After extraction and purification, natural gas must travel over long distances – under high pressure – from oil and gas production fields to industry users as well as end customers for the transportation of natural gas.
Pipeline transportation was invented to help make the delivery of natural gas to their destinations safer, more cost-effective, and quicker. However, more than a few technical difficulties arose from this distribution mode.
When natural gas – or any other type of gas – is transported over long distances, it experiences significant pressure loss. It is also exposed to lots of impurities lurking within the transportation channels.
To overcome these challenges, compression stations were invented and brought into play. This article covers compressor stations’ primary role when transporting natural gas from the fields to the market.
What is a Compression Station?
A compression station is an industrial facility designed to stabilize the flow rate and pressure of gases within a pipeline network at required optimal levels to obtain maximum carrying capacity. When natural gas travels through a pipeline, several factors – such as friction, distance, and elevation differences – slow its movement and reduce its pressure, causing it to expand.
An appropriately operated and strategically-positioned natural gas compression station efficiently collects the gas that reaches it, re-pressurizes the gas to minimize its volume, and then channels it – by re-establishing the correct flow speed that propels it – to numerous end processes and industries. This makes compression facilities an integral part of the natural gas pipeline network.
The number of natural gas compressor stations required along a particular pipeline varies significantly, depending mainly on the conditions and the local environment. But on average, one natural gas compression station is needed every 40-70 miles to maintain proper flow. Compression can mainly be achieved through piston-driven reciprocating compressors powered by electric motors, reciprocating engines, or turbines.
The number of compressor stations and their sizes varies, depending significantly on the volume of the natural gas to be processed and the distance.
Components of a Gas Compressor Station
Natural gas usually enters a compressor station via the station yard piping and finds its way through filters and scrubbers to eliminate solids, liquids, or other particulate matter within the gas stream.
As soon as the stream of natural gas is clean, it is directed efficiently through extra yard piping to individual compressors. Computers are primarily responsible for regulating the number of units and flow required to handle all scheduled system flow requirements.
Most compressor units used in this system operate in parallel, with individual compressors providing the necessary additional pressure before the natural gas back into the pipeline after restoring its full operational pressure.
If the needed boost in pressure is incredibly high, several compressors are employed in stages – in serial fashion – to achieve the desired pressure within stages.
Compressing natural gas usually generates unwanted heat, which is dissipated as soon as possible to cool the gas stream before it leaves the compressor facility. The temperature of the natural gas increases by 7 to 8 degrees for every 100 pounds per square inch (psi) increase in pressure.
This is why aerial cooler systems are installed in most compressor stations to dissipate excess heat. The heat that is also generated via the operation of each compressor unit dissipates through a sealed coolant system very similar to that of an automotive radiator.
Compressor Stations in Wet Gas Areas
In areas producing NGLs (natural gas liquids) or wet gas areas, significant changes in temperature and pressure may cause some of the liquids to drop out. These liquids are usually captured in tanks and then trucked off the site. The captured liquids – drip gas or natural gasoline – are often used as a motor gasoline blend.
Natural gas turbine units or conventional piston engines drive gas-powered compressors. Most compressor stations supply a small portion of the natural gas that flows through the station. It is common for some areas to power compressor stations electrically for security or environmental reasons.
There are only significant operational and site design differences between competing compressor engine technologies, including unique sound and air emissions.
How Many Compressor Units are in a Station?
There could be one or more individual compressor units at a particular station. These compressor units can be installed in the open or housed in a building to facilitate sound management and maintenance. Newer compressor units are frequently housed one per building, though it is common to find multiple compressor units within one large building.
Compressor buildings are specially constructed, incorporating shielded exhaust systems and insulated walls. They also have advanced fan technology for dampening noise or sound. Newly constructed compressor structures can incorporate these unique features where local, state, or federal regulations require comprehensive noise mitigation.
Compression Station Yards
Compression station yards are mostly larger than transmission line compressors because of the multiple pipelines entering the complex and the extra equipment required for filtering and removing liquids from the gas stream.
Other vital components that make up a compressor complex include:
- Gas metering equipment
- Backup generators
- Safety and system monitoring controls
- Gas filtration systems
In some cases, odorization equipment for adding mercaptan – which furnishes the natural gas with a distinctive sulfurous odor – may be present.
Natural gas is an odorless and colorless gas, so mercaptan, an odorant, is usually added to gas streams as an extra safety mechanism. But this must be done under local, state, and federal laws, especially areas requiring transmission lines in areas that are densely populated.
Conclusion
The compression station is an integral part of an industrial facility or natural gas pipeline network transporting natural gas from the oil and gas fields to the market. The primary role of a natural gas compression station is to stabilize the flow rate and pressure of gases within pipeline networks during the transportation of natural gas. This helps the pipeline network maintain its maximum carrying capacity as it delivers natural gas to end users and industries.
Don’t miss out on the latest industry insights and updates from KB Delta. Consider us for parts servicing the natural gas industry, ranging from valve assemblies to steel and thermoplastics.