Compressor stations are an integral part of the natural gas pipeline network that helps to reduce pressure and maintain flow in transporting natural gas from individual well sites. As natural gas moves through the pipeline, it is slowed by distance, friction and elevation differences. Compressor stations help these issues be resolved strategically placed within gathering or transportation pipelines so they can continue on their journey to market.

Understanding Natural Gas Compressor Stations

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How Compressor Stations Work

Natural gas enters a compressor station and is cleaned of liquids, solids, and particulates. The natural gas stream then goes through more piping to individual compressors, where computers regulate the number required to handle system requirements. On high-pressure occasions (like when you're cooking), several units can be operated in stages to provide needed pressure on an incremental basis ((Figure 1). When necessary, this process also works from the bottom-up, which provides for a gradual increase in flow at startup as opposed to outputting all available volume immediately upon demand

Natural gas needs to be cooled before leaving a compressor facility to cool down the stream. This happens by compressing it and dissipating heat at 100 PSI increments. Most compressor stations have aerial coolers for this task (after-coolers). The individual units generate heat which is then cooled with sealed radiators similar to those in an automobile engine - these are called 'before' coolers.

In wet gas areas, where the production of natural gas liquids (NGLs) is high, changes in pressure and temperature cause some of the NGLs to fall out. The NGLs that have fallen out are captured in tanks and trucked off-site for future use. It's called natural gasoline or drip gas since it is often used to blend with motor gasoline.

Most compressor stations are fueled by a portion of the natural gas flowing through them; however, there may be locations where all or just some units can only run using electricity primarily for environmental reasons or security reasons like location isolation from society on military bases, etc. Nevertheless, sites explicitly designed for electrical power generation will have different air emissions than those powered by conventional piston engines, which rely on combustion-driven pistons vs turbine-powered compressors driven electrically but emit sound at higher levels due to their design features geared towards acoustic containment rather than engine attenuation via mufflers like human ears do not hear well over long distances.

Stationary compressors are often housed in buildings to facilitate maintenance and sound management. But the newest units may be located one per building, as well. The walls of these buildings generally have insulation for better noise isolation and advanced fan technology that dampens the sound from inside and outside. In recent years, new construction projects have incorporated this design characteristic where local regulations require it; however, they vary significantly in their approaches when not required by law.

Compressor station yards for gathering lines are often larger than transmission line compressors due to multiple pipelines coming into the complex and, in some cases, equipment needed to filter out liquids from gas. Other components of a compressor complex include backup generators, metering equipment (to measure how much natural gas is passing through), and filtration systems that remove impurities like water droplets or dirt particles before it enters the pipeline system. In addition, there may be odorization facilities on-site; these sites will add mercaptan - also known as "sulphurous" chemicals- which provide distinctive sulphurous odours that warn us if there's a leak.

The Permitting and Regulatory Framework

Gathering pipelines are subject to permitting and regulation at the federal or provincial level, while interprovincial transmission systems come under either of these levels depending on the type of pipeline. A gathering line is any pipe that gathers gas from smaller lines in a region; an interstate transmission system is any line that carries gas across multiple provinces. The purpose, not size, defines whether it's a gathering or an intrastate transmission line.

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Compressor Stations within the Gathering System

Gathering lines are smaller diameter pipelines that take natural gas from the wellhead to a processing facility or interconnect with a more extensive pipeline. These gathering lines are regulated at the provincial level, and compressor stations in this system of pipes also fall under regulation.

Natural gas in a gathering system can arrive at the compressor station with various pressures depending on the force of wells feeding it and how much gas travels from the wellhead to compressors. Regardless of these pressures, the natural gas needs to be regulated or compressed to enter an interstate transmission system at 800-1200 psi (pounds per square inch). Gathering systems have extensive facilities of 6-12 compressors because there are often significant requirements for compression within them. In addition, as more wells are drilled in an area, these buildings need to scale up as more demand for reduction exists. A typical permanent land requirement for a gathering system compressor is 5 acres, but they may exceed this if slopes exist or other factors are considered.

Compressor Stations within the Interstate Transmission System

A transmission pipeline is a wide-diameter, long-distance pipe that brings natural gas from the production area to market. These pipes can sometimes travel clear across the country. The Federal Energy Regulatory Commission has authority over the construction and operation of interprovincial pipelines.

Natural gas within the pipeline is usually pressurized at 800 to 1,200 psi. To ensure that gas flows optimally, it must be periodically compressed and pushed through the pipeline. However, friction and elevation differences slow the gas and reduce pressure, so compressor stations are typically placed 40-70 miles apart along the pipeline to boost pressure for optimal performance. A typical facility may consist of two compressor units (one operational one as backup) with a single building consisting of four acres or less of land required for a permanent location.

Natural gas within an interstate transmission system is generally already pressurized at 800-1200 PSI--to keep it flowing optimally, periodic compression boosts are needed every few miles on most pipelines stretching across states or countries; because they only offer increases in pressures, these facilities generally need much smaller footprints than gathering systems which require more energy-intensive processes like compression boosting; this means you can have compressors spaced about 70mi apart providing their localized benefits without disrupting other parts of your network; when using 50kW generators that recycle excess heat & power production into natural resources.

Learn More From Your Natural Gas Experts

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Over the last few years, there has been an increase in demand for clean energy sources. Natural gas power generation is a good choice for many industries looking for an efficient primary or backup source of power that is more environmentally friendly than traditional fuels. But what are the main advantages of this type of power generation, and is it a suitable solution for your industry?

Why Are Natural Gas Liquids Important?

Higher prices on crude oil have led to increased demand for these products, making drilling in liquid-rich resources more profitable than it once was due to their high content rate of natural gas liquids (NGL). Natural gas liquids have high value as separate products and have many different applications.

Depending on their vapour pressure, natural gas liquids are categorized into three main types:

Low vapour pressure NGL (condensate);
Intermediate vapour pressure NGL (natural gasoline);
High vapour pressure NGL (liquefied petroleum gas).

Based on their applications, there are many different types of natural gas liquids:

Ethane (C2H6) - Applications for ethane include plastics production and petrochemical feedstock- as raw materials fed into an industrial process to produce a new product. Some of the end products of these processes are plastics, detergents, and antifreeze.
Butanes (C4H10) - Butane can be blended with other fuels, such as gasoline and propane. Such a blend produces synthetic rubber for tires and lighter fuel. Pure butane is also used in refrigeration in its liquid form. When combined with propane, butane becomes liquified petroleum gas (LPG).
Isobutane (C4H10) - Isobutane is used in various industrial applications, including as a refinery feedstock and petrochemical feedstock. Some well-known end-use products include aerosols and refrigerants.
Propane (C3H8) - Propane has a number of applications and uses. Residential and commercial heating is just one example. Propane is also used as cooking fuel. Some vehicle owners also use propane as fuel for their cars.
Pentanes (C5H12) - Pentanes are mainly used in natural gasoline and as a blowing agent for polystyrene foam. There is also a special category, called Pentane Plus (also known as natural gasoline), which is blended with vehicle fuel and exported for bitumen production.

Industries Using Natural Gas Liquids

Each type of natural gas liquid has its own primary sector of use. As their applications vary, the primary sectors for NGLs can also be different:

Ethane is primarily used in the industrial sector.
Propane is used in the industrial, residential and commercial sectors.
Butane is mainly used for transportation and in the industrial sector.
The application of the isobutanes is mostly in the industrial sector.
Pentane and Pentane Plus are used for transportation.

How Are Natural Gas Liquids Extracted?

There are two methods for removing NGLs from the natural gas stream: absorption and cryogenic expansion.

The Absorption Method

The absorption method for NGL extraction is very similar to how dehydration works. The primary difference lies in the usage of absorbing the oil in NGL absorption instead of glycol in the process of dehydration.

The absorption method is used when it is necessary to pick up heavier natural gas liquids like butane and pentane because the absorbing oil has an affinity with them. The absorption process occurs in an "absorption tower" where the gas comes into contact with absorbing oil which soaks up most of the natural gas liquids. Then the mixture of absorption oil and NGLs is heated to a temperature higher than the boiling point for the NGLs, but below the boiling point of the oil.

This process yields a recovery of 75% butanes and 85-90% natural gasoline from the natural gas feedstock.

The Cryogenic Expansion Process

The lighter hydrocarbons, unlike the heavier NGLs, are harder to recover from the natural gas feedstocks. This is where the cryogenic expansion process comes into place. In this process, the temperature of natural gas is lowered to -120 degrees Fahrenheit by using external cooling agents. One of the most common and at the same time effective methods of cooling natural gas is the turbo expander process.

This process uses an expansion turbine to quickly drop the temperature of the gas, causing the natural gas liquids to start condensing. Apart from being efficient, this method can also save some serious energy costs by converting a portion of the released energy.

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What Is NGL Fractionation?

The fractionation process is used in natural gas processing plants to separate the natural gas liquids into individual products. Fractionation works based on the different boiling points of the different hydrocarbons in the stream. This process consists of a series of steps, starting from the lighter NGLs being taken out from the natural gas stream.

The fractionation is the second step in the process of natural gas treatment. The first step includes the extraction of the liquids from the natural gas. And the second is the separation of these liquids into their base components, such as ethane, propane, butane, and methane.

At 24/7 Compression, we are proud to be a trusted wholesaler of gas compression parts and equipment for many different industries. We offer flexible solutions to our clients, including new build and used compressor packages, rental packages and full services. We have multiple locations in Alberta and British Columbia, so don't hesitate to reach out and let's discuss how we can help. Contact us today!

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