In this video, we're going to follow the pipes on a typical natural gas
compression station and explain how each piece of equipment works.
This is the inlet pipe on this compressor station. The pipe coming from underground
carries natural gas from many different sites. At this point,
over 500 well sites are flowing into this station with a flow volume over 45 MMCFD.
Also leading into the main inlet on this site are two pig receivers from two different lines.
All the process fluid that the pig is pushing through from the pig launcher
moves into the main inlet pipeline with the natural gas.
On the PIG receiver, the pig trap closure is where an operator would remove pig from the line.
The PIG-SIG will indicate that a pig has arrived.
Next on the pipeline is an emergency shutdown valve, or ESD. If someone were to press an
ESD button, or if the system were over pressure, this will shut-in the system.
In the event of an ESD closure, the bypass line will be used to slowly increase the pressure to
resume operation, so the system is not pressurized too quickly during startup.
During regular operation, natural gas is coming into the station at 40-45
PSI. When leaving the station, the final pressure will be between 1250-1300 PSI.
The slug catcher is designed to handle the large volume of fluid that the pig
pushes into the station. It also helps to separate water and hydrocarbon liquids that
may condense out of the gas stream as the gas cools and moves through the pipeline.
The large amounts of hydrocarbon liquids and water that the pig pushes into the slug catcher
travels to storage tanks on this location.
At this point, a site may use an emulsion breaker to aid this separation process of resources.
After the slug catcher, you may notice more pipes with empty end connections.
This station is built to be modular and allow for other equipment to be added in the future
if the producer decided it was necessary for increased capacity.
After much of the initial fluids have been removed,
the natural gas moves into a second vessel – a filter separator.
A filter separator removes impurities such as pipe scale, water, iron sulfide,
liquid hydrocarbons, compressor lube oil and sulfur products from natural gas. A filter
separator differs from a standard separator vessel in that it uses filter elements to
remove contaminants rather than using mechanical devices and other principles of separation.
For more on filter separator operation, watch our video specific to that vessel.
This filter separator has a liquid boot design where the liquids fall into the lower portion
of the vessel. This is a 2-stage separator, not to be confused with a 2-phase separator.
In the first stage liquids fallout and their levels are controlled by this level controller.
In the second stage when the gas passes through the filters,
the liquids drop on the other side of the boot and are controlled by a second level controller.
The gas then flows into the suction header and into individual inlets for each compressor.
This pilot is monitoring and controlling the suction of the compressor.
The compressor operates most efficiently in a certain window of condition. The suction
control valve and pilot prevent the compressor from going down on high or low suction pressure.
After the suction control valve, the natural gas travels through underground pipelines
into the inlet scrubber of the compressor that is located on the other side of a sound barrier wall.
Large compressors like these are found at compressor stations where
high volumes of gas are being gathered from multiple wells over a large area
or from a large pipeline. These stations help move gas from one side of the country to the other.
The size and number of compressors found at these stations vary based on the pressures,
volume of gas to be moved and the distance it must travel to the next station.
You can learn more about the function and flow path
of compressors with our other videos specific to that topic.
After the natural gas has been compressed,
the higher pressure allows it to be discharged into a smaller pipeline at the same flow rate.
Also coming off the main discharge line is a recirculation line.
This can be used if the gas needs to run back through the compressor again.
The discharge line from each compressor travels into the discharge header
which then enters a vertical separator.
After the natural gas has been compressed and then cooled, more condensation will be present
in the gas stream. This vertical separator is removing those condensed liquids from the gas.
Another filter separator is used to remove more impurities such as pipe scale, water,
iron sulfide, liquid hydrocarbons, compressor lube oil and sulfur products from natural gas.
There is a lot of equipment needed for the dehydration process. Natural gas only travels
through the inlet scrubber and the contactor. On this site, these two vessels are combined
into one unit. All the other equipment is used to regenerate the glycol used in the dehydration
process and is located slightly farther away, connected by underground pipelines.
For more about dehydration and the equipment needed see our other videos on that topic.
The next vessel is a Glycol After Scrubber. The function is to capture any glycol that the gas
sweeps out of the tower due to foaming. This could be caused by high Ph levels
or a high temperature differential between the gas and glycol.
When the natural gas exits the glycol after scrubber, it moves back into discharge
pipeline and travels underground to the next compressor station or destination.
The gas flare is used to destroy excess gas during startup or shutdown processes
and when pressure needs to be relieved from equipment.
This site was expanded to handle an increased production from additional wells.
The new higher volume was great enough to require additional equipment, rather than replacing it
with larger vessels. This also allows for even more increase in production in the future.
This additional equipment is an almost identical setup to what was just discussed
with some exceptions like a larger slug catcher and the number of compressors.
The purpose of these vessels and components is to take the raw natural gas from many sources,
clean and pressurize the gas and send it miles away to the next station or gas processing plant.