How Do We Get Natural Gas?
When we turn on an oven burner or turn up the thermostat to our home heating system, we generally give little thought to what powers those home appliances. But for us to enjoy the comfort they bring to our lives, a natural gas system must be put into place. You may be asking “how do we get natural gas into our homes?” What process is used in transporting natural gas from the well to our homes? Unlike propane, we don’t have a truck deliver it and unlike our electric power, we don’t see a lot of pipes above the ground. Natural gas that is recovered from a well site is transported via pipe-lines to a processing facility. Once the natural gas is processed, the finished product must be delivered to the consumer (you and me). How does natural gas get from the well to the processing plant and from the processing plant into our homes and businesses? In this article, we will cover how this whole process works.
You will never see trucks hauling natural gas from one point to another, as you may with liquid propane. Pipelines are the method used to transport natural gas from one destination to another. There are two variables that determine the flow rate of gas along these pipe-lines. The first thing that affects the volume of gas moved along these pipelines is the size of the pipe itself. The larger the pipeline, the more volume it can handle. Second, the pressure within the pipeline determines how fast natural gas flows along the line. With no pressure, there will be no flow. The amount of pressure within the pipelines is measured in pounds per square inch. A small line will be limited in the amount of gas it can carry, even with a higher pressure applied.
Gathering Gas From Wells
The production from each well will vary. The picture to the left is a finished natural gas well. This rig has a very small footprint and is called a christmas tree. The gas collected at each well site has to be collected and carried to the processing facility. These facilities are normally relatively close to the wells. As the natural gas moves closer to the processing facility, gas from other wells is combined. The pipeline that begins at the well site will be smaller than the pipe-lines that reach a central collecting point. The structure of the pipelines is kind of like a tree, where the branches are smaller, the farther they are from the base. As the pipeline increases in size, it has the ability to carry more gas. If production increases, pressure can be increased to move the gas along at a higher rate.
Due to friction within the pipelines, the flow may slow down. As this happens, pressure needs to be boosted to keep the gas moving smoothly. One or more field compressors are needed along the way to boost the pressure and get the gas to the processing plant. Most of the compressors used in this gathering system utilize a combustion engine with a turbine, which increases the pressure. These compressors typically use a small amount of the natural gas from their own line for their operation.
The Processing Facility
A processing facility is used to remove impurities like water, carbon dioxide and sulfur from the gas. If left inside the pipes, they might corrode the pipeline. If inert gases, such as helium were left in the pipeline, it would also reduce the energy value of the natural gas.
The processing plants also remove other usable gases such as propane and butane. These gases are then used for other applications.
Natural Gas Transmission System
Natural gas often has to be transported thousands of miles across the country from the areas of production to local distribution companies. The natural gas transmission system is composed of more than 272,000 miles of pipelines which act like interstate highways for gas. These huge steel pipes are between 20 and 42 inches in diameter. To move the natural gas along these massive pipelines, the lines are pressurized between 200 pounds and 1,500 pounds per square inch. The pressure varies depending on the area of operation. Much of the 42 inch pipeline is pressurized at about 1,000 psi. At this pressure, a 50 mile stretch, this pipe will contain about 200 million cubic feet of gas. That is enough natural gas to power a kitchen stove for over 2,000 years. The heavy-steel construction of the pipelines is designed to handle much higher pressure than is actually used. In highly populated areas, the system is designed to handle more than twice the pressure that is used.
Since the pipelines are run across long distances, many of them are buried on the property of landowners. The gas companies have to lease a right of way from the property owners, where the pipe is placed. This right of way is usually about 100 feet wide. Areas where the pipe is buried, there are restrictions on construction, to minimize the potential for any accidental damage. Sometimes, two or more large steel-pipes are run parallel to each other. This provides a much higher delivery capacity during times of peak demand.
Compressor stations are positioned roughly every fifty to sixty miles to boost the pressure as the gas slows in its movement. This resistance is caused by friction as the gas moves along the steel pipe. These compressor stations boost the pressure and keep the gas moving. Many of these stations are automated, which means they kick on or off as needed. Each station is also monitored and controlled by a central control room, which remotely operates shut-off valves all along this transmission system. As a result, efficiency is optimized and a safe environment is maintained. Natural gas travels through this transmission system at a speed of up to thirty miles per hour, so it takes the gas quite some time to get from state to state. When demand decreases, by lowering the pressure on the pipeline, the company can actually use the transmission lines to store gas until the demand increases. This volume of gas in the pipe is called “linepack.” With this system in place, fluctuations in usage don’t negatively impact supply and demand. In fact, it makes the system much more flexible.
As the transmission pipeline comes to a local gas utility, a “gate station” is used. A gate station reduces the pressure from transmission levels of 200 to 1,500 pounds, to distribution levels, which are from ¼ pound to 200 pounds. This is also where an odorant called mercaptan is added. The flow rate of gas that flows through the gate station is monitored. The ownership of the natural gas is transferred to the local utility company. It is their obligation at this point to get the gas to the end user.
The Distribution System
As gas leaves the gate stations, it travels in lines that are anywhere from 2” to more than 24” in diameter. During the distribution process, regulators are used to control the pressure and to drop it low enough for consumer use. Many of these regulators are controlled remotely by the utility company which optimizes efficiency in the gas delivery process. As the natural gas gets closer to the consumer, the pipe line diameter generally gets smaller in diameter and the pressure is lowered.
The gas utility company monitors the flow rates as well as the pressure at various points along the way, ensuring they stay below the maximum level throughout the delivery system. If for some reason a regulator fails and doesn’t lower the pressure significantly enough, there are built in relief valves that will vent this gas harmlessly into the atmosphere.
Normally, multiple grids are interconnected to the distribution mains so that if the utility company needs to do maintenance on specific lines, they don’t have to shut off the gas supply to their customers. Shut-off valves are strategically placed so they can control the flow of gas remotely.
Getting Natural Gas to the End User
Hopefully, this description of the natural gas delivery system has been helpful in answering the question “how do we get natural gas?” The next time you turn on that appliance, you will have an idea how the natural gas was produced, processed, and delivered to your home. It may also give you a better appreciation for those who make it possible for you to use.