is known as pipeline-quality dry natural gas.
Once natural gas comes out of the wellhead, any oil and water present in the gas is removed either at the wellhead or at a nearby processing facility. Once the natural gas is transported to a nearby natural gas processing facility, other non-NGL liquids, such as sulfur, helium, and carbon dioxide, are removed, and then the NGLs are removed. The process of separating the NGLs from the natural gas stream is a complicated process involving multiple steps. Once NGLs are separated from the natural gas stream, they must then themselves be separated.
The process of separating various NGLs is called fractionation. Since each molecule (ethane, propane, etc.) has a different boiling point, the hydrocarbon stream goes through multiple fractionators, each with a different temperature. This removes a different NGL at each step, starting with the lightest hydrocarbons and working up to the heaviest. Typically ethane is removed first, followed by propane, butane, and isobutane. After these NGLs are removed and the natural gas meets the pipeline quality standards for the pipeline it will be transported on, it is sent to natural gas utilities, power generators, and industrial customers.
WHAT ARE NGLS USED FOR?
Of the approximately 1.36 billion barrels of U.S. NGLs produced in 2017, 33 percent was propane, 38 percent ethane, 12 percent pentane, 8 percent normal butane and 9 percent was isobutane.
NGLs are used for a variety of purposes in almost all sectors of the U.S. economy. Ethane is used almost exclusively in the production of ethylene, which is then turned into plastics. Propane is mostly used for heating and as a petrochemical feedstock. Butane and isobutane are typically blended into petroleum products to create various fuels.
| NGL | Applications | Main Sectors |
|---|---|---|
| Ethane | Ethylene for plastics production; petrochemical feedstock | Industrial |
| Propane | Residential and commercial heating; cooking fuel; petrochemical feedstock | Industrial, Residential, Commercial |
| Butane | Petrochemical feedstock; blending with propane or gasoline | Industrial, Transportation |
| Isobutane | Refinery feedstock; petrochemical feedstock | Industrial |
| Pentane | Natural gasoline; blowing agent for polystyrene foam | Transportation |
| Pentanes Plug | Blending with vehicle fuel; exported for bitumen production | Transportation |
The largest customer for NGLs, particularly ethane, is the chemical industry. Ethane is valuable because the industry uses it to create ethylene (ethylene loading solutions), which is the raw ingredient in most types of plastics. The complex process of converting ethane into ethylene is called cracking. Ethane cracker facilities heat the gas to approximately 1,500 degrees Fahrenheit to change the chemical composition of the ethane molecules resulting predominantly in ethylene. The ethylene is then cooled rapidly so it can be transported via pipelines in its liquid state.” Other chemicals can then be added to create entirely new compounds that are made into many of the consumer products we use every day.
In addition to ethylene, other chemicals derived from NGLs include propylene, benzene, methanol, and butadiene. Although we may not recognize their names immediately, these products are building blocks in consumer items and applications most of us use daily.
There are many immediate benefits of increased U.S. domestic natural gas production: lower costs for home heating and electricity; reduced emissions from power generation plants as they switch from coal and oil to natural gas, and a decreased reliance on foreign countries for energy. However, the secondary benefits of the domestic gas boom are also incredibly important to the U.S. economy. Increased domestic natural gas, oil, and NGL production are strengthening the refining and petrochemical industry, restoring the manufacturing sector, and making America a global energy superpower.
