Natural gas is essential both as a clean energy source and as a chemical feedstock in the manufacture of plastics. However, before it reaches the consumer, it has to go through many steps known as processing natural gas. These steps are essential for recovering valuable components contained in the gas and the efficient transport of gas over long distances via the pipeline.
What Is Natural Gas?
Processing natural gas is a tricky industrial process utilized to purify natural gas that is extracted from underground gas fields. This process separates impurities and other non-methane fluids and hydrocarbons to produce pure methane (CH4), also known as dry pipeline-quality natural gas. Commercial, Industrial, and even residential consumers utilize this processed natural gas as fuel.
Natural gas in its final state utilized by the consumer is very different from the type of gas found underneath the earth. Raw natural gas is full of impurities, whereas the final product after processing is pure methane. These impurities incorporate nitrogen, oil, hydrates, carbon dioxide, water vapor, hydrogen sulfide, and heavy hydrocarbons that consist primarily of butane, pentane, ethane, and propane.
While some of this processing is completed at the well site, the other process is completed at the processing plant. Before natural gas enters the pipeline, eliminating most or all impurities is still required. Processing natural gas as a whole requires several separate steps; however, there are four primary processes: oil, water, condensate removal, hydrogen and carbon dioxide removal, dehydration, and the removal of NGL.
Processing Natural Gas
The natural gas utilized by consumers in its final state varies significantly from the natural gas underground. The final product contains almost pure methane; however, raw natural gas contains a variety of impurities. Impurities incorporate carbon dioxide, hydrogen sulfide, oil, water vapor, nitrogen, hydrates, and heavier hydrocarbons, consisting mostly of ethane, butane, propane, and pentanes.
While some gas treatments are done at the well site, the final processing takes place at a gas processing plant. Removal of all or most impurities is needed before entering the pipeline. Even though natural gas processing has several steps, the primary processes include separation, carbon dioxide and hydrogen sulfide removal, dehydration, and NGL recovery.
- Large-Particle Impurities
- When the gas leaves the well site, the first step for processing natural gas is eliminating all of the water and condensates. Typically, this step is performed at the site of the well. However, scrubbers and heaters are first implemented to reduce temperature drops in the gas and remove large-particle types of impurities.
- Separating Oil from Gas
- Next, a conventional separator is utilized to separate the oil from the gas. The separator comprises a closed tank that uses the force of gravity to separate liquids and solids. When this process is not achieved with gravity alone, separators use high pressure to cool the gas, which then is transferred through a high-pressure liquid to remove a quantity of the water and any remaining oil.
- Gas “Sweetening”
- When condensates, water, and oil have been removed from the natural gas, carbon dioxide and hydrogen sulfide must also be removed. This step in the process is additionally known as “sweetening” the gas. This is due to sulfur’s strong or “sour” scent. This step is crucial because hydrogen sulfide in itself is corrosive and even lethal.
- While product specifications and regulations to prevent sulfur effects are put forth by the National Agency of Corrosion Engineers, additionally known as NACE International, the Occupational Safety and Health Administration, OSHA, requires these additional preventative measures.
- Once the hydrogen sulfide and carbon dioxide have been removed, next comes the dehydration of the natural gas. This step is important to remove any excess water that can create freezing, corrosion, and hydrates issues, which do not meet pipeline standards.
- Next, water vapor is removed through the adsorption process. Adsorption is just the condensing and collection of water vapor on the surface or a passive dehydration system. Finally, it is the removal of water vapor utilizes a dehydrating agent.
- Mercury Removal
- This step isn’t always expedient; however, high mercury levels cause environmental pollution and aluminum heat exchanger corrosion. Therefore, when deemed necessary, two forms of mercury removal take place in regenerative and nonregenerative processes.
- The regenerative use alumina or sulfur-activated carbon, whereas the second uses silver located on a molecular sieve.
- Nitrogen Rejection
- Nitrogen, a non-flammable inert gas, decreases natural gas’s overall temperature. The gross heating value of natural gas should maintain a level of 900 to 1200 BTU (British thermal units). Purified natural gas maintains a level of 1010 btu.
- In most cases, the heating value is generally too low to meet pipeline standards where there should be the presence of nitrogen. Eliminating nitrogen from natural gas is called nitrogen rejection.
- NGL Recovery
- NGLs or Natural gas liquids are heavy in hydrocarbons, incorporating natural gasoline, butane, iso-butane, propane, and ethane. Even though natural gas liquids hold a high BTU, they aren’t of pipeline quality. However, these products are imperative when they are sold separately. Therefore, natural gas liquids should be removed in an NGL recovery process.
- The first step of this recovery process includes the removal of all present NGLs from the natural gas. This is achieved by cooling gas temperature. This cooling transforms vapor into liquid, making a case for easy removal. The process additionally removes hydrates and decreases the gross heating value.
- When the natural gas liquids are extracted, they are divided into their individual end products. This step is further known as fractionation. Natural gas liquids that are separated have high selling values and are advantageous in various use cases.
- The separating of pentanes, propane, butanes, and ethane by volatility is accomplished with a piece of equipment known as the fractionator train.
Importance of Natural Gas
As the world strives to diversify its energy mix into a single source, natural gas and the natural gas process are increasingly becoming important.
Not only is natural gas viewed as “lower carbon” contrasted to other fossil fuels, but the construction of natural gas process plants is also considered to be relatively quick (2 years). Thus, the International Energy Agency (IEA) forecasts the share of natural gas in the global energy mix to increase up to 2% annually until 2020.
This growth has increased natural gas dependency in a variety of uses. For example, natural gas is used in the power sector and industrial heat generation, ammonia in fertilization, and LNG in the transportation division for long-haul trucks or CNG (compressed natural gas).
Name: Rachel Lockard
I am Rachel Lockard, Marketing Head at Tailwater Technical Consultant. Tailwater Technical Consulting was founded in 2019 as a full-service engineering solutions provider for the Oil & Gas industry and leading consulting firms for Oil & Gas services in the USA.