A compressor station is a facility which helps the movement of gas from one location to another in a pipeline system. Gases typically transported over long distances in this way include

natural gas Natural gas (also fossil gas, methane gas, and gas) is a naturally occurring compound of gaseous hydrocarbons, primarily methane (95%), small amounts of higher alkanes, and traces of carbon dioxide and nitrogen, hydrogen sulfide and helium ...

methane Methane ( , ) is a chemical compound with the chemical formula (one carbon atom bonded to four hydrogen atoms). It is a group-14 hydride, the simplest alkane, and the main constituent of natural gas. The abundance of methane on Earth makes ...

ethylene Ethylene (IUPAC name: ethene) is a hydrocarbon which has the formula or . It is a colourless, flammable gas with a faint "sweet and musky" odour when pure. It is the simplest alkene (a hydrocarbon with carbon–carbon bond, carbon–carbon doub ...

hydrogen Hydrogen is a chemical element; it has chemical symbol, symbol H and atomic number 1. It is the lightest and abundance of the chemical elements, most abundant chemical element in the universe, constituting about 75% of all baryon, normal matter ...

ammonia Ammonia is an inorganic chemical compound of nitrogen and hydrogen with the chemical formula, formula . A Binary compounds of hydrogen, stable binary hydride and the simplest pnictogen hydride, ammonia is a colourless gas with a distinctive pu ...

and

carbon dioxide Carbon dioxide is a chemical compound with the chemical formula . It is made up of molecules that each have one carbon atom covalent bond, covalently double bonded to two oxygen atoms. It is found in a gas state at room temperature and at norma ...

. While being transported through a pipeline the gas pressure gradually decreases due to frictional effects and needs to be periodically repressurized at intervals of about . Siting of compressor stations is dependent on terrain, accessibility and whether there are other tie-ins such as gas wells in the vicinity. Frequent elevation changes and a greater number of gas wells will require more compressor stations. The compressor station, also called a pumping station, is the "engine" that powers a long-distance gas pipelines. As the name suggests, the station compresses the gas (increasing its pressure) thereby providing additional energy to move it through the pipeline. The

compressor A compressor is a mechanical device that increases the pressure of a gas by reducing its volume. An air compressor is a specific type of gas compressor. Many compressors can be staged, that is, the gas is compressed several times in steps o ...

is driven by an electric motor or an engine fueled by some of the natural gas bled from the pipeline or liquid fuel such as diesel. Companies install compressor stations along a pipeline route. The size of the station and the number of compressors (pumps) varies, based on the diameter of the pipe and the volume of gas to be moved. Nevertheless, the basic components of a station are similar. Natural gas may move through a pipeline system typically at speeds of up to 25 mph (11.2 m/s), depending on pressures and pipeline diameters. For a pipeline system operating at a nominal pressure of 1000 psi (such as the UK

National Transmission System The United Kingdom's National Transmission System (NTS) is the network of gas pipelines that supply gas to about forty power stations and large industrial users from natural gas terminals situated on the coast, and to gas distribution companies ...

) compressor stations compress the gas from about 48 bar (700 psi) to 65 bar (950 psi). Compressor stations generally operate at a pressure ratio of 1:1.4. During compression the gas may increase in temperature from 5 °C (41°F) to 45 °C (113°F). Limiting the pressure ratio ensures that the temperature rise across the compressors is not high enough to require after-coolers to prevent damage to the pipeline protective coatings.

Liquid Separators

As the pipeline enters the compressor station the gas passes through scrubbers, strainers or filter separators. These are vessels designed to remove any free liquids or solid particles from the gas before it enters the compressors. Though the pipeline is carrying “dry gas,” some water and hydrocarbon liquids may condense out of the gas stream as the gas cools and moves through the pipeline. Any liquids that may be produced are collected and stored for sale or disposal. A piping system directs the gas from the separators to the gas compressor for compression.

Prime Movers

There are three commonly used types of engines that drive the compressors and are known as "prime movers": * Gas turbine / Centrifugal Compressor uses a natural gas-fired

turbine A turbine ( or ) (from the Greek , ''tyrbē'', or Latin ''turbo'', meaning vortex) is a rotary mechanical device that extracts energy from a fluid flow and converts it into useful work. The work produced can be used for generating electrical ...

to turn a

centrifugal compressor Centrifugal compressors, sometimes called impeller compressors or radial compressors, are a sub-class of dynamic axisymmetric work-absorbing turbomachinery. They achieve pressure rise by adding energy to the continuous flow of fluid through th ...

. The centrifugal compressor is similar to a large fan inside a case, which pumps the gas as the fan turns. A small portion of natural gas from the pipeline is burned to power the turbine. * Electric Motor/Centrifugal Compressor uses a centrifugal compressor driven by a high voltage

electric motor An electric motor is a machine that converts electrical energy into mechanical energy. Most electric motors operate through the interaction between the motor's magnetic field and electric current in a electromagnetic coil, wire winding to gene ...

. An electrified compressor may still require an air permit, as regulations vary by location an applicability analysis should be conducted whenever a compressor station will be constructed. A reliable source of electric power must be available and near the station. * Reciprocating Engine/Reciprocating Compressor uses a large piston engine resembling an

automobile engine There are a wide variety of propulsion systems available or potentially available for automobiles and other vehicles. Options included internal combustion engines fueled by petrol, diesel, propane, or natural gas; hybrid vehicles, plug-in hybr ...

, but much larger. Commonly known as “,” these engines are fueled by natural gas from the pipeline. Reciprocating pistons, located in cylinder cases, compress the gas. The compressor pistons and the power pistons are connected to a common crankshaft. The advantage of reciprocating compressors is that the volume of gas flowing through the pipeline can be adjusted incrementally to meet changes in customer demand.

Pigging facilities

As the pipeline enters the compressor station a

pig The pig (''Sus domesticus''), also called swine (: swine) or hog, is an omnivorous, domesticated, even-toed, hoofed mammal. It is named the domestic pig when distinguishing it from other members of the genus '' Sus''. Some authorities cons ...

receiver may be installed to receive pigs sent down the pipeline from an upstream facility. An intelligent pig, travelling at the prevailing gas velocity, measures the wall thickness of the pipeline and identifies areas of corrosion or defects. As the pipeline leaves the compressor station a pig launcher may be installed to send pigs down the pipeline to the next facility.

References

{{Fuel gas Natural gas infrastructure Natural gas technology

Liquid Separators

Prime Movers

Pigging facilities

See also

References