Valves in action -
Pilot-operated pressure reducing valve RP 810
Pressure reduction in a gas compressor station
Natural gas is of major importance to meet the increasing worldwide demand for fossil fuels. However, it is much more difficult to transport than oil is because a relatively large volume must be moved.
If the gas is to be conveyed by pipelines, which can often be hundreds of kilometres long, liquefaction of the gas is not convenient. It would make more sense to increase the pressure to such an extent that large quantities of gas can be pumped through the pipelines. Normally, pressure values of approximately 100 bar are obtained. Big turbo compressors augment the natural gas pressure to some 100 bar before it starts its journey through a pipeline. In spite of the low gas viscosity, pressure losses will naturally occur over time owing to the large distances to be surmounted and the differences in altitude that will reduce part of the gas pressure. Therefore, so-called pressure boosting stations are installed every 100 to 150 km, because each time the pressure drops the gas is further expanded and te volume will rise.
Consequently, the gas must flow faster, which will entail further pressure losses. Without the use of pressure boosting stations the gas would not reach the end of the pipeline or would not have the required volume flow. A pressure boosting station is a very complex small plant with a relatively simple task. On the one side of such plant the incoming pipelines are arranged, in which the gas only features a pressure of approximately 80 bar. The plant is equipped with large turbo compressors. Now part of the gas is branched off and led to a gas turbine where it is used as fuel. The gas turbine, in turn, propels a turbo compressor which again compresses the gas that remained in the pipeline and brings it to a higher pressure level. Downstream of the turbo compressor, the heated gas is led through large coolers in order to again remove the heat that was put in during compression. The gas turbine of the plant requires a relatively low inlet pressure of approximately 2 - 3 bar whilst there is a gas pressure of abt. 80 through to 85 bar within the incoming pipeline. Such high pipeline pressure must not act directly on the combustion chamber, otherwise the latter would be destroyed.
Mankenberg’s RP 810 pressure reducing valves and SV 4 safety valves have the task of reducing the higher pipeline pressure to approximately 2 - 3 bar. First of all, the incoming gas is led through a filter, which is to protect the downstream regulating valves and gas turbines from contaminants coming from the pipeline. After that the gas pressure is reduced in two steps: firstly from 85 bar to approximately 20 - 25 bar and subsequently to approximately 2 - 3 bar. The Mankenberg RP 810 regulating valve is employed for this purpose. When selecting the regulating valves, the customer attaches great importance to high regulating accuracy. Therefore, Mankenberg‘s pilot-operated control valves are particularly suitable because the high regulating accuracy has been combined with hydraulic damping. The latter has the advantage that it compensates oscillations from the system preventing upswings of the entire system and the transfer of vibrations to the gas turbine. The filters integrated in the control valve further increase the operational reliability of the complete system because they prevent clogging caused by possibly existing dirt particles. Thus the customer receives a highly precise control valve whose design allows for an extended operational lifespan with long maintenance intervals.
