The transmission of natural gas involves losses due to friction, which results in the decrease of pressure. In order to maintain continuous transmission and increase transmission capacities, pressure must be raised. This is the function of the compressor stations installed at the end points of the pipelines. Our system operates centrifugal compressors that are driven by high-performance gas turbines, similar to the ones used in aircrafts, in 8 locations: Beregdaróc, Nemesbikk, Hajdúszoboszló, Városföld, Csanádpalota, Szada, Báta and Mosonmagyaróvár
Natural gas is transmitted at high pressure (40–75 bars). This pressure is 20–40 times as large as the pressure in the rubber tires of cars and equals to the pressure that could be found 400–700 meters below sea level.
In the long-distance pipelines used for gas transmission the flowing gas is in contact with the internal walls of the pipelines and therefore it whirls and is exposed to friction, which consistently reduces pressure. In order to maintain continuous gas transmission and increase transmission capacities, pressure has to be raised. This is the function of the compressors installed along the long-distance pipelines.
At the compressor stations, centrifugal compressors driven by high-performance gas turbines are used to increase the pressure.
The operation of these equipment units is similar to the functioning of the turbines that power airplanes, whereas centrifugal compressors show resemblance to the chargers used in car engines.
Operating principle of the gas turbine
Operating principle of the gas turbine used at the stations.
The multi-stage axial air compressors suck ambient air through the filters and while rotating it compresses the air to 10–20 bar pressure. The compressed air flows into the combustion space, where natural gas used as the fuel is added and mixed. In the combustion space designed with respect to the type of the gas turbine, the mixture of the gas and air is burnt. The hot combustion gases flow through the stages of the gas generator and gradually deliver part of their internal energy, which triggers the rotation of the gas generator and the air compressor that is installed on the same axle. This is how the operation of the gas turbine becomes continuous.
On the rotator of the axial compressor, there are curved, airfoil-shaped, twisted rotating blades in several rows, followed by lines of similarly airfoil-shaped stator blades curved in the opposite direction. Every row of rotating blades is followed by a set of stator blades. A line of rotating blades and the row of stator blades thereafter is collectively called a stage.
During the process, considerable energy remains in the hot combustion gas. It further flows through the stages of the so-called power turbine, which is driven by the gas delivering its residual energy. The power turbine rotates the centrifugal compressor unit, which serves the transmission of natural gas.
There is no mechanical link between the gas generator and the power turbine, meaning that they are rotated – as described above – by the hot combustion gases that pass through them.
In the spiral casing, there is an axle-mounted rotator, the so-called blade wheel rotating, and it consists of a disk-shaped rear panel with curved blades installed on the panel, as well as a front panel, if any. The gas enters the equipment via the port on the top of the spiral casing. The gas is driven towards the appropriate direction by the guide vanes after the suction stub of the spiral casing. The gas flow accelerates in the rotator. The gas exits the impeller radially, the spiral casing collects and directs the outflowing gas towards the discharge stub – in fact a diffusor (a pipeline section of increasing cross-section) – where the gas flow decelerates, and a part of its kinetic energy is converted into potential energy: its pressure increases.
Operating principle of the compressor station
The mechanical units operated at the compressor station are usually connected to common suction and discharge lines. The operation of the equipment units depends on the given gas transmission function. In the domestic system, the pressure of the natural gas is increased from 35–40 bars to 60–75 bars on the average. While passing through the compressors, the temperature of the gas increases, because the internal sides of the long-distance pipelines are covered with protective coating, which is safeguarded by only allowing gas of adequate temperature to enter. For this reason, the warmer natural gas needs to be cooled down on a gas chiller.
For the safe and continuous functioning of the station, a number of auxiliary systems have to be operated without interruption. The operating parameters can be continuously controlled and changed – if necessary – via the installed remote surveillance system.
The compressor installed in the building of the Hajdúszoboszló compressor station with mechanical units and the gas chiller