As it passes through a pipeline, natural gas is strongly pressured. The natural gas must be compressed on a regular basis along the pipeline to keep it pressurized. Compressor stations, where gas is compressed by a turbine, a motor, or an engine, are used to do this.
Natural gas must be compressed and pushed through the interstate pipeline system on a regular basis to ensure optimal flow.
Friction and elevation changes diminish the pressure within the pipeline over long distances, slowing the flow of gas. Compressor stations play an important role in this. Hundreds of compressor stations are located across North America, typically 50 to 70 miles apart along the transmission pipeline system, and provide a needed “boost” to help the gas go from one location to the next. These stations are operational 24 hours a day, 365 days a year, and are also supervised by highly qualified employees 24 hours a day, seven days a week. Hundreds of compressor stations are located across the United States and play an important role in the natural gas transmission system, which has been demonstrated to be the safest and most dependable mode of natural gas transportation.
Safety and Emergency Shutdowns
To protect the public, staff, and our facilities, compressor stations use a range of safety methods and practices.
Every station, for example, has an emergency shutdown system that shuts down the compressors, separates and vents the compressor station gas pipes, and diverts gas away from the station.
At a centralized gas control center, highly-trained people monitor all compressor stations around the clock. In addition, as required by Department of Transportation rules, all emergency shutdown systems are completely checked every year.
We also cooperate closely with first responders to ensure that they are aware of our operations and can help if an emergency arises.
Air Quality
Compressor stations are highly regulated establishments that must adhere to stringent safety and air quality regulations.
The gas compressors are powered by turbines that use low-emission technology and are fueled by clean-burning natural gas. Under current federal standards, the turbines must be designed to emit 25 ppmvd (parts per million by volume, dry basis) of nitrogen oxide (NOx) during normal operation. During normal operation, new turbines are supposed to emit NOx at a rate of 9 ppmvd. This is much less than what federal and state rules require.
Furthermore, if natural gas is discharged from the compressor station during yearly testing or an emergency shutdown, the natural gas a mixture of hydrocarbons, predominantly methane will rise and dissipate safely as it is absorbed into the atmosphere.
Noise and Odor
When operating at full load, the Federal Energy Regulatory Commission (FERC) requires that the station’s noise levels do not exceed an average day-night sound level (Ldn) of 55 decibels (dBA) at the nearest noise sensitive area, such as residences, schools, hospitals, churches, playgrounds, and camping facilities.
Before and after construction, noise surveys are undertaken to ensure that the federal noise levels are not exceeded. The average residential dishwasher produces 50 decibels of sound.
Natural gas has no odor or color. For safety concerns, an odorant called Mercaptan is introduced into some natural gas pipelines. Mercaptan emits a distinct stench, similar to rotten eggs, that aids in the identification and detection of a leak. It is non-toxic and will disperse on its own. The odor from the Mercaptan may be noticed during annual testing of the emergency shutdown system or in the unlikely event that an emergency shutdown occurs. If minute residues of Mercaptan separate from natural gas that has risen and been absorbed into the atmosphere, the scent of the odorant may linger in some situations.
What method is used to pressurize gas lines?
The essential premise of the natural gas delivery system is that gas flows from higher to lower pressure. In a pipeline, the pressure is measured in pounds per square inch.
The natural gas is piped from the well into “gathering” lines, which look like tree branches and get larger as they get closer to the central collection site.
To transport the gas to the pipeline or processing plant, a collection system may require one or more field compressors. A compressor is a machine that uses a turbine or an internal combustion engine to create pressure in order to “push” gas down the pipes. The majority of compressors in the natural gas distribution system run on natural gas from their own lines.
Some natural gas gathering systems contain a processing facility that removes contaminants like water, carbon dioxide, or sulfur that could damage a pipeline, as well as inert gases like helium that would lower the gas’s energy value. Small amounts of propane and butane can also be removed at processing plants. These gases are employed in a variety of applications, including chemical feedstocks.
Natural gas is transported from the collection system to the transmission system, which is made up of around 272,000 miles of high-strength steel pipe.
These massive natural gas transmission lines are comparable to the nation’s interstate highway system for automobiles. They transport significant amounts of natural gas from production regions to local distribution businesses over thousands of miles (LDCs). Depending on the sort of area in which the pipeline is running, the pressure of gas in each segment of line normally ranges from 200 pounds to 1,500 pounds per square inch. Pipelines are designed and built to handle far more pressure than is ever attained in the system as a safety measure. Pipelines in densely populated areas, for example, operate at less than half of their intended pressure.
Many large interstate pipelines are “looped,” meaning they run parallel to each other in the same right of way. This ensures maximum capacity during peak demand periods.
Compressor stations are spaced every 50 to 60 miles along each pipeline to compensate for the pressure loss caused by the natural gas traveling through the steel pipe. Many compressor stations are fully automated, allowing them to be started and stopped from the pipeline’s central control center. Shut-off valves along the transmission line can also be controlled remotely from the control room. The system’s operators keep precise operating data on each compressor station and alter the mix of engines running on a regular basis to improve efficiency and safety.
Because natural gas travels at up to 30 miles per hour through the transmission system, it takes several days for gas from Texas to reach a utility receipt point in the Northeast. There are several linkages with other pipelines and utility systems along the way, providing system operators with a great level of flexibility in moving gas.
About 200 million cubic feet of gas is contained in a 50-mile piece of 42-inch transmission line operating at about 1,000 pounds of pressure, enough to operate a kitchen range for more than 2,000 years. The “linepack” refers to the amount of gas in the pipe.
A pipeline company can store gas by raising and lowering the pressure on any pipeline segment during periods when there is less demand at the pipeline’s terminus. Using linepack in this fashion helps pipeline operators to efficiently handle hourly demand swings.
Natural gas pipelines and utilities rely on highly complex computer models of customer demand for natural gas, which link daily and hourly consumption patterns to seasonal and environmental factors. That’s why customers can rely on natural gas’s dependability: when it’s required, it’s there.
When natural gas travels through a transmission pipeline and arrives at a local gas utility, it typically goes through a “gate station.” Gate stations are widely used by utilities to receive gas from a variety of sites and pipelines. There are three purposes for gate stations. To begin, they lower the line pressure from transmission levels (200 to 1,500 pounds) to distribution levels (from 1/4 pound to 200 pounds). Then an odorant is introduced, which has the unique sour scent associated with natural gas, allowing customers to detect even minute amounts of gas. Finally, the gate station determines the amount of gas received by the utility by measuring the flow rate of the gas.
Natural gas flows from the gate station into distribution lines, or “mains,” that range in diameter from 2 inches to more than 24 inches. There are sections of each distribution system that run at various pressures, with regulators controlling the pressure. The utility can remotely operate some regulators to vary pressures in different portions of the system to improve efficiency. In general, the smaller the pipe diameter and the lower the pressure, the closer natural gas goes to a client.
In general, the gas utility’s central control center monitors flow rates and pressures at various places across its system on a continuous basis. The operators must ensure that sufficient flow rates and pressures of gas reach each customer in order to fuel equipment and appliances. They also ensure that the pressures in the monitored areas of the system remain below the maximum pressure. The pressure in distribution lines is often less than one-fifth of their design pressure.
Regulators manage the flow of gas as it passes through the system, shifting it from higher to lower pressures. If a regulator detects a drop in pressure below a preset level, it will open to enable additional gas to flow. When pressure rises above a preset level, the regulator closes to compensate. Relief valves are installed on pipelines as an added safety measure to expel gas to the atmosphere if necessary.
To assess the network’s delivery capacity and ensure that all customers receive adequate gas supplies at or above the minimum pressure level required by their gas appliances, sophisticated computer systems are utilized.
With strategically placed shut-off valves, distribution mains are interconnected in numerous grid configurations. During maintenance and emergency situations, these valves reduce the need for customers to be inconvenienced.
A service line transports natural gas from the main to a home or business. The natural gas utility is usually in charge of maintaining and operating gas pipelines and facilities up to the gas meter in the home. The client is responsible for any equipment and gas supply pipes downstream of the home meter.
When the gas reaches the meter of a client, it passes through another pressure regulator, which reduces the pressure to less than 1/4 pound if necessary. Some service lines transport gas that has already been compressed to a very low pressure. This is the usual pressure for natural gas in a domestic piping system, which is lower than the pressure caused by a child blowing bubbles in a glass of milk through a straw. When you turn on a gas heater or stove, the gas pressure is slightly higher than the air pressure, so gas pours out of the burner and ignites in that famous clear blue flame.
What is the pressure at which natural gas is delivered?
Natural gas pressure delivered to the home is approximately 1/4 pound per square inch. First, the natural gas must be transferred at greater pressures through huge pipelines that connect the well field to the local provider.
Is it necessary to compress natural gas?
Natural gas vehicles are becoming more common on the road, particularly in municipal and commercial uses. Natural gas, on the other hand, must be compressed before it can be used as a motor fuel. This, among other things, allows for more fuel to be stored per volume.
Is natural gas transported through pipelines as a liquid?
Steel or plastic tubes are used to construct oil pipelines, which are normally buried. Oil is transported through pipelines by pump stations located along the route. Natural gas (and other gaseous fuels) are compressed into liquids called Natural Gas Liquids (NGLs). Carbon steel is used to construct natural gas pipelines. The transfer of hydrogen through a pipe is known as hydrogen pipeline transport. Pipelines are one of the safest modes of material transfer as compared to road or rail, and as a result, military attacks against pipelines are common.
Is natural gas on the rise or on the decline?
Natural gas is always lighter than air, therefore if it escapes from a burner or a leaking fitting, it will rise in the room. Propane, on the other hand, is heavier than air and will settle in a basement or other low-lying location. When the gas mixture is richer than 10%, incomplete combustion can occur.
How long should a gas line be able to maintain pressure?
Gas lines must maintain a specific psi for the period of time specified by local codes in order to pass pressure testing. There will be some natural peaks and decreases in the pressure of the gas line when testing for leaks.
Standard gas line inspections often call for lines to be held at three times their working pressure for at least 30 minutes. Typically, if a test of 20 psi on the gas line results in a loss of around 2 psi, the lines are acceptable. In contrast, if the line loses more than 10% of its pressure, it may be leaking. After a 30 minute or even a 24-hour test, this may be true.
Gas line changes are also influenced by environmental conditions. Heat causes line pressures to rise, whereas cold temperatures cause pressure to fall. These situations improve as the days and seasons pass. It’s usual to see decreases overnight, and they don’t always mean there’s a problem with the line.
What is the depth at which a natural gas pipeline is buried?
On private land, service lines on distribution systems must be 12 inches deep, and 18 inches deep along roads and streets. The burial depth is only for installation, and there is no need in federal rules that it be maintained over time.
What causes natural gas to smell?
Natural gas is odorless. To give it its unmistakable “rotten egg” smell, gas companies add a harmless chemical called mercaptan. In Connecticut, all natural gas and propane pipeline gas is odorized.