This study compares two natural gas compressor facility vent header designs—one designed with steady-state calculations and one designed with a transient analysis. The steady-state design will also be analyzed with the transient software to determine how the design might perform in an emergency. The example facility used for this study is based on an operating compressor facility in the Barnett Shale area near Ft. Worth, TX. It includes 8 automated block valves, 16 pressure relief valves, and the piping that connects it to the blow down silencer. The predicted venting performance for each design is also compared to the actual venting performance at the example facility.
During start-up, shut-down, and in emergency situations natural gas facilities are designed to release the gas in the station piping to a vent gas header system. In an emergency such as a fire or over pressure condition, quickly releasing the pressure on the station piping reduces the risk of a serious explosion. The vent gas system may take the gas to a flare or to a blow-down silencer—depending on the quality of the gas and the sensitivity of the surrounding area. Inlets to the vent gas header include automated block valves, which are opened manually or by set points in the station's programming. There are also pressure relief valves on the vent header, which open if the pressure in the piping exceeds the set point. Vent gas headers are designed to move a large amount of gas in a short amount of time at very low pressures. Correctly sizing the vent header piping is critical to avoid excessive back pressure, which can delay the evacuation of the gas from the station piping. This paper examines the differences in designing vent headers using steady state calculations versus transient analysis