Natural-gas processing

Natural-gas processing is a complex industrial process designed to clean raw natural gas by separating impurities and various non-methane hydrocarbons and fluids to produce what is known as pipeline quality dry natural gas. Natural-gas processing begins at the well head. The composition of the raw natural gas extracted from producing wells depends on the type, depth, and location of the underground deposit and the geology of the area. Natural gas processing is a necessary step to ensure the safety, reliability, and marketability of natural gas.

Overview

The main purpose of natural-gas processing is to purify the raw natural gas by removing contaminants such as solids, water, carbon dioxide (CO2), hydrogen sulfide (H2S), and higher molecular mass hydrocarbons. Some of the substances which contaminate natural gas have economic value and are further processed or sold. A fully operational natural-gas processing plant delivers pipeline-quality dry natural gas that can be used as fuel by residential, commercial, and industrial consumers.

Process

The processing of natural gas involves several critical steps:

Removal of Solid Particles

Initially, solid particles such as sand, dust, and other sediments are removed through a series of filters and separators.

Condensate Separation

Natural gas contains various hydrocarbon liquids. These liquids are removed through condensation and separation processes.

Dehydration

Water vapor is removed from natural gas to prevent the formation of hydrates and corrosion in pipelines. This is typically achieved using glycol dehydration or solid desiccant dehydration.

Sweetening

Sour gas, which contains hydrogen sulfide (H2S), must be treated to remove H2S, a process known as sweetening. This is commonly done using amine gas treating.

Carbon Dioxide Removal

Carbon dioxide (CO2) is also removed from natural gas to prevent corrosion and to meet the specifications for pipeline transportation. Techniques include amine treating and membrane separation.

Nitrogen Rejection

Nitrogen, which can dilute the heating value of the gas, is removed using cryogenic distillation or adsorption processes.

Hydrocarbon Dew Point Control

Controlling the hydrocarbon dew point of natural gas is necessary to meet pipeline specifications and to prevent condensation of heavy hydrocarbons during transportation.

Products

The main product of natural-gas processing is pipeline-quality dry natural gas. By-products can include:

• Natural Gas Liquids (NGLs) - Ethane, propane, butanes, and natural gasoline separated from the natural gas.
• Sulfur - Recovered when sweetening the gas stream.
• Condensate - Liquid hydrocarbons recovered during processing.

Environmental Considerations

Natural-gas processing has environmental impacts, including the emission of greenhouse gases (GHGs) and air pollutants. Technologies and practices such as carbon capture and storage (CCS) and reduced emissions from flares and vents can mitigate some of these impacts.

Economic Aspects

The economics of natural-gas processing are influenced by the composition of the raw gas, the market value of the by-products, and the cost of processing. Efficient and effective processing technologies can improve the profitability of natural gas production.

See Also

• Natural gas
• Hydrocarbon dew point
• Amine gas treating
• Carbon capture and storage