Compressor Station

The oil and gas industry uses two main types of compressors: reciprocating and screw.
A natural gas reciprocating compressor uses pistons and positive displacement to compress the gas. Gas enters the manifold, flows into the compression cylinder, then discharges at a higher pressure.
In the video, we show the inner workings and the flow path of a 3-stage reciprocating compressor. The inlet flow, or "suction side," of the compressor starts at 30 psi and 80°F. It enters the inlet scrubber and any free liquids fall out. There are three stages of compression on a reciprocating compressor.
At the first stage of compression, the pistons will compress the gas to 155 psi and the temperature will increase to 260°F. As it exits the first stage it goes into the intercooler. This cools the gas to down to 120°F.
The heating and cooling of the gas along with the compression makes more liquids fall out of the gas. From here it enters another scrubber so that liquids can fall out.
The second stage of compression increases the pressure to 490 psi and the temperature also heats up to 270°F. from there it's back through the cooler to get the temperature back down to 120°F. with more pressure and cooling there's more liquids that will fall out in the last scrubber.
The third stage of compression gets the pressure up to 1200 psi and 240°F. Once again, the hot gas will go through the cooler and exit the at the discharge at 120°F. Some producers will run the compressed gas through one last scrubber to give any remaining liquids a place to drop out.

A screw compressor uses two meshing helical screws or rotors to compress the gas. Gas enters the suction side and moves through the threads. As it does it is compressed, and this compressed natural gas then exits at the discharge side at a higher pressure.
Screw compressors are typically used for lower pressure and lower volume like a VRU.

Centrifugal compressors, sometimes called impeller compressors or radial compressors, are a sub-class of dynamic axisymmetric work-absorbing turbomachinery. They achieve pressure rise by adding energy to the continuous flow of fluid through the rotor/impeller.
Here are the main benefits that centrifugal compressors offer:
●Centrifugal compressors provide optimum combination of high flow with low energy consumption lowers specific energy requirements for large flows and Class 0 Oil Free air quality as per standard ISO 8573-1.
●The multi-stage compression method keeps air relatively cooler than other methods with higher pressure ratio per stage. Lower air temperature is efficient to compress and maximum machine reliability is ensured.
●Longer service intervals due to fewer rubbing parts and high-grade stainless-steel coolers with epoxy coated air path for minimum corrosion.
●Faster maintenance thanks to simplified connection like water manifolds, Horizontal split gear box and integrated components - oil lubrication system on the main shaft or no external instrument air connections need.
●Superior AGMA Q13 quality gears (aircraft quality) for longer lifetime, less mechanical losses, and lower noise. Full individual component interchangeability available.
●Exclusive backward lean impeller design offer operation flexibility with turndown ratio up to 35%.
●Accurate Servo motor-controlled Inlet Guide Vanes to offer precise positioning for optimal flow control.
●Remote monitoring and control of operation parameters, receiving alerts on mobile devices to maximize uptime.
●Compact and light unit for its class with lower total cost of ownership.

A Directed Inspection and Maintenance (DI&M) Program allows you to use a cost-friendly way to find, detect, and fix the leakage of components at the compressor station.
The program centers on a baseline survey of identifying and quantifying leaks.
First off, repairs are carried out to fix the leaking components. But the fixes are carried out on components that are profitable to repair, hence, they offer cost-effective benefits.
In the same vein, these are components with the highest potential to leak.
After this survey, other surveys can be carried out with reliance on the data obtained from previous surveys. These surveys help operators to focus on components that could potentially leak in the future and maybe more profitable to fix.

Part of the DI&M program includes the use of leak screening techniques as well as leak measurement techniques.
Here 's a detailed breakdown of either of these.

1. Soap Bubble Screening
This is an inexpensive and fast leak screening technique where soap is used to find loose fittings and connections. The loose fittings can be tightened immediately to stop leakage.
However, the process begins with spraying a solution of soap on small components including threaded connections. This technique helps in fixing leaks and confirming the tightness of a repair.
On the other hand, the soaping technique could take operators an hour to check 100 components.
2. Electronic Screening Technique
This technique involves the use of small hand-held gas detectors to check for gas leaks.
Sniffing devices can also be used in the process.
On the other hand, the gas detectors used in the process feature thermal conductivity and catalytic oxidation sensors. These sensors detect when certain gases are present. This method is also more preferable for larger openings that cannot be screened using the soaping technique.
However, 50 components per hour may be checked by the electronic screening technique, which makes the soaping technique faster.
3. Organic Vapor Analyzers (Ovas) and Toxic Vapor Analyzers (Tvas)
Hydrocarbon detectors such as Organic Vapor Analyzers (OVAs) and Toxic Vapor Analyzers (TVAs) are useful devices in detecting leaks.
For starters, OVAs are flame ionization detectors (FID) that measure the concentration of organic vapors between a range of 9 to 10,000 parts per million (ppm).
TVAs, on the other hand, combine photoionization detector (PID) with FID to aid in the measurement of organic vapors and at concentrations that are above 10,000 ppm.
4. Infrared Cameras
Infrared cameras can also detect when there is gas emission in components at the compressor station. These cameras operate by converting scanned regions into a moving image in real-time.
To that effect, it makes gas plumes visible as these gases absorb infrared light.
IR cameras help in the fast screening of components, hence, hundreds can be screened in an hour.
Also, components located in confined or elevated spaces can be screened remotely from a location that is accessible that is within a viewing distance.

Aside from detecting leakage in components of the compressor station, it is also important to measure the volume of leakages from these components.
The ability to measure these leaks will ensure that resources and manpower are targeted towards significant leaks that will be most profitable to repair.
Some leak measurement techniques you can rely on are:
1. Toxic Vapor Analyzers (TVAs)
Toxic Vapor Analyzers (TVAs) serve to predict the mass leak rate.
The measurement of concentration in ppm is then changed to mass emissions rate with the help of the correlation equation.
There is, however a downside to this measurement since the correlation equations are not tailored to a particular site.
2. Bagging Techniques
These techniques help in the measurement of mass emissions as a result of equipment leakage.
Here, a bag is used to cover the leaking component or its opening, before nitrogen or any other inert carrier gas is passed through the bag using a known flow rate.
As the carrier gas reaches equilibrium, the gas sample is taken from the bag and its methane concentration is measured. The methane concentration of the sample found on the bag as well as the carrier gas flow rate are used for the mass emission rate calculation.