Natural gas is a valuable energy resource that is used for various purposes, from heating and cooking to electricity generation. However, the natural gas that is extracted from underground is not pure enough for direct use. It needs to undergo a series of processes to remove impurities and separate valuable components. One crucial step in this process is the extraction and fractionation of Natural Gas Liquids (NGLs). In this article, we will delve deeper into the world of NGLs, their components, extraction methods, and the importance of fractionation in the midstream sector.
What are Natural Gas Liquids (NGLs)?
Natural Gas Liquids (NGLs) are hydrocarbons that are found in natural gas streams along with methane, the primary component of natural gas. NGLs are composed of various components, including ethane (C2), propane (C3), iso-butane (iC4), normal butane (nC4), natural gasoline (C5-C6), and pentanes (C5) and heavier molecules (C6-C9). These components have different boiling points and properties, making them valuable for different applications.
NGLs are usually extracted from natural gas because they have significant commercial value and can be used for various purposes. Ethane is a crucial feedstock for petrochemical industries, propane is widely used for heating and cooking, butanes are used as blendstocks in gasoline production, and natural gasoline is used in gasoline blending, specialty solvent production, and as a diluent for syncrude production. The extraction of NGLs not only provides valuable products but also improves the quality of the remaining natural gas, making it suitable for further processing or direct use.
There are two primary methods for extracting NGLs from natural gas: the absorption method and the cryogenic expander process. These methods are used depending on the specific composition and requirements of the natural gas stream. (shameless plug: Rogue Edge Members have access to our natural gas processing calculator – providing REAL TIME insight into recoveries and the true economic value for the full Natural Gas Stream)
The absorption method for NGL extraction is similar to the absorption process used for dehydration. However, instead of using glycol, an absorbing oil is used to separate NGLs from the natural gas stream. The absorbing oil has an affinity for NGLs, similar to how glycol has an affinity for water. When the natural gas is passed through an absorption tower, it comes into contact with the absorbing oil. The absorbing oil absorbs a high volume of NGLs from the gas stream, becoming “rich” in NGLs. The rich oil is then sent to a lean oil still, where the mixture of absorption oil and NGLs is heated to a temperature higher than the boiling point of the NGLs but below that of the oil. This process allows for the recovery of approximately 75% of butanes and 85-90% of natural gasoline from the natural gas feedstock. Refrigeration can be used to target specific NGLs, such as propane, and improve the extraction efficiency.
Cryogenic Expansion Process
The cryogenic expansion process is employed when it is necessary to extract lighter hydrocarbons, such as ethane, from the natural gas stream. Cryogenic processes involve lowering the temperature of the gas stream to extremely low levels, around -120 degrees Fahrenheit. The most effective technique for achieving this is the turbo expander process. The natural gas stream is cooled using external refrigerants, and then an expansion turbine rapidly expands the chilled gases. This rapid expansion causes the temperature of the natural gas to drop significantly, condensing ethane and other hydrocarbons while methane remains in its gaseous form. The recovery of ethane in the cryogenic expansion process can reach approximately 90-95%. Moreover, the energy released during the expansion of the natural gas stream can be utilized to recompress the gaseous methane effluent, resulting in energy cost savings associated with ethane extraction. (shameless plug: Rogue Edge Members have access our outlook for Ethane elections – allowing midstream providers and producers to see if they should Recover Ethane or Reject Ethane)
The extraction of NGLs from the natural gas stream not only produces cleaner and purer natural gas but also provides valuable hydrocarbons that can be used in various industries. The extracted gas can serve as a feedstock for Liquid Natural Gas (LNG) production, which has its own set of applications and benefits.
NGL Fractionation: Separating Valuable Components
Once NGLs have been extracted from the natural gas stream, they need to be separated into their individual components to be used effectively. This separation process is known as fractionation and is essential for maximizing the value of the NGLs.
Fractionation is based on the different boiling points of the various hydrocarbons in the NGL stream. The process involves a series of steps, starting with the removal of the lighter NGLs and progressing to the separation of heavier components. There are specific fractionators dedicated to each hydrocarbon. Here are the key steps involved in NGL fractionation:
Deethanizer – Ethane Removal
The deethanizer is the first fractionator in the process. Its primary function is to separate ethane from the NGL stream. Ethane has a lower boiling point compared to other NGL components, allowing it to be easily separated. The deethanizer operates by heating the NGL stream and condensing the ethane, which can then be collected separately.
Depropanizer – Propane Removal
The depropanizer is responsible for removing propane from the NGL stream. Propane has a slightly higher boiling point than ethane, making it the next component to be separated. The depropanizer works in a similar way to the deethanizer, with the propane condensing at the appropriate temperature and being collected as a separate product.
Debutanizer – Butanes Removal
The debutanizer is used to separate butanes (both iso-butane and normal butane) from the remaining NGL stream. Butanes have higher boiling points compared to ethane and propane. The debutanizer operates at a higher temperature to condense and collect the butanes, leaving the pentanes and heavier hydrocarbons in the NGL stream.
Butane Splitter or Deisobutanizer – Separating Iso and Normal Butanes
In some cases, it is necessary to separate iso-butane and normal butane from each other. This is achieved through a process called butane splitting or deisobutanizer. The butane splitter operates at specific temperatures and pressures to selectively condense and separate the iso-butane and normal butane components.
The remaining NGL stream after the butanes have been separated is known as natural gasoline. Natural gasoline is a mixture of pentanes (C5) and heavier molecules (C6-C9). It serves various purposes, including gasoline blending, specialty solvent production, feedstock for ethanol production, and as a diluent for syncrude production.
Fractionation is a critical process in the midstream sector of the natural gas industry. It enables the separation of different NGL components, each with its unique value and application. The separated NGLs can be sold individually, providing raw materials for petrochemical plants, enhancing oil recovery in oil wells, and serving as sources of energy. The fractionated NGLs play a vital role in various industries, from plastics manufacturing to gasoline production.
The Importance of Natural Gas Processing
Natural gas processing is a crucial step in the midstream sector of the natural gas industry. It involves the extraction of NGLs and the fractionation of these valuable components. Natural gas processing plants are typically located in natural gas producing regions, where the extracted gas is transported through a network of gathering pipelines. (shameless plug: Rogue Edge Members have access to fundamental supply/demand for Natural Gas, Ethane, Propane, Iso Butane, Normal Butane, and Natural Gasoline – along with forward pricing for each commodity in the energy space.)
Gathering and Transporting Natural Gas
Before natural gas can be processed, it needs to be gathered and transported from the wellhead to the processing plant. Gathering pipelines, which are small-diameter and low-pressure pipes, are used to transport the extracted natural gas to the processing plants. A complex gathering system can consist of thousands of miles of pipelines, connecting the processing plant to numerous wells in the area. The gathering pipelines ensure the efficient and safe transportation of the natural gas to the processing facilities.
Processing Natural Gas
Once the natural gas reaches the processing plant, it undergoes a series of processes to remove impurities and separate the valuable components. The primary goal of natural gas processing is to produce “pipeline quality” dry natural gas, which meets the specifications imposed by major transportation pipelines. These specifications ensure the safe and efficient transport of the natural gas to end users. (shameless plug: Did we mention that Rogue Edge Members have access to processing economics???)
The processing of natural gas involves several steps, including the removal of impurities like water vapor, hydrogen sulfide (H2S), carbon dioxide, helium, nitrogen, and other compounds. The purification process varies depending on the specific impurities present in the natural gas stream. For example, water vapor can be removed through dehydration using absorption or adsorption methods.
Oil and Condensate Removal
In some cases, natural gas is produced along with crude oil or condensate. To process and transport the associated dissolved natural gas, it needs to be separated from the oil. This separation process can be achieved through various techniques, such as conventional separators or low-temperature separators (LTX). The separation of oil and natural gas is typically done at or near the wellhead, ensuring the efficient extraction of both resources.
Water vapor is another impurity that needs to be removed from the natural gas stream during processing. The presence of water vapor can lead to the formation of natural gas hydrates, which can obstruct the passage of natural gas through pipelines and valves. To prevent hydrate formation, natural gas is dehydrated using either absorption or adsorption processes. Glycol dehydration and solid-desiccant dehydration are two commonly used methods for removing water vapor from the natural gas stream.
Separation of NGLs
During natural gas processing, NGLs are separated from the gas stream to maximize their value and ensure the production of pipeline-quality dry natural gas. The extraction of NGLs involves methods like absorption and cryogenic expansion. These methods target specific NGLs, such as ethane, propane, and butanes, and separate them from the natural gas stream. The recovered NGLs can then be further processed or sold separately, depending on their specific applications.
Natural gas processing plays a crucial role in the midstream sector, ensuring the production of clean and valuable natural gas. It involves the extraction and fractionation of NGLs, which have numerous commercial applications and provide raw materials for various industries. The processing of natural gas also improves the quality of the remaining gas, making it suitable for further processing or direct use.
Natural gas processing and the fractionation of NGLs are vital steps in the midstream sector of the natural gas industry. These processes involve the extraction, separation, and purification of valuable components from the natural gas stream. NGLs, including ethane, propane, iso-butane, normal butane, natural gasoline, and pentanes, are extracted through methods like absorption and cryogenic expansion. Fractionation further separates these components, maximizing their value and enabling their use in various industries. (shameless plug: Rogue Edge Members can learn about Natural Gas Processing through our state of the art and AFFORDABLE platform with energy financials and fundamentals.)
Natural gas processing ensures the production of clean and pure natural gas, suitable for further processing or direct use. It involves the removal of impurities like water vapor, oil, and condensate, as well as the separation of NGLs. The processed natural gas can then be transported through pipelines to end users, providing a reliable and efficient source of energy.
Understanding the importance of natural gas processing and fractionation is crucial for the midstream sector and the overall natural gas industry. These processes not only enhance the value of natural gas but also contribute to the production of essential products and the growth of various industries.
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