It is worth noting that there is a type of air compressor that is easily confused with a natural gas compressor, and that is a natural gas air compressor. Unlike the common traditional air compressors that use electricity or fuel as energy, it uses natural gas. As a high-quality energy source, natural gas is not only cheap, but also has little impact on the environment.

It is now being used more and more widely. But it is not a natural gas compressor, and it cannot be used to compress natural gas, because it is just a type of ordinary air compressor, and its compression medium is still air.

How piston natural gas compressors work

Natural gas enters the compressor through the air inlet and enters the compression chamber. There is a piston inside the compression chamber, which is driven by an electric motor or a diesel engine. When the piston moves downward, the volume of the compression chamber increases, and the gas enters the chamber through the air inlet.

As the piston moves upward, the volume of the compression chamber decreases, the gas is compressed, and the pressure of the gas gradually increases. The piston natural gas compressor uses the up and down movement of the piston in the compression chamber to compress the gas into high-pressure gas. This type of compressor is usually widely used in natural gas filling stations, natural gas storage depots and other fields.

How rotary screw natural gas compressors work

The working principle of rotary screw gas compressor is based on the special shape and movement of the screw. When the two screws rotate, the working chamber sealed by their gears pushes the gas forward. As the two screws rotate around their axes, their gears push against the gas, compressing it. As the screws rotate, the gas is pushed into the closed space between the other screws.

When the gas is compressed to the required pressure, the valve opens and the compression is completed. Screw gas compressors are widely used in oil and gas exploration, production, pipeline transportation and other links.

How centrifugal natural gas compressors work

Centrifugal compression technology is a common compression technology. Its main features are simple structure, reliable performance and high efficiency. This technology is suitable for natural gas compression scenarios in the low and medium pressure range. The structure and working principle of the centrifugal compressor are very similar to those of the centrifugal blower.

However, its working principle is fundamentally different from that of the piston and screw compressors. It does not increase the pressure of the gas by reducing the cylinder volume, but relies on the change of kinetic energy to increase the gas pressure. In the centrifugal compressor, when the gas enters the unit, it is sucked in by the rotation of the centrifugal wheel and rotates in the gap between the wheel cover and the centrifugal wheel.

The air gains kinetic energy due to the centrifugal force, and at the same time, the gas in the wheel cover gains more kinetic energy due to the high-speed circular motion. Finally, part of the kinetic energy will be converted into gas pressure, and the gas is compressed.

CNG compressors for drainage and gas extraction

During the process of natural gas production, the gas reservoir will experience pressure depletion. In order to maintain the pressure of the gas reservoir and continue production, a CNG compressor is needed for pressurization.

The gas lift process is to inject high-pressure gas into the well with the help of CNG compressor, reduce the pressure gradient from the injection point to the wellhead, and then reduce the bottom hole back pressure, increase the production pressure difference, thereby increasing the fluid flow rate, increasing the liquid carrying capacity of natural gas, and then draining the bottom liquid, so that the flooded well can resume production and finally achieve continuous or intermittent production of drainage and gas production. CNG compressors play a vital role in this process.

CNG compressors for gas gathering and processing

As gas wells are continuously mined, the parallel port pressure will also decrease. When the pressure drops below the pressure of the gas gathering system, boosting equipment is needed to input the produced natural gas into the gas gathering pipeline network. The types of CNG compressors suitable for high-pressure gas gathering processes are mainly reciprocating compressors.

In the process of designing the unit, the important technical parameters are mainly outlet pressure, inlet pressure and exhaust volume. In the boosting scheme of the gas gathering station, the compressor outlet pressure must be greater than or equal to the operating pressure of the branch line and the trunk line to ensure that the boosted natural gas can smoothly enter the branch line and the trunk line.

The inlet pressure is determined by the bottom hole pressure at the end of the gas field boosting stable production period. The compressor is installed in or near the gas gathering station, and the inlet pressure is required to be basically consistent with the natural gas inlet pressure from the gas well.

Finally, the single unit power is determined according to the total processing scale of the station and the number of compressors.

Generally, the number of compressors for each gas gathering station is preferably 3~5. The compressor used for gas gathering and processing does not have high pressure requirements, generally below 8MPa, and the power level is determined according to the natural gas processing volume requirements of the gas gathering station. The general single-unit power is within 3500kW.

CNG compressors for pipeline transportation

Long-distance natural gas pipelines need to build natural gas boosting stations along the way. Only by multiple multi-stage boosting by compressors can long-distance transportation of natural gas be achieved. CNG compressors are often likened to the “heart” of natural gas pipeline transportation. There are two types of natural gas compressors commonly used for pipeline transportation: reciprocating and centrifugal.

The specific type to be used needs to be determined based on the pipeline boosting conditions and the environmental conditions for installing the natural gas compressor. Generally speaking, the reciprocating type is suitable for unstable working conditions, high or ultra-high pressure and small flow rate; while the centrifugal type is suitable for large processing volume and small fluctuation range of processing volume (variation range between 70% and 120%).

According to the current development trend of newly built natural gas transmission pipelines at home and abroad (high pressure, large diameter and high flow), the use of centrifugal types will become more and more extensive.（data source: www.compressor.cn）

• After compressing the gas, the floor space occupied can be reduced, the storage density can be increased, and the storage can be safer and more reliable.
• After compressing the gas, the gas can be directly transported to a farther place through a pipeline, reducing the transportation cost.
• After compressing natural gas into high-pressure gas, it can be better used in gas water heaters, natural gas engines and other application fields.
• By compressing natural gas to a certain pressure to increase its density and reduce its volume, it becomes a new type of fuel with high energy storage density and stability. Compared with ordinary natural gas, compressed natural gas can reduce 80% of nitrogen oxide emissions and 99% of particulate pollutant emissions, and is more environmentally friendly.
• Compressed natural gas has a wide range of applications. Compared with traditional petroleum energy, it has higher storage density, emission reduction advantages and safety, and is one of the new fuels developed at home and abroad.