It consists of a simple closed tank, where the force of gravity serves to separate the heavier liquids like oil, and the lighter gases, like natural gas. They usually liquefy at the surface (at atmospheric pressure) and are produced separately as natural gas liquids (NGLs), either in field separators or in gas processing plants. According to the Gas Processors Association, these two processes account for around 90 percent of total natural gas liquids production. The process for removing hydrogen sulfide from sour gas is commonly referred to as ‘sweetening’ the gas. Either of these compounds, in liquid form, will absorb sulfur compounds from natural gas as it passes through. Why natural gas gathering and processing are important for MLPs Real Estate Natural gas processing is a purification method used on raw natural gas after it is extracted from a well. This rapid expansion of the gas allows for the lowering of the temperature in the separator. While absorption methods can extract almost all of the heavier NGLs, the lighter hydrocarbons, such as ethane, are often more difficult to recover from the natural gas stream. Methane is the gas found in natural gas, and natural gas processing is used to remove other gases and impurities. The process used to accomplish this task is called fractionation. M.R. Sulfur can be sold and used if reduced to its elemental form. Natural gas that comes from oil wells is typically termed ‘associated gas’. A new innovation in this process has been the addition of flash tank separator-condensers. In these cases, separation of oil and gas is relatively easy, and the two hydrocarbons are sent separate ways for further processing. ‹ Natural Gas Composition and Specifications, Lesson 1: Introduction to Petroleum Refining and Crude Oil Composition, Lesson 2: Properties and Classification of Crude Oil, Lesson 7: Catalytic Conversion Processes Part 1, Lesson 8: Catalytic Conversion Processes Part 2, Lesson 11: Past and Future of Petroleum Refining, Natural Gas Composition and Specifications, Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License, Department of Energy and Mineral Engineering, Department of Materials Science and Engineering, Department of Meteorology and Atmospheric Science, Earth and Environmental Systems Institute, iMPS in Renewable Energy and Sustainability Policy Program Office, BA in Energy and Sustainability Policy Program Office, 2217 Earth and Engineering Sciences Building, University Park, Pennsylvania 16802, NGL Recovery, Separation, Fractionation, and Treatment of Natural Gas Liquids. In certain instances, it is economic to simply leave the lighter NGLs in the natural 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. In addition to processing done at the wellhead and at centralized processing plants, some final processing is also sometimes accomplished at ‘straddle extraction plants’. In all, the Claus process is usually able to recover 97 percent of the sulfur that has been removed from the natural gas stream. In this process, external refrigerants are used to cool the natural gas stream. The behavior of natural gas, whether pure methane or a mixture of volatile hydrocarbons and the nonhydrocarbons nitrogen, carbon dioxide, and hydrogen sulfide, must be understood by the engineer who is designing the operating equipment for its production, processing, and transportation. Most of the liquid, free water associated with extracted natural gas is removed by simple separation methods at or near the wellhead. To learn about the basics of natural gas, including its composition, click here. The sour gas is run through a tower, which contains the amine solution. In this case, however, amine solutions are used to remove the hydrogen sulfide. Although dry pipeline quality natural gas is virtually identical across different geographic areas, raw natural gas from different regions may have different compositions and separation requirements. For information on the production of sulfur in the United States, visit the USGS here. An important part of natural gas processing is the removal of sour components, such as H 2 S and CO 2 from natural gas. In order to decrease the amount of methane and other compounds that are lost, flash tank separator-condensers work to remove these compounds before the glycol solution reaches the boiler. Natural Gas Processing and Treating. The Pennsylvania State University © 2020. Please send comments or suggestions on accessibility to the site editor. 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 scrubbers remove sand and other large-particle impurities. Abstract. Natural gas hydrates are crystalline ice-like solids or semi-solids that can impede the passage of natural gas through valves and pipes. Condensate and water removal [6]. Our gas processing plants process upstream natural gas from offshore Peninsular Malaysia for consumption of customers in the power generation sector as well as various industries such as petrochemicals. Natural gas processing consists of separating all of the various hydrocarbons and fluids from the pure natural gas, to produce what is known as ‘pipeline quality’ dry natural gas. Similar to using absorption for dehydration, using a different absorbing oil for hydrocarbons. Cryogenic processes are also used to extract NGLs from natural gas. To reduce the occurrence of hydrates, small natural gas-fired heating units are typically installed along the gathering pipe wherever it is likely that hydrates may form. This solution has an affinity for sulfur, and absorbs it much like glycol absorbing water. In addition to separating oil and some condensate from the wet gas stream, it is necessary to remove most of the associated water. Natural gas is a fossil fuel, though the global warming emissions from its combustion are much lower than those from coal or oil. The next logical step is NGL (Natural Gas Liquids) extraction and fractionation. With natural gas that contains even low quantities of water, natural gas hydrates have a tendency to form when temperatures drop. The ‘rich’ absorption oil, now containing NGLs, exits the absorption tower through the bottom. Second, these natural gas liquids must be separated themselves, down to their base components. The first step in natural gas processing is to separate the raw natural gas from the water and condensate. According to the American Gas Association’s Gas Facts 2000, there was an estimated 36,100 miles of gathering system pipelines in the U.S. in 1999. Natural gas, as it is used by consumers, is much different from the natural gas that is brought from underground up to the wellhead. In addition, raw natural gas contains water vapor, hydrogen sulfide (H2S), carbon dioxide, helium, nitrogen, and other compounds. Many of the innovations we have developed, like the use of plate-fin exchangers and packings in cryogenic columns, remain today as standard designs in the industry. Butane Splitter or Deisobutanizer - separates iso and n-butanes. These hydrates are solid or semi-solid compounds, resembling ice like crystals. There are two principle amine solutions used, monoethanolamine (MEA) and diethanolamine (DEA). Once absorbed, the glycol particles become heavier and sink to the bottom of the contactor where they are removed. Since it is such a polluting and harmful substance, further filtering, incineration, and ‘tail gas’ clean up efforts ensure that well over 98 percent of the sulfur is recovered. A complex gathering system can consist of thousands of miles of pipes, interconnecting the processing plant to upwards of 100 wells in the area. For over 40 years, Exterran has had a proven legacy of outstanding plant performance, innovation and accountability for all phases of your project. To learn more about glycol dehydration, visit the Gas Technology Institute’s website here. In addition to losing a portion of the natural gas that was extracted, this venting contributes to air pollution and the greenhouse effect. Natural gas processing plants. By varying the pressure of the gas in various sections of the separator, it is possible to vary the temperature, which causes the oil and some water to be condensed out of the wet gas stream. There are two principle techniques for removing NGLs from the natural gas stream: the absorption method and the cryogenic expander process. Natural gas is considered the dominant worldwide bridge between fossil fuels of today and future resources of tomorrow. The natural gas used by consumers is composed almost entirely of methane. After leaving the gas well, the first step in processing natural gas is removing oil, water, and condensates. However, if it is economic to extract ethane and other lighter hydrocarbons, cryogenic processes are required for high recovery rates. Like the process for NGL extraction and glycol dehydration, the amine solution used can be regenerated (that is, the absorbed sulfur is removed), allowing it to be reused to treat more sour gas. Natural Gas Processing; We offer reliable solutions across the natural gas value chain through a broad technology portfolio that includes gas conditioning and treating, fractionation, deep ethane extraction and LPG recovery, and liquid product treating. While some of the needed processing can be accomplished at or near the wellhead (field processing), the complete processing of natural gas takes place at a processing plant, usually located in a natural gas producing region. This process allows for the recovery of about 90 to 95 percent of the ethane originally in the gas stream. The entire fractionation process is broken down into steps, starting with the removal of the lighter NGLs from the stream. The project was completed on a very fast track schedule (kick-off to commissioning took just over 4 months). However, natural gas found at the wellhead, although still composed primarily of methane, is by no means as pure. This means that, when in contact with a stream of natural gas that contains water, glycol will serve to ‘steal’ the water out of the gas stream. Two basic steps: 1) Extraction, 2) Fractionation. ]A. J. Kidnay and W. R. Parrish, Fundamentals of Natural Gas Processing, CRC Press, Boca Raton, FL, 2006, p.16. NGL from highly sour gases may need additional treatment to remove mercaptans and other sulfur species before NGL leaves the processing plant. The glycol solution, bearing all of the water stripped from the natural gas, is put through a specialized boiler designed to vaporize only the water out of the solution. Riazi, S. Eser, J. L. Peña Díez, and S. S. Agrawal, “Introduction” In Petroleum Refining and Natural Gas Processing, Editors: M. R. Riazi, S. Eser, J. L. Peña, S. S. Agrawal, ASTM International, West Conshohocken, PA, 2013, p.12. Although most sour gas sweetening involves the amine absorption process, it is also possible to use solid desiccants like iron sponges to remove the sulfide and carbon dioxide. Typical desiccants include activated alumina or a granular silica gel material. These processes are dictated by the profitability metric referred to … Hydrogen & syngas plants. While the ethane, propane, butane, and pentanes must be removed from natural gas, this does not mean that they are all ‘waste products’. The natural gas, having been stripped of most of its water content, is then transported out of the dehydrator. [6. Gas wells typically produce raw natural gas by itself, while condensate wells produce free natural gas along with a semi-liquid hydrocarbon condensate. The basic absorption process above can be modified to improve its effectiveness, or to target the extraction of specific NGLs. After removing the acid gases, the natural gas stream is sent to a dehydration unit to remove water typically by absorption in a glycol unit, followed by mercury removal (by adsorption on activated carbons or other sorbents), and nitrogen rejection either cryogenically, or by adsorption, or absorption depending on the nitrogen concentration. As well as absorbing water from the wet gas stream, the glycol solution occasionally carries with it small amounts of methane and other compounds found in the wet gas. It is instrumental in ensuring that the natural gas intended for use is as clean and pure as possible, making it the clean burning and environmentally sound energy choice. A generalized natural gas flow diagram is shown in Figure 12.2 [7]. To learn more about the fractionation of NGLs, click here. In general, natural gas processing includes the following steps: In addition to these processes, it is often necessary to install scrubbers and heaters at or near the wellhead. [7.] These plants are located on major pipeline systems. It is now a mixture of absorption oil, propane, butanes, pentanes, and other heavier hydrocarbons. That is, the mixed stream of different NGLs must be separated out. Department of Energy’s Office of Fossil Energy, Natural Gas – From Wellhead to Burner Tip. These separators use pressure differentials to cool the wet natural gas and separate the oil and condensate. Click here to learn about the transportation of natural gas. Natural gas is one of the world’s most important sources of energy. In many instances, natural gas is dissolved in oil underground primarily due to the pressure that the formation is under. This process is known simply as the ‘amine process’, or alternatively as the Girdler process, and is used in 95 percent of U.S. gas sweetening operations. Most produced gas must be treated before the consumer can use it, and there were nearly 2,000 gas processing plants operating around the world as of mid-2006. 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